file which includes the original illustrations4 ,see #chbdf-;h4htm or #chbdf-;h4zip3 7https3_/_/www4gutenberg4org_/cache_/epu b_/#chbdf_/pg#chbdf-;images4html7 or 7https3_/_/www4gutenberg4org_/files_/#ch bdf_/chbdf-;h4zip7 ,,heroes ,,of ,,science4 ,chemists by ,m4 ,m4 ,,pattison ,,muir1 ,m4,a41 ,f4,r4,s4,e41 ,fellow1 and ,praelector in ,chemistry1 of ,gonville and ,caius ,college1 ,cambridge4 ,published under the ,direction of the ,committee of ,general ,literature and ,education ,appointed by the ,society for ,promoting ,christian ,knowledge4 ,london3 ,society for ,promoting ,christian ,knowledge1 ,northumberland ,avenue1 ,charing ,cross2 #dc1 ,queen ,victoria ,street1 ,e4,c42 #bf1 ,st4 ,george's ,place1 ,hyde ,park ,corner1 ,s4,w4 ,brighton3 #ace1 ,north ,street4 ,new ,york3 ,e4 ,j4 ,b4 ,young ,co4 #ahhc4 ,the discoveries of great men never leave us2 they are immortal2 they contain those eternal truths which survive the shock of empires1 outlive the struggles of rival creeds1 and witness the decay of successive religions4--,,buckle4 ,he who studies ,nature has continually the exquisite pleasure of discerning or half discerning and divining laws2 regularities glimmer through an appearance of confusion1 analogies between phenomena of a different order suggest themselves and set the imagination in motion2 the mind is haunted with the sense of a vast unity not yet discoverable or nameable4 ,there is food for contemplation which never runs short2 you gaze at an object which is always growing clearer1 and yet always1 in the very act of growing clearer1 presenting new mysteries4--,,the ,,author ,,of ,,ecce ,,homo4 ,je laenger ich lebe1 desto mehr verlern' ich das ,gelernte1 naemlich die ,systeme4--,,jean ,,paul ,,richter4 ,,preface4 ,i have endeavoured in this book to keep to the lines laid down for me by the ,publication ,committee of the ,society1 viz4 to exhibit1 by selected biographies1 the progress of chemistry from the beginning of the inductive method until the present time4 ,the progress of chemistry has been made the central theme2 around this ,i have tried to group short accounts of the lives of those who have most assisted this progress by their labours4 ,this method of treatment1 if properly conducted1 exhibits the advances made in science as intimately connected with the lives and characters of those who studied it1 and also impresses on the reader the continuity of the progress of natural knowledge4 ,the lives of a few chemists have been written2 of others there are1 however1 only scanty notices to be found4 ,the materials for this book have been collected chiefly from the following works3-- ,kopp's ,geschichte der ,chemie4 ,thomson's ,history of ,chemistry4 ,ladenburg's ,entwickelungsgeschichte der ,chemie4 ,wurtz's ,history of the ,atomic ,theory4 ,watts's ,dictionary of ,chemistry4 ,whewell's ,history of the ,inductive ,sciences4 ,rodwell's ,birth of ,chemistry2 ,inquiry into the ,hermetic ,mystery and ,alchemy 7,london1 #ahej72 ,popular ,treatises on ,science written during the ,middle ,ages1 edited for the ,historical ,society of ,science by ,thomas ,wright1 ,m4,a4 7,london1 #ahda72 ,ripley ,reviv'd2 or1 ,an ,exposition upon ,sir ,george ,ripley's ,hermetico-,poetical ,works1 by ,eirenaeus ,philalethes 7,london1 #afgh72 ,tripus ,aureus1 hoc est ,tres ,tractates ,chymici ,selectissimi 7,frankfurt1 #afah74 ,alchemy2 article in ,encyclopaedia ,britannica4 ,boyle's ,sceptical ,chymist4 ,biographie ,universelle2 for notices of ,berzelius and ,lavoisier4 ,english ,cyclopaedia2 for notices of ,black1 ,berzelius and ,lavoisier4 ,black's ,lectures1 with ,memoir3 edited by ,dr4 ,robinson4 ,priestley's ,memoirs3 written partly by himself4 ,priestley's works on ,air1 etc4 ,lavoisier's ,oeuvres4 ,dalton's ,life1 by ,dr4 ,henry2 ,life1 by ,dr4 ,r4 ,angus ,smith2 ,new ,system of ,chemical ,philosophy4 ,davy's ,collected ,works2 with ,life1 by his brother2 ,life1 by ,dr4 ,paris4 ,berzelius's ,lehrbuch1 and various dissertations4 ,woehler's ,jugenderinnerungen eines ,chemikers4 ,graham's ,collected ,memoirs4 ,sketch of ,graham's life1 in ,chemical ,society's ,journal4 ,life-,work of ,liebig1 by ,a4 ,w4 ,hofmann4 ,dumas1 by ,a4 ,w4 ,hofmann4 ,various dissertations by ,liebig and ,dumas in ,annalen1 and elsewhere4 ,my warmest thanks are due to my friend1 ,mr4 ,francis ,rye1 for the great assistance he has given me in correcting the proof-sheets4 ,m4 ,m4 ,,pattison ,,muir4 ,,cambridge1 ,april1 #ahhc4 ,,contents4 ,,page ,,introductory #a ,,chapter ,i4 ,,alchemy3 ,,and ,,the ,,dawn ,,of ,,chemistry4 ,beginnings of natural knowledge--,chemistry in the ,middle ,ages--,alchemy--,the phlogistic theory #e ,,chapter ,,ii4 ,,establishment ,,of ,,chemistry ,,as ,a ,,science--,,period ,,of ,,black1 ,,priestley ,,and ,,lavoisier4 ,introduction of accurate measurements into chemistry--,black's researches on alkalis and on fixed air--,his conception of heat--,priestley's experiments on airs--,his discovery of oxygen--,lavoisier1 the founder of the science of chemistry--,he clearly establishes a connection between composition and properties of bodies #cj ,,chapter ,,iii4 ,,establishment ,,of ,,general ,,principles ,,of ,,chemical ,,science--,,period ,,of ,,dalton4 ,dalton's training in physical science--,he revives and renders quantitative the atomic theory--,the term atom is applied by him to elements and compounds alike--,his rules for chemical synthesis #ajf ,,chapter ,,iv4 ,,establishment ,,of ,,general ,,principles ,,of ,,chemical ,,science 7continued7--,,period ,,of ,,davy ,,and ,,berzelius4 ,electro-chemistry--,the dualistic theory developed by ,berzelius--,davy's work on acids1 alkalis1 and salts--,he proves chlorine to be an element--,his discovery of the safety-lamp #aee ,,chapter ,v4 ,,the ,,work ,,of ,,graham4 ,graham traces the movements of molecules--,he distinguishes between colloids and cystalloids--,dialysis #bcb ,,chapter ,,vi4 ,,rise ,,and ,,progress ,,of ,,organic ,,chemistry--,,period ,,of ,,liebig ,,and ,,dumas4 ,the barrier between inorganic and organic chemistry begins to be broken down--,woehler prepares urea--,dumas opposes the dualistic system of ,berzelius--,liebig's conception of compound radicles--,his work in animal and agricultural chemistry #beb ,,chapter ,,vii4 ,,modern ,,chemistry4 ,the relations between composition and properties of bodies are developed and rendered more definite--,physical methods are more largely made use of in chemistry--,spectroscopic analysis #bid ,,chapter ,,viii4 ,,summary ,,and ,,conclusion #caf ,,heroes ,,of ,,science4 ,,introductory4 ,as we trace the development of any branch of natural knowledge we find that there has been a gradual progress from vague and fanciful to accurate and definite views of ,nature4 ,we find that as man's conceptions of natural phenomena become more accurate they also for a time become more limited1 but that this limitation is necessary in order that facts may be correctly classified1 and so there may be laid the basis for generalizations which1 being definite1 shall also be capable of expansion4 ,at first ,nature is strange2 she is full of wonderful and fearful appearances4 ,man is overwhelmed by the sudden and apparently irregular outbreaks of storms1 by the capricious freaks of thunder and lightning1 by the awful and unannounced devastations of the volcano or the earthquake2 he believes himself to be surrounded by an invisible array of beings more powerful than himself1 but1 like himself1 changeable in their moods and easily provoked to anger4 ,after a time he begins to find that it is possible to trace points of connection between some of the appearances which had so overpowered or perplexed him4 ,the huntsman observes that certain kinds of plants always grow where the game which he pursues is chiefly to be found2 from the appearance of the sky at morning and evening the fisherman is able to tell whether there will follow weather suitable for him to set out in his fishing-boat2 the tiller of the ground begins to feel sure that if he sow the seed in the well-dug soil and water it in proper seasons he will certainly reap the harvest in due time4 ,and thus man comes to believe that natural events follow each other in a fixed order2 there arises a conscious reference on his part of certain effects to certain definite causes4 ,accurate knowledge has begun4 ,as knowledge of natural appearances advances there comes a time when men devote themselves chiefly to a careful study of some one class of facts2 they try to consider that part of ,nature with which they are mostly concerned as separate from all other parts of ,nature4 ,thus the various branches of natural knowledge begin to have each a distinct existence4 ,these branches get more and more subdivided1 each division is more accurately studied1 and so a great number of facts is accumulated in many classes4 ,then we usually find that a master mind arises1 who shows the connection which exists between the different parts of each division of natural knowledge1 who takes a wide1 far-reaching view of the whole range of the province of knowledge which he studies1 and who1 at the same time1 is able to hold in his vision all the important details of each branch of which that province is composed4 ,and thus we again get wide views of ,nature4 ,but these are very different from the vague1 dim and hesitating notions in which natural knowledge had its beginnings4 ,in this later time men see that ,nature is both simple and complex2 that she is more wonderful than their fathers dreamed1 but that through all the complexity there runs a definite purpose2 that the apparently separate facts are bound together by definite laws1 and that to discover this purpose and these laws is possible for man4 ,as we trace this progress in the various branches of natural knowledge we are struck with the fact that each important advance is generally accomplished by one or two leading men2 we find that it becomes possible to group the history of each period round a few central figures2 and we also learn that the character of the work done by each of these men of note is dependent on the nature and training of the individual man4 ,it will be my endeavour in the following pages to give an account of the advance of chemical science1 grouping the facts in each stage of progress round the figures of one or two men who were prominent in that period4 ,for the purposes of this book it will be necessary that ,i should sketch only the most important periods in the story of chemical progress1 and that in each of these ,i should fill in the prominent points alone4 ,i shall therefore select three periods in the progress of this science1 and try to give an account of the main work done in each of these4 ,and the periods will be3-- ,i4 ,the period wherein1 chiefly by the work of ,black1 ,priestley and ,lavoisier1 the aim of chemical science was defined and the essential characters of the phenomena to be studied were clearly stated4 ,,ii4 ,the period during which1 chiefly by the labours of ,dalton1 ,berzelius and ,davy1 the great central propositions of the science were laid down and were developed into a definite theory4 ,as belonging in great extent to this period1 although chronologically later1 ,i shall also consider the work of ,graham4 ,,iii4 ,the period when1 chiefly owing to advances made in organic chemistry1 broader and more far-reaching systems of classification were introduced1 and the propositions laid down in the preceding period were modified and strengthened4 ,the workers in this period were very numerous2 ,i shall chiefly consider these two--,liebig and ,dumas4 ,i shall conclude with a brief sketch of some of the important advances of chemical science in more recent times1 and a summary of the characteristics of each of the three periods4 ,,chapter ,i4 ,,alchemy3 ,,and ,,the ,,dawn ,,of ,,chemistry4 ,early chemistry was not a science4 ,the ancient chemists dealt chiefly with what we should now call chemical manufactures2 they made glass1 cleaned leather1 dyed cloth purple and other colours1 extracted metals from their ores1 and made alloys of metals4 ,no well-founded explanations of these processes could be expected either from men who simply used the recipes of their predecessors1 or from philosophers who studied natural science1 not by the help of accurate experiments1 but by the unaided light of their own minds4 ,at somewhat later times chemistry assumed a very important place in the general schemes propounded by philosophers4 ,change is vividly impressed on all man's surroundings3 the endeavour to find some resting-place amidst the chaos of circumstances1 some unchanging substance beneath the ever-changing appearances of things1 has always held a prominent place with those who study the phenomena of the world which surrounds them4 ,in the third and fourth centuries of our era much attention was given to the art which professed to explain the changes of ,nature4 ,religion1 philosophy1 and what we should now call natural science1 were at that time closely intermingled2 the scheme of things which then1 and for several centuries after that time1 exerted a powerful influence over the minds of many thinkers was largely based on the conception of a fundamental unity underlying and regulating the observed dissimilarities of the universe4 ,thus1 in the ,emerald ,table of ,hermes1 which was held in much repute in the ,middle ,ages1 we read-- ,true1 without error1 certain and most true3 that which is above is as that which is below1 and that which is below is as that which is above1 for performing the miracles of the ,one ,thing2 and as all things were from one1 by the mediation of one1 so all things arose from this one thing by adaptation3 the father of it is the ,sun1 the mother of it is the ,moon1 the wind carried it in its belly1 the nurse of it is the ,earth4 ,this is the father of all perfection1 the consummation of the whole world4 ,and again1 in a later writing we have laid down the basis of the art of alchemy in the proposition that there abides in nature a certain pure matter1 which1 being discovered and brought by art to perfection1 converts to itself proportionally all imperfect bodies that it touches4 ,to discover this fundamental principle1 this ,one ,thing1 became the object of all research4 ,earth and the heavens were supposed to be bound together by the all-pervading presence of the ,one ,thing2 he who should attain to a knowledge of this precious essence would possess all wisdom4 ,to the vision of those who pursued the quest for the ,one ,thing the whole universe was filled by one ever-working spirit1 concealed now by this1 now by that veil of sense1 ever escaping identification in any concrete form1 yet certainly capable of being apprehended by the diligent searcher4 ,analogy was the chief guide in this search4 ,if it were granted that all natural appearances were manifestations of the activity of one essential principle1 then the vaguest and most far-fetched analogies between the phenomena of nature might1 if properly followed up1 lead to the apprehension of this hidden but everywhere present essence4 ,the history of alchemy teaches1 in the most striking manner1 the dangers which beset this method of pursuing the study of ,nature2 this history teaches us that analogies1 unless founded on carefully and accurately determined facts1 are generally utterly misleading in natural science4 ,let us consider the nature of the experimental evidence which an alchemist of the fourth or fifth century could produce in favour of his statement that transmutation of one kind of matter into another is of constant occurrence in ,nature4 ,the alchemist heated a quantity of water in an open glass vessel2 the water slowly disappeared1 and when it was all gone there remained in the vessel a small quantity of a white earthy solid substance4 ,what could this experiment teach save that water was changed into earth and air8 ,the alchemist then plunged a piece of red-hot iron into water placed under a bell-shaped glass vessel2 some of the water seemed to be changed into air1 and a candle1 when brought into the bell1 caused the air therein to take fire4 ,therefore1 concluded the experimenter1 water is proved to be changeable into fire4 ,a piece of lead was then strongly heated in the air2 it lost its lustre and became changed into a reddish-white powder1 very unlike lead in its properties2 this powder was then heated in a convenient vessel with a little wheat1 whereupon the lead was again produced4 ,therefore1 said the alchemist1 lead is destroyed by fire1 but it can be reproduced from its ashes by the help of heat and a few grains of corn4 ,the experimenter would now proceed to heat a quantity of a mineral containing lead in an open vessel made of pulverized bones2 the lead slowly disappeared1 and at the close of the experiment a button of silver remained4 ,might he not triumphantly assert that he had transmuted lead into silver8 ,in order that the doctrine of the transmutation of metals might rest on yet surer evidence1 the alchemist placed a piece of copper in spirits of nitre 7nitric acid72 the metal disappeared2 into the green liquid thus produced he then placed a piece of iron2 the copper again made its appearance1 while the iron was removed4 ,he might now well say that if lead was thus demonstrably changed into silver1 and copper into iron1 it was1 to say the least1 extremely probable that any metal might be changed into any other provided the proper means for producing the change could be discovered4 ,but the experimental alchemist had a yet stranger transmutation wherewith to convince the most sceptical4 ,he poured mercury in a fine stream on to melted sulphur2 at once the mercury and the sulphur disappeared1 and in their place was found a solid substance black as the raven's wing4 ,he then heated this black substance in a closed vessel1 when it also disappeared1 and in its place there was found1 deposited on the cooler part of the vessel1 a brilliantly red-coloured solid4 ,this experiment taught lessons alike to the alchemist1 the philosopher1 and the moralist of these times4 ,the alchemist learned that to change one kind of matter into another was an easy task3 the philosopher learned that the prevalence of change or transmutation is one of the laws of ,nature3 and the moralist learned that evil is not wholly evil1 but contains also some germs of good2 for was not the raven-black substance emblematical of the evil1 and the red-coloured matter of the good principle of things8#a ,on such experimental evidence as this the building of alchemy was reared4 ,a close relationship was believed to prevail through the whole phenomena of ,nature4 ,what more natural then than to regard the changes which occur among the forms of matter on this earth as intimately connected with the changes which occur among the heavenly bodies8 ,man has ever been overawed by the majesty of the stars2 yet he has not failed to notice that the movements of these bodies are apparently capricious4 ,the moon has always been to him a type of mutability2 only in the sun has he seemed to find a settled resting-point4 ,now1 when we remember that in the alchemical scheme of things the material earth and material heavens1 the intellectual1 the moral1 and the spiritual world were regarded as one great whole1 the parts of which were continuously acting and reacting on each other1 we cannot wonder that the alchemist should regard special phenomena which he observed in his laboratory1 or special forms of matter which he examined1 as being more directly than other phenomena or other forms of matter1 under the influence of the heavenly bodies4 ,this connection became gradually more apparent to the student of alchemy1 until at last it was fixed in the language and the symbols which he employed4 ,thus the sun 7,sol7 was represented by a circle1 which likewise became the symbol for gold1 as being the most perfect metal4 ,the moon 7,luna7 was ever changing2 she was represented by a half-circle1 which also symbolized the pale metal silver4 ,copper and iron were regarded as belonging to the same class of metals as gold1 but their less perfect nature was denoted by the sign or 4 ,tin and lead belonged to the lunar class1 but like copper they were supposed to be imperfect metals4 ,mercury was at once solar and lunar in its properties4 ,these suppositions were summed up in such alchemical symbols as are represented below-- ,illustration3 ,sol4 ,gold4 ,illustration3 ,luna4 ,silver4 ,illustration3 ,venus4 ,copper4 ,illustration3 ,mars4 ,iron4 ,illustration3 ,jupiter4 ,tin4 ,illustration3 ,saturn4 ,lead4 ,illustration3 ,mercury4 ,quicksilver4 ,many of the alchemical names remain to the present time2 thus in pharmacy the name lunar caustic is applied to silver nitrate1 and the symptoms indicative of lead-poisoning are grouped together under the designation of saturnine cholic4 ,but as the times advanced the older and nobler conception of alchemy became degraded4 ,if it be true1 the later alchemists urged1 that all things suffer change1 but that a changeless essence or principle underlies all changing things1 and that the presence of more or less of this essence confers on each form of matter its special properties1 it follows that he who can possess himself of this principle will be able to transmute any metal into any other2 he will be able to change any metal into gold4 ,now1 as the possession of gold has always carried with it the means of living luxuriously1 it is easy to understand how1 when this practical aspect of alchemy had taken firm root in men's minds1 the pursuit of the art became for all1 except a few lofty and noble spirits1 synonymous with the pursuit of wealth4 ,so that we shall not1 ,i think1 much err if we describe the chemistry of the later ,middle ,ages as an effort to accumulate facts on which might be founded the art of making gold4 ,in one respect this was an advance4 ,in the early days of alchemy there had been too much trusting to the mental powers for the manufacture of natural facts3 chemists now actually worked in laboratories2 and very hard did many of these alchemists work4 ,paracelsus says of the alchemists1 ,they are not given to idleness1 nor go in a proud habit1 or plush and velvet garments1 often showing their rings upon their fingers1 or wearing swords with silver hilts by their sides1 or fine and gay gloves upon their hands2 but diligently follow their labours1 sweating whole days and nights by their furnaces4 ,they do not spend their time abroad for recreation1 but take delight in their laboratory4 ,they put their fingers amongst coals1 into clay and filth1 not into gold rings4 ,they are sooty and black like smiths and miners1 and do not pride themselves upon clean and beautiful faces4 ,by thus taking delight in their laboratories the later alchemists gathered together many facts2 but their work centred round one idea1 viz4 that metals might all be changed into gold1 and this idea was the result rather of intellectual guessing than of reasoning on established facts of ,nature4 ,one of the most famous alchemists of the ,middle ,ages was born at ,einsiedeln1 in ,switzerland1 in #adic4 ,his name1 when paraphrased into ,greek1 became ,paracelsus4 ,this man1 some of whose remarks have just been quoted1 acquired great fame as a medical practitioner1 and also as a lecturer on medicine3 he travelled throughout the greater part of ,europe1 and is supposed to have been taught the use of several new medicines by the ,arabian physicians whom he met in ,spain4 ,with an over-weening sense of his own powers1 with an ardent and intemperate disposition1 revolting against all authority in medicine or science1 ,paracelsus yet did a good work in calling men to the study of ,nature as the only means whereby natural science could be advanced4 ,alchemy has but one aim and object1 ,paracelsus taught3 to extract the quintessence of things1 and to prepare arcana and elixirs which may serve to restore to man the health and soundness he has lost4 ,he taught that the visible universe is but an outer shell or covering1 that there is a spirit ever at work underneath this veil of phenomena2 but that all is not active3 to separate the active function 7the spirit7 of this outside shell from the passive was1 he said1 the proper province of alchemy4 ,paracelsus strongly insisted on the importance of the changes which occur when a substance burns1 and in doing this he prepared the way for ,stahl and the phlogistic chemists4 ,however we may admire the general conceptions underlying the work of the earlier alchemists1 we must admit that the method of study which they adopted could lead to very few results of lasting value2 and ,i think we may add that1 however humble the speculations of these older thinkers might appear1 this humility was for the most part only apparent4 ,these men were encompassed 7as we are7 by unexplained appearances3 they were every moment reminded that man is not the measure of all things2 and by not peering too anxiously into the mysteries around them1 by drawing vague conclusions from partially