,transcriber's ,note3 ,,do ,,not ,,try ,,this ,,at ,,home4 ,this e-text comes in three different forms3 unicode 7,,utf-#h71 ,latin-#a and ascii-#g4 ,use the one that works best on your text reader4 --,if 80 displays as a single character1 and apostrophes and quotation marks are 8curly0 or angled1 you have the utf-#h version 7best74 ,if any part of this paragraph displays as garbage1 try changing your text reader's 8character set0 or 8file encoding04 ,if that doesn't work1 proceed to3 --,in the ,latin-#a version1 80 is two letters1 but the word 8ariform0 is usually written with dieresis 7dots7 over the 8e01 and 80 is a single letter4 ,apostrophes and quotation marks will be straight 78typewriter0 form74 ,again1 if you see any garbage in this paragraph and can't get it to display properly1 use3 --,the ,,ascii-#g or rock-bottom version4 ,all necessary text will still be there2 it just won't be as pretty4 ,the full caption of each ,plate is given after its first mention in the text--generally a few pages before the ,plate's physical appearance1 as specified in the caption4 ,many terms used in this book are different from today's standard terminology4 ,note in particular3 oxy-muriatic acid the element chlorine phosphat of lime calcium diphosphate or the element calcium glucium the element beryllium muriatic acid hydrochloric acid muriat of lime calcium chloride oxymuriate of potash potassium chlorate carbonic acid carbon dioxide ,further details and more examples are at the end of the e-text4 ,each ,volume had its own table of contents4 ,they have been merged for this e-text1 but the ,vol4 ,,ii title page was retained4 ,some ,conversations were renumbered between the #dth and #eth edition1 resulting in the apparent disappearance of ,conversations ,,xi and ,,xii4 ,typographical errors are listed at the end of the text4 99 99 99 99 99 99 99 99 99 99 99 99 99 99 ,,conversations ,,on ,,chemistry2 ,in ,which ,the ,elements ,of ,that ,science ,are ,familiarly ,explained ,and ,illustrated ,by ,experiments4 ,,in ,,two ,,volumes4 ,the ,fifth ,edition1 revised1 corrected1 and considerably enlarged4 ,,vol4 ,i4 ,,on ,,simple ,,bodies4 ,london3 ,printed ,for ,longman1 ,hurst1 ,rees1 ,orme1 and ,brown1 ,paternoster-,row4 #ahag4 ,printed by ,a4 ,strahan1 ,printers-,street1 ,london4 ,,advertisement4 ,the ,author1 in this fifth edition1 has endeavoured to give an account of the principal discoveries which have been made within the last four years in ,chemical ,science1 and of the various important applications1 such as the gas-lights1 and the miner's-lamp1 to which they have given rise4 ,but in regard to doctrines or principles1 the work has undergone no material alteration4 ,london1 ,july1 #ahag4 ,,preface4 ,in venturing to offer to the public1 and more particularly to the female sex1 an ,introduction to ,chemistry1 the author1 herself a woman1 conceives that some explanation may be required2 and she feels it the more necessary to apologise for the present undertaking1 as her knowledge of the subject is but recent1 and as she can have no real claims to the title of chemist4 ,on attending for the first time experimental lectures1 the author found it almost impossible to derive any clear or satisfactory information from the rapid demonstrations which are usually1 and perhaps necessarily1 crowded into popular courses of this kind4 ,but frequent opportunities having afterwards occurred of conversing with a friend on the subject of chemistry1 and of repeating a variety of experiments1 she became better acquainted with the principles of that science1 and began to feel highly interested in its pursuit4 ,it was then that she perceived1 in attending the excellent lectures delivered at the ,royal ,institution1 by the present ,professor of ,chemistry1 the great advantage which her previous knowledge of the subject1 slight as it was1 gave her over others who had not enjoyed the same means of private instruction4 ,every fact or experiment attracted her attention1 and served to explain some theory to which she was not a total stranger2 and she had the gratification to find that the numerous and elegant illustrations1 for which that school is so much distinguished1 seldom failed to produce on her mind the effect for which they were intended4 ,hence it was natural to infer1 that familiar conversation was1 in studies of this kind1 a most useful auxiliary source of information2 and more especially to the female sex1 whose education is seldom calculated to prepare their minds for abstract ideas1 or scientific language4 ,as1 however1 there are but few women who have access to this mode of instruction2 and as the author was not acquainted with any book that could prove a substitute for it1 she thought that it might be useful for beginners1 as well as satisfactory to herself1 to trace the steps by which she had acquired her little stock of chemical knowledge1 and to record1 in the form of dialogue1 those ideas which she had first derived from conversation4 ,but to do this with sufficient method1 and to fix upon a mode of arrangement1 was an object of some difficulty4 ,after much hesitation1 and a degree of embarrassment1 which1 probably1 the most competent chemical writers have often felt in common with the most superficial1 a mode of division was adopted1 which1 though the most natural1 does not always admit of being strictly pursued--it is that of treating first of the simplest bodies1 and then gradually rising to the most intricate compounds4 ,it is not the author's intention to enter into a minute vindication of this plan4 ,but whatever may be its advantages or inconveniences1 the method adopted in this work is such1 that a young pupil1 who should occasionally recur to it1 with a view to procure information on particular subjects1 might often find it obscure or unintelligible2 for its various parts are so connected with each other as to form an uninterrupted chain of facts and reasonings1 which will appear sufficiently clear and consistent to those only who may have patience to go through the whole work1 or have previously devoted some attention to the subject4 ,it will1 no doubt1 be observed1 that in the course of these ,conversations1 remarks are often introduced1 which appear much too acute for the young pupils1 by whom they are supposed to be made4 ,of this fault the author is fully aware4 ,but1 in order to avoid it1 it would have been necessary either to omit a variety of useful illustrations1 or to submit to such minute explanations and frequent repetitions1 as would have rendered the work tedious1 and therefore less suited to its intended purpose4 ,in writing these pages1 the author was more than once checked in her progress by the apprehension that such an attempt might be considered by some1 either as unsuited to the ordinary pursuits of her sex1 or ill-justified by her own recent and imperfect knowledge of the subject4 ,but1 on the one hand1 she felt encouraged by the establishment of those public institutions1 open to both sexes1 for the dissemination of philosophical knowledge1 which clearly prove that the general opinion no longer excludes women from an acquaintance with the elements of science2 and1 on the other1 she flattered herself that whilst the impressions made upon her mind1 by the wonders of ,nature1 studied in this new point of view1 were still fresh and strong1 she might perhaps succeed the better in communicating to others the sentiments she herself experienced4 ,the reader will soon perceive1 in perusing this work1 that he is often supposed to have previously acquired some slight knowledge of natural philosophy1 a circumstance1 indeed1 which appears very desirable4 ,the author's original intention was to commence this work by a small tract1 explaining1 on a plan analogous to this1 the most essential rudiments of that science4 ,this idea she has since abandoned2 but the manuscript was ready1 and might1 perhaps1 have been printed at some future period1 had not an elementary work of a similar description1 under the tide of 8,scientific ,dialogues10 been pointed out to her1 which1 on a rapid perusal1 she thought very ingenious1 and well calculated to answer its intended object4 ,contents ,of ,the ,first ,volume4 ,,on ,,simple ,,bodies4 ,,conversation ,i4 ,page ,,on ,,the ,,general ,,principles ,,of ,,chemistry4 #a ,connexion between ,chemistry and ,natural ,philosophy4 --,improved ,state of modern ,chemistry4 --,its use in the ,arts4 --,the general ,objects of ,chemistry4 --,definition of ,elementary ,bodies4 --,definition of ,decomposition4 --,integrant and ,constituent ,particles4 --,distinction between ,simple and ,compound ,bodies4 --,classification of ,simple ,bodies4 --,of ,chemical ,affinity1 or ,attraction of ,composition4 --,examples of ,composition and ,decomposition4 ,,conversation ,,ii4 ,,on ,,light ,,and ,,heat4 #bf ,light and ,heat capable of being separated4 --,dr4 ,herschel's ,experiments4 --,phosphorescence4 --,of ,caloric4 --,its two ,modifications4 --,free ,caloric4 --,of the three different ,states of ,bodies1 solid1 fluid1 and aeriform4 --,dilatation of solid ,bodies4 --,pyrometer4 --,dilatation of ,fluids4 --,thermometer4 --,dilatation of ,elastic ,fluids4 --,air ,thermometer4 --,equal ,diffusion of ,caloric4 --,cold a ,negative ,quality4 --,professor ,prevost's ,theory of the ,radiation of ,heat4 --,professor ,pictet's ,experiments on the ,reflexion of ,heat4 --,mr4 ,leslie's ,experiments on the ,radiation of ,heat4 ,,conversation ,,iii4 ,,continuation ,,of ,,the ,,subject4 #gj ,of the different ,power of ,bodies to conduct ,heat4 --,attempt to account for this ,power4 --,count ,rumford's ,theory of the non-conducting ,power of ,fluids4 --,phenomena of ,boiling4 --,of ,solution in general4 --,solvent ,power of ,water4 --,difference between ,solution and ,mixture4 --,solvent ,power of ,caloric4 --,of ,clouds1 ,rain1 ,dr4 ,wells' theory of ,dew1 ,evaporation1 c4 --,influence of ,atmospherical ,pressure on ,evaporation4 --,ignition4 ,,conversation ,,iv4 ,,on ,,combined ,,caloric1 ,,comprehending ,,specific ,,heat ,,and ,,latent ,,heat4 #abb ,of ,specific ,heat4 --,of the different ,capacities of ,bodies for ,heat4 --,specific ,heat not perceptible by the ,senses4 --,how to be ascertained4 --,of ,latent ,heat4 --,distinction between ,latent and ,specific ,heat4 --,phenomena attending the ,melting of ,ice and the ,formation of ,vapour4 --,phenomena attending the ,formation of ,ice1 and the ,condensation of ,elastic ,fluids4 --,instances of ,condensation1 and consequent ,disengagement of ,heat1 produced by ,mixtures1 by the ,slaking of ,lime4 --,general ,remarks on ,latent ,heat4 --,explanation of the ,phenomena of ,ether boiling1 and ,water freezing1 at the same ,temperature4 --,of the ,production of ,cold by ,evaporation4 --,calorimeter4 --,meteorological ,remarks4 ,,conversation ,v4 ,,on ,,the ,,chemical ,,agencies ,,of ,,electricity4 #afj ,of ,positive and ,negative ,electricity4 --,galvani's ,discoveries4 --,voltaic ,battery4 --,electrical ,machine4 --,theory of ,voltaic ,excitement4 ,,conversation ,,vi4 ,,on ,,oxygen ,,and ,,nitrogen4 #aha ,the ,atmosphere composed of ,oxygen and ,nitrogen in the ,state of ,gas4 --,definition of ,gas4 --,distinction between ,gas and ,vapour4 --,oxygen essential to ,combustion and ,respiration4 --,decomposition of the ,atmosphere by ,combustion4 --,nitrogen ,gas obtained by this ,process4 --,of ,oxygenation in general4 --,of the ,oxydation of ,metals4 --,oxygen ,gas obtained from ,oxyd of ,manganese4 --,description of a ,water-,bath for collecting and preserving ,gases4 --,combustion of ,iron ,wire in ,oxygen ,gas4 --,fixed and volatile ,products of ,combustion4 --,patent ,lamps4 --,decomposition of the ,atmosphere by ,respiration4 --,recomposition of the ,atmosphere4 ,,conversation ,,vii4 ,,on ,,hydrogen4 #bad ,of ,hydrogen4 --,of the ,formation of ,water by the ,combustion of ,hydrogen4 --,of the ,decomposition of ,water4 --,detonation of ,hydrogen ,gas4 --,description of ,lavoisier's ,apparatus for the formation of ,water4 --,hydrogen ,gas essential to the ,production of ,flame4 --,musical ,tones produced by the ,combustion of ,hydrogen ,gas within a ,glass ,tube4 --,combustion of ,candles explained4 --,gas lights4 --,detonation of ,hydrogen ,gas in ,soap ,bubbles4 --,air ,balloons4 --,meteorological ,phenomena ascribed to ,hydrogen ,gas4 --,miner's ,lamp4 ,transcriber's ,note3 ,the final two pages of the ,table of ,contents for ,volume ,i were missing2 everything after 8,decomposition of ,water0 was supplied from earlier and later editions1 compared against the body text4 ,the section marked 8,diamond0 7,conv4 ,,ix7 was called 8,diamond is ,carbon7e7 in a state of perfect purity0 in the #dth edn41 8,diamond0 alone in later editions4 ,,conversation ,,viii4 ,,on ,,sulphur ,,and ,,phosphorus4 #bef ,natural ,history of ,sulphur4 --,sublimation4 --,alembic4 --,combustion of ,sulphur in ,atmospheric ,air4 --,of ,acidification in general4 --,nomenclature of the ,acids4 --,combustion of ,sulphur in ,oxygen ,gas4 --,sulphuric ,acid4 --,sulphurous ,acid4 --,decomposition of ,sulphur4 --,sulphurated ,hydrogen ,gas4 --,harrogate1 or ,hydro-sulphurated ,waters4 --,phosphorus4 --,history of its ,discovery4 --,its ,combustion in ,oxygen ,gas4 --,phosphoric ,acid4 --,phosphorus ,acid4 --,eudiometer4 --,combination of ,phosphorus with ,sulphur4 --,phosphorated ,hydrogen ,gas4 --,nomenclature of ,binary ,compounds4 --,phosphoret of ,lime burning under ,water4 ,,conversation ,,ix4 ,,on ,,carbon4 #bhb ,method of obtaining pure ,charcoal4 --,method of making common ,charcoal4 --,pure ,carbon not to be obtained by ,art4 --,diamond4 --,properties of ,carbon4 --,combustion of ,carbon4 --,production of ,carbonic ,acid ,gas4 --,carbon susceptible of only one ,degree of ,acidification4 --,gaseous ,oxyd of ,carbon4 --,of ,seltzer ,water and other ,mineral ,waters4 --,effervescence4 --,decomposition of ,water by ,carbon4 --,of ,fixed and ,essential ,oils4 --,of the ,combustion of ,lamps and ,candles4 --,vegetable ,acids4 --,of the ,power of ,carbon to revive ,metals4 ,,conversation ,x4 ,,on ,,metals4 #cad ,natural ,history of ,metals4 --,of ,roasting1 ,smelting1 c4 --,oxydation of metals by the ,atmosphere4 --,change of ,colours produced by different degrees of ,oxydation4 --,combustion of ,metals4 --,perfect ,metals burnt by ,electricity only4 --,some ,metals revived by ,carbon and other ,combustibles4 --,perfect ,metals revived by ,heat alone4 --,of the ,oxydation of certain ,metals by the ,decomposition of ,water4 ,power of ,acids to promote this ,effect4 --,oxydation of ,metals by ,acids4 --,metallic ,neutral ,salts4 --,previous oxydation of the ,metal requisite4 --,crystallisation4 --,solution distinguished from ,dissolution4 --,five metals susceptible of acidification4 --,meteoric ,stones4 --,alloys1 ,soldering1 ,plating1 c4 --,of ,arsenic1 and of the caustic ,effects of ,oxygen4 --,of ,verdigris1 ,sympathetic ,ink1 c4 --,of the new ,metals discovered by ,sir ,h4 ,davy4 ,contents ,of ,the ,second ,volume4 ,,on ,,compound ,,bodies4 ,,conversation ,,xiii4 ,page ,,on ,,the ,,attraction ,,of ,,composition4 #a ,of the laws which regulate the ,phenomena of the ,attraction of ,composition4 --#a4 ,it takes place only between ,bodies of a different ,nature4 --#b4 ,between the most minute ,particles only4 --#c4 ,between #b1 #c1 #d1 or more ,bodies4 --,of ,compound or ,neutral ,salts4 --#d4 ,produces a ,change of ,temperature4 --#e4 ,the ,properties which characterise ,bodies in their separate ,state1 destroyed by ,combination4 --#f4 ,the ,force of ,attraction estimated by that which is required by the ,separation of the ,constituents4 --#g4 ,bodies have amongst themselves different ,degrees of ,attraction4 --,of simple elective and double elective ,attractions4 --,of quiescent and divellent ,forces4 --,law of definite ,proportions4 --,decomposition of ,salts by ,voltaic ,electricity4 ,,conversation ,,xiv4 ,,on ,,alkalies4 #ai ,of the ,composition and general ,properties of the ,alkalies4 --,of ,potash4 --,manner of preparing it4 --,pearlash4 --,soap4 --,carbonat of ,potash4 --,chemical ,nomenclature4 --,solution of ,potash4 --,of ,glass4 --,of ,nitrat of ,potash or ,saltpetre4 --,effect of ,alkalies on ,vegetable ,colours4 --,of ,soda4 --,of ,ammonia or ,volatile ,alkali4 --,muriat of ,ammonia4 --,ammoniacal ,gas4 --,composition of ,ammonia4 --,hartshorn and ,sal ,volatile4 --,combustion of ,ammoniacal ,gas4 ,,conversation ,,xv4 ,,on ,,earths4 #dd ,composition of the ,earths4 --,of their ,incombustibility4 --,form the ,basis of all ,minerals4 --,their ,alkaline ,properties4 --,silex2 its ,properties and ,uses in the ,arts4 --,alumine2 its ,uses in ,pottery1 c4 --,alkaline ,earths4 --,barytes4 --,lime2 its extensive chemical ,properties and ,uses in the ,arts4 --,magnesia4 --,strontian4 ,,conversation ,,xvi4 ,,on ,,acids4 #fi ,nomenclature of the ,acids4 --,of the ,classification of ,acids4 --#ast ,class --,acids of simple and known ,radicals1 or ,mineral ,acids4 --#b;d ,class --,acids of double ,radicals1 or ,vegetable ,acids4 --#c;d ,class --,acids of triple ,radicals or ,animal ,acids4 --,of the ,decomposition of ,acids of the #ast ,class by ,combustible bodies4 ,,conversation ,,xvii4 ,,of ,,the ,,sulphuric ,,and ,,phosphoric ,,acids3 ,,or1 ,,the ,,combinations ,,of ,,oxygen ,,with ,,sulphur ,,and ,,with ,,phosphorus2 ,,and ,,of ,,the ,,sulphats ,,and ,,phosphats4 #hj ,of the ,sulphuric ,acid4 --,combustion of ,animal or ,vegetable ,bodies by this ,acid4 --,method of preparing it4 -- ,the ,sulphurous ,acid obtained in the ,form of ,gas4 --,may be obtained from ,sulphuric ,acid4 --,may be reduced to ,sulphur4 --,is absorbable by ,water4 --,destroys ,vegetable ,colours4 --,oxyd of ,sulphur4 --,of ,salts in general4 --,sulphats4 --,sulphat of ,potash1 or ,sal ,polychrest4 --,cold produced by the melting of ,salts4 --,sulphat of ,soda1 or ,glauber's ,salt4 --,heat evolved during the ,formation of ,salts4 --,crystallisation of ,salts4 --,water of ,crystallisation4 --,efflorescence and ,deliquescence of ,salts4 --,sulphat of ,lime1 ,gypsum or ,plaister of ,paris4 --,sulphat of ,magnesia4 --,sulphat of ,alumine1 or ,alum4 --,sulphat of ,iron4 --,of ,ink4 --,of the ,phosphoric and ,phosphorous ,acids4 --,phosphorus obtained from ,bones4 --,phosphat of ,lime4 ,,conversation ,,xviii4 ,,of ,,the ,,nitric ,,and ,,carbonic ,,acids3 ,,or ,,the ,,combination ,,of ,,oxygen ,,with ,,nitrogen ,,and ,,with ,,carbon2 ,,and ,,of ,,the ,,nitrats ,,and ,,carbonats4 #ajj ,nitrogen susceptible of various ,degrees of ,acidification4 --,of the ,nitric ,acid4 --,its ,nature and ,composition discovered by ,mr4 ,cavendish4 --,obtained from ,nitrat of ,potash4 --,aqua ,fortis4 --,nitric ,acid may be converted into ,nitrous ,acid4 --,nitric ,oxyd ,gas4 --,its ,conversion into ,nitrous ,acid ,gas4 --,used as an ,eudiometrical ,test4 --,gaseous ,oxyd of ,nitrogen1 or exhilarating ,gas1 obtained from ,nitrat of ,ammonia4 --,its singular ,effects on being respired4 --,nitrats4 --,of ,nitrat of ,potash1 ,nitre or ,saltpetre4 --,of ,gunpowder4 --,causes of ,detonation4 --,decomposition of ,nitre4 --,deflagration4 --,nitrat of ,ammonia4 --,nitrat of ,silver4 --,of the ,carbonic ,acid4 --,formed by the ,combustion of ,carbon4 --,constitutes a component ,part of the ,atmosphere4 --,exhaled in some ,caverns4 --,grotto del ,cane4 --,great ,weight of this ,gas4 --,produced from calcareous ,stones by ,sulphuric ,acid4 --,deleterious ,effects of this ,gas when respired4 --,sources which keep up a ,supply of this ,gas in the ,atmosphere4 --,its ,effects on ,vegetation4 --,of the ,carbonats of ,lime2 ,marble1 ,chalk1 ,shells1 ,spars1 and calcareous ,stones4 ,,conversation ,,xix4 ,,on ,,the ,,boracic1 ,,fluoric1 ,,muriatic1 ,,and ,,oxygenated ,,muriatic ,,acids2 ,,and ,,on ,,muriats4 #aca ,on the ,boracic ,acid4 --,its ,decomposition by ,sir ,h4 ,davy4 --,its ,basis ,boracium4 --,its ,recomposition4 --,its ,uses in the ,arts4 --,borax or ,borat of ,soda4 --,of the ,fluoric ,acid4 --,obtained from ,fluor2 corrodes ,siliceous ,earth2 its supposed ,composition4 --,fluorine2 its supposed ,basis4 --,of the ,muriatic ,acid4 --,obtained from ,muriats4 --,its gaseous ,form4 --,is absorbable by ,water4 --,its ,decomposition4 --,is susceptible of a stronger ,degree of ,oxygenation4 --,oxygenated ,muriatic ,acid4 --,its gaseous ,form and other ,properties4 --,combustion of ,bodies in this ,gas4 --,it dissolves ,gold4 --,composition of ,aqua ,regia4 --,oxygenated ,muriatic ,acid destroys all ,colours4 --,sir ,h4 ,davy's ,theory of the ,nature of ,muriatic and ,oxymuriatic ,acid4 --,chlorine4 --,used for ,bleaching and for ,fumigations4 --,its offensive ,smell1 c4 --,muriats4 --,muriat of ,soda1 or common ,salt4 --,muriat of ,ammonia4 --,oxygenated ,muriat of ,potash4 --,detonates with ,sulphur1 ,phosphorus1 c4 --,experiment of burning ,phosphorus under ,water by means of this ,salt and of ,sulphuric ,acid4 ,,conversation ,,xx4 ,,on ,,the ,,nature ,,and ,,composition ,,of ,,vegetables4 #afb ,of organised ,bodies4 --,of the ,functions of ,vegetables4 --,of the ,elements of ,vegetables4 --,of the ,materials of ,vegetables4 --,analysis of ,vegetables4 --,of ,sap4 --,mucilage1 or ,gum4 --,sugar4 --,manna1 and ,honey4 --,gluten4 --,vegetable ,oils4 --,fixed ,oils1 ,linseed1 ,nut1 and ,olive ,oils4 --,volatile ,oils1 forming ,essences and ,perfumes4 --,camphor4 --,resins and ,varnishes4 --,pitch1 ,tar1 ,copal1 ,mastic1 c4 --,gum ,resins4 --,myrrh1 ,assaftida1 c4 --,caoutchouc1 or ,gum ,elastic4 --,extractive colouring ,matter2 its ,use in the ,arts of ,dyeing and ,painting4 --,tannin2 its ,use in the ,art of preparing ,leather4 --,woody ,fibre4 --,vegetable ,acids4 --,the ,alkalies and ,salts contained in ,vegetables4 ,,conversation ,,xxi4 ,,on ,,the ,,decomposition ,,of ,,vegetables4 #bjb ,of ,fermentation in general4 --,of the ,saccharine ,fermentation1 the ,product of which is ,sugar4 --,of the ,vinous ,fermentation1 the ,product of which is ,wine4 --,alcohol1 or ,spirit of ,wine4 --,analysis of ,wine by ,distillation4 --,of ,brandy1 ,rum1 ,arrack1 ,gin1 c4 --,tartrit of ,potash1 or ,cream of ,tartar4 --,liqueurs4 --,chemical ,properties of ,alcohol4 --,its ,combustion4 --,of ,ether4 --,of the ,acetous ,fermentation1 the ,product of which is ,vinegar4 --,fermentation of ,bread4 --,of the ,putrid ,fermentation1 which reduces ,vegetables to their ,elements4 --,spontaneous ,succession of these ,fermentations4 --,of ,vegetables said to be petrified4 --,of ,bitumens3 ,naphtha1 ,asphaltum1 ,jet1 ,coal1 ,succin1 or ,yellow ,amber4 --,of ,fossil ,wood1 ,peat1 and ,turf4 ,,conversation ,,xxii4 ,,history ,,of ,,vegetation4 #bdc ,connexion between the ,vegetable and ,animal ,kingdoms4 --,of ,manures4 --,of ,agriculture4 --,inexhaustible ,sources of ,materials for the ,purposes of ,agriculture4 --,of sowing ,seed4 --,germination of the ,seed4 --,function of the ,leaves of ,plants4 --,effects of ,light and ,air on ,vegetation4 --,effects of ,water on ,vegetation4 --,effects of ,vegetation on the ,atmosphere4 --,formation of ,vegetable ,materials by the ,organs of ,plants4 --,vegetable ,heat4 --,of the ,organs of ,plants4 --,of the ,bark1 consisting of ,epidermis1 ,parenchyma1 and ,cortical ,layers4 --,of ,alburnum1 or ,wood4 --,leaves1 ,flowers1 and ,seeds4 --,effects of the ,season on ,vegetation4 --,vegetation of ,evergreens in ,winter4 ,,conversation ,,xxiii4 ,,on ,,the ,,composition ,,of ,,animals4 #bgf ,elements of ,animals4 --,of the principal ,materials of ,animals1 viz4 --,gelatine1 ,albumen1 ,fibrine1 ,mucus4 --,of ,animal ,acids4 --,of ,animal ,colours1 ,prussian ,blue1 ,carmine1 and ,ivory ,black4 ,,conversation ,,xxiv4 ,,on ,,the ,,animal ,,economy4 #big ,of the principal ,animal ,organs4 --,of ,bones1 ,teeth1 ,horns1 ,ligaments1 and ,cartilage4 --,of the ,muscles1 constituting the ,organs of ,motion4 --,of the ,vascular ,system1 for the ,conveyance of ,fluids4 --,of the ,glands1 for the ,secretion of ,fluids4 --,of the ,nerves1 constituting the ,organs of ,sensation4 --,of the ,cellular ,substance which connects the several ,organs4 --,of the ,skin4 ,,conversation ,,xxv4 ,,on ,,animalisation1 ,,nutrition1 ,,and ,,respiration4 #cad ,digestion4 --,solvent ,power of the ,gastric ,juice4 --,formation of a ,chyle4 --,its ,assimilation1 or ,conversion into ,blood4 --,of ,respiration4 --,mechanical ,process of ,respiration4 --,chemical ,process of ,respiration4 --,of the ,circulation of the ,blood4 --,of the ,functions of the ,arteries1 the ,veins1 and the ,heart4 --,of the ,lungs4 --,effects of ,respiration on the ,blood4 ,,conversation ,,xxvi4 ,,on ,,animal ,,heat2 ,,and ,,of ,,various ,,animal ,,products4 #ccf ,of the ,analogy of ,combustion and ,respiration4 --,animal ,heat evolved in the ,lungs4 --,animal ,heat evolved in the ,circulation4 --,heat produced by ,fever4 --,perspiration4 --,heat produced by ,exercise4 --,equal ,temperature of ,animals at all ,seasons4 --,power of the ,animal ,body to resist the ,effects of ,heat4 --,cold produced by ,perspiration4 --,respiration of ,fish and of ,birds4 --,effects of ,respiration on ,muscular ,strength4 --,of several ,animal ,products1 viz4 ,milk1 ,butter1 and ,cheese2 ,spermaceti2 ,ambergris2 ,wax2 ,lac2 ,silk2 ,musk2 ,civet2 ,castor4 --,of the putrid ,fermentation4 --,conclusion4 ,,conversations ,,on ,,chemistry4 ,,conversation ,i4 ,,on ,,the ,,general ,,principles ,,of ,,chemistry4 ,,mrs4 ,b4 ,as you have now acquired some elementary notions of ,,natural ,,philosophy1 ,i am going to propose to you another branch of science1 to which ,i am particularly anxious that you should devote a share of your attention4 ,this is ,,chemistry1 which is so closely connected with ,natural ,philosophy1 that the study of the one must be incomplete without some knowledge of the other2 for1 it is obvious that we can derive but a very imperfect idea of bodies from the study of the general laws by which they are governed1 if we remain totally ignorant of their intimate nature4 ,,caroline4 ,to confess the truth1 ,mrs4 ,b41 ,i am not disposed to form a very favourable idea of chemistry1 nor do ,i expect to derive much entertainment from it4 ,i prefer the sciences which exhibit nature on a grand scale1 to those that are confined to the minuti of petty details4 ,can the studies which we have lately pursued1 the general properties of matter1 or the revolutions of the heavenly bodies1 be compared to the mixing up of a few insignificant drugs8 ,i grant1 however1 there may be entertaining experiments in chemistry1 and should not dislike to try some of them3 the distilling1 for instance1 of lavender1 or rose water 4 4 4 4 4 4 ,,mrs4 ,b4 ,i rather imagine1 my dear ,caroline1 that your want of taste for chemistry proceeds from the very limited idea you entertain of its object4 ,you confine the chemist's laboratory to the narrow precincts of the apothecary's and perfumer's shops1 whilst it is subservient to an immense variety of other useful purposes4 ,besides1 my dear1 chemistry is by no means confined to works of art4 ,nature also has her laboratory1 which is the universe1 and there she is incessantly employed in chemical operations4 ,you are surprised1 ,caroline1 but ,i assure you that the most wonderful and the most interesting phenomena of nature are almost all of them produced by chemical powers4 ,what ,bergman1 in the introduction to his history of chemistry1 has said of this science1 will give you a more just and enlarged idea of it4 ,the knowledge of nature may be divided1 he observes1 into three periods4 ,the first was that in which the attention of men was occupied in learning the external forms and characters of objects1 and this is called ,natural ,history4 ,in the second1 they considered the effects of bodies acting on each other by their mechanical power1 as their weight and motion1 and this constitutes the science of ,natural ,philosophy4 ,the third period is that in which the properties and mutual action of the elementary parts of bodies was investigated4 ,this last is the science of ,,chemistry1 and ,i have no doubt you will soon agree with me in thinking it the most interesting4 ,you may easily conceive1 therefore1 that without entering into the minute details of practical chemistry1 a woman may obtain such a knowledge of the science as will not only throw an interest on the common occurrences of life1 but will enlarge the sphere of her ideas1 and render the contemplation of nature a source of delightful instruction4 ,,caroline4 ,if this is the case1 ,i have certainly been much mistaken in the notion ,i had formed of chemistry4 ,i own that ,i thought it was chiefly confined to the knowledge and preparation of medicines4 ,,mrs4 ,b4 ,that is only a branch of chemistry which is called ,pharmacy2 and1 though the study of it is certainly of great importance to the world at large1 it belongs exclusively to professional men1 and is therefore the last that ,i should advise you to pursue4 ,,emily4 ,but1 did not the chemists formerly employ themselves in search of the philosopher's stone1 or the secret of making gold8 ,,mrs4 ,b4 ,these were a particular set of misguided philosophers1 who dignified themselves with the name of ,alchemists1 to distinguish their pursuits from those of the common chemists1 whose studies were confined to the knowledge of medicines4 ,but1 since that period1 chemistry has undergone so complete a revolution1 that1 from an obscure and mysterious art1 it is now become a regular and beautiful science1 to which art is entirely subservient4 ,it is true1 however1 that we are indebted to the alchemists for many very useful discoveries1 which sprung from their fruitless attempts to make gold1 and which1 undoubtedly1 have proved of infinitely greater advantage to mankind than all their chimerical pursuits4 ,the modern chemists1 instead of directing their ambition to the vain attempt of producing any of the original substances in nature1 rather aim at analysing and imitating her operations1 and have sometimes succeeded in forming combinations1 or effecting decompositions1 no instances of which occur in the chemistry of ,nature4 ,they have little reason to regret their inability to make gold1 whilst1 by their innumerable inventions and discoveries1 they have so greatly stimulated industry and facilitated labour1 as prodigiously to increase the luxuries as well as the necessaries of life4 ,,emily4 ,but1 ,i do not understand by what means chemistry can facilitate labour2 is not that rather the province of the mechanic8 ,,mrs4 ,b4 ,there are many ways by which labour may be rendered more easy1 independently of mechanics2 but even the machine1 the most wonderful in its effects1 the ,steam-engine1 cannot be understood without the assistance of chemistry4 ,in agriculture1 a chemical knowledge of the nature of soils1 and of vegetation1 is highly useful2 and1 in those arts which relate to the comforts and conveniences of life1 it would be endless to enumerate the advantages which result from the study of this science4 ,,caroline4 ,but1 pray1 tell us more precisely in what manner the discoveries of chemists have proved so beneficial to society8 ,,mrs4 ,b4 ,that would be an injudicious anticipation2 for you would not comprehend the nature of such discoveries and useful applications1 as well as you will do hereafter4 ,without a due regard to method1 we cannot expect to make any progress in chemistry4 ,i wish to direct your observations chiefly to the chemical operations of ,nature2 but those of ,art are certainly of too high importance to pass unnoticed4 ,we shall therefore allow them also some share of our attention4 ,,emily4 ,well1 then1 let us now set to work regularly4 ,i am very anxious to begin4 ,,mrs4 ,b4 ,the object of chemistry is to obtain a knowledge of the intimate nature of bodies1 and of their mutual action on each other4 ,you find therefore1 ,caroline1 that this is no narrow or confined science1 which comprehends every thing material within our sphere4 ,,caroline4 ,on the contrary1 it must be inexhaustible2 and ,i am a loss to conceive how any proficiency can be made in a science whose objects are so numerous4 ,,mrs4 ,b4 ,if every individual substance were formed of different materials1 the study of chemistry would1 indeed1 be endless2 but you must observe that the various bodies in nature are composed of certain elementary principles1 which are not very numerous4 ,,caroline4 ,yes2 ,i know that all bodies are composed of fire1 air1 earth1 and water2 ,i learnt that many years ago4 ,,mrs4 ,b4 ,but you must now endeavour to forget it4 ,i have already informed you what a great change chemistry has undergone since it has become a regular science4 ,within these thirty years especially1 it has experienced an entire revolution1 and it is now proved1 that neither fire1 air1 earth1 nor water1 can be called elementary bodies4 ,for an elementary body is one that has never been decomposed1 that is to say1 separated into other substances2 and fire1 air1 earth1 and water1 are all of them susceptible of decomposition4 ,,emily4 ,i thought that decomposing a body was dividing it into its minutest parts4 ,and if so1 ,i do not understand why an elementary substance is not capable of being decomposed1 as well as any other4 ,,mrs4 ,b4 ,you have misconceived the idea of decomposition2 it is very different from mere division4 ,the latter simply reduces a body into parts1 but the former separates it into the various ingredients1 or materials1 of which it is composed4 ,if we were to take a loaf of bread1 and separate the several ingredients of which it is made1 the flour1 the yeast1 the salt1 and the water1 it would be very different from cutting or crumbling the loaf into pieces4 ,,emily4 ,i understand you now very well4 ,to decompose a body is to separate from each other the various elementary substances of which it consists4 ,,caroline4 ,but flour1 water1 and other materials of bread1 according to our definition1 are not elementary substances8 ,,mrs4 ,b4 ,no1 my dear2 ,i mentioned bread rather as a familiar comparison1 to illustrate the idea1 than as an example4 ,the elementary substances of which a body is composed are called the constituent parts of that body2 in decomposing it1 therefore1 we separate its constituent parts4 ,if1 on the contrary1 we divide a body by chopping it to pieces1 or even by grinding or pounding it to the finest powder1 each of these small particles will still consist of a portion of the several constituent parts of the whole body3 these are called the integrant parts2 do you understand the difference8 ,,emily4 ,yes1 ,i think1 perfectly4 ,we decompose a body into its constituent parts2 and divide it into its integrant parts4 ,,mrs4 ,b4 ,exactly so4 ,if therefore a body consists of only one kind of substance1 though it may be divided into its integrant parts1 it is not possible to decompose it4 ,such bodies are therefore called simple or elementary1 as they are the elements of which all other bodies are composed4 ,compound bodies are such as consist of more than one of these elementary principles4 ,,caroline4 ,but do not fire1 air1 earth1 and water1 consist1 each of them1 but of one kind of substance8 ,,mrs4 ,b4 ,no1 my dear2 they are every one of them susceptible of being separated into various simple bodies4 ,instead of four1 chemists now reckon upwards of forty elementary substances4 ,the existence of most of these is established by the clearest experiments2 but1 in regard to a few of them1 particularly the most subtle agents of nature1 heat1 light1 and electricity1 there is yet much uncertainty1 and ,i can only give you the opinion which seems most probably deduced from the latest discoveries4 ,after ,i have given you a list of the elementary bodies1 classed according to their properties1 we shall proceed to examine each of them separately1 and then consider them in their combinations with each other4 ,excepting the more general agents of nature1 heat1 light1 and electricity1 it would seem that the simple form of bodies is that of a metal4 ,,caroline4 ,you astonish me6 ,i thought the metals were only one class of minerals1 and that there were besides1 earths1 stones1 rocks1 acids1 alkalies1 vapours1 fluids1 and the whole of the animal and vegetable kingdoms4 ,,mrs4 ,b4 ,you have made a tolerably good enumeration1 though ,i fear not arranged in the most scientific order4 ,all these bodies1 however1 it is now strongly believed1 may be ultimately resolved into metallic substances4 ,your surprise at this circumstance is not singular1 as the decomposition of some of them1 which has been but lately accomplished1 has excited the wonder of the whole philosophical world4 ,but to return to the list of simple bodies--these being usually found in combination with oxygen1 ,i shall class them according to their properties when so combined4 ,this will1 ,i think1 facilitate their future investigation4 ,,emily4 ,pray what is oxygen8 ,,mrs4 ,b4 ,a simple body2 at least one that is supposed to be so1 as it has never been decomposed4 ,it is always found united with the negative electricity4 ,it will be one of the first of the elementary bodies whose properties ,i shall explain to you1 and1 as you will soon perceive1 it is one of the most important in nature2 but it would be irrelevant to enter upon this subject at present4 ,we must now confine our attention to the enumeration and classification of the simple bodies in general4 ,they may be arranged as follows3 ,,class ,i4 ,comprehending the imponderable agents1 viz4 ,,heat or ,,caloric1 ,,light1 ,,electricity4 ,,class ,,ii4 ,comprehending agents capable of uniting with inflammable bodies1 and in most instances of effecting their combustion4 ,,oxygen1 ,,chlorine1 ,,iodine499 ,footnote 993 ,it has been questioned by some eminent chemists1 whether these two last agents should not be classed among the inflammable bodies1 as they are capable of combining with oxygen1 as well as with inflammable bodies4 ,but they seem to be more distinctly characterised by their property of supporting combustion than by any other quality4 ,,class ,,iii4 ,comprehending bodies capable of uniting with oxygen1 and1 forming with it various compounds4 ,this class may be divided as follows3 ,,division #a4 ,,hydrogen1 forming water4 ,,division #b4 ,bodies forming acids4 ,,nitrogen1 forming nitric acid4 ,,sulphur1 forming sulphuric acid4 ,,phosphorus1 forming phosphoric acid4 ,,carbon1 forming carbonic acid4 ,,boracium1 forming boracic acid4 ,,fluorium1 forming fluoric acid4 ,,muriatium1 forming muriatic acid4 ,,division #c4 ,metallic bodies forming alkalies4 ,,potassium1 forming potash4 ,,sodium1 forming soda4 ,,ammonium1 forming ammonia4 ,,division #d4 ,metallic bodies forming earths4 ,,calcium1 or metal forming lime4 ,,magnium1 forming magnesia4 ,,barium1 forming barytes4 ,,strontium1 forming strontites4 ,,silicium1 forming silex4 ,,alumium1 forming alumine4 ,,yttrium1 forming yttria4 ,,glucium1 forming glucina4 ,,zirconium1 forming zirconi499 ,footnote 993 ,of all these earths1 three or four only have as yet been distinctly decomposed4 ,,division #e4 ,metals1 either naturally metallic1 or yielding their oxygen to carbon or to heat alone4 ,subdivision #a4 ,malleable ,metals4 ,,gold1 ,,platina1 ,,palladium1 ,,silver99 ,,mercury ,,tin1 ,,copper1 ,,iron1 ,,lead1 ,,nickel1 ,,zinc4 ,footnote 993 ,these first four metals have commonly been distinguished by the appellation of perfect or noble metals1 on account of their possessing the characteristic properties of ductility1 malleability1 inalterability1 and great specific gravity1 in an eminent degree4 ,footnote 3 ,mercury1 in its liquid state1 cannot1 of course1 be called a malleable metal4 ,but when frozen1 it possesses a considerable degree of malleability4 ,subdiv4 #b4 ,brittle ,metals4 ,,arsenic1 ,,bismuth1 ,,antimony1 ,,manganese1 ,,tellurium1 ,,cobalt1 ,,tungsten1 ,,molybdenum1 ,,titanium1 ,,chrome1 ,,uranium1 ,,columbium or ,,tantalium1 ,,iridium1 ,,osmium1 ,,rhodium499 ,footnote 993 ,these last four or five metallic bodies are placed under this class for the sake of arrangement1 though some of their properties have not been yet fully investigated4 ,,caroline4 ,oh1 what a formidable list6 ,you will have much to do to explain it1 ,mrs4 ,b42 for ,i assure you it is perfectly unintelligible to me1 and ,i think rather perplexes than assists me4 ,,mrs4 ,b4 ,do not let that alarm you1 my dear2 ,i hope that hereafter this classification will appear quite clear1 and1 so far from perplexing you1 will assist you in arranging your ideas4 ,it would be in vain to attempt forming a division that would appear perfectly clear to a beginner3 for you may easily conceive that a chemical division being necessarily founded on properties with which you are almost wholly unacquainted1 it is impossible that you should at once be able to understand its meaning or appreciate its utility4 ,but1 before we proceed further1 it will be necessary to give you some idea of chemical attraction1 a power on which the whole science depends4 ,chemical ,attraction1 or the ,attraction of ,composition1 consists in the peculiar tendency which bodies of a different nature have to unite with each other4 ,it is by this force that all the compositions1 and decompositions1 are effected4 ,,emily4 ,what is the difference between chemical attraction1 and the attraction of cohesion1 or of aggregation1 which you often mentioned to us1 in former conversations8 ,,mrs4 ,b4 ,the attraction of cohesion exists only between particles of the same nature1 whether simple or compound2 thus it unites the particles of a piece of metal which is a simple substance1 and likewise the particles of a loaf of bread which is a compound4 ,the attraction of composition1 on the contrary1 unites and maintains1 in a state of combination1 particles of a dissimilar nature2 it is this power that forms each of the compound particles of which bread consists2 and it is by the attraction of cohesion that all these particles are connected into a single mass4 ,,emily4 ,the attraction of cohesion1 then1 is the power which unites the integrant particles of a body3 the attraction of composition that which combines the constituent particles4 ,is it not so8 ,,mrs4 ,b4 ,precisely3 and observe that the attraction of cohesion unites particles of a similar nature1 without changing their original properties2 the result of such an union1 therefore1 is a body of the same kind as the particles of which it is formed2 whilst the attraction of composition1 by combining particles of a dissimilar nature1 produces compound bodies1 quite different from any of their constituents4 ,if1 for instance1 ,i pour on the piece of copper1 contained in this glass1 some of this liquid 7which is called nitric acid71 for which it has a strong attraction1 every particle of the copper will combine with a particle of acid1 and together they will form a new body1 totally different from either the copper or the acid4 ,do you observe the internal commotion that already begins to take place8 ,it is produced by the combination of these two substances2 and yet the acid has in this case to overcome not only the resistance which the strong cohesion of the particles of copper opposes to their combination with it1 but also to overcome the weight of the copper1 which makes it sink to the bottom of the glass1 and prevents the acid from having such free access to it as it would if the metal were suspended in the liquid4 ,,emily4 ,the acid seems1 however1 to overcome both these obstacles without difficulty1 and appears to be very rapidly dissolving the copper4 ,,mrs4 ,b4 ,by this means it reduces the copper into more minute parts than could possibly be done by any mechanical power4 ,but as the acid can act only on the surface of the metal1 it will be some time before the union of these two bodies will be completed4 ,you may1 however1 already see how totally different this compound is from either of its ingredients4 ,it is neither colourless1 like the acid1 nor hard1 heavy1 and yellow like the copper4 ,if you tasted it1 you would no longer perceive the sourness of the acid4 ,it has at present the appearance of a blue liquid2 but when the union is completed1 and the water with which the acid is diluted is evaporated1 the compound will assume the form of regular crystals1 of a fine blue colour1 and perfectly transparent994 ,of these ,i can shew you a specimen1 as ,i have prepared some for that purpose4 ,footnote 993 ,these crystals are more easily obtained from a mixture of sulphuric with a little nitric acid4 ,,caroline4 ,how very beautiful they are1 in colour1 form1 and transparency6 ,,emily4 ,nothing can be more striking than this example of chemical attraction4 ,,mrs4 ,b4 ,the term attraction has been lately introduced into chemistry as a substitute for the word affinity1 to which some chemists have objected1 because it originated in the vague notion that chemical combinations depended upon a certain resemblance1 or relationship1 between particles that are disposed to unite2 and this idea is not only imperfect1 but erroneous1 as it is generally particles of the most dissimilar nature1 that have the greatest tendency to combine4 ,,caroline4 ,besides1 there seems to be no advantage in using a variety of terms to express the same meaning2 on the contrary it creates confusion2 and as we are well acquainted with the term ,attraction in natural philosophy1 we had better adopt it in chemistry likewise4 ,,mrs4 ,b4 ,if you have a clear idea of the meaning1 ,i shall leave you at liberty to express it in the terms you prefer4 ,for myself1 ,i confess that ,i think the word ,attraction best suited to the general law that unites the integrant particles of bodies2 and ,affinity better adapted to that which combines the constituent particles1 as it may convey an idea of the preference which some bodies have for others1 which the term attraction of composition does not so well express4 ,,emily4 ,so ,i think2 for though that preference may not result from any relationship1 or similitude1 between the particles 7as you say was once supposed71 yet1 as it really exists1 it ought to be expressed4 ,,mrs4 ,b4 ,well1 let it be agreed that you may use the terms affinity1 chemical attraction and attraction of composition1 indifferently1 provided you recollect that they have all the same meaning4 ,,emily4 ,i do not conceive how bodies can be decomposed by chemical attraction4 ,that this power should be the means of composing them1 is very obvious2 but that it should1 at the same time1 produce exactly the contrary effect1 appears to me very singular4 ,,mrs4 ,b4 ,to decompose a body is1 you know1 to separate its constituent parts1 which1 as we have just observed1 cannot be done by mechanical means4 ,,emily4 ,no3 because mechanical means separate only the integrant particles2 they act merely against the attraction of cohesion1 and only divide a compound into smaller parts4 ,,mrs4 ,b4 ,the decomposition of a body is performed by chemical powers4 ,if you present to a body composed of two principles1 a third1 which has a greater affinity for one of them than the two first have for each other1 it will be decomposed1 that is1 its two principles will be separated by means of the third body4 ,let us call two ingredients1 of which the body is composed1 ,a and ,b4 ,if we present to it another ingredient ,c1 which has a greater affinity for ,b than that which unites ,a and ,b1 it necessarily follows that ,b will quit ,a to combine with ,c4 ,the new ingredient1 therefore1 has effected a decomposition of the original body ,a ,b2 ,a has been left alone1 and a new compound1 ,b ,c1 has been formed4 ,,emily4 ,we might1 ,i think1 use the comparison of two friends1 who were very happy in each other's society1 till a third disunited them by the preference which one of them gave to the new-comer4 ,,mrs4 ,b4 ,very well4 ,i shall now show you how this takes place in chemistry4 ,let us suppose that we wish to decompose the compound we have just formed by the combination of the two ingredients1 copper and nitric acid2 we may do this by presenting to it a piece of iron1 for which the acid has a stronger attraction than for copper2 the acid will1 consequently1 quit the copper to combine with the iron1 and the copper will be what the chemists call precipitated1 that is to say1 it will be thrown down in its separate state1 and reappear in its simple form4 ,in order to produce this effect1 ,i shall dip the blade of this knife into the fluid1 and1 when ,i take it out1 you will observe1 that1 instead of being wetted with a bluish liquid1 like that contained in the glass1 it will be covered with a thin coat of copper4 ,,caroline4 ,so it is really6 but then is it not the copper1 instead of the acid1 that has combined with the iron blade8 ,,mrs4 ,b4 ,no2 you are deceived by appearances3 it is the acid which combines with the iron1 and1 in so doing1 deposits or precipitates the copper on the surface of the blade4 ,,emily4 ,but1 cannot three or more substances combine together1 without any of them being precipitated8 ,,mrs4 ,b4 ,that is sometimes the case2 but1 in general1 the stronger affinity destroys the weaker2 and it seldom happens that the attraction of several substances for each other is so equally balanced as to produce such complicated compounds4 ,,caroline4 ,but1 pray1 ,mrs4 ,b41 what is the cause of the chemical attraction of bodies for each other8 ,it appears to me more extraordinary or unnatural1 if ,i may use the expression1 than the attraction of cohesion1 which unites particles of a similar nature4 ,,mrs4 ,b4 ,chemical attraction may1 like that of cohesion or gravitation1 be one of the powers inherent in matter which1 in our present state of knowledge1 admits of no other satisfactory explanation than an immediate reference to a divine cause4 ,sir ,h4 ,davy1 however1 whose important discoveries have opened such improved views in chemistry1 has suggested an hypothesis which may throw great light upon that science4 ,he supposes that there are two kinds of electricity1 with one or other of which all bodies are united4 ,these we distinguish by the names of positive and negative electricity2 those bodies are disposed to combine1 which possess opposite electricities1 as they are brought together by the attraction which these electricities have for each other4 ,but1 whether this hypothesis be altogether founded on truth or not1 it is impossible to question the great influence of electricity in chemical combinations4 ,,emily4 ,so1 that we must suppose that the two electricities always attract each other1 and thus compel the bodies in which they exist to combine8 ,,caroline4 ,and may not this be also the cause of the attraction of cohesion8 ,,mrs4 ,b4 ,no1 for in particles of the same nature the same electricities must prevail1 and it is only the different or opposite electric fluids that attract each other4 ,,caroline4 ,these electricities seem to me to be a kind of chemical spirit1 which animates the particles of bodies1 and draws them together4 ,,emily4 ,if it is known1 then1 with which of the electricities bodies are united1 it can be inferred which will1 and which will not1 combine together8 ,,mrs4 ,b4 ,certainly4 --,i should not omit to mention1 that some doubts have been entertained whether electricity be really a material agent1 or whether it might not be a power inherent in bodies1 similar to1 or1 perhaps identical with1 attraction4 ,,emily4 ,but what then would be the electric spark which is visible1 and must therefore be really material8 ,,mrs4 ,b4 ,what we call the electric spark1 may1 ,sir ,h4 ,davy says1 be merely the heat and light1 or fire produced by the chemical combinations with which these phenomena are always connected4 ,we will not1 however1 enter more fully on this important subject at present1 but reserve the principal facts which relate to it to a future conversation4 ,before we part1 however1 ,i must recommend you to fix in your memory the names of the simple bodies1 against our next interview4 ,,conversation ,,ii4 ,,on ,,light ,,and ,,heat ,,or ,,caloric4 ,,caroline4 ,we have learned by heart the names of all the simple bodies which you have enumerated1 and we are now ready to enter on the examination of each of them successively4 ,you will begin1 ,i suppose1 with ,,light8 ,,mrs4 ,b4 ,respecting the nature of light we have little more than conjectures4 ,it is considered by most philosophers as a real substance1 immediately emanating from the sun1 and from all luminous bodies1 from which it is projected in right lines with prodigious velocity4 ,light1 however1 being imponderable1 it cannot be confined and examined by itself2 and therefore it is to the effects it produces on other bodies1 rather than to its immediate nature1 that we must direct our attention4 ,the connection between light and heat is very obvious2 indeed1 it is such1 that it is extremely difficult to examine the one independently of the other4 ,,emily4 ,but1 is it possible to separate light from heat2 ,i thought they were only different degrees of the same thing1 fire8 ,,mrs4 ,b4 ,i told you that fire was not now considered as a simple element4 ,whether light and heat be altogether different agents1 or not1 ,i cannot pretend to decide2 but1 in many cases1 light may be separated from heat4 ,the first discovery of this was made by a celebrated ,swedish chemist1 ,scheele4 ,another very striking illustration of the separation of heat and light was long after pointed out by ,dr4 ,herschell4 ,this philosopher discovered that these two agents were emitted in the rays of the sun1 and that heat was less refrangible than light2 for1 in separating the different coloured rays of light by a prism 7as we did some time ago71 he found that the greatest heat was beyond the spectrum1 at a little distance from the red rays1 which1 you may recollect1 are the least refrangible4 ,,emily4 ,i should like to try that experiment4 ,,mrs4 ,b4 ,it is by no means an easy one3 the heat of a ray of light1 refracted by a prism1 is so small1 that it requires a very delicate thermometer to distinguish the difference of the degree of heat within and without the spectrum4 ,for in this experiment the heat is not totally separated from the light1 each coloured ray retaining a certain portion of it1 though the greatest part is not sufficiently refracted to fall within the spectrum4 ,,emily4 ,i suppose1 then1 that those coloured rays which are the least refrangible1 retain the greatest quantity of heat8 ,,mrs4 ,b4 ,they do so4 ,,emily4 ,though ,i no longer doubt that light and heat can be separated1 ,dr4 ,herschell's experiment does not appear to me to afford sufficient proof that they are essentially different2 for light1 which you call a simple body1 may likewise be divided into the various coloured rays4 ,,mrs4 ,b4 ,no doubt there must be some difference in the various coloured rays4 ,even their chemical powers are different4 ,the blue rays1 for instance1 have the greatest effect in separating oxygen from bodies1 as was found by ,scheele2 and there exist also1 as ,dr4 ,wollaston has shown1 rays more refrangible than the blue1 which produce the same chemical effect1 and1 what is very remarkable1 are invisible4 ,,emily4 ,do you think it possible that heat may be merely a modification of light8 ,,mrs4 ,b4 ,that is a supposition which1 in the present state of natural philosophy1 can neither be positively affirmed nor denied4 ,let us1 therefore1 instead of discussing theoretical points1 be contented with examining what is known respecting the chemical effects of light4 ,light is capable of entering into a kind of transitory union with certain substances1 and this is what has been called phosphorescence4 ,bodies that are possessed of this property1 after being exposed to the sun's rays1 appear luminous in the dark4 ,the shells of fish1 the bones of land animals1 marble1 limestone1 and a variety of combinations of earths1 are more or less powerfully phosphorescent4 ,,caroline4 ,i remember being much surprised last summer with the phosphorescent appearance of some pieces of rotten wood1 which had just been dug out of the ground2 they shone so bright that ,i at first supposed them to be glow-worms4 ,,emily4 ,and is not the light of a glow-worm of a phosphorescent nature8 ,,mrs4 ,b4 ,it is a very remarkable instance of phosphorescence in living animals2 this property1 however1 is not exclusively possessed by the glow-worm4 ,the insect called the lanthorn-fly1 which is peculiar to warm climates1 emits light as it flies1 producing in the dark a remarkably sparkling appearance4 ,but it is more common to see animal matter in a dead state possessed of a phosphorescent quality2 sea fish is often eminently so4 ,,emily4 ,i have heard that the sea has sometimes had the appearance of being illuminated1 and that the light is supposed to proceed from the spawn of fishes floating on its surface4 ,,mrs4 ,b4 ,this light is probably owing to that or some other animal matter4 ,sea water has been observed to become luminous from the substance of a fresh herring having been immersed in it2 and certain insects1 of the ,medusa kind1 are known to produce similar effects4 ,but the strongest phosphorescence is produced by chemical compositions prepared for the purpose1 the most common of which consists of oyster shells and sulphur1 and is known by the name of ,canton's ,phosphorus4 ,,emily4 ,i am rather surprised1 ,mrs4 ,b41 that you should have said so much of the light emitted by phosphorescent bodies without taking any notice of that which is produced by burning bodies4 ,,mrs4 ,b4 ,the light emitted by the latter is so intimately connected with the chemical history of combustion1 that ,i must defer all explanation of it till we come to the examination of that process1 which is one of the most interesting in chemical science4 ,light is an agent capable of producing various chemical changes4 ,it is essential to the welfare both of the animal and vegetable kingdoms2 for men and plants grow pale and sickly if deprived of its salutary influence4 ,it is likewise remarkable for its property of destroying colour1 which renders it of great consequence in the process of bleaching4 ,,emily4 ,is it not singular that light1 which in studying optics we were taught to consider as the source and origin of colours1 should have also the power of destroying them8 ,,caroline4 ,it is a fact1 however1 that we every day experience2 you know how it fades the colours of linens and silks4 ,,emily4 ,certainly4 ,and ,i recollect that endive is made to grow white instead of green1 by being covered up so as to exclude the light4 ,but by what means does light produce these effects8 ,,mrs4 ,b4 ,this ,i cannot attempt to explain to you until you have obtained a further knowledge of chemistry4 ,as the chemical properties of light can be accounted for only in their reference to compound bodies1 it would be useless to detain you any longer on this subject2 we may therefore pass on to the examination of heat1 or caloric1 with which we are somewhat better acquainted4 ,,heat and ,,light may be always distinguished by the different sensations they produce1 ,light affects the sense of sight2 ,caloric that of feeling2 the one produces ,vision1 the other the sensation of ,heat4 ,caloric is found to exist in a variety of forms or modifications1 and ,i think it will be best to consider it under the two following heads1 viz4 #a4 ,,free ,,or ,,radiant ,,caloric4 #b4 ,,combined ,,caloric4 ,the first1 ,,free or ,,radiant ,,caloric1 is also called ,,heat ,,of ,,temperature2 it comprehends all heat which is perceptible to the senses1 and affects the thermometer4 ,,emily4 ,you mean such as the heat of the sun1 of fire1 of candles1 of stoves2 in short1 of every thing that burns8 ,,mrs4 ,b4 ,and likewise of things that do not burn1 as1 for instance1 the warmth of the body2 in a word1 all heat that is sensible1 whatever may be its degree1 or the source from which it is derived4 ,,caroline4 ,what then are the other modifications of caloric8 ,it must be a strange kind of heat that cannot be perceived by our senses4 ,,mrs4 ,b4 ,none of the modifications of caloric should properly be called heat2 for heat1 strictly speaking1 is the sensation produced by caloric1 on animated bodies2 this word1 therefore1 in the accurate language of science1 should be confined to express the sensation4 ,but custom has adapted it likewise to inanimate matter1 and we say the heat of an oven1 the heat of the sun1 without any reference to the sensation which they are capable of exciting4 ,it was in order to avoid the confusion which arose from thus confounding the cause and effect1 that modern chemists adopted the new word caloric1 to denote the principle which produces heat2 yet they do not always1 in compliance with their own language1 limit the word heat to the expression of the sensation1 since they still frequently employ it in reference to the other modifications of caloric which are quite independent of sensation4 ,,caroline4 ,but you have not yet explained to us what these other modifications of caloric are4 ,,mrs4 ,b4 ,because you are not acquainted with the properties of free caloric1 and you know that we have agreed to proceed with regularity4 ,one of the most remarkable properties of free caloric is its power of dilating bodies4 ,this fluid is so extremely subtle1 that it enters and pervades all bodies whatever1 forces itself between their particles1 and not only separates them1 but frequently drives them asunder to a considerable distance from each other4 ,it is thus that caloric dilates or expands a body so as to make it occupy a greater space than it did before4 ,,emily4 ,the effect it has on bodies1 therefore1 is directly contrary to that of the attraction of cohesion2 the one draws the particles together1 the other drives them asunder4 ,,mrs4 ,b4 ,precisely4 ,there is a continual struggle between the attraction of aggregation1 and the expansive power of caloric2 and from the action of these two opposite forces1 result all the various forms of matter1 or degrees of consistence1 from the solid1 to the liquid and ariform state4 ,and accordingly we find that most bodies are capable of passing from one of these forms to the other1 merely in consequence of their receiving different quantities of caloric4 ,,caroline4 ,that is very curious2 but ,i think ,i understand the reason of it4 ,if a great quantity of caloric is added to a solid body1 it introduces itself between the particles in such a manner as to overcome1 in a considerable degree1 the attraction of cohesion2 and the body1 from a solid1 is then converted into a fluid4 ,,mrs4 ,b4 ,this is the case whenever a body is fused or melted2 but if you add caloric to a liquid1 can you tell me what is the consequence8 ,,caroline4 ,the caloric forces itself in greater abundance between the particles of the fluid1 and drives them to such a distance from each other1 that their attraction of aggregation is wholly destroyed3 the liquid is then transformed into vapour4 ,,mrs4 ,b4 ,very well2 and this is precisely the case with boiling water1 when it is converted into steam or vapour1 and with all bodies that assume an ariform state4 ,,emily4 ,i do not well understand the word ariform8 ,,mrs4 ,b4 ,any elastic fluid whatever1 whether it be merely vapour or permanent air1 is called ariform4 ,but each of these various states1 solid1 liquid1 and ariform1 admit of many different degrees of density1 or consistence1 still arising 7chiefly at least7 from the different quantities of caloric the bodies contain4 ,solids are of various degrees of density1 from that of gold1 to that of a thin jelly4 ,liquids1 from the consistence of melted glue1 or melted metals1 to that of ether1 which is the lightest of all liquids4 ,the different elastic fluids 7with which you are not yet acquainted7 are susceptible of no less variety in their degrees of density4 ,,emily4 ,but does not every individual body also admit of different degrees of consistence1 without changing its state8 ,,mrs4 ,b4 ,undoubtedly2 and this ,i can immediately show you by a very simple experiment4 ,this piece of iron now exactly fits the frame1 or ring1 made to receive it2 but if heated red hot1 it will no longer do so1 for its dimensions will be so much increased by the caloric that has penetrated into it1 that it will be much too large for the frame4 ,the iron is now red hot2 by applying it to the frame1 we shall see how much it is dilated4 ,,emily4 ,considerably so indeed6 ,i knew that heat had this effect on bodies1 but ,i did not imagine that it could be made so conspicuous4 ,,mrs4 ,b4 ,by means of this instrument 7called a ,pyrometer7 we may estimate1 in the most exact manner1 the various dilatations of any solid body by heat4 ,the body we are now going to submit to trial is this small iron bar2 ,i fix it to this apparatus1 7,,plate ,i4 ,fig4 #a47 and then heat it by lighting the three lamps beneath it3 when the bar expands1 it increases in length as well as thickness2 and1 as one end communicates with this wheel-work1 whilst the other end is fixed and immoveable1 no sooner does it begin to dilate than it presses against the wheel-work1 and sets in motion the index1 which points out the degrees of dilatation on the dial-plate4 ,illustration3 ,plate ,i4 ,vol4 ,i4 p4 #ch4 ,fig4 #a4 ,pyrometer4 ,a4,a ,bar of ,metal4 #a4b4c ,lamps burning4 ,b4,b ,wheel work4 ,c ,index4 ,fig4 #b ,a4,a ,glass tubes with bulbs4 ,b4,b ,glasses of water in which they are immersed4 ,,emily4 ,this is1 indeed1 a very curious instrument2 but ,i do not understand the use of the wheels3 would it not be more simple1 and answer the purpose equally well1 if the bar1 in dilating1 pressed against the index1 and put it in motion without the intervention of the wheels8 ,,mrs4 ,b4 ,the use of the wheels is merely to multiply the motion1 and therefore render the effect of the caloric more obvious2 for if the index moved no more than the bar increased in length1 its motion would scarcely be perceptible2 but by means of the wheels it moves in a much greater proportion1 which therefore renders the variations far more conspicuous4 ,by submitting different bodies to the test of the pyrometer1 it is found that they are far from dilating in the same proportion4 ,different metals expand in different degrees1 and other kinds of solid bodies vary still more in this respect4 ,but this different susceptibility of dilatation is still more remarkable in fluids than in solid bodies1 as ,i shall show you4 ,i have here two glass tubes1 terminated at one end by large bulbs4 ,we shall fill the bulbs1 the one with spirit of wine1 the other with water4 ,i have coloured both liquids1 in order that the effect may be more conspicuous4 ,the spirit of wine1 you see1 dilates by the warmth of my hand as ,i hold the bulb4 ,,emily4 ,it certainly does1 for ,i see it is rising into the tube4 ,but water1 it seems1 is not so easily affected by heat2 for scarcely any change is produced on it by the warmth of the hand4 ,,mrs4 ,b4 ,true2 we shall now plunge the bulbs into hot water1 7,,plate ,i4 ,fig4 #b47 and you will see both liquids rise in the tubes2 but the spirit of wine will ascend highest4 ,,caroline4 ,how rapidly it expands6 ,now it has nearly reached the top of the tube1 though the water has hardly begun to rise4 ,,emily4 ,the water now begins to dilate4 ,are not these glass tubes1 with liquids rising within them1 very like thermometers8 ,,mrs4 ,b4 ,a thermometer is constructed exactly on the same principle1 and these tubes require only a scale to answer the purpose of thermometers3 but they would be rather awkward in their dimensions4 ,the tubes and bulbs of thermometers1 though of various sizes1 are in general much smaller than these2 the tube too is hermetically closed1 and the air excluded from it4 ,the fluid most generally used in thermometers is mercury1 commonly called quicksilver1 the dilatations and contractions of which correspond more exactly to the additions1 and subtractions1 of caloric1 than those of any other fluid4 ,,caroline4 ,yet ,i have often seen coloured spirit of wine used in thermometers4 ,,mrs4 ,b4 ,the expansions and contractions of that liquid are not quite so uniform as those of mercury2 but in cases in which it is not requisite to ascertain the temperature with great precision1 spirit of wine will answer the purpose equally well1 and indeed in some respects better1 as the expansion of the latter is greater1 and therefore more conspicuous4 ,this fluid is used likewise in situations and experiments in which mercury would be frozen2 for mercury becomes a solid body1 like a piece of lead or any other metal1 at a certain degree of cold3 but no degree of cold has ever been known to freeze spirit of wine4 ,a thermometer1 therefore1 consists of a tube with a bulb1 such as you see here1 containing a fluid whose degrees of dilatation and contraction are indicated by a scale to which the tube is fixed4 ,the degree which indicates the boiling point1 simply means that1 when the fluid is sufficiently dilated to rise to this point1 the heat is such that water exposed to the same temperature will boil4 ,when1 on the other hand1 the fluid is so much condensed as to sink to the freezing point1 we know that water will freeze at that temperature4 ,the extreme points of the scales are not the same in all thermometers1 nor are the degrees always divided in the same manner4 ,in different countries philosophers have chosen to adopt different scales and divisions4 ,the two thermometers most used are those of ,fahrenheit1 and of ,reaumur2 the first is generally preferred by the ,english1 the latter by the ,french4 ,,emily4 ,the variety of scale must be very inconvenient1 and ,i should think liable to occasion confusion1 when ,french and ,english experiments are compared4 ,,mrs4 ,b4 ,the inconvenience is but very trifling1 because the different gradations of the scales do not affect the principle upon which thermometers are constructed4 ,when we know1 for instance1 that ,fahrenheit's scale is divided into #bab degrees1 in which #cb corresponds with the freezing point1 and #bab with the point of boiling water3 and that ,reaumur's is divided only into #hj degrees1 in which #j denotes the freezing point1 and #hj that of boiling water1 it is easy to compare the two scales together1 and reduce the one into the other4 ,but1 for greater convenience1 thermometers are sometimes constructed with both these scales1 one on either side of the tube2 so that the correspondence of the different degrees of the two scales is thus instantly seen4 ,here is one of these scales1 7,,plate ,,ii4 ,fig4 #a47 by which you can at once perceive that each degree of ,reaumur's corresponds to #b of ,fahrenheit's division4 ,but ,i believe the ,french have1 of late1 given the preference to what they call the centigrade scale1 in which the space between the freezing and the boiling point is divided into #ajj degrees4 ,illustration3 ,plate ,,ii4 ,vol4 ,i4 p4 #db4 ,fig4 #a4 ,thermometer4 ,fahrenheit's ,scale4 ,reaumur's ,scale4 ,boiling point of ,water ,freezing point of ,water ,fig4 #b4 ,differential ,thermometer4 ,,caroline4 ,that seems to me the most reasonable division1 and ,i cannot guess why the freezing point is called #cb1 or what advantage is derived from it4 ,,mrs4 ,b4 ,there really is no advantage in it2 and it originated in a mistaken opinion of the instrument-maker1 ,fahrenheit1 who first constructed these thermometers4 ,he mixed snow and salt together1 and produced by that means a degree of cold which he concluded was the greatest possible1 and therefore made his scale begin from that point4 ,between that and boiling water he made #bab degrees1 and the freezing point was found to be at #cb4 ,,emily4 ,are spirit of wine1 and mercury1 the only liquids used in the construction of thermometers8 ,,mrs4 ,b4 ,i believe they are the only liquids now in use1 though some others1 such as linseed oil1 would make tolerable thermometers3 but for experiments in which a very quick and delicate test of the changes of temperature is required1 air is the fluid sometimes employed4 ,the bulb of air thermometers is filled with common air only1 and its expansion and contraction are indicated by a small drop of any coloured liquor1 which is suspended within the tube1 and moves up and down1 according as the air within the bulb and tube expands or contracts4 ,but in general1 air thermometers1 however sensible to changes of temperature1 are by no means accurate in their indications4 ,i can1 however1 show you an air thermometer of a very peculiar construction1 which is remarkably well adapted for some chemical experiments1 as it is equally delicate and accurate in its indications4 ,,caroline4 ,it looks like a double thermometer reversed1 the tube being bent1 and having a large bulb at each of its extremities4 7,,plate ,,ii4 ,fig4 #b47 ,,emily4 ,why do you call it an air thermometer2 the tube contains a coloured liquid8 ,,mrs4 ,b4 ,but observe that the bulbs are filled with air1 the liquid being confined to a portion of the tube1 and answering only the purpose of showing1 by its motion in the tube1 the comparative dilatation or contraction of the air within the bulbs1 which afford an indication of their relative temperature4 ,thus if you heat the bulb ,a1 by the warmth of your hand1 the fluid will rise towards the bulb ,b1 and the contrary will happen if you reverse the experiment4 ,but if1 on the contrary1 both tubes are of the same temperature1 as is the case now1 the coloured liquid1 suffering an equal pressure on each side1 no change of level takes place4 ,,caroline4 ,this instrument appears1 indeed1 uncommonly delicate4 ,the fluid is set in motion by the mere approach of my hand4 ,,mrs4 ,b4 ,you must observe1 however1 that this thermometer cannot indicate the temperature of any particular body1 or of the medium in which it is immersed2 it serves only to point out the difference of temperature between the two bulbs1 when placed under different circumstances4 ,for this reason it has been called differential thermometer4 ,you will see by-and-bye to what particular purposes this instrument applies4 ,,emily4 ,but do common thermometers indicate the exact quantity of caloric contained either in the atmosphere1 or in any body with which they are in contact8 ,,mrs4 ,b4 ,no3 first1 because there are other modifications of caloric which do not affect the thermometer2 and1 secondly1 because the temperature of a body1 as indicated by the thermometer1 is only relative4 ,when1 for instance1 the thermometer remains stationary at the freezing point1 we know that the atmosphere 7or medium in which it is placed1 whatever it may be7 is as cold as freezing water2 and when it stands at the boiling point1 we know that this medium is as hot as boiling water2 but we do not know the positive quantity of heat contained either in freezing or boiling water1 any more than we know the real extremes of heat and cold2 and consequently we cannot determine that of the body in which the thermometer is placed4 ,,caroline4 ,i do not quite understand this explanation4 ,,mrs4 ,b4 ,let us compare a thermometer to a well1 in which the water rises to different heights1 according as it is more or less supplied by the spring which feeds it3 if the depth of the well is unfathomable1 it must be impossible to know the absolute quantity of water it contains2 yet we can with the greatest accuracy measure the number of feet the water has risen or fallen in the well at any time1 and consequently know the precise quantity of its increase or diminution1 without having the least knowledge of the whole quantity of water it contains4 ,,caroline4 ,now ,i comprehend it very well2 nothing appears to me to explain a thing so clearly as a comparison4 ,,emily4 ,but will thermometers bear any degree of heat8 ,,mrs4 ,b4 ,no2 for if the temperature were much above the highest degree marked on the scale of the thermometer1 the mercury would burst the tube in an attempt to ascend4 ,and at any rate1 no thermometer can be applied to temperatures higher than the boiling point of the liquid used in its construction1 for the steam1 on the liquid beginning to boil1 would burst the tube4 ,in furnaces1 or whenever any very high temperature is to be measured1 a pyrometer1 invented by ,wedgwood1 is used for that purpose4 ,it is made of a certain composition of baked clay1 which has the peculiar property of contracting by heat1 so that the degree of contraction of this substance indicates the temperature to which it has been exposed4 ,,emily4 ,but is it possible for a body to contract by heat8 ,i thought that heat dilated all bodies whatever4 ,,mrs4 ,b4 ,this is not an exception to the rule4 ,you must recollect that the bulk of the clay is not compared1 whilst hot1 with that which it has when cold2 but it is from the change which the clay has undergone by having been heated that the indications of this instrument are derived4 ,this change consists in a beginning fusion which tends to unite the particles of clay more closely1 thus rendering it less pervious or spongy4 ,clay is to be considered as a spongy body1 having many interstices or pores1 from its having contained water when soft4 ,these interstices are by heat lessened1 and would by extreme heat be entirely obliterated4 ,,caroline4 ,and how do you ascertain the degrees of contraction of ,wedgwood's pyrometer8 ,,mrs4 ,b4 ,the dimensions of a piece of clay are measured by a scale graduated on the side of a tapered groove1 formed in a brass ruler2 the more the clay is contracted by the heat1 the further it will descend into the narrow part of the tube4 ,before we quit the subject of expansion1 ,i must observe to you that1 as liquids expand more readily than solids1 so elastic fluids1 whether air or vapour1 are the most expansible of all bodies4 ,it may appear extraordinary that all elastic fluids whatever1 undergo the same degree of expansion from equal augmentations of temperature4 ,,emily4 ,i suppose1 then1 that all elastic fluids are of the same density8 ,,mrs4 ,b4 ,very far from it2 they vary in density1 more than either liquids or solids4 ,the uniformity of their expansibility1 which at first may appear singular1 is1 however1 readily accounted for4 ,for if the different susceptibilities of expansion of bodies arise from their various degrees of attraction of cohesion1 no such difference can be expected in elastic fluids1 since in these the attraction of cohesion does not exist1 their particles being on the contrary possessed of an elastic or repulsive power2 they will therefore all be equally expanded by equal degrees of caloric4 ,,emily4 ,true2 as there is no power opposed to the expansive force of caloric in elastic bodies1 its effect must be the same in all of them4 ,,mrs4 ,b4 ,let us now proceed to examine the other properties of free caloric4 ,free caloric always tends to diffuse itself equally1 that is to say1 when two bodies are of different temperatures1 the warmer gradually parts with its heat to the colder1 till they are both brought to the same temperature4 ,thus1 when a thermometer is applied to a hot body1 it receives caloric2 when to a cold one1 it communicates part of its own caloric1 and this communication continues until the thermometer and the body arrive at the same temperature4 ,,emily4 ,cold1 then1 is nothing but a negative quality1 simply implying the absence of heat4 ,,mrs4 ,b4 ,not the total absence1 but a diminution of heat2 for we know of no body in which some caloric may not be discovered4 ,,caroline4 ,but when ,i lay my hand on this marble table ,i feel it positively cold1 and cannot conceive that there is any caloric in it4 ,,mrs4 ,b4 ,the cold you experience consists in the loss of caloric that your hand sustains in an attempt to bring its temperature to an equilibrium with the marble4 ,if you lay a piece of ice upon it1 you will find that the contrary effect will take place2 the ice will be melted by the heat which it abstracts from the marble4 ,,caroline4 ,is it not in this case the air of the room1 which being warmer than the marble1 melts the ice8 ,,mrs4 ,b4 ,the air certainly acts on the surface which is exposed to it1 but the table melts that part with which it is in contact4 ,,caroline4 ,but why does caloric tend to an equilibrium8 ,it cannot be on the same principle as other fluids1 since it has no weight8 ,,mrs4 ,b4 ,very true1 ,caroline1 that is an excellent objection4 ,you might also1 with some propriety1 object to the term equilibrium being applied to a body that is without weight2 but ,i know of no expression that would explain my meaning so well4 ,you must consider it1 however1 in a figurative rather than a literal sense2 its strict meaning is an equal diffusion4 ,we cannot1 indeed1 well say by what power it diffuses itself equally1 though it is not surprising that it should go from the parts which have the most to those which have the least4 ,this subject is best explained by a theory suggested by ,professor ,prevost of ,geneva1 which is now1 ,i believe1 generally adopted4 ,according to this theory1 caloric is composed of particles perfectly separate from each other1 every one of which moves with a rapid velocity in a certain direction4 ,these directions vary as much as imagination can conceive1 the result of which is1 that there are rays or lines of these particles moving with immense velocity in every possible direction4 ,caloric is thus universally diffused1 so that when any portion of space happens to be in the neighbourhood of another1 which contains more caloric1 the colder portion receives a quantity of calorific rays from the latter1 sufficient to restore an equilibrium of temperature4 ,this radiation does not only take place in free space1 but extends also to bodies of every kind4 ,thus you may suppose all bodies whatever constantly radiating caloric3 those that are of the same temperature give out and absorb equal quantities1 so that no variation of temperature is produced in them2 but when one body contains more free caloric than another1 the exchange is always in favour of the colder body1 until an equilibrium is effected2 this you found to be the case when the marble table cooled your hand1 and again when it melted the ice4 ,,caroline4 ,this reciprocal radiation surprises me extremely2 ,i thought1 from what you first said1 that the hotter bodies alone emitted rays of caloric which were absorbed by the colder2 for it seems unnatural that a hot body should receive any caloric from a cold one1 even though it should return a greater quantity4 ,,mrs4 ,b4 ,it may at first appear so1 but it is no more extraordinary than that a candle should send forth rays of light to the sun1 which1 you know1 must necessarily happen4 ,,caroline4 ,well1 ,mrs4 ,b--1 ,i believe that ,i must give up the point4 ,but ,i wish ,i could see these rays of caloric2 ,i should then have greater faith in them4 ,,mrs4 ,b4 ,will you give no credit to any sense but that of sight8 ,you may feel the rays of caloric which you receive from any body of a temperature higher than your own2 the loss of the caloric you part with in return1 it is true1 is not perceptible2 for as you gain more than you lose1 instead of suffering a diminution1 you are really making an acquisition of caloric4 ,it is1 therefore1 only when you are parting with it to a body of a lower temperature1 that you are sensible of the sensation of cold1 because you then sustain an absolute loss of caloric4 ,,emily4 ,and in this case we cannot be sensible of the small quantity of heat we receive in exchange from the colder body1 because it serves only to diminish the loss4 ,,mrs4 ,b4 ,very well1 indeed1 ,emily4 ,professor ,pictet1 of ,geneva1 has made some very interesting experiments1 which prove not only that caloric radiates from all bodies whatever1 but that these rays may be reflected1 according to the laws of optics1 in the same manner as light4 ,i shall repeat these experiments before you1 having procured mirrors fit for the purpose2 and it will afford us an opportunity of using the differential thermometer1 which is particularly well adapted for these experiments4 --,i place an iron bullet1 7,,plate ,,iii4 ,fig4 #a47 about two inches in diameter1 and heated to a degree not sufficient to render it luminous1 in the focus of this large metallic concave mirror4 ,the rays of heat which fall on this mirror are reflected1 agreeably to the property of concave mirrors1 in a parallel direction1 so as to fall on a similar mirror1 which1 you see1 is placed opposite to the first1 at the distance of about ten feet2 thence the rays converge to the focus of the second mirror1 in which ,i place one of the bulbs of this thermometer4 ,now1 observe in what manner it is affected by the caloric which is reflected on it from the heated bullet4 --,the air is dilated in the bulb which we placed in the focus of the mirror1 and the liquor rises considerably in the opposite leg4 ,illustration3 ,plate ,,iii4 ,vol4 ,i4 p4 #ed ,mr4 ,pictet's ,apparatus for the ,reflection of ,heat4 ,fig4 #a4 ,a4,a4 ,b4,b ,concave mirrors fixed on stands4 ,c ,heated ,bullet placed in the focus of the mirror ,a4 ,d ,thermometer1 with its bulb placed in the focus of the mirror ,b4 #a4b4c4d ,rays of ,caloric radiating from the bullet falling on the mirror ,a4 #e4f4g4h ,the same rays reflected from the mirror ,a to the mirror ,b4 #i4aj4aa4ab ,the same rays reflected by the mirror ,b to the ,thermometer4 ,,emily4 ,but would not the same effect take place1 if the rays of caloric from the heated bullet fell directly on the thermometer1 without the assistance of the mirrors8 ,,mrs4 ,b4 ,the effect would in that case be so trifling1 at the distance at which the bullet and the thermometer are from each other1 that it would be almost imperceptible4 ,the mirrors1 you know1 greatly increase the effect1 by collecting a large quantity of rays into a focus2 place your hand in the focus of the mirror1 and you will find it much hotter there than when you remove it nearer to the bullet4 ,,emily4 ,that is very true2 it appears extremely singular to feel the heat diminish in approaching the body from which it proceeds4 ,,caroline4 ,and the mirror which produces so much heat1 by converging the rays1 is itself quite cold4 ,,mrs4 ,b4 ,the same number of rays that are dispersed over the surface of the mirror are collected by it into the focus2 but1 if you consider how large a surface the mirror presents to the rays1 and1 consequently1 how much they are diffused in comparison to what they are at the focus1 which is little more than a point1 ,i think you can no longer wonder that the focus should be so much hotter than the mirror4 ,the principal use of the mirrors in this experiment is1 to prove that the calorific emanation is reflected in the same manner as light4 ,,caroline4 ,and the result1 ,i think1 is very conclusive4 ,,mrs4 ,b4 ,the experiment may be repeated with a wax taper instead of the bullet1 with a view of separating the light from the caloric4 ,for this purpose a transparent plate of glass must be interposed between the mirrors2 for light1 you know1 passes with great facility through glass1 whilst the transmission of caloric is almost wholly impeded by it4 ,we shall find1 however1 in this experiment1 that some few of the calorific rays pass through the glass together with the light1 as the thermometer rises a little2 but1 as soon as the glass is removed1 and a free passage left to the caloric1 it will rise considerably higher4 ,,emily4 ,this experiment1 as well as that of ,dr4 ,herschell's1 proves that light and heat may be separated2 for in the latter experiment the separation was not perfect1 any more than in that of ,mr4 ,pictet4 ,,caroline4 ,i should like to repeat this experiment1 with the difference of substituting a cold body instead of the hot one1 to see whether cold would not be reflected as well as heat4 ,,mrs4 ,b4 ,that experiment was proposed to ,mr4 ,pictet by an incredulous philosopher like yourself1 and he immediately tried it by substituting a piece of ice in the place of the heated bullet4 ,,caroline4 ,well1 ,mrs4 ,b41 and what was the result8 ,,mrs4 ,b4 ,that we shall see2 ,i have procured some ice for the purpose4 ,,emily4 ,the thermometer falls considerably6 ,,caroline4 ,and does not that prove that cold is not merely a negative quality1 implying simply an inferior degree of heat8 ,the cold must be positive1 since it is capable of reflection4 ,,mrs4 ,b4 ,so it at first appeared to ,mr4 ,pictet2 but upon a little consideration he found that it afforded only an additional proof of the reflection of heat3 this ,i shall endeavour to explain to you4 ,according to ,mr4 ,prevost's theory1 we suppose that all bodies whatever radiate caloric2 the thermometer used in these experiments therefore emits calorific rays in the same manner as any other substance4 ,when its temperature is in equilibrium with that of the surrounding bodies1 it receives as much caloric as it parts with1 and no change of temperature is produced4 ,but when we introduce a body of a lower temperature1 such as a piece of ice1 which parts with less caloric than it receives1 the consequence is1 that its temperature is raised1 whilst that of the surrounding bodies is proportionally lowered4 ,,emily4 ,if1 for instance1 ,i was to bring a large piece of ice into this room1 the ice would in time be melted1 by absorbing caloric from the general radiation which is going on throughout the room2 and as it would contribute very little caloric in return for what is absorbed1 the room would necessarily be cooled by it4 ,,mrs4 ,b4 ,just so2 and as in consequence of the mirrors1 a more considerable exchange of rays takes place between the ice and the thermometer1 than between these and any of the surrounding bodies1 the temperature of the thermometer must be more lowered than that of any other adjacent object4 ,,caroline4 ,i confess ,i do not perfectly understand your explanation4 ,,mrs4 ,b4 ,this experiment is exactly similar to that made with the heated bullet3 for1 if we consider the thermometer as the hot body 7which it certainly is in comparison to the ice71 you may then easily understand that it is by the loss of the calorific rays which the thermometer sends to the ice1 and not by any cold rays received from it1 that the fall of the mercury is occasioned3 for the ice1 far from emitting rays of cold1 sends forth rays of caloric1 which diminish the loss sustained by the thermometer4 ,let us say1 for instance1 that the radiation of the thermometer towards the ice is equal to #bj1 and that of the ice towards the thermometer to #aj3 the exchange in favour of the ice is as #bj is to #aj1 or the thermometer absolutely loses #aj1 whilst the ice gains #aj4 ,,caroline4 ,but if the ice actually sends rays of caloric to the thermometer1 must not the latter fall still lower when the ice is removed8 ,,mrs4 ,b4 ,no2 for the space that the ice occupied1 admits rays from all the surrounding bodies to pass through it2 and those being of the same temperature as the thermometer1 will not affect it1 because as much heat now returns to the thermometer as radiates from it4 ,,caroline4 ,i must confess that you have explained this in so satisfactory a manner1 that ,i cannot help being convinced now that cold has no real claim to the rank of a positive being4 ,,mrs4 ,b4 ,before ,i conclude the subject of radiation ,i must observe to you that different bodies1 7or rather surfaces17 possess the power of radiating caloric in very different degrees4 ,some very curious experiments have been made by ,mr4 ,leslie on this subject1 and it was for this purpose that he invented the differential thermometer2 with its assistance he ascertained that black surfaces radiate most1 glass next1 and polished surfaces the least of all4 ,,emily4 ,supposing these surfaces1 of course1 to be all of the same temperature4 ,,mrs4 ,b4 ,undoubtedly4 ,i will now show you the very simple and ingenious apparatus1 by means of which he made these experiments4 ,this cubical tin vessel or canister1 has each of its sides externally covered with different materials2 the one is simply blackened2 the next is covered with white paper2 the third with a pane of glass1 and in the fourth the polished tin surface remains uncovered4 ,we shall fill this vessel with hot water1 so that there can be no doubt but that all its sides will be of the same temperature4 ,now let us place it in the focus of one of the mirrors1 making each of its sides front it in succession4 ,we shall begin with the black surface4 ,,caroline4 ,it makes the thermometer which is in the focus of the other mirror rise considerably4 ,let us turn the paper surface towards the mirror4 ,the thermometer falls a little1 therefore of course this side cannot emit or radiate so much caloric as the blackened side4 ,,emily4 ,this is very surprising2 for the sides are exactly of the same size1 and must be of the same temperature4 ,but let us try the glass surface4 ,,mrs4 ,b4 ,the thermometer continues falling1 and with the plain surface it falls still lower2 these two surfaces therefore radiate less and less4 ,,caroline4 ,i think ,i have found out the reason of this4 ,,mrs4 ,b4 ,i should be very happy to hear it1 for it has not yet 7to my knowledge7 been accounted for4 ,,caroline4 ,the water within the vessel gradually cools1 and the thermometer in consequence gradually falls4 ,,mrs4 ,b4 ,it is true that the water cools1 but certainly in much less proportion than the thermometer descends1 as you will perceive if you now change the tin surface for the black one4 ,,caroline4 ,i was mistaken certainly1 for the thermometer rises again now that the black surface fronts the mirror4 ,,mrs4 ,b4 ,and yet the water in the vessel is still cooling1 ,caroline4 ,,emily4 ,i am surprised that the tin surface should radiate the least caloric1 for a metallic vessel filled with hot water1 a silver teapot1 for instance1 feels much hotter to the hand than one of black earthen ware4 ,,mrs4 ,b4 ,that is owing to the different power which various bodies possess for conducting caloric1 a property which we shall presently examine4 ,thus1 although a metallic vessel feels warmer to the hand1 a vessel of this kind is known to preserve the heat of the liquid within1 better than one of any other materials2 it is for this reason that silver teapots make better tea than those of earthen ware4 ,,emily4 ,according to these experiments1 light-coloured dresses1 in cold weather1 should keep us warmer than black clothes1 since the latter radiate so much more than the former4 ,,mrs4 ,b4 ,and that is actually the case4 ,,emily4 ,this property1 of different surfaces to radiate in different degrees1 appears to me to be at variance with the equilibrium of caloric2 since it would imply that those bodies which radiate most1 must ultimately become coldest4 ,suppose that we were to vary this experiment1 by using two metallic vessels full of boiling water1 the one blackened1 the other not2 would not the black one cool the first8 ,,caroline4 ,true2 but when they were both brought down to the temperature of the room1 the interchange of caloric between the canisters and the other bodies of the room being then equal1 their temperatures would remain the same4 ,,emily4 ,i do not see why that should be the case2 for if different surfaces of the same temperature radiate in different degrees when heated1 why should they not continue to do so when cooled down to the temperature of the room8 ,,mrs4 ,b4 ,you have started a difficulty1 ,emily1 which certainly requires explanation4 ,it is found by experiment that the power of absorption corresponds with and is proportional to that of radiation2 so that under equal temperatures1 bodies compensate for the greater loss they sustain in consequence of their greater radiation by their greater absorption2 so that if you were to make your experiment in an atmosphere heated like the canisters1 to the temperature of boiling water1 though it is true that the canisters would radiate in different degrees1 no change of temperature would be produced in them1 because they would each absorb caloric in proportion to their respective radiation4 ,,emily4 ,but would not the canisters of boiling water also absorb caloric in different degrees in a room of the common temperature8 ,,mrs4 ,b4 ,undoubtedly they would4 ,but the various bodies in the room would not1 at a lower temperature1 furnish either of the canisters with a sufficiency of caloric to compensate for the loss they undergo2 for1 suppose the black canister to absorb #djj rays of caloric1 whilst the metallic one absorbed only #bjj2 yet if the former radiate #hjj1 whilst the latter radiates only #djj1 the black canister will be the first cooled down to the temperature of the room4 ,but from the moment the equilibrium of temperature has taken place1 the black canister1 both receiving and giving out #djj rays1 and the metallic one #bjj1 no change of temperature will take place4 ,,emily4 ,i now understand it extremely well4 ,but what becomes of the surplus of calorific rays1 which good radiators emit and bad radiators refuse to receive2 they must wander about in search of a resting-place8 ,,mrs4 ,b4 ,they really do so2 for they are rejected and sent back1 or1 in other words1 reflected by the bodies which are bad radiators of caloric2 and they are thus transmitted to other bodies which happen to lie in their way1 by which they are either absorbed or again reflected1 according as the property of reflection1 or that of absorption1 predominates in these bodies4 ,,caroline4 ,i do not well understand the difference between radiating and reflecting caloric1 for the caloric that is reflected from a body proceeds from it in straight lines1 and may surely be said to radiate from it8 ,,mrs4 ,b4 ,it is true that there at first appears to be a great analogy between radiation and reflection1 as they equally convey the idea of the transmission of caloric4 ,but if you consider a little1 you will perceive that when a body radiates caloric1 the heat which it emits not only proceeds from1 but has its origin in the body itself4 ,whilst when a body reflects caloric1 it parts with none of its own caloric1 but only reflects that which it receives from other bodies4 ,,emily4 ,of this difference we have very striking examples before us1 in the tin vessel of water1 and the concave mirrors2 the first radiates its own heat1 the latter reflect the heat which they receive from other bodies4 ,,caroline4 ,now1 that ,i understand the difference1 it no longer surprises me that bodies which radiate1 or part with their own caloric freely1 should not have the power of transmitting with equal facility that which they receive from other bodies4 ,,emily4 ,yet no body can be said to possess caloric of its own1 if all caloric is originally derived from the sun4 ,,mrs4 ,b4 ,when ,i speak of a body radiating its own caloric1 ,i mean that which it has absorbed and incorporated either immediately from the sun's rays1 or through the medium of any other substance4 ,,caroline4 ,it seems natural enough that the power of absorption should be in opposition to that of reflection1 for the more caloric a body receives1 the less it will reject4 ,,emily4 ,and equally so that the power of radiation should correspond with that of absorption4 ,it is1 in fact1 cause and effect2 for a body cannot radiate heat without having previously absorbed it2 just as a spring that is well fed flows abundantly4 ,,mrs4 ,b4 ,fluids are in general very bad radiators of caloric2 and air neither radiates nor absorbs caloric in any sensible degree4 ,we have not yet concluded our observations on free caloric4 ,but ,i shall defer1 till our next meeting1 what ,i have further to say on this subject4 ,i believe it will afford us ample conversation for another interview4 ,,conversation ,,iii4 ,,continuation ,,of ,,the ,,subject4 ,,mrs4 ,b4 ,in our last conversation1 we began to examine the tendency of caloric to restore an equilibrium of temperature4 ,this property1 when once well understood1 affords the explanation of a great variety of facts which appeared formerly unaccountable4 ,you must observe1 in the first place1 that the effect of this tendency is gradually to bring all bodies that are in contact to the same temperature4 ,thus1 the fire which burns in the grate1 communicates its heat from one object to another1 till every part of the room has an equal proportion of it4 ,,emily4 ,and yet this book is not so cold as the table on which it lies1 though both are at an equal distance from the fire1 and actually in contact with each other1 so that1 according to your theory1 they should be exactly of the same temperature4 ,,caroline4 ,and the hearth1 which is much nearer the fire than the carpet1 is certainly the colder of the two4 ,,mrs4 ,b4 ,if you ascertain the temperature of these several bodies by a thermometer 7which is a much more accurate test than your feeling71 you will find that it is exactly the same4 ,,caroline4 ,but if they are of the same temperature1 why should the one feel colder than the other8 ,,mrs4 ,b4 ,the hearth and the table feel colder than the carpet or the book1 because the latter are not such good conductors of heat as the former4 ,caloric finds a more easy passage through marble and wood1 than through leather and worsted2 the two former will therefore absorb heat more rapidly from your hand1 and consequently give it a stronger sensation of cold than the two latter1 although they are all of them really of the same temperature4 ,,caroline4 ,so1 then1 the sensation ,i feel on touching a cold body1 is in proportion to the rapidity with which my hand yields its heat to that body8 ,,mrs4 ,b4 ,precisely2 and1 if you lay your hand successively on every object in the room1 you will discover which are good1 and which are bad conductors of heat1 by the different degrees of cold you feel4 ,but1 in order to ascertain this point1 it is necessary that the several substances should be of the same temperature1 which will not be the case with those that are very near the fire1 or those that are exposed to a current of cold air from a window or door4 ,,emily4 ,but what is the reason that some bodies are better conductors of heat than others8 ,,mrs4 ,b4 ,this is a point not well ascertained4 ,it has been conjectured that a certain union or adherence takes place between the caloric and the particles of the body through which it passes4 ,if this adherence be strong1 the body detains the heat1 and parts with it slowly and reluctantly2 if slight1 it propagates it freely and rapidly4 ,the conducting power of a body is therefore1 inversely1 as its tendency to unite with caloric4 ,,emily4 ,that is to say1 that the best conductors are those that have the least affinity for caloric4 ,,mrs4 ,b4 ,yes2 but