,transcriber's ,note3 ,underscores before and after a word or phrase indicate italics in the original text1 however1 they are also used to designate a subscript4 ,equal signs before and after a word or phrase indicate bold in the original text4 ,carat characters are used to designate a superscript4 ,small capitals have been converted to ,,solid capitals4 ,illustrations have been moved so they do not break up paragraphs4 ,old or antiquated spellings have been preserved4 ,typographical errors have been silently corrected but other variations in spelling and punctuation remain unaltered4 ,,the ,,gases ,,of ,,the ,,atmosphere ,illustration ,illustration3 ,,stephen ,,hales4 ,,the ,,gases ,,of ,,the ,,atmosphere ,,the ,,history ,,of ,,their ,,discovery ,,by ,,william ,,ramsay1 ,f4,r4,s4 ,,professor ,,of ,,chemistry ,,in ,,university ,,college1 ,,london ,,with ,,portraits ,london ,,macmillan ,,and ,,co41 ,,ltd4 ,,new ,,york3 ,,the ,,macmillan ,,co4 #ahif ,all rights reserved 8,modern discoveries have not been made by large collections of facts1 with subsequent discussion1 separation1 and resulting deduction of a truth thus rendered perceptible4 ,a few facts have suggested an hypothesis1 which means a supposition proper to explain them4 ,the necessary results of this supposition are worked out1 and then1 and not till then1 other facts are examined to see if their ulterior results are found in ,nature40 --,,de ,,morgan1 ,a ,budget of ,paradoxes1 ed4 #ahgb1 p4 #ee4 ,,preface ,the discovery of new elementary gas in the atmosphere in #ahid aroused much interest1 and public attention has again been directed to the air1 which was1 for many centuries1 a fruitful field for speculation and conjecture4 ,the account of this discovery1 communicated to the ,royal ,society in ,january #ahie1 was1 however1 necessarily couched in scientific language2 and many matters of interest to the chemist and physicist were written in an abbreviated style1 in the knowledge that the passages describing them would be easily understood by the experts to whom the communication was primarily addressed4 ,but persons without any special scientific training have frequently expressed to me the hope that an account of the discovery would be published1 in which the conclusions drawn from the physical behaviour of argon should be accompanied by a full account of the reasoning on which they are based4 ,an endeavour to fulfil this request is to be found in the following pages4 ,and as the history of the discovery of the better known constituents of the atmosphere is of itself of great interest1 and leads up to an acquaintance with the new stranger1 who has so long been with us incognito1 an effort has here been made to tell the tale of the air in popular language4 ,,contents ,,chapter ,i ,,page ,,the ,,experiments ,,and ,,speculations ,,of ,,boyle1 ,,mayow1 ,,and ,,hales #a ,,chapter ,,ii 8,,fixed ,,air0 ,,and 8,,mephitic ,,air0--,,their ,,discovery ,,by ,,black ,,and ,,by ,,rutherford #ch ,,chapter ,,iii ,,the ,,discovery ,,of 8,,dephlogisticated ,,air0 ,,by ,,priestley ,,and ,,by ,,scheele--,,the ,,overthrow ,,of ,,the ,,phlogistic ,,theory ,,by ,,lavoisier #fh ,,chapter ,,iv 8,,phlogisticated ,,air0 ,,investigated ,,by ,,cavendish--,,his ,,discovery ,,of ,,the ,,composition ,,of ,,water #aai ,,chapter ,v ,,the ,,discovery ,,of ,,argon #adf ,,chapter ,,vi ,,the ,,properties ,,of ,,argon #aha ,,chapter ,,vii ,,the ,,position ,,of ,,argon ,,among ,,the ,,elements #baf ,,list ,,of ,,portraits ,,stephen ,,hales ,frontispiece ,,robert ,,boyle ,to face page #h ,,john ,,mayow #ag ,,joseph ,,black #dh ,,daniel ,,rutherford #fb ,,joseph ,,priestley #gb ,,antoine ,,auguste ,,lavoisier #ajb ,,hon4 ,,henry ,,cavendish #aba ,,chapter ,i ,,the ,,experiments ,,and ,,speculations ,,of ,,boyle1 ,,mayow1 ,,and ,,hales ,to tell the story of the development of men's ideas regarding the nature of atmospheric air is in great part to write a history of chemistry and physics4 ,this history is an attractive and varied one3 in its early stages it was expressed in the quaint terms of ancient mythology1 while in its later developments it illustrates the advantage of careful experimental inquiry4 ,the human mind is apt to reason from insufficient premisses2 and we meet with many instances of incorrect conclusions1 based upon experiment1 it is true1 but upon experiment inadequate to support their burden4 ,further research has often proved the reasoning of the ,schoolmen to be futile2 not indeed from want of logical method1 but because important premisses had been overlooked4 ,among the errors which misled the older speculators1 three stand out conspicuously4 ,these are-- ,first1 ,the confusion of one gas with another4 ,since gases are for the most part colourless1 and always transparent1 they make less impression on the senses than liquids or solids do4 ,it was difficult to believe in the substantiality of bodies which could not be seen1 but the existence of which had to be inferred from the testimony of other senses2 indeed1 in certain instances only by the sense of touch1 for many gases possess neither smell nor taste4 ,this peculiarity led1 in past ages1 to the notion that air possessed a semi-spiritual nature2 that its substantiality was less than that of other objects more accessible to our senses4 ,we meet with a relic of this view in words still in common use4 ,thus the ,greek words 1 ,i blow1 and 1 a spirit or ghost1 are closely connected2 in ,latin we have spiro1 ,i breathe1 and spiritus1 the human spirit2 in ,english1 the words ghost and gust are cognate4 ,and the same connection can be traced in similar words in many other languages4 ,our sense of smell is affected by extremely minute traces of gases and vapours--traces so small as to be unrecognisable by any other method of perception1 direct or indirect4 ,a piece of musk retains its fragrant odour for years1 and the most delicate balance fails to detect any appreciable loss of weight in it4 ,we are capable of smelling gases only3 liquids and solids1 if introduced into the nostrils1 irritate the olfactory nerves1 but do not stimulate them so as to incite the sense of smell2 yet the admixture of a minute trace of some odorous vapour with air appears entirely to change its properties4 ,the effect of inhaling such air1 although sometimes pleasant1 is very different from the sensation produced by pure inodorous air1 and such admixtures were in olden times naturally taken to be air modified in its properties4 ,but such modifications are obviously almost infinite in number1 for varieties of scent are excessively numerous2 and it was therefore perhaps deemed useless to attempt to investigate such a substance as air1 whose properties could change in so inexplicable and mysterious a manner4 ,owing1 therefore1 to its elusive and1 as it were1 semi-spiritual properties1 and to its unexpected changes of character1 it was long before its true nature was discovered4 ,it had not escaped observation that 8air0 obtained by distilling animal and vegetable matter1 or by the action of acids on iron and zinc1 differed from ordinary air by being inflammable2 but such 8airs0 were regarded as atmospheric air1 modified in some manner1 as it is modified when perfumed4 ,and 8airs0 escaping from fermenting liquids1 or produced by the action of acids on carbonates1 were neglected4 ,for long no attempt was made to catch them2 and the frothing and bubbling were regarded as a species of boiling1 as is still seen in the use of our word 8fermentation0 7fervere1 to boil74 ,second1 ,erroneous ideas regarding the phenomena of combustion4 ,while it was recognised that a burning candle was extinguished if placed in a confined space1 its extinction was attributed not to the absence of air1 but to the impossibility of the escape of flame4 ,indeed1 flame was regarded as possessing the same semi-spiritual1 semi-material nature as air4 ,together with earth and water1 air and flame or fire formed the four elementary principles of the ,ancients2 and all substances--stones1 metals1 animals1 and vegetables--were regarded as partaking of the properties of these elements1 and often as being constituted of the latter in varying proportions1 according as they were cold and dry 7earth71 cold and moist 7water71 hot and moist 7air71 or hot and dry 7fire74 ,it is not within the scope of this book to enter into details regarding such ancient views4 ,those who are interested in the matter will find them expounded in ,kopps' ,history of ,chemistry1 ,rodwell's ,dawn of ,chemistry1 ,e4 von ,mayer's ,history of ,chemistry1 and in other similar works4 ,but we shall be obliged to consider the later developments of such ideas in the phlogistic theory1 by means of which all chemical changes connected with combustion were interpreted from the latter part of the seventeenth to the end of the eighteenth century4 ,with erroneous views regarding the nature of combustion1 and ignorance as to the part played by the atmosphere in the phenomena of burning1 the true nature of air was undiscoverable4 ,third1 ,the lack of attention to gain or loss of weight4 ,it was in past times not recognised that nothing could be created and nothing destroyed4 ,in popular language1 a candle is destroyed when it is burned1 nothing visible being produced from it4 ,the products1 we now know1 are gaseous and invisible1 and possessed of greater weight than the unburnt candle2 but for want of careful experiment1 it was formerly concluded that the candle1 when burnt1 was annihilated4 ,the formation of a cloud in a cloudless sky2 the growth of vegetables in earth1 from which1 apparently1 they did not derive their substance2 and the reputed growth of metalliferous lodes in mines--these were all adduced as proofs of the creative power of ,nature4 ,with such ideas1 therefore1 the necessity of controlling the gain or loss of material during experiment1 by determining gain or loss of weight1 did not appear imperative2 and hence but few quantitative experiments were made1 and little importance was attached to these few4 ,it had1 for example1 long been noticed that certain metals gained weight when burned and converted into a 8calx10 or1 as we should now say1 a metallic oxide1 but such gain in weight was not regarded as of any consequence4 ,when considered in relation to the supposed loss of 8phlogiston0 suffered by a metal on being converted into a calx1 it was explained by the hypothesis that phlogiston possessed 8levity0--the antithesis of gravity--and that the calx weighed more than the metal1 owing to its having lost a principle which was repelled instead of being attracted by the earth4 ,among the most remarkable early attempts to elucidate the true nature of air1 we meet with one by the ,hon4 ,robert ,boyle1 who published about the middle of the seventeenth century his ,memoirs for a ,general ,history of the ,air4 ,boyle was one of the most distinguished scientific men of his own1 or indeed of any1 age1 and in his spirit of calm philosophical inquiry he was far in advance of his contemporaries4 ,he was born in the early part of the year #afbf1 in ,ireland1 whither his father1 ,richard ,boyle1 had emigrated at the age of twenty-two4 ,boyle's mother1 daughter of ,sir ,geoffrey ,fenton1 principal ,secretary of ,state for ,ireland1 died while he was still a child4 ,yet she must have lived in the recollection of her son ,robert1 for he wrote3 8,to be such parents' son1 and not their eldest1 was a happiness that our ,philarethes 7himself7 would mention with great expressions of gratitude2 his birth so suiting his inclinations and designs1 that had he been permitted an election1 his choice would scarce have altered ,god's discernment40 ,in those days of early development1 ,boyle had finished his school-days at ,eton by his twelfth year4 ,he informs us that he devoured books omnivorously1 and could hardly be induced to join in games4 ,the next six years of his life he spent on the ,continent with his elder brother2 and on his father's death1 which happened when he was abroad1 he returned to ,england1 and settled at ,stalbridge1 in ,dorsetshire1 where he had inherited a manor4 ,here he passed most of his life in great retirement1 with only an occasional visit to ,london2 for though he lived through troublous times1 he avoided politics4 ,indeed1 he is known only to have appeared once on a public platform1 and that was in defence of the ,royal ,society1 then in its infancy1 from attacks made upon it by some too scrupulously loyal ,churchmen4 ,illustration3 ,,robert ,,boyle4 ,boyle did not confine his attention exclusively to scientific pursuits3 he interested himself deeply in theology1 and published numerous tracts on religious subjects4 ,he wrote with equal ease in ,english1 ,french1 and ,latin1 and his books appeared simultaneously in the first and last of these languages4 ,his researches are remarkable for their wide range and for the boldness of his conceptions4 ,but ,boyle1 ingenious though he was1 was unable to fathom the mystery of atmospheric air4 ,his views regarding it are succinctly stated by him in his ,memoirs for a ,general ,history of the ,air1 and in the same work he sums up the views of the ,ancients4 ,his words are3 8,the ,schools teach the air to be a warm and moist element1 and consequently a simple and homogeneous body4 ,many modern philosophers have1 indeed1 justly given up this elementary purity in the air1 yet few seem to think it a body so greatly compounded as it really appears to be4 ,the atmosphere1 they allow1 is not absolutely pure1 but with them it differs from true and simple air only as turbid water from clear4 ,our atmosphere1 in my opinion1 consists not wholly of purer aether1 or subtile matter which is diffused thro' the universe1 but in great number of numberless exhalations of the terraqueous globe2 and the various materials that go to compose it1 with perhaps some substantial emanations from the celestial bodies1 make up together1 not a bare indetermined feculancy1 but a confused aggregate of different effluvia4 ,one principal sort of these effluvia in the atmosphere ,i take to be saline1 which float variously among the rest in that vast ocean2 for they seem not to be equally mixed therein1 but are to be found of different kinds1 in different quantities and places1 in different seasons4444 ,many men talk much of a volatile nitre in the air1 as the only salt wherewith that fluid is impregnated4 ,i must own the air1 in many places1 seems to abound in corpuscles of a nitrous nature2 but ,i don't find it proved by experiments to possess a volatile nitre4 ,in all my experiments upon salt-peter1 ,i found it difficult to raise that salt by a gentle heat2 and spirits of nitre1 which is drawn by means of a vehement one1 has quite different properties from crude nitre1 or the supposed volatile kind in the air1 for 'tis exceeding corrosive40#a ,boyle then proceeds to collect and comment on the effluvia from volcanoes and from decaying vegetables and animals1 and proposes tests for the presence of such ingredients4 ,he even attributes the darkening of silver chloride to its being a reagent for certain salts present in air at one time and not at another1 and draws attention to the sulphurous smell produced by 8thunder40 ,farther on 7p4 #fa7 he writes3 8,the generality of men are so accustomed to judge of things by their senses1 that because the air is invisible they ascribe but little to it1 and think it but one remove from nothing4 ,and this fluid is even by the ,schoolmen considered only as a receptacle of visible bodies1 without exerting any action on them unless by its manifest qualities1 heat and moisture2 tho'1 for my part1 ,i allow it other faculties1 and among them1 such as are generative1 maturative1 and corruptive2 and that1 too1 in respect not only of animals and bodies of a light texture1 but even of salts and minerals40 ,in another place 7p4 #ag7 he states3 8,i conjecture that the atmospherical air consists of three different kinds of corpuscles3 the first1 those numberless particles which1 in the form of vapours or dry exhalations1 ascend from the earth1 water1 minerals1 vegetables1 animals1 etc42 in a word1 whatever substances are elevated by the celestial or subterraneal heat1 and thence diffused into the atmosphere4 ,the second may be yet more subtile1 and consist of those exceedingly minute atoms the magnetical effluvia of the earth1 with other innumerable particles sent out from the bodies of the celestial luminaries1 and causing1 by their impulse1 the idea of light in us4 ,the third sort is its characteristic and essential property1 ,i mean permanently elastic parts40 ,boyle also relates experiments designed to 8produce what appears to be air02 and he describes the production1 by the action of oil-of-vitriol on steel filings1 of 8air0 7now known as hydrogen7 which possessed the property of elasticity2 although he failed to notice its inflammability4 ,he further obtained carbon dioxide by the fermentation of raisins1 and probably also hydrogen chloride in the gaseous form by breaking a bulb containing 8some good spirit-of-salt0 in a vacuous receiver4 ,the result of shrewd reasoning power1 applied1 however1 to imperfect observations1 is well illustrated by the following passages3 8,for tho'1 by reason of its great thinness and of its being1 in its usual state1 devoid both of taste and smell1 air seems wholly unfit to be a menstruum or solvent2 yet it may have a dissolving1 or at least a consuming1 power on many bodies1 especially such as are peculiarly disposed to admit its operations4 ,for the air has a great advantage by the vast quantity of it that may come to work1 in proportion to the bodies exposed thereto4444 ,thus we find a rust on copper that has been long exposed to the air40#b ,boyle1 shortly after1 describes the production of 8an efflorescence of a vitriolic nature0 on marcasite 7or sulphide of iron7 which has been exposed to the air2 and he relates that the 8ore of alum1 robb'd of its salt1 will in tract of time recover it by being exposed to the air1 as we are assured by the experienced ,agricola40 ,to account for such actions1 and for combustion1 he proceeds 7p4 #ha73 8,the difficulty we find in keeping flame and fire alive1 tho' but for a little time1 without air1 renders it suspicious that there may be dispersed thro' the rest of the atmosphere some odd substance1 either of a solar1 astral1 or other foreign nature2 on account whereof the air is so necessary to the subsistance of flame4444 ,it also seems by the sudden wasting or spoiling of this fine substance1 whatever it be1 that the bulk of it is but very small in proportion to the air it impregnates with its vertue2 for after the extinction of the flame1 the air in the receiver was not visibly alter'd2 and for ought ,i could perceive by several ways of judging1 the air retained either all1 or at least the far greatest part1 of its elasticity2 which ,i take to be its most genuine and distinguishing property4 ,and this undestroyed springyness of the air1 with the necessity of fresh air to the life of hot animals1 suggest a great suspicion of some vital substance1 if ,i may so call it1 diffused thro' the air2 whether it be a volatile nitre1 or rather some anonymous substance1 sidereal or subterraneal2 tho' not improbably of kin to that which seems so necessary to the maintenance of the other flames40 ,the experimental part of ,boyle's work relates to the oxidation of cuprous to cupric compounds1 with the change of colour from brown to blue or green1 either in ammoniacal or in hydrochloric acid solution2 and he goes so far as to prove that two ounces of marcasites broken into small lumps1 and kept in a room 8freely accessible to the air1 which was esteemed to be very pure10 for somewhat less than seven weeks1 gained above twelve grains by oxidation4 ,in his ,memoirs for a ,general ,history of the ,air1 ,boyle draws up a programme of research1 of the carrying out of which1 however1 there is no record4 ,he proposes 7p4 #bc73 8#a4 ,to produce air by fermentation in well clos'd receivers4 8,to produce air by fermentation in sealed glasses4 8,to separate air from liquors by boiling4 8,to separate air from liquors by the air-pump4 8,to produce air by corrosion1 especially with spirit of vinegar4 8,to separate air by animal and sulphureous dissolvants4 8,to obtain air in an exhausted receiver by burning-glasses and red-hot irons4 8,to produce air out of gunpowder and other nitrous bodies4 8#b4 ,to examine the produced aerial substances by their preserving or reviving animals1 flame1 fire1 the light of rotten wood1 and of fish4 8,to examine it by its elasticity1 and the duration thereof4 8,to do the same by its weight1 and its elevating the fumes of liquors40 ,we shall all agree that if ,boyle had successfully carried out such experiments1 our knowledge of the true nature of air would have come quite a century before it did4 ,some of these experiments were indeed made by ,john ,mayow1 his contemporary1 whose work and speculations we shall now proceed to consider4 ,john ,mayow was born in the parish of ,st4 ,dunstan1 ,london1 in #afde4 ,his family was originally ,cornish1 having come from ,bree1 in ,cornwall4 ,he entered ,wadham ,college1 ,oxford1 at the early age of sixteen1 and was shortly afterwards made a probationer-fellow of ,all ,souls' ,college4 ,after the usual three years of study1 he took his degree in ,law2 but not being attracted by the legal profession1 he turned his attention to medicine1 and became a medical practitioner at ,bath1 where he lived during the fashionable season4 ,when not more than twenty-three years of age1 he wrote two essays on ,respiration1 ascribing the inflation of the lungs to the action of the intercostal muscles4 ,these 8,tractatus duo0 were published in #affh4 ,some years later he produced the treatise on which his fame rests2 it is entitled 8,tractatus quinque medico-physici1 quorum primus agit de sal-nitro et spiritu nitro-areo2 secundus1 de respiratione2 tertius1 de respiratione foetus in utero et ovo2 quartus1 de motu musculari1 et spiritibus animalibus2 ultimus1 de rhachitide2 studio ,joh4 ,mayow1 ,,ll4,d4 ,medici1 nec non ,coll4 ,omn4 ,anim4 in ,univ4 ,oxon4 ,socii4 ,oxonii e ,theatro ,sheldoniano1 ,an4 ,dom4 ,,mdclxxiv40 ,the work was dedicated to ,sir ,henry ,coventry4 ,it was inserted in an abridged form in the ,philosophical ,transactions of the ,royal ,society1 some time after its publication1 but received only scant recognition1 for the fame of ,newton and ,boyle overshadowed the labours of less well-known investigators4 ,and ,mayow did not live to press his discoveries on the attention of his contemporaries1 for he died in #afgi1 five years after the publication of his tracts1 in his thirty-fourth year4 ,little is known of ,mayow's domestic life1 save that he married shortly before his death4 ,his scientific work proves that if he had been granted the usual span of life1 his extraordinary genius would have furthered the knowledge of the true explanation of the nature of air1 and its function in supporting combustion and respiration1 and that his views would have been accepted more than a century before ,lavoisier--with fuller knowledge1 and with the scientific position which at once gained a hearing--forced precisely similar doctrines upon the attention of the scientific world4 ,illustration3 ,john ,mayow4 ,mayow was a contemporary of ,boyle1 and frequently made use of ,boyle's experiments in support of the theories which he advanced4 ,curiously enough1 while ,boyle seems to have read ,mayow's work1 he does not appear to have been favourably impressed by his conclusions4 ,boyle1 at the age of fifty-two1 had doubtless formed his own opinions1 and was unwilling that they should be disturbed by the speculations1 well founded though they were1 of so young a man4 ,and shortly after ,mayow's death1 the views of ,becher1 one of his contemporaries1 expounded and made definite by ,stahl1 regarding the nature of combustion1 were universally received4 ,after ,lavoisier's theories had overthrown these false views1 attention was again directed to ,mayow's tracts by ,johann ,andreas ,scherer1 in a work published at ,vienna in #agic1 and also by ,dr4 ,yeats in #agih4 ,scherer gives a careful analysis of ,mayow's work1 somewhat altering the order of his paragraphs1 with a paraphrase in ,german of the ,latin text1 which he quotes in full4 ,yeats' treatise is more especially concerned with the medical aspect of ,mayow's work1 although it also deals with the purely chemical portion at considerable length4 ,in the following account of ,mayow's researches1 free use has been made of both of these works1 as well as of his own 8,tracts40 ,mayow's contributions to the chemistry of the atmosphere may be classified thus3-- #a4 ,the atmosphere consists of particles of two kinds of gases at least3 one of these1 termed 8nitro-aerial particles10 is necessary for the support of life and for the combustion of inflammable bodies2 while the other1 left after this constituent has been removed1 is incapable of supporting either life or combustion4 ,the portion which is necessary for life enters1 during respiration1 into the blood4 ,it is the chief cause of motion in animals and in plants4 #b4 ,these 8nitro-aerial particles0 are also present in saltpetre or nitre1 as can be shown by mixing inflammable substances1 such as sulphur and charcoal1 with nitre to form gunpowder1 filling a tube with the powder1 and1 after setting it on fire1 immediately plunging the open end of the tube under water4 ,the sulphur and charcoal will be as completely consumed as if burned in the open air4 ,such combustion might1 however1 be ascribed to a 8sulphureous0 constituent in saltpetre2 by 8sulphureous0 is to be understood combustible1 for those substances capable of burning were imagined to contain a 8sulphur0 which gave them that property4 ,that nitre does not contain such 8sulphur0 can be shown by exposing it alone to heat1 when no change takes place1 except fusion4 ,besides1 nitre is compounded of 8spirit of nitre0 or nitric acid and pure alkali1 neither of which contains a combustible sulphur2 hence the particles of fire-air must be present in nitre in no small amount4 ,but it is probable that it is the spirit of nitre which contains such fire-air particles1 because1 as will be shown later1 they are not present in the alkali4 ,one difficulty occurs to ,mayow4 ,how is it that so large a quantity of gas as is necessary to support combustion can be contained in a relatively small bulk of saltpetre8 ,he tries whether a solution of saltpetre evolves air-bubbles when placed in a vacuum1 and finds that it effervesces less than pure water does4 ,he also prepares saltpetre by mixing nitric acid and alkali in a vacuum2 a brisk effervescence occurs1 and the dried-up salt is ordinary saltpetre4 ,hence saltpetre cannot contain elastic air4 ,mayow consequently draws a distinction between 8air0 and 8air-particles40 ,the residue left after the 8fire-air10 or spiritus igneo-aerius1 has been removed from ordinary air by breathing or by combustion is proved to be lighter than the fire-air itself2 because a mouse dies sooner if kept at the top of air in a confined bell-jar than at the bottom2 and a candle goes out sooner4 ,here the conclusion is right1 although the reason given is wrong2 for it is the temperature of the respired air which makes it rise1 and not the fact that it is specifically lighter than the oxygen4 ,metallic antimony gains in weight when it is set on fire by a lens1 and burns2 if this gain in weight1 ,mayow remarks1 is not due to the absorption of nitro-aerial particles and to the fire1 it is difficult to say to what it is due4 ,the reason why substances burn so violently in nitre compared with air1 is because of the proximity of the fire-air particles2 and these are evidently due to the nitric acid1 because the residue--the alkali--if mixed with sulphur and inflamed1 does not produce ignition4 #c4 ,all acids contain fire-air particles1 for acids have great similarity to each other4 ,this is shown as follows3--,antimony made into a calx by the sun's rays with a burning-glass gives the same calx as when it is evaporated repeatedly with nitric acid and converted into 8,bezoar-mineral10 i4e4 oxide of antimony4 ,and iron-rust obtained from sulphide of iron appears to be formed by the union of the fire-air particles with the metallic 8sulphur0 of the iron4 ,it has up till now been believed that sulphuric acid is an ingredient of common sulphur4 ,but this is unlikely1 for sulphur has a sweetish1 and not an acid taste4 ,moreover1 quite a different substance from a vitriol 7or sulphate7 is obtained by melting together alkali and sulphur2 and no effervescence takes place during its preparation4 ,sulphur1 too1 is precipitated out of the 8liver of sulphur0 7potassium persulphide7 by the addition of sulphuric acid4 ,now1 were sulphuric acid contained in sulphur1 it would hinder the union of the sulphur with the alkali4 ,it is to be noticed that the volatile sulphuric acid1 from the combustion of sulphur1 is produced in the following way3--8,the flame of the burning sulphur consists1 like every other flame1 in the violent motion of the sulphur particles with that of the nitro-aerial particles2 hence the sulphur particles1 at first solid1 become sharp and acid1 and probably form the ordinary #8spirit of sulphur' 7sulphuric acid74 ,if this be not so1 ,i know not in what manner this acid can be produced2 for1 as has been shown1 it is very improbable that it previously existed in the mass of the sulphur before its deflagration4 ,such a change also1 in all probability1 takes place in pyrites1 when it is converted to green vitriol2 because pyrites yields sulphur on distillation2 and the green vitriol on distillation gives sulphuric acid1 leaving red colcothar 7iron oxide7 behind40 ,similarly1 nitre appears to be a triple salt1 formed by the union of the fiery part of air with a salt-like substance existing in the earthy material1 together forming nitric acid2 and this added to earthy salts 7alkali7 yields ordinary nitre4 8,i have tried to show that all acids consist of certain saline particles rendered fluid by the nitro-aerial particles40 #d4 ,boyle has shown that a flame is extinguished more rapidly in a vacuous space than in a confined space containing air2 this is obviously due to absence of nourishment in the air1 rather than to its choking by its own vapours2 for in the vacuous vessel there is evidently more space for such noxious vapours than in the air-filled vessel1 and yet the flame is more rapidly extinguished4 ,moreover1 no combustible matter can be kindled in a vacuum by means of a burning-glass4 ,but it must not be concluded that this fire-air constitutes the whole of ordinary air2 because a candle goes out in air confined in a glass while a large quantity of air is still contained in it4 ,while gunpowder burns owing to the fire-air particles which it contains1 and requires no sustenance from external air1 the combustion of vegetables is supported partly by the igno-aerial particles which they themselves contain1 partly by those of the external air4 ,air which has supported combustion loses to some extent its elasticity 7i4e4 diminishes in volume71 as shown by the burning of a candle in air confined over water4 ,this is to be ascribed partly to actual loss of elasticity1 partly to the absorption of the fire-air4 ,the loss of volume amounts to about three per cent of the whole quantity of air taken4 ,all this is exceedingly clear1 and in accordance with our modern views1 but ,mayow's mind is somewhat confused with reference to flame and heat1 since he imagined that the diminution of the volume of air in which combustible substances have been burned is due to the escape of heat2 and inasmuch as a rise of temperature was known to increase the volume of air1 so a loss of heat should1 in his opinion1 produce the opposite effect4 ,the fire-air particles are apparently regarded as a sort of compound of heat with matter 7as indeed in a certain sense they are72 and by combustion or by respiration both are removed4 ,the loss of volume is to be explained by the removal of both from the air1 and the gain in weight by the union of the matter with the combustible body1 such as antimony4 ,such is a brief account of ,mayow's views on the nature of atmospheric air4 ,but the tale would be incomplete without mention of the fact that he prepared a gas by the action of nitric acid on iron1 viz4 nitric oxide1 which1 when introduced into ordinary air confined over water1 decreased its volume2 and he found that further admission of nitric oxide produced no further diminution in the volume of the air4 ,a very little more1 and he would have recognised in this a means of analysing air1 and depriving it wholly of its oxygen4 ,he goes so far as to speculate that a compound is formed between the nitric oxide and the oxygen1 but the solubility of gases in water appears not to have struck him as important4 ,he notices1 however1 that the combination of the two gases is attended by rise of temperature1 and is in so far analogous to combustion4 ,it would lead us too far to consider in detail ,mayow's theories of fermentation and of respiration4 ,suffice it to say that he ascribes the production of animal heat to the consumption of his fire-air particles by the animal1 and remarks that the pulse is heightened by respiration4 ,this view was in opposition to that held by his contemporaries1 viz4 that the purpose of respiration was to cool the blood4 ,it is impossible to avoid being impressed with the clearness and justice of ,mayow's inferential reasoning4 ,all that was wanting was the discovery of oxygen and carbon dioxide1 and the identification of the first with his fire-air1 and of the second with one of the products of combustion4 ,but these discoveries were not made until a century after his death4 ,had he lived1 there can be little doubt that1 unless discouraged by the want of appreciation with which his ideas were received1 he would have continued to labour in the fruitful fields from which he had already reaped so rich a harvest4 ,before leaving the seventeenth century1 it is perhaps fitting to mention the name of ,jean ,rey1 a ,french physician1 who wrote in #afcj concerning the gain in weight of tin and lead when calcined4 ,while ,rey exhibited some leaning towards the modern methods of experimentation1 he still lay fettered in the bonds of medival scholasticism4 ,in discussing the weight of air and fire1 he finds occasion to consider the question whether a vacuum can exist4 ,his words are so quaint that they are worth quoting3 8,it is quite certain that in the bounds of ,nature a vacuum1 which is nothing1 can find no place4 ,there is no power in ,nature from which nothing could have made the universe1 and none which could reduce the universe to nothing3 that requires the same virtue4 ,now the matter would be otherwise if there could be a vacuum4 ,for if it could be here1 it could also be there2 and being here and there1 why not elsewhere8 and why not everywhere8 ,thus the universe could reach annihilation by its own forces2 but to ,him alone who could make it is the glory of being able to compass its destruction40 ,and since air cannot be drawn down by a vacuum1 it must descend by virtue of its own weight when it fills a hole4 ,and hence1 as air has weight1 tin and lead gain in weight when they combine with air4 ,it will be admitted that this is very inferior to the speculations and deductions of ,boyle and ,mayow4 ,the next stage in the history of our subject