examined appearances1 they seemed at once to admit their own powerlessness and the greatness of ,nature4 ,but ,i think we shall find1 as we proceed with our story1 that this is not the true kind of reverence1 and that he is the really humble student of ,nature who refuses to overlook any fact1 however small1 because he feels the tremendous significance of every part of the world of wonders which it is his business and his happiness to explore4 ,as examples of the kind of explanation given by alchemists of those aspects of ,nature which they professed to study1 ,i give two quotations from translations of the writings of ,basil ,valentine and ,paracelsus1 who flourished in the first half of the fifteenth and sixteenth centuries respectively4 ,think most diligently about this2 often bear in mind1 observe and comprehend that all minerals and metals together1 in the same time1 and after the same fashion1 and of one and the same principal matter1 are produced and generated4 ,that matter is no other than a mere vapour1 which is extracted from the elementary earth by the superior stars1 or by a sidereal distillation of the macrocosm2 which sidereal hot infusion1 with an airy sulphureous property1 descending upon inferiors1 so acts and operates as that there is implanted1 spiritually and invisibly1 a certain power and virtue in those metals and minerals2 which fume1 moreover1 resolves in the earth into a certain water wherefrom all metals are thenceforth generated and ripened to their perfection1 and thence proceeds this or that metal or mineral1 according as one of the three principles acquires dominion and they have much or little of sulphur and salt1 or an unequal mixture of these2 whence some metals are fixed1 that is1 constant or stable2 and some are volatile and easily changeable1 as is seen in gold1 silver1 copper1 iron1 tin and lead4 ,the life of metals is a secret fatness2 of salts1 the spirit of aqua fortis2 of pearls1 their splendour2 of marcasites and antimony1 a tingeing metalline spirit2 of arsenics1 a mineral and coagulated poison4 ,the life of all men is nothing else but an astral balsam1 a balsamic impression1 and a celestial invisible fire1 an included air1 and a tingeing spirit of salt4 ,i cannot name it more plainly1 although it is set out by many names4 ,when the alchemists gave directions for making the stone which was to turn all it touched into gold1 they couched them in such strange and symbolical language as this3 ,after our serpent has been bound by her chain1 penetrated with the blood of our green dragon1 and driven nine or ten times through the combustible fire into the elementary air1 if you do not find her to be exceeding furious and extremely penetrating1 it is a sign that you do not hit our subject1 the notion of the homogenea1 or their proportion2 if this furious serpent does not come over in a cloud and turn into our virgin milk1 or argentine water1 not corrosive at all and yet insensibly and invisibly devouring everything that comes near it1 it is plainly to be seen that you err in the notion of our universal menstruum4 ,or1 again1 what could any reasonable man make of this8 ,in the green lion's bed the sun and moon are born2 they are married and beget a king4 ,the king feeds on the lion's blood1 which is the king's father and mother1 who are at the same time his brother and sister4 ,i fear ,i betray the secret1 which ,i promised my master to conceal in dark speech from any one who knows not how to rule the philosopher's fire4 ,concerning the same lion1 another learned author says that though called a lion1 it is not an animal substance1 but for its transcendant force1 and the rawness of its origin1 it is called the green lion4 ,but he adds in a moment of confidence3 ,this horrid beast has so many names1 that unless ,god direct the searcher it is impossible to distinguish him4 ,and once more4 ,take our two serpents1 which are to be found everywhere on the face of the earth3 tie them in a love-knot and shut them up in the ,arabian caraha4 ,this is the first labour2 but the next is more difficult4 ,thou must encamp against them with the fire of nature1 and be sure thou dost bring thy line round about4 ,circle them in and stop all avenues that they find no relief4 ,continue this siege patiently1 and they turn into an ugly venomous black toad1 which will be transformed to a horrible devouring dragon1 creeping and weltering in the bottom of her cave without wings4 ,touch her not by any means1 for there is not on earth such a vehement transcending poison4 ,as thou hast begun so proceed1 and this dragon will turn into a swan4 ,henceforth ,i will show thee how to fortify thy fire till the phoenix appear3 it is a red bird of a most deep colour1 with a shining fiery hue4 ,feed this bird with the fire of his father and the ether of his mother3 for the first is meat and the second is drink1 and without this last he attains not to his full glory4 ,be sure to understand this secret1 etc41 etc4 ,the alchemists spoke of twelve gates through which he who would attain to the palace of true art must pass3 these twelve gates were to be unlocked by twelve keys1 descriptions of which1 couched in strange and symbolical language1 were given in alchemical treatises4 ,thus in ,ripley reviv'd#b we read that ,canon ,ripley1 of ,bridlington1 who lived in the time of ,edward ,,iv41 sang thus of the first gate1 which was ,calcination3-- ,the battle's fought1 the conquest won1 ,the ,lyon dead reviv'd2 ,the eagle's dead which did him slay1 ,and both of sense depriv'd4 ,the showers cease1 the dews which fell ,for six weeks do not rise2 ,the ugly toad that did so swell ,with swelling bursts and dies4 ,and of the third gate1 or ,conjunction1 we find the ,canon saying-- ,he was a king1 yet dead as dead could be2 ,his sister a queen1 ,who when her brother she did breathless see1 ,the like was never seen1 ,she cryes ,until her eyes ,with over-weeping were waxed dim-- ,so long till her tears ,reach'd up to her ears3 ,the queen sunk1 but the king did swim4 ,in some books these gates and keys are symbolically represented in drawings1 e4g4 in a pamphlet by ,paracelsus1 called ,tripus ,aureus1 hoc est ,tres ,tractates chymici selectissimi4 7,frankfurt1 #afah47 ,it is evident that a method of studying ,nature which resulted in such dim and hazy explanations as these was eminently fitted to produce many who pretended to possess secrets by the use of which they could bring about startling results beyond the power of ordinary men2 and1 at the same time1 the almost universal acceptance of such statements as those ,i have quoted implied the existence in men generally of a wondrous readiness to believe anything and everything4 ,granted that a man by sweating whole days and nights by his furnaces can acquire knowledge which gives him great power over his fellows1 it necessarily follows that many will be found ready to undergo these days and nights of toil4 ,and when we find that this supposed knowledge is hidden under a mask of strange and mystical signs and language1 we may confidently assert that there will be many who learn to repeat these strange terms and use these mystical signs without attempting to penetrate to the truths which lie behind--without1 indeed1 believing that the mystical machinery which they use has any real meaning at all4 ,we find1 as a matter of fact1 that the age of the alchemists produced many deceivers1 who1 by mumbling incantations and performing a few tricks1 which any common conjuror would now despise1 were able to make crowds of men believe that they possessed a supernatural power to control natural actions1 and1 under this belief1 to make them part with their money and their substance4 ,one respectable physician of the ,hague1 who entertained a peripatetic alchemist1 complains that the man entered his best-furnished room without wiping his shoes1 although they were full of snow and dirt4 ,however1 the physician was rewarded1 as the stranger gave him1 out of his philosophical commiseration1 as much as a turnip seed in size of the much-wished-for stone of wisdom4 ,that the alchemist of popular belief was a man who used a jargon of strange and high-sounding words1 that he might the better deceive those whom he pretended to help1 is evident from the literature of the sixteenth and seventeenth centuries4 ,in the play of the ,alchymist ,ben ,jonson draws the character of ,subtle as that of a complete scoundrel1 whose aim is to get money from the pockets of those who are stupid enough to trust him1 and who never hesitates to use the basest means for this end4 ,from the speeches of ,subtle we may learn the kind of jargon employed by the men who pretended that they could cure diseases and change all baser metals into gold4 ,subtle4 ,name the vexations and the martyrizations of metals in the work4 ,face4 ,sir1 putrefaction1 ,solution1 ablution1 sublimation1 ,cohobation1 calcination1 ceration1 and ,fixation4 ,sub4 ,and when comes vivification8 ,face4 ,after mortification4 ,sub4 ,what's cohobation8 ,face4 ',tis the pouring on ,your aqua regis1 and then drawing him off1 ,to the trine circle of the seven spheres4 99 99 99 99 99 ,sub4 ,and what's your mercury8 ,face4 ,a very fugitive2 he will be gone1 sir4 ,sub4 ,how know you him8 ,pace4 ,by his viscosity1 ,his oleosity1 and his suscitability4 ,even in the fourteenth century1 ,chaucer 7in the ,canon's ,yeoman's ,tale7 depicts the alchemist as a mere cunning knave4 ,a priest is prevailed on to give the alchemist money1 and is told that he will be shown the change of base metal into gold4 ,the alchemist busies himself with preparations1 and sends the priest to fetch coals4 ,and whil he besy was1 this feendly wrecche1 ,this false chanoun 7the foule feende him fecche7 ,out of his bosom took a bechen cole ,in which ful subtilly was maad an hole1 ,and therein put was of silver lymayle ,an unce1 and stopped was withoute fayle ,the hole with wex1 to keep the lymayle in4 ,and understondith1 that this false gyn ,was not maad there1 but it was maad before4 ,this false gyn having been put in the crucible and burned with the rest of the ingredients1 duly let out its silver lymayle 7filings71 which appeared in the shape of a small button of silver1 and so accomplished the false chanoun's end of deceiving his victim4 ,the alchemists accumulated many facts3 they gained not a little knowledge concerning the appearances of ,nature1 but they were dominated by a single idea4 ,living in the midst of an extremely complex order of things1 surrounded by a strange and apparently capricious succession of phenomena1 they were convinced that the human intelligence1 directed and aided by the teachings of the ,church1 would guide them through the labyrinth4 ,and so they entered on the study of ,nature with preconceived notions and foregone conclusions3 enthusiastic and determined to know although many of them were1 they nevertheless failed because they refused to tread the only path which leads to true advances in natural science--the path of unprejudiced accurate experiment1 and of careful reasoning on experimentally determined facts4 ,and even when they had become convinced that their aims were visionary1 they could not break free from the vicious system which bound them4 444 ,i am broken and trained ,to my old habits3 they are part of me4 ,i know1 and none so well1 my darling ends ,are proved impossible3 no less1 no less1 ,even now what humours me1 fond fool1 as when ,their faint ghosts sit with me and flatter me1 ,and send me back content to my dull round4#c ,one of the most commonly occurring and most noticeable changes in the properties of matter is that which proceeds when a piece of wood1 or a candle1 or a quantity of oil burns4 ,the solid wood1 or candle1 or the liquid oil slowly disappears1 and this disappearance is attended with the visible formation of flame4 ,even the heavy fixed metals1 tin or lead1 may be caused to burn2 light is produced1 a part of the metal seems to disappear1 and a white 7or reddish7 solid1 very different from the original metal1 remains4 ,the process of burning presents all those peculiarities which are fitted to strike an observer of the changes of ,nature2 that is1 which are fitted to strike a chemist--for chemistry has always been recognized as having for its object to explain the changes which matter undergoes4 ,the chemists of the seventeenth and eighteenth centuries were chiefly occupied in trying to explain this process of burning or combustion4 ,van ,helmont 7#aegg-afdd71 who was a physician and chemist of ,brussels1 clearly distinguished between common air and other airs or gases produced in different ways4 ,robert ,hooke 7#afce-agjc71 one of the original ,fellows of the ,royal ,society1 in the ,micographia1 or ,philosophical ,description of ,minute ,bodies1 published in #affe1 concluded from the results of numerous experiments that there exists in common air a peculiar kind of gas1 similar to1 or perhaps identical with the gas or air which is got by heating saltpetre2 and he further supposed that when a solid burns1 it is dissolved by 7or we should now say1 it is converted into a gas by combining with7 this peculiar constituent of the air4 ,john ,mayow 7#afde-afgi71 a physician of ,oxford1 experimented on the basis of facts established by ,hooke4 ,he showed that when a substance1 e4g4 a candle1 burns in air1 the volume of air is thereby lessened4 ,to that portion of the air which had dissolved the burned substance he gave the name of nitre-air1 and he argued that this air exists in condensed form in nitre1 because sulphur burns when heated with nitre in absence of common air4 ,mayow added the most important fact--a fact which was forgotten by many later experimenters--that the solid substance obtained by burning a metal in air weighs more than the metal itself did before burning4 ,he explained this increase in weight by saying that the burning metal absorbs particles of nitre-air from the atmosphere4 ,thus ,hooke and ,mayow had really established the fact that common air consists of more than one definite kind of matter--in other words1 that common air is not an element2 but until recent times the term element or elementary principle was used without any definite meaning4 ,when we say that the ancients and the alchemists recognized four elements--earth1 air1 fire1 and water--we do not attach to the word element the same definite meaning as when we now say1 ,iron is an element4 ,from earth1 air1 fire and water other substances were obtained2 or it might be possible to resolve other substances into one or more of these four4 ,but even to such a word as substance or matter no very definite meaning could be attached4 ,although1 therefore1 the facts set forth by ,hooke and ,mayow might now justify the assertion that air is not an element1 they did not1 in the year #afgj1 necessarily convey this meaning to men's minds4 ,the distinction between element and compound was much more clearly laid down by the ,hon4 ,robert ,boyle 7#afbg-afia71 whose chemical work was wonderfully accurate and thorough1 and whose writings are characterized by acute scientific reasoning4 ,we shall again return to these terms element and compound4 ,but the visible and striking phenomenon in most processes of burning is the production of light and sometimes of flame4 ,the importance of the fact that the burned substance 7when a solid7 weighs more than the unburned substance was overshadowed by the apparent importance of the outward part of the process1 which could scarcely be passed over by any observer4 ,there appears to be an outrush of something from the burning substance4 ,there is an outrush of something1 said ,becher and ,stahl1 and this something is the principle of fire4 ,the principle of fire1 they said1 is of a very subtle nature2 its particles1 which are always in very rapid motion1 can penetrate any substance1 however dense4 ,when metals burn--the argument continued--they lose this principle of fire2 when the burned metal--or calx as it was usually called--is heated with charcoal it regains this principle1 and so the metal is re-formed from the calx4 ,thus arose the famous theory of phlogiston 7from ,greek1 burned71 which served as a central nucleus round which all chemical facts were grouped for nearly a hundred years4 ,john ,joachim ,becher was born at ,speyer in #afce1 and died in #afhb2 in his chemical works1 the most important of which is the ,physica ,subterranea1 he retained the alchemical notion that the metals are composed of three principles--the nitrifiable1 the combustible1 and the mercurial--and taught that during calcination the combustible and mercurial principles are expelled1 while the nitrifiable remains in the calx4 ,george ,ernest ,stahl--born at ,anspach in #affj1 and died at ,berlin in #agcd--;had regard chiefly to the principles which escape during the calcination of metals1 and simplifying1 and at the same rendering more definite the idea of ,becher1 he conceived and enunciated the theory of phlogiston4 ,but if something 7name it phlogiston or call it by any other name you please7 is lost by a metal when the metal is burned1 how is it that the loss of this thing is attended with an increase in the weight of the matter which loses it8 ,either the theory of phlogiston must be abandoned1 or the properties of the thing called phlogiston must be very different from those of any known kind of matter4 ,stahl replied1 phlogiston is a principle of levity2 the presence of phlogiston in a substance causes that substance to weigh less than it did before it received this phlogiston4 ,in criticizing this strange statement1 we must remember that in the middle of the seventeenth century philosophers in general were not firmly convinced of the truth that the essential character of matter is that it possesses weight1 nor of the truth that it is impossible to destroy or to create any quantity of matter however small4 ,it was not until the experimental work of ,lavoisier became generally known that chemists were convinced of these truths4 ,nevertheless1 the opponents of the ,stahlian doctrine were justified in asking for further explanations--in demanding that some other facts analogous to this supposed fact1 viz4 that a substance can weigh less than nothing1 should be experimentally established4 ,the phlogistic theory however maintained its ground2 we shall find that it had a distinct element of truth in it1 but we shall also find that it did harm to scientific advance4 ,this theory was a wide and sweeping generalization from a few facts2 it certainly gave a central idea around which some facts might be grouped1 and it was not very difficult1 by slightly cutting down here and slightly adding there1 to bring many new discoveries within the general theory4 ,we now know that in order to explain the process of combustion much more accurate knowledge was required than the chemists of the seventeenth century possessed2 but we ought to be thankful to these chemists1 and notably to ,stahl1 that they did not hesitate to found a generalization on the knowledge they had4 ,almost everything propounded in natural science has been modified as man's knowledge of nature has become wider and more accurate2 but it is because the scientific student of nature uses the generalizations of to-day as stepping-stones to the better theories of to-morrow1 that science grows from more to more4 ,looking at the state of chemistry about the middle of the eighteenth century1 we find that the experiments1 and especially the measurements1 of ,hooke and ,mayow had laid a firm basis of fact concerning the process of combustion1 but that the phlogistic theory1 which appeared to contradict these facts1 was supreme2 that the existence of airs1 or gases1 different from common air was established1 but that the properties of these airs were very slightly and very inaccurately known2 that ,boyle had distinguished element from compound and had given definite meanings to these terms1 but that nevertheless the older and vaguer expression1 elementary principle1 was generally used2 and lastly1 that very few measurements of the masses of the different kinds of matter taking part in chemical changes had yet been made4 ,,footnotes3 #a ,i have borrowed these illustrations of the alchemical1 experimental method from ,m4 ,hoefer's ,histoire de la ,chimie1 quoted in the ,encyclopaedia ,brittanica1 art4 ,alchemy4 #b ,ripley reviv'd3 or an exposition upon ,sir ,george ,ripley's ,hermetico-poetical works1 by ,eirenaeus ,philalethes4 ,london1 #afgh4 #c ,browning's ,paracelsus4 ,,chapter ,,ii4 ,,establishment ,,of ,,chemistry ,,as ,a ,,science--,,period ,,of ,,black1 ,,priestley ,,and ,,lavoisier4 ,joseph ,black1 #agbh-agii4 ,joseph1 ,priestley1 #agcc-ahjd4 ,antoine ,laurent ,lavoisier1 #agdc-agid4 ,during this period of advance1 which may be broadly stated as comprising the last half of the eighteenth century1 the aim and scope of chemical science were clearly indicated by the labours of ,black1 ,priestley and ,lavoisier4 ,the work of these men dealt chiefly with the process of combustion4 ,black and ,priestley finally proved the existence of airs or gases different from common air1 and ,lavoisier applied these discoveries to give a clear explanation of what happens when a substance burns4 99 99 99 99 99 ,,joseph ,,black was born near ,bordeaux in the year #agbh4 ,his father was of ,scottish family1 but a native of ,belfast2 his mother was the daughter of ,mr4 ,gordon1 of ,hilhead in ,aberdeenshire4 ,we are told by ,dr4 ,robison1 in his preface to ,black's ,lectures1 that ,john ,black1 the father of ,joseph1 was a man of most amiable manners1 candid and liberal in his sentiments1 and of no common information4 ,at the age of twelve ,black was sent home to a school at ,belfast2 after spending six years there he went to the ,university of ,glasgow in the year #agdf4 ,little is known of his progress at school or at the university1 but judging from his father's letters1 which his son preserved1 he seems to have devoted himself to study4 ,while at ,glasgow he was attracted to the pursuit of physical science1 and chose medicine as a profession4 ,becoming a pupil of ,dr4 ,cullen1 he was much impressed with the importance of chemical knowledge to the student of medicine4 ,dr4 ,cullen appears to have been one of the first to take large and philosophical views of the scope of chemical science1 and to attempt to raise chemistry from the rank of a useful art to that of a branch of natural philosophy4 ,such a man must have been attracted by the young student1 whose work was already at once accurate in detail and wide in general scope4 ,in the notes of work kept by ,black at this time are displayed those qualities of methodical arrangement1 perseverance and thoroughness which are so prominent in his published investigations and lectures4 ,in one place we find1 says his biographer1 many disjointed facts and records of diverse observations1 but the next time he refers to the same subjects we generally have analogous facts noted and some conclusions drawn--we have the beginnings of knowledge4 ,having once entered on an investigation ,black works it out steadily until he gets definite results4 ,his earlier notes are concerned chiefly with heat and cold2 about #ageb he begins to make references to the subject of fixed air4 ,about #agej ,black went to ,edinburgh ,university to complete his medical studies1 and here he was again fortunate in finding a really scientific student occupying the chair of natural philosophy4 ,the attention of medical men was directed at this time to the action of limewater as a remedy for stone in the bladder4 ,all the medicines which were of any avail in mitigating the pain attendant on this disease more or less resembled the caustic ley of the soap-boilers 7or as we should now call it caustic potash or soda74 ,these caustic medicines were mostly prepared by the action of quicklime on some other substance1 and quicklime was generally supposed to derive its caustic1 or corrosive properties from the fire which was used in changing ordinary limestone into quicklime4 ,when quicklime was heated with fixed alkalis 7i4e4 with potassium or sodium carbonate71 it changed these substances into caustic bodies which had a corrosive action on animal matter2 hence it was concluded that the quicklime had derived a power--or some said had derived igneous matter--from the fire1 and had communicated this to the fixed alkalis1 which thereby acquired the property of corroding animal matter4 ,black thought that he might be able to lay hold of this igneous matter supposed to be taken by the limestone from the fire2 but he found that limestone loses weight when changed into quicklime4 ,he then dissolved limestone 7or chalk7 in spirits of salt 7hydrochloric acid71 and compared the loss of weight undergone by the chalk in this process with the loss suffered by an equal quantity of chalk when strongly heated4 ,this investigation led ,black to a fuller study of the action of heat on chalk and on mild magnesia 7or as we now say1 magnesium carbonate74 ,in order that his experiments