the term affinity is objectionable in this case1 because1 as that word is used to express a chemical attraction 7which can be destroyed only by decomposition71 it cannot be applicable to the slight and transient union that takes place between free caloric and the bodies through which it passes2 an union which is so weak1 that it constantly yields to the tendency which caloric has to an equilibrium4 ,now you clearly understand1 that the passage of caloric1 through bodies that are good conductors1 is much more rapid than through those that are bad conductors1 and that the former both give and receive it more quickly1 and therefore1 in a given time1 more abundantly1 than bad conductors1 which makes them feel either hotter or colder1 though they may be1 in fact1 both of the same temperature4 ,,caroline4 ,yes1 ,i understand it now2 the table1 and the book lying upon it1 being really of the same temperature1 would each receive1 in the same space of time1 the same quantity of heat from my hand1 were their conducting powers equal2 but as the table is the best conductor of the two1 it will absorb the heat from my hand more rapidly1 and consequently produce a stronger sensation of cold than the book4 ,,mrs4 ,b4 ,very well1 my dear2 and observe1 likewise1 that if you were to heat the table and the book an equal number of degrees above the temperature of your body1 the table1 which before felt the colder1 would now feel the hotter of the two2 for1 as in the first case it took the heat most rapidly from your hand1 so it will now impart heat most rapidly to it4 ,thus the marble table1 which seems to us colder than the mahogany one1 will prove the hotter of the two to the ice2 for1 if it takes heat more rapidly from our hands1 which are warmer1 it will give out heat more rapidly to the ice1 which is colder4 ,do you understand the reason of these apparently opposite effects8 ,,emily4 ,perfectly4 ,a body which is a good conductor of caloric1 affords it a free passage2 so that it penetrates through that body more rapidly than through one which is a bad conductor2 and consequently1 if it is colder than your hand1 you lose more caloric1 and if it is hotter1 you gain more than with a bad conductor of the same temperature4 ,,mrs4 ,b4 ,but you must observe that this is the case only when the conductors are either hotter or colder than your hand2 for1 if you heat different conductors to the temperature of your body1 they will all feel equally warm1 since the exchange of caloric between bodies of the same temperature is equal4 ,now1 can you tell me why flannel clothing1 which is a very bad conductor of heat1 prevents our feeling cold8 ,,caroline4 ,it prevents the cold from penetrating 4 4 4 4 4 4 4 4 ,,mrs4 ,b4 ,but you forget that cold is only a negative quality4 ,,caroline4 ,true2 it only prevents the heat of our bodies from escaping so rapidly as it would otherwise do4 ,,mrs4 ,b4 ,now you have explained it right2 the flannel rather keeps in the heat1 than keeps out the cold4 ,were the atmosphere of a higher temperature than our bodies1 it would be equally efficacious in keeping their temperature at the same degree1 as it would prevent the free access of the external heat1 by the difficulty with which it conducts it4 ,,emily4 ,this1 ,i think1 is very clear4 ,heat1 whether external or internal1 cannot easily penetrate flannel2 therefore in cold weather it keeps us warm2 and if the weather was hotter than our bodies1 it would keep us cool4 ,,mrs4 ,b4 ,the most dense bodies are1 generally speaking1 the best conductors of heat2 probably because the denser the body the greater are the number of points or particles that come in contact with caloric4 ,at the common temperature of the atmosphere a piece of metal will feel much colder than a piece of wood1 and the latter than a piece of woollen cloth2 this again will feel colder than flannel2 and down1 which is one of the lightest1 is at the same time one of the warmest bodies4 ,,caroline4 ,this is1 ,i suppose1 the reason that the plumage of birds preserves them so effectually from the influence of cold in winter8 ,,mrs4 ,b4 ,yes2 but though feathers in general are an excellent preservative against cold1 down is a kind of plumage peculiar to aquatic birds1 and covers their chest1 which is the part most exposed to the water2 for though the surface of the water is not of a lower temperature than the atmosphere1 yet1 as it is a better conductor of heat1 it feels much colder1 consequently the chest of the bird requires a warmer covering than any other part of its body4 ,besides1 the breasts of aquatic birds are exposed to cold not only from the temperature of the water1 but also from the velocity with which the breast of the bird strikes against it2 and likewise from the rapid evaporation occasioned in that part by the air against which it strikes1 after it has been moistened by dipping from time to time into the water4 ,if you hold a finger of one hand motionless in a glass of water1 and at the same time move a finger of the other hand swiftly through water of the same temperature1 a different sensation will be soon perceived in the different fingers4 ,most animal substances1 especially those which ,providence has assigned as a covering for animals1 such as fur1 wool1 hair1 skin1 c4 are bad conductors of heat1 and are1 on that account1 such excellent preservatives against the inclemency of winter1 that our warmest apparel is made of these materials4 ,,emily4 ,wood is1 ,i dare say1 not so good a conductor as metal1 and it is for that reason1 no doubt1 that silver teapots have always wooden handles4 ,,mrs4 ,b4 ,yes2 and it is the facility with which metals conduct caloric that made you suppose that a silver pot radiated more caloric than an earthen one4 ,the silver pot is in fact hotter to the hand when in contact with it2 but it is because its conducting power more than counterbalances its deficiency in regard to radiation4 ,we have observed that the most dense bodies are in general the best conductors2 and metals1 you know1 are of that class4 ,porous bodies1 such as the earths and wood1 are worse conductors1 chiefly1 ,i believe1 on account of their pores being filled with air2 for air is a remarkably bad conductor4 ,,caroline4 ,it is a very fortunate circumstance that air should be a bad conductor1 as it tends to preserve the heat of the body when exposed to cold weather4 ,,mrs4 ,b4 ,it is one of the many benevolent dispensations of ,providence1 in order to soften the inclemency of the seasons1 and to render almost all climates habitable to man4 ,in fluids of different densities1 the power of conducting heat varies no less remarkably2 if you dip your hand into this vessel full of mercury1 you will scarcely conceive that its temperature is not lower than that of the atmosphere4 ,,caroline4 ,indeed ,i know not how to believe it1 it feels so extremely cold4 --,but we may easily ascertain its true temperature by the thermometer4 --,it is really not colder than the air2--the apparent difference then is produced merely by the difference of the conducting power in mercury and in air4 ,,mrs4 ,b4 ,yes2 hence you may judge how little the sense of feeling is to be relied on as a test of the temperature of bodies1 and how necessary a thermometer is for that purpose4 ,it has indeed been doubted whether fluids have the power of conducting caloric in the same manner as solid bodies4 ,count ,rumford1 a very few years since1 attempted to prove1 by a variety of experiments1 that fluids1 when at rest1 were not at all endowed with this property4 ,,caroline4 ,how is that possible1 since they are capable of imparting cold or heat to us2 for if they did not conduct heat1 they would neither take it from1 nor give it to us8 ,,mrs4 ,b4 ,count ,rumford did not mean to say that fluids would not communicate their heat to solid bodies2 but only that heat does not pervade fluids1 that is to say1 is not transmitted from one particle of a fluid to another1 in the same manner as in solid bodies4 ,,emily4 ,but when you heat a vessel of water over the fire1 if the particles of water do not communicate heat to each other1 how does the water become hot throughout8 ,,mrs4 ,b4 ,by constant agitation4 ,water1 as you have seen1 expands by heat in the same manner as solid bodies2 the heated particles of water1 therefore1 at the bottom of the vessel1 become specifically lighter than the rest of the liquid1 and consequently ascend to the surface1 where1 parting with some of their heat to the colder atmosphere1 they are condensed1 and give way to a fresh succession of heated particles ascending from the bottom1 which having thrown off their heat at the surface1 are in their turn displaced4 ,thus every particle is successively heated at the bottom1 and cooled at the surface of the liquid2 but as the fire communicates heat more rapidly than the atmosphere cools the succession of surfaces1 the whole of the liquid in time becomes heated4 ,,caroline4 ,this accounts most ingeniously for the propagation of heat upwards4 ,but suppose you were to heat the upper surface of a liquid1 the particles being specifically lighter than those below1 could not descend3 how therefore would the heat be communicated downwards8 ,,mrs4 ,b4 ,if there were no agitation to force the heated surface downwards1 ,count ,rumford assures us that the heat would not descend4 ,in proof of this he succeeded in making the upper surface of a vessel of water boil and evaporate1 while a cake of ice remained frozen at the bottom4 ,,caroline4 ,that is very extraordinary indeed6 ,,mrs4 ,b4 ,it appears so1 because we are not accustomed to heat liquids by their upper surface2 but you will understand this theory better if ,i show you the internal motion that takes place in liquids when they experience a change of temperature4 ,the motion of the liquid itself is indeed invisible from the extreme minuteness of its particles2 but if you mix with it any coloured dust1 or powder1 of nearly the same specific gravity as the liquid1 you may judge of the internal motion of the latter by that of the coloured dust it contains4 --,do you see the small pieces of amber moving about in the liquid contained in this phial8 ,,caroline4 ,yes1 perfectly4 ,,mrs4 ,b4 ,we shall now immerse the phial in a glass of hot water1 and the motion of the liquid will be shown1 by that which it communicates to the amber4 ,,emily4 ,i see two currents1 the one rising along the sides of the phial1 the other descending in the centre3 but ,i do not understand the reason of this4 ,,mrs4 ,b4 ,the hot water communicates its caloric1 through the medium of the phial1 to the particles of the fluid nearest to the glass2 these dilate and ascend laterally to the surface1 where1 in parting with their heat1 they are condensed1 and in descending1 form the central current4 ,,caroline4 ,this is indeed a very clear and satisfactory experiment2 but how much slower the currents now move than they did at first8 ,,mrs4 ,b4 ,it is because the circulation of particles has nearly produced an equilibrium of temperature between the liquid in the glass and that in the phial4 ,,caroline4 ,but these communicate laterally1 and ,i thought that heat in liquids could be propagated only upwards4 ,,mrs4 ,b4 ,you do not take notice that the heat is imparted from one liquid to the other1 through the medium of the phial itself1 the external surface of which receives the heat from the water in the glass1 whilst its internal surface transmits it to the liquid it contains4 ,now take the phial out of the hot water1 and observe the effect of its cooling4 ,,emily4 ,the currents are reversed2 the external current now descends1 and the internal one rises4 --,i guess the reason of this change3-- the phial being in contact with cold air instead of hot water1 the external particles are cooled instead of being heated2 they therefore descend and force up the central particles1 which1 being warmer1 are consequently lighter4 ,,mrs4 ,b4 ,it is just so4 ,count ,rumford hence infers that no alteration of temperature can take place in a fluid1 without an internal motion of its particles1 and as this motion is produced only by the comparative levity of the heated particles1 heat cannot be propagated downwards4 ,but though ,i believe that ,count ,rumford's theory as to heat being incapable of pervading fluids is not strictly correct1 yet there is1 no doubt1 much truth in his observation1 that the communication is materially promoted by a motion of the parts2 and this accounts for the cold that is found to prevail at the bottom of the lakes in ,switzerland1 which are fed by rivers issuing from the snowy ,alps4 ,the water of these rivers being colder1 and therefore more dense than that of the lakes1 subsides to the bottom1 where it cannot be affected by the warmer temperature of the surface2 the motion of the waves may communicate this temperature to some little depth1 but it can descend no further than the agitation extends4 ,,emily4 ,but when the atmosphere is colder than the lake1 the colder surface of the water will descend1 for the very reason that the warmer will not4 ,,mrs4 ,b4 ,certainly3 and it is on this account that neither a lake1 nor any body of water whatever1 can be frozen until every particle of the water has risen to the surface to give off its caloric to the colder atmosphere2 therefore the deeper a body of water is1 the longer will be the time it requires to be frozen4 ,,emily4 ,but if the temperature of the whole body of water be brought down to the freezing point1 why is only the surface frozen8 ,,mrs4 ,b4 ,the temperature of the whole body is lowered1 but not to the freezing point4 ,the diminution of heat1 as you know1 produces a contraction in the bulk of fluids1 as well as of solids4 ,this effect1 however1 does not take place in water below the temperature of #dj degrees1 which is #h degrees above the freezing point4 ,at that temperature1 therefore1 the internal motion1 occasioned by the increased specific gravity of the condensed particles1 ceases2 for when the water at the surface no longer condenses1 it will no longer descend1 and leave a fresh surface exposed to the atmosphere3 this surface alone1 therefore1 will be further exposed to its severity1 and will soon be brought down to the freezing point1 when it becomes ice1 which being a bad conductor of heat1 preserves the water beneath a long time from being affected by the external cold4 ,,caroline4 ,and the sea does not freeze1 ,i suppose1 because its depth is so great1 that a frost never lasts long enough to bring down the temperature of such a great body of water to #dj degrees8 ,,mrs4 ,b4 ,that is one reason why the sea1 as a large mass of water1 does not freeze4 ,but1 independently of this1 salt water does not freeze till it is cooled much below #cb degrees1 and with respect to the law of condensation1 salt water is an exception1 as it condenses even many degrees below the freezing point4 ,when the caloric of fresh water1 therefore1 is imprisoned by the ice on its surface1 the ocean still continues throwing off heat into the atmosphere1 which is a most signal dispensation of ,providence to moderate the intensity of the cold in winter4 ,,caroline4 ,this theory of the non-conducting power of liquids1 does not1 ,i suppose1 hold good with respect to air1 otherwise the atmosphere would not be heated by the rays of the sun passing through it8 ,,mrs4 ,b4 ,nor is it heated in that way4 ,the pure atmosphere is a perfectly transparent medium1 which neither radiates1 absorbs1 nor conducts caloric1 but transmits the rays of the sun to us without in any way diminishing their intensity4 ,the air is therefore not more heated1 by the sun's rays passing through it1 than diamond1 glass1 water1 or any other transparent medium4 ,,caroline4 ,that is very extraordinary6 ,are glass windows not heated then by the sun shining on them8 ,,mrs4 ,b4 ,no2 not if the glass be perfectly transparent4 ,a most convincing proof that glass transmits the rays of the sun without being heated by them is afforded by the burning lens1 which by converging the rays to a focus will set combustible bodies on fire1 without its own temperature being raised4 ,,emily4 ,yet1 ,mrs4 ,b41 if ,i hold a piece of glass near the fire it is almost immediately warmed by it2 the glass therefore must retain some of the caloric radiated by the fire8 ,is it that the solar rays alone pass freely through glass without paying tribute8 ,it seems unaccountable that the radiation of a common fire should have power to do what the sun's rays cannot accomplish4 ,,mrs4 ,b4 ,it is not because the rays from the fire have more power1 but rather because they have less1 that they heat glass and other transparent bodies4 ,it is true1 however1 that as you approach the source of heat the rays being nearer each other1 the heat is more condensed1 and can produce effects of which the solar rays1 from the great distance of their source1 are incapable4 ,thus we should find it impossible to roast a joint of meat by the sun's rays1 though it is so easily done by culinary heat4 ,yet caloric emanated from burning bodies1 which is commonly called culinary heat1 has neither the intensity nor the velocity of solar rays4 ,all caloric1 we have said1 is supposed to proceed originally from the sun2 but after having been incorporated with terrestrial bodies1 and again given out by them1 though its nature is not essentially altered1 it retains neither the intensity nor the velocity with which it first emanated from that luminary2 it has therefore not the power of passing through transparent mediums1 such as glass and water1 without being partially retained by those bodies4 ,,emily4 ,i recollect that in the experiment on the reflection of heat1 the glass skreen which you interposed between the burning taper and the mirror1 arrested the rays of caloric1 and suffered only those of light to pass through it4 ,,caroline4 ,glass windows1 then1 though they cannot be heated by the sun shining on them1 may be heated internally by a fire in the room8 ,but1 ,mrs4 ,b41 since the atmosphere is not warmed by the solar rays passing through it1 how does it obtain heat2 for all the fires that are burning on the surface of the earth would contribute very little towards warming it8 ,,emily4 ,the radiation of heat is not confined to burning bodies3 for all bodies1 you know1 have that property2 therefore1 not only every thing upon the surface of the earth1 but the earth itself1 must radiate heat2 and this terrestrial caloric1 not having1 ,i suppose1 sufficient power to traverse the atmosphere1 communicates heat to it4 ,,mrs4 ,b4 ,your inference is extremely well drawn1 ,emily2 but the foundation on which it rests is not sound2 for the fact is1 that terrestrial or culinary heat1 though it cannot pass through the denser transparent mediums1 such as glass or water1 without loss1 traverses the atmosphere completely3 so that all the heat which the earth radiates1 unless it meet with clouds or any foreign body to intercept its passage1 passes into the distant regions of the universe4 ,,caroline4 ,what a pity that so much heat should be wasted6 ,,mrs4 ,b4 ,before you are tempted to object to any law of nature1 reflect whether it may not prove to be one of the numberless dispensations of ,providence for our good4 ,if all the heat which the earth has received from the sun1 since the creation had been accumulated in it1 its temperature by this time would1 no doubt1 have been more elevated than any human being could have borne4 ,,caroline4 ,i spoke indeed very inconsiderately4 ,but1 ,mrs4 ,b41 though the earth1 at such a high temperature1 might have scorched our feet1 we should always have had a cool refreshing air to breathe1 since the radiation of the earth does not heat the atmosphere4 ,,emily4 ,the cool air would have afforded but very insufficient refreshment1 whilst our bodies were exposed to the burning radiation of the earth4 ,,mrs4 ,b4 ,nor should we have breathed a cool air2 for though it is true that heat is not communicated to the atmosphere by radiation1 yet the air is warmed by contact with heated bodies1 in the same manner as solids or liquids4 ,the stratum of air which is immediately in contact with the earth is heated by it2 it becomes specifically lighter and rises1 making way for another stratum of air which is in its turn heated and carried upwards2 and thus each successive stratum of air is warmed by coming in contact with the earth4 ,you may perceive this effect in a sultry day1 if you attentively observe the strata of air near the surface of the earth2 they appear in constant agitation1 for though it is true the air is itself invisible1 yet the sun shining on the vapours floating in it1 render them visible1 like the amber dust in the water4 ,the temperature of the surface of the earth is therefore the source from whence the atmosphere derives its heat1 though it is communicated neither by radiation1 nor transmitted from one particle of it to another by the conducting power2 but every particle of air must come in contact with the earth in order to receive heat from it4 ,,emily4 ,wind then by agitating the air should contribute to cool the earth and warm the atmosphere1 by bringing a more rapid succession of fresh strata of air in contact with the earth1 and yet in general wind feels cooler than still air8 ,,mrs4 ,b4 ,because the agitation of the air carries off heat from the surface of our bodies more rapidly than still air1 by occasioning a greater number of points of contact in a given time4 ,,emily4 ,since it is from the earth and not the sun that the atmosphere receives its heat1 ,i no longer wonder that elevated regions should be colder than plains and valleys2 it was always a subject of astonishment to me1 that in ascending a mountain and approaching the sun1 the air became colder instead of being more heated4 ,,mrs4 ,b4 ,at the distance of about a hundred million of miles1 which we are from the sun1 the approach of a few thousand feet makes no sensible difference1 whilst it produces a very considerable effect with regard to the warming the atmosphere at the surface of the earth4 ,,caroline4 ,yet as the warm air rises from the earth and the cold air descends to it1 ,i should have supposed that heat would have accumulated in the upper regions of the atmosphere1 and that we should have felt the air warmer as we ascended8 ,,mrs4 ,b4 ,the atmosphere1 you know1 diminishes in density1 and consequently in weight1 as it is more distant from the earth2 the warm air1 therefore1 rises only till it meets with a stratum of air of its own density2 and it will not ascend into the upper regions of the atmosphere until all the parts beneath have been previously heated4 ,the length of summer even in warm climates does not heat the air sufficiently to melt the snow which has accumulated during the winter on very high mountains1 although they are almost constantly exposed to the heat of the sun's rays1 being too much elevated to be often enveloped in clouds4 ,,emily4 ,these explanations are very satisfactory2 but allow me to ask you one more question respecting the increased levity of heated liquids4 ,you said that when water was heated over the fire1 the particles at the bottom of the vessel ascended as soon as heated1 in consequence of their specific levity3 why does not the same effect continue when the water boils1 and is converted into steam8 and why does the steam rise from the surface1 instead of the bottom of the liquid8 ,,mrs4 ,b4 ,the steam or vapour does ascend from the bottom1 though it seems to arise from the surface of the liquid4 ,we shall boil some water in this ,florence flask1 7,,plate ,,iv4 ,fig4 #a47 in order that you may be well acquainted with the process of ebullition2--you will then see1 through the glass1 that the vapour rises in bubbles from the bottom4 ,we shall make it boil by means of a lamp1 which is more convenient for this purpose than the chimney fire4 ,illustration3 ,plate ,,iv4 ,vol4 ,i4 p4 #hd4 ,fig4 #a4 ,pneumatic ,pump4 ,ether evaporated water frozen in the air pump4 ,a ,phial of ,ether4 ,b ,glass vessel containing water4 ,c4,c ,thermometers one in the ,ether1 the other in the water4 ,fig4 #b4 ,boiling water in a flask over a ,patent lamp4 ,,emily4 ,i see some small bubbles ascend1 and a great many appear all over the inside of the flask2 does the water begin to boil already8 ,,mrs4 ,b4 ,no2 what you now see are bubbles of air1 which were either dissolved in the water1 or attached to the inner surface of the flask1 and which1 being rarefied by the heat1 ascend in the water4 ,,emily4 ,but the heat which rarefies the air inclosed in the water must rarefy the water at the same time2 therefore1 if it could remain stationary in the water when both were cold1 ,i do not understand why it should not when both are equally heated8 ,,mrs4 ,b4 ,air being much less dense than water1 is more easily rarefied2 the former1 therefore1 expands to a great extent1 whilst the latter continues to occupy nearly the same space2 for water dilates comparatively but very little without changing its state and becoming vapour4 ,now that the water in the flask begins to boil1 observe what large bubbles rise from the bottom of it4 ,,emily4 ,i see them perfectly2 but ,i wonder that they have sufficient power to force themselves through the water4 ,,caroline4 ,they must rise1 you know1 from their specific levity4 ,,mrs4 ,b4 ,you are right1 ,caroline2 but vapour has not in all liquids 7when brought to the degree of vaporization7 the power of overcoming the pressure of the less heated surface4 ,metals1 for instance1 mercury excepted1 evaporate only from the surface2 therefore no vapour will ascend from them till the degree of heat which is necessary to form it has reached the surface2 that is to say1 till the whole of the liquid is brought to a state of ebullition4 ,,emily4 ,i have observed that steam1 immediately issuing from the spout of a teakettle1 is less visible than at a further distance from it2 yet it must be more dense when it first evaporates1 than when it begins to diffuse itself in the air4 ,,mrs4 ,b4 ,when the steam is first formed1 it is so perfectly dissolved by caloric1 as to be invisible4 ,in order however to understand this1 it will be necessary for me to enter into some explanation respecting the nature of ,,solution4 ,solution takes place whenever a body is melted in a fluid4 ,in this operation the body is reduced to such a minute state of division by the fluid1 as to become invisible in it1 and to partake of its fluidity2 but in common solutions this happens without any decomposition1 the body being only divided into its integrant particles by the fluid in which it is melted4 ,,caroline4 ,it is then a mode of destroying the attraction of aggregation4 ,,mrs4 ,b4 ,undoubtedly4 --,the two principal solvent fluids are water1 and caloric4 ,you may have observed that if you melt salt in water1 it totally disappears1 and the water remains clear1 and transparent as before2 yet though the union of these two bodies appears so perfect1 it is not produced by any chemical combination2 both the salt and the water remain unchanged2 and if you were to separate them by evaporating the latter1 you would find the salt in the same state as before4 ,,emily4 ,i suppose that water is a solvent for solid bodies1 and caloric for liquids8 ,,mrs4 ,b4 ,liquids of course can only be converted into vapour by caloric4 ,but the solvent power of this agent is not at all confined to that class of bodies2 a great variety of solid substances are dissolved by heat3 thus metals1 which are insoluble in water1 can be dissolved by intense heat1 being first fused or converted into a liquid1 and then rarefied into an invisible vapour4 ,many other bodies1 such as salt1 gums1 c4 yield to either of these solvents4 ,,caroline4 ,and that1 no doubt1 is the reason why hot water will melt them so much better than cold water8 ,,mrs4 ,b4 ,it is so4 ,caloric may1 indeed1 be considered as having1 in every instance1 some share in the solution of a body by water1 since water1 however low its temperature may be1 always contains more or less caloric4 ,,emily4 ,then1 perhaps1 water owes its solvent power merely to the caloric contained in it8 ,,mrs4 ,b4 ,that1 probably1 would be carrying the speculation too far2 ,i should rather think that water and caloric unite their efforts to dissolve a body1 and that the difficulty or facility of effecting this1 depend both on the degree of attraction of aggregation to be overcome1 and on the arrangement of the particles which are more or less disposed to be divided and penetrated by the solvent4 ,,emily4 ,but have not all liquids the same solvent power as water8 ,,mrs4 ,b4 ,the solvent power of other liquids varies according to their nature1 and that of the substances submitted to their action4 ,most of these solvents1 indeed1 differ essentially from water1 as they do not merely separate the integrant particles of the bodies which they dissolve1 but attack their constituent principles by the power of chemical attraction1 thus producing a true decomposition4 ,these more complicated operations we must consider in another place1 and confine our attention at present to the solutions by water and caloric4 ,,caroline4 ,but there are a variety of substances which1 when dissolved in water1 make it thick and muddy1 and destroy its transparency4 ,,mrs4 ,b4 ,in this case it is not a solution1 but simply a mixture4 ,i shall show you the difference between a solution and a mixture1 by putting some common salt into one glass of water1 and some powder of chalk into another2 both these substances are white1 but their effect on the water will be very different4 ,,caroline4 ,very different indeed6 ,the salt entirely disappears and leaves the water transparent1 whilst the chalk changes it into an opaque liquid like milk4 ,,emily4 ,and would lumps of chalk and salt produce similar effects on water8 ,,mrs4 ,b4 ,yes1 but not so rapidly2 salt is1 indeed1 soon melted though in a lump2 but chalk1 which does not mix so readily with water1 would require a much greater length of time2 ,i therefore preferred showing you the experiment with both substances reduced to powder1 which does not in any respect alter their nature1 but facilitates the operation merely by presenting a greater quantity of surface to the water4 ,i must not forget to mention a very curious circumstance respecting solutions1 which is1 that a fluid is not nearly so much increased in bulk by holding a body in solution1 as it would by mere mixture with the body4 ,,caroline4 ,that seems impossible2 for two bodies cannot exist together in the same space4 ,,mrs4 ,b4 ,two bodies may1 by condensation1 occupy less space when in union than when separate1 and this ,i can show you by an easy experiment4 ,this phial1 which contains some salt1 ,i shall fill with water1 pouring it in quickly1 so as not to dissolve much of the salt2 and when it is quite full ,i cork it4 --,if ,i now shake the phial till the salt is dissolved1 you will observe that it is no longer full4 ,,caroline4 ,i shall try to add a little more salt4 --,but now1 you see1 ,mrs4 ,b41 the water runs over4 ,,mrs4 ,b4 ,yes2 but observe that the last quantity of salt you put in remains solid at the bottom1 and displaces the water2 for it has already melted all the salt it is capable of holding in solution4 ,this is called the point of saturation2 and the water in this case is said to be saturated with salt4 ,,emily4 ,i think ,i now understand the solution of a solid body by water perfectly3 but ,i have not so clear an idea of the solution of a liquid by caloric4 ,,mrs4 ,b4 ,it is probably of a similar nature2 but as caloric is an invisible fluid1 its action as a solvent is not so obvious as that of water4 ,caloric1 we may conceive1 dissolves water1 and converts it into vapour by the same process as water dissolves salt2 that is to say1 the particles of water are so minutely divided by the caloric as to become invisible4 ,thus1 you are now enabled to understand why the vapour of boiling water1 when it first issues from the spout of a kettle1 is invisible2 it is so1 because it is then completely dissolved by caloric4 ,but the air with which it comes in contact1 being much colder than the vapour1 the latter yields to it a quantity of its caloric4 ,the particles of vapour being thus in a great measure deprived of their solvent1 gradually collect1 and become visible in the form of steam1 which is water in a state of imperfect solution2 and if you were further to deprive it of its caloric1 it would return to its original liquid state4 ,,caroline4 ,that ,i understand very well4 ,if you hold a cold plate over a tea-urn1 the steam issuing from it will be immediately converted into drops of water by parting with its caloric to the plate2 but in what state is the steam1 when it becomes invisible by being diffused in the air8 ,,mrs4 ,b4 ,it is not merely diffused1 but is again dissolved by the air4 ,,emily4 ,the air1 then1 has a solvent power1 like water and caloric8 ,,mrs4 ,b4 ,this was formerly believed to be the case4 ,but it appears from more recent enquiries that the solvent power of the atmosphere depends solely upon the caloric contained in it4 ,sometimes the watery vapour diffused in the atmosphere is but imperfectly dissolved1 as is the case in the formation of clouds and fogs2 but if it gets into a region sufficiently warm1 it becomes perfectly invisible4 ,,emily4 ,can any water dissolve in the atmosphere without its being previously converted into vapour by boiling8 ,,mrs4 ,b4 ,unquestionably2 and this constitutes the difference between vaporization and evaporation4 ,water1 when heated to the boiling point1 can no longer exist in the form of water1 and must necessarily be converted into vapour or steam1 whatever may be the state and temperature of the surrounding medium2 this is called vaporization4 ,but the atmosphere1 by means of the caloric it contains1 can take up a certain portion of water at any temperature1 and hold it in a state of solution4 ,this is simply evaporation4 ,thus the atmosphere is continually carrying off moisture from the surface of the earth1 until it is saturated with it4 ,,caroline4 ,that is the case1 no doubt1 when we feel the atmosphere damp4 ,,mrs4 ,b4 ,on the contrary1 when the moisture is well dissolved it occasions no humidity3 it is only when in a state of imperfect solution and floating in the atmosphere1 in the form of watery vapour1 that it produces dampness4 ,this happens more frequently in winter than in summer2 for the lower the temperature of the atmosphere1 the less water it can dissolve2 and in reality it never contains so much moisture as in a dry hot summer's day4 ,,caroline4 ,you astonish me6 ,but why1 then1 is the air so dry in frosty weather1 when its temperature is at the lowest8 ,,emily4 ,this1 ,i conjecture1 proceeds not so much from the moisture being dissolved1 as from its being frozen2 is not that the case8 ,,mrs4 ,b4 ,it is2 and the freezing of the watery vapour which the atmospheric heat could not dissolve1 produces what is called a hoar frost2 for the particles descend in freezing1 and attach themselves to whatever they meet with on the surface of the earth4 ,the tendency of free caloric to an equilibrium1 together with its solvent power1 are likewise connected with the phenomena of rain1 of dew1 c4 ,when moist air of a certain temperature happens to pass through a colder region of the atmosphere1 it parts with a portion of its heat to the surrounding air2 the quantity of caloric1 therefore1 which served to keep the water in a state of vapour1 being diminished1 the watery particles approach each other1 and form themselves into drops of water1 which being heavier than the atmosphere1 descend to the earth4 ,there are also other circumstances1 and particularly the variation in the weight of the atmosphere1 which may contribute to the formation of rain4 ,this1 however1 is an intricate subject1 into which we cannot more fully enter at present4 ,,emily4 ,in what manner do you account for the formation of dew8 ,,mrs4 ,b4 ,dew is a deposition of watery particles or minute drops from the atmosphere1 precipitated by the coolness of the evening4 ,,caroline4 ,this precipitation is owing1 ,i suppose1 to the cooling of the atmosphere1 which prevents its retaining so great a quantity of watery vapour in solution as during the heat of the day4 ,,mrs4 ,b4 ,such was1 from time immemorial1 the generally received opinion respecting the cause of dew2 but it has been very recently proved by a course of ingenious experiments of ,dr4 ,wells1 that the deposition of dew is produced by the cooling of the surface of the earth1 which he has shown to take place previously to the cooling of the atmosphere2 for on examining the temperature of a plot of grass just before the dew-fall1 he found that it was considerably colder than the air a few feet above it1 from which the dew was shortly after precipitated4 ,,emily4 ,but why should the earth cool in the evening sooner than the atmosphere8 ,,mrs4 ,b4 ,because it parts with its heat more readily than the air2 the earth is an excellent radiator of caloric1 whilst the atmosphere does not possess that property1 at least in any sensible degree4 ,towards evening1 therefore1 when the solar heat declines1 and when after sunset it entirely ceases1 the earth rapidly cools by radiating heat towards the skies2 whilst the air has no means of parting with its heat but by coming into contact with the cooled surface of the earth1 to which it communicates its caloric4 ,its solvent power being thus reduced1 it is unable to retain so large a portion of watery vapour1 and deposits those pearly drops which we call dew4 ,,emily4 ,if this be the cause of dew1 we need not be apprehensive of receiving any injury from it2 for it can be deposited only on surfaces that are colder than the atmosphere1 which is never the case with our bodies4 ,,mrs4 ,b4 ,very true2 yet ,i would not advise you for this reason to be too confident of escaping all the ill effects which may arise from exposure to the dew2 for it may be deposited on your clothes1 and chill you afterwards by its evaporation from them4 ,besides1 whenever the dew is copious1 there is a chill in the atmosphere which it is not always safe to encounter4 ,,caroline4 ,wind1 then1 must promote the deposition of dew1 by bringing a more rapid succession of particles of air in contact with the earth1 just as it promotes the cooling of the earth and warming of the atmosphere during the heat of the day8 ,,mrs4 ,b4 ,yes2 provided the wind be unattended with clouds1 for these accumulations of moisture not only prevent the free radiation of the earth towards the upper regions1 but themselves radiate towards the earth2 under these circumstances much less dew is formed than on fine clear nights1 when the radiation of the earth passes without obstacle through the atmosphere to the distant regions of space1 whence it receives no caloric in exchange4 ,the dew continues to be deposited during the night1 and is generally most abundant towards morning1 when the contrast between the temperature of the earth and that of the air is greatest4 ,after sunrise the equilibrium of temperature between these two bodies is gradually restored by the solar rays passing freely through the atmosphere to the earth2 and later in the morning the temperature of the earth gains the ascendency1 and gives out caloric to the air by contact1 in the same manner as it receives it from the air during the night4 --,can you tell me1 now1 why a bottle of wine taken fresh from the cellar 7in summer particularly71 will soon be covered with dew2 and even the glasses into which the wine is poured will be moistened with a similar vapour8 ,,emily4 ,the bottle being colder than the surrounding air1 must absorb caloric from it2 the moisture therefore which that air contained becomes visible1 and forms the dew which is deposited on the bottle4 ,,mrs4 ,b4 ,very well1 ,emily4 ,now1 ,caroline1 can you inform me why1 in a warm room1 or close carriage1 the contrary effect takes place2 that is to say1 that the inside of the windows is covered with vapour8 ,,caroline4 ,i have heard that it proceeds from the breath of those within the room or the carriage2 and ,i suppose it is occasioned by the windows which1 being colder than the breath1 deprive it of part of its caloric1 and by this means convert it into watery vapour4 ,,mrs4 ,b4 ,you have both explained it extremely well4 ,bodies attract dew in proportion as they are good radiators of caloric1 as it is this quality which reduces their temperature below that of the atmosphere2 hence we find that little or no dew is deposited on rocks1 sand1 water2 while grass and living vegetables1 to which it is so highly beneficial1 attract it in abundance--another remarkable instance of the wise and bountiful dispensations of ,providence4 ,,emily4 ,and we may again observe it in the abundance of dew in summer1 and in hot climates1 when its cooling effects are so much required2 but ,i do not understand what natural cause increases the dew in hot weather8 ,,mrs4 ,b4 ,the more caloric the earth receives during the day1 the more it will radiate afterwards1 and consequently the more rapidly its temperature will be reduced in the evening1 in comparison to that of the atmosphere4 ,in the ,west-,indies especially1 where the intense heat of the day is strongly contrasted with the coolness of the evening1 the dew is prodigiously abundant4 ,during a drought1 the dew is less plentiful1 as the earth is not sufficiently supplied with moisture to be able to saturate the atmosphere4 ,,caroline4 ,i have often observed1 ,mrs4 ,b41 that when ,i walk out in frosty weather1 with a veil over my face1 my breath freezes upon it4 ,pray what is the reason of that8 ,,mrs4 ,b4 ,it is because the cold air immediately seizes on the caloric of your breath1 and1 by robbing it of its solvent1 reduces it to a denser fluid1 which is the watery vapour that settles on your veil1 and there it continues parting with its caloric till it is brought down to the temperature of the atmosphere1 and assumes the form of ice4 ,you may1 perhaps1 have observed that the breath of animals1 or rather the moisture contained in it1 is visible in damp weather1 or during a frost4 ,in the former case1 the atmosphere being over-saturated with moisture1 can dissolve no more4 ,in the latter1 the cold condenses it into visible vapour2 and for the same reason1 the steam arising from water that is warmer than the atmosphere1 becomes visible4 ,have you never taken notice of the vapour rising from your hands after having dipped them into warm water8 ,,caroline4 ,frequently1 especially in frosty weather4 ,,mrs4 ,b4 ,we have already observed that pressure is an obstacle to evaporation3 there are liquids that contain so great a quantity of caloric1 and whose particles consequently adhere so slightly together1 that they may be rapidly converted into vapour without any elevation of temperature1 merely by taking off the weight of the atmosphere4 ,in such liquids1 you perceive1 it is the pressure of the atmosphere alone that connects their particles1 and keeps them in a liquid state4 ,,caroline4 ,i do not well understand why the particles of such fluids should be disunited and converted into vapour1 without any elevation of temperature1 in spite of the attraction of cohesion4 ,,mrs4 ,b4 ,it is because the degree of heat at which we usually observe these fluids is sufficient to overcome their attraction of cohesion4 ,ether is of this description2 it will boil and be converted into vapour1 at the common temperature of the air1 if the pressure of the atmosphere be taken off4 ,,emily4 ,i thought that ether would evaporate without either the pressure of the atmosphere being taken away1 or heat applied2 and that it was for that reason so necessary to keep it carefully corked up8 ,,mrs4 ,b4 ,it is true it will evaporate1 but without ebullition2 what ,i am now speaking of is the vaporization of ether1 or its conversion into vapour by boiling4 ,i am going to show you how suddenly the ether in this phial will be converted into vapour1 by means of the air-pump4 --,observe with what rapidity the bubbles ascend1 as ,i take off the pressure of the atmosphere4 ,,caroline4 ,it positively boils3 how singular to see a liquid boil without heat6 ,,mrs4 ,b4 ,now ,i shall place the phial of ether in this glass1 which it nearly fits1 so as to leave only a small space1 which ,i fill with water2 and in this state ,i put it again under the receiver4 7,,plate ,,iv4 ,fig4 #a4799 ,you will observe1 as ,i exhaust the air from it1 that whilst the ether boils1 the water freezes4 ,footnote 993 ,two pieces of thin glass tubes1 sealed at one end1 might answer this purpose better4 ,the experiment1 however1 as here described1 is difficult1 and requires a very nice apparatus4 ,but if1 instead of phials or tubes1 two watch-glasses be used1 water may be frozen almost instantly in the same manner4 ,the two glasses are placed over one another1 with a few drops of water interposed between them1 and the uppermost glass is filled with ether4 ,after working the pump for a minute or two1 the glasses are found to adhere strongly together1 and a thin layer of ice is seen between them4 ,,caroline4 ,it is indeed wonderful to see water freeze in contact with a boiling fluid6 ,,emily4 ,i am at a loss to conceive how the ether can pass to the state of vapour without an addition of caloric4 ,does it not contain more caloric in a state of vapour1 than in a state of liquidity8 ,,mrs4 ,b4 ,it certainly does2 for though it is the pressure of the atmosphere which condenses it into a liquid1 it is by forcing out the caloric that belongs to it when in an ariform state4 ,,emily4 ,you have1 therefore1 two difficulties to explain1 ,mrs4 ,b4 --,first1 from whence the ether obtains the caloric necessary to convert it into vapour when it is relieved from the pressure of the atmosphere2 and1 secondly1 what is the reason that the water1 in which the bottle of ether stands1 is frozen8 ,,caroline4 ,now1 ,i think1 ,i can answer both these questions4 ,the ether obtains the addition of caloric required1 from the water in the glass2 and the loss of caloric1 which the latter sustains1 is the occasion of its freezing4 ,,mrs4 ,b4 ,you are perfectly right2 and if you look at the thermometer which ,i have placed in the water1 whilst ,i am working the pump1 you will see that every time bubbles of vapour are produced1 the mercury descends2 which proves that the heat of the water diminishes in proportion as the ether boils4 ,,emily4 ,this ,i understand now very well2 but if the water freezes in consequence of yielding its caloric to the ether1 the equilibrium of heat must1 in this case1 be totally destroyed4 ,yet you have told us1 that the exchange of caloric between two bodies of equal temperature1 was always equal2 how1 then1 is it that the water1 which was originally of the same temperature as the ether1 gives out caloric to it1 till the water is frozen1 and the ether made to boil8 ,,mrs4 ,b4 ,i suspected that you would make these objections2 and1 in order to remove them1 ,i enclosed two thermometers in the air-pump2 one which stands in the glass of water1 the other in the phial of ether2 and you may see that the equilibrium of temperature is not destroyed2 for as the thermometer descends in the water1 that in the ether sinks in the same manner2 so that both thermometers indicate the same temperature1 though one of them is in a boiling1 the other in a freezing liquid4 ,,emily4 ,the ether1 then1 becomes colder as it boils8 ,this is so contrary to common experience1 that ,i confess it astonishes me exceedingly4 ,,caroline4 ,it is1 indeed1 a most extraordinary circumstance4 ,but pray1 how do you account for it8 ,,mrs4 ,b4 ,i cannot satisfy your curiosity at present2 for before we can attempt to explain this apparent paradox1 it is necessary to become acquainted with the subject of ,,latent ,,heat3 and that1 ,i think1 we must defer till our next interview4 ,,caroline4 ,i believe1 ,mrs4 ,b41 that you are glad to put off the explanation2 for it must be a very difficult point to account for4 ,,mrs4 ,b4 ,i hope1 however1 that ,i shall do it to your complete satisfaction4 ,,emily4 ,but before we part1 give me leave to ask you one question4 ,would not water1 as well as ether1 boil with less heat1 if deprived of the pressure of the atmosphere8 ,,mrs4 ,b4 ,undoubtedly4 ,you must always recollect that there are two forces to overcome1 in order to make a liquid boil or evaporate2 the attraction of aggregation1 and the weight of the atmosphere4 ,on the summit of a high mountain 7as ,mr4 ,de ,saussure ascertained on ,mount ,blanc7 much less heat is required to make water boil1 than in the plain1 where the weight of the atmosphere is greater499 ,indeed if the weight of the atmosphere be entirely removed by means of a good air-pump1 and if water be placed in the exhausted receiver1 it will evaporate so fast1 however cold it maybe1 as to give it the appearance of boiling from the surface4 ,but without the assistance of the air-pump1 ,i can show you a very pretty experiment1 which proves the effect of the pressure of the atmosphere in this respect4 ,observe1 that this ,florence flask is about half full of water1 and the upper half of invisible vapour1 the water being in the act of boiling4 --,i take it from the lamp1 and cork it carefully--the water1 you see1 immediately ceases boiling4 --,i shall now dip the flask into a bason of cold water4 ,footnote 993 ,on the top of ,mount ,blanc1 water boiled when heated only to #ahg degrees1 instead of #bab degrees4 ,footnote 3 ,the same effect may be produced by wrapping a cold wet linen cloth round the upper part of the flask4 ,in order to show how much the water cools whilst it is boiling1 a thermometer1 graduated on the tube itself1 may be introduced into the bottle through the cork4 ,,caroline4 ,but look1 ,mrs4 ,b41 the hot water begins to boil again1 although the cold water must rob it more and more of its caloric6 ,what can be the reason of that8 ,,mrs4 ,b4 ,let us examine its temperature4 ,you see the thermometer immersed in it remains stationary at #ahj degrees1 which is about #cj degrees below the boiling point4 ,when ,i took the flask from the lamp1 ,i observed to you that the upper part of it was filled with vapour2 this being compelled to yield its caloric to the cold water1 was again condensed into water-- ,what1 then1 filled the upper part of the flask8 ,,emily4 ,nothing2 for it was too well corked for the air to gain admittance1 and therefore the upper part of the flask must be a vacuum4 ,,mrs4 ,b4 ,the water below1 therefore1 no longer sustains the pressure of the atmosphere1 and will consequently boil at a much lower temperature4 ,thus1 you see1 though it had lost many degrees of heat1 it began boiling again the instant the vacuum was formed above it4 ,the boiling has now ceased1 the temperature of the water being still farther reduced2 if it had been ether1 instead of water1 it would have continued boiling much longer1 for ether boils1 under the usual atmospheric pressure1 at a temperature as low as #ajj degrees2 and in a vacuum it boils at almost any temperature2 but water being a more dense fluid1 requires a more considerable quantity of caloric to make it evaporate quickly1 even when the pressure of the atmosphere is removed4 ,,emily4 ,what proportion of vapour can the atmosphere contain in a state of solution8 ,,mrs4 ,b4 ,i do not know whether it has been exactly ascertained by experiment2 but at any rate this proportion must vary1 both according to the temperature and the weight of the atmosphere2 for the lower the temperature1 and the greater the pressure1 the smaller must be the proportion of vapour that the atmosphere can contain4 ,to conclude the subject of free caloric1 ,i should mention ,ignition1 by which is meant that emission of light which is produced in bodies at a very high temperature1 and which is the effect of accumulated caloric4 ,,emily4 ,you mean1 ,i suppose1 that light which is produced by a burning body8 ,,mrs4 ,b4 ,no3 ignition is quite independent of combustion4 ,clay1 chalk1 and indeed all incombustible substances1 may be made red hot4 ,when a body burns1 the light emitted is the effect of a chemical change which takes place1 whilst ignition is the effect of caloric alone1 and no other change than that of temperature is produced in the ignited body4 ,all solid bodies1 and most liquids1 are susceptible of ignition1 or1 in other words1 of being heated so as to become luminous2 and it is remarkable that this takes place pretty nearly at the same temperature in all bodies1 that is1 at about #hjj degrees of ,fahrenheit's scale4 ,,emily4 ,but how can liquids attain so high a temperature1 without being converted into vapour8 ,,mrs4 ,b4 ,by means of confinement and pressure4 ,water confined in a strong iron vessel 7called ,papin's digester7 can have its temperature raised to upwards of #djj degrees4 ,sir ,james ,hall has made some very curious experiments on the effects of heat assisted by pressure2 by means of strong gun-barrels1 he succeeded in melting a variety of substances which were considered as infusible3 and it is not unlikely that1 by similar methods1 water itself might be heated to redness4 ,,emily4 ,i am surprised at that3 for ,i thought that the force of steam was such as to destroy almost all mechanical resistance4 ,,mrs4 ,b4 ,the expansive force of steam is prodigious2 but in order to subject water to such high temperatures1 it is prevented by confinement from being converted into steam1 and the expansion of heated water is comparatively trifling4 --,but we have dwelt so long on the subject of free caloric1 that we must reserve the other modifications of that agent to our next meeting1 when we shall endeavour to proceed more rapidly4 ,,conversation ,,iv4 ,,on ,,combined ,,caloric1 ,,comprehending ,,specific ,,and ,,latent ,,heat4 ,,mrs4 ,b4 ,we are now to examine the other modifications of caloric4 ,,caroline4 ,i am very curious to know of what nature they can be2 for ,i have no notion of any kind of heat that is not perceptible to the senses4 ,,mrs4 ,b4 ,in order to enable you to understand them1 it will be necessary to enter into some previous explanations4 ,it has been discovered by modern chemists1 that bodies of a different nature1 heated to the same temperature1 do not contain the same quantity of caloric4 ,,caroline4 ,how could that be ascertained8 ,have you not told us that it is impossible to discover the absolute quantity of caloric which bodies contain8 ,,mrs4 ,b4 ,true2 but at the same time ,i said that we were enabled to form a judgment of the proportions which bodies bore to each other in this respect4 ,thus it is found that1 in order to raise the temperature of different bodies the same number of degrees1 different quantities of caloric are required for each of them4 ,if1 for instance1 you place a pound of lead1 a pound of chalk1 and a pound of milk1 in a hot oven1 they will be gradually heated to the temperature of the oven2 but the lead will attain it first1 the chalk next1 and the milk last4 ,,caroline4 ,that is a natural consequence of their different bulks2 the lead being the smallest body1 will be heated soonest1 and the milk1 which is the largest1 will require the longest time4 ,,mrs4 ,b4 ,that explanation will not do1 for if the lead be the least in bulk1 it offers also the least surface to the caloric1 the quantity of heat therefore which can enter into it in the same space of time is proportionally smaller4 ,,emily4 ,why1 then1 do not the three bodies attain the temperature of the oven at the same time8 ,,mrs4 ,b4 ,it is supposed to be on account of the different capacity of these bodies for caloric4 ,,caroline4 ,what do you mean by the capacity of a body for caloric8 ,,mrs4 ,b4 ,i mean a certain disposition of bodies to require more or less caloric for raising their temperature to any degree of heat4 ,perhaps the fact may be thus explained3 ,let us put as many marbles into this glass as it will contain1 and pour some sand over them--observe how the sand penetrates and lodges between them4 ,we shall now fill another glass with pebbles of various forms--you see that they arrange themselves in a more compact manner than the marbles1 which1 being globular1 can touch each other by a single point only4 ,the pebbles1 therefore1 will not admit so much sand between them2 and consequently one of these glasses will necessarily contain more sand than the other1 though both of them be equally full4 ,,caroline4 ,this ,i understand perfectly4 ,the marbles and the pebbles represent two bodies of different kinds1 and the sand the caloric contained in them2 it appears very plain1 from this comparison1 that one body may admit of more caloric between its particles than another4 ,,mrs4 ,b4 ,you can no longer be surprised1 therefore1 that bodies of a different capacity for caloric should require different proportions of that fluid to raise their temperatures equally4 ,,emily4 ,but ,i do not conceive why the body that contains the most caloric should not be of the highest temperature2 that is to say1 feel hot in proportion to the quantity of caloric it contains8 ,,mrs4 ,b4 ,the caloric that is employed in filling the capacity of a body1 is not free caloric2 but is imprisoned as it were in the body1 and is therefore imperceptible3 for we can feel only the caloric which the body parts with1 and not that which it retains4 ,,caroline4 ,it appears to me very extraordinary that heat should be confined in a body in such a manner as to be imperceptible4 ,,mrs4 ,b4 ,if you lay your hand on a hot body1 you feel only the caloric which leaves it1 and enters your hand2 for it is impossible that you should be sensible of that which remains in the body4 ,the thermometer1 in the same manner1 is affected only by the free caloric which a body transmits to it1 and not at all by that which it does not part with4 ,,caroline4 ,i begin to understand it3 but ,i confess that the idea of insensible heat is so new and strange to me1 that it requires some time to render it familiar4 ,,mrs4 ,b4 ,call it insensible caloric1 and the difficulty will appear much less formidable4 ,it is indeed a sort of contradiction to call it heat1 when it is so situated as to be incapable of producing that sensation4 ,yet this modification of caloric is commonly called ,,specific ,,heat4 ,,caroline4 ,but it certainly would have been more correct to have called it specific caloric4 ,,emily4 ,i do not understand how the term specific applies to this modification of caloric8 ,,mrs4 ,b4 ,it expresses the relative quantity of caloric which different species of bodies of the same weight and temperature are capable of containing4 ,this modification is also frequently called heat of capacity1 a term perhaps preferable1 as it explains better its own meaning4 ,you now understand1 ,i suppose1 why the milk and chalk required a longer portion of time than the lead to raise their temperature to that of the oven8 ,,emily4 ,yes3 the milk and chalk having a greater capacity for caloric than the lead1 a greater proportion of that fluid became insensible in those bodies3 and the more slowly1 therefore1 their temperature was raised4 ,,caroline4 ,but might not this difference proceed from the different conducting powers of heat in these three bodies1 since that which is the best conductor must necessarily attain the temperature of the oven first8 ,,mrs4 ,b4 ,very well observed1 ,caroline4 ,this objection would be insurmountable1 if we could not1 by reversing the experiment1 prove that the milk1 the chalk1 and the lead1 actually absorbed different quantities of caloric1 and we know that if the different time they took in heating1 proceeded merely from their different conducting powers1 they would each have acquired an equal quantity of caloric4 ,,caroline4 ,certainly4 ,but how can you reverse this experiment8 ,,mrs4 ,b4 ,it may be done by cooling the several bodies to the same degree in an apparatus adapted to receive and measure the caloric which they give out4 ,thus1 if you plunge them into three equal quantities of water1 each at the same temperature1 you will be able to judge of the relative quantity of caloric which the three bodies contained1 by that1 which1 in cooling1 they communicated to their respective portions of water3 for the same quantity of caloric which they each absorbed to raise their temperature1 will abandon them in lowering it2 and on examining the three vessels of water1 you will find the one in which you immersed the lead to be the least heated2 that which held the chalk will be the next2 and that which contained the milk will be heated the most of all4 ,the celebrated ,lavoisier has invented a machine to estimate1 upon this principle1 the specific heat of bodies in a more perfect manner2 but ,i cannot explain it to you1 till you are acquainted with the next modification of caloric4 ,,emily4 ,the more dense a body is1 ,i suppose1 the less is its capacity for caloric8 ,,mrs4 ,b4 ,this is not always the case with bodies of different nature2 iron1 for instance1 contains more specific heat than tin1 though it is more dense4 ,this seems to show that specific heat does hot merely depend upon the interstices between the particles2 but1 probably1 also upon some peculiar constitution of the bodies which we do not comprehend4 ,,emily4 ,but1 ,mrs4 ,b41 it would appear to me more proper to compare bodies by measure1 rather than by weight1 in order to estimate their specific heat4 ,why1 for instance1 should we not compare pints of milk1 of chalk1 and of lead1 rather than pounds of those substances2 for equal weights may be composed of very different quantities8 ,,mrs4 ,b4 ,you are mistaken1 my dear2 equal weight must contain equal quantities of matter2 and when we wish to know what is the relative quantity of caloric1 which substances of various kinds are capable of containing under the same temperature1 we must compare equal weights1 and not equal bulks of those substances4 ,bodies of the same weight may undoubtedly be of very different dimensions2 but that does not change their real quantity of matter4 ,a pound of feathers does not contain one atom more than a pound of lead4 ,,caroline4 ,i have another difficulty to propose4 ,it appears to me1 that if the temperature of the three bodies in the oven did not rise equally1 they would never reach the same degree2 the lead would always keep its advantage over the chalk and milk1 and would perhaps be boiling before the others had attained the temperature of the oven4 ,i think you might as well say that1 in the course of time1 you and ,i should be of the same age8 ,,mrs4 ,b4 ,your comparison is not correct1 ,caroline4 ,as soon as the lead reached the temperature of the oven1 it would remain stationary2 for it would then give out as much heat as it would receive4 ,you should recollect that the exchange of radiating heat1 between two bodies of equal temperature1 is equal3 it would be impossible1 therefore1 for the lead to accumulate heat after having attained the temperature of the oven2 and that of the chalk and milk therefore would ultimately arrive at the same standard4 ,now ,i fear that this will not hold good with respect to our ages1 and that1 as long as ,i live1 ,i shall never cease to keep my advantage over you4 ,,emily4 ,i think that ,i have found a comparison for specific heat1 which is very applicable4 ,suppose that two men of equal weight and bulk1 but who required different quantities of food to satisfy their appetites1 sit down to dinner1 both equally hungry2 the one would consume a much greater quantity of provisions than the other1 in order to be equally satisfied4 ,,mrs4 ,b4 ,yes1 that is very fair2 for the quantity of food necessary to satisfy their respective appetites1 varies in the same manner as the quantity of caloric requisite to raise equally the temperature of different bodies4 ,,emily4 ,the thermometer1 then1 affords no indication of the specific heat of bodies8 ,,mrs4 ,b4 ,none at all3 no more than satiety is a test of the quantity of food eaten4 ,the thermometer1 as ,i have repeatedly said1 can be affected only by free caloric1 which alone raises the temperature of bodies4 ,but there is another mode of proving the existence of specific heat1 which affords a very satisfactory illustration of that modification4 ,this1 however1 ,i did not enlarge upon before1 as ,i thought it might appear to you rather complicated4 --,if you mix two fluids of different temperatures1 let us say the one at #ej degrees1 and the other at #ajj degrees1 of what temperature do you suppose the mixture will be8 ,,caroline4 ,it will be no doubt the medium between the two1 that is to say1 #ge degrees4 ,,mrs4 ,b4 ,that will be the case if the two bodies happen to have the same capacity for caloric2 but if not1 a different result will be obtained4 ,thus1 for instance1 if you mix together a pound of mercury1 heated at #ej degrees1 and a pound of water heated at #ajj degrees1 the temperature of the mixture1 instead of being #ge degrees1 will be #hj degrees2 so that the water will have lost only #ab degrees1 whilst the mercury will have gained #ch degrees2 from which you will conclude that the capacity of mercury for heat is less than that of water4 ,,caroline4 ,i wonder that mercury should have so little specific heat4 ,did we not see it was a much better conductor of heat than water8 ,,mrs4 ,b4 ,and it is precisely on that account that its specific heat is less4 ,for since the conductive power of bodies depends1 as we have observed before1 on their readiness to receive heat and part with it1 it is natural to expect that those bodies which are the worst conductors should absorb the most caloric before they are disposed to part with it to other bodies4 ,but let us now proceed to ,,latent ,,heat4 ,,caroline4 ,and pray what kind of heat is that8 ,,mrs4 ,b4 ,it is another modification of combined caloric1 which is so analogous to specific heat1 that most chemists make no distinction between them2 but ,mr4 ,pictet1 in his ,essay on ,fire1 has so clearly discriminated them1 that ,i am induced to adopt his view of the subject4 ,we therefore call latent heat that portion of insensible caloric which is employed in changing the state of bodies2 that is to say1 in converting solids into liquids1 or liquids2 into vapour4 ,when a body changes its state from solid to liquid1 or from liquid to vapour1 its expansion occasions a sudden and considerable increase of capacity for heat1 in consequence of which it immediately absorbs a quantity of caloric1 which becomes fixed in the body which it has transformed2 and1 as it is perfectly concealed from our senses1 it has obtained the name of latent heat4 ,,caroline4 ,i think it would be much more correct to call this modification latent caloric instead of latent heat1 since it does not excite the sensation of heat4 ,,mrs4 ,b4 ,this modification of heat was discovered and named by ,dr4 ,black long before the ,french chemists introduced the term caloric1 and we must not presume to alter it1 as it is still used by much better chemists than ourselves4 ,and1 besides1 you are not to suppose that the nature of heat is altered by being variously modified3 for if latent heat and specific heat do not excite the same sensations as free caloric1 it is owing to their being in a state of confinement1 which prevents them from acting upon our organs2 and consequently1 as soon as they are extricated from the body in which they are imprisoned1 they return to their state of free caloric4 ,,emily4 ,but ,i do not yet clearly see in what respect latent heat differs from specific heat2 for they are both of them imprisoned and concealed in bodies4 ,,mrs4 ,b4 ,specific heat is that which is employed in filling the capacity of a body for caloric1 in the state in which this body actually exists2 while latent heat is that which is employed only in effecting a change of state1 that is1 in converting bodies from a solid to a liquid1 or from a liquid to an ariform state4 ,but ,i think that1 in a general point of view1 both these modifications might be comprehended under the name of heat of capacity1 as in both cases the caloric is equally engaged in filling the capacities of bodies4 ,i shall now show you an experiment1 which ,i hope will give you a clear idea of what is understood by latent heat4 ,the snow which you see in this phial has been cooled by certain chemical means 7which ,i cannot well explain to you at present71 to #e or #f degrees below the freezing point1 as you will find indicated by the thermometer which is placed in it4 ,we shall expose it to the heat of a lamp1 and you will see the thermometer gradually rise1 till it reaches the freezing point---- ,,emily4 ,but there it stops1 ,mrs4 ,b41 and yet the lamp burns just as well as before4 ,why is not its heat communicated to the thermometer8 ,,caroline4 ,and the snow begins to melt1 therefore it must be rising above the freezing point8 ,,mrs4 ,b4 ,the heat no longer affects the thermometer1 because it is wholly employed in converting the ice into water4 ,as the ice melts1 the caloric becomes latent in the new-formed liquid1 and therefore cannot raise its temperature2 and the thermometer will consequently remain stationary1 till the whole of the ice be melted4 ,,caroline4 ,now it is all melted1 and the thermometer begins to rise again4 ,,mrs4 ,b4 ,because the conversion of the ice into water being completed1 the caloric no longer becomes latent2 and therefore the heat which the water now receives raises its temperature1 as you find the thermometer indicates4 ,,emily4 ,but ,i do not think that the thermometer rises so quickly in the water as it did in the ice1 previous to its beginning to melt1 though the lamp burns equally well8 ,,mrs4 ,b4 ,that is owing to the different specific heat of ice and water4 ,the capacity of water for caloric being greater than that of ice1 more heat is required to raise its temperature1 and therefore the thermometer rises slower in the water than in the ice4 ,,emily4 ,true2 you said that a solid body always increased its capacity for heat by becoming fluid2 and this is an instance of it4 ,,mrs4 ,b4 ,yes1 and the latent heat is that which is absorbed in consequence of the greater capacity which the water has for heat1 in comparison to ice4 ,i must now tell you a curious calculation founded on that consideration4 ,i have before observed to you that though the thermometer shows us the comparative warmth of bodies1 and enables us to determine the same point at different times and places1 it gives us no idea of the absolute quantity of heat in any body4 ,we cannot tell how low it ought to fall by the privation of all heat1 but an attempt has been made to infer it in the following manner4 ,it has been found by experiment1 that the capacity of water for heat1 when compared with that of ice1 is as #aj to #i1 so that1 at the same temperature1 ice contains one tenth of caloric less than water4 ,by experiment also it is observed1 that in order to melt ice1 there must be added to it as much heat1 as would1 if it did not melt it1 raise its temperature #adj degrees4 ,this quantity of heat is therefore absorbed when the ice1 by being converted into water1 is made to contain one-ninth more caloric than it did before4 ,therefore #adj degrees is a ninth part of the heat contained in ice at #cj degrees2 and the point of zero1 or the absolute privation of heat1 must consequently be #abfj degrees below #cb degrees4 ,this mode of investigating so curious a question is ingenious1 but its correctness is not yet established by similar calculations for other bodies4 ,the points of absolute cold1 indicated by this method in various bodies1 are very remote from each other2 it is however possible1 that this may arise from some imperfection in the experiments4 ,,caroline4 ,it is indeed very ingenious--but we must now attend to our present experiment4 ,the water begins to boil1 and the thermometer is again stationary4 ,,mrs4 ,b4 ,well1 ,caroline1 it is your turn to explain the phenomenon4 ,,caroline4 ,it is wonderfully curious6 ,the caloric is now busy in changing the water into steam1 in which it hides itself1 and becomes insensible4 ,this is another example of latent heat1 producing a change of form4 ,at first it converted a solid body into a liquid1 and now it turns the liquid into vapour6 ,,mrs4 ,b4 ,you see1 my dear1 how easily you have become acquainted with these modifications of insensible heat1 which at first appeared so unintelligible4 ,if1 now1 we were to reverse these changes1 and condense the vapour into water1 and the water into ice1 the latent heat would re-appear entirely1 in the form of free caloric4 ,,emily4 ,pray do let us see the effect of latent heat returning to its free state4 ,,mrs4 ,b4 ,for the purpose of showing this1 we need simply conduct the vapour through this tube into this vessel of cold water1 where it will part with its latent heat and return to its liquid form4 ,,emily4 ,how rapidly the steam heats the water6 ,,mrs4 ,b4 ,that is because it does not merely impart its free caloric to the water1 but likewise its latent heat4 ,this method of heating liquids1 has been turned to advantage1 in several economical establishments4 ,the steam-kitchens1 which are getting into such general use1 are upon the same principle4 ,the steam is conveyed through a pipe in a similar manner1 into the several vessels which contain the provisions to be dressed1 where it communicates to them its latent caloric1 and returns to the state of water4 ,count ,rumford makes great use of this principle in many of his fire-places3 his grand maxim is to avoid all unnecessary waste of caloric1 for which purpose he confines the heat in such a manner1 that not a particle of it shall unnecessarily escape2 and while he economises the free caloric1 he takes care also to turn the latent heat to advantage4 ,it is thus that he is enabled to produce a degree of heat superior to that which is obtained in common fire-places1 though he employs less fuel4 ,,emily4 ,when the advantages of such contrivances are so clear and plain1 ,i cannot understand why they are not universally used4 ,,mrs4 ,b4 ,a long time is always required before innovations1 however useful1 can be reconciled with the prejudices of the vulgar4 ,,emily4 ,what a pity it is that there should be a prejudice against new inventions2 how much more rapidly the world would improve1 if such useful discoveries were immediately and universally adopted6 ,,mrs4 ,b4 ,i believe1 my dear1 that there are as many novelties attempted to be introduced1 the adoption of which would be prejudicial to society1 as there are of those which would be beneficial to it4 ,the well-informed1 though by no means exempt from error1 have an unquestionable advantage over the illiterate1 in judging what is likely or not to prove serviceable2 and therefore we find the former more ready to adopt such discoveries as promise to be really advantageous1 than the latter1 who having no other test of the value of a novelty but time and experience1 at first oppose its introduction4 ,the well-informed1 however1 are frequently disappointed in their most sanguine expectations1 and the prejudices of the vulgar1 though they often retard the progress of knowledge1 yet sometimes1 it must be admitted1 prevent the propagation of error4 --,but we are deviating from our subject4 ,we have converted steam into water1 and are now to change water into ice1 in order to render the latent heat sensible1 as it escapes from the water on its becoming solid4 ,for this purpose we must produce a degree of cold that will make water freeze4 ,,caroline4 ,that must be very difficult to accomplish in this warm room4 ,,mrs4 ,b4 ,not so much as you think4 ,there are certain chemical mixtures which produce a rapid change from the solid to the fluid state1 or the reverse1 in the substances combined1 in consequence of which change latent heat is either extricated or absorbed4 ,,emily4 ,i do not quite understand you4 ,,mrs4 ,b4 ,this snow and salt1 which you see me mix together1 are melting rapidly2 heat1 therefore1 must be absorbed by the mixture1 and cold produced4 ,,caroline4 ,it feels even colder than ice1 and yet the snow is melted4 ,this is very extraordinary4 ,,mrs4 ,b4 ,the cause of the intense cold of the mixture is to be attributed to the change from a solid to a fluid state4 ,the union of the snow and salt produces a new arrangement of their particles1 in consequence of which they become liquid2 and the quantity of caloric1 required to effect this change1 is seized upon by the mixture wherever it can be obtained4 ,this eagerness of the mixture for caloric1 during its liquefaction1 is such1 that it converts part of its own free caloric into latent heat1 and it is thus that its temperature is lowered4 ,,emily4 ,whatever you put in this mixture1 therefore1 would freeze8 ,,mrs4 ,b4 ,yes2 at least any fluid that is susceptible of freezing at that temperature4 ,i have prepared this mixture of salt and snow for the purpose of freezing the water from which you are desirous of seeing the latent heat escape4 ,i have put a thermometer in the glass of water that is to be frozen1 in order that you may see how it cools4 ,,caroline4 ,the thermometer descends1 but the heat which the water is now losing1 is its free1 not its latent heat4 ,,mrs4 ,b4 ,certainly2 it does not part with its latent heat till it changes its state and is converted into ice4 ,,emily4 ,but here is a very extraordinary circumstance6 ,the thermometer is fallen below the freezing point1 and yet the water is not frozen4 ,,mrs4 ,b4 ,that is always the case previous to the freezing of water when it is in a state of rest4 ,now it begins to congeal1 and you may observe that the thermometer again rises to the freezing point4 ,,caroline4 ,it appears to me very strange that the thermometer should rise the very moment that the water freezes2 for it seems to imply that the water was colder before it froze than when in the act of freezing4 ,,mrs4 ,b4 ,it is so2 and after our long dissertation on this circumstance1 ,i did not think it would appear so surprising to you4 ,reflect a little1 and ,i think you will discover the reason of it4 ,,caroline4 ,it must be1 no doubt1 the extrications of latent heat1 at the instant the water freezes1 that raises the temperature4 ,,mrs4 ,b4 ,certainly2 and if you now examine the thermometer1 you will find that its rise was but temporary1 and lasted only during the disengagement of the latent heat--now that all the water is frozen it falls again1 and will continue to fall till the ice and mixture are of an equal temperature4 ,,emily4 ,and can you show us any experiments in which liquids1 by being mixed1 become solid1 and disengage latent heat8 ,,mrs4 ,b4 ,i could show you several2 but you are not yet sufficiently advanced to understand them well4 ,i shall1 however1 try one1 which will afford you a striking instance of the fact4 ,the fluid which you see in this phial consists of a quantity of a certain salt called muriat of lime1 dissolved in water4 ,now1 if ,i pour into it a few drops of this other fluid1 called sulphuric acid1 the whole1 or very nearly the whole1 will be instantaneously converted into a solid mass4 ,,emily4 ,how white it turns6 ,i feel the latent heat escaping1 for the bottle is warm1 and the fluid is changed to a solid white substance like chalk6 ,,caroline4 ,this is1 indeed1 the most curious experiment we have seen yet4 ,but pray what is that white vapour that ascends from the mixture8 ,,mrs4 ,b4 ,you are not yet enough of a chemist to understand that4 --,but take care1 ,caroline1 do not approach too near it1 for it has a very pungent smell4 ,i shall show you another instance similar to that of the water1 which you observed to become warmer as it froze4 ,i have in this phial a solution of a salt called sulphat of soda or ,glauber's salt1 made very strong1 and corked up when it was hot1 and kept without agitation till it became cold1 as you may feel the phial is4 ,now when ,i take out the cork and let the air fall upon it1 7for being closed when boiling1 there was a vacuum in the upper part7 observe that the salt will suddenly crystallize4 4 4 4 ,,caroline4 ,surprising6 how beautifully the needles of salt have shot through the whole phial6 ,,mrs4 ,b4 ,yes1 it is very striking--but pray do not forget the object of the experiment4 ,feel how warm the phial has become by the conversion of part of the liquid into a solid4 ,,emily4 ,quite warm ,i declare6 this is a most curious experiment of the disengagement of latent heat4 ,,mrs4 ,b4 ,the slakeing of lime is another remarkable instance of the extrication of latent heat4 ,have you never observed how quick-lime smokes when water is poured upon it1 and how much heat it produces8 ,,caroline4 ,yes2 but ,i do not understand what change of state takes place in the lime that occasions its giving out latent heat2 for the quick-lime1 which is solid1 is 7if ,i recollect right7 reduced to powder1 by this operation1 and is1 therefore1 rather expanded than condensed4 ,,mrs4 ,b4 ,it is from the water1 not the lime1 that the latent heat is set free4 ,the water incorporates with1 and becomes solid in the lime2 in consequence of which1 the heat1 which kept it in a liquid state1 is disengaged1 and escapes in a sensible form4 ,,caroline4 ,i always thought that the heat originated in the lime4 ,it seems very strange that water1 and cold water too1 should contain so much heat4 ,,emily4 ,after this extrication of caloric1 the water must exist in a state of ice in the lime1 since it parts with the heat which kept it liquid4 ,,mrs4 ,b4 ,it cannot properly be called ice1 since ice implies a degree of cold1 at least equal to the freezing point4 ,yet as water1 in combining with lime1 gives out more heat than in freezing1 it must be in a state of still greater solidity in the lime1 than it is in the form of ice2 and you may have observed that it does not moisten or liquefy the lime in the smallest degree4 ,,emily4 ,but1 ,mrs4 ,b41 the smoke that rises is white2 if it was only pure caloric which escaped1 we might feel1 but could not see it4 ,,mrs4 ,b4 ,this white vapour is formed by some of the particles of lime1 in a state of fine dust1 which are carried off by the caloric4 ,,emily4 ,in all changes of state1 then1 a body either absorbs or disengages latent heat8 ,,mrs4 ,b4 ,you cannot exactly say absorbs latent heat1 as the heat becomes latent only on being confined in the body2 but you may say1 generally1 that bodies1 in passing from a solid to a liquid form1 or from the liquid state to that of vapour1 absorb heat2 and that when the reverse takes place1 heat is disengaged499 ,footnote 993 ,this rule1 if not universal1 admits of very few exceptions4 ,,emily4 ,we can now1 ,i think1 account for the ether boiling1 and the water freezing in vacuo1 at the same temperature4 ,footnote 3 ,see page #ajb4 ,,mrs4 ,b4 ,let me hear how you explain it4 ,,emily4 ,the latent heat1 which the water gave out in freezing1 was immediately absorbed by the ether1 during its conversion into vapour2 and therefore1 from a latent state in one liquid1 it passed into a latent state in the other4 ,,mrs4 ,b4 ,but this only partly accounts for the result of the experiment2 it remains to be explained why the temperature of the ether1 while in a state of ebullition1 is brought down to the freezing temperature of the water4 --,it is because the ether1 during its evaporation1 reduces its own temperature1 in the same proportion as that of the water1 by converting its free caloric into latent heat3 so that1 though one liquid boils1 and the other freezes1 their temperatures remain in a state of equilibrium4 ,,emily4 ,but why does not water1 as well as ether1 reduce its own temperature by evaporating8 ,,mrs4 ,b4 ,the fact is that it does1 though much less rapidly than ether4 ,thus1 for instance1 you may often have observed1 in the heat of summer1 how much any particular spot may be cooled by watering1 though the water used for that purpose be as warm as the air itself4 ,indeed so much cold may be produced by the mere evaporation of water1 that the inhabitants of ,india1 by availing themselves of the most favourable circumstances for this process which their warm climate can afford1 namely1 the cool of the night1 and situations most exposed to the night breeze1 succeed in causing water to freeze1 though the temperature of the air be as high as #fj degrees4 ,the water is put into shallow earthen trays1 so as to expose an extensive surface to the process of evaporation1 and in the morning1 the water is found covered with a thin cake of ice1 which is collected in sufficient quantity to be used for purposes of luxury4 ,,caroline4 ,how delicious it must be to drink liquids so cold in those tropical climates6 ,but1 ,mrs4 ,b41 could we not try that experiment8 ,,mrs4 ,b4 ,if we were in the country1 ,i have no doubt but that we should be able to freeze water1 by the same means1 and under similar circumstances4 ,but we can do it immediately1 upon a small scale1 in this very room1 in which the thermometer stands at #gj degrees4 ,for this purpose we need only place some water in a little cup under the receiver of the air-pump 7,,plate ,v4 fig4 #a471 and exhaust the air from it4 ,what will be the consequence1 ,caroline8 ,illustration3 ,plate ,v4 ,vol4 ,i4 page #ach4 ,fig4 #a4 ,the air-pump receiver for ,mr4 ,leslie's experiment4 ,c a saucer with sulphuric ,acid4 ,b a glass or earthen cup containing ,water4 ,d a stand for the cup with its legs made of ,glass4 ,a a ,thermometer4 ,fig4 #b4 ,dr4 ,wollaston's ,cryophorus4 ,fig4 #e4 ,dr4 ,marcet's mode of using the ,cryophorus4 ,fig4 #c4 #d4 the different parts of ,fig4 #e4 seen separate4 ,,caroline4 ,of course the water will evaporate more quickly1 since there will no longer be any atmospheric pressure on its surface3 but will this be sufficient to make the water freeze8 ,,mrs4 ,b4 ,probably not1 because the vapour will not be carried off fast enough2 but this will be accomplished without difficulty if we introduce into the receiver 7fig4 #a471 in a saucer1 or other large shallow vessel1 some strong sulphuric acid1 a substance which has a great attraction for water1 whether in the form of vapour1 or in the liquid state4 ,this attraction is such that the acid will instantly absorb the moisture as it rises from the water1 so as to make room for the formation of fresh vapour2 this will of course hasten the process1 and the cold produced from the rapid evaporation of the water1 will1 in a few minutes1 be sufficient to freeze its surface499 ,we shall now exhaust the air from the receiver4 ,footnote 993 ,this experiment was first devised by ,mr4 ,leslie1 and has since been modified in a variety of forms4 ,,emily4 ,thousands of small bubbles already rise through the water from the internal surface of the cup2 what is the reason of this8 ,,mrs4 ,b4 ,these are bubbles of air which were partly attached to the vessel1 and partly diffused in the water itself2 and they expand and rise in consequence of the atmospheric pressure being removed4 ,,caroline4 ,see1 ,mrs4 ,b42 the thermometer in the cup is sinking fast2 it has already descended to #dj degrees6 ,,emily4 ,the water seems now and then violently agitated on the surface1 as if it was boiling2 and yet the thermometer is descending fast6 ,,mrs4 ,b4 ,you may call it boiling1 if you please1 for this appearance is1 as well as boiling1 owing to the rapid formation of vapour2 but here1 as you have just observed1 it takes place from the surface1 for it is only when heat is applied to the bottom of the vessel that the vapour is formed there4 --,now crystals of ice are actually shooting all over the surface of the water4 ,,caroline4 ,how beautiful it is6 ,the surface is now entirely frozen--but the thermometer remains at #cb degrees4 ,,mrs4 ,b4 ,and so it will1 conformably with our doctrine of latent heat1 until the whole of the water is frozen2 but it will then again begin to descend lower and lower1 in consequence of the evaporation which goes on from the surface of the ice4 ,,emily4 ,this is a most interesting experiment2 but it would be still more striking if no sulphuric acid were required4 ,,mrs4 ,b4 ,i will show you a freezing instrument1 contrived by ,dr4 ,wollaston1 upon the same principle as ,mr4 ,leslie's experiment1 by which water may be frozen by its own evaporation alone1 without the assistance of sulphuric acid4 ,this tube1 which1 as you see 7,,plate ,v4 fig4 #b471 is terminated at each extremity by a bulb1 one of which is half full of water1 is internally perfectly exhausted of air2 the consequence of this is1 that the water in the bulb is always much disposed to evaporate4 ,this evaporation1 however1 does not proceed sufficiently fast to freeze the water2 but if the empty ball be cooled by some artificial means1 so as to condense quickly the vapour which rises from the water1 the process may be thus so much promoted as to cause the water to freeze in the other ball4 ,dr4 ,wollaston has called this instrument ,cryophorus4 ,,caroline4 ,so that cold seems to perform here the same part which the sulphuric acid acted in ,mr4 ,leslie's experiment8 ,,mrs4 ,b4 ,exactly so2 but let us try the experiment4 ,,emily4 ,how will you cool the instrument8 ,you have neither ice nor snow4 ,,mrs4 ,b4 ,true3 but we have other means of effecting this499 ,you recollect what an intense cold can be produced by the evaporation of ether in an exhausted receiver4 ,we shall inclose the bulb in this little bag of fine flannel 7fig4 #c471 then soke it in ether1 and introduce it into the receiver of the air-pump4 7,fig4 #e47 ,for this purpose we shall find it more convenient to use a cryophorus of this shape 7fig4 #d471 as its elongated bulb passes easily through a brass plate which closes the top of the receiver4 ,if we now exhaust the receiver quickly1 you will see1 in less than a minute1 the water freeze in the other bulb1 out of the receiver4 ,footnote 993 ,this mode of making the experiment was proposed1 and the particulars detailed1 by ,dr4 ,marcet1 in the #cdth vol4 of ,nicholson's ,journal1 page #aai4 ,,emily4 ,the bulb already looks quite dim1 and small drops of water are condensing on its surface4 ,,caroline4 ,and now crystals of ice shoot all over the water4 ,this is1 indeed1 a very curious experiment6 ,,mrs4 ,b4 ,you will see1 some other day1 that1 by a similar method1 even quicksilver may be frozen4 --,but we cannot at present indulge in any further digression4 ,having advanced so far on the subject of heat1 ,i may now give you an account of the calorimeter1 an instrument invented by ,lavoisier1 upon the principles just explained1 for the purpose of estimating the specific heat of bodies4 ,it consists of a vessel1 the inner surface of which is lined with ice1 so as to form a sort of hollow globe of ice1 in the midst of which the body1 whose specific heat is to be ascertained1 is placed4 ,the ice absorbs caloric from this body1 till it has brought it down to the freezing point2 this caloric converts into water a certain portion of the ice which runs out through an aperture at the bottom of the machine2 and the quantity of ice changed to water is a test of the quantity of caloric which the body has given out in descending from a certain temperature to the freezing point4 ,,caroline4 ,in this apparatus1 ,i suppose1 the milk1 chalk1 and lead1 would melt different quantities of ice1 in proportion to their different capacities for caloric8 ,,mrs4 ,b4 ,certainly3 and thence we are able to ascertain1 with precision1 their respective capacities for heat4 ,but the calorimeter affords us no more idea of the absolute quantity of heat contained in a body1 than the thermometer2 for though by means of it we extricate both the free and combined caloric1 yet we extricate them only to a certain degree1 which is the freezing point2 and we know not how much they contain of either below that point4 ,,emily4 ,according to the theory of latent heat1 it appears to me that the weather should be warm when it freezes1 and cold in a thaw3 for latent heat is liberated from every substance that it freezes1 and such a large supply of heat must warm the atmosphere2 whilst1 during a thaw1 that very quantity of free heat must be taken from the atmosphere1 and return to a latent state in the bodies which it thaws4 ,,mrs4 ,b4 ,your observation is very natural2 but consider that in a frost the atmosphere is so much colder than the earth1 that all the caloric which it takes from the freezing bodies is insufficient to raise its temperature above the freezing point2 otherwise the frost must cease4 ,but if the quantity of latent heat extricated does not destroy the frost1 it serves to moderate the suddenness of the change of temperature of the atmosphere1 at the commencement both of frost1 and of a thaw4 ,in the first instance1 its extrication diminishes the severity of the cold2 and1 in the latter1 its absorption moderates the warmth occasioned by a thaw3 it even sometimes produces a discernible chill1 at the breaking up of a frost4 ,,caroline4 ,but what are the general causes that produce those sudden changes in the weather1 especially from hot to cold1 which we often experience8 ,,mrs4 ,b4 ,this question would lead us into meteorological discussions1 to which ,i am by no means competent4 ,one circumstance1 however1 we can easily understand4 ,when the air has passed over cold countries1 it will probably arrive here at a temperature much below our own1 and then it must absorb heat from every object it meets with1 which will produce a general fall of temperature4 ,,caroline4 ,but pray1 now that we know so much of the effects of heat1 will you inform us whether it is really a distinct body1 or1 as ,i have heard1 a peculiar kind of motion produced in bodies8 ,,mrs4 ,b4 ,as ,i before told you1 there is yet much uncertainty as to the nature of these subtle agents4 ,but ,i am inclined to consider heat not as mere motion1 but as a separate substance4 ,late experiments too appear to make it a compound body1 consisting of the two electricities1 and in our next conversation ,i shall inform you of the principal facts on which that opinion is founded4 ,,conversation ,v4 ,,on ,,the ,,chemical ,,agencies ,,of ,,electricity4 ,,mrs4 ,b4 ,before we proceed further it will be necessary to give you some account of certain properties of electricity1 which have of late years been discovered to have an essential connection with the phenomena of chemistry4 ,,caroline4 ,it is ,,electricity1 if ,i recollect right1 which comes next in our list of simple substances8 ,,mrs4 ,b4 ,i have placed electricity in that list1 rather from the necessity of classing it somewhere1 than from any conviction that it has a right to that situation1 for we are as yet so ignorant of its intimate nature1 that we are unable to determine1 not only whether it is simple or compound1 but whether it is in fact a material agent2 or1 as ,sir ,h4 ,davy has hinted1 whether it may not be merely a property inherent in matter4 ,as1 however1 it is necessary to adopt some hypothesis for the explanation of the discoveries which this agent has enabled us to make1 ,i have chosen the opinion1 at present most prevalent1 which supposes the existence of two kinds of electricity1 distinguished by the names of positive and negative electricity4 ,,caroline4 ,well1 ,i must confess1 ,i do not feel nearly so interested in a science in which so much uncertainty prevails1 as in those which rest upon established principles2 ,i never was fond of electricity1 because1 however beautiful and curious the phenomena it exhibits may be1 the theories1 by which they were explained1 appeared to me so various1 so obscure and inadequate1 that ,i always remained dissatisfied4 ,i was in hopes that the new discoveries in electricity had thrown so great a light on the subject1 that every thing respecting it would now have been clearly explained4 ,,mrs4 ,b4 ,that is a point which we are yet far from having attained4 ,but1 in spite of the imperfection of our theories1 you will be amply repaid by the importance and novelty of the subject4 ,the number of new facts which have already been ascertained1 and the immense prospect of discovery which has lately been opened to us1 will1 ,i hope1 ultimately lead to a perfect elucidation of this branch of natural science2 but at present you must be contented with studying the effects1 and in some degree explaining the phenomena1 without aspiring to a precise knowledge of the remote cause of electricity4 ,you have already obtained some notions of electricity3 in our present conversation1 therefore1 ,i shall confine myself to that part of the science which is of late discovery1 and is more particularly connected with chemistry4 ,it was a trifling and accidental circumstance which first gave rise to this new branch of physical science4 ,galvani1 a professor of natural philosophy at ,bologna1 being engaged 7about twenty years ago7 in some experiments on muscular irritability1 observed1 that when a piece of metal was laid on the nerve of a frog1 recently dead1 whilst the limb supplied by that nerve rested upon some other metal1 the limb suddenly moved1 on a communication being made between the two pieces of metal4 ,,emily4 ,how is this communication made8 ,,mrs4 ,b4 ,either by bringing the two metals into contact1 or by connecting them by means of a metallic conductor4 ,but without subjecting a frog to any cruel experiments1 ,i can easily make you sensible of this kind of electric action4 ,here is a piece of zinc1 7one of the metals ,i mentioned in the list of elementary bodies7--put it under your tongue1 and this piece of silver upon your tongue1 and let both the metals project a little beyond the tip of the tongue--very well--now make the projecting parts of the metals touch each other1 and you will instantly perceive a peculiar sensation4 ,,emily4 ,indeed ,i did1 a singular taste1 and ,i think a degree of heat3 but ,i can hardly describe it4 ,,mrs4 ,b4 ,the action of these two pieces of metal on the tongue is1 ,i believe1 precisely similar to that made on the nerve of a frog4 ,i shall not detain you by a detailed account of the theory by which ,galvani attempted to account for this fact1 as his explanation was soon overturned by subsequent experiments1 which proved that ,galvanism 7the name this new power had obtained7 was nothing more than electricity4 ,galvani supposed that the virtue of this new agent resided in the nerves of the frog1 but ,volta1 who prosecuted this subject with much greater success1 shewed that the phenomena did not depend on the organs of the frog1 but upon the electrical agency of the metals1 which is excited by the moisture of the animal1 the organs of the frog being only a delicate test of the presence of electric influence4 ,,caroline4 ,i suppose1 then1 the saliva of the mouth answers the same purpose as the moisture of the frog1 in exciting the electricity of the pieces of silver and zinc with which ,emily tried the experiment on her tongue4 ,,mrs4 ,b4 ,precisely4 ,it does not appear1 however1 necessary that the fluid used for this purpose should be of an animal nature4 ,water1 and acids very much diluted by water1 are found to be the most effectual in promoting the developement of electricity in metals2 and1 accordingly1 the original apparatus which ,volta first constructed for this purpose1 consisted of a pile or succession of plates of zinc and copper1 each pair of which was connected by pieces of cloth or paper impregnated with water2 and this instrument1 from its original inconvenient structure and limited strength1 has gradually arrived at its present state of power and improvement1 such as is exhibited in the ,voltaic battery4 ,in this apparatus1 a specimen of which you see before you 7,,plate ,,vi4 fig4 #a471 the plates of zinc and copper are soldered together in pairs1 each pair being placed at regular distances in wooden troughs and the interstices being filled with fluid4 ,illustration3 ,plate ,,vi4 p4 #aea4 ,fig4 #a4 ,voltaic ,battery4 ,fig4 #b4 ,fig4 #d4 ,fig4 #a4 #b4 #d4 ,voltaic ,batteries ,fig4 #c4 ,electrical ,machine4 ,a the ,cylinder4 ,b the ,conductor4 ,r the ,rubber4 ,c the ,chain4 ,,caroline4 ,though you will not allow us to enquire into the precise cause of electricity1 may we not ask in what manner the fluid acts on the metals so as to produce it8 ,,mrs4 ,b4 ,the action of the fluid on the metals1 whether water or acid be used1 is entirely of a chemical nature4 ,but whether electricity is excited by this chemical action1 or whether it is produced by the contact of the two metals1 is a point upon which philosophers do not yet perfectly agree4 ,,emily4 ,but can the mere contact of two metals1 without any intervening fluid1 produce electricity8 ,,mrs4 ,b4 ,yes1 if they are afterwards separated4 ,it is an established fact1 that when two metals are put in contact1 and afterwards separated1 that which has the strongest attraction for oxygen exhibits signs of positive1 the other of negative electricity4 ,,caroline4 ,it seems then but reasonable to infer that the power of the ,voltaic battery should arise from the contact of the plates of zinc and copper4 ,,mrs4 ,b4 ,it is upon this principle that ,volta and ,sir ,h4 ,davy explain the phenomena of the pile2 but notwithstanding these two great authorities1 many philosophers entertain doubts on the truth of this theory4 ,the principal difficulty which occurs in explaining the phenomena of the ,voltaic battery on this principle1 is1 that two such plates show no signs of different states of electricity whilst in contact1 but only on being separated after contact4 ,now in the ,voltaic battery1 those plates that are in contact always continue so1 being soldered together3 and they cannot therefore receive a succession of charges4 ,besides1 if we consider the mere disturbance of the balance of electricity by the contact of the plates1 as the sole cause of the production of ,voltaic electricity1 it remains to be explained how this disturbed balance becomes an inexhaustible source of electrical energy1 capable of pouring forth a constant and copious supply of electrical fluid1 though without any means of replenishing itself from other sources4 ,this subject1 it must be owned1 is involved in too much obscurity to enable us to speak very decidedly in favour of any theory4 ,but1 in order to avoid perplexing you with different explanations1 ,i shall confine myself to one which appears to me to be least encumbered with difficulties1 and most likely to accord with truth499 ,this theory supposes the electricity to be excited by the chemical action of the acid on the zinc2 but you