is the consideration of the work of ,stephen ,hales and of ,joseph ,priestley4 ,both of these philosophers were essentially experimentalists4 ,while both discovered gases and prepared them in a more or less pure state1 ,hales had no theory to guide him1 and concluded as the result of his researches that air was possessed of 8a chaotic nature02 for he did not recognise his gases as different kinds of matter1 but supposed them all to be modified air4 ,priestley1 on the other hand1 was an adherent of the theory of phlogiston1 and interpreted all his experiments by its help4 ,hales was a country clergyman1 interested in botany1 and undertook researches on air in order to gain knowledge of the growth and development of plants4 ,priestley was also a divine1 who amused himself with experiments during the intervals of composing sermons or writing controversial pamphlets on disputed doctrines4 ,both possessed the experimental faculty1 and both employed it to good purpose4 ,hales' chief work is entitled 8,statical ,essays1 containing ,vegetable ,staticks2 or an account of ,statical ,experiments on the ,sap in ,vegetables1 being an ,essay towards a ,natural ,history of ,vegetation3 of use to those who are curious in the ,culture and ,improvement of ,gardening1 etc43 ,also1 a specimen of an attempt to analyse the air by a great ,variety of ,chymiostatical ,experiments1 which were read at several meetings before the ,royal ,society4 ,by ,stephen ,hales1 ,d4,d41 ,f4,r4,s41 ,rector of ,farringdon1 ,hampshire1 and ,minister of ,teddington1 ,middlesex40 ,in his 8,introduction0 ,hales reveals his method of research4 ,the determination of weight and volume was at that date especially necessary2 for want of numerical data the experimental researches of the time were of a somewhat vague character1 and it often happened that the conclusions drawn from them were incorrect4 ,hence it is with a feeling of satisfaction that we read 7vol4 i4 p4 #b73-- 8,and since we are assured that the all-wise ,creator has observed the most exact proportions of number1 weight1 and measure in the make of all things1 the most likely way1 therefore1 to get any insight into the nature of those parts of the creation which come within our observation must in all reason be to number1 weigh1 and measure4 ,and we have much encouragement to pursue this method of searching into the nature of things1 from the great success which has attended any attempts of this kind40 ,for ,god has 8comprehended the dust of the earth in a measure1 and weighed the mountains in scales1 and the hills in a balance40 ,from experiments on the rise of sap in plants1 many of them very ingenious and well adapted to secure their end1 and which are still regarded by botanists as classic1 ,hales noticed that a quantity of air was inspired by plants4 ,in order to ascertain the composition and amount of this air1 the process of distillation was resorted to2 for ,hales remarks3 8,that elasticity is no immutable property of air is further evident from these experiments2 because it were impossible for such great quantities of it to be confined in the substances of animals and vegetables1 in an elastick state1 without rending their constituent parts with a vast explosion0 7,preface1 p4 viii474 ,hence1 concluding that the air absorbed by plants and animals could be recovered by their distillation1 ,hales proceeded to distil a great number of substances of animal and vegetable origin1 such as hogs' blood1 tallow1 a fallow-deer's horn1 oystershell1 oak1 wheat1 peas1 amber1 tobacco1 camphor1 aniseed oil1 honey1 beeswax1 sugar1 ,newcastle coal1 earth1 chalk1 pyrites1 a mixture of salt and bone-ash1 of nitre and bone-ash1 tartar1 compound aquafortis1 and a number of other substances4 ,he collected the 8air0 in each case over water1 and gave numerical data to show what proportion the air bore by weight to the substance from which it had been obtained4 ,he even tried to compare the weight of ordinary air with that of air from distilled tartar2 but his experiment led to no positive conclusion1 because of the crudeness of his appliances4 ,the compressibility or 8elasticity0 of the air from tartar1 however1 was found to be identical with that of common air4 ,hales does not appear to have made any special experiments on the properties of his various airs1 by trying whether they supported combustion1 whether they were themselves combustible1 etc4 ,we see from this list that he had under his hands mixtures of hydrocarbons1 carbon dioxide1 probably sulphur dioxide1 hydrochloric acid and ammonia 7both1 however1 dissolving in water as they were formed71 oxides of nitrogen1 possibly chlorine1 and1 as minium or red-lead was one of the substances he tried1 oxygen in a more or less pure state4 ,it must be remembered that in all cases the gas obtained was mixed with the air originally present in the retort4 ,he next proceeded to produce 8air0 by the fermentation of grain1 of raisins1 and of other fruits2 this 8air0 obviously was carbon dioxide more or less pure4 ,it is curious to note here that he anticipated ,lord ,kelvin in devising a sounding-lead which should register the depth of the sea by the compression of air1 the distance to which the air had receded along the tube being shown by the entry of treacle4 ,he successfully carried out a sounding by means of his apparatus4 ,the next series of experiments related to the generation of 8air0 by the action of acids on metals4 ,aqua-regia and gold1 aqua-regia and antimony1 aquafortis and iron1 dilute oil-of-vitriol and iron1 yielded gases which contracted on standing in contact with water4 ,this1 in the case of the oxides of nitrogen1 is to be ascribed to their reacting with the oxygen of the air accidentally present in the receiver2 but in the last case ,hales noticed that the gas absorbed in cold weather was re-evolved on rise of temperature1 as one would expect with hydrogen4 ,these experiments led him to investigate the action of certain mixtures on ordinary air4 ,thus a mixture of spirits of hartshorn 7or ammonia7 with iron filings absorbed #a cubic inches of air1 and one with copper filings1 twice as much4 ,further1 a mixture of iron filings and brimstone absorbed in two days no less than #ai cubic inches of air4 ,but it is disappointing to find that1 in spite of all the experimental facts which ,hales accumulated1 he was unable to make use of them4 ,the prejudice in favour of the unity and identity of all these 8airs0 was too great for him to overcome4 ,true1 he sometimes theorises a little1 as for example when he remarks 7p4 #bhe73--8;,if fire was a particular kind of body inherent in sulphur 7i4e4 combustible matter of all kinds71 as ,mr4 ,homberg1 ,mr4 ,lemery1 and some others imagine1 then such sulphureous bodies1 when ignited1 should rarefy and dilute all the circumambient air2 whereas it is found by many of the preceding experiments1 that acid sulphureous fuel constantly attracts and condenses a considerable part of the circumambient elastick air3 an argument that there is no fire endued with peculiar properties inherent in sulphur2 and also that the heat of fire consists principally in the brisk vibrating action and re-action between the elastick repelling air and the strongly attracting acid sulphur1 which sulphur in its ,analysis is found to contain an inflammable oil1 an acid salt1 a very fix'd earth1 and a little metal40 ,enough has now been said to give a fair idea of ,stephen ,hales' researches4 ,it will suffice if his conclusions be stated in his own words 7p4 #cad73-- 8,thus1 upon the whole1 we see that air abounds in animal1 vegetable1 and mineral substances2 in all which it bears a considerable part2 if all the parts of matter were only endued with a strongly attracting power1 whole nature would then immediately become one unactive cohering lump2 wherefore it was absolutely necessary1 in order to the actuating and enlivening this vast mass of attracting matter1 that there should be everywhere intermix'd with it a due proportion of strongly repelling elastick particles1 which might enliven the whole mass1 by the incessant action between them and the attracting particles2 and since these elastick particles are continually in great abundance reduced by the power of the strong attracters1 from an elastick to a fixt state1 it was therefore necessary that these particles should be endued with a property of resuming their elastick state1 whenever they were disengaged from that mass in which they were fixt1 that thereby this beautiful frame of things might be maintained in a continual round of the production and dissolution of animal and vegetable bodies4 8,the air is very instrumental in the production and growth of animals and vegetables1 both by invigorating their several juices while in an elastick active state1 and also by greatly contributing in a fix'd state to the union and firm connection of several constituent parts of those bodies1 viz4 their water1 salt1 sulphur1 and earth4 ,this band of union1 in conjunction with the external air1 is also a very powerful agent in the dissolution and corruption of the same bodies2 for it makes one in every fermenting mixture2 the action and re-action of the aerial and sulphureous particles is1 in many fermenting mixtures1 so great as to excite a burning heat1 and in others a sudden flame2 and it is1 we see1 by the like action and re-action of the same principles1 in fuel and the ambient air1 that common culinary fires are produced and maintained4 8,tho' the force of its elasticity is so great as to be able to bear a prodigious pressure1 without losing that elasticity1 yet we have1 from the foregoing ,experiments1 evident proof that its elasticity is easily1 and in great abundance destroyed2 and is thereby reduced to a fixt state by the strong attraction of the acid sulphureous particles which arise either from fire or from fermentation2 and therefore elasticity is not an essential immutable property of air-particles2 but they are1 we see1 easily changed from an elastick to a fixt state1 by the strong attraction of the acid1 sulphureous1 and saline particles which abound in air4 ,whence it is reasonable to conclude that our atmosphere is a ,chaos1 consisting not only of elastick1 but also of unelastick air-particles1 which in plenty float in it1 as well as the sulphureous1 saline1 watery1 and earthy particles1 which are no ways capable of being thrown off into a permanently elastick state1 like those particles which constitute true permanent air4 ,since1 then1 air is found so manifestly to abound in almost all natural bodies2 since we find it so operative and active a principle in every chymical operation2 since its constituent parts are of so durable a nature1 that the most violent action of fire or fermentation cannot induce such an alteration of its texture as thereby to disqualify it from resuming1 either by the means of fire or fermentation1 its former elastick state2 unless in the case of vitrification1 when1 with the vegetable ,salt and ,nitre in which it is incorporated1 it may1 perhaps1 some of it1 with other chymical principles1 be immutably fixt1--since then this is the case1 may we not with good reason adopt this now fixt1 now volatile ,proteus among the chymical principles1 and that a very active one1 as well as acid sulphur2 notwithstanding it has hitherto been overlooked and rejected by chymists1 as no way intitled to that denomination80 ,this quotation shows us how little ,mayow's shrewd reasoning and well-devised experiments had impressed the thinkers of his age4 ,while ,hales quotes frequently from ,boyle's and ,newton's works1 his reference to ,mayow is meagre2 nor does he adopt any one of ,mayow's conclusions4 ,one would have thought that1 having prepared so many gases by means of apparatus well adapted to their purpose1 and having observed that certain substances introduced into air produced contraction1 he would have drawn the conclusion that such 8airs0 were essentially different kinds of matter4 ,but the 8,proteus0 was too much for him2 and he left the subject practically in the same state of 8,chaos0 in which he found it4 #a ,memoirs for a ,general ,history of the ,air2 ,shaw's ,abridgment of ,boyle's works1 edition #agbe1 vol4 iii4 p4 #bf4 #b 8,suspicions about some hidden qualities of the ,air10 ibid4 p4 #gg4 ,,chapter ,,ii 8,,fixed ,,air0 ,,and 8,,mephitic ,,air0--,,their ,,discovery ,,by ,,black ,,and ,,by ,,rutherford ,before relating the history of the discoveries of ,black1 ,rutherford1 and ,priestley1 it will be appropriate to give an account of a theory which professed to explain the phenomena of combustion1 and with it the conversion of metals into calces1 and the reduction of these calces to the reguline or metallic state4 ,like other theories1 it was slow in developing4 ,its germ is to be traced to the writings of ,johann ,baptist van ,helmont of ,brabant1 ,seigneur of ,merode1 ,royenboch1 ,oorshot1 and ,pellines1 who was born in ,brussels in #aegg4 ,he adopted a fantastical creation of ,paracelsus1 the archaeus1 a kind of demon which1 by means of fermentation1 draws together all the particles of matter4 ,believing that water was the true principle and origin of everything 7for he had succeeded in producing a willow tree1 weighing #afd lbs41 from water alone1 the earth in which it grew having neither gained nor lost appreciably in weight71 he conceived that it was acted on by a ferment or principle pre-existing in the seed developed by it1 and exhaling an odour by which the archaeus was attracted4 ,water undergoing the action of this ferment developed a vapour1 to which van ,helmont gave the name of 8gas40 ,a 8gas0 was a substance intermediate between spirit and matter1 and the word was probably derived from ,geist1 the common ,german word for spirit4 ,another word introduced by him to denote the life-principle of the stars was ,blas1 connected probably with blasen1 to blow1 and our ,english word blast4 ,it is curious to notice how the idea of an archaeus survived down to later times under the name of a 8life-principle0--a conception that all organic substances must necessarily owe their origin to life itself1 and not to the usual chemical and physical transformations4 ,van ,helmont was acquainted with various kinds of gases1 as appears from his treatise 8,de ,flatibus40 ,his gas sylvestre was evolved from fermenting liquors1 and he knew that it was formed during the combustion of charcoal1 and also that it was present in the ,grotto del ,cane near ,naples4 ,he was likewise acquainted with combustible gases1 which he named gas pingue1 gas siccum1 or gas fuliginosum4 ,these principles of van ,helmont's apparently suggested to his successors1 ,becher and ,stahl1 the notion of a principle inherent in every combustible substance1 which was lost during combustion4 ,the development of this--the phlogistic--theory is almost wholly due to the latter chemist1 and indeed it is difficult to trace ,becher's share in it4 ,george ,ernest ,stahl was born at ,anspach in #affj2 he studied and graduated in medicine at ,halle1 and in #afid he was appointed second professor of medicine at that ,university1 where he continued to teach for twenty-two years4 ,his most important work was his ,fundamenta chymiae dogmaticae et experimentale4 ,his theoretical views are contained in the last part of this work4 ,he there treats of zymotechnia1 or fermentation2 halotechnia1 or the production of salts2 and pyrotechnia1 or the doctrine of combustion4 ,it is the last of these sections which gives an account of the doctrine of phlogiston4 ,the fundamental conception of this doctrine is that all combustible bodies are compounds4 ,during combustion one of these constituents1 common to all1 was dissipated and escaped1 while the other1 sometimes an acid1 sometimes an earthy powder or calx1 remained behind4 ,thus sulphur and phosphorus1 when burnt1 give acids2 and the metals form calces4 ,non-combustible substances1 such as lime1 were imagined to be calces1 and it was supposed that if phlogiston were restored to them1 they too would be converted into metals4 ,this combustible principle was thought to be inherent in all combustible bodies whatsoever2 it corresponds in kind with the 8sulphur0 of more ancient writers1 but differs from the latter inasmuch as no very precise ideas were entertained of the identity of the 8sulphur0 which conferred on the substances containing it as a constituent1 or possessing it as a property1 their power of combustion4 ,it was also made more definite by ,stahl that substances capable of burning or conversion into calces are compounds containing phlogiston in combination with other substances4 ,stahl can hardly be credited with more than the invention of the term 8phlogiston10 and with bringing the subject in a clear and definite form before his contemporaries4 ,for ,stahl wrote in #agbj2 and we find ,mayow1 in #afgd1 entering into an elaborate argument to prove that sulphuric acid is not contained in sulphur1 but that it is produced by the union of the sulphur with his fire-air particles4 ,but ,stahl amplified the doctrine which ,mayow had controverted1 in pointing out that if such substances as phosphorus1 sulphur1 or metals are heated1 they burn1 and are changed into phosphoric acid1 sulphuric acid1 or 8calces02 and reciprocally1 if phosphoric acid1 sulphuric acid1 or a calx such as that of tin or lead1 is heated with matter rich in phlogiston1 such as charcoal1 pitcoal1 sugar1 flour1 etc41 phlogiston is restored to the burnt substance1 and the original material1 phosphorus1 sulphur1 tin1 or lead1 is reproduced4 ,the idea at once captivated the minds of the chemists of that age1 who received it with approbation1 and devised experiments designed to extend the applications of the theory and to confirm its truth4 ,substances were not supposed always to be completely deprived of phlogiston by combustion4 ,indeed1 if the phlogiston were removed wholly1 or nearly so1 it was by no means easy to restore it4 ,thus the calx of zinc1 or of iron1 which was regarded as nearly devoid of phlogiston1 is difficult to reduce to the metallic state by ignition with substances rich in phlogiston1 such as coal or charcoal4 ,the addition of phlogiston alters the appearance of the substance as regards colour or metallic lustre1 and these vary according to the proportion of phlogiston present4 ,there existed no very definite idea regarding the appearance or properties of phlogiston itself4 ,becher's name for it was terra pinguis1 and it was represented by ,becher and by ,stahl as a dry substance of an earthy nature1 consisting of very fine particles1 which were capable of being set into violent motion2 this idea was derived partly from the fact that combustion is usually accompanied by flame1 which was supposed to be produced by the motion of the particles of the body1 communicated to it by the phlogiston4 ,it must not be forgotten that at this time it was perfectly well known that metals gain weight on calcination4 ,jean ,rey was quite aware of this1 and ,boyle relates an experiment to show that tin gains weight when converted into calx2 and it will be remembered that ,mayow made experiments on the ignition of antimony by the aid of a burning-glass1 and rightly conjectured that the substance produced was the same as that formed by treating it with nitric acid1 and subsequent ignition4 ,boyle's view was that calx of tin was a compound of tin and heat2 ,mayow's more correct view was that calx of antimony was a compound of antimony and fire-air4 ,but in spite of these well-proved facts1 the adherents of the theory of phlogiston ignored them1 and it does not appear to have occurred to ,becher or to ,stahl that they were inconsistent with their theories4 ,when this difficulty was stated1 which was not until a much later date1 a lame explanation of a metaphysical nature1 and in itself contradictory1 was all that could be offered4 ,it was that phlogiston is endowed with the contrary of gravity or weight1 i4e4 levity or absolute lightness4 ,this means1 of course1 that it is repelled by the earth4 ,but if repelled by matter1 how comes it that it enters into combination with matter8 ,for it could not remain united if its property were to repel and not to attract4 ,notwithstanding this1 however1 the idea satisfied some as to the gain in weight which metals undergo in changing into calces4 ,it is indeed astonishing that men of such great ability and acumen as ,black and ,cavendish should have so long lain under the yoke of this absurd theory4 ,it is probable that1 in the case of these two great chemists1 they stated their results in terms of the theory1 partly because they were content to express the facts to which they wished to call attention in this manner1 partly because they were not in a position to replace the theory by a more rational one4 ,it is not easy to revolutionise a language1 even though its vocabulary be a restricted one4 ,the object of writing is to convey thoughts to others2 and it is certainly more convenient to make use of terms understood by others1 even if they only imperfectly convey the meaning which it is desired to express1 than to attempt a revolution which will probably be unsuccessful1 and even if successful1 will at all events take time4 ,it is not so difficult to understand ,priestley's attitude1 which we shall have to consider later2 for ,priestley was first of all an experimentalist1 and was captivated more by the acquisition of a new fact than by assigning to that fact its proper place in the cosmogony of nature4 ,the influence of the phlogistic theory on the knowledge of the nature of air was of such a kind as to retard its progress4 ,for how could that knowledge be furthered1 when the most active constituent of air was represented by a negation8 ,it may be said that it is easy to be wise after the event1--in this case the discovery of oxygen2 but here was a theory which was in contradiction to many known facts1 and which furnished but a lame explanation of phenomena1 and which had been anticipated by another theory1 subsequently proved to be correct4 ,its sole support was the authority of its inventors or adapters1 and the deeply-ingrained notions of centuries4 ,we may read from it a lesson that it is wiser to seek out facts which test and prove a theory rather than those which support it1 and we may learn for the hundredth time the folly of relying on authority1 however ancient and associated with famous names it may be4 ,this was happily expressed by ,boyle when he wrote3#c 8,for ,i am wont to judge of opinions as of coins3 ,i consider much less in any one that ,i am to receive1 whose inscription it bears1 than what metal 'tis made of4 ',tis indifferent enough to me whether 'twas stamped many years or ages since1 or came but yesterday from the mint4 ,nor do ,i regard how many or how few hands it has passed through1 provided ,i know by the touchstone whether or no it be genuine1 and does or does not deserve to have been current4 ,for if1 on due proof1 it appears to be good1 its having been long1 and by many1 received for such1 will not tempt me to refuse it4 ,but if ,i find it counterfeit1 neither the prince's image nor superscription1 nor the multitude of hands it has passed through1 will engage me to receive it4 ,and one disfavouring trial1 well made1 will much more discredit it with me than all these spurious things ,i have named can recommend it40 ,it has been necessary to enter at some length into the nature of the phlogistic theory1 because the discoveries of the time were expressed in its language4 ,the fire-air or vital air of ,mayow was termed dephlogisticated air2 i4e4 air wholly deprived of the power of burning1 or air more capable of supporting combustion than ordinary air2 while airs capable of burning were supposed to be more or less highly charged with phlogiston2 indeed1 at one time1 it was imagined that hydrogen was phlogiston itself4 ,it is to ,joseph ,black that the discovery of carbon dioxide1 that constituent of air first to be definitely recognised1 if we except ,mayow's early work1 is generally ascribed4 ,but we must remember that it had been prepared by ,becher and by ,hales1 and had been doubtless obtained in an impure state by many others4 ,it will be seen that ,black's work was so complete1 and established the identity of this gas in so definite a manner1 that his right to be named as its true discoverer can hardly be questioned4 ,black was born near ,bordeaux in #agbh4 ,his father1 a wine-merchant1 was originally a native of ,belfast1 being descended from a ,scottish family which had been settled there for some time4 ,when twelve years of age4 ,black returned to ,belfast1 and received his education in the local grammar-school1 afterwards proceeding to the ,university of ,glasgow in #agdf1 at the age of eighteen4 ,he was a pupil of ,dr4 ,cullen1 then ,lecturer on ,chemistry at the ,college there1 who is mentioned by ,professor ,thomas ,thomson1 in his ,history of ,chemistry1 as an excellent and instructive lecturer4 ,black intended to choose the career of medicine1 and he indeed practised occasionally as a medical man during the greater part of his life4 ,illustration3 ,,joseph ,,black4 ,he began his medical studies in ,edinburgh in the year #agea1 and in #agee he published1 as his thesis for the degree of ,m4,d41 the work which has rendered his name famous4 ,it appears that as early as #ageb he had been occupied with investigations on quicklime1 which was then attracting attention as a remedy for urinary calculi4 ,opinion was divided regarding its virtue4 ,in a manuscript copy of notes of ,black's lectures1 which the author is so fortunate as to possess1 he mentions that his attention was directed to the subject through the rival views of ,drs4 ,alston and ,whytt4 ,it was not long before he proved that1 in opposition to the commonly received notion1 quicklime had gained nothing from the fire in which it was made1 but that the limestone used for its preparation had lost nearly half its weight in becoming caustic4 ,he also attempted successfully to trap the escaping gas1 and again placed it in presence of lime1 confining it over water4 ,instead of any escape of material when the lime became mild1 8nothing escapes--the cup rises considerably by absorbing air40 ,and in his notes1 a few pages farther on1 he compares the loss of weight undergone by limestone on being calcined1 with its loss on being dissolved in muriatic acid4 ,these experiments appear from his journal to have been made before ,november #ageb4 ,his thesis was not published1 however1 until #agee4 ,immediately after1 in #agef1 he succeeded ,dr4 ,cullen as ,professor in ,glasgow1 where he remained until #agff4 ,during these ten years he began and made great progress with his well-known researches on the heat of fusion of ice1 and the heat of vaporisation of water1 or1 as he termed them1 the 8latent heats0 of water and of steam4 ,in #agff1 ,dr4 ,cullen was appointed ,professor of ,medicine in the ,university of ,edinburgh1 and ,black again succeeded him as ,professor of ,chemistry4 ,there he lectured until #agig1 when he retired from public life2 he died as peacefully as he had lived1 in #agii1 in the seventy-first year of his age4 ,thomson1 who relates these particulars1 was one of his last students2 he writes3--8,i never listened to any lectures with so much pleasure as to his2 and it was the elegant simplicity of his manner1 the perfect clearness of his statements1 and the vast quantity of information which he contrived in this way to communicate1 that delighted me4444 ,his illustrations were just sufficient to answer completely the object in view1 and no more40 ,black's original thesis for his degree was entitled ,experiments upon ,magnesia ,alba1 ,quicklime1 and other ,alcaline ,substances4 ,it was published in #agee1 and several times reprinted4 ,it is now to be had in a convenient form as one of the 8,alembic ,club ,reprints40 ,it was the custom in those days to administer alkalies as a remedy for urinary calculi2 and about the year #agej lime-water was tried as a substitute4 ,opinion was divided as regarded its efficacy2 and it was with the view of preparing a better remedy that ,black undertook researches on magnesia alba4 ,black prepared magnesia from 8bittern10 which remains in the pans after the crystallisation of salt from sea-water1 and also from ,epsom salts1 8which is evidently composed of magnesia and the vitriolic acid40 ,the magnesia is thrown down from the sulphate as carbonate1 by the addition of pearl ashes1 at the temperature of ebullition1 the soluble product being 8vitriolated tartar10 or potassium sulphate4 ,he describes how 8magnesia is quickly dissolved with effervescence or explosion of air1 by the acids of vitriol1 nitre1 and of common salt1 and by distilled vinegar10 and gives an account of the properties of the sulphate1 nitrate1 chloride1 and acetate4 ,he subsequently heated this magnesia1 and found that it lost 8a remarkable proportion of its weight in the fire10 and his 8attempts were directed to the investigation of this volatile part40 ,the residue in the retort did not effervesce on the addition of acids2 hence the volatile part had been driven away by the heat4 8,chemists have often observed1 in their distillations1 that part of the body has vanished from their senses1 notwithstanding the utmost care to retain it2 and they have always found1 upon further inquiry1 that subtile part to be air1 which1 having been imprisoned in the body1 under a solid form1 was set free1 and rendered fluid and elastic by the fire4 ,we may safely conclude that the volatile matter lost in the calcination of magnesia is mostly air2 and hence the calcined magnesia does not emit air1 or make an effervescence when mixed with acids40 ,magnesia1 thus freed from 8air0 by ignition1 was dissolved in 8spirit of vitriol0 and thrown down with an alkali4 ,its weight was nearly equal to that which it possessed before calcination1 and it again effervesced with acids4 8,the air seems to have been furnished by the alkali1 from which it was separated by the acid2 for ,dr4 ,hales has clearly proved that alkaline salts contain a large quantity of fixed air1 which they emit in great abundance when joined to a pure acid4 ,in the present case1 the alkali is really joined to an acid1 but without any visible emission of air3 and yet the air is not retained in it2 for the neutral salt1 into which it is converted1 is the same in quantity1 and in every other respect1 as if the acid employed had not been previously saturated with magnesia1 but offered to the alkali in its pure state1 and had driven the air out of it in their conflict4 ,it seems1 therefore1 evident that the air was forced from the alkali by the acid1 and lodged itself in the magnesia40 ,after an account of some experiments showing that magnesia is not identical with lime or with alumina1 he proceeds3--8,it is sufficiently clear that the calcareous earths in their native state1 and that the alkalis and magnesia in their ordinary condition1 contain a large quantity of fixed air2 and this air certainly adheres to them with considerable force1 since a strong fire is necessary to separate it from magnesia1 and the strongest is not sufficient to expel it entirely from fixed alkalis1 or take away their power of effervescing with acid salts4 8,these considerations led me to conclude that the relation between fixed air and alkaline substances was somewhat similar to the relation between these and acids3 that as the calcareous earths and alkalis attract acids strongly1 and can be saturated with them1 so they also attract fixed air1 and are1 in their ordinary state1 saturated with it2 and when we mix an acid with an alkali1 or with an absorbent earth1 that the air is then set at liberty1 and breaks out with violence2 because the alkaline body attracts it more weakly than it does the acid1 and because the acid and air cannot both be joined to the same body at the same time4444 ,crude lime was therefore considered as a peculiar acrid earth1 rendered mild by its union with fixed air2 and quicklime as the same earth1 in which1 by having separated the air1 we discover that acrimony or attraction for water1 for animal1 vegetable1 and for inflammable substances40 ,the solubility of slaked lime in water is next discussed4 ,if a solution of lime 8be exposed to the open air1 the particles of quicklime which are nearest the surface gradually attract the particles of fixed air which float in the atmosphere40 ,black next points out that1 on mixing magnesia alba with lime-water1 the air leaves the magnesia and joins itself to the lime2 and as both magnesia and calcium carbonate are insoluble in water1 the water is left pure4 ,similarly quicklime deprives alkalies of their air and renders them caustic4 ,and it follows that if caustic alkali be added to a salt of magnesia or of lime1 it will separate the magnesia or the calcareous earth from the acid1 in a condition free from 8air0 but combined with water4 ,in order to show that the 8air0 which exists in combination with lime or alkalies is not the air which is contained in solution in water1 lime-water was placed under an air-pump1 along with an equal quantity of pure water2 on making a vacuum1 an approximately equal amount of air was evolved from each4 8,quicklime1 therefore1 does not attract air when in its most ordinary form1 but is capable of being joined to one particular species only1 which is dispersed through the atmosphere1 either in the shape of an exceedingly subtile powder1 or more probably in that of an elastic fluid4 ,to this ,i have given the name of fixed air1 and perhaps very improperly2 but ,i thought it better to use a word already familiar in philosophy than to invent a new name1 before we be more fully acquainted with the nature and properties of this substance1 which will probably be the subject of my further inquiry40 ,the next proceeding was to render 8mild alkali0 caustic by means of lime1 and to determine that nearly the same amount of acid is required to saturate the caustic alkali as to saturate the mild alkali from which the caustic alkali had been prepared4 ,on exposure to air for a fortnight1 the caustic alkali again became mild1 owing to its absorption of fixed air4 ,careful experiments were made to prove that such caustic alkali contains no lime1 and does not therefore owe its causticity and corrosive properties to the presence of that ingredient4 ,the volatile alkali 7ammonium carbonate7 was also rendered caustic1 and ,black 8obtained an exceedingly volatile and acrid spirit1 which neither effervesced with acids nor altered in the least the transparency of lime-water2 and although very strong was lighter than water1 and floated upon it like spirit of wine40 ,after a description of some unsuccessful attempts to render mild alkalies caustic by heat alone 7i4e4 to expel carbon dioxide from potassium carbonate71 ,black examines the action of the 8sedative salt0 or boracic acid on mild alkalies1 by rubbing them together in presence of some water4 ,at first there is no effervescence1 but on adding successive quantities of boracic acid1 brisk effervescence finally takes place1 borax being formed4 8,this phenomenon may be explained by considering the fixed alkalis as not perfectly saturated with air 444 if they expel a small quantity of air from some of the salt1 this air is at the same time absorbed by such of the contiguous particles as are destitute of it40 ,and on 8exposing a small quantity of a pure vegetable fixed alkali 7carbonate of soda7 to the air1 in a broad and shallow vessel1 