might be complete and his conclusions well established1 he delayed taking the degree of ,doctor of ,medicine for three years4 ,he graduated as ,m4 ,d4 in #agee1 and presented his thesis on ,magnesia ,alba1 ,quicklime and other ,alkaline ,substances1 which contained the results of what is probably the first accurately quantitative examination of a chemical action which we possess4 ,black prepared mild magnesia 7magnesium carbonate7 by boiling together solutions of ,epsom salts 7magnesium sulphate7 and fixed alkali 7potassium carbonate74 ,he showed that when mild magnesia is heated-- #a4 ,it is much decreased in bulk4 #b4 ,it loses weight 7twelve parts become five1 according to ,black74 #c4 ,it does not precipitate lime from solutions of that substance in acids 7,black had already shown that mild magnesia does precipitate lime74 ,he then strongly heated a weighed quantity of mild magnesia in a retort connected with a receiver2 a few drops of water were obtained in the receiver1 but the magnesia lost six or seven times as much weight as the weight of the water produced4 ,black then recalls the experiments of ,hales1 wherein airs other than common air had been prepared1 and concludes that the loss of weight noticed when mild magnesia is calcined is probably due to expulsion1 by the heat1 of some kind of air4 ,dissolving some of his mild magnesia in acid he noticed that effervescence occurred1 and from this he concluded that the same air which1 according to his hypothesis1 is expelled by heat1 is also driven out from the mild magnesia by the action of acid4 ,he then proceeded to test this hypothesis4 ,one hundred and twenty grains of mild magnesia were strongly calcined2 the calcined matter1 amounting to seventy grains1 was dissolved in dilute oil of vitriol1 and this solution was mixed with common fixed alkali 7potassium carbonate74 ,the solid which was thus produced was collected1 washed and weighed2 it amounted to a trifle less than one hundred and twenty grains1 and possessed all the properties--detailed by ,black--of the original mild magnesia4 ,but this is exactly the result which ought to have occurred according to his hypothesis4 ,the next step in the investigation was to collect the peculiar air which ,black had proved to be evolved during the calcination of mild magnesia4 ,to this substance he gave the name of fixed air1 because it was fixed or held by magnesia4 ,black established the existence of this air in the expired breath of animals1 and also showed that it was present in the air evolved during vinous fermentation4 ,he demonstrated several of its properties2 among these1 the fact that animals die when placed in this air4 ,an air with similar properties was obtained by calcining chalk4 ,black held that the chemical changes which occur when chalk is calcined are exactly analogous to those which he had proved to take place when magnesia is strongly heated4 ,chalk ought therefore to lose weight when calcined2 the residue ought to neutralize an acid without evolution of any gas1 and the quantity of acid thus neutralized ought to be the same as would be neutralized by the uncalcined chalk2 lastly1 it ought to be possible to recover the uncalcined chalk by adding a fixed alkali to a solution of the calcined chalk or quicklime4 ,the actual results which ,black obtained were as follows3-- ,one hundred and twenty grains of chalk were dissolved in dilute muriatic 7hydrochloric7 acid2 #dba grains of the acid were needed to neutralize the chalk1 and #dh grains of fixed air were evolved4 ,one hundred and twenty grains of the same specimen of chalk were strongly calcined1 and then dissolved in dilute muriatic acid2 #dad grains of the acid were required to neutralize the calcined chalk4 ,the difference between #dba and #dad is very slight2 considering the state of practical chemistry at ,black's time1 we may well agree with him that he was justified in the conclusion that equal weights of calcined and of uncalcined chalk neutralize the same amount of acid4 ,one hundred and twenty grains of the same specimen of chalk were again strongly heated2 the calcined chalk1 amounting to #fh grains1 was digested with a solution of fixed alkali in water4 ,the substance thus obtained1 when washed and dried1 weighed #aah grains1 and had all the properties of ordinary chalk4 ,therefore1 said ,black1 it is possible to recover the whole of the chalk originally present before calcination1 by adding a fixed alkali to the calcined chalk or quicklime4 ,at this time it was known that water dissolves quicklime1 but it was generally held that only about one-fourth 7or perhaps a little more7 of any specimen of quicklime could be dissolved by water1 however much water was employed4 ,black's researches had led him to regard quicklime as a homogeneous chemical compound2 he concluded that as water undoubtedly dissolves quicklime to some extent1 any specimen of this substance1 provided it be pure1 must be wholly soluble in water4 ,carefully conducted experiments proved that ,black's conclusion was correct4 ,black had thus proved that quicklime is a definite substance1 with certain fixed properties which characterize it and mark it off from all other substances2 that by absorbing1 or combining with another definite substance 7fixed air71 quicklime is changed into a third substance1 namely chalk1 which is also characterized by properties as definite and marked as those of quicklime or fixed air4 ,black1 quite as much as the alchemists1 recognized the fact that change is continually proceeding in ,nature2 but he clearly established the all-important conclusion that these natural changes proceed in definite order1 and that it is possible by careful experiment and just reasoning to acquire a knowledge of this order4 ,he began the great work of showing that1 as in other branches of natural science1 so also in chemistry1 which is pre-eminently the study of the changes of ,nature1 the only distinct meaning of that word 7natural7 is stated1 fixed1 or settled 7,butler's ,analogy1 published #agcf74 ,this research by ,black is a model of what scientific work ought to be4 ,he begins with a few observations of some natural phenomenon2 these he supplements by careful experiments1 and thus establishes a sure basis of fact2 he then builds on this basis a general hypothesis1 which he proceeds to test by deducing from it certain necessary conclusions1 and proving1 or disproving1 these by an appeal to ,nature4 ,this is the scientific method2 it is common sense made accurate4 ,very shortly after the publication of the thesis on magnesia and quicklime1 a vacancy occurred in the chemical chair in ,glasgow ,university1 and ,black was appointed ,professor of ,anatomy and ,lecturer on ,chemistry4 ,as he did not feel fully qualified to lecture on anatomy1 he made an arrangement to exchange subjects with the ,professor of ,medicine1 and from this time he delivered lectures on chemistry and on ,the ,institutes of ,medicine4 ,black devoted a great deal of care and time to the teaching duties of his chair4 ,his chemical experimental researches were not much advanced after this time2 but he delivered courses of lectures in which new light was thrown on the whole range of chemical science4 ,in the years between #agei and #agfc ,black examined the phenomena of heat and cold1 and gave an explanation1 founded on accurate experiments1 of the thermal changes which accompany the melting of solids and the vaporization of liquids4 ,if pieces of wood1 lead and ice be taken by the hand from a box in which they have been kept cold1 the wood feels cold to the touch1 the lead feels colder than the wood1 and the ice feels colder than the lead2 hence it was concluded that the hand receives cold from the wood1 more cold from the lead1 and most cold from the ice4 ,black however showed that the wood really takes away heat from the hand1 but that as the wood soon gets warmed1 the process stops before long2 that the lead1 not being so quickly warmed as the wood1 takes away more heat from the hand than the wood does1 and that the ice takes away more heat than either wood or lead4 ,black thought that the heat which is taken by melting ice from a warm body remains in the water which is produced2 as soon as winter came he proceeded to test this supposition by comparing the times required to melt one pound of ice and to raise the temperature of one pound of water through one degree1 the source of heat being the same in each case4 ,he also compared the time required to lower the temperature of one pound of water through one degree with that required to freeze one pound of ice-cold water4 ,he found that in order to melt one pound of ice without raising its temperature1 as much heat had to be added to the ice as sufficed to raise the temperature of one pound of water through about #adj degrees of ,fahrenheit's thermometer4 ,but this heat which has been added to the ice to convert it into water is not indicated by the thermometer4 ,black called this latent heat4 ,the experimental data and the complete theory of latent heat were contained in a paper read by ,black to a private society which met in the ,university of ,glasgow1 on ,april #bc1 #agfb2 but it appears that ,black was accustomed to teach the theory in his ordinary lectures before this date4 ,the theory of latent heat ought also to explain the phenomena noticed when liquid water is changed into steam4 ,black applied his theory generally to this change1 but did not fully work out the details and actually measure the quantity of heat which is absorbed by water at the boiling point before it is wholly converted into steam at the same temperature1 until some years later when he had the assistance of his pupil and friend ,james ,watt4 ,taking a survey of the phenomena of ,nature1 ,black insisted on the importance of these experimentally established facts--that before ice melts it must absorb a large quantity of heat1 and before water is vaporized it must absorb another large quantity of heat1 which amounts of heat are restored to surrounding substances when water vapour again becomes liquid water and when liquid water is congealed to ice4 ,he allows his imagination to picture the effects of these properties of water in modifying and ameliorating the climates of tropical and of ,northern countries4 ,in his lectures he says1 ,here we can also trace another magnificent train of changes which are nicely accommodated to the wants of the inhabitants of this globe4 ,in the equatorial regions1 the oppressive heat of the sun is prevented from a destructive accumulation by copious evaporation4 ,the waters1 stored with their vaporific heat1 are then carried aloft into the atmosphere till the rarest of the vapour reaches the very cold regions of the air1 which immediately forms a small portion of it into a fleecy cloud4 ,this also further tempers the scorching heat by its opacity1 performing the acceptable office of a screen4 ,from thence the clouds are carried to the inland countries1 to form the sources in the mountains which are to supply the numberless streams that water the fields4 ,and by the steady operation of causes1 which are tolerably uniform1 the greater part of the vapours passes on to the circumpolar regions1 there to descend in rains and dews2 and by this beneficent conversion into rain by the cold of those regions1 each particle of steam gives up the heat which was latent in it4 ,this is immediately diffused1 and softens the rigour of those less comfortable climates4 ,in the year #agff ,black was appointed ,professor of ,chemistry in the ,university of ,edinburgh1 in which position he remained till his death in #agii4 ,during these thirty-three years he devoted himself chiefly to teaching and to encouraging the advance of chemical science4 ,he was especially careful in the preparation of his elementary lectures1 being persuaded that it was of the utmost importance that his pupils should be well grounded in the principles of chemistry4 ,his health had never been robust1 and as he grew old he was obliged to use great care in his diet2 his simple and methodical character and habits made it easy for him to live on the plainest food1 and to take meals and exercise at stated times and in fixed quantities4 ,black's life closed1 as was fitting1 in a quiet and honoured old age4 ,he had many friends1 but lived pretty much alone--he was never married4 ,on the #bfth of ,november #agii1 being at table with his usual fare1 some bread1 a few prunes and a measured quantity of milk diluted with water1 and having the cup in his hand when the last stroke of his pulse was to be given1 he had set it down on his knees1 which were joined together1 and kept it steady with his hand1 in the manner of a person perfectly at ease2 and in this attitude he expired1 without spilling a drop1 and without a writhe in his countenance1 as if an experiment had been required to show to his friends the facility with which he departed4 ,black was characterized by moderation and sobriety of thought2 he had a great sense of the fitness of things--of what is called by the older writers propriety4 ,but he was by no means a dull companion2 he enjoyed general society1 and was able to bear a part in any kind of conversation4 ,a thorough student of ,nature1 he none the less did not wish to devote his whole time to laboratory work or to the labours of study2 indeed he seems to have preferred the society of well-cultivated men and women to that of specialists in his own or other branches of natural science4 ,but with his true scientific peers he doubtless appeared at his best4 ,among his more intimate friends were the famous political economist ,adam ,smith1 and the no less celebrated philosopher ,david ,hume4 ,dr4 ,hutton1 one of the earliest workers in geology1 was a particular friend of ,black2 his friendship with ,james ,watt began when ,watt was a student in his class1 and continued during his life4 ,with such men as his friends1 and engaged in the study of ,nature--that boundless subject which one can never know to the full1 but which one can always know a little more year by year--,black's life could not but be happy4 ,his example and his teaching animated his students2 he was what a university professor ought to be1 a student among students1 but yet a teacher among pupils4 ,his work gained for him a place in the first rank of men of science2 his clearness of mind1 his moderation1 his gentleness1 his readiness to accept the views of others provided these views were well established on a basis of experimentally determined facts1 fitted him to be the centre of a circle of scientific students who looked on him as at once their teacher and their friend4 ,as a lecturer ,black was eminently successful4 ,he endeavoured to make all his lectures plain and intelligible2 he enlivened them by many experiments designed simply to illustrate the special point which he had in view4 ,he abhorred ostentatious display and trickiness in a teacher4 ,black was strongly opposed to the use of hypotheses in science4 ,dr4 ,robison 7the editor of his lectures7 tells that when a student in ,edinburgh he met ,black1 who became interested in him from hearing him speak somewhat enthusiastically in favour of one of the lecturers in the university4 ,black impressed on him the necessity of steady experimental work in natural science1 gave him a copy of ,newton's ,optics as a model after which scientific work ought to be conducted1 and advised him to reject1 even without examination1 any hypothetical explanation1 as a mere waste of time and ingenuity4 ,but1 when we examine ,black's own work1 we see that by hypothetical explanations he meant vague guesses4 ,he himself made free use of scientific 7i4e4 of exact7 hypotheses2 indeed the history of science tells us that without hypotheses advance is impossible4 ,black taught by his own researches that science is not an array of facts1 but that the object of the student of ,nature is to explain facts4 ,but the method generally in vogue before the time of ,black was to gather together a few facts1 or what seemed to be facts1 and on these to raise a vast superstructure of vain imaginings4 ,naturalists had scarcely yet learned that ,nature is very complex1 and that guessing and reasoning on guesses1 with here and there an observation added1 was not the method by which progress was to be made in learning the lessons written in this complex book of ,nature4 ,in place of this loose and slipshod method ,black insisted that the student must endeavour to form a clear mental image of every phenomenon which he studied4 ,such an image could be obtained only by beginning with detailed observation and experiment4 ,from a number of definite mental images the student must put together a picture of the whole natural phenomenon under examination2 perceiving that something was wanted here1 or that the picture was overcrowded there1 he must again go to ,nature and gain fresh facts1 or sometimes prove that what had been accepted as facts had no real existence1 and so at length he would arrive at a true representation of the whole process4 ,so anxious was ,black to define clearly what he knew and professed to teach1 that he preferred to call his lectures ,on the ,effects of ,heat and ,mixtures1 rather than to announce them as ,a ,systematic ,course on ,chemistry4 ,his introductory lecture on ,heat in ,general is very admirable2 the following quotation will serve to show the clearness of his style and the methodical but yet eminently suggestive manner of his teaching3-- ,of ,heat in ,general4 ,that this extensive subject may be treated in a profitable manner1 ,i propose-- ,first4 ,to ascertain what ,i mean by the word heat in these lectures4 ,secondly4 ,to explain the meaning of the term cold1 and ascertain the real difference between heat and cold4 ,thirdly4 ,to mention some of the attempts which have been made to discover the nature of heat1 or to form an idea of what may be the immediate cause of it4 ,fourthly and lastly4 ,i shall begin to describe sensible effects produced by heat on the bodies to which it is communicated4 ,any person who reflects on the ideas which we annex to the word heat will perceive that this word is used for two meanings1 or to express two different things4 ,it either means a sensation excited in our organs1 or a certain quality1 affection1 or condition of the bodies around us1 by which they excite in us that sensation4 ,the word is used in the first sense when we say1 we feel heat2 in the second1 when we say1 there is heat in the fire or in a hot stone4 ,there cannot be a sensation of heat in the fire1 or in the hot stone1 but the matter of the fire1 or of the stone1 is in a state or condition by which it excites in us the sensation of heat4 ,now1 in beginning to treat of heat and its effects1 ,i propose to use the word in this second sense only2 or as expressing that state1 condition1 or quality of matter by which it excites in us the sensation of heat4 ,this idea of heat will be modified a little and extended as we proceed1 but the meaning of the word will continue at bottom the same1 and the reason of the modification will be easily perceived4 ,black's manner of dealing with the phenomenon of combustion illustrates the clearness of the conceptions which he formed of natural phenomena1 and shows moreover the thoroughly unbiased nature of his mind4 ,as soon as he had convinced himself that the balance of evidence was in favour of the new 7antiphlogistic7 theory1 he gave up those doctrines in which he had been trained1 and accepted the teaching of the ,french chemists2 but he did not--as some with less well-balanced minds might do--regard the new theory as a final statement1 but rather as one stage nearer the complete explanation which future experiments and future reasoning would serve to establish4 ,in his lectures on combustion ,black first of all establishes the facts1 that when a body is burned it is changed into a kind 7or kinds7 of matter which is no longer inflammable2 that the presence of air is needed for combustion to proceed2 that the substance must be heated to a certain degree before combustion or inflammation begins2 that this degree of heat 7or we should now say this degree of temperature7 differs for each combustible substance2 that the supply of air must be renewed if the burning is to continue2 and that the process of burning produces a change in the quality of the air supplied to the burning body4 ,he then states the phlogistic interpretation of these phenomena3 that combustion is caused by the outrush from the burning body of a something called the principle of fire1 or phlogiston4 ,black then proceeds to demonstrate certain other facts3--,when the substances produced by burning phosphorus or sulphur are heated with carbon 7charcoal7 the original phosphorus or sulphur is reproduced4 ,this reproduction is due1 according to the phlogistic chemists1 to the giving back1 by carbon1 of the phlogiston which had escaped during the burning4 ,hence carbon contains much phlogiston4 ,but as a similar reproduction of phosphorus or sulphur1 from the substances obtained by burning these bodies1 can be accomplished by the use of substances other than carbon1 it is evident that these other substances also contain much phlogiston1 and1 moreover1 that the phlogiston contained in all these substances is one and the same principle4 ,what then1 he asks1 is this principle which can so escape1 and be so restored by the action of various substances8 ,he then proceeds as follows3-- ,but when we inquire further1 and endeavour to learn what notion was formed of the nature of this principle1 and what qualities it was supposed to have in its separate state1 we find this part of the subject very obscure and unsatisfactory1 and the opinions very unsettled4 ,the elder chemists1 and the alchemists1 considered sulphur as the universal inflammable principle1 or at least they chose to call the inflammable part of all bodies1 that are more or less inflammable1 by the name of their sulphur4444 ,the famous ,german chemist ,becher was1 ,i believe1 the first who rejected the notion of sulphur being the principle of inflammability in bodies4444 ,his notion of the nature of the pure principle of inflammability was afterwards more fully explained and supported by ,professor ,stahl1 who1 agreeably to the doctrine of ,becher1 represented the principle of inflammability as a dry substance1 or of an earthy nature1 the particles of which were exquisitely subtile1 and were much disposed to be agitated and set in motion with inconceivable velocity4444 ,the opinion of ,becher and ,stahl concerning this terra secunda1 or terra inflammabilis1 or phlogiston1 was that the atoms of it are1 more than all others1 disposed to be affected with an excessively swift whirling motion 7motus vorticillaris74 ,the particles of other elementary substances are likewise liable to be affected with the same sort of motion1 but not so liable as those of terra secunda2 and when the particles of any body are agitated with this sort of motion1 the body exhibits the phenomena of heat1 or ignition1 or inflammation according to the violence and rapidity of the motion4444 ,becher and ,stahl1 therefore1 did not suppose that heat depended on the abundance of a peculiar matter1 such as the matter of heat or fire is now supposed to be1 but on a peculiar motion of the particles of matter4444 ,this very crude opinion of the earthy nature of the principle of inflammability appears to have been deduced from a quality of many of the inflammable substances1 by which they resist the action of water as a solvent4 ,the greater number of the earthy substances are little1 or not at all1 soluble in water4444 ,and when ,becher and ,stahl found those compounds1 which they supposed contained phlogiston in the largest quantity1 to be insoluble in water1 although the other matter1 with which the phlogiston was supposed to be united1 was1 in its separate state1 exceedingly soluble in that fluid1 they concluded that a dry nature1 or an incapability to be combined with water1 was an eminent quality of their phlogiston2 and this was what they meant by calling it an earth or earthy substance4444 ,but these authors supposed1 at the same time1 that the particles of this dry and earthy phlogiston were much disposed to be excessively agitated with a whirling motion2 which whirling motion1 exerted in all directions from the bodies in which phlogiston is contained1 produced the phenomena of inflammation4 ,this appears to have been the notion formed by ,becher and ,stahl1 concerning the nature of the principle of inflammability1 or the phlogiston2 a notion which seems the least entitled to the name of explanation of anything we can think of4 ,i presume that few persons can form any clear conception of this whirling motion1 or1 if they can1 are able to explain to themselves how it produces1 or can produce1 anything like the phenomena of heat or fire4 ,black then gives a clear account of the experiments of ,priestley and ,lavoisier 7see pp4 #eh1 #ei1 and #hg-hi71 which established the presence1 