are yet such novices in chemistry1 that ,i think it will be necessary to give you some previous explanation of the nature of this action4 ,all metals have a strong attraction for oxygen1 and this element is found in great abundance both in water and in acids4 ,the action of the diluted acid on the zinc consists therefore in its oxygen combining with it1 and dissolving its surface4 ,footnote 993 ,this mode of explaining the phenomena of the ,voltaic pile is called the chemical theory of electricity1 because it ascribes the cause of these phenomena to certain chemical changes which take place during their appearance4 ,in the preceding edition of this work1 the same theory was presented in a more elaborate1 but less easy form than it is in this4 ,the mode of viewing the subject which is here sketched was long since suggested by ,dr4 ,bostock1 of whose theory1 however1 this is by no means to be considered as a complete statement4 ,,caroline4 ,in the same manner ,i suppose as we saw an acid dissolve copper8 ,,mrs4 ,b4 ,yes2 but in the ,voltaic battery the diluted acid is not strong enough to produce so complete an effect2 it acts only on the surface of the zinc1 to which it yields its oxygen1 forming upon it a film or crust1 which is a compound of the oxygen and the metal4 ,,emily4 ,since there is so strong a chemical attraction between oxygen and metals1 ,i suppose they are naturally in different states of electricity8 ,,mrs4 ,b4 ,yes2 it appears that all metals are united with the positive1 and that oxygen is the grand source of the negative electricity4 ,,caroline4 ,does not then the acid act on the plates of copper1 as well as on those of zinc8 ,,mrs4 ,b4 ,no2 for though copper has an affinity for oxygen1 it is less strong than that of zinc2 and therefore the energy of the acid is only exerted upon the zinc4 ,it will be best1 ,i believe1 in order to render the action of the ,voltaic battery more intelligible1 to confine our attention at first to the effect produced on two plates only4 7,,plate ,,vi4 fig4 #b47 ,if a plate of zinc be placed opposite to one of copper1 or any other metal less attractive of oxygen1 and the space between them 7suppose of half an inch in thickness71 be filled with an acid or any fluid capable of oxydating the zinc1 the oxydated surface will have its capacity for electricity diminished1 so that a quantity of electricity will be evolved from that surface4 ,this electricity will be received by the contiguous fluid1 by which it will be transmitted to the opposite metallic surface1 the copper1 which is not oxydated1 and is therefore disposed to receive it2 so that the copper plate will thus become positive1 whilst the zinc plate will be in the negative state4 ,this evolution of electrical fluid however will be very limited2 for as these two plates admit of but very little accumulation of electricity1 and are supposed to have no communication with other bodies1 the action of the acid1 and further developement of electricity1 will be immediately stopped4 ,,emily4 ,this action1 ,i suppose1 can no more continue to go on1 than that of a common electrical machine1 which is not allowed to communicate with other bodies8 ,,mrs4 ,b4 ,precisely2 the common electrical machine1 when excited by the friction of the rubber1 gives out both the positive and negative electricities4-- 7,,plate ,,vi4 ,fig4 #c47 ,the positive1 by the rotation of the glass cylinder1 is conveyed into the conductor1 whilst the negative goes into the rubber4 ,but unless there is a communication made between the rubber and the ground1 but a very inconsiderable quantity of electricity can be excited2 for the rubber1 like the plates of the battery1 has too small a capacity to admit of an accumulation of electricity4 ,unless therefore the electricity can pass out of the rubber1 it will not continue to go into it1 and consequently no additional accumulation will take place4 ,now as one kind of electricity cannot be given out without the other1 the developement of the positive electricity is stopped as well as that of the negative1 and the conductor therefore cannot receive a succession of charges4 ,,caroline4 ,but does not the conductor1 as well as the rubber1 require a communication with the earth1 in order to get rid of its electricity8 ,,mrs4 ,b4 ,no2 for it is susceptible of receiving and containing a considerable quantity of electricity1 as it is much larger than the rubber1 and therefore has a greater capacity2 and this continued accumulation of electricity in the conductor is what is called a charge4 ,,emily4 ,but when an electrical machine is furnished with two conductors to receive the two electricities1 ,i suppose no communication with the earth is required8 ,,mrs4 ,b4 ,certainly not1 until the two are fully charged2 for the two conductors will receive equal quantities of electricity4 ,,caroline4 ,i thought the use of the chain had been to convey the electricity from the ground into the machine8 ,,mrs4 ,b4 ,that was the idea of ,dr4 ,franklin1 who supposed that there was but one kind of electricity1 and who1 by the terms positive and negative 7which he first introduced71 meant only different quantities of the same kind of electricity4 ,the chain was in that case supposed to convey electricity from the ground through the rubber into the conductor4 ,but as we have adopted the hypothesis of two electricities1 we must consider the chain as a vehicle to conduct the negative electricity into the earth4 ,,emily4 ,and are both kinds of electricity produced whenever electricity is excited8 ,,mrs4 ,b4 ,yes1 invariably4 ,if you rub a tube of glass with a woollen cloth1 the glass becomes positive1 and the cloth negative4 ,if1 on the contrary1 you excite a stick of sealing-wax by the same means1 it is the rubber which becomes positive1 and the wax negative4 ,but with regard to the ,voltaic battery1 in order that the acid may act freely on the zinc1 and the two electricities be given out without interruption1 some method must be devised1 by which the plates may part with their electricities as fast as they receive them4 --,can you think of any means by which this might be effected8 ,,emily4 ,would not two chains or wires1 suspended from either plate to the ground1 conduct the electricities into the earth1 and thus answer the purpose8 ,,mrs4 ,b4 ,it would answer the purpose of carrying off the electricity1 ,i admit2 but recollect1 that though it is necessary to find a vent for the electricity1 yet we must not lose it1 since it is the power which we are endeavouring to obtain4 ,instead1 therefore1 of conducting it into the ground1 let us make the wires1 from either plate1 meet3 the two electricities will thus be brought together1 and will combine and neutralize each other2 and as long as this communication continues1 the two plates having a vent for their respective electricities1 the action of the acid will go on freely and uninterruptedly4 ,,emily4 ,that is very clear1 so far as two plates only are concerned2 but ,i cannot say ,i understand how the energy of the succession of plates1 or rather pairs of plates1 of which the ,galvanic trough is composed1 is propagated and accumulated throughout a battery8 ,,mrs4 ,b4 ,in order to shew you how the intensity of the electricity is increased by increasing the number of plates1 we will examine the action of four plates2 if you understand these1 you will readily comprehend that of any number whatever4 ,in this figure 7,,plate ,,vi4 ,fig4 #d471 you will observe that the two central plates are united2 they are soldered together1 7as we observed in describing the ,voltaic trough17 so as to form but one plate which offers two different surfaces1 the one of copper1 the other of zinc4 ,now you recollect that1 in explaining the action of two plates1 we supposed that a quantity of electricity was evolved from the surface of the first zinc plate1 in consequence of the action of the acid1 and was conveyed by the interposed fluid to the copper plate1 ,no4 #b1 which thus became positive4 ,this copper plate communicates its electricity to the contiguous zinc plate1 ,no4 #c1 in which1 consequently1 some accumulation of electricity takes place4 ,when1 therefore1 the fluid in the next cell acts upon the zinc plate1 electricity is extricated from it in larger quantity1 and in a more concentrated form1 than before4 ,this concentrated electricity is again conveyed by the fluid to the next pair of plates1 ,no4 #d and #e1 when it is farther increased by the action of the fluid in the third cell1 and so on1 to any number of plates of which the battery may consist2 so that the electrical energy will continue to accumulate in proportion to the number of double plates1 the first zinc plate of the series being the most negative1 and the last copper plate the most positive4 ,,caroline4 ,but does the battery become more and more strongly charged1 merely by being allowed to stand undisturbed8 ,,mrs4 ,b4 ,no1 for the action will soon stop1 as was explained before1 unless a vent be given to the accumulated electricities4 ,this is easily done1 however1 by establishing a communication by means of the wires 7,fig4 #a471 between the two ends of the battery3 these being brought into contact1 the two electricities meet and neutralize each other1 producing the shock and other effects of electricity2 and the action goes on with renewed energy1 being no longer obstructed by the accumulation of the two electricities which impeded its progress4 ,,emily4 ,is it the union of the two electricities which produces the electric spark8 ,,mrs4 ,b4 ,yes2 and it is1 ,i believe1 this circumstance which gave rise to ,sir ,h4 ,davy's opinion that caloric may be a compound of the two electricities4 ,,caroline4 ,yet surely caloric is very different from the electrical spark8 ,,mrs4 ,b4 ,the difference may consist probably only in intensity3 for the heat of the electric spark is considerably more intense1 though confined to a very minute spot1 than any heat we can produce by other means4 ,,emily4 ,is it quite certain that the electricity of the ,voltaic battery is precisely of the same nature as that of the common electrical machine8 ,,mrs4 ,b4 ,undoubtedly2 the shock given to the human body1 the spark1 the circumstance of the same substances which are conductors of the one being also conductors of the other1 and of those bodies1 such as glass and sealing-wax1 which are non-conductors of the one1 being also non-conductors of the other1 are striking proofs of it4 ,besides1 ,sir ,h4 ,davy has shewn in his ,lectures1 that a ,leyden jar1 and a common electric battery1 can be charged with electricity obtained from a ,voltaic battery1 the effect produced being perfectly similar to that obtained by a common machine4 ,dr4 ,wollaston has likewise proved that similar chemical decompositions are effected by the electric machine and by the ,voltaic battery2 and has made other experiments which render it highly probable1 that the origin of both electricities is essentially the same1 as they show that the rubber of the common electrical machine1 like the zinc in the ,voltaic battery1 produces the two electricities by combining with oxygen4 ,,caroline4 ,but ,i do not see whence the rubber obtains oxygen1 for there is neither acid nor water used in the common machine1 and ,i always understood that the electricity was excited by the friction4 ,,mrs4 ,b4 ,it appears that by friction the rubber obtains oxygen from the atmosphere1 which is partly composed of that element4 ,the oxygen combines with the amalgam of the rubber1 which is of a metallic nature1 much in the same way as the oxygen of the acid combines with the zinc in the ,voltaic battery1 and it is thus that the two electricities are disengaged4 ,,caroline4 ,but1 if the electricities of both machines are similar1 why not use the common machine for chemical decompositions8 ,,mrs4 ,b4 ,though its effects are similar to those of the ,voltaic battery1 they are incomparably weaker4 ,indeed ,dr4 ,wollaston1 in using it for chemical decompositions1 was obliged to act upon the most minute quantities of matter1 and though the result was satisfactory in proving the similarity of its effects to those of the ,voltaic battery1 these effects were too small in extent to be in any considerable degree applicable to chemical decomposition4 ,,caroline4 ,how terrible1 then1 the shock must be from a ,voltaic battery1 since it is so much more powerful than an electrical machine6 ,,mrs4 ,b4 ,it is not nearly so formidable as you think2 at least it is by no means proportional to the chemical effect4 ,the great superiority of the ,voltaic battery consists in the large quantity of electricity that passes2 but in regard to the rapidity or intensity of the charge1 it is greatly surpassed by the common electrical machine4 ,it would seem that the shock or sensation depends chiefly upon the intensity2 whilst1 on the contrary1 for chemical purposes1 it is quantity which is required4 ,in the ,voltaic battery1 the electricity1 though copious1 is so weak as not to be able to force its way through the fluid which separates the plates1 whilst that of a common machine will pass through any space of water4 ,,caroline4 ,would not it be possible to increase the intensity of the ,voltaic battery till it should equal that of the common machine8 ,,mrs4 ,b4 ,it can actually be increased till it imitates a weak electrical machine1 so as to produce a visible spark when accumulated in a ,leyden jar4 ,but it can never be raised sufficiently to pass through any considerable extent of air1 because of the ready communication through the fluids employed4 ,by increasing the number of plates of a battery1 you increase its intensity1 whilst1 by enlarging the dimensions of the plates1 you augment its quantity2 and1 as the superiority of the battery over the common machine consists entirely in the quantity of electricity produced1 it was at first supposed that it was the size1 rather than the number of plates that was essential to the augmentation of power4 ,it was1 however1 found upon trial1 that the quantity of electricity produced by the ,voltaic battery1 even when of a very moderate size1 was sufficiently copious1 and that the chief advantage in this apparatus was obtained by increasing the intensity1 which1 however1 still falls very short of that of the common machine4 ,i should not omit to mention1 that a very splendid1 and1 at the same time1 most powerful battery1 was1 a few years ago1 constructed under the direction of ,sir ,h4 ,davy1 which he repeatedly exhibited in his course of electro-chemical lectures4 ,it consists of two thousand double plates of zinc and copper1 of six square inches in dimensions1 arranged in troughs of ,wedgwood-ware1 each of which contains twenty of these plates4 ,the troughs are furnished with a contrivance for lifting the plates out of them in a very convenient and expeditious manner499 ,footnote 993 ,a model of this mode of construction is exhibited in ,,plate ,,xiii4 ,fig4 #a4 ,,caroline4 ,well1 now that we understand the nature of the action of the ,voltaic battery1 ,i long to hear an account of the discoveries to which it has given rise4 ,,mrs4 ,b4 ,you must restrain your impatience1 my dear1 for ,i cannot with any propriety introduce the subject of these discoveries till we come to them in the regular course of our studies4 ,but1 as almost every substance in nature has already been exposed to the influence of the ,voltaic battery1 we shall very soon have occasion to notice its effects4 ,,conversation ,,vi4 ,,on ,,oxygen ,,and ,,nitrogen4 ,,mrs4 ,b4 ,to-day we shall examine the chemical properties of the ,,atmosphere4 ,,caroline4 ,i thought that we were first to learn the nature of ,,oxygen1 which come next in our table of simple bodies8 ,,mrs4 ,b4 ,and so you shall2 the atmosphere being composed of two principles1 ,,oxygen and ,,nitrogen1 we shall proceed to analyse it1 and consider its component parts separately4 ,,emily4 ,i always thought that the atmosphere had been a very complicated fluid1 composed of all the variety of exhalations from the earth4 ,,mrs4 ,b4 ,such substances may be considered rather as heterogeneous and accidental1 than as forming any of its component parts2 and the proportion they bear to the whole mass is quite inconsiderable4 ,,atmospherical ,,air is composed of two gasses1 known by the names of ,,oxygen ,,gas and ,,nitrogen or ,,azotic ,,gas4 ,,emily4 ,pray what is a gas8 ,,mrs4 ,b4 ,the name of gas is given to any fluid capable of existing constantly in an aeriform state1 under the pressure and at the temperature of the atmosphere4 ,,caroline4 ,is not water1 or any other substance1 when evaporated by heat1 called gas8 ,,mrs4 ,b4 ,no1 my dear2 vapour is1 indeed1 an elastic fluid1 and bears a strong resemblance to a gas2 there are1 however1 several points in which they essentially differ1 and by which you may always distinguish them4 ,steam1 or vapour1 owes its elasticity merely to a high temperature1 which is equal to that of boiling water4 ,and it differs from boiling water only by being united with more caloric1 which1 as we before explained1 is in a latent state4 ,when steam is cooled1 it instantly returns to the form of water2 but air1 or gas1 has never yet been rendered liquid or solid by any degree of cold4 ,,emily4 ,but does not gas1 as well as vapour1 owe its elasticity to caloric8 ,,mrs4 ,b4 ,it was the prevailing opinion2 and the difference of gas or vapour was thought to depend on the different manner in which caloric was united with the basis of these two kinds of elastic fluids4 ,in vapour1 it was considered as in a latent state2 in gas1 it was said to be chemically combined4 ,but the late researches of ,sir ,h4 ,davy have given rise to a new theory respecting gasses2 and there is now reason to believe that these bodies owe their permanently elastic state1 not solely to caloric1 but likewise to the prevalence of either the one or the other of the two electricities4 ,,emily4 ,when you speak1 then1 of the simple bodies oxygen and nitrogen1 you mean to express those substances which are the basis of the two gasses8 ,,mrs4 ,b4 ,yes1 in strict propriety1 for they can properly be called gasses only when brought to an aeriform state4 ,,caroline4 ,in what proportions are they combined in the atmosphere8 ,,mrs4 ,b4 ,the oxygen gas constitutes a little more than one-fifth1 and the nitrogen gas a little less than four-fifths4 ,when separated1 they are found to possess qualities totally different from each other4 ,for oxygen gas is essential both to respiration and combustion1 while neither of these processes can be performed in nitrogen gas4 ,,caroline4 ,but if nitrogen gas is unfit for respiration1 how does it happen that the large proportion of it which enters into the composition of the atmosphere is not a great impediment to breathing8 ,,mrs4 ,b4 ,we should breathe more freely than our lungs could bear1 if we respired oxygen gas alone4 ,the nitrogen is no impediment to respiration1 and probably1 on the contrary1 answers some useful purpose1 though we do not know in what manner it acts in that process4 ,,emily4 ,and by what means can the two gasses1 which compose the atmospheric air1 be separated8 ,,mrs4 ,b4 ,there are many ways of analysing the atmosphere3 the two gasses may be separated first by combustion4 ,,emily4 ,you surprise me6 how is it possible that combustion should separate them8 ,,mrs4 ,b4 ,i should previously remind you that oxygen is supposed to be the only simple body naturally combined with negative electricity4 ,in all the other elements the positive electricity prevails1 and they have consequently1 all of them1 an attraction for oxygen499 ,footnote 993 ,if chlorine or oxymuriatic gas be a simple body1 according to ,sir ,h4 ,davy's view of the subject1 it must be considered as an exception to this statement2 but this subject cannot be discussed till the properties and nature of chlorine come under examination4 ,,caroline4 ,oxygen the only negatively electrified body6 that surprises me extremely2 how then are the combinations of the other bodies performed1 if1 according to your explanation of chemical attraction1 bodies are supposed only to combine in virtue of their opposite states of electricity8 ,,mrs4 ,b4 ,observe that ,i said1 that oxygen was the only simple body1 naturally negative4 ,compound bodies1 in which oxygen prevails over the other component parts1 are also negative1 but their negative energy is greater or less in proportion as the oxygen predominates4 ,those compounds into which oxygen enters in less proportion than the other constituents1 are positive1 but their positive energy is diminished in proportion to the quantity of oxygen which enters into their composition4 ,all bodies1 therefore1 that are not already combined with oxygen1 will attract it1 and1 under certain circumstances1 will absorb it from the atmosphere1 in which case the nitrogen gas will remain alone1 and may thus be obtained in its separate state4 ,,caroline4 ,i do not understand how a gas can be absorbed8 ,,mrs4 ,b4 ,it is only the oxygen1 or basis of the gas1 which is absorbed2 and the two electricities escaping1 that is to say1 the negative from the oxygen1 the positive from the burning body1 unite and produce caloric4 ,,emily4 ,and what becomes of this caloric8 ,,mrs4 ,b4 ,we shall make this piece of dry wood attract oxygen from the atmosphere1 and you will see what becomes of the caloric4 ,,caroline4 ,you are joking1 ,mrs4 ,b--2 you do not mean to decompose the atmosphere with a piece of dry stick8 ,,mrs4 ,b4 ,not the whole body of the atmosphere1 certainly2 but if we can make this piece of wood attract any quantity of oxygen from it1 a proportional quantity of atmospherical air will be decomposed4 ,,caroline4 ,if wood has so strong an attraction for oxygen1 why does it not decompose the atmosphere spontaneously8 ,,mrs4 ,b4 ,it is found by experience1 that an elevation of temperature is required for the commencement of the union of the oxygen and the wood4 ,this elevation of temperature was formerly thought to be necessary1 in order to diminish the cohesive attraction of the wood1 and enable the oxygen to penetrate and combine with it more readily4 ,but since the introduction of the new theory of chemical combination1 another cause has been assigned1 and it is now supposed that the high temperature1 by exalting the electrical energies of bodies1 and consequently their force of attraction1 facilitates their combination4 ,,emily4 ,if it is true1 that caloric is composed of the two electricities1 an elevation of temperature must necessarily augment the electric energies of bodies4 ,,mrs4 ,b4 ,i doubt whether that would be a necessary consequence2 for1 admitting this composition of caloric1 it is only by its being decomposed that electricity can be produced4 ,sir ,h4 ,davy1 however1 in his numerous experiments1 has found it to be an almost invariable rule that the electrical energies of bodies are increased by elevation of temperature4 ,what means then shall we employ to raise the temperature of the wood1 so as to enable it to attract oxygen from the atmosphere8 ,,caroline4 ,holding it near the fire1 ,i should think1 would answer the purpose4 ,,mrs4 ,b4 ,it may1 provided you hold it sufficiently close to the fire2 for a very considerable elevation of temperature is required4 ,,caroline4 ,it has actually taken fire1 and yet ,i did not let it touch the coals1 but ,i held it so very close that ,i suppose it caught fire merely from the intensity of the heat4 ,,mrs4 ,b4 ,or you might say1 in other words1 that the caloric which the wood imbibed1 so much elevated its temperature1 and exalted its electric energy1 as to enable it to attract oxygen very rapidly from the atmosphere4 ,,emily4 ,does the wood absorb oxygen while it is burning8 ,,mrs4 ,b4 ,yes1 and the heat and light are produced by the union of the two electricities which are set at liberty1 in consequence of the oxygen combining with the wood4 ,,caroline4 ,you astonish me6 the heat of a burning body proceeds then as much from the atmosphere as from the body itself8 ,,mrs4 ,b4 ,it was supposed that the caloric1 given out during combustion1 proceeded entirely1 or nearly so1 from the decomposition of the oxygen gas2 but1 according to ,sir ,h4 ,davy's new view of the subject1 both the oxygen gas1 and the combustible body1 concur in supplying the heat and light1 by the union of their opposite electricities4 ,,emily4 ,i have not yet met with any thing in chemistry that has surprised or delighted me so much as this explanation of combustion4 ,i was at first wondering what connection there could be between the affinity of a body for oxygen and its combustibility2 but ,i think ,i understand it now perfectly4 ,,mrs4 ,b4 ,combustion then1 you see1 is nothing more than the rapid combination of a body with oxygen1 attended by the disengagement of light and heat4 ,,emily4 ,but are there no combustible bodies whose attraction for oxygen is so strong1 that they will combine with it1 without the application of heat8 ,,caroline4 ,that cannot be2 otherwise we should see bodies burning spontaneously4 ,,mrs4 ,b4 ,but there are some instances of this kind1 such as phosphorus1 potassium1 and some compound bodies1 which ,i shall hereafter make you acquainted with4 ,these bodies1 however1 are prepared by art1 for in general1 all the combustions that could occur spontaneously1 at the temperature of the atmosphere1 have already taken place2 therefore new combustions cannot happen without the temperature of the body being raised4 ,some bodies1 however1 will burn at a much lower temperature than others4 ,,caroline4 ,but the common way of burning a body is not merely to approach it to one already on fire1 but rather to put the one in actual contact with the other1 as when ,i burn this piece of paper by holding it in the flame of the fire4 ,,mrs4 ,b4 ,the closer it is in contact with the source of caloric1 the sooner will its temperature be raised to the degree necessary for it to burn4 ,if you hold it near the fire1 the same effect will be produced2 but more time will be required1 as you found to be the case with the piece of stick4 ,,emily4 ,but why is it not necessary to continue applying caloric throughout the process of combustion1 in order to keep up the electric energy of the wood1 which is required to enable it to combine with the oxygen8 ,,mrs4 ,b4 ,the caloric which is gradually produced by the two electricities during combustion1 keeps up the temperature of the burning body2 so that when once combustion has begun1 no further application of caloric is required4 ,,caroline4 ,since ,i have learnt this wonderful theory of combustion1 ,i cannot take my eyes from the fire2 and ,i can scarcely conceive that the heat and light1 which ,i always supposed to proceed entirely from the coals1 are really produced as much by the atmosphere4 ,,emily4 ,when you blow the fire1 you increase the combustion1 ,i suppose1 by supplying the coals with a greater quantity of oxygen gas8 ,,mrs4 ,b4 ,certainly2 but of course no blowing will produce combustion1 unless the temperature of the coals be first raised4 ,a single spark1 however1 is sometimes sufficient to produce that effect2 for1 as ,i said before1 when once combustion has commenced1 the caloric disengaged is sufficient to elevate the temperature of the rest of the body1 provided that there be a free access of oxygen4 ,it however sometimes happens that if a fire be ill made1 it will be extinguished before all the fuel is consumed1 from the very circumstance of the combustion being so slow that the caloric disengaged is insufficient to keep up the temperature of the fuel4 ,you must recollect that there are three things required in order to produce combustion2 a combustible body1 oxygen1 and a temperature at which the one will combine with the other4 ,,emily4 ,you said that combustion was one method of decomposing the atmosphere1 and obtaining the nitrogen gas in its simple state2 but how do you secure this gas1 and prevent it from mixing with the rest of the atmosphere8 ,,mrs4 ,b4 ,it is necessary for this purpose to burn the body within a close vessel1 which is easily done4 --,we shall introduce a small lighted taper 7,,plate ,,vii4 ,fig4 #a47 under this glass receiver1 which stands in a bason over water1 to prevent all communication with the external air4 ,illustration3 ,plate ,,vii4 ,vol4 ,i4 p4 #aha4 ,fig4 #a4 ,combustion of a taper under a receiver4 ,fig4 #b4 ,a ,retort on a stand4 ,fig4 #c4 ,preparation of oxygen gas4 ,a ,furnace4 ,b ,earthen ,retort in the furnace4 ,c ,water bath4 ,d ,receiver4 ,e4,e ,tube conveying the gas from the ,retort through the water into the ,receiver4 ,f4,f4,f ,shelf perforated on which the ,receiver stands4 ,fig4 #d4 ,combustion of iron wire in oxygen gas4 ,,caroline4 ,how dim the light burns already6 --,it is now extinguished4 ,,mrs4 ,b4 ,can you tell us why it is extinguished8 ,,caroline4 ,let me consider4 --,the receiver was full of atmospherical air2 the taper1 in burning within it1 must have combined with the oxygen contained in that air1 and the caloric that was disengaged produced the light of the taper4 ,but when the whole of the oxygen was absorbed1 the whole of its electricity was disengaged2 consequently no more caloric could be produced1 the taper ceased to burn1 and the flame was extinguished4 ,,mrs4 ,b4 ,your explanation is perfectly correct4 ,,emily4 ,the two constituents of the oxygen gas being thus disposed of1 what remains under the receiver must be pure nitrogen gas8 ,,mrs4 ,b4 ,there are some circumstances which prevent the nitrogen gas1 thus obtained1 from being perfectly pure2 but we may easily try whether the oxygen has disappeared1 by putting another lighted taper under it4 --,you see how instantaneously the flame is extinguished1 for want of oxygen to supply the negative electricity required for the formation of caloric2 and were you to put an animal under the receiver1 it would immediately be suffocated4 ,but that is an experiment which ,i do not think your curiosity will tempt you to try4 ,,emily4 ,certainly not4 --,but look1 ,mrs4 ,b41 the receiver is full of a thick white smoke4 ,is that nitrogen gas8 ,,mrs4 ,b4 ,no1 my dear2 nitrogen gas is perfectly transparent and invisible1 like common air4 ,this cloudiness proceeds from a variety of exhalations1 which arise from the burning taper1 and the nature of which you cannot yet understand4 ,,caroline4 ,the water within the receiver has now risen a little above its level in the bason4 ,what is the reason of this8 ,,mrs4 ,b4 ,with a moment's reflection1 ,i dare say1 you would have explained it yourself4 ,the water rises in consequence of the oxygen gas within it having been destroyed1 or rather decomposed1 by the combustion of the taper4 ,,caroline4 ,then why did not the water rise immediately when the oxygen gas was destroyed8 ,,mrs4 ,b4 ,because the heat of the taper1 whilst burning1 produced a dilatation of the air in the vessel1 which at first counteracted this effect4 ,another means of decomposing the atmosphere is the oxygenation of certain metals4 ,this process is very analogous to combustion2 it is1 indeed1 only a more general term to express the combination of a body with oxygen4 ,,caroline4 ,in what respect1 then1 does it differ from combustion8 ,,mrs4 ,b4 ,the combination of oxygen in combustion is always accompanied by a disengagement of light and heat2 whilst this circumstance is not a necessary consequence of simple oxygenation4 ,,caroline4 ,but how can a body absorb oxygen without the combination of the two electricities which produce caloric8 ,,mrs4 ,b4 ,oxygen does not always present itself in a gaseous state2 it is a constituent part of a vast number of bodies1 both solid and liquid1 in which it exists in a much denser state than in the atmosphere2 and from these bodies it may be obtained without much disengagement of caloric4 ,it may likewise1 in some cases1 be absorbed from the atmosphere without any sensible production of light and heat2 for1 if the process be slow1 the caloric is disengaged in such small quantities1 and so gradually1 that it is not capable of producing either light or heat4 ,in this case the absorption of oxygen is called oxygenation or oxydation1 instead of combustion1 as the production of sensible light and heat is essential to the latter4 ,,emily4 ,i wonder that metals can unite with oxygen2 for1 as they are so dense1 their attraction of aggregation must be very great2 and ,i should have thought that oxygen could never have penetrated such bodies4 ,,mrs4 ,b4 ,their strong attraction for oxygen counterbalances this obstacle4 ,most metals1 however1 require to be made red-hot before they are capable of attracting oxygen in any considerable quantity4 ,by this combination they lose most of their metallic properties1 and fall into a kind of powder1 formerly called calx1 but now much more properly termed an oxyd2 thus we have oxyd of lead1 oxyd of iron1 c4 ,,emily4 ,and in the ,voltaic battery1 it is1 ,i suppose1 an oxyd of zinc1 that is formed by the union of the oxygen with that metal8 ,,mrs4 ,b4 ,yes1 it is4 ,,caroline4 ,the word oxyd1 then1 simply means a metal combined with oxygen8 ,,mrs4 ,b4 ,yes2 but the term is not confined to metals1 though chiefly applied to them4 ,any body whatever1 that has combined with a certain quantity of oxygen1 either by means of oxydation or combustion1 is called an oxyd1 and is said to be oxydated or oxygenated4 ,,emily4 ,metals1 when converted into oxyds1 become1 ,i suppose1 negative8 ,,mrs4 ,b4 ,not in general2 because in most oxyds the positive energy of the metal more than counterbalances the native energy of the oxygen with which it combines4 ,this black powder is an oxyd of manganese1 a metal which has so strong an affinity for oxygen1 that it attracts that substance from the atmosphere at any known temperature3 it is therefore never found in its metallic form1 but always in that of an oxyd1 in which state1 you see1 it has very little of the appearance of a metal4 ,it is now heavier than it was before oxydation1 in consequence of the additional weight of the oxygen with which it has combined4 ,,caroline4 ,i am very glad to hear that2 for ,i confess ,i could not help having some doubts whether oxygen was really a substance1 as it is not to be obtained in a simple and palpable state2 but its weight is1 ,i think1 a decisive proof of its being a real body4 ,,mrs4 ,b4 ,it is easy to estimate its weight1 by separating it from the manganese1 and finding how much the latter has lost4 ,,emily4 ,but if you can take the oxygen from the metal1 shall we not then have it in its palpable simple state8 ,,mrs4 ,b4 ,no2 for ,i can only separate the oxygen from the manganese1 by presenting to it some other body1 for which it has a greater affinity than for the manganese4 ,caloric affording the two electricities is decomposed1 and one of them uniting with the oxygen1 restores it to the ariform state4 ,,emily4 ,but you said just now1 that manganese would attract oxygen from the atmosphere in which it is combined with the negative electricity2 how1 therefore1 can the oxygen have a superior affinity for that electricity1 since it abandons it to combine with the manganese8 ,,mrs4 ,b4 ,i give you credit for this objection1 ,emily2 and the only answer ,i can make to it is1 that the mutual affinities of metals for oxygen1 and of oxygen for electricity1 vary at different temperatures2 a certain degree of heat will1 therefore1 dispose a metal to combine with oxygen1 whilst1 on the contrary1 the former will be compelled to part with the latter1 when the temperature is further increased4 ,i have put some oxyd of manganese into a retort1 which is an earthen vessel with a bent neck1 such as you see here4 7,,plate ,,vii4 ,fig4 #b47 --,the retort containing the manganese you cannot see1 as ,i have enclosed it in this furnace1 where it is now red-hot4 ,but1 in order to make you sensible of the escape of the gas1 which is itself invisible1 ,i have connected the neck of the retort with this bent tube1 the extremity of which is immersed in this vessel of water4 7,,plate ,,vii4 ,fig4 #c47 --,do you see the bubbles of air rise through the water8 ,,caroline4 ,perfectly4 ,this1 then1 is pure oxygen gas2 what a pity it should be lost6 ,could you not preserve it8 ,,mrs4 ,b4 ,we shall collect it in this receiver4 --,for this purpose1 you observe1 ,i first fill it with water1 in order to exclude the atmospherical air2 and then place it over the bubbles that issue from the retort1 so as to make them rise through the water to the upper part of the receiver4 ,,emily4 ,the bubbles of oxygen gas rise1 ,i suppose1 from their specific levity8 ,,mrs4 ,b4 ,yes2 for though oxygen forms rather a heavy gas1 it is light compared to water4 ,you see how it gradually displaces the water from the receiver4 ,it is now full of gas1 and ,i may leave it inverted in water on this shelf1 where ,i can keep the gas as long as ,i choose1 for future experiments4 ,this apparatus 7which is indispensable in all experiments in which gases are concerned7 is called a water-bath4 ,,caroline4 ,it is a very clever contrivance1 indeed2 equally simple and useful4 ,how convenient the shelf is for the receiver to rest upon under water1 and the holes in it for the gas to pass into the receiver6 ,i long to make some experiments with this apparatus4 ,,mrs4 ,b4 ,i shall try your skill that way1 when you have a little more experience4 ,i am now going to show you an experiment1 which proves1 in a very striking manner1 how essential oxygen is to combustion4 ,you will see that iron itself will burn in this gas1 in the most rapid and brilliant manner4 ,,caroline4 ,really6 ,i did not know that it was possible to burn iron4 ,,emily4 ,iron is a simple body1 and you know1 ,caroline1 that all simple bodies are naturally positive1 and therefore must have an affinity for oxygen4 ,,mrs4 ,b4 ,iron will1 however1 not burn in atmospherical air without a very great elevation of temperature2 but it is eminently combustible in pure oxygen gas2 and what will surprise you still more1 it can be set on fire without any considerable rise of temperature4 ,you see this spiral iron wire--,i fasten it at one end to this cork1 which is made to fit an opening at the top of the glass-receiver4 7,,plate ,,vii4 ,fig4 #d47 ,,emily4 ,i see the opening in the receiver2 but it is carefully closed by a ground glass-stopper4 ,,mrs4 ,b4 ,that is in order to prevent the gas from escaping2 but ,i shall take out the stopper1 and put in the cork1 to which the wire hangs4 --,now ,i mean to burn this wire in the oxygen gas1 but ,i must fix a small piece of lighted tinder to the extremity of it1 in order to give the first impulse to combustion2 for1 however powerful oxygen is in promoting combustion1 you must recollect that it cannot take place without some elevation of temperature4 ,i shall now introduce the wire into the receiver1 by quickly changing the stoppers4 ,,caroline4 ,is there no danger of the gas escaping while you change the stoppers8 ,,mrs4 ,b4 ,oxygen gas is a little heavier than atmospherical air1 therefore it will not mix with it very rapidly2 and1 if ,i do not leave the opening uncovered1 we shall not lose any---- ,,caroline4 ,oh1 what a brilliant and beautiful flame6 ,,emily4 ,it is as white and dazzling as the sun6 --,now a piece of the melted wire drops to the bottom3 ,i fear it is extinguished2 but no1 it burns again as bright as ever4 ,,mrs4 ,b4 ,it will burn till the wire is entirely consumed1 provided the oxygen is not first expended3 for you know it can burn only while there is oxygen to combine with it4 ,,caroline4 ,i never saw a more beautiful light4 ,my eyes can hardly bear it6 ,how astonishing to think that all this caloric was contained in the small quantity of gas and iron that was enclosed in the receiver2 and that1 without producing any sensible heat6 ,,caroline4 ,how wonderfully quick combustion goes on in pure oxygen gas6 ,but pray1 are these drops of burnt iron as heavy as the wire was before8 ,,mrs4 ,b4 ,they are even heavier2 for the iron1 in burning1 has acquired exactly the weight of the oxygen which has disappeared1 and is now combined with it4 ,it has become an oxyd of iron4 ,,caroline4 ,i do not know what you mean by saying that the oxygen has disappeared1 ,mrs4 ,b41 for it was always invisible4 ,,mrs4 ,b4 ,true1 my dear2 the expression was incorrect4 ,but though you could not see the oxygen gas1 ,i believe you had no doubt of its presence1 as the effect it produced on the wire was sufficiently evident4 ,,caroline4 ,yes1 indeed2 yet you know it was the caloric1 and not the oxygen gas itself1 that dazzled us so much4 ,,mrs4 ,b4 ,you are not quite correct in your turn1 in saying the caloric dazzled you2 for caloric is invisible2 it affects only the sense of feeling2 it was the light which dazzled you4 ,,caroline4 ,true2 but light and caloric are such constant companions1 that it is difficult to separate them1 even in idea4 ,,mrs4 ,b4 ,the easier it is to confound them1 the more careful you should be in making the distinction4 ,,caroline4 ,but why has the water now risen1 and filled part of the receiver8 ,,mrs4 ,b4 ,indeed1 ,caroline1 ,i did not suppose you would have asked such a question6 ,i dare say1 ,emily1 you can answer it4 ,,emily4 ,let me reflect 4 4 4 4 4 4 ,the oxygen has combined with the wire2 the caloric has escaped2 consequently nothing can remain in the receiver1 and the water will rise to fill the vacuum4 ,,caroline4 ,i wonder that ,i did not think of that4 ,i wish that we had weighed the wire and the oxygen gas before combustion2 we might then have found whether the weight of the oxyd was equal to that of both4 ,,mrs4 ,b4 ,you might try the experiment if you particularly wished it2 but ,i can assure you1 that1 if accurately performed1 it never fails to show that the additional weight of the oxyd is precisely equal to that of the oxygen absorbed1 whether the process has been a real combustion1 or a simple oxygenation4 ,,caroline4 ,but this cannot be the case with combustions in general2 for when any substance is burnt in the common air1 so far from increasing in weight1 it is evidently diminished1 and sometimes entirely consumed4 ,,mrs4 ,b4 ,but what do you mean by the expression consumed8 ,you cannot suppose that the smallest particle of any substance in nature can be actually destroyed4 ,a compound body is decomposed by combustion2 some of its constituent parts fly off in a gaseous form1 while others remain in a concrete state2 the former are called the volatile1 the latter the fixed products of combustion4 ,but if we collect the whole of them1 we shall always find that they exceed the weight of the combustible body1 by that of the oxygen which has combined with them during combustion4 ,,emily4 ,in the combustion of a coal fire1 then1 ,i suppose that the ashes are what would be called the fixed product1 and the smoke the volatile product8 ,,mrs4 ,b4 ,yet when the fire burns best1 and the quantity of volatile products should be the greatest1 there is no smoke2 how can you account for that8 ,,emily4 ,indeed ,i cannot2 therefore ,i suppose that ,i was not right in my conjecture4 ,,mrs4 ,b4 ,not quite3 ashes1 as you supposed1 are a fixed product of combustion2 but smoke1 properly speaking1 is not one of the volatile products1 as it consists of some minute undecomposed particles of the coals that are carried off by the heated air without being burnt1 and are either deposited in the form of soot1 or dispersed by the wind4 ,smoke1 therefore1 ultimately1 becomes one of the fixed products of combustion4 ,and you may easily conceive that the stronger the fire is1 the less smoke is produced1 because the fewer particles escape combustion4 ,on this principle depends the invention of ,argand's ,patent ,lamps2 a current of air is made to pass through the cylindrical wick of the lamp1 by which means it is so plentifully supplied with oxygen1 that scarcely a particle of oil escapes combustion1 nor is there any smoke produced4 ,,emily4 ,but what then are the volatile products of combustion8 ,,mrs4 ,b4 ,various new compounds1 with which you are not yet acquainted1 and which being converted by caloric either into vapour or gas1 are invisible2 but they can be collected1 and we shall examine them at some future period4 ,,caroline4 ,there are then other gases1 besides the oxygen and nitrogen gases4 ,,mrs4 ,b4 ,yes1 several3 any substance that can assume and maintain the form of an elastic fluid at the temperature of the atmosphere1 is called a gas4 ,we shall examine the several gases in their respective places2 but we must now confine our attention to those that compose the atmosphere4 ,i shall show you another method of decomposing the atmosphere1 which is very simple4 ,in breathing1 we retain a portion of the oxygen1 and expire the nitrogen gas2 so that if we breathe in a closed vessel1 for a certain length of time1 the air within it will be deprived of its oxygen gas4 ,which of you will make the experiment8 ,,caroline4 ,i should be very glad to try it4 ,,mrs4 ,b4 ,very well2 breathe several times through this glass tube into the receiver with which it is connected1 until you feel that your breath is exhausted4 ,,caroline4 ,i am quite out of breath already6 ,,mrs4 ,b4 ,now let us try the gas with a lighted taper4 ,,emily4 ,it is very pure nitrogen gas1 for the taper is immediately extinguished4 ,,mrs4 ,b4 ,that is not a proof of its being pure1 but only of the absence of oxygen1 as it is that principle alone which can produce combustion1 every other gas being absolutely incapable of it4 ,,emily4 ,in the methods which you have shown us1 for decomposing the atmosphere1 the oxygen always abandons the nitrogen2 but is there no way of taking the nitrogen from the oxygen1 so as to obtain the latter pure from the atmosphere8 ,,mrs4 ,b4 ,you must observe1 that whenever oxygen is taken from the atmosphere1 it is by decomposing the oxygen gas2 we cannot do the same with the nitrogen gas1 because nitrogen has a stronger affinity for caloric than for any other known principle3 it appears impossible therefore to separate it from the atmosphere by the power of affinities4 ,but if we cannot obtain the oxygen gas1 by this means1 in its separate state1 we have no difficulty 7as you have seen7 to procure it in its gaseous form1 by taking it from those substances that have absorbed it from the atmosphere1 as we did with the oxyd of manganese4 ,,emily4 ,can atmospherical air be recomposed1 by mixing due proportions of oxygen and nitrogen gases8 ,,mrs4 ,b4 ,yes3 if about one part of oxygen gas be mixed with about four parts of nitrogen gas1 atmospherical air is produced499 ,footnote 993 ,the proportion of oxygen in the atmosphere varies from #ba to #bb per cent4 ,,emily4 ,the air1 then1 must be an oxyd of nitrogen8 ,,mrs4 ,b4 ,no1 my dear2 for there must be a chemical combination between oxygen and nitrogen in order to produce an oxyd2 whilst in the atmosphere these two substances are separately combined with caloric1 forming two distinct gases1 which are simply mixed in the formation of the atmosphere4 ,i shall say nothing more of oxygen and nitrogen at present1 as we shall continually have occasion to refer to them in our future conversations4 ,they are both very abundant in nature2 nitrogen is the most plentiful in the atmosphere1 and exists also in all animal substances2 oxygen forms a constituent part1 both of the animal and vegetable kingdoms1 from which it may be obtained by a variety of chemical means4 ,but it is now time to conclude our lesson4 ,i am afraid you have learnt more to-day than you will be able to remember4 ,,caroline4 ,i assure you that ,i have been too much interested in it1 ever to forget it4 ,in regard to nitrogen there seems to be but little to remember2 it makes a very insignificant figure in comparison to oxygen1 although it composes a much larger portion of the atmosphere4 ,,mrs4 ,b4 ,perhaps this insignificance you complain of may arise from the compound nature of nitrogen1 for though ,i have hitherto considered it as a simple body1 because it is not known in any natural process to be decomposed1 yet from some experiments of ,sir ,h4 ,davy1 there appears to be reason for suspecting that nitrogen is a compound body1 as we shall see afterwards4 ,but even in its simple state1 it will not appear so insignificant when you are better acquainted with it2 for though it seems to perform but a passive part in the atmosphere1 and has no very striking properties1 when considered in its separate state1 yet you will see by-and-bye what a very important agent it becomes1 when combined with other bodies4 ,but no more of this at present2 we must reserve it for its proper place4 ,,conversation ,,vii4 ,,on ,,hydrogen4 ,,caroline4 ,the next simple bodies we come to are ,,chlorine and ,,iodine4 ,pray what kinds of substances are these2 are they also invisible8 ,,mrs4 ,b4 ,no2 for chlorine1 in the state of gas1 has a distinct greenish colour1 and is therefore visible2 and iodine1 in the same state1 has a beautiful claret-red colour4 ,the knowledge of these two bodies1 however1 and the explanation of their properties1 imply various considerations1 which you would not yet be able to understand2 we shall therefore defer their examination to some future conversation1 and we shall pass on to the next simple substance1 ,,hydrogen1 which we cannot1 any more than oxygen1 obtain in a visible or palpable form4 ,we are acquainted with it only in its gaseous state1 as we are with oxygen and nitrogen4 ,,caroline4 ,but in its gaseous state it cannot be called a simple substance1 since it is combined with heat and electricity8 ,,mrs4 ,b4 ,true1 my dear2 but as we do not know in nature of any substance which is not more or less combined with caloric and electricity1 we are apt to say that a substance is in its pure state when combined with those agents only4 ,hydrogen was formerly called inflammable air1 as it is extremely combustible1 and burns with a great flame4 ,since the invention of the new nomenclature1 it has obtained the name of hydrogen1 which is derived from two ,greek words1 the meaning of which is1 to produce water4 ,,emily4 ,and how does hydrogen produce water8 ,,mrs4 ,b4 ,by its combustion4 ,water is composed of eighty-five parts1 by weight1 of oxygen1 combined with fifteen parts of hydrogen2 or of two parts1 by bulk of hydrogen gas1 to one part of oxygen gas4 ,,caroline4 ,really6 is it possible that water should be a combination of two gases1 and that one of these should be inflammable air6 ,hydrogen must be a most extraordinary gas that will produce both fire and water4 ,,emily4 ,but ,i thought you said that combustion could take place in no gas but oxygen8 ,,mrs4 ,b4 ,do you recollect what the process of combustion consists in8 ,,emily4 ,in the combination of a body with oxygen1 with disengagement of light and heat4 ,,mrs4 ,b4 ,therefore when ,i say that hydrogen is combustible1 ,i mean that it has an affinity for oxygen2 but1 like all other combustible substances1 it cannot burn unless supplied with oxygen1 and also heated to a proper temperature4 ,,caroline4 ,the simply mixing fifteen parts of hydrogen1 with eighty-five parts of oxygen gas1 will not1 therefore1 produce water8 ,,mrs4 ,b4 ,no2 water being a much denser fluid than gases1 in order to reduce these gases to a liquid1 it is necessary to diminish the quantity of caloric or electricity which maintains them in an elastic form4 ,,emily4 ,that ,i should think might be done by combining the oxygen and hydrogen together2 for in combining they would give out their respective electricities in the form of caloric1 and by this means would be condensed4 ,,caroline4 ,but you forget1 ,emily1 that in order to make the oxygen and hydrogen combine1 you must begin by elevating their temperature1 which increases1 instead of diminishing1 their electric energies4 ,,mrs4 ,b4 ,emily is1 however1 right2 for though it is necessary to raise their temperature1 in order to make them combine1 as that combination affords them the means of parting with their electricities1 it is eventually the cause of the diminution of electric energy4 ,,caroline4 ,you love to deal in paradoxes to-day1 ,mrs4 ,b4 --,fire1 then1 produces water8 ,,mrs4 ,b4 ,the combustion of hydrogen gas certainly does2 but you do not seem to have remembered the theory of combustion so well as you thought you would4 ,can you tell me what happens in the combustion of hydrogen gas8 ,,caroline4 ,the hydrogen combines with the oxygen1 and their opposite electricities are disengaged in the form of caloric4 --,yes1 ,i think ,i understand it now--by the loss of this caloric1 the gases are condensed into a liquid4 ,,emily4 ,water1 then1 ,i suppose1 when it evaporates and incorporates with the atmosphere1 is decomposed and converted into hydrogen and oxygen gases8 ,,mrs4 ,b4 ,no1 my dear--there you are quite mistaken3 the decomposition of water is totally different from its evaporation2 for in the latter case 7as you should recollect7 water is only in a state of very minute division2 and is merely suspended in the atmosphere1 without any chemical combination1 and without any separation of its constituent parts4 ,as long as these remain combined1 they form ,,water1 whether in a state of liquidity1 or in that of an elastic fluid1 as vapour1 or under the solid form of ice4 ,in our experiments on latent heat1 you may recollect that we caused water successively to pass through these three forms1 merely by an increase or diminution of caloric1 without employing any power of attraction1 or effecting any decomposition4 ,,caroline4 ,but are there no means of decomposing water8 ,,mrs4 ,b4 ,yes1 several3 charcoal1 and metals1 when heated red hot1 will attract the oxygen from water1 in the same manner as they will from the atmosphere4 ,,caroline4 ,hydrogen1 ,i see1 is like nitrogen1 a poor dependant friend of oxygen1 which is continually forsaken for greater favourites4 ,,mrs4 ,b4 ,the connection1 or friendship1 as you choose to call it1 is much more intimate between oxygen and hydrogen1 in the state of water1 than between oxygen and nitrogen1 in the atmosphere2 for1 in the first case1 there is a chemical union and condensation of the two substances2 in the latter1 they are simply mixed together in their gaseous state4 ,you will find1 however1 that1 in some cases1 nitrogen is quite as intimately connected with oxygen1 as hydrogen is4 --,but this is foreign to our present subject4 ,,emily4 ,water1 then1 is an oxyd1 though the atmospherical air is not8 ,,mrs4 ,b4 ,it is not commonly called an oxyd1 though1 according to our definition1 it may1 no doubt1 be referred to that class of bodies4 ,,caroline4 ,i should like extremely to see water decomposed4 ,,mrs4 ,b4 ,i can gratify your curiosity by a much more easy process than the oxydation of charcoal or metals3 the decomposition of water by these latter means takes up a great deal of time1 and is attended with much trouble2 for it is necessary that the charcoal or metal should be made red hot in a furnace1 that the water should pass over them in a state of vapour1 that the gas formed should be collected over the water-bath1 c4 ,in short1 it is a very complicated affair4 ,but the same effect may be produced with the greatest facility1 by the action of the ,voltaic battery1 which this will give me an opportunity of exhibiting4 ,,caroline4 ,i am very glad of that1 for ,i longed to see the power of this apparatus in decomposing bodies4 ,,mrs4 ,b4 ,for this purpose ,i fill this piece of glass-tube 7,,plate ,,viii4 fig4 #a47 with water1 and cork it up at both ends2 through one of the corks ,i introduce that wire of the battery which conveys the positive electricity2 and the wire which conveys the negative electricity is made to pass through the other cork1 so that the two wires approach each other sufficiently near to give out their respective electricities4 ,illustration3 ,plate ,,viii4 ,vol4 ,i4 p4 #bjf ,fig4 #a4 ,apparatus for the decomposition of water by the ,voltaic ,battery4 ,fig4 #b4 ,apparatus for decomposing water by ,voltaic ,electricity obtaining the gasses separate4 ,fig4 #c4 ,apparatus for preparing collecting hydrogen gas4 ,fig4 #d4 ,receiver full of hydrogen gas inverted over water4 ,fig4 #e ,slow combustion of hydrogen gas4 ,fig4 #f4 ,apparatus for illustrating the formation of water by the combustion of hydrogen gas4 ,fig4 #g4 ,apparatus for producing harmonic sounds by the combustion of hydrogen gas4 ,,caroline4 ,it does not appear to me that you approach the wires so near as you did when you made the battery act by itself4 ,,mrs4 ,b4 ,water being a better conductor of electricity than air1 the two wires will act on each other at a greater distance in the former than in the latter4 ,,emily4 ,now the electrical effect appears3 ,i see small bubbles of air emitted from each wire4 ,,mrs4 ,b4 ,each wire decomposes the water1 the positive by combining with its oxygen which is negative1 the negative by combining with its hydrogen which is positive4 ,,caroline4 ,that is wonderfully curious6 ,but what are the small bubbles of air8 ,,mrs4 ,b4 ,those that appear to proceed from the positive wire1 are the result of the decomposition of the water by that wire4 ,that is to say1 the positive electricity having combined with some of the oxygen of the water1 the particles of hydrogen which were combined with that portion of oxygen are set at liberty1 and appear in the form of small bubbles of gas or air4 ,,emily4 ,and ,i suppose the negative fluid having in the same manner combined with some of the hydrogen of the water1 the particles of oxygen that were combined with it1 are set free1 and emitted in a gaseous form4 ,,mrs4 ,b4 ,precisely so4 ,but ,i should not forget to observe1 that the wires used in this experiment are made of platina1 a metal which is not capable of combining with oxygen2 for otherwise the wire would combine with the oxygen1 and the hydrogen alone would be disengaged4 ,,caroline4 ,but could not water be decomposed without the electric circle being completed8 ,if1 for instance1 you immersed only the positive wire in the water1 would it not combine with the oxygen1 and the hydrogen gas be given out8 ,,mrs4 ,b4 ,no2 for as you may recollect1 the battery cannot act unless the circle be completed2 since the positive wire will not give out its electricity1 unless attracted by that of the negative wire4 ,,caroline4 ,i understand it now4 --,but look1 ,mrs4 ,b41 the decomposition of the water which has now been going on for some time1 does not sensibly diminish its quantity--what is the reason of that8 ,,mrs4 ,b4 ,because the quantity decomposed is so extremely small4 ,if you compare the density of water with that of the gases into which it is resolved1 you must be aware that a single drop of water is sufficient to produce thousands of such small bubbles as those you now perceive4 ,,caroline4 ,but in this experiment1 we obtain the oxygen and hydrogen gases mixed together4 ,is there any means of procuring the two gases separately8 ,,mrs4 ,b4 ,they can be collected separately with great ease1 by modifying a little the experiment4 ,thus if instead of one tube1 we employ two1 as you see here1 7c1 d1 ,,plate ,,viii4 fig4 #b47 both tubes being closed at one end1 and open at the other2 and if after filling these tubes with water1 we place them standing in a glass of water 7e71 with their open end downwards1 you will see that the moment we connect the wires 7a1 b7 which proceed upwards from the interior of each tube1 the one with one end of the battery1 and the other with the other end1 the water in the tubes will be decomposed2 hydrogen will be given out round the wire in the tube connected with the positive end of the battery1 and oxygen in the other2 and these gases will be evolved1 exactly in the proportions which ,i have before mentioned1 namely1 two measures of hydrogen for one of oxygen4 ,we shall now begin the experiment1 but it will be some time before any sensible quantity of the gases can be collected4 ,,emily4 ,the decomposition of water in this way1 slow as it is1 is certainly very striking2 but ,i confess that ,i should be still more gratified1 if you could shew it us on a larger scale1 and by a quicker process4 ,i am sorry that the decomposition of water by charcoal or metals is attended with so much inconvenience4 ,,mrs4 ,b4 ,water may be decomposed by means of metals without any difficulty2 but for this purpose the intervention of an acid is required4 ,thus1 if we add some sulphuric acid 7a substance with the nature of which you are not yet acquainted7 to the water which the metal is to decompose1 the acid disposes the metal to combine with the oxygen of the water so readily and abundantly1 that no heat is required to hasten the process4 ,of this ,i am going to shew you an instance4 ,i put into this bottle the water that is to be decomposed1 as also the metal that is to effect that decomposition by combining with the oxygen1 and the acid which is to facilitate the combination of the metal and the oxygen4 ,you will see with what violence these will act on each other4 ,,caroline4 ,but what metal is it that you employ for this purpose8 ,,mrs4 ,b4 ,it is iron2 and it is used in the state of filings1 as these present a greater surface to the acid than a solid piece of metal4 ,for as it is the surface of the metal which is acted upon by the acid1 and is disposed to receive the oxygen produced by the decomposition of the water1 it necessarily follows that the greater is the surface1 the more considerable is the effect4 ,the bubbles which are now rising are hydrogen gas---- ,,caroline4 ,how disagreeably it smells6 ,,mrs4 ,b4 ,it is indeed unpleasant1 though1 ,i believe1 not particularly hurtful4 ,we shall not1 however1 suffer any more to escape1 as it will be wanted for experiments4 ,i shall1 therefore1 collect it in a glass-receiver1 by making it pass through this bent tube1 which will conduct it into the water-bath4 7,,plate ,,viii4 fig4 #c47 ,,emily4 ,how very rapidly the gas escapes6 it is perfectly transparent1 and without any colour whatever4 --,now the receiver is full---- ,,mrs4 ,b4 ,we shall1 therefore1 remove it1 and substitute another in its place4 ,but you must observe1 that when the receiver is full1 it is necessary to keep it inverted with the mouth under water1 otherwise the gas would escape4 ,and in order that it may not be in the way1 ,i introduce within the bath1 under the water1 a saucer1 into which ,i slide the receiver1 so that it can be taken out of the bath and conveyed any where1 the water in the saucer being equally effectual in preventing its escape as that in the bath4 7,,plate ,,viii4 fig4 #d47 ,,emily4 ,i am quite surprised to see what a large quantity of hydrogen gas can be produced by such a small quantity of water1 especially as oxygen is the principal constituent of water4 ,,mrs4 ,b4 ,in weight it is2 but not in volume4 ,for though the proportion1 by weight1 is nearly six parts of oxygen to one of hydrogen1 yet the proportion of the volume of the gases1 is about one part of oxygen to two of hydrogen2 so much heavier is the former than the latter4 ,,caroline4 ,but why is the vessel in which the water is decomposed so hot8 ,as the water changes from a liquid to a gaseous form1 cold should be produced instead of heat4 ,,mrs4 ,b4 ,no2 for if one of the constituents of water is converted into a gas1 the other becomes solid in combining with the metal4 ,,emily4 ,in this case1 then1 neither heat nor cold should be produced8 ,,mrs4 ,b4 ,true3 but observe that the sensible heat which is disengaged in this operation1 is not owing to the decomposition of the water1 but to an extrication of heat produced by the mixture of water and sulphuric acid4 ,i will mix some water and sulphuric acid together in this glass1 that you may feel the surprising quantity of heat that is disengaged by their union--now take hold of the glass---- ,,caroline4 ,indeed ,i cannot2 it feels as hot as boiling water4 ,i should have imagined there would have been heat enough disengaged to have rendered the liquid solid4 ,,mrs4 ,b4 ,as1 however1 it does not produce that effect1 we cannot refer this heat to the modification called latent heat4 ,we may1 however1 ,i think1 consider it as heat of capacity1 as the liquid is condensed by its loss2 and if you were to repeat the experiment1 in a graduated tube1 you would find that the two liquids1 when mixed1 occupy considerably less space than they did separately4 --,but we will reserve this to another opportunity1 and attend at present to the hydrogen gas which we have been producing4 ,if ,i now set the hydrogen gas1 which is contained in this receiver1 at liberty all at once1 and kindle it as soon as it comes in contact with the atmosphere1 by presenting it to a candle1 it will so suddenly and rapidly decompose the oxygen gas1 by combining with its basis1 that an explosion1 or a detonation 7as chemists commonly call it71 will be produced4 ,for this purpose1 ,i need only take up the receiver1 and quickly present its open mouth to the candle---- so 4 4 4 4 ,,caroline4 ,it produced only a sort of hissing noise1 with a vivid flash of light4 ,i had expected a much greater report4 ,,mrs4 ,b4 ,and so it would have been1 had the gases been closely confined at the moment they were made to explode4 ,if1 for instance1 we were to put in this bottle a mixture of hydrogen gas and atmospheric air2 and if1 after corking the bottle1 we should kindle the mixture by a very small orifice1 from the sudden dilatation of the gases at the moment of their combination1 the bottle must either fly to pieces1 or the cork be blown out with considerable violence4 ,,caroline4 ,but in the experiment which we have just seen1 if you did not kindle the hydrogen gas1 would it not equally combine with the oxygen8 ,,mrs4 ,b4 ,certainly not2 for1 as ,i have just explained to you1 it is necessary that the oxygen and hydrogen gases be burnt together1 in order to combine chemically and produce water4 ,,caroline4 ,that is true2 but ,i thought this was a different combination1 for ,i see no water produced4 ,,mrs4 ,b4 ,the water resulting from this detonation was so small in quantity1 and in such a state of minute division1 as to be invisible4 ,but water certainly was produced2 for oxygen is incapable of combining with hydrogen in any other proportions than those that form water2 therefore water must always be the result of their combination4 ,if1 instead of bringing the hydrogen gas into sudden contact with the atmosphere 7as we did just now7 so as to make the whole of it explode the moment it is kindled1 we allow but a very small surface of gas to burn in contact with the atmosphere1 the combustion goes on quietly and gradually at the point of contact1 without any detonation1 because the surfaces brought together are too small for the immediate union of gases4 ,the experiment is a very easy one4 ,this phial1 with a narrow neck1 7,,plate ,,viii4 fig4 #e47 is full of hydrogen gas1 and is carefully corked4 ,if ,i take out the cork without moving the phial1 and quickly approach the candle to the orifice1 you will see how different the result will be---- ,,emily4 ,how prettily it burns1 with a blue flame6 ,the flame is gradually sinking within the phial--now it has entirely disappeared4 ,but does not this combustion likewise produce water8 ,,mrs4 ,b4 ,undoubtedly4 ,in order to make the formation of the water sensible to you1 ,i shall procure a fresh supply of hydrogen gas1 by putting into this bottle 7,,plate ,,viii4 fig4 #f47 iron filings1 water1 and sulphuric acid1 materials similar to those which we have just used for the same purpose4 ,i shall then cork up the bottle1 leaving only a small orifice in the cork1 with a piece of glass-tube fixed to it1 through which the gas will issue in a continued rapid stream4 ,,caroline4 ,i hear already the hissing of the gas through the tube1 and ,i can feel a strong current against my hand4 ,,mrs4 ,b4 ,this current ,i am going to kindle with the candle--see how vividly it burns---- ,,emily4 ,it burns like a candle with a long flame4 ,but why does this combustion last so much longer than in the former experiment8 ,,mrs4 ,b4 ,the combustion goes on uninterruptedly as long as the new gas continues to be produced4 ,now if ,i invert this receiver over the flame1 you will soon perceive its internal surface covered with a very fine dew1 which is pure water---- ,,caroline4 ,yes1 indeed2 the glass is now quite dim with moisture6 ,how glad ,i am that we can see the water produced by this combustion4 ,,emily4 ,it is exactly what ,i was anxious to see2 for ,i confess ,i was a little incredulous4 ,,mrs4 ,b4 ,if ,i had not held the glass-bell over the flame1 the water would have escaped in the state of vapour1 as it did in the former experiment4 ,we have here1 of course1 obtained but a very small quantity of water2 but the difficulty of procuring a proper apparatus1 with sufficient quantities of gases1 prevents my showing it you on a larger scale4 ,the composition of water was discovered about the same period1 both by ,mr4 ,cavendish1 in this country1 and by the celebrated ,french chemist ,lavoisier4 ,the latter invented a very perfect and ingenious apparatus to perform1 with great accuracy1 and upon a large scale1 the formation of water by the combination of oxygen and hydrogen gases4 ,two tubes1 conveying due proportions1 the one of oxygen1 the other of hydrogen gas1 are inserted at opposite sides of a large globe of glass1 previously exhausted of air2 the two streams of gas are kindled within the globe1 by the electrical spark1 at the point where they come in contact2 they burn together1 that is to say1 the hydrogen combines with the oxygen1 the caloric is set at liberty1 and a quantity of water is produced exactly equal1 in weight1 to that of the two gases introduced into the globe4 ,,caroline4 ,and what was the greatest quantity of water ever formed in this apparatus8 ,,mrs4 ,b4 ,several ounces2 indeed1 very nearly a pound1 if ,i recollect right2 but the operation lasted many days4 ,,emily4 ,this experiment must have convinced all the world of the truth of the discovery4 ,pray1 if improper proportions of the gases were mixed and set fire to1 what would be the result8 ,,mrs4 ,b4 ,water would equally be formed1 but there would be a residue of either one or other of the gases1 because1 as ,i have already told you1 hydrogen and oxygen will combine only in the proportions requisite for the formation of water4 ,,emily4 ,look1 ,mrs4 ,b41 our experiment with the ,voltaic battery 7,,plate ,,viii4 fig4 #b47 has made great progress2 a quantity of gas has been formed in each tube1 but in one of them there is twice as much gas as in the other4 ,,mrs4 ,b4 ,yes2 because1 as ,i said before1 water is composed of two volumes of hydrogen to one of oxygen--and if we should now mix these gases together and set fire to them by an electrical spark1 both gases would entirely disappear1 and a small quantity of water would be formed4 ,there is another curious effect produced by the combustion of hydrogen gas1 which ,i shall show you1 though ,i must acquaint you first1 that ,i cannot well explain the cause of it4 ,for this purpose1 ,i must put some materials into our apparatus1 in order to obtain a stream of hydrogen gas1 just as we have done before4 ,the process is already going on1 and the gas is rushing through the tube--,i shall now kindle it with the taper---- ,,emily4 ,it burns exactly as it did before---- ,what is the curious effect which you were mentioning8 ,,mrs4 ,b4 ,instead of the receiver1 by means of which we have just seen the drops of water form1 we shall invert over the flame this piece of tube1 which is about two feet in length1 and one inch in diameter 7,,plate ,,viii4 fig4 #g472 but you must observe that it is open at both ends4 ,,emily4 ,what a strange noise it makes6 something like the olian harp1 but not so sweet4 ,,caroline4 ,it is very singular1 indeed2 but ,i think rather too powerful to be pleasing4 ,and is not this sound accounted for8 ,,mrs4 ,b4 ,that the percussion of glass1 by a rapid stream of gas1 should produce a sound1 is not extraordinary3 but the sound here is so peculiar1 that no other gas has a similar effect4 ,perhaps it is owing to a brisk vibratory motion of the glass1 occasioned by the successive formation and condensation of small drops of water on the sides of the glass tube1 and the air rushing in to replace the vacuum formed499 ,footnote 993 ,this ingenious explanation was first suggested by ,dr4 ,delarive4 --,see ,journals of the ,royal ,institution1 vol4 i4 p4 #bei4 ,,caroline4 ,how very much this flame resembles the burning of a candle4 ,,mrs4 ,b4 ,the burning of a candle is produced by much the same means4 ,a great deal of hydrogen is contained in candles1 whether of tallow or wax4 ,this hydrogen being converted into gas by the heat of the candle1 combines with the oxygen of the atmosphere1 and flame and water result from this combination4 ,so that1 in fact1 the flame of a candle is owing to the combustion of hydrogen gas4 ,an elevation of temperature1 such as is produced by a lighted match or taper1 is required to give the first impulse to the combustion2 but afterwards it goes on of itself1 because the candle finds a supply of caloric in the successive quantities of heat which results from the union of the two electricities given out by the gases during their combustion4 ,but there are other circumstances connected with the combustion of candles and lamps1 which ,i cannot explain to you till you are acquainted with carbon1 which is one of their constituent parts4 ,in general1 however1 whenever you see flame1 you may infer that it is owing to the formation and burning of hydrogen gas992 for flame is the peculiar mode of burning hydrogen gas1 which1 with only one or two apparent exceptions1 does not belong to any other combustible4 ,footnote 993 ,or rather1 hydro-carbonat1 a gas composed of hydrogen and carbon1 which will be noticed under the head ,carbon4 ,,emily4 ,you astonish me6 ,i understood that flame was the caloric produced by the union of the two electricities1 in all combustions whatever8 ,,mrs4 ,b4 ,your error proceeded from your vague and incorrect idea of flame2 you have confounded it with light and caloric in general4 ,flame always implies caloric1 since it is produced by the combustion of hydrogen gas2 but all caloric does not imply flame4 ,many bodies burn with intense heat without producing flame4 ,coals1 for instance1 burn with flame until all the hydrogen which they contain is evaporated2 but when they afterwards become red hot1 much more caloric is disengaged than when they produce flame4 ,,caroline4 ,but the iron wire1 which you burnt in oxygen gas1 appeared to me to emit flame2 yet1 as it was a simple metal1 it could contain no hydrogen8 ,,mrs4 ,b4 ,it produced a sparkling dazzling blaze of light1 but no real flame4 ,,emily4 ,and what is the cause of the regular shape of the flame of a candle8 ,,mrs4 ,b4 ,the regular stream of hydrogen gas which exhales from its combustible matter4 ,,caroline4 ,but the hydrogen gas must1 from its great levity1 ascend into the upper regions of the atmosphere2 why therefore does not the flame continue to accompany it8 ,,mrs4 ,b4 ,the combustion of the hydrogen gas is completed at the point where the flame terminates2 it then ceases to be hydrogen gas1 as it is converted by its combination with oxygen into watery vapour2 but in a state of such minute division as to be invisible4 ,,caroline4 ,i do not understand what is the use of the wick of a candle1 since the hydrogen gas burns so well without it8 ,,mrs4 ,b4 ,the combustible matter of the candle must be decomposed in order to emit the hydrogen gas1 and the wick is instrumental in effecting this decomposition4 ,its combustion first melts the combustible matter1 and 4 4 4 4 ,,caroline4 ,but in lamps the combustible matter is already fluid1 and yet they also require wicks8 ,,mrs4 ,b4 ,i am going to add that1 afterwards1 the burning wick 7by the power of capillary attraction7 gradually draws up the fluid to the point where combustion takes place2 for you must have observed that the wick does not burn quite to the bottom4 ,,caroline4 ,yes2 but ,i do not understand why it does not4 ,,mrs4 ,b4 ,because the air has not so free an access to that part of the wick which is immediately in contact with the candle1 as to the part just above1 so that the heat there is not sufficient to produce its decomposition2 the combustion therefore begins a little above this point4 ,,caroline4 ,but1 ,mrs4 ,b41 in those beautiful lights1 called gas-lights1 which are now seen in many streets1 and will1 ,i hope1 be soon adopted every where1 ,i can perceive no wick at all4 ,how are these lights managed8 ,,mrs4 ,b4 ,i am glad you have put me in mind of saying a few words on this very useful and interesting improvement4 ,in this mode of lighting1 the gas is conveyed to the extremity of a tube1 where it is kindled1 and burns as long as the supply continues4 ,there is1 therefore1 no occasion for a wick1 or any other fuel whatever4 ,,emily4 ,but how is all this gas procured in such large quantities8 ,,mrs4 ,b4 ,it is obtained from coal1 by distillation4 --,coal1 when exposed to heat in a close vessel1 is decomposed2 and hydrogen1 which is one of its constituents1 rises in the state of gas1 combined with another of its component parts1 carbon1 forming a compound gas1 called ,hydrocarbonat1 the nature of which we shall again have an opportunity of noticing when we treat of carbon4 ,this gas1 like hydrogen1 is perfectly transparent1 invisible1 and highly inflammable2 and in burning it emits that vivid light which you have so often observed4 ,,caroline4 ,and does the process for procuring it require nothing but heating the coals1 and conveying the gas through tubes8 ,,mrs4 ,b4 ,nothing else2 except that the gas must be made to pass1 immediately at its formation1 through two or three large vessels of water1 in which it deposits some other ingredients1 and especially water1 tar1 and oil1 which also arise from the distillation of coals4 ,the gas-light apparatus1 therefore1 consists simply in a large iron vessel1 in which the coals are exposed to the heat of a furnace1--some reservoirs of water1 in which the gas deposits its impurities1--and tubes that convey it to the desired spot1 being propelled with uniform velocity through the tubes by means of a certain degree of pressure which is made upon the reservoir4 ,,emily4 ,what an admirable contrivance6 ,do you not think1 ,mrs4 ,b41 that it will soon get into universal use8 ,,mrs4 ,b4 ,most probably1 as to the lighting of streets1 offices1 and public places1 as it far surpasses any former invention for that purpose2 but as to the interior of private houses1 this mode of lighting has not yet been sufficiently tried to know whether it will be found generally desirable1 either in regard to economy or convenience4 ,it may1 however1 be considered as one of the happiest applications of chemistry to the comforts of life2 and there is every reason to suppose that it will answer the full extent of public1 expectation4 ,i have another experiment to show you with hydrogen gas1 which ,i think will entertain you4 ,have you ever blown bubbles with soap and water8 ,,emily4 ,yes1 often1 when ,i was a child2 and ,i used to make them float in the air by blowing them upwards4 ,,mrs4 ,b4 ,we shall fill some such bubbles with hydrogen gas1 instead of atmospheric air1 and you will see with what ease and rapidity they will ascend1 without the assistance of blowing1 from the lightness of the gas4 --,will you mix some soap and water whilst ,i fill this bladder with the gas contained in the receiver which stands on the shelf in the water-bath8 ,,caroline4 ,what is the use of the brass-stopper and turn-cock at the top of the receiver8 ,,mrs4 ,b4 ,it is to afford a passage to the gas when required4 ,there is1 you see1 a similar stop-cock fastened to this bladder1 which is made to fit that on the receiver4 ,i screw them one on the other1 and now turn the two cocks1 to open a communication between the receiver and the bladder2 then1 by sliding the receiver off the shelf1 and gently sinking it into the bath1 the water rises in the receiver and forces the gas into the bladder4 7,,plate ,,ix4 fig4 #a47 ,illustration3 ,plate ,,ix4 ,vol4 ,i4 p4 #bbh ,fig4 #a4 ,apparatus for transferring gases from a ,receiver into a bladder4 ,fig4 #b4 ,apparatus for blowing ,soap bubbles4 ,,caroline4 ,yes1 ,i see the bladder swell as the water rises in the receiver4 ,,mrs4 ,b4 ,i think that we have already a sufficient quantity in the bladder for our purpose2 we must be careful to stop both the cocks before we separate the bladder from the receiver1 lest the gas should escape4 --,now ,i must fix a pipe to the stopper of the bladder1 and by dipping its mouth into the soap and water1 take up a few drops--then ,i again turn the cock1 and squeeze the bladder in order to force the gas into the soap and water at the mouth of the pipe4 7,,plate ,,ix4 fig4 #b47 ,,emily4 ,there is a bubble--but it bursts before it leaves the mouth of the pipe4 ,,mrs4 ,b4 ,we must have patience and try again2 it is not so easy to blow bubbles by means of a bladder1 as simply with the breath4 ,,caroline4 ,perhaps there is not soap enough in the water2 ,i should have had warm water1 it would have dissolved the soap better4 ,,emily4 ,does not some of the gas escape between the bladder and the pipe8 ,,mrs4 ,b4 ,no1 they are perfectly air tight2 we shall succeed presently1 ,i dare say4 ,,caroline4 ,now a bubble ascends2 it moves with the rapidity of a balloon4 ,how beautifully it refracts the light6 ,,emily4 ,it has burst against the ceiling--you succeed now wonderfully2 but why do they all ascend and burst against the ceiling8 ,,mrs4 ,b4 ,hydrogen gas is so much lighter than atmospherical air1 that it ascends rapidly with its very light envelope1 which is burst by the force with which it strikes the ceiling4 ,air-balloons are filled with this gas1 and if they carried no other weight than their covering1 would ascend as rapidly as these bubbles4 ,,caroline4 ,yet their covering must be much heavier than that of these bubbles8 ,,mrs4 ,b4 ,not in proportion to the quantity of gas they contain4 ,i do not know whether you have ever been present at the filling of a large balloon4 ,the apparatus for that purpose is very simple4 ,it consists of a number of vessels1 either jars or barrels1 in which the materials for the formation of the gas are mixed1 each of these being furnished with a tube1 and communicating with a long flexible pipe1 which conveys the gas into the balloon4 ,,emily4 ,but the fire-balloons which were first invented1 and have been since abandoned1 on account of their being so dangerous1 were constructed1 ,i suppose1 on a different principle4 ,,mrs4 ,b4 ,they were filled simply with atmospherical air1 considerably rarefied by heat2 and the necessity of having a fire underneath the balloon1 in order to preserve the rarefaction of the air within it1 was the circumstance productive of so much danger4 ,if you are not yet tired of experiments1 ,i have another to show you4 ,it consists in filling soap-bubbles with a mixture of hydrogen and oxygen gases1 in the proportions that form water2 and afterwards setting fire to them4 ,,emily4 ,they will detonate1 ,i suppose8 ,,mrs4 ,b4 ,yes1 they will4 ,as you have seen the method of transferring the gas from the receiver into the bladder1 it is not necessary to repeat it4 ,i have therefore provided a bladder which contains a due proportion of oxygen and hydrogen gases1 and we have only to blow bubbles with it4 ,,caroline4 ,here is a fine large bubble rising--shall ,i set fire to it with the candle8 ,,mrs4 ,b4 ,if you please 4 4 4 4 ,,caroline4 ,heavens1 what an explosion6 --,it was like the report of a gun3 ,i confess it frightened me much4 ,i never should have imagined it could be so loud4 ,,emily4 ,and the flash was as vivid as lightning4 ,,mrs4 ,b4 ,the combination of the two gases takes place during that instant of time that you see the flash1 and hear the detonation4 ,,emily4 ,this has a strong resemblance to thunder and lightning4 ,,mrs4 ,b4 ,these phenomena1 however1 are generally of an electrical nature4 ,yet various meteorological effects may be attributed to accidental detonations of hydrogen gas in the atmosphere2 for nature abounds with hydrogen3 it constitutes a very considerable portion of the whole mass of water belonging to our globe1 and from that source almost every other body obtains it4 ,it enters into the composition of all animal substances1 and of a great number of minerals2 but it is most abundant in vegetables4 ,from this immense variety of bodies1 it is often spontaneously disengaged2 its great levity makes it rise into the superior regions of the atmosphere2 and when1 either by an electrical spark1 or any casual elevation of temperature1 it takes fire1 it may produce such meteors or luminous appearances as are occasionally seen in the atmosphere4 ,of this kind are probably those broad flashes which we often see on a summer-evening1 without hearing any detonation4 ,,emily4 ,every flash1 ,i suppose1 must produce a quantity of water8 ,,caroline4 ,and this water1 naturally1 descends in the form of rain8 ,,mrs4 ,b4 ,that probably is often the case1 though it is not a necessary consequence2 for the water may be dissolved by the atmosphere1 as it descends towards the lower regions1 and remain there in the form of clouds4 ,the application of electrical attraction to chemical phenomena is likely to lead to many very interesting discoveries in meteorology2 for electricity evidently acts a most important part in the atmosphere4 ,this subject however1 is1 as yet1 not sufficiently developed for me to venture enlarging upon it4 ,the phenomena of the atmosphere are far from being well understood2 and even with the little that is known1 ,i am but imperfectly acquainted4 ,but before we take leave of hydrogen1 ,i must not omit to mention to you a most interesting discovery of ,sir ,h4 ,davy1 which is connected with this subject4 ,,caroline4 ,you allude1 ,i suppose1 to the new miner's lamp1 which has of late been so much talked of8 ,i have long been desirous of knowing what that discovery was1 and what purpose it was intended to answer4 ,,mrs4 ,b4 ,it often happens in coal-mines1 that quantities of the gas1 called by chemists hydro-carbonat1 or by the miners fire-damp1 7the same from which the gas-lights are obtained17 ooze out from fissures in the beds of coal1 and fill the cavities in which the men are at work2 and this gas being inflammable1 the consequence is1 that when the men approach those places with a lighted candle1 the gas takes fire1 and explosions happen which destroy the men and horses employed in that part of the colliery1 sometimes in great numbers4 ,,emily4 ,what tremendous accidents these must be6 ,but whence does that gas originate8 ,,mrs4 ,b4 ,being the chief product of the combustion of coal1 no wonder that inflammable gas should occasionally appear in situations in which this mineral abounds1 since there can be no doubt that processes of combustion are frequently taking place at a great depth under the surface of the earth2 and therefore those accumulations of gas may arise either from combustions actually going on1 or from former combustions1 the gas having perhaps been confined there for ages4 ,,caroline4 ,and how does ,sir ,h4 ,davy's lamp prevent those dreadful explosions8 ,,mrs4 ,b4 ,by a contrivance equally simple and ingenious2 and one which does no less credit to the philosophical views from which it was deduced1 than to the philanthropic motives from which the enquiry sprung4 ,the principle of the lamp is shortly this3 ,it was ascertained1 two or three years ago1 both by ,mr4 ,tennant and by ,sir ,humphry himself1 that the combustion of inflammable gas could not be propagated through small tubes2 so that if a jet of an inflammable gaseous mixture1 issuing from a bladder or any other vessel1 through a small tube1 be set fire to1 it burns at the orifice of the tube1 but the flame never penetrates into the vessel4 ,it is upon this fact that ,sir ,humphry's safety-lamp is founded4 ,,emily4 ,but why does not the flame ever penetrate through the tube into the vessel from which the gas issues1 so as to explode at once the whole of the gas8 ,,mrs4 ,b4 ,because1 no doubt1 the inflamed gas is so much cooled in its passage through a small tube as to cease to burn before the combustion reaches the reservoir4 ,,caroline4 ,and how can this principle be applied to the construction of a lamp8 ,,mrs4 ,b4 ,nothing easier4 ,you need only suppose a lamp enclosed all round in glass or horn1 but having a number of small open tubes at the bottom1 and others at the top1 to let the air in and out4 ,now1 if such a lamp or lanthorn be carried into an atmosphere capable of exploding1 an explosion or combustion of the gas will take place within the lamp2 and although the vent afforded by the tubes will save the lamp from bursting1 yet1 from the principle just explained1 the combustion will not be propagated to the external air through the tubes1 so that no farther consequence will ensue4 ,,emily4 ,and is that all the mystery of that valuable lamp8 ,,mrs4 ,b4 ,no2 in the early part of the enquiry a lamp of this kind was actually proposed2 but it was but a rude sketch compared to its present state of improvement4 ,sir ,h4 ,davy1 after a succession of trials1 by which he brought his lamp nearer and nearer to perfection1 at last conceived the happy idea that if the lamp were surrounded with a wire-work or wire-gauze1 of a close texture1 instead of glass or horn1 the tubular contrivance ,i have just described would be entirely superseded1 since each of the interstices of the gauze would act as a tube in preventing the propagation of explosions2 so that this pervious metallic covering would answer the various purposes of transparency1 of permeability to air1 and of protection against explosion4 ,this idea1 ,sir ,humphry immediately submitted to the test of experiment1 and the result has answered his most sanguine expectations1 both in his laboratory and in the collieries1 where it has already been extensively tried4 ,and he has now the happiness of thinking that his invention will probably be the means of saving every year a number of lives1 which would have been lost in digging out of the bowels of the earth one of the most valuable necessaries of life4 ,here is one of these lamps1 every part of which you will at once comprehend4 7,see ,,plate ,x4 fig4 #a47 ,illustration3 ,plate ,x4 ,fig4 #a4 ,a4 the cistern containing the ,oil ,b4 the rim or screw by which the gauze cage is fixed to the cistern4 ,c4 apperture for supplying ,oil4 ,e4 a wire for trimming the wick4 ,d4 ,f4 the wire gauze cylinder4 ,g4 a double top4 ,fig4 #b4 ,a4 the reservoir of condensed air4 ,b4 the condensing ,syringe4 ,c4 the bladder for ,oxygen4 ,d4 the moveable jet4 ,,caroline4 ,how very simple and ingenious6 ,but ,i do not yet well see why an explosion taking place within the lamp should not communicate to the external air around it1 through the interstices of the wire8 ,,mrs4 ,b4 ,this has been and is still a subject of wonder1 even to philosophers2 and the only mode they have of explaining it is1 that flame or ignition cannot pass through a fine wire-work1 because the metallic wire cools the flame sufficiently to extinguish it in passing through the gauze4 ,this property of the wire-gauze is quite similar to that of the tubes which ,i mentioned on introducing the subject2 for you may consider each interstice of the gauze as an extremely short tube of a very small diameter4 ,,emily4 ,but ,i should expect the wire would often become red-hot1 by the burning of the gas within the lamp8 ,,mrs4 ,b4 ,and this is actually the case1 for the top of the lamp is very apt to become red-hot4 ,but1 fortunately1 inflammable gaseous mixtures cannot be exploded by red-hot wire1 the intervention of actual flame being required for that purpose2 so that the wire does not set fire to the explosive gas around it4 ,,emily4 ,i can understand that2 but if the wire be red-hot1 how can it cool the flame within1 and prevent its passing through the gauze8 ,,mrs4 ,b4 ,the gauze1 though red-hot1 is not so hot as the flame by which it has been heated2 and as metallic wire is a good conductor1 the heat does not much accumulate in it1 as it passes off quickly to the other parts of the lamp1 as well as to any contiguous bodies4 ,,caroline4 ,this is indeed a most interesting discovery1 and one which shows at once the immense utility with which science may be practically applied to some of the most important purposes4 ,,conversation ,,viii4 ,,on ,,sulphur ,,and ,,phosphorus4 ,,mrs4 ,b4 ,,sulphur is the next substance that comes under our consideration4 ,it differs in one essential point from the preceding1 as it exists in a solid form at the temperature of the atmosphere4 ,,caroline4 ,i am glad that we have at last a solid body to examine2 one that we can see and touch4 ,pray1 is it not with sulphur that the points of matches are covered1 to make them easily kindle8 ,,mrs4 ,b4 ,yes1 it is2 and you therefore already know that sulphur is a very combustible substance4 ,it is seldom discovered in nature in a pure unmixed state2 so great is its affinity for other substances1 that it is almost constantly found combined with some of them4 ,it is most commonly united with metals1 under various forms1 and is separated from them by a very simple process4 ,it exists likewise in many mineral waters1 and some vegetables yield it in various proportions1 especially those of the cruciform tribe4 ,it is also found in animal matter2 in short1 it may be discovered in greater or less quantity1 in the mineral1 vegetable1 and animal kingdoms4 ,,emily4 ,i have heard of flowers of sulphur1 are they the produce of any plant8 ,,mrs4 ,b4 ,by no means3 they consist of nothing more than common sulphur1 reduced to a very fine powder by a process called sublimation4 --,you see some of it in this phial2 it is exactly the same substance as this lump of sulphur1 only its colour is a paler yellow1 owing to its state of very minute division4 ,,emily4 ,pray what is sublimation8 ,,mrs4 ,b4 ,it is the evaporation1 or1 more properly speaking1 the volatilisation of solid substances1 which1 in cooling1 condense again in a concrete form4 ,the process1 in this instance1 must be performed in a closed vessel1 both to prevent combustion1 which would take place if the access of air were not carefully precluded1 and likewise in order to collect the substance after the operation4 ,as it is rather a slow process1 we shall not try the experiment now2 but you will understand it perfectly if ,i show you the apparatus used for the purpose4 7,,plate ,,xi4 fig4 #a47 ,some lumps of sulphur are put into a receiver of this kind1 which is called a cucurbit4 ,its shape1 you see1 somewhat resembles that of a pear1 and is open at the top1 so as to adapt itself exactly to a kind of conical receiver of this sort1 called the head4 ,the cucurbit1 thus covered with its head1 is placed over a sand-bath2 this is nothing more than a vessel full of sand1 which is kept heated by a furnace1 such as you see here1 so as to preserve the apparatus in a moderate and uniform temperature4 ,the sulphur then soon begins to melt1 and immediately after this1 a thick white smoke rises1 which is gradually deposited within the head1 or upper part of the apparatus1 where it condenses against the sides1 somewhat in the form of a vegetation1 whence it has obtained the name of flowers of sulphur4 ,this apparatus1 which is called an alembic1 is highly useful in all kinds of distillations1 as you will see when we come to treat of those operations4 ,alembics are not commonly made of glass1 like this1 which is applicable only to distillations upon a very small scale4 ,those used in manufactures are generally made of copper1 and are1 of course1 considerably larger4 ,the principal construction1 however1 is always the same1 although their shape admits of some variation4 ,illustration3 ,plate ,,xi4 ,vol4 ,i4 p4 #bcg4 ,fig4 #a4 ,sublimation of ,sulphur4 ,a ,alembic4 ,b ,sand-bath4 ,c ,furnace4 ,fig4 #b4 ,eudiometer4 ,fig4 #c4 ,decomposition of water by ,carbon4 ,a ,retort containing water4 ,b ,lamp to heat the water4 ,c4,c ,porcelain tube containing ,carbone4 ,d ,furnace through which the tube passes4 ,e ,receiver for the gas produced4 ,f ,water bath4 ,,caroline4 ,what is the use of that neck1 or tube1 which bends down from the upper piece of the apparatus8 ,,mrs4 ,b4 ,it is of no use in sublimations2 but in distillations 7the general object of which is to evaporate1 by heat1 in closed vessels1 the volatile parts of a compound body1 and to condense them again into a liquid17 it serves to carry off the condensed fluid1 which otherwise would fall back into the cucurbit4 ,but this is rather foreign to our present subject4 ,let us return to the sulphur4 ,you now perfectly understand1 ,i suppose1 what is meant by sublimation8 ,,emily4 ,i believe ,i do4 ,sublimation appears to consist in destroying1 by means of heat1 the attraction of aggregation of the particles of a solid body1 which are thus volatilised2 and as soon as they lose the caloric which produced that effect1 they are deposited in the form of a fine powder4 ,,caroline4 ,it seems to me to be somewhat similar to the transformation of water into vapour1 which returns to its liquid state when deprived of caloric4 ,,emily4 ,there is this difference1 however1 that the sulphur does not return to its former state1 since1 instead of lumps1 it changes to a fine powder4 ,,mrs4 ,b4 ,chemically speaking1 it is exactly the same substance1 whether in the form of lump or powder4 ,for if this powder be melted again by heat1 it will1 in cooling1 be restored to the same solid state in which it was before its sublimation4 ,,caroline4 ,but if there be no real change1 produced by the sublimation of the sulphur1 what is the use of that operation8 ,,mrs4 ,b4 ,it divides the sulphur into very minute parts1 and thus disposes it to enter more readily into combination with other bodies4 ,it is used also as a means of purification4 ,,caroline4 ,sublimation appears to me like the beginning of combustion1 for the completion of which one circumstance only is wanting1 the absorption of oxygen4 ,,mrs4 ,b4 ,but that circumstance is every thing4 ,no essential alteration is produced in sulphur by sublimation2 whilst in combustion it combines with the oxygen1 and forms a new compound totally different in every respect from sulphur in its pure state4 --,we shall now burn some sulphur1 and you will see how very different the result will be4 ,for this purpose ,i put a small quantity of flowers of sulphur into this cup1 and place it in a dish1 into which ,i have poured a little water3 ,i now set fire to the sulphur with the point of this hot wire2 for its combustion will not begin unless its temperature be considerably raised4 --,you see that it burns with a faint blueish flame2 and as ,i invert over it this receiver1 white fumes arise from the sulphur1 and fill the vessel4 --,you will soon perceive that the water is rising within the receiver1 a little above its level in the plate4 --,well1 ,emily1 can you account for this8 ,,emily4 ,i suppose that the sulphur has absorbed the oxygen from the atmospherical air within the receiver1 and that we shall find some oxygenated sulphur in the cup4 ,as for the white smoke1 ,i am quite at a loss to guess what it may be4 ,,mrs4 ,b4 ,your first conjecture is very right3 but you are mistaken in the last2 for nothing will be left in the cup4 ,the white vapour is the oxygenated sulphur1 which assumes the form of an elastic fluid of a pungent and offensive smell1 and is a powerful acid4 ,here you see a chemical combination of oxygen and sulphur1 producing a true gas1 which would continue such under the pressure and at the temperature of the atmosphere1 if it did not unite with the water in the plate1 to which it imparts its acid taste1 and all its acid properties4 --,you see1 now1 with what curious effects the combustion of sulphur is attended4 ,,caroline4 ,this is something quite new2 and ,i confess that ,i do not perfectly understand why the sulphur turns acid4 ,,mrs4 ,b4 ,it is because it unites with oxygen1 which is the acidifying principle4 ,and1 indeed1 the word oxygen is derived from two ,greek words signifying to produce an acid4 ,,caroline4 ,why1 then1 is not water1 which contains such a quantity of oxygen1 acid8 ,,mrs4 ,b4 ,because hydrogen1 which is the other constituent of water1 is not susceptible of acidification4 --,i believe it will be necessary1 before we proceed further1 to say a few words of the general nature of acids1 though it is rather a deviation from our plan of examining the simple bodies separately1 before we consider them in a state of combination4 ,acids may be considered as a peculiar class of burnt bodies1 which during their combustion1 or combination with oxygen1 have acquired very characteristic properties4 ,they are chiefly discernible by their sour taste1 and by turning red most of the blue vegetable colours4 ,these two properties are common to the whole class of acids2 but each of them is distinguished by other peculiar qualities4 ,every acid consists of some particular substance1 7which constitutes its basis1 and is different in each17 and of oxygen1 which is common to them all4 ,,emily4 ,but ,i do not clearly see the difference between acids and oxyds4 ,,mrs4 ,b4 ,acids were1 in fact1 oxyds1 which1 by the addition of a sufficient quantity of oxygen1 have been converted into acids4 ,for acidification1 you must observe1 always implies previous oxydation1 as a body must have combined with the quantity of oxygen requisite to constitute it an oxyd1 before it can combine with the greater quantity that is necessary to render it an acid4 ,,caroline4 ,are all oxyds capable of being converted into acids8 ,,mrs4 ,b4 ,very far from it2 it is only certain substances which will enter into that peculiar kind of union with oxygen that produces acids1 and the number of these is proportionally very small2 but all burnt bodies may be considered as belonging either to the class of oxyds1 or to that of acids4 ,at a future period1 we shall enter more at large into this subject4 ,at present1 ,i have but one circumstance further to point out to your observation respecting acids3 it is1 that most of them are susceptible of two degrees of acidification1 according to the different quantities of oxygen with which their basis combines4 ,,emily4 ,and how are these two degrees of acidification