for the space of two months10 crystals were obtained1 which possessed a milder taste than that of ordinary salt of tartar1 which effervesced with acids more violently than usual1 and which could not be mixed with the smallest portion of boracic acid without emitting a sensible quantity of air 7hydrogen sodium carbonate74 ,it therefore follows that such alkaline substances have an attraction for fixed air2 and this was proved by mixing magnesia alba in fine powder with caustic alkali1 and shaking for some time4 ,the magnesia was converted into the variety which did not effervesce with acids1 and the alkali was rendered mild1 like a solution of salt of tartar4 ,these are the principal results of ,black's researches1 and he concludes with a table of affinity of acids for fixed alkali1 calcareous earth1 volatile alkali1 and magnesia1 contrasting it with the affinity possessed by fixed air for the same bases4 ,it was the habit of the ,scottish students to pass down notes taken during the lectures of their professors from one generation to another4 ,as the lectures were generally read1 and not delivered extempore1 the process resulted in an almost verbatim report of the actual words of the lecturer4 ,one of these copies of lectures1 bearing the date #aggh1 gives an account of the experiments which have been described1 in words almost identical with those used in the thesis of #agee4 ,black appears to have shown his class this air1 made1 however1 according to ,hales' plan1 by heating magnesium carbonate in a bent gun-barrel1 and collected over water in the usual way4 ,he demonstrated its weight by pouring it from one vessel to another1 and showed that it extinguished the flame of a candle4 ,he mentions also that in #ageb he discovered that this air is the same as choke-damp1 and that it is fatal to animal life4 ,he speaks of the ,grotto del ,cane1 and observes that fixed air is produced by fermentation1 and by the burning of charcoal1 and showed to his class experiments in which air from each source is shaken with lime-water1 giving a turbidity of carbonate4 ,the well-known experiment of inspiring air through lime-water1 which1 owing to the small amount of carbonic anhydride it contains1 does not produce a turbidity1 and expiring through lime-water1 showing the formation of carbon dioxide in the lungs1 is described and performed4 ,he next describes ,cavendish's experiments on the solubility of fixed air and its density1 and researches by ,dr4 ,brownrigg and ,dr4 ,gahn of ,sweden on its occurrence in mineral waters4 ,he also explains how calcareous petrifactions are produced by the escape of fixed air from water1 which then deposits its dissolved calcium carbonate1 present in solution as bicarbonate4 ,the deposit of iron from chalybeate waters is ascribed to the same cause1 and the explanation is attributed to ,mr4 ,lane4 8,upon the whole10 these manuscript notes relate1 8this sort of air is quite distinct from common air1 though it is commonly mixed with it in small quantity40 8,with regard to its origin1 when treating of inflammable substances and metals ,i shall consider this more completely4 ,i shall now only hint that it is a vital air1 changed by some matter1 seemingly the principle of inflammability4 ,this appears from several phenomena when an animal or burning body is enclosed with a certain quantity of this air1 until it is changed as much as possible40 ,the air is diminished in volume by the breathing of the animal or by the burning of the candle4 ,and ,dr4 ,priestley has found that 8growing vegetables had the power of restoring this sort of air to common or vital air again1 which must be by their taking away some matter which it had received from the burning body or animal40 ,black's account of fixed air and its properties is the first example we possess of a clear and well-reasoned series of experimental researches1 where nothing was taken on trust1 but everything was made the subject of careful quantitative measurement4 ,it was not long since ,hales had pronounced air to be a chaotic mixture of effluvia4 ,black showed that common air contains a small amount of fixed air1 and that fixed air must be considered as a fluid differing in many of its properties from common air1 especially in its being absorbed by quicklime and by alkalies4 ,it must be remembered that at that time carbon was not recognised as an element2 and hence1 though ,black knew that fixed air was a product of the combustion of charcoal1 he did not attribute it to the union of carbon with oxygen1 although the sentence quoted above closely approaches to the truth4 ,the discovery of nitrogen was next in the order of time4 ,it was made by ,daniel ,rutherford1 a pupil of ,black's1 and at his instigation1 and its description formed a thesis for his degree of ,doctor of ,medicine4 ,daniel ,rutherford was born at ,edinburgh on ,november #crd1 #agdi4 ,he was the son of a medical man1 ,dr4 ,john ,rutherford1 one of the founders of the ,medical ,school in that city4 ,he was educated at ,edinburgh ,university1 and after graduating in ,arts1 became a medical student1 taking his degree of ,m4,d4 in #aggb4 ,his diploma was obtained on #abth ,september4 ,he then travelled for three years in ,england1 ,france1 and ,italy1 and in #agge he returned to his native town1 where he practised his profession4 ,in #aghf he succeeded ,dr4 ,john ,hope in the ,chair of ,botany in his ,university1 but he did not on that account resign his practice4 ,he was president of the ,royal ,college of ,physicians of ,edinburgh from #agif to #agih4 ,during the greater part of his life he suffered from gout2 he died in #ahai1 at the age of seventy4 ,rutherford does not seem to have pursued the study of chemistry further3 his duties led him into other fields4 ,his genial1 pleasant face1 seen in the portrait by ,raeburn1 shows him to have possessed a happy disposition2 and he is said to have maintained until his death his friendship with ,black1 and his interest in the progress which science was then rapidly making4 ,the title of ,rutherford's dissertation1 of which ,i have been able to find a copy only in the ,british ,museum1 is ,dissertatio ,inauguralis de aere fixo dicto1 aut mephitico4 ,it was published at ,edinburgh in #aggb1 seventeen years after ,black's memorable dissertation on ,fixed ,air4 ,as will be seen shortly1 it precedes ,priestley's and ,scheele's writings by a year or two4 ,evidently ,black had noticed that a residue was left after the combustion of carbonaceous bodies in air1 and absorption of the fixed air produced by the combustion1 and had suggested to ,rutherford1 then a student of his1 the advantage of further investigating the matter1 and ascertaining the properties of the residual gas4 ,illustration3 ,,daniel ,,rutherford4 ,rutherford begins his essay with an apt quotation from ,lucretius3-- ,denique res omnes debent in corpore habere ,ara1 quandoquidem rara sunt corpora et ar ,omnibus est rebus circumdatus appositusque4 ,he next proceeds to define the atmosphere as a pellucid thin fluid1 in which clouds float and vapours rise4 ,its necessity for animal and vegetable life is acknowledged by all4 ,it possesses weight and elasticity4 ,it can be fixed by other bodies2 but the air obtained from them by distillation differs from ordinary vital1 salubrious air1 and is often termed mephitic or poisonous4 ,after acknowledging his debt to his illustrious preceptor ,black1 he proceeds to quote from the latter to the effect that mephitic or fixed air is the air which proves fatal to animals and extinguishes fire2 which is easily absorbed by quicklime and by alkaline salts2 which occurs in the ,grotto del ,cane1 and in mineral waters2 and which is produced during exhalation from the lungs1 by combustion1 and during certain kinds of fermentation4 ,its density1 compared with that of ordinary air1 is as #ae or #af to #i2 hence it can be kept for some time in an open glass1 and a candle lowered into it is extinguished4 ,it has an agreeable taste and smell2 and it changes the colour of syrup of violets from blue to purple4 ,it prevents putrefaction1 but putrefied bodies are not made fresh by it4 ,it possesses the power of combining with lime1 which acquires new properties as the result of its action4 ,rutherford then recalls ,black's experiments on lime and on magnesia1 pointing out how these bases absorb fixed air1 and how it can be recovered from them and from its compounds with alkalies1 sometimes by heat1 and always by the action of acids4 ,rutherford next describes experiments which show that a mouse1 placed in atmospheric air1 and left till dead1 diminishes the volume of the air by one-tenth2 and that the residual air1 on treatment with alkali1 loses one-eleventh of its volume4 ,the residue extinguishes the flame of a candle2 but tinder continues to smoulder in it for a short time4 ,it is thus proved that after the whole of the fixed air has been withdrawn by alkalies1 the residue is still incapable of supporting life and combustion4 ,some burning bodies deprive air of its 8salubrity0 more easily than others4 ,the phosphorus of urine continues to glow in air in which a candle has ceased to burn1 or in which charcoal has burned until it is extinguished4 ,even after the absorption of all fixed air by alkalies1 phosphorus burns1 emitting clouds of the dry acid of phosphorus1 which can be absorbed by lime-water4 8,it therefore appears that pure air is not converted into mephitic air by force of combustion1 but that this air rather takes its rise or is thrown out from the body thus resolved4 ,and from this it is permissible to draw the conclusion that that unwholesome air is composed of atmospheric air in union with1 and1 so to say1 saturated with1 phlogiston4 ,and this conjecture is confirmed by the fact that air which has served for the calcination of metals is similar1 and has clearly taken away from them their phlogiston40 ,such air differs from the air evolved from metals by the action of acids1 which is more thoroughly impregnated with phlogiston2 and also from that from decaying flesh1 which is a mixture of mephitic air and combustible air4 ,he proceeds3--8,i had intended to add something regarding the composition of mephitic air1 and to seek for a reason for its unwholesome effects1 but ,i have not been able to find out anything with certainty4 ,certain experiments appear to show1 however1 that it consists of atmospheric air in union with phlogistic material2 for it is never produced except from bodies which abound in inflammable parts3 the phlogiston appears to escape from such bodies when they become converted into the calces of metals4 ,i say from phlogistic material1 because1 as already mentioned1 pure phlogiston1 in combination with common air1 can be seen to yield another kind of air viz4 hydrogen4444 ,i have lately heard that ,priestley believes that vegetables growing in mephitic air dispel its noxious ingredients1 or1 as it were1 extract them1 and restore its original wholesomeness2 and that mephitic air1 added to air from putrid flesh1 partly mitigates its unwholesome character4 ,but ,i have been unable to try such experiments40 ,we see1 then1 that ,rutherford's claims to the discovery of nitrogen amount to this3--he removed the oxygen from ordinary air by combustibles such as charcoal1 phosphorus1 or a candle2 and having got rid of the carbon dioxide1 in those cases when it was formed1 by alkali or lime1 he obtained a residue1 now known as nitrogen4 ,his view of the nature of this gas1 in the phlogistic language of the time1 was that the burning bodies had given up some of their 8phlogistic material0 to the air1 which was thus altered4 ,nitrogen was 8phlogisticated air10 even though incombustible2 hydrogen1 too1 was phlogisticated air1 but air produced by the union of pure phlogiston with atmospheric air4 ,the step taken by ,rutherford1 under ,black's guidance1 was an advance1 though not a great one1 in the development of the theory of the true nature of air2 and he may be well credited with the discovery of nitrogen4 #c ,a ,free ,inquiry into the ,vulgar ,notion of ,nature2 ,prefatory remarks4 ,,chapter ,,iii ,,the ,,discovery ,,of 8,,dephlogisticated ,,air0 ,,by ,,priestley ,,and ,,by ,,scheele--,,the ,,overthrow ,,of ,,the ,,phlogistic ,,theory ,,by ,,lavoisier ,we have seen that ,stephen ,hales must have prepared oxygen1 among the numerous gases and mixtures of gases which he extracted from various substances2 for1 among the many materials which he heated1 one was red-lead4 ,the red-lead of that day1 however1 must have contained carbonate1 because1 as we shall see1 ,priestley always obtained a mixture of oxygen and carbon dioxide from that source4 ,in the account of his researches1 ,hales only incidentally mentions the collection of gas from minium2 and he appears to have made no experiments with the object of ascertaining its properties4 ,the discovery of oxygen was made nearly simultaneously by ,priestley and ,scheele1 though it appears from the recent publication of ,scheele's laboratory notes by ,baron ,nordenskjld that ,scheele had in reality anticipated ,priestley by about two years4 ,his researches1 however1 were not published until a year after ,priestley had given to the world an account of his experiments4 ,priestley had no theory to defend2 his experiments were undertaken in an almost haphazard manner1 probably as a relaxation4 8,for my own part10 he says1#d 8,i will frankly acknowledge that1 at the commencement of the experiments recited in this section1 ,i was so far from having formed any hypothesis that led to the discoveries made in pursuing them1 that they would have appeared very improbable to me had ,i been told of them2 and when the decisive facts did at length obtrude themselves upon my notice1 it was very slowly1 and with great hesitation1 that ,i yielded to the evidence of my senses40 ,on the other hand1 ,scheele was engaged in forming a theory of the nature of fire4 ,he writes3#e--8;,i perceived the necessity of a knowledge of fire1 because without this it is impossible to make any experiment2 and without fire or heat1 it is impossible to utilise the action of any solvent4 ,i began1 therefore1 to dismiss from my mind all explanations of fire1 and undertook a series of experiments in order to gain as full knowledge as possible of these lovely phenomena4 ,i ere long found1 however1 that it was not possible to form any correct opinion concerning the appearances which fire exhibits1 without a knowledge of the air4 ,after a series of experiments1 ,i saw that air really is concerned in the mixture termed fire1 and that it is a constituent of flame and sparks4 ,i learned1 moreover1 that such a treatise on fire as this could not be compiled with thoroughness without also taking air into consideration40 ,scheele's views concerning fire need not be mentioned here2 but his researches on air are so methodical and so complete as to command our entire admiration4 ,they remind us of those of ,mayow1 and had the latter lived a little longer1 they would not improbably have been carried out by him4 ,since1 however1 ,priestley had the advantage of priority of publication1 we shall commence with an account of his researches4 99 99 99 99 99 ,joseph ,priestley was born in #agcc at ,fieldheads1 about six miles from ,leeds4 ,his father1 a maker and dresser of woollen cloth1 lost his wife when his son ,joseph was about six years of age2 and being poor1 his sister1 ,mrs4 ,keighley1 offered to bring up the boy4 ,the early associations of the lad were closely connected with dissent2 and after some time spent at a public school in the neighbourhood1 he was sent1 in #ageb1 to the ,academy at ,daventry1 in which he was trained for the ministry4 ,there he gained some knowledge of mechanics and metaphysics1 and also acquired some acquaintance with ,chaldee1 ,syriac1 and ,arabic1 besides being a competent ,french and ,german scholar4 ,after leaving the ,academy1 he settled at ,needham in ,suffolk1 as assistant in a small meeting-house1 where his income was not over #cj a year4 ,his views were1 however1 too liberal for his hearers2 and after some years he moved to ,nantwich in ,cheshire1 where he preached and also taught a school4 ,here his income was improved1 though still miserably small2 yet he managed to buy some books1 a small air-pump1 and an electrical machine4 ,he subsequently removed to ,warrington1 being employed there in teaching and in literary work2 among his writings was a ,history of ,electricity1 which first brought him into notice1 and which procured for him the degree of ,,ll4,d4 of ,edinburgh1 thus giving him a right to the title of ,doctor1 by which he was always afterwards known4 ,at ,warrington1 too1 he married4 ,we next find him being asked in #agfg to take the pastorship of ,millhill ,chapel at ,leeds1 a call which he accepted4 ,the chapel was next door to a brewery1 and this circumstance first induced him to take up the subject of the chemistry of gases1 which has made his name famous4 ,here too he published his ,history of ,discoveries relative to ,light and ,colours4 ,after six years spent at ,leeds1 he became librarian to the ,earl of ,shelburne 7afterwards ,marquis of ,lansdowne7 and travelled with him on the ,continent4 ,while with ,lord ,shelburne he published the first three volumes of ,experiments on ,air1 and carried out investigations which were recorded in a fourth volume1 published after his removal to ,birmingham4 ,after some years spent in this way1 he was pensioned off1 and settled as minister of a meeting-house in ,birmingham1 where he employed his time partly in theological controversy1 and partly in prosecuting researches in chemistry4 ,he published during this period another three volumes giving a description of his experiments on air1 and communicated several papers to the ,philosophical ,transactions of the ,royal ,society1 of which he had been made a ,fellow4 ,towards the year #agij he was so unfortunate as to attack ,burke's book on the ,french ,revolution2 and this had the effect of rousing popular opinion against him1 more especially that of the local clergy1 whose political views he had frequently opposed4 ,during the riots which took place at ,birmingham in #agia1 his house was burned1 and he was obliged to escape to ,london under an assumed name4 ,after some years spent in the charge of a meeting-house at ,hackney1 he left ,england for ,america4 ,his opinions1 though by no means uncommon at the present day1 were so antagonistic to those of his ,english contemporaries that he was cut by his ,fellows of the ,royal ,society1 and he therefore resigned his ,fellowship4 ,and this feeling was in no way lessened by the action of the ,french ,government of the time1 which made him a ,citizen of the ,republic1 and even chose him as a member of their ,legislative ,assembly4 ,arriving in ,america in #agie1 he was well received1 and settled at ,northumberland1 not far from ,philadelphia4 ,there he died in #ahjd4 ,illustration3 ,,joseph ,,priestley4 ,in ,priestley's work on gases he employed the form of apparatus which had been used by ,mayow a century before4 ,such apparatus is indeed generally used now3 the flasks with bent delivery-tubes1 the ,wolff's bottles with two necks1 and the pneumatic trough filled with water or mercury were his chief utensils4 ,by means of such apparatus1 gases can be collected in a state of comparative purity3 they can be easily transferred from one vessel to another1 and substances which it is desired to submit to their action can be readily introduced4 ,scheele1 on the other hand1 employed less convenient methods3 his gases were generally collected in bladders1 and their transference to bottles must have been attended with the introduction of atmospheric air4 ,scheele's method was to allow a certain amount of gas to escape from the generating flask in order to expel air2 an empty bladder was then tied over the neck1 and the gas entered the bladder4 ,when he wished to transfer the gas to a bottle1 the bladder was tied at some distance from the neck1 and its loose open end was secured by a string round the neck of a bottle full of water4 ,the string confining the gas was then untied1 and the bottle was inverted2 the water ran into the bladder and was replaced by gas4 ,a cork was also enclosed in the bladder1 and it was possible to push this cork into the neck of the bottle and re-tie the string which confined the gas2 and then1 by loosing the string which secured the bottle to the bladder1 the full bottle could be conveyed away4 ,this process is obviously a clumsy one1 although in ,scheele's hands it yielded splendid results2 and the methods which ,priestley had borrowed from ,mayow have attested their superiority by their survival4 ,the first gas which ,priestley investigated was 8nitrous gas10 or1 as it is now named1 nitric oxide4 ,it had previously been prepared by ,mayow 7see p4 #be7 by the action of nitric acid on iron2 and ,mayow had made the important observation that when it was introduced into ordinary air confined over water1 the volume of the air was decreased1 and a rise of temperature occurred4 ,but ,mayow did not apply his discovery to the analysis of air1 though he rightly conjectured that the reason of the decrease in volume of the latter was due to combination between the nitric oxide and his 8fire-air particles40 ,it was left for ,priestley to rediscover this fact1 and to apply it to the analysis of air1 or1 as he expressed it1 to the determination of its 8goodness40 ,priestley's use of a mercurial trough enabled him to collect and investigate various kinds of airs1 among others 8marine acid air0 or gaseous hydrogen chloride1 a gas differing entirely in properties from ordinary air4 ,this made his mind familiar with the thought that different kinds of air exist1 not necessarily modifications of atmospheric air4 ,he had previously from his experiments come to the conclusion that 8atmospheric air is not an unalterable thing1 for that the phlogiston with which it becomes loaded from bodies burning in it1 and animals breathing it1 and various other chemical processes1 so far alters and depraves it1 as to render it altogether unfit for inflammation1 respiration1 and other purposes to which it is subservient2 and ,i had discovered that agitation in water1 the process of vegetation1 and probably other natural processes1 by taking out the superfluous phlogiston1 restore it to its natural purity4 ,but ,i own ,i had no idea of the possibility of going any farther in this way1 and thereby procuring air purer than the best common air40 ,on the #ast of ,august #aggd1 ,priestley heated by means of a burning-glass red oxide of mercury4 ,this was produced by heating mercury until it oxidised1 and therefore had been untouched by acids1 or by any substance which could have 8imparted phlogiston0 to atmospheric air4 ,the resulting air was insoluble in water1 and supported combustion better than common air1 for a candle burned more brightly1 and a piece of red-hot wood sparkled in it4 ,this air he also produced from 8red precipitate10 the product of heating nitrate of mercury2 and at the same time from red-lead1 or minium4 ,it differed from 8modified nitrous air10 in which a candle also burns brightly1 inasmuch as shaking with water the gases produced after a candle had burned for some time in it did not deprive it of its power of supporting combustion2 nor did it diminish the bulk of common air1 as the nitrous air does in some degree4 ,priestley here refers to a mixture obtained by distilling nitrates1 which is essentially a mixture of nitric peroxide with oxygen4 ,a candle burns in such a mixture1 depriving the nitric peroxide of part of its oxygen1 and converting it into nitric oxide mixed with nitrogen4 ,nitric oxide1 deprived of the excess of peroxide by shaking with water1 with which the peroxide reacts and is absorbed1 is no longer capable of supporting the combustion of a candle2 and when added to ordinary air it combines with its oxygen1 again forming nitric peroxide1 which in its turn is absorbed by water4 ,priestley's experiments were performed at intervals from ,august #aggd till ,march #agge1 and at that date it occurred to him to mix with his dephlogisticated air some nitric oxide over water2 absorption took place1 and he concluded that he might assume his new air to be respirable4 ,and what surprised him especially was1 that even after addition of nitric oxide and agitation with water1 the residue still supported the combustion of a candle4 ,a mouse1 too1 lived half an hour in the new air1 and revived after being removed2 whereas similar experiments with an equal volume of common air had shown that1 after respiring it for a quarter of an hour1 a mouse was indisputably dead4 ,even after the mouse had breathed it for so long a time1 it was still capable of supporting the combustion of a candle2 and this induced him to add more nitric oxide to the respired air1 when he found that a further contraction occurred4 ,he reintroduced the same unfortunate mouse into the remainder of the air--a portion to which nitric oxide had not been added--when it lived for another half-hour1 and was quite vigorous when withdrawn4 ,subsequent experiments with nitric oxide showed that air from red precipitate or from 8mercurius calcinatus0 7red oxide of mercury in each case1 although prepared in different ways7 was 8between four and five times as good as common air40 ,he proceeds3#f--8;,being now satisfied with respect to the nature of this new species of air1 viz4 that being capable of taking more phlogiston from nitrous air1 it therefore originally contains less of this principle1 my next inquiry was1 by what means it comes to be so pure1 or1 philosophically speaking1 to be so much dephlogisticated40 ,he therefore went on to heat the various oxides of lead1 but without any special results worth chronicling4 ,on moistening red-lead with nitric acid1 however1 and distilling the mixture1 he obtained1 in successive operations1 air which was 8five times as good0 as common air4 ,this process formed lead nitrate1 which on distillation yielded nitric peroxide and oxygen2 the gas was1 of course1 collected over water1 which absorbed the peroxide1 allowing pure oxygen to pass4 ,he found that red-lead was not the only 8earth0 which produced this effect2 but that 8flowers of zinc0 7zinc oxide71 chalk1 slaked lime1 and other substances also gave a gas1 when distilled with nitric acid1 which was 8better0 than common air4 ,in some cases he broke up nitric acid by heat into water1 nitric peroxide1 and oxygen2 in others he heated nitrates4 ,his conclusion is3 8,atmospherical air1 or the thing we breathe1 consists of the nitrous acid and earth1 with so much phlogiston as is necessary to its elasticity2 and likewise so much more as is required to bring it from its state of perfect purity to the mean condition in which we find it40#g ,when such experiments were made by heating nitrates in a gun-barrel1 8phlogisticated air0 was obtained4 ,this was nitrogen1 for the iron had reduced the oxides of the latter1 and combining with their oxygen1 had formed nitrogen2 moreover1 it had absorbed to a greater or less extent the oxygen simultaneously produced4 ,having concluded that respirable air was a compound of nitrous acid1 phlogiston1 and earth1 ,priestley endeavoured to ascertain what was the nature of this earth4 ,he concludes 8that the metallic earths1 if free from phlogiston1 are the most proper1 and next to them the calcareous earths40 8,dephlogisticated air may be procured from any kind of earth with which the spirit of nitre will unite40 ,a few quantitative experiments would surely have refuted this erroneous conclusion4 ,those which he attempted to make were very crude4 ,a bladder 7of which he does not give the capacity7 was filled with ,phlogisticated air1 and weighed #g dwts4 #ae grs4 ,nitrous air #g #af ,common air #g #ag ,dephlogisticated air #g #ai ,he concludes 7taking into consideration that inflammable air is very light7 8that the less phlogiston any kind of air contains1 the heavier it is2 and the more phlogiston it contains1 the lighter it is40#h ,strange that this should not have led to the rejection of the phlogistic hypothesis6 ,priestley had the curiosity to breathe his 8good0 air4 ,he says3 8,my reader will not wonder that1 after having ascertained the superior goodness of dephlogisticated air by mice living in it1 and the other tests above mentioned1 ,i should have the curiosity to taste it myself4 ,i have gratified that curiosity by breathing it1 drawing it through a glass syphon1 and by this means ,i reduced a large jar full of it to the standard of common air4 ,the feeling of it to my lungs was not sensibly different from that of common air1 but ,i fancied that my breast felt peculiarly light and easy for some time afterwards4 ,who can tell but that in time this pure air may become a fashionable article in luxury8 ,hitherto only two mice and myself have had the privilege of breathing it40#i ,it will be seen from this account that ,priestley's work was to some extent that of an amateur4 ,he performed experiments1 often without any definite object2 and he was not always successful in devising theories4 ,as before remarked1 his chemical pursuits were to him a recreation1 and were undertaken during the intervals of his necessary work4 ,his mind was therefore not given over to them alone2 and this is to be seen from the character of his writings4 ,his style is a delightfully familiar one3 he exposes his inmost thoughts with perfect frankness1 and his writings are therefore very readable4--,we have now to compare his work with that of his contemporary1 ,scheele1 whose mission in life was that of a chemist2 and the reader will be interested in noting the different points of view which these two eminent discoverers adopted4 99 99 99 99 99 ,carl ,wilhelm ,scheele was born on the #ith of ,december #agdb in ,stralsund1 the capital of ,swedish ,pomerania1 where his father was a merchant and a burgess4 ,he was the seventh of eleven children4 ,after receiving his education1 partly in a private school1 partly in the public school 7gymnasium7 at ,stralsund1 he was apprenticed at the age of fourteen to the apothecary ,bauch in ,gothenburg4 ,in those days an apothecary was in large measure a manufacturer as well as a retailer of drugs4 ,he had to prepare his medicines in a pure state from very impure materials1 as well as to mix them in order to carry out prescriptions2 and1 indeed1 he himself often1 as sometimes happens still1 ventured to prescribe in mild cases4 ,scheele's master taught him such methods1 and in addition instructed him in the use of the chemical symbols in vogue at that date2 these he afterwards freely employed in his manuscripts1 and this renders them exceedingly difficult to decipher4 ,there still exists a catalogue of the drugs his master kept2 many of them are of a fantastic nature1 such as 8ointment of vipers01 8human brain prepared without heat01 etc42 but among them were many of the well-known salts of metals1 and the commoner acids1 besides phosphorus1 sulphur1 rock-crystal1 some ores1 and some carbon compounds2 for example1 benzoic acid and camphor4 ,there was a fair chemical library1 which included the works of ,boerhaave and ,lemery1 and his master devoted much pains to his instruction4 ,in a letter to ,scheele's father1 however1 he expressed a fear that too great devotion to study and experimental work would undermine the health of a growing lad4 ,in #agfe the business was sold1 and ,scheele obtained a situation in ,malm with an apothecary named ,kjellstrm4 ,his master testified that he had extraordinary application and ability1 and related that he was in the habit of criticising all that he read1 saying of one statement1 8,this may be the case02 of another1 8,this is wrong02 of a third1 8,i shall look into this40 ,his memory was prodigious3 he is said never to have forgotten anything which he had read relating to his favourite subject4 ,he took little interest in anything else1 and both his employers appear to have encouraged him to the utmost in his favourite pursuit4 ,in #agfh he left ,malm for ,stockholm2 but here the exigencies of his duties interfered with his leisure for experimentation4 ,while there1 in conjunction with his friend ,retzius1 he discovered tartaric acid1 which up till then had never been separated from tartar1 its potassium salt4 ,here too he made investigations on the acid of fluor-spar 7hydrofluoric acid72 but finding his time too greatly occupied with routine work1 he took a situation at ,upsala1 the seat of the largest university of ,sweden1 in #aggj4 ,at that time ,bergman was ,professor of ,chemistry there1 and ,linnaeus occupied the ,chair of ,botany2 both had then achieved a wide reputation4 ,with ,bergman he soon established close relations1 and ,retzius wrote that it was difficult to say which was pupil and which teacher4 ,while at ,upsala he wrote his great work on ,fire and ,air1 which we shall shortly have to consider4 ,from his laboratory notes it appears that before #aggc he had obtained oxygen by the ignition of silver carbonate1 red mercuric oxide1 nitre1 magnesium nitrate1 and from a mixture of arsenic acid and manganese dioxide4 ,here too he discovered chlorine1 and made researches on manganese1 arsenic1 and baryta4 ,in #agge he was elected a member of the ,royal ,swedish ,academy of ,sciences1 an honour which much improved his social status4 ,in the same year he became manager of a business at ,kping1 where he passed the rest of his days1 in spite of urgent appeals to engage in more remunerative work2 indeed1 he was strongly pressed to go to ,berlin1 and also1 it is said1 to ,london1 for his publications had led to his recognition as one of the greatest chemists of the age4 ,his book on ,fire and ,air was not published for some years after the manuscript had been in the printer's hands4 ,we learn from his letters that he was much afraid of being anticipated in his discoveries1 as indeed events showed that he had reason to be4 ,from his letters and from the verdict of his contemporaries1 ,scheele is depicted as an amiable and honourable man1 singularly free from vanity and selfishness4 ,unfortunately no portrait of him has survived4 ,his last memoir on the action of sunlight on nitric acid was published in #aghf2 he died suddenly at the early age of forty-three in ,may of that year1 two days after his marriage to ,sara ,margaretha ,pohl4 ,his devotion to science had told on his health1 and his death was caused by a complication of diseases4 ,yet he was during his life1 as after his death1 regarded as one of the greatest of chemists3 his great knowledge1 extraordinary aptitude in experimenting1 and high intellectual powers placed him among the foremost men of science of his day4 ,near the beginning of his ,treatise on ,air and ,fire1#aj ,scheele defines air4 ,it is that fluid invisible substance which we continually breathe2 which surrounds the whole surface of the earth1 is very elastic1 and possesses weight4 8,it is always filled with an astonishing quantity of all kinds of exhalations1 which are so finely divided in it that they are scarcely visible1 even in the sun's rays40#aa ,it also contains another elastic substance resembling air1 termed aerial acid by ,bergman 7identical with ,black's fixed air74 ,since atmospheric air has not been completely converted into fixed air by admixture of foreign materials1 8,i hope ,i do not err if ,i assume as many kinds of air as experiment reveals to me4 ,for when ,i have collected an elastic fluid1 and