in common air1 of a peculiar kind of gas which is especially concerned in the processes of combustion2 he emphasizes the fact that a substance increases in weight when it is burned2 and he gives a simple and clear statement of that explanation of combustion which is now accepted by all1 and which does not require that the existence of any principle of fire should be assumed4 ,it is important to note that ,black clearly connects the physical fact that heat is absorbed1 or evolved1 by a substance during combustion1 with the chemical changes which are brought about in the properties of the substance burned4 ,he concludes with an admirable contrast between the phlogistic theory and the theory of ,lavoisier1 which shows how wide1 and at the same time how definite1 his conceptions were4 ,black never speaks contemptuously of a theory which he opposes4 ,according to this theory 7i4e4 the theory of ,lavoisier71 the inflammable bodies1 sulphur for example1 or phosphorus1 are simple substances4 ,the acid into which they are changed by inflammation is a compound4 ,the chemists1 on the contrary 7i4e4 the followers of ,stahl71 consider the inflammable bodies as compounds1 and the uninflammable matter as more simple4 ,in the common theory the heat and light are supposed to emanate from1 or to be furnished by1 the burning body4 ,but1 in ,mr4 ,lavoisier's theory1 both are held to be furnished by the air1 of which they are held to be constituent parts1 or ingredients1 while in its state of fire-supporting air4 ,black was not a brilliant discoverer1 but an eminently sound and at the same time imaginative worker2 whatever he did he did well1 but he did not exhaust any field of inquiry4 ,many of the facts established by him have served as the basis of important work done by those who came after him4 ,the number of new facts added by ,black to the data of chemistry was not large2 but by his lectures--which are original dissertations of the highest value--he did splendid service in advancing the science of chemistry4 ,black possessed that which has generally distinguished great men of science1 a marked honesty of character2 and to this he added comprehensiveness of mental vision3 he saw beyond the limits of the facts which formed the foundations of chemical science in his day4 ,he was not a fact-collector1 but a philosopher4 99 99 99 99 99 ,,joseph ,,priestley1 the son of ,jonas ,priestley1 a maker and dresser of woollen cloth1 was born at ,fieldhead1 near ,leeds1 in the year #agcc4 ,his mother1 who was the daughter of a farmer near ,wakefield1 died when he was seven years old4 ,from that time he was brought up by a sister of his father1 who was possessed of considerable private means4 ,priestley's surroundings in his young days were decidedly religious1 and evidently gave a tone to his whole after life4 ,we shall find that ,priestley's work as a man of science can scarcely be separated from his theological and metaphysical work4 ,his cast of mind was decidedly metaphysical2 he was altogether different from ,black1 who1 as we have seen1 was a typical student of natural phenomena4 ,the house of ,priestley's aunt was a resort for all the ,dissenting ministers of that part of the county4 ,she herself was strictly ,calvinistic in her theological views1 but not wholly illiberal4 ,priestley's early schooling was chiefly devoted to learning languages2 he acquired a fair knowledge of ,latin1 a little ,greek1 and somewhat later he learned the elements of ,hebrew4 ,at one time he thought of going into trade1 and therefore1 as he tells us in his ,memoirs1 he acquired some knowledge of ,french1 ,italian and ,high ,dutch4 ,with the help of a friend1 a ,dissenting minister1 he learned something of geometry1 mathematics and natural philosophy1 and also got some smattering of the ,chaldee and ,syriac tongues4 ,at the age of nineteen ,priestley went to an academy at ,daventry4 ,the intellectual atmosphere here seems to have been suitable to the rapid development of ,priestley's mind4 ,great freedom of discussion was allowed2 even during the teachers' lectures the students were permitted to ask whatever questions and to make whatever remarks they pleased2 and they did it1 ,priestley says1 with the greatest1 but without any offensive1 freedom4 ,the students were required to read and to give an account of the more important arguments for and against the questions discussed in the teachers' lectures4 ,theological disputations appear to have been the favourite topics on which the students exercised their ingenuity among themselves4 ,priestley tells us that he saw reason to embrace what is generally called the heterodox side of almost every question4 ,leaving this academy1 ,priestley went1 in #agee1 as assistant to the ,dissenting minister at ,needham1 in ,suffolk4 ,here he remained for three years1 living on a salary of about ,l#cj a year1 and getting more and more into bad odour because of his peculiar theological views4 ,from ,needham he moved to ,nantwich1 in ,cheshire1 where he was more comfortable1 and1 having plenty of work to do1 he had little time for abstruse speculations4 ,school work engaged most of his time at ,nantwich2 he also began to collect a few scientific instruments1 such as an electrical machine and an air-pump4 ,these he taught his scholars to use and to keep in good order4 ,he gave lectures on natural phenomena1 and encouraged his scholars to make experiments and sometimes to exhibit their experiments before their parents and friends4 ,he thus extended the reputation of his school and implanted in his scholars a love of natural knowledge4 ,in the year #agfa ,priestley removed to ,warrington1 to act as tutor in a newly established academy1 where he taught languages--a somewhat wide subject1 as it included lectures on ,the ,theory of ,languages1 on ,oratory and ,criticism1 and on ,the ,history1 ,laws1 and ,constitution of ,england4 ,he says1 ,it was my province to teach elocution1 and also logic and ,hebrew4 ,the first of these ,i retained1 but after a year or two ,i exchanged the two last articles with ,dr4 ,aikin for the civil law1 and one year ,i gave a course of lectures on anatomy4 ,during his stay at ,warrington1 which lasted until #agfg1 ,priestley married a daughter of ,mr4 ,isaac ,wilkinson1 an ironmaster of ,wrexham1 in ,wales4 ,he describes his wife as a woman of an excellent understanding much improved by reading1 of great fortitude and strength of mind1 and of a temper in the highest degree affectionate and generous1 feeling strongly for others and little for herself1 also greatly excelling in everything relating to household affairs4 ,about this time ,priestley met ,dr4 ,franklin more than once in ,london4 ,his conversation seems to have incited ,priestley to a further study of natural philosophy4 ,he began to examine electrical phenomena1 and this led to his writing and publishing a ,history of ,electricity1 in the course of which he found it necessary to make new experiments4 ,the publication of the results of these experiments brought him more into notice among scientific men1 and led to his election as a ,fellow of the ,royal ,society1 and to his obtaining the degree of ,,ll4,d4 from the ,university of ,edinburgh4 ,in the year #agfg ,priestley removed to ,leeds1 where he spent six years as minister of ,millhill ,chapel4 ,he was able to give freer expression to his theological views in ,leeds than could be done in smaller places1 such as ,needham and ,nantwich4 ,during this time he wrote and published many theological and metaphysical treatises4 ,but1 what is of more importance to us1 he happened to live near a brewery4 ,now1 the accidental circumstances1 as we call them1 of ,priestley's life were frequently of the greatest importance in their effects on his scientific work4 ,black had established the existence and leading properties of fixed air about twelve or thirteen years before the time when ,priestley came to live near the brewery in ,leeds4 ,he had shown that this fixed air is produced during alcoholic fermentation4 ,priestley knowing this used to collect the fixed air which came off from the vats in the neighbouring brewery1 and amuse himself with observing its properties4 ,but removing from this part of the town his supplies of fixed air were stopped4 ,as however he had become interested in working with airs1 he began to make fixed air for himself from chalk1 and in order to collect this air he devised a very simple piece of apparatus which has played a most important part in the later development of the chemistry of gases1 or pneumatic chemistry4 ,priestley's pneumatic trough is at this day to be found in every laboratory2 it is extremely simple and extremely perfect4 ,a dish of glass1 or earthenware1 or wood is partly filled with water2 a shelf runs across the dish at a little distance beneath the surface of the water2 a wide-mouthed bottle is filled with water and placed1 mouth downwards1 over a hole in this shelf4 ,the gas which is to be collected in this bottle is generated in a suitable vessel1 from which a piece of glass or metal tubing passes under the shelf and stops just where the hole is made4 ,the gas which comes from the apparatus bubbles up into the bottle1 drives out the water1 and fills the bottle4 ,when the bottle is full of gas1 it is moved to one side along the shelf1 and another bottle filled with water is put in its place4 ,as the mouth of each bottle is under water there is no connection between the gas inside and the air outside the bottle2 the gas may therefore be kept in the bottle until the experimenter wants it4 7,see ,fig4 #a4 which is reduced from the cut in ,priestley's ,air47 ,illustration3 ,fig4 #a4 ,priestley tells us that at this time he knew very little chemistry1 but he thinks that this was a good thing1 else he might not have been led to make so many new discoveries as he did afterwards make4 ,experimenting with fixed air1 he found that water could be caused to dissolve some of the gas4 ,in #aggb he published a pamphlet on the method of impregnating water with fixed air2 this solution of fixed air in water was employed medicinally1 and from this time we date the manufacture of artificial mineral waters4 ,the next six years of ,priestley's life 7#aggc-aggi7 are very important in the history of chemistry2 it was during these years that much of his best work on various airs was performed4 ,during this time he lived as a kind of literary companion 7nominally as librarian7 with the ,earl of ,shelburne 7afterwards ,marquis of ,lansdowne47 ,his wife and family--he had now three children--lived at ,calne1 in ,wiltshire1 near ,lord ,shelburne's seat of ,bowood4 ,priestley spent most of the summer months with his family1 and the greater part of each winter with ,lord ,shelburne at his ,london residence2 during this time he also travelled in ,holland and ,germany1 and visited ,paris in #aggd4 ,in a paper published in ,november #aggb1 ,priestley says that he examined a specimen of air which he had extracted from saltpetre above a year before this date4 ,this air had by some means or other become noxious1 but1 he supposed1 had been restored to its former wholesome state1 so as to effervesce with nitrous air 7in modern language1 to combine with nitric oxide7 and to admit a candle to burn in it1 in consequence of agitation with water4 ,he tells us1 in his ,observations on ,air 7#aggi71 that at this time he was altogether in the dark as to the nature of this air obtained from saltpetre4 ,in ,august #aggd1 he was amusing himself by observing the action of heat on various substances--without any particular view1 he says1 except that of extracting air from a variety of substances by means of a burning lens in quicksilver1 which was then a new process with me1 and which ,i was very proud of--when he obtained from red precipitate 7oxide of mercury7 an air in which a candle burned with a remarkably vigorous flame4 ,the production of this peculiar air surprised me more than ,i can well express2 ,i was utterly at a loss how to account for it4 ,at first he thought that the specimen of red precipitate from which the air had been obtained was not a proper preparation1 but getting fresh specimens of this salt1 he found that they all yielded the same kind of air4 ,having satisfied himself by experiment that this peculiar air had all the properties of common air1 only in much greater perfection1 he gave to it the name of dephlogisticated air4 ,later experiments taught him that the same air might be obtained from red lead1 from manganese oxide1 etc41 by the action of heat1 and from various other salts by the action of acids4 ,priestley evidently regards the new dephlogisticated air simply as very pure ordinary air2 indeed1 he seems to look on all airs1 or gases1 as easily changeable one into the other4 ,he always interprets his experimental results by the help of the theory of phlogiston4 ,one would indeed think from ,priestley's papers that the existence of this substance phlogiston was an unquestioned and unquestionable fact4 ,thus1 he says in the preface to his ,experiments on ,air3 ,if any opinion in all the modern doctrine concerning air be well founded1 it is certainly this1 that nitrous air is highly charged with phlogiston1 and that from this quality only it renders pure air noxious4444 ,if ,i have completely ascertained anything at all relating to air it is this4 ,priestley thought that very pure air would take away phlogiston from some metals without the help of heat or any acid1 and thus cause these metals to rust4 ,he therefore placed some clean iron nails in dephlogisticated air standing over mercury2 after three months he noticed that about one-tenth of the air in the vessel had disappeared1 and he concluded1 although no rust appeared1 that the dephlogisticated air had as a fact withdrawn phlogiston from the iron nails4 ,this is the kind of reasoning which ,black described to his pupils as mere waste of time and ingenuity4 ,the experiment with the nails was made in #aggi2 at this time1 therefore1 ,priestley had no conception as to what his dephlogisticated air really was4 ,trying a great many experiments1 and finding that the new air was obtained by the action of acids on earthy substances1 ,priestley was inclined to regard this air1 and if this then all other airs1 as made up of an acid 7or acids7 and an earthy substance4 ,we now know how completely erroneous this conclusion was1 but we must remember that in ,priestley's time chemical substances were generally regarded as of no very definite or fixed composition2 that almost any substance1 it was supposed1 might be changed into almost any other2 that no clear meaning was attached to the word element2 and that few1 if any1 careful measurements of the quantities of different kinds of matter taking part in chemical actions had yet been made4 ,but at the same time we cannot forget that the books of ,hooke and ,mayow had been published years before this time1 and that twenty years before ,priestley began his work on airs1 ,black had published his exact1 scientific investigation on fixed air4 ,although we may agree with ,priestley that1 had he made himself acquainted with what others had done before he began his own experiments1 he might not have made so many new discoveries as he did1 yet one cannot but think that his discoveries1 although fewer1 would have been more accurate4 ,we are told by ,priestley that1 when he was in ,paris in #aggd1 he exhibited the method of obtaining dephlogisticated air from red precipitate to ,lavoisier and other ,french chemists4 ,we shall see hereafter what important results to science followed from this visit to ,lavoisier4 ,let us shortly review ,priestley's answer to the question1 ,what happens when a substance burns in air8 ,beginning to make chemical experiments when he had no knowledge of chemistry1 and being an extremely rapid worker and thinker1 he naturally adopted the prevalent theory1 and as naturally interpreted the facts which he discovered in accordance with this theory4 ,when a substance burns1 phlogiston1 it was said1 rushes out of it4 ,but why does rapid burning only take place in air8 ,because1 said ,priestley1 air has a great affinity for phlogiston1 and draws it out of the burning substance4 ,what then becomes of this phlogiston8 we next inquire4 ,the answer is1 obviously it remains in the air around the burning body1 and this is proved by the fact that this air soon becomes incapable of supporting the process of burning1 it becomes phlogisticated4 ,now1 if phlogisticated air cannot support combustion1 the greater the quantity of phlogiston in air1 the less will it support burning2 but we know that if a substance is burnt in a closed tube containing air1 the air which remains when the burning is quite finished at once extinguishes a lighted candle4 ,priestley also proved that an air can be obtained by heating red precipitate1 characterized by its power of supporting combustion with great vigour4 ,what is this but common air completely deprived of phlogiston8 ,it is dephlogisticated air4 ,now1 if common air draws phlogiston out of substances1 surely this dephlogisticated air will even more readily do the same4 ,that it really does this ,priestley thought he had proved by his experiment with clean iron nails 7see p4 #fj74 ,water was regarded as a substance which1 like air1 readily combined with phlogiston2 but ,priestley thought that a candle burned less vigorously in dephlogisticated air which had been shaken with water than in the same air before this treatment2 hence he concluded that phlogiston had been taken from the water4 ,after ,cavendish had discovered 7or rather rediscovered7 hydrogen1 and had established the fact that this air is extremely inflammable1 most chemists began to regard this gas as pure or nearly pure phlogiston1 or1 at least1 as a substance very highly charged with phlogiston4 ,now1 said ,priestley1 when a metal burns phlogiston rushes out of it2 if ,i restore this phlogiston to the metallic calx1 ,i shall convert it back into the metal4 ,he then showed by experiment that when calx of iron is heated with hydrogen1 the hydrogen disappears and the metal iron is produced4 ,he seemed1 therefore1 to have a large experimental basis for his answer to the question1 ,what happens when a substance burns8 ,but at a later time it was proved that iron was also produced by heating the calx of iron with carbon4 ,the antiphlogistic chemists regarded fixed air as composed of carbon and dephlogisticated air2 the phlogisteans said it was a substance highly charged with phlogiston4 ,the antiphlogistic school said that calx of iron is composed of iron and dephlogisticated air2 the phlogisteans said it was iron deprived of its phlogiston4 ,here was surely an opportunity for a crucial experiment3 when calx of iron is heated with carbon1 and iron is produced1 there must either be a production of fixed air 7which is a non-inflammable gas1 and forms a white solid substance when brought into contact with limewater71 or there must be an outrush of phlogiston from the carbon4 ,the experiment was tried3 a gas was produced which had no action on limewater and which was very inflammable2 what could this be but phlogiston1 already recognized by this very property of extreme inflammability8 ,thus the phlogisteans appeared to triumph4 ,but if we examine these experiments made by ,priestley with the light thrown on them by subsequent research1 we find that they bear the interpretation which he put on them only because they were not accurate2 thus1 two gases are inflammable1 but it by no means follows that these gases are one and the same4 ,we must have more accurate knowledge of the properties of these gases4 ,the air around a burning body1 such as iron1 after a time loses the power of supporting combustion2 but this is merely a qualitative fact4 ,accurately to trace the change in the properties of this air1 it is absolutely necessary that exact measurements should be made2 when this is done1 we find that the volume of air diminishes during the combustion1 that the burning body gains weight1 and that this gain in weight is just equal to the loss in weight undergone by the air4 ,when the inflammable gas produced by heating calx of iron with carbon was carefully and quantitatively analyzed1 it was found to consist of carbon and oxygen 7dephlogisticated air71 but to contain these substances in a proportion different from that in which they existed in fixed air4 ,it was a new kind of air or gas2 it was not hydrogen4 ,this account of ,priestley's experiments and conclusions regarding combustion shows how easy it is in natural science to interpret experimental results1 especially when these results are not very accurate1 in accordance with a favourite theory2 and it also illustrates one of the lessons so emphatically taught by all scientific study1 viz4 the necessity of suspending one's judgment until accurate measurements have been made1 and the great wisdom of then judging cautiously4 ,about #aggi ,priestley left ,lord ,shelburne1 and went as minister of a chapel to ,birmingham1 where he remained until #agia4 ,during his stay in ,birmingham1 ,priestley had a considerable amount of pecuniary help from his friends4 ,he had from ,lord ,shelburne1 according to an agreement made when he entered his service1 an annuity of ,l#aej a year for life2 some of his friends raised a sum of money annually for him1 in order that he might be able to prosecute his researches without the necessity of taking pupils4 ,during the ten years or so after he settled in ,birmingham1 ,priestley did a great deal of chemical work1 and made many discoveries1 almost entirely in the field of pneumatic chemistry4 ,besides the discovery of dephlogisticated air 7or oxygen7 which has been already described1 ,priestley discovered and gave some account of the properties of nitrous air 7nitric acid71 vitriolic acid air 7sulphur dioxide71 muriatic acid air 7hydrochloric acid71 and alkaline air 7ammonia71 etc4 ,in the course of his researches on the last-named air he showed1 that when a succession of electric sparks is passed through this gas a great increase in the volume of the gas occurs4 ,this fact was further examined at a later time by ,berthollet1 who1 by measuring the increase in volume undergone by a measured quantity of ammonia gas1 and determining the nature of the gases produced by the passage of the electric sparks1 proved that ammonia is a compound of hydrogen and nitrogen1 and that three volumes of the former gas combine with one volume of the latter to produce two volumes of ammonia gas4 ,priestley's experiments on inflammable air--or hydrogen--are important and interesting4 ,the existence of this substance as a definite kind of air had been proved by the accurate researches of ,cavendish in #agff4 ,priestley drew attention to many actions in which this inflammable air is produced1 chiefly to those which take place between acids and metals4 ,he showed that inflammable air is not decomposed by electric sparks2 but he thought that it was decomposed by long-continued heating in closed tubes made of lead-glass4 ,priestley regarded inflammable air as an air containing much phlogiston4 ,he found that tubes of lead-glass1 filled with this air1 were blackened when strongly heated for a long time1 and he explained this by saying that the lead in the glass had a great affinity for phlogiston1 and drew it out of the inflammable air4 ,when inflammable air burns in a closed vessel containing common air1 the latter after a time loses its property of supporting combustion4 ,priestley gave what appeared to be a fairly good explanation of this fact1 when he said that the inflammable air parted with phlogiston1 which1 becoming mixed with the ordinary air in the vessel1 rendered it unable to support the burning of a candle4 ,he gave a few measurements in support of this explanation2 but we now know that the method of analysis which he employed was quite untrustworthy4 ,thinking that by measuring the extent to which the phlogistication 7we would now say the deoxidation7 of common air was carried by mixing measured quantities of common and inflammable airs and exploding this mixture1 he might be able to determine the amount of phlogiston in a given volume of inflammable air1 he mixed the two airs in glass tubes1 through the sides of which he had cemented two pieces of wire1 sealed the tubes1 and exploded the mixture by passing electric sparks from wire to wire4 ,the residual air now contained1 according to ,priestley1 more phlogiston1 and therefore relatively less dephlogisticated air than before the explosion4 ,he made various measurements of the quantities of dephlogisticated air in the tubes1 but without getting any constant results4 ,he noticed that after the explosions the insides of the tubes were covered with moisture4 ,at a later time he exploded a mixture of dephlogisticated and inflammable airs 7oxygen and hydrogen7 in a copper globe1 and recorded the fact that after the explosion the globe contained a little water4 ,priestley was here apparently on the eve of a great discovery4 ,in looking for one thing1 says ,priestley1 ,i have generally found another1 and sometimes a thing of much more value than that which ,i was in quest of4 ,had he performed the experiment of exploding dephlogisticated and inflammable airs with more care1 and had he made sure that the airs used were quite dry before the explosion1 he would probably have found a thing of indeed much more value than that of which he was in quest2 he would probably have discovered the compound nature of water--a discovery which was made by ,cavendish three or four years after these experiments described by ,priestley4 ,some very curious observations were made by ,priestley regarding the colour of the gas obtained by heating spirit of nitre 7i4e4 nitric acid74 ,he showed that a yellow gas or air is obtained by heating colourless liquid spirit of nitre in a sealed glass tube1 and that as the heating is continued the colour of the gas gets darker1 until it is finally very dark orange red4 ,these experiments have found an explanation only in quite recent times4 ,another discovery made by ,priestley while in ,birmingham1 viz4 that an acid is formed when electric sparks are passed through ordinary air for some time1 led1 in the hands of ,cavendish--an experimenter who was as careful and deliberate as ,priestley was rapid and careless--to the demonstration of the composition of nitric acid4 ,many observations were made by ,priestley on the effects of various airs on growing plants and living animals2 indeed1 one of his customary methods of testing different airs was to put a mouse into each and watch the effects of the air on its breathing4 ,he grew sprigs of mint in common air1 in dephlogisticated air 7oxygen71 and in phlogisticated air 7nitrogen1 but probably not pure72 the sprig in the last-named air grew best1 while that in the dephlogisticated air soon appeared sickly4 ,he also showed that air which has been rendered noxious by the burning of a candle in it1 or by respiration or putrefaction1 could be restored to its original state by the action of growing plants4 ,he thought that the air was in the first instance rendered noxious by being impregnated with phlogiston1 and that the plant restored the air by removing this phlogiston4 ,thus ,priestley distinctly showed that 7to use his own words7 it is very probable that the injury which is continually done to the atmosphere by the respiration of such a number of animals as breathe it1 and the putrefaction of such vast masses1 both of vegetable and animal substances1 exposed to it1 is1 in part at least1 repaired by the vegetable creation4 ,but from want of quantitative experiments he failed to give any just explanation of the process whereby this reparation is accomplished4 ,during his stay in ,birmingham1 ,priestley was busily engaged1 as was his wont during life1 in writing metaphysical and theological treatises and pamphlets4 ,at this time the minds of men in ,england were much excited by the events of the ,french ,revolution1 then being enacted before them4 ,priestley and some of his friends were known to sympathize with the ,french people in this great struggle1 as they had been on the side of the ,americans in the ,war of ,independence4 ,priestley's political opinions had1 in fact1 always been more advanced than the average opinion of his age2 by some he was regarded as a dangerous character4 ,but if we read what he lays down as a fundamental proposition in the ,essay on the ,first ,principles of ,civil ,government 7#agfh71 we cannot surely find anything very startling4 ,it must be understood1 whether it be expressed or not1 that all people live in society for their mutual advantage2 so that the good and happiness of the members1 that is the majority of the members of any state1 is the great standard by which everything relating to that state must be finally determined4 ,and though it may be supposed that a body of people may be bound by a voluntary resignation of all their rights to a single person1 or to a few1 it can never be supposed that the resignation is obligatory on their posterity1 because it is manifestly contrary to the good of the whole that it should be so4 ,priestley proposed many political reforms1 but he was decidedly of opinion that these ought to be brought about gradually4 ,he was in favour of abolishing all religious ,state establishments1 and was a declared enemy to the ,church of ,england4 ,his controversies with the clergy of ,birmingham helped to stir up a section of public opinion against him1 and to bring about the condemnation of his writings in many parts of the country2 he was also unfortunate in making an enemy of ,mr4 ,burke1 who spoke against him and his writings in the ,house of ,commons4 ,in the year #agia1 the day of the anniversary of the taking of the ,bastille was celebrated by some of ,priestley's friends in ,birmingham4 ,on that day a senseless mob1 raising the cry of ,church and ,king1 caused a riot in the town4 ,finding that they were not checked by those in authority1 they after a time attacked and burned ,dr4 ,priestley's meeting-house1 and then destroyed his dwelling-house1 and the houses of several other ,dissenters in the town4 ,one of his sons barely escaped with his life4 ,he himself found it necessary to leave ,birmingham for ,london1 as he considered his life to be in danger4 ,many of his manuscripts1 his library1 and much of his apparatus were destroyed1 and his house was burned4 ,a congregation at ,hackney had the courage at this time to invite ,priestley to become their minister4 ,here he remained for about three years1 ministering to the congregation1 and pursuing his chemical and other experiments with the help of apparatus and books which had been supplied by his friends1 and by the expenditure of part of the sum1 too small to cover his losses1 given him by ,government in consideration of the damage done to his property in the riots at ,birmingham4 ,but finding himself more and more isolated and lonely1 especially after the departure of his three sons to ,america1 which occurred during these years1 he at last resolved to follow them1 and spend the remainder of his days in the ,new ,world4 ,although ,priestley had been very badly treated by a considerable section of the ,english people1 yet he left his native country without any resentment or ill will4 ,when the time for reflection1 he says1 shall come1 my countrymen will1 ,i am confident1 do me more justice4 ,he left ,england in #agie1 and settled at ,northumberland1 in ,pennsylvania1 about a hundred and thirty miles north-west of ,philadelphia4 ,by the help of his friends in ,england he was enabled to build a house and establish a laboratory and a library2 an income was also secured sufficient to maintain him in moderate comfort4 ,the chair of chemistry in the ,university of ,philadelphia was offered to him1 and he was also invited to the charge of a ,unitarian chapel in ,new ,york2 but he preferred to remain quietly at work in his laboratory and library1 rather than again to enter into the noisy battle of life4 ,in ,america he published several writings4 ,of his chemical discoveries made after leaving ,england1 the most important was that an inflammable gas is obtained by heating metallic calces with carbon4 ,the production of this gas was regarded by ,priestley as an indisputable proof of the justness of the theory of phlogiston 7see pp4 #fc1 #fd74 ,his health began to give way about #ahja2 gradually his strength declined1 and in ,february #ahjd1 the end came quietly and peacefully4 ,a list of the books and pamphlets published by ,priestley on theological1 metaphysical1 philological1 historical1 educational and scientific subjects would fill several pages of this book4 ,his industry was immense4 ,to accomplish the vast amount of work which he did required the most careful outlay of time4 ,in his ,memoirs1 partly written by himself1 he tells us that he inherited from his parents a happy temperament of body and mind2 his father especially was always in good spirits1 and could have been happy in a workhouse4 ,his paternal ancestors had1 as a race1 been healthy and long-lived4 ,he was not himself robust as a youth1 yet he was always able to study3 ,i have never found myself1 he says1 less disposed or less qualified for mental exertion of any kind at one time of the day more than another2 but all seasons have been equal to me1 early or late1 before dinner or after4 ,his peculiar evenness of disposition enabled him quickly to recover from the effects of any unpleasant occurrence2 indeed1 he assures us that the most perfect satisfaction often came a day or two after an event that afflicted me the most1 and without any change having taken place in the state of things4 ,another circumstance which tended to make life easy to him was his fixed resolution1 that in any controversy in which he might be engaged1 he would frankly acknowledge every mistake he perceived himself to have fallen into4 ,priestley's scientific work is marked by rapidity of execution4 ,the different parts do not hang together well2 we are presented with a brilliant series of discoveries1 but we do not see the connecting strings of thought4 ,we are not then astonished when he tells us that sometimes he forgot that he had made this or that experiment1 and repeated what he had done weeks before4 ,he says that he could not work in a hurry1 and that he was therefore always methodical2 but he adds that he sometimes blamed himself for doing to-day what had better have been put off until to-morrow4 ,many of his most startling discoveries were the results of chance operations1 not of themes worked out and applied4 ,he was led to the discovery of oxygen1 he says1 by a succession of extraordinary accidents4 ,but that he was able to take advantage of the chance observations1 and from these to advance to definite facts1 constitutes the essential difference between him and ordinary plodding investigators4 ,although he rarely1 if ever1 saw all the bearings of his own discoveries1 although none of his experiments was accurately worked out to its conclusion1 yet he did see1 rapidly and as it appeared almost at one glance1 something of their meanings1 and this something was enough to urge him on to fresh experimental work4 ,although we now condemn ,priestley's theories as quite erroneous1 yet we must admire his undaunted devotion to experiment4 ,he was a true student of science in one essential point1 viz4 ,nature was for him the first and the last court of appeal4 ,he theorized and speculated much1 he experimented rapidly and not accurately1 but he was ever appealing to natural facts2 and in doing this he could not but lay some foundation which should remain4 ,the facts discovered by him are amongst the very corner-stones on which the building of chemical science was afterwards raised4 ,so enthusiastic was ,priestley in the prosecution of his experiments1 that when he began1 he tells us1 ,i spent all the money ,i could possibly raise1 carried on by my ardour in philosophical investigation1 and entirely regardless of consequences1 except so far as never to contract any debts4 ,he seems all through his life to have been perfectly free from anxiety about money affairs4 ,priestley's manner of work shows how kindly and genial he was4 ,he trained himself to talk and think and write with his family by the fireside2 nothing but reading aloud1 or speaking without interruption1 was an obstruction to his work4 ,priestley was just the man who was wanted in the early days of chemical science4 ,by the vast number1 variety and novelty of his experimental results1 he astonished scientific men--he forcibly drew attention to the science in which he laboured so hard2 by the brilliancy of some of his experiments he obliged chemists to admit that a new field of research was opened before them1 and the instruments for the prosecution of this research were placed in their hands2 and even by the unsatisfactoriness of his reasoning he drew attention to the difficulties and contradictions of the theories which then prevailed in chemistry4 ,that the work of ,priestley should bear full fruit it was necessary that a greater than he should interpret it1 and should render definite that which ,priestley had but vaguely shown to exist4 ,the man who did this1 and who in doing it really established chemistry as a science1 was ,lavoisier4 ,but before considering the work of ,lavoisier1 ,i should like to point out that many of the physical characters of common air had been clearly established in the later years of the seventeenth century by the ,honourable ,robert ,boyle4 ,in the ,sceptical ,chymist1 published in #affa1 ,mr4 ,boyle had established the fact that air is a material substance possessed of weight1 that this air presses on the surface of all things1 and that by removing part of the air in an enclosed space the pressure within that space is diminished4 ,he had demonstrated that the boiling point of water is dependent on the pressure of the air on the surface of the water4 ,having boiled some water a pretty while1 that by the heat it might be freed from the latitant air1 he placed the vessel containing the hot water within the receiver of an arrangement which he had invented for sucking air out of an enclosed space2 as soon as he began to suck out air from this receiver1 the water boiled as if it had stood over a very quick fire4444 ,once1 when the air had been drawn out1 the liquor did1 upon a single exsuction1 boil so long with prodigiously vast bubbles1 that the effervescence lasted almost as long as was requisite for the rehearsing of a ,pater noster4 ,boyle had gone further than the qualitative fact that the volume of an enclosed quantity of air alters with changes in the pressure to which that air is subjected2 he had shown by simple and accurate experiments that the volume varies inversely as the pressure4 ,he had established the generalization of so much importance in physical science now known as ,boyle's law4 ,the work of the ,honourable ,henry ,cavendish will be considered in some detail in the book on ,the ,physicists belonging to this series1 but ,i must here briefly allude to the results of his experiments on air published in the ,philosophical ,transactions for #aghd and #aghe4 ,cavendish held the ordinary view that when a metal burns in air1 the air is thereby phlogisticated2 but why is it1 he asked1 that the volume of air is decreased by this process8 ,it was very generally said that fixed air was produced during the calcination of metals1 and was absorbed by the calx4 ,but ,cavendish instituted a series of experiments which proved that no fixed air could be obtained from metallic calces4 ,in #agff inflammable air 7hydrogen7 was discovered by ,cavendish2 he now proved that when this air is exploded with dephlogisticated air 7oxygen71 water is produced4 ,he showed that when these two airs are mixed in about the proportion of two volumes of hydrogen to one volume of oxygen1 the greater part1 if not the whole of the airs is condensed into water by the action of the electric spark4 ,he then proceeded to prove by experiments that when common air is exploded with inflammable air water is likewise produced1 and phlogisticated air 7i4e4 nitrogen7 remains4 ,priestley and ,cavendish had thus distinctly established the existence of three kinds of air1 viz4 dephlogisticated air1 phlogisticated air1 and inflammable air4 ,cavendish had shown that when the last named is exploded with common air water is produced 7which is composed of dephlogisticated and inflammable airs71 and phlogisticated air remains4 ,common air had thus been proved to consist of these two--phlogisticated and dephlogisticated airs 7nitrogen and oxygen74 ,applying these results to the phenomenon of the calcination of metals1 ,cavendish gave reasons for thinking that the metals act towards common air in a manner analogous to that in which inflammable air acts--that they withdraw dephlogisticated and leave phlogisticated air2 but1 as he was a supporter of the phlogistic theory1 he rather preferred to say that the burning metals withdraw dephlogisticated air and phlogisticate that which remains2 in other words1 while admitting that a metal in the process of burning gains dephlogisticated air1 he still thought that the metal also loses something2 viz4 phlogiston4 ,that ,cavendish in #aghc-hd had proved air to consist of two distinct gases1 and water to be produced by the union of two gases1 must be remembered as we proceed with the story of the discoveries of ,lavoisier4 99 99 99 99 99 ,,antoine ,,laurent ,,lavoisier1 born in ,paris in #agdc1 was the son of a wealthy merchant1 who1 judging from his friendship with many of the men of science of that day1 was probably of a scientific bent of mind1 and who certainly showed that he was a man of sense by giving his son the best education which he could obtain4 ,after studying in the ,mazarin ,college1 ,lavoisier entered on a course of training in physical1 astronomical1 botanical and chemical science4 ,the effects of this training in the accurate methods of physics are apparent in the chemical researches of ,lavoisier4 ,at the age of twenty-one ,lavoisier wrote a memoir which gained the prize offered by the ,french ,government for the best and most economical method of lighting the streets of a large city4 ,while making experiments1 the results of which were detailed in this paper1 ,lavoisier lived for six weeks in rooms lighted only by artificial light1 in order that his eyesight might become accustomed to small differences in the intensities of light from various sources4 ,when he was twenty-five years old ,lavoisier was elected a member of the ,academy of ,sciences4 ,during the next six years 7#agfh-aggd7 he published various papers1 some on chemical1 some on geological1 and some on mathematical subjects4 ,indeed at this time1 although an ardent cultivator of natural science1 he appears to have been undecided as to which branch of science he should devote his strength4 ,the accuracy and thoroughness of ,lavoisier's work1 and the acuteness of his reasoning powers1 are admirably illustrated in two papers1 published in the ,memoirs of the ,academy for #aggj1 on the alleged conversion of water into earth4 ,when water is boiled for a long time in a glass vessel a considerable quantity of white siliceous earth is found in the vessel4 ,this apparent conversion or transmutation of water into earthy matter was quite in keeping with the doctrines which had been handed down from the times of the alchemists2 the experiment was generally regarded as conclusively proving the possibility of changing water into earth4 ,lavoisier found that after heating water for a hundred and one days in a closed and weighed glass vessel1 there was no change in the total weight of the vessel and its contents2 when he poured out the water and evaporated it to dryness1 he obtained #bj4d grains of solid earthy matter2 but he also found1 what had been before overlooked1 that the glass vessel had lost weight4 ,the actual loss amounted to #ag4d grains4 ,the difference between this and the weight of the earthy matter in the water1 viz4 three grains1 was set down 7and as we now know justly set down7 by ,lavoisier to errors of experiment4 ,lavoisier therefore concluded that water1 when boiled1 is not changed into earth1 but that a portion of the earthy matter of which glass is composed is dissolved by the water4 ,this conclusion was afterwards confirmed by the ,swedish chemist ,scheele1 who proved that the composition of the earthy matter found in the water is identical with that of some of the constituents of glass4 ,by this experiment ,lavoisier proved the old alchemical notion of transmutation to be erroneous2 he showed that water is not transmuted into earth1 but that each of these substances is possessed of definite properties which belong to it and to it only4 ,he established the all-important generalization--which subsequent research has more amply confirmed1 until it is to-day accepted as the very foundation of every branch of physical science--that in no process of change is there any alteration in the total mass of matter taking part in that change4 ,the glass vessel in which ,lavoisier boiled water for so many days lost weight2 but the matter lost by the glass was found dissolved in the water4 ,we know that this generalization holds good in all chemical changes4 ,solid sulphur may be converted into liquid oil of vitriol1 but it is only by the sulphur combining with other kinds of matter2 the weight of oil of vitriol produced is always exactly equal to the sum of the weights of the sulphur1 hydrogen and oxygen which have combined to form it4 ,the colourless gases1 hydrogen and oxygen1 combine1 and the limpid liquid water is the result2 but the weight of the water produced is equal to the sum of the weights of hydrogen and oxygen which combined together4 ,it is impossible to overrate the importance of the principle of the conservation of mass1 first definitely established by ,lavoisier4 ,some time about the year #aggj ,lavoisier turned his attention seriously to chemical phenomena4 ,in #aggd he published a volume entitled ,essays ,physical and ,chemical1 wherein he gave an historical account of all that had been done on the subject of airs from the time of ,paracelsus to the year #aggd1 and added an account of his own experiments1 in which he had established the facts that a metal in burning absorbs air1 and that when the metallic calx is reduced to metal by heating with charcoal1 an air is produced of the same nature as the fixed air of ,dr4 ,black4 ,in ,november #aggb ,lavoisier deposited a sealed note in the hands of the ,secretary to the ,academy of ,sciences4 ,this note was opened on the #ast of ,may #aggc1 and found to run as follows#d3-- ,about eight days ago ,i discovered that sulphur in burning1 far from losing1 augments in weight2 that is to say1 that from one pound of sulphur much more than one pound of vitriolic acid is obtained1 without reckoning the humidity of the air4 ,phosphorus presents the same phenomenon4 ,this augmentation of weight arises from a great quantity of air which becomes fixed during the combustion1 and which combines with the vapours4 ,this discovery1 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 augmentation of weight in the calces of metals proceeded from the same cause4 ,the experiment fully confirmed my conjectures4 ,i operated the reduction of litharge in closed vessels with ,hale's 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 one thousand times greater than that of the litharge employed4 ,as this discovery appears to me one of the most interesting which has been made since ,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 experiments4 ,,lavoisier4 ,paris1 #aath ,november #aggb4 ,in his paper ,on the ,calcination of ,tin in ,closed ,vessels1 and on the ,cause of ,increase of ,weight acquired by the ,metal during this ,process 7published in #aggd71 we see and admire ,lavoisier's manner of working4 ,a weighed quantity 7about half a pound7 of tin was heated to melting in a glass retort1 the beak of which was drawn out to a very small opening2 the air within the retort having expanded1 the opening was closed by melting the glass before the blowpipe4 ,the weight of retort and tin was now noted2 the tin was again heated to its melting point1 and kept at this temperature as long as the process of calcination appeared to proceed2 the retort and its contents were then allowed to cool and again weighed4 ,no change was caused by the heating process in the total weight of the whole apparatus4 ,the end of the retort beak was now broken off2 air rushed in with a hissing sound4 ,the retort and contents were again weighed1 and the increase over the weight at the moment of sealing the retort was noted4 ,the calcined tin in the retort was now collected and weighed4 ,it was found that the increase in the weight of the tin was equal to the weight of the air which rushed into the retort4 ,hence ,lavoisier concluded that the calcination of tin was accompanied by an absorption of air1 and that the difference between the weights of the tin and the calx of tin was equal to the weight of air absorbed2 but he states that probably only a part of the air had combined with the tin1 and that hence air is not a simple substance1 but is composed of two or more constituents4 ,between the date of this publication and that of ,lavoisier's next paper on combustion we know that ,priestley visited ,paris4 ,in his last work1 ,the ,doctrine of ,phlogiston established 7published in #ahjj71 ,priestley says1 ,having made the discovery of dephlogisticated air some time before ,i was in ,paris in #aggd1 ,i mentioned it at the table of ,mr4 ,lavoisier1 when most of the philosophical people in the city were present2 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 that ,i had got it from precipitatum per se1 and also from red lead4 ,in #agge ,lavoisier's paper1 ,on the ,nature of the ,principle which combines with the ,metals during their ,calcination1 and which augments their ,weight1 was read before the ,academy4 ,the preparation and properties of an air obtained1 in ,november #aggd1 from red precipitate are described1 but ,priestley's name is not mentioned4 ,it seems probable1 however1 that ,lavoisier learned the existence and the mode of preparation of this air from ,priestley2#e but we have seen that even in #aggi ,priestley was quite in the dark as to the true nature of the air discovered by him 7p4 #fj74 ,in papers published in the next three or four years ,lavoisier gradually defined and more thoroughly explained the phenomenon of combustion4 ,he burned phosphorus in a confined volume of air1 and found that about one-fourth of the air disappeared1 that the residual portion of air was unable to support combustion or to sustain animal life1 that the phosphorus was converted into a white substance deposited on the sides of the vessel in which the experiment was performed1 and that for each grain of phosphorus used about two and a half grains of this white solid were obtained4 ,he further described the properties of the substance produced by burning phosphorus1 gave it the name of phosphoric acid1 and described some of the substances formed by combining it with various bases4 ,the burning of candles in air was about this time studied by ,lavoisier4 ,he regarded his experiments as proving that the air which remained after burning a candle1 and in which animal life could not be sustained1 was really present before the burning2 that common air consisted of about one-fourth part of dephlogisticated air and three-fourths of azotic air 7i4e4 air incapable of sustaining life72 and that the burning candle simply combined with1 and so removed the former of these1 and at the same time produced more or less fixed air4 ,in his treatise on chemistry ,lavoisier describes more fully his proof that the calcination of a metal consists in the removal1 by the metal1 of dephlogisticated air 7or oxygen7 from the atmosphere1 and that the metallic calx is simply a compound of metal and oxygen4 ,the experiments are strictly quantitative and are thoroughly conclusive4 ,he placed four ounces of pure mercury in a glass balloon1 the neck of which dipped beneath the surface of mercury in a glass dish1 and then passed a little way up into a jar containing fifty cubic inches of air1 and standing in the mercury in the dish4 ,there was thus free communication between the air in the balloon and that in the glass jar1 but no communication between the air inside and that outside the whole apparatus4 ,the mercury in the balloon was heated nearly to its boiling point for twelve days1 during which time red-coloured specks gradually formed on the surface of the metal2 at the end of this time it was found that the air in the glass jar measured between forty-two and forty-three cubic inches4 ,the red specks when collected amounted to forty-five grains2 they were heated in a very small retort connected with a graduated glass cylinder containing mercury4 ,between seven and eight cubic inches of pure dephlogisticated air 7oxygen7 were obtained in this cylinder1 and forty-one and a half grains of metallic mercury remained when the decomposition of the red substance was completed4 ,the conclusion drawn by ,lavoisier from these experiments was that mercury1 when heated nearly to boiling in contact with air1 withdraws oxygen from the air and combines with this gas to form red precipitate1 and that when the red precipitate which has been thus formed is strongly heated1 it parts with the whole of its oxygen1 and is changed back again into metallic mercury4 ,lavoisier had now 7#aggg-gh7 proved that the calces of mercury1 tin and lead are compounds of these metals with oxygen2 and that the oxygen is obtained from the atmosphere when the metal burns4 ,but the phlogistic chemistry was not yet overthrown4 ,we have seen that the upholders of phlogiston believed that in the inflammable air of ,cavendish they had at last succeeded in obtaining the long-sought-for phlogiston4 ,now they triumphantly asked1 ,why1 when metals dissolve in diluted vitriolic or muriatic acid with evolution of inflammable air1 are calces of these metals produced8 ,and they answered as triumphantly1 ,because these metals lose phlogiston by this process1 and we know that a calx is a metal deprived of its phlogiston4 ,lavoisier contented himself with observing that a metallic calx always weighed more than the metal from which it was produced2 and that as inflammable air1 although much lighter than common air1 was distinctly possessed of weight1 it was not possible that a metallic calx could be metal deprived of inflammable air4 ,he had given a simple explanation of the process of calcination1 and had proved1 by accurate experiments1 that this explanation was certainly true in some cases4 ,although all the known facts about solution of metals in acids could not as yet be brought within his explanation1 yet none of these facts was absolutely contradictory of that explanation4 ,he was content to wait for further knowledge4 ,and to gain this further knowledge he set about devising and performing new experiments4 ,the upholders of the theory of phlogiston laid considerable stress on the fact that metals are produced by heating metallic calces in inflammable air2 the air is absorbed1 they said1 and so the metal is reproduced4 ,it was obviously of the utmost importance that ,lavoisier should learn more about this inflammable air1 and especially that he should know exactly what happened when this air was burned4 ,he therefore prepared to burn a large quantity of inflammable air1 arranging the experiment so that he should be able to collect and examine the product of this burning1 whatever should be the nature of that product4 ,but at this time the news was brought to ,paris that ,cavendish had obtained water by burning mixtures of inflammable and dephlogisticated airs4 ,this must have been a most exciting announcement to ,lavoisier2 he saw how much depended on the accuracy of this statement1 and as a true student of ,nature1 he at once set about to prove or disprove it4 ,on the #bdth of ,june #aghc1 in the presence of the ,king and several notabilities 7including ,sir ,charles ,blagden1 ,secretary of the ,royal ,society1 who had told ,lavoisier of the experiments of ,cavendish71 ,lavoisier and ,laplace burned inflammable and dephlogisticated airs1 and obtained water4 ,as the result of these experiments they determined that one volume of dephlogisticated air combines with #a4ia volumes of inflammable air to form water4 ,a little later ,lavoisier completed the proof of the composition of water by showing that when steam is passed through a tube containing iron filings kept red hot1 inflammable air is evolved and calx of iron remains in the tube4 ,lavoisier could now explain the conversion of a metallic calx into metal by the action of inflammable air2 this air decomposes the calx--that is1 the metallic oxide--combines with its oxygen to form water1 and so the metal is produced4 ,when a metal is dissolved in diluted vitriolic or muriatic acid a calx is formed1 because1 according to ,lavoisier1 the water present is decomposed by the metal1 inflammable air is evolved1 and the dephlogisticated air of the water combines with the metal forming a calx1 which then dissolves in the acid4 ,lavoisier now studied the properties of the compounds produced by burning phosphorus1 sulphur and carbon in dephlogisticated air4 ,he found that solutions of these compounds in water had a more or less sour taste and turned certain blue colouring matters red2 but these were the properties regarded as especially belonging to acids4 ,these products of combustion in dephlogisticated air were therefore acids2 but as phosphorus1 carbon and sulphur were not themselves acids1 the acid character of the substances obtained by burning these bodies in dephlogisticated air must be due to the presence in them of this air4 ,hence ,lavoisier concluded that this air is the substance the presence of which in a compound confers acid properties on that compound4 ,this view of the action of dephlogisticated air he perpetuated in the name oxygen 7from ,greek1 acid-producer71 which he gave to dephlogisticated air1 and by which name this gas has ever since been known4 ,priestley was of opinion that the atmosphere is rendered noxious by the breathing of animals1 because it is thereby much phlogisticated1 and he thought that his experiments rendered it very probable that plants are able to purify this noxious air by taking away phlogiston from it 7see p4 #fi74 ,but ,lavoisier was now able to give a much more definite account of the effects on the atmosphere of animal and vegetable life4 ,he had already shown that ordinary air contains oxygen and azote 7nitrogen71 and that the former is alone concerned in the process of combustion4 ,he was now able to show that animals during respiration draw in air into their lungs3 that a portion of the oxygen is there combined with carbon to form carbonic acid gas 7as the fixed air of ,black was now generally called71 which is again expired along with unaltered azote4 ,respiration was thus proved to be a process chemically analogous to that of calcination4 ,thus1 about the year #aghd-he1 the theory of phlogiston appeared to be quite overthrown4 ,the arguments of its upholders1 after this time1 were not founded on facts2 they consisted of fanciful interpretations of crudely performed experiments4 ,cavendish was the only opponent to be dreaded by the supporters of the new chemistry4 ,but we have seen that although ,cavendish retained the language of the phlogistic theory 7see pp4 #gh1 #gi7 as in his opinion equally applicable to the facts of combustion with that of the new or ,lavoisierian theory1 he nevertheless practically admitted the essential point of the latter1 viz4 that calces are compounds of metal and oxygen 7or dephlogisticated air74 ,although ,cavendish was the first to show that water is produced when the two gases hydrogen and oxygen are exploded together1 it would yet appear that he did not fully grasp the fact that water is a compound of these two gases2 it was left to ,lavoisier to give a clear statement of this all-important fact1 and thus to remove the last prop from under the now tottering1 but once stately edifice built by ,stahl and his successors4 ,the explanation given by ,lavoisier of combustion was to a great extent based on a conception of element and compound very different from that of the older chemists4 ,in the ,sceptical ,chymist 7#affa7 ,boyle had argued strongly against the doctrine of the four elementary principles1 earth1 air1 fire and water1 as held by the vulgar chymists4 ,the existence of these principles1 or some of them1 in every compound substance was firmly held by most chemists in ,boyle's time4 ,they argued thus3 when a piece of green wood bums1 the existence in the wood of the principle of fire is made evident by the flame1 of the principle of air by the smoke which ascends1 of that of water by the hissing and boiling sound1 and of the principle of earth by the ashes which remain when the burning is finished4#f ,boyle combated the inference that because a flame is visible round the burning wood1 and a light air or smoke ascends from it1 therefore these principles were contained in the wood before combustion began4 ,he tried to prove by experiments that one substance may be obtained from another in which the first substance did not already exist2 thus1 he heated water for a year in a closed glass vessel1 and obtained solid particles heavier than1 and as he supposed formed from1 the water4 ,we have already learned the true interpretation of this experiment from the work of ,lavoisier4 ,boyle grew various vegetables in water only1 and thought that he had thus changed water into solid vegetable matter4 ,he tells travellers' tales of the growth of pieces of iron and other metals in the earth or while kept in underground cellars4 ,we now know how erroneous in most points this reasoning was1 but we must admit that ,boyle established one point most satisfactorily1 viz4 that because earth1 or air1 or fire1 or water is obtained by heating or otherwise decomposing a substance1 it does not necessarily follow that the earth1 or air1 or fire1 or water existed as such in the original substance4 ,he overthrew the doctrine of elementary principles held by the vulgar chymists4 ,defining elements as certain primitive and simple bodies which1 not being made of any other bodies1 or of one another1 are the ingredients of which all those called perfectly mixt bodies are immediately compounded1 and into which they are ultimately resolved1 ,boyle admitted the possible existence1 but thought that the facts known at his time did not warrant the assertion of the certain existence1 of such elements4 ,the work of ,hooke and ,mayow on combustion tended to strengthen this definition of element given by ,boyle4 ,black1 as we have seen1 clearly proved that certain chemical substances were possessed of definite and unvarying composition and properties2 and ,lavoisier1 indirectly by his explanation of combustion1 and directly in his ,treatise on ,chemistry1 laid down the definition of element which is now universally adopted4 ,an element is a substance from which no simpler forms of matter--that is1 no forms of matter each weighing less than the original substance--have as yet been obtained4 ,in the decade #aggd-aghd chemical science was thus established on a sure foundation by ,lavoisier4 ,like most great builders1 whether of physical or mental structures1 he used the materials gathered by those who came before him1 but the merit of arranging these materials into a well-laid foundation1 on which the future building might firmly rest1 is due to him alone4 ,the value of ,lavoisier's work now began to be recognized by his fellow-chemists in ,france4 ,in #aghe ,berthollet1 one of the most rising of the younger ,french chemists1 declared himself a convert to the views of ,lavoisier on combustion4 ,fourcroy1 another member of the ,academy1 soon followed the example of ,berthollet4 ,fourcroy1 knowing the weakness of his countrymen1 saw that if the new views could be made to appear as especially the views of ,frenchmen1 the victory would be won2 he therefore gave to the theory of ,lavoisier the name ,la chimie ,francaise4 ,although this name was obviously unfair to ,lavoisier1 it nevertheless caused the antiphlogistic theory to be identified with the ,french chemists1 and succeeded in impressing the ,french public generally with the idea that to hold to the old theory was to be a traitor to the glory of one's country4 ,m4 de ,morveau1 who held a prominent place both in politics and science1 was invited to ,paris1 and before long was persuaded to embrace the new theory4 ,this conversion--for the whole matter was managed as if it had been a political intrigue rather than a philosophical inquiry--was of great importance to ,lavoisier and his friends4 ,m4 de ,morveau was editor of the chemical part of the ,encyclopedie ,methodique2 in that part of this work which had appeared before #aghd ,de ,morveau had skilfully opposed the opinions of ,lavoisier1 but in the second part of the work he introduced an advertisement announcing the change in his opinions on the subject of combustion1 and giving his reasons for this change4 ,the importance of having a definite language in every science is apparent at each step of advance4 ,lavoisier found great difficulty in making his opinions clear because he was obliged to use a language which had been introduced by the phlogistic chemists1 and which bore the impress of that theory on most of its terms4 ,about the years #aghe-aghg1 ,lavoisier1 ,berthollet1 ,fourcroy and ,de ,morveau drew up a new system of chemical nomenclature4 ,the fundamental principles of that system have remained as those of every nomenclature since proposed4 ,they are briefly these3-- ,an element is a substance from which no form of matter simpler than itself has as yet been obtained4 ,every substance is to be regarded as an element until it is proved to be otherwise4 ,the name of every compound is to tell of what elements the substance is composed1 and it is to express as far as possible the relative amounts of the elements which go to form the compound4 ,thus the compounds of oxygen with any other element were called oxides1 e4g4 iron oxide1 mercury oxide1 tin oxide1 etc4 ,when two oxides of iron came to be known1 one containing more oxygen relatively to the amount of iron present than the other1 that with the greater quantity of oxygen was called iron peroxide1 and that with the smaller quantity iron protoxide4 ,we now generally prefer to use the name of the element other than oxygen in adjectival form1 and to indicate the relatively smaller or greater quantity of oxygen present by modifications in the termination of this adjective4 ,thus iron protoxide is now generally known as ferrous oxide1 and iron peroxide as ferric oxide4 ,but the principles laid down by the four ,french chemists in #aghe-aghg remain as the groundwork of our present system of nomenclature4 ,the antiphlogistic theory was soon adopted by all ,french chemists of note4 ,we have already seen that ,black1 with his usual candour and openness to conviction1 adopted and taught this theory1 and we are assured by ,dr4 ,thomas ,thomson that when he attended ,black's classes1 nine years after the publication of the ,french system of nomenclature1 that system was in general use among the chemical students of the university4 ,the older theory was naturally upheld by the countrymen of the distinguished ,stahl after it had been given up in ,france4 ,in the year #agib ,klaproth1 who was then ,professor of ,chemistry in ,berlin1 proposed to the ,berlin ,academy of ,sciences to repeat the more important experiments on which the ,lavoisierian theory rested1 before the ,academy4 ,his offer was accepted1 and from that time most of the ,berlin chemists declared themselves in favour of the new theory4 ,by the close of last century the teaching of ,lavoisier regarding combustion found almost universal assent among chemists4 ,but this teaching carried with it1 as necessary parts1 the fundamental distinction between element and compound2 the denial of the existence of principles or essences2 the recognition of the study of actually occurring reactions between substances as the basis on which all true chemical knowledge was to be built2 and the full acknowledgment of the fact that matter is neither created nor destroyed1 but only changed as to its form1 in any chemical reaction4 ,of ,lavoisier's other work ,i can only mention the paper on ,specific ,heats contributed by ,laplace and ,lavoisier to the ,memoirs of the ,academy for #aghj4 ,in this paper is described the ice calorimeter1 whereby the amount of heat given out by a substance in cooling from one definite temperature to another is determined1 by measuring the amount of ice converted into water by the heated substance in cooling through the stated interval of temperature4 ,the specific heats of various substances1 e4g4 iron1 glass1 mercury1 quicklime1 etc41 were determined by the help of this instrument4 ,as we read the record of work done by ,lavoisier during the years between #aggd and #agid--work which must have involved a great amount of concentrated thought as well as the expenditure of much time--we find it hard to realize that the most tremendous political and social revolution which the modern world has seen was raging around him during this time4 ,in the earlier days of the ,french ,revolution1 and in the time immediately preceding that movement1 many minds had been stirred to see the importance of the study of ,nature2 but it was impossible that natural science should continue to flourish when the tyrant ,robespierre had begun the ,reign of ,terror4 ,the roll of those who perished during this time contains no more illustrious name than that of ,antoine ,laurent ,lavoisier4 ,in the year #agid ,lavoisier1 who had for some time acted as a fermier-general under the ,government1 was accused of mixing with the tobacco water and other ingredients hurtful to the health of the citizens4 ,on this pretext he and some of his colleagues were condemned to death4 ,for some days ,lavoisier found a hiding-place among his friends1 but hearing that his colleagues had been arrested1 he delivered himself up to the authorities1 only asking that the death sentence should not be executed until he had completed the research in which he was engaged2 not that he was unwilling to part with life1 but because he thought the results would be for the good of humanity4 ,the ,republic has no need of chemists2 the course of justice cannot be suspended1 was the reply4 ,on the #hth of ,may #agid1 the guillotine did its work2 and in his fifty-first year ,lavoisier joined the majority4 ,to the honour of the ,academy of which he was so illustrious a member it is recorded that a deputation of his fellow-workers in science1 braving the wrath of ,robespierre1 penetrated to the dungeons of the prison and placed a wreath on the grave of their comrade4 99 99 99 99 99 ,the period of the infancy of chemical science which ,i have now briefly described is broadly contemporaneous with the second half of the eighteenth century4 ,at this time the minds of men were greatly stirred4 ,opinions and beliefs consecrated by the assent of generations of men were questioned or denied2 the pretensions of civil and ecclesiastical authorities were withstood2 assertions however strongly made1 and by whatever authority supported1 were met by demands for reasons4 ,in ,france this revolt against mere authority was especially marked4 ,led by the great thinker ,voltaire1 the ,french philosophers attacked the generally accepted views in moral1 theological and historical matters4 ,a little later they began to turn with eager attention and hope to the facts of external ,nature4 ,physical science was cultivated with wonderful vigour and with surprising success4 ,in the sciences of heat and light we have at this time the all-important works of ,fourier1 ,prevost and ,fresnel2 in geology and natural history we have ,buffon and ,cuvier2 the name of ,bichat marks the beginning of biological science1 and chemistry takes rank as a science only from the time of ,lavoisier4 ,from the philosophers an interest in natural science spread through the mass of the people4 ,about the year #ahgj the lecture-rooms of the great teachers of chemistry1 astronomy1 electricity1 and even anatomy were crowded with ladies and gentlemen of fashion in the ,french capital4 ,a similar state of matters was noticeable in this country4 ,dr4 ,black's lecture theatre was filled by an audience which comprised many young men of good position4 ,to know something of chemistry became an essential part of the training of all who desired to be liberally educated4 ,the secrets of ,nature were now rapidly explored2 astonishing advances were made1 and as a matter of course much opposition was raised4 ,in this active1 inquiring atmosphere the young science of chemistry grew towards maturity4 ,priestley1 ever seeking for new facts1 announcing discovery after discovery1 attacking popular belief in most matters1 yet satisfied to interpret his scientific discoveries in terms of the hypothesis with which he was most familiar1 was the pioneer of the advancing science4 ,he may be compared to the advance-guard sent forward by the explorers of a new country with orders to clear a way for the main body3 his work was not to level the rough parts of the way1 or to fill in the miry places with well-laid metal1 but rather rapidly to make a road as far into the heart of the country as possible4 ,and we have seen how well he did the work4 ,in his discovery of various kinds of airs1 notably of oxygen1 he laid the basis of the great generalizations of ,lavoisier1 and1 what was perhaps of even more importance1 he introduced a new method into chemistry4 ,he showed the existence of a new and unexplored region4 ,before his time1 ,hooke and ,mayow had proved the existence of more than one kind of air1 but the chemistry of gases arose with the discoveries of ,priestley4 ,although ,black's chief research1 on fixed air and on latent heat1 was completed fifteen or twenty years before ,priestley's discovery of oxygen1 yet the kind of work done by ,black1 and its influence on chemical science1 mark him as coming after ,priestley in order of development4 ,we have seen that the work of ,black was characterized by thoroughness and suggestiveness4 ,the largeness of scope1 the breadth of view1 of this great philosopher are best illustrated in his discourses on heat2 he there leads us with him in his survey of the domain of ,nature1 and although he tells us that hypotheses are a mere waste of time1 we find that it is by the strength of his imagination that he commands assent4 ,but he never allows the imagination to degenerate into fanciful guesses2 he vigorously tests the fundamental facts of his theory1 and then he uses the imagination in developing