distinguished8 ,,mrs4 ,b4 ,by the peculiar properties which result from them4 ,the acid we have just made is the first or weakest degree of acidification1 and is called sulphureous acid2 if it were fully saturated with oxygen1 it would be called sulphuric acid4 ,you must therefore remember1 that in this1 as in all acids1 the first degree of acidification is expressed by the termination in ous2 the stronger1 by the termination in ic4 ,,caroline4 ,and how is the sulphuric acid made8 ,,mrs4 ,b4 ,by burning sulphur in pure oxygen gas1 and thus rendering its combustion much more complete4 ,i have provided some oxygen gas for this purpose2 it is in that bottle1 but we must first decant the gas into the glass receiver which stands on the shelf in the bath1 and is full of water4 ,,caroline4 ,pray1 let me try to do it1 ,mrs4 ,b4 ,,mrs4 ,b4 ,it requires some little dexterity--hold the bottle completely under water1 and do not turn the mouth upwards1 till it is immediately under the aperture in the shelf1 through which the gas is to pass into the receiver1 and then turn it up gradually4 --,very well1 you have only let a few bubbles escape1 and that must be expected at a first trial4 --,now ,i shall put this piece of sulphur into the receiver1 through the opening at the top1 and introduce along with it a small piece of lighted tinder to set fire to it4 --,this requires being done very quickly1 lest the atmospherical air should get in1 and mix with the pure oxygen gas4 ,,emily4 ,how beautifully it burns6 ,,caroline4 ,but it is already buried in the thick vapour4 ,this1 ,i suppose1 is sulphuric acid8 ,,emily4 ,are these acids always in a gaseous state8 ,,mrs4 ,b4 ,sulphureous acid1 as we have already observed1 is a permanent gas1 and can be obtained in a liquid form only by condensing it in water4 ,in its pure state1 the sulphureous acid is invisible1 and it now appears in the form of a white smoke1 from its combining with the moisture4 ,but the vapour of sulphuric acid1 which you have just seen to rise during the combustion1 is not a gas1 but only a vapour1 which condenses into liquid sulphuric acid1 by losing its caloric4 ,but it appears from ,sir ,h4 ,davy's experiments1 that this formation and condensation of sulphuric acid requires the presence of water1 for which purpose the vapour is received into cold water1 which may afterwards be separated from the acid by evaporation4 ,sulphur has hitherto been considered as a simple substance2 but ,sir ,h4 ,davy has suspected that it contains a small portion of hydrogen1 and perhaps also of oxygen4 ,on submitting sulphur to the action of the ,voltaic battery1 he observed that the negative wire gave out hydrogen2 and the existence of hydrogen in sulphur was rendered still more probable by his observing that a small quantity of water was produced during the combustion of sulphur4 ,,emily4 ,and pray of what nature is sulphur when perfectly pure8 ,,mrs4 ,b4 ,sulphur has probably never been obtained perfectly free from combination1 so that its radical may possibly possess properties very different from those of common sulphur4 ,it has been suspected to be of a metallic nature2 but this is mere conjecture4 ,before we quit the subject of sulphur1 ,i must tell you that it is susceptible of combining with a great variety of substances1 and especially with hydrogen1 with which you are already acquainted4 ,hydrogen gas can dissolve a small portion of it4 ,,emily4 ,what6 can a gas dissolve a solid substance8 ,,mrs4 ,b4 ,yes2 a solid substance may be so minutely divided by heat1 as to become soluble in a gas3 and there are several instances of it4 ,but you must observe1 that1 in this case1 a chemical union or combination of the sulphur with the hydrogen gas is produced4 ,in order to effect this1 the sulphur must be strongly heated in contact with the gas2 the heat reduces the sulphur to such a state of extreme division1 and diffuses it so thoroughly through the gas1 that they combine and incorporate together4 ,and as a proof that there must be a chemical union between the sulphur and the gas1 it is sufficient to remark that they are not separated when the sulphur loses the caloric by which it was volatilized4 ,besides1 it is evident1 from the peculiar fetid smell of this gas1 that it is a new compound totally different from either of its constituents2 it is called sulphuretted hydrogen gas1 and is contained in great abundance in sulphureous mineral waters4 ,,caroline4 ,are not the ,harrogate waters of this nature8 ,,mrs4 ,b4 ,yes2 they are naturally impregnated with sulphuretted hydrogen gas1 and there are many other springs of the same kind1 which shows that this gas must often be formed in the bowels of the earth by spontaneous processes of nature4 ,,caroline4 ,and could not such waters be made artificially by impregnating common water with this gas8 ,,mrs4 ,b4 ,yes2 they can be so well imitated1 as perfectly to resemble the ,harrogate waters4 ,sulphur combines likewise with phosphorus1 and with the alkalies1 and alkaline earths1 substances with which you are yet unacquainted4 ,we cannot1 therefore1 enter into these combinations at present4 ,in our next lesson we shall treat of phosphorus4 ,,emily4 ,may we not begin that subject to-day2 this lesson has been so short8 ,,mrs4 ,b4 ,i have no objection1 if you are not tired4 ,what do you say1 ,caroline8 ,,caroline4 ,i am as desirous as ,emily of prolonging the lesson to-day1 especially as we are to enter on a new subject2 for ,i confess that sulphur has not appeared to me so interesting as the other simple bodies4 ,,mrs4 ,b4 ,perhaps you may find phosphorus more entertaining4 ,you must not1 however1 be discouraged when you meet with some parts of a study less amusing than others2 it would answer no good purpose to select the most pleasing parts1 since1 if we did not proceed with some method1 in order to acquire a general idea of the whole1 we could scarcely expect to take interest in any particular subjects4 ,,phosphorus4 ,,phosphorus is considered as a simple body2 though1 like sulphur1 it has been suspected of containing hydrogen4 ,it was not known by the earlier chemists4 ,it was first discovered by ,brandt1 a chemist of ,hamburgh1 whilst employed in researches after the philosopher's stone2 but the method of obtaining it remained a secret till it was a second time discovered both by ,kunckel and ,boyle1 in the year #afhj4 ,you see a specimen of phosphorus in this phial2 it is generally moulded into small sticks of a yellowish colour1 as you find it here4 ,,caroline4 ,i do not understand in what the discovery consisted2 there may be a secret method of making an artificial composition1 but how can you talk of making a substance which naturally exists8 ,,mrs4 ,b4 ,a body may exist in nature so closely combined with other substances1 as to elude the observation of chemists1 or render it extremely difficult to obtain it in its separate state4 ,this is the case with phosphorus1 which is always so intimately combined with other substances1 that its existence remained unnoticed till ,brandt discovered the means of obtaining it free from other combinations4 ,it is found in all animal substances1 and is now chiefly extracted from bones1 by a chemical process4 ,it exists also in some plants1 that bear a strong analogy to animal matter in their chemical composition4 ,,emily4 ,but is it never found in its pure separate state8 ,,mrs4 ,b4 ,never1 and this is the reason that it has remained so long undiscovered4 ,phosphorus is eminently combustible2 it melts and takes fire at the temperature of one hundred degrees1 and absorbs in its combustion nearly once and a half its own weight of oxygen4 ,,caroline4 ,what6 will a pound of phosphorus consume a pound and half of oxygen8 ,,mrs4 ,b4 ,so it appears from accurate experiments4 ,i can show you with what violence it combines with oxygen1 by burning some of it in that gas4 ,we must manage the experiment in the same manner as we did the combustion of sulphur4 ,you see ,i am obliged to cut this little bit of phosphorus under water1 otherwise there would be danger of its taking fire by the heat of my fingers4 ,i now put into the receiver1 and kindle it by means of a hot wire4 ,,emily4 ,what a blaze6 ,i can hardly look at it4 ,i never saw any thing so brilliant4 ,does it not hurt your eyes1 ,caroline8 ,,caroline4 ,yes2 but still ,i cannot help looking at it4 ,a prodigious quantity of oxygen must indeed be absorbed1 when so much light and caloric are disengaged6 ,,mrs4 ,b4 ,in the combustion of a pound of phosphorus1 a sufficient quantity of caloric is set free to melt upwards of a hundred pounds of ice2 this has been computed by direct experiments with the calorimeter4 ,,emily4 ,and is the result of this combustion1 like that of sulphur1 an acid8 ,,mrs4 ,b4 ,yes2 phosphoric acid4 ,and had we duly proportioned the phosphorus and the oxygen1 they would have been completely converted into phosphoric acid1 weighing together1 in this new state1 exactly the sum of their weights separately4 ,the water would have ascended into the receiver1 on account of the vacuum formed1 and would have filled it entirely4 ,in this case1 as in the combustion of sulphur1 the acid vapour formed is absorbed and condensed in the water of the receiver4 ,but when this combustion is performed without any water or moisture being present1 the acid then appears in the form of concrete whitish flakes1 which are1 however1 extremely ready to melt upon the least admission of moisture4 ,,emily4 ,does phosphorus1 in burning in atmospherical air1 produce1 like sulphur1 a weaker sort of the same acid8 ,,mrs4 ,b4 ,no3 for it burns in atmospherical air1 nearly at the same temperature as in pure oxygen gas2 and it is in both cases so strongly disposed to combine with the oxygen1 that the combustion is perfect1 and the product similar2 only in atmospherical air1 being less rapidly supplied with oxygen1 the process is performed in a slower manner4 ,,caroline4 ,but is there no method of acidifying phosphorus in a slighter manner1 so as to form phosphorus acid8 ,,mrs4 ,b4 ,yes1 there is4 ,when simply exposed to the atmosphere1 phosphorus undergoes a kind of slow combustion at any temperature above zero4 ,,emily4 ,but is not the process in this case rather an oxydation than a combustion8 ,for if the oxygen is too slowly absorbed for a sensible quantity of light and heat to be disengaged1 it is not a true combustion4 ,,mrs4 ,b4 ,the case is not as you suppose3 a faint light is emitted which is very discernible in the dark2 but the heat evolved is not sufficiently strong to be sensible3 a whitish vapour arises from this combustion1 which1 uniting with water1 condenses into liquid phosphorus acid4 ,,caroline4 ,is it not very singular that phosphorus should burn at so low a temperature in atmospherical air1 whilst it does not burn in pure oxygen without the application of heat8 ,,mrs4 ,b4 ,so it at first appears4 ,but this circumstance seems to be owing to the nitrogen gas of the atmosphere4 ,this gas dissolves small particles of phosphorus1 which being thus minutely divided and diffused in the atmospherical air1 combines with the oxygen1 and undergoes this slow combustion4 ,but the same effect does not take place in oxygen gas1 because it is not capable of dissolving phosphorus2 it is therefore necessary1 in this case1 that heat should be applied to effect that division of particles1 which1 in the former instance1 is produced by the nitrogen4 ,,emily4 ,i have seen letters written with phosphorus1 which are invisible by day-light1 but may be read in the dark by their own light4 ,they look as if they were written with fire2 yet they do not seem to burn4 ,,mrs4 ,b4 ,but they do really burn2 for it is by their slow combustion that the light is emitted2 and phosphorus acid is the result of this combustion4 ,phosphorus is sometimes used as a test to estimate the purity of atmospherical air4 ,for this purpose1 it is burnt in a graduated tube1 called an ,eudiometer 7,,plate ,,xi4 fig4 #b471 and from the quantity of air which the phosphorus absorbs1 the proportion of oxygen in the air examined is deduced2 for the phosphorus will absorb all the oxygen1 and the nitrogen alone will remain4 ,,emily4 ,and the more oxygen is contained in the atmosphere1 the purer1 ,i suppose1 it is esteemed8 ,,mrs4 ,b4 ,certainly4 ,phosphorus1 when melted1 combines with a great variety of substances4 ,with sulphur it forms a compound so extremely combustible1 that it immediately takes fire on coming in contact with the air4 ,it is with this composition that phosphoric matches are prepared1 which kindle as soon as they are taken out of their case and are exposed to the air4 ,,emily4 ,i have a box of these curious matches2 but ,i have observed1 that in very cold weather1 they will not take fire without being previously rubbed4 ,,mrs4 ,b4 ,by rubbing them you raise their temperature2 for1 you know1 friction is one of the means of extricating heat4 ,,emily4 ,will phosphorus combine with hydrogen gas1 as sulphur does8 ,,mrs4 ,b4 ,yes2 and the compound gas which results from this combination has a smell still more fetid than the sulphuretted hydrogen2 it resembles that of garlic4 ,the phosphoretted hydrogen gas has this remarkable peculiarity1 that it takes fire spontaneously in the atmosphere1 at any temperature4 ,it is thus1 probably1 that are produced those transient flames1 or flashes of light1 called by the vulgar ,will-of-the ,whisp1 or more properly ,ignes-fatui1 which are often seen in church-yards1 and places where the putrefactions of animal matter exhale phosphorus and hydrogen gas4 ,,caroline4 ,country people1 who are so much frightened by those appearances1 would soon be reconciled to them1 if they knew from what a simple cause they proceed4 ,,mrs4 ,b4 ,there are other combinations of phosphorus that have also very singular properties1 particularly that which results from its union with lime4 ,,emily4 ,is there any name to distinguish the combination of two substances1 like phosphorus and lime1 neither of which are oxygen1 and which cannot therefore produce either an oxyd or an acid8 ,,mrs4 ,b4 ,the names of such combinations are composed from those of their ingredients1 merely by a slight change in their termination4 ,thus the combination of sulphur with lime is called a sulphuret1 and that of phosphorus1 a phosphuret of lime4 ,this latter compound1 ,i was going to say1 has the singular property of decomposing water1 merely by being thrown into it4 ,it effects this by absorbing the oxygen of water1 in consequence of which bubbles of hydrogen gas ascend1 holding in solution a small quantity of phosphorus4 ,,emily4 ,these bubbles then are phosphoretted hydrogen gas8 ,,mrs4 ,b4 ,yes2 and they produce the singular appearance of a flash of fire issuing from water1 as the bubbles kindle and detonate on the surface of the water1 at the instant that they come in contact with the atmosphere4 ,,caroline4 ,is not this effect nearly similar to that produced by the combination of phosphorus and sulphur1 or1 more properly speaking1 the phosphuret of sulphur8 ,,mrs4 ,b4 ,yes2 but the phenomenon appears more extraordinary in this case1 from the presence of water1 and from the gaseous form of the combustible compound4 ,besides1 the experiment surprises by its great simplicity4 ,you only throw a piece of phosphoret of lime into a glass of water1 and bubbles of fire will immediately issue from it4 ,,caroline4 ,cannot we try the experiment8 ,,mrs4 ,b4 ,very easily3 but we must do it in the open air2 for the smell of the phosphorated hydrogen gas is so extremely fetid1 that it would be intolerable in the house4 ,but before we leave the room1 we may produce1 by another process1 some bubbles of the same gas1 which are much less offensive4 ,there is in this little glass retort a solution of potash in water2 ,i add to it a small piece of phosphorus4 ,we must now heat the retort over the lamp1 after having engaged its neck under water--you see it begins to boil2 in a few minutes bubbles will appear1 which take fire and detonate as they issue from the water4 ,,caroline4 ,there is one--and another4 ,how curious it is6 --,but ,i do not understand how this is produced4 ,,mrs4 ,b4 ,it is the consequence of a display of affinities too complicated1 ,i fear1 to be made perfectly intelligible to you at present4 ,in a few words1 the reciprocal action of the potash1 phosphorus1 caloric1 and water are such1 that some of the water is decomposed1 and the hydrogen gas thereby formed carries off some minute particles of phosphorus1 with which it forms phosphoretted hydrogen gas1 a compound which spontaneously takes fire at almost any temperature4 ,,emily4 ,what is that circular ring of smoke which slowly rises from each bubble after its detonation8 ,,mrs4 ,b4 ,it consists of water and phosphoric acid in vapour1 which are produced by the combustion of hydrogen and phosphorus4 ,,conversation ,,ix4 ,,on ,,carbon4 ,,caroline4 ,to-day1 ,mrs4 ,b41 ,i believe we are to learn the nature and properties of ,,carbon4 ,this substance is quite new to me2 ,i never heard it mentioned before4 ,,mrs4 ,b4 ,not so new as you imagine2 for carbon is nothing more than charcoal in a state of purity1 that is to say1 unmixed with any foreign ingredients4 ,,caroline4 ,but charcoal is made by art1 ,mrs4 ,b41 and a body consisting of one simple substance cannot be fabricated8 ,,mrs4 ,b4 ,you again confound the idea1 of making a simple body1 with that of separating it from a compound4 ,the chemical processes by which a simple body is obtained in a state of purity1 consist in unmaking the compound in which it is contained1 in order to separate from it the simple substance in question4 ,the method by which charcoal is usually obtained1 is1 indeed1 commonly called making it2 but1 upon examination1 you will find this process to consist simply in separating it from other substances with which it is found combined in nature4 ,carbon forms a considerable part of the solid matter of all organised bodies2 but it is most abundant in the vegetable creation1 and it is chiefly obtained from wood4 ,when the oil and water 7which are other constituents of vegetable matter7 are evaporated1 the black1 porous1 brittle substance that remains1 is charcoal4 ,,caroline4 ,but if heat be applied to the wood in order to evaporate the oil and water1 will not the temperature of the charcoal be raised so as to make it burn2 and if it combines with oxygen1 can we any longer call it pure8 ,,mrs4 ,b4 ,i was going to say1 that1 in this operation1 the air must be excluded4 ,,caroline4 ,how then can the vapour of the oil and water fly off8 ,,mrs4 ,b4 ,in order to produce charcoal in its purest state 7which is1 even then1 but a less imperfect sort of carbon71 the operation should be performed in an earthen retort4 ,heat being applied to the body of the retort1 the evaporable part of the wood will escape through its neck1 into which no air can penetrate as long as the heated vapour continues to fill it4 ,and if it be wished to collect these volatile products of the wood1 this can easily be done by introducing the neck of the retort into the water-bath apparatus1 with which you are acquainted4 ,but the preparation of common charcoal1 such as is used in kitchens and manufactures1 is performed on a much larger scale1 and by an easier and less expensive process4 ,,emily4 ,i have seen the process of making common charcoal4 ,the wood is ranged on the ground in a pile of a pyramidical form1 with a fire underneath2 the whole is then covered with clay1 a few holes only being left for the circulation of air4 ,,mrs4 ,b4 ,these holes are closed as soon as the wood is fairly lighted1 so that the combustion is checked1 or at least continues but in a very imperfect manner2 but the heat produced by it is sufficient to force out and volatilize1 through the earthy cover1 most part of the oily and watery principles of the wood1 although it cannot reduce it to ashes4 ,,emily4 ,is pure carbon as black as charcoal8 ,,mrs4 ,b4 ,the purest charcoal we can prepare is so2 but chemists have never yet been able to separate it entirely from hydrogen4 ,sir ,h4 ,davy says1 that the most perfect carbon that is prepared by art contains about five per cent4 of hydrogen2 he is of opinion1 that if we could obtain it quite free from foreign ingredients1 it would be metallic1 in common with other simple substances4 ,but there is a form in which charcoal appears1 that ,i dare say will surprise you4 --,this ring1 which ,i wear on my finger1 owes its brilliancy to a small piece of carbon4 ,,caroline4 ,surely1 you are jesting1 ,mrs4 ,b48 ,,emily4 ,i thought your ring was diamond8 ,,mrs4 ,b4 ,it is so4 ,but diamond is nothing more than carbon in a crystallized state4 ,,emily4 ,that is astonishing6 ,is it possible to see two things apparently more different than diamond and charcoal8 ,,caroline4 ,it is1 indeed1 curious to think that we adorn ourselves with jewels of charcoal6 ,,mrs4 ,b4 ,there are many other substances1 consisting chiefly of carbon1 that are remarkably white4 ,cotton1 for instance1 is almost wholly carbon4 ,,caroline4 ,that1 ,i own1 ,i could never have imagined6 --,but pray1 ,mrs4 ,b41 since it is known of what substance diamond and cotton are composed1 why should they not be manufactured1 or imitated1 by some chemical process1 which would render them much cheaper1 and more plentiful than the present mode of obtaining them8 ,,mrs4 ,b4 ,you might as well1 my dear1 propose that we should make flowers and fruit1 nay1 perhaps even animals1 by a chemical process2 for it is known of what these bodies consist1 since every thing which we are acquainted with in nature is formed from the various simple substances that we have enumerated4 ,but you must not suppose that a knowledge of the component parts of a body will in every case enable us to imitate it4 ,it is much less difficult to decompose bodies1 and discover of what materials they are made1 than it is to recompose them4 ,the first of these processes is called analysis1 the last synthesis4 ,when we are able to ascertain the nature of a substance by both these methods1 so that the result of one confirms that of the other1 we obtain the most complete knowledge of it that we are capable of acquiring4 ,this is the case with water1 with the atmosphere1 with most of the oxyds1 acids1 and neutral salts1 and with many other compounds4 ,but the more complicated combinations of nature1 even in the mineral kingdom1 are in general beyond our reach1 and any attempt to imitate organised bodies must ever prove fruitless2 their formation is a secret that rests in the bosom of the ,creator4 ,you see1 therefore1 how vain it would be to attempt to make cotton by chemical means4 ,but1 surely1 we have no reason to regret our inability in this instance1 when nature has so clearly pointed out a method of obtaining it in perfection and abundance4 ,,caroline4 ,i did not imagine that the principle of life could be imitated by the aid of chemistry2 but it did not appear to me ridiculous to suppose that chemists might attain a perfect imitation of inanimate nature4 ,,mrs4 ,b4 ,they have succeeded in this point in a variety of instances2 but1 as you justly observe1 the principle of life1 or even the minute and intimate organisation of the vegetable kingdom1 are secrets that have almost entirely eluded the researches of philosophers2 nor do ,i imagine that human art will ever be capable of investigating them with complete success4 ,,emily4 ,but diamond1 since it consists of one simple unorganised substance1 might be1 one would think1 perfectly imitable by art8 ,,mrs4 ,b4 ,it is sometimes as much beyond our power to obtain a simple body in a state of perfect purity1 as it is to imitate a complicated combination2 for the operations by which nature separates bodies are frequently as inimitable as those which she uses for their combination4 ,this is the case with carbon2 all the efforts of chemists to separate it entirely from other substances have been fruitless1 and in the purest state in which it can be obtained by art1 it still retains a portion of hydrogen1 and probably of some other foreign ingredients4 ,we are ignorant of the means which nature employs to crystallize it4 ,it may probably be the work of ages1 to purify1 arrange1 and unite the particles of carbon in the form of diamond4 ,here is some charcoal in the purest state we can procure it3 you see that it is a very black1 brittle1 light1 porous substance1 entirely destitute of either taste or smell4 ,heat1 without air1 produces no alteration in it1 as it is not volatile2 but1 on the contrary1 it invariably remains at the bottom of the vessel after all the other parts of the vegetable are evaporated4 ,,emily4 ,yet carbon is1 no doubt1 combustible1 since you say that charcoal would absorb oxygen if air were admitted during its preparation8 ,,caroline4 ,unquestionably4 ,besides1 you know1 ,emily1 how much it is used in cooking4 ,but pray what is the reason that charcoal burns without smoke1 whilst a wood fire smokes so much8 ,,mrs4 ,b4 ,because1 in the conversion of wood into charcoal1 the volatile particles of the former have been evaporated4 ,,caroline4 ,yet ,i have frequently seen charcoal burn with flame2 therefore it must1 in that case1 contain some hydrogen4 ,,mrs4 ,b4 ,very true2 but you must recollect that charcoal1 especially that which is used for common purposes1 is not perfectly pure4 ,it generally retains some remains of the various other component parts of vegetables1 and hydrogen particularly1 which accounts for the flame in question4 ,,caroline4 ,but what becomes of the carbon itself during its combustion8 ,,mrs4 ,b4 ,it gradually combines with the oxygen of the atmosphere1 in the same way as sulphur and phosphorus1 and1 like those substances1 it is converted into a peculiar acid1 which flies off in a gaseous form4 ,there is this difference1 however1 that the acid is not1 in this instance1 as in the two cases just mentioned1 a mere condensable vapour1 but a permanent elastic fluid1 which always remains in the state of gas1 under any pressure and at any temperature4 ,the nature of this acid was first ascertained by ,dr4 ,black1 of ,edinburgh2 and1 before the introduction of the new nomenclature1 it was called fixed air4 ,it is now distinguished by the more appropriate name of carbonic acid gas4 ,,emily4 ,carbon1 then1 can be volatilized by burning1 though1 by heat alone1 no such effect is produced8 ,,mrs4 ,b4 ,yes2 but then it is no longer simple carbon1 but an acid of which carbon forms the basis4 ,in this state1 carbon retains no more appearance of solidity or corporeal form1 than the basis of any other gas4 ,and you may1 ,i think1 from this instance1 derive a more clear idea of the basis of the oxygen1 hydrogen1 and nitrogen gases1 the existence of which1 as real bodies1 you seemed to doubt1 because they were not to be obtained simply in a solid form4 ,,emily4 ,that is true2 we may conceive the basis of the oxygen1 and of the other gases1 to be solid1 heavy substances1 like carbon2 but so much expanded by caloric as to become invisible4 ,,caroline4 ,but does not the carbonic acid gas partake of the blackness of charcoal8 ,,mrs4 ,b4 ,not in the least4 ,blackness1 you know1 does not appear to be essential to carbon1 and it is pure carbon1 and not charcoal1 that we must consider as the basis of carbonic acid4 ,we shall make some carbonic acid1 and1 in order to hasten the process1 we shall burn the carbon in oxygen gas4 ,,emily4 ,but do you mean then to burn diamond8 ,,mrs4 ,b4 ,charcoal will answer the purpose still better1 being softer and more easy to inflame2 besides the experiments on diamond are rather expensive4 ,,caroline4 ,but is it possible to burn diamond8 ,,mrs4 ,b4 ,yes1 it is2 and in order to effect this combustion1 nothing more is required than to apply a sufficient degree of heat by means of the blow-pipe1 and of a stream of oxygen gas4 ,indeed it is by burning diamond that its chemical nature has been ascertained4 ,it has long been known as a combustible substance1 but it is within these few years only that the product of its combustion has been proved to be pure carbonic acid4 ,this remarkable discovery is due to ,mr4 ,tennant4 ,now let us try to make some carbonic acid4 --,will you1 ,emily1 decant some oxygen gas from this large jar into the receiver in which we are to burn the carbon2 and ,i shall introduce this small piece of charcoal1 with a little lighted tinder1 which will be necessary to give the first impulse to the combustion4 ,,emily4 ,i cannot conceive how so small a piece of tinder1 and that but just lighted1 can raise the temperature of the carbon sufficiently to set fire to it2 for it can produce scarcely any sensible heat1 and it hardly touches the carbon4 ,,mrs4 ,b4 ,the tinder thus kindled has only heat enough to begin its own combustion1 which1 however1 soon becomes so rapid in the oxygen gas1 as to raise the temperature of the charcoal sufficiently for this to burn likewise1 as you see is now the case4 ,,emily4 ,i am surprised that the combustion of carbon is not more brilliant2 it does not give out near so much light or caloric as phosphorus1 or sulphur4 ,yet since it combines with so much oxygen1 why is not a proportional quantity of light and heat disengaged from the decomposition of the oxygen gas1 and the union of its electricity with that of the charcoal8 ,,mrs4 ,b4 ,it is not surprising that less light and heat should be liberated in this than in almost any other combustion1 since the oxygen1 instead of entering into a solid or liquid combination1 as it does in the phosphoric and sulphuric acids1 is employed in forming another elastic fluid2 it therefore parts with less of its caloric4 ,,emily4 ,true2 and1 on second consideration1 it appears1 on the contrary1 surprising that the oxygen should1 in its combination with carbon1 retain a sufficient portion of caloric to maintain both substances in a gaseous state4 ,,caroline4 ,we may then judge of the degree of solidity in which oxygen is combined in a burnt body1 by the quantity of caloric liberated during its combustion8 ,,mrs4 ,b4 ,yes2 provided that you take into the account the quantity of oxygen absorbed by the combustible body1 and observe the proportion which the caloric bears to it4 ,,caroline4 ,but why should the water1 after the combustion of carbon1 rise in the receiver1 since the gas within it retains an ariform state8 ,,mrs4 ,b4 ,because the carbonic acid gas is gradually absorbed by the water2 and this effect would be promoted by shaking the receiver4 ,,emily4 ,the charcoal is now extinguished1 though it is not nearly consumed2 it has such an extraordinary avidity for oxygen1 ,i suppose1 that the receiver did not contain enough to satisfy the whole4 ,,mrs4 ,b4 ,that is certainly the case2 for if the combustion were performed in the exact proportions of #bh parts of carbon to #gb of oxygen1 both these ingredients would disappear1 and #ajj parts of carbonic acid would be produced4 ,,caroline4 ,carbonic acid must be a very strong acid1 since it contains so great a proportion of oxygen8 ,,mrs4 ,b4 ,that is a very natural inference2 yet it is erroneous4 ,for the carbonic is the weakest of all the acids4 ,the strength of an acid seems to depend upon the nature of its basis1 and its mode of combination1 as well as upon the proportion of the acidifying principle4 ,the same quantity of oxygen that will convert some bodies into strong acids1 will only be sufficient simply to oxydate others4 ,,caroline4 ,since this acid is so weak1 ,i think chemists should have called it the carbonous1 instead of the carbonic acid4 ,,emily4 ,but1 ,i suppose1 the carbonous acid is still weaker1 and is formed by burning carbon in atmospherical air4 ,,mrs4 ,b4 ,it has been lately discovered1 that carbon may be converted into a gas1 by uniting with a smaller proportion of oxygen2 but as this gas does not possess any acid properties1 it is no more than an oxyd2 it is called gaseous oxyd of carbon4 ,,caroline4 ,pray is not carbonic acid a very wholesome gas to breathe1 as it contains so much oxygen8 ,,mrs4 ,b4 ,on the contrary1 it is extremely pernicious4 ,oxygen1 when in a state of combination with other substances1 loses1 in almost every instance1 its respirable properties1 and the salubrious effects which it has on the animal economy when in its unconfined state4 ,carbonic acid is not only unfit for respiration1 but extremely deleterious if taken into the lungs4 ,,emily4 ,you know1 ,caroline1 how very unwholesome the fumes of burning charcoal are reckoned4 ,,caroline4 ,yes2 but1 to confess the truth1 ,i did not consider that a charcoal fire produced carbonic acid gas4 --,can this gas be condensed into a liquid8 ,,mrs4 ,b4 ,no3 for1 as ,i told you before1 it is a permanent elastic fluid4 ,but water can absorb a certain quantity of this gas1 and can even be impregnated with it1 in a very strong degree1 by the assistance of agitation and pressure1 as ,i am going to show you4 ,i shall decant some carbonic acid gas into this bottle1 which ,i fill first with water1 in order to exclude the atmospherical air2 the gas is then introduced through the water1 which you see it displaces1 for it will not mix with it in any quantity1 unless strongly agitated1 or allowed to stand over it for some time4 ,the bottle is now about half full of carbonic acid gas1 and the other half is still occupied by the water4 ,by corking the bottle1 and then violently shaking it1 in this way1 ,i can mix the gas and water together4 --,now will you taste it8 ,,emily4 ,it has a distinct acid taste4 ,,caroline4 ,yes1 it is sensibly sour1 and appears full of little bubbles4 ,,mrs4 ,b4 ,it possesses likewise all the other properties of acids1 but1 of course1 in a less degree than the pure carbonic acid gas1 as it is so much diluted by water4 ,this is a kind of artificial ,seltzer water4 ,by analysing that which is produced by nature1 it was found to contain scarcely any thing more than common water impregnated with a certain proportion of carbonic acid gas4 ,we are1 therefore1 able to imitate it1 by mixing those proportions of water and carbonic acid4 ,here1 my dear1 is an instance1 in which1 by a chemical process1 we can exactly copy the operations of nature2 for the artificial ,seltzer waters can be made in every respect similar to those of nature2 in one point1 indeed1 the former have an advantage1 since they may be prepared stronger1 or weaker1 as occasion requires4 ,,caroline4 ,i thought ,i had tasted such water before4 ,but what renders it so brisk and sparkling8 ,,mrs4 ,b4 ,this sparkling1 or effervescence1 as it is called1 is always occasioned by the action of an elastic fluid escaping from a liquid2 in the artifical ,seltzer water1 it is produced by the carbonic acid1 which being lighter than the water in which it was strongly condensed1 flies off with great rapidity the instant the bottle is uncorked2 this makes it necessary to drink it immediately4 ,the bubbling that took place in this bottle was but trifling1 as the water was but very slightly impregnated with carbonic acid4 ,it requires a particular apparatus to prepare the gaseous artificial mineral waters4 ,,emily4 ,if1 then1 a bottle of ,seltzer water remains for any length of time uncorked1 ,i suppose it returns to the state of common water8 ,,mrs4 ,b4 ,the whole of the carbonic acid gas1 or very nearly so1 will soon disappear2 but there is likewise in ,seltzer water a very small quantity of soda1 and of a few other saline or earthy ingredients1 which will remain in the water1 though it should be kept uncorked for any length of time4 ,,caroline4 ,i have often heard of people drinking soda-water4 ,pray what sort of water is that8 ,,mrs4 ,b4 ,it is a kind of artificial ,seltzer water1 holding in solution1 besides the gaseous acid1 a particular saline substance1 called soda1 which imparts to the water certain medicinal qualities4 ,,caroline4 ,but how can these waters be so wholesome1 since carbonic acid is so pernicious8 ,,mrs4 ,b4 ,a gas1 we may conceive1 though very prejudicial to breathe1 may be beneficial to the stomach4 --,but it would be of no use to attempt explaining this more fully at present4 ,,caroline4 ,are waters never impregnated with other gases8 ,,mrs4 ,b4 ,yes2 there are several kinds of gaseous waters4 ,i forgot to tell you that waters have1 for some years past1 been prepared1 impregnated both with oxygen and hydrogen gases4 ,these are not an imitation of nature1 but are altogether obtained by artificial means4 ,they have been lately used medicinally1 particularly on the continent1 where1 ,i understand1 they have acquired some reputation4 ,,emily4 ,if ,i recollect right1 ,mrs4 ,b41 you told us that carbon was capable of decomposing water2 the affinity between oxygen and carbon must1 therefore1 be greater than between oxygen and hydrogen8 ,,mrs4 ,b4 ,yes2 but this is not the case unless their temperature be raised to a certain degree4 ,it is only when carbon is red-hot1 that it is capable of separating the oxygen from the hydrogen4 ,thus1 if a small quantity of water be thrown on a red-hot fire1 it will increase rather than extinguish the combustion2 for the coals or wood 7both of which contain a quantity of carbon7 decompose the water1 and thus supply the fire both with oxygen and hydrogen gases4 ,if1 on the contrary1 a large mass of water be thrown over the fire1 the diminution of heat thus produced is such1 that the combustible matter loses the power of decomposing the water1 and the fire is extinguished4 ,,emily4 ,i have heard that fire-engines sometimes do more harm than good1 and that they actually increase the fire when they cannot throw water enough to extinguish it4 ,it must be owing1 no doubt1 to the decomposition of the water by the carbon during the conflagration4 ,,mrs4 ,b4 ,certainly4 --,the apparatus which you see here 7,,plate ,,xi4 fig4 #c471 may be used to exemplify what we have just said4 ,it consists in a kind of open furnace1 through which a porcelain tube1 containing charcoal1 passes4 ,to one end of the tube is adapted a glass retort with water in it2 and the other end communicates with a receiver placed on the water-bath4 ,a lamp being applied to the retort1 and the water made to boil1 the vapour is gradually conveyed through the red-hot charcoal1 by which it is decomposed2 and the hydrogen gas which results from this decomposition is collected in the receiver4 ,but the hydrogen thus obtained is far from being pure2 it retains in solution a minute portion of carbon1 and contains also a quantity of carbonic acid4 ,this renders it heavier than pure hydrogen gas1 and gives it some peculiar properties2 it is distinguished by the name of carbonated hydrogen gas4 ,,caroline4 ,and whence does it obtain the carbonic acid that is mixed with it8 ,,emily4 ,i believe ,i can answer that question1 ,caroline4 --,from the union of the oxygen 7proceeding from the decomposed water7 with the carbon1 which1 you know1 makes carbonic acid4 ,,caroline4 ,true2 ,i should have recollected that4 --,the product of the decomposition of water by red-hot charcoal1 therefore1 is carbonated hydrogen gas1 and carbonic acid gas4 ,,mrs4 ,b4 ,you are perfectly right now4 ,carbon is frequently found combined with hydrogen in a state of solidity1 especially in coals1 which owe their combustible nature to these two principles4 ,,emily4 ,is it the hydrogen1 then1 that produces the flame of coals8 ,,mrs4 ,b4 ,it is so2 and when all the hydrogen is consumed1 the carbon continues to burn without flame4 ,but again1 as ,i mentioned when speaking of the gas-lights1 the hydrogen gas produced by the burning of coals is not pure2 for1 during the combustion1 particles of carbon are successively volatilized with the hydrogen1 with which they form what is called a hydro-carbonat1 which is the principal product of this combustion4 ,carbon is a very bad conductor of heat2 for this reason1 it is employed 7in conjunction with other ingredients7 for coating furnaces and other chemical apparatus4 ,,emily4 ,pray what is the use of coating furnaces8 ,,mrs4 ,b4 ,in most cases1 in which a furnace is used1 it is necessary to produce and preserve a great degree of heat1 for which purpose every possible means are used to prevent the heat from escaping by communicating with other bodies1 and this object is attained by coating over the inside of the furnace with a kind of plaster1 composed of materials that are bad conductors of heat4 ,carbon1 combined with a small quantity of iron1 forms a compound called plumbago1 or black-lead1 of which pencils are made4 ,this substance1 agreeably to the nomenclature1 is a carburet of iron4 ,,emily4 ,why1 then1 is it called black-lead8 ,,mrs4 ,b4 ,it is an ancient name given to it by ignorant people1 from its shining metallic appearance2 but it is certainly a most improper name for it1 as there is not a particle of lead in the composition4 ,there is only one mine of this mineral1 which is in ,cumberland4 ,it is supposed to approach as nearly to pure carbon as the best prepared charcoal does1 as it contains only five parts of iron1 unadulterated by any other foreign ingredients4 ,there is another carburet of iron1 in which the iron1 though united only to an extremely small proportion of carbon1 acquires very remarkable properties2 this is steel4 ,,caroline4 ,really2 and yet steel is much harder than iron8 ,,mrs4 ,b4 ,but carbon is not ductile like iron1 and therefore may render the steel more brittle1 and prevent its bending so easily4 ,whether it is that the carbon1 by introducing itself into the pores of the iron1 and1 by filling them1 makes the metal both harder and heavier2 or whether this change depends upon some chemical cause1 ,i cannot pretend to decide4 ,but there is a subsequent operation1 by which the hardness of steel is very much increased1 which simply consists in heating the steel till it is red-hot1 and then plunging it into cold water4 ,carbon1 besides the combination just mentioned1 enters into the composition of a vast number of natural productions1 such1 for instance1 as all the various kinds of oils1 which result from the combination of carbon1 hydrogen1 and caloric1 in various proportions4 ,,emily4 ,i thought that carbon1 hydrogen1 and caloric1 formed carbonated hydrogen gas8 ,,mrs4 ,b4 ,that is the case when a small portion of carbonic acid gas is held in solution by hydrogen gas4 ,different proportions of the same principles1 together with the circumstances of their union1 produce very different combinations2 of this you will see innumerable examples4 ,besides1 we are not now talking of gases1 but of carbon and hydrogen1 combined only with a quantity of caloric sufficient to bring them to the consistency of oil or fat4 ,,caroline4 ,but oil and fat are not of the same consistence8 ,,mrs4 ,b4 ,fat is only congealed oil2 or oil1 melted fat4 ,the one requires a little more heat to maintain it in a fluid state than the other4 ,have you never observed the fat of meat turned to oil by the caloric it has imbibed from the fire8 ,,emily4 ,yet oils in general1 as salad-oil1 and lamp-oil1 do not turn to fat when cold8 ,,mrs4 ,b4 ,not at the common temperature of the atmosphere1 because they retain too much caloric to congeal at that temperature2 but if exposed to a sufficient degree of cold1 their latent heat is extricated1 and they become solid fat substances4 ,have you never seen salad oil frozen in winter8 ,,emily4 ,yes2 but it appears to me in that state very different from animal fat4 ,,mrs4 ,b4 ,the essential constituent parts of either vegetable or animal oils are the same1 carbon and hydrogen2 their variety arises from the different proportions of these substances1 and from other accessory ingredients that may be mixed with them4 ,the oil of a whale1 and the oil of roses1 are1 in their essential constituent parts1 the same2 but the one is impregnated with the offensive particles of animal matter1 the other with the delicate perfume of a flower4 ,the difference of fixed oils1 and volatile or essential oils1 consists also in the various proportions of carbon and hydrogen4 ,fixed oils are those which will not evaporate without being decomposed2 this is the case with all common oils1 which contain a greater proportion of carbon than the essential oils4 ,the essential oils 7which comprehend the whole class of essences and perfumes7 are lighter2 they contain more equal proportions of carbon and hydrogen1 and are volatilized or evaporated without being decomposed4 ,,emily4 ,when you say that one kind of oil will evaporate1 and the other be decomposed1 you mean1 ,i suppose1 by the application of heat8 ,,mrs4 ,b4 ,not necessarily2 for there are oils that will evaporate slowly at the common temperature of the atmosphere2 but for a more rapid volatilization1 or for their decomposition1 the assistance of heat is required4 ,,caroline4 ,i shall now remember1 ,i think1 that fat and oil are really the same substances1 both consisting of carbon and hydrogen2 that in fixed oils the carbon preponderates1 and heat produces a decomposition2 while1 in essential oils1 the proportion of hydrogen is greater1 and heat produces a volatilization only4 ,,emily4 ,i suppose the reason why oil burns so well in lamps is because its two constituents are so combustible8 ,,mrs4 ,b4 ,certainly2 the combustion of oil is just the same as that of a candle2 if tallow1 it is only oil in a concrete state2 if wax1 or spermaceti1 its chief chemical ingredients are still hydrogen and carbon4 ,,emily4 ,i wonder1 then1 there should be so great a difference between tallow and wax8 ,,mrs4 ,b4 ,i must again repeat1 that the same substances1 in different proportions1 produce results that have sometimes scarcely any resemblance to each other4 ,but this is rather a general remark that ,i wish to impress upon your minds1 than one which is applicable to the present case2 for tallow and wax are far from being very dissimilar2 the chief difference consists in the wax being a purer compound of carbon and hydrogen than the tallow1 which retains more of the gross particles of animal matter4 ,the combustion of a candle1 and that of a lamp1 both produce water and carbonic acid gas4 ,can you tell me how these are formed8 ,,emily4 ,let me reflect 4 4 4 4 ,both the candle and lamp burn by means of fixed oil--this is decomposed as the combustion goes on2 and the constituent parts of the oil being thus separated1 the carbon unites to a portion of oxygen from the atmosphere to form carbonic acid gas1 whilst the hydrogen combines with another portion of oxygen1 and forms with it water4 --,the products1 therefore1 of the combustion of oils are water and carbonic acid gas4 ,,caroline4 ,but we see neither water nor carbonic acid produced by the combustion of a candle4 ,,mrs4 ,b4 ,the carbonic acid gas1 you know1 is invisible1 and the water being in a state of vapour1 is so likewise4 ,emily is perfectly correct in her explanation1 and ,i am very much pleased with it4 ,all the vegetable acids consist of various proportions of carbon and hydrogen1 acidified by oxygen4 ,gums1 sugar1 and starch1 are likewise composed of these ingredients2 but1 as the oxygen which they contain is not sufficient to convert them into acids1 they are classed with the oxyds1 and called vegetable oxyds4 ,,caroline4 ,i am very much delighted with all these new ideas2 but1 at the same time1 ,i cannot help being apprehensive that ,i may forget many of them4 ,,mrs4 ,b4 ,i would advise you to take notes1 or1 what would answer better still1 to write down1 after every lesson1 as much of it as you can recollect4 ,and1 in order to give you a little assistance1 ,i shall lend you the heads or index1 which ,i occasionally consult for the sake of preserving some method and arrangement in these conversations4 ,unless you follow some such plan1 you cannot expect to retain nearly all that you learn1 how great soever be the impression it may make on you at first4 ,,emily4 ,i will certainly follow your advice4 --,hitherto ,i have found that ,i recollected pretty well what you have taught us2 but the history of carbon is a more extensive subject than any of the simple bodies we have yet examined4 ,,mrs4 ,b4 ,i have little more to say on carbon at present2 but hereafter you will see that it performs a considerable part in most chemical operations4 ,,caroline4 ,that is1 ,i suppose1 owing to its entering into the composition of so great a variety of substances8 ,,mrs4 ,b4 ,certainly2 it is the basis1 you have seen1 of all vegetable matter2 and you will find that it is very essential to the process of animalization4 ,but in the mineral kingdom also1 particularly in its form of carbonic acid1 we shall often discover it combined with a great variety of substances4 ,in chemical operations1 carbon is particularly useful1 from its very great attraction for oxygen1 as it will absorb this substance from many oxygenated or burnt bodies1 and thus deoxygenate1 or unburn them1 and restore them to their original combustible state4 ,,caroline4 ,i do not understand how a body can be unburnt1 and restored to its original state4 ,this piece of tinder1 for instance1 that has been burnt1 if by any means the oxygen were extracted from it1 would not be restored to its former state of linen2 for its texture is destroyed by burning1 and that must be the case with all organized or manufactured substances1 as you observed in a former conversation4 ,,mrs4 ,b4 ,a compound body is decomposed by combustion in a way which generally precludes the possibility of restoring it to its former state2 the oxygen1 for instance1 does not become fixed in the tinder1 but it combines with its volatile parts1 and flies off in the shape of gas1 or watery vapour4 ,you see1 therefore1 how vain it would be to attempt the recomposition of such bodies4 ,but1 with regard to simple bodies1 or at least bodies whose component parts are not disturbed by the process of oxygenation or deoxygenation1 it is often possible to restore them1 after combustion1 to their original state4 --,the metals1 for instance1 undergo no other alteration by combustion than a combination with oxygen2 therefore1 when the oxygen is taken from them1 they return to their pure metallic state4 ,but ,i shall say nothing further of this at present1 as the metals will furnish ample subject for another morning2 and they are the class of simple bodies that come next under consideration4 ,,conversation ,x4 ,,on ,,metals4 ,,mrs4 ,b4 ,the ,,metals1 which we are now to examine1 are bodies of a very different nature from those which we have hitherto considered4 ,they do not1 like the bases of gases1 elude the immediate observation of our senses2 for they are the most brilliant1 the most ponderous1 and the most palpable substances in nature4 ,,caroline4 ,i doubt1 however1 whether the metals will appear to us so interesting1 and give us so much entertainment as those mysterious elements which conceal themselves from our view4 ,besides1 they cannot afford so much novelty2 they are bodies with which we are already so well acquainted4 ,,mrs4 ,b4 ,you are not aware1 my dear1 of the interesting discoveries which were a few years ago made by ,sir ,h4 ,davy respecting this class of bodies4 ,by the aid of the ,voltaic battery1 he has obtained from a variety of substances1 metals before unknown1 the properties of which are equally new and curious4 ,we shall begin1 however1 by noticing those metals with which you profess to be so well acquainted4 ,but the acquaintance1 you will soon perceive1 is but very superficial2 and ,i trust that you will find both novelty and entertainment in considering the metals in a chemical point of view4 ,to treat of this subject fully1 would require a whole course of lectures2 for metals form of themselves a most important branch of practical chemistry4 ,we must1 therefore1 confine ourselves to a general view of them4 ,these bodies are seldom found naturally in their metallic form3 they are generally more or less oxygenated or combined with sulphur1 earths1 or acids1 and are often blended with each other4 ,they are found buried in the bowels of the earth in most parts of the world1 but chiefly in mountainous districts1 where the surface of the globe has suffered from the earthquakes1 volcanos1 and other convulsions of nature4 ,they are spread in strata or beds1 called veins1 and these veins are composed of a certain quantity of metal1 combined with various earthy substances1 with which they form minerals of different nature and appearance1 which are called ores4 ,,caroline4 ,i now feel quite at home1 for my father has a lead-mine in ,yorkshire1 and ,i have heard a great deal about veins of ore1 and of the roasting and smelting of the lead2 but1 ,i confess1 that ,i do not understand in what these operations consist4 ,,mrs4 ,b4 ,roasting is the process by which the volatile parts of the ore are evaporated2 smelting1 that by which the pure metal is afterwards separated from the earthy remains of the ore4 ,this is done by throwing the whole into a furnace1 and mixing with it certain substances that will combine with the earthy parts and other foreign ingredients of the ore2 the metal being the heaviest1 falls to the bottom1 and runs out by proper openings in its pure metallic state4 ,,emily4 ,you told us in a preceding lesson that metals had a great affinity for oxygen4 ,do they not1 therefore1 combine with oxygen1 when strongly heated in the furnace1 and run out in the state of oxyds8 ,,mrs4 ,b4 ,no2 for the scori1 or oxyd1 which soon forms on the surface of the fused metal1 when it is oxydable1 prevents the air from having any further influence on the mass2 so that neither combustion nor oxygenation can take place4 ,,caroline4 ,are all the metals equally combustible8 ,,mrs4 ,b4 ,no2 their attraction for oxygen varies extremely4 ,there are some that will combine with it only at a very high temperature1 or by the assistance of acids2 whilst there are others that oxydate spontaneously and with great rapidity1 even at the lowest temperature2 such is in particular manganese1 which scarcely ever exists in the metallic state1 as it immediately absorbs oxygen on being exposed to the air1 and crumbles to an oxyd in the course of a few hours4 ,,emily4 ,is not that the oxyd from which you extracted the oxygen gas8 ,,mrs4 ,b4 ,it is3 so that1 you see1 this metal attracts oxygen at a low temperature1 and parts with it when strongly heated4 ,,emily4 ,is there any other metal that oxydates at the temperature of the atmosphere8 ,,mrs4 ,b4 ,they all do1 more or less1 excepting gold1 silver1 and platina4 ,copper1 lead1 and iron1 oxydate slowly in the air1 and cover themselves with a sort of rust1 a process which depends on the gradual conversion of the surface into an oxyd4 ,this rusty surface preserves the interior metal from oxydation1 as it prevents the air from coming in contact with it4 ,strictly speaking1 however1 the word rust applies only to the oxyd1 which forms on the surface of iron1 when exposed to air and moisture1 which oxyd appears to be united with a small portion of carbonic acid4 ,,emily4 ,when metals oxydate from the atmosphere without an elevation of temperature1 some light and heat1 ,i suppose1 must be disengaged1 though not in sufficient quantities to be sensible4 ,,mrs4 ,b4 ,undoubtedly2 and1 indeed1 it is not surprising that in this case the light and heat should not be sensible1 when you consider how extremely slow1 and1 indeed1 how imperfectly1 most metals oxydate by mere exposure to the atmosphere4 ,for the quantity of oxygen with which metals are capable of combining1 generally depends upon their temperature2 and the absorption stops at various points of oxydation1 according to the degree to which their temperature is raised4 ,,emily4 ,that seems very natural2 for the greater the quantity of caloric introduced into a metal1 the more will its positive electricity be exalted1 and consequently the stronger will be its affinity for oxygen4 ,,mrs4 ,b4 ,certainly4 ,when the metal oxygenates with sufficient rapidity for light and heat to become sensible1 combustion actually takes place4 ,but this happens only at very high temperatures1 and the product is nevertheless an oxyd2 for though1 as ,i have just said1 metals will combine with different proportions of oxygen1 yet with the exception of only five of them1 they are not susceptible of acidification4 ,metals change colour during the different degrees of oxydation which they undergo4 ,lead1 when heated in contact with the atmosphere1 first becomes grey2 if its temperature be then raised1 it turns yellow1 and a still stronger heat changes it to red4 ,iron becomes successively a green1 brown1 and white oxyd4 ,copper changes from brown to blue1 and lastly green4 ,,emily4 ,pray1 is the white lead with which houses are painted prepared by oxydating lead8 ,,mrs4 ,b4 ,not merely by oxydating1 but by being also united with carbonic acid4 ,it is a carbonat of lead4 ,the mere oxyd of lead is called red lead4 ,litharge is another oxyd of lead1 containing less oxygen4 ,almost all the metallic oxyds are used as paints4 ,the various sorts of ochres consist chiefly of iron more or less oxydated4 ,and it is a remarkable circumstance1 that if you burn metals rapidly1 the light or flame they emit during combustion partakes of the colours which the oxyd successively assumes4 ,,caroline4 ,how is that accounted for1 ,mrs4 ,b48 ,for light1 you know1 does not proceed from the burning body1 but from the decomposition of the oxygen gas8 ,,mrs4 ,b4 ,the correspondence of the colour of the light with that of the oxyd which emits it1 is1 in all probability1 owing to some particles of the metal which are volatilised and carried off by the caloric4 ,,caroline4 ,it is then a sort of metallic gas4 ,,emily4 ,why is it reckoned so unwholesome to breathe the air of a place in which metals are melting8 ,,mrs4 ,b4 ,perhaps the notion is too generally entertained4 ,but it is true with respect to lead1 and some other noxious metals1 because1 unless care be taken1 the particles of the oxyd which are volatilised by the heat are inhaled in with the breath1 and may produce dangerous effects4 ,i must show you some instances of the combustion of metals2 it would require the heat of a furnace to make them burn in the common air1 but if we supply them with a stream of oxygen gas1 we may easily accomplish it4 ,,caroline4 ,but it will still1 ,i suppose1 be necessary in some degree to raise their temperature8 ,,mrs4 ,b4 ,this1 as you shall see1 is very easily done1 particularly if the experiment be tried upon a small scale4 --,i begin by lighting this piece of charcoal with the candle1 and then increase the rapidity of its combustion by blowing upon it with a blow-pipe4 7,,plate ,,xii4 fig4 #a47 ,illustration3 ,plate ,,xii4 ,apparatus for the combustion of metals by means of oxygen gas4 ,fig4 #a4 ,igniting charcoal with a taper blow-pipe4 ,fig4 #b4 ,combustion of metals by means of a blow-pipe conveying a stream of oxygen gas from a gas holder4 ,,emily4 ,that ,i do not understand2 for it is not every kind of air1 but merely oxygen gas1 that produces combustion4 ,now you said that in breathing we inspired1 but did not expire oxygen gas4 ,why1 therefore1 should the air which you breathe through the blow-pipe promote the combustion of the charcoal8 ,,mrs4 ,b4 ,because the air1 which has but once passed through the lungs1 is yet but little altered1 a small portion only of its oxygen being destroyed2 so that a great deal more is gained by increasing the rapidity of the current1 by means of the blow-pipe1 than is lost in consequence of the air passing once through the lungs1 as you shall see-- ,,emily4 ,yes1 indeed1 it makes the charcoal burn much brighter4 ,,mrs4 ,b4 ,whilst it is red-hot1 ,i shall drop some iron filings on it1 and supply them with a current of oxygen gas1 by means of this apparatus1 7,,plate ,,xii4 fig #b47 which consists simply of a closed tin cylindrical vessel1 full of oxygen gas1 with two apertures and stop-cocks1 by one of which a stream of water is thrown into the vessel through a long funnel1 whilst by the other the gas is forced out through a blow-pipe adapted to it1 as the water gains admittance4 --,now that ,i pour water into the funnel1 you may hear the gas issuing from the blow-pipe--,i bring the charcoal close to the current1 and drop the filings upon it-- ,,caroline4 ,they emit much the same vivid light as the combustion of the iron wire in oxygen gas4 ,,mrs4 ,b4 ,the process is1 in fact1 the same2 there is only some difference in the mode of conducting it4 ,let us burn some tin in the same manner--you see that it is equally combustible4 --,let us now try some copper-- ,,caroline4 ,this burns with a greenish flame2 it is1 ,i suppose1 owing to the colour of the oxyd8 ,,emily4 ,pray1 shall we not also burn some gold8 ,,mrs4 ,b4 ,that is not in our power1 at least in this way4 ,gold1 silver1 and platina1 are incapable of being oxydated by the greatest heat that we can produce by the common method4 ,it is from this circumstance1 that they have been called perfect metals4 ,even these1 however1 have an affinity for oxygen2 but their oxydation or combustion can be performed only by means of acids or by electricity4 ,the spark given out by the ,voltaic battery produces at the point of contact a greater degree of heat than any other process2 and it is at this very high temperature only that the affinity of these metals for oxygen will enable them to act on each other4 ,i am sorry that ,i cannot show you the combustion of the perfect metals by this process1 but it requires a considerable ,voltaic battery4 ,you will see these experiments performed in the most perfect manner1 when you attend the chemical lectures of the ,royal ,institution4 ,but in the mean time ,i can1 without difficulty1 show you an ingenious apparatus lately contrived for the purpose of producing intense heats1 the power of which nearly equals that of the largest ,voltaic batteries4 ,it simply consists1 you see1 in a strong box1 made of iron or copper1 7,,plate ,x4 fig4 #b47 to which may be adapted this air-syringe or condensing-pump1 and a stop-cock terminating in a small orifice similar to that of a blow-pipe4 ,by working the condensing syringe1 up and down in this manner1 a quantity of air is accumulated in the vessel1 which may be increased to almost any extent2 so that if we now turn the stop-cock1 the condensed air will rush out1 forming a jet of considerable force2 and if we place the flame of a lamp in the current1 you will see how violently the flame is driven in that direction4 ,,caroline4 ,it seems to be exactly the same effect as that of a blow-pipe worked by the mouth1 only much stronger4 ,,emily4 ,yes2 and this new instrument has this additional advantage1 that it does not fatigue the mouth and lungs like the common blow-pipe1 and requires no art in blowing4 ,,mrs4 ,b4 ,unquestionably2 but yet this blow-pipe would be of very limited utility1 if its energy and power could not be greatly increased by some other contrivance4 ,can you imagine any mode of producing such an effect8 ,,emily4 ,could not the reservoir be charged with pure oxygen1 instead of common air1 as in the case of the gas-holder8 ,,mrs4 ,b4 ,undoubtedly2 and this is precisely the contrivance ,i allude to4 ,the vessel need only be supplied with air from a bladder full of oxygen1 instead of the air of the room1 and this1 you see1 may be easily done by screwing the bladder on the upper part of the syringe1 so that in working the syringe the oxygen gas is forced from the bladder into the condensing vessel4 ,,caroline4 ,with the aid of this small apparatus1 therefore1 we could obtain the same effects as those we have just produced with the gas-holder1 by means of a column of water forcing the gas out of it8 ,,mrs4 ,b4 ,yes2 and much more conveniently so4 ,but there is a mode of using this apparatus by which more powerful effects still may be obtained4 ,it consists in condensing in the reservoir1 not oxygen alone1 but a mixture of oxygen and hydrogen in the exact proportion in which they unite to produce water2 and then kindling the jet formed by the mixed gases4 ,the heat disengaged by this combustion1 without the help of any lamp1 is probably the most intense known2 and various effects are said to have been obtained from it which exceed all expectation4 ,,caroline4 ,but why should we not try this experiment8 ,,mrs4 ,b4 ,because it is not exempt from danger2 the combustion 7notwithstanding various contrivances which have been resorted to with a view to prevent accident7 being apt to penetrate into the inside of the vessel1 and to produce a dangerous and violent explosion4 --,we shall1 therefore1 now proceed in our subject4 ,,caroline4 ,i think you said the oxyds of metals could be restored to their metallic state8 ,,mrs4 ,b4 ,yes2 this is called reviving a metal4 ,metals are in general capable of being revived by charcoal1 when heated red hot1 charcoal having a greater attraction for oxygen than the metals4 ,you need only1 therefore1 decompose1 or unburn the oxyd1 by depriving it of its oxygen1 and the metal will be restored to its pure state4 ,,emily4 ,but will the carbon1 by this operation1 be burnt1 and be converted into carbonic acid8 ,,mrs4 ,b4 ,certainly4 ,there are other combustible substances to which metals at a high temperature will part with their oxygen4 ,they will also yield it to each other1 according to their several degrees of attraction for it2 and if the oxygen goes into a more dense state in the metal which it enters1 than it existed in that which it quits1 a proportional disengagement of caloric will take place4 ,,caroline4 ,and cannot the oxyds of gold1 silver1 and platina1 which are formed by means of acids or of the electric fluid1 be restored to their metallic state8 ,,mrs4 ,b4 ,yes1 they may2 and the intervention of a combustible body is not required2 heat alone will take the oxygen from them1 convert it into a gas1 and revive the metal4 ,,emily4 ,you said that rust was an oxyd of iron2 how is it1 then1 that water1 or merely dampness1 produces it1 which1 you know1 it very frequently does on steel grates1 or any iron instruments8 ,,mrs4 ,b4 ,in that case the metal decomposes the water1 or dampness 7which is nothing but water in a state of vapour71 and obtains the oxygen from it4 ,,caroline4 ,i thought that it was necessary to bring metals to a very high temperature to enable them to decompose water4 ,,mrs4 ,b4 ,it is so1 if it is required that the process should be performed rapidly1 and if any considerable quantity is to be decomposed4 ,rust1 you knew1 is sometimes months in forming1 and then it is only the surface of the metal that is oxydated4 ,,emily4 ,metals1 then1 that do not rust1 are incapable of spontaneous oxydation1 either by air or water8 ,,mrs4 ,b4 ,yes2 and this is the case with the perfect metals1 which1 on that account1 preserve their metallic lustre so well4 ,,emily4 ,are all metals capable of decomposing water1 provided their temperature be sufficiently raised8 ,,mrs4 ,b4 ,no2 a certain degree of attraction is requisite1 besides the assistance of heat4 ,water1 you recollect1 is composed of oxygen and hydrogen2 and1 unless the affinity of the metal for oxygen be stronger than that of hydrogen1 it is in vain that we raise its temperature1 for it cannot take the oxygen from the hydrogen4 ,iron1 zinc1 tin1 and antimony1 have a stronger affinity for oxygen than hydrogen has1 therefore these four metals are capable of decomposing water4 ,but hydrogen having an advantage over all the other metals with respect to its affinity for oxygen1 it not only withholds its oxygen from them1 but is even capable1 under certain circumstances1 of taking the oxygen from the oxyds of these metals4 ,,emily4 ,i confess that ,i do not quite understand why hydrogen can take oxygen from those metals that do not decompose water4 ,,caroline4 ,now ,i think ,i do perfectly4 ,lead1 for instance1 will not decompose water1 because it has not so strong an attraction for oxygen as hydrogen has4 ,well1 then1 suppose the lead to be in a state of oxyd2 hydrogen will take the oxygen from the lead1 and unite with it to form water1 because hydrogen has a stronger attraction for oxygen1 than oxygen has for lead2 and it is the same with all the other metals which do not decompose water4 ,,emily4 ,i understand your explanation1 ,caroline1 very well2 and ,i imagine that it is because lead cannot decompose water that it is so much employed for pipes for conveying that fluid4 ,,mrs4 ,b4 ,certainly2 lead is1 on that account1 particularly appropriate to such purposes2 whilst1 on the contrary1 this metal1 if it was oxydable by water1 would impart to it very noxious qualities1 as all oxyds of lead are more or less pernicious4 ,but1 with regard to the oxydation of metals1 the most powerful mode of effecting it is by means of acids4 ,these1 you know1 contain a much greater proportion of oxygen than either air or water2 and will1 most of them1 easily yield it to metals4 ,thus1 you recollect1 the zinc plates of the ,voltaic battery are oxydated by the acid and water1 much more effectually than by water alone4 ,,caroline4 ,and ,i have often observed that if ,i drop vinegar1 lemon1 or any acid on the blade of a knife1 or on a pair of scissars1 it will immediately produce a spot of rust4 ,,emily4 ,metals have1 then1 three ways of obtaining oxygen2 from the atmosphere1 from water1 and from acids4 ,,mrs4 ,b4 ,the two first you have already witnessed1 and ,i shall now show you how metals take the oxygen from an acid4 ,this bottle contains nitric acid2 ,i shall pour some of it over this piece of copper-leaf 4 4 4 4 4 4 4 ,,caroline4 ,oh1 what a disagreeable smell6 ,,emily4 ,and what is it that produces the effervescency and that thick yellow vapour8 ,,mrs4 ,b4 ,it is the acid1 which being abandoned by the greatest part of its oxygen1 is converted into a weaker acid1 which escapes in the form of gas4 ,,caroline4 ,and whence proceeds this heat8 ,,mrs4 ,b4 ,indeed1 ,caroline1 ,i think you might now be able to answer that question yourself4 ,,caroline4 ,perhaps it is that the oxygen enters into the metal in a more solid state than it existed in the acid1 in consequence of which caloric is disengaged4 ,,mrs4 ,b4 ,if the combination of the oxygen and the metal results from the union of their opposite electricities1 of course caloric must be given out4 ,,emily4 ,the effervescence is over2 therefore ,i suppose that the metal is now oxydated4 ,,mrs4 ,b4 ,yes4 ,but there is another important connection between metals and acids1 with which ,i must now make you acquainted4 ,metals1 when in the state of oxyds1 are capable of being dissolved by acids4 ,in this operation they enter into a chemical combination with the acid1 and form an entirely new compound4 ,,caroline4 ,but what difference is there between the oxydation and the dissolution of the metal by an acid8 ,,mrs4 ,b4 ,in the first case1 the metal merely combines with a portion of oxygen taken from the acid1 which is thus partly deoxygenated1 as in the instance you have just seen2 in the second case1 the metal1 after being previously oxydated1 is actually dissolved in the acid1 and enters into a chemical combination with it1 without producing any further decomposition or effervescence4 --,this complete combination of an oxyd and an acid forms a peculiar and important class of compound salts4 ,,emily4 ,the difference between an oxyd and a compound salt1 therefore1 is very obvious3 the one consists of a metal and oxygen2 the other of an oxyd and an acid4 ,,mrs4 ,b4 ,very well3 and you will be careful to remember that the metals are incapable of entering into this combination with acids1 unless they are previously oxydated2 therefore1 whenever you bring a metal in contact with an acid1 it will be first oxydated and afterwards dissolved1 provided that there be a sufficient quantity of acid for both operations4 ,there are some metals1 however1 whose solution is more easily accomplished1 by diluting the acid in water2 and the metal will1 in this case1 be oxydated1 not by the acid1 but by the water1 which it will decompose4 ,but in proportion as the oxygen of the water oxydates the surface of the metal1 the acid combines with it1 washes it off1 and leaves a fresh surface for the oxygen to act upon3 then other coats of oxyd are successively formed1 and rapidly dissolved by the acid1 which continues combining with the new-formed surfaces of oxyd till the whole of the metal is dissolved4 ,during this process the hydrogen gas of the water is disengaged1 and flies off with effervescence4 ,,emily4 ,was not this the manner in which the sulphuric acid assisted the iron filings in decomposing water8 ,,mrs4 ,b4 ,exactly2 and it is thus that several metals1 which are incapable alone of decomposing water1 are enabled to do it by the assistance of an acid1 which1 by continually washing off the covering of oxyd1 as it is formed1 prepares a fresh surface of metal to act upon the water4 ,,caroline4 ,the acid here seems to act a part not very different from that of a scrubbing-brush4 --,but pray would not this be a good method of cleaning metallic utensils8 ,,mrs4 ,b4 ,yes2 on some occasions a weak acid1 as vinegar1 is used for cleaning copper4 ,iron plates1 too1 are freed from the rust on their surface by diluted muriatic acid1 previous to their being covered with tin4 ,you must remember1 however1 that in this mode of cleaning metals the acid should be quickly afterwards wiped off1 otherwise it would produce fresh oxyd4 ,,caroline4 ,let us watch the dissolution of the copper in the nitric acid2 for ,i am very impatient to see the salt that is to result from it4 ,the mixture is now of a beautiful blue colour2 but there is no appearance of the formation of a salt2 it seems to be a tedious operation4 ,,mrs4 ,b4 ,the crystallisation of the salt requires some length of time to be completed2 if1 however1 you are so impatient1 ,i can easily show you a metallic salt already formed4 ,,caroline4 ,but that would not satisfy my curiosity half so well as one of our own manufacturing4 ,,mrs4 ,b4 ,it is one of our own preparing that ,i mean to show you4 ,when we decomposed water a few days since1 by the oxydation of iron filings through the assistance of sulphuric acid1 in what did the process consist8 ,,caroline4 ,in proportion as the water yielded its oxygen to the iron1 the acid combined with the new-formed oxyd1 and the hydrogen escaped alone4 ,,mrs4 ,b4 ,very well2 the result1 therefore1 was a compound salt1 formed by the combination of sulphuric acid with oxyd of iron4 ,it still remains in the vessel in which the experiment was performed4 ,fetch it1 and we shall examine it4 ,,emily4 ,what a variety of processes the decomposition of water1 by a metal and an acid1 implies2 #ast1 the decomposition of the water2 #b;dly1 the oxydation of the metal2 and #c;dly1 the formation of a compound salt4 ,,caroline4 ,here it is1 ,mrs4 ,b4 --,what beautiful green crystals6 ,but we do not perceive any crystals in the solution of copper in nitrous acid8 ,,mrs4 ,b4 ,because the salt is now suspended in the water which the nitrous acid contains1 and will remain so till it is deposited in consequence of rest and cooling4 ,,emily4 ,i am surprised that a body so opake as iron can be converted into such transparent crystals4 ,,mrs4 ,b4 ,it is the union with the acid that produces the transparency2 for if the pure metal were melted1 and afterwards permitted to cool and crystallise1 it would be found just as opake as before4 ,,emily4 ,i do not understand the exact meaning of crystallisation8 ,,mrs4 ,b4 ,you recollect that when a solid body is dissolved either by water or caloric it is not decomposed2 but that its integrant parts are only suspended in the solvent4 ,when the solution is made in water1 the integrant particles of the body will1 on the water being evaporated1 again unite into a solid mass by the force of their mutual attraction4 ,but when the body is dissolved by caloric alone1 nothing more is necessary1 in order to make its particles reunite1 than to reduce its temperature4 ,and1 in general1 if the solvent1 whether water or caloric1 be slowly separated by evaporation or by cooling1 and care taken that the particles be not agitated during their reunion1 they will arrange themselves in regular masses1 each individual substance assuming a peculiar form or arrangement2 and this is what is called crystallisation4 ,,emily4 ,crystallisation1 therefore1 is simply the reunion of the particles of a solid body that has been dissolved in a fluid4 ,,mrs4 ,b4 ,that is a very good definition of it4 ,but ,i must not forget to observe1 that heat and water may unite their solvent powers2 and1 in this case1 crystallisation may be hastened by cooling1 as well as by evaporating the liquid4 ,,caroline4 ,but if the body dissolved is of a volatile nature1 will it not evaporate with the fluid8 ,,mrs4 ,b4 ,a crystallised body held in solution only by water is scarcely ever so volatile as the fluid itself1 and care must be taken to manage the heat so that it may be sufficient to evaporate the water only4 ,i should not omit also to mention that bodies1 in crystallising from their watery solution1 always retain a small portion of water1 which remains confined in the crystal in a solid form1 and does not reappear unless the body loses its crystalline state4 ,this is called the water of crystallisation4 ,but you must observe1 that whilst a body may be separated from its solution in water or caloric simply by cooling or by evaporation1 an acid can be taken from a metal with which it is combined only by stronger affinities1 which produce a decomposition4 ,,emily4 ,are the perfect metals susceptible of being dissolved and converted into compound salts by acids8 ,,mrs4 ,b4 ,gold is acted upon by only one acid1 the oxygenated muriatic1 a very remarkable acid1 which1 when in its most concentrated state1 dissolves gold or any other metal1 by burning them rapidly4 ,gold can1 it is true1 be dissolved likewise by a mixture of two acids1 commonly called aqua regia2 but this mixed solvent derives that property from containing the peculiar acid which ,i have just mentioned4 ,platina is also acted upon by this acid only2 silver is dissolved by nitric acid4 ,,caroline4 ,i think you said that some of the metals might be so strongly oxydated as to become acid8 ,,mrs4 ,b4 ,there are five metals1 arsenic1 molybdena1 chrome1 tungsten1 and columbium1 which are susceptible of combining with a sufficient quantity of oxygen to be converted into acids4 ,,caroline4 ,acids are connected with metals in such a variety of ways1 that ,i am afraid of some confusion in remembering them4 --,in the first place1 acids will yield their oxygen to metals4 ,secondly1 they will combine with them in their state of oxyds1 to form compound salts2 and lastly1 several of the metals are themselves susceptible of acidification4 ,,mrs4 ,b4 ,very well2 but though metals have so great an affinity for acids1 it is not with that class of bodies alone that they will combine4 ,they are most of them1 in their simple state1 capable of uniting with sulphur1 with phosphorus1 with carbon1 and with each other2 these combinations1 according to the nomenclature which was explained to you on a former occasion1 are called sulphurets1 phosphorets1 carburets1 c4 ,the metallic phosphorets offer nothing very remarkable4 ,the sulphurets form the peculiar kind of mineral called pyrites1 from which certain kinds of mineral waters1 as those of ,harrogate1 derive their chief chemical properties4 ,in this combination1 the sulphur1 together with the iron1 have so strong an attraction for oxygen1 that they obtain it both from the air and from water1 and by condensing it in a solid form1 produce the heat which raises the temperature of the water in such a remarkable degree4 ,,emily4 ,but if pyrites obtain oxygen from water1 that water must suffer a decomposition1 and hydrogen gas be evolved4 ,,mrs4 ,b4 ,that is actually the case in the hot springs alluded to1 which give out an extremely fetid gas1 composed of hydrogen impregnated with sulphur4 ,,caroline4 ,if ,i recollect right1 steel and plumbago1 which you mentioned in the last lesson1 are both carburets of iron8 ,,mrs4 ,b4 ,yes2 and they are the only carburets of much consequence4 ,a curious combination of metals has lately very much attracted the attention of the scientific world3 ,i mean the meteoric stones that fall from the atmosphere4 ,they consist principally of native or pure iron1 which is never found in that state in the bowels of the earth2 and contain also a small quantity of nickel and chrome1 a combination likewise new in the mineral kingdom4 ,these circumstances have led many scientific persons to believe that those substances have fallen from the moon1 or some other planet1 while others are of opinion either that they are formed in the atmosphere1 or are projected into it by some unknown volcano on the surface of our globe4 ,,caroline4 ,i have heard much of these stones1 but ,i believe many people are of opinion that they are formed on the surface of the earth1 and laugh at their pretended celestial origin4 ,,mrs4 ,b4 ,the fact of their falling is so well ascertained1 that ,i think no person who has at all investigated the subject1 can now entertain any doubt of it4 ,specimens of these stones have been discovered in all parts of the world1 and to each of them some tradition or story of its fall has been found connected4 ,and as the analysis of all those specimens affords precisely the same results1 there is strong reason to conjecture that they all proceed from the same source4 ,it is to ,mr4 ,howard that philosophers are indebted for having first analysed these stones1 and directed their attention to this interesting subject4 ,,caroline4 ,but pray1 ,mrs4 ,b41 how can solid masses of iron and nickel be formed from the atmosphere1 which consists of the two airs1 nitrogen and oxygen8 ,,mrs4 ,b4 ,i really do not see how they could1 and think it much more probable that they fall from the moon4 --,but we must not suffer this digression to take up too much of our time4 ,the combinations of metals with each other are called alloys2 thus brass is an alloy of copper and zinc2 bronze1 of copper and tin1 c4 ,,emily4 ,and is not pewter also a combination of metal8 ,,mrs4 ,b4 ,it is4 ,the pewter made in this country is mostly composed of tin1 with a very small proportion of zinc and lead4 ,,caroline4 ,block-tin is a kind of pewter1 ,i believe8 ,,mrs4 ,b4 ,properly speaking1 block-tin means tin in blocks1 or square massive ingots2 but in the sense in which it is used by ignorant workmen1 it is iron plated with tin1 which renders it more durable1 as tin will not so easily rust4 ,tin alone1 however1 would be too soft a metal to be worked for common use1 and all tin-vessels and utensils are in fact made of plates of iron1 thinly coated with tin1 which prevents the iron from rusting4 ,,caroline4 ,say rather oxydating1 ,mrs4 ,b4 --,rust is a word that should be exploded in chemistry4 ,,mrs4 ,b4 ,take care1 however1 not to introduce the word oxydate1 instead of rust1 in general conversation2 for you would probably not be understood1 and you might be suspected of affectation4 ,metals differ very much in their affinity for each other2 some will not unite at all1 others readily combine together1 and on this property of metals the art of soldering depends4 ,,emily4 ,what is soldering8 ,,mrs4 ,b4 ,it is joining two pieces of metal together1 by a more fusible metal interposed between them4 ,thus tin is a solder for lead2 brass1 gold1 or silver1 are solder for iron1 c4 ,,caroline4 ,and is not plating metals something of the same nature8 ,,mrs4 ,b4 ,in the operation of plating1 two metals are united1 one being covered with the other1 but without the intervention of a third2 iron or copper may thus be covered with gold or silver4 ,,emily4 ,mercury appears to me of a very different nature from the other metals4 ,,mrs4 ,b4 ,one of its greatest peculiarities is1 that it retains a fluid state at the temperature of the atmosphere4 ,all metals are fusible at different degrees of heat1 and they have likewise each the property of freezing or becoming solid at a certain fixed temperature4 ,mercury congeals only at seventy-two degrees below the freezing point4 ,,emily4 ,that is to say1 that in order to freeze1 it requires a temperature of seventy-two degrees colder than that at which water freezes4 ,,mrs4 ,b4 ,exactly so4 ,,caroline4 ,but is the temperature of the atmosphere ever so low as that8 ,,mrs4 ,b4 ,yes1 often in ,siberia2 but happily never in this part of the globe4 ,here1 however1 mercury may be congealed by artificial cold2 ,i mean such intense cold as can be produced by some chemical mixtures1 or by the rapid evaporation of ether under the air-pump499 ,footnote 993 ,by a process analogous to that described1 page #aee4 of this volume4 ,,caroline4 ,and can mercury be made to boil and evaporate8 ,,mrs4 ,b4 ,yes1 like any other liquid2 only it requires a much greater degree of heat4 ,at the temperature of six hundred degrees1 it begins to boil and evaporate like water4 ,mercury combines with gold1 silver1 tin1 and with several other metals2 and1 if mixed with any of them in a sufficient proportion1 it penetrates the solid metal1 softens it1 loses its own fluidity1 and forms an amalgam1 which is the name given to the combination of any metal with mercury1 forming a substance more or less solid1 according as the mercury or the other metal predominates4 ,,emily4 ,in the list of metals there are some whose names ,i have never before heard mentioned4 ,,mrs4 ,b4 ,besides those which ,sir ,h4 ,davy has obtained1 there are several that have been recently discovered1 whose properties are yet but little known1 as for instance1 titanium1 which was discovered by the ,rev4 ,mr4 ,gregor1 in the tin-mines of ,cornwall2 columbium or tantalium1 which has lately been discovered by ,mr4 ,hatchett2 and osmium1 iridium1 palladium1 and rhodium1 all of which ,dr4 ,wollaston and ,mr4 ,tennant found mixed in minute quantities with crude platina1 and the distinct existence of which they proved by curious and delicate experiments4 ,,caroline4 ,arsenic has been mentioned amongst the metals4 ,i had no notion that it belonged to that class of bodies1 for ,i had never seen it but as a powder1 and never thought of it but as a most deadly poison4 ,,mrs4 ,b4 ,in its pure metallic state1 ,i believe1 it is not so poisonous2 but it has such a great affinity for oxygen1 that it absorbs it from the atmosphere at its natural temperature3 you have seen it1 therefore1 only in its state of oxyd1 when1 from its combination with oxygen1 it has acquired its very poisonous properties4 ,,caroline4 ,is it possible that oxygen can impart poisonous qualities8 ,that valuable substance which produces light and fire1 and which all bodies in nature are so eager to obtain8 ,,mrs4 ,b4 ,most of the metallic oxyds are poisonous1 and derive this property from their union with oxygen4 ,the white lead1 so much used in paint1 owes its pernicious effects to oxygen4 ,in general1 oxygen1 in a concrete state1 appears to be particularly destructive in its effects on flesh or any animal matter2 and those oxyds are most caustic that have an acrid burning taste1 which proceeds from the metal having but a slight affinity for oxygen1 and therefore easily yielding it to the flesh1 which it corrodes and destroys4 ,,emily4 ,what is the meaning of the word caustic1 which you have just used8 ,,mrs4 ,b4 ,it expresses that property which some bodies possess1 of disorganizing and destroying animal matter1 by operating a kind of combustion1 or at least a chemical decomposition4 ,you must often have heard of caustic used to burn warts1 or other animal excrescences2 most of these bodies owe their destructive power to the oxygen with which they are combined4 ,the common caustic1 called lunar caustic1 is a compound formed by the union of nitric acid and silver2 and it is supposed to owe its caustic qualities to the oxygen contained in the nitric acid4 ,,caroline4 ,but1 pray1 are not acids still more caustic than oxyds1 as they contain a greater proportion of oxygen8 ,,mrs4 ,b4 ,some of the acids are2 but the caustic property of a body depends not only upon the quantity of oxygen which it contains1 but also upon its slight affinity for that principle1 and the consequent facility with which it yields it4 ,,emily4 ,is not this destructive property of oxygen accounted for8 ,,mrs4 ,b4 ,it proceeds probably from the strong attraction of oxygen for hydrogen2 for if the one rapidly absorb the other from the animal fibre1 a disorganisation of the substance must ensue4 ,,emily4 ,caustics are1 then1 very properly said to burn the flesh1 since the combination of oxygen and hydrogen is an actual combustion4 ,,caroline4 ,now1 ,i think1 this effect would be more properly termed an oxydation1 as there is no disengagement of light and heat4 ,,mrs4 ,b4 ,but there really is a sensation of heat produced by the action of caustics4 ,,emily4 ,if oxygen is so caustic1 why does not that which is contained in the atmosphere burn us8 ,,mrs4 ,b4 ,because it is in a gaseous state1 and has a greater attraction for its electricity than for the hydrogen of our bodies4 ,besides1 should the air be slightly caustic1 we are in a great measure sheltered from its effects by the skin2 you know how much a wound1 however trifling1 smarts on being exposed to it4 ,,caroline4 ,it is a curious idea1 however1 that we should live in a slow fire4 ,but1 if the air was caustic1 would it not have an acrid taste8 ,,mrs4 ,b4 ,it possibly may have such a taste2 though in so slight a degree1 that custom has rendered it insensible4 ,,caroline4 ,and why is not water caustic8 ,when ,i dip my hand into water1 though cold1 it ought to burn me from the caustic nature of its oxygen4 ,,mrs4 ,b4 ,your hand does not decompose the water2 the oxygen in that state is much better supplied with hydrogen than it would be by animal matter1 and if its causticity depend on its affinity for that principle1 it will be very far from quitting its state of water to act upon your hand4 ,you must not forget that oxyds are caustic in proportion as the oxygen adheres slightly to them4 ,,emily4 ,since the oxyd of arsenic is poisonous1 its acid1 ,i suppose1 is fully as much so8 ,,mrs4 ,b4 ,yes2 it is one of the strongest poisons in nature4 ,,emily4 ,there is a poison called verdigris1 which forms on brass and copper when not kept very clean2 and this1 ,i have heard1 is an objection to these metals being made into kitchen utensils4 ,is this poison likewise occasioned by oxygen8 ,,mrs4 ,b4 ,it is produced by the intervention of oxygen2 for verdigris is a compound salt formed by the union of vinegar and copper2 it is of a beautiful green colour1 and much used in painting4 ,,emily4 ,but1 ,i believe1 verdigris is often formed on copper when no vinegar has been in contact with it4 ,,mrs4 ,b4 ,not real verdigris1 but compound salts1 somewhat resembling it1 may be produced by the action of any acid on copper4 ,the solution of copper in nitric acid1 if evaporated1 affords a salt which produces an effect on tin that will surprise you1 and ,i have prepared some from the solution we made before1 that ,i might show it to you4 ,i shall first sprinkle some water on this piece of tin-foil1 and then some of the salt4 --,now observe that ,i fold it up suddenly1 and press it into one lump4 ,,caroline4 ,what a prodigious vapour issues from it--and sparks of fire ,i declare6 ,,mrs4 ,b4 ,i thought it would surprise you4 ,the effect1 however1 ,i dare say you could account for1 since it is merely the consequence of the oxygen of the salt rapidly entering into a closer combination with the tin4 ,there is also a beautiful green salt too curious to be omitted2 it is produced by the combination of cobalt with muriatic acid1 which has the singular property of forming what is called sympathetic ink4 ,characters written with this solution are invisible when cold1 but when a gentle heat is applied1 they assume a fine bluish green colour4 ,,caroline4 ,i think one might draw very curious landscapes with the assistance of this ink2 ,i would first make a water-colour drawing of a winter-scene1 in which the trees should be leafless1 and the grass scarcely green3 ,i would then trace all the verdure with the invisible ink1 and whenever ,i chose to create spring1 ,i should hold it before the fire1 and its warmth would cover the landscape with a rich verdure4 ,,mrs4 ,b4 ,that will be a very amusing experiment1 and ,i advise you by all means to try it4 ,transcriber's ,note3 ,several cobalt compounds1 including the cobalt chloride described here1 are still in use as invisible 78sympathetic07 inks4 ,they are safe if used appropriately4 ,before we part1 ,i must introduce to your acquaintance the curious metals which ,sir ,h4 ,davy has recently discovered4 ,the history of these extraordinary bodies is yet so much in its infancy1 that ,i shall confine myself to a very short account of them2 it is more important to point out to you the vast1 and apparently inexhaustible1 field of research which has been thrown open to our view by ,sir ,h4 ,davy's memorable discoveries1 than to enter into a minute account of particular bodies or experiments4 ,,caroline4 ,but ,i have heard that these discoveries1 however splendid and extraordinary1 are not very likely to prove of any great benefit to the world1 as they are rather objects of curiosity than of use4 ,,mrs4 ,b4 ,such may be the illiberal conclusions of the ignorant and narrow-minded2 but those who can duly estimate the advantages of enlarging the sphere of science1 must be convinced that the acquisition of every new fact1 however unconnected it may at first appear with practical utility1 must ultimately prove beneficial to mankind4 ,but these remarks are scarcely applicable to the present subject2 for some of the new metals have already proved eminently useful as chemical agents1 and are likely soon to be employed in the arts4 ,for the enumeration of these metals1 ,i must refer you to our list of simple bodies2 they are derived from the alkalies1 the earths1 and three of the acids1 all of which had been hitherto considered as undecompoundable or simple bodies4 ,when ,sir ,h4 ,davy first turned his attention to the effects of the ,voltaic battery1 he tried its power on a variety of compound bodies1 and gradually brought to light a number of new and interesting facts1 which led the way to more important discoveries4 ,it would be highly interesting to trace his steps in this new department of science1 but it would lead us too far from our principal object4 ,a general view of his most remarkable discoveries is all that ,i can aim at1 or that you could1 at present1 understand4 ,the facility with which compound bodies yielded to the ,voltaic electricity1 induced him to make trial of its effects on substances hitherto considered as simple1 but which he suspected of being compound1 and his researches were soon crowned with the most complete success4 ,the body which he first submitted to the ,voltaic battery1 and which had never yet been decomposed1 was one of the fixed alkalies1 called potash4 ,this substance gave out an elastic fluid at the positive wire1 which was ascertained to be oxygen1 and at the negative wire1 small globules of a very high metallic lustre1 very similar in appearance to mercury2 thus proving that potash1 which had hitherto been considered as a simple incombustible body1 was in fact a metallic oxyd2 and that its incombustibility proceeded from its being already combined with oxygen4 ,,emily4 ,i suppose the wires used in this experiment were of platina1 as they were when you decomposed water2 for if of iron1 the oxygen would have combined with the wire1 instead of appearing in the form of gas4 ,,mrs4 ,b4 ,certainly3 the metal1 however1 would equally have been disengaged4 ,sir ,h4 ,davy has distinguished this new substance by the name of ,,potassium1 which is derived from that of the alkali1 from which it is procured4 ,i have some small pieces of it in this phial1 but you have already seen it1 as it is the metal which we burnt in contact with sulphur4 ,,emily4 ,what is the liquid in which you keep it8 ,,mrs4 ,b4 ,it is naptha1 a bituminous liquid1 with which ,i shall hereafter make you acquainted4 ,it is almost the only fluid in which potassium can be preserved1 as it contains no oxygen1 and this metal has so powerful an attraction for oxygen1 that it will not only absorb it from the air1 but likewise from water1 or any body whatever that contains it4 ,,emily4 ,this1 then1 is one of the bodies that oxydates spontaneously without the application of heat8 ,,mrs4 ,b4 ,yes2 and it has this remarkable peculiarity that it attracts oxygen much more rapidly from water than from air2 so that when thrown into water1 however cold1 it actually bursts into flame4 ,i shall now throw a small piece1 about the size of a pin's head1 on this drop of water4 ,,caroline4 ,it instantaneously exploded1 producing a little flash of light6 this is1 indeed1 a most curious substance6 ,,mrs4 ,b4 ,by its combustion it is reconverted into potash2 and as potash is now decidedly a compound body1 ,i shall not enter into any of its properties till we have completed our review of the simple bodies2 but we may here make a few observations on its basis1 potassium4 ,if this substance is left in contact with air1 it rapidly returns to the state of potash1 with a disengagement of heat1 but without any flash of light4 ,,emily4 ,but is it not very singular that it should burn better in water than in air8 ,,caroline4 ,i do not think so3 for if the attraction of potassium for oxygen is so strong that it finds no more difficulty in separating it from the hydrogen in water1 than in absorbing it from the air1 it will no doubt be more amply and rapidly supplied by water than by air4 ,,mrs4 ,b4 ,that cannot1 however1 be precisely the reason1 for when potassium is introduced under water1 without contact of air1 the combustion is not so rapid1 and indeed1 in that case1 there is no luminous appearance2 but a violent action takes place1 much heat is excited1 the potash is regenerated1 and hydrogen gas is evolved4 ,potassium is so eminently combustible1 that instead of requiring1 like other metals1 an elevation of temperature1 it will burn rapidly in contact with water1 even below the freezing point4 ,this you may witness by throwing a piece on this lump of ice4 ,,caroline4 ,it again exploded with flame1 and has made a deep hole in the ice4 ,,mrs4 ,b4 ,this hole contains a solution of potash2 for the alkali being extremely soluble1 disappears in the water at the instant it is produced4 ,its presence1 however1 may be easily ascertained1 alkalies having the property of changing paper1 stained with turmeric1 to a red colour2 if you dip one end of this slip of paper into the hole in the ice you will see it change colour1 and the same1 if you wet it with the drop of water in which the first piece of potassium was burnt4 ,,caroline4 ,it has indeed changed the paper from yellow to red4 ,,mrs4 ,b4 ,this metal will burn likewise in carbonic acid gas1 a gas that had always been supposed incapable of supporting combustion1 as we were unacquainted with any substance that had a greater attraction for oxygen than carbon4 ,potassium1 however1 readily decomposes this gas1 by absorbing its oxygen1 as ,i shall show you4 ,this retort is filled with carbonic acid gas4 --,i will put a small piece of potassium in it2 but for this combustion a slight elevation of temperature is required1 for which purpose ,i shall hold the retort over the lamp4 ,,caroline4 ,now it has taken fire1 and burns with violence6 ,it has burst the retort4 ,,mrs4 ,b4 ,here is the piece of regenerated potash2 can you tell me why it is become so black8 ,,emily4 ,no doubt it is blackened by the carbon1 which1 when its oxygen entered into combination with the potassium1 was deposited on its surface4 ,,mrs4 ,b4 ,you are right4 ,this metal is perfectly fluid at the temperature of one hundred degrees2 at fifty degrees it is solid1 but soft and malleable2 at thirty-two degrees it is hard and brittle1 and its fracture exhibits an appearance of confused crystallization4 ,it is scarcely more than half as heavy as water2 its specific gravity being about six when water is reckoned at ten2 so that this metal is actually lighter than any known fluid1 even than ether4 ,potassium combines with sulphur and phosphorus1 forming sulphurets and phosphurets2 it likewise forms alloys with several metals1 and amalgamates with mercury4 ,,emily4 ,but can a sufficient quantity of potassium be obtained1 by means of the ,voltaic battery1 to admit of all its properties and relations to other bodies being satisfactorily ascertained8 ,,mrs4 ,b4 ,not easily2 but ,i must not neglect to inform you that a method of obtaining this metal in considerable quantities has since been discovered4 ,two eminent ,french chemists1 ,thenard and ,gay ,lussac1 stimulated by the triumph which ,sir ,h4 ,davy had obtained1 attempted to separate potassium from its combination with oxygen1 by common chemical means1 and without the aid of electricity4 ,they caused red hot potash in a state of fusion to filter through iron turnings in an iron tube1 heated to whiteness4 ,their experiment was crowned with the most complete success2 more potassium was obtained by this single operation1 that could have been collected in many weeks by the most diligent use of the ,voltaic battery4 ,,emily4 ,in this experiment1 ,i suppose1 the oxygen quitted its combination with the potassium to unite with the iron turnings8 ,,mrs4 ,b4 ,exactly so2 and the potassium was thus obtained in its simple state4 ,from that time it has become a most convenient and powerful instrument of deoxygenation in chemical experiments4 ,this important improvement1 engrafted on ,sir ,h4 ,davy's previous discoveries1 served but to add to his glory1 since the facts which he had established1 when possessed of only a few atoms of this curious substance1 and the accuracy of his analytical statements1 were all confirmed when an opportunity occurred of repeating his experiments upon this substance1 which can now be obtained in unlimited quantities4 ,,caroline4 ,what a satisfaction ,sir ,h4 ,davy must have felt1 when by an effort of genius he succeeded in bringing to light and actually giving existence1 to these curious bodies1 which without him might perhaps have ever remained concealed from our view6 ,,mrs4 ,b4 ,the next substance which ,sir ,h4 ,davy submitted to the influence of the ,voltaic battery was ,soda1 the other fixed alkali1 which yielded to the same powers of decomposition2 from