observe concerning it that its expansive power is increased by heat and diminished by cold1 while it still uniformly retains its elastic fluidity1 but also discover in it properties and behaviour different from those of common air1 then ,i consider myself justified in believing that this is a peculiar kind of air4 ,i say that air thus collected must retain its elasticity even in the greatest cold1 because otherwise an innumerable multitude of varieties of air would have to be assumed1 since it is very probable that all substances can be converted by excessive heat into a vapour resembling air40#ab ,after defining the properties characteristic of air1 namely1 its power of supporting combustion1 its diminution by one third or one quarter during the combustion of any substance which does not produce any fluid resembling air1 its insolubility in water1 its power of supporting life1 and the fact of its being favourable to the growth of plants1 ,scheele demonstrates that air must consist of at least two elastic fluids4 ,this he proves by exposing it to 8liver of sulphur0 7polysulphide of potassium71 when six parts out of twenty were absorbed4 ,he obtained the same result by employing a solution of sulphur in caustic potash1 and also by polysulphide of calcium1 prepared by boiling lime-water with sulphur1 and by means of yellow sulphide of ammonium4 ,nitric oxide1 8the nitrous air which arises on the dissolution of metals in nitrous acid10 produces a similar contraction1 and so also do oil of turpentine and 8drying oils0 in general4 ,dippel's animal oil1 obtained by distilling bones1 and ferrous hydroxide1 produced from 8vitriol of iron0 and 8caustic ley10 or ferrous sulphate and caustic potash1 may also be used as absorbents2 as may also iron filings moistened with water1 a solution of iron in vinegar1 and a solution of cuprous chloride4 8,in none of the foregoing kinds of air can a candle burn or the smallest spark glow40 ,he accounts for these results by the theory that all such absorbents contain phlogiston1 which is attracted by the air1 and1 combining with it1 diminishes its bulk4 ,the alkalies and lime attract the vitriolic acid of the sulphides used1 and the air attracts the phlogiston4 8,but whether the phlogiston which was lost by the substances was still present in the air left behind in the bottle1 or whether the air which was lost had united and fixed itself with the materials1 such as liver of sulphur1 oils1 etc41 are questions of importance40#ac ,the conclusion that such air1 which had received phlogiston and had contracted in volume1 ought to be specifically heavier than common air was1 however1 rudely dissipated by experiment4 ,the air must therefore contain two fluids1 one of which does not manifest the least attraction for phlogiston1 while the other is peculiarly disposed to such attraction4 8,but where this latter kind of air has gone to1 after it has united with the inflammable substance1 is a question which must be decided by further experiments1 and not by conjectures40#ad ,to decide this question1 ,scheele burned in air substances such as phosphorus1 which do not produce by their combustion any kind of 8air40 ,the result was that the air lost #i volumes out of an original #cj1 or about one-third of its bulk4 ,a flame of hydrogen burning in air caused it to lose one-fifth of its volume4 ,on burning a candle1 some spirits of wine1 or some charcoal1 in a confined quantity of air1 very little1 if any1 diminution of volume was noticed2 but on shaking the air with milk of lime1 contraction ensued1 but not to the same extent as when phosphorus was burnt in it4 ,this greatly puzzled ,scheele2 we now know that such combustibles are not able to remove all the oxygen1 but that they are extinguished when only a portion of each has entered into combination4 ,here1 again1 however1 his memory comes to his help1 for he says1 8,it is known that one part of aerial acid mixed with ten parts of ordinary air extinguishes fire2 and there are here in addition1 expanded by the heat of the flame and surrounding the latter1 the watery vapours produced by the destruction of those oily substances4 ,it is these two elastic fluids1 separating themselves from such a flame1 which present no small hindrance to the fire which would otherwise burn much longer1 especially since there is here no current of air by means of which they can be driven away from the flame4 ,when the aerial acid is separated from this air by milk of lime1 then a candle can burn in it again1 though only for a very short time40#ae ,thus the question was correctly solved4 ,scheele's acumen led him at once to make experiments admirably adapted to discover the true reason2 he was not turned aside by any imaginary difficulties1 but went straight to the point4 ,he next burned sulphur in confined air1 and found little alteration of volume1 but on shaking with clear lime-water1 absorption took place1 and one-sixth of the air was removed4 8,the lime-water was not in the least precipitated in this case1 an indication that sulphur gives out no aerial acid during its combustion1 but another substance resembling air2 this is the volatile acid of sulphur1 which occupies again the empty space produced by the union of the inflammable substance with air40#af ,the next set of experiments were devised 8to prove that ordinary air1 consisting of two kinds of elastic fluids1 can be compounded again1 after these have been separated from one another by means of phlogiston40 8,i have already stated that ,i was not able to find again the lost air4 ,one might indeed object that the lost air remains in the residual air which can no more unite with phlogiston2 for1 since ,i have found that it is lighter than ordinary air1 it might be believed that the phlogiston1 united with this air1 makes it lighter1 as appears to be known already from other experiments4 ,but since phlogiston is a substance1 which always presupposes some weight1 ,i much doubt whether such hypothesis has any foundation40#ag ,he had formerly conjectured that hydrogen1 the 8air0 obtained by the action of vitriol on zinc1 might be phlogiston2 8still1 other experiments are contrary to this40 ,scheele next directs attention to acid of nitre1 and points out that when prepared in absence of organic material1 it is nearly colourless2 but that if phlogiston be given to it1 it becomes red4 ,at the end of a distillation of pure nitre with pure sulphuric acid1 however1 red fumes are produced3 8,where does the acid now obtain its phlogiston8 ,there is the difficulty40 ,he collected some of this 8red air0 in a bladder containing milk of lime1 to prevent its corrosive action2 and having tried whether the resulting gas1 which was now no longer red1 would support combustion1 8the candle began to burn with a large flame1 whereby it gave out such a bright light that it was sufficient to dazzle the eyes4 ,i mixed one part of this air with three parts of that air in which fire would not burn2 ,i had here an air which was like the ordinary air in every respect4 ,since this air is necessarily required for the origination of fire1 and makes up about the third part of our common air1 ,i shall call it after this1 for the sake of shortness1 ,fire-air2 but the other air1 which is not in the least serviceable for the fiery phenomena1 ,i shall designate after this with the name already known1 ,vitiated air40#ah ,how history repeats itself6 ,here is ,scheele1 in #aggb1 reproducing ,mayow's name 8fire-air particles0 for the same substance of which ,mayow had inferred the existence a century before1 and which he had pointed out as being present in the acid of nitre1 as well as in common air4 ,this air is not a 8dry acid of nitre converted into elastic vapours10 for it does not produce nitre with alkalies2 moreover1 it can be prepared from substances which have nothing in common with nitre1 no compound of nitre having been used during their preparation4 ,scheele next describes experiments proving that 8fire-air0 is produced by the distillation of black oxide of manganese with concentrated oil of vitriol1 or with the 8phosphorus acid of urine0 7phosphoric acid71 by distilling nitrate of magnesium1 made by dissolving the 8white magnesia employed in medicine0 7magnesium carbonate7 in aquafortis 7nitric acid71 or by distilling 8mercurial nitre0 7mercuric nitrate74 ,the cheapest and the best method of producing 8fire-air0 is to distil purified nitre in a glass retort4 ,but ,scheele also obtained it from 8calx of silver0 7silver carbonate7 prepared from silver nitrate and 8alkali of tartar0 7potassium carbonate72 during this process he got aerial acid1 which had been present originally in the alkali of tartar2 but it was easily removed by means of milk of lime4 ,similarly1 8calx of gold10 obtained from a solution of gold with 8alkali of tartar10 gave 8fire-air0 when heated2 but no aerial acid1 for that air escapes during the precipitation of the 8calx40 ,the brown-red precipitate obtained by adding 8alkali of tartar0 to 8corrosive sublimate0 7potassium carbonate to mercuric chloride1 giving a basic carbonate of mercury and potassium chloride7 yielded a mixture of fire-air and aerial acid when heated4 ,but if the 8calx of mercury0 had been prepared by means of the 8acid of nitre10 or in modern language by heating mercuric nitrate1 a pure 8fire-air10 unmixed with 8aerial acid10 was the product4 ,and lastly1 arsenic acid1 when heated1 gave ordinary white arsenic together with 8fire-air40 ,this fire-air was completely absorbed by 8liver of sulphur0 7a polysulphide of potassium1 formed by heating together potassium carbonate and sulphur72 and a mixture of four parts of 8fire-air0 with fourteen parts of 8vitiated air0 lost the whole of its fire-air on standing for fourteen days in contact with liver of sulphur4 ,dippel's animal oil1 and burning phosphorus1 charcoal1 and sulphur1 all absorbed 8fire-air0--completely if it was pure1 incompletely if it was mixed with 8vitiated air02 in short1 the identity of 8fire-air0 prepared from calces1 etc41 with that in ordinary air was completely established4 ,as 8vitiated air0 is lighter than ordinary air1 it follows that 8fire-air0 must be heavier2 and experiment proved this to be the case4 ,to completely disprove the possible contention that nitre was necessary for the production of 8fire-air10 some 8calx of mercury0 7or red oxide71 which had been prepared by boiling mercury for a long time in contact with air1 was heated4 ,the products were metallic mercury and 8fire-air04 8,this is a remarkable circumstance1 that the fire-air which had previously removed from the mercury its phlogiston in a slow calcination1 gives the same phlogiston up to it again1 when the calx is simply made red-hot40#ai ,is it not remarkable that the true explanation should not have forced itself upon ,scheele's mind1 which was so acute1 and so capable of forming true deductions8 ,the next set of experiments dealt with the phenomena of respiration4 ,a rat1 confined in air until it died1 polluted the air with one-thirtieth of aerial acid4 ,respiration from ,scheele's own lungs had the same effect4 ,a few flies1 bees1 and caterpillars also polluted the air in the same way4 ,peas1 roots1 herbs1 and flowers all converted about one-fourth part of ordinary air into 8aerial acid04 8,these are accordingly strange circumstances1 that the air is not noticeably absorbed by animals endowed with lungs1 contains in it very little aerial acid1 and yet extinguishes fire4 ,on the other hand1 insects and plants alter the air in exactly the same way1 but still they convert the fourth part of it into aerial acid40#bj ,and so he makes experiments which prove that it is the fire-air which is converted into 8aerial acid0 by peas2 and that 8fire-air0 is absorbed by fresh blood1 and acquires no aerial acid from it4 ,and1 further1 he was able to breathe fire-air for a long time1 especially if a 8handful of potashes0 was put into the bladder4 ,a couple of large bees1 confined in 8fire-air10 along with milk of lime1 consumed practically the whole of the air in eight days4 ,but plants1 confined in 8fire-air10 along with milk of lime1 would not grow2 however1 they yielded a little aerial acid4 ,scheele is again puzzled here by the circumstance that the blood and the lungs have not the same action on air as insects and plants1 inasmuch as the former convert it into vitiated air1 and the latter into aerial acid4 ,we now know that air will not support life of warm-blooded animals when the oxygen falls below a certain not very small amount1 while insects appear to be capable of exhausting the oxygen to a great extent2 and it is probable that the plants1 under the unnatural circumstances in which they were placed1 gave off a considerable amount of carbon dioxide4 ,scheele's explanation in terms of phlogiston is not successful4 ,he wrote3--8,i am inclined to believe that fire-air consists of a subtle acid substance united with phlogiston1 and it is probable that all acids derive their origin from fire-air4 ,now if this air penetrates into plants1 these must attract the phlogiston1 and consequently the acid1 which manifests itself as aerial acid1 must be produced40#ba ,this is reversing what may be termed the true explanation on the basis of the phlogistic theory4 ,for ,scheele supposes that oxygen contains phlogiston1 and by losing it1 yields carbon dioxide4 ,on the other hand1 the consistent explanation would be that carbon is carbonic acid plus phlogiston1 and that when it burns it loses phlogiston and becomes carbonic acid again4 ,we see how confused the phlogistic ideas became after the discovery of oxygen1 and how ripe the time was for ,lavoisier to formulate the views which are now universally accepted4 ,in the concluding sections of his treatise ,scheele describes experiments which prove the solubility of 8fire-air0 in water2 he mentions a convenient test for free oxygen in solution1 viz4 a mixture of ferrous sulphate and lime1 which turns dark green1 and finally rust-coloured1 when added to water containing oxygen2 and he shows that water is deprived of oxygen by the presence of a leech1 kept in it for two days4 ,it is impossible not to recognise in ,scheele one of the most acute intellects and able experimenters whom the world has ever seen4 ,and although we cannot but feel surprise that his discoveries did not lead him to take the step of renouncing the hypothesis of phlogiston1 it must be borne in mind that the doctrine was surrounded with the halo of old age1 and sanctioned by many names of great repute in their time4 ,we shall see later that ,cavendish1 one of the greatest of ,english chemists1 on weighing the rival theories1 decided in favour of the phlogistic hypothesis4 ,the actual escape of flame1 a visible entity1 from a burning substance1 may have had much to do with this decision2 and the uncertainty concerning the nature of heat1 and the doubt whether it was not a form of imponderable matter1 may have led both ,scheele and ,cavendish to retain the older views4 ,it was ,lavoisier who first dared to throw off the shackles of tradition2 and this he did before oxygen had been discovered1 as early as #aggb4 99 99 99 99 99 ,antoine ,auguste ,lavoisier was born in ,paris on the #bfth of ,august #agdc4 ,his father was wealthy1 and spared no expense on his education4 ,in his twenty-first year he obtained a gold medal from the ,academy of ,sciences for an essay on the best method of lighting the streets of ,paris1 but it was some years before he made definite choice of his subject4 ,he published memoirs relating to geology and to mathematics1 before the fame of ,black's and ,priestley's discoveries reached him and induced him to turn his attention to scientific chemistry4 ,lavoisier's life was divided between his researches and the performance of public duties4 ,in his twenty-fifth year he was elected a ,member of the ,french ,academy of ,sciences1 and1 somewhat later1 became its treasurer4 ,he drew up numerous reports for the ,government on questions on the borderland of ,science and ,technology2 for example1 on the preparation of paper for bills1 which would not admit of forgery2 on experimental agriculture2 and on the manufacture of gunpowder4 ,in #agga he married ,marie ,anna ,pierette ,paulze1 the daughter of a 8fermier-gnral0 or collector of ,government revenue2 and after his death1 she became the wife of ,count ,rumford1 another distinguished scientific man4 ,made a 8fermier-gnral0 himself1 it was during his tenure of this office that ,lavoisier was accused--along with others holding similar positions--of misappropriating revenue moneys1 with the result that1 under the dictatorship of the infamous ,robespierre1 he and twenty-eight of those who held like office were guillotined publicly1 on the #hth of ,may #agid4 ,it is stated that ,lavoisier's last plea1 presented by ,hall--for permission to finish a research--was refused by ,coffinhal1 with the brutal phrase1 8,la ,republique n'a pas besoin de savants2 il faut que la justice suive son cours40 ,within twenty-four hours the execution took place4 ,lavoisier was a tall1 handsome man1 with a remarkably pleasing face4 ,he possessed great influence1 and used it all for good4 ,the first account which we possess of ,lavoisier's revolutionary ideas1 for revolutionary they were then deemed1 was in a sealed note1 placed in the hands of the ,secretary of the ,academy on the #ast of ,november #aggb4 ,it is to the following effect3-- 8,about eight days ago1 ,i discovered that sulphur1 when burned1 instead of losing weight1 gains weight2 that is to say1 from one pound of sulphur much more than one pound of vitriolic acid is produced1 not counting the moisture gained from the air4 ,phosphorus presents the same phenomenon4 ,this increase of weight is due to a great quantity of air which becomes fixed during the combustion1 and which combines with the vapours4 ,this discovery1 which ,i confirmed by experiments which ,i regard as decisive1 led me to think that what is observed in the combustion of sulphur and phosphorus might likewise take place with respect to all the bodies which augment in weight by combustion and calcination2 and ,i was persuaded that the gain of weight in calces of metals proceeded from the same cause4 ,experiment fully confirmed my conjectures4 ,i effected the reduction of litharge in closed vessels with ,hales' apparatus1 and ,i observed that at the moment of the passage of the calx into the metallic state1 there was a disengagement of air in considerable quantity1 and that this air formed a volume at least a thousand times greater than that of the litharge employed4 ,as this discovery appears to me to be one of the most interesting which has been made since the time of ,stahl1 ,i thought it expedient to secure to myself the property1 by depositing the present note in the hands of the ,secretary of the ,academy1 to remain secret till the period when ,i shall publish my experiments40 ,,lavoisier4 8,,paris1 #aath ,november #aggb40 ,illustration3 ,,antoine ,,auguste ,,lavoisier4 ,there is no account in ,hales' work of his reducing litharge in closed vessels4 ,it is to be presumed that ,lavoisier heated in a retort a mixture of litharge and charcoal1 and that the air which he speaks of was a mixture of oxides of carbon4 ,this account does not inform us of ,lavoisier's views on combustion1 but merely shows the date at which he had first obtained what he supposed were results new to science4 ,we recognise that ,mayow had anticipated him in this4 ,it was not until ,priestley1 when dining with him in the autumn of #aggd 7being in ,paris with ,lord ,shelburne at the time71 had informed ,lavoisier of his discovery of 8dephlogisticated0 air1 that the ideas of the latter upon the subject became precise4 ,priestley's own words are3--8,having made the discovery some time before ,i was in ,paris1 in the year #aggd1 ,i mentioned it at the table of ,mr4 ,lavoisier1 when most of the philosophical people of the city were present1 saying that it was a kind of air in which a candle burned much better than in common air1 but ,i had not then given it any name4 ,at this all the company1 and ,mr4 and ,mrs4 ,lavoisier as much as any1 expressed great surprise4 ,i told them ,i had gotten it from precipitate per se1 and also from red-lead4 ,speaking ,french very imperfectly1 and being little acquainted with the terms of chemistry1 ,i said plombe rouge1 which was not understood till ,mr4 ,macquer said ,i must mean minium40 ,shortly after this1 ,lavoisier repeated ,priestley's experiments and confirmed their truth2 and this led to the true explanation of experiments of which an account is given in the ,memoirs of the ,french ,academy for #aggd1 and which were fundamental in their character4 ,they referred to the calcination of tin in hermetically-sealed retorts4 ,the tin was placed in a retort which was heated on a sand-bath until the metal had melted4 ,the beak of the retort1 previously drawn out into a capillary1 was then sealed1 the air expelled having been collected and its weight noted4 ,the retort was then cooled and weighed4 ,it was again heated1 and the temperature was maintained until the calcination of the tin stopped4 ,with a large retort the calcination was more complete than when a smaller one was employed1 this implying that the degree to which the calcination proceeded was dependent upon the amount of air present4 ,after cooling the retort a second time1 it was again weighed1 when it was found to have undergone no change of weight4 ,the beak was then broken1 and air entered with a hissing noise4 ,the gain in weight was now about #aj grains with a large retort4 ,the tin and its calx were next weighed1 and it was found that the gain in weight of the tin was always equal to the loss of weight of the air in the retort1 measured by the quantity of air which entered on breaking the beak of the retort1 less the air driven out of the retort before hermetically sealing it4 ,from this ,lavoisier concluded that calx of tin is a compound of tin and air4 ,lavoisier's next research1 communicated to the ,academy in #agge1 and published in #aggh1 was entitled 8,on the ,nature of the ,principle which combines with ,metals during their ,calcination1 and which increases their ,weight40 ,in this he describes experiments showing that when metallic calces are converted into metals by heating with charcoal1 a quantity of fixed air is expelled2 and here for the first time he points out that fixed air is a compound of carbon with the elastic fluid contained in the calx4 ,he then describes the preparation of oxygen by ,priestley's process of heating red oxide of mercury 7mercurius precipitatus per se71 and shows that the red oxide1 when heated with charcoal1 manifests the properties of a true calx1 inasmuch as metallic mercury is formed1 and a large quantity of fixed air is produced4 ,his next paper1 which appeared in #aggg in the ,mmoires of the ,academy1 deals with the combustion of phosphorus2 and here he recapitulates ,rutherford's experiments1 and shows that one-fifth of the air disappears1 and that the residue1 to which he gave the name 8mouffette atmosphrique10 is incapable of supporting combustion4 ,it will be remembered that ,rutherford named this residue 8phlogisticated air10 inasmuch as he imagined it to have absorbed phlogiston from the burning phosphorus2 ,scheele1 too1 had made a similar experiment with a similar result4 ,from these observations1 ,lavoisier concluded that air consists of a mixture or compound of two gases1 one capable of absorption by burning bodies1 the other incapable of supporting combustion4 ,this paper was immediately followed by another1 also published in #aggg4 ,its title is1 8,on the ,combustion of ,candles in ,atmospheric ,air1 and in ,air eminently respirable40 ,in this memoir he distinguishes between four kinds of air3--#a1 ,atmospheric air1 in which we live and which we breathe4 #b1 ,pure air1 alone fit for breathing1 constituting about one-fourth of atmospheric air1 and termed by ,priestley 8dephlogisticated air40 #c1 ,azotic gas1 identical with ,rutherford's 8mephitic air10 and of which the properties were then unknown4 #d1 ,fixed air1 which he proposed to call 8acide crayeux10 or acid of chalk1 discovered twenty-five years previously by ,black4 ,by this time his theory was well developed4 ,he accounted for the phenomena of combustion without having recourse to the phlogistic hypothesis3 the calx was produced by the union of the metal with the active constituent of air2 and when carbonaceous material burned1 the carbon united with this same constituent1 producing fixed air4 ,but there were still difficulties in his way3 it was known that in dissolving metals in dilute vitriol or muriatic acid1 a combustible and very light air was evolved2 and that the metals were thereby converted into calces in combination with the respective acids4 ,this fact was not explained even by the supporters of the phlogistic theory1 but it had the effect of preventing them from accepting ,lavoisier's views4 ,some considered that hydrogen and phlogiston were identical1 and that on dissolving a metal the calx was formed by the escape of the phlogiston2 while others had a hazy idea that hydrogen was a compound of water and phlogiston2 but of this more hereafter4 ,lavoisier's objection to such a theory was that the calx was heavier than the metal1 and that hydrogen1 though light1 still possessed weight4#bb ,moreover1 he had ascertained that the calces of mercury1 tin1 and lead are compounds of these metals with active air1 and that as fixed air is produced by heating such calces with carbon1 fixed air must be a compound of carbon and vital air1 or1 as he named it1 the 8oxygine principle10 inasmuch as its combination with phosphorus1 sulphur1 and carbon resulted in the formation of acids 71 an acid74 ,in #aggg he read another memoir1 8,on the ,solution of ,mercury in ,vitriolic ,acid1 and on the ,resolution of that ,acid into ,aeriform ,sulphurous ,acid1 and into ,air eminently respirable40 ,priestley had already shown that this process yielded sulphur dioxide2 ,lavoisier carried the temperature higher1 and1 decomposing the sulphate of mercury1 produced metallic mercury1 sulphur dioxide1 and oxygen4 ,it appeared therefore that sulphurous differed from sulphuric acid in containing a smaller proportion of oxygen4 ,he also experimented with iron pyrites1 and his experiments recall those of ,boyle4 ,boyle found that 8marcasite10 a disulphide of iron1 on exposure to air1 gained in weight1 while vitriol of iron was formed4 ,lavoisier performed the same experiment1 not 8in a very pure air10 as ,boyle did when he left the pyrites exposed in a quiet dust-free room1 but in a confined quantity of ordinary air2 and he found that the air was rendered incapable of supporting combustion1 or1 in other words1 its oxygen was removed4 ,in the same volume of the ,memoirs of the ,academy for #aggh1 another of ,lavoisier's papers--8,on ,combustion in ,general0--is to be found4 ,in this he showed that oxygen gas is the only substance which supports combustion2 that during the burning of combustible substances in air a portion of the oxygen disappears1 and converts the burning substance into one of two kinds of compounds3 either an acid1 such as sulphuric acid from sulphur1 phosphoric acid from phosphorus1 or carbonic acid from carbon 7for in those days the term 8acid0 was applied to what we now term an anhydride72 or in the case of metals a calx1 or compound of oxygen with the metal4 ,the processes are analogous1 but differ in the rate at which they take place2 for the calcination of metals is a much slower operation than the combustion of sulphur or phosphorus4 ,it is the rapidity of the action which leads to actual inflammation4 ,he next examined and attacked the theory of phlogiston1 and maintained that the existence of phlogiston is purely hypothetical1 and quite unnecessary for the explanation of the phenomena4 ,but his papers were received with doubt4 ,the change demanded was too great2 the trammels of custom were too firmly bound4 ,he gained no converts4 ,until the true nature of hydrogen had been explained1 the attack on the phlogistic theory could not be said to be complete4 ,this combination of hydrogen and oxygen to form water was first proved by ,cavendish4 ,and as soon as ,sir ,charles ,blagden1 in #aghc1 had communicated ,cavendish's results to ,lavoisier1 the latter at once saw their bearing on the new theory which he was endeavouring to uphold1 and perceived how they would give a final blow to the adherents of the theory of phlogiston4 ,for it had been frequently adduced as an objection to his new views1 that they were incapable of explaining why hydrogen should be evolved during the solution of metals in acids1 or why it should be absorbed during the reduction of calces to the metallic state4 ,lavoisier at once repeated ,cavendish's experiments on a large scale1 and was assisted on that occasion by ,laplace1 ,sir ,charles ,blagden also being present4 ,a considerable quantity of water was produced1 and the volumes of the combining gases were found to be #a of oxygen to #aia of hydrogen4 ,shortly after1 in conjunction with ,meunier1 he performed the converse operation1 in decomposing steam by passing it over iron wire heated to redness in a porcelain tube4 ,the iron withdrew the oxygen from the water1 while the hydrogen passed on and was collected in the gasholder4 ,the explanation of the solution of metals in acids was now easy3 it depended on the decomposition of water4 ,while the oxygen united with the metal to form a calx1 the hydrogen was evolved2 the calx dissolved in the acid1 forming a salt of the metal4 ,and the operation of producing hydrogen by the action of steam on red-hot iron met with an equally simple explanation3 the oxygen and iron united to form an oxide--the ancient ethiops martial--while the hydrogen escaped4 ,the converse took place during the reduction of a calx to the metallic state by hydrogen4 ,here the hydrogen seized on the oxygen of the calx1 removed it in the form of water1 and the metal was left4 ,these experiments were due to ,cavendish2 all that ,lavoisier did was to show the true nature of the phenomena4 ,the opponents of the new doctrines1 ,priestley chief among them1 did their best to disprove the view that water was a compound of oxygen and hydrogen4 ,but in vain4 ,many of ,lavoisier's opponents had to admit the justice of his views2 and in #aghg ,de ,morveau1 ,berthollet1 and ,fourcroy joined ,lavoisier in reconstructing the nomenclature of chemistry on a new basis1 which is substantially that in use at the present day4 ,black1 too1 was a convert1 but ,priestley and ,cavendish remained true to their old faith1 and one of ,priestley's last acts was to publish a defence of the phlogistic theory4 ,we shall see later how ,cavendish carefully considered the rival theories1 and what reasons induced him to cast his vote for the older one4 ,among the numerous memoirs which ,lavoisier communicated to the ,academy during the ten years between #aggb and #aghb1 one still remains to be mentioned4 ,it was published as early as #aggg1 but it must be remembered that many of these memoirs were antedated4 ,it referred to the respiration of animals2 and ,lavoisier concluded1 on the ground that the phenomena of respiration are essentially similar to those of combustion and calcination1 that the only portion of the air which supports animal life is the oxygen4 ,the azote or nitrogen is inhaled along with the oxygen1 but is exhaled unaltered4 ,the oxygen1 however1 is gradually converted into carbonic acid2 and when a certain amount1 but by no means the whole1 has been thus changed1 the air becomes unfit for respiration4 ,if the carbonic acid is withdrawn by means of lime-water or caustic alkali1 the residue is air poor in oxygen1 and the azote is the same as that left after the calcination of metals1 or the burning of a candle1 in air4 ,at the time of his impeachment1 ,lavoisier was engaged in experiments on perspiration1 along with ,sguin4 ,he had nearly finished his experimental work1 but had drawn up no account of it4 ,his request that his life might be prolonged until he had compiled a statement of his results was refused2 but ,sguin1 who was fortunately spared1 undertook the task4 ,the facts collected do not1 however1 bear directly on our subject1 and shall not be further alluded to here4 ,this account of ,lavoisier's researches would be incomplete without a reference to his text-book of chemistry1 ,trait lmentaire de ,chimie1 in which his views are stated in order1 and with great clearness4 ,the nomenclature current at the time was so cumbrous1 that it was almost1 if not quite1 impossible for the supporters of the new theory to express their meaning in an intelligible manner4 ,de ,morveau had suggested a nomenclature for salts2 ,black1 too1 had invented one2 but neither of these systems was adapted to represent the new views4 ,it was partly with the object of avoiding such embarrassment that ,lavoisier wrote his ,treatise4 ,he begins with a clear statement of what is generally termed 8the states of matter0--solid1 liquid1 and gaseous--and points out that solids and liquids are almost all capable of change into the aeriform state by the addition of 8caloric40 ,proceeding next to the consideration of the nature of air1 he shows that it must necessarily contain all those gases capable of existence at the ordinary temperature2 and he explains how water-vapour must be one of them1 seeing that even though water is a liquid at the ordinary temperature1 it is capable1 like many other liquids1 of existing as vapour1 when mixed with other gases4 ,he next treats of the analysis of air1 and describes his classical experiment of heating four ounces of mercury for twelve days in a retort communicating with a bell-shaped receiver1 standing in a mercury trough4 ,having marked the initial height of the air in the jar by means of a piece of gummed paper1 he found that1 after twelve days' heating close to the boiling-point1 the air had diminished in volume by about one-sixth1 and that the mercury had become covered with a red deposit of mercurius calcinatus per se1 which1 when collected1 weighed #de grains4 ,the residual air in the retort and in the jar was incapable of supporting life or combustion2 but the red precipitate1 when heated1 lost #c grains of its weight1 yielding #da grains of metallic mercury1 while it evolved #g or #h cubic inches of oxygen1 capable of supporting the combustion of a candle vividly1 and of causing charcoal to burn with a crackling noise1 throwing out sparks4 ,oxygen was thus successfully separated from air1 and obtained from it in a pure condition for the first time1 in a single series of operations4 ,in ,lavoisier we see a master mind1 not only capable of devising and executing beautiful experiments1 but of assimilating those of others1 and deducing from them their true meaning4 ,although his additions to the known chemical compounds were few in number1 and cannot be compared with those of ,scheele or of ,priestley1 yet his reasoning in disproof of the phlogistic theory was so accurate and so exact that it rapidly secured conviction4 ,with the exceptions already mentioned1 almost all the eminent chemists of the day accepted his conclusions2 and one1 ,kirwan1 who had written a formal treatise in defence of the phlogistic theory1 was so fair-minded1 that after his work had been translated into ,french and published with comments1 he acknowledged that the old theory was dead1 and that truth had conquered4 ,it