the necessary consequences of these facts4 ,to ,black we owe not only the first rigorously accurate chemical investigation1 but also the establishment of just ideas concerning the nature of heat4 ,but ,lavoisier came before us as a greater than either ,priestley or ,black4 ,to great accuracy and great breadth of view he added wonderful power of generalizing2 with these1 aided by marked mental activity and1 on the whole1 favourable external circumstances1 he was able finally to overthrow the loose opinions regarding combustion and elementary principles which prevailed before his time1 and so to establish chemistry as one of the natural sciences4 ,at the close of the first period of advance we find that the sphere of chemistry has been defined2 that the object of the science has been laid down1 as being to find an explanation of the remarkable changes noticed in the properties of bodies2 that as a first step towards the wished-for explanation1 all material substances have been divided by the chemist into elements and compounds2 that an element has been defined as any kind of matter from a given weight of which no simpler forms of matter--that is1 no kinds of matter each weighing less than the original matter--have as yet been obtained2 that the great principle of the indestructibility of matter has been established1 viz4 that however the properties of matter may be altered1 yet the total mass 7or quantity7 remains unchanged2 and lastly1 we find that an explanation of one important class of chemical changes--those changes which occur when substances burn--has been found4 ,and we have also learned that the method by which these results were obtained was this--to go to ,nature1 to observe and experiment accurately1 to consider carefully the results of these experiments1 and so to form a general hypothesis2 by the use of the mental powers1 and notably by the use of the imagination1 to develop the necessary deductions from this hypothesis2 and finally1 to try these deductions by again inquiring from ,nature whether these things were so4 ,before the time which we have been considering the paths of chemical science had scarcely yet been trodden4 ,each discovery was full of promise1 each advance displayed the possibility of further progress2 the atmosphere was filled as with a mighty rushing wind ready to sweep away the old order of things4 ,the age was an age of doubt and of freedom from the trammels of authority2 it was a time eminently suited for making advances in natural knowledge4 ,in the unceasing activity of ,priestley and ,lavoisier we may trace the influence of the restlessness of the age2 but in the quietness and strength of the best work of these men1 and notably in the work of ,black2 in the calmness with which ,priestley bore his misfortunes at ,birmingham2 in the noble words of ,lavoisier1 ,i am not unwilling to part with life1 but ,i ask time to finish my experiments1 because the results will1 ,i believe1 be for the good of humanity--we see the truth of the assertion made by one who was himself a faithful student of ,nature-- ,nature never did betray ,the heart that loved her4 ,,footnotes3 #d ,the translation is taken from ,thomson's ,history of ,chemistry4 #e ,nevertheless1 in other places ,lavoisier most readily acknowledges the merits of ,priestley4 #f ,a similar method of reasoning was employed so far back as the tenth century3 thus1 in an ,anglo-,saxon ,manual of ,astronomy we read1 ,there is no corporeal thing which has not in it the four elements1 that is1 air and fire1 earth and water4444 ,take a stick and rub it on something1 it becomes hot directly with the fire which lurks in it2 burn one end1 then goeth the moisture out at the other end with the smoke4 ,,chapter ,,iii4 ,,establishment ,,of ,,general ,,principles ,,of ,,chemical ,,science--,,period ,,of ,,dalton4 ,john ,dalton1 #agff-ahdd4 ,the progress of chemical knowledge became so rapid in the early years of the present century1 that although ,i have in this chapter called the time immediately succeeding that of ,lavoisier the period of ,john ,dalton1 and although ,i shall attempt to describe the advances made by this philosopher without considering those of his contemporaries ,davy and ,berzelius1 yet ,i must insist on the facts that this arrangement is made purely for the sake of convenience1 and that many of the discoveries of ,davy1 ,berzelius and others came in order of time before1 or followed close upon the publication of ,dalton's atomic theory4 ,nevertheless1 as the work of these men belongs in its essence to the modern period1 and as the promulgation of the atomic theory by ,dalton marks the beginning of this period1 it seems better that we should have a clear conception of what was done by this chemist before proceeding to consider the advances made by his contemporaries and successors4 99 99 99 99 99 ,,john ,,dalton1 the second of three children of ,joseph and ,deborah ,dalton1 was born at ,eaglesfield1 a village near ,cockermouth1 in ,cumberland1 on the #eth of ,september #agff4 ,one of the first meeting-houses established by the ,society of ,friends is to be found in ,eaglesfield4 ,the ,dalton family had been settled for several generations on a small copyhold estate in this village4 ,the first of them to join the ,friends was the grandfather of ,john ,dalton2 his descendants remained faithful adherents of this society4 ,dalton attended the village schools of ,eaglesfield and the neighbourhood until he was eleven years old1 by which time1 in addition to learning reading1 writing and arithmetic1 he had gone through a course of mensuration1 surveying1 navigation1 etc4 ,at the age of ten his taste for measurements and calculations began to be remarked by those around him2 this taste was encouraged by ,mr4 ,robinson1 a relative of ,dalton1 who recognizing the indomitable perseverance of the boy appears to have taken some care about this time in directing his mathematical studies4 ,at the early age of twelve ,dalton affixed to the door of his father's house a large sheet of paper whereon he announced that he had opened a school for youth of both sexes2 also that paper1 pens and ink were sold within4 ,the boy-teacher had little authority over his pupils1 who challenged their master to fight in the graveyard1 and broke the windows of the room into which they had been locked till their tasks should be learned4 ,when he was fifteen years old ,dalton removed to ,kendal1 where he continued for eleven or twelve years1 at first as assistant-master1 and then1 along with his elder brother ,jonathan1 as principal of a boarding school for boys4 ,it was announced by the brothers that in this school youth will be carefully instructed in ,english1 ,latin1 ,greek and ,french2 also writing1 arithmetic1 merchants' accounts and the mathematics4 ,the school was not very successful4 ,both brothers were hard1 inflexible1 and ungainly in their habits1 and neither was fitted to become a successful teacher of boys3 of the two1 ,john had the gentler disposition1 and was preferred by the boys2 besides1 his mind was so occupied by mathematics that their faults escaped his notice4 ,during this time ,dalton employed his leisure in learning ,latin1 ,greek and ,french1 and in pursuing his studies in mathematics and natural philosophy4 ,he became a frequent contributor to the ,gentlemen's ,diary1 a paper which received problems of various kinds--chiefly mathematical--and presented prizes for their successful solution4 ,besides setting and answering mathematical problems in this journal1 and also in the ,ladies' ,diary1 ,dalton sometimes ventured into the wider fields of mental phenomena4 ,it seems strange to read that1 even at the age of twenty-six1 ,dalton should occupy his leisure time composing answers to such queries as these3-- ,whether1 to a generous mind1 is the conferring or receiving an obligation1 the greater pleasure8 ,is it possible for a person of sensibility and virtue1 who has once felt the passion of love in the fullest extent that the human heart is capable of receiving it 7being by death or some other circumstance for ever deprived of the object of its wishes71 ever to feel an equal passion for any other object8 ,in his answer to the second of these queries1 ,dalton carefully framed two hypotheses1 and as carefully drew conclusions from each4 ,the question in the ,diary was by ,mira2 if ,mira were a rapturous maiden she would not derive much comfort from the cold and mathematical answer by ,mr4 ,john ,dalton of ,kendal4 ,at ,kendal ,dalton made the acquaintance of ,mr4 ,gough1 who was about eight years older than ,dalton1 and had been blind from the age of two4 ,mr4 ,gough1 we are assured by ,dalton1 was a perfect master of the ,latin1 ,greek and ,french tongues2 he understood well all the different branches of mathematics2 there was no branch of natural philosophy but what he was well acquainted with2 he knew by the touch1 taste and smell1 almost every plant within twenty miles of ,kendal4 ,to the friendship of this remarkable man ,dalton owed much2 with his help he acquired a fair knowledge of the classical languages1 and he it was who set ,dalton the example of keeping a regular record of weather observations4 ,on the #bdth of ,march #aghg ,dalton made his first entry in a book which he entitled ,observations on the ,weather1 etc42 the last entry in this book he made fifty-seven years later on the evening preceding his death4 ,the importance of ,dalton's meteorological observations1 as leading him to the conception of the atomic theory1 will be noticed as we proceed4 ,in the year #agic ,dalton1 who was now twenty-seven years of age1 was invited to ,manchester to become tutor in the mathematical and natural philosophy department of a college recently established by influential ,dissenters in that town4 ,eighty pounds for the session of ten months was guaranteed him2 and he was provided with rooms and commons in the college at a charge of ,l#bg #ajs4 per session4 ,he held this appointment for six years1 when he retired1 and continuing to live in ,manchester devoted himself to researches in natural philosophy1 gaining a living by giving private lessons in mathematics and physical science at a charge of #bs4 #f;d4 per hour1 or #as4 #f;d4 each if more than two pupils attended at the same time4 ,dalton was elected a ,fellow of the ,literary and ,philosophical ,society of ,manchester in the year #agid2 and from the time of his retiring from the tutorship of ,manchester ,new ,college till the close of his life he spent a great part of his time in a room in the society's house in ,george ,street1 in studying and teaching4 ,the fifty years thus spent are marked by few outward events4 ,the history of ,dalton's life from this time is the history of the development of his intellect1 and the record of his scientific discoveries4 ,on one occasion during ,dalton's stay at ,kendal1 as he was about to make a visit to his native village1 he bethought himself that the present of a pair of silken hose would be acceptable to his mother4 ,he accordingly purchased a pair marked newest fashion2 but his mother's remark1 ,thou hast brought me a pair of grand hose1 ,john2 but what made thee fancy so light a colour8 ,i can never show myself at meeting in them1 rather disconcerted him1 as to his eyes the hose were of the orthodox drab colour4 ,his mother insisted that the stockings were as red as a cherry4 ,john's brother upheld the drab side of the dispute2 so the neighbours were called in1 and gave their decision that the hose were varra fine stuff1 but uncommon scarlety4 ,from this time ,dalton made observations on the peculiarities of his own vision and that of others1 and in his first paper read before the ,literary and ,philosophical ,society in #agid1 he described these peculiarities4 ,he says1 ,since the year #agij the occasional study of botany obliged me to attend more to colour than before4 ,with respect to colours that were white1 yellow1 or green1 ,i readily assented to the appropriate term2 blue1 purple1 pink and crimson appeared rather less distinguishable1 being1 according to my idea1 all referable to blue4 ,i have often seriously asked a person whether a flower was blue or pink1 but was generally considered to be in jest4 ,dalton's colour-blindness was amusingly illustrated at a later time1 when having been created ,d4,c4,l4 by the ,university of ,oxford he continued to wear the red robes of his degree for some days2 and when his attention was drawn to the somewhat strange phenomenon1 even in a university town1 of an elderly gentleman in the dress of a ,quaker perambulating the town day after day in a scarlet robe1 he remarked that to him the gown appeared to be of the same colour as the green trees4 ,dalton's work during the next six or eight years dealt chiefly with problems suggested by his meteorological observations2 he published a volume on ,meteorological ,observations and ,essays1 chiefly occupied with descriptions of the instruments employed1 more especially of the thermometer and barometer1 and an instrument for determining the dew-point of air4 ,by this time he had established the existence of a connection of some kind between magnetism and the aurora1 and had thus laid the foundations of a most important branch of meteorology4 ,in #agii1 in a note to a paper on rain and dew1 he begins his work on aqueous vapour in the atmosphere by proving that water vapour exists as such in the air4 ,this paper is quickly followed by another on the conducting power of water for heat4 ,a very important paper was published in #ahja1 on the ,constitution of ,mixed ,gases1 etc41 wherein ,dalton asserted that the total pressure of a mixture of two gases on the walls of the containing vessel is equal to the sum of the pressures of each gas2 in other words1 that if one gas is removed the pressure now exerted by the remaining gas is exactly the same as was exerted by that gas in the original mixture4 ,in a paper published much later 7#ahbf71 when his views and experiments on this subject were matured1 he writes3 ,it appears to me as completely demonstrated as any physical principle1 that whenever two or more 444 gases or vapours 444 are put together1 either into a limited or unlimited space1 they will finally be arranged each as if it occupied the whole space1 and the others were not present2 the nature of the fluids and gravitation being the only efficacious agents4 ,this conclusion was followed out and extended in a paper published in #ahjc1 on the absorption of gases by water and other liquids1 wherein he states that the amount of each gas mechanically dissolved by a liquid from a mixture of gases depends only on the quantity of that gas in the mixture1 the other gases exerting no influence in this respect4 ,dalton now considered the variation in the pressures of various gases caused by increasing or decreasing temperature1 and then proceeded to discuss the relations which exist between the volumes of gases and the temperature at which these volumes are measured4 ,he concluded that all elastic fluids under the same pressure expand equally by heat3 and he adds the very important remark1 ,it seems1 therefore1 that general laws respecting the absolute quantity and the nature of heat are more likely to be derived from the study of elastic fluids than of other substances--a remark the profound truth of which has been emphasized by each step in the advances made in our conception of the nature of heat since the time of ,dalton4 ,in these papers on the ,constitution of ,mixed ,gases ,dalton also describes and illustrates a method whereby the actual amount of water vapour in a given bulk of atmospheric air may be found from a knowledge of the dew-point of that air1 that is1 the temperature at which the deposition of water in the liquid form begins4 ,the introduction of this method for finding the humidity of air marks an important advance in the history of meteorology4 ,in this series of papers published within the first three years of the present century ,dalton evidently had before his mind's eye a picture of a gas as a quantity of matter built up of small but independent particles2 he constantly speaks of pressures between the small particles of elastic fluids1 of these particles as repelling each other1 etc4 ,in his ,new ,system he says1 ,a vessel full of any pure elastic fluid presents to the imagination a picture like one full of small shot4 ,it is very important to notice that ,dalton makes use of this conception of small particles to explain purely physical experiments and operations4 ,although we know that during these years he was thinking much of chemical combinations1 yet we find that it was his observations on the weather which led him to the conception--a purely physical conception--of each chemically distinct gas as being built up of a vast number of small1 equally heavy particles4 ,a consideration of these papers by ,dalton on the constitution of mixed gases shows us the method which he pursued in his investigations4 ,the progress of philosophical knowledge1 he says1 is advanced by the discovery of new and important facts2 but much more when these facts lead to the establishment of general laws4 ,dalton always strove to attain to general laws4 ,the facts which he describes are frequently inaccurate2 he was singularly deficient in manipulation1 and he cannot claim a high place as a careful experimenter4 ,he was however able to draw general conclusions of wide applicability4 ,he seems sometimes to have stated a generalization in definite form before he had obtained any experimental verification of it4 ,in the year #ahjb ,dalton conducted an examination of air from various localities1 and concluded that one hundred volumes of air are composed of twenty-one volumes of oxygen and seventy-nine volumes of nitrogen4 ,this appears to have been his first piece of purely chemical work4 ,but in the next year he again returns to physical phenomena4 ,in the paper already referred to1 on the absorption of gases by water and other liquids1 published in this year1 he had stated that ,all gases that enter into water and other liquids by means of pressure1 and are wholly disengaged again by the removal of that pressure1 are mechanically mixed with the liquid1 and not chemically combined with it4 ,but if this be so1 why1 he asked1 does not water mechanically dissolve the same bulk of every kind of gas8 ,the answer which he gives to this question is found at the close of the paper2 to the student of chemistry it is very important3-- ,this question ,i have duly considered1 and though ,i am not yet able to satisfy myself completely1 ,i am nearly persuaded that the circumstance depends upon the weight and number of the ultimate particles of the several gases1 those whose particles are lightest and single being least absorbable1 and the others more1 accordingly as they increase in weight and complexity4 ,an inquiry into the relative weights of the ultimate particles of bodies is a subject1 as far as ,i know1 entirely new4 ,i have lately been prosecuting this inquiry with remarkable success4 ,the principle cannot be entered upon in this paper2 but ,i shall just subjoin the results1 as far as they appear to be ascertained by my experiments4 ,then follows a ,table of the relative weights of the ultimate particles of gaseous and other bodies4 ,the following numbers1 among others1 are given3-- ,hydrogen #a ,sulphur #ad4d ,oxygen #e4e ,alcohol #ae4a ,azote #d4b ,nitrous oxide #ac4g ,phosphorus #g4b ,ether #i4f ,here is the beginning of the atomic theory2 and yet ,dalton's strictly chemical experimental work lies in the future4 ,the scope of the theory is defined in that sentence--,an inquiry into the relative weights of the ultimate particles of bodies4 ,his paper on mixed gases is illustrated by a plate1#g which shows how vividly ,dalton at this time pictured to himself a quantity of gas as composed of many little particles1 and how clearly he recognized the necessity of regarding all the particles of each elementary gas as alike1 but as differing from those of every other elementary gas4 ,in #ahjd ,dalton was invited to deliver a course of lectures in the ,royal ,institution of ,london1 on heat1 mixed gases and similar subjects4 ,in these lectures he expounded his views on the constitution of gases1 on absorption of gases by liquids1 etc4 ,these views drew much attention in this and other countries4 ,they are busy with them1 he writes in #ahjd1 at ,london1 ,edinburgh1 ,paris and in various parts of ,germany1 some maintaining one side and some another4 ,the truth will surely out at last4 ,illustration3 ,fig4 #b ,dalton's love of numerical calculations is noticeable in a trivial circumstance which he mentions in a letter from ,london to his brother4 ,he tried to count the number of coaches which he met in going to the ,friends' morning meeting3 this he assures his brother he effected with tolerable precision4 ,the number was one hundred and four4 ,during vacation time ,dalton usually made a walking excursion in the ,lake district4 ,he was extremely fond of mountain scenery1 but generally combined the pursuit of science with that of pleasure2 he carried his meteorological instruments with him1 determined the dew-point at various altitudes1 and measured mountain heights by the aid of his barometer4 ,sometimes however he refused to have anything to do with science4 ,a companion in one of these excursions says that he was like a schoolboy enjoying a holiday1 mocking the cuckoos1 putting up and chasing the hares1 stopping from time to time to point out some beautiful view1 or loitering to chat with passing pedestrians4 ,this side of ,dalton's nature was not often apparent4 ,in him the quiet1 hard-working student generally appeared prominently marked2 but on the half-holiday which he allowed himself on each ,thursday afternoon1 in order to enjoy the society of a few friends and to engage in his favourite amusement of a game at bowls1 he laid aside something of the quietness1 regularity and decorum which usually characterized him4 ,when it came to his turn to bowl he threw his whole soul into the game1444 and it was not a little amusing to spectators to see him running after the ball across the green1 stooping down as if talking to it1 and waving his hands from one side to the other exactly as he wished the line of the ball to be1 and manifesting the most intense interest in its coming near to the point at which he aimed4 ,from the year #ahjc-d ,dalton becomes more and more a worker in chemistry4 ,the establishment of the atomic theory now engaged most of his time and attention4 ,the results of his investigation of the primary laws which seem to obtain in regard to heat and to chemical combinations appeared in his ,new ,system of ,chemical ,philosophy1 ,part ,i4 of which1 ,on ,heat1 on the ,constitution of ,bodies and on ,chemical ,synthesis1 was published in #ahjh4 ,we have now arrived at the time when ,dalton's inquiry into the relative weights of the ultimate particles of bodies was in his opinion sufficiently advanced for presentation to the scientific world2 but ,i think we shall do better to postpone our consideration of this great inquiry until we have completed our review of the chief events in the life of ,dalton1 other than this the greatest event of all4 ,dalton did not look for rewards--he desired only the just fame of one who sought for natural truths2 but after the publication of the ,new ,system rewards began to come to him4 ,in #ahag he was elected a corresponding member of the ,french ,academy of ,sciences4 ,in #ahbb1 when his fame as a philosophical chemist was fully established1 ,dalton visited ,paris4 ,this visit gave him great pleasure4 ,he was constantly in the society of the great men who then so nobly represented the dignity of natural science in ,france2 ,laplace1 ,cuvier1 ,biot1 ,arago1 ,gay-,lussac1 ,milne-,edwards and others were his friends4 ,for some time after this visit he was more vivacious and communicative than usual1 and we are told by one who lived in the same house as he1 ,we frequently bantered him with having become half a ,frenchman4 ,dalton especially valued the friendship of ,clementine ,cuvier1 daughter of the great naturalist1 with whom he became acquainted during his visit to ,paris4 ,all through life he greatly delighted in the society of cultivated women1 and his warmest friendships were with gentlewomen4 ,at one time1 shortly after going to ,manchester1 he was much taken by a widow lady who combined great personal charms with considerable mental culture4 ,during my captivity1 he writes to a friend1 which lasted about a week1 ,i lost my appetite1 and had other symptoms of bondage about me1 as incoherent discourse1 etc41 but have now happily regained my freedom4 ,the society of men who like himself were actively engaged in the investigation of natural science was also a source of much pleasure to ,dalton4 ,such men used to visit him in ,manchester1 so that in the house of the ,rev4 ,mr4 ,johns1 in whose family he lived1 there were found from time to time some of the greatest