this alkali too1 a metallic substance was obtained1 very analogous in its properties to that which had been discovered in potash2 ,sir ,h4 ,davy has called it ,,sodium4 ,it is rather heavier than potassium1 though considerably lighter than water2 it is not so easily fusible as potassium4 ,encouraged by these extraordinary results1 ,sir ,h4 ,davy next performed a series of beautiful experiments on ,ammonia1 or the volatile alkali1 which1 from analogy1 he was led to suspect might also contain oxygen4 ,this he soon ascertained to be the fact1 but he has not yet succeeded in obtaining the basis of ammonia in a separate state2 it is from analogy1 and from the power which the volatile alkali has1 in its gaseous form1 to oxydate iron1 and also from the amalgams which can be obtained from ammonia by various processes1 that the proofs of that alkali being also a metallic oxyd are deduced4 ,thus1 then1 the three alkalies1 two of which had always been considered as simple bodies1 have now lost all claim to that title1 and ,i have accordingly classed the alkalies amongst the compounds1 whose properties we shall treat of in a future conversation4 ,,emily4 ,what are the other newly discovered metals which you have alluded to in your list of simple bodies8 ,,mrs4 ,b4 ,they are the metals of the earths which became next the object of ,sir ,h4 ,davy's researches2 these bodies had never yet been decomposed1 though they were strongly suspected not only of being compounds1 but of being metallic oxyds4 ,from the circumstance of their incombustibility it was conjectured1 with some plausibility1 that they might possibly be bodies that had been already burnt4 ,,caroline4 ,and metals1 when oxydated1 become1 to all appearance1 a kind of earthy substance4 ,,mrs4 ,b4 ,they have1 besides1 several features of resemblance with metallic oxyds2 ,sir ,h4 ,davy had therefore great reason to be sanguine in his expectations of decomposing them1 and he was not disappointed4 ,he could not1 however1 succeed in obtaining the basis of the earths in a pure separate state2 but metallic alloys were formed with other metals1 which sufficiently proved the existence of the metallic basis of the earths4 ,the last class of new metallic bodies which ,sir ,h4 ,davy discovered was obtained from the three undecompounded acids1 the boracic1 the fluoric1 and the muriatic acids2 but as you are entirely unacquainted with these bodies1 ,i shall reserve the account of their decomposition till we come to treat of their properties as acids4 ,thus in the course of two years1 by the unparalleled exertions of a single individual1 chemical science has assumed a new aspect4 ,bodies have been brought to light which the human eye never before beheld1 and which might have remained eternally concealed under their impenetrable disguise4 ,it is impossible at the present period to appreciate to their full extent the consequences which science or the arts may derive from these discoveries2 we may1 however1 anticipate the most important results4 ,in chemical analysis we are now in possession of more energetic agents of decomposition than were ever before known4 ,in geology new views are opened1 which will probably operate a revolution in that obscure and difficult science4 ,it is already proved that all the earths1 and1 in fact1 the solid surface of this globe1 are metallic bodies mineralized by oxygen1 and as our planet has been calculated to be considerably more dense upon the whole than on the surface1 it is reasonable to suppose that the interior part is composed of a metallic mass1 the surface of which only has been mineralized by the atmosphere4 ,the eruptions of volcanos1 those stupendous problems of nature1 admit now of an easy explanation4 ,for if the bowels of the earth are the grand recess of these newly discovered inflammable bodies1 whenever water penetrates into them1 combustions and explosions must take place2 and it is remarkable that the lava which is thrown out1 is the very kind of substance which might be expected to result from these combustions4 ,i must now take my leave of you2 we have had a very long conversation to-day1 and ,i hope you will be able to recollect what you have learnt4 ,at our next interview we shall enter on a new subject4 ,,end ,,of ,,the ,,first ,,volume4 ,printed by ,a4 ,strahan1 ,printers-,street1 ,london4 99 99 99 99 99 99 99 99 99 ,,conversations ,,on ,,chemistry2 ,in ,which ,the ,elements ,of ,that ,science ,are ,familiarly ,explained ,and ,illustrated ,by ,experiments4 ,,in ,,two ,,volumes4 ,the ,fifth ,edition1 revised1 corrected1 and considerably enlarged4 ,,vol4 ,,ii4 ,,on ,,compound ,,bodies4 ,london3 ,printed ,for ,longman1 ,hurst1 ,rees1 ,orme1 and ,brown1 ,paternoster-,row4 #ahag4 ,,conversation ,,xiii4 ,,on ,,the ,,attraction ,,of ,,composition4 ,,mrs4 ,b4 ,having completed our examination of the simple or elementary bodies1 we are now to proceed to those of a compound nature2 but before we enter on this extensive subject1 it will be necessary to make you acquainted with the principal laws by which chemical combinations are governed4 ,you recollect1 ,i hope1 what we formerly said of the nature of the attraction of composition1 or chemical attraction1 or affinity1 as it is also called8 ,,emily4 ,yes1 ,i think perfectly2 it is the attraction that subsists between bodies of a different nature1 which occasions them to combine and form a compound1 when they come in contact1 and1 according to ,sir ,h4 ,davy's opinion1 this effect is produced by the attraction of the opposite electricities1 which prevail in bodies of different kinds4 ,,mrs4 ,b4 ,very well2 your definition comprehends the first law of chemical attraction1 which is1 that it takes place only between bodies of a different nature2 as1 for instance1 between an acid and an alkali2 between oxygen and a metal1 c4 ,,caroline4 ,that we understand of course2 for the attraction between particles of a similar nature is that of aggregation1 or cohesion1 which is independent of any chemical power4 ,,mrs4 ,b4 ,the #b;d law of chemical attraction is1 that it takes place only between the most minute particles of bodies2 therefore1 the more you divide the particles of the bodies to be combined1 the more readily they act upon each other4 ,,caroline4 ,that is again a circumstance which we might have supposed1 for the finer the particles of the two substances are1 the more easily and perfectly they will come in contact with each other1 which must greatly facilitate their union4 ,it was for this purpose1 you said1 that you used iron filings1 in preference to wires or pieces of iron1 for the decomposition of water4 ,,mrs4 ,b4 ,it was once supposed that no mechanical power could divide bodies into particles sufficiently minute for them to act on each other2 and that1 in order to produce the extreme division requisite for a chemical action1 one1 if not both of the bodies1 should be in a fluid state4 ,there are1 however1 a few instances in which two solid bodies1 very finely pulverized1 exert a chemical action on one another2 but such exceptions to the general rule are very rare indeed4 ,,emily4 ,in all the combinations that we have hitherto seen1 one of the constituents has1 ,i believe1 been either liquid or ariform4 ,in combustions1 for instance1 the oxygen is taken from the atmosphere1 in which it existed in the state of gas2 and whenever we have seen acids combine with metals or with alkalies1 they were either in a liquid or an ariform state4 ,,mrs4 ,b4 ,the #c;d law of chemical attraction is1 that it can take place between two1 three1 four1 or even a greater number of bodies4 ,,caroline4 ,oxyds and acids are bodies composed of two constituents2 but ,i recollect no instance of the combination of a greater number of principles4 ,,mrs4 ,b4 ,the compound salts1 formed by the union of the metals with acids1 are composed of three principles4 ,and there are salts formed by the combination of the alkalies with the earths which are of a similar description4 ,,caroline4 ,are they of the same kind as the metallic salts8 ,,mrs4 ,b4 ,yes2 they are very analogous in their nature1 although different in many of their properties4 ,a methodical nomenclature1 similar to that of the acids1 has been adopted for the compound salts4 ,each individual salt derives its name from its constituent parts1 so that every name implies a knowledge of the composition of the salt4 ,the three alkalies1 the alkaline earths1 and the metals1 are called salifiable bases or radicals2 and the acids1 salifying principles4 ,the name of each salt is composed both of that of the acid and the salifiable base2 and it terminates in at or it1 according to the degree of the oxygenation of the acid4 ,thus1 for instance1 all those salts which are formed by the combination of the sulphuric acid with any of the salifiable bases are called sulphats1 and the name of the radical is added for the specific distinction of the salt2 if it be potash1 it will compose a sulphat of potash2 if ammonia1 sulphat of ammonia1 c4 ,,emily4 ,the crystals which we obtained from the combination of iron and sulphuric acid were therefore sulphat of iron8 ,,mrs4 ,b4 ,precisely2 and those which we prepared by dissolving copper in nitric acid1 nitrat of copper1 and so on4 --,but this is not all2 if the salt be formed by that class of acids which ends in ous1 7which you know indicates a less degree of oxygenation17 the termination of the name of the salt will be in it1 as sulphit of potash1 sulphit of ammonia1 c4 ,,emily4 ,there must be an immense number of compound salts1 since there is so great a variety of salifiable radicals1 as well as of salifying principles4 ,,mrs4 ,b4 ,their real number cannot be ascertained1 since it increases every day4 ,but we must not proceed further in the investigation of the compound salts1 until we have completed the examination of the nature of the ingredients of which they are composed4 ,the #dth law of chemical attraction is1 that a change of temperature always takes place at the moment of combination4 ,this arises from the extrication of the two electricities in the form of caloric1 which takes place when bodies unite2 and also sometimes in part from a change of capacity of the bodies for heat1 which always takes place when the combination is attended with an increase of density1 but more especially when the compound passes from the liquid to the solid form4 ,i shall now show you a striking instance of a change of temperature from chemical union1 merely by pouring some nitrous acid on this small quantity of oil of turpentine--the oil will instantly combine with the oxygen of the acid1 and produce a considerable change of temperature4 ,,caroline4 ,what a blaze6 ,the temperature of the oil and the acid must be greatly raised1 indeed1 to produce such a violent combustion4 ,,mrs4 ,b4 ,there is1 however1 a peculiarity in this combustion1 which is1 that the oxygen1 instead of being derived from the atmosphere alone1 is principally supplied by the acid itself4 ,,emily4 ,and are not all combustions instances of the change of temperature produced by the chemical combination of two bodies8 ,,mrs4 ,b4 ,undoubtedly2 when oxygen loses its gaseous form1 in order to combine with a solid body1 it becomes condensed1 and the caloric evolved produces the elevation of temperature4 ,the specific gravity of bodies is at the same time altered by chemical combination2 for in consequence of a change of capacity for heat1 a change of density must be produced4 ,,caroline4 ,that was the case with the sulphuric acid and water1 which1 by being mixed together1 gave out a great deal of heat1 and increased in density4 ,,mrs4 ,b4 ,the #eth law of chemical attraction is1 that the properties which characterise bodies1 when separate1 are altered or destroyed by their combination4 ,,caroline4 ,certainly2 what1 for instance1 can be so different from water as the hydrogen and oxygen gases8 ,,emily4 ,or what more unlike sulphat of iron than iron or sulphuric acid8 ,,mrs4 ,b4 ,every chemical combination is an illustration of this rule4 ,but let us proceed-- ,the #fth law is1 that the force of chemical affinity between the constituents of a body is estimated by that which is required for their separation4 ,this force is not always proportional to the facility with which bodies unite2 for manganese1 for instance1 which1 you know1 is so much disposed to unite with oxygen that it is never found in a metallic state1 yields it more easily than any other metal4 ,,emily4 ,but1 ,mrs4 ,b41 you speak of estimating the force of attraction between bodies1 by the force required to separate them2 how can you measure these forces8 ,,mrs4 ,b4 ,they cannot be precisely measured1 but they are comparatively ascertained by experiment1 and can be represented by numbers which express the relative degrees of attraction4 ,the #gth law is1 that bodies have amongst themselves different degrees of attraction4 ,upon this law1 7which you may have discovered yourselves long since17 the whole science of chemistry depends2 for it is by means of the various degrees of affinity which bodies have for each other1 that all the chemical compositions and decompositions are effected4 ,every chemical fact or experiment is an instance of the same kind2 and whenever the decomposition of a body is performed by the addition of any single new substance1 it is said to be effected by simple elective attractions4 ,but it often happens that no simple substance will decompose a body1 and that1 in order to effect this1 you must offer to the compound a body which is itself composed of two1 or sometimes three principles1 which would not1 each separately1 perform the decomposition4 ,in this case there are two new compounds formed in consequence of a reciprocal decomposition and recomposition4 ,all instances of this kind are called double elective attractions4 ,,caroline4 ,i confess ,i do not understand this clearly4 ,,mrs4 ,b4 ,you will easily comprehend it by the assistance of this diagram1 in which the reciprocal forces of attraction are represented by numbers3 ,original ,compound ,sulphat of ,soda4 ,soda #h ,sulphuric ,acid ,quies- cent ,result ,result ,nitrat #g ,divellent ,attractions #f #ac ,sulphat of ,soda of ,lime ,attrac- tions ,nitric ,acid #d ,lime -- #ab ,original ,compound ,nitrat of ,lime4 ,we here suppose that we are to decompose sulphat of soda2 that is1 to separate the acid from the alkali2 if1 for this purpose1 we add some lime1 in order to make it combine with the acid1 we shall fail in our attempt1 because the soda and the sulphuric acid attract each other by a force which is superior1 and 7by way of supposition7 is represented by the number #h2 while the lime tends to unite with this acid by an affinity equal only to the number #f4 ,it is plain1 therefore1 that the sulphat of soda will not be decomposed1 since a force equal to #h cannot be overcome by a force equal only to #f4 ,,caroline4 ,so far1 this appears very clear4 ,,mrs4 ,b4 ,if1 on the other hand1 we endeavour to decompose this salt by nitric acid1 which tends to combine with soda1 we shall be equally unsuccessful1 as nitric acid tends to unite with the alkali by a force equal only to #g4 ,in neither of these cases of simple elective attraction1 therefore1 can we accomplish our purpose4 ,but let us previously combine together the lime and nitric acid1 so as to form a nitrat of lime1 a compound salt1 the constituents of which are united by a power equal to #d4 ,if then we present this compound to the sulphat of soda1 a decomposition will ensue1 because the sum of the forces which tend to preserve the two salts in their actual state is not equal to that of the forces which tend to decompose them1 and to form new combinations4 ,the nitric acid1 therefore1 will combine with the soda1 and the sulphuric acid with the lime4 ,,caroline4 ,i understand you now very well4 ,this double effect takes place because the numbers #h and #d1 which represent the degrees of attraction of the constituents of the two original salts1 make a sum less than the numbers #g and #f1 which represent the degrees of attraction of the two new compounds that will in consequence be formed4 ,,mrs4 ,b4 ,precisely so4 ,,caroline4 ,but what is the meaning of quiescent and divellent forces1 which are written in the diagram8 ,,mrs4 ,b4 ,quiescent forces are those which tend to preserve compounds in a state of rest1 or such as they actually are3 divellent forces1 those which tend to destroy that state of combination1 and to form new compounds4 ,these are the principal circumstances relative to the doctrine of chemical attractions1 which have been laid down as rules by modern chemists2 a few others might be mentioned respecting the same theory1 but of less importance1 and such as would take us too far from our plan4 ,i should1 however1 not omit to mention that ,mr4 ,berthollet1 a celebrated ,french chemist1 has questioned the uniform operation of elective attraction1 and has advanced the opinion1 that1 in chemical combinations1 the changes which take place depend not only upon the affinities1 but also1 in some degree1 on the respective quantities of the substances concerned1 on the heat applied during the process1 and some other circumstances4 ,,caroline4 ,in that case1 ,i suppose1 there would hardly be two compounds exactly similar1 though composed of the same materials8 ,,mrs4 ,b4 ,on the contrary1 it is found that a remarkable uniformity prevails1 as to proportions1 between the ingredients of bodies of similar composition4 ,thus water1 as you may recollect to have seen in a former conversation1 is composed of two volumes of hydrogen gas to one of oxygen1 and this is always found to be precisely the proportion of its constituents1 from whatever source the water be derived4 ,the same uniformity prevails with regard to the various salts2 the acid and alkali1 in each kind of salt1 being always found to combine in the same proportions4 ,sometimes1 it is true1 the same acid1 and the same alkali1 are capable of making two distinct kinds of salts2 but in all these cases it is found that one of the salts contains just twice1 or in some instances1 thrice as much acid1 or alkali1 as the other4 ,,emily4 ,if the proportions in which bodies combine are so constant and so well defined1 how can ,mr4 ,berthollet's remark be reconciled with this uniform system of combination8 ,,mrs4 ,b4 ,great as that philosopher's authority is in chemistry1 it is now generally supposed that his doubts on this subject were in a great degree groundless1 and that the exceptions he has observed in the laws of definite proportions1 have been only apparent1 and may be accounted for consistently with those laws4 ,,caroline4 ,pray1 ,mrs4 ,b41 can you decompose a salt by means of electricity1 in the same way as we decompose water8 ,,mrs4 ,b4 ,undoubtedly2 and ,i am glad this question occurred to you1 because it gives me an opportunity of showing you some very interesting experiments on the subject4 ,if we dissolve a quantity1 however small1 of any salt in a glass of water1 and if we plunge into it the extremities of the wires which proceed from the two ends of the ,voltaic battery1 the salt will be gradually decomposed1 the acid being attracted by the positive1 and the alkali by the negative wire4 ,,emily4 ,but how can you render that decomposition perceptible8 ,,mrs4 ,b4 ,by placing in contact with the extremities of each wire1 in the solution1 pieces of paper stained with certain vegetable colours1 which are altered by the contact of an acid or an alkali4 ,thus this blue vegetable preparation called litmus becomes red when touched by an acid2 and the juice of violets becomes green by the contact of an alkali4 ,but the experiment can be made in a much more distinct manner1 by receiving the extremities of the wires into two different vessels1 so that the alkali shall appear in one vessel and the acid in the other4 ,,caroline4 ,but then the ,voltaic circle will not be completed2 how can any effect be produced8 ,,mrs4 ,b4 ,you are right2 ,i ought to have added that the two vessels must be connected together by some interposed substance capable of conducting electricity4 ,a piece of moistened cotton-wick answers this purpose very well4 ,you see that the cotton 7,,plate ,,xiii4 fig4 #b4 c47 has one end immersed in one glass and the other end in the other1 so as to establish a communication between any fluids contained in them4 ,we shall now put into each of the glasses a little glauber salt1 or sulphat of soda1 7which consists of an acid and an alkali17 and then we shall fill the glasses with water1 which will dissolve the salt4 ,let us now connect the glasses by means of the wires 7e1 d17 with the two ends of the battery1 thus 4 4 4 4 ,illustration3 ,plate ,,xiii4 ,vol4 ,,ii4 page #af4 ,fig4 #a4 ,voltaic ,battery of improved construction with the ,plates out of the ,cells4 ,fig4 #b4 #c #d4 ,instances of ,chemical decomposition by the ,voltaic ,battery4 ,,caroline4 ,the wires are already giving out small bubbles2 is this owing to the decomposition of the salt8 ,,mrs4 ,b4 ,no2 these are bubbles produced by the decomposition of the water1 as you saw in a former experiment4 ,in order to render the separation of the acid from the alkali visible1 ,i pour into the glass 7a71 which is connected with the positive wire1 a few drops of a solution of litmus1 which the least quantity of acid turns red2 and into the other glass 7b71 which is connected with the negative wire1 ,i pour a few drops of the juice of violets 4 4 4 4 ,,emily4 ,the blue solution is already turning red all round the wire4 ,,caroline4 ,and the violet solution is beginning to turn green4 ,this is indeed very singular6 ,,mrs4 ,b4 ,you will be still more astonished when we vary the experiment in this manner3-- ,these three glasses 7fig4 #c4 f1 g1 h17 are1 as in the former instance1 connected together by wetted cotton1 but the middle one alone contains a saline solution1 the two others containing only distilled water1 coloured as before by vegetable infusions4 ,yet1 on making the connection with the battery1 the alkali will appear in the negative glass 7h71 and the acid in the positive glass 7f71 though neither of them contained any saline matter4 ,,emily4 ,so that the acid and alkali must be conveyed right and left from the central glass1 into the other glasses1 by means of the connecting moistened cotton8 ,,mrs4 ,b4 ,exactly so2 and you may render the experiment still more striking1 by putting into the central glass 7k1 fig4 #c47 an alkaline solution1 the glauber salt being placed into the negative glass 7l71 and the positive glass 7i7 containing only water4 ,the acid will be attracted by the positive wire 7m71 and will actually appear in the vessel 7i71 after passing through the alkaline solution 7k71 without combining with it1 although1 you know1 acids and alkalies are so much disposed to combine4 --,but this conversation has already much exceeded our usual limits1 and we cannot enlarge more upon this interesting subject at present4 ,,conversation ,,xiv4 ,,on ,,alkalies4 ,,mrs4 ,b4 ,having now given you some idea of the laws by which chemical attractions are governed1 we may proceed to the examination of bodies which are formed in consequence of these attractions4 ,the first class of compounds that present themselves to our notice1 in our gradual ascent to the most complicated combinations1 are bodies composed of only two principles4 ,the sulphurets1 phosphurets1 carburets1 c4 are of this description2 but the most numerous and important of these compounds are the combinations of oxygen with the various simple substances with which it has a tendency to unite4 ,of these you have already acquired some knowledge1 but it will be necessary to enter into further particulars respecting the nature and properties of those most deserving our notice4 ,of this class are the ,,alkalies and the ,,earths1 which we shall successively examine4 ,we shall first take a view of the alkalies1 of which there are three1 viz4 ,,potash1 ,,soda1 and ,,ammonia4 ,the two first are called fixed alkalies1 because they exist in a solid form at the temperature of the atmosphere1 and require a great heat to be volatilised4 ,they consist1 as you already know1 of metallic bases combined with oxygen4 ,in potash1 the proportions are about eighty-six parts of potassium to fourteen of oxygen2 and in soda1 seventy-seven parts of sodium to twenty-three of oxygen4 ,the third alkali1 ammonia1 has been distinguished by the name of volatile alkali1 because its natural form is that of gas4 ,its composition is of a more complicated nature1 of which we shall speak hereafter4 ,some of the earths bear so strong a resemblance in their properties to the alkalies1 that it is difficult to know under which head to place them4 ,the celebrated ,french chemist1 ,fourcroy1 has classed two of them 7barytes and strontites7 with the alkalies2 but as lime and magnesia have almost an equal title to that rank1 ,i think it better not to separate them1 and therefore have adopted the common method of classing them with the earths1 and of distinguishing them by the name of alkaline earths4 ,the general properties of alkalies are1 an acrid burning taste1 a pungent smell1 and a caustic action on the skin and flesh4 ,,caroline4 ,i wonder they should be caustic1 ,mrs4 ,b41 since they contain so little oxygen4 ,,mrs4 ,b4 ,whatever substance has an affinity for any one of the constituents of animal matter1 sufficiently powerful to decompose it1 is entitled to the appellation of caustic4 ,the alkalies1 in their pure state1 have a very strong attraction for water1 for hydrogen1 and for carbon1 which1 you know1 are the constituent principles of oil1 and it is chiefly by absorbing these substances from animal matter that they effect its decomposition2 for1 when diluted with a sufficient quantity of water1 or combined with any oily substance1 they lose their causticity4 ,but1 to return to the general properties of alkalies--they change1 as we have already seen1 the colour of syrup of violets1 and other blue vegetable infusions1 to green2 and have1 in general1 a very great tendency to unite with acids1 although the respective qualities of these two classes of bodies form a remarkable contrast4 ,we shall examine the result of the combination of acids and alkalies more particularly hereafter4 ,it will be sufficient at present to inform you1 that whenever acids are brought in contact with alkalies1 or alkaline earths1 they unite with a remarkable eagerness1 and form compounds perfectly different from either of their constituents2 these bodies are called neutral or compound salts4 ,the dry white powder which you see in this phial is pure caustic ,,potash2 it is very difficult to preserve it in this state1 as it attracts1 with extreme avidity1 the moisture from the atmosphere1 and if the air were not perfectly excluded1 it would1 in a very short time1 be actually melted4 ,,emily4 ,it is then1 ,i suppose1 always found in a liquid state8 ,,mrs4 ,b4 ,no2 it exists in nature in a great variety of forms and combinations1 but is never found in its pure separate state2 it is combined with carbonic acid1 with which it exists in every part of the vegetable kingdom1 and is most commonly obtained from the ashes of vegetables1 which are the residue that remains after all the other parts have been volatilised by combustion4 ,,caroline4 ,but you once said1 that after all the volatile parts of a vegetable were evaporated1 the substance that remained was charcoal8 ,,mrs4 ,b4 ,i am surprised that you should still confound the processes of volatilisation and combustion4 ,in order to procure charcoal1 we evaporate such parts as can be reduced to vapour by the operation of heat alone2 but when we burn the vegetable1 we burn the carbon also1 and convert it into carbonic acid gas4 ,,caroline4 ,that is true2 ,i hope ,i shall make no more mistakes in my favourite theory of combustion4 ,,mrs4 ,b4 ,potash derives its name from the pots in which the vegetables1 from which it was obtained1 used formerly to be burnt2 the alkali remained mixed with the ashes at the bottom1 and was thence called potash4 ,,emily4 ,the ashes of a wood-fire1 then1 are potash1 since they are vegetable ashes8 ,,mrs4 ,b4 ,they always contain more or less potash1 but are very far from consisting of that substance alone1 as they are a mixture of various earths and salts which remain after the combustion of vegetables1 and from which it is not easy to separate the alkali in its pure form4 ,the process by which potash is obtained1 even in the imperfect state in which it is used in the arts1 is much more complicated than simple combustion4 ,it was once deemed impossible to separate it entirely from all foreign substances1 and it is only in chemical laboratories that it is to be met with in the state of purity in which you find it in this phial4 ,wood-ashes are1 however1 valuable for the alkali which they contain1 and are used for some purposes without any further preparation4 ,purified in a certain degree1 they make what is commonly called pearlash1 which is of great efficacy in taking out grease1 in washing linen1 c42 for potash combines readily with oil or fat1 with which it forms a compound well known to you under the name of soap4 ,,caroline4 ,really6 ,then ,i should think it would be better to wash all linen with pearlash than with soap1 as1 in the latter case1 the alkali being already combined with oil1 must be less efficacious in extracting grease4 ,,mrs4 ,b4 ,its effect would be too powerful on fine linen1 and would injure its texture2 pearlash is therefore only used for that which is of a strong coarse kind4 ,for the same reason you cannot wash your hands with plain potash2 but1 when mixed with oil in the form of soap1 it is soft as well as cleansing1 and is therefore much better adapted to the purpose4 ,caustic potash1 as we already observed1 acts on the skin1 and animal fibre1 in virtue of its attraction for water and oil1 and converts all animal matter into a kind of saponaceous jelly4 ,,emily4 ,are vegetables the only source from which potash can be derived8 ,,mrs4 ,b4 ,no3 for though far most abundant in vegetables1 it is by no means confined to that class of bodies1 being found also on the surface of the earth1 mixed with various minerals1 especially with earths and stones1 whence it is supposed to be conveyed into vegetables by the roots of the plant4 ,it is also met with1 though in very small quantities1 in some animal substances4 ,the most common state of potash is that of carbonat2 ,i suppose you understand what that is8 ,,emily4 ,i believe so2 though ,i do not recollect that you ever mentioned the word before4 ,if ,i am not mistaken1 it must be a compound salt1 formed by the union of carbonic acid with potash4 ,,mrs4 ,b4 ,very true2 you see how admirably the nomenclature of modern chemistry is adapted to assist the memory2 when you hear the name of a compound1 you necessarily learn what are its constituent parts2 and when you are acquainted with these constituents1 you can immediately name the compound which they form4 ,,caroline4 ,pray1 how were bodies arranged and distinguished before this nomenclature was introduced8 ,,mrs4 ,b4 ,chemistry was then a much more difficult study2 for every substance had an arbitrary name1 which it derived either from the person who discovered it1 as ,glauber's salts for instance2 or from some other circumstance relative to it1 though quite unconnected with its real nature1 as potash4 ,these names have been retained for some of the simple bodies2 for as this class is not numerous1 and therefore can easily be remembered1 it has not been thought necessary to change them4 ,,emily4 ,yet ,i think it would have rendered the new nomenclature more complete to have methodised the names of the elementary1 as well as of the compound bodies1 though it could not have been done in the same manner4 ,but the names of the simple substances might have indicated their nature1 or1 at least1 some of their principal properties2 and if1 like the acids and compound salts1 all the simple bodies had a similar termination1 they would have been immediately known as such4 ,so complete and regular a nomenclature would1 ,i think1 have given a clearer and more comprehensive view of chemistry than the present1 which is a medley of the old and new terms4 ,,mrs4 ,b4 ,but you are not aware of the difficulty of introducing into science an entire set of new terms2 it obliges all the teachers and professors to go to school again1 and if some of the old names1 that are least exceptionable1 were not left as an introduction to the new ones1 few people would have had industry and perseverance enough to submit to the study of a completely new language2 and the inferior classes of artists1 who can only act from habit and routine1 would1 at least for a time1 have felt material inconvenience from a total change of their habitual terms4 ,from these considerations1 ,lavoisier and his colleagues1 who invented the new nomenclature1 thought it most prudent to leave a few links of the old chain1 in order to connect it with the new one4 ,besides1 you may easily conceive the inconvenience which might arise from giving a regular nomenclature to substances1 the simple nature of which is always uncertain2 for the new names might1 perhaps1 have proved to have been founded in error4 ,and1 indeed1 cautious as the inventors of the modern chemical language have been1 it has already been found necessary to modify it in many respects4 ,in those few cases1 however1 in which new terms have been adopted to designate simple bodies1 these names have been so contrived as to indicate one of the chief properties of the body in question2 this is the case with oxygen1 which1 as ,i explained to you1 signifies generator of acids2 and hydrogen generator of water4 ,if all the elementary bodies had a similar termination1 as you propose1 it would be necessary to change the name of any that might hereafter be found of a compound nature1 which would be very inconvenient in this age of discovery4 ,but to return to the alkalies4 --,we shall now try to melt some of this caustic potash in a little water1 as a circumstance occurs during its solution very worthy of observation4 --,do you feel the heat that is produced8 ,,caroline4 ,yes1 ,i do2 but is not this directly contrary to our theory of latent heat1 according to which heat is disengaged when fluids become solid1 and cold produced when solids are melted8 ,,mrs4 ,b4 ,the latter is really the case in all solutions2 and if the solution of caustic alkalies seems to make an exception to the rule1 it does not1 ,i believe1 form any solid objection to the theory4 ,the matter may be explained thus3 ,when water first comes in contact with the potash1 it produces an effect similar to the slaking of lime1 that is1 the water is solidified in combining with the potash1 and thus loses its latent heat2 this is the heat that you now feel1 and which is1 therefore1 produced not by the melting of the solid1 but by the solidification of the fluid4 ,but when there is more water than the potash can absorb and solidify1 the latter then yields to the solvent power of the water2 and if we do not perceive the cold produced by its melting1 it is because it is counterbalanced by the heat previously disengaged499 ,a very remarkable property of potash is the formation of glass by its fusion with siliceous earth4 ,you are not yet acquainted with this last substance1 further than its being in the list of simple bodies4 ,it is sufficient1 for the present1 that you should know that sand and flint are chiefly composed of it2 alone1 it is infusible1 but mixed with potash1 it melts when exposed to the heat of a furnace1 combines with the alkali1 and runs into glass4 ,footnote 993 ,this defence of the general theory1 however plausible1 is liable to some obvious objections4 ,the phenomenon might perhaps be better accounted for by supposing that a solution of alkali in water has less capacity for heat than either water or alkali in their separate state4 ,,caroline4 ,who would ever have supposed that the same substance which converts transparent oil into such an opake body as soap1 should transform that opake substance1 sand1 into transparent glass6 ,,mrs4 ,b4 ,the transparency1 or opacity of bodies1 does not1 ,i conceive1 depend so much upon their intimate nature1 as upon the arrangement of their particles3 we cannot have a more striking instance of this1 than is afforded by the different states of carbon1 which1 though it commonly appears in the form of a black opake body1 sometimes assumes the most dazzling transparent form in nature1 that of diamond1 which1 you recollect1 is carbon1 and which1 in all probability1 derives its beautiful transparency from the peculiar arrangement of its particles during their crystallisation4 ,,emily4 ,i never should have supposed that the formation of glass was so simple a process as you describe it4 ,,mrs4 ,b4 ,it is by no means an easy operation to make perfect glass2 for if the sand1 or flint1 from which the siliceous earth is obtained1 be mixed with any metallic particles1 or other substance1 which cannot be vitrified1 the glass will be discoloured1 or defaced1 by opake specks4 ,,caroline4 ,that1 ,i suppose1 is the reason why objects so often appear irregular and shapeless through a common glass-window4 ,,mrs4 ,b4 ,this species of imperfection proceeds1 ,i believe1 from another cause4 ,it is extremely difficult to prevent the lower part of the vessels1 in which the materials of glass are fused1 from containing a more dense vitreous matter than the upper1 on account of the heavier ingredients falling to the bottom4 ,when this happens1 it occasions the appearance of veins or waves in the glass1 from the difference of density in its several parts1 which produces an irregular refraction of the rays of light that pass through it4 ,another species of imperfection sometimes arises from the fusion not being continued for a length of time sufficient to combine the two ingredients completely1 or from the due proportion of potash and silex 7which are as two to one7 not being carefully observed2 the glass1 in those cases1 will be liable to alteration from the action of the air1 of salts1 and especially of acids1 which will effect its decomposition by combining with the potash1 and forming compound salts4 ,,emily4 ,what an extremely useful substance potash is6 ,,mrs4 ,b4 ,besides the great importance of potash in the manufactures of glass and soap1 it is of very considerable utility in many of the other arts1 and in its combinations with several acids1 particularly the nitric1 with which it forms saltpetre4 ,,caroline4 ,then saltpetre must be a nitrat of potash8 ,but we are not yet acquainted with the nitric acid8 ,,mrs4 ,b4 ,we shall therefore defer entering into the particulars of these combinations till we come to a general review of the compound salts4 ,in order to avoid confusion1 it will be better at present to confine ourselves to the alkalies4 ,,emily4 ,cannot you show us the change of colour which you said the alkalies produced on blue vegetable infusions8 ,,mrs4 ,b4 ,yes2 very easily4 ,i shall dip a piece of white paper into this syrup of violets1 which1 you see1 is of a deep blue1 and dyes the paper of the same colour4 --,as soon as it is dry1 we shall dip it into a solution of potash1 which1 though itself colourless1 will turn the paper green-- ,,caroline4 ,so it has1 indeed6 ,and do the other alkalies produce a similar effect8 ,,mrs4 ,b4 ,exactly the same4 --,we may now proceed to ,,soda1 which1 however important1 will detain us but a very short time2 as in all its general properties it very strongly resembles potash2 indeed1 so great is their similitude1 that they have been long confounded1 and they can now scarcely be distinguished1 except by the difference of the salts which they form with acids4 ,the great source of this alkali is the sea1 where1 combined with a peculiar acid1 it forms the salt with which the waters of the ocean are so strongly impregnated4 ,,emily4 ,is not that the common table salt8 ,,mrs4 ,b4 ,the very same2 but again we must postpone entering into the particulars of this interesting combination1 till we treat of the neutral salts4 ,soda may be obtained from common salt2 but the easiest and most usual method of procuring it is by the combustion of marine plants1 an operation perfectly analogous to that by which potash is obtained from vegetables4 ,,emily4 ,from what does soda derive its name8 ,,mrs4 ,b4 ,from a plant called by us soda1 and by the ,arabs kali1 which affords it in great abundance4 ,kali has1 indeed1 given its name to the alkalies in general4 ,,caroline4 ,does soda form glass and soap in the same manner as potash8 ,,mrs4 ,b4 ,yes1 it does2 it is of equal importance in the arts1 and is even preferred to potash for some purposes2 but you will not be able to distinguish their properties till we examine the compound salts which they form with acids2 we must therefore leave soda for the present1 and proceed to ,,ammonia1 or the ,,volatile ,,alkali4 ,,emily4 ,i long to hear something of this alkali2 is it not of the same nature as hartshorn8 ,,mrs4 ,b4 ,yes1 it is1 as you will see by-and-bye4 ,this alkali is seldom found in nature in its pure state2 it is most commonly extracted from a compound salt1 called sal ammoniac1 which was formerly imported from ,ammonia1 a region of ,libya1 from which both these salts and the alkali derive their names4 ,the crystals contained in this bottle are specimens of this salt1 which consists of a combination of ammonia and muriatic acid4 ,,caroline4 ,then it should be called muriat of ammonia2 for though ,i am ignorant what muriatic acid is1 yet ,i know that its combination with ammonia cannot but be so called2 and ,i am surprised to see sal ammoniac inscribed on the label4 ,,mrs4 ,b4 ,that is the name by which it has been so long known1 that the modern chemists have not yet succeeded in banishing it altogether2 and it is still sold under that name by druggists1 though by scientific chemists it is more properly called muriat of ammonia4 ,,caroline4 ,both the popular and the common name should be inscribed on labels--this would soon introduce the new nomenclature4 ,,emily4 ,by what means can the ammonia be separated from the muriatic acid8 ,,mrs4 ,b4 ,by chemical attractions2 but this operation is too complicated for you to understand1 till you are better acquainted with the agency of affinities4 ,,emily4 ,and when extracted from the salt1 what kind of substance is ammonia8 ,,mrs4 ,b4 ,its natural form1 at the temperature of the atmosphere1 when free from combination1 is that of gas2 and in this state it is called ammoniacal gas4 ,but it mixes very readily with water1 and can be thus obtained in a liquid form4 ,,caroline4 ,you said that ammonia was more complicated in its composition than the other alkalies2 pray of what principles does it consist8 ,,mrs4 ,b4 ,it was discovered a few years since1 by ,berthollet1 a celebrated ,french chemist1 that it consisted of about one part of hydrogen to four parts of nitrogen4 ,having heated ammoniacal gas under a receiver1 by causing the electrical spark to pass repeatedly through it1 he found that it increased considerably in bulk1 lost all its alkaline properties1 and was actually converted into hydrogen and nitrogen gases2 and from the latest and most accurate experiments1 the proportions appear to be1 one volume of nitrogen gas to three of hydrogen gas4 ,,caroline4 ,ammonia1 therefore1 has not1 like the two other alkalies1 a metallic basis8 ,,mrs4 ,b4 ,it is believed it has1 though it is extremely difficult to reconcile that idea with what ,i have just stated of its chemical nature4 ,but the fact is1 that although this supposed metallic basis of ammonia has never been obtained distinct and separate1 yet both ,professor ,berzelius1 of ,stockholm1 and ,sir ,h4 ,davy1 have succeeded in forming a combination of mercury with the basis of ammonia1 which has so much the appearance of an amalgam1 that it strongly corroborates the idea of ammonia having a metallic basis499 ,but these theoretical points are full of difficulties and doubts1 and it would be useless to dwell any longer upon them4 ,let us therefore return to the properties of volatile alkali4 ,ammoniacal gas is considerably lighter than oxygen gas1 and only about half the weight of atmospherical air4 ,it possesses most of the properties of the fixed alkalies2 but cannot be of so much use in the arts on account of its volatile nature4 ,it is1 therefore1 never employed in the manufacture of glass1 but it forms soap with oils equally as well as potash and soda2 it resembles them likewise in its strong attraction for water2 for which reason it can be collected in a receiver over mercury only4 ,footnote 993 ,this amalgam is easily obtained1 by placing a globule of mercury upon a piece of muriat1 or carbonat of ammonia1 and electrifying this globule by the ,voltaic battery4 ,the globule instantly begins to expand to three or four times its former size1 and becomes much less fluid1 though without losing its metallic lustre1 a change which is ascribed to the metallic basis of ammonia uniting with the mercury4 ,this is an extremely curious experiment4 ,,caroline4 ,i do not understand this8 ,,mrs4 ,b4 ,do you recollect the method which we used to collect gases in a glass-receiver over water8 ,,caroline4 ,perfectly4 ,,mrs4 ,b4 ,ammoniacal gas has so strong a tendency to unite with water1 that1 instead of passing through that fluid1 it would be instantaneously absorbed by it4 ,we can therefore neither use water for that purpose1 nor any other liquid of which water is a component part2 so that1 in order to collect this gas1 we are obliged to have recourse to mercury1 7a liquid which has no action upon it17 and a mercurial bath is used instead of a water bath1 such as we employed on former occasions4 ,water impregnated with this gas is nothing more than the fluid which you mentioned at the beginning of the conversation--hartshorn2 it is the ammoniacal gas escaping from the water which gives it so powerful a smell4 ,,emily4 ,but there is no appearance of effervescence in hartshorn4 ,,mrs4 ,b4 ,because the particles of gas that rise from the water are too subtle and minute for their effect to be visible4 ,water diminishes in density1 by being impregnated with ammoniacal gas2 and this augmentation of bulk increases its capacity for caloric4 ,,emily4 ,in making hartshorn1 then1 or impregnating water with ammonia1 heat must be absorbed1 and cold produced8 ,,mrs4 ,b4 ,that effect would take place if it was not counteracted by another circumstance2 the gas is liquefied by incorporating with the water1 and gives out its latent heat4 ,the condensation of the gas more than counterbalances the expansion of the water2 therefore1 upon the whole1 heat is produced4 --,but if you dissolve ammoniacal gas with ice or snow1 cold is produced4 --,can you account for that8 ,,emily4 ,the gas1 in being condensed into a liquid1 must give out heat2 and1 on the other hand1 the snow or ice1 in being rarefied into a liquid1 must absorb heat2 so that1 between the opposite effects1 ,i should have supposed the original temperature would have been preserved4 ,,mrs4 ,b4 ,but you have forgotten to take into the account the rarefaction of the water 7or melted ice7 by the impregnation of the gas2 and this is the cause of the cold which is ultimately produced4 ,,caroline4 ,is the sal volatile 7the smell of which so strongly resembles hartshorn7 likewise a preparation of ammonia8 ,,mrs4 ,b4 ,it is carbonat of ammonia dissolved in water2 and which1 in its concrete state1 is commonly called salts of hartshorn4 ,ammonia is caustic1 like the fixed alkalies1 as you may judge by the pungent effects of hartshorn1 which cannot be taken internally1 nor applied to delicate external parts1 without being plentifully diluted with water4 --,oil and acids are very excellent antidotes for alkaline poisons2 can you guess why8 ,,caroline4 ,perhaps1 because the oil combines with the alkali1 and forms soap1 and thus destroys its caustic properties2 and the acid converts it into a compound salt1 which1 ,i suppose1 is not so pernicious as caustic alkali4 ,,mrs4 ,b4 ,precisely so4 ,ammoniacal gas1 if it be mixed with atmospherical air1 and a burning taper repeatedly plunged into it1 will burn with a large flame of a peculiar yellow colour4 ,,emily4 ,but pray tell me1 can ammonia be procured from this ,lybian salt only8 ,,mrs4 ,b4 ,so far from it1 that it is contained in1 and may be extracted from1 all animal substances whatever4 ,hydrogen and nitrogen are two of the chief constituents of animal matter2 it is therefore not surprising that they should occasionally meet and combine in those proportions that compose ammonia4 ,but this alkali is more frequently generated by the spontaneous decomposition of animal substances2 the hydrogen and nitrogen gases that arise from putrefied bodies combine1 and form the volatile alkali4 ,muriat of ammonia1 instead of being exclusively brought from ,lybia1 as it originally was1 is now chiefly prepared in ,europe1 by chemical processes4 ,ammonia1 although principally extracted from this salt1 can also be produced by a great variety of other substances4 ,the horns of cattle1 especially those of deer1 yield it in abundance1 and it is from this circumstance that a solution of ammonia in water has been called hartshorn4 ,it may likewise be procured from wool1 flesh1 and bones2 in a word1 any animal substance whatever yields it by decomposition4 ,we shall now lay aside the alkalies1 however important the subject may be1 till we treat of their combination with acids4 ,the next time we meet we shall examine the earths4 ,,conversation ,,xv4 ,,on ,,earths4 ,,mrs4 ,b4 ,the ,,earths1 which we are to-day to examine1 are nine in number3 ,,silex1 ,,alumine1 ,,barytes1 ,,lime1 ,,magnesia1 ,,strontites1 ,,yttria1 ,,glucina1 ,,zirconia4 ,the last three are of late discovery2 their properties are but imperfectly known2 and1 as they have not yet been applied to use1 it will be unnecessary to enter into any particulars respecting them2 we shall confine our remarks1 therefore1 to the first five4 ,they are composed1 as you have already learnt1 of a metallic basis combined with oxygen2 and1 from this circumstance1 are incombustible4 ,,caroline4 ,yet ,i have seen turf burnt in the country1 and it makes an excellent fire2 the earth becomes red hot1 and produces a very great quantity of heat4 ,,mrs4 ,b4 ,it is not the earth that burns1 my dear1 but the roots1 grass1 and other remnants of vegetables that are intermixed with it4 ,the caloric1 which is produced by the combustion of these substances1 makes the earth red hot1 and this being a bad conductor of heat1 retains its caloric a long time2 but were you to examine it when cooled1 you would find that it had not absorbed one particle of oxygen1 nor suffered any alteration from the fire4 ,earth is1 however1 from the circumstance just mentioned1 an excellent radiator of heat1 and owes its utility1 when mixed with fuel1 solely to that property4 ,it is in this point of view that ,count ,rumford has recommended balls of incombustible substances to be arranged in fire-places1 and mixed with the coals1 by which means the caloric disengaged by the combustion of the latter is more perfectly reflected into the room1 and an expense of fuel is saved4 ,,emily4 ,i expected that the list of earths would be much more considerable4 ,when ,i think of the great variety of soils1 ,i am astonished that there is not a greater number of earths to form them4 ,,mrs4 ,b4 ,you might1 indeed1 almost confine that number to four2 for barytes1 strontites1 and the others of late discovery1 act but so small a part in this great theatre1 that they cannot be reckoned as essential to the general formation of the globe4 ,and you must not confine your idea of earths to the formation of soil2 for rock1 marble1 chalk1 slate1 sand1 flint1 and all kinds of stones1 from the precious jewels to the commonest pebbles2 in a word1 all the immense variety of mineral products1 may be referred to some of these earths1 either in a simple state1 or combined the one with the other1 or blended with other ingredients4 ,,caroline4 ,precious stones composed of earth6 ,that seems very difficult to conceive4 ,,emily4 ,is it more extraordinary than that the most precious of all jewels1 diamond1 should be composed of carbon8 ,but diamond forms an exception1 ,mrs4 ,b42 for1 though a stone1 it is not composed of earth4 ,,mrs4 ,b4 ,i did not specify the exception1 as ,i knew you were so well acquainted with it4 ,besides1 ,i would call a diamond a mineral rather than a stone1 as the latter term always implies the presence of some earth4 ,,caroline4 ,i cannot conceive how such coarse materials can be converted into such beautiful productions4 ,,mrs4 ,b4 ,we are very far from understanding all the secret resources of nature2 but ,i do not think the spontaneous formation of the crystals1 which we call precious stones1 one of the most difficult phenomena to comprehend4 ,by the slow and regular work of ages1 perhaps of hundreds of ages1 these earths may be gradually dissolved by water1 and as gradually deposited by their solvent in the undisturbed process of crystallisation4 ,the regular arrangement of their particles1 during their reunion in a solid mass1 gives them that brilliancy1 transparency1 and beauty1 for which they are so much admired2 and renders them in appearance so totally different from their rude and primitive ingredients4 ,,caroline4 ,but how does it happen that they are spontaneously dissolved1 and afterwards crystallised8 ,,mrs4 ,b4 ,the scarcity of many kinds of crystals1 as rubies1 emeralds1 topazes1 c4 shows that their formation is not an operation very easily carried on in nature4 ,but cannot you imagine that when water1 holding in solution some particles of earth1 filters through the crevices of hills or mountains1 and at length dribbles into some cavern1 each successive drop may be slowly evaporated1 leaving behind it the particle of earth which it held in solution8 ,you know that crystallisation is more regular and perfect1 in proportion as the evaporation of the solvent is slow and uniform2 nature1 therefore1 who knows no limit of time1 has1 in all works of this kind1 an infinite advantage over any artist who attempts to imitate such productions4 ,,emily4 ,i can now conceive that the arrangement of the particles of earth1 during crystallisation1 may be such as to occasion transparency1 by admitting a free passage to the rays of light2 but ,i cannot understand why crystallised earths should assume such beautiful colours as most of them do4 ,sapphire1 for instance1 is of a celestial blue2 ruby1 a deep red2 topaz1 a brilliant yellow8 ,,mrs4 ,b4 ,nothing is more simple than to suppose that the arrangement of their particles is such1 as to transmit some of the coloured rays of light1 and to reflect others1 in which case the stone must appear of the colour of the rays which it reflects4 ,but besides1 it frequently happens that the colour of a stone is owing to a mixture of some metallic matter4 ,,caroline4 ,pray1 are the different kinds of precious stones each composed of one individual earth1 or are they formed of a combination of several earths8 ,,mrs4 ,b4 ,a great variety of materials enters into the composition of most of them2 not only several earths1 but sometimes salts and metals4 ,the earths1 however1 in their simple state1 frequently form very beautiful crystals2 and1 indeed1 it is in that state only that they can be obtained perfectly pure4 ,,emily4 ,is not the ,derbyshire spar produced by the crystallisation of earths1 in the way you have just explained8 ,i have been in some of the subterraneous caverns where it is found1 which are similar to those you have described4 ,,mrs4 ,b4 ,yes2 but this spar is a very imperfect specimen of crystallisation2 it consists of a variety of ingredients confusedly blended together1 as you may judge by its opacity1 and by the various colours and appearances which it exhibits4 ,but1 in examining the earths in their most perfect and agreeable form1 we must not lose sight of that state in which they are commonly found1 and which1 if less pleasing to the eye1 is far more interesting by its utility4 ,all the earths are more or less endowed with alkaline properties2 but there are four1 barytes1 magnesia1 lime1 and strontites1 which are called alkaline earths1 because they possess those qualities in so great a degree1 as to entitle them1 in most respects1 to the rank of alkalies4 ,they combine and form compound salts with acids1 in the same way as alkalies2 they are1 like them1 susceptible of a considerable degree of causticity1 and are acted upon in a similar manner by chemical tests4 --,the remaining earths1 silex and alumine1 with one or two others of late discovery1 are in some degree more earthy1 that is to say1 they possess more completely the properties common to all the earths1 which are1 insipidity1 dryness1 unalterableness in the fire1 infusibility1 c4 ,,caroline4 ,yet1 did you not tell us that silex1 or siliceous earth1 when mixed with an alkali1 was fusible1 and run into glass8 ,,mrs4 ,b4 ,yes1 my dear2 but the characteristic properties of earths1 which ,i have mentioned1 are to be considered as belonging to them in a state of purity only2 a state in which they are very seldom to be met with in nature4 --,besides these general properties1 each earth has its own specific characters1 by which it is distinguished from any other substance4 --,let us therefore review them separately4 ,,silex1 or ,,silica1 abounds in flint1 sand1 sandstone1 agate1 jasper1 c42 it forms the basis of many precious stones1 and particularly of those which strike fire with steel4 ,it is rough to the touch1 scratches and wears away metals2 it is acted upon by no acid but the fluoric1 and is not soluble in water by any known process2 but nature certainly dissolves it by means with which we are unacquainted1 and thus produces a variety of siliceous crystals1 and amongst these rock crystal1 which is the purest specimen of this earth4 ,silex appears to have been intended by ,providence to form the solid basis of the globe1 to serve as a foundation for the original mountains1 and give them that hardness and durability which has enabled them to resist the various revolutions which the surface of the earth has successively undergone4 ,from these mountains siliceous rocks have1 during the course of ages1 been gradually detached by torrents of water1 and brought down in fragments2 these1 in the violence and rapidity of their descent1 are sometimes crumbled to sand1 and in this state form the beds of rivers and of the sea1 chiefly composed of siliceous materials4 ,sometimes the fragments are broken without being pulverised by their fall1 and assume the form of pebbles1 which gradually become rounded and polished4 ,,emily4 ,pray what is the true colour of silex1 which forms such a variety of different coloured substances8 ,sand is brown1 flint is nearly black1 and precious stones are of all colours4 ,,mrs4 ,b4 ,pure silex1 such as is found only in the chemist's laboratory1 is perfectly white1 and the various colours which it assumes1 in the different substances you have just mentioned1 proceed from the different ingredients with which it is mixed in them4 ,,caroline4 ,i wonder that silex is not more valuable1 since it forms the basis of so many precious stones4 ,,mrs4 ,b4 ,you must not forget that the value we set upon precious stones depends in a great measure upon the scarcity with which nature affords them2 for1 were those productions either common or perfectly imitable by art1 they would no longer1 notwithstanding their beauty1 be so highly esteemed4 ,but the real value of siliceous earth1 in many of the most useful arts1 is very extensive4 ,mixed with clay1 it forms the basis of all the various kinds of earthen ware1 from the most common utensils to the most refined ornaments4 ,,emily4 ,and we must recollect its importance in the formation of glass with potash4 ,,mrs4 ,b4 ,nor should we omit to mention1 likewise1 many other important uses of silex1 such as being the chief ingredient of some of the most durable cements1 of mortar1 c4 ,i said before1 that siliceous earth combined with no acid but the fluoric2 it is for this reason that glass is liable to be attacked by that acid only1 which1 from its strong affinity for silex1 forces that substance from its combination with the potash1 and thus destroys the glass4 ,we will now hasten to proceed to the other earths1 for ,i am rather apprehensive of your growing weary of this part of our subject4 ,,caroline4 ,the history of the earths is not quite so entertaining as that of the simple substances4 ,,mrs4 ,b4 ,perhaps not2 but it is absolutely indispensable that you should know something of them2 for they form the basis of so many interesting and important compounds1 that their total omission would throw great obscurity on our general outline of chemical science4 ,we shall1 however1 review them in as cursory a manner as the subject can admit of4 ,,alumine derives its name from a compound salt called alum1 of which it forms the basis4 ,,caroline4 ,but it ought to be just the contrary1 ,mrs4 ,b42 the simple body should give1 instead of taking1 its name from the compound4 ,,mrs4 ,b4 ,that is true2 but as the compound salt was known long before its basis was discovered1 it was very natural that when the earth was at length separated from the acid1 it should derive its name from the compound from which it was obtained4 ,however1 to remove your scruples1 we will call the salt according to the new nomenclature1 sulphat of alumine4 ,from this combination1 alumine may be obtained in its pure state2 it is then soft to the touch1 makes a paste with water1 and hardens in the fire4 ,in nature1 it is found chiefly in clay1 which contains a considerable proportion of this earth2 it is very abundant in fuller's earth1 slate1 and a variety of other mineral productions4 ,there is indeed scarcely any mineral substance more useful to mankind than alumine4 ,in the state of clay1 it forms large strata of the earth1 gives consistency to the soil of valleys1 and of all low and damp spots1 such as swamps and marshes4 ,the beds of lakes1 ponds1 and springs1 are almost entirely of clay2 instead of allowing of the filtration of water1 as sand does1 it forms an impenetrable bottom1 and by this means water is accumulated in the caverns of the earth1 producing those reservoirs whence springs issue1 and spout out at the surface4 ,,emily4 ,i always thought that these subterraneous reservoirs of water were bedded by some hard stone1 or rock1 which the water could not penetrate4 ,,mrs4 ,b4 ,that is not the case2 for in the course of time water would penetrate1 or wear away silex1 or any other kind of stone1 while it is effectually stopped by clay1 or alumine4 ,the solid compact soils1 such as are fit for corn1 owe their consistence in a great measure to alumine2 this earth is therefore used to improve sandy or chalky soils1 which do not retain a sufficient quantity of water for the purpose of vegetation4 ,alumine is the most essential ingredient in all potteries4 ,it enters into the composition of brick1 as well as that of the finest porcelain2 the addition of silex and water hardens it1 renders it susceptible of a degree of vitrification1 and makes it perfectly fit for its various purposes4 ,,caroline4 ,i can scarcely conceive that brick and china should be made of the same materials4 ,,mrs4 ,b4 ,brick consists almost entirely of baked clay2 but a certain proportion of silex is essential to the formation of earthen or stone ware4 ,in common potteries sand is used for that purpose2 a more pure silex is1 ,i believe1 necessary for the composition of porcelain1 as well as a finer kind of clay2 and these materials are1 no doubt1 more carefully prepared1 and curiously wrought1 in the one case than in the other4 ,porcelain owes its beautiful semitransparency to a commencement of vitrification4 ,,emily4 ,but the commonest earthen-ware1 though not transparent1 is covered with a kind of glazing4 ,,mrs4 ,b4 ,that precaution is equally necessary for use as for beauty1 as the ware would be liable to be spoiled and corroded by a variety of substances1 if not covered with a coating of this kind4 ,in porcelain it consists of enamel1 which is a fine white opake glass1 formed of metallic oxyds1 sand1 salts1 and such other materials as are susceptible of vitrification4 ,the glazing of common earthen-ware is made chiefly of oxyd of lead1 or sometimes merely of salt1 which1 when thinly spread over earthen vessels1 will1 at a certain heat1 run into opake glass4 ,,caroline4 ,and of what nature are the colours which are used for painting porcelain8 ,,mrs4 ,b4 ,they are all composed of metallic oxyds1 so that these colours1 instead of receiving injury from the application of fire1 are strengthened and developed by its action1 which causes them to undergo different degrees of oxydation4 ,alumine and silex are not only often combined by art1 but they have in nature a very strong tendency to unite1 and are found combined1 in different proportions1 in various gems and other minerals4 ,indeed1 many of the precious stones1 such as ruby1 oriental sapphire1 amethyst1 c4 consist chiefly of alumine4 ,we may now proceed to the alkaline earths1 ,i shall say but a few words on ,,barytes1 as it is hardly ever used1 except in chemical laboratories4 ,it is remarkable for its great weight1 and its strong alkaline properties1 such as destroying animal substances1 turning green some blue vegetable colours1 and showing a powerful attraction for acids2 this last property it possesses to such a degree1 particularly with regard to the sulphuric acid1 that it will always detect its presence in any substance or combination whatever1 by immediately uniting with it1 and forming a sulphat of barytes4 ,this renders it a very valuable chemical test4 ,it is found pretty abundantly in nature in the state of carbonat1 from which the pure earth can be easily separated4 ,the next earth we have to consider is ,,lime4 ,this is a substance of too great and general importance to be passed over so slightly as the last4 ,lime is strongly alkaline4 ,in nature it is not met with in its simple state1 as its affinity for water and carbonic acid is so great1 that it is always found combined with these substances1 with which it forms the common lime-stone2 but it is separated in the kiln from these ingredients1 which are volatilised whenever a sufficient degree of heat is applied4 ,,emily4 ,pure lime1 then1 is nothing but lime-stone1 which has been deprived1 in the kiln1 of its water and carbonic acid8 ,,mrs4 ,b4 ,precisely3 in this state it is called quick-lime1 and it is so caustic1 that it is capable of decomposing the dead bodies of animals very rapidly1 without their undergoing the process of putrefaction4 --,i have here some quick lime1 which is kept carefully corked up in a bottle to prevent the access of air2 for were it at all exposed to the atmosphere1 it would absorb both moisture and carbonic acid gas from it1 and be soon slaked4 ,here is also some lime-stone--we shall pour a little water on each1 and observe the effects that result from it4 ,,caroline4 ,how the quick-lime hisses6 ,it is become excessively hot6 --,it swells1 and now it bursts and crumbles to powder1 while the water appears to produce no kind of alteration on the lime-stone4 ,,mrs4 ,b4 ,because the lime-stone is already saturated with water1 whilst the quick-lime1 which has been deprived of it in the kiln1 combines with it with very great avidity1 and produces this prodigious disengagement of heat1 the cause of which ,i formerly explained to you2 do you recollect it8 ,,emily4 ,yes2 you said that the heat did not proceed from the lime1 but from the water which was solidified1 and thus parted with its heat of liquidity4 ,,mrs4 ,b4 ,very well4 ,if we continue to add successive quantities of water to the lime after being slaked and crumbled as you see1 it will then gradually be diffused in the water1 till it will at length be dissolved in it1 and entirely disappear2 but for this purpose it requires no less than #gjj times its weight of water4 ,this solution is called lime-water4 ,,caroline4 ,how very small1 then1 is the proportion of lime dissolved6 ,,mrs4 ,b4 ,barytes is still of more difficult solution2 it dissolves only in #ijj times its weight of water3 but it is much more soluble in the state of crystals4 ,the liquid contained in this bottle is lime-water2 it is often used as a medicine1 chiefly1 ,i believe1 for the purpose of combining with1 and neutralising1 the superabundant acid which it meets with in the stomach4 ,,emily4 ,i am surprised that it is so perfectly clear2 it does not at all partake of the whiteness of the lime4 ,,mrs4 ,b4 ,have you forgotten that1 in solutions1 the solid body is so minutely subdivided by the fluid as to become invisible1 and therefore will not in the least degree impair the transparency of the solvent8 ,i said that the attraction of lime for carbonic acid was so strong1 that it would absorb it from the atmosphere4 ,we may see this effect by exposing a glass of lime-water to the air2 the lime will then separate from the water1 combine with the carbonic acid1 and re-appear on the surface in the form of a white film1 which is carbonat of lime1 commonly called chalk4 ,,caroline4 ,chalk is1 then1 a compound salt6 ,i never should have supposed that those immense beds of chalk1 that we see in many parts of the country1 were a salt4 --,now1 the white film begins to appear on the surface of the water2 but it is far from resembling hard solid chalk4 ,,mrs4 ,b4 ,that is owing to its state of extreme division2 in a little time it will collect into a more compact mass1 and subside at the bottom of the glass4 ,if you breathe into lime-water1 the carbonic acid1 which is mixed with the air that you expire1 will produce the same effect4 ,it is an experiment very easily made2 --,i shall pour some lime-water into this glass tube1 and1 by breathing repeatedly into it1 you will soon perceive a precipitation of chalk-- ,,emily4 ,i see already a small white cloud formed4 ,,mrs4 ,b4 ,it is composed of minute particles of chalk2 at present it floats in the water1 but it will soon subside4 ,carbonat of lime1 or chalk1 you see1 is insoluble in water1 since the lime which was dissolved re-appears when converted into chalk2 but you must take notice of a very singular circumstance1 which is1 that chalk is soluble in water impregnated with carbonic acid4 ,,caroline4 ,it is very curious1 indeed1 that carbonic acid gas should render lime soluble in one instance1 and insoluble in the other6 ,,mrs4 ,b4 ,i have here a bottle of ,seltzer water1 which1 you know1 is strongly impregnated with carbonic acid3-- let us pour a little of it into a glass of lime-water4 ,you see that it immediately forms a precipitation of carbonat of lime8 ,,emily4 ,yes1 a white cloud appears4 ,,mrs4 ,b4 ,i shall now pour an additional quantity of the ,seltzer water into the lime-water-- ,,emily4 ,how singular6 ,the cloud is re-dissolved1 and the liquid is again transparent4 ,,mrs4 ,b4 ,all the mystery depends upon this circumstance1 that carbonat of lime is soluble in carbonic acid1 whilst it is insoluble in water2 the first quantity of carbonic acid1 therefore1 which ,i introduce into the lime-water1 was employed in forming the carbonat of lime1 which remained visible1 until an additional quantity of carbonic acid dissolved it4 ,thus1 you see1 when the lime and carbonic acid are in proper proportions to form chalk1 the white cloud appears1 but when the acid predominates1 the chalk is no sooner formed than it is dissolved4 ,,caroline4 ,that is now the case2 but let us try whether a further addition of lime-water will again precipitate the chalk4 ,,emily4 ,it does1 indeed6 ,the cloud re-appears1 because1 ,i suppose1 there is now no more of the carbonic acid than is necessary to form chalk2 and1 in order to dissolve the chalk1 a superabundance of acid is required4 ,,mrs4 ,b4 ,we have1 ,i think1 carried this experiment far enough2 every repetition would but exhibit the same appearances4 ,lime combines with most of the acids1 to which the carbonic 7as being the weakest7 readily yields it2 but these combinations we shall have an opportunity of noticing more particularly hereafter4 ,it unites with phosphorus1 and with sulphur1 in their simple state2 in short1 of all the earths1 lime is that which nature employs most frequently1 and most abundantly1 in its innumerable combinations4 ,it is the basis of all calcareous earths and stones2 we find it likewise in the animal and the vegetable creations4 ,,emily4 ,and in the arts is not lime of very great utility8 ,,mrs4 ,b4 ,scarcely any substance more so2 you know that it is a most essential requisite in building1 as it constitutes the basis of all cements1 such as mortar1 stucco1 plaister1 c4 ,lime is also of infinite importance in agriculture2 it lightens and warms soils that are too cold1 and compact1 in consequence of too great a proportion of clay4 --,but it would be endless to enumerate the various purposes for which it is employed2 and you know enough of it to form some idea of its importance2 we shall1 therefore1 now proceed to the third alkaline earth1 ,,magnesia4 ,,caroline4 ,i am already pretty well acquainted with that earth2 it is a medicine4 ,,mrs4 ,b4 ,it is in the state of carbonat that magnesia is usually employed medicinally2 it then differs but little in appearance from its simple form1 which is that of a very fine light white powder4 ,it dissolves in #bjjj times its weight of water1 but forms with acids extremely soluble salts4 ,it has not so great an attraction for acids as lime1 and consequently yields them to the latter4 ,it is found in a great variety of mineral combinations1 such as slate1 mica1 amianthus1 and more particularly in a certain lime stone1 which has lately been discovered by ,mr4 ,tennant to contain it in very great quantities4 ,it does not attract and solidify water1 like lime3 but when mixed with water and exposed to the atmosphere1 it slowly absorbs carbonic acid from the latter1 and thus loses its causticity4 ,its chief use in medicine is1 like that of lime1 derived from its readiness to combine with1 and neutralise1 the acid which it meets with in the stomach4 ,,emily4 ,yet1 you said that it was taken in the state of carbonat1 in which case it has already combined with an acid8 ,,mrs4 ,b4 ,yes2 but the carbonic is the last of all the acids in the order of affinities2 it will therefore yield the magnesia to any of the others4 ,it is1 however1 frequently taken in its caustic state as a remedy for flatulence4 ,combined with sulphuric acid1 magnesia forms another and more powerful medicine1 commonly called ,epsom salt4 ,,caroline4 ,and properly1 sulphat of magnesia1 ,i suppose8 ,pray why was it ever called ,epsom salt8 ,,mrs4 ,b4 ,because there is a spring in the neighbourhood of ,epsom which contains this salt in great abundance4 ,the last alkaline earth which we have to mention is ,,strontian1 or ,,strontites1 discovered by ,dr4 ,hope a few years ago4 ,it so strongly resembles barytes in its properties1 and is so sparingly found in nature1 and of so little use in the arts1 that it will not be necessary to enter into any particulars respecting it4 ,one of the remarkable characteristic properties of strontites is1 that its salts1 when dissolved in spirit of wine1 tinge the flame of a deep red1 or blood colour4 ,,conversation ,,xvi4 ,,on ,,acids4 ,,mrs4 ,b4 ,we may now proceed to the acids4 ,of the metallic oxyds1 you have already acquired some general notions4 ,this subject1 though highly interesting in its details1 is not of sufficient importance to our concise view of chemistry1 to be particularly treated of2 but it is absolutely necessary that you should be better acquainted with the acids1 and likewise with their combinations with the alkalies1 which form the triple compounds called ,,neutral ,,salts4 ,the class of acids is characterised by very distinct properties4 ,they all change blue vegetable infusions to a red colour3 they are all more or less sour to the taste2 and have a general tendency to combine with the earths1 alkalies1 and metallic oxyds4 ,you have1 ,i believe1 a clear idea of the nomenclature by which the base 7or radical7 of the acid1 and the various degrees of acidification1 are expressed8 ,,emily4 ,yes1 ,i think so2 the acid is distinguished by the name of its base1 and its degree of oxydation1 that is1 the quantity of oxygen it contains1 by the termination of that name in ous or ic2 thus sulphureous acid is that formed by the smallest proportion of oxygen combined with sulphur2 sulphuric acid that which results from the combination of sulphur with the greatest quantity of oxygen4 ,,mrs4 ,b4 ,a still greater latitude may1 in many cases1 be allowed to the proportions of oxygen than can be combined with acidifiable radicals2 for several of these radicals are susceptible of uniting with a quantity of oxygen so small as to be insufficient to give them the properties of acids2 in these cases1 therefore1 they are converted into oxyds4 ,such is sulphur1 which by exposure to the atmosphere with a degree of heat inadequate to produce inflammation1 absorbs a small proportion of oxygen1 which colours it red or brown4 ,this1 therefore1 is the first degree of oxygenation of sulphur2 the #b;d converts it into sulphurous acid2 the #c;d into the sulphuric acid2 and #dthly1 if it was found capable of combining with a still larger proportion of oxygen1 it would then be termed super-oxygenated sulphuric acid4 ,,emily4 ,are these various degrees of oxygenation common to all the acids8 ,,mrs4 ,b4 ,no2 they vary much in this respect3 some are susceptible of only one degree of oxygenation2 others1 of two1 or three2 there are but very few that will admit of more4 ,,caroline4 ,the modern nomenclature must be of immense advantage in pointing out so easily the nature of the acids1 and their various degrees of oxygenation4 ,,mrs4 ,b4 ,till lately many of the acids had not been decomposed2 but analogy afforded so strong a proof of their compound nature1 that ,i never could reconcile myself to classing them with the simple bodies1 though this division has been adopted by several chemical writers4 ,at present there are only the muriatic and the fluoric acids1 which have not had their bases distinctly separated4 ,,caroline4 ,we have heard of a great variety of acids2 pray how many are there in all8 ,,mrs4 ,b4 ,i believe there are reckoned at present thirty-four1 and their number is constantly increasing1 as the science improves2 but the most important1 and those to which we shall almost entirely confine our attention1 are but few4 ,i shall1 however1 give you a general view of the whole2 and then we shall more particularly examine those that are the most essential4 ,this class of bodies was formerly divided into mineral1 vegetable1 and animal acids1 according to the substances from which they were commonly obtained4 ,,caroline4 ,that1 ,i should think1 must have been an excellent arrangement2 why was it altered8 ,,mrs4 ,b4 ,because in many cases it produced confusion4 ,in which class1 for instance1 would you place carbonic acid8 ,,caroline4 ,now ,i see the difficulty4 ,i should be at a loss where to place it1 as you have told us that it exists in the animal1 vegetable1 and mineral kingdoms4 ,,emily4 ,there would be the same objection with respect to phosphoric acid1 which1 though obtained chiefly from bones1 can also1 you said1 be found in small quantities in stones1 and likewise in some plants4 ,,mrs4 ,b4 ,you see1 therefore1 the propriety of changing this mode of classification4 ,these objections do not exist in the present nomenclature2 for the composition and nature of each individual acid is in some degree pointed out1 instead of the class of bodies from which it is extracted2 and1 with regard to the more general division of acids1 they are classed under these three heads3 ,first1 ,acids of known or supposed simple bases1 which are formed by the union of these bases with oxygen4 ,they are the following3 ,the ,sulphuric ,carbonic ,nitric ,phosphoric ,arsenical ,acids1 of known and simple bases4 ,tungstenic ,molybdenic ,boracic ,fluoric ,muriatic ,this class comprehends the most anciently known and most important acids4 ,the sulphuric1 nitric1 and muriatic were formerly1 and are still frequently1 called mineral acids4 #b;dly1 ,acids that have double or binary radicals1 and which consequently consist of triple combinations4 ,these are the vegetable acids1 whose common radical is a compound of hydrogen and carbon4 ,,caroline4 ,but if the basis of all the vegetable acids be the same1 it should form but one acid2 it may indeed combine with different proportions of oxygen1 but the nature of the acid must be the same4 ,,mrs4 ,b4 ,the only difference that exists in the basis of vegetable acids1 is the various proportions of hydrogen and carbon from which they are severally composed4 ,but this is enough to produce a number of acids apparently very dissimilar4 ,that they do not1 however1 differ essentially1 is proved by their susceptibility of being converted into each other1 by the addition or subtraction of a portion of hydrogen or of carbon4 ,the names of these acids are1 ,the ,acetic ,oxalic ,tartarous ,citric ,malic ,acids1 of double bases1 being of vegetable origin4 ,gallic ,mucous ,benzoic ,succinic ,camphoric ,suberic ,the #c;d class of acids consists of those which have triple radicals1 and are therefore of a still more compound nature4 ,this class comprehends the animal acids1 which are1 ,the ,lactic ,prussic ,formic ,acids1 of triple bases1 or animal acids4 ,bombic ,sebacic ,zoonic ,lithic ,i have given you this summary account or enumeration of the acids1 as you may find it more satisfactory to have at once an outline or a general notion of the extent of the subject2 but we shall now confine ourselves to the first class1 which requires our more immediate attention2 and defer the few remarks which we shall have to make on the others1 till we treat of the chemistry of the animal and vegetable kingdoms4 ,the acids of simple and known radicals are all capable of being decomposed by combustible bodies1 to which they yield their oxygen4 ,if1 for instance1 ,i pour a drop of sulphuric acid on this piece of iron1 it will produce a spot of rust1 you know what that is8 ,,caroline4 ,yes2 it is an oxyd1 formed by the oxygen of the acid combining with the iron4 ,,mrs4 ,b4 ,in this case you see the sulphur deposits the oxygen by which it was acidified on the metal4 ,and again1 if we pour some acid on a compound combustible substance1 7we shall try it on this piece of wood17 it will combine with one or more of the constituents of that substance1 and occasion a decomposition4 ,,emily4 ,it has changed the colour of the wood to black4 ,how is that8 ,,mrs4 ,b4 ,the oxygen deposited by the acid has burnt it2 you know that wood in burning becomes black before it is reduced to ashes4 ,whether it derives the oxygen which burns it from the atmosphere1 or from any other source1 the chemical effect on the wood is the same4 ,in the case of real combustion1 wood becomes black1 because it is reduced to the state of charcoal by the evaporation of its other constituents4 ,but can you tell me the reason why wood turns black when burnt by the application of an acid8 ,,caroline4 ,first1 tell me what are the ingredients of wood8 ,,mrs4 ,b4 ,hydrogen and carbon are the chief constituents of wood1 as of all other vegetable substances4 ,,caroline4 ,well1 then1 ,i suppose that the oxygen of the acid combines with the hydrogen of the wood1 to form water2 and that the carbon of the wood1 remaining alone1 appears of its usual black colour4 ,,mrs4 ,b4 ,very well indeed1 my dear2 that is certainly the most plausible explanation4 ,,emily4 ,would not this be a good method of making charcoal8 ,,mrs4 ,b4 ,it would be an extremely expensive1 and1 ,i believe1 very imperfect method2 for the action of the acid on the wood1 and the heat produced by it1 are far from sufficient to deprive the wood of all its evaporable parts4 ,,caroline4 ,what is the reason that vinegar1 lemon1 and the acid of fruits1 do not produce this effect on wood8 ,,mrs4 ,b4 ,they are vegetable acids1 whose bases are composed of hydrogen and carbon2 the oxygen1 therefore1 will not be disposed to quit this radical1 where it is already united with hydrogen4 ,the strongest of these may1 perhaps1 yield a little of their oxygen to the wood1 and produce a stain upon it2 but the carbon will not be sufficiently uncovered to assume its black colour4 ,indeed1 the several mineral acids themselves possess this power of charring wood in very different degrees4 ,,emily4 ,cannot vegetable acids be decomposed1 by any combustibles8 ,,mrs4 ,b4 ,no2 because their radical is composed of two substances which have a greater attraction for oxygen than any known body4 ,,caroline4 ,and are those strong acids1 which burn and decompose wood1 capable of producing similar effects on the skin and flesh of animals8 ,,mrs4 ,b4 ,yes2 all the mineral acids1 and one of them more especially1 possess powerful caustic qualities4 ,they actually corrode and destroy the skin and flesh2 but they do not produce upon these exactly the same alteration they do on wood1 probably because there is a great proportion of nitrogen and other substances in animal matter1 which prevents the separation of carbon from being so conspicuous4 ,,conversation ,,xvii4 ,,of ,,the ,,sulphuric ,,and ,,phosphoric ,,acids2 ,,or ,,the ,,combinations ,,of ,,oxygen ,,with ,,sulphur ,,and ,,phosphorus2 ,,and ,,of ,,the ,,sulphats ,,and ,,phosphats4 ,,mrs4 ,b4 ,in addition to the general survey which we have taken of acids1 ,i think you will find it interesting to examine individually a few of the most important of them1 and likewise some of their principal combinations with the alkalies1 alkaline earths1 and metals4 ,the first of the acids1 in point of importance1 is the ,,sulphuric1 formerly called oil of vitriol4 ,,caroline4 ,i have known it a long time by that name1 but had no idea that it was the same fluid as sulphuric acid4 ,what resemblance or connection can there be between oil of vitriol and this acid8 ,,mrs4 ,b4 ,vitriol is the common name for sulphat of iron1 a salt which is formed by the combination of sulphuric acid and iron2 the sulphuric acid was formerly obtained by distillation from this salt1 and it very naturally received its name from the substance which afforded it4 ,,caroline4 ,but it is still usually called oil of vitriol8 ,,mrs4 ,b4 ,yes2 a sufficient length of time has not yet elapsed1 since the invention of the new nomenclature1 for it to be generally disseminated2 but1 as it is adopted by all scientific chemists1 there is every reason to suppose that it will gradually become universal4 ,when ,i received this bottle from the chemists1 oil of vitriol was inscribed on the label2 but1 as ,i knew you were very punctilious in regard to the nomenclature1 ,i changed it1 and substituted the words sulphuric acid4 ,,emily4 ,this acid has neither colour nor smell1 but it appears much thicker than water4 ,,mrs4 ,b4 ,it is nearly twice as heavy as water1 and has1 you see1 an oily consistence4 ,,caroline4 ,and it is probably from this circumstance that it has been called an oil1 for it can have no real claim to that name1 as it does not contain either hydrogen or carbon1 which are the essential constituents of oil4 ,,mrs4 ,b4 ,certainly2 and therefore it would be the more absurd to retain a name which owed its origin to such a mistaken analogy4 ,sulphuric acid1 in its purest state1 would probably be a concrete substance1 but its attraction for water is such1 that it is impossible to obtain that acid perfectly free from it2 it is1 therefore1 always seen in a liquid form1 such as you here find it4 ,one of the most striking properties of sulphuric acid is that of evolving a considerable quantity of heat when mixed with water2 this ,i have already shown you4 ,,emily4 ,yes1 ,i recollect it2 but what was the degree of heat produced by that mixture8 ,,mrs4 ,b4 ,the thermometer may be raised by it to #cjj degrees1 which is considerably above the temperature of boiling water4 ,,caroline4 ,then water might be made to boil in that mixture8 ,,mrs4 ,b4 ,nothing more easy1 provided that you employ sufficient quantities of acid and of water1 and in the due proportions4 ,the greatest heat is produced by a mixture of one part of water to four of the acid3 we shall make a mixture of these proportions1 and immerse in it this thin glass tube1 which is full of water4 ,,caroline4 ,the vessel feels extremely hot1 but the water does not boil yet4 ,,mrs4 ,b4 ,you must allow some time for the heat to penetrate the tube1 and raise the temperature of the water to the boiling point-- ,,caroline4 ,now it boils--and with increasing violence4 ,,mrs4 ,b4 ,but it will not continue boiling long2 for the mixture gives out heat only while the particles of the water and the acid are mutually penetrating each other3 as soon as the new arrangement of those particles is effected1 the mixture will gradually cool1 and the water return to its former temperature4 ,you have seen the manner in which sulphuric acid decomposes all combustible substances1 whether animal1 vegetable1 or mineral1 and burns them by means of its oxygen8 ,,caroline4 ,i have very unintentionally repeated the experiment on my gown1 by letting a drop of the acid fall upon it1 and it has made a stain1 which1 ,i suppose1 will never wash out4 ,,mrs4 ,b4 ,no1 certainly2 for before you can put it into water1 the spot will become a hole1 as the acid has literally burnt the muslin4 ,,caroline4 ,so it has1 indeed6 ,well1 ,i will fasten the stopper1 and put the bottle away1 for it is a dangerous substance4 --,oh1 now ,i have done worse still1 for ,i have spilt some on my hand6 ,,mrs4 ,b4 ,it is then burned1 as well as your gown1 for you know that oxygen destroys animal as well as vegetable matters2 and1 as far as the decomposition of the skin of your finger is effected1 there is no remedy2 but by washing it immediately in water1 you will dilute the acid1 and prevent any further injury4 ,,caroline4 ,it feels extremely hot1 ,i assure you4 ,,mrs4 ,b4 ,you have now learned1 by experience1 how cautiously this acid must be used4 ,you will soon become acquainted with another acid1 the nitric1 which1 though it produces less heat on the skin1 destroys it still quicker1 and makes upon it an indelible stain4 ,you should never handle any substances of this kind1 without previously dipping your fingers in water1 which will weaken their caustic effects4 ,but1 since you will not repeat the experiment1 ,i must put in the stopper1 for the acid attracts the moisture from the atmosphere1 which would destroy its strength and purity4 ,,emily4 ,pray1 how can sulphuric acid be extracted from sulphat of iron by distillation8 ,,mrs4 ,b4 ,the process of distillation1 you know1 consists in separating substances from one another by means of their different degrees of volatility1 and by the introduction of a new chemical agent1 caloric4 ,thus1 if sulphat of iron be exposed in a retort to a proper degree of heat1 it will be decomposed1 and the sulphuric acid will be volatilised4 ,,emily4 ,but now that the process of forming acids by the combustion of their radicals is known1 why should not this method be used for making sulphuric acid8 ,,mrs4 ,b4 ,this is actually done in most manufactures2 but the usual method of preparing sulphuric acid does not consist in burning the sulphur in oxygen gas 7as we formerly did by the way of experiment71 but in heating it together with another substance1 nitre1 which yields oxygen in sufficient abundance to render the combustion in common air rapid and complete4 ,,caroline4 ,this substance1 then1 answers the same purpose as oxygen gas8 ,,mrs4 ,b4 ,exactly4 ,in manufactures the combustion is performed in a leaden chamber1 with water at the bottom1 to receive the vapour and assist its condensation4 ,the combustion is1 however1 never so perfect but that a quantity of sulphureous acid is formed at the same time2 for you recollect that the sulphureous acid1 according to the chemical nomenclature1 differs from the sulphuric only by containing less oxygen4 ,from its own powerful properties1 and from the various combinations into which it enters1 sulphuric acid is of great importance in many of the arts4 ,it is used also in medicine in a state of great dilution2 for were it taken internally1 in a concentrated state1 it would prove a most dangerous poison4 ,,caroline4 ,i am sure it would burn the throat and stomach4 ,,mrs4 ,b4 ,can you think of any thing that would prove an antidote to this poison8 ,,caroline4 ,a large draught of water to dilute it4 ,,mrs4 ,b4 ,that would certainly weaken the caustic power of the acid1 but it would increase the heat to an intolerable degree4 ,do you recollect nothing that would destroy its deleterious properties more effectually8 ,,emily4 ,an alkali might1 by combining with it2 but1 then1 a pure alkali is itself a poison1 on account of its causticity4 ,,mrs4 ,b4 ,there is no necessity that the alkali should be caustic4 ,soap1 in which it is combined with oil2 or magnesia1 either in the state of carbonat1 or mixed with water1 would prove the best antidotes4 ,,emily4 ,in those cases then1 ,i suppose1 the potash and the magnesia would quit their combinations to form salts with the sulphuric acid8 ,,mrs4 ,b4 ,precisely4 ,we may now make a few observations on the sulphureous acid1 which we have found to be the product of sulphur slowly and imperfectly burnt4 ,this acid is distinguished by its pungent smell1 and its gaseous form4 ,,caroline4 ,its ariform state is1 ,i suppose1 owing to the smaller proportion of oxygen1 which renders it lighter than sulphuric acid8 ,,mrs4 ,b4 ,probably2 for by adding oxygen to the weaker acid1 it may be converted into the stronger kind4 ,but this change of state may also be connected with a change of affinity with regard to caloric4 ,,emily4 ,and may sulphureous acid be obtained from sulphuric acid by a diminution of oxygen8 ,,mrs4 ,b4 ,yes2 it can be done by bringing any combustible substance in contact with the acid4 ,this decomposition is most easily performed by some of the metals2 these absorb a portion of the oxygen from the sulphuric acid1 which is thus converted into the sulphureous1 and flies off in its gaseous form4 ,,caroline4 ,and cannot the sulphureous acid itself be decomposed and reduced to sulphur8 ,,mrs4 ,b4 ,yes2 if this gas be heated in contact with charcoal1 the oxygen of the gas will combine with it1 and the pure sulphur is regenerated4 ,sulphureous acid is readily absorbed by water2 and in this liquid state it is found particularly useful in bleaching linen and woollen cloths1 and is much used in manufactures for those purposes4 ,i can show you its effect in destroying colours1 by taking out vegetable stains--,i think ,i see a spot on your gown1 ,emily1 on which we may try the experiment4 ,,emily4 ,it is the stain of mulberries2 but ,i shall be almost afraid of exposing my gown to the experiment1 after seeing the effect which the sulphuric acid produced on that of ,caroline-- ,,mrs4 ,b4 ,there is no such danger from the sulphureous2 but the experiment must be made with great caution1 for1 during the formation of sulphureous acid by combustion1 there is always some sulphuric produced4 ,,caroline4 ,but where is your sulphureous acid8 ,,mrs4 ,b4 ,we may easily prepare some ourselves1 simply by burning a match2 we must first wet the stain with water1 and now hold it in this way1 at a little distance1 over the lighted match3 the vapour that arises from it is sulphureous acid1 and the stain1 you see1 gradually disappears4 ,,emily4 ,i have frequently taken out stains by this means1 without understanding the nature of the process4 ,but why is it necessary to wet the stain before it is exposed to the acid fumes8 ,,mrs4 ,b4 ,the moisture attracts and absorbs the sulphureous acid2 and it serves likewise to dilute any particles of sulphuric acid which might injure the linen4 ,sulphur is susceptible of a third combination with oxygen1 in which the proportion of the latter is too small to render the sulphur acid4 ,it acquires this slight oxygenation by mere exposure to the atmosphere1 without any elevation of temperature3 in this case1 the sulphur does not change its natural form1 but is only discoloured1 being changed to red or brown2 and in this state it is an oxyd of sulphur4 ,before we take leave of the sulphuric acid1 we shall say a few words of its principal combinations4 ,it unites with all the alkalies1 alkaline earths and metals1 to form compound salts4 ,,caroline4 ,pray1 give me leave to interrupt you for a moment3 you have never mentioned any other salts than the compound or neutral salts2 is there no other kind8 ,,mrs4 ,b4 ,the term salt has been used1 from time immemorial1 as a kind of general name for any substance that has savour1 odour1 is soluble in water1 and crystallisable1 whether it be of an acid1 an alkaline1 or compound nature2 but the compound salts alone retain that appellation in modern chemistry4 ,the most important of the salts1 formed by the combinations of the sulphuric acid1 are1 first1 sulphat of potash1 formerly called sal polychrest3 this is a very bitter salt1 much used in medicine2 it is found in the ashes of most vegetables1 but it may be prepared artificially by the immediate combination of sulphuric acid and potash4 ,this salt is easily soluble in boiling water4 ,solubility is1 indeed1 a property common to all salts2 and they always produce cold in melting4 ,,emily4 ,that must be owing to the caloric which they absorb in passing from a solid to a fluid form4 ,,mrs4 ,b4 ,that is1 certainly1 the most probable explanation4 ,sulphat of soda1 commonly called ,glauber's salt1 is another medicinal salt1 which is still more bitter than the preceding4 ,we must prepare some of these compounds1 that you may observe the phenomena which take place during their formation4 ,we need only pour some sulphuric acid over the soda which ,i have put into this glass4 ,,caroline4 ,what an amazing heat is disengaged6 --,i thought you said that cold was produced by the melting of salts8 ,,mrs4 ,b4 ,but you must observe that we are now making1 not melting a salt4 ,heat is disengaged during the formation of compound salts1 and a faint light is also emitted1 which may sometimes be perceived in the dark4 ,,emily4 ,and is this heat and light produced by the union of the opposite electricities of the alkali and the acid8 ,,mrs4 ,b4 ,no doubt it is1 if that theory be true4 ,,caroline4 ,the union of an acid and an alkali is then an actual combustion8 ,,mrs4 ,b4 ,not precisely1 though there is certainly much analogy in these processes4 ,,caroline4 ,will this sulphat of soda become solid8 ,,mrs4 ,b4 ,we have not1 ,i suppose1 mixed the acid and the alkali in the exact proportions that are required for the formation of the salt1 otherwise the mixture would have been almost immediately changed to a solid mass2 but1 in order to obtain it in crystals1 as you see it in this bottle1 it would be necessary first to dilute it with water1 and afterwards to evaporate the water1 during which operation the salt would gradually crystallise4 ,,caroline4 ,but of what use is the addition of water1 if it is afterwards to be evaporated8 ,,mrs4 ,b4 ,when suspended in water1 the acid and the alkali are more at liberty to act on each other1 their union is more complete1 and the salt assumes the regular form of crystals during the slow evaporation of its solvent4 ,sulphat of soda liquefies by heat1 and effloresces in the air4 ,,emily4 ,pray what is the meaning of the word effloresces8 ,i do not recollect your having mentioned it before4 ,,mrs4 ,b4 ,a salt is said to effloresce when it loses its water of crystallisation on being exposed to the atmosphere1 and is thus gradually converted into a dry powder3 you may observe that these crystals of sulphat of soda are far from possessing the transparency which belongs to their crystalline state2 they are covered with a white powder1 occasioned by their having been exposed to the atmosphere1 which has deprived their surface of its lustre1 by absorbing its water of crystallisation4 ,salts are1 in general1 either efflorescent or deliquescent3 this latter property is precisely the reverse of the former2 that is to say1 deliquescent salts absorb water from the atmosphere1 and are moistened and gradually melted by it4 ,muriat of lime is an instance of great deliquescence4 ,,emily4 ,but are there no salts that have the same degree of attraction for water as the atmosphere1 and that will consequently not be affected by it8 ,,mrs4 ,b4 ,yes2 there are many such salts1 as1 for instance1 common salt1 sulphat of magnesia1 and a variety of others4 ,sulphat of lime is very frequently met with in nature1 and constitutes the well-known substance called gypsum1 or plaster of ,paris4 ,sulphat of magnesia1 commonly called ,epsom salt1 is another very bitter medicine1 which is obtained from sea-water and from several springs1 or may be prepared by the direct combination of its ingredients4 ,we have formerly mentioned sulphat of alumine as constituting the common alum2 it is found in nature chiefly in the neighbourhood of volcanos1 and is particularly useful in the arts1 from its strong astringent qualities4 ,it is chiefly employed by dyers and calico-printers1 to fix colours2 and is used also in the manufacture of some kinds of leather4 ,sulphuric acid combines also with the metals4 ,,caroline4 ,one of these combinations1 sulphat of iron1 we are already well acquainted with4 ,,mrs4 ,b4 ,that is the most important metallic salt formed by sulphuric acid1 and the only one that we shall here notice4 ,it is of great use in the arts2 and1 in medicine1 it affords a very valuable tonic3 it is of this salt that most of those preparations called steel medicines are composed4 ,,caroline4 ,but does any carbon enter into these compositions to form steel8 ,,mrs4 ,b4 ,not an atom3 they are1 therefore1 very improperly called steel3 but it is the vulgar appellation1 and medical men themselves often comply with the general custom4 ,sulphat of iron may be prepared1 as you have seen1 by dissolving iron in sulphuric acid2 but it is generally obtained from the natural production called ,pyrites1 which being a sulphuret of iron1 requires only exposure to the atmosphere to be oxydated1 in order to