will be interesting now to trace ,cavendish's part in developing the history of the discovery of the constituents of air1 and to note his arguments in favour of the phlogistic theory4 ,although ,cavendish never publicly acknowledged its insufficiency1 yet he had ceased to occupy himself with chemical problems at the time when its adoption was universal1 and his true opinions have never been recorded4 #d ,experiments and ,observations on ,different ,kinds of ,air1 vol4 ii4 ,by ,joseph ,priestley1 ,,ll4,d41 ,f4,r4,s4 ,second edition 7#aggf71 p4 #bi4 #e ,chemical ,treatise on ,air and ,fire 7#aggg71 #c4 #f ,loc4 cit4 p4 #df4 #g ,loc4 cit4 p4 #ee4 #h ,loc4 cit4 p4 #id4 #i ,loc4 cit4 p4 #ajb4 #aj ,the accurate translation of ,scheele's ,treatise published by the ,alembic ,club 7,william ,f4 ,clay1 #ahid7 has been made use of here4 #aa #d4 #ab #e4 #ac #af4 #ad #af4 #ae #bb4 #af #bc4 #ag #bd4 #ah #bi4 #ai #hj4 #bj #hg4 #ba #ic4 #bb ,this1 as previously remarked1 had already been noticed4 ,in ,maquer's lmens de ,chymie-pratique1 published in #ageb1 a work which ran through many editions1 we read 7p4 #cjg73 8,there happens during all these calcinations1 and especially in that of lead1 a very strange phenomenon for which it is very difficult to assign a reason4 ,it is that those bodies1 which lose no small proportion of their substance1 whether by the dissipation of phlogiston1 or because part of the metal is exhaled as vapour1 yield calces increased in weight after calcination2 and this increase is by no means inconsiderable4444 ,physicists and chemists have devised many ingenious systems to account for this phenomenon1 but no one of them is absolutely satisfactory4 ,as no well-established theory has been devised1 we shall not undertake to attempt an explanation of this singular fact40 ,,chapter ,,iv 8,,phlogisticated ,,air0 ,,investigated ,,by ,,cavendish--,,his ,,discovery ,,of ,,the ,,composition ,,of ,,water ,while ,lavoisier was engaged in experiments on oxygen1 ,cavendish1 too1 was devoting his attention to the constituents of air1 but in a somewhat different manner4 ,his early experiments led him to the discovery of the composition of water2 and it has already been pointed out how necessary a knowledge of the true nature of hydrogen is to the understanding of the phenomena of combustion4 ,his second paper deals with the inactive constituent of air1 the mephitic portion1 now known as nitrogen or azote4 ,but before considering these1 a sketch of his life will prove of interest4 ,the ,honourable ,henry ,cavendish was a very singular man1 retiring and uncommunicative to a degree2 hence little is known of his early life4 ,he was the elder son of ,lord ,charles ,cavendish1 who was the third son of the second ,duke of ,devonshire4 ,his only brother1 ,frederick1 was also an eccentric1 but a very benevolent man1 and the two brothers1 though they seldom met1 lived on excellent terms with each other4 ,henry ,cavendish was born at ,nice in ,october #agca4 ,his mother died when he was two years old4 ,nothing is known of his childhood and youth1 save that he attended ,hackney ,school from #agdb to #agdi1 and that he went to ,cambridge in the end of #agdi1 and remained till #agec1 without taking a degree4 ,after leaving ,cambridge1 it is supposed that he lived in ,london for ten years4 ,it is known that his allowance from his father amounted to #ejj a year1 and that his rooms were a set of stables fitted up for his accommodation4 ,it is probable that this was his own choice1 and that he made use of them chiefly as a laboratory and a workshop4 ,although at his father's death and by the legacy of an aunt he acquired a large fortune1 he never spent more than a fraction of it4 ,he left more than a million sterling to his relative1 ,lord ,george ,cavendish2 but they saw each other only once a year1 and the interview seldom lasted more than ten minutes4 ,the writer of his obituary notice1 ,m4 ,biot1 epigrammatically said3--8,il tait le plus riche de tous les savans1 et le plus savant de tous les riches40 ,illustration3 ,h4 ,cavendish ,he was a regular attendant at the meetings of the ,royal ,society1 of which he was made a ,fellow in #agfj1 and was a constant diner at the ,royal ,society ,club4 ,it is said that he used to talk to his neighbour at table so long as others did not join in the conversation2 but if the conversation took a general turn1 he was silent4 ,his death took place in ,february #ahaj1 and was as solitary as his life4 ,it is related by his servant that ,cavendish1 on feeling his end approaching1 dismissed him from the room1 telling him to come back in half an hour4 ,he disobeyed instructions1 and1 being anxious1 found some pretext to enter the room4 ,cavendish ordered him away in a voice of displeasure2 and on returning1 the man found his master dead4 ,such a life demands our pity2 yet1 if an object of human life is to give pleasure to its possessor1 we can hardly say that ,cavendish's was a failure4 ,ordinary mortals have a craving for the sympathy of their fellows2 ,cavendish appears to have been devoid of any such sensation4 ,indeed1 his experiments were in many cases not published until long after they had been made4 ,he appears to have carried on his work for his own information1 and to have been indifferent to the impression which his labours made on his fellow-men4 ,yet his inquiries cover a more extensive field than those of almost any other man of science4 ,they begin with experiments on arsenic1 by which he endeavoured to determine the difference between the element arsenic and its two oxides4 ,he held that arsenic acid was more thoroughly 8deprived of phlogiston0 than arsenious acid 7i4e4 more highly oxidised72 and on the same occasion he studied the effect of the addition of air to nitric oxide1 produced by the action of nitric acid on the element arsenic and on arsenious oxide4 ,his next experiments related to heat2 and had he published them1 he would doubtless have anticipated ,black in his discovery of latent heat4 ,his paper on 8,factitious ,airs10 published in the ,philosophical ,transactions for #agff1 deals with the properties of hydrogen1 carbon dioxide1 and the gases produced by the destructive distillation of organic substances4 ,as we shall see later1 he supposed that hydrogen1 generated by the action of acids on metals1 came out of the metal1 and was an unknown principle in combination with phlogiston1 if indeed it was not phlogiston itself2 and this idea is not absurd1 for many metals1 and indeed a very large number of minerals1 evolve hydrogen when heated1 the gas having been 8occluded0 in their pores4 ,in #aggb he communicated privately to ,dr4 ,priestley the results of a series of experiments dealing with nitrogen4 ,to prepare it1 he passed air repeatedly over red-hot charcoal1 and absorbed the resulting carbon dioxide in potash4 ,the residue was nitrogen4 ,his description of it is3--8,the specific gravity of this air was found to differ very little from that of common air2 of the two it seemed rather lighter4 ,it extinguished flame1 and rendered common air unfit for making bodies burn in the same manner as fixed air1 but in a less degree1 as a candle which burned about #hj seconds in pure common air1 and which went out immediately in common air mixed with #f_/eeths of fixed air1 burned about #bf seconds in common air mixed with the same proportion of this burnt air40#bc ,he named it1 as usual1 8mephitic air10 and it is certain that1 although ,cavendish did not publish his results1 his discovery was not later in date than ,rutherford's4 ,dealing next with the phenomena observed when that curious fish1 the torpedo1 produces shocks1 he ascribed them to the discharge of electricity1 and he was the first to distinguish between intensity1 or potential1 and quantity of electricity1 a distinction now familiar to all4 ,it was in #aggg that he commenced his beautiful 8,experiments on ,air10 the first account of which was published in #aghc4 ,they led to the discovery of the constant quantitative composition of the atmosphere1 of the compound nature of water1 and of the composition of nitric acid1 and pointed the way to the recent discovery of argon4 ,in determining the composition of the atmosphere1 ,cavendish made use of nitric oxide in presence of water1 as a means of removing oxygen4 ,this process1 originally devised by ,mayow1 was rediscovered by ,priestley1 who employed it to ascertain the 8goodness0 of various samples of air2 in ,cavendish's hands it became an accurate quantitative method4 ,the title of his paper1 published in the ,philosophical ,transactions for #aghc1 is 8,of a new ,eudiometer40 ,the term 8eudiometer10 signifying 8measurer of goodness10 was devised when it was supposed that ordinary air presented considerable variations in its power of supporting respiration and combustion1 according to the seasons1 and according to the place from which it was collected4 ,dr4 ,ingenhousz had found a greater absorption when air from near the sea-coast was tested by ,priestley's method with nitric oxide1 than when town-air was employed2 and he ascribed the salubrious nature of sea-air to its being richer in 8vital air40 ,the ,abb ,fontana1 too1 had made similar experiments1 and had come to similar conclusions4 ,cavendish modified ,fontana's apparatus1 rendering it capable of giving more accurate results2 and during the last half of the year #agha he analysed the air collected on sixty days1 some fine1 some wet1 and some foggy4 ,he also collected air from different localities1 sometimes at ,marlborough ,street1 sometimes at ,kensington1 which was then a country village4 ,the results of his analyses establish as the composition of air1 freed from carbon dioxide by potash3 #giaf per cent of phlogisticated air 7nitrogen74 #bjhd per cent of dephlogisticated air 7oxygen74 ,this result does not differ materially from those obtained by the best modern analyses1 which give1 within very small variations3 #gijd per cent of nitrogen and argon1 #bjif per cent of oxygen1 after absorption of carbon dioxide1 ammonia1 and water-vapour4 ,in the following year1 #aghd1 ,cavendish published the first of his great memoirs1 entitled ,experiments on ,air4 ,his experiments were made principally 8with a view to find out the cause of the diminution which common air is well known to suffer by all the various ways in which it is phlogisticated1 and to discover what becomes of the air thus lost or condensed40 ,cavendish chose processes for 8phlogisticating0 air in the course of which no fixed air should be produced4 ,he therefore avoided the use of animal and vegetable materials1 and confined himself to combustibles1 such as sulphur or phosphorus1 to the calcination of metals1 the explosion of inflammable air1 and the mixture of nitrous air4 ,he adds as a suggestion1 8,perhaps it may be supposed that ,i ought to add to these the electric spark2 but ,i think it much more likely that the phlogistication of the air1 and production of fixed air1 in this process is owing to the burning of some inflammable matter in the apparatus40 ,we shall see later what magnificent results arose from this last mode of 8phlogisticating0 air4 ,he begins with an account of a repetition of an experiment of ,mr4 ,waltire's1 related by ,priestley1 in which a mixture of hydrogen and air was exploded in a copper vessel1 with the result that they observed a loss of a few grains in weight2 it is also stated by ,waltire that if the explosion took place in a glass vessel1 it became dewy1 8which confirmed an opinion he had long entertained1 that common air deposits its moisture by phlogistication40 ,but ,cavendish1 using a glass vessel of much greater capacity than ,waltire's1 could remark no change of weight2 and he concluded that #dbc measures of hydrogen1 or 8inflammable air0 as he named it1 are 8nearly sufficient to completely phlogisticate #ajjj of common air1 and that the bulk of the air remaining after the explosion is then very little more than ths of the common air employed2 so that1 as common air cannot be reduced to a much less bulk than that1 by any method of phlogistication1 we may safely conclude that1 when they are mixed in this proportion and exploded1 almost all the inflammable air1 and about th part of the common air1 lose their elasticity1 and are condensed into the dew which lines the glass4 8,the better to examine the nature of this #8dew1' #ejj1jjj grain measures of inflammable air were burnt with about #b times that quantity of common air1 and the burnt air made to pass through a glass cylinder #h feet long and about of an inch in diameter1 in order to deposit the dew04 8,by this means upwards of #ace grains of water were condensed in the cylinder1 which had no taste or smell1 and which left no sensible sediment when evaporated to dryness1 neither did it yield any pungent smell during the evaporation2 in short1 it seemed pure water04 8,and by this experiment it appears that this dew is plain water1 and consequently that almost all the inflammable and about th of the common air are turned into pure water40 ,but on firing little by little a mixture of 8dephlogisticated air0 or oxygen1 obtained from red precipitate 7that is1 mercuric oxide prepared by heating the nitrate71 with twice its volume of 8inflammable air0 or hydrogen1 the resulting water was acid to the taste1 and on evaporation with alkali gave a small quantity--about #b grains--of nitre4 ,cavendish suspected that the acid came from the nitrate of mercury in his red precipitate1 and1 to test this1 procured his oxygen from other sources--from red-lead and sulphuric acid1 and from the leaves of plants--but still with the same result2 nitric acid was formed4 ,repeating the experiment so as to have present an excess of hydrogen1 he found that no acid was produced4 8,from the foregoing experiments it appears that when a mixture of inflammable and dephlogisticated air is exploded in such proportion that the burnt air is not much phlogisticated1 the condensed liquor contains a little acid1 which is always of the nitrous kind1 whatever substance the dephlogisticated air is procured from2 but if the proportion be such that the burnt air is almost entirely phlogisticated1 the condensed liquor is not at all acid1 but seems pure water1 without any addition whatever2 and as1 when they are mixed in that proportion1 very little air remains after the explosion1 almost the whole being condensed1 it follows that almost the whole of the inflammable and dephlogisticated air is converted into pure water40 ,the quantity of uncombined gas was so small that it must be regarded as an impurity4 8,there can be little doubt that it proceeds only from the impurities mixed with the dephlogisticated and inflammable air1 and consequently that if those airs could be obtained perfectly pure1 the whole would be condensed40 ,the next paragraph is interesting4 8,during the last summer also of #agha a friend of mine gave some account of them these experiments to ,mr4 ,lavoisier1 as well as of the conclusion drawn from them1 that dephlogisticated air is only water deprived of phlogiston2 but at that time1 so far was ,mr4 ,lavoisier from thinking any such opinion warranted1 that1 till he was prevailed upon to repeat the experiment himself1 he found some difficulty in believing that nearly the whole of the two airs could be converted into water40 ,and next comes an important deduction4 8,phlogisticated air appears to be nothing else than the nitrous acid united to phlogiston2 for when nitre is deflagrated with charcoal1 the acid is almost entirely converted into this kind of air40 ,this is the first statement of the true relation between nitrogen and nitric acid2 we should now state the matter by the expression1 8,nitrogen is nothing else than nitric acid deprived of oxygen40 ,and the further deduction is made that 8it is well known that nitrous acid is also converted by phlogistication into nitrous air1 in which respect there seems a considerable analogy between that and the vitriolic acid2 for this acid1 when united to a smaller proportion of phlogiston1 forms the volatile sulphurous acid and vitriolic acid air1 both of which1 by exposure to the atmosphere1 lose their phlogiston1 though not very fast1 and are turned back into the vitriolic acid2 but when united to a greater proportion of phlogiston1 it forms sulphur1 which shows no signs of acidity40 8,in like manner the nitrous acid1 united to a certain quantity of phlogiston1 forms nitrous acid and nitrous air1 which readily quit their phlogiston to common air2 but when united to a different1 in all probability a larger quantity1 it forms phlogisticated air1 which shows no signs of acidity1 and is still less disposed to part with its phlogiston than sulphur40 ,but the origin of the acid in water made from inflammable and dephlogisticated air was still unexplained4 ,to settle this point ,cavendish added to an explosive mixture of oxygen and hydrogen a tenth of its volume of nitrogen1 and found that the water was much more strongly acid2 and if hydrogen was much in excess1 a still greater amount of nitric acid was produced4 ,after relating these experiments he proceeds3-- 8,from what has been said there seems the utmost reason to think that dephlogisticated air is only water deprived of its phlogiston1 and that inflammable air1 as was before said1 is either phlogisticated water or else pure phlogiston1 but in all probability the former40 ,in a foot-note he gives his reason for the choice1 viz4 that it requires a red-heat to cause hydrogen and oxygen to combine1 while nitrous air combines with oxygen at the ordinary temperature2 now1 if hydrogen were pure phlogiston1 one would expect it to combine more readily than nitrous gas1 which has been shown to be a compound of nitric acid with phlogiston4 ,it seems inexplicable that dephlogisticated air should refuse to unite at the ordinary temperature with pure phlogiston1 when it is able to extract it from substances with which it has an affinity4 ,hence it is unlikely that hydrogen is phlogiston itself4 ,and a few paragraphs farther on ,cavendish very nearly discards the phlogistic theory by this statement3 8,instead of saying air is phlogisticated or dephlogisticated by any means1 it would be more strictly just to say1 it is deprived of1 or receives1 an addition of dephlogisticated air2 but as the other expression is convenient1 and can scarcely be considered as improper1 ,i shall still frequently make use of it in the remainder of this paper40 ,and now we come to the consideration of ,lavoisier's new theory1 and its rejection in favour of the old one of phlogiston4 ,it is curious to follow the reasoning which made such an exceptionally acute thinker as ,cavendish deliberately reject the true explanation4 ,cavendish first states his results in ,lavoisier's terms3-- 8,according to this hypothesis1 we must suppose that water consists of inflammable air united to dephlogisticated air2 that nitrous air1 vitriolic acid air 7sulphur dioxide71 and the phosphoric acid are also combinations of phlogisticated air1 sulphur1 and phosphorus with dephlogisticated air2 and that the two former1 by a further addition of the same substance1 are reduced to the common nitrous and vitriolic acids2 that the metallic calces consist of the metals themselves united to the same substance1 commonly1 however1 with a mixture of fixed air2 that on exposing the calces of the perfect metals to a sufficient heat1 all the dephlogisticated air is driven off1 and the calces are restored to their metallic form2 but as the calces of the imperfect metals are vitrified by heat1 instead of recovering the metallic form1 it should seem as if all the dephlogisticated air could not be recovered from them by heat alone4 ,in like manner1 according to this hypothesis1 the rationale of the production of dephlogisticated air from red precipitate is1 that during the solution of the quicksilver in the acid and the subsequent calcination1 the acid is decompounded1 and quits part of its dephlogisticated air to the quicksilver1 whence it comes over in the form of nitrous air1 and leaves the quicksilver behind united to dephlogisticated air1 which1 by a further increase of heat1 is driven off1 while the quicksilver resumes its metallic form4 ,in procuring dephlogisticated air from nitre1 the acid is also decompounded2 but with this difference1 that it suffers some of its dephlogisticated air to escape1 while it remains united to the alkali itself in the form of phlogisticated nitrous acid4 ,as to the production of dephlogisticated air from plants1 it may be said that vegetable substances consist chiefly of three different bases1 one of which hydrogen1 when united to dephlogisticated air1 forms water2 another carbon fixed air2 and the third phlogisticated air nitrogen2 and that1 by means of vegetation1 each of these substances are decomposed1 and yield their dephlogisticated air2 and that1 in burning1 they again acquire dephlogisticated air1 and are restored to their pristine form4 8,it seems1 therefore1 from what has been said1 as if the phenomena of nature might be explained very well on this principle1 without the help of phlogiston2 and indeed1 as adding dephlogisticated air to a body comes to the same thing as depriving it of its phlogiston and adding water to it1 and as there are perhaps no bodies destitute of water1 and as ,i know no way by which phlogiston may be transferred from one body to another1 without leaving it uncertain whether water is not at the same time transferred1 it will be very difficult to determine by experiment which of these opinions is the truest2 but as the commonly-received principle of phlogiston explains all phenomena1 at least as well as ,mr4 ,lavoisier's1 ,i have adhered to that40 8,another thing which ,mr4 ,lavoisier endeavours to prove is that dephlogisticated air is the acidifying principle4 ,from what has been explained1 it appears that this is no more than saying that acids lose their acidity by uniting to phlogiston1 which1 with regard to the nitrous1 vitriolic1 phosphoric1 and arsenical acids1 is certainly true04 8,but as to the marine acid and acid of tartar1 it does not appear that they are capable of losing their acidity by any union with phlogiston40 ,here ,cavendish does not consider the question of gain of weight on loss of phlogiston1 or if he does1 he must ascribe it to simultaneous entry of water4 ,and experimental research at that time was not far enough advanced to enable him to decide finally as to the truth of this hypothesis4 ,in his next memoir1 read before the ,royal ,society on ,june #bnd1 #aghe1 ,cavendish relates experiments on the passage of electric sparks through air1 the experiment having first been tried by ,priestley4 ,priestley says3#bd--8,lastly1 the same effect i4e4 the diminution of the volume of common air1 ,i find1 is produced by the electric spark1 though ,i had no expectation of this event when ,i made the experiment40 ,and again3--8,at the time of my former publication1 ,i had found that taking the electric spark in given quantities of several kinds of air had a very remarkable effect on them1 that it diminished common air and made it noxious1 making it deposit its fixed air exactly like any phlogistic process2 from whence ,i concluded that the electric matter either is or contains phlogiston40 ,cavendish had mentioned this process casually as one of the methods of phlogisticating air2 in beginning his second paper he says3--8,i now find that1 though ,i was right in supposing the phlogistication of the air does not proceed from phlogiston communicated to it by the electric spark1 and that no part of the air is converted into fixed air2 yet that the real cause of the diminution is very different from what ,i suspected1 and depends upon the conversion of phlogisticated air into nitrous acid40 ,the apparatus he used was very simple4 ,it consisted of a glass siphon filled with mercury1 each leg dipping into a glass likewise containing mercury2 the air was admitted by a gas-pipette into the bend of the siphon1 and on connecting the mercury in one of the glasses with a ball placed near the prime conductor of an electric machine1 and the other with the earth1 sparks could be made to pass from the mercury in one limb to that in the other4 ,the product obtained by passing sparks through air in this manner turned litmus red1 and gave rise to no cloud in lime-water1 while the air was reduced to two-thirds of its original volume2 nor did the lime-water give a precipitate on introducing some fixed air1 this showing that it had been saturated by an acid4 ,it was found1 too1 that 8soap-lees10 or solution of caustic potash1 if present1 diminished the volume more rapidly than did lime-water2 and repeated trials proved that 8when five parts of pure dephlogisticated air were mixed with three parts of common air1 almost the whole of the air was made to disappear40 ,the nitrate of potassium thus produced caused paper soaked in it and dried to deflagrate2 and it contained no sulphuric acid4 8,there is no reason to think that any other acid entered into it except the nitrous40 ,but it gave a precipitate with silver nitrate2 and ,cavendish1 suspecting that this was silver nitrite1 prepared some potassium nitrite by heating the nitrate2 on comparing the white precipitate which this solution gave with silver nitrate with that obtained from his 8soap-lees10 he found them identical4 ,there was therefore no 8muriatic acid0 present1 which would have yielded chloride of silver1 of appearance somewhat similar to the nitrite4 ,as it had previously been shown to be probable that phlogisticated air is nitrous air united with phlogiston1 and that nitrous air is nitric acid united with phlogiston1 8we may safely conclude that in the present experiments the phlogisticated air was enabled1 by means of the electric spark1 to unite to1 or form a chemical combination with1 the dephlogisticated air1 and was thereby reduced to nitrous acid1 which united to the soap-lees and formed a solution of nitre2 for in these experiments the two airs actually disappeared1 and nitrous acid was actually formed in their room04 8,a further confirmation of the above-mentioned opinion is that1 as far as ,i can perceive1 no diminution of air is produced when the electric spark is passed either through pure dephlogisticated air or through perfectly phlogisticated air1 which indicates a necessity of a combination of these two airs to produce the acid4 ,moreover1 it was found in the last experiment that the quantity of nitre procured was the same that the soap-lees would have produced if saturated with nitrous acid2 which shows that the production of the nitre was not owing to any decomposition of the soap-lees40 ,nothing more clearly shows the care with which ,cavendish reasoned than these last quotations4 ,no loophole is left unstopped2 every precaution is taken to make the proof as faultless as it is possible for a proof to be4 ,but this was not enough4 ,it was necessary for ,cavendish to show that1 so far as he could ascertain it experimentally1 all the phlogisticated air was capable of combining with dephlogisticated air to form nitre4 ,this he next proceeded to do4 8,as far as the experiments hitherto published extend1 we scarcely know more of the phlogisticated part of our atmosphere than that it is not diminished by lime-water1 caustic alkalies1 or nitrous air2 that it is unfit to support fire or maintain life in animals2 and that its specific gravity is not much less than that of common air2 so that though the nitrous acid1 by being united to phlogiston1 is converted into air possessed of these properties1 and consequently1 though it was reasonable to suppose that part at least of the phlogisticated air of the atmosphere consists of this acid united to phlogiston1 yet it might fairly be doubted whether the whole is of this kind1 or whether there are not in reality many different substances confounded together by us under the name of dephlogisticated air4 ,i therefore made an experiment to determine whether the whole of a given portion of the phlogisticated air of the atmosphere could be reduced to nitrous acid1 or whether there was not a part of a different nature from the rest1 which would refuse to undergo that change4 ,the foregoing experiments1 indeed1 in some measure decided this point1 as much the greatest part of the air let up into the tube lost its elasticity2 yet1 as some remained unabsorbed1 it did not appear for certain whether that was of the same nature as the rest or not4 ,for this purpose ,i diminished a similar mixture of dephlogisticated and common air in the same manner as before1 till it was reduced to a small part of its original bulk4 ,i then1 in order to decompound as much as ,i could of the phlogisticated air which remained in the tube1 added some dephlogisticated air to it1 and continued the spark until no further diminution took place4 ,having by these means condensed as much as ,i could of the phlogisticated air1 ,i let up some solution of liver of sulphur to absorb the dephlogisticated air2 after which only a small bubble of air remained unabsorbed1 which certainly was not more than #a_/abjth of the bulk of the phlogisticated air let up into the tube2 so that1 if there is any part of the phlogisticated air of our atmosphere which differs from the rest1 and cannot be reduced to nitrous acid1 we may safely conclude that it is not more than #a_/abjth part of the whole40 ,we shall afterwards see that this is a marvellously close estimate4 ,there is actually #a_/hdth part of the supposed nitrogen of the air which will not combine with oxygen when sparked with it in presence of potash4 ,but there still remained1 in ,cavendish's opinion1 one point unproved4 ,it was still conceivable that the potash might contain some 8inflammable matter0 which would diminish the air on sparking1 and therefore oxygen nearly pure was sparked in presence of potash2 but only a very small diminution of volume occurred1 owing probably to some nitrogen present as an impurity in the oxygen4 ,water was substituted for potash with the same result2 but if litmus was added to the water the colour was discharged1 and lime-water introduced into the tube gave a cloud1 showing that 8the litmus1 if not burnt1 was at least decompounded1 so as to lose entirely its purple colour and to yield fixed air2 so that1 though soap-lees cannot be decompounded by the process1 yet the solution of litmus can1 and so very likely might the solutions of many other combustible substances40 ,such are the chemical researches of ,cavendish4 ,of all experimenters on the subject he was undoubtedly the greatest1 though ,mayow and ,scheele were near rivals4 ,but his researches were so complete that it is scarcely possible to criticise4 ,he was not content with partial results3 every point was proved and re-proved1 and every possibility of erroneous conclusion was allowed for4 ,it is curious that he did not employ the balance to check his results4 ,had he done so he could not have remained an adherent of the phlogistic theory4 ,although1 as we have seen1 he was perfectly acquainted with the method in which his results were interpreted by ,lavoisier1 he chose the old well-trodden path leading to the wilderness of distorted facts4 ,lavoisier tried to repeat ,cavendish's experiments1 but without success2 and in #aghh the last part of his ,experiments on ,air was published1 in which he recorded the successful repetition by a ,committee of the ,royal ,society of the conversion of nitrogen into nitric acid by the electric spark in presence of oxygen and potash4 ,his remaining papers deal with meteorological and astronomical subjects4 ,one1 published in #agij1 refers to the height of a remarkable aurora seen in #aghd2 another to the civil year of the ,hindoos2 and another to a method for reducing lunar distances4 ,and in #agih his famous memoir on the density of the earth appeared4 ,it would be quite beyond the province of this book to enter into any detail regarding it2 but it may be remarked in passing that the method consisted in measuring1 by means of a torsion balance1 the attraction of one leaden ball for another1 and that recent experiments1 made with the utmost refinement1 have barely altered the number which he obtained1 #ed1 to #eebg4 ,his last paper1 on an improvement in a machine for dividing astronomical instruments1 was published in #ahji1 the year before his death4 ,nothing has been said here regarding the rival claims of ,watt to the discovery of the composition of water1 and little need be said4 ,the discovery was made by both in #aghd1 yet ,cavendish visited ,watt at ,birmingham in #aghe1 and was apparently on the best of terms with him2 and ,watt1 as proved by ,cavendish's diary1 showed him many of his devices connected with the steam-engine4 ,there can be no doubt that ,watt had also discovered that when hydrogen and oxygen are exploded together water is the sole product1 but he coupled the phenomenon with views involving the material nature of heat1 or caloric1 as it was then called1 which ,cavendish repudiated4 ,cavendish's later work was carried out in a villa at ,clapham1 which was fitted as a laboratory1 workshop1 and observatory1 but he had a town-house near the ,british ,museum1 at the corner of ,gower ,street and ,montague ,place4 ,he had also a library in ,dean ,street1 ,soho1 which was available for any scientific man who chose to present himself4 ,so singular were ,cavendish's habits that when he wished a book he went to this house and borrowed it as from a public library1 giving a receipt for it4 ,of all men1 ,cavendish was probably the most singular1 but there can be no question of his extraordinary genius4 #bc ,brit4 ,assoc4 ,report1 #ahci1 p4 #fd4 #bd ,experiments and ,observations on ,different ,kinds of ,air1 vol4 i4 p4 #aha1 and vol4 ii4 p4 #bch4 ,second edition1 #aggf4 ,,chapter ,v ,,the ,,discovery ,,of ,,argon ,with the advent of ,lavoisier's system of representing the phenomena of combustion1 and the expression in his terms of the various changes resulting in air when metals are oxidised1 and when carbonaceous substances burn1 the investigation of air was abandoned4 ,it was no longer regarded as a mysterious element1 possessed of 8chaotic0 properties1 but was held to be a mixture of oxygen1 nitrogen1 and small quantities of carbon dioxide and water vapour1 together with a trace of ammonia4 ,more exact determinations of the proportion between its oxygen and so-called nitrogen than ,cavendish had made by the nitric oxide method were carried out in #ahjd by ,gay-,lussac and ,humboldt1 by explosion with measured quantities of hydrogen1 according to the method suggested by ,volta2 and they concluded1 from a large number of analyses made on specimens collected in all weathers and from various localities1 that #ajj volumes of air contained #ba volumes of oxygen and #gi volumes of nitrogen4 ,these experiments1 too1 led ,gay-,lussac to the conviction that oxygen and hydrogen unite to form water in the exact proportion of one volume of the former to two volumes of the latter2 and he published1 some years later1 accounts of numerous experiments of the same kind1 as the result of which he found that1 when two gases combine or react with each other1 they do so in some simple number of volumes2 for example1 one to one1 one to two1 or one to three4 ,the almost constant relation between the volumes of oxygen and nitrogen in air made it appear not unlikely1 in the opinion of some1 that air was a compound1 and not a mixture2 for the law of combination in definite proportions