form the salt2 this1 therefore1 is much the most easy way of procuring it on a large scale4 ,,emily4 ,i am surprised to find that both acids and compound salts are generally obtained from their various combinations1 rather than from the immediate union of their ingredients4 ,,mrs4 ,b4 ,were the simple bodies always at hand1 their combinations would naturally be the most convenient method of forming compounds2 but you must consider that1 in most instances1 there is great difficulty and expense in obtaining the simple ingredients from their combinations2 it is1 therefore1 often more expedient to procure compounds from the decomposition of other compounds4 ,but1 to return to the sulphat of iron4 --,there is a certain vegetable acid called ,gallic acid1 which has the remarkable property of precipitating this salt black--,i shall pour a few drops of the gallic acid into this solution of sulphat of iron-- ,,caroline4 ,it is become as black as ink6 ,,mrs4 ,b4 ,and it is ink in reality4 ,common writing ink is a precipitate of sulphat of iron by gallic acid2 the black colour is owing to the formation of gallat of iron1 which being insoluble1 remains suspended in the fluid4 ,this acid has also the property of altering the colour of iron in its metallic state4 ,you may frequently see its effect on the blade of a knife1 that has been used to cut certain kinds of fruits4 ,,caroline4 ,true2 and that is1 perhaps1 the reason that a silver knife is preferred to cut fruits2 the gallic acid1 ,i suppose1 does not act upon silver4 --,is this acid found in all fruits8 ,,mrs4 ,b4 ,it is contained1 more or less1 in the rind of most fruits and roots1 especially the radish1 which1 if scraped with a steel or iron knife1 has its bright red colour changed to a deep purple1 the knife being at the same time blackened4 ,but the vegetable substance in which the gallic acid most abounds is nutgall1 a kind of excrescence that grows on oaks1 and from which the acid is commonly obtained for its various purposes4 ,,mrs4 ,b4 ,we now come to the ,,phosphoric and ,,phosphorous ,,acids4 ,in treating of phosphorus1 you have seen how these acids may be obtained from it by combustion8 ,,emily4 ,yes2 but ,i should be much surprised if it was the usual method of obtaining them1 since it is so very difficult to procure phosphorus in its pure state4 ,,mrs4 ,b4 ,you are right1 my dear2 the phosphoric acid1 for general purposes1 is extracted from bones1 in which it is contained in the state of phosphat of lime2 from this salt the phosphoric acid is separated by means of the sulphuric1 which combines with the lime4 ,in its pure state1 phosphoric acid is either liquid or solid1 according to its degree of concentration4 ,among the salts formed by this acid1 phosphat of lime is the only one that affords much interest2 and this1 we have already observed1 constitutes the basis of all bones4 ,it is also found in very small quantities in some vegetables4 ,,conversation ,,xviii4 ,,of ,,the ,,nitric ,,and ,,carbonic ,,acids3 ,,or ,,the ,,combinations ,,of ,,oxygen ,,with ,,nitrogen ,,and ,,carbon2 ,,and ,,of ,,the ,,nitrats ,,and ,,carbonats4 ,,mrs4 ,b4 ,i am almost afraid of introducing the subject of the ,,nitric ,,acid1 as ,i am sure that ,i shall be blamed by ,caroline for not having made her acquainted with it before4 ,,caroline4 ,why so1 ,mrs4 ,b48 ,,mrs4 ,b4 ,because you have long known its radical1 which is nitrogen or azote2 and in treating of that element1 ,i did not even hint that it was the basis of an acid4 ,,caroline4 ,and what could be your reason for not mentioning this acid sooner8 ,,mrs4 ,b4 ,i do not know whether you will think the reason sufficiently good to acquit me2 but the omission1 ,i assure you1 did not proceed from negligence4 ,you may recollect that nitrogen was one of the first simple bodies which we examined2 you were then ignorant of the theory of combustion1 which ,i believe was1 for the first time1 mentioned in that lesson2 and therefore it would have been in vain1 at that time1 to have attempted to explain the nature and formation of acids4 ,,caroline4 ,i wonder1 however1 that it never occurred to us to enquire whether nitrogen could be acidified2 for1 as we knew it was classed among the combustible bodies1 it was natural to suppose that it might produce an acid4 ,,mrs4 ,b4 ,that is not a necessary consequence2 for it might combine with oxygen only in the degree requisite to form an oxyd4 ,but you will find that nitrogen is susceptible of various degrees of oxygenation1 some of which convert it merely into an oxyd1 and others give it all the acid properties4 ,the acids1 resulting from the combination of oxygen and nitrogen1 are called the ,,nitrous and ,,nitric acids4 ,we will begin with the ,,nitric1 in which nitrogen is in the highest state of oxygenation4 ,this acid naturally exists in the form of gas2 but is so very soluble in water1 and has so great an affinity for it1 that one grain of water will absorb and condense ten grains of acid gas1 and form the limpid fluid which you see in this bottle4 ,,caroline4 ,what a strong offensive smell it has6 ,,mrs4 ,b4 ,this acid contains a greater abundance of oxygen than any other1 but it retains it with very little force4 ,,emily4 ,then it must be a powerful caustic1 both from the facility with which it parts with its oxygen1 and the quantity which it affords8 ,,mrs4 ,b4 ,very well1 ,emily2 both cause and effect are exactly such as you describe3 nitric acid burns and destroys all kinds of organised matter4 ,it even sets fire to some of the most combustible substances4 --,we shall pour a little of it over this piece of dry warm charcoal--you see it inflames it immediately2 it would do the same with oil of turpentine1 phosphorus1 and several other very combustible bodies4 ,this shows you how easily this acid is decomposed by combustible bodies1 since these effects must depend upon the absorption of its oxygen4 ,nitric acid has been used in the arts from time immemorial1 but it is only within these twenty-five years that its chemical nature has been ascertained4 ,the celebrated ,mr4 ,cavendish discovered that it consisted of about #aj parts of nitrogen and #be of oxygen499 ,these principles1 in their gaseous state1 combine at a high temperature2 and this may be effected by repeatedly passing the electrical spark through a mixture of the two gases4 ,footnote 993 ,the proportion stated by ,sir ,h4 ,davy1 in his ,chemical ,researches1 is as #a to #b4chi4 ,,emily4 ,the nitrogen and oxygen gases1 of which the atmosphere is composed1 do not combine1 ,i suppose1 because their temperature is not sufficiently elevated8 ,,caroline4 ,but in a thunder-storm1 when the lightning repeatedly passes through them1 may it not produce nitric acid8 ,we should be in a strange situation1 if a violent storm should at once convert the atmosphere into nitric acid4 ,,mrs4 ,b4 ,there is no danger of it1 my dear2 the lightning can affect but a very small portion of the atmosphere1 and though it were occasionally to produce a little nitric acid1 yet this never could happen to such an extent as to be perceivable4 ,,emily4 ,but how could the nitric acid be known1 and used1 before the method of combining its constituents was discovered8 ,,mrs4 ,b4 ,before that period the nitric acid was obtained1 and it is indeed still extracted1 for the common purposes of art1 from the compound salt which it forms with potash1 commonly called nitre4 ,,caroline4 ,why is it so called8 ,pray1 ,mrs4 ,b41 let these old unmeaning names be entirely given up1 by us at least2 and let us call this salt nitrat of potash4 ,,mrs4 ,b4 ,with all my heart2 but it is necessary that ,i should1 at least1 mention the old names1 and more especially those which are yet in common use2 otherwise1 when you meet with them1 you would not be able to understand their meaning4 ,,emily4 ,and how is the acid obtained from this salt8 ,,mrs4 ,b4 ,by the intervention of sulphuric acid1 which combines with the potash1 and sets the nitric acid at liberty4 ,this ,i can easily show you1 by mixing some nitrat of potash and sulphuric acid in this retort1 and heating it over a lamp2 the nitric acid will come over in the form of vapour1 which we shall collect in a glass bell4 ,this acid1 diluted in water1 is commonly called aqua fortis1 if ,caroline will allow me to mention that name4 ,,caroline4 ,i have often heard that aqua fortis will dissolve almost all metals2 it is no doubt because it yields its oxygen so easily4 ,,mrs4 ,b4 ,yes2 and from this powerful solvent property1 it derived the name of aqua fortis1 or strong water4 ,do you not recollect that we oxydated1 and afterwards dissolved1 some copper in this acid8 ,,emily4 ,if ,i remember right1 the nitrat of copper was the first instance you gave us of a compound salt4 ,,caroline4 ,can the nitric acid be completely decomposed and converted into nitrogen and oxygen8 ,,emily4 ,that cannot be the case1 ,caroline2 since the acid can be decomposed only by the combination of its constituents with other bodies4 ,,mrs4 ,b4 ,true2 but caloric is sufficient for this purpose4 ,by making the acid pass through a red hot porcelain tube1 it is decomposed2 the nitrogen and oxygen regain the caloric which they had lost in combining1 and are thus both restored to their gaseous state4 ,the nitric acid may also be partly decomposed1 and is by this means converted into ,,nitrous ,,acid4 ,,caroline4 ,this conversion must be easily effected1 as the oxygen is so slightly combined with the nitrogen4 ,,mrs4 ,b4 ,the partial decomposition of nitric acid is readily effected by most metals2 but it is sufficient to expose the nitric acid to a very strong light to make it give out oxygen gas1 and thus be converted into nitrous acid4 ,of this acid there are various degrees1 according to the proportions of oxygen which it contains2 the strongest1 and that into which the nitric is first converted1 is of a yellow colour1 as you see in this bottle4 ,,caroline4 ,how it fumes when the stopper is taken out6 ,,mrs4 ,b4 ,the acid exists naturally in a gaseous state1 and is here so strongly concentrated in water1 that it is constantly escaping4 ,here is another bottle of nitrous acid1 which1 you see1 is of an orange red2 this acid is weaker1 the nitrogen being combined with a smaller quantity of oxygen2 and with a still less proportion of oxygen it is an olive-green colour1 as it appears in this third bottle4 ,in short1 the weaker the acid1 the deeper is its colour4 ,nitrous acid acts still more powerfully on some inflammable substances than the nitric4 ,,emily4 ,i am surprised at that1 as it contains less oxygen4 ,,mrs4 ,b4 ,but1 on the other hand1 it parts with its oxygen much more readily3 you may recollect that we once inflamed oil with this acid4 ,the next combinations of nitrogen and oxygen form only oxyds of nitrogen1 the first of which is commonly called nitrous air2 or more properly nitric oxyd gas4 ,this may be obtained from nitric acid1 by exposing the latter to the action of metals1 as in dissolving them it does not yield the whole of its oxygen1 but retains a portion of this principle sufficient to convert it into this peculiar gas1 a specimen of which ,i have prepared1 and preserved within this inverted glass bell4 ,,emily4 ,it is a perfectly invisible elastic fluid4 ,,mrs4 ,b4 ,yes2 and it may be kept any length of time in this manner over water1 as it is not1 like the nitric and nitrous acids1 absorbable by it4 ,it is rather heavier than atmospherical air1 and is incapable of supporting either combustion or respiration4 ,i am going to incline the glass gently on one side1 so as to let some of the gas escape-- ,,emily4 ,how very curious6 --,it produces orange fumes like the nitrous acid6 that is the more extraordinary1 as the gas within the glass is perfectly invisible4 ,,mrs4 ,b4 ,it would give me much pleasure if you could make out the reason of this curious change without requiring any further explanation4 ,,caroline4 ,it seems1 by the colour and smell1 as if it were converted into nitrous acid gas3 yet that cannot be1 unless it combines with more oxygen2 and how can it obtain oxygen the very instant it escapes from the glass8 ,,emily4 ,from the atmosphere1 no doubt4 ,is it not so1 ,mrs4 ,b48 ,,mrs4 ,b4 ,you have guessed it2 as soon as it comes in contact with the atmosphere1 it absorbs from it the additional quantity of oxygen necessary to convert it into nitrous acid gas4 ,and1 if ,i now remove the bottle entirely from the water1 so as to bring at once the whole of the gas into contact with the atmosphere1 this conversion will appear still more striking-- ,,emily4 ,look1 ,caroline1 the whole capacity of the bottle is instantly tinged of an orange colour6 ,,mrs4 ,b4 ,thus1 you see1 it is the most easy process imaginable to convert nitrous oxyd gas into nitrous acid gas4 ,the property of attracting oxygen from the atmosphere1 without any elevation of temperature1 has occasioned this gaseous oxyd being used as a test for ascertaining the degree of purity of the atmosphere4 ,i am going to show you how it is applied to this purpose4 --,you see this graduated glass tube1 which is closed at one end1 7,,plate ,x4 ,fig4 #b47 --,i first fill it with water1 and then introduce a certain measure of nitrous gas1 which1 not being absorbable by water1 passes through it1 and occupies the upper part of the tube4 ,i must now add rather above two-thirds of oxygen gas1 which will just be sufficient to convert the nitrous oxyd gas into nitrous acid gas4 ,,caroline4 ,so it has6 --,i saw it turn of an orange colour2 but it immediately afterwards disappeared entirely1 and the water1 you see1 has risen1 and almost filled the tube4 ,,mrs4 ,b4 ,that is because the acid gas is absorbable by water1 and in proportion as the gas impregnates the water1 the latter rises in the tube4 ,when the oxygen gas is very pure1 and the required proportion of nitrous oxyd gas very exact1 the whole is absorbed by the water2 but if any other gas be mixed with the oxygen1 instead of combining with the nitrous oxygen1 it will remain and occupy the upper part of the tube2 or1 if the gases be not in the due proportion1 there will be a residue of that which predominates4 --,before we leave this subject1 ,i must not forget to remark that nitrous acid may be formed by dissolving nitrous oxyd gas in nitric acid4 ,this solution may be effected simply by making bubbles of nitrous oxyd gas pass through nitric acid4 ,,emily4 ,that is to say1 that nitrogen at its highest degree of oxygenation1 being mixed with nitrogen at its lowest degree of oxygenation1 will produce a kind of intermediate substance1 which is nitrous acid4 ,,mrs4 ,b4 ,you have stated the fact with great precision4 --,there are various other methods of preparing nitrous oxyd1 and of obtaining it from compound bodies2 but it is not necessary to enter into these particulars4 ,it remains for me only to mention another curious modification of oxygenated nitrogen1 which has been distinguished by the name of gaseous oxyd of nitrogen4 ,it is but lately that this gas has been accurately examined1 and its properties have been investigated chiefly by ,sir ,h4 ,davy4 ,it has obtained also the name of exhilarating gas1 from the very singular property which that gentleman has discovered in it1 of elevating the animal spirits1 when inhaled into the lungs1 to a degree sometimes resembling delirium or intoxication4 ,,caroline4 ,is it respirable1 then8 ,,mrs4 ,b4 ,it can scarcely be called respirable1 as it would not support life for any length of time2 but it may be breathed for a few moments without any other effects1 than the singular exhilaration of spirits ,i have just mentioned4 ,it affects different people1 however1 in a very different manner4 ,some become violent1 even outrageous3 others experience a languor1 attended with faintness2 but most agree in opinion1 that the sensations it excites are extremely pleasant4 ,,caroline4 ,i think ,i should like to try it--how do you breathe it8 ,,mrs4 ,b4 ,by collecting the gas in a bladder1 to which a short tube with a stop-cock is adapted2 this is applied to the mouth with one hand1 whilst the nostrils are kept closed with the other1 that the common air may have no access4 ,you then alternately inspire1 and expire the gas1 till you perceive its effects4 ,but ,i cannot consent to your making the experiment2 for the nerves are sometimes unpleasantly affected by it1 and ,i would not run any risk of that kind4 ,,emily4 ,i should like1 at least1 to see somebody breathe it2 but pray by what means is this curious gas obtained8 ,,mrs4 ,b4 ,it is procured from nitrat of ammonia1 an artificial salt which yields this gas on the application of a gentle heat4 ,i have put some of the salt into a retort1 and by the aid of a lamp the gas will be extricated4-- ,,caroline4 ,bubbles of air begin to escape through the neck of the retort into the water apparatus2 will you not collect them8 ,,mrs4 ,b4 ,the gas that first comes over need not be preserved1 as it consists of little more than the common air that was in the retort2 besides1 there is always in this experiment a quantity of watery vapour which must come away before the nitrous oxyd appears4 ,,emily4 ,watery vapour6 ,whence does that proceed8 ,there is no water in nitrat of ammonia8 ,,mrs4 ,b4 ,you must recollect that there is in every salt a quantity of water of crystallisation1 which may be evaporated by heat alone4 ,but1 besides this1 water is actually generated in this experiment1 as you will see presently4 ,first tell me1 what are the constituent parts of nitrat of ammonia8 ,,emily4 ,ammonia1 and nitric acid3 this salt1 therefore1 contains three different elements1 nitrogen and hydrogen1 which produce the ammonia2 and oxygen1 which1 with nitrogen1 forms the acid4 ,,mrs4 ,b4 ,well then1 in this process the ammonia is decomposed2 the hydrogen quits the nitrogen to combine with some of the oxygen of the nitric acid1 and forms with it the watery vapour which is now coming over4 ,when that is effected1 what will you expect to find8 ,,emily4 ,nitrous acid instead of nitric acid1 and nitrogen instead of ammonia4 ,,mrs4 ,b4 ,exactly so2 and the nitrous acid and nitrogen combine1 and form the gaseous oxyd of nitrogen1 in which the proportion of oxygen is #cg parts to #fc of nitrogen4 ,you may have observed1 that for a little while no bubbles of air have come over1 and we have perceived only a stream of vapour condensing as it issued into the water4 --,now bubbles of air again make their appearance1 and ,i imagine that by this time all the watery vapour is come away1 and that we may begin to collect the gas4 ,we may try whether it is pure1 by filling a phial with it1 and plunging a taper into it--yes1 it will do now1 for the taper burns brighter than in the common air1 and with a greenish flame4 ,,caroline4 ,but how is that8 ,i thought no gas would support combustion but oxygen or chlorine4 ,,mrs4 ,b4 ,or any gas that contains oxygen1 and is ready to yield it1 which is the case with this in a considerable degree2 it is not1 therefore1 surprising that it should accelerate the combustion of the taper4 ,you see that the gas is now produced in great abundance2 we shall collect a large quantity of it1 and ,i dare say that we shall find some of the family who will be curious to make the experiment of respiring it4 ,whilst this process is going on1 we may take a general survey of the most important combinations of the nitric and nitrous acids with the alkalies4 ,the first of these is nitrat of potash1 commonly called nitre or saltpetre4 ,,caroline4 ,is not that the salt with which gunpowder is made8 ,,mrs4 ,b4 ,yes4 ,gunpowder is a mixture of five parts of nitre to one of sulphur1 and one of charcoal4 --,nitre from its great proportion of oxygen1 and from the facility with which it yields it1 is the basis of most detonating compositions4 ,,emily4 ,but what is the cause of the violent detonation of gunpowder when set fire to8 ,,mrs4 ,b4 ,detonation may proceed from two causes2 the sudden formation or destruction of an elastic fluid4 ,in the first case1 when either a solid or liquid is instantaneously converted into an elastic fluid1 the prodigious and sudden expansion of the body strikes the air with great violence1 and this concussion produces the sound called detonation4 ,,caroline4 ,that ,i comprehend very well2 but how can a similar effect be produced by the destruction of a gas8 ,,mrs4 ,b4 ,a gas can be destroyed only by condensing it to a liquid or solid state2 when this takes place suddenly1 the gas1 in assuming a new and more compact form1 produces a vacuum1 into which the surrounding air rushes with great impetuosity2 and it is by that rapid and violent motion that the sound is produced4 ,in all detonations1 therefore1 gases are either suddenly formed1 or destroyed4 ,in that of gunpowder1 can you tell me which of these two circumstances takes place8 ,,emily4 ,as gunpowder is a solid1 it must1 of course1 produce the gases in its detonation2 but how1 ,i cannot tell4 ,,mrs4 ,b4 ,the constituents of gunpowder1 when heated to a certain degree1 enter into a number of new combinations1 and are instantaneously converted into a variety of gases1 the sudden expansion of which gives rise to the detonation4 ,,caroline4 ,and in what instance does the destruction or condensation of gases produce detonation8 ,,mrs4 ,b4 ,i can give you one with which you are well acquainted2 the sudden combination of the oxygen and hydrogen gases4 ,,caroline4 ,true2 ,i recollect perfectly that hydrogen detonates with oxygen when the two gases are converted into water4 ,,mrs4 ,b4 ,but let us return to the nitrat of potash4 --,this salt is decomposed when exposed to heat1 and mixed with any combustible body1 such as carbon1 sulphur1 or metals1 these substances oxydating rapidly at the expense of the nitrat4 ,i must show you an instance of this4 --,i expose to the fire some of the salt in a small iron ladle1 and1 when it is sufficiently heated1 add to it some powdered charcoal2 this will attract the oxygen from the salt1 and be converted into carbonic acid4-- ,,emily4 ,but what occasions that crackling noise1 and those vivid flashes that accompany it8 ,,mrs4 ,b4 ,the rapidity with which the carbonic acid gas is formed occasions a succession of small detonations1 which1 together with the emission of flame1 is called deflagration4 ,nitrat of ammonia we have already noticed1 on account of the gaseous oxyd of nitrogen which is obtained from it4 ,nitrat of silver is the lunar caustic1 so remarkable for its property of destroying animal fibre1 for which purpose it is often used by surgeons4 --,we have said so much on a former occasion1 on the mode in which caustics act on animal matter1 that ,i shall not detain you any longer on this subject4 ,we now come to the ,,carbonic ,,acid1 which we have already had many opportunities of noticing4 ,you recollect that this acid may be formed by the combustion of carbon1 whether in its imperfect state of charcoal1 or in its purest form of diamond4 ,and it is not necessary1 for this purpose1 to burn the carbon in oxygen gas1 as we did in the preceding lecture2 for you need only light a piece of charcoal and suspend it under a receiver on the water bath4 ,the charcoal will soon be extinguished1 and the air in the receiver will be found mixed with carbonic acid4 ,the process1 however1 is much more expeditious if the combustion be performed in pure oxygen gas4 ,,caroline4 ,but how can you separate the carbonic acid1 obtained in this manner1 from the air with which it is mixed8 ,,mrs4 ,b4 ,the readiest mode is to introduce under the receiver a quantity of caustic lime1 or caustic alkali1 which soon attracts the whole of the carbonic acid to form a carbonat4 --,the alkali is found increased in weight1 and the volume of the air is diminished by a quantity equal to that of the carbonic acid which was mixed with it4 ,,emily4 ,pray is there no method of obtaining pure carbon from carbonic acid8 ,,mrs4 ,b4 ,for a long time it was supposed that carbonic acid was not decompoundable2 but ,mr4 ,tennant discovered1 a few years ago1 that this acid may be decomposed by burning phosphorus in a closed vessel with carbonat of soda or carbonat of lime3 the phosphorus absorbs the oxygen from the carbonat1 whilst the carbon is separated in the form of a black powder4 ,this decomposition1 however1 is not effected simply by the attraction of the phosphorus for oxygen1 since it is weaker than that of charcoal2 but the attraction of the alkali of lime for the phosphoric acid1 unites its power at the same time4 ,,caroline4 ,cannot we make that experiment8 ,,mrs4 ,b4 ,not easily2 it requires being performed with extreme nicety1 in order to obtain any sensible quantity of carbon1 and the experiment is much too delicate for me to attempt it4 ,but there can be no doubt of the accuracy of ,mr4 ,tennant's results2 and all chemists now agree1 that one hundred parts of carbonic acid gas consists of about twenty-eight parts of carbon to seventy-two of oxygen gas4 ,but if you recollect1 we decomposed carbonic acid gas the other day by burning potassium in it4 ,,caroline4 ,true1 so we did2 and found the carbon precipitated on the regenerated potash4 ,,mrs4 ,b4 ,carbonic acid gas is found very abundantly in nature2 it is supposed to form about one thousandth part of the atmosphere1 and is constantly produced by the respiration of animals2 it exists in a great variety of combinations1 and is exhaled from many natural decompositions4 ,it is contained in a state of great purity in certain caves1 such as the ,grotto del ,cane1 near ,naples4 ,,emily4 ,i recollect having read an account of that grotto1 and of the cruel experiments made on the poor dogs1 to gratify the curiosity of strangers4 ,but ,i understood that the vapour exhaled by this cave was called fixed air4 ,,mrs4 ,b4 ,that is the name by which carbonic acid was known before its chemical composition was discovered4 --,this gas is more destructive of life than any other2 and if the poor animals that are submitted to its effects are not plunged into cold water as soon as they become senseless1 they do not recover4 ,it extinguishes flame instantaneously4 ,i have collected some in this glass1 which ,i will pour over the candle4 ,,caroline4 ,this is extremely singular--it seems to extinguish it as it were by enchantment1 as the gas is invisible4 ,i never should have imagined that gas could have been poured like a liquid4 ,,mrs4 ,b4 ,it can be done with carbonic acid only1 as no other gas is sufficiently heavy to be susceptible of being poured out in the atmospherical air without mixing with it4 ,,emily4 ,pray by what means did you obtain this gas8 ,,mrs4 ,b4 ,i procured it from marble4 ,carbonic acid gas has so strong an attraction for all the alkalies and alkaline earths1 that these are always found in nature in the state of carbonats4 ,combined with lime1 this acid forms chalk1 which may be considered as the basis of all kinds of marbles1 and calcareous stones4 ,from these substances carbonic acid is easily separated1 as it adheres so slightly to its combinations1 that the carbonats are all decomposable by any of the other acids4 ,i can easily show you how ,i obtained this gas2 ,i poured some diluted sulphuric acid over pulverised marble in this bottle 7the same which we used the other day to prepare hydrogen gas71 and the gas escaped through the tube connected with it2 the operation still continues1 as you may easily perceive-- ,,emily4 ,yes1 it does2 there is a great fermentation in the glass vessel4 ,what singular commotion is excited by the sulphuric acid taking possession of the lime1 and driving out the carbonic acid6 ,,caroline4 ,but did the carbonic acid exist in a gaseous state in the marble8 ,,mrs4 ,b4 ,certainly not2 the acid1 when in a state of combination1 is capable of existing in a solid form4 ,,caroline4 ,whence1 then1 does it obtain the caloric necessary to convert it into gas8 ,,mrs4 ,b4 ,it may be supplied in this case from the mixture of sulphuric acid and water1 which produces an evolution of heat1 even greater than is required for the purpose2 since1 as you may perceive by touching the glass vessel1 a considerable quantity of the caloric disengaged becomes sensible4 ,but a supply of caloric may be obtained also from a diminution of capacity for heat1 occasioned by the new combination which takes place2 and1 indeed1 this must be the case when other acids are employed for the disengagement of carbonic acid gas1 which do not1 like the sulphuric1 produce heat on being mixed with water4 ,carbonic acid may likewise be disengaged from its combinations by heat alone1 which restores it to its gaseous state4 ,,caroline4 ,it appears to me very extraordinary that the same gas1 which is produced by the burning of wood and coals1 should exist also in such bodies as marble1 and chalk1 which are incombustible substances4 ,,mrs4 ,b4 ,i will not answer that objection1 ,caroline1 because ,i think ,i can put you in a way of doing it yourself4 ,is carbonic acid combustible8 ,,caroline4 ,why1 no--because it is a body that has been already burnt2 it is carbon only1 and not the acid1 that is combustible4 ,,mrs4 ,b4 ,well1 and what inference do you draw from this8 ,,caroline4 ,that carbonic acid cannot render the bodies with which it is united combustible2 but that simple carbon does1 and that it is in this elementary state that it exists in wood1 coals1 and a great variety of other combustible bodies4 --,indeed1 ,mrs4 ,b41 you are very ungenerous2 you are not satisfied with convincing me that my objections are frivolous1 but you oblige me to prove them so myself4 ,,mrs4 ,b4 ,you must confess1 however1 that ,i make ample amends for the detection of error1 when ,i enable you to discover the truth4 ,you1 understand1 now1 ,i hope1 that carbonic acid is equally produced by the decomposition of chalk1 or by the combustion of charcoal4 ,these processes are certainly of a very different nature2 in the first case the acid is already formed1 and requires nothing more than heat to restore it to its gaseous state2 whilst1 in the latter1 the acid is actually made by the process of combustion4 ,,caroline4 ,i understand it now perfectly4 ,but ,i have just been thinking of another difficulty1 which1 ,i hope1 you will excuse my not being able to remove myself4 ,how does the immense quantity of calcareous earth1 which is spread all over the globe1 obtain the carbonic acid with which it is combined8 ,,mrs4 ,b4 ,the question is1 indeed1 not very easy to answer2 but ,i conceive that the general carbonisation of calcareous matter may have been the effect of a general combustion1 occasioned by some revolution of our globe1 and producing an immense supply of carbonic acid1 with which the calcareous matter became impregnated2 or that this may have been effected by a gradual absorption of carbonic acid from the atmosphere4 --,but this would lead us to discussions which we cannot indulge in1 without deviating too much from our subject4 ,,emily4 ,how does it happen that we do not perceive the pernicious effects of the carbonic acid which is floating in the atmosphere8 ,,mrs4 ,b4 ,because of the state of very great dilution in which it exists there4 ,but can you tell me1 ,emily1 what are the sources which keep the atmosphere constantly supplied with this acid8 ,,emily4 ,i suppose the combustion of wood1 coals1 and other substances1 that contain carbon4 ,,mrs4 ,b4 ,and also the breath of animals4 ,,caroline4 ,the breath of animals6 ,i thought you said that this gas was not at all respirable1 but on the contrary1 extremely poisonous4 ,,mrs4 ,b4 ,so it is2 but although animals cannot breathe in carbonic acid gas1 yet1 in the process of respiration1 they have the power of forming this gas in their lungs2 so that the air which we expire1 or reject from the lungs1 always contains a certain proportion of carbonic acid1 which is much greater than that which is commonly found in the atmosphere4 ,,caroline4 ,but what is it that renders carbonic acid such a deadly poison8 ,,mrs4 ,b4 ,the manner in which this gas destroys life1 seems to be merely by preventing the access of respirable air2 for carbonic acid gas1 unless very much diluted with common air1 does not penetrate into the lungs1 as the windpipe actually contracts and refuses it admittance4 --,but we must dismiss this subject at present1 as we shall have an opportunity of treating of respiration much more fully1 when we come to the chemical functions of animals4 ,,emily4 ,is carbonic acid as destructive to the life of vegetables as it is to that of animals8 ,,mrs4 ,b4 ,if a vegetable be completely immersed in it1 ,i believe it generally proves fatal to it2 but mixed in certain proportions with atmospherical air1 it is1 on the contrary1 very favourable to vegetation4 ,you remember1 ,i suppose1 our mentioning the mineral waters1 both natural and artificial1 which contain carbonic acid gas8 ,,caroline4 ,you mean the ,seltzer water8 ,,mrs4 ,b4 ,that is one of those which are the most used2 there are1 however1 a variety of others into which carbonic acid enters as an ingredient3 all these waters are usually distinguished by the name of acidulous or gaseous mineral waters4 ,the class of salts called carbonats is the most numerous in nature2 we must pass over them in a very cursory manner1 as the subject is far too extensive for us to enter on it in detail4 ,the state of carbonat is the natural state of a vast number of minerals1 and particularly of the alkalies and alkaline earths1 as they have so great an attraction for the carbonic acid1 that they are almost always found combined with it2 and you may recollect that it is only by separating them from this acid1 that they acquire that causticity and those striking qualities which ,i have formerly described4 ,all marbles1 chalks1 shells1 calcareous spars1 and lime-stones of every description1 are neutral salts1 in which lime1 their common basis1 has lost all its characteristic properties4 ,,emily4 ,but if all these various substances are formed by the union of lime with carbonic acid1 whence arises their diversity of form and appearance8 ,,mrs4 ,b4 ,both from the different proportions of their component parts1 and from a variety of foreign ingredients which may be occasionally blended with them3 the veins and colours of marbles1 for instance1 proceed from a mixture of metallic substances2 silex and alumine also frequently enter into these combinations4 ,the various carbonats1 therefore1 that ,i have enumerated1 cannot be considered as pure unadulterated neutral salts1 although they certainly belong to that class of bodies4 ,,conversation ,,xix4 ,,on ,,the ,,boracic1 ,,fluoric1 ,,muriatic1 ,,and ,,oxygenated ,,muriatic ,,acids2 ,,and ,,on ,,muriats4 --,,on ,,iodine ,,and ,,iodic ,,acid4 ,,mrs4 ,b4 ,we now come to the three remaining acids with simple bases1 the compound nature of which1 though long suspected1 has been but recently proved4 ,the chief of these is the muriatic2 but ,i shall first describe the two others1 as their bases have been obtained more distinctly than that of the muriatic acid4 ,you may recollect ,i mentioned the ,,boracic ,,acid4 ,this is found very sparingly in some parts of ,europe1 but for the use of manufactures we have always received it from the remote country of ,thibet1 where it is found in some lakes1 combined with soda4 ,it is easily separated from the soda by sulphuric acid1 and appears in the form of shining scales1 as you see here4 ,,caroline4 ,i am glad to meet with an acid which we need not be afraid to touch2 for ,i perceive1 from your keeping it in a piece of paper1 that it is more innocent than our late acquaintance1 the sulphuric and nitric acids4 ,,mrs4 ,b4 ,certainly2 but being more inert1 you will not find its properties so interesting4 ,however1 its decomposition1 and the brilliant spectacle it affords when its basis again unites with oxygen1 atones for its want of other striking qualities4 ,sir ,h4 ,davy succeeded in decomposing the boracic acid1 7which had till then been considered as undecompoundable17 by various methods4 ,on exposing this acid to the ,voltaic battery1 the positive wire gave out oxygen1 and on the negative wire was deposited a black substance1 in appearance resembling charcoal4 ,this was the basis of the acid1 which ,sir ,h4 ,davy has called ,boracium1 or ,boron4 ,the same substance was obtained in more considerable quantities1 by exposing the acid to a great heat in an iron gun-barrel4 ,a third method of decomposing the boracic acid consisted in burning potassium in contact with it in vacuo4 ,the potassium attracts the oxygen from the acid1 and leaves its basis in a separate state4 ,the recomposition of this acid ,i shall show you1 by burning some of its basis1 which you see here1 in a retort full of oxygen gas4 ,the heat of a candle is all that is required for this combustion4-- ,,emily4 ,the light is astonishingly brilliant1 and what beautiful sparks it throws out6 ,,mrs4 ,b4 ,the result of this combustion is the boracic acid1 the nature of which1 you see1 is proved both by analytic and synthetic means4 ,its basis has not1 it is true1 a metallic appearance2 but it makes very hard alloys with other metals4 ,,emily4 ,but pray1 ,mrs4 ,b41 for what purpose is the boracic acid used in manufactures8 ,,mrs4 ,b4 ,its principal use is in conjunction with soda1 that is1 in the state of borat of soda1 which in the arts is commonly called borax4 ,this salt has a peculiar power of dissolving metallic oxyds1 and of promoting the fusion of substances capable of being melted2 it is accordingly employed in various metallic arts2 it is used1 for example1 to remove the oxyd from the surface of metals1 and is often employed in the assaying of metallic ores4 ,let us now proceed to the ,,fluoric ,,acid4 ,this acid is obtained from a substance which is found frequently in mines1 and particularly in those of ,derbyshire1 called fluor1 a name which it acquired from the circumstance of its being used to render the ores of metals more fluid when heated4 ,,caroline4 ,pray is not this the ,derbyshire spar1 of which so many ornaments are made8 ,,mrs4 ,b4 ,the same2 but though it has long been employed for a variety of purposes1 its nature was unknown until ,scheele1 the great ,swedish chemist1 discovered that it consisted of lime united with a peculiar acid1 which obtained the name of fluoric acid4 ,it is easily separated from the lime by the sulphuric acid1 and unless condensed in water1 ascends in the form of gas4 ,a very peculiar property of this acid is its union with siliceous earths1 which ,i have already mentioned4 ,if the distillation of this acid is performed in glass vessels1 they are corroded1 and the siliceous part of the glass comes over1 united with the gas2 if water is then admitted1 part of the silex is deposited1 as you may observe in this jar4 ,,caroline4 ,i see white flakes forming on the surface of the water2 is that silex8 ,,mrs4 ,b4 ,yes it is4 ,this power of corroding glass has been used for engraving1 or rather etching1 upon it4 ,the glass is first covered with a coat of wax1 through which the figures to be engraved are to be scratched with a pin2 then pouring the fluoric acid over the wax1 it corrodes the glass where the scratches have been made4 ,,caroline4 ,i should like to have a bottle of this acid1 to make engravings4 ,,mrs4 ,b4 ,but you could not have it in a glass bottle1 for in that case the acid would be saturated with silex1 and incapable of executing an engraving2 the same thing would happen were the acid kept in vessels of porcelain or earthen-ware2 this acid must therefore be both prepared and preserved in vessels of silver4 ,if it be distilled from fluor spar and vitriolic acid1 in silver or leaden vessels1 the receiver being kept very cold during the distillation1 it assumes the form of a dense fluid1 and in that state is the most intensely corrosive substance known4 ,this seems to be the acid combined with a little water4 ,it may be called hydro-fluoric acid2 and ,sir ,h4 ,davy has been led1 from some late experiments on the subject1 to consider pure fluoric acid as a compound of a certain unknown principle1 which he calls fluorine1 with hydrogen4 ,sir ,h4 ,davy has also attempted to decompose the fluoric acid by burning potassium in contact with it2 but he has not yet been able by this or any other method1 to obtain its basis in a distinct separate state4 ,we shall conclude our account of the acids with that of the ,,muriatic ,,acid1 which is perhaps the most curious and interesting of all of them4 ,it is found in nature combined with soda1 lime1 and magnesia4 ,muriat of soda is the common sea-salt1 and from this substance the acid is usually disengaged by means of the sulphuric acid4 ,the natural state of the muriatic acid is that of an invisible permanent gas1 at the common temperature of the atmosphere2 but it has a remarkably strong attraction for water1 and assumes the form of a whitish cloud whenever it meets any moisture to combine with4 ,this acid is remarkable for its peculiar and very pungent smell1 and possesses1 in a powerful degree1 most of the acid properties4 ,here is a bottle containing muriatic acid in a liquid state4 ,,caroline4 ,and how is it liquefied8 ,,mrs4 ,b4 ,by impregnating water with it2 its strong attraction for water makes it very easy to obtain it in a liquid form4 ,now1 if ,i open the phial1 you may observe a kind of vapour rising from it1 which is muriatic acid gas1 of itself invisible1 but made apparent by combining with the moisture of the atmosphere4 ,,emily4 ,have you not any of the pure muriatic acid gas8 ,,mrs4 ,b4 ,this jar is full of that acid in its gaseous state--it is inverted over mercury instead of water1 because1 being absorbable by water1 this gas cannot be confined by it4 --,i shall now raise the jar a little on one side1 and suffer some of the gas to escape4 --,you see that it immediately becomes visible in the form of a cloud4 ,,emily4 ,it must be1 no doubt1 from its uniting with the moisture of the atmosphere1 that it is converted into this dewy vapour4 ,,mrs4 ,b4 ,certainly2 and for the same reason1 that is to say1 its extreme eagerness to unite with water1 this gas will cause snow to melt as rapidly as an intense fire4 ,this acid proved much more refractory when ,sir ,h4 ,davy attempted to decompose it than the other two undecompounded acids4 ,it is singular that potassium will burn in muriatic acid1 and be converted into potash1 without decomposing the acid1 and the result of this combustion is a muriat of potash2 for the potash1 as soon as it is regenerated1 combines with the muriatic acid4 ,,caroline4 ,but how can the potash be regenerated if the muriatic acid does not oxydate the potassium8 ,,mrs4 ,b4 ,the potassium1 in this process1 obtains oxygen from the moisture with which the muriatic acid is always combined1 and accordingly hydrogen1 resulting from the decomposition of the moisture1 is invariably evolved4 ,,emily4 ,but why not make these experiments with dry muriatic acid8 ,,mrs4 ,b4 ,dry acids cannot be acted on by the ,voltaic battery1 because acids are non-conductors of electricity1 unless moistened4 ,in the course of a number of experiments which ,sir ,h4 ,davy made upon acids in a state of dryness1 he observed that the presence of water appeared always necessary to develop the acid properties1 so that acids are not even capable of reddening vegetable blues if they have been carefully deprived of moisture4 ,this remarkable circumstance led him to suspect1 that water1 instead of oxygen1 may be the acidifying principle2 but this he threw out rather as a conjecture than as an established point4 ,sir ,h4 ,davy obtained very curious results from burning potassium in a mixture of phosphorus and muriatic acid1 and also of sulphur and muriatic acid2 the latter detonates with great violence4 ,all his experiments1 however1 failed in presenting to his view the basis of the muriatic acid1 of which he was in search2 and he was at last induced to form an opinion respecting the nature of this acid1 which ,i shall presently explain4 ,,emily4 ,is this acid susceptible of different degrees of oxygenation8 ,,mrs4 ,b4 ,yes1 for though we cannot deoxygenate this acid1 yet we may add oxygen to it4 ,,caroline4 ,why1 then1 is not the least degree of oxygenation of the acid called the muriatous1 and the higher degree the muriatic acid8 ,,mrs4 ,b4 ,because1 instead of becoming1 like other acids1 more dense1 and more acid by an addition of oxygen1 it is rendered on the contrary more volatile1 more pungent1 but less acid1 and less absorbable by water4 ,these circumstances1 therefore1 seem to indicate the propriety of making an exception to the nomenclature4 ,the highest degree of oxygenation of this acid has been distinguished by the additional epithet of oxygenated1 or1 for the sake of brevity1 oxy1 so that it is called the oxygenated1 or oxy-muriatic acid4 ,this likewise exists in a gaseous form1 at the temperature of the atmosphere2 it is also susceptible of being absorbed by water1 and can be congealed1 or solidified1 by a certain degree of cold4 ,,emily4 ,and how do you obtain the oxy-muriatic acid8 ,,mrs4 ,b4 ,in various ways2 but it may be most conveniently obtained by distilling liquid muriatic acid over oxyd of manganese1 which supplies the acid with the additional oxygen4 ,one part of the acid being put into a retort1 with two parts of the oxyd of manganese1 and the heat of a lamp applied1 the gas is soon disengaged1 and may be received over water1 as it is but sparingly absorbed by it4 --,i have collected some in this jar-- ,,caroline4 ,it is not invisible1 like the generality of gases2 for it is of a yellowish colour4 ,,mrs4 ,b4 ,the muriatic acid extinguishes flame1 whilst1 on the contrary1 the oxy-muriatic makes the flame larger1 and gives it a dark red colour4 ,can you account for this difference in the two acids8 ,,emily4 ,yes1 ,i think so2 the muriatic acid will not supply the flame with the oxygen necessary for its support2 but when this acid is further oxygenated1 it will part with its additional quantity of oxygen1 and in this way support combustion4 ,,mrs4 ,b4 ,that is exactly the case2 indeed the oxygen added to the muriatic acid1 adheres so slightly to it1 that it is separated by mere exposure to the sun's rays4 ,this acid is decomposed also by combustible bodies1 many of which it burns1 and actually inflames1 without any previous increase of temperature4 ,,caroline4 ,that is extraordinary1 indeed6 ,i hope you mean to indulge us with some of these experiments8 ,,mrs4 ,b4 ,i have prepared several glass jars of oxy-muriatic acid gas for that purpose4 ,in the first we shall introduce some ,dutch gold leaf4 --,do you observe that it takes fire8 ,,emily4 ,yes1 indeed it does--how wonderful it is6 ,it became immediately red hot1 but was soon smothered in a thick vapour4 ,,caroline4 ,what a disagreeable smell6 ,,mrs4 ,b4 ,we shall try the same experiment with phosphorus in another jar of this acid4 --,you had better keep your handkerchief to your nose when ,i open it--now let us drop into it this little piece of phosphorus-- ,,caroline4 ,it burns really2 and almost as brilliantly as in oxygen gas6 ,but1 what is most extraordinary1 these combustions take place without the metal or phosphorus being previously lighted1 or even in the least heated4 ,,mrs4 ,b4 ,all these curious effects are owing to the very great facility with which this acid yields oxygen to such bodies as are strongly disposed to combine with it4 ,it appears extraordinary indeed to see bodies1 and metals in particular1 melted down and inflamed1 by a gas without any increase of temperature1 either of the gas1 or of the combustible4 ,the phenomenon1 however1 is1 you see1 well accounted for4 ,,emily4 ,why did you burn a piece of ,dutch gold leaf rather than a piece of any other metal8 ,,mrs4 ,b4 ,because1 in the first place1 it is a composition of metals 7consisting chiefly of copper7 which burns readily2 and ,i use a thin metallic leaf in preference to a lump of metal1 because it offers to the action of the gas but a small quantity of matter under a large surface4 ,filings1 or shavings1 would answer the purpose nearly as well2 but a lump of metal1 though the surface would oxydate with great rapidity1 would not take fire4 ,pure gold is not inflamed by oxy-muriatic acid gas1 but it is rapidly oxydated1 and dissolved by it2 indeed1 this acid is the only one that will dissolve gold4 ,,emily4 ,this1 ,i suppose1 is what is commonly called aqua regia1 which you know is the only thing that will act upon gold4 ,,mrs4 ,b4 ,that is not exactly the case either2 for aqua regia is composed of a mixture of muriatic acid and nitric acid4 --,but1 in fact1 the result of this mixture is the formation of oxy-muriatic acid1 as the muriatic acid oxygenates itself at the expence of the nitric2 this mixture1 therefore1 though it bears the name of nitro-muriatic acid1 acts on gold merely in virtue of the oxy-muriatic acid which it contains4 ,sulphur1 volatile oils1 and many other substances1 will burn in the same manner in oxy-muriatic acid gas2 but ,i have not prepared a sufficient quantity of it1 to show you the combustion of all these bodies4 ,,caroline4 ,there are several jars of the gas yet remaining4 ,,mrs4 ,b4 ,we must reserve these for future experiments4 ,the oxy-muriatic acid does not1 like other acids1 redden the blue vegetable colours2 but it totally destroys any colour1 and turns all vegetables perfectly white4 ,let us collect some vegetable substances to put into this glass1 which is full of gas4 ,,emily4 ,here is a sprig of myrtle-- ,,caroline4 ,and here some coloured paper-- ,,mrs4 ,b4 ,we shall also put in this piece of scarlet riband1 and a rose-- ,,emily4 ,their colours begin to fade immediately6 ,but how does the gas produce this effect8 ,,mrs4 ,b4 ,the oxygen combines with the colouring matter of these substances1 and destroys it2 that is to say1 destroys the property which these colours had of reflecting only one kind of rays1 and renders them capable of reflecting them all1 which1 you know1 will make them appear white4 ,old prints may be cleaned by this acid1 for the paper will be whitened without injury to the impression1 as printer's ink is made of materials 7oil and lamp black7 which are not acted upon by acids4 ,this property of the oxy-muriatic acid has lately been employed in manufactures in a variety of bleaching processes2 but for these purposes the gas must be dissolved in water1 as the acid is thus rendered much milder and less powerful in its effects2 for1 in a gaseous state1 it would destroy the texture1 as well as the colour of the substance submitted to its action4 ,,caroline4 ,look at the things which we put into the gas2 they have now entirely lost their colour6 ,,mrs4 ,b4 ,the effect of the acid is almost completed2 and1 if we were to examine the quantity that remains1 we should find it to consist chiefly of muriatic acid4 ,the oxy-muriatic acid has been used to purify the air in fever hospitals and prisons1 as it burns and destroys putrid effluvia of every kind4 ,the infection of the small-pox is likewise destroyed by this gas1 and matter that has been submitted to its influence will no longer generate that disorder4 ,,caroline4 ,indeed1 ,i think the remedy must be nearly as bad as the disease2 the oxy-muriatic acid has such a dreadfully suffocating smell4 ,,mrs4 ,b4 ,it is certainly extremely offensive2 but by keeping the mouth shut1 and wetting the nostrils with liquid ammonia1 in order to neutralize the vapour as it reaches the nose1 its prejudicial effects may be in some degree prevented4 ,at any rate1 however1 this mode of disinfection can hardly be used in places that are inhabited4 ,and as the vapour of nitric acid1 which is scarcely less efficacious for this purpose1 is not at all prejudicial1 it is usually preferred on such occasions4 ,,caroline4 ,you have not told us yet what is ,sir ,h4 ,davy's new opinion respecting the nature of muriatic acid1 to which you alluded a few minutes ago8 ,,mrs4 ,b4 ,true2 ,i avoided noticing it then1 because you could not have understood it without some previous knowledge of the oxy-muriatic acid1 which ,i have but just introduced to your acquaintance4 ,sir ,h4 ,davy's idea is that muriatic acid1 instead of being a compound1 consisting of an unknown basis and oxygen1 is formed by the union of oxy-muriatic gas with hydrogen4 ,,emily4 ,have you not told us just now that oxy-muriatic gas was itself a compound of muriatic acid and oxygen8 ,,mrs4 ,b4 ,yes2 but according to ,sir ,h4 ,davy's hypothesis1 oxy-muriatic gas is considered as a simple body1 which contains no oxygen--as a substance of its own kind1 which has a great analogy to oxygen in most of its properties1 though in others it differs entirely from it4 --,according to this view of the subject1 the name of oxy-muriatic acid can no longer be proper1 and therefore ,sir ,h4 ,davy has adopted that of chlorine1 or chlorine gas1 a name which is simply expressive of its greenish colour2 and in compliance with that philosopher's theory1 we have placed chlorine in our table among the simple bodies4 ,,caroline4 ,but what was ,sir ,h4 ,davy's reason for adopting an opinion so contrary to that which had hitherto prevailed8 ,,mrs4 ,b4 ,there are many circumstances which are favourable to the new doctrine2 but the clearest and simplest fact in its support is1 that if hydrogen gas and oxy-muriatic gas be mixed together1 both these gases disappear1 and muriatic acid gas is formed4 ,,emily4 ,that seems to be a complete proof2 is it not considered as perfectly conclusive8 ,,mrs4 ,b4 ,not so decisive as it appears at first sight2 because it is argued by those who still incline to the old doctrine1 that muriatic acid gas1 however dry it may be1 always contains a certain quantity of water1 which is supposed essential to its formation4 ,so that1 in the experiment just mentioned1 this water is supplied by the union of the hydrogen gas with the oxygen of the oxy-muriatic acid2 and therefore the mixture resolves itself into the base of muriatic acid and water1 that is1 muriatic acid gas4 ,,caroline4 ,i think the old theory must be the true one2 for otherwise how could you explain the formation of oxy-muriatic gas1 from a mixture of muriatic acid and oxyd of manganese8 ,,mrs4 ,b4 ,very easily2 you need only suppose that in this process the muriatic acid is decomposed2 its hydrogen unites with the oxygen of the manganese to form water1 and the chlorine appears in its separate state4 ,,emily4 ,but how can you explain the various combustions which take place in oxy-muriatic gas1 if you consider it as containing no oxygen8 ,,mrs4 ,b4 ,we need only suppose that combustion is the result of intense chemical action2 so that chlorine1 like oxygen1 in combining with bodies1 forms compounds which have less capacity for caloric than their constituent principles1 and1 therefore1 caloric is evolved at the moment of their combination4 ,,emily4 ,if1 then1 we may explain every thing by either theory1 to which of the two shall we give the preference8 ,,mrs4 ,b4 ,it will1 perhaps1 be better to wait for more positive proofs1 if such can be obtained1 before we decide positively upon the subject4 ,the new doctrine has certainly gained ground very rapidly1 and may be considered as nearly established2 but several competent judges still refuse their assent to it1 and until that theory is very generally adopted1 it may be as well for us still occasionally to use the language to which chemists have long been accustomed4 --,but let us proceed to the examination of salts formed by muriatic acid4 ,among the compound salts formed by muriatic acid1 the muriat of soda1 or common salt1 is the most interesting499 ,the uses and properties of this salt are too well known to require much comment4 ,besides the pleasant flavour it imparts to the food1 it is very wholesome1 when not used to excess1 as it assists the process of digestion4 ,sea-water is the great source from which muriat of soda is extracted by evaporation4 ,but it is also found in large solid masses in the bowels of the earth1 in ,england1 and in many other parts of the world4 ,footnote 993 ,according to ,sir ,h4 ,davy's views of the nature of the muriatic and oxy-muriatic acids1 dry muriat of soda is a compound of sodium and chlorine1 for it may be formed by the direct combination of oxy-muriatic gas and sodium4 ,in his opinion1 therefore1 what we commonly call muriat of soda contains neither soda nor muriatic acid4 ,,emily4 ,i thought that salts1 when solid1 were always in the state of crystals2 but the common table-salt is in the form of a coarse white powder4 ,,mrs4 ,b4 ,crystallisation depends1 as you may recollect1 on the slow and regular reunion of particles dissolved in a fluid2 common sea-salt is only in a state of imperfect crystallisation1 because the process by which it is prepared is not favourable to the formation of regular crystals4 ,but if you dissolve it1 and afterwards evaporate the water slowly1 you will obtain a regular crystallisation4 ,muriat of ammonia is another combination of this acid1 which we have already mentioned as the principal source from which ammonia is derived4 ,i can at once show you the formation of this salt by the immediate combination of muriatic acid with ammonia4 --,these two glass jars contain1 the one muriatic acid gas1 the other ammoniacal gas1 both of which are perfectly invisible--now1 if ,i mix them together1 you see they immediately form an opake white cloud1 like smoke4 --,if a thermometer was placed in the jar in which these gases are mixed1 you would perceive that some heat is at the same time produced4 ,,emily4 ,the effects of chemical combinations are1 indeed1 wonderful6 --,how extraordinary it is that two invisible bodies should become visible by their union6 ,,mrs4 ,b4 ,this strikes you with astonishment1 because it is a phenomenon which nature seldom exhibits to our view2 but the most common of her operations are as wonderful1 and it is their frequency only that prevents our regarding them with equal admiration4 ,what would be more surprising1 for instance1 than combustion1 were it not rendered so familiar by custom8 ,,emily4 ,that is true4 --,but pray1 ,mrs4 ,b41 is this white cloud the salt that produces ammonia8 ,how different it is from the solid muriat of ammonia which you once showed us6 ,,mrs4 ,b4 ,it is the same substance which first appears in the state of vapour1 but will soon be condensed by cooling against the sides of the jar1 in the form of very minute crystals4 ,we may now proceed to the oxy-muriats4 ,in this class of salts the oxy-muriat of potash is the most worthy of our attention1 for its striking properties4 ,the acid1 in this state of combination1 contains a still greater proportion of oxygen than when alone4 ,,caroline4 ,but how can the oxy-muriatic acid acquire an increase of oxygen by combining with potash8 ,,mrs4 ,b4 ,it does not really acquire an additional quantity of oxygen1 but it loses some of the muriatic acid1 which produces the same effect1 as the acid which remains is proportionably super-oxygenated499 ,if this salt be mixed1 and merely rubbed together with sulphur1 phosphorus1 charcoal1 or indeed any other combustible1 it explodes strongly4 ,footnote 993 ,according to ,sir ,h4 ,davy's new views1 just explained1 oxy-muriat of potash is a compound of chlorine with oxyd of potassium4 ,,caroline4 ,like gun-powder1 ,i suppose1 it is suddenly converted into elastic fluids8 ,,mrs4 ,b4 ,yes2 but with this remarkable difference1 that no increase of temperature1 any further than is produced by gentle friction1 is required in this instance4 ,can you tell me what gases are generated by the detonation of this salt with charcoal8 ,,emily4 ,let me consider 4 4 4 4 4 ,the oxy-muriatic acid parts with its excess of oxygen to the charcoal1 by which means it is converted into muriatic acid gas2 whilst the charcoal1 being burnt by the oxygen1 is changed to carbonic acid gas4 --,what becomes of the potash ,i cannot tell4 ,,mrs4 ,b4 ,that is a fixed product which remains in the vessel4 ,,caroline4 ,but since the potash does not enter into the new combinations1 ,i do not understand of what use it is in this operation4 ,would not the oxy-muriatic acid and the charcoal produce the same effect without it8 ,,mrs4 ,b4 ,no2 because there would not be that very great concentration of oxygen which the combination with the potash produces1 as ,i have just explained4 ,i mean to show you this experiment1 but ,i would advise you not to repeat it alone2 for if care be not taken to mix only very small quantities at a time1 the detonation will be extremely violent1 and may be attended with dangerous effects4 ,you see ,i mix an exceedingly small quantity of the salt with a little powdered charcoal1 in this ,wedgwood mortar1 and rub them together with the pestle-- ,,caroline4 ,heavens6 ,how can such a loud explosion be produced by so small a quantity of matter8 ,,mrs4 ,b4 ,you must consider that an extremely small quantity of solid substance may produce a very great volume of gases2 and it is the sudden evolution of these which occasions the sound4 ,,emily4 ,would not oxy-muriat of potash make stronger gunpowder than nitrat of potash8 ,,mrs4 ,b4 ,yes2 but the preparation1 as well as the use of this salt1 is attended with so much danger1 that it is never employed for that purpose4 ,,caroline4 ,there is no cause to regret it1 ,i think2 for the common gunpowder is quite sufficiently destructive4 ,,mrs4 ,b4 ,i can show you a very curious experiment with this salt2 but it must again be on condition that you will never attempt to repeat it by yourselves4 ,i throw a small piece of phosphorus into this glass of water2 then a little oxy-muriat of potash2 and1 lastly1 ,i pour in 7by means of this funnel1 so as to bring it in contact with the two other ingredients at the bottom of the glass7 a small quantity of sulphuric acid-- ,,caroline4 ,this is1 indeed1 a beautiful experiment6 ,the phosphorus takes fire and burns from the bottom of the water4 ,,emily4 ,how wonderful it is to see flame bursting out under water1 and rising through it6 ,pray1 how is this accounted for8 ,,mrs4 ,b4 ,cannot you find it out1 ,caroline8 ,,emily4 ,stop--,i think ,i can explain it4 ,is it not because the sulphuric acid decomposes the salt by combining with the potash1 so as to liberate the oxy-muriatic acid gas by which the phosphoric is set on fire8 ,,mrs4 ,b4 ,very well1 ,emily2 and with a little more reflection you would have discovered another concurring circumstance1 which is1 that an increase of temperature is produced by the mixture of the sulphuric acid and water1 which assists in promoting the combustion of the phosphorus4 ,i must1 before we part1 introduce to your acquaintance the newly-discovered substance ,,iodine1 which you may recollect we placed next to oxygen and chlorine in our table of simple bodies4 ,,caroline4 ,is this also a body capable of maintaining combustion like oxygen and chlorine8 ,,mrs4 ,b4 ,it is2 and although it does not so generally disengage light and heat from inflammable bodies1 as oxygen and chlorine do1 yet it is capable of combining with most of them2 and sometimes1 as in the instance of potassium and phosphorus1 the combination is attended with an actual appearance of light and heat4 ,,caroline4 ,but what sort of a substance is iodine3 what is its form1 and colour8 ,,mrs4 ,b4 ,it is a very singular body1 in many respects4 ,at the ordinary temperature of the atmosphere1 it commonly appears in the form of blueish black crystalline scales1 such as you see in this tube4 ,,caroline4 ,they shine like black lead1 and some of the scales have the shape of lozenges4 ,,mrs4 ,b4 ,that is actually the form which the crystals of iodine often assume4 ,but if we heat them gently1 by holding the tube over the flame of a candle1 see what a change takes place in them4 ,,caroline4 ,how curious6 ,they seem to melt1 and the tube immediately fills with a beautiful violet vapour4 ,but look1 ,mrs4 ,b41 the same scales are now appearing at the other end of the tube4 ,,mrs4 ,b4 ,this is in fact a sublimation of iodine1 from one part of the tube to another2 but with this remarkable peculiarity1 that1 while in the gaseous state1 iodine assumes that bright violet colour1 which1 as you may already perceive1 it loses as the tube cools1 and the substance resumes its usual solid form4 --,it is from the violet colour of the gas that iodine has obtained its name4 ,,caroline4 ,but how is this curious substance obtained8 ,,mrs4 ,b4 ,it is found in the ley of ashes of sea-weeds1 after the soda has been separated by crystallisation2 and it is disengaged by means of sulphuric acid1 which expels it from the alkaline ley in the form of a violet gas1 which may be collected and condensed in the way you have just seen4 --,this interesting discovery was made in the year #ahab1 by ,m4 ,courtois1 a manufacturer of saltpetre at ,paris4 ,,caroline4 ,and pray1 ,mrs4 ,b41 what is the proof of iodine being a simple body8 ,,mrs4 ,b4 ,it is considered as a simple body1 both because it is not capable of being resolved into other ingredients2 and because it is itself capable of combining with other bodies1 in a manner analogous to oxygen and chlorine4 ,the most curious of these combinations is that which it forms with hydrogen gas1 the result of which is a peculiar gaseous acid4 ,,caroline4 ,just as chlorine and hydrogen gas form muriatic acid8 ,in this respect chlorine and iodine seem to bear a strong analogy to each other4 ,,mrs4 ,b4 ,that is indeed the case2 so that if the theory of the constitution of either of these two bodies be true1 it must be true also in regard to the other2 if erroneous in the one1 the theory must fall in both4 ,but it is now time to conclude2 we have examined such of the acids and salts as ,i conceived would appear to you most interesting4 --,i shall not enter into any particulars respecting the metallic acids1 as they offer nothing sufficiently striking for our present purpose4 ,,conversation ,,xx4 ,,on ,,the ,,nature ,,and ,,composition ,,of ,,vegetables4 ,,mrs4 ,b4 ,we have hitherto treated only of the simplest combinations of elements1 such as alkalies1 earths1 acids1 compound salts1 stones1 c42 all of which belong to the mineral kingdom4 ,it is time now to turn our attention to a more complicated class of compounds1 that of ,,organised ,,bodies1 which will furnish us with a new source of instruction and amusement4 ,,emily4 ,by organised bodies1 ,i suppose1 you mean the vegetable and animal creation8 ,i have1 however1 but a very vague idea of the word organisation1 and ,i have often wished to know more precisely what it means4 ,,mrs4 ,b4 ,organised bodies are such as are endowed by nature with various parts1 peculiarly constructed and adapted to perform certain functions connected with life4 ,thus you may observe1 that mineral compounds are formed by the simple effect of mechanical or chemical attraction1 and may appear to some to be in a great measure the productions of chance2 whilst organised bodies bear the most striking and impressive marks of design1 and are eminently distinguished by that unknown principle1 called life1 from which the various organs derive the power of exercising their respective functions4 ,,caroline4 ,but in what manner does life enable these organs to perform their several functions8 ,,mrs4 ,b4 ,that is a mystery which1 ,i fear1 is enveloped in such profound darkness that there is very little hope of our ever being able to unfold it4 ,we must content ourselves with examining the effects of this principle2 as for the cause1 we have been able only to give it a name1 without attaching any other meaning to it than the vague and unsatisfactory idea of au unknown agent4 ,,caroline4 ,and yet ,i think ,i can form a very clear idea of life4 ,,mrs4 ,b4 ,pray let me hear how you would define it8 ,,caroline4 ,it is perhaps more easy to conceive than to express--let me consider-- ,is not life the power which enables both the animal and the vegetable creation to perform the various functions which nature has assigned to them8 ,,mrs4 ,b4 ,i have nothing to object to your definition2 but you will allow me to observe1 that you have only mentioned the effects which the unknown cause produces1 without giving us any notion of the cause itself4 ,,emily4 ,yes1 ,caroline1 you have told us what life does1 but you have not told us what it is4 ,,mrs4 ,b4 ,we may study its operations1 but we should puzzle ourselves to no purpose by attempting to form an idea of its real nature4 ,we shall begin with examining its effects in the vegetable world1 which constitutes the simplest class of organised bodies2 these we shall find distinguished from the mineral creation1 not only by their more complicated nature1 but by the power which they possess within themselves1 of forming new chemical arrangements of their constituent parts1 by means of appropriate organs4 ,thus1 though all vegetables are ultimately composed of hydrogen1 carbon1 and oxygen1 7with a few other occasional ingredients17 they separate and combine these principles by their various organs1 in a thousand ways1 and form1 with them1 different kinds of juices and solid parts1 which exist ready made in vegetables1 and may1 therefore1 be considered as their immediate materials4 ,these are3 ,sap1 ,mucilage1 ,sugar1 ,fecula1 ,gluten1 ,fixed ,oil1 ,volatile ,oil1 ,camphor1 ,resins1 ,gum ,resins1 ,balsams1 ,caoutchouc1 ,extractive colouring ,matter1 ,tannin1 ,woody ,fibre1 ,vegetable ,acids1 c4 ,,caroline4 ,what a long list of names6 ,i did not suppose that a vegetable was composed of half so many ingredients4 ,,mrs4 ,b4 ,you must not imagine that every one of these materials is formed in each individual plant4 ,i only mean to say1 that they are all derived exclusively from the vegetable kingdom4 ,,emily4 ,but does each particular part of the plant1 such as the root1 the bark1 the stem1 the seeds1 the leaves1 consist of one of these ingredients only1 or of several of them combined together8 ,,mrs4 ,b4 ,i believe there is no part of a plant which can be said to consist solely of any one particular ingredient2 a certain number of vegetable materials must always be combined for the formation of any particular part1 7of a seed for instance17 and these combinations are carried on by sets of vessels1 or minute organs1 which select from other parts1 and bring together1 the several principles required for the development and growth of those particular parts which they are intended to form and to maintain4 ,,emily4 ,and are not these combinations always regulated by the laws of chemical attraction8 ,,mrs4 ,b4 ,no doubt2 the organs of plants cannot force principles to combine that have no attraction for each other2 nor can they compel superior attractions to yield to those of inferior power2 they probably act rather mechanically1 by bringing into contact such principles1 and in such proportions1 as will1 by their chemical combination1 form the various vegetable products4 ,,caroline4 ,we may then consider each of these organs as a curiously constructed apparatus1 adapted for the performance of a variety of chemical processes4 ,,mrs4 ,b4 ,exactly so4 ,as long as the plant lives and thrives1 the carbon1 hydrogen1 and oxygen1 7the chief constituents of its immediate materials17 are so balanced and connected together1 that they are not susceptible of entering into other combinations2 but no sooner does death take place1 than this state of equilibrium is destroyed1 and new combinations produced4 ,,emily4 ,but why should death destroy it2 for these principles must remain in the same proportions1 and consequently1 ,i should suppose1 in the same order of attractions8 ,,mrs4 ,b4 ,you must remember1 that in the vegetable1 as well as in the animal kingdom1 it is by the principle of life that the organs are enabled to act2 when deprived of that agent or stimulus1 their power ceases1 and an order of attractions succeeds similar to that which would take place in mineral or unorganised matter4 ,,emily4 ,it is this new order of attractions1 ,i suppose1 that destroys the organisation of the plant after death2 for if the same combinations still continued to prevail1 the plant would always remain in the state in which it died8 ,,mrs4 ,b4 ,and that1 you know1 is never the case2 plants may be partially preserved for some time after death1 by drying2 but in the natural course of events they all return to the state of simple elements2 a wise and admirable dispensation of ,providence1 by which dead plants are rendered fit to enrich the soil1 and become subservient to the nourishment of living vegetables4 ,,caroline4 ,but we are talking of the dissolution of plants1 before we have examined them in their living state4 ,,mrs4 ,b4 ,that is true1 my dear4 ,but ,i wished to give you a general idea of the nature of vegetation1 before we entered into particulars4 ,besides1 it is not so irrelevant as you suppose to talk of vegetables in their dead state1 since we cannot analyse them without destroying life2 and it is only by hastening to submit them to examination1 immediately after they have ceased to live1 that we can anticipate their natural decomposition4 ,there are two kinds of analysis of which vegetables are susceptible2 first1 that which separates them into their immediate materials1 such as sap1 resin1 mucilage1 c42 secondly1 that which decomposes them into their primitive elements1 as carbon1 hydrogen1 and oxygen4 ,,emily4 ,is there not a third kind of analysis of plants1 which consists in separating their various parts1 as the stem1 the leaves1 and the several organs of the flower8 ,,mrs4 ,b4 ,that1 my dear1 is rather the department of the botanist2 we shall consider these different parts of plants only1 as the organs by which the various secretions or separations are performed2 but we must first examine the nature of these secretions4 ,the sap is the principal material of vegetables1 since it contains the ingredients that nourish every part of the plant4 ,the basis of this juice1 which the roots suck up from the soil1 is water2 this holds in solution the various other ingredients required by the several parts of the plant1 which are gradually secreted from the sap by the different organs appropriated to that purpose1 as it passes them in circulating through the plant4 ,mucus1 or mucilage1 is a vegetable substance1 which1 like all the others1 is secreted from the sap2 when in excess1 it exudes from trees in the form of gum4 ,,caroline4 ,is that the gum so frequently used instead of paste or glue8 ,,mrs4 ,b4 ,it is2 almost all fruit-trees yield some sort of gum1 but that most commonly used in the arts is obtained from a species of acacia-tree in ,arabia1 and is called gum arabic2 it forms the chief nourishment of the natives of those parts1 who obtain it in great quantities from incisions which they make in the trees4 ,,caroline4 ,i did not know that gum was eatable4 ,,mrs4 ,b4 ,there is an account of a whole ship's company being saved from starving by feeding on the cargo1 which was gum senegal4 ,i should not1 however1 imagine1 that it would be either a pleasant or a particularly eligible diet to those who have not1 from their birth1 been accustomed to it4 ,it is1 however1 frequently taken medicinally1 and considered as very nourishing4 ,several kinds of vegetable acids may be obtained1 by particular processes1 from gum or mucilage1 the principal of which is called the mucous acid4 ,sugar is not found in its simple state in plants1 but is always mixed with gum1 sap1 or other ingredients2 this saccharine matter is to be met with in every vegetable1 but abounds most in roots1 fruits1 and particularly in the sugar-cane4 ,,emily4 ,if all vegetables contain sugar1 why is it extracted exclusively from the sugar-cane8 ,,mrs4 ,b4 ,because it is both most abundant in that plant1 and most easily obtained from it4 ,besides1 the sugars produced by other vegetables differ a little in their nature4 ,during the late troubles in the ,west-,indies1 when ,europe was but imperfectly supplied with sugar1 several attempts were made to extract it from other vegetables1 and very good sugar was obtained from parsnips and from carrots2 but the process was too expensive to carry this enterprize to any extent4 ,,caroline4 ,i should think that sugar might be more easily obtained from sweet fruits1 such as figs1 dates1 c4 ,,mrs4 ,b4 ,probably2 but it would be still more expensive1 from the high price of those fruits4 ,,emily4 ,pray1 in what manner is sugar obtained from the sugar-cane8 ,,mrs4 ,b4 ,the juice of this plant is first expressed by passing it between two cylinders of iron4 ,it is then boiled with lime-water1 which makes a thick scum rise to the surface4 ,the clarified liquor is let off below and evaporated to a very small quantity1 after which it is suffered to crystallise by standing in a vessel1 the bottom of which is perforated with holes1 that are imperfectly stopped1 in order that the syrup may drain off4 ,the sugar obtained by this process is a coarse brown powder1 commonly called raw or moist sugar2 it undergoes another operation to be refined and converted into loaf sugar4 ,for this purpose it is dissolved in water1 and afterwards purified by an animal fluid called albumen4 ,white of eggs chiefly consist of this fluid1 which is also one of the constituent parts of blood2 and consequently eggs1 or bullocks' blood1 are commonly used for this purpose4 ,the albuminous fluid being diffused through the syrup1 combines with all the solid impurities contained in it1 and rises with them to the surface1 where it forms a thick scum2 the clear liquor is then again evaporated to a proper consistence1 and poured into moulds1 in which1 by a confused crystallisation1 it forms loaf-sugar4 ,but an additional process is required to whiten it2 to this effect the mould is inverted1 and its open base is covered with clay1 through which water is made to pass2 the water slowly trickling through the sugar1 combines with and carries off the colouring matter4 ,,caroline4 ,i am very glad to hear that the blood that is used to purify sugar does not remain in it2 it would be a disgusting idea4 ,i have heard of some improvements by the late ,mr4 ,howard1 in the process of refining sugar4 ,pray what are they8 ,,mrs4 ,b4 ,it would be much too long to give you an account of the process in detail4 ,but the principal improvement relates to the mode of evaporating the syrup1 in order to bring it to the consistency of sugar4 ,instead of boiling the syrup in a large copper1 over a strong fire1 ,mr4 ,howard carries off the water by means of a large air-pump1 in a way similar to that used in ,mr4 ,leslie's experiment for freezing water by evaporation2 that is1 the syrup being exposed to a vacuum1 the water evaporates quickly1 with no greater heat than that of a little steam1 which is introduced round the boiler4 ,the air-pump is of course of large dimensions1 and is worked by a steam engine4 ,a great saving is thus obtained1 and a striking instance afforded of the power of science in suggesting useful economical improvements4 ,,emily4 ,and pray how is sugar-candy and barley-sugar prepared8 ,,mrs4 ,b4 ,candied sugar is nothing more than the regular crystals1 obtained by slow evaporation from a solution of sugar4 ,barley-sugar is sugar melted by heat1 and afterwards cooled in moulds of a spiral form4 ,sugar may be decomposed by a red heat1 and1 like all other vegetable substances1 resolved into carbonic acid and hydrogen4 ,the formation and the decomposition of sugar afford many very interesting particulars1 which we shall fully examine1 after having gone through the other materials of vegetables4 ,we shall find that there is reason to suppose that sugar is not1 like the other materials1 secreted from the sap by appropriate organs2 but that it is formed by a peculiar process with which you are not yet acquainted4 ,,caroline4 ,pray1 is not honey of the same nature as sugar8 ,,mrs4 ,b4 ,honey is a mixture of saccharine matter and gum4 ,,emily4 ,i thought that honey was in some measure an animal substance1 as it is prepared by the bees4 ,,mrs4 ,b4 ,it is rather collected by them from flowers1 and conveyed to their store-houses1 the hives4 ,it is the wax only that undergoes a real alteration in the body of the bee1 and is thence converted into an animal substance4 ,manna is another kind of sugar1 which is united with a nauseous extractive matter1 to which it owes its peculiar taste and colour4 ,it exudes like gum from various trees in hot climates1 some of which have their leaves glazed by it4 ,the next of the vegetable materials is fecula2 this is the general name given to the farinaceous substance contained in all seeds1 and in some roots1 as the potatoe1 parsnip1 c4 ,it is intended by nature for the first aliment of the young vegetable2 but that of one particular grain is become a favourite and most common food of a large part of mankind4 ,,emily4 ,you allude1 ,i suppose1 to bread1 which is made of wheat-flower8 ,,mrs4 ,b4 ,yes4 ,the fecula of wheat contains also another vegetable substance which seems peculiar to that seed1 or at least has not as yet been obtained from any other4 ,this is gluten1 which is of a sticky1 ropy1 elastic nature2 and it is supposed to be owing to the viscous qualities of this substance1 that wheat-flour forms a much better paste than any other4 ,,emily4 ,gluten1 by your description1 must be very like gum8 ,,mrs4 ,b4 ,in their sticky nature they certainly have some resemblance2 but gluten is essentially different from gum in other points1 and especially in its being insoluble in water1 whilst gum1 you know1 is extremely soluble4 ,the oils contained in vegetables all consist of hydrogen and carbon in various proportions4 ,they are of two kinds1 fixed and volatile1 both of which we formerly mentioned4 ,do you remember in what the difference between fixed and volatile oil consists8 ,,emily4 ,if ,i recollect rightly1 the former are decomposed by heat1 whilst the latter are merely volatilised by it4 ,,mrs4 ,b4 ,very well4 ,fixed oil is contained only in the seeds of plants1 excepting in the olive1 in which it is produced in1 and expressed from1 the fruit4 ,we have already observed that seeds contain also fecula2 these two substances1 united with a little mucilage1 form the white substance contained in the seeds or kernels of plants1 and is destined for the nourishment of the young plant1 to which the seed gives birth4 ,the milk of almonds1 which is expressed from the seed of that name1 is composed of these three substances4 ,,emily4 ,pray1 of what nature is the linseed oil which is used in painting8 ,,mrs4 ,b4 ,it is a fixed oil1 obtained from the seed of flax4 ,nut oil1 which is frequently used for the same purpose1 is expressed from walnuts4 ,olive oil is that which is best adapted to culinary purposes4 ,,caroline4 ,and what are the oils used for burning8 ,,mrs4 ,b4 ,animal oils most commonly2 but the preference given to them is owing to their being less expensive2 for vegetable oils burn equally well1 and are more pleasant1 as their smell is not offensive4 ,,emily4 ,since oil is so good a combustible1 what is the reason that lamps so frequently require trimming8 ,,mrs4 ,b4 ,this sometimes proceeds from the construction of the lamp1 which may not be sufficiently favourable to a perfect combustion2 but there is certainly a defect in the nature of oil itself1 which renders it necessary for the best-constructed lamps to be occasionally trimmed4 ,this defect arises from a portion of mucilage which it is extremely difficult to separate from the oil1 and which being a bad combustible1 gathers round the wick1 and thus impedes its combustion1 and consequently dims the light4 ,,caroline4 ,but will not oils burn without a wick8 ,,mrs4 ,b4 ,not unless their temperature be elevated to five or six hundred degrees2 the wick answers this purpose1 as ,i think ,i once before explained to you4 ,the oil rises between the fibres of the cotton by capillary attraction1 and the heat of the burning wick volatilises it1 and brings it successively to the temperature at which it is combustible4 ,,emily4 ,i suppose the explanation which you have given with regard to the necessity of trimming lamps1 applies also to candles1 which so often require snuffing8 ,,mrs4 ,b4 ,i believe it does2 at least1 in some degree4 ,but besides the circumstance just explained1 the common sorts of oils are not very highly combustible1 so that the heat produced by a candle1 which is a coarse kind of animal oil1 being insufficient to volatilise them completely1 a quantity of soot is gradually deposited on the wick1 which dims the light1 and retards the combustion4 ,,caroline4 ,wax candles then contain no incombustible matter1 since they do not require snuffing8 ,,mrs4 ,b4 ,wax is a much better combustible than tallow1 but still not perfectly so1 since it likewise contains some particles that are unfit for burning2 but when these gather round the wick1 7which in a wax light is comparatively small17 they weigh it down on one side1 and fall off together with the burnt part of the wick4 ,,caroline4 ,as oils are such good combustibles1 ,i wonder that they should require so great an elevation of temperature before they begin to burn8 ,,mrs4 ,b4 ,though fixed oils will not enter into actual combustion below the temperature of about four hundred degrees1 yet they will slowly absorb oxygen at the common temperature of the atmosphere4 ,hence arises a variety of changes in oils which modify their properties and uses in the arts4 ,if oil simply absorbs1 and combines with oxygen1 it thickens and changes to a kind of wax4 ,this change is observed to take place on the external parts of certain vegetables1 even during their life4 ,but it happens in many instances that the oil does not retain all the oxygen which it attracts1 but that part of it combines with1 or burns1 the hydrogen of the oil1 thus forming a quantity of water1 which gradually goes off by evaporation4 ,in this case the alteration of the oil consists not only in the addition of a certain quantity of oxygen1 but in the diminution of the hydrogen4 ,these oils are distinguished by the name of drying oils4 ,linseed1 poppy1 and nut-oils1 are of this description4 ,,emily4 ,i am well acquainted with drying oils1 as ,i continually use them in painting4 ,but ,i do not understand why the acquisition of oxygen on one hand1 and a loss of hydrogen on the other1 should render them drying8 ,,mrs4 ,b4 ,this1 ,i conceive1 may arise from two reasons2 either from the oxygen which is added being less favourable to the state of fluidity than the hydrogen1 which is subtracted2 or from this additional quantity of oxygen giving rise to new combinations1 in consequence of which the most fluid parts of the oil are liberated and volatilised4 ,for the purpose of painting1 the drying quality of oil is further increased by adding a quantity of oxyd of lead to it1 by which means it is more rapidly oxygenated4 ,the rancidity of oil is likewise owing to their oxygenation4 ,in this case a new order of attraction takes place1 from which a peculiar acid is formed1 called the sebacic acid4 ,,caroline4 ,since the nature and composition of oil is so well known1 pray could not oil be actually made1 by combining its principles8 ,,mrs4 ,b4 ,that is by no means a necessary consequence2 for there are innumerable varieties of compound bodies which we can decompose1 although we are unable to reunite their ingredients4 ,this1 however1 is not the case with oil1 as it has very lately been discovered1 that it is possible to form oil1 by a peculiar process1 from the action of oxygenated muriatic acid gas on hydro-carbonate4 ,we now pass to the volatile or essential oils4 ,these form the basis of all the vegetable perfumes1 and are contained1 more or less1 in every part of the plant excepting the seed2 they are1 at least1 never found in that part of the seed which contains the embrio plant4 ,,emily4 ,the smell of flowers1 then1 proceeds from volatile oil8 ,,mrs4 ,b4 ,certainly2 but this oil is often most abundant in the rind of fruits1 as in oranges1 lemons1 c4 from which it may be extracted by the slightest pressure2 it is found also in the leaves of plants1 and even in the wood4 ,,caroline4 ,is it not very plentiful in the leaves of mint1 and of thyme1 and all the sweet-smelling herbs8 ,,mrs4 ,b4 ,yes1 remarkably so2 and in geranium leaves also1 which have a much more powerful odour than the flowers4 ,the perfume of sandal fans is an instance of its existence in wood4 ,in short1 all vegetable odours or perfumes are produced by the evaporation of particles of these volatile oils4 ,,emily4 ,they are1 ,i suppose1 very light1 and of very thin consistence1 since they are so volatile8 ,,mrs4 ,b4 ,they vary very much in this respect1 some of them being as thick as butter1 whilst others are as fluid as water4 ,in order to be prepared for perfumes1 or essences1 these oils are first properly purified1 and then either distilled with spirit of wine1 as in the case with lavender water1 or simply mixed with a large proportion of water1 as is often done with regard to peppermint4 ,frequently1 also1 these odoriferous waters are prepared merely by soaking the plants in water1 and distilling4 ,the water then comes over impregnated with the volatile oil4 ,,caroline4 ,such waters are frequently used to take spots of grease out of cloth1 or silk2 how do they produce that effect8 ,,mrs4 ,b4 ,by combining with the substance that forms these stains2 for volatile oils1 and likewise the spirit in which they are distilled1 will dissolve wax1 tallow1 spermaceti1 and resins2 if1 therefore1 the spot proceeds from any of these substances1 it will remove it4 ,insects of every kind have a great aversion to perfumes1 so that volatile oils are employed with success in museums for the preservation of stuffed birds and other species of animals4 ,,caroline4 ,pray does not the powerful smell of camphor proceed from a volatile oil8 ,,mrs4 ,b4 ,camphor seems to be a substance of its own kind1 remarkable by many peculiarities4 ,but if not exactly of the same nature as volatile oil1 it is at least very analogous to it4 ,it is obtained chiefly from the camphor-tree1 a species of laurel which grows in ,china1 and in the ,indian isles1 from the stem and roots of which it is extracted4 ,small quantities have also been distilled from thyme1 sage1 and other aromatic plants2 and it is deposited in pretty large quantities by some volatile oils after long standing4 ,it is extremely volatile and inflammable4 ,it is insoluble in water1 but is soluble in oils1 in which state1 as well as in its solid form1 it is frequently applied to medicinal purposes4 ,amongst the particular properties of camphor1 there is one too singular to be passed over in silence4 ,if you take a small piece of camphor1 and place it on the surface of a bason of pure water1 it will immediately begin to move round and round with great rapidity2 but if you pour into the bason a single drop of any odoriferous fluid1 it will instantly put a stop to this motion4 ,you can at any time try this very simple experiment2 but you must not expect that ,i shall be able to account for this phenomenon1 as nothing satisfactory has yet been advanced for its explanation4 ,,caroline4 ,it is very singular indeed2 and ,i will certainly try the experiment4 ,pray what are resins1 which you just now mentioned8 ,,mrs4 ,b4 ,they are volatile oils1 that have been acted on1 and peculiarly modified1 by oxygen4 ,,caroline4 ,they are1 therefore1 oxygenated volatile oils8 ,,mrs4 ,b4 ,not exactly2 for the process does not appear to consist so much in the oxygenation of the oil1 as in the combustion of a portion of its hydrogen1 and a small portion of its carbon4 ,for when resins are artificially made by the combination of volatile oils with oxygen1 the vessel in which the process is performed is bedewed with water1 and the air included within is loaded with carbonic acid4 ,,emily4 ,this process must be1 in some respects1 similar to that for preparing drying oils8 ,,mrs4 ,b4 ,yes2 and it is by this operation that both of them acquire a greater degree of consistence4 ,pitch1 tar1 and turpentine1 are the most common resins2 they exude from the pine and fir trees4 ,copal1 mastic1 and frankincense1 are also of this class of vegetable substances4 ,,emily4 ,is it of these resins that the mastic and copal varnishes1 so much used in painting1 are made8 ,,mrs4 ,b4 ,yes4 ,dissolved either in oil1 or in alcohol1 resins form varnishes4 ,from these solutions they may be precipitated by water1 in which they are insoluble4 ,this ,i can easily show you4 --,if you will pour some water into this glass of mastic varnish1 it will combine with the alcohol in which the resin is dissolved1 and the latter will be precipitated in the form of a white cloud-- ,,emily4 ,it is so4 ,and yet how is it that pictures or drawings1 varnished with this solution1 may safely be washed with water8 ,,mrs4 ,b4 ,as the varnish dries1 the alcohol evaporates1 and the dry varnish or resin which remains1 not being soluble in water1 will not be acted on by it4 ,there is a class of compound resins called gum-resins1 which are precisely what their name denotes1 that is to say1 resins combined with mucilage4 ,myrrh and assaftida are of this description4 ,,caroline4 ,is it possible that a substance of so disagreeable a smell as assaftida can be formed from a volatile oil8 ,,mrs4 ,b4 ,the odour of volatile oils is by no means always grateful4 ,onions and garlic derive their smell from volatile oils1 as well as roses and lavender4 ,there is still another form under which volatile oils present themselves1 which is that of balsams4 ,these consist of resinous juices combined with a peculiar acid1 called the benzoic acid4 ,balsams appear to have been originally volatile oils1 the oxygenation of which has converted one part into a resin1 and the other part into an acid1 which1 combined together1 form a balsam2 such are the balsams of ,peru1 ,tolu1 c4 ,we shall now take leave of the oils and their various modifications1 and proceed to the next vegetable substance1 which is caoutchouc4 ,this is a white milky glutinous fluid1 which acquires consistence1 and blackens in drying1 in which state it forms the substance with which you are so well acquainted1 under the name of gum-elastic4 ,,caroline4 ,i am surprised to hear that gum-elastic was ever white1 or ever fluid6 ,and from what vegetable is it procured8 ,,mrs4 ,b4 ,it is obtained from two or three different species of trees1 in the ,east-,indies1 and ,south-,america1 by making incisions in the stem4 ,the juice is collected as it trickles from these incisions1 and moulds of clay1 in the form of little bottles of gum-elastic1 are dipped into it4 ,a layer of this juice adheres to the clay and dries on it2 and several layers are successively added by repeating this till the bottle is of sufficient thickness4 ,it is then beaten to break down the clay1 which is easily shaken out4 ,the natives of the countries where this substance is produced sometimes make shoes and boots of it by a similar process1 and they are said to be extremely pleasant and serviceable1 both from their elasticity1 and their being water-proof4 ,the substance which comes next in our enumeration of the immediate ingredients of vegetables1 is extractive matter4 ,this is a term1 which1 in a general sense1 may be applied to any substance extracted from vegetables2 but it is more particularly understood to relate to the extractive colouring matter of plants4 ,a great variety of colours are prepared from the vegetable kingdom1 both for the purposes of painting and of dying2 all the colours called lakes are of this description2 but they are less durable than mineral colours1 for1 by long exposure to the atmosphere1 they either darken or turn yellow4 ,,emily4 ,i know that in painting1 the lakes are reckoned far less durable colours than the ochres2 but what is the reason of it8 ,,mrs4 ,b4 ,the change which takes place in vegetable colours is owing chiefly to the oxygen of the atmosphere slowly burning their hydrogen1 and leaving1 in some measure1 the blackness of the carbon exposed4 ,such change cannot take place in ochre1 which is altogether a mineral substance4 ,vegetable colours have a stronger affinity for animal than for vegetable substances1 and this is supposed to be owing to a small quantity of nitrogen which they contain4 ,thus1 silk and worsted will take a much finer vegetable dye than linen and cotton4 ,,caroline4 ,dying1 then1 is quite a chemical process8 ,,mrs4 ,b4 ,undoubtedly4 ,the condition required to form a good dye is1 that the colouring matter should be precipitated1 or fixed1 on the substance to be dyed1 and should form a compound not soluble in the liquids to which it will probably be exposed4 ,thus1 for instance1 printed or dyed linens or cottons must be able to resist the action of soap and water1 to which they must necessarily be subject in washing2 and woollens and silks should withstand the action of grease and acids1 to which they may accidentally be exposed4 ,,caroline4 ,but if linen and cotton have not a sufficient affinity for colouring matter1 how are they made to resist the action of washing1 which they always do when they are well printed8 ,,mrs4 ,b4 ,when the substance to be dyed has either no affinity for the colouring matter1 or not sufficient power to retain it1 the combination is effected1 or strengthened1 by the intervention of a third substance1 called a mordant1 or basis4 ,the mordant must have a strong affinity both for the colouring matter and the substance to be dyed1 by which means it causes them to combine and adhere together4 ,,caroline4 ,and what are the substances that perform the office of thus reconciling the two adverse parties8 ,,mrs4 ,b4 ,the most common mordant is sulphat of alumine1 or alum4 ,oxyds of tin and iron1 in the state of compound salts1 are likewise used for that purpose4 ,tannin is another vegetable ingredient of great importance in the arts4 ,it is obtained chiefly from the bark of trees2 but it is found also in nut-galls1 and in some other vegetables4 ,,emily4 ,is that the substance commonly called tan1 which is used in hot-houses8 ,,mrs4 ,b4 ,tan is the prepared bark in which the peculiar substance1 tannin1 is contained4 ,but the use of tan in hot-houses is of much less importance than in the operation of tanning1 by which skin is converted into leather4 ,,emily4 ,pray1 how is this operation performed8 ,,mrs4 ,b4 ,various methods are employed for this purpose1 which all consist in exposing skin to the action of tannin1 or of substances containing this principle1 in sufficient quantities1 and disposed to yield it to the skin4 ,the most usual way is to infuse coarsely powdered oak bark in water1 and to keep the skin immersed in this infusion for a certain length of time4 ,during this process1 which is slow and gradual1 the skin is found to have increased in weight1 and to have acquired a considerable tenacity and impermeability to water4 ,this effect may be much accelerated by using strong saturations of the tanning principle 7which can be extracted from bark71 instead of employing the bark itself4 ,but this quick mode of preparation does not appear to make equally good leather4 ,tannin is contained in a great variety of astringent vegetable substances1 as galls1 the rose-tree1 and wine2 but it is nowhere so plentiful as in bark4 ,all these substances yield it to water1 from which it may be precipitated by a solution of isinglass1 or glue1 with which it strongly unites and forms an insoluble compound4 ,hence its valuable property of combining with skin 7which consists chiefly of glue71 and of enabling it to resist the action of water4 ,,emily4 ,might we not see that effect by pouring a little melted isinglass into a glass of wine1 which you say contains tannin8 ,,mrs4 ,b4 ,yes4 ,i have prepared a solution of isinglass for that very purpose4 --,do you observe the thick muddy precipitate8 --,that is the tannin combined with the isinglass4 ,,caroline4 ,this precipitate must then be of the same nature as leather8 ,,mrs4 ,b4 ,it is composed of the same ingredients2 but the organisation and texture of the skin being wanting1 it has neither the consistence nor the tenacity of leather4 ,,caroline4 ,one might suppose that men who drink large quantities of red wine stand a chance of having the coats of their stomachs converted into leather1 since tannin has so strong an affinity for skin4 ,,mrs4 ,b4 ,it is not impossible but that the coats of their stomachs may be1 in some measure1 tanned1 or hardened by the constant use of this liquor2 but you must remember that where a number of other chemical agents are concerned1 and1 above all1 where life exists1 no certain chemical inference can be drawn4 ,i must not dismiss this subject1 without mentioning a recent discovery of ,mr4 ,hatchett1 which relates to it4 ,this gentleman found that a substance very similar to tannin1 possessing all its leading properties1 and actually capable of tanning leather1 may be produced by exposing carbon1 or any substance containing carbonaceous matter1 whether vegetable1 animal1 or mineral1 to the action of nitric acid4 ,,caroline4 ,and is not this discovery very likely to be of use to manufactures8 ,,mrs4 ,b4 ,that is very doubtful1 because tannin1 thus artificially prepared1 must probably always be more expensive than that which is obtained from bark4 ,but the fact is extremely curious1 as it affords one of those very rare instances of chemistry being able to imitate the proximate principles of organised bodies4 ,the last of the vegetable materials is woody fibre2 it is the hardest part of plants4 ,the chief source from which this substance is derived is wood1 but it is also contained1 more or less1 in every solid part of that plant4 ,it forms a kind of skeleton of the part to which it belongs1 and retains its shape after all the other materials have disappeared4 ,it consists chiefly of carbon1 united with a small proportion of salts1 and the other constituents common to all vegetables4 ,,emily4 ,it is of woody fibre1 then1 that the common charcoal is made8 ,,mrs4 ,b4 ,yes4 ,charcoal1 as you may recollect1 is obtained from wood1 by the separation of all its evaporable parts4 ,before we take leave of the vegetable materials1 it will be proper1 at least1 to enumerate the several vegetable acids which we either have had1 or may have occasion to mention4 ,i believe ,i formerly told you that their basis1 or radical1 was uniformly composed of hydrogen and carbon1 and that their difference consisted only in the various proportions of oxygen which they contained4 ,the following are the names of the vegetable acids3 ,the ,mucous ,acid1 obtained from gum or mucilage2 ,suberic - - - from cork2 ,camphoric - - - from camphor2 ,benzoic - - - from balsams2 ,gallic - - - from galls1 bark1 c4 ,malic - - - from ripe fruits2 ,citric - - - from lemon juice2 ,oxalic - - - from sorrel2 ,succinic - - - from amber2 ,tartarous - - - from tartrit of potash3 ,acetic - - - from vinegar4 ,they are all decomposable by heat1 soluble in water1 and turn vegetable blue colours red4 ,the succinic1 the tartarous1 and the acetous acids1 are the products of the decomposition of vegetables2 we shall1 therefore1 reserve their examination for a future period4 ,the oxalic acid1 distilled from sorrel1 is the highest term of vegetable acidification2 for1 if more oxygen be added to it1 it loses its vegetable nature1 and is resolved into carbonic acid and water2 therefore1 though all the other acids may be converted into the oxalic by an addition of oxygen1 the oxalic itself is not susceptible of a further degree of oxygenation2 nor can it be made1 by any chemical processes1 to return to a state of lower acidification4 ,to conclude this subject1 ,i have only to add a few words on the gallic acid4 4 4 4 4 ,,caroline4 ,is not this the same acid before mentioned1 which forms ink1 by precipitating sulphat of iron from its solution8 ,,mrs4 ,b4 ,yes4 ,though it is usually extracted from galls1 on account of its being most abundant in that vegetable substance1 it may also be obtained from a great variety of plants4 ,it constitutes what is called the astringent principle of vegetables2 it is generally combined with tannin1 and you will find that an infusion of tea1 coffee1 bark1 red-wine1 or any vegetable substance that contains the astringent principle1 will make a black precipitate with a solution of sulphat of iron4 ,,caroline4 ,but pray what are galls8 ,,mrs4 ,b4 ,they are excrescences which grow on the bark of young oaks1 and are occasioned by an insect which wounds the bark of trees1 and lays its eggs in the aperture4 ,the lacerated vessels of the tree then discharge their contents1 and form an excrescence1 which affords a defensive covering for these eggs4 ,the insect1 when come to life1 first feeds on this excrescence1 and some time afterward eats its way out1 as it appears from a hole which is formed in all gall-nuts that no longer contain an insect4 ,it is in hot climates only that strongly astringent gall-nuts are found2 those which are used for the purpose of making ink are brought from ,aleppo4 ,,emily4 ,but are not the oak-apples1 which grow on the leaves of the oak in this country1 of a similar nature8 ,,mrs4 ,b4 ,yes2 only they are an inferior species of galls1 containing less of the astringent principle1 and therefore less applicable to useful purposes4 ,,caroline4 ,are the vegetable acids never found but in their pure uncombined state8 ,,mrs4 ,b4 ,by no means2 on the contrary1 they are frequently met with in the state of compound salts2 these1 however1 are in general not fully saturated with the salifiable bases1 so that the acid predominates2 and1 in this state1 they are called acidulous salts4 ,of this kind is the salt called cream of tartar4 ,,caroline4 ,is not the salt of lemon1 commonly used to take out ink-spots and stains1 of this nature8 ,,mrs4 ,b4 ,no2 that salt consists of the oxalic acid1 combined with a little potash4 ,it is found in that state in sorrel4 ,,caroline4 ,and pray how does it take out ink-spots8 ,,mrs4 ,b4 ,by uniting with the iron1 and rendering it soluble in water4 ,besides the vegetable materials which we have enumerated1 a variety of other substances1 common to the three kingdoms1 are found in vegetables1 such as potash1 which was formerly supposed to belong exclusively to plants1 and was1 in consequence1 called the vegetable alkali4 ,sulphur1 phosphorus1 earths1 and a variety of metallic oxyds1 are also found in vegetables1 but only in small quantities4 ,and we meet sometimes with neutral salts1 formed by the combination of these ingredients4 ,,conversation ,,xxi4 ,,on ,,the ,,decomposition ,,of ,,vegetables4 ,,caroline4 ,the account which you have given us1 ,mrs4 ,b41 of the materials of vegetables1 is1 doubtless1 very instructive2 but it does not completely satisfy my curiosity4 ,i wish to know how plants obtain the principles from which their various materials are formed2 by what means these are converted into vegetable matter1 and how they are connected with the life of the plant8 ,,mrs4 ,b4 ,this implies nothing less than a complete history of the chemistry and physiology of vegetation1 subjects on which we have yet but very imperfect notions4 ,still ,i hope that ,i shall be able1 in some measure1 to satisfy your curiosity4 ,but1 in order to render the subject more intelligible1 ,i must first make you acquainted with the various changes which vegetables undergo1 when the vital power no longer enables them to resist the common laws of chemical attraction4 ,the composition of vegetables being more complicated than that of minerals1 the former more readily undergo chemical changes than the latter3 for the greater the variety of attractions1 the more easily is the equilibrium destroyed1 and a new order of combinations introduced4 ,,emily4 ,i am surprised that vegetables should be so easily susceptible of decomposition2 for the preservation of the vegetable kingdom is certainly far more important than that of minerals4 ,,mrs4 ,b4 ,you must consider1 on the other hand1 how much more easily the former is renewed than the latter4 ,the decomposition of the vegetable takes place only after the death of the plant1 which1 in the common course of nature1 happens when it has yielded fruit and seeds to propagate its species4 ,if1 instead of thus finishing its career1 each plant was to retain its form and vegetable state1 it would become an useless burden to the earth and its inhabitants4 ,when vegetables1 therefore1 cease to be productive1 they cease to live1 and nature then begins her process of decomposition1 in order to resolve them into their chemical constituents1 hydrogen1 carbon1 and oxygen2 those simple and primitive ingredients1 which she keeps in store for all her combinations4 ,,emily4 ,but since no system of combination can be destroyed1 except by the establishment of another order of attractions1 how can the decomposition of vegetables reduce them to their simple elements8 ,,mrs4 ,b4 ,it is a very long process1 during which a variety of new combinations are successively established and successively destroyed3 but1 in each of these changes1 the ingredients of vegetable matter tend to unite in a more simple order of compounds1 till they are at length brought to their elementary state1 or1 at least1 to their most simple order of combinations4 ,thus you will find that vegetables are in the end almost entirely reduced to water and carbonic acid2 the hydrogen and carbon dividing the oxygen between them1 so as to form with it these two substances4 ,but the variety of intermediate combinations that take place during the several stages of the decomposition of vegetables1 present us with a new set of compounds1 well worthy of our examination4 ,,caroline4 ,how is it possible that vegetables1 while putrefying1 should produce any thing worthy of observation8 ,,mrs4 ,b4 ,they are susceptible of undergoing certain changes before they arrive at the state of putrefaction1 which is the final term of decomposition2 and of these changes we avail ourselves for particular and important purposes4 ,but1 in order to make you understand this subject1 which is of considerable importance1 ,i must explain it more in detail4 ,the decomposition of vegetables is always attended by a violent internal motion1 produced by the disunion of one order of particles1 and the combination of another4 ,this is called ,,fermentation4 ,there are several periods at which this process stops1 so that a state of rest appears to be restored1 and the new order of compounds fairly established4 ,but1 unless means be used to secure these new combinations in their actual state1 their duration will be but transient1 and a new fermentation will take place1 by which the compound last formed will be destroyed2 and another1 and less complex order1 will succeed4 ,,emily4 ,the fermentations1 then1 appear to be only the successive steps by which a vegetable descends to its final dissolution4 ,,mrs4 ,b4 ,precisely so4 ,your definition is perfectly correct4 ,,caroline4 ,and how many fermentations1 or new arrangements1 does a vegetable undergo before it is reduced to its simple ingredients8 ,,mrs4 ,b4 ,chemists do not exactly agree in this point2 but there are1 ,i think1 four distinct fermentations1 or periods1 at which the decomposition of vegetable matter stops and changes its course4 ,but every kind of vegetable matter is not equally susceptible of undergoing all these fermentations4 ,there are likewise several circumstances required to produce fermentation4 ,water and a certain degree of heat are both essential to this process1 in order to separate the particles1 and thus weaken their force of cohesion1 that the new chemical affinities may be brought into action4 ,,caroline4 ,in frozen climates1 then1 how can the spontaneous decomposition of vegetables take place8 ,,mrs4 ,b4 ,it certainly cannot2 and1 accordingly1 we find scarcely any vestiges of vegetation where a constant frost prevails4 ,,caroline4 ,one would imagine that1 on the contrary1 such spots would be covered with vegetables2 for1 since they cannot be decomposed1 their number must always increase4 ,,mrs4 ,b4 ,but1 my dear1 heat and water are quite as essential to the formation of vegetables1 as they are to their decomposition4 ,besides1 it is from the dead vegetables1 reduced to their elementary principles1 that the rising generation is supplied with sustenance4 ,no young plant1 therefore1 can grow unless its predecessors contribute both to its formation and support2 and these not only furnish the seed from which the new plant springs1 but likewise the food by which it is nourished4 ,,caroline4 ,under the torrid zone1 therefore1 where water is never frozen1 and the heat is very great1 both the processes of vegetation and of fermentation must1 ,i suppose1 be extremely rapid8 ,,mrs4 ,b4 ,not so much as you imagine3 for in such climates great part of the water which it requires for these processes is in an ariform state1 which is scarcely more conducive either to the growth or formation of vegetables than that of ice4 ,in those latitudes1 therefore1 it is only in low damp situations1 sheltered by woods from the sun's rays1 that the smaller tribes of vegetables can grow and thrive during the dry season1 as dead vegetables seldom retain water enough to produce fermentation1 but are1 on the contrary1 soon dried up by the heat of the sun1 which enables them to resist that process2 so that it is not till the fall of the autumnal rains 7which are very violent in such climates71 that spontaneous fermentation can take place4 ,the several fermentations derive their names from their principal products4 ,the first is called the saccharine fermentation1 because its product is sugar4 ,,caroline4 ,but sugar1 you have told us1 is found in all vegetables2 it cannot1 therefore1 be the product of their decomposition4 ,,mrs4 ,b4 ,it is true that this fermentation is not confined to the decomposition of vegetables1 as it continually takes place during their life2 and1 indeed1 this circumstance has1 till lately1 prevented it from being considered as one of the fermentations4 ,but the process appears so analogous to the other fermentations1 and the formation of sugar1 whether in living or dead vegetable matter is so evidently a new compound1 proceeding from the destruction of the previous order of combinations1 and essential to the subsequent fermentations1 that it is now1 ,i believe1 generally esteemed the first step1 or necessary preliminary1 to decomposition1 if not an actual commencement of that process4 ,,caroline4 ,i recollect your hinting to us that sugar was supposed not to be secreted from the sap1 in the same manner as mucilage1 fecula1 oil1 and the other ingredients of vegetables4 ,,mrs4 ,b4 ,it is rather from these materials1 than from the sap itself1 that sugar is formed2 and it is developed at particular periods1 as you may observe in fruits1 which become sweet in ripening1 sometimes even after they have been gathered4 ,life1 therefore1 is not essential to the formation of sugar1 whilst on the contrary1 mucilage1 fecula1 and the other vegetable materials that are secreted from the sap by appropriate organs1 whose powers immediately depend on the vital principle1 cannot be produced but during the existence of that principle4 ,,emily4 ,the ripening of fruits is1 then1 their first step to destruction1 as well as their last towards perfection8 ,,mrs4 ,b4 ,exactly4 --,a process analogous to the saccharine fermentation takes place also during the cooking of certain vegetables4 ,this is the case with parsnips1 carrots1 potatoes1 c4 in which sweetness is developed by heat and moisture2 and we know that if we carried the process a little farther1 a more complete decomposition would ensue4 ,the same process takes place also in seeds previous to their sprouting4 ,,caroline4 ,how do you reconcile this to your theory1 ,mrs4 ,b48 ,can you suppose that a decomposition is the necessary precursor of life8 ,,mrs4 ,b4 ,that is indeed the case4 ,the materials of the seed must be decomposed1 and the seed disorganized1 before a plant can sprout from it4 ,seeds1 besides the embrio plant1 contain 7as we have already observed7 fecula1 oil1 and a little mucilage4 ,these substances are destined for the nourishment of the future plant2 but they undergo some change before they can be fit for this function4 ,the seeds1 when buried in the earth1 with a certain degree of moisture and of temperature1 absorb water1 which dilates them1 separates their particles1 and introduces a new order of attractions1 of which sugar is the product4 ,the substance of the seed is thus softened1 sweetened1 and converted into a sort of white milky pulp1 fit for the nourishment of the embrio plant4 ,the saccharine fermentation of seeds is artificially produced1 for the purpose of making malt1 by the following process3-- ,a quantity of barley is first soaked in water for two or three days3 the water being afterwards drained off1 the grain heats spontaneously1 swells1 bursts1 sweetens1 shows a disposition to germinate1 and actually sprouts to the length of an inch1 when the process is stopped by putting it into a kiln1 where it is well dried at a gentle heat4 ,in this state it is crisp and friable1 and constitutes the substance called malt1 which is the principal ingredient of beer4 ,,emily4 ,but ,i hope you will tell us how malt is made into beer8 ,,mrs4 ,b4 ,certainly2 but ,i must first explain to you the nature of the second fermentation1 which is essential to that operation4 ,this is called the vinous fermentation1 because its product is wine4 ,,emily4 ,how very different the decomposition of vegetables is from what ,i had imagined6 ,the products of their disorganisation appear almost superior to those which they yield during their state of life and perfection4 ,,mrs4 ,b4 ,and do you not1 at the same time1 admire the beautiful economy of ,nature1 which1 whether she creates1 or whether she destroys1 directs all her operations to some useful and benevolent purpose8 --,it appears that the saccharine fermentation is extremely favourable1 if not absolutely essential1 as a previous step1 to the vinous fermentation2 so that if sugar be not developed during the life of the plant1 the saccharine fermentation must be artificially produced before the vinous fermentation can take place4 ,this is the case with barley1 which does not yield any sugar until it is made into malt2 and it is in that state only that it is susceptible of undergoing the vinous fermentation by which it is converted into beer4 ,,caroline4 ,but if the product of the vinous fermentation is always wine1 beer cannot have undergone that process1 for beer is certainly not wine4 ,,mrs4 ,b4 ,chemically speaking1 beer may be considered as the wine of grain4 ,for it is the product of the fermentation of malt1 just as wine is that of the fermentation of grapes1 or other fruits4 ,the consequence of the vinous fermentation is the decomposition of the saccharine matter1 and the formation of a spirituous liquor from the constituents of the sugar4 ,but1 in order to promote this fermentation1 not only water and a certain degree of heat are necessary1 but also some other vegetable ingredients1 besides the sugar1 as fecula1 mucilage1 acids1 salts1 extractive matter1 c4 all of which seem to contribute to this process2 and give to the liquor its peculiar taste4 ,,emily4 ,it is1 perhaps1 for this reason that wine is not obtained from the fermentation of pure sugar2 but that fruits are chosen for that purpose1 as they contain not only sugar1 but likewise the other vegetable ingredients which promote the vinous fermentation1 and give the peculiar flavour4 ,,mrs4 ,b4 ,certainly4 ,and you must observe also1 that the relative quantity of sugar is not the only circumstance to be considered in the choice of vegetable juices for the formation of wine2 otherwise the sugar-cane would be best adapted for that purpose4 ,it is rather the manner and proportion in which the sugar is mixed with other vegetable ingredients that influences the production and qualities of wine4 ,and it is found that the juice of the grape not only yields the most considerable proportion of wine1 but that it likewise affords it of the most grateful flavour4 ,,emily4 ,i have seen a vintage in ,switzerland1 and ,i do not recollect that heat was applied1 or water added1 to produce the fermentation of the grapes4 ,,mrs4 ,b4 ,the common temperature of the atmosphere in the cellars in which the juice of the grape is fermented is sufficiently warm for this purpose2 and as the juice contains an ample supply of water1 there is no occasion for any addition of it4 ,but when fermentation is produced in dry malt1 a quantity of water must necessarily be added4 ,,emily4 ,but what are precisely the changes that happen during the vinous fermentation8 ,,mrs4 ,b4 ,the sugar is decomposed1 and its constituents are recombined into two new substances2 the one a peculiar liquid substance1 called alcohol or spirit of wine1 which remains in the fluid2 the other1 carbonic acid gas1 which escapes during the fermentation4 ,wine1 therefore1 as ,i before observed1 in a general point of view1 may be considered as a liquid of which alcohol constitutes the essential part4 ,and the varieties of strength and flavour of the different kinds of wine are to be attributed to the different qualities of the fruits from which they are obtained1 independently of the sugar4 ,,caroline4 ,i am astonished to hear that so powerful a liquid as spirit of wine should be obtained from so mild a substance as sugar4 ,,mrs4 ,b4 ,can you tell me in what the principal difference consists between alcohol and sugar8 ,,caroline4 ,let me reflect 4 4 4 4 4 ,sugar consists of carbon1 hydrogen1 and oxygen4 ,if carbonic acid be subtracted from it1 during the formation of alcohol1 the latter will contain less carbon and oxygen than sugar does2 therefore hydrogen must be the prevailing principle of alcohol4 ,,mrs4 ,b4 ,it is exactly so4 ,and this very large proportion of hydrogen accounts for the lightness and combustible property of alcohol1 and of spirits in general1 all of which consist of alcohol variously modified4 ,,emily4 ,and can sugar be recomposed from the combination of alcohol and carbonic acid8 ,,mrs4 ,b4 ,chemists have never been able to succeed in effecting this2 but from analogy1 ,i should suppose such a recomposition possible4 ,let us now observe more particularly the phenomena that take place during the vinous fermentation4 ,at the commencement of this process1 heat is evolved1 and the liquor swells considerably from the formation of the carbonic acid1 which is disengaged in such prodigious quantities as would be fatal to any person who should unawares inspire it2 an accident which has sometimes happened4 ,if the fermentation be stopped by putting the liquor into barrels1 before the whole of the carbonic acid is evolved1 the wine is brisk1 like ,champagne1 from the carbonic acid imprisoned in it1 and it tastes sweet1 like cyder1 from the sugar not being completely decomposed4 ,,emily4 ,but ,i do not understand why heat should be evolved during this operation4 ,for1 as there is a considerable formation of gas1 in which a proportionable quantity of heat must become insensible1 ,i should have imagined that cold1 rather than heat1 would have been produced4 ,,mrs4 ,b4 ,it appears so on first consideration2 but you must recollect that fermentation is a complicated chemical process2 and that1 during the decompositions and recompositions attending it1 a quantity of chemical heat may be disengaged1 sufficient both to develope the gas1 and to effect an increase of temperature4 ,when the fermentation is completed1 the liquid cools and subsides1 the effervescence ceases1 and the thick1 sweet1 sticky juice of the fruit is converted into a clear1 transparent1 spirituous liquor1 called wine4 ,,emily4 ,how much ,i regret not having been acquainted with the nature of the vinous fermentation1 when ,i had an opportunity of seeing the process6 ,,mrs4 ,b4 ,you have an easy method of satisfying yourself in that respect by observing the process of brewing1 which1 in every essential circumstance1 is similar to that of making wine1 and is really a very curious chemical operation4 ,although we cannot actually make wine at this moment1 it will be easy to show you the mode of analyzing it4 ,this is done by distillation4 ,when wine of any kind is submitted to this operation1 it is found to contain brandy1 water1 tartar1 extractive colouring matter1 and some vegetable acids4 ,i have put a little port wine into this alembic of glass 7,,plate ,,xiv4 ,fig4 #a471 and on placing the lamp under it1 you will soon see the spirit and water successively come over-- ,illustration3 ,plate ,,xiv4 ,vol4 ,,ii4 p4 #bac4 ,fig4 #a4 ,a ,alembic4 ,b ,lamp4 ,c ,wine glass4 ,fig4 #b4 ,alcohol blowpipe4 ,d the ,lamp4 ,e the vessel in which the ,alcohol is boiling4 ,f a safety valve4 ,g the inflamed jet or steam of alcohol directed towards a glass tube ,h4 ,,emily4 ,but you do not mention alcohol amongst the products of the distillation of wine2 and yet that is its most essential ingredient8 ,,mrs4 ,b4 ,the alcohol is contained in the brandy which is now coming over1 and dropping from the still4 ,brandy is nothing more than a mixture of alcohol and water2 and in order to obtain the alcohol pure1 we must again distil it from brandy4 ,,caroline4 ,i have just taken a drop on my finger2 it tastes like strong brandy1 but it is without colour1 whilst brandy is of a deep yellow4 ,,mrs4 ,b4 ,it is not so naturally2 in its pure state brandy is colourless1 and it obtains the yellow tint you observe1 by extracting the colouring matter from the new oaken casks in which it is kept4 ,but if it does not acquire the usual tinge in this way1 it is the custom to colour the brandy used in this country artificially1 with a little burnt sugar1 in order to give it the appearance of having been long kept4 ,,caroline4 ,and is rum also distilled from wine8 ,,mrs4 ,b4 ,by no means2 it is distilled from the sugar-cane1 a plant which contains so great a quantity of sugar1 that it yields more alcohol than almost any other vegetable4 ,after the juice of the cane has been pressed out for making sugar1 what still remains in the bruised cane is extracted by water1 and this watery solution of sugar is fermented1 and produces rum4 ,the spirituous liquor called arack is in a similar manner distilled from the product of the vinous fermentation of rice4 ,,emily4 ,but rice has no sweetness2 does it contain any sugar8 ,,mrs4 ,b4 ,like barley and most other seeds1 it is insipid until it has undergone the saccharine fermentation2 and this1 you must recollect1 is always a previous step to the vinous fermentation in those vegetables in which sugar is not already formed4 ,brandy may in the same manner be obtained from malt4 ,,caroline4 ,you mean from beer1 ,i suppose2 for the malt must have previously undergone the vinous fermentation4 ,,mrs4 ,b4 ,beer is not precisely the product of the vinous fermentation of malt4 ,for hops are a necessary ingredient for the formation of that liquor2 whilst brandy is distilled from pure fermented malt4 ,but brandy might1 no doubt1 be distilled from beer as well as from any other liquor that has undergone the vinous fermentation2 for since the basis of brandy is alcohol1 it may be obtained from any liquid that contains that spirituous substance4 ,,emily4 ,and pray1 from what vegetable is the favourite spirit of the lower orders of people1 gin1 extracted8 ,,mrs4 ,b4 ,the spirit 7which is the same in all fermented liquors7 may be obtained from any kind of grain2 but the peculiar flavour which distinguishes gin is that of juniper berries1 which are distilled together with the grain-- ,i think the brandy contained in the wine which we are distilling must1 by this time1 be all come over4 ,yes--taste the liquid that is now dropping from the alembic-- ,,caroline4 ,it is perfectly insipid1 like water4 ,,mrs4 ,b4 ,it is water1 which1 as ,i was telling you1 is the second product of wine1 and comes over after all the spirit1 which is the lightest part1 is distilled4 --,the tartar and extractive colouring matter we shall find in a solid form at the bottom of the alembic4 ,,emily4 ,they look very like the lees of wine4 ,,mrs4 ,b4 ,and in many respects they are of a similar nature2 for lees of wine consist chiefly of tartrit of potash2 a salt which exists in the juice of the grape1 and in many other vegetables1 and is developed only by the vinous fermentation4 ,during this operation it is precipitated1 and deposits itself on the internal surface of the cask in which the wine is contained4 ,it is much used in medicine1 and in various arts1 particularly dying1 under the name of cream of tartar1 and it is from this salt that the tartarous acid is obtained4 ,,caroline4 ,but the medicinal cream of tartar is in appearance quite different from these dark-coloured dregs2 it is perfectly colourless4 ,,mrs4 ,b4 ,because it consists of the pure salts only1 in its crystallised form2 whilst in the instance before us it is mixed with the deep-coloured extractive matter1 and other foreign ingredients4 ,,emily4 ,pray cannot we now obtain pure alcohol from the brandy which we have distilled8 ,,mrs4 ,b4 ,we might2 but the process would be tedious3 for in order to obtain alcohol perfectly free from water1 it is necessary to distil1 or1 as the distillers call it1 rectify it several times4 ,you must therefore allow me to produce a bottle of alcohol that has been thus purified4 ,this is a very important ingredient1 which has many striking properties1 besides its forming the basis of all spirituous liquors4 ,,emily4 ,it is alcohol1 ,i suppose1 that produces intoxication8 ,,mrs4 ,b4 ,certainly2 but the stimulus and momentary energy it gives to the system1 and the intoxication it occasions when taken in excess1 are circumstances not yet accounted for4 ,,caroline4 ,i thought that it produced these effects by increasing the rapidity of the circulation of the blood2 for drinking wine or spirits1 ,i have heard1 always quickens the pulse4 ,,mrs4 ,b4 ,no doubt2 the spirit1 by stimulating the nerves1 increases the action of the muscles2 and the heart1 which is one of the strongest muscular organs1 beats with augmented vigour1 and propels the blood with accelerated quickness4 ,after such a strong excitation the frame naturally suffers a proportional degree of depression1 so that a state of debility and languor is the invariable consequence of intoxication4 ,but though these circumstances are well ascertained1 they are far from explaining why alcohol should produce such effects4 ,,emily4 ,liqueurs are the only kind of spirits which ,i think pleasant4 ,pray of what do they consist8 ,,mrs4 ,b4 ,they are composed of alcohol1 sweetened with syrup1 and flavoured with volatile oil4 ,the different kinds of odoriferous spirituous waters are likewise solutions of volatile oil in alcohol1 as lavender water1 eau de ,cologne1 c4 ,the chemical properties of alcohol are important and numerous4 ,it is one of the most powerful chemical agents1 and is particularly useful in dissolving a variety of substances1 which are soluble neither by water nor heat4 ,,emily4 ,we have seen it dissolve copal and mastic to form varnishes2 and these resins are certainly not soluble in water1 since water precipitates them from their solution in alcohol4 ,,mrs4 ,b4 ,i am happy to find that you recollect these circumstances so well4 ,the same experiment affords also an instance of another property of alcohol1--its tendency to unite with water2 for the resin is precipitated in consequence of losing the alcohol1 which abandons it from its preference for water4 ,it is attended also1 as you may recollect1 with the same peculiar circumstance of a disengagement of heat and consequent diminution of bulk1 which we have supposed to be produced by a mechanical penetration of particles by which latent heat is forced out4 ,alcohol unites thus readily not only with resins and with water1 but with oils and balsams2 these compounds form the extensive class of elixirs1 tinctures1 quintessences1 c4 ,,emily4 ,i suppose that alcohol must be highly combustible1 since it contains so large a proportion of hydrogen8 ,,mrs4 ,b4 ,extremely so2 and it will burn at a very moderate temperature4 ,,caroline4 ,i have often seen both brandy and spirit of wine burnt2 they produce a great deal of flame1 but not a proportional quantity of heat1 and no smoke whatever4 ,,mrs4 ,b4 ,the last circumstance arises from their combustion being complete2 and the disproportion between the flame and heat shows you that these are by no means synonymous4 ,the great quantity of flame proceeds from the combustion of the hydrogen to which1 you know1 that manner of burning is peculiar4 --,have you not remarked also that brandy and alcohol will burn without a wick8 --,they take fire at so low a temperature1 that this assistance is not required to concentrate the heat and volatilise the fluid4 ,,caroline4 ,i have sometimes seen brandy burnt by merely heating it in a spoon4 ,,mrs4 ,b4 ,the rapidity of the combustion of alcohol may1 however1 be prodigiously increased by first volatilising it4 ,an ingenious instrument has been constructed on this principle to answer the purpose of a blow-pipe1 which may be used for melting glass1 or other chemical purposes4 ,it consists of a small metallic vessel 7,,plate ,,xiv4 ,fig4 #b471 of a spherical shape1 which contains the alcohol1 and is heated by the lamp beneath it2 as soon as the alcohol is volatilised1 it passes through the spout of the vessel1 and issues just above the wick of the lamp1 which immediately sets fire to the stream of vapour1 as ,i shall show you-- ,,emily4 ,with what amazing violence it burns6 ,the flame of alcohol1 in the state of vapour1 is1 ,i fancy1 much hotter than when the spirit is merely burnt in a spoon8 ,,mrs4 ,b4 ,yes2 because in this way the combustion goes on much quicker1 and1 of course1 the heat is proportionally increased4 --,observe its effect on this small glass tube1 the middle of which ,i present to the extremity of the flame1 where the heat is greatest4 ,,caroline4 ,the glass1 in that spot1 is become red hot1 and bends from its own weight4 ,,mrs4 ,b4 ,i have now drawn it asunder1 and am going to blow a ball at one of the heated ends2 but ,i must previously close it up1 and flatten it with this little metallic instrument1 otherwise the breath would pass through the tube without dilating any part of it4 --,now1 ,caroline1 will you blow strongly into the tube whilst the closed end is red hot4 ,,emily4 ,you blowed too hard2 for the ball suddenly dilated to a great size1 and then burst in pieces4 ,,mrs4 ,b4 ,you will be more expert another time2 but ,i must caution you1 should you ever use this blow-pipe1 to be very careful that the combustion of the alcohol does not go on with too great violence1 for ,i have seen the flame sometimes dart out with such force as to reach the opposite wall of the room1 and set the paint on fire4 ,there is1 however1 no danger of the vessel bursting1 as it is provided with a safety tube1 which affords an additional vent for the vapour of alcohol when required4 ,the products of the combustion of alcohol consist in a great proportion of water1 and a small quantity of carbonic acid4 ,there is no smoke or fixed remains whatever4 --,how do you account for that1 ,emily8 ,,emily4 ,i suppose that the oxygen which the alcohol absorbs in burning1 converts its hydrogen into water and its carbon into carbonic acid gas1 and thus it is completely consumed4 ,,mrs4 ,b4 ,very well4 --,ether1 the lightest of all fluids1 and with which you are well acquainted1 is obtained from alcohol1 of which it forms the lightest and most volatile part4 ,,emily4 ,ether1 then1 is to alcohol1 what alcohol is to brandy8 ,,mrs4 ,b4 ,no3 there is an essential difference4 ,in order to obtain alcohol from brandy1 you need only deprive the latter of its water2 but for the formation of ether1 the alcohol must be decomposed1 and one of its constituents partly subtracted4 ,i leave you to guess which of them it is-- ,,emily4 ,it cannot be hydrogen1 as ether is more volatile than alcohol1 and hydrogen is the lightest of all its ingredients3 nor do ,i suppose that it can be oxygen1 as alcohol contains so small a proportion of that principle2 it is1 therefore1 most probably1 carbon1 a diminution of which would not fail to render the new compound more volatile4 ,,mrs4 ,b4 ,you are perfectly right4 ,the formation of ether consists simply in subtracting from the alcohol a certain proportion of carbon2 this is effected by the action of the sulphuric1 nitric1 or muriatic acids1 on alcohol4 ,the acid and carbon remain at the bottom of the vessel1 whilst the decarbonised alcohol flies off in the form of a condensable vapour1 which is ether4 ,ether is the most inflammable of all fluids1 and burns at so slow a temperature that the heat evolved during its combustion is more than is required for its support1 so that a quantity of ether is volatilised1 which takes fire1 and gradually increases the violence of the combustion4 ,sir ,humphry ,davy has lately discovered a very singular fact respecting the vapour of ether4 ,if a few drops of ether be poured into a wine-glass1 and a fine platina wire1 heated almost to redness1 be held suspended in the glass1 close to the surface of the ether1 the wire soon becomes intensely red-hot1 and remains so for any length of time4 ,we may easily try the experiment4 4 4 4 4 ,,caroline4 ,how very curious6 ,the wire is almost white hot1 and a pungent smell rises from the glass4 ,pray how is this accounted for8 ,,mrs4 ,b4 ,this is owing to a very peculiar property of the vapour of ether1 and indeed of many other combustible gaseous bodies4 ,at a certain temperature lower than that of ignition1 these vapours undergo a slow and imperfect combustion1 which does not give rise1 in any sensible degree1 to the phenomena of light and flame1 and yet extricates a quantity of caloric sufficient to react upon the wire and make it red-hot1 and the wire in its turn keeps up the effect as long as the emission of vapour continues4 ,,caroline4 ,but why should not an iron or silver wire produce the same effect8 ,,mrs4 ,b4 ,because either iron or silver1 being much better conductors of heat than platina1 the heat is carried off too fast by those metals to allow the accumulation of caloric necessary to produce the effect in question4 ,ether is so light that it evaporates at the common temperature of the atmosphere2 it is therefore necessary to keep it confined by a well ground glass stopper4 ,no degree of cold known has ever frozen it4 ,,caroline4 ,is it not often taken medicinally8 ,,mrs4 ,b4 ,yes2 it is one of the most effectual antispasmodic medicines1 and the quickness of its effects1 as such1 probably depends on its being instantly converted into vapour by the heat of the stomach1 through the intervention of which it acts on the nervous system4 ,but the frequent use of ether1 like that of spirituous liquors1 becomes prejudicial1 and1 if taken to excess1 it produces effects similar to those of intoxication4 ,we may now take our leave of the vinous fermentation1 of which1 ,i hope1 you have acquired a clear idea2 as well as of the several products that are derived from it4 ,,caroline4 ,though this process appears1 at first sight1 so much complicated1 it may1 ,i think1 be summed up in a few words1 as it consists in the conversion of sugar and fermentable bodies into alcohol and carbonic acid1 which give rise both to the formation of wine1 and of all kinds of spirituous liquors4 ,,mrs4 ,b4 ,we shall now proceed to the acetous fermentation1 which is thus called1 because it converts wine into vinegar1 by the formation of the acetous acid1 which is the basis or radical of vinegar4 ,,caroline4 ,but is not the acidifying principle of the acetous acid the same as that of all other acids1 oxygen8 ,,mrs4 ,b4 ,certainly2 and on that account the contact of air is essential to this fermentation1 as it affords the necessary supply of oxygen4 ,vinegar1 in order to obtain pure acetous acid from it1 must be distilled and rectified by certain processes4 ,,emily4 ,but pray1 ,mrs4 ,b41 is not the acetous acid frequently formed without this fermentation taking place8 ,is it not1 for instance1 contained in acid fruits1 and in every substance that becomes sour8 ,,mrs4 ,b4 ,no1 not in fruits2 you confound it with the citric1 the malic1 the oxalic1 and other vegetable acids1 to which living vegetables owe their acidity4 ,but whenever a vegetable substance turns sour1 after it has ceased to live1 the acetous acid is developed by means of the acetous fermentation1 in which the substance advances a step towards its final decomposition4 ,amongst the various instances of acetous fermentation1 that of bread is usually classed4 ,,caroline4 ,but the fermentation of bread is produced by yeast2 how does that effect it8 ,,mrs4 ,b4 ,it is found by experience that any substance that has already undergone a fermentation1 will readily excite it in one that is susceptible of that process4 ,if1 for instance1 you mix a little vinegar with wine1 that is intended to be acidified1 it will absorb oxygen more rapidly1 and the process be completed much sooner1 than if left to ferment spontaneously4 ,thus yeast1 which is a product of the fermentation of beer1 is used to excite and accelerate the fermentation of malt1 which is to be converted into beer1 as well as that of paste which is to be made into bread4 ,,caroline4 ,but if bread undergoes the acetous fermentation1 why is it not sour8 ,,mrs4 ,b4 ,it acquires a certain savour which corrects the heavy insipidity of flour1 and may be reckoned a first degree of acidification2 or if the process were carried further1 the bread would become decidedly acid4 ,there are1 however1 some chemists who do not consider the fermentation of bread as being of the acetous kind1 but suppose that it is a process of fermentation peculiar to that substance4 ,the putrid fermentation is the final operation of ,nature1 and her last step towards reducing organised bodies to their simplest combinations4 ,all vegetables spontaneously undergo this fermentation after death1 provided there be a sufficient degree of heat and moisture1 together with access of air2 for it is well known that dead plants may be preserved by drying1 or by the total exclusion of air4 ,,caroline4 ,but do dead plants undergo the other fermentation previous to this last2 or do they immediately suffer the putrid fermentation8 ,,mrs4 ,b4 ,that depends on a variety of circumstances1 such as the degrees of temperature and of moisture1 the nature of the plant itself1 c4 ,but if you were carefully to follow and examine the decomposition of plants from their death to their final dissolution1 you would generally find a sweetness developed in the seeds1 and a spirituous flavour in the fruits 7which have undergone the saccharine fermentation71 previous to the total disorganisation and separation of the parts4 ,,emily4 ,i have sometimes remarked a kind of spirituous taste in fruits that were over ripe1 especially oranges2 and this was just before they became rotten4 ,,mrs4 ,b4 ,it was then the vinous fermentation which had succeeded the saccharine1 and had you followed up these changes attentively1 you would probably have found the spirituous taste followed by acidity1 previous to the fruit passing to the state of putrefaction4 ,when the leaves fall from the trees in autumn1 they do not 7if there is no great moisture in the atmosphere7 immediately undergo a decomposition1 but are first dried and withered2 as soon1 however1 as the rain sets in1 fermentation commences1 their gaseous products are imperceptibly evolved into the atmosphere1 and their fixed remains mixed with their kindred earth4 ,wood1 when exposed to moisture1 also undergoes the putrid fermentation and becomes rotten4 ,,emily4 ,but ,i have heard that the dry rot1 which is so liable to destroy the beams of houses1 is prevented by a current of air2 and yet you said that air was essential to the putrid fermentation8 ,,mrs4 ,b4 ,true2 but it must not be in such a proportion to the moisture as to dissolve the latter1 and this is generally the case when the rotting of wood is prevented or stopped by the free access of air4 ,what is commonly called dry rot1 however1 is not ,i believe a true process of putrefaction4 ,it is supposed to depend on a peculiar kind of vegetation1 which1 by feeding on the wood1 gradually destroys it4 ,straw and all other kinds of vegetable matter undergo the putrid fermentation more rapidly when mixed with animal matter4 ,much heat is evolved during this process1 and a variety of volatile products are disengaged1 as carbonic acid and hydrogen gas1 the latter of which is frequently either sulphurated or phosphorated4 --,when all these gases have been evolved1 the fixed products1 consisting of carbon1 salts1 potash1 c4 form a kind of vegetable earth1 which makes very fine manure1 as it is composed of those elements which form the immediate materials of plants4 ,,caroline4 ,pray are not vegetables sometimes preserved from decomposition by petrification8 ,i have seen very curious specimens of petrified vegetables1 in which state they perfectly preserve their form and organisation1 though in appearance they are changed to stone4 ,,mrs4 ,b4 ,that is a kind of metamorphosis1 which1 now that you are tolerably well versed in the history of mineral and vegetable substances1 ,i leave to your judgment to explain4 ,do you imagine that vegetables can be converted into stone8 ,,emily4 ,no1 certainly2 but they might perhaps be changed to a substance in appearance resembling stone4 ,,mrs4 ,b4 ,it is not so1 however1 with the substances that are called petrified vegetables2 for these are really stone1 and generally of the hardest kind1 consisting chiefly of silex4 ,the case is this3 when a vegetable is buried under water1 or in wet earth1 it is slowly and gradually decomposed4 ,as each successive particle of the vegetable is destroyed1 its place is supplied by a particle of siliceous earth1 conveyed thither by the water4 ,in the course of time the vegetable is entirely destroyed1 but the silex has completely replaced it1 having assumed its form and apparent texture1 as if the vegetable itself were changed to stone4 ,,caroline4 ,that is very curious6 and ,i suppose that petrified animal substances are of the same nature8 ,,mrs4 ,b4 ,precisely4 ,it is equally impossible for either animal or vegetable substances to be converted into stone4 ,they may be reduced1 as we find they are1 by decomposition1 to their constituent elements1 but cannot be changed to elements1 which do not enter into their composition4 ,there are1 however1 circumstances which frequently prevent the regular and final decomposition of vegetables2 as1 for instance1 when they are buried either in the sea1 or in the earth1 where they cannot undergo the putrid fermentation for want of air4 ,in these cases they are subject to a peculiar change1 by which they are converted into a new class of compounds1 called bitumens4 ,,caroline4 ,these are substances ,i never heard of before4 ,,mrs4 ,b4 ,you will find1 however1 that some of them are very familiar to you4 ,bitumens are vegetables so far decomposed as to retain no organic appearance2 but their origin is easily detected by their oily nature1 their combustibility1 the products of their analysis1 and the impressions of the forms of leaves1 grains1 fibres of wood1 and even of animals1 which they frequently bear4 ,they are sometimes of an oily liquid consistence1 as the substance called naptha1 in which we preserved potassium2 it is a fine transparent colourless fluid1 that issues out of clays in some parts of ,persia4 ,but more frequently bitumens are solid1 as asphaltum1 a smooth1 hard1 brittle substance1 which easily melts1 and forms1 in its liquid state1 a beautiful dark brown colour for oil painting4 ,jet1 which is of a still harder texture1 is a peculiar bitumen1 susceptible of so fine a polish1 that it is used for many ornamental purposes4 ,coal is also a bituminous substance1 to the composition of which both the mineral and animal kingdoms seem to concur4 ,this most useful mineral appears to consist chiefly of vegetable matter1 mixed with the remains of marine animals and marine salts1 and occasionally containing a quantity of sulphuret of iron1 commonly called pyrites4 ,,emily4 ,it is1 ,i suppose1 the earthly1 the metallic1 and the saline parts of coals1 that compose the cinders or fixed products of their combustion2 whilst the hydrogen and carbon1 which they derive from vegetables1 constitute their volatile products4 ,,caroline4 ,pray is not coke1 7which ,i have heard is much used in some manufactures17 also a bituminous substance8 ,,mrs4 ,b4 ,no2 it is a kind of fuel artificially prepared from coals4 ,it consists of coals reduced to a substance analogous to charcoal1 by the evaporation of their bituminous parts4 ,coke1 therefore1 is composed of carbon1 with some earthy and saline ingredients4 ,succin1 or yellow amber1 is a bitumen which the ancients called electrum1 from whence the word electricity is derived1 as that substance is peculiarly1 and was once supposed to be exclusively1 electric4 ,it is found either deeply buried in the bowels of the earth1 or floating on the sea1 and is supposed to be a resinous body which has been acted on by sulphuric acid1 as its analysis shows it to consist of ah oil and an acid4 ,the oil is called oil of amber1 the acid the succinic4 ,,emily4 ,that oil ,i have sometimes used in painting1 as it is reckoned to change less than the other kinds of oils4 ,,mrs4 ,b4 ,the last class of vegetable substances that have changed their nature are fossil-wood1 peat1 and turf4 ,these are composed of wood and roots of shrubs1 that are partly decomposed by being exposed to moisture under ground1 and yet1 in some measure1 preserve their form and organic appearance4 ,the peat1 or black earth of the moors1 retains but few vestiges of the roots to which it owes its richness and combustibility1 these substances being in the course of time reduced to the state of vegetable earth4 ,but in turf the roots of plants are still discernible1 and it equally answers the purpose of fuel4 ,it is the combustible used by the poor in heathy countries1 which supply it abundantly4 ,it is too late this morning to enter upon the history of vegetation4 ,we shall reserve this subject1 therefore1 for our next interview1 when ,i expect that it will furnish us with ample matter for another conversation4 ,,conversation ,,xxii4 ,,history ,,of ,,vegetation4 ,,mrs4 ,b4 ,the ,,vegetable ,,kingdom may be considered as the link which unites the mineral and animal creation into one common chain of beings2 for it is through the means of vegetation alone that mineral substances are introduced into the animal system1 since1 generally speaking1 it is from vegetables that all animals ultimately derive their sustenance4 ,,caroline4 ,i do not understand that2 the human species subsists as much on animal as on vegetable food1 and there are some carnivorous animals that will eat only animal food4 ,,mrs4 ,b4 ,that is true2 but you do not consider that those that live on animal food1 derive their sustenance equally1 though not so immediately1 from vegetables4 ,the meat that we eat is formed from the herbs of the field1 and the prey of carnivorous animals proceeds1 either directly or indirectly1 from the same source4 ,it is1 therefore1 through this channel that the simple elements become a part of the animal frame4 ,we should in vain attempt to derive nourishment from carbon1 hydrogen1 and oxygen1 either in their separate state1 or combined in the mineral kingdom2 for it is only by being united in the form of vegetable combination1 that they become capable of conveying nourishment4 ,,emily4 ,vegetation1 then1 seems to be the method which ,nature employs to prepare the food of animals8 ,,mrs4 ,b4 ,that is certainly its principal object4 ,the vegetable creation does not exhibit more wisdom in that admirable system of organisation1 by which it is enabled to answer its own immediate ends of preservation1 nutrition1 and propagation1 than in its grand and ultimate object of forming those arrangements and combinations of principles1 which are so well adapted for the nourishment of animals4 ,,emily4 ,but ,i am very curious to know whence vegetables obtain those principles which form their immediate materials8 ,,mrs4 ,b4 ,this is a point on which we are yet so much in the dark1 that ,i cannot hope fully to satisfy your curiosity2 but what little ,i know on this subject1 ,i will endeavour to explain to you4 ,the soil1 which1 at first view1 appears to be the aliment of vegetables1 is found1 on a closer investigation1 to be little more than the channel through which they receive their nourishment2 so that it is very possible to rear plants without any earth or soil4 ,,caroline4 ,of that we have an instance in the hyacinth and other bulbous roots1 which will grow and blossom beautifully in glasses of water4 ,but ,i confess ,i should think it would be difficult to rear trees in a similar manner4 ,,mrs4 ,b4 ,no doubt it would1 as it is the burying of the roots in the earth that supports the stem of the tree4 ,but this office1 besides that of affording a vehicle for food1 is far the most important part which the earthy portion of the soil performs in the process of vegetation2 for we can discover1 by analysis1 but an extremely small proportion of earth in vegetable compounds4 ,,caroline4 ,but if earths do not afford nourishment1 why is it necessary to be so attentive to the preparation of the soil8 ,,mrs4 ,b4 ,in order to impart to it those qualities which render it a proper vehicle for the food of the plant4 ,water is the chief nourishment of vegetables2 if1 therefore1 the soil be too sandy1 it will not retain a quantity of water sufficient to supply the roots of the plants4 ,if1 on the contrary1 it abound too much with clay1 the water will lodge in such quantities as to threaten a decomposition of the roots4 ,calcareous soils are1 upon the whole1 the most favourable to the growth of plants3 soils are1 therefore1 usually improved by chalk1 which1 you may recollect1 is a carbonat of lime4 ,different vegetables1 however1 require different kinds of soils4 ,thus rice demands a moist retentive soil2 potatoes a soft sandy soil2 wheat a firm and rich soil4 ,forest trees grow better in fine sand than in a stiff clay2 and a light ferruginous soil is best suited to fruit-trees4 ,,caroline4 ,but pray what is the use of manuring the soil8 ,,mrs4 ,b4 ,manure consists of all kinds of substances1 whether of vegetable or animal origin1 which have undergone the putrid fermentation1 and are consequently decomposed1 or nearly so1 into their elementary principles4 ,and it is requisite that these vegetable matters should be in a state of decay1 or approaching decomposition4 ,the addition of calcareous earth1 in the state of chalk or lime1 is beneficial to such soils1 as it accelerates the dissolution of vegetable bodies4 ,now1 ,i ask you1 what is the utility of supplying the soil with these decomposed substances8 ,,caroline4 ,it is1 ,i suppose1 in order to furnish vegetables with the principles which enter into their composition4 ,for manures not only contain carbon1 hydrogen1 and oxygen1 but by their decomposition supply the soil with these principles in their elementary form4 ,,mrs4 ,b4 ,undoubtedly2 and it is for this reason that the finest crops are produced in fields that were formerly covered with woods1 because their soil is composed of a rich mould1 a kind of vegetable earth1 which abounds in those principles4 ,,emily4 ,this accounts for the plentifulness of the crops produced in ,america1 where the country was but a few years since covered with wood4 ,,caroline4 ,but how is it that animal substances are reckoned to produce the best manure8 ,does it not appear much more natural that the decomposed elements of vegetables should be the most appropriate to the formation of new vegetables8 ,,mrs4 ,b4 ,the addition of a much greater proportion of nitrogen1 which constitutes the chief difference between animal and vegetable matter1 renders the composition of the former more complicated1 and consequently more favourable to decomposition4 ,the use of animal substances is chiefly to give the first impulse to the fermentation of the vegetable ingredients that enter into the composition of manures4 ,the manure of a farm-yard is of that description2 but there is scarcely any substance susceptible of undergoing the putrid fermentation that will not make good manure4 ,the heat produced by the fermentation of manure is another circumstance which is extremely favourable to vegetation2 yet this heat would be too great if the manure was laid on the ground during the height of fermentation2 it is used in this state only for hot-beds1 to produce melons1 cucumbers1 and such vegetables as require a very high temperature4 ,,caroline4 ,a difficulty has just occurred to me which ,i do not know how to remove4 ,since all organised bodies are1 in the common course of nature1 ultimately reduced to their elementary state1 they must necessarily in that state enrich the soil1 and afford food for vegetation4 ,how is it1 then1 that agriculture1 which cannot increase the quantity of those elements that are required to manure the earth1 can increase its produce so wonderfully as is found to be the case in all cultivated countries8 ,,mrs4 ,b4 ,it is by suffering none of these decaying bodies to be dissipated1 but in applying them duly to the soil4 ,it is by a judicious preparation of the soil1 which consists in fitting it either for the general purposes of vegetation1 or for that of the particular seed which is to be sown4 ,thus1 if the soil be too wet1 it may be drained2 if too loose and sandy1 it may be rendered more consistent and retentive of water by the addition of clay or loam2 it may be enriched by chalk1 or any kind of calcareous earth4 ,on soils thus improved1 manures will act with double efficacy1 and if attention be paid to spread them on the ground at a proper season of the year1 to mix them with the soil so that they may be generally diffused through it1 to destroy the weeds which might appropriate these nutritive principles to their own use1 to remove the stones which would impede the growth of the plant1 c4 we may obtain a produce an hundred fold more abundant than the earth would spontaneously supply4 ,,emily4 ,we have a very striking instance of this in the scanty produce of uncultivated commons1 compared to the rich crops of meadows which are occasionally manured4 ,,caroline4 ,but1 ,mrs4 ,b41 though experience daily proves the advantage of cultivation1 there is still a difficulty which ,i cannot get over4 ,a certain quantity of elementary principles exist in nature1 which it is not in the power of man either to augment or diminish4 ,of these principles you have taught us that both the animal and vegetable creation are composed4 ,now the more of them is taken up by the vegetable kingdom1 the less1 it would seem1 will remain for animals2 and1 therefore1 the more populous the earth becomes1 the less it will produce4 ,,mrs4 ,b4 ,your reasoning is very plausible2 but experience every where contradicts the inference you would draw from it2 for we find that the animal and vegetable kingdoms1 instead of thriving1 as you would suppose1 at each other's expense1 always increase and multiply together4 ,for you should recollect that animals can derive the elements of which they are formed only through the medium of vegetables4 ,and you must allow that your conclusion would be valid only if every particle of the several principles that could possibly be spared from other purposes were employed in the animal and vegetable creations4 ,now we have reason to believe that a much greater proportion of these principles than is required for such purposes remains either in an elementary state1 or engaged in a less useful mode of combination in the mineral kingdom4 ,possessed of such immense resources as the atmosphere and the waters afford us1 for oxygen1 hydrogen1 and carbon1 so far from being in danger of working up all our simple materials1 we cannot suppose that we shall ever bring agriculture to such a degree of perfection as to require the whole of what these resources could supply4 ,nature1 however1 in thus furnishing us with an inexhaustible stock of raw materials1 leaves it in some measure to the ingenuity of man to appropriate them to its own purposes4 ,but1 like a kind parent1 she stimulates him to exertion1 by setting the example and pointing out the way4 ,for it is on the operations of nature that all the improvements of art are founded4 ,the art of agriculture consists1 therefore1 in discovering the readiest method of obtaining the several principles1 either from their grand sources1 air and water1 or from the decomposition of organised bodies2 and in appropriating them in the best manner to the purposes of vegetation4 ,,emily4 ,but1 among the sources of nutritive principles1 ,i am surprised that you do not mention the earth itself1 as it contains abundance of coals1 which are chiefly composed of carbon4 ,,mrs4 ,b4 ,though coals abound in carbon1 they cannot1 on account of their hardness and impermeable texture1 be immediately subservient to the purposes of vegetation4 ,,emily4 ,no2 but by their combustion carbonic acid is produced2 and this entering into various combinations on the surface of the earth1 may1 perhaps1 assist in promoting vegetation4 ,,mrs4 ,b4 ,probably it may in some degree2 but at any rate the quantity of nourishment which vegetables may derive from that source can be but very trifling1 and must entirely depend on local circumstances4 ,,caroline4 ,perhaps the smoky atmosphere of ,london is the cause of vegetation being so forward and so rich in its vicinity8 ,,mrs4 ,b4 ,i rather believe that this circumstance proceeds from the very ample supply of manure1 assisted1 perhaps1 by the warmth and shelter which the town affords4 ,far from attributing any good to the smoky atmosphere of ,london1 ,i confess ,i like to anticipate the time when we shall have made such progress in the art of managing combustion1 that every particle of carbon will be consumed1 and the smoke destroyed at the moment of its production4 ,we may then expect to have the satisfaction of seeing the atmosphere of ,london as clear as that of the country4 --,but to return to our subject3 ,i hope that you are now convinced that we shall not easily experience a deficiency of nutritive elements to fertilise the earth1 and that1 provided we are but industrious in applying them to the best advantage by improving the art of agriculture1 no limits can be assigned to the fruits that we may expect to reap from our labours4 ,,caroline4 ,yes2 ,i am perfectly satisfied in that respect1 and ,i can assure you that ,i feel already much more interested in the progress and improvement of agriculture4 ,,emily4 ,i have frequently thought that the culture of the land was not considered as a concern of sufficient importance4 ,manufactures always take the lead2 and health and innocence are frequently sacrificed to the prospect of a more profitable employment4 ,it has often grieved me to see the poor manufacturers crowded together in close rooms1 and confined for the whole day to the most uniform and sedentary employment1 instead of being engaged in that innocent and salutary kind of labour1 which ,nature seems to have assigned to man for the immediate acquirement of comfort1 and for the preservation of his existence4 ,i am sure that you agree with me in thinking so1 ,mrs4 ,b48 ,,mrs4 ,b4 ,i am entirely of your opinion1 my dear1 in regard to the importance of agriculture2 but as the conveniences of life1 which we are all enjoying1 are not derived merely from the soil1 ,i am far from wishing to depreciate manufactures4 ,besides1 as the labour of one man is sufficient to produce food for several1 those whose industry is not required in tillage must do something in return for the food that is provided for them4 ,they exchange1 consequently1 the accommodations for the necessaries of life4 ,thus the carpenter and the weaver lodge and clothe the peasant1 who supplies them with their daily bread4 ,the greater stock of provisions1 therefore1 which the husbandman produces1 the greater is the quantity of accommodation which the artificer prepares4 ,such are the happy effects which naturally result from civilised society4 ,it would be wiser1 therefore1 to endeavour to improve the situation of those who are engaged in manufactures1 than to indulge in vain declamations on the hardships to which they are too frequently exposed4 ,but we must not yet take our leave of the subject of agriculture2 we have prepared the soil1 it remains for us now to sow the seed4 ,in this operation we must be careful not to bury it too deep in the ground1 as the access of air is absolutely necessary to its germination2 the earth must1 therefore1 lie loose and light over it1 in order that the air may penetrate4 ,hence the use of ploughing and digging1 harrowing and raking1 c4 ,a certain degree of heat and moisture1 such as usually takes place in the spring1 is likewise necessary4 ,,caroline4 ,one would imagine you were going to describe the decomposition of an old plant1 rather than the formation of a new one2 for you have enumerated all the requisites of fermentation4 ,,mrs4 ,b4 ,do you forget1 my dear1 that the young plant derives its existence from the destruction of the seed1 and that it is actually by the saccharine fermentation that the latter is decomposed8 ,,caroline4 ,true2 ,i wonder that ,i did not recollect that4 ,the temperature and moisture required for the germination of the seed is then employed in producing the saccharine fermentation within it8 ,,mrs4 ,b4 ,certainly4 ,but1 in order to understand the nature of germination1 you should be acquainted with the different parts of which the seed is composed4 ,the external covering or envelope contains1 besides the germ of the future plant1 the substance which is to constitute its first nourishment2 this substance1 which is called the parenchyma1 consists of fecula1 mucilage1 and oil1 as we formerly observed4 ,the seed is generally divided into two compartments1 called lobes1 or cotyledons1 as is exemplified by this bean 7,,plate ,,xv4 ,fig4 #a47--the dark-coloured kind of string which divides the lobes is called the radicle1 as it forms the root of the plant1 and it is from a contiguous substance1 called plumula1 which is enclosed within the lobes1 that the stem arises4 ,the figure and size of the seed depend very much upon the cotyledons2 these vary in number in different seeds2 some have only one1 as wheat1 oats1 barley1 and all the grasses2 some have three1 others six4 ,but most seeds1 as1 for instance1 all the varieties of beans1 have two cotyledons4 ,when the seed is buried in the earth1 at any temperature above #dj degrees1 it imbibes water1 which softens and swells the lobes2 it then absorbs oxygen1 which combines with some of its carbon1 and is returned in the form of carbonic acid4 ,this loss of carbon increases the comparative proportion of hydrogen and oxygen in the seed1 and excites the saccharine fermentation1 by which the parenchymatous matter is converted into a kind of sweet emulsion4 ,in this form it is carried into the radicle by vessels appropriated to that purpose2 and in the mean time1 the fermentation having caused the seed to burst1 the cotyledons are rent asunder1 the radicle strikes into the ground and becomes the root of the plant1 and hence the fermented liquid is conveyed to the plumula1 whose vessels have been previously distended by the heat of the fermentation4 ,the plumula being thus swelled1 as it were1 by the emulsive fluid1 raises itself and springs up to the surface of the earth1 bearing with it the cotyledons1 which1 as soon as they come in contact with the air1 spread themselves1 and are transformed into leaves4 --,if we go into the garden1 we shall probably find some seeds in the state which ,i have described-- ,illustration3 ,plate ,,xv4 ,vol4 ,,ii4 p4 #bej ,germination4 ,fig4 #a #b4 ,a4,b ,cotyledons4 ,c ,envelope4 ,d ,radicle4 ,fig4 #c4 ,a4,b ,cotyledons4 ,c ,plumula4 ,d ,radicle4 ,fig4 #d4 ,a4,b4 ,cotyledons4 ,c ,plumula4 ,d ,radicle4 ,fig4 #e4 ,apparatus to illustrate the mechanism of breathing4 ,a4,a ,glass ,bell4 ,b ,bladder representing the lungs4 ,c ,bladder representing the ,diaphragm4 ,,emily4 ,here are some lupines that are just making their appearance above ground4 ,,mrs4 ,b4 ,we shall take up several of them to observe their different degrees of progress in vegetation4 ,here is one that has but recently burst its envelope--do you see the little radicle striking downwards8 7,,plate ,,xv4 ,fig4 #b47 ,in this the plumula is not yet visible4 ,but here is another in a greater state of forwardness--the plumula1 or stem1 has risen out of the ground1 and the cotyledons are converted into seed leaves4 7,,plate ,,xv4 ,fig4 #c47 ,,caroline4 ,these leaves are very thick and clumsy1 and unlike the other leaves1 which ,i perceive are just beginning to appear4 ,,mrs4 ,b4 ,it is because they retain the remains of the parenchyma1 with which they still continue to nourish the young plant1 as it has not yet sufficient roots and strength to provide for its sustenance from the soil4 --,but1 in this third lupine 7,,plate ,,xv4 ,fig4 #d471 the radicle had sunk deep into the earth1 and sent out several shoots1 each of which is furnished with a mouth to suck up nourishment from the soil2 the function of the original leaves1 therefore1 being no longer required1 they are gradually decaying1 and the plumula is become a regular stem1 shooting out small branches1 and spreading its foliage4 ,,emily4 ,there seems to be a very striking analogy between a seed and an egg2 both require an elevation of temperature to be brought to life2 both at first supply with aliment the organised being which they produce2 and as soon as this has attained sufficient strength to procure its own nourishment1 the egg-shell breaks1 whilst in the plant the seed-leaves fall off4 ,,mrs4 ,b4 ,there is certainly some resemblance between these processes2 and when you become acquainted with animal chemistry1 you will frequently be struck with its analogy to that of the vegetable kingdom4 ,as soon as the young plant feeds from the soil1 it requires the assistance of leaves1 which are the organs by which it throws off its super-abundant fluid2 this secretion is much more plentiful in the vegetable than in the animal creation1 and the great extent of surface of the foliage of plants is admirably calculated for carrying it on in sufficient quantities4 ,this transpired fluid consists of little more than water4 ,the sap1 by this process1 is converted into a liquid of greater consistence1 which is fit to be assimilated to its several parts4 ,,emily4 ,vegetation1 then1 must be essentially injured by destroying the leaves of the plant8 ,,mrs4 ,b4 ,undoubtedly2 it not only diminishes the transpiration1 but also the absorption by the roots2 for the quantity of sap absorbed is always in proportion to the quantity of fluid thrown off by transpiration4 ,you see1 therefore1 the necessity that a young plant should unfold its leaves as soon as it begins to derive its nourishment from the soil2 and1 accordingly1 you will find that those lupines which have dropped their seed-leaves1 and are no longer fed by the parenchyma1 have spread their foliage1 in order to perform the office just described4 ,but ,i should inform you that this function of transpiration seems to be confined to the upper surface of the leaves1 whilst1 on the contrary1 the lower surface1 which is more rough and uneven1 and furnished with a kind of hair or down1 is destined to absorb moisture1 or such other ingredients as the plant derives from the atmosphere4 ,as soon as a young plant makes its appearance above ground1 light1 as well as air1 becomes necessary to its preservation4 ,light is essential to the development of the colours1 and to the thriving of the plant4 ,you may have often observed what a predilection vegetables have for the light4 ,if you make any plants grow in a room1 they all spread their leaves1 and extend their branches towards the windows4 ,,caroline4 ,and many plants close up their flowers as soon as it is dark4 ,,emily4 ,but may not this be owing to the cold and dampness of the evening air8 ,,mrs4 ,b4 ,that does not appear to be the case2 for in a course of curious experiments1 made by ,mr4 ,senebier1 of ,geneva1 on plants which he reared by lamp-light1 he found that the flowers closed their petals whenever the lamps were extinguished4 ,,emily4 ,but pray1 why is air essential to vegetation1 plants do not breathe it like animals8 ,,mrs4 ,b4 ,at least not in the same manner2 but they certainly derive some principles from the atmosphere1 and yield others to it4 ,indeed1 it is chiefly owing to the action of the atmosphere and the vegetable kingdom on each other1 that the air continues always fit for respiration4 ,but you will understand this better when ,i have explained the effect of water on plants4 ,i have said that water forms the chief nourishment of plants2 it is the basis not only of the sap1 but of all the vegetable juices4 ,water is the vehicle which carries into the plant the various salts and other ingredients required for the formation and support of the vegetable system4 ,nor is this all2 part of the water itself is decomposed by the organs of the plant2 the hydrogen becomes a constituent part of oil1 of extract1 of colouring matter1 c4 whilst a portion of the oxygen enters into the formation of mucilage1 of fecula1 of sugar1 and of vegetable acids4 ,but the greater part of the oxygen1 proceeding from the decomposition of the water1 is converted into a gaseous state by the caloric disengaged from the hydrogen during its condensation in the formation of the vegetable materials4 ,in this state the oxygen is transpired by the leaves of plants when exposed to the sun's rays4 ,thus you find that the decomposition of water1 by the organs of the plant1 is not only a means of supplying it with its chief ingredient1 hydrogen1 but at the same time of replenishing the atmosphere with oxygen1 a principle which requires continual renovation1 to make up for the great consumption of it occasioned by the numerous oxygenations1 combustions1 and respirations1 that are constantly taking place on the surface of the globe4 ,,emily4 ,what a striking instance of the harmony of nature4 ,,mrs4 ,b4 ,and how admirable the design of ,providence1 who makes every different part of the creation thus contribute to the support and renovation of each other6 ,but the intercourse of the vegetable and animal kingdoms through the medium of the atmosphere extends still further4 ,animals1 in breathing1 not only consume the oxygen of the air1 but load it with carbonic acid1 which1 if accumulated in the atmosphere1 would1 in a short time1 render it totally unfit for respiration4 ,here the vegetable kingdom again interferes2 it attracts and decomposes the carbonic acid1 retains the carbon for its own purposes1 and returns the oxygen for ours4 ,,caroline4 ,how interesting this is6 ,i do not know a more beautiful illustration of the wisdom which is displayed in the laws of nature4 ,,mrs4 ,b4 ,faint and imperfect as are the ideas which our limited perceptions enable us to form of divine wisdom1 still they cannot fail to inspire us with awe and admiration4 ,what1 then1 would be our feelings1 were the complete system of nature at once displayed before us6 ,so magnificent a scene would probably be too great for our limited and imperfect comprehension1 and it is no doubt among the wise dispensations of ,providence1 to veil the splendour of a glory with which we should be overpowered4 ,but it is well suited to the nature of a rational being to explore1 step by step1 the works of the creation1 to endeavour to connect them into harmonious systems2 and1 in a word1 to trace in the chain of beings1 the kindred ties and benevolent design which unites its various links1 and secure its preservation4 ,,caroline4 ,but of what nature are the organs of plants which are endued with such wonderful powers8 ,,mrs4 ,b4 ,they are so minute that their structure1 as well as the mode in which they perform their functions1 generally elude our examination2 but we may consider them as so many vessels or apparatus appropriated to perform1 with the assistance of the principle of life1 certain chemical processes1 by means of which these vegetable compounds are generated4 ,we may1 however1 trace the tannin1 resins1 gum1 mucilage1 and some other vegetable materials1 in the organised arrangement of plants1 in which they form the bark1 the wood1 the leaves1 flowers1 and seeds4 ,the bark is composed of the epidermis1 the parenchyma1 and the cortical layers4 ,the epidermis is the external covering of the plant4 ,it is a thin transparent membrane1 consisting of a number of slender fibres1 crossing each other1 and forming a kind of net-work4 ,when of a white glossy nature1 as in several species of trees1 in the stems of corn and of seeds1 it is composed of a thin coating of siliceous earth1 which accounts for the strength and hardness of those long and slender stems4 ,sir ,h4 ,davy was led to the discovery of the siliceous nature of the epidermis of such plants1 by observing the singular phenomenon of sparks of fire emitted by the collision of ratan canes with which two boys were fighting in a dark room4 ,on analysing the epidermis of the cane1 he found it to be almost entirely siliceous4 ,,caroline4 ,with iron then1 a cane1 ,i suppose1 will strike fire very easily8 ,,mrs4 ,b4 ,i understand that it will4 --,in ever-greens the epidermis is mostly resinous1 and in some few plants is formed of wax4 ,the resin1 from its want of affinity for water1 tends to preserve the plant from the destructive effects of violent rains1 severe climates1 or inclement seasons1 to which this species of vegetables is peculiarly exposed4 ,,emily4 ,resin must preserve wood just like a varnish1 as it is the essential ingredient of varnishes8 ,,mrs4 ,b4 ,yes2 and by this means it prevents likewise all unnecessary expenditure of moisture4 ,the parenchyma is immediately beneath the epidermis2 it is that green rind which appears when you strip a branch of any tree or shrub of its external coat of bark4 ,the parenchyma is not confined to the stem or branches1 but extends over every part of the plant4 ,it forms the green matter of the leaves1 and is composed of tubes filled with a peculiar juice4 ,the cortical layers are immediately in contact with the wood2 they abound with tannin and gallic acid1 and consist of small vessels through which the sap descends after being elaborated in the leaves4 ,the cortical layers are annually renewed1 the old bark being converted into wood4 ,,emily4 ,but through what vessels does the sap ascend8 ,,mrs4 ,b4 ,that function is performed by the tubes of the alburnum1 or wood1 which is immediately beneath the cortical layers4 ,the wood is composed of woody fibre1 mucilage1 and resin4 ,the fibres are disposed in two ways2 some of them longitudinally1 and these form what is called the silver grain of the wood4 ,the others1 which are concentric1 are called the spurious grain4 ,these last are disposed in layers1 from the number of which the age of the tree may be computed1 a new one being produced annually by the conversion of the bark into wood4 ,the oldest1 and consequently most internal part of the alburnum1 is called heart-wood2 it appears to be dead1 at least no vital functions are discernible in it4 ,it is through the tubes of the living alburnum that the sap rises4 ,these1 therefore1 spread into the leaves1 and there communicate with the extremities of the vessels of the cortical layers1 into which they pour their contents4 ,,caroline4 ,of what use1 then1 are the tubes of the parenchyma1 since neither the ascending nor descending sap passes through them8 ,,mrs4 ,b4 ,they are supposed to perform the important function of secreting from the sap the peculiar juices from which the plant more immediately derives its nourishment4 ,these juices are very conspicuous1 as the vessels which contain them are much larger than those through which the sap circulates4 ,the peculiar juices of plants differ much in their nature1 not only in different species of vegetables1 but frequently in different parts of the same individual plant3 they are sometimes saccharine1 as in the sugar-cane1 sometimes resinous1 as in firs and evergreens1 sometimes of a milky appearance1 as in the laurel4 ,,emily4 ,i have often observed1 that in breaking a young shoot1 or in bruising a leaf of laurel1 a milky juice will ooze out in great abundance4 ,,mrs4 ,b4 ,and it is by making incisions in the bark that pitch1 tar1 and turpentine are obtained from fir-trees4 ,the durability of this species of wood is chiefly owing to the resinous nature of its peculiar juices4 ,the volatile oils have1 in a great measure1 the same preservative effects1 as they defend the parts1 with which they are connected1 from the attack of insects4 ,this tribe seems to have as great an aversion to perfumes1 as the human species have delight in them4 ,they scarcely ever attack any odoriferous parts of plants1 and it is not uncommon to see every leaf of a tree destroyed by a blight1 whilst the blossoms remain untouched4 ,cedar1 sandal1 and all aromatic woods1 are on this account of great durability4 ,,emily4 ,but the wood of the oak1 which is so much esteemed for its durability1 has1 ,i believe1 no smell4 ,does it derive this quality from its hardness alone8 ,,mrs4 ,b4 ,not entirely2 for the chesnut1 though considerably harder and firmer than the oak1 is not so lasting4 ,the durability of the oak is1 ,i believe1 in a great measure owing to its having very little heart-wood1 the alburnum preserving its vital functions longer than in other trees4 ,,caroline4 ,if incisions are made into the alburnum and cortical layers1 may not the ascending and descending sap be procured in the same manner as the peculiar juice is from the vessels of the parenchyma8 ,,mrs4 ,b4 ,yes2 but in order to obtain specimens of these fluids1 in any quantity1 the experiment must be made in the spring1 when the sap circulates with the greatest energy4 ,for this purpose a small bent glass tube should be introduced into the incision1 through which the sap may flow without mixing with any of the other juices of the tree4 ,from the bark the sap will flow much more plentifully than from the wood1 as the ascending sap is much more liquid1 more abundant1 and more rapid in its motion than that which descends2 for the latter having been deprived by the operation of the leaves of a considerable part of its moisture1 contains a much greater proportion of solid matter1 which retards its motion4 ,it does not appear that there is any excess of descending sap1 as none ever exudes from the roots of plants2 this process1 therefore1 seems to be carried on only in proportion to the wants of the plant1 and the sap descends no further1 and in no greater quantity1 than is required to nourish the several organs4 ,therefore1 though the sap rises and descends in the plant1 it does not appear to undergo a real circulation4 ,the last of the organs of plants is the flower1 or blossom1 which produces the fruits and seed4 ,these may be considered as the ultimate purpose of nature in the vegetable creation4 ,from fruits and seeds animals derive both a plentiful source of immediate nourishment1 and an ample provision for the reproduction of the same means of subsistence4 ,the seed which forms the final product of mature plants1 we have already examined as constituting the first rudiments of future vegetation4 ,these are the principal organs of vegetation1 by means of which the several chemical processes which are carried on during the life of the plant are performed4 ,,emily4 ,but how are the several principles which enter into the composition of vegetables so combined by the organs of the plant as to be converted into vegetable matter8 ,,mrs4 ,b4 ,by chemical processes1 no doubt2 but the apparatus in which they are performed is so extremely minute as completely to elude our examination4 ,we can form an opinion1 therefore1 only by the result of these operations4 ,the sap is evidently composed of water1 absorbed by the roots1 and holding in solution the various principles which it derives from the soil4 ,from the roots the sap ascends through the tubes of the alburnum into the stem1 and thence branches out to every extremity of the plant4 ,together with the sap circulates a certain quantity of carbonic acid1 which is gradually disengaged from the former by the internal heat of the plant4 ,,caroline4 ,what6 have vegetables a peculiar heat1 analogous to animal heat8 ,,mrs4 ,b4 ,it is a circumstance that has long been suspected2 but late experiments have decided beyond a doubt that vegetable heat is considerably above that of unorganised matter in winter1 and below it in summer4 ,the wood of a tree is about sixty degrees1 when the thermometer is seventy or eighty degrees4 ,and the bark1 though so much exposed1 is seldom below forty in winter4 ,it is from the sap1 after it has been elaborated by the leaves1 that vegetables derive their nourishment2 in its progress through the plant from the leaves to the roots1 it deposits in the several sets of vessels with which it communicates1 the materials on which the growth and nourishment of each plant depends4 ,it is thus that the various peculiar juices1 saccharine1 oily1 mucous1 acid1 and colouring1 are formed2 as also the more solid parts1 fecula1 woody fibre1 tannin1 resins1 concrete salts2 in a word1 all the immediate materials of vegetables1 as well as the organised parts of plants1 which latter1 besides the power of secreting these from the sap for the general purpose of the plant1 have also that of applying them to their own particular nourishment4 ,,emily4 ,but why should the process of vegetation take place only at one season of the year1 whilst a total inaction prevails during the other8 ,,mrs4 ,b4 ,heat is such an important chemical agent1 that its effect1 as such1 might perhaps alone account for the impulse which the spring gives to vegetation4 ,but1 in order to explain the mechanism of that operation1 it has been supposed that the warmth of the spring dilates the vessels of plants1 and produces a kind of vacuum1 into which the sap 7which had remained in a state of inaction in the trunk during the winter7 rises3 this is followed by the ascent of the sap contained in the roots1 and room is thus made for fresh sap1 which the roots1 in their turn1 pump up from the soil4 ,this process goes on till the plant blossoms and bears fruit1 which terminates its summer career3 but when the cold weather sets in1 the fibres and vessels contract1 the leaves wither1 and are no longer able to perform their office of transpiration2 and1 as this secretion stops1 the roots cease to absorb sap from the soil4 ,if the plant be an annual1 its life then terminates2 if not1 it remains in a state of torpid inaction during the winter2 or the only internal motion that takes place is that of a small quantity of resinous juice1 which slowly rises from the stem into the branches1 and enlarges their buds during the winter4 ,,caroline4 ,yet1 in evergreens1 vegetation must continue throughout the year4 ,,mrs4 ,b4 ,yes2 but in winter it goes on in a very imperfect manner1 compared to the vegetation of spring and summer4 ,we have dwelt much longer on the history of vegetable chemistry than ,i had intended2 but we have at length1 ,i think1 brought the subject to a conclusion4 ,,caroline4 ,i rather wonder that you did not reserve the account of the fermentations for the conclusion2 for the decomposition of vegetables naturally follows their death1 and can hardly1 it seems1 be introduced with so much propriety at any other period4 ,,mrs4 ,b4 ,it is difficult to determine at what point precisely it may be most eligible to enter on the history of vegetation2 every part of the subject is so closely connected1 and forms such an uninterrupted chain1 that it is by no means easy to divide it4 ,had ,i begun with the germination of the seed1 which1 at first view1 seems to be the most proper arrangement1 ,i could not have explained the nature and fermentation of the seed1 or have described the changes which manure must undergo1 in order to yield the vegetable elements4 ,to understand the nature of germination1 it is necessary1 ,i think1 previously to decompose the parent plant1 in order to become acquainted with the materials required for that purpose4 ,i hope1 therefore1 that1 upon second consideration1 you will find that the order which ,i have adopted1 though apparently less correct1 is in fact the best calculated for the elucidation of the subject4 ,,conversation ,,xxiii4 ,,on ,,the ,,composition ,,of ,,animals4 ,,mrs4 ,b4 ,we are now come to the last branch of chemistry1 which comprehends the most complicated order of compound beings4 ,this is the animal creation1 the history of which cannot but excite the highest degree of curiosity and interest1 though we often fail in attempting to explain the laws by which it is governed4 ,,emily4 ,but since all animals ultimately derive their nourishment from vegetables1 the chemistry of this order of beings must consist merely in the conversion of vegetable into animal matter4 ,,mrs4 ,b4 ,very true2 but the manner in which this is effected is1 in a great measure1 concealed from our observation4 ,this process is called animalisation1 and is performed by peculiar organs4 ,the difference of the animal and vegetable kingdoms does not however depend merely on a different arrangement of combinations4 ,a new principle abounds in the animal kingdom1 which is but rarely and in very small quantities found in vegetables2 this is nitrogen4 ,there is likewise in animal substances a greater and more constant proportion of phosphoric acid1 and other saline matters4 ,but these are not essential to the formation of animal matter4 ,,caroline4 ,animal compounds contain1 then1 four fundamental principles2 oxygen1 hydrogen1 carbon1 and nitrogen8 ,,mrs4 ,b4 ,yes2 and these form the immediate materials of animals1 which are gelatine1 albumen1 and fibrine4 ,,emily4 ,are those all8 ,i am surprised that animals should be composed of fewer kinds of materials than vegetables2 for they appear much more complicated in their organisation4 ,,mrs4 ,b4 ,their organisation is certainly more perfect and intricate1 and the ingredients that occasionally enter into their composition are more numerous4 ,but notwithstanding the wonderful variety observable in the texture of the animal organs1 we find that the original compounds1 from which all the varieties of animal matter are derived1 may be reduced to the three heads just mentioned4 ,animal substances being the most complicated of all natural compounds1 are most easily susceptible of decomposition1 as the scale of attractions increases in proportion to the number of constituent principles4 ,their analysis is1 however1 both difficult and imperfect2 for as they cannot be examined in their living state1 and are liable to alteration immediately after death1 it is probable that1 when submitted to the investigation of a chemist1 they are always more or less altered in their combinations and properties1 from what they were1 whilst they made part of the living animal4 ,,emily4 ,the mere diminution of temperature1 which they experience by the privation of animal heat1 must1 ,i should suppose1 be sufficient to derange the order of attractions that existed during life4 ,,mrs4 ,b4 ,that is one of the causes1 no doubt3 but there are many other circumstances which prevent us from studying the nature of living animal substances4 ,we must therefore1 in a considerable degree1 confine our researches to the phenomena of these compounds in their inanimate state4 ,these three kinds of animal matter1 gelatine1 albumen1 and fibrine1 form the basis of all the various parts of the animal system2 either solid1 as the skin1 flesh1 nerves1 membranes1 cartilages1 and bones2 or fluid1 as blood1 chyle1 milk1 mucus1 the gastric and pancreatic juices1 bile1 perspiration1 saliva1 tears1 c4 ,,caroline4 ,is it not surprising that so great a variety of substances1 and so different in their nature1 should yet all arise from so few materials1 and from the same original elements8 ,,mrs4 ,b4 ,the difference in the nature of various bodies depends1 as ,i have often observed to you1 rather on their state of combination1 than on the materials of which they are composed4 ,thus1 in considering the chemical nature of the creation in a general point of view1 we observe that it is throughout composed of a very small number of elements4 ,but when we divide it into the three kingdoms1 we find that1 in the mineral1 the combinations seem to result from the union of elements casually brought together2 whilst in the vegetable and animal kingdoms1 the attractions are peculiarly and regularly produced by appropriate organs1 whose action depends on the vital principle4 ,and we may further observe1 that by means of certain spontaneous changes and decompositions1 the elements of one kind of matter become subservient to the reproduction of another2 so that the three kingdoms are intimately connected1 and constantly contributing to the preservation of each other4 ,,emily4 ,there is1 however1 one very considerable class of elements1 which seems to be confined to the mineral kingdom3 ,i mean metals4 ,,mrs4 ,b4 ,not entirely2 they are found1 though in very minute quantities1 both in the vegetable and animal kingdoms4 ,a small portion of earths and sulphur enters also into the composition of organised bodies4 ,phosphorus1 however1 is almost entirely confined to the animal kingdom2 and nitrogen1 but with few exceptions1 is extremely scarce in vegetables4 ,let us now proceed to examine the nature of the three principal materials of the animal system4 ,gelatine1 or jelly1 is the chief ingredient of skin1 and of all the membranous parts of animals4 ,it may be obtained from these substances1 by means of boiling water1 under the forms of glue1 size1 isinglass1 and transparent jelly4 ,,caroline4 ,but these are of a very different nature2 they cannot therefore be all pure gelatine4 ,,mrs4 ,b4 ,not entirely1 but very nearly so4 ,glue is extracted from the skin of animals4 ,size is obtained either from skin in its natural state1 or from leather4 ,isinglass is gelatine procured from a particular species of fish2 it is1 you know1 of this substance that the finest jelly is made1 and this is done by merely dissolving the isinglass in boiling water1 and allowing the solution to congeal4 ,,emily4 ,the wine1 lemon1 and spices1 are1 ,i suppose1 added only to flavour the jelly8 ,,mrs4 ,b4 ,exactly so4 ,,caroline4 ,but jelly is often made of hartshorn shavings1 and of calves' feet2 do these substances contain gelatine8 ,,mrs4 ,b4 ,yes4 ,gelatine may be obtained from almost any animal substance1 as it enters more or less into the composition of all of them4 ,the process for obtaining it is extremely simple1 as it consists merely in boiling the substance that contains it with water4 ,the gelatine dissolves in water1 and may be attained of any degree of consistence or strength1 by evaporating this solution4 ,bones in particular produce it very plentifully1 as they consist of phosphat of lime combined or cemented by gelatine4 ,horns1 which are a species of bone1 will yield abundance of gelatine4 ,the horns of the hart are reckoned to produce gelatine of the finest quality2 they are reduced to the state of shavings in order that the jelly may be more easily extracted by the water4 ,it is of hartshorn shavings that the jellies for invalids are usually made1 as they are of very easy digestion4 ,,caroline4 ,it appears singular that hartshorn1 which yields such a powerful ingredient as ammonia1 should at the same time produce so mild and insipid a substance as jelly8 ,,mrs4 ,b4 ,and 7what is more surprising7 it is from the gelatine of bones that ammonia is produced4 ,you must observe1 however1 that the processes by which these two substances are obtained from bones are very different4 ,by the simple action of water and heat1 the gelatine is separated2 but in order to procure the ammonia1 or what is commonly called hartshorn1 the bones must be distilled1 by which means the gelatine is decomposed1 and hydrogen and nitrogen combined in the form of ammonia4 ,so that the first operation is a mere separation of ingredients1 whilst the second requires a chemical decomposition4 ,,caroline4 ,but when jelly is made from hartshorn shavings1 what becomes of the phosphat of lime which constitutes the other part of bones8 ,,mrs4 ,b4 ,it is easily separated by straining4 ,but the jelly is afterwards more perfectly purified1 and rendered transparent1 by adding white of egg1 which being coagulated by heat1 rises to the surface along with any impurities4 ,,emily4 ,i wonder that bones are not used by the common people to make jelly2 a great deal of wholesome nourishment1 might1 ,i should suppose1 be procured from them1 though the jelly would perhaps not be quite so good as if made from hartshorn shavings8 ,,mrs4 ,b4 ,there is a prejudice among the poor against a species of food that is usually thrown to the dogs2 and as we cannot expect them to enter into chemical considerations1 it is in some degree excusable4 ,besides1 it requires a prodigious quantity of fuel to dissolve bones and obtain the gelatine from them4 ,the solution of bones in water is greatly promoted by an accumulation of heat4 ,this may be effected by means of an extremely strong metallic vessel1 called ,papin's digester1 in which the bones and water are enclosed1 without any possibility of the steam making its escape4 ,a heat can thus be applied much superior to that of boiling water2 and bones1 by this means1 are completely reduced to a pulp4 ,but the process still consumes too much fuel to be generally adopted among the lower classes4 ,,caroline4 ,and why should not a manufacture be established for grinding or macerating bones1 or at least for reducing them to the state of shavings1 when ,i suppose they would dissolve as readily as hartshorn shavings8 ,,mrs4 ,b4 ,they could not be collected clean for such a purpose1 but they are not lost1 as they are used for making hartshorn and sal ammoniac2 and such is the superior science and industry of this country1 that we now send sal ammoniac to the ,levant1 though it originally came to us from ,egypt4 ,,emily4 ,when jelly is made of isinglass1 does it leave no sediment8 ,,mrs4 ,b4 ,no2 nor does it so much require clarifying1 as it consists almost entirely of pure gelantine1 and any foreign matter that is mixed with it1 is thrown off during the boiling in the form of scum4 --,these are processes which you may see performed in great perfection in the culinary laboratory1 by that very able and most useful chemist the cook4 ,,caroline4 ,to what an immense variety of purposes chemistry is subservient6 ,,emily4 ,it appears1 in that respect1 to have an advantage over most other arts and sciences2 for these1 very often1 have a tendency to confine the imagination to their own particular object1 whilst the pursuit of chemistry is so extensive and diversified1 that it inspires a general curiosity1 and a desire of enquiring into the nature of every object4 ,,caroline4 ,i suppose that soup is likewise composed of gelatine2 for1 when cold1 it often assumes the consistence of jelly8 ,,mrs4 ,b4 ,not entirely2 for though soups generally contain a quantity of gelatine1 the most essential ingredient is a mucous or extractive matter1 a peculiar animal substance1 very soluble in water1 which has a strong taste1 and is more nourishing than gelatine4 ,the various kinds of portable soup consist of this extractive matter in a dry state1 which1 in order to be made into soup1 requires only to be dissolved in water4 ,gelatine1 in its solid state1 is a semiductile transparent substance1 without either taste or smell4 --,when exposed to heat1 in contact with air and water1 it first swells1 then fuses1 and finally burns4 ,you may have seen the first part of this operation performed in the carpenter's glue-pot4 ,,caroline4 ,but you said that gelatine had no smell1 and glue has a very disagreeable one4 ,,mrs4 ,b4 ,glue is not pure gelatine2 as it is not designed for eating1 it is prepared without attending to the state of the ingredients1 which are more or less contaminated by particles that have become putrid4 ,gelatine may be precipitated from its solution in water by alcohol4 --,we shall try this experiment with a glass of warm jelly4 --,you see that the gelatine subsides by the union of the alcohol and the water4 ,,emily4 ,how is it1 then1 that jelly is flavoured with wine1 without producing any precipitation8 ,,mrs4 ,b4 ,because the alcohol contained in wine is already combined with water1 and other ingredients1 and is therefore not at liberty to act upon the jelly as when in its separate state4 ,gelatine is soluble both in acids and in alkalies2 the former1 you know1 are frequently used to season jellies4 ,,caroline4 ,among the combinations of gelatine we must not forget one which you formerly mentioned2 that with tannin1 to form leather4 ,,mrs4 ,b4 ,true2 but you must observe that leather can be produced only by gelatine in a membranous state2 for though pure gelatine and tannin will produce a substance chemically similar to leather1 yet the texture of the skin is requisite to make it answer the useful purposes of that substance4 ,the next animal substance we are to examine is albumen2 this1 although constituting a part of most of the animal compounds1 is frequently found insulated in the animal system2 the white of egg1 for instance1 consists almost entirely of albumen2 the substance that composes the nerves1 the serum1 or white part of the blood1 and the curds of milk1 are little else than albumen variously modified4 ,in its most simple state1 albumen appears in the form of a transparent viscous fluid1 possessed of no distinct taste or smell2 it coagulates at the low temperature of #afe degrees1 and1 when once solidified1 it will never return to its fluid state4 ,sulphuric acid and alcohol are each of them capable of coagulating albumen in the same manner as heat1 as ,i am going to show you4 ,,emily4 ,exactly so4 --,pray1 ,mrs4 ,b41 what kind of action is there between albumen and silver8 ,i have sometimes observed1 that if the spoon with which ,i eat an egg happens to be wetted1 it becomes tarnished4 ,,mrs4 ,b4 ,it is because the white of egg 7and1 indeed1 albumen in general7 contains a little sulphur1 which1 at the temperature of an egg just boiled1 will decompose the drop of water that wets the spoon1 and produce sulphurated hydrogen gas1 which has the property of tarnishing silver4 ,we may now proceed to fibrine4 ,this is an insipid and inodorous substance1 having somewhat the appearance of fine white threads adhering together2 it is the essential constituent of muscles or flesh1 in which it is mixed with and softened by gelatine4 ,it is insoluble both in water and alcohol1 but sulphuric acid converts it into a substance very analogous to gelatine4 ,these are the essential and general ingredients of animal matter2 but there are other substances1 which1 though not peculiar to the animal system1 usually enter into its composition1 such as oils1 acids1 salts1 c4 ,animal oil is the chief constituent of fat2 it is contained in abundance in the cream of milk1 whence it is obtained in the form of butter4 ,,emily4 ,is animal oil the same in its composition as vegetable oils8 ,,mrs4 ,b4 ,not the same1 but very analogous4 ,the chief difference is that animal oil contains nitrogen1 a principle which seldom enters into the composition of vegetable oils1 and never in so large a proportion4 ,there are a few animal acids1 that is to say1 acids peculiar to animal matter1 from which they are almost exclusively obtained4 ,the animal acids have triple bases of hydrogen1 carbon1 and nitrogen4 ,some of them are found native in animal matter2 others are produced during its decomposition4 ,those that we find ready formed are3 ,the bombic acid1 which is obtained from silk-worms4 ,the formic acid1 from ants4 ,the lactic acid1 from the whey of milk4 ,the sebacic1 from oil or fat4 ,those produced during the decomposition of animal substances by heat1 are the prussic and zoonic acids4 ,this last is produced by the roasting of meat1 and gives it a brisk flavour4 ,,caroline4 ,the class of animal acids is not very extensive8 ,,mrs4 ,b4 ,no2 nor are they1 generally speaking1 of great importance4 ,the prussic acid is1 ,i think1 the only one sufficiently interesting to require any further comment4 ,it can be formed by any artificial process1 without the presence of any animal matter2 and it may likewise be obtained from a variety of vegetables1 particularly those of the narcotic kind1 such as poppies1 laurel1 