had by this time been enunciated by ,professor ,thomas ,thomson1 ,dalton's intimate friend4 ,but between the numbers #ba and #gi there exists no such simple ratio2 and1 moreover1 on artificially producing air by mixing oxygen and nitrogen1 there are none of the usual phenomena which characterise the formation of a compound3 there is no rise or fall of temperature1 nor does the product differ in any way in properties from the constituents4 ,and in #ahdf ,bunsen showed that the proportion between oxygen and nitrogen is not a constant one1 but that the oxygen varies between #bjig and #bjhd2 the experimental error did not exceed #jjc volume1 while the difference found amounted to #jac volume4 ,regnault1 ,angus ,smith1 ,a4 ,r4 ,leeds1 and von ,jolly confirmed these results at later dates1 from analyses of air collected from all parts of the world4 ,that air contains ammonia was first observed by ,scheele4 ,he found that the stopper of a bottle containing muriatic acid1 when exposed to air became covered with a film or deposit which he recognised to be sal ammoniac1 or ammonium chloride4 ,the amount of ammonia in atmospheric air is1 however1 exceedingly small1 and it is best detected in rain-water1 which dissolves it2 thus the air is considerably poorer in ammonia after a shower4 ,the ammonia1 small though its proportion is1 plays a great part1 although not an exclusive one1 in yielding to plants their supply of nitrogen4 ,the rain1 percolating through the soil1 leaves the ammonia behind1 in some form of combination2 and it is then attacked by the nitrifying ferments and converted into nitrates1 from which the plants derive the nitrogen which forms part of their substance1 in combination with carbon1 oxygen1 and hydrogen4 ,there are also traces of nitric and nitrous acids in air1 which are apparently in combination with ammonia4 ,while the ammonia has been found to vary between #ja and #ajj volumes per million volumes of air--the latter number refers to ,manchester streets--nitrous and nitric acids are present in still smaller amounts2 and in spite of the widespread opinion that ozone is contained in air1 its occurrence is still a matter of dispute4 ,that some powerful oxidising agent such as ozone or hydrogen peroxide is present appears certain2 but the characteristic test for ozone--the formation of peroxide of silver on exposure of metallic silver to its influence--has never been successful4 ,on the other hand1 a small quantity of hydrogen dioxide--also1 like water1 a compound of oxygen and hydrogen1 but one containing more oxygen than water--appears to be almost constantly present in air4 ,its amount is also extremely minute3 it does not exceed one part per million4 ,its presence in air was discovered by ,schnbein4 ,the atmosphere further contains dust1 some of which appears to consist largely of metallic iron1 which is conjectured to be of extraterrestrial origin--minute meteorites in fact--and also the spores of micro-organisms2 but these spores1 however important from a biological or a sanitary point of view1 hardly come within the scope of the chemical composition of air4 ,they serve to emphasise the conjectures of ,boyle and of ,scheele that air may contain 8corpuscles0 of all sorts1 some in the form of dry exhalations1 while other innumerable particles may be sent out from the celestial luminaries4 99 99 99 99 99 ,up to within the last few years it was supposed that the constituents of air had all been discovered4 ,but ,lord ,rayleigh and ,professor ,william ,ramsay have recently found that the supposed nitrogen of the air is in reality a mixture of nitrogen with a new gaseous element1 to which they have given the name 8argon10 on account of its chemical inactivity 71 idle1 inactive74 ,in his presidential address to ,section ,a of the ,british ,association at ,southampton in #ahhb1 ,lord ,rayleigh alluded to an investigation which he had begun on the densities of hydrogen and oxygen1 relatively to each other4 ,the object of the research was to discover whether the atomic weights of these gases1 determinable from their densities and from the proportions by volume in which they combine1 was actually as #a to #af1 or whether some fractional number was necessary to express the weight of an atom of oxygen relatively to that of hydrogen4 ,in #ahhh his first account of the determination was published in the ,proceedings of the ,royal ,society4 ,in #ahhi he published a continuation of his first paper1 and in #ahib he gave his final results2 the number obtained was #aehhb for the atomic weight of oxygen1 calculated from its density1 hydrogen being taken as #a4 ,in #ahic further experiments on densities were published1#be those of oxygen and nitrogen being specially considered with reference to the density of air4 ,he found the weights of one litre of oxygen1 nitrogen1 and air to be ,oxygen #adbieb grams 8,nitrogen0 #abegah ,air #abicbg ,a simple calculation leads to the composition of purified air4 ,the percentage of oxygen must be #bjida1 and that of 8nitrogen0 #gijei1 in order to give a mixture of which the weight of a litre is #abicbg4 ,now1 this corresponds with the results of the best analyses1 quoted above4 ,and the accuracy of these determinations of density is confirmed by this means1 as well as by results of other experiments made by ,leduc1 von ,jolly1 and ,morley4 ,but ,lord ,rayleigh was not content to prepare his gases by one process only4 ,the oxygen1 of which the mean value of the weight of a litre is given above1 was prepared in three different ways3 by the electrolysis of water1 by heating chlorates1 and by heating potassium permanganate4 ,the results showed that the only difference which could be detected1 and that an extremely minute one1 must be attributed to experimental error4 ,the actual weights of the contents of his globe were-- ,electrolysis1 ,may #ahib #bfbgb grams #bfbga ,heating chlorates1 ,may #ahib #bfbfi ,june #bfbfi ,heating permanganate1 ,january #ahic #bfbga ,these numbers are subject to a deduction of #jjjjef1 due to the fact that when the globe was empty of air1 its capacity was somewhat reduced1 owing to the external pressure of the atmosphere4 ,it was next deemed necessary to test whether nitrogen was homogeneous by preparing it too by several different methods4 ,in the same paper ,lord ,rayleigh 7p4 #adf7 mentions that nitrogen1 prepared from ammonia1 its compound with hydrogen1 is somewhat lighter than 8atmospheric nitrogen10 the deficiency in weight amounting to about #a part in #bjj4 ,now it is evident from inspection of the numbers quoted above1 that the accuracy of the density determination may be trusted to within #a part in #aj1jjj1 and that the balance would detect a discrepancy one-fiftieth of that observed in the densities of 8atmospheric0 and 8chemical0 nitrogen4 ,in a letter to ,nature1 ,lord ,rayleigh asked for suggestions from chemists as to the reason of this curious anomaly1 but his letter went without reply4 ,he himself was inclined to believe that the difference was due to the decomposition of some of the ordinary molecules of nitrogen1 usually believed to consist of two atoms in union with each other1 into molecules consisting of one atom2 and as it is held that equal numbers of molecules inhabit the same volume1 temperature and pressure being equal1 if the total number of molecules in his globe were increased by the splitting of some double-atom molecules into single-atom molecules1 the effect would be that1 owing to an admixture of some lighter molecules1 the density would be somewhat reduced4 ,but two other suppositions were entertained as possible4 ,the oxygen might have been imperfectly removed from the nitrogen derived from the atmosphere2 or1 on the other hand1 the nitrogen from ammonia might conceivably have retained traces of hydrogen4 ,in the former case1 the nitrogen would have an increased weight owing to admixture of some heavier oxygen2 in the latter1 a diminished weight1 due to the presence of the lighter hydrogen4 ,the first of these suppositions is out of the question1 inasmuch as it would have required that the nitrogen should contain one-thirtieth of its volume of oxygen1 or one-sixth of that present in air1 in order that its density should be raised by one two-hundredth2 for the densities of oxygen and nitrogen are not so very different4 ,the second supposition was negatived by introducing hydrogen purposely1 and removing it by passing the gas over red-hot copper oxide1 which oxidises the hydrogen to water4 ,this yielded nitrogen of the same density as that which had not undergone that treatment4 ,one other possibility was considered3 the atmospheric nitrogen might contain some molecules of greater complexity than two-atom molecules1 say ,n#c-molecules4 ,now it is known that when oxygen is electrified by the passage of a rain of small sparks through it1 it acquires new properties3 it possesses an odour1 and attacks metallic mercury and silver4 ,and this product1 ozone1 has been shown to consist of three-atom molecules of oxygen1 by various experiments of which an account cannot be given here4 ,it was not inconceivable that if such a 8silent electric discharge0 were to be passed through 8atmospheric0 nitrogen1 it might increase the number of such three-atom molecules1 and might render the gas still denser2 or if passed through 8chemical0 nitrogen1 it might increase its density so as to make it equal to that of 8atmospheric0 nitrogen4 ,lord ,rayleigh made such experiments1 but without changing the density in the least3 the nitrogen from ammonia or from oxides of nitrogen1 which has been termed 8chemical0 nitrogen1 still remained too light by about one two-hundredth1 and the atmospheric nitrogen still remained too heavy by the same amount4 ,at this stage ,professor ,ramsay asked and received permission to make some experiments on the nitrogen of the atmosphere1 with the view of explaining its anomalous behaviour4 ,he had several years before made experiments on the possibility of causing nitrogen and hydrogen to combine directly1 by passing the mixture over heated metals2 among these was magnesium1 and although no direct combination to any great extent was observed1 still it was noticed that magnesium was a good absorbent for nitrogen1 when that gas was passed over the red-hot filings of the metal4 ,this process was therefore applied to the absorption of 8atmospheric0 nitrogen1 in order to find out whether any portion of it was different from the rest4 ,the plan adopted was to heat turnings of magnesium1 which can be made very thin and loose1 to redness in a tube of hard glass1 in contact with the nitrogen of the atmosphere1 carefully purified from oxygen1 which would otherwise have also combined with the metallic magnesium4 ,as absorption proceeded1 more nitrogen was admitted from a reservoir1 and after a certain quantity had been absorbed1 the residual gas was extracted from the tube by a mercury pump1 and weighed4 ,the amount weighed was very small1--smaller perhaps than had up till then been thought possible1 if accurate results were to be obtained4 ,but here large differences were to be looked for4 ,only #dj cubic centimetres--the twenty-fifth part of a litre--was weighed2 and its weight was only #jjej gram4 ,but with careful weighing the error should not exceed one five-hundredth of the amount weighed2 and if there were to be any increase in density1 that increase should be expected greatly to exceed this small fraction4 ,the first weighing--in ,may #ahid--showed that the nitrogen had increased in density by reason of the operations1 and instead of being fourteen times as heavy as hydrogen1 it was nearly fifteen times as heavy4 ,illustration3 ,,fig4 #a4 ,the result was encouraging1 and led to the probability of the nitrogen being altered in some way1 or of the presence of some new component of the atmosphere4 ,an experiment was therefore begun on a larger scale1 the atmospheric nitrogen being passed backwards and forwards from one large glass gasholder ,a to another ,b1 through a tube filled with magnesium heated to redness ,g1 to absorb nitrogen2 over red-hot copper oxide 7a7 7b71 so that any carbonaceous matter such as dust should be oxidised to carbon dioxide and water2 and these1 if produced1 were absorbed by placing in the train of tubes1 one filled with a mixture of soda and lime ,f and ,i1 to absorb any carbon dioxide which might possibly be formed1 and two filled with pentoxide of phosphorus ,d and ,h1 to dry the gas1 so that water-vapour1 carried along with the gas from the gasholders 7which contained water7 might be removed before the gas passed over the red-hot magnesium2 for water acts on hot magnesium1 forming oxide of magnesium and hydrogen1 and the gas would have become contaminated with the latter had this precaution not been taken4 ,the process was continued for ten days1 by which time most of the nitrogen had become absorbed4 ,the apparatus was then somewhat altered1 so as to make it possible to work with a smaller quantity of gas2 but the tubes destined to absorb nitrogen1 hydrogen1 etc41 were filled with the same materials as before4 ,in a few days more the volume was reduced to one-seventh of what it had been when the transference to the smaller apparatus was made1 or about one-eightieth of the original volume of the atmospheric nitrogen taken4 ,the gas was then weighed1 this time in a larger bulb1 the weight being #jbaij gram2 and such is the possibility of precision in weighing on a good balance1 that a difference of one two-thousandth of the whole weight was detectable4 ,the density of the gas was now found to be #afa4 ,at this stage it was still believed that the new gas was an ozone-like modification of nitrogen1 difficult to attack by magnesium4 ,it was supposed that just as oxygen1 when exposed to an electric discharge1 undergoes a cleavage of its molecules1 two-atom molecules becoming one-atom molecules for an instant1 which then unite to form three-atom molecules1 so the action of the magnesium on the nitrogen might be to withdraw one atom of nitrogen from the two-atom molecule1 leaving a single uncombined atom1 which might not improbably find two partners1 each of its own kind1 to form with them a three-atom molecule--a sort of nitrogen-ozone1 in fact4 ,hence it was resolved to continue the absorption with fresh magnesium for a still longer time1 in the hope of its being possible to isolate the three-atom nitrogen molecules4 ,but it became apparent that the bright metallic magnesium was now not much attacked2 and on estimating the total amount of nitrogen absorbed1 by treating the compound of nitrogen and magnesium with water1 and liberating the nitrogen as ammonia1 it appeared that only a small quantity of magnesium nitride had been formed4 ,the density of this further purified gas was again determined1 when it was found that a litre now weighed #agjed gram1 corresponding to a density of #aijhf4 ,a portion of this gas was mixed with oxygen and exposed to a rain of electric sparks in presence of caustic soda2 in fact1 ,cavendish's old plan of causing nitrogen to combine was now resorted to4 ,contraction occurred1 and on removing the excess of oxygen1 the diminution of volume was found to amount to #aed per cent of the original volume taken4 ,making the supposition that the gas of density #ai still contained nitrogen1 and allowing for its influencing the density1 it followed that the pure gas should be twenty times as heavy as hydrogen4 ,a tube such as is usually employed in examining the spectra of gases at low pressures was next filled with the gas of density #ai4 ,such a tube1 called a ,pflcker's tube1 after its inventor1 contains wires of platinum sealed through at each end1 where it is about half an inch in width2 the middle portion of the tube is about #c inches long1 and its bore is a fine capillary4 ,when the platinum wires are connected with the secondary terminals of a ,ruhmkorff's coil1 and the tube is partially exhausted1 a brilliant glow appears in the capillary portion4 ,if viewed through a glass prism1 different gases show different sets of coloured lines crossing the usual gradation of colours of the spectrum4 ,thus hydrogen exhibits three striking lines1 one bright red1 one peacock blue1 and one violet2 nitrogen shows a large number of somewhat hazy bands1 red1 orange1 yellow1 and yellow-green in colour1 besides a number of bands of a violet colour2 but the new gas1 while exhibiting the bands characteristic of nitrogen1 showed in addition certain groups of red and green lines which did not appear to belong to the spectrum of any known gas4 ,illustration3 ,,fig4 #b4 ,while these experiments were in progress1 ,lord ,rayleigh was occupied in preparing nitrogen from other sources1 and in determining its density2 and in every case it was evident that nitrogen from all sources except the atmosphere weighed somewhat less than atmospheric nitrogen4 ,he therefore proceeded to repeat ,cavendish's experiment1 and like ,cavendish1 he obtained a small residue of gas which would not disappear on sparking with oxygen1 in presence of caustic soda4 ,the sparks1 as they passed1 could be observed through a spectroscope 7which consists of an arrangement of prisms and lenses so designed as to examine the components of the light emitted by the sparks71 and he1 too1 was struck with the unusual character of the spectrum4 ,his experiments proved1 besides1 that the amount of residue was roughly proportional to the amount of air taken2 thus1 beginning with #ej cubic centimetres of air1 the residue was #jcb cubic centimetre2 and from #e cubic centimetres of air1 only #jjf cubic centimetre of gas was obtained4 ,these small amounts are not proportional to the quantities of air taken2 but1 as will afterwards be seen1 the discrepancy is owing to the solubility of the new gas in water4 ,still they served to show that from a comparatively large amount of air1 more of the new gas could be obtained than from a smaller amount4 ,at this stage the two discoverers joined forces1 and letters passed almost daily between them1 describing the results of experiments which one or other had made4 ,and just prior to the meeting of the ,british ,association at ,oxford in ,august #ahie1 it was decided that the proof of the existence of a new constituent gas in air was sufficiently clear to render it advisable to make to the ,association a short announcement of the discovery4 ,the statement was received with surprise and interest2 chemists were naturally somewhat incredulous that air1 a substance of which the composition had been so long and so carefully studied1 should yield anything new4 ,one of the audience inquired whether the name of this new substance had been discovered2 as a matter of fact it was then under consideration4 ,but it was still conceivable1 although improbable1 that the new gas was being produced by the very processes designed for its separation1 and attention was first turned to devising a complete proof of its actual presence in air4 ,now it is known that the rates of diffusion of gases through a narrow opening1 or through a number of minute holes1 such as exist in a pipe of porous clay1 e4g4 a tobacco-pipe stem1 are in inverse proportion to the square roots of the densities of the gases4 ,oxygen is1 in round numbers1 sixteen times as dense as hydrogen2 the square roots of #af and #a being #d and #a1 it was found by ,graham1 who first carefully investigated this subject1 that four times as much hydrogen would pass through a porous diaphragm1 in a given time1 as oxygen4 ,the compound of hydrogen and oxygen1 however1 in the state of gas1 viz4 steam1 is not separated by such a process into its constituents2 it diffuses as such1 and since it is nine times as dense as hydrogen1 the relative rates of diffusion of steam and hydrogen are as #a3 #i1 or as #a to #c2 that is1 for every #c parts of hydrogen passing through such a septum1 #a part of steam would pass in the same time4 ,an experiment was therefore devised1 in which a large quantity of air was made to stream slowly through a long train of stems of churchwarden tobacco-pipes1 placed inside a glass tube1 the latter being closed at each end1 except for the entrance and exit tubes of the tobacco-pipes2 in the encasing glass tube a vacuum was maintained1 and the gases1 passing through the walls of the pipe-stems1 were pumped off and discharged4 ,according to what has just been said1 these should be the lighter gases1 nitrogen and oxygen1 which ought to pass through the porous stems more quickly than the supposed heavier constituent of air2 while the air issuing from the end of the train of pipes should contain relatively more of the heavier constituent1 and should in consequence have a greater weight than an equal volume of air4 ,but it was obviously convenient to remove the oxygen before weighing this sample of altered air1 and this was done in the usual way by passing the mixed gases over red-hot copper4 ,it was found that such nitrogen was even heavier than ordinary atmospheric nitrogen2 not much1 it is true1 but still consistently heavier4 ,the denser constituent could1 in fact1 be concentrated by this means4 ,the proof was therefore indubitable that the new gas existed in air as such4 ,there is another method of proof1 however1 which was not left untried4 ,experiment showed that the solubility of the new gas in water is considerably greater than that of nitrogen1 although less than that of oxygen4 ,in #ajj volumes of water at the ordinary temperature1 about #ae volumes of nitrogen will dissolve1 about #de volumes of oxygen1 and about #d volumes of the new gas1 to which the name finally chosen for it1 8argon10 may now be applied4 ,now the proportion in which the constituents of a mixture of gases will dissolve in a solvent is conditioned first by their relative solubilities1 and second1 by their relative proportion4 ,thus1 if air be considered to be simply a mixture of #a volume of oxygen and #d volumes of nitrogen1 the gas extracted from water which has been shaken with air will have the composition-- ,oxygen #a x #de #de volumes ,nitrogen #d x #ae #fj ,so that the proportion of oxygen to nitrogen in such a mixture of gases is considerably greater than in air3 instead of being approximately #a to #d1 it is nearly #de to #f4 ,the discovery of this law concerning the composition of the gases dissolved in liquids was due to ,dr4 ,henry1 one of the biographers of ,dalton4 ,the gases can be almost entirely extracted by boiling the water4 ,but to boil large quantities of water at one operation in a vessel suitable for collecting the escaping gas is not easy4 ,it is much simpler to cause the water to pass slowly through a can below which there is a powerful flame1 so that the water in its passage becomes heated to the boiling-point1 and gives off its gas before it escapes4 ,of course the gas collected contained oxygen1 but this was easily removed by the usual method of passing it over red-hot copper4 ,the density of the residual gas was determined1 and it was found to be at least as much greater than that of 8atmospheric0 nitrogen as the density of 8atmospheric0 nitrogen exceeded that from chemical sources4 ,hence it was to be concluded that the new constituent of air1 argon1 was being concentrated by dissolving air in water1 and extracting the dissolved mixture of gases4 ,a third proof that argon exists in air will be given farther on4 ,illustration3 ,,fig4 #c4 ,in order that the properties of the newly-discovered gas1 argon1 might be thoroughly investigated1 it was necessary to prepare it on a much larger scale than had hitherto been attempted1 and this was carried out by the two processes for removing the oxygen and nitrogen which have been already described4 ,supposing the new gas to have the density #bj compared with oxygen as #af1 the density of the atmospheric mixture of nitrogen and argon compared with that of nitrogen alone shows that air should1 roughly speaking1 contain less than one part of argon in one hundred4 ,hence1 to obtain a litre of argon1 it was necessary to work up a large quantity of atmospheric nitrogen4 ,now1 as has just been said1 there are two ways of doing this4 7#a7 ,one is to produce an electric flame between two pieces of stout platinum in air1 confined in a large glass balloon of about #f litres capacity1 over a weak solution of caustic soda4 ,for this purpose a very powerful rapidly alternating current is necessary4 ,the latest1 and apparently the best1 method of carrying this out1 was described by ,lord ,rayleigh in his ,royal ,institution lecture in ,january #ahif4 ,the neck of the balloon is placed downwards1 and connected by means of a glass tube1 passing through a cork which closes the neck1 with a rotating fan or paddle-wheel with curved blades1 which forces through the tube a weak solution of caustic soda2 another tube1 also entering through the cork1 conveys away the excess of soda to the fan1 whence it is again forced into the balloon4 ,the soda solution makes a fountain in the balloon1 and flows in a uniform stream down its sides1 covering its inner surface with a thin layer of liquid4 ,through the cork the two electrodes1 with their thick platinum terminals1 enter2 and there is another tube besides1 which conveys into the balloon a mixture of air and oxygen in such proportions that they combine completely on exposure to the flame4 ,the layer of soda solution plays a double part4 ,it prevents the undue heating of the glass balloon1 which otherwise must be sunk in running water in order to keep it cool2 and it exposes a very large and constantly renewed surface of soda to the nitrous fumes which are produced by the combination of the nitrogen and the oxygen1 and so removes them as quickly as they are formed4 ,it appears probable that the union results initially in the formation of nitric oxide1 ,,no1 which then unites partially with oxygen to form some nitrogen peroxide1 ,,no#b4 ,this is absorbed by the soda1 giving a mixture of nitrite and nitrate of sodium1 ,na,n,o#b and ,na,n,o#c4 ,working in this way1 from #g to #h litres of mixed gases can be made to combine per hour4 ,the rapidly alternating current is best obtained by the use of a transformer2 and as the heating effect on the platinum terminals is very great1 they must be made of stout rods4 7#b7 ,to prepare a large quantity of argon by the absorption of atmospheric nitrogen by magnesium is a somewhat tedious process4 ,the air must be first freed from oxygen by means of red-hot copper1 and the atmospheric nitrogen collected in a gasholder4 ,long tubes of combustion-glass tubing1 which stands a bright red heat without becoming deformed1 are packed with magnesium turnings and heated to redness in long gas furnaces1 such as are used in organic analyses2 and through these the 8atmospheric nitrogen10 dried by passage over soda-lime and phosphorus pentoxide1 is then passed4 ,the magnesium begins to glow at that end of the tube nearest the entrance1 owing to its combination with nitrogen1 and a hot ring is seen to travel slowly down the tube to the other end1 marking the place where such combustion is in progress4 ,the gas issuing from the tube is collected in a small gasholder4 ,when one tube of magnesium is exhausted1 another is substituted for it4 ,each tube is capable of absorbing about seven litres of nitrogen1 so that to obtain a litre of argon about one hundred litres of 8atmospheric nitrogen0 must be employed1 and about fourteen tubes of magnesium are required4 ,m4 ,maquenne1 who has prepared the nitrides of several metals1 has stated that a mixture of lime and magnesium1 yielding metallic calcium1 is more easily manipulated than pure magnesium1 owing to the absorption of the nitrogen at a lower temperature4 ,the process has not been tried on a large scale1 but if the temperature of combination of magnesium and nitrogen could be thus reduced1 it would much facilitate the operation1 for the greatest care has to be taken not to overheat the combustion tube1 else it softens1 and blows into holes4 ,porcelain tubes are attacked by the magnesium1 and crack on cooling2 and iron tubes are difficult to clean out4 ,this preliminary operation does not yield pure argon2 it merely removes a large portion of the nitrogen4 ,to free the argon from the remainder1 it is caused to circulate 7by means of a specially contrived mercury-pump1 where each drop of mercury in falling down a narrow glass tube carries before it a small bubble of gas7 through tubes containing red-hot copper1 red-hot copper oxide1 red-hot magnesium1 and cold soda-lime and phosphoric anhydride4 ,the copper serves to remove traces of oxygen2 the copper oxide yields up its oxygen to any hydrogen or carbon compound--dust and the like--which may happen to be present2 the soda-lime absorbs any carbon dioxide produced by the combustion of the carbon compounds1 and at the same time partially dries the gas2 while the phosphoric anhydride effectually dries the gas1 previous to its passage over the red-hot magnesium1 which in its turn removes the nitrogen4 ,it is necessary to continue this circulation for several days before the litre of gas is entirely freed from nitrogen4 ,it is difficult to choose between these two methods3 both are troublesome1 and require a considerable time1 but in an ordinary laboratory the latter is probably the more easily set in operation1 for the former requires a suitable electric current1 and power1 so as to rotate the water-fan4 ,up to the present date1 the only sources which have yielded argon are atmospheric air1 gases extracted from mineral waters or from springs1 one meteorite1 and a few rare minerals4 ,no animal or vegetable substance appears to contain it4 ,experiments were made in the summer of #ahie by ,mr4 ,george ,mac,donald and ,mr4 ,alexander ,kellas1 in order to decide whether argon was a constituent of any living matter4 ,some peas were reduced to powder and dried2 the carbon and hydrogen of the peas were burned to carbon dioxide and water by heating with oxide of copper1 and under these circumstances the nitrogen is evolved in the state of gas4 ,had argon been contained in the vegetable1 it too would have accompanied the nitrogen4 ,the nitrogen was then1 as usual1 absorbed for the most part by means of magnesium1 and the small unabsorbed residue was mixed with oxygen and exposed to electric sparks for many hours1 in presence of caustic soda4 ,there was no residue left after absorbing the excess oxygen3 the gas was completely removed4 ,similar experiments carried out on animal tissue led to a similar conclusion4 ,two mice were chloroformed1 and when dead they were dried in an oven until all the moisture of their bodies was completely driven off1 and it was possible to reduce them to powder4 ,it is interesting to note that one of these mice contained #gc per cent of water1 and the other #gje per cent4 ,the dried animals yielded about #aa per cent of their weight of nitrogen4 ,absolutely no residue of gas was obtained on causing this nitrogen to combine2 hence it appears to be a legitimate conclusion that neither animal nor vegetable tissue contains any appreciable amount of argon4 ,but these experiments lead to a further result4 ,they show that nitrogen1 procured from its compounds1 when treated in the same way as atmospheric nitrogen1 yields no trace of argon4 ,and it must therefore be taken as proved without doubt that argon is actually present in the atmosphere as such1 and is not produced by any process to which the nitrogen has been submitted in order to extract it4 ,this point having been settled1 the actual percentage of argon in atmospheric air next invited inquiry4 ,it is by no means very easy to absorb quantitatively the whole of the nitrogen from an accurately measured sample of air1 for small gains and losses are apt to occur4 ,it is necessary to keep the air out of contact with water as much as possible1 because argon1 being more soluble than nitrogen1 dissolves in larger proportional amount in the water1 and is thereby partially removed4 ,the air was therefore entirely manipulated over mercury4 ,the processes were like those previously employed3 most of the nitrogen was removed with magnesium1 and the residue was freed from all nitrogen by sparking with oxygen4 ,experiments directed to this end were carried out by ,mr4 ,kellas in ,professor ,ramsay's laboratory1 and independently by ,m4 ,h4 ,schloesing in ,paris4 ,the results were identical4 8,atmospheric nitrogen0 consists of pure nitrogen mixed with #aahf per cent of its volume of argon4 ,it is now possible1 knowing the percentage of argon in atmospheric nitrogen and its density 7#aiid71 to calculate whether ,lord ,rayleigh's determinations of the density of atmospheric nitrogen were correct4 ,the weight of one litre of pure nitrogen is #abeaa gram1 and of argon1 #aghah gram2 hence a litre of a mixture of #ihhad volumes of nitrogen with #aahf volume of argon must possess the weight #abegd gram4 ,the actual number found by ,lord ,rayleigh was #abegb gram1 which is almost exactly identical with the number calculated4 ,mineral waters1 as a rule1 contain small quantities of argon mixed with oxygen1 nitrogen1 carbon dioxide1 and in some cases sulphuretted hydrogen and helium1 a gas of which more hereafter4 ,the waters actually examined were the ,bath waters1 which contain much nitrogen1 a little argon1 and a trace of helium2 the ,buxton waters1 containing nitrogen and a little argon2 the water from 8,allhusen's ,well10 ,middlesborough1 which evolved gas of an inflammable nature consisting mainly of nitrogen1 but also containing marsh-gas1 and argon to the extent of ,o#d per cent2 water from boiling springs in ,iceland evolved gas containing somewhat more argon than air does1 viz4 #aad per cent2 and lastly1 water from the ,harrogate sulphur springs yielded a gas largely consisting of a mixture of sulphuretted hydrogen1 carbon dioxide and nitrogen1 but giving also an appreciable amount of argon4 ,such determinations show that argon is not merely confined to the atmosphere above the earth1 but that it penetrates the earth and is contained in subterraneous water4 ,these results have been obtained by ,lord ,rayleigh1 ,professor ,ramsay1 ,mr4 ,travers1 and ,mr4 ,kellas4#bf ,similar experiments have been made by ,dr4 ,bouchard in ,paris#bg on effervescing waters from ,cauterets in the ,pyrenees4 ,one of those springs yielded a mixture of nitrogen with a small amount of argon and helium2 another yielded only nitrogen and argon2 while a third gave nitrogen and helium4 ,such are1 up to the present1 the sources of argon4 ,it has been several times stated that the element helium1 which is closely allied to argon in its physical properties1 and in its inertness1 is a normal constituent of our atmosphere1 although in very small amount4 ,this1 however1 is not the case4 ,for the argon of the atmosphere has been very carefully examined for helium in two ways4 ,first1 ,lord ,rayleigh dissolved a large quantity of argon in water1 leaving only a minute bubble undissolved4 ,now while #ajjj parts of water dissolve #dj parts of argon1 they dissolve only #g parts of helium2 and if helium were present1 it should be found in the residue4 ,but careful spectroscopic examination failed to reveal the characteristic lines of helium4 ,next1 ,professor ,ramsay and ,dr4 ,collie diffused argon fractionally2 and as the densities of argon and helium are very different 7#b and #bj71 the helium should have been visible in the first portion which diffused4 ,there was no trace to be detected4 ,but1 further1 they submitted this portion of argon to a discharge of electricity for several hours in a vacuum-tube provided with platinum electrodes4 ,this process1 as they proved1 carries out the helium with the platinum which is splashed on to the sides of the tube4 ,the argon was then removed by pumping it off in the cold4 ,on heating the splashed-off platinum1 no helium spectrum could be observed4 ,in a similar experiment1 in which a very minute trace of helium had been added to the argon1 there was no difficulty in detecting the helium on heating the tube4 ,the conclusion therefore follows that no helium is present in our atmosphere4 ,it is1 besides1 exceedingly improbable that helium should be present4 ,for1 as shown by ,dr4 ,johnstone ,stoney1 the rate of motion of a molecule of hydrogen is so rapid that1 on finding its way to the confines of the atmosphere1 it would escape1 and travel through space until it found a planet of sufficient attractive force to hold it4 ,the same is true of helium4 ,were helium present in the atmosphere1 it would ultimately leave us for the sun1 or for some planet of much greater mass than the earth4 ,this conception of ,dr4 ,stoney's tallies with the observation that the moon1 a planet of small mass1 is devoid of an atmosphere1 and that the sun1 a body with a mass #cjj1jjj times as great as the earth1 shows in its chromosphere the spectra both of hydrogen and of helium with great brilliancy4 ,it is now of interest to inquire what are the properties of argon and how it is related to other elements4 #be ,proc4 ,roy4 ,soc4 vol4 liii4 p4 #acd4 #bf ,proc4 ,roy4 ,soc4 vol4 lix4 p4 #fh4 ,phil4 ,trans4 vol4 clxxxvi4 p4 #bbg4 #bg ,compt4 rend4 vol4 cxxi4 p4 #cid4 ,,chapter ,,vi ,,the ,,properties ,,of ,,argon ,the density of a gas is one of its most characteristic and important properties4 ,avogadro's law1 which postulates that equal volumes of gases1 at equal temperature and pressure1 contain equal numbers of molecules1 renders it possible to compare the weights of the molecules by determining the relative weights of the gases4 ,thus1 as the ratio between the densities of nitrogen and oxygen is #g to #h1 a single molecule of nitrogen1 the smallest portion which can exist in freedom1 uncombined with other elements1 is ths of the weight of a single molecule of oxygen4 ,hence a determination of the density of argon leads directly to a knowledge of the relative weight of a single molecule of this gas4 ,but with what should the density of argon be compared8 ,what gas must serve as the standard of density8 ,to answer this question1 it is necessary to give a short sketch of the development of chemical theory regarding the atomic weights of elements and their relative volumes4 ,dalton proposed to adopt as the unit of atomic weight the weight of the lightest atom1 namely1 that of hydrogen4 ,taking1 for example1 water as one substance containing hydrogen1 its percentage composition by weight is-- ,hydrogen #aaaa per cent ,oxygen #hhhh ,if the smallest portion of water capable of free existence contains one atom of hydrogen and one of oxygen1 then placing the weight of an atom of hydrogen as unity1 the weight of an atom of oxygen is eight times as great4 ,and although we do not know the absolute weight of any single atom1 we are justified in supposing that an atom of oxygen is eight times as heavy as an atom of hydrogen4 ,but have we any right to make the assumption that a molecule of water contains one atom of each element8 ,dalton came to the conclusion that this supposition was a justifiable one2 but there are strong reasons against it4 ,we have already seen that ,cavendish discovered approximately1 and that ,gay-,lussac and ,humboldt determined accurately1 that when hydrogen and oxygen unite to form water1 two volumes of the former combine with one of the latter4 ,now it appears improbable on the face of it that any given volume of hydrogen should contain only half as many particles as an equal volume of oxygen2 and it is still more improbable1 when we take into consideration 7#a7 ,boyle's discovery that if the pressure on a gas be increased1 the volume of the gas1 whatever it may be1 diminishes in like proportion2 and 7#b7 ,gay-,lussac's and ,dalton's discovery1 that all gases1 when equally raised in temperature1 expand equally4 ,it would be very remarkable if one gas1 containing twice as many particles in unit volume as another1 should show exactly similar behaviour towards pressure and temperature4 ,hence it appeared not unreasonable to suppose that the composition of water was expressed by one particle of oxygen in union with two particles of hydrogen4 7,the word 8particle0 is here used in the meaning of 8small portion02 such particles may be molecules or they may be atoms47 ,when steam is formed by the union of hydrogen with oxygen1 it has a volume equal not to the sum of the volumes of the hydrogen and the oxygen1 but to two-thirds of the sum1 or equal to that of the hydrogen alone1 or twice that of the oxygen4 ,and as steam1 like hydrogen and oxygen1 follows ,boyle's and ,gay-,lussac's laws1 it must be supposed that in the steam there are as many particles as in the hydrogen from which it was formed4 ,but the particles of steam must necessarily be more complex than those of the hydrogen1 inasmuch as the steam contains oxygen as well as hydrogen4 ,these difficulties may1 however1 be easily overcome by the following supposition1 which was first formulated by ,avogadro in #ahaa4 ,the ordinary particles of hydrogen and of oxygen are complex1 each containing at least two atoms1 or smaller particles1 which usually exist in combination with each other1 or with atoms of some other element4 ,two volumes of hydrogen1 therefore1 contain twice as many particles as one volume of oxygen2 to such particles the name 8molecules0 is now universally applied4 ,and as these molecules are themselves each made up of two smaller particles1 now termed 8atoms10 there exist in two volumes of hydrogen twice as many atoms as in one volume of oxygen4 ,on combination1 the atoms in the molecules of hydrogen and oxygen rearrange themselves1 so that two atoms of hydrogen and one atom of oxygen combine to form a molecule of water-vapour1 containing three atoms4 ,the steam now contains as many molecules as did the hydrogen before combination2 but whereas the molecules of hydrogen originally consisted of two atoms each1 the molecules of steam contain three atoms4 ,it is this which causes the contraction from three volumes to two when hydrogen and oxygen molecules exchange partners in forming water molecules4 ,of course the difficulty would meet with an equally good explanation if it were supposed that the hydrogen molecules and the oxygen molecules each contained four atoms1 or eight atoms2 but there is no need to increase the complexity of the molecule1 and the assumption that these molecules are 8diatomic0 completely serves the purpose4 ,the composition of water is therefore believed to be two atoms of hydrogen in combination with one atom of oxygen2 and when hydrogen and oxygen unite to form water1 a transaction similar to an exchange of partners is supposed to occur2 the atoms of hydrogen and oxygen are imagined to leave their partners of like kind1 and to rearrange themselves so that groups of atoms1 or molecules1 each containing two atoms of hydrogen and one of oxygen1 are formed4 ,to such an arrangement the formula ,h#b,o is applied1 while ordinary hydrogen molecules may be represented as ,h#b1 and molecules of oxygen as ,o#b4 ,it has been shown already 7p4 #aej7 how ,lord ,rayleigh obtained the number #aehhb for the density of oxygen compared with that of hydrogen4 ,to determine the atomic weights of elements1 the usual process has been to analyse their oxides1 for only a few elements form compounds with hydrogen4 ,thus the analysis of copper oxide yields the numbers-- ,copper #giif per cent ,oxygen #bjjd ,and as no compound of copper and hydrogen is known which lends itself to analysis1 the atomic weight of copper is necessarily referred to that of oxygen4 ,if the atomic weight of hydrogen be taken as unity1 that of oxygen1 from ,lord ,rayleigh's determination1 must be #aehhb1 because1 in comparing the weights of equal volumes of the gases1 a comparison is made of the weights of equal numbers of molecules2 and as it is reasonable to suppose that each molecule of hydrogen and of oxygen contains two atoms1 the number #aehhb represents the weight of an atom of oxygen compared with that of an atom of hydrogen taken as #a4 ,but this number has not been regarded as sufficiently established by experiment4 ,other observers 7for the importance of this ratio has been acknowledged since the beginning of the century7 have obtained results differing from that given above1 although not to any great extent4 ,and as it is a matter of indifference what basis or standard be taken for atomic weights1 which represent only relative numbers1 it is common to accept the atomic weight of oxygen as #af1 in which case that of hydrogen1 if ,lord ,rayleigh's determination of its density be regarded as accurate1 would be #ajjgd4 ,hence if we place the atomic weight of oxygen as #af1 that of copper would be #fccd4 ,and as with copper1 so with most other elements4 ,it is very seldom that the atomic weight of an element has been directly compared with that of hydrogen2 it is1 in fact1 almost always ascertained by analysis of its chloride1 bromide1 or oxide2 and the atomic weights of chlorine and bromine have been very carefully compared with that of oxygen4 ,there is1 besides1 another convenience in accepting #af as the atomic weight of oxygen3 it is that many atomic weights are then represented by whole numbers instead of by fractions2 thus1 sulphur has the atomic weight #cb1 if oxygen be made #af1 whereas1 if it were #aehhb1 the atomic weight of sulphur would be #cagfd1 a number much more difficult to remember4 ,we see then that it is convenient to refer the density of argon to oxygen taken as #af4 ,the density obtained by ,professor ,ramsay in ,february #ahie1 using a globe of small capacity 7only #afj cubic centimetres71 was #aiid2 exactly the same result was given by ,lord ,rayleigh's experiments in ,june #ahie on argon prepared by means of the electric discharge1 with a balloon of much greater capacity1 which held over two litres of gas4 ,now as a molecule of oxygen consists of two atoms1 the weight of a molecule is twice the atomic weight1 or #cb2 and as a given volume of argon must contain as many molecules as the same volume of oxygen1 the weight of a molecule of argon must be twice #aiid1 or #cihh4 ,but this gives no information regarding the relative weight of an atom of argon4 ,to ascertain this important quantity two methods may be chosen4 ,one is to make compounds of the element1 and this will be first considered4 ,since an atom of an element is defined as the smallest amount which can exist in combination1 then1 if numerous compounds of an element be examined1 that one which contains proportionally the least amount of the element may be regarded as containing an atom1 unless there are reasons to the contrary4 ,for example1 reverting to the former instance of water1 the relative proportions by weight of oxygen and hydrogen are1 in round numbers1 #af to #b4 ,reasons have already been given showing why its formula should be ,h#b,o and not ,,ho2 its molecule must contain two atoms of hydrogen4 ,but another compound of oxygen and hydrogen is known in which the proportions are #af parts by weight of oxygen to #a part by weight of hydrogen4 ,here also there are reasons for believing that this compound1 hydrogen peroxide1 contains two atoms of hydrogen2 whence it follows that it must contain two atoms of oxygen1 or #cb parts by weight to #b parts by weight of hydrogen1 and must therefore have the formula ,h#b,o#b4 ,no other compound of oxygen and hydrogen is known2 and it may be stated briefly that no compound of oxygen with any element whatever is known in which less than #af parts by weight enters1 compared1 of course1 with the atomic weight of the other element or elements in the compound4 ,hence #af is accepted on this ground as the atomic weight of oxygen4 ,if now it were possible to prepare compounds of argon1 similar reasoning might be applied to them1 and that compound containing least argon would be regarded as indicating its atomic weight4 ,many attempts were therefore made to induce argon to enter into combination4 ,and the consistent failure of these attempts led to the choice of the name 8argon0 or 8idle0 for the newly discovered element4 ,the methods employed to prepare argon free from nitrogen1 namely1 by exposing the mixed gases to the action of oxygen in a discharge of electric sparks1 and by passing them over red-hot magnesium1 show that it cannot be induced to combine with one of the most electro-negative of elements1 oxygen1 and one of the most electro-positive1 magnesium4 ,it also refuses to combine with hydrogen or with chlorine when sparked with these gases2 nor is it absorbed or altered in volume by passage through a red-hot tube along with the vapours of phosphorus1 sulphur1 tellurium1 or sodium4 ,red-hot caustic soda1 or a red-hot mixture of soda and lime1 which attacks the exceedingly refractory metal platinum1 was without action on argon4 ,the combined influence of oxygen and an alkali in the shape of fused potassium nitrate or red-hot peroxide of sodium was also without effect4 ,gold would1 however1 have resisted such action1 but it would have been attacked by the next agent tried1 viz4 persulphide of sodium and calcium4 ,this mixture was exposed at a red-heat to a current of argon1 again without result4 ,nascent chlorine1 or chlorine at the moment of liberation1 obtained from a mixture of nitric and hydrochloric acids1 and from permanganate of potassium and hydrochloric acid1 was without action4 ,a mixture of argon with fluorine1 the most active of all the elements1 was exposed to a rain of electric sparks by ,m4 ,moissan1 the distinguished chemist who first succeeded in preparing large quantities of fluorine in a pure state1 without his observing any sign of chemical combination4 ,an attempt was also made to cause argon to combine with carbon by making an electric arc between two rods of carbon in an atmosphere of argon4 ,it was at first believed that combination had taken place1 for expansion occurred1 the final volume of gas being larger than the volume taken2 but subsequent experiments have shown that the expansion was due to the formation of some oxide of carbon from the oxygen adhering to the carbon rods4 ,on absorption of this oxide by the usual absorbent1 a mixture of cuprous chloride and ammonia1 the argon was recovered unchanged4 ,m4 ,berthelot1 the celebrated ,french chemist1 has stated that1 on exposing argon mixed with benzene vapour to a rain of electric sparks1 he has succeeded in causing argon to combine4 ,its volume certainly decreases1 but whether this decrease is to be attributed to true combination or not is very doubtful4 ,the benzene is converted into a resinous mass1 which coats the walls of the tube2 and it is not improbable that the argon may be dissolved1 or even mechanically retained1 in the resinous deposit4 ,helium1 a gas closely resembling argon in properties1 may be made to enter into a similar combination with metallic platinum1 if combination it can be called2 but the amount absorbed in both cases is extremely minute1 and the gas is evolved unchanged on heating the resin or the metal4 ,professor ,ramsay has also made experiments on the action of a silent electric discharge upon a mixture of argon with the vapour of carbon tetrachloride2 the latter decomposes1 giving1 not a resin1 but crystals of hexachlorobenzene and free chlorine2 but the volume of the argon was unchanged4 ,it was all recovered without loss4 ,lastly1 the rare elements titanium and uranium have been heated to redness in a current of argon with no alteration or absorption of the gas4 ,in short1 all likely agents have been tried as absorbents for argon1 but in no case has any true chemical combination been obtained4 ,these failures to produce compounds make it impossible to gain any knowledge regarding the atomic weight of argon by a study of its compounds1 for it forms none4 ,it is1 indeed1 in the highest degree improbable that1 had compounds existed1 none should have been found in ,nature4 ,there are1 it is true1 a few elements1 such as platinum and those resembling it1 which always occur native1 i4e4 in the elementary state2 but even they yield to the attack of the agents tried with argon4 ,it cannot1 of course1 be stated with absolute certainty that no element can combine with argon2 but it appears at least improbable that any compounds will be formed4 ,it was therefore necessary to adopt some other method in attempting to determine the atomic weight of argon1--some method dependent on its physical rather than its chemical properties1 for argon1 unlike almost all other elements1 appears to be devoid of chemical properties4 ,in order better to follow the train of reasoning based on experiment1 it will be well to begin with an account of why the atomic weight of mercury is accepted as #bjj4 ,the amount of mercury which combines with #af parts by weight of oxygen is easily found by heating a weighed quantity of oxide of mercury1 as ,priestley and ,scheele did1 and weighing the residue of metal4 ,the results of the most accurate experiments show that #bjjcf grams of mercury combine with #af grams of oxygen1 and if the compound consists of one atom of each element1 #bjjcf must be the atomic weight of mercury4 ,the first idea which naturally occurs is to find out the relative weight of mercury gas4 ,this has been done1 and it is found to have the ratio to that of oxygen of #ajj to #af4 ,doubling these numbers will give the molecular weights1 since a molecule of oxygen consists of two atoms1 and must therefore possess twice the weight of one atom4 ,we thus obtain the numbers #bjj and #cb as the molecular weights of mercury and oxygen respectively4 ,it might therefore be concluded that #bjj is not the true atomic weight of mercury1 but #ajj1 and that the compound of mercury with oxygen contains not one but two atoms of mercury1 and should therefore be represented by the formula ,hg#b,o1 not ,hg,o4 ,but on surveying all known compounds of mercury1 there is not one which contains less than #bjj parts by weight of mercury in a molecule of the compound1 or in which the mercury cannot be conceived to replace #b parts by weight of hydrogen4 ,and on weighing as gases the compounds of mercury with other elements1 where such compounds do not decompose on heating like the oxide1 the amount of mercury present must be always taken as #bjj1 in order to add up to the molecular weight found4 ,for example1 a compound of mercury with carbon and hydrogen1 named mercury methide1 has a density of #abj compared with oxygen taken as #af1 hence the comparative weight of its molecule must be #bdj4 ,now it is known to contain two atoms of carbon and six atoms of hydrogen1 the atomic weights of which are #bd #f #cj4 ,and deducting #cj from #bdj1 #baj remains as an approximation to the atomic weight of mercury4 ,it might1 it is true1 be the weight of two atoms of mercury1 but if so it is singular that no compound contains a smaller proportion2 and there is another reason1 which follows immediately1 that leads us to believe that #bjj is correctly taken as the true weight of an atom4 ,it was discovered by ,dulong and ,petit1 early in the century1 that the higher the atomic weight of an element the less heat is required to raise its temperature through a given number of degrees4 ,this heat can be measured by dropping a fragment of the element1 carefully weighed and heated to a known temperature1 into a known weight of cold water1 and ascertaining what rise of temperature the water undergoes1 owing to the heat communicated to it by the element4 ,these comparative amounts of heat1 if water is chosen as the standard1 are termed specific heats4 ,and as the specific heats of elements have been found by experiment to be inversely as their atomic weights1 the product of the specific heat of any element and its atomic weight will give a constant number4 ,if the quantity of element weighed is one gram1 and its rise of temperature one degree1 the numerical value of this product is about #fd4 ,now the specific heat of mercury has been found to equal #jjcb2 that is to say1 it requires only a fraction of the value of #jjcb of heat to raise the temperature of say #a gram of mercury through one degree1 whereas the amount of heat necessary to raise #a gram of water through one degree is represented by the number #a4 ,hence this number1 #jjcb1 multiplied by the atomic weight of mercury1 should yield the product #fd2 and it is seen at once that that number must be #bjj1 for #bjj #jjcb #fd4 ,this is an additional reason for believing that the atomic weight of mercury must be represented by the number #bjj4 ,we come next to a confirmatory piece of evidence which greatly strengthens the view that the atomic weight of mercury must be #bjj2 but before entering into detail let us see what an atomic weight of #bjj involves4 ,the density of mercury gas is #ajj1 and its molecular weight must be #bjj4 ,but if its atomic weight is also #bjj1 it follows of necessity that its molecule and its atom must be identical2 that unlike oxygen and hydrogen1 its molecule consists1 not of two atoms1 but of one single atom4 ,there is nothing strange in this conclusion2 there is no evident reason why single atoms should not act as molecules1 or independent particles1 able to exist in a free state1 uncombined with each other or with any other molecules4 ,the specific heat of a gas is measured in much the same manner as that of a solid4 ,a known volume of the gas is caused to pass through a spiral tube1 heated to a certain definite high temperature2 it then enters a vessel containing a known weight of water1 traverses a spiral tube immersed in the water1 and parts with its heat to the water4 ,knowing1 therefore1 the weight of the gas and its initial temperature1 and also the rise of temperature of the water1 the specific heat of the gas can be compared with that required to raise an equal weight of water through one degree4 ,but gases are found to possess two specific heats4 ,if the volume of the gas is kept constant1 so that the gas does not contract during its loss of heat1 one number for its specific heat is obtained2 while if it is allowed to alter its volume a higher figure represents its specific heat4 ,it will be necessary to consider the cause of this difference1 in order to understand what conclusions can be drawn respecting the molecular nature of argon from a determination of the ratio between its two specific heats--that at constant pressure and that at constant volume4 ,if a gas is allowed to expand into a vertical cylinder so as to drive up a piston loaded with a weight1 it is said to 8do work40 ,the work is measured by the weight on the piston1 and also by the height to which it is raised4 ,thus1 if the weight is one pound1 and the height one foot1 one foot-pound of work is done2 if the mass is one gram and the height one centimetre1 one gram-centimetre of work is done4 ,during this process the gas must expand2 and if it were enclosed in some form of casing through which heat could not pass--we know of no such casing1 but we can contrive casings through which heat passes very slowly--the temperature of the gas would fall during its expansion1 and it would lose heat4 ,for each loss of one heat-unit or calory--i4e4 the amount of heat given off by #a gram of water in cooling through #a ,centigrade--the gas would perform #db1chj gram-centimetres of work2 it would raise a weight of nearly #d kilograms1 or about #i lbs41 through #a centimetre1 or nearly half an inch4 ,when a gas expands into the atmosphere it may be regarded as 8raising the atmosphere0 through a certain height1 for the atmosphere possesses weight1 equal on the average to #ajcc grams on each square centimetre of the earth's surface1 or between #ae and #af lbs4 on each square inch4 ,suppose a quantity of air1 weighing #a gram1 to be enclosed in a long cylindrical tube of one square centimetre in section4 ,at the usual pressure of the atmosphere on the earth's surface1 and at #j ,centigrade1 the volume of the air would be #ggcc cubic centimetres2 and1 as the sectional area of the tube is #a square centimetre1 the air would occupy #ggcc centimetres' length of the tube4 ,if heat be given to this air1 so that its temperature is raised from #j to #a1 it will expand1 as ,gay-,lussac showed1 by #a_/bgcrd of its volume4 ,now the product of #ggcc and #a_/bgc is #bhc centimetres2 the level of the surface of the air will rise in the tube through that amount4 ,in doing so it will perform the work of raising #ajcc grams through #bhc centimetres1 or #bibg gram-centimetres4 ,careful measurements have shown that1 in order to do this work1 heat to the amount of #jjfib calory must be given to the gas4 ,but it has been found that to heat the air through one degree1 without allowing it to expand1 requires #jafhc calory2 that is1 the same amount of heat which would raise a gram of air through one degree1 its volume being kept constant1 will raise a gram of water through #jafhc2 or1 in other words1 the specific heat of air is #jafhc4 ,but if allowed to expand1 more heat is required--an additional #jjfib calory must be given it2 consequently its specific heat at constant pressure is greater2 it is actually the sum of these two numbers1 #jafhc #jjfib #jbcge4 ,we have thus-- ,specific heat at constant pressure #jbcge volume #jafhc ,ratio between these numbers3 #jbcge_/jafhc #ada ,this ratio is termed the ratio between the specific heats of air1 and such a ratio is represented usually by the letter 4 ,but it is not necessary to determine both kinds of specific heat in order to arrive at a knowledge of the value of this ratio4 ,one plan1 adopted by ,gay-,lussac and ,dsormes at the suggestion of ,laplace1#bh is to actually measure the fall of temperature by allowing a known volume of gas1 of which the weight can of course be deduced1 to expand from a pressure somewhat higher than that of the atmosphere to atmospheric pressure4 ,it is true that heat will rapidly flow in through the walls of the vessel2 but by choosing a sufficiently large vessel1 and surrounding its walls with badly-conducting material1 the entry of heat will be so slow that it may1 for practical purposes1 be neglected4 ,the number for this ratio1 actually found by ,gay-,lussac and ,welters for air1 was #acgf2 but subsequent and more accurate experiments have given as a result #adje1 which is almost identical with that calculated above4 ,this method1 however1 can be employed only when an unlimited supply of gas is at disposal1 for it entails the use of large vessels1 and the compressed gas must be allowed to escape into the atmosphere1 and is lost4 ,there is1 fortunately1 another method by which the same results can be obtained1 and which requires only a small amount of gas4 ,sir ,isaac ,newton calculated that the velocity of sound in a gas was dependent on its pressure and on its density1 in such a manner that c 7p_/d71 where c stands for velocity 7celerity71 p for pressure1 and d for density4 ,when waves of sound are transmitted through air1 the air is compressed in parts and rarefied in parts1 in such a manner that compression follows rarefaction very rapidly1 that part which is compressed at one instant being rarefied at the next1 compressed again at a third1 and rarefied at a fourth1 and so on4 ,laplace was the first to point out that during such rapid changes of pressure as occur while a sound-wave is passing1 the pressure will not rise proportionally to the density1 as would be the case if ,boyle's law were followed2 for on sudden rise of pressure the temperature of the compressed portion of the gas will be increased2 and1 correspondingly1 on sudden fall of pressure1 the wave of compression having passed1 the temperature will fall4 ,he showed that instead of two pressures being inversely proportional to their two volumes1 under such circumstances1 as they are according to ,boyle's law1 or p_/p#a v#a_/v1 they must be inversely proportional to the volumes raised to a power1 the numerical expression of which is the ratio of the specific heats of the two gases1 1 thus3 p_/p#a 7v#a_/v72 or as v#a 3 v 33 d 3 d#a1 c 7 p_/d71 and c#b;d_/p4 ,the ratio of the two specific heats can therefore be determined by finding the velocity of sound in the gas1 and by noting at the same time its density and its pressure4 ,to determine the velocity of sound in a gas1 it is not necessary to adopt the plan which has been successfully carried out with air2 that is1 to make a sudden sound at one spot and to measure the interval of time which the sound takes to travel to another spot some miles distant4 ,there is a simpler method1 depending on the fact that the lengths of the waves of compression and rarefaction are proportional to the velocity of the sound4 ,so that1 knowing the velocity of sound in air1 the velocity in any other gas may be found by determining the relative length of the sound-waves in air and in that gas4 ,illustration3 ,,fig4 #d4 ,the simple apparatus with which such determinations are made is due to the physicist ,kundt4 ,it consists of a glass tube1 through one end of which a glass rod passes1 so that half the rod is enclosed in the tube1 while the other half projects outside it4 ,in the experiments on argon1 the rod was sealed into the tube2 in other cases1 it is better to attach it with indiarubber1 or to cause the rod to pass through a cork4 ,the open end of the tube is connected with a supply of the gas1 so that1 after the tube has been pumped empty of air1 the gas1 in a pure and dry condition1 can be admitted4 ,some light powder 7and for this purpose lycopodium dust--the dried spores of a species of fungus--is best7 is placed in the tube1 and distributed uniformly throughout it1 so that when the latter is in a horizontal position1 a streak of the powder lies along it from end to end4 ,the portion of rod outside the tube is rubbed with a rag wetted with alcohol1 when it emits a shrill tone or squeak1 due to longitudinal vibrations2 the pitch of the tone depends1 naturally1 on the length of the rod1 a long rod giving a deeper tone than a short one4 ,the vibrations of the rod set the gas in the tube in motion1 and the sound-waves are conveyed from end to end of the tube through the gas4 ,as the tube is closed at the end through which the gas was admitted1 these waves echo back through it2 and a great deal of care must be taken to make the echo strengthen the waves1 so that the compressions produced by the back waves are coincident in position with the compressions produced by the forward waves travelling onwards from the rod4 ,the gas1 could we see it1 would represent portions compressed and portions rarefied at regular intervals along the tube4 ,where the gas is compressed1 it gathers the lycopodium dust together in small heaps1 the position of each heap signifying a node of compression4 ,hence1 comparing the distances between the nodes of compression for any gas and for air1 we find the relative wave-lengths of sound in the two gases2 and1 as the velocity of sound in air has been accurately measured1 we thus determine the velocity of sound-waves in the gas under experiment4 ,such experiments were made by ,kundt and by his co-worker ,warburg on mercury gas1 and they found that in this case the value of was #afg2 that is1 in the equation c#b;d_/p the value #afg had to be ascribed to 1 in order to render it equal to the product of the square of the velocity into the density1 divided by the pressure4 ,similar experiments with argon led to the same result as ,kundt and ,warburg found for mercury gas2 but the calculation becomes more simple if it is allowable to take for granted that the elasticity1 or alteration of pressure produced by unit alteration of volume1 is identical in the case of argon and air4 ,the full equations are-- nair cair 7p_/d77#a at7air1 and nargon cargon 7p_/d77#a at7argon1 where n is the number of vibrations per second1 the wave-length of sound1 and a the coefficient of the expansion of a gas for a rise of #a in temperature1 t1 viz4 #jjjcfg4 ,now if the expression p 7#a at7 can be shown to be identical for argon and for air1 the value of for argon can be calculated by the very simple proportion-- #b;dair 3 #b;dargon 33 #adjh 3 argon4 ,this involved a measurement of the rate of rise of pressure of argon1 p1 per degree of rise of temperature1 t2 or1 in other words1 the verification of ,boyle's and ,gay-,lussac's laws for argon2 and this research was successfully carried out by ,dr4 ,randall of the ,johns ,hopkins ,university of ,baltimore1 ,u4,s4,a41 and ,dr4 ,kuenen1 of ,leyden1 working in ,professor ,ramsay's laboratory4#bi ,they made use of a constant volume thermometer1 and measured the rise of pressure corresponding to a definite rise of temperature1 comparing the gases argon and helium in this respect with air4 ,the values found between #j and #ajj for air1 argon1 and helium were-- ,one volume air1 heated from #j to #ajj1 raises pressure in the proportion of #a to #acffc ,argon #acffh ,helium #acffe ,it may therefore be taken for certain that1 within the limits of experimental error1 the value of the expression p7#a at7 is identical for all three gases4 ,we see1 then1 that for argon1 as for mercury gas1 the value of 1 the ratio between the specific heats at constant volume and at constant pressure1 is #a to #aff1 whereas for air1 hydrogen1 oxygen1 nitrogen1 carbon monoxide1 and nitric oxide1 it is #a to #ad4 ,we have now to consider what conclusion can be drawn from this difference4 ,on the usually accepted theory of the constitution of matter1 it is held that atoms may be regarded as spheres1 hard1 elastic1 smooth1 and practically incompressible4 ,true1 we really know little or nothing regarding the properties of such particles1 if particles there be2 but in considering their behaviour it is necessary to make certain suppositions1 and to see whether observed facts can be pictured to our minds in accordance with such postulates4 ,if1 from the known behaviour of large masses1 conclusions can be drawn regarding small masses1 and if these conclusions harmonise with what is found to be the behaviour of large numbers of small masses acting at once1 the justice of the supposition is1 although not proved1 at least rendered defensible as one mode of regarding natural phenomena4 ,molecules1 on this supposition1 may consist of single atoms1 or they may consist of pairs of such atoms1 joined in some fashion like the bulged ends of a dumb-bell2 or lastly1 they may consist of greater numbers of atoms arranged in some different manner1 the arrangement depending on their relative size and attraction for each other4 ,it must be clearly understood1 however1 that such mental pictures are not to be taken as actually representing the true constitution of matter1 but merely as attempts to picture such forms as will allow of our drawing conclusions regarding their behaviour from known configurations of large masses4 ,the molecules of gases are imagined to be in a state of continual motion1 up and down1 backwards and forwards1 and from side to side4 ,it is true that they must also move in directions which cannot be described by any of these expressions1 but such other directions may be conceived as partaking more or less of motions