c4 ,but it is commonly obtained from blood1 by strongly heating that substance with caustic potash2 the alkali attracts the acid from the blood1 and forms with it a prussiat of potash4 ,from this state of combination the prussic acid can be obtained pure by means of other substances which have the power of separating it from the alkali4 ,,emily4 ,but if this acid does not exist ready formed in blood1 how can the alkali attract it from it8 ,,mrs4 ,b4 ,it is the triple basis only of this acid that exists in the blood2 and this is developed and brought to the state of acid1 during the combustion4 ,the acid therefore is first formed1 and it afterwards combines with the potash4 ,,emily4 ,now ,i comprehend it4 ,but how can the prussic acid be artificially made8 ,,mrs4 ,b4 ,by passing ammoniacal gas over red-hot charcoal2 and hence we learn that the constituents of this acid are hydrogen1 nitrogen1 and carbon4 ,the two first are derived from the volatile alkali1 the last from the combustion of the charcoal4 ,,caroline4 ,but this does not accord with the system of oxygen being the principle of acidity4 ,,mrs4 ,b4 ,the colouring matter of prussian blue is called an acid1 because it unites with alkalies and metals1 and not from any other characteristic properties of acids2 perhaps the name is not strictly appropriate4 ,but this circumstance1 together with some others of the same kind1 has induced several chemists to think that oxygen may not be the exclusive generator of acids4 ,sir ,h4 ,davy1 ,i have already informed you1 was led by his experiments on dry acids to suspect that water might be essential to acidity4 ,and it is the opinion of some chemists that acidity may possibly depend rather on the arrangement than on the presence of any particular principles4 ,but we have not yet done with the prussic acid4 ,it has a strong affinity for metallic oxyds1 and precipitates the solutions of iron in acids of a blue colour4 ,this is the prussian blue1 or prussiat of iron1 so much used in the arts1 and with which ,i think you must be acquainted4 ,,emily4 ,yes1 ,i am2 it is much used in painting1 both in oil and in water colours2 but it is not reckoned a permanent oil-colour4 ,,mrs4 ,b4 ,that defect arises1 ,i believe1 in general1 from its being badly prepared1 which is the case when the iron is not so fully oxydated as to form a red oxyd4 ,for a solution of green oxyd of iron 7in which the metal is more slightly oxydated71 makes only a pale green1 or even a white precipitate1 with prussiat of potash2 and this gradually changes to blue by being exposed to the air1 as ,i can immediately show you4 ,,caroline4 ,it already begins to assume a pale blue colour4 ,but how does the air produce this change8 ,,mrs4 ,b4 ,by oxydating the iron more perfectly4 ,if we pour some nitrous acid on it1 the prussian blue colour will be immediately produced1 as the acid will yield its oxygen to the precipitate1 and fully saturate it with this principle1 as you shall see4 ,,caroline4 ,it is very curious to see a colour change so instantaneously4 ,,mrs4 ,b4 ,hence you perceive that prussian blue cannot be a permanent colour1 unless prepared with red oxyd of iron1 since by exposure to the atmosphere it gradually darkens1 and in a short time is no longer in harmony with the other colours of the painting4 ,,caroline4 ,but it can never become darker1 by exposure to the atmosphere1 than the true prussian blue1 in which the oxyd is perfectly saturated8 ,,mrs4 ,b4 ,certainly not4 ,but in painting1 the artist not reckoning upon partial alterations in his colours1 gives his blue tints that particular shade which harmonises with the rest of the picture4 ,if1 afterwards1 those tints become darker1 the harmony of the colouring must necessarily be destroyed4 ,,caroline4 ,pray1 of what nature is the paint called carmine8 ,,mrs4 ,b4 ,it is an animal colour prepared from cochineal1 an insect1 the infusion of which produces a very beautiful red4 ,,caroline4 ,whilst we are on the subject of colours1 ,i should like to learn what ivory black is8 ,,mrs4 ,b4 ,it is a carbonaceous substance obtained by the combustion of ivory4 ,a more common species of black is obtained from the burning of bone4 ,,caroline4 ,but during the combustion of ivory or bone1 the carbon1 ,i should have imagined1 must be converted into carbonic acid gas1 instead of this black substance8 ,,mrs4 ,b4 ,in this1 as in most combustions1 a considerable part of the carbon is simply volatilised by the heat1 and again obtained concrete on cooling4 ,this colour1 therefore1 may be called the soot produced by the burning of ivory or bone4 ,,conversation ,,xxiv4 ,,on ,,the ,,animal ,,economy4 ,,mrs4 ,b4 ,we have now acquired some idea of the various materials that compose the animal system2 but if you are curious to know in what manner these substances are formed by the animal organs1 from vegetable1 as well as from animal substances1 it will be necessary to have some previous knowledge of the nature and functions of these organs1 without which it is impossible to form any distinct idea of the process of animalisation and nutrition4 ,,caroline4 ,i do not exactly understand the meaning of the word animalisation8 ,,mrs4 ,b4 ,animalisation is the process by which the food is assimilated1 that is to say1 converted into animal matter2 and nutrition is that by which the food thus assimilated is rendered subservient to the purposes of nourishing and maintaining the animal system4 ,,emily4 ,this1 ,i am sure1 must be the most interesting of all the branches of chemistry6 ,,caroline4 ,so ,i think2 particularly as ,i expect that we shall hear something of the nature of respiration1 and of the circulation of the blood8 ,,mrs4 ,b4 ,these functions undoubtedly occupy a most important place in the history of the animal economy4 --,but ,i must previously give you a very short account of the principal organs by which the various operations of the animal system are performed4 ,these are3 ,the ,bones2 ,muscles1 ,blood vessels1 ,lymphatic vessels1 ,glands1 and ,nerves4 ,the bones are the most solid part of the animal frame1 and in a great measure determine its form and dimensions4 ,you recollect1 ,i suppose1 what are the ingredients which enter into their composition8 ,,caroline4 ,yes2 phosphat of lime1 cemented by gelatine4 ,,mrs4 ,b4 ,during the earliest period of animal life1 they consist almost entirely of gelatinous membrane having the form of the bones1 but of a loose spongy texture1 the cells or cavities of which are destined to be filled with phosphat of lime2 it is the gradual acquisition of this salt which gives to the bones their subsequent hardness and durability4 ,infants first receive it from their mother's milk1 and afterwards derive it from all animal and from most vegetable food1 especially farinaceous substances1 such as wheat-flour1 which contain it in sensible quantities4 ,a portion of the phosphat1 after the bones of the infant have been sufficiently expanded and solidified1 is deposited in the teeth1 which consist at first only of a gelatinous membrane or case1 fitted for the reception of this salt2 and which1 after acquiring hardness within the gum1 gradually protrude from it4 ,,caroline4 ,how very curious this is2 and how ingeniously nature has first provided for the solidification of such bones as are immediately wanted1 and afterwards for the formation of the teeth1 which would not only be useless1 but detrimental in infancy6 ,,mrs4 ,b4 ,in quadrupeds the phosphat of lime is deposited likewise in their horns1 and in the hair or wool with which they are generally clothed4 ,in birds it serves also to harden the beaks and the quills of their feathers4 ,when animals are arrived at a state of maturity1 and their bones have acquired a sufficient degree of solidity1 the phosphat of lime which is taken with the food is seldom assimilated1 excepting when the female nourishes her young2 it is then all secreted into the milk1 as a provision for the tender bones of the nursling4 ,,emily4 ,so that whatever becomes superfluous to one being1 is immediately wanted by another2 and the child acquires strength precisely by the species of nourishment which is no longer necessary to the mother4 ,nature is1 indeed1 an admirable economist6 ,,caroline4 ,pray1 ,mrs4 ,b41 does not the disease in the bones of children1 called the rickets1 proceed from a deficiency of phosphat of lime8 ,,mrs4 ,b4 ,i have heard that this disease may arise from two causes2 it is sometimes occasioned by the growth of the muscles being too rapid in proportion to that of the bones4 ,in this case the weight of the flesh is greater than the bones can support1 and presses upon them so as to produce a swelling of the joints1 which is the great indication of the rickets4 ,the other cause of this disorder is supposed to be an imperfect digestion and assimilation of the food1 attended with an excess of acid1 which counteracts the formation of phosphat of lime4 ,in both instances1 therefore1 care should be taken to alter the child's diet1 not merely by increasing the quantity of aliment containing phosphat of lime1 but also by avoiding all food that is apt to turn acid on the stomach1 and to produce indigestion4 ,but the best preservative against complaints of this kind is1 no doubt1 good nursing3 when a child has plenty of air and exercise1 the digestion and assimilation will be properly performed1 no acid will be produced to interrupt these functions1 and the muscles and bones will grow together in just proportions4 ,,caroline4 ,i have often heard the rickets attributed to bad nursing1 but ,i never could have guessed what connection there was between exercise and the formation of the bones4 ,,mrs4 ,b4 ,exercise is generally beneficial to all the animal functions4 ,if man is destined to labour for his subsistence1 the bread which he earns is scarcely more essential to his health and preservation than the exertions by which he obtains it4 ,those whom the gifts of fortune have placed above the necessity of bodily labour are compelled to take exercise in some mode or other1 and when they cannot convert it into an amusement1 they must submit to it as a task1 or their health will soon experience the effects of their indolence4 ,,emily4 ,that will never be my case3 for exercise1 unless it becomes fatigue1 always gives me pleasure2 and1 so far from being a task1 is to me a source of daily enjoyment4 ,i often think what a blessing it is1 that exercise1 which is so conducive to health1 should be so delightful2 whilst fatigue1 which is rather hurtful1 instead of pleasure1 occasions painful sensations4 ,so that fatigue1 no doubt1 was intended to moderate our bodily exertions1 as satiety puts a limit to our appetites4 ,,mrs4 ,b4 ,certainly4 --,but let us not deviate too far from our subject4 --,the bones are connected together by ligaments1 which consist of a white thick flexible substance1 adhering to their extremities1 so far as to secure the joints firmly1 though without impeding their motion4 ,and the joints are moreover covered by a solid1 smooth1 elastic1 white substance1 called cartilage1 the use of which is to allow1 by its smoothness and elasticity1 the bones to slide easily over one another1 so that the joints may perform their office without difficulty or detriment4 ,over the bones the muscles are placed2 they consist of bundles of fibres which terminate in a kind of string1 or ligament1 by which they are fastened to the bones4 ,the muscles are the organs of motion2 by their power of dilatation and contraction they put into action the bones1 which act as levers1 in all the motions of the body1 and form the solid support of its various parts4 ,the muscles are of various degrees of strength or consistence in different species of animals4 ,the mammiferous tribe1 or those that suckle their young1 seem in this respect to occupy an intermediate place between birds and cold-blooded animals1 such as reptiles and fishes4 ,,emily4 ,the different degrees of firmness and solidity in the muscles of these several species of animals proceed1 ,i imagine1 from the different nature of the food on which they subsist8 ,,mrs4 ,b4 ,no2 that is not supposed to be the case3 for the human species1 who are of the mammiferous tribe1 live on more substantial food than birds1 and yet the latter exceed them in muscular strength4 ,we shall hereafter attempt to account for this difference2 but let us now proceed in the examination of the animal functions4 ,the next class of organs is that of the vessels of the body1 the office of which is to convey the various fluids throughout the frame4 ,these vessels are innumerable4 ,the most considerable of them are those through which the blood circulates1 which are of two kinds3 the arteries1 which convey it from the heart to the extremities of the body1 and the veins1 which bring it back into the heart4 ,besides these1 there are a numerous set of small transparent vessels1 destined to absorb and convey different fluids into the blood2 they are generally called the absorbent or lymphatic vessels3 but it is to a portion of them only that the function of conveying into the blood the fluid called lymph is assigned4 ,,emily4 ,pray what is the nature of that fluid8 ,,mrs4 ,b4 ,the nature and use of the lymph have1 ,i believe1 never been perfectly ascertained2 but it is supposed to consist of matter that has been previously animalised1 and which1 after answering the purpose for which it was intended1 must1 in regular rotation1 make way for the fresh supplies produced by nourishment4 ,the lymphatic vessels pump up this fluid from every part of the system1 and convey it into the veins to be mixed with the blood which runs through them1 and which is commonly called venous blood4 ,,caroline4 ,but does it not again enter into the animal system through that channel8 ,,mrs4 ,b4 ,not entirely2 for the venous blood does not return into the circulation until it has undergone a peculiar change1 in which it throws off whatever is become useless4 ,another set of absorbent vessels pump up the chyle from the stomach and intestines1 and convey it1 after many circumvolutions1 into the great vein near the heart4 ,,emily4 ,pray what is chyle8 ,,mrs4 ,b4 ,it is the substance into which food is converted by digestion4 ,,caroline4 ,one set of the absorbent vessels1 then1 is employed in bringing away the old materials that are no longer fit for use2 whilst the other set is busy in conveying into the blood the new materials that are to replace them4 ,,emily4 ,what a great variety of ingredients must enter into the composition of the blood8 ,,mrs4 ,b4 ,you must observe that there is also a great variety of substances to be secreted from it4 ,we may compare the blood to a general receptacle or storehouse for all kinds of commodities1 which are afterwards fashioned1 arranged1 and disposed of as circumstances require4 ,there is another set of absorbent vessels in females which is destined to secrete milk for the nourishment of the young4 ,,emily4 ,pray is not milk very analogous in its composition to blood2 for1 since the nursling derives its nourishment from that source only1 it must contain every principle which the animal system requires8 ,,mrs4 ,b4 ,very true4 ,milk is found1 by its analysis1 to contain the principal materials of animal matter1 albumen1 oil1 and phosphat of lime2 so that the suckling has but little trouble to digest and assimilate this nourishment4 ,but we shall examine the composition of milk more fully afterwards4 ,in many parts of the body numbers of small vessels are collected together in little bundles called glands1 from a ,latin word meaning acorn1 on account of the resemblance which some of them bear in shape to that fruit4 ,the function of the glands is to secrete1 or separate certain matters from the blood4 ,the secretions are not only mechanical1 but chemical separations from the blood2 for the substances thus formed1 though contained in the blood1 are not ready combined in that fluid4 ,the secretions are of two kinds1 those which form peculiar animal fluids1 as bile1 tears1 saliva1 c42 and those which produce the general materials of the animal system1 for the purpose of recruiting and nourishing the several organs of the body2 such as albumen1 gelatine1 and fibrine2 the latter may be distinguished by the name of nutritive secretions4 ,,caroline4 ,i am quite astonished to hear that all the secretions should be derived from the blood4 ,,emily4 ,i thought that the bile was produced by the liver8 ,,mrs4 ,b4 ,so it is2 but the liver is nothing more than a very large gland1 which secretes the bile from the blood4 ,the last of the animal organs which we have mentioned are the nerves2 these are the vehicles of sensation1 every other part of the body being1 of itself1 totally insensible4 ,,caroline4 ,they must then be spread through every part of the frame1 for we are every where susceptible of feeling4 ,,emily4 ,excepting the nails and the hair4 ,,mrs4 ,b4 ,and those are almost the only parts in which nerves cannot be discovered4 ,the common source of all the nerves is the brain2 thence they descend1 some of them through different holes of the skull1 but the greatest part through the back bone1 and extend themselves by innumerable ramifications throughout the whole body4 ,they spread themselves over the muscles1 penetrate the glands1 wind round the vascular system1 and even pierce into the interior of the bones4 ,it is most probably through them that the communication is carried on between the mind and the other parts of the body2 but in what manner they are acted on by the mind1 and made to re-act on the body1 is still a profound secret4 ,many hypotheses have been formed on this very obscure subject1 but they are all equally improbable1 and it would be useless for us to waste our time in conjectures on an enquiry1 which1 in all probability1 is beyond the reach of human capacity4 ,,caroline4 ,but you have not mentioned those particular nerves that form the senses of hearing1 seeing1 smelling1 and tasting8 ,,mrs4 ,b4 ,they are considered as being of the same nature as those which are dispersed over every part of the body1 and constitute the general sense of feeling4 ,the different sensations which they produce arise from their peculiar situation and connection with the several organs of taste1 smell1 and hearing4 ,,emily4 ,but these senses appear totally different from that of feeling8 ,,mrs4 ,b4 ,they are all of them sensations1 but variously modified according to the nature of the different organs in which the nerves are situated4 ,for1 as we have formerly observed1 it is by contact only that the nerves are affected4 ,thus odoriferous particles must strike upon the nerves of the nose1 in order to excite the sense of smelling2 in the same manner that taste is produced by the particular substance coming in contact with the nerves of the palate4 ,it is thus also that the sensation of sound is produced by the concussion of the air striking against the auditory nerve2 and sight is the effect of the light falling upon the optic nerve4 ,these various senses1 therefore1 are affected only by the actual contact of particles of matter1 in the same manner as that of feeling4 ,the different organs of the animal body1 though easily separated and perfectly distinct1 are loosely connected together by a kind of spongy substance1 in texture somewhat resembling net-work1 called the cellular membrane2 and the whole is covered by the skin4 ,the skin1 as well as the bark of vegetables1 is formed of three coats4 ,the external one is called the cuticle or epidermis2 the second1 which is called the mucous membrane1 is of a thin soft texture1 and consists of a mucous substance1 which in negroes is black1 and is the cause of their skin appearing of that colour4 ,,caroline4 ,is then the external skin of negroes white like ours8 ,,mrs4 ,b4 ,yes2 but as the cuticle is transparent1 as well as porous1 the blackness of the mucous membrane is visible through it4 ,the extremities of the nerves are spread over this skin1 so that the sensation of feeling is transmitted through the cuticle4 ,the internal covering of the muscles1 which is properly the skin1 is the thickest1 the toughest1 and most resisting of the whole2 it is this membrane which is so essential in the arts1 by forming leather when combined with tannin4 ,the skin which covers the animal body1 as well as those membranes that form the coats of the vessels1 consists almost exclusively of gelatine2 and is capable of being converted into glue1 size1 or jelly4 ,the cavities between the muscles and the skin are usually filled with fat1 which lodges in the cells of the membranous net before mentioned1 and gives to the external form 7especially in the human figure7 that roundness1 smoothness1 and softness1 so essential to beauty4 ,,emily4 ,and the skin itself is1 ,i think1 a very ornamental part of the human frame1 both from the fineness of its texture1 and the variety and delicacy of its tints4 ,,mrs4 ,b4 ,this variety and harmonious graduation of colours1 proceed1 not so much from the skin itself1 as from the internal organs which transmit their several colours through it1 these being only softened and blended by the colour of the skin1 which is uniformly of a yellowish white4 ,thus modified1 the darkness of the veins appears of a pale blue colour1 and the floridness of the arteries is changed to a delicate pink4 ,in the most transparent parts1 the skin exhibits the bloom of the rose1 whilst where it is more opake its own colour predominates2 and at the joints1 where the bones are most prominent1 their whiteness is often discernible4 ,in a word1 every part of the human frame seems to contribute to its external grace2 and this not merely by producing a pleasing variety of tints1 but by a peculiar kind of beauty which belongs to each individual part4 ,thus it is to the solidity and arrangement of the bones that the human figure owes the grandeur of its stature1 and its firm and dignified deportment4 ,the muscles delineate the form1 and stamp it with energy and grace2 and the soft substance which is spread over them smooths their ruggedness1 and gives to the contours the gentle undulations of the line of beauty4 ,every organ of sense is a peculiar and separate ornament2 and the skin1 which polishes the surface1 and gives it that charm of colouring so inimitable by art1 finally conspires to render the whole the fairest work of the creation4 ,but now that we have seen in what manner the animal frame is formed1 let us observe how it provides for its support1 and how the several organs1 which form so complete a whole1 are nourished and maintained4 ,this will lead us to a more particular explanation of the internal organs3 here we shall not meet with so much apparent beauty1 because these parts were not intended by nature to be exhibited to view2 but the beauty of design1 in the internal organisation of the animal frame1 is1 if possible1 still more remarkable than that of the external parts4 ,we shall defer this subject till our next interview4 ,,conversation ,,xxv4 ,,on ,,animalisation1 ,,nutrition1 ,,and ,,respiration4 ,,mrs4 ,b4 ,we have now learnt of what materials the animal system is composed1 and have formed some idea of the nature of its organisation4 ,in order to complete the subject1 it remains for us to examine in what manner it is nourished and supported4 ,vegetables1 we have observed1 obtain their nourishment from various substances1 either in their elementary state1 or in a very simple state of combination2 as carbon1 water1 and salts1 which they pump up from the soil2 and carbonic acid and oxygen1 which they absorb from the atmosphere4 ,animals1 on the contrary1 feed on substances of the most complicated kind2 for they derive their sustenance1 some from the animal creation1 others from the vegetable kingdom1 and some from both4 ,,caroline4 ,and there is one species of animals1 which1 not satisfied with enjoying either kind of food in its simple state1 has invented the art of combining them together in a thousand ways1 and of rendering even the mineral kingdom subservient to its refinements4 ,,emily4 ,nor is this all2 for our delicacies are collected from the various climates of the earth1 so that the four quarters of the globe are often obliged to contribute to the preparation of our simplest dishes4 ,,caroline4 ,but the very complicated substances which constitute the nourishment of animals1 do not1 ,i suppose1 enter into their system in their actual state of combination8 ,,mrs4 ,b4 ,so far from it1 that they not only undergo a new arrangement of their parts1 but a selection is made of such as are most proper for the nourishment of the body1 and those only enter into the system1 and are animalised4 ,,emily4 ,and by what organs is this process performed8 ,,mrs4 ,b4 ,chiefly by the stomach1 which is the organ of digestion1 and the prime regulator of the animal frame4 ,digestion is the first step towards nutrition4 ,it consists in reducing into one homogeneous mass the various substances that are taken as nourishment2 it is performed by first chewing and mixing the solid aliment with the saliva1 which reduces it to a soft mass1 in which state it is conveyed into the stomach1 where it is more completely dissolved by the gastric juice4 ,this fluid 7which is secreted into the stomach by appropriate glands7 is so powerful a solvent that scarcely any substances will resist its action4 ,,emily4 ,the coats of the stomach1 however1 cannot be attacked by it1 otherwise we should be in danger of having them destroyed when the stomach was empty4 ,,mrs4 ,b4 ,they are probably not subject to its action2 as long1 at least1 as life continues4 ,but it appears1 that when the gastric juice has no foreign substance to act upon1 it is capable of occasioning a degree of irritation in the coats of the stomach1 which produces the sensation of hunger4 ,the gastric juice1 together with the heat and muscular action of the stomach1 converts the aliment into an uniform pulpy mass called chyme4 ,this passes into the intestines1 where it meets with the bile and some other fluids1 by the agency of which1 and by the operation of other causes hitherto unknown1 the chyme is changed into chyle1 a much thinner substance1 somewhat resembling milk1 which is pumped by immense numbers of small absorbent vessels spread over the internal surface of the intestines4 ,these1 after many circumvolutions1 gradually meet and unite into large branches1 till they at length collect the chyle into one vessel1 which pours its contents into the great vein near the heart1 by which means the food1 thus prepared1 enters into the circulation4 ,,caroline4 ,but ,i do not yet clearly understand how the blood1 thus formed1 nourishes the body and supplies all the secretions8 ,,mrs4 ,b4 ,before this can be explained to you1 you must first allow me to complete the formation of the blood4 ,the chyle may1 indeed1 be considered as forming the chief ingredient of blood2 but this fluid is not perfect until it has passed through the lungs1 and undergone 7together with the blood that has already circulated7 certain necessary changes that are effected by ,,respiration4 ,,caroline4 ,i am very glad that you are going to explain the nature of respiration3 ,i have often longed to understand it1 for though we talk incessantly of breathing1 ,i never knew precisely what purpose it answered4 ,,mrs4 ,b4 ,it is indeed one of the most interesting processes imaginable2 but1 in order to understand this function well1 it will be necessary to enter into some previous explanations4 ,tell me1 ,emily1 --what do you understand by respiration8 ,,emily4 ,respiration1 ,i conceive1 consists simply in alternately inspiring air into the lungs1 and expiring it from them4 ,,mrs4 ,b4 ,your answer will do very well as a general definition4 ,but1 in order to form a tolerably clear notion of the various phenomena of respiration1 there are many circumstances to be taken into consideration4 ,in the first place1 there are two things to be distinguished in respiration1 the mechanical and the chemical part of the process4 ,the mechanism of breathing depends on the alternate expansions and contractions of the chest1 in which the lungs are contained4 ,when the chest dilates1 the cavity is enlarged1 and the air rushes in at the mouth1 to fill up the vacuum formed by this dilatation2 when it contracts1 the cavity is diminished1 and the air forced out again4 ,,caroline4 ,i thought that it was the lungs that contracted and expanded in breathing8 ,,mrs4 ,b4 ,they do likewise2 but their action is only the consequence of that of the chest4 ,the lungs1 together with the heart and largest blood vessels1 in a manner fill up the cavity of the chest2 they could not1 therefore1 dilate if the chest did not previously expand2 and1 on the other hand1 when the chest contracts1 it compresses the lungs and forces the air out of them4 ,,caroline4 ,the lungs1 then1 are like bellows1 and the chest is the power that works them4 ,,mrs4 ,b4 ,precisely so4 ,here is a curious little figure 7,,plate ,,xv4 ,fig4 #e471 that will assist me in explaining the mechanism of breathing4 ,,caroline4 ,what a droll figure6 a little head fixed upon a glass bell1 with a bladder tied over the bottom of it6 ,,mrs4 ,b4 ,you must observe that there is another bladder within the glass1 the neck of which communicates with the mouth of the figure--this represents the lungs contained within the chest2 the other bladder1 which you see is tied loose1 represents a muscular membrane1 called the diaphragm1 which separates the chest from the lower part of the body4 ,by the chest1 therefore1 ,i mean that large cavity in the upper part of the body contained within the ribs1 the neck1 and the diaphragm2 this membrane is muscular1 and capable of contraction and dilatation4 ,the contraction may be imitated by drawing the bladder tight over the bottom of the receiver1 when the air in the bladder1 which represents the lungs1 will be forced out through the mouth of the figure-- ,,emily4 ,see1 ,caroline1 how it blows the flame of the candle in breathing6 ,,mrs4 ,b4 ,by letting the bladder loose again1 we imitate the dilatation of the diaphragm1 and the cavity of the chest being enlarged1 the lungs expand1 and the air rushes in to fill them4 ,,emily4 ,this figure1 ,i think1 gives a very clear idea of the process of breathing4 ,,mrs4 ,b4 ,it illustrates tolerably well the action of the lungs and diaphragm2 but those are not the only powers that are concerned in enlarging or diminishing the cavity of the chest2 the ribs are also possessed of a muscular motion for the same purpose2 they are alternately drawn in1 edgeways1 to assist the contraction1 and stretched out1 like the hoops of a barrel1 to contribute to the dilatation of the chest4 ,,emily4 ,i always supposed that the elevation and depression of the ribs were the consequence1 not the cause of breathing4 ,,mrs4 ,b4 ,it is exactly the reverse4 ,the muscular action of the diaphragm1 together with that of the ribs1 are the causes of the contraction and expansion of the chest2 and the air rushing into1 and being expelled from the lungs1 are only consequences of those actions4 ,,caroline4 ,i confess that ,i thought the act of breathing began by opening the mouth for the air to rush in1 and that it was the air alone1 which1 by alternately rushing in and out1 occasioned the dilatations and contractions of the lungs and chest4 ,,mrs4 ,b4 ,try the experiment of merely opening your mouth2 the air will not rush in1 till by an interior muscular action you produce a vacuum--yes1 just so1 your diaphragm is now dilated1 and the ribs expanded4 ,but you will not be able to keep them long in that state4 ,your lungs and chest are already resuming their former state1 and expelling the air with which they had just been filled4 ,this mechanism goes on more or less rapidly1 but1 in general1 a person at rest and in health will breathe between fifteen and twenty-five times in a minute4 ,we may now proceed to the chemical effects of respiration2 but1 for this purpose1 it is necessary that you should previously have some notion of the circulation of the blood4 ,tell me1 ,caroline1 what do you understand by the circulation of the blood8 ,,caroline4 ,i am delighted that you come to that subject1 for it is one that has long excited my curiosity4 ,but ,i cannot conceive how it is connected with respiration4 ,the idea ,i have of the circulation is1 that the blood runs from the heart through the veins all over the body1 and back again to the heart4 ,,mrs4 ,b4 ,i could hardly have expected a better definition from you2 it is1 however1 not quite correct1 for you do not distinguish the arteries from the veins1 which1 as we have already observed1 are two distinct sets of vessels1 each having its own peculiar functions4 ,the arteries convey the blood from the heart to the extremities of the body2 and the veins bring it back into the heart4 ,this sketch will give you an idea of the manner in which some of the principal veins and arteries of the human body branch out of the heart1 which may be considered as a common centre to both sets of vessels4 ,the heart is a kind of strong elastic bag1 or muscular cavity1 which possesses a power of dilating and contracting itself1 for the purposes of alternately receiving and expelling the blood1 in order to carry on the process of circulation4 ,,emily4 ,why are the arteries in this drawing painted red1 and the veins purple8 ,,mrs4 ,b4 ,it is to point out the difference of the colour of the blood in these two sets of vessels4 ,,caroline4 ,but if it is the same blood that flows from the arteries into the veins1 how can its colour be changed8 ,,mrs4 ,b4 ,this change arises from various circumstances4 ,in the first place1 during its passage through the arteries1 the blood undergoes a considerable alteration1 some of its constituent parts being gradually separated from it for the purpose of nourishing the body1 and of supplying the various secretions4 ,the consequence of this is1 that the florid arterial colour of the blood changes by degrees to a deep purple1 which is its constant colour in the veins4 ,on the other hand1 the blood is recruited during its return through the veins by the fresh chyle1 or imperfect blood1 which has been produced by food2 and it receives also lymph from the absorbent vessels1 as we have before mentioned4 ,in consequence of these several changes1 the blood returns to the heart in a state very different from that in which it left it4 ,it is loaded with a greater proportion of hydrogen and carbon1 and is no longer fit for the nourishment of the body1 or other purposes of circulation4 ,,emily4 ,and in this state does it mix in the heart with the pure florid blood that runs into the arteries8 ,,mrs4 ,b4 ,no4 ,the heart is divided into two cavities or compartitions1 called the right and left ventricles4 ,the left ventricle is the receptacle for the pure arterial blood previous to its circulation2 whilst the venous1 or impure blood1 which returns to the heart after having circulated1 is received into the right ventricle1 previous to its purification1 which ,i shall presently explain4 ,,caroline4 ,for my part1 ,i always thought that the same blood circulated again and again through the body1 without undergoing any change4 ,,mrs4 ,b4 ,yet you must have supposed that the blood circulated for some purpose8 ,,caroline4 ,i knew that it was indispensable to life2 but had no idea of its real functions4 ,,mrs4 ,b4 ,but now that you understand that the blood conveys nourishment to every part of the body1 and supplies the various secretions1 you must be sensible that it cannot constantly answer these objects without being proportionally renovated and purified4 ,,caroline4 ,but does not the chyle answer this purpose8 ,,mrs4 ,b4 ,only in part4 ,it renovates the nutritive principles of the blood1 but does not relieve it from the superabundance of water and carbon with which it is encumbered4 ,,emily4 ,how1 then1 is this effected8 ,,mrs4 ,b4 ,by ,,respiration4 ,this is one of the grand mysteries which modern chemistry has disclosed4 ,when the venous blood enters the right ventricle of the heart1 it contracts by its muscular power1 and throws the blood through a large vessel into the lungs1 which are contiguous1 and through which it circulates by millions of small ramifications4 ,here it comes in contact with the air which we breathe4 ,the action of the air on the blood in the lungs is1 indeed1 concealed1 from our immediate observation2 but we are able to form a tolerably accurate judgment of it from the changes which it effects not only in the blood1 but also on the air expired4 ,the air1 after passing through the lungs1 is found to contain all the nitrogen inspired1 but to have lost part of its oxygen1 and to have acquired a portion of watery vapour and of carbonic acid gas4 ,hence it is inferred1 that when the air comes in contact with the venous blood in the lungs1 the oxygen attracts from it the superabundant quantity of carbon with which it has impregnated itself during the circulation1 and converts it into carbonic acid4 ,this gaseous acid1 together with the redundant moisture from the lungs991 being then expired1 the blood is restored to its former purity1 that is1 to the state of arterial blood1 and is thus again enabled to perform its various functions4 ,footnote 993 ,the quantity of moisture discharged by the lungs in #bd hours1 may be computed at eight or nine ounces4 ,,caroline4 ,this is truly wonderful6 ,of all that we have yet learned1 ,i do not recollect any thing that has appeared to me so curious and interesting4 ,i almost believe that ,i should like to study anatomy now1 though ,i have hitherto had so disgusting an idea of it4 ,pray1 to whom are we indebted for these beautiful discoveries8 ,,mrs4 ,b4 ,priestley and ,crawford1 in this country1 and ,lavoisier1 in ,france1 are the principal inventors of the theory of respiration4 ,of late years the subject has been farther illustrated and simplified by the accurate experiments of ,messrs4 ,allen and ,pepys4 ,but the still more important and more admirable discovery of the circulation of the blood was made long before by our immortal countryman ,harvey4 ,,emily4 ,indeed ,i never heard any thing that delighted me so much as this theory of respiration4 ,but ,i hope1 ,mrs4 ,b41 that you will enter a little more into particulars before you dismiss so interesting a subject4 ,we left the blood in the lungs to undergo the salutary change3 but how does it thence spread to all the parts of the body8 ,,mrs4 ,b4 ,after circulating through the lungs1 the blood is collected into four large vessels1 by which it is conveyed into the left ventricle of the heart1 whence it is propelled to all the different parts of the body by a large artery1 which gradually ramifies into millions of small arteries through the whole frame4 ,from the extremities of these little ramifications the blood is transmitted to the veins1 which bring it back to the heart and lungs1 to go round again and again in the manner we have just described4 ,you see1 therefore1 that the blood actually undergoes two circulations2 the one1 through the lungs1 by which it is converted into pure arterial blood2 the other1 or general circulation1 by which nourishment is conveyed to every part of the body2 and these are both equally indispensable to the support of animal life4 ,,emily4 ,but whence proceeds the carbon with which the blood is impregnated when it comes into the lungs8 ,,mrs4 ,b4 ,carbon exists in a greater proportion in blood than in organised animal matter4 ,the blood1 therefore1 after supplying its various secretions1 becomes loaded with an excess of carbon1 which is carried off by respiration2 and the formation of new chyle from the food affords a constant supply of carbonaceous matter4 ,,caroline4 ,i wonder what quantity of carbon may be expelled from the blood by respiration in the course of #bd hours8 ,,mrs4 ,b4 ,it appears by the experiments of ,messrs4 ,allen and ,pepys that about #dj1jjj cubic inches of carbonic acid gas are emitted from the lungs of a healthy person1 daily2 which is equivalent to eleven ounces of solid carbon every #bd hours4 ,,emily4 ,what an immense quantity6 ,and pray how much of carbonic acid gas do we expel from our lungs at each expiration8 ,,mrs4 ,b4 ,the quantity of air which we take into our lungs at each inspiration1 is about #dj cubic inches1 which contain a little less than #aj cubic inches of oxygen2 and of those #aj inches1 one-eighth is converted into carbonic acid gas on passing once through the lungs991 a change which is sufficient to prevent air which has only been breathed once from suffering a taper to burn in it4 ,footnote 993 ,the bulk of carbonic acid gas formed by respiration1 is exactly the same as that of the oxygen gas which disappears4 ,,caroline4 ,pray1 how does the air come in contact with the blood in the lungs8 ,,mrs4 ,b4 ,i cannot answer this question without entering into an explanation of the nature and structure of the lungs4 ,you recollect that the venous blood1 on being expelled from the right ventricle1 enters the lungs to go through what we may call the lesser circulation2 the large trunk or vessel that conveys it branches out1 at its entrance into the lungs1 into an infinite number of very fine ramifications4 ,the windpipe1 which conveys the air from the mouth into the lungs1 likewise spreads out into a corresponding number of air vessels1 which follow the same course as the blood vessels1 forming millions of very minute air-cells4 ,these two sets of vessels are so interwoven as to form a sort of net-work1 connected into a kind of spongy mass1 in which every particle of blood must necessarily come in contact with a particle of air4 ,,caroline4 ,but since the blood and the air are contained in different vessels1 how can they come into contact8 ,,mrs4 ,b4 ,they act on each other through the membrane which forms the coats of these vessels2 for although this membrane prevents the blood and the air from mixing together in the lungs1 yet it is no impediment to their chemical action on each other4 ,,emily4 ,are the lungs composed entirely of blood vessels and air vessels8 ,,mrs4 ,b4 ,i believe they are1 with the addition only of nerves and of a small quantity of the cellular substance before mentioned1 which connects the whole into an uniform mass4 ,,emily4 ,pray1 why are the lungs always spoken of in the plural number8 ,are there more than one8 ,,mrs4 ,b4 ,yes2 for though they form but one organ1 they really consist of two compartments called lobes1 which are enclosed in separate membranes or bags1 each occupying one side of the chest1 and being in close contact with each other1 but without communicating together4 ,this is a beautiful provision of nature1 in consequence of which1 if one of the lobes be wounded1 the other performs the whole process of respiration till the first is healed4 ,the blood1 thus completed1 by the process of respiration1 forms the most complex of all animal compounds1 since it contains not only the numerous materials necessary to form the various secretions1 as saliva1 tears1 c4 but likewise all those that are required to nourish the several parts of the body1 as the muscles1 bones1 nerves1 glands1 c4 ,,emily4 ,there seems to be a singular analogy between the blood of animals and the sap of vegetables2 for each of these fluids contains the several materials destined for the nutrition of the numerous class of bodies to which they respectively belong4 ,,mrs4 ,b4 ,nor is the production of these fluids in the animal and vegetable systems entirely different2 for the absorbent vessels1 which pump up the chyle from the stomach and intestines1 may be compared to the absorbents of the roots of plants1 which suck up the nourishment from the soil4 ,and the analogy between the sap and the blood may be still further traced1 if we follow the latter in the course of its circulation2 for1 in the living animal1 we find every where organs which are possessed of a power to secrete from the blood and appropriate to themselves the ingredients requisite for their support4 ,,caroline4 ,but whence do these organs derive their respective powers8 ,,mrs4 ,b4 ,from a peculiar organisation1 the secret of which no one has yet been able to unfold4 ,but it must be ultimately by means of the vital principle that both their mechanical and chemical powers are brought into action4 ,i cannot dismiss the subject of circulation without mentioning perspiration1 a secretion which is immediately connected with it1 and acts a most important part in the animal economy4 ,,caroline4 ,is not this secretion likewise made by appropriate glands8 ,,mrs4 ,b4 ,no2 it is performed by the extremities of the arteries1 which penetrate through the skin and terminate under the cuticle1 through the pores of which the perspiration issues4 ,when this fluid is not secreted in excess1 it is insensible1 because it is dissolved by the air as it exudes from the pores2 but when it is secreted faster than it can be dissolved1 it becomes sensible1 as it assumes its liquid state4 ,,emily4 ,this secretion bears a striking resemblance to the transpiration of the sap of plants4 ,they both consist of the most fluid part1 and both exude from the surface by the extremities of the vessels through which they circulate4 ,,mrs4 ,b4 ,and the analogy does not stop there2 for1 since it has been ascertained that the sap returns into the roots of the plants1 the resemblance between the animal and vegetable circulation is become still more obvious4 ,the latter1 however1 is far from being complete1 since1 as we observed before1 it consists only in a rising and descending of the sap1 whilst in animals the blood actually circulates through every part of the system4 ,we have now1 ,i think1 traced the process of nutrition1 from the introduction of the food into the stomach to its finally becoming a constituent part of the animal frame4 ,this will1 therefore1 be a fit period to conclude our present conversation4 ,what further remarks we have to make on the animal economy shall be reserved for our next interview4 ,,conversation ,,xxvi4 ,,on ,,animal ,,heat2 ,,and ,,on ,,various ,,animal ,,products4 ,,emily4 ,since our last interview1 ,i have been thinking much of the theory of respiration2 and ,i cannot help being struck with the resemblance which it appears to bear to the process of combustion4 ,for in respiration1 as in most cases of combustion1 the air suffers a change1 and a portion of its oxygen combines with carbon1 producing carbonic acid gas4 ,,mrs4 ,b4 ,i am much pleased that this idea has occurred to you3 these two processes appear so very analogous1 that it has been supposed that a kind of combustion actually takes place in the lungs2 not of the blood1 but of the superfluous carbon which the oxygen attracts from it4 ,,caroline4 ,a combustion in our lungs6 that is a curious idea indeed6 ,but1 ,mrs4 ,b41 how can you call the action of the air on the blood in the lungs combustion1 when neither light nor heat are produced by it8 ,,emily4 ,i was going to make the same objection4 --,yet ,i do not conceive how the oxygen can combine with the carbon1 and produce carbonic acid1 without disengaging heat8 ,,mrs4 ,b4 ,the fact is1 that heat is disengaged499 ,whether any light be evolved1 ,i cannot pretend to determine2 but that heat is produced in considerable and very sensible quantities is certain1 and this is the principal1 if not the only source of ,,animal ,,heat4 ,footnote 993 ,it has been calculated that the heat produced by respiration in #ab hours1 in the lungs of a healthy person1 is such as would melt about #ajj pounds of ice4 ,,emily4 ,how wonderful6 that the very process which purifies and elaborates the blood1 should afford an inexhaustible supply of internal heat8 ,,mrs4 ,b4 ,this is the theory of animal heat in its original simplicity1 such nearly as it was first proposed by ,black and ,lavoisier4 ,it was equally clear and ingenious2 and was at first generally adopted4 ,but it was objected1 on second consideration1 that if the whole of the animal heat was evolved in the lungs1 it would necessarily be much less in the extremities of the body than immediately at its source2 which is not found to be the case4 ,this objection1 however1 which was by no means frivolous1 is now satisfactorily removed by the following consideration3-- ,venous blood has been found by experiment to have less capacity for heat than arterial blood2 whence it follows that the blood1 in gradually passing from the arterial to the venous state1 during the circulation1 parts with a portion of caloric1 by means of which heat is diffused through every part of the body4 ,,emily4 ,more and more admirable6 ,,caroline4 ,the cause of animal heat was always a perfect mystery to me1 and ,i am delighted with its explanation4 --,but pray1 ,mrs4 ,b41 can you tell me what is the reason of the increase of heat that takes place in a fever8 ,,emily4 ,is it not because we then breathe quicker1 and therefore more heat is disengaged in the system8 ,,mrs4 ,b4 ,that may be one reason3 but ,i should think that the principal cause of the heat experienced in fevers1 is1 that there is no vent for the caloric which is generated in the body4 ,one of the most considerable secretions is the insensible perspiration2 this is constantly carrying off caloric in a latent state2 but during the hot stage of a fever1 the pores are so contracted1 that all perspiration ceases1 and the accumulation of caloric in the body occasions those burning sensations which are so painful4 ,,emily4 ,this is1 no doubt1 the reason why the perspiration that often succeeds the hot stage of a fever affords so much relief4 ,if ,i had known this theory of animal heat when ,i had a fever last summer1 ,i think ,i should have found some amusement in watching the chemical processes that were going on within me4 ,,caroline4 ,but exercise likewise produces animal heat1 and that must be quite in a different manner4 ,,mrs4 ,b4 ,not so much so as you think2 for the more exercise you take1 the more the body is stimulated1 and requires recruiting4 ,for this purpose the circulation of the blood is quickened1 the breath proportionably accelerated1 and consequently a greater quantity of caloric evolved4 ,,caroline4 ,true2 after running very fast1 ,i gasp for breath1 my respiration is quick and hard1 and it is just then that ,i begin to feel hot4 ,,emily4 ,it would seem1 then1 that violent exercise should produce fever4 ,,mrs4 ,b4 ,not if the person is in a good state of health2 for the additional caloric is then carried off by the perspiration which succeeds4 ,,emily4 ,what admirable resources nature has provided for us6 ,by the production of animal heat she has enabled us to keep up the temperature of our bodies above that of inanimate objects2 and whenever this source becomes too abundant1 the excess is carried off by perspiration4 ,,mrs4 ,b4 ,it is by the same law of nature that we are enabled1 in all climates1 and in all seasons1 to preserve our bodies of an equal temperature1 or at least very nearly so4 ,,caroline4 ,you cannot mean to say that our bodies are of the same temperature in summer1 and in winter1 in ,england1 and in the ,west-,indies4 ,,mrs4 ,b4 ,yes1 ,i do2 at least if you speak of the temperature of the blood1 and the internal parts of the body2 for those parts that are immediately in contact with the atmosphere1 such as the hands and face1 will occasionally get warmer1 or colder1 than the internal or more sheltered parts4 ,but if you put the bulb of a thermometer in your mouth1 which is the best way of ascertaining the real temperature of your body1 you will scarcely perceive any difference in its indication1 whatever may be the difference of temperature of the atmosphere4 ,,caroline4 ,and when ,i feel overcome by heat1 ,i am really not hotter than when ,i am shivering with cold8 ,,mrs4 ,b4 ,when a person in health feels very hot1 whether from internal heat1 from violent exercise1 or from the temperature of the atmosphere1 his body is certainly a little warmer than when he feels very cold2 but this difference is much smaller than our sensations would make us believe2 and the natural standard is soon restored by rest and by perspiration4 ,it is chiefly the external parts that are warmer1 and ,i am sure that you will be surprised to hear that the internal temperature of the body scarcely ever descends below ninety-five or ninety-six degrees1 and seldom attains one hundred and four or one hundred and five degrees1 even in the most violent fevers4 ,,emily4 ,the greater quantity of caloric1 therefore1 that we receive from the atmosphere in summer1 cannot raise the temperature of our bodies beyond certain limits1 as it does that of inanimate bodies1 because an excess of caloric is carried off by perspiration4 ,,caroline4 ,but the temperature of the atmosphere1 and consequently that of inanimate bodies1 is surely never so high as that of animal heat8 ,,mrs4 ,b4 ,i beg your pardon4 ,frequently in the ,east and ,west ,indies1 and sometimes in the southern parts of ,europe1 the atmosphere is above ninety-eight degrees1 which is the common temperature of animal heat4 ,indeed1 even in this country1 it occasionally happens that the sun's rays1 setting full on an object1 elevate its temperature above that point4 ,in illustration of the power which our bodies have to resist the effects of external heat1 ,sir ,charles ,blagden1 with some other gentlemen1 made several very curious experiments4 ,he remained for some time in an oven heated to a temperature not much inferior to that of boiling water1 without suffering any other inconvenience than a profuse perspiration1 which he supported by drinking plentifully4 ,,emily4 ,he could scarcely consider the perspiration as an inconvenience1 since it saved him from being baked by giving vent to the excess of caloric4 ,,caroline4 ,i always thought1 ,i confess1 that it was from the heat of the perspiration that we suffered in summer4 ,,mrs4 ,b4 ,you now find that you are quite mistaken4 ,whenever evaporation takes place1 cold1 you know1 is produced in consequence of a quantity of caloric being carried off in a latent state2 this is the case with perspiration1 and it is in this way that it affords relief4 ,it is on that account also that we are so apt to catch cold1 when in a state of profuse perspiration4 ,it is for the same reason that tea is often refreshing in summer1 though it appears to heat you at the moment you drink it4 ,,emily4 ,and in winter1 on the contrary1 tea is pleasant on account of its heat4 ,,mrs4 ,b4 ,yes2 for we have then rather to guard against a deficiency than an excess of caloric1 and you do not find that tea will excite perspiration in winter1 unless after dancing1 or any other violent exercise4 ,,caroline4 ,what is the reason that it is dangerous to eat ice after dancing1 or to drink any thing cold when one is very hot8 ,,mrs4 ,b4 ,because the loss of heat arising from the perspiration1 conjointly with the chill occasioned by the cold draught1 produce more cold than can be borne with safety1 unless you continue to use the same exercise after drinking that you did before2 for the heat occasioned by the exercise will counteract the effects of the cold drink1 and the danger will be removed4 ,you may1 however1 contrary to the common notion1 consider it as a rule1 that cold liquids may1 at all times1 be drunk with perfect safety1 however hot you may feel1 provided you are not at the moment in a state of great perspiration1 and on condition that you keep yourself in gentle exercise afterwards4 ,,emily4 ,but since we are furnished with such resources against the extremes of heat or cold1 ,i should have thought that all climates would have been equally wholesome4 ,,mrs4 ,b4 ,that is true1 in a certain degree1 with regard to those who have been accustomed to them from birth2 for we find that the natives of those climates1 which we consider as most deleterious1 are as healthy as ourselves2 and if such climates are unwholesome to those who are habituated to a more moderate temperature1 it is because the animal economy does not easily accustom itself to considerable changes4 ,,caroline4 ,but pray1 ,mrs4 ,b41 if the circulation preserves the body of an uniform temperature1 how does it happen that animals are sometimes frozen8 ,,mrs4 ,b4 ,because1 if more heat be carried off by the atmosphere than the circulation can supply1 the cold will finally prevail1 the heart will cease to beat1 and the animal will be frozen4 ,and1 likewise1 if the body remained long exposed to a degree of heat1 greater than the perspiration could carry off1 it would at last lose the power of resisting its destructive influence4 ,,caroline4 ,fish1 ,i suppose1 have no animal heat1 but only partake of the temperature of the water in which they live8 ,,emily4 ,and their coldness1 no doubt1 proceeds from their not breathing8 ,,mrs4 ,b4 ,all kinds of fish breathe more or less1 though in a much smaller degree than land animals4 ,nor are they entirely destitute of animal heat1 though1 for the same reason1 they are much colder than other creatures4 ,they have comparatively but a very small quantity of blood1 therefore but very little oxygen is required1 and a proportionally small quantity of animal heat is generated4 ,,caroline4 ,but how can fish breathe under water8 ,,mrs4 ,b4 ,they breathe by means of the air which is dissolved in the water1 and if you put them into water deprived of air by boiling1 they are soon suffocated4 ,if a fish is confined in a vessel of water closed from the air1 it soon dies2 and any fish put in afterwards would be killed immediately1 as all the air had been previously consumed4 ,,caroline4 ,are there any species of animals that breathe more than we do8 ,,mrs4 ,b4 ,yes2 birds1 of all animals1 breathe the greatest quantity of air in proportion to their size2 and it is to this that they are supposed to owe the peculiar firmness and strength of their muscles1 by which they are enabled to support the violent exertion of flying4 ,this difference between birds and fish1 which may be considered as the two extremes of the scale of muscular strength1 is well worth observing4 ,birds residing constantly in the atmosphere1 surrounded by oxygen1 and respiring it in greater proportions than any other species of animals1 are endowed with a superior degree of muscular strength1 whilst the muscles of fish1 on the contrary1 are flaccid and oily2 these animals are comparatively feeble in their motions1 and their temperature is scarcely above that of the water in which they live4 ,this is1 in all probability1 owing to their imperfect respiration2 the quantity of hydrogen and carbon1 that is in consequence accumulated in their bodies1 forms the oil which is so strongly characteristic of that species of animals1 and which relaxes and softens the small quantity of fibrine which their muscles contain4 ,,caroline4 ,but1 ,mrs4 ,b41 there are some species of birds that frequent both elements1 as1 for instance1 ducks and other water fowl4 ,of what nature is the flesh of these8 ,,mrs4 ,b4 ,such birds1 in general1 make but little use of their wings2 if they fly1 it is but feebly1 and only to a short distance4 ,their flesh1 too1 partakes of the oily nature1 and even in taste sometimes resembles that of fish4 ,this is the case not only with the various kinds of water fowls1 but with all other amphibious animals1 as the otter1 the crocodile1 the lizard1 c4 ,,caroline4 ,and what is the reason that reptiles are so deficient in muscular strength8 ,,mrs4 ,b4 ,it is because they usually live under ground1 and seldom come into the atmosphere4 ,they have imperfect1 and sometimes no discernible organs of respiration2 they partake therefore of the soft oily nature of fish2 indeed1 many of them are amphibious1 as frogs1 toads1 and snakes1 and very few of them find any difficulty in remaining a length of time under water4 ,whilst1 on the contrary1 the insect tribe1 that are so strong in proportion to their size1 and alert in their motions1 partake of the nature of birds1 air being their peculiar element1 and their organs of respiration being comparatively larger than in other classes of animals4 ,i have now given you a short account of the principal animal functions4 ,however interesting the subject may appear to you1 a fuller investigation of it would1 ,i fear1 lead us too far from our object4 ,,emily4 ,yet ,i shall not quit it without much regret2 for of all the branches of chemistry1 it is certainly the most curious and most interesting4 ,,caroline4 ,but1 ,mrs4 ,b41 ,i must remind you that you promised to give us some account of the nature of milk4 ,,mrs4 ,b4 ,true4 ,there are several other animal productions that deserve likewise to be mentioned4 ,we shall begin with milk1 which is certainly the most important and the most interesting of all the animal secretions4 ,milk1 like all other animal substances1 ultimately yields by analysis oxygen1 hydrogen1 carbon1 and nitrogen4 ,these are combined in it under the forms of albumen1 gelatine1 oil1 and water4 ,but milk contains1 besides1 a considerable portion of phosphat of lime1 the purposes of which ,i have already pointed out4 ,,caroline4 ,yes2 it is this salt which serves to nourish the tender bones of the suckling4 ,,mrs4 ,b4 ,to reduce milk to its elements1 would be a very complicated1 as well as useless operation2 but this fluid1 without any chemical assistance1 may be decomposed into three parts1 cream1 curds1 and whey4 ,these constituents of milk have but a very slight affinity for each other1 and you find accordingly that cream separates from milk by mere standing4 ,it consists chiefly of oil1 which being lighter than the other parts of the milk1 gradually rises to the surface4 ,it is of this1 you know1 that butter is made1 which is nothing more than oxygenated cream4 ,,caroline4 ,butter1 then1 is somewhat analogous to the waxy substance formed by the oxygenation of vegetable oils4 ,,mrs4 ,b4 ,very much so4 ,,emily4 ,but is the cream oxygenated by churning8 ,,mrs4 ,b4 ,its oxygenation commences previous to churning1 merely by standing exposed to the atmosphere1 from which it absorbs oxygen4 ,the process is afterwards completed by churning2 the violent motion which this operation occasions brings every particle of cream in contact with the atmosphere1 and thus facilitates its oxygenation4 ,,caroline4 ,but the effect of churning1 ,i have often observed in the dairy1 is to separate the cream into two substances1 butter and butter-milk4 ,,mrs4 ,b4 ,that is to say1 in proportion as the oily particles of the cream become oxygenated1 they separate from the other constituent parts of the cream in the form of butter4 ,so by churning you produce1 on the one hand1 butter1 or oxygenated oil2 and1 on the other1 butter-milk1 or cream deprived of oil4 ,but if you make butter by churning new milk instead of cream1 the butter-milk will then be exactly similar in its properties to creamed or skimmed milk4 ,,caroline4 ,yet butter-milk is very different from common skimmed milk4 ,,mrs4 ,b4 ,because you know it is customary1 in order to save time and labour1 to make butter from cream alone4 ,in this case1 therefore1 the butter-milk is deprived of the creamed milk1 which contains both the curd and whey4 ,besides1 in consequence of the milk remaining exposed to the atmosphere during the separation of the cream1 the latter becomes more or less acid1 as well as the butter-milk which it yields in churning4 ,,emily4 ,why should not the butter be equally acidified by oxygenation8 ,,mrs4 ,b4 ,animal oil is not so easily acidified as the other ingredients of milk4 ,butter1 therefore1 though usually made of sour cream1 is not sour itself1 because the oily part of the cream had not been acidified4 ,butter1 however1 is susceptible of becoming acid by an excess of oxygen2 it is then said to be rancid1 and produces the sebacic acid1 the same as that which is obtained from fat4 ,,emily4 ,if that be the case1 might not rancid butter be sweetened by mixing with it some substance that would take the acid from it8 ,,mrs4 ,b4 ,this idea has been suggested by ,sir ,h4 ,davy1 who supposes1 that if rancid butter were well washed in an alkaline solution1 the alkali would separate the acid from the butter4 ,,caroline4 ,you said just now that creamed milk consisted of curd and whey4 ,pray how are these separated8 ,,mrs4 ,b4 ,they may be separated by standing for a certain length of time exposed to the atmosphere2 but this decomposition may be almost instantaneously effected by the chemical agency of a variety of substances4 ,alkalies1 rennet991 and indeed almost all animal substances1 decompose milk by combining with the curds4 ,acids and spirituous liquors1 on the other hand1 produce a decomposition by combining with the whey4 ,in order1 therefore1 to obtain the whey pure1 rennet1 or alkaline substances1 must be used to attract the curds from it4 ,but if it be wished to obtain the curds pure1 the whey must be separated by acids1 wine1 or other spirituous liquors4 ,footnote 993 ,rennet is the name given to a watery infusion of the coats of the stomach of a sucking calf4 ,its remarkable efficacy in promoting coagulation is supposed to depend on the gastric juice with which it is impregnated4 ,,emily4 ,this is a very useful piece of information2 for ,i find white-wine whey1 which ,i sometimes take when ,i have a cold1 extremely heating2 now1 if the whey were separated by means of an alkali instead of wine1 it would not produce that effect4 ,,mrs4 ,b4 ,perhaps not4 ,but ,i would strenuously advise you not to place too much reliance on your slight chemical knowledge in medical matters4 ,i do not know why whey is not separated from curd by rennet1 or by an alkali1 for the purpose which you mention2 but ,i strongly suspect that there must be some good reason why the preparation by means of wine is generally preferred4 ,i can1 however1 safely point out to you a method of obtaining whey without either alkali1 rennet1 or wine2 it is by substituting lemon juice1 a very small quantity of which will separate it from the curds4 ,whey1 as an article of diet1 is very wholesome1 being remarkable light of digestion4 ,but its effect1 taken medicinally1 is chiefly1 ,i believe1 to excite perspiration1 by being drunk warm on going to bed4 ,from whey a substance may be obtained in crystals by evaporation1 called sugar of milk4 ,this substance is sweet to the taste1 and in its composition is so analogous to common sugar1 that it is susceptible of undergoing the vinous fermentation4 ,,caroline4 ,why then is not wine1 or alcohol1 made from whey8 ,,mrs4 ,b4 ,the quantity of sugar contained in milk is so trifling1 that it can hardly answer that purpose4 ,i have heard of only one instance of its being used for the production of a spirituous liquor1 and this is by the ,tartan ,arabs2 their abundance of horses1 as well as their scarcity of fruits1 has introduced the fermentation of mares' milk1 by which they produce a liquor called koumiss4 ,whey is likewise susceptible of being acidified by combining with oxygen from the atmosphere4 ,it then produces the lactic acid1 which you may recollect is mentioned amongst the animal acids1 as the acid of milk4 ,let us now see what are the properties of curds4 ,,emily4 ,i know that they are made into cheese2 but ,i have heard that for that purpose they are separated from the whey by rennet1 and yet this you have just told us is not the method of obtaining pure curds8 ,,mrs4 ,b4 ,nor are pure curds so well adapted for the formation of cheese4 ,for the nature and flavour of the cheese depend1 in a great measure1 upon the cream or oily matter which is left in the curds2 so that if every particle of cream be removed from the curds1 the cheese is scarcely eatable4 ,rich cheeses1 such as cream and ,stilton cheeses1 derive their excellence from the quantity1 as well as the quality1 of the cream that enters into their composition4 ,,caroline4 ,i had no idea that milk was such an interesting compound4 ,in many respects there appears to me to be a very striking analogy between milk and the contents of an egg1 both in respect to their nature and their use4 ,they are1 each of them1 composed of the various substances necessary for the nourishment of the young animal1 and equally destined for that purpose4 ,,mrs4 ,b4 ,there is1 however1 a very essential difference4 ,the young animal is formed1 as well as nourished1 by the contents of the egg-shell2 whilst milk serves as nutriment to the suckling1 only after it is born4 ,there are several peculiar animal substances which do not enter into the general enumeration of animal compounds1 and which1 however1 deserve to be mentioned4 ,spermaceti is of this class2 it is a kind of oily substance obtained from the head of the whale1 which1 however1 must undergo a certain preparation before it is in a fit state to be made into candles4 ,it is not much more combustible than tallow1 but it is pleasanter to burn1 as it is less fusible and less greasy4 ,ambergris is another peculiar substance derived from a species of whale4 ,it is1 however1 seldom obtained from the animal itself1 but is generally found floating on the surface of the sea4 ,wax1 you know1 is a concrete oil1 the peculiar product of the bee1 part of the constituents of which may probably be derived from flowers1 but so prepared by the organs of the bee1 and so mixed with its own substance1 as to be decidedly an animal product4 ,bees' wax is naturally of a yellow colour1 but it is bleached by long exposure to the atmosphere1 or may be instantaneously whitened by the oxy-muriatic acid4 ,the combustion of wax is far more perfect than that of tallow1 and consequently produces a greater quantity of light and heat4 ,lac is a substance very similar to wax in the manner of its formation2 it is the product of an insect1 which collects its ingredients from flowers1 apparently for the purpose of protecting its eggs from injury4 ,it is formed into cells1 fabricated with as much skill as those of the honey-comb1 but differently arranged4 ,the principal use of lac is in the manufacture of sealing-wax1 and in making varnishes and lacquers4 ,musk1 civet1 and castor1 are other particular productions1 from different species of quadrupeds4 ,the two first are very powerful perfumes2 the latter has a nauseous smell and taste1 and is only used medicinally4 ,,caroline4 ,is it from this substance that castor oil is obtained8 ,,mrs4 ,b4 ,no4 ,far from it1 for castor oil is a vegetable oil1 expressed from the seeds of a particular plant2 and has not the least resemblance to the medicinal substance obtained from the castor4 ,silk is a peculiar secretion of the silk-worm1 with which it builds its nest or cocoon4 ,this insect was originally brought to ,europe from ,china4 ,silk1 in its chemical nature1 is very similar to the hair and wool of animals2 whilst in the insect it is a fluid1 which is coagulated1 apparently by uniting with oxygen1 as soon as it comes in contact with the air4 ,the moth of the silk-worm ejects a liquor which appears to contain a particular acid1 called bombic1 the properties of which are but very little known4 ,,emily4 ,before we conclude the subject of the animal economy1 shall we not learn by what steps dead animals return to their elementary state8 ,,mrs4 ,b4 ,animal matter1 although the most complicated of all natural substances1 returns to its elementary state by one single spontaneous process1 the putrid fermentation4 ,by this1 the albumen1 fibrine1 c4 are slowly reduced to the state of oxygen1 hydrogen1 nitrogen1 and carbon2 and thus the circle of changes through which these principles have passed is finally completed4 ,they first quitted their elementary form1 or their combination with unorganised matter1 to enter into the vegetable system4 ,hence they were transmitted to the animal kingdom2 and from this they return1 again to their primitive simplicity1 soon to re-enter the sphere of organised existence4 ,when all the circumstances necessary to produce fermentation do not take place1 animal1 like vegetable matter1 is liable to a partial or imperfect decomposition1 which converts it into a combustible substance very like spermaceti4 ,i dare say that ,caroline1 who is so fond of analogies1 will consider this as a kind of animal bitumen4 ,,caroline4 ,and why should ,i not1 since the processes which produce these substances are so similar8 ,,mrs4 ,b4 ,there is1 however1 one considerable difference2 the state of bitumen seems permanent1 whilst that of animal substances1 thus imperfectly decomposed1 is only transient2 and unless precautions be taken to preserve them in that state1 a total dissolution infallibly ensues4 ,this circumstance1 of the occasional conversion of animal matter into a kind of spermaceti1 is of late discovery4 ,a manufacture has in consequence been established near ,bristol1 in which1 by exposing the carcases of horses and other animals for a length of time under water1 the muscular parts are converted into this spermaceti-like substance4 ,the bones afterwards undergo a different process to produce hartshorn1 or1 more properly1 ammonia1 and phosphorus2 and the skin is prepared for leather4 ,thus art contrives to enlarge the sphere of useful purposes1 for which the elements were intended by nature2 and the productions of the several kingdoms are frequently arrested in their course1 and variously modified1 by human skill1 which compels them to contribute1 under new forms1 to the necessities or luxuries of man4 ,but all that we enjoy1 whether produced by the spontaneous operations of nature1 or the ingenious efforts of art1 proceed alike from the goodness of ,providence4 --,to ,,god alone man owes the admirable faculties which enable him to improve and modify the productions of nature1 no less than those productions themselves4 ,in contemplating the works of the creation1 or studying the inventions of art1 let us1 therefore1 never forget the ,divine ,source from which they proceed2 and thus every acquisition of knowledge will prove a lesson of piety and virtue4 ,,index4 ,a ,absorbent vessels1 ii4 #cjd ,absorption of caloric1 i4 #ei4 #ff ,acetic acid1 ii4 #ge4 #aig ,acetous fermentation1 ii4 #bcb ---- acid1 ii4 #aic4 #bcb ,acidulous gaseous mineral waters1 ii4 #abi ---- salts1 ii4 #bjj ,acids1 i4 #bfb4 ii4 #fi ,aeriform1 i4 #cf ,affinity1 i4 #ai4 ii4 #a ,agate1 ii4 #ea ,agriculture1 ii4 #beb ,air1 i4 #ahb4 ii4 #bfb ,albumen1 ii4 #bgg4 #bhh ,alburnum1 ii4 #bfg ,alchemists1 i4 #d ,alcohol1 or spirit of wine1 ii4 #bae4 #bbb ,alembic1 i4 #beh ,alkalies1 ii4 #ai ,alkaline earths1 ii4 #ej4 #eh ,alloys1 i4 #cdd ,alum1 or sulphat of alumine1 ii4 #ee4 #ie ,alumine1 ii4 #ed ,alumium1 i4 #ac ,amalgam1 i4 #cdg ,ambergris1 ii4 #ceh ,amethyst1 ii4 #eh ,amianthus1 ii4 #ff ,ammonia1 or volatile alkali1 i4 #cfc4 ii4 #bj4 #ce ,ammoniacal gas1 ii4 #cf ,ammonium1 i4 #ac ,analysis1 i4 #bhg ---- of vegetables1 ii4 #afe ,animals1 ii4 #bgf ,animal acids1 ii4 #ge4 #bij ---- colours1 ii4 #bib ---- heat1 ii4 #ccg ---- oil1 ii4 #agh4 #bhc ,animalization1 ii4 #bgf4 #big4 #cae ,antidotes1 ii4 #da4 #hg ,antimony1 i4 #ad ,aqua fortis1 ii4 #aje ---- regia1 i4 #cdj4 ii4 #add ,arrack1 ii4 #bbj ,argand's ,lamp1 i4 #bjh ,arsenic1 i4 #ad4 #cdj4 #cdh ,arteries1 ii4 #cjd4 #cbc ,arterial blood1 ii4 #cje4 #cbf4 #cch ,asphaltum1 ii4 #bdj ,assaftida1 ii4 #ahh ,assimilation1 ii4 #bih ,astringent principle1 ii4 #aih ,atmosphere1 i4 #ij4 #aha4 ii4 #bfb ,atmospherical air1 i4 #ahb ,attraction of aggregation1 or cohesion1 i4 #af4 ii4 #b ---- of composition1 i4 #af4 ii4 #a ,azot1 or nitrogen1 i4 #ahb1 ii4 #ajj ,azotic gas1 i4 #ahb ,b ,balsams1 ii4 #afe4 #ahh ,balloons1 i4 #bde ,bark1 ii4 #aic4 #bfe ,barytes1 ii4 #dd4 #eh4 #fa ,bases of acids1 i4 #bfc4 ii4 #fi ---- gases1 i4 #ahc ---- salts1 ii4 #e ,beer1 ii4 #bab4 #bbj ,benzoic acid1 ii4 #gd4 #aig ,bile1 ii4 #cjh ,birds1 ii4 #cdg ,bismuth1 i4 #ad ,bitumens1 ii4 #bci ,black lead1 or plumbago1 i4 #cjd ,bleaching1 i4 #cb4 ii4 #hi4 #adj4 ,blow-pipe1 i4 #cbd4 ii4 #bbf ,blood1 ii4 #cjf4 #cag ,blood-vessels1 ii4 #bih ,boiling water1 i4 #ic ,bombic acid1 ii4 #ge4 #bij ,bones1 ii4 #bih1 #bii ,boracic acid1 i4 #cfe4 ii4 #aca ,boracium1 i4 #ac4 ii4 #acb ,borat of soda1 ii4 #acc ,brandy1 ii4 #bah ,brass1 i4 #cdd ,bread1 ii4 #bcc ,bricks1 ii4 #ef ,brittle-metals1 i4 #ad ,bronze1 i4 #cda ,butter1 ii4 #cea ,butter-milk1 ii4 #ceb ,c ,calcareous earths1 ii4 #fe ---- stones1 ii4 #abc ,calcium1 i4 #ac ,caloric1 i4 #ab4 #cc ----1 absorption of1 i4 #ff ----1 conductors of1 i4 #gj ----1 combined1 i4 #abb ----1 expansive power of i4 #ce ----1 equilibrium of1 i4 #ej ----1 reflexion of1 i4 #ed4 #fg ----1 radiation of1 i4 #eb4 #fa ----1 solvent power of1 i4 #if4 #ajb ----1 capacity for1 i4 #abd ,calorimeter1 i4 #aef ,calx1 i4 #ahc ,camphor1 ii4 #afe4 #ahe ,camphoric acid1 ii4 #gd4 #aig ,caoutchouc1 ii4 #afe4 #ahi ,carbonats1 ii4 #be4 #abi ,carbonat of ammonia1 ii4 #da ---- lead1 i4 #cbj ---- lime1 ii4 #ei4 #acj ---- magnesia1 ii4 #fg ---- potash1 ii4 #be ,carbonated hydrogen gas1 i4 #cjb ,carbon1 i4 #bhb4 ii4 #cbi ,carbonic acid1 i4 #bij4 #cei4 ii4 #cbg ,carburet of iron1 i4 #cjd4 #cdb ,carmine1 ii4 #bie ,cartilage1 ii4 #cjc ,castor1 ii4 #cei ,cellular membrane1 ii4 #caa ,caustics1 i4 #cdi ,chalk1 ii4 #fb4 #abc ,charcoal1 i4 #bhb ,cheese1 ii4 #cef ,chemical attraction1 i4 #ae4 ii4 #i ,chemistry1 i4 #c ,chest1 ii4 #cah ,china1 ii4 #ed ,chlorine1 i4 #bad ,chrome1 i4 #ad4 #cdj ,chyle1 ii4 #cje4 #cag ,chyme1 ii4 #caf ,citric acid1 ii4 #gd4 #aig ,circulation of the blood1 ii4 #cbb ,civet1 ii4 #cei ,clay1 i4 #dh4 ii4 #ee ,coke1 ii4 #bda ,coal1 ii4 #bdj4 #beb ,cobalt1 i4 #ad ,cochineal1 ii4 #bie ,cold1 i4 #ej4 #eh ---- from evaporation1 i4 #ajb4 #aac4 #aej ,colours of metallic oxyds1 i4 #cai ,columbium1 i4 #ad4 #cdj4 #cdh ,combined caloric1 i4 #abb ,combustion1 i4 #aij ----1 volatile products of1 i4 #bjg ----1 fixed products of1 i4 #bjg ----1 of alcohol1 ii4 #bbe ----1 of ammoniacal gas1 ii4 #db ----1 of boracium1 ii4 #acc ----1 by oxymuriatic acid or chlorine1 ii4 #adb ----1 of carbon1 i4 #bhi ----1 of coals1 i4 #bjg4 #big ----1 of charcoal by nitric acid1 ii4 #ajb ----1 of candles1 i4 #bcf4 #cji4 ii4 #agi ----1 of diamonds1 i4 #bib ----1 of ether1 ii4 #bcj ----1 of hydrogen1 i4 #bbi4 ----1 of iron1 i4 #bjj4 #cbb ----1 of metals1 i4 #cba ----1 of oils1 i4 #bjh4 ii4 #agh4 #cji ----1 of oil of turpentine by nitrous acid1 ii4 #f ----1 of phosphorus1 i4 #bgb ----1 of sulphur1 i4 #bfa ---- of potassium1 i4 #ceh4 ii4 #acb4 #ach1 #aci ,compound bodies1 i4 #i4 ii4 #ad ---- or neutral salts i4 #ccc4 ii4 #d ,conductors of heat1 i4 #ga ----1 solids1 i4 #gc ----1 fluids1 i4 #gh ----1 ,count ,rumford's theory1 i4 #gi ,constituent parts1 i4 #i ,copper1 i4 #ad4 #cca ,copal1 ii4 #ahg4 #bbd ,cortical layers1 ii4 #bfe4 #bfg ,cotyledons1 or lobes1 ii4 #bef ,cream1 ii4 #cea ,cream of tartar1 or tartrit of potash1 ii4 #bjj4 #bbb ,cryophorus1 i4 #aed ,crystallisation1 i4 #cch4 ii4 #dg ,cucurbit1 i4 #beh ,culinary heat1 i4 #hh ,curd1 ii4 #cea4 #ced ,cuticle1 or epidermis1 ii4 #caj ,d ,decomposition1 i4 #h4 #bj ---- of atmospherical air1 i4 #aha4 #bji ---- of water by the ,voltaic battery1 i4 #bbj ---- of salts by the ,voltaic battery1 ii4 #ad ---- of water by metals1 i4 #bbe4 #ccd ---- ---- by carbon1 i4 #cja ---- of vegetables1 ii4 #bjb ---- of potash1 i4 #cef ---- of soda1 i4 #ef ---- of ammonia1 i4 #cfc4 ii4 #cg ---- of the boracic acid1 ii4 #acb ---- of the fluoric acid1 ii4 #acf ---- of the muriatic acid1 ii4 #aci ,deflagration1 ii4 #aah ,definite proportions1 ii4 #ac ,deliquescence1 ii4 #ie ,detonation1 i4 #bai4 ii4 #aaf ,dew1 i4 #aje ,diamond1 i4 #bhe ,diaphragm1 ii4 #cbj ,digestion1 ii4 #caf ,dissolution of metals1 i4 #afe4 #caf4 #ccc ,distillation1 i4 #bei4 ii4 #bah ---- of red wine1 ii4 #bah ,divellent forces1 ii4 #ab ,division1 i4 #g ,drying oils1 ii4 #aha ,dying1 ii4 #aia ,e ,earths1 ii4 #dd ,earthen-ware1 ii4 #ec4 #eg ,effervescence1 i4 #bih ,efflorescence1 ii4 #id ,elastic fluids1 i4 #cg ,electricity1 i4 #ab4 #be4 #afj4 #bbj4 ii4 #aci ,electric machine1 i4 #afi ,elective attractions1 ii4 #i ,elementary bodies1 i4 #h4 #ab ,elixirs1 tinctures1 or quintessences1 ii4 #bbe ,enamel1 ii4 #eg ,epidermis of vegetables1 ii4 #bfi ---- of animals1 ii4 #caj ,epsom salts1 ii4 #fc4 #ie ,equilibrium of caloric1 i4 #ej ,essences1 i4 #cjg4 ii4 #ahc4 #bbd ,essential1 or volatile oils1 i4 #cjg4 ii4 #ahc ,ether1 i4 #aaa4 ii4 #bbi ,evaporation1 i4 #ajc ,evergreens1 ii4 #bgd ,eudiometer1 i4 #bgf ,expansion of caloric1 i4 #cf ,extractive colouring matter1 ii4 #afe4 #aij ,f ,falling stones1 i4 #cai ,fat1 i4 #cjf4 ii4 #caa ,feathers1 ii4 #cjj ,fecula1 ii4 #agf ,fermentation1 ii4 #bje ,fibrine1 ii4 #bgg4 #bhi ,fire1 i4 #g4 #bg ,fish1 ii4 #cdf ,fixed air1 or carbonic acid1 i4 #bij4 ii4 #abe ---- alkalies1 ii4 #bj ---- oils1 i4 #cjg4 ii4 #afe4 #agg ---- products of combustion1 i4 #bjg ,flame1 i4 #bcg ,flint1 ii4 #cj4 #ea ,flower or blossom1 ii4 #bga ,fluoric acid1 ii4 #ed4 #acd ,fluorium1 or ,fluorine1 i4 #ab4 ii4 #acf ,formic acid1 ii4 #bij ,fossil wood1 ii4 #bdb ,frankincense1 ii4 #ahg ,free or radiant caloric1 or heat of temperature1 i4 #cc ,freezing mixtures1 i4 #adb ---- by evaporation1 i4 #ajd4 #aej1 c4 ,frost1 i4 #id ,fruit1 ii4 #bga ,fuller's earth1 ii4 #ee ,furnace1 i4 #cjd ,g ,galls1 ii4 #aii ,gallat of iron1 ii4 #ih ,gallic acid1 ii4 #gd4 #aig1 #aih ,galvanism1 i4 #afc ,gas1 i4 #ahb ,gas-lights1 i4 #bdj ,gaseous oxyd of carbon1 i4 #bif ---- nitrogen1 ii4 #aaa ,gastric juice1 ii4 #caf ,gelatine1 or jelly1 ii4 #bgg4 #bhj ,germination1 ii4 #bef ,gin1 ii4 #bba ,glands1 ii4 #bih4 #cjg ,glass1 ii4 #cj ,glauber's salts1 or sulphat of soda1 ii4 #ib ,glazing1 ii4 #eg ,glucium1 i4 #ac ,glue1 ii4 #bha4 #bhg ,gluten1 ii4 #afe4 #agg ,gold1 i4 #ad4 #cbc ,gum1 ii4 #agj ---- arabic1 ii4 #agj ---- elastic1 or caoutchouc1 ii4 #ahi ---- resins1 ii4 #afe4 #ahh ,gunpowder1 ii4 #aaf ,gypsum1 or plaister of ,paris1 or sulphat of lime1 ii4 #ie ,h ,hair1 ii4 #cjj ,harrogate water1 i4 #bfh4 #cda ,hartshorn1 ii4 #ce4 #ci4 #bha4 #bhe ,heart1 ii4 #cbc ---- wood1 ii4 #bfh ,heat1 i4 #bf4 #cc ---- of capacity1 i4 #abg4 #ace ---- of temperature1 i4 #cc ,honey1 ii4 #age ,horns1 ii4 #bhb4 #cjj ,hydro-carbonat1 i4 #bda4 #cjc ,hydrogen1 i4 #bad ---- gas1 i4 #bae ,i ,jasper1 ii4 #ea ,ice1 i4 #ach ,jelly1 ii4 #bha ,jet1 ii4 #bdj ,ignes fatui1 i4 #bgg ,ignition1 i4 #aai ,imponderable agents1 i4 #ab ,inflammable air1 i4 #bae ,ink1 ii4 #ih4 #aii ,insects1 ii4 #cdi ,integrant pans1 i4 #i ,iridium1 i4 #ad ,iron1 i4 #ad4 #cai4 #cbh ,isinglass1 ii4 #aid4 #bhe ,ivory black1 ii4 #bie ,iodine1 i4 #bad4 ii4 #aeg ,k ,kali1 ii4 #cd ,koumiss1 ii4 #cef ,l ,lac1 ii4 #ceh ,lactic acid1 ii4 #ge4 #bij4 #cef ,lakes1 colours1 ii4 #aij ,latent heat1 i4 #acc ,lavender water1 ii4 #ahd4 #bbd ,lead1 i4 #ad4 #cah4 #ccj ,leather1 ii4 #aic4 #bhg ,leaves1 ii4 #bfj ,life1 ii4 #aei4 #afh ,ligaments1 ii4 #cjc ,light1 i4 #ab4 #bf4 ii4 #bfa ,lightning1 i4 #bdh ,lime1 ii4 #ei ---- water1 ii4 #fa ,limestone1 ii4 #fj ,linseed oil1 ii4 #agh ,liqueurs1 ii4 #bbd ,liver1 ii4 #cjh ,lobes1 ii4 #bef4 #ccb ,lunar caustic1 or nitrat of silver1 i4 #cej4 ii4 #aai ,lungs1 ii4 #cai4 #ccj ,lymph1 ii4 #cjd ,lymphatic vessels1 ii4 #cjd ,m ,magnesia1 ii4 #dd4 #ff ,magnium1 i4 #ac ,malic acid1 ii4 #gd4 #aig ,malt1 ii4 #baa ,malleable metals1 i4 #ad ,manganese1 i4 #ad4 #cag ,manna1 ii4 #agf ,manure1 ii4 #bdg ,marble1 ii4 #abc ,marine acid1 or muriatic acid1 ii4 #acf ,mastic1 ii4 #ahg4 #bbd ,materials of animals1 ii4 #bgg ---- of vegetables1 ii4 #afe ,mercury1 i4 #ad4 #cdf ----1 new mode of freezing1 i4 #aee4 #cdg ,metallic acids1 i4 #cdj ---- oxyds1 i4 #caf ,metals1 i4 #ab4 #cad ,meteoric stones1 i4 #cdb ,mica1 ii4 #ff ,milk1 ii4 #bii4 #cjf4 #cej ,minerals1 i4 #cae4 ii4 #dd4 #aeh ,mineral waters1 i4 #bif4 ii4 #abi ---- acids1 ii4 #gc ,miner's lamp1 i4 #bdi ,mixture1 i4 #ii ,molybdena1 i4 #ad4 #cdj ,mordant1 ii4 #afe4 #aib ,mortar1 ii4 #ec4 #fe ,mucilage1 ii4 #agj ,mucous acid1 ii4 #gd4 #aga4 #aig ---- membrane1 ii4 #caa ,muriatic acid1 or marine acid1 ii4 #acf ,muriats1 ii4 #aea ,muriat of ammonia1 ii4 #ce4 #aeb ---- lime1 i4 #ajj ---- soda1 or common salt1 ii4 #acf4 #aea ---- potash1 ii4 #ach ,muriatium1 i4 #ac ,muscles of animals1 ii4 #bih4 #cjc ,musk1 ii4 #cei ,myrrh1 ii4 #ahh ,n4 ,naphtha1 i4 #ceg4 ii4 #bdj ,negative electricity1 i4 #be4 #afa4 #ahe ,nerves1 ii4 #bgi4 #bih4 #cjh ,neutral1 or compound salts1 i4 #ccc4 ii4 #d4 #bb4 #fi ,nickel1 i4 #ac4 #cdc ,nitre1 or nitrat of potash1 or saltpetre1 ii4 #cb4 #ajd4 #aaf ,nitric acid1 ii4 #ajj ,nitrogen1 or azot1 i4 #aha4 ii4 #ajj ---- gas1 i4 #ahb4 #baa ,nitro-muriatic acid1 or aqua regia1 ii4 #add ,nitrous acid gas1 ii4 #aja4 #ajf ---- air1 or nitrit oxyd gas1 ii4 #ajg ,nitrats1 ii4 #aaf ,nitrat of copper1 ii4 #e ---- ammonia1 ii4 #aac4 #aah ---- potash1 or nitre1 or saltpetre1 ii4 #cb4 #ajd4 #aaf ---- silver1 or lunar caustic1 ii4 #ai ,nomenclature of acids1 i4 #bfd4 ii4 #fi ---- compound salts1 ii4 #d4 #bb ---- other binary compounds1 i4 #bgh ,nut-galls1 ii4 #ih4 #aii ,nut-oil1 ii4 #agh ,nutrition1 ii4 #big ,o ,ochres1 i4 #cbj ,oils1 i4 #bhe4 ii4 #cjf ,oil of amber1 ii4 #bda ---- vitriol1 or sulphuric acid1 ii4 #hj ,olive oil1 ii4 #agh ,ores1 i4 #cae ,organized bodies1 ii4 #aei ,organs of animals1 ii4 #bij4 #caj ---- vegetables1 ii4 #aei4 #bfe4 #bga ,osmium1 i4 #ad4 #cdh ,oxalic acid1 ii4 #gd4 #aig ,oxyds1 i4 #aih ,oxyd of manganese1 i4 #aag4 #cag ---- iron1 i4 #bjd4 #cai ---- lead1 i4 #cai ---- sulphur1 ii4 #ia ,oxydation1 or oxygenation1 i4 #aif ,oxygen1 i4 #aa4 #aha4 #bja4 #baa ---- gas1 or vital air1 i4 #ahb4 #bja ,oxy-muriatic acid1 ii4 #adj ,oxy-muriats1 ii4 #aec ,oxy-muriat of potash1 ii4 #aee ,p ,palladium1 i4 #ac4 #cdh ,papin's digester1 i4 #abj4 ii4 #bhd ,parenchyma1 ii4 #bef4 #bff ,particles1 i4 #af ,pearlash1 ii4 #bd ,peat1 ii4 #bdb ,peculiar juice of plants1 ii4 #bfh ,perfect metals1 i4 #ad4 #cbd ,perfumes1 i4 #cjh4 ii4 #ahc ,perspiration1 ii4 #ccc4 #cbi ,petrification1 ii4 #bcg ,pewter1 i4 #cdd ,pharmacy1 i4 #ad ,phosphat of lime1 ii4 #ii4 #bii ,phosphorated hydrogen gas1 i4 #bgg ,phosphorescence1 i4 #bi ,phosphoric acid1 i4 #bgc4 ii4 #ii ,phosphorous acid1 i4 #bgd4 ii4 #ii ,phosphorus1 i4 #bgj ,phosphoret of lime1 i4 #bgh4 #cda ---- sulphur1 i4 #bgi4 #cda ,pitch1 ii4 #ahg ,plaster1 ii4 #fe ,platina1 i4 #ad4 #cbc ,plating1 i4 #cde ,plumbago1 or black lead1 i4 #cjd ,plumula1 ii4 #beg ,porcelain1 ii4 #ef ,positive electricity1 i4 #be4 #afa4 #ahe ,potassium1 i4 #ac4 #ceg4 ii4 #ae ,pottery1 ii4 #ef ,potash1 i4 #cef4 ii4 #bb ,precipitate1 i4 #bb ,pressure of the atmosphere1 i4 #aab4 #aaf ,printer's ink1 ii4 #add ,prussiat of iron1 or prussian blue1 ii4 #bia ---- potash1 ii4 #bia ,prussic acid1 ii4 #ge4 #bij ,putrid fermentation1 ii4 #bce4 #cfj ,pyrites1 i4 #cda4 ii4 #ig ,pyrometer1 i4 #ch4 #db ,q ,quick lime1 ii4 #ei ,quiescent forces1 ii4 #ab ,r ,radiation of caloric1 i4 #eb ----1 ,prevost's theory1 i4 #eb ----1 ,pictet's explanations1 i4 #ed ----1 ,leslie's illustrations1 i4 #fa ,radicals1 ii4 #e4 #fi ,radicle2 or root1 ii4 #beg ,rain1 i4 #ajd ,rancidity1 ii4 #ahb ,rectification1 ii4 #bbc ,reflexion of caloric1 i4 #ed4 #fd ,reptiles1 ii4 #cdi ,resins1 ii4 #afe1 #ahf4 #bff ,respiration1 ii4 #cag4 #cbf ,reviving of metals1 i4 #cbg ,rhodium1 i4 #ad4 #cdh ,roasting metals1 i4 #caf ,rock crystal1 ii4 #fa ,ruby1 ii4 #ec ,rum1 ii4 #bai ,rust1 i4 #cah4 #cbh ,s ,saccharine fermentation1 ii4 #bjh ,sal ammoniac1 or muriat of ammonia1 ii4 #ce ---- polychrest1 or sulphat of potash1 ii4 #ia ---- volatile1 or carbonat of ammonia1 ii4 #da ,salifiable bases1 ii4 #e ,salifying principles1 ii4 #e ,saltpetre1 or nitre1 or nitrat of potash1 ii4 #cb4 #ajd4 #aaf ,salt1 ii4 #ia ,sand1 ii4 #cj4 #ea ,sandstone1 ii4 #ea ,sap of plants1 ii4 #afe4 #bfj4 #bfb4 #bgj4 #bgb ,sapphire1 ii4 #eh ,saturation1 i4 #aja4 ,sapphire1 ii4 #eh ,saturation1 i4 #aja ,seas1 temperature of1 i4 #cc4 ,sebacic acid1 ii4 #ge4 #ahb4 #bij4 #cec ,secretions1 ii4 #cjg ,seeds of plants1 ii4 #baj4 #bga ,seltzer water1 i4 #bhi4 ii4 #fc4 #abi ,senses1 ii4 #caj ,silex1 or silica1 ii4 #cj4 #ea ,silicium1 i4 #ac4 ,silk1 ii4 #cei ,silver1 i4 #cba ,simple bodies1 i4 #aj4 #ab ,size1 ii4 #bha ,skin1 ii4 #bgi4 #caj4 #aic ,slakeing of lime1 i4 #adg4 ii4 #ef ,slate1 ii4 #ea4 #ff ,smelting metals1 i4 #caf ,smoke i4 #bjh ,soap1 ii4 #bd ,soda1 i4 #cfc4 ii4 #cc ---- water1 i4 #bii ,sodium1 i4 #ac4 #cfc ,soils1 i4 #db4 ii4 #bde ,soldering1 i4 #cde ,solubility1 ii4 #ib ,solution1 i4 #if ---- by the air1 i4 #ajb ---- of potash1 ii4 #bh ,specific heat1 i4 #abf ,spermaceti1 ii4 #ceh ,spirits1 ii4 #cac ,steam1 i4 #adj4 #ahb ,steel1 i4 #cje ,stomach1 ii4 #cae ,stones1 ii4 #df ,stucco1 ii4 #fe ,strontites1 ii4 #dd4 #fh ,strontium1 i4 #ac ,suberic acid1 ii4 #gd4 #aig ,sublimation1 i4 #beg ,succin1 or yellow amber1 ii4 #bda ,succinic acid1 ii4 #gd4 #aig4 #bda ,sugar1 ii4 #afe4 #agd4 #bjh ---- of milk1 ii4 #cee ,sulphats1 ii4 #e4 #ia ,super oxygenated sulphuric acid1 ii4 #gj4 ,sulphat of alumine1 or alum1 ii4 #ed4 #ie ---- barytes1 ii4 #eh ---- iron1 ii4 #if ---- lime1 or gypsum1 or plaster of ,paris1 ii4 #ie ---- magnesia1 or ,epsom salt1 ii4 #fg4 #ie ---- potash1 or sal polychrest1 ii4 #ia ---- soda1 or ,glauber's salts1 ii4 #ib ,sulphur1 i4 #bef ---- flowers of1 i4 #beg ,sulphurated hydrogen gas1 i4 #afe4 #bfh ,sulphurets1 i4 #cda ,sulphurous acid1 i4 #bed4 ii4 #hh ,sulphuric acid1 i4 #gd4 ii4 #bfe ,sympathetic ink1 i4 #ced ,synthesis1 i4 #bhg ,t ,tan1 ii4 #aib ,tannin1 ii4 #afe4 #aib ,tar1 ii4 #ahg ,tartarous acid1 ii4 #gd4 #aig ,tartrit of potash1 ii4 #bbb ,teeth1 ii4 #cjj ,tellurium1 i4 #ad ,temperature1 i4 #cc ,thaw1 i4 #aeh ,thermometers1 i4 #dj ----1 ,fahrenheit's1 i4 #db ----1 ,reaumur's1 i4 #db ----1 ,centigrade1 i4 #dc ----1 air1 i4 #dd ----1 differential1 i4 #df ,thunder1 i4 #bdh ,tin1 i4 #ad4 #cdd ,titanium1 i4 #ad4 #cdh ,turf1 ii4 #bdb ,turpentine1 ii4 #ahg ,transpiration of plants1 ii4 #bfj ,tungsten1 i4 #ad4 #cdj ,v ,vapour1 i4 #cf4 #di4 #ic4 #ahb ,vaporisation1 i4 #ajc ,varnishes1 ii4 #ahg ,vegetables1 ii4 #aeh ,vegetable acid1 i4 #caj4 ii4 #gd4 #aig ---- colours1 ii4 #aij ---- heat1 ii4 #bgb ---- oils1 ii4 #agg ,veins1 ii4 #cjd4 #cbc4 ,venous blood1 ii4 #cje4 #cbf4 #cch ,ventricles1 ii4 #cbd ,verdigris1 i4 #ceb ,vessels1 ii4 #cjd ,vinegar1 ii4 #bcb ,vinous fermentation1 ii4 #bab ,vital air1 or oxygen gas1 i4 #ahb ,vitriol1 or sulphat of iron1 ii4 #ha ,volatile oils1 i4 #cjg4 ii4 #afe4 #ahc4 #bbd4 #bfi ---- products of combustion1 i4 #bjg ---- alkali1 i4 #cfc4 ii4 #bj4 #ce ,voltaic battery1 i4 #afd4 #bbj4 #cef4 ii4 #ae ,u ,uranium1 i4 #ad ,w ,water1 i4 #bae4 ii4 #bfb ----1 decomposition of1 by electricity1 i4 #bjj4 #bbe ----1 condensation of1 i4 #cb ---- of the sea1 i4 #hf ----1 boiling1 i4 #ic ----1 solution by1 i4 #if ---- of crystallisation1 i4 #cci ,wax1 i4 #cji4 ii4 #ahj4 #ceh ,whey1 ii4 #cea ,wine1 ii4 #bab ,wood1 ii4 #bfg ,woody fibre1 ii4 #aef4 #aif4 #bfg ,wool1 ii4 #cjj ,y ,yeast1 ii4 #bcd4 ,yttria1 ii4 #dd4 ,yttrium1 i4 #ac4 ,z ,zinc1 ii4 #ad4 #cdd ,zirconia1 ii4 #dd ,zirconium1 i4 #ad ,zoonic acid1 ii4 #ge4 #bbj ,,end4 ,printed by ,a4 ,strahan1 ,printers-,street1 ,london 99 99 99 99 99 99 99 99 99 99 99 99 99 99 ,terminology oxy-muriatic acid chlorine 7proposed as an element in #ahae3 see ,conversation ,,xix7 8columbium or tantalium0 niobium and tantalum 7the two elements always occur together1 and were not recognized as separate until much later in the #aith century7 phosphat of lime calcium diphosphate or calcium 7the element calcium was isolated in #ahjh1 but is named only once in this #ahag edition7 glucium beryllium 7,humphry ,davy's name for the element7 muriatic acid hydrochloric acid 7still called 8muriatic acid0 for some commercial uses7 muriat of lime calcium chloride oxymuriate of potash potassium chlorate muriat of soda sodium chloride 7table salt7 carbonic acid carbon dioxide ,note also3 simple body1 fundamental principle element fecula starch 7usually spelled 8fcula07 spirit of wine alcohol philosopher scientist arts industry1 manufacture1 crafts etc4 7seldom 8fine arts07 ,some essential concepts relating to living things--photosynthesis1 microorganisms1 the cell1 proteins--are either unknown or not mentioned4 ,the atom theory had been proposed1 but not by ,humphry ,davy2 it is not mentioned in this book4 ,the word 8explode0 is used at least once in its orginal1 figurative sense 78a word that should be exploded in chemistry07 but far more often in its later1 concrete one4 ,the word 8explosion0 is always used concretely 78an explosion1 or a detonation as chemists commonly call it074 ,calculated ,values3 8the point of zero1 or the absolute privation of heat1 must consequently be #abfj degrees below #cb degrees0 -#abbh ,f4 ,the calculation is based on wrong premises2 the correct figure is about -#dfj ,f or -#bgc ,c4 8,mercury congeals only at seventy-two degrees below the freezing point40 -#dj ,f1 which is also -#dj ,c4 ,this figure is correct1 though approximate4 8,the proportion stated by ,sir ,h4 ,davy1 in his ,chemical ,researches1 is as #a to #b4chi40 8ammonia consisted of about one part of hydrogen to four parts of nitrogen4444 and from the latest and most accurate experiments1 the proportions appear to be1 one volume of nitrogen gas to three of hydrogen gas0 ,these and similar calculations involving weight and volume make more sense when one knows the elements' atomic weights4 ,for nitric acid1 ,,hno#c1 the figures are #a3ad3dh1 giving a proportion closer to #a3c4e4 ,for ammonia1 ,,nh#c 7not #d71 the figures are #ad3c4 8,the oxalic acid1 distilled from sorrel1 is the highest term of vegetable acidification2 for1 if more oxygen be added to it1 it loses its vegetable nature1 and is resolved into carbonic acid and water20 ,oxalic acid ,h#b;,c#b,o#d2 carbonic acid 7carbon dioxide7 ,,co#b4 ,h#b;,c#b,o#d ,o becomes ,h#b,o ,,co#b ,,co#b4 99 99 99 99 99 99 99 99 99 ,contents3 ,numbering and ,changes ,the #crd and #dth editions used the same ,conversation numbering4 ,changes between the #dth and #eth 7present text7 edition are shown4 ,some illustrations were also changed4 ,volume ,i3 ,on ,simple ,bodies 7,i1 ,,ii1 ,,iii no change7 ,,iv4 ,on ,specific ,heat1 ,latent ,heat1 and ,chemical ,heat4 ,,iv4 ,on ,combined ,caloric1 ,comprehending ,specific ,heat and ,latent ,heat4 -- ,v4 ,new ,chapter ,on ,the ,chemical ,agencies ,of ,electricity4 ,v4 ,,vi4 ,on ,oxygen ,and ,nitrogen4 ,,vi4 ,,vii4 ,on ,hydrogen4 #eth edn3 adds sections on ,gas lights and ,miner's ,lamp ,,vii4 ,,viii4 ,on ,sulphur ,and ,phosphorus4 #eth edn3 adds section on ,decomposition of ,sulphur ,,viii4 ,on ,carbone4 ,,ix4 ,on ,carbon4 #dth edn3 ,section 8,diamond is ,carbon in a ,state of perfect purity02 later edn3 8,diamond0 alone ,,ix4 ,x4 ,on ,metals4 ,x4 ,,xiv4 ,on ,alkalies4 ,,xi4 ,,xv4 ,on ,earths4 #eth edn3 both moved to ,vol4 ,,ii4 ,volume ,,ii4 ,on ,compound ,bodies ,,xii4 ,,xiii4 ,on ,the ,attraction ,of ,composition4 #eth edn4 ,,xiv1 ,,xv #dth edn4 ,x1 ,,xi ,,xiii4 ,on ,compound ,bodies4 ,,xvi4 ,on ,acids4 ,most of ,,xiii1 ,on ,compound ,bodies1 became ,,xvi1 ,on ,acids4 ,some introductory material was moved to ,,xiv1 ,on ,alkalies4 ,,xiv4 ,on ,the ,combinations of ,oxygen with ,sulphur and with ,phosphorus2 and of the ,sulphats ,and ,phosphats4 ,,xvii4 ,of the ,sulphuric and ,phosphoric ,acids3 or1 ,the ,combinations of 4444 ,,xv4 ,on ,the ,combination of ,oxygen ,with ,nitrogen and with ,carbone2 and of ,the ,nitrats ,and ,carbonats4 ,,xviii4 ,of ,the ,nitric ,and ,carbonic ,acids3 ,or ,the ,combination 444 ,,xvi4 ,on ,muriatic ,and ,oxygenated ,muriatic ,acids2 and on ,muriats4 ,,xix4 ,on ,the ,boracic1 ,fluoric1 ,muriatic1 and ,oxygenated ,muriatic ,acids2 and on ,muriats4 ,,xvii4 ,,xx4 ,on ,the ,nature ,and ,composition ,of ,vegetables4 7remaining ,conversations3 #dth edn4 #c #eth edn47 99 99 99 99 99 99 99 99 99 ,,errata ,inconsistencies are generally unchanged2 see end of ,errata list4 ,two items are noted in the printed ,errata1 immediately after the ,contents for ,vol4 ,i3 ,vol4 ,i4 page #ef4 last line but one1 for 8caloric10 read 8calorific40 #agi4 ,note1 for 8,plate ,,xii40 r4 8,plate ,,xiii40 ,i4#ef ,the principal use of the mirrors in this experiment is1 to prove that the calorific emanation 444 ,i4#agi fn4 ,a model of this mode of construction is exhibited in ,,plate ,,xiii4 ,fig4 #a4 ,errata ,noted by ,transcriber3 ,contents ,,ii 444 ,dr4 ,herschel's ,experiments body text has 8,herschell0 ,,xiv 444 ,hartshorn and ,sal ,volatile ad ,conversation ,i ,emily the electric spark which is visible1 and aud ,conversation ,,ii ,mrs4 ,b41 parenthesis 7,,plate ,i4 ,fig4 #a47 ,fig4 ,i4 ,mrs4 ,b4 it has been called differential thermometer missing 8the08 ,mrs4 ,b41 parenthesis 7,,plate ,,iii4 ,fig4 #a47 ,fig4 ,i4 ,emily the tin surface should radiate the least caloric carolic ,conversation ,,iii ,emily the glass skreen spelling unchanged ,mrs4 ,b41 parenthesis 7,,plate ,,iv4 ,fig4 #a47 error for ,fig4 #b4 ,plate ,,iv caption ,thermometers one in the ,ether1 the other invisible comma after 8,thermometers08 ,mrs4 ,b4 he found that it was considerably colder is was ,conversation ,,iv ,caroline ,but how can you reverse this experiment8 printed 8expe-_/periment0 at line break ,mrs4 ,b4 instead of being #ge degrees1 will be #hj degrees error for #hh8 ,emily1 footnote ,see page #ajb4 in ,conversation ,,iii ,mrs4 ,b4 then soke it in ether spelling unchanged ,conversation ,v ,mrs4 ,b4 at regular distances in wooden troughs throughs ,caroline the nature of the action of the ,voltaic battery ,votaic ,conversation ,,vi ,caroline the nature of ,,oxygen1 which come next in our table error for 8comes08 ,conversation ,,vii ,mrs4 ,b41 parenthesis 7c1 d1 ,,plate ,,viii4 fig4 #b47 fig4 #b1 ,caroline be soon adopted every where1 every where4 ,plate ,x ,c4 apperture for supplying ,oil4 spelling unchanged ,conversation ,,viii ,mrs4 ,b4 sulphur is a very combustible substance sulpur ,mrs4 ,b4 ,i now put into the receiver missing 8it08 ,emily ,what is 444 after its detonation8 4 for 8 ,conversation ,,ix ,mrs4 ,b4 we are to burn the carbon bnrn ,mrs4 ,b4 since they may be prepared thay ,mrs4 ,b4 artificial ,seltzer water artifical ,conversation ,x ,mrs4 ,b4 increase the rapidity of its combustion of of ,caroline a pair of scissars spelling unchanged ,mrs4 ,b4 as well as by evaporating the liquid4 8 for 4 ,mrs4 ,b41 footnote page #aee4 of this volume near the end of ,conversation ,,iv ,caroline amongst the metals4 ,i had no notion 1 for 4 ,emily ,but is it not very singular singulr ,mrs4 ,b4 ,thenard and ,gay ,lussac usually hyphenated3 8,gay-,lussac0 ,conversation ,,xiii ,emily 444 render that decomposition perceptible8 4 for 8 ,conversation ,,xiv ,mrs4 ,b4 an acrid burning taste on acrid ,caroline according to which heat is disengaged t in 8heat0 invisible ,mrs4 ,b4 one volume of nitrogen gas to three of hydrogen gas text has 8oxygen0 for 8hydrogen0 ,conversation ,,xv ,mrs4 ,b4 so many interesting and important compounds interesing ,caroline ,and of what nature 444 painting porcelain8 4 for 8 speaker's name missing2 supplied from other editions ,conversation ,,xvi ,mrs4 ,b4 combined with acidifiable radicals acidificiable ,mrs4 ,b4 this power of charring wood charing ,conversation ,,xviii ,caroline not mentioning this acid printed 8mention-_/this0 at line break ,mrs4 ,b4 7footnote7 #a to #b4chi4 printed 8#b1chi03 no other decimal numbers occur in the text1 but a comma appears once as a thousands separator ,mrs4 ,b4 ,you1 understand1 now1 ,i hope1 all commas in original ,conversation ,,xx ,mrs4 ,b4 of vegetables2 we shall1 therefore 1 for 2 ,conversation ,,xxi ,mrs4 ,b4 the compound last formed will be destroyed2 detroyed ,mrs4 ,b4 in such climates great part of the water missing 8a0 before 8great08 ,mrs4 ,b4 a state of debility and languor langour ,mrs4 ,b41 parenthesis 7,,plate ,,xiv4 ,fig4 #b47 ,,plate ,,xiii4 ,mrs4 ,b4 burns at so slow a temperature text unchanged3 error for 8low0 or correct as printed8 ,mrs4 ,b4 the poor in heathy countries not an error3 8heath-y01 not 8healthy0 ,conversation ,,xxii ,mrs4 ,b41 parenthesis 7,,plate ,,xv4 ,fig4 #d47 ,,plate ,,xiv4 ,mrs4 ,b4 so many vessels or apparatus not an error3 8apparatus0 is the ,latin plural form ,mrs4 ,b4 chesnut common variant spelling ,conversation ,,xxiii ,mrs4 ,b4 pure gelatine gelantine ,conversation ,,xxv ,mrs4 ,b4 ,the muscular action of the diaphragm diaphram ,conversation ,,xxvi ,mrs4 ,b4 the air had been previously consumed previouly ,mrs4 ,b4 this is by the ,tartan ,arabs text unchanged3 ,tartar8 ,mrs4 ,b4 or studying the inventions of art1 let us1 therefore 2 for 1 ,index ,arrack body text has 8arack0 ,cold ---- from evaporation1 i4 #ajb4 #aac4 #aej volume number missing ,culinary heat1 i4 #hh volume number missing ,decomposition ---- of ammonia1 i4 #cfc4 ii4 #cg ammonnia2 8i0 invisible ,frankincense ,francincense ,freezing mixtures ---- by evaporation1 i4 #ajd4 #aej1 c4 volume number invisible ,glue1 ii4 #bha4 #bhg volume number missing ,n4 anomalous 4 unchanged ,phosphorous acid1 i4 #bgd4 ii4 #ii volume ,i body text always has 8,phosphorus acid0 ,sulphat ---- lime1 or gypsum1 or gypsum of ,sulphur ---- flowers of1 i4 #beg volume number missing ,thermometers ----1 ,centigrade1 i4 #dc ,centrigade ,thermometers ----1 differential1 i4 #df differentiial ,v1 ,u alphabetized as shown ,zirconia1 ii4 #dd ,zicornia ,zirconium1 i4 #ad ,zicornium 444 #ac ,inconsistencies and variant spellings3 ,standard spellings in this book include3 bason1 judgment1 embrio1 volcanos 7plural71 potatoe 7singular7 ,inconsistencies include3 capitalization of 8,fig40 or 8fig40 hyphenization of words such as 8oxy-muriatic0 8glauber salt0 and 8,glauber's salt0 both occur ,variant forms include3 opake1 opaque ariform1 aeriform 7with and without dieresis7 gasses1 gases phosphoret1 phosphuret 7but always carburet7 ,libya1 ,lybia dy7e7ing from 8dye0 nap7h7tha pla7i7ster slak7e7ing earthen-ware1 earthen ware 8sulphurous01 8naphtha0 are used in the ,contents and the ,index2 8sulphureous01 8naptha0 in the body text forms in 8-xion0 7such as 8connexion07 appear only in the ,contents and the ,index ,volume ,i has more archaic forms than ,volume ,,ii3 8shew01 8inclose0 are sometimes used instead of 8show01 8enclose0 8carbone0 with final 8e0 appears in one ,plate caption4 7,in the same plate's header1 the 8e0 appears to have been removed by the engraver47 8develope7ment70 is more common in ,volume ,i1 8develop7ment70 in ,volume ,,ii 8-ize0 and 8-yze0 forms 7for later 8-ise0 and 8-yse07 are common in ,volume ,i1 rare in ,volume ,,ii except in the ,index ,the 8,dr4 ,marcet0 mentioned in a few footnotes and figure captions is the author's husband4 ,humphry ,davy 78,sir ,h4 ,davy07 was knighted in #ahab1 between the #crd and #dth editions of the book4 ,reminder3 ,,do ,,not ,,try ,,this ,,at ,,home4 99 99 99 99 99 99 99 99 99 99 99 99 99 99