in the three directions specified2 i4e4 in being resolvable into these4 ,to these motions have been applied the term 8degrees of freedom40 ,such motions through space1 in which the molecule is transported from one position in space to another1 form three of the possible six degrees of freedom which a molecule may possess1 and the molecules are said to possess 8energy of translation0 in virtue of this motion4 ,the other three consist in rotations in three planes at right angles to each other4 ,now1 it can be shown that the product of pressure and volume of a gas1 pv1 is equal to rds of the energy of translation of all molecules of the gas1 or pv 7,,nr71 where ,n stands for the number of molecules in unit volume1 and ,r for their energy of translation2 inasmuch as a pressure diminishing a volume is of the nature of work1 or energy4 ,for one gram of air at ,o ,c4 and #gf cms4 pressure 7normal temperature and pressure71 the pressure 7p71 measured in grams per square centimetre1 is #ajcc1 and the volume 7v7 is #ggcc cubic centimetres2 and the raising of the temperature through #a1 as was shown before1 requires #bibg gram-centimetres of work4 ,further1 since the product of pressure into volume is equal to rds of the energy due to motion1 or the translational energy of the gas1 ,,nr #c_/bpv #c_/b #bibg #dcia gram-centimetres4 ,dividing this number by #db1chj1 the mechanical equivalent of heat1 or the number of gram-centimetres corresponding to one calory1 the quotient is #jajdj calory4 ,if the energy of the air were due to the translational motion of its molecules1 we should expect this number1 #jajdj1 to stand for the specific heat of air at constant volume2 but it has been found equal to #jafhc1 as already shown4 ,we have seen that to convert specific heat at constant volume into specific heat at constant pressure #jjfib must be added4 ,hence at constant pressure the specific heat of such an ideal gas should be #jagcb4 ,and the relation between specific heat at constant volume and that at constant pressure should be #jajdj to #jagcb1 or #a to #a4 ,the conclusion to be drawn from these numbers for air1 #jafhc and #jbcge1 which bear to each other the ratio of #a3 #ada1 is that air cannot be such an ideal gas2 that in communicating heat to it some of that heat must be employed in performing some kind of work other than that of raising its temperature4 ,what this work may possibly be we shall consider later4 ,but ,kundt and ,warburg found1 from their experiments on the ratio between the specific heats of mercury gas1 this ideal ratio1 #a to #a2 and ,professor ,ramsay obtained the same ideal ratio1 or one very close to it indeed1 #a to #afei1 for argon4 ,he subsequently found this ideal ratio also to hold for helium 7#a to #afeb71 and it must therefore be concluded that such gases possess only three degrees of freedom2 or1 in other words1 their molecules1 when heated1 expend all the energy imparted to them in translational motion through space4 ,this is the consequence which we should infer from the supposition that such molecules are hard1 smooth1 elastic spheres4 ,were they each composed of two atoms1 we should have to picture them as dumbbell-like structures2 and here we enter on a theoretical conception put forward by ,professor ,boltzmann1 but which has not been accepted universally by physicists4 ,illustration3 ,,fig4 #e4 ,illustration3 ,,fig4 #f4 ,boltzmann imagines that to the three 8degrees of freedom0 of a single atom molecule there may be added1 provided the molecule consists of two atoms1 two other degrees of freedom1 namely1 freedom to rotate about two planes at right angles to each other4 ,the knobs at the end of each imaginary dumb-bell may revolve round a central point in the handle joining them1 and it is clear that they may revolve in one horizontal and in one vertical plane1 as shown in ,fig4 #e4 ,such diatomic molecules are said to possess five 8degrees of freedom40 ,they will not1 it is supposed1 rotate round the line joining the centres of the spheres1 because1 as before said1 the atoms are pictured as perfectly smooth4 ,but if the molecules are triatomic1 as1 for example1 ,,co#b or ,n#b,o1 they will have six degrees of freedom1 for with the addition of an additional atom they have an additional plane of rotation 7see ,fig4 #f74 ,boltzmann has attempted to show that the ratio of the specific heats of diatomic molecules should be as #a to #ad4 ,in actual fact it approximates to that number4 ,for the commoner gases it is-- ,oxygen #adjb ,nitrogen #adaa ,hydrogen #adab ,carbon monoxide #adah ,in all cases the numbers are too large1 and this is a serious difficulty1 because any tendency to rotate round the central line would cause the values to be less1 not greater than #ad4 ,for triatomic molecules the calculated value of is #a1 but in actual fact the ratio in the case of triatomic molecules1 such as ,h#b,o1 ,,co#b1 ,n#b,o1 etc41 is always less than #a4 ,these speculations stand on a basis very different from the first conception1 namely1 that all heat must be employed in communicating translational motion to molecules of mercury gas1 argon1 and helium1 and it appears that the atoms of these three elements must necessarily be regarded as having the properties of smooth elastic spheres4 ,the atoms and the molecules must in their several cases be identical4 ,and1 inasmuch as the chemical evidence regarding mercury leads to the same conclusion1 it appears legitimate to infer that argon and helium must also be monatomic elements4 #bh ,mchanique cleste1 vol4 v4 p4 #abc4 #bi ,proc4 ,roy4 ,soc4 vol4 lix4 p4 #fc4 ,,chapter ,,vii ,,the ,,position ,,of ,,argon ,,among ,,the ,,elements ,from what has been said in the preceding chapter there can be no doubt that the molecular weight of argon is #cihh4 ,we have now to consider what this conclusion involves4 ,taken in conjunction with the fact that the ratio between its specific heat at constant volume and that at constant pressure is #a1 it follows that energy imparted to it is employed solely in communicating translational motion to its molecules4 ,in the case of mercury gas such behaviour is taken as evidence that the conclusion following from the formulae of its compounds1 from the density of its compounds in the gaseous state1 and from its own vapour-density1 as well as from its specific heat in the liquid state1 namely1 that its molecules are monatomic1 is correct4 ,is it legitimate to conclude that because argon in the gaseous state has the same ratio of specific heats1 therefore it also is a monatomic gas8 ,the conclusion will depend on our conception of an atom and a molecule1 and in the present state of our ignorance regarding these abstract entities no positive answer can be given4 ,it appears certain that1 on raising the temperature of argon1 very little1 if any1 energy is absorbed in imparting vibrational motion to its molecules2 and our choice lies between our ability or inability to conceive of a molecule so constituted as to be incapable of internal motion4 ,if there be any truth underlying ,professor ,boltzmann's conception1 a molecule of argon cannot consist of any complex structure of atoms1 otherwise it would possess more than three degrees of freedom1 and heat would be utilised in causing rotational motions4 ,as we know for a fact that the ratio between the specific heats of gases diminishes with the increasing complexity of their molecules1 perhaps the safest conclusion is the one adopted by the discoverers of argon1 that the balance of evidence drawn from this source is in favour of its monatomic nature4 ,but this hypothesis raises difficulties which are not lightly to be met4 ,these difficulties arise from a consideration of the position of argon when it is classified with other elements4 ,in #ahfc ,mr4 ,john ,newlands pointed out in a letter to the ,chemical ,news that if the elements be arranged in the order of their atomic weights in a tabular form1 they fall naturally into such groups that elements similar to each other in chemical behaviour occur in the same columns4 ,this idea was elaborated farther in #ahfi by ,professor ,mendeleff of ,st4 ,petersburg and by the late ,professor ,lothar ,meyer1 and the table may be made to assume the subjoined form 7the atomic weights are given with only approximate accuracy73-- ,,the ,,elements ,,arranged ,,in ,,the ,,periodic ,,system4 ---------------------------------------- --------------------- ,lithium #gj;,beryllium #ia;,boron #aaj;,carbon #abj ,sodium #bcj,magnesium #bdc;,aluminium #bgj,silicon #bhc ,potassium #cia;,calcium #dja,scandium #dda,titanium #dha ,rubidium #hee,strontium #hge,yttrium #hij,zirconium #ijj ,caesium #acbi;,barium #acgj,lanthanum #adbc;,cerium #adjc 8 #agjj8 #agb #j,ytterbium #agcj8 #aggj 8 #bbaj8 #bbej8 #bcjj,thorium #bcbd ---------------------------------------- --------------------- ---------------------------------------- ----------------- ,hydrogen #aja;,helium #db ,nitrogen #adj,oxygen #afj;,fluorine #aij8 ,phosphorus #caj,sulphur #cba;,chlorine #cee;,argon #cii ,arsenic #gea,selenium #gij;,bromine #hjj8 ,antimony #abjc,tellurium #abfc;,iodine #abfi8 ,erbium #affj8 #afgj8 #afij8 ,bismuth #bjha8 #badj8 #baij8 ---------------------------------------- ----------------- ---------------------------------------- ------------------ ,lithium #gj;,beryllium #ia;,boron #aaj;,carbon #abj ,sodium #bcj,magnesium #bdc;,aluminium #bgj,silicon #bhc ,copper #fcd,zinc #fec;,gallium #fii;,germanium #gbc ,silver #ajgi;,cadmium #aaba;,indium #aacg,tin #aaia 8 #aefj8 #aehj8 #aeij,terbium #afbj8 ,gold #aigb,mercury #bjjb,thallium #bjdb,lead #bjfi ---------------------------------------- ------------------ ---------------------------------------- ----------------------- ,hydrogen #aja;,helium #db ,nitrogen #adj,oxygen #afj;,fluorine #aij8 ,phosphorus #caj,sulphur #cba;,chlorine #cee;,argon #cii ,iron #efj ,vanadium #ead;,chromium #ebc,manganese #eej;,cobalt #ehg ,nickel #ehf ,ruthenium #ajaf ,niobium #idj,molybdenum #ieg8 #ajjj,rhodium #ajcj ,palladium #ajfc ,neodymium #adjh,praseodymium #adcf,samarium #aejj8 #aeb1 #aec1 #aed ,osmium #aiac ,tantalum #ahbe,tungsten #ahdj8 #aijj;,iridium #aicj ,platinum #aidc 8 ,uranium #bdjj8 #bddj ---------------------------------------- ----------------------- ,the elements in the first column all agree in that they are white soft substances1 with metallic lustre1 but tarnish rapidly in air1 owing to the action of water-vapour2 they are all violently attacked by water1 and they are without exception monads1 that is1 they replace hydrogen in its compounds atom for atom4 ,the elements in column two are also all white metals1 attacked by water with more or less ease2 but in their case one atom replaces two atoms of hydrogen1 whence they are called dyads1 or bivalent elements 7worth two74 ,and so on with the other columns4 ,all elements in vertical columns exhibit chemical similarity1 and1 indeed1 are often strikingly like in properties4 ,the subdivision1 produced by folding the loose page1 is intended to show that the elements represented on it have a double set of resemblances4 ,but there are various anomalous and inexplicable phenomena still attached to this arrangement of elements4 ,for example1 copper1 although it replaces one atom of hydrogen in some of its compounds1 and is thus a monad1 forms more numerous and more stable compounds in acting as a dyad and replacing two atoms of hydrogen4 ,gold1 which belongs to the same column1 is at once univalent and tervalent2 mercury1 both univalent and bivalent2 thallium1 univalent and tervalent2 tin and lead1 bivalent and quadrivalent1 and so on4 ,it is as if some elements had a tendency to enter a column not their own4 ,again1 on comparing the atomic weights of the elements1 it is seen that the differences are far from being regular4 ,as a rule1 the difference in the vertical columns between any single element and the one following it is approximately #af1 or some multiple of #af4 ,thus we have lithium1 sodium1 and potassium2 beryllium1 magnesium1 and calcium2 boron1 aluminium1 and scandium2 carbon and silicon2 oxygen and sulphur2 fluorine and chlorine--all with a difference of #af approximately4 ,but here we come to a break3 silicon and titanium1 phosphorus and vanadium1 sulphur and chromium1 chlorine and manganese1 each show a difference of about #bj4 ,passing on1 between the atomic weights of potassium1 rubidium1 and caesium there is a difference of about #af #c2 a similar difference between calcium1 strontium1 and barium2 between scandium and yttrium2 between titanium1 zirconium1 and cerium1 and so on2 but with wider and wider divergence from the supposed constant1 #dh #af #c4 ,in short1 we have a seeming regularity1 but only a very approximate one--a regularity1 in fact1 in which a vivid imagination must play a conspicuous part in order to detect it4 ,now1 up to the present1 no reason has been suggested to account for the divergence from this irregular regularity1 which a little expenditure of time will enable any one to trace through all these numbers4 ,but one thing has been remarked2 there is the same seeming regularity between certain physical properties of elements and their compounds3 their specific volumes1 their melting-points1 their refractive indices1 and other properties vary from member to member of the same column in a manner bearing more or less similarity to the periodic variation of the atomic weights4 ,it happens that among compounds of carbon we are acquainted with series of compounds which1 in variation of molecular weights and gradation of properties1 bear a striking resemblance to the elements thus arranged4 ,thus we have the series3-- ,,ch#d ,methane #af ,c#b;,h#f ,ethane #cj ,c#c;,h#h ,propane #dd ,c#d;,h#aj ,butane #eh ,c#e;,h#ab ,pentane #gb and a host of others up to a compound of the formula ,c#cj;,h#fb2 in each case there is a constant difference of #ad between the molecular weight of any one hydrocarbon and that immediately preceding or succeeding it in the column4 ,such a series is termed a homologous series4 ,the analogy is very tempting2 to suppose that a similar constant difference should exist in the relations of the atomic weights of the elements1 and that they too are undecomposable compounds of two unknown elements1 is an attractive hypothesis1 but one for which there exists no proof2 indeed1 it is rendered improbable by the irregularities just pointed out4 ,but there is one noticeable feature in the periodic arrangement of the elements4 ,it is1 that although the differences are irregular 7e4g4 between ,b #aa and ,c #ab the difference is #a1 while between ,o #af and ,f #ai the difference is #c71 yet there is no marked displacement in the order of arrangements of the elements1 inasmuch as no element has an atomic weight lower than that preceding it in the horizontal line4 ,it was for some time supposed that tellurium and iodine were thus misplaced2 and indeed it is even now not quite established that they are not1 but the balance of evidence is in favour of tellurium having a lower atomic weight than iodine4 ,argon1 however1 is a marked exception4 ,with an atomic weight of #cihh1 its natural position would lie between those of potassium and calcium2 but there is no room for it4 ,and for this reason considerable doubts have been thrown on the validity of the conclusion to be drawn from the found ratio of its specific heats1 #a1 viz4 that its molecule and its atom are identical4 ,if it were a diatomic gas1 like chlorine or hydrogen1 its atomic weight would be #aiid1 and it would find a fitting position after fluorine and before sodium4 ,and the difference between its atomic weight and that of helium1 to which the atomic weight #ba would for the same reasons then attach1 would be #aghd1 one not incomparable with #af4 ,but1 as before remarked1 it is difficult1 if not altogether impossible1 to conceive of a diatomic structure to which all energy imparted in the form of heat should result in translational motion1 and as a matter of fact none such is known4 ,there are two methods of escape from this dilemma4 ,if the gases termed argon and helium are not single elements1 but mixtures of monatomic elements1 then what has been termed their atomic weights will represent the mean of the atomic weights of two or more elements1 taken in the proportion in which they occur4 ,for example1 supposing that argon is a mixture of an element of atomic weight #cg with one of atomic weight #hb1 the found atomic weight1 nearly #dj1 would imply a mixture of #icc per cent of the lighter1 with #fg per cent of the heavier element4 ,we must therefore carefully examine all evidence for or against the supposition that argon is a mixture of elements4 ,it is well known that elements with high atomic weights have1 as a rule1 higher boiling-points than those with low atomic weights in the same columns4 ,perhaps the most striking case is that of the elements fluorine1 chlorine1 bromine1 and iodine4 ,whereas fluorine has never been liquefied 7chiefly owing to difficulties of manipulation1 due to its extraordinarily energetic action on almost every element and compound71 chlorine boils at -#ajb1 bromine at #ei1 and iodine at #ahd4 ,and if a mixture of chlorine and bromine gases be cooled1 the bromine1 if present in sufficient amount1 will condense first1 in a fairly pure state1 little chlorine condensing with it4 ,but in a mixture containing only #g per cent of bromine with #ic per cent of chlorine 7analogous to a mixture of the two supposed constituents of the argon mixture7 the pressure of the bromine gas in the mixture would be only #g_/ajjths of the normal pressure1 or #ecb millimetres4 ,at this pressure the boiling-point of bromine is about -#e1 so that1 on cooling to that temperature1 bromine would begin to show signs of liquefaction4 ,this is1 however1 still nearly #ajj above the boiling-point of chlorine2 and there would therefore be no difficulty whatever in detecting such a percentage of bromine in a mixture of chlorine and bromine gases on cooling the mixture to a moderately low temperature4#cj ,argon has been liquefied4 ,a sample of pure argon was sent by ,professor ,ramsay to ,professor ,olszewski of ,cracow1 well known for his accurate researches at low temperatures2 and he found the boiling-point of argon at atmospheric pressure to be -#ahfi1 and its melting-point to be -#ahif4 ,there was no appearance of liquid before the boiling-point was reached1 nor was there any alteration of temperature as the argon boiled away1 and these are signs of a single substance1 not of a mixture2 moreover1 the melting-point was a definite one2 and here again1 mixtures never melt suddenly1 but always show signs of softening before melting4 ,so far as this evidence goes1 therefore1 it points to the conclusion that argon is not a mixture of two elements4 ,other evidence may be sought for in the spectrum of argon1 which was carefully examined by ,mr4 ,crookes4 ,it consists of a great number of lines1 extending all through the spectrum1 from far down in the red to far beyond the visible violet2 the invisible lines were examined by the aid of photography1 for ultraviolet light1 although invisible to the eye1 impresses a photographic plate4 ,the most striking feature of this spectrum is the change which can be produced in it by altering the intensity of the electric discharge which is passed through the tube containing argon at a low pressure4 ,by interposing a ,leyden jar between the secondary terminals of the induction-coil from which sparks are taken through the gas1 the colour of the light in the tube changes from a brilliant red to an equally brilliant blue4 ,a large number of lines in the red spectrum disappear1 on interposing the jar1 while many lines in the blue-green1 blue1 and violet part of the spectrum1 invisible before1 shine out with great brilliancy4 ,there is no other gas in which a similar alteration of intensity of discharge produces such a marked difference1 although in many gases1 supposed to be simple substances1 similar changes may be produced4 ,so far as we know at present1 however1 such a change cannot be definitely ascribed to the presence of a mixture of two elements1 although it is in itself a very remarkable phenomenon4 ,on the other hand1 ,professors ,runge and ,paschen1 in a paper communicated to the ,royal ,academy of ,science of ,berlin in ,july #ahie1 have adduced reasons for concluding that helium1 the gas from clveite1 is a mixture2 it appears to show lines belonging to two spectra1 each series of lines exhibiting certain regularities4 ,but this1 although an important conclusion in itself1 has no direct bearing on the question of the simplicity of argon4 ,one method of separating the constituents of a mixture is by taking advantage of their different solubilities in water1 or in some other appropriate solvent4 ,and as argon was found to have the solubility of #d volumes in #ajj of water1 while helium is very sparingly soluble1 only #jg volume per #ajj1 it is not unreasonable to suppose that1 if argon consisted of a mixture of elements in argon1 one should be more soluble than another4 ,exhaustive experiments in this direction have still to be carried out2 but ,lord ,rayleigh has made experiments which render it very improbable that any separation into its constituents1 if it be a mixture1 can be thus effected4 ,wishing to ascertain if there were any helium in the air1 he shook up atmospheric argon with water1 until a very small fraction remained undissolved4 ,the spectrum of this small residue was identical with that of the original argon1 from which it would appear that this method1 at least1 is incapable of effecting any separation4 ,a completely decisive proof that argon is not a mixture has just been furnished by experiments carried out by ,dr4 ,collie and ,professor ,ramsay1 in which a large quantity of argon was submitted to fractional diffusion4 ,from what was said on p4 #afb1 it will be seen that if argon consisted of a mixture of two gases of different densities1 such a process should separate the mixture more or less completely into its two constituents4 ,after a long series of diffusions1 however1 the density of that portion of argon passing first through the porous plug1 which would have been less had any gas of lower density been present1 was found to be identical with that of the last portions of gas4 ,on the other hand1 by aid of the same diffusion-apparatus1 a fair separation of oxygen 7density #af7 from carbon dioxide 7density #bb7 was effected1 although1 as the reader will observe1 the densities of these two gases do not differ greatly4 ,hence1 if argon consists of two kinds of matter they must have the same density1 and hence the same molecular weights1 and the difficulty is not removed4 ,but as the spectrum of the first and last portions was the same and was identical with that of argon1 this supposition is improbable4 ,the evidence is therefore distinctly against the supposition that argon is a mixture of two or more elements4 ,there is1 however1 another possible method of accounting for the high atomic weight of argon1 which1 if it could be reduced by a few units1 would fall into its place after chlorine and before potassium4 ,it is that argon consists of a mixture of many monatomic1 with comparatively few diatomic1 molecules4 ,if there were only about #ejj molecules of diatomic argon in every #aj1jjj molecules of the gas1 its density1 supposing it to consist entirely of monatomic molecules1 would be #ai1 and its atomic and molecular weights #ch1 a number which would fit between the atomic weight of chlorine1 #cee1 and that of potassium1 #cia4 ,several instances of this kind are known4 ,chlorine itself1 when heated to high temperatures1 changes from diatomic to monatomic molecules1 and the density decreases with the change4 ,for example1 at #ajjj the found density of chlorine is #bg1 implying a molecular weight of #ed2 now #ed is neither the weight of a monatomic molecule of chlorine1 viz4 #cee1 nor of a diatomic molecule1 which is #ga2 but it corresponds to that of a mixture of monatomic and diatomic molecules4 ,here fall of temperature causes combination of monatomic molecules with each other to form diatomic molecules2 and rise of temperature increases the number of monatomic molecules1 at the expense of the diatomic molecules4 ,is there no sign of similar behaviour with argon8 ,it has already been mentioned that the rise of pressure of argon with rise of temperature has been carefully measured by ,drs4 ,randall and ,kuenen1 and that it is quite normal2 no sign of splitting has been observed4 ,but the range of temperature was not great 7it was only from #j to #bhj71 and it is quite possible that the change1 if there was one1 was so minute as to have escaped detection4 ,again1 a more delicate method of detecting such a change is in the measurement of the ratio of the specific heats4 ,the most trustworthy number obtained was #afei for the ratio1 instead of #affg1 the theoretical figure4 ,a mixture of #e per cent of diatomic molecules should have reduced this ratio to #afdh4 ,here the evidence is1 however1 inconclusive4 ,but on the whole1 the presumption is against the hypothesis that argon is a mixture of monatomic with diatomic molecules4 ,it still remains for us1 therefore1 to account for the fact that in the periodic table there is no place for argon1 provided it be insisted on that the elements must follow each other in the numerical order of their atomic weights4 ,if the numbers in the table actually showed regular intervals1 or if there were any regularity to be detected in their differences1 argon might be regarded as of wholly exceptional behaviour4 ,but this is not so4 ,argon is an extreme instance of divergence1 but similar divergences1 though not of equal magnitude1 are common4 ,in attempting to offer an explanation of such anomalies1 it must be remembered that the question is in itself a far-reaching one2 and that although argon has served to direct attention anew to the anomalies of the periodic table1 yet these anomalies existed before argon was discovered4 ,it is necessary above all things to be clear as to what is under discussion4 ,we speak of 8atomic weights10 or 8atomic masses40 ,what is meant precisely by these expressions8 ,by mass1 we understand that property of a body1 in virtue of which1 when acted on by a certain force for a certain time1 it acquires a certain velocity4 ,the product of the mass into half the velocity squared1 or ,,mv#b 7where ,m and ,v stand respectively for mass and for velocity71 is what is termed kinetic energy4 ,if the mass chosen be #a gram1 and the velocity #a centimetre per second1 the unit of energy is the product2 it is termed an erg4 ,the same unit of energy1 the erg1 is derived by the action of unit force1 termed #a dyne1 through unit length1 #a centimetre4 ,we have thus two equations1 where ,f and ,l represent force and length1 ,kinetic ,energy 7,,mv7#b and ,linear ,energy ,,fl4 ,now we choose mass as a unit of measure of the quantity of material2 and we are justified in doing so1 because experiments have shown that material1 confined in a closed space1 does not appreciably alter its mass4 ,the mass is proportional to the weight1 generally measured as the force exerted at some definite latitude on the earth's surface1 tending to pull the body towards the centre of the earth4 ,this force is equal to about #iha dynes at ,london4 ,there is no known reason why mass and weight should be proportional to each other2 for the cause of the attraction of the earth has never been satisfactorily elucidated4 ,we therefore use weight1 or the attraction of the earth1 as a convenient means of determining the relative masses of two objects4 ,hence it appears rational to prefer the expression 8atomic weight0 to 8atomic mass10 seeing that the former represents the actual result of experiment1 and also because we are dealing in atomic weights with relative numbers4 ,but this is really a matter of choice4 ,the atomic weights therefore represent the relative masses in which the elements generally unite4 ,they often1 however1 unite in multiples of these weights1 as formulated by ,dalton's second law4 ,the weights1 arranged in numerical order in columns1 give us the periodic table4 ,now energy can be measured in other units besides those of force and mass4 ,heat is one form of energy1 and it is measured by an interval of temperature1 and by a property which we term specific heat4 ,it happens that the latter property varies1 not with the mass of the substance heated1 but with its atom1 so that all elements have approximately the same atomic heat2 that is1 quantities of elements proportional in mass to their atomic weights require approximately equal increments of heat to raise their temperature through an equal interval1 say #a4 ,this is the formulation of ,dulong and ,petit's law previously alluded to4 ,but here we meet with irregularities1 which have up till now defied classification4 ,the heat imparted to an aggregation of atoms is not expended solely in raising their temperature2 other work is done also1 as is generally supposed1 in the nature of expansion1 or separation of parts1 as in overcoming the attraction between the atoms in the molecule1 or in imparting special motion to the atoms2 such work1 however1 involves an expenditure of energy which is either very small in proportion to the total energy imparted as heat1 or is nearly the same for all elements4 ,at present we cannot decide between these alternatives1 owing to the lack of knowledge of the nature of liquids and solids4 ,the main fact1 however1 is incontestable3 that the heat energy required to raise different elements through the same interval of temperature is the same1 not for equal masses or weights of the substances1 but for their atomic masses4 ,again1 many compounds when dissolved in water conduct an electric current1 while they themselves are decomposed2 and the different ingredients of the compound are often deposited at the points where the electric current enters or leaves the liquid4 ,where they are not so deposited1 it is usually because of their action on the solvent water4 ,now ,faraday found that when elements are deposited1 equal quantities of electricity are conveyed either by equal numbers of atoms or by some simple fraction of these numbers4 ,to this fraction we apply the term valency4 ,thus we say that an atom of oxygen is bivalent1 or a dyad1 because it conveys twice as much electricity through the liquid in which it is present as an atom of hydrogen1 which is termed univalent1 or a monad4 ,here we see a direct connection between the conveyance of an electric charge and the atomic weight4 ,the electric unit of quantity is in fact defined as that which can be conveyed by a certain weight of hydrogen1 by #h times that weight of oxygen1 by #ajh times that weight of silver1 and so on4 ,therefore the electrical unit is connected1 not with unit of mass1 or with the gravitational unit1 but with the atomic unit4 ,we have therefore a number of systems1 each capable of being equated to a unit of energy1 but of which the terms are in some as yet unknown way related to each other1 and often more directly than they can be related to mass and weight4 ,this relation is only an approximate one in the case of specific heats2 it appears to be an absolute one in the conveyance of electrical energy4 ,the arrangement of the elements in the periodic table must therefore be considered by the light of such general views4 ,i would venture to suggest1 as a tentative method of solving this problem1 that it be considered whether mass or weight are such invariable properties of matter as have generally been taken for granted4 ,that the relative weights or masses in which elements combine always retain their invariable proportion is true1 so far as we can determine2 but it must be remembered that we cannot cause them to combine except under a very limited series of conditions4 ,for example1 the act of combination equalises the temperature of two combining atoms2 it also1 in all probability1 equalises their electrical charges4 ,it is a legitimate speculation whether1 could we maintain a difference in their temperature or in their electric potential1 their atomic weights might not also change4 ,indeed1 we are ignorant whether mass is changed by alteration of temperature4 ,experiments made by ,sir ,john ,airy1 and interpreted by ,professor ,hicks1 appear to show that variation of temperature is not without some influence on gravitational attraction4 ,others by ,professor ,landolt point in the same direction4 ,it therefore appears to me not impossible that the mass of the atoms may be affected by the various and different properties which they possess1 some to a greater1 some to a lesser extent4 ,it must be admitted that atoms differ from each other in the readiness with which they combine with those of the same kind to form molecules2 and that molecules of different elements differ from each other in their capacity to form molecular aggregates4 ,take1 for example1 such cases as caesium and fluorine1 each intensely active1 but towards different objects3 caesium the most electro-positive of the metals1 and fluorine the most electro-negative of elements4 ,surely their activity must be due to some cause which cannot but exert influence on their other properties1 such as their mass and their gravitational attraction1 as it doubtless has influence on their specific heats1 and on many of their other physical properties4 ,and contrast these instances with helium and with argon1 the most indifferent of substances1 the atoms of which are unwilling1 and apparently unable1 to pair even with themselves2 it is hardly conceivable that these peculiarities should leave their other1 and1 as we are in the habit of thinking1 invariable1 properties unaffected4 ,i venture to suggest that these powers of combination1 due to some configuration or to some attractive force1 tend to lessen the gravitational attraction by which we measure their atomic weights2 that helium and argon1 which possess little1 if any1 of such power to combine1 show what may be termed the normal atomic weights1 inasmuch as their gravitational attraction is subject to no deduction attributable to their reacting powers4 ,i cannot but think that1 when some numerical values are assigned to this combinational power1 it will be found that they will so increase their atomic weights as to display that regularity which1 so far as we can see at present1 is conspicuous by its absence4 ,i am aware that these suggestions are of a wholly speculative character2 and yet ,i venture to put them forward in the firm conviction that no true progress in knowledge has ever been made without such speculations4 ,it was the speculative phlogistic theory which combined phenomena apparently so distinct as the burning of a candle and the rusting of iron4 ,it is true that that theory is now a phantom of the past1 yet it served its purpose in directing attention to phenomena of a similar character4 ,it would be easy to multiply instances of the kind2 in almost every case some useful object has been served by speculation preceding exact knowledge4 ,the object of science1 as indeed of inquiry in all departments of human interest1 is to reconcile the world of man with the world of nature1 and to endeavour to know in part that of which we hope one day to attain to a perfect knowledge4 ,,the ,,end #cj ,these considerations would hold on the assumption that no combination takes place between chlorine and bromine4 ,printed by ,r4 ,r4 ,,clark1 ,,limited1 ,edinburgh4