philosophers in ,europe4 ,dalton was elected a ,fellow of the ,royal ,society in #ahbb1 and four years later he became the first recipient of one of the ,royal ,medals1 then founded by the ,king 7,george ,,iv474 ,in #ahcj he was elected one of the eight foreign ,associates of the ,french ,academy1 an honour which is generally regarded as the highest that can be bestowed on any man of science4 ,dalton was one of the original members of the ,british ,association for the ,advancement of ,science1 and he attended most of the meetings from the first held in ,york in #ahca to that held in ,manchester two years before his death4 ,at the ,oxford meeting of #ahcb he was created ,d4,c4,l4 by the ,university1 and two years later the ,university of ,edinburgh honoured herself by enrolling his name on the list of her doctors of law4 ,about this time some of ,dalton's scientific friends1 who considered his work of great national importance1 endeavoured to obtain a pension for him from the civil list4 ,at the meeting of the ,british ,association held at ,cambridge in #ahcc1 the president1 ,professor ,sedgwick1 was able to announce that ,his ,majesty1 willing to manifest his attachment to science1 and his regard for a character like that of ,dr4 ,dalton1 had graciously conferred on him1 out of the funds of the civil list1 a substantial mark of his royal favour4 ,the substantial mark of royal favour1 the announcement of which ,dalton received with his customary quietness and simplicity of manner1 consisted of a pension of ,l#aej per annum1 which was increased three years later to ,l#cjj4 ,the second part of ,volume ,i4 of his ,new ,system was published by ,dalton in #ahaj1 and the second volume of the same work in #ahbg4 ,in #ahdd a paper by him was read before the ,british ,association1 in which he announced some important discoveries with regard to the water in crystallizable salts1 and thus brought a new class of facts within the range of the atomic theory4 ,he was seized with paralysis in #ahcg1 but recovered to a great extent2 a second attack in #ahdd however completely prostrated him4 ,on the #afth of ,july in that year he made the last entry in his book of ,observations on the ,weather--,little rain2 next morning he became insensible and quietly passed away4 99 99 99 99 99 ,it is as the founder of the chemical atomic theory that ,dalton must ever be remembered by all students of physical and chemical science4 ,to the ,greek philosophers ,leucippus and ,democritus 7flourished about #ddj-djj ,b4,c47 we owe the conception that ,the bodies which we see and handle1 which we can set in motion or leave at rest1 which we can break in pieces and destroy1 are composed of smaller bodies1 which we cannot see or handle1 which are always in motion1 and which can neither be stopped1 nor broken in pieces1 nor in any way destroyed or deprived of the least of their properties 7,clerk ,maxwell74 ,the heavier among these small indivisible bodies or atoms were regarded as always moving downwards4 ,by collisions between these and the lighter ascending atoms lateral movements arose4 ,by virtue of the natural law 7as they said7 that things of like weight and shape must come to the same place1 the atoms of the various elements came together2 thus larger masses of matter were formed2 these again coalesced1 and so finally worlds came into existence4 ,this doctrine was extended by ,epicurus 7#cdj-bgj ,b4,c471 whose teaching is preserved for us in the poem of ,lucretius 7#ie-eb ,b4,c471 ,de ,rerum ,natura2 he ascribed to the atoms the power of deviating from a straight line in their descending motion4 ,on this hypothesis ,epicurus built a general theory to explain all material and spiritual phenomena4 ,the ceaseless change and decay in everything around them was doubtless one of the causes which led men to this conception of atoms as indivisible1 indestructible substances which could never wear out and could never be changed4 ,but even here rest could not be found2 the mind was obliged to regard these atoms as always in motion4 ,the dance of the dust-motes in the sunbeam was to ,lucretius the result of the more complex motion whereby the atoms which compose that dust are agitated4 ,in his dream as told by ,tennyson-- ,a void was made in ,nature3 all her bonds ,cracked3 and ,i saw the flaring atom-streams ,and torrents of her myriad universe1 ,ruining along the illimitable inane1 ,fly on to clash together again1 and make ,another and another frame of things ,for ever4 ,the central quest of the physicist1 from the days of ,democritus to the present time1 has been to explain the conception of atom--to develop more clearly the observed properties of the things which are seen and which may be handled as dependent on the properties of those things which cannot be seen1 but which yet exist4 ,for two thousand years he has been trying to penetrate beneath the ever-changing appearances of ,nature1 and to find some surer resting-place whence he may survey these shifting pictures as they pass before his mental vision4 ,the older atomists thought to find this resting-place1 not in the atoms themselves1 but in the wide spaces which they supposed to exist between the worlds3-- ,the lucid interspace of world and world ,where never creeps a cloud1 or moves a wind1 ,nor ever falls the least white star of snow1 ,nor ever lowest roll of thunder moans1 ,nor sound of human sorrow mounts to mar ,their sacred everlasting calm4 ,to the modern student of science the idea of absolute rest appears unthinkable2 but in the most recent outcome of the atomic theory--in the vortex atoms of ,helmholtz and ,thomson--he thinks he perceives the very foundation stones of the material universe4 ,newton conceived the atom as a solid1 massy1 hard1 impenetrable1 movable particle4 ,to the mind of ,d4 ,bernoulli the pressure exerted by a gas on the walls of a vessel enclosing it was due to the constant bombardment of the walls by the atoms of which the gas consisted4 ,atomic motion was the leading idea in the explanation of heat given by ,rumford and ,davy1 and now universally accepted2 and1 as we have seen1 ,dalton was himself accustomed to regard all elastic fluids 7i4e4 gases7 as consisting of vast numbers of atoms4 ,but in the year #ahjb or so1 ,dalton thought that by the study of chemical combinations it would be possible to determine the relative weights of atoms4 ,assume that any elementary gas is composed of small1 indivisible1 equally heavy parts2 assume that the weight of an atom of one element is different from that of the atom of any other element2 and1 lastly1 assume that when elements combine the atom of the compound so produced is built up of the atoms of the various elements4 ,make these assumptions1 and it follows that the relative weights of two or more elements which combine together must represent the relative weights of the atoms of these elements4 ,we know that the fixity of composition of chemical compounds had been established before this time1 largely by the labours of ,black and ,lavoisier4 ,fixity of composition had however been called in question by ,berthollet1 who held that elements combine together in very varying quantities2 that1 in fact1 in place of there being two or three1 or a few definite compounds of1 say1 iron and oxygen1 there exists a graduated series of such bodies2 and that the amount of iron which combines with oxygen depends chiefly on such physical conditions as the temperature1 the pressure1 etc41 under which the chemical action occurs4 ,but by the date of the publication of the first part of ,dalton's ,new ,system1 the long dispute between ,berthollet and ,proust regarding fixity of composition of compounds had nearly closed in favour of the latter chemist1 who strongly upheld the affirmative side of the argument4 ,but if ,dalton's assumptions are correct1 it is evident that when two elements form more than one compound1 the quantity of element ,a in one of these must be a simple multiple of the quantity in the other of these compounds2 because there must be a greater number of atoms of element ,a in the atom of one compound than in that of the other compound1 and an elementary atom is assumed to be indivisible4 ,hence it follows that if one element be taken as a standard1 it must be possible to affix to any other element a certain number which shall express the smallest quantity of that element which combines with one part by weight of the standard element2 and this number shall also represent how many times the atom of the given element is heavier than the atom of the standard element1 the weight of which has been taken to be one4 ,if this element forms two compounds with the standard element1 the amount of this element in the second compound must be expressed by a simple multiple of the number assigned to this element1 because it is not possible1 according to the fundamental assumptions of the theory1 to form a compound by the combination of fractions of elementary atoms4 ,by pondering on the facts regarding chemical combinations which had been established by various workers previous to the year #ahjb1 ,dalton had apparently come to such conclusions as those now indicated4 ,in his paper on the properties of the gases constituting the atmosphere1 read to the ,manchester ,society on ,november #ab1 #ahjb1 he stated that one hundred measures of common air would combine with thirty-six measures of nitrous gas in a narrow tube to produce an oxide of nitrogen1 but with seventy-two measures of the same gas in a wide vessel to produce another oxide of nitrogen4 ,these facts1 he says1 clearly point out the theory of the process3 the elements of oxygen may combine with a certain portion of nitrous gas1 or with twice that portion1 but with no intermediate quantity4 ,in the concluding paragraph of his paper on absorption of gases by liquids1 read on ,october #ba1 #ahjc1 we found 7see p4 #aaf7 that he had got so far in his inquiry into the relative weights of the ultimate particles of bodies as to give a table of twenty-one such weights4 ,about this time ,dalton made analyses of two gaseous compounds of carbon--olefiant gas and carburetted hydrogen or marsh-gas4 ,he found that both are compounds of carbon and hydrogen2 that in one #d4c parts by weight of carbon are combined with one part by weight of hydrogen1 and in the other the same amount 7#d4c7 of carbon is combined with two parts by weight of hydrogen4#h ,this was a striking confirmation of his views regarding combination in multiple proportions1 which views followed as a necessary deduction from the atomic hypothesis4 ,from this time he continued to develop and extend this hypothesis1 and in the year #ahjh he published his ,new ,system of ,chemical ,philosophy4 ,the first detailed account of the atomic theory was however given to the chemical world the year before ,dalton's book appeared4 ,during a conversation with ,dalton in the autumn of #ahjd ,dr4 ,thomas ,thomson learned the fundamental points of the new theory1 and in the third edition of his ,system of ,chemistry1 published in #ahjg1 he gave an account of ,dalton's views regarding the composition of bodies4 ,in the same year a paper by ,thomson appeared in the ,philosophical ,transactions1 wherein it was experimentally proved that oxalic acid combines with strontia to form two distinct compounds1 one of which contains twice as much oxalic acid as the other1 the amount of strontia being the same in both4 ,analyses of the oxalates of potash1 published about the same time by ,wollaston1 afforded another illustration of the law of multiple proportions1 and drew the attention of chemists to ,dalton's theory4 ,but the new theory was opposed by several very eminent chemists1 notably by ,sir ,humphry ,davy4 ,in the autumn of #ahjg ,wollaston1 ,thomson and ,davy were present at the dinner of the ,royal ,society ,club1 at the ,crown and ,anchor1 in the ,strand4 ,after dinner1 these three chemists discussed the new theory for an hour and a half1 ,wollaston and ,thomson trying to convince ,davy of the truth of ,dalton's theory2 but so far from being convinced1 he went away1 if possible1 more prejudiced against it than ever4 ,soon after this ,wollaston succeeded in convincing ,mr4 ,davis ,gilbert 7afterwards ,president of the ,royal ,society7 of the justness of the atomic theory1 and he in turn so placed the facts and the reasoning before ,davy1 that from this time he became a supporter of the new theory4 ,in order that the atomic theory should be fruitful of results1 it was now necessary that the values of the atomic weights of many elements should be carefully determined4 ,let us consider what knowledge must be acquired before the value to be assigned to the atomic weight of an element can be found4 ,hydrogen was the element chosen as a standard by ,dalton4 ,he assumed that the atom of hydrogen weighs #a2 the atomic weight of any other element is therefore a number which tells how many times the atom of that element is heavier than the atom of hydrogen4 ,thus1 when ,dalton said the atomic weight of oxygen is #h1 he meant that the atom of oxygen is eight times heavier than that of hydrogen4 ,how was this number obtained8 ,accurate analyses of water show that in this liquid one part by weight of hydrogen is combined with eight parts by weight of oxygen2 but 7it is said7 as the atom of hydrogen weighs #a1 the atom of oxygen must weigh #h4 ,in drawing this conclusion it is assumed that the atom1 or smallest particle1 of water is built up of one atom of hydrogen and one atom of oxygen4 ,let it be assumed that the atom of water contains two atoms of hydrogen and one of oxygen1 then the latter atom must weigh sixteen times as much as each atom of hydrogen2 let it be assumed that three atoms of hydrogen combine with one atom of oxygen to form an atom of water1 then the weight of the oxygen atom must be twenty-four times that of the hydrogen atom4 ,any one of these assumptions will equally satisfy the figures obtained by analyzing water 7#a3 #h #b3 #af #c3 #bd74 ,now1 had we any method whereby we could determine how many times an atom of water is heavier than an atom of hydrogen we should be able to determine which of the foregoing assumptions is correct1 and therefore to determine the atomic weight of oxygen4 ,hence1 before the atomic weight of an element can be determined1 there must be found some method for determining the atomic weights of compounds of that element4 ,unless this can be done the atomic theory is of little avail in chemistry4 ,i conceive it to be one of the signal merits of ,dalton that he so clearly lays down rules1 the best which could be devised at his time1 for determining the atomic weights of compounds1 or1 what is the same thing1 for determining the number of elementary atoms in one atom of any compound4 ,in his ,new ,system he says that he wishes to show the importance of ascertaining the relative weights of the ultimate particles both of simple and compound bodies1 the number of simple elementary particles which constitute one compound particle1 and the number of less compound particles which enter into the formation of one more compound particle4 ,considering compounds of two elements1 he divides these into binary1 ternary1 quaternary1 etc41 according as the compound atom contains two1 three1 four1 etc41 atoms of the elements4 ,he then proceeds thus-- ,the following general rules may be adopted as guides in all our investigations respecting chemical synthesis3-- #ast4 ,when only one combination of two bodies can be obtained1 it must be presumed to be a binary one1 unless some cause appear to the contrary4 #bnd4 ,when two combinations are observed1 they must be presumed to be a binary and a ternary4 #crd4 ,when three combinations are obtained1 we may expect one to be binary and the other two ternary4 #dth4 ,when four combinations are observed1 we should expect one binary1 two ternary1 and one quaternary1 etc4 ,only one compound of hydrogen and oxygen was then known2 hence it was presumed to be a binary compound1 i4e4 a compound the smallest particle of which consisted of one atom of hydrogen and one atom of oxygen2 and hence1 from the data already given on page #acj1 it followed that the atomic weight of oxygen was #h4 ,two compounds of carbon and oxygen were known1 each containing six parts by weight of carbon1 in one case united with eight1 and in the other case with sixteen parts by weight of oxygen4 ,from ,dalton's rules one of these was a binary1 and the other a ternary compound2 but as the atomic weight of oxygen had already been determined to be #h1 that compound of carbon and oxygen containing eight of oxygen combined with six of carbon was decided to be binary1 and that containing sixteen of oxygen 7i4e4 two atoms7 to be ternary2 and hence the atomic weight of carbon was determined to be #f4 ,in the second part of the ,new ,system ,dalton1 guided by these rules1 determined experimentally the atomic weights of a great many substances2 but this was not the kind of work suited to ,dalton's genius4 ,his analytical determinations were generally inaccurate2 nevertheless1 he clearly showed how the values of the atomic weights of elements ought to be established1 and he obtained results sufficiently accurate to confirm his general theory4 ,to make accurate determinations of the relative weights of elementary atoms was one of the tasks reserved for the great ,swedish chemist ,berzelius 7see pp4 #afb-agj74 ,when we examine ,dalton's rules we must confess that they appear somewhat arbitrary4 ,he does not give reasons for his assertion that when only one combination of two bodies can be obtained1 it must be presumed to be a binary one4 ,why may it not be ternary or quaternary8 ,why must the atom of water be built up of one atom of hydrogen combined with one atom of oxygen8 ,or1 when two compounds are known containing the same pair of elements1 why must one be binary and the other ternary8 ,or1 even assuming that this must be justified by facts1 does it follow that ,dalton's interpretation of the atomic structure of the two oxides of carbon is necessarily correct8 ,these oxides contain #f of carbon #h of oxygen1 and #f of carbon #af of oxygen1 respectively4 ,take the second1 #f3 #af #c3 #h2 assume this to be a binary compound of one atom of oxygen 7weighing #h7 with one atom of carbon 7weighing #c71 then the other will be a ternary compound containing one atom of oxygen 7#h7 and two atoms of carbon 7#f74 ,hence it appears that ,dalton's rules were too arbitrary1 and that they were insufficient to determine with certainty the atomic weights of some of the elements4 ,nevertheless1 without some such rules as those of ,dalton1 no great advances could have been made in applying the atomic theory to the facts of chemical combination2 and ,dalton's rules were undoubtedly founded on wide considerations4 ,in the appendix to ,volume ,,ii4 of his ,new ,system he expressly states that before the number of atoms of two elements present in the atom of a compound can be determined1 it is necessary that many combinations should be examined1 not only of these elements with each other1 but also of each of these with other elements2 and he tells us that to gather together facts bearing on this general question of chemical synthesis was the object of his work from the time of the promulgation of the atomic theory4 ,when we find that ,dalton applied the term atom to the small particles of compound bodies1 we at once see that by atom he could not always mean that which cannot be cut2 he simply meant the smallest particle of a substance which exhibits the properties of that substance4 ,a mass of water vapour was conceived by ,dalton as like a mass of small shot4 ,each shot exhibited the characteristic chemical properties of water vapour2 it differed from the large quantity of vapour only in mass2 but if one of these little pieces of shot were divided--as ,dalton1 of course1 knew it could be divided--smaller pieces of matter would be produced4 ,but these would no longer be water2 they would be new kinds of matter4 ,they are called oxygen and hydrogen4 ,as aids towards gaining a clear conception of the atom of a compound as a definite building1 ,dalton made diagrammatic representations of the hypothetical structures of some of these atoms3 the following plate is copied from the ,new ,system3--,a represents an atom of alum2 ,b1 an atom of nitrate of alumina2 ,c1 of barium chloride2 ,d1 of barium nitrate2 ,e1 of calcium chloride2 ,f calcium nitrate2 ,g1 of calcium sulphate2 ,h1 potassium carbonate2 ,i1 of potash2 and ,k1 an atom of soda4 ,illustration3 ,fig4 #c4 ,but ,i think if we consider this application of the term atom to elements and compounds alike1 we shall see objections to it4 ,when an atom of a compound is divided the smaller particles so produced are each very different in chemical properties from the atom which has just been divided4 ,we may1 if we choose1 assume that the atom of an element could in like manner be divided1 and that the products of this division would be different from the elementary atoms2 but such a division of an elementary atom has not as a matter of fact been yet accomplished1 unless we class among elements substances such as potash and soda1 which for many years were universally regarded as elements1 and rightly so regarded because they had not been decomposed4 ,in ,dalton's nomenclature then1 the term atom is applied alike to a small particle with definite properties known to be divisible into smaller particles1 each with properties different from those of the undivided particle1 and to a small particle which1 so far as our knowledge goes1 cannot be divided into any particle smaller than or different from itself4 ,nevertheless1 if the atomic theory was to be victorious1 it was necessary that it should be applied to elements and compounds alike4 ,until a clear conception should be obtained1 and expressed in accurate language1 of the differences in structure of the ultimate particles of compounds and of elements1 it was perhaps better to apply the term atom to both alike4 ,these two difficulties--7#a7 the difficulty of attaching to the term atom a precise meaning applicable to elements and compounds alike1 and 7#b7 the difficulty of determining the number of elementary atoms in the atom of a given compound1 and hence of determining the relative weights of elementary atoms themselves--were for many years stumbling-blocks in the path of the upholders of the ,daltonian theory4 ,the very great difficulty of clearly comprehending the full meaning of ,dalton's proposed theory becomes apparent when we learn that within three years from the publication of ,part ,i4 of the ,new ,system1 facts were made known by the ,french chemist ,gay-,lussac1 and the true interpretation of these facts was announced by the ,italian chemist ,avogadro1 which facts and interpretation were sufficient to clear away both the difficulties ,i have just mentioned2 but that nevertheless it is only within the last ten or fifteen years that the true meaning of the facts established by ,gay-,lussac and the interpretation given by ,avogadro have been generally recognized4 ,in #ahji ,gay-,lussac1 in a memoir on the combination of gaseous bodies1 proved that gases combine chemically in simple proportions by volume1 and that the volume of the product always bears a simple relation to the volumes of the combining gases4 ,thus1 he showed that two volumes of hydrogen combine with one volume of oxygen to form two volumes of water vapour2 that one volume of nitrogen combines with three volumes of hydrogen to form two volumes of ammonia gas1 and so on4 ,now1 as elements combine atom with atom1 the weights of these combining volumes of elements must represent the relative weights of the atoms of the same elements4 ,in #ahaa ,avogadro distinguished between the ultimate particles of compounds and elements4 ,let a gaseous element1 ,a1 combine with another gaseous element1 ,b1 to form a gaseous compound1 ,c2 then ,avogadro supposed that the little particles of ,a and the little particles of ,b 7,dalton's atoms7 split up1 each into two or more smaller particles1 and that these smaller particles then combine together to form particles of the compound ,c4 ,the smaller particles produced by splitting a ,daltonian elementary atom were regarded by ,avogadro as all identical in properties1 but these very small particles could not exist uncombined either with each other or with very small particles of some other element4 ,when the atom of a compound is decomposed1 ,avogadro pictured this atom as splitting into smaller particles of two or three or more different kinds1 according as the compound had contained two or three or different elements4 ,to ,avogadro's mental vision an elementary gas appeared as built up of a great many little particles1 each exhibiting in miniature all the properties of the gas4 ,the gas might be heated1 or cooled1 or otherwise physically altered1 but each of the little particles remained intact2 the moment however that this gas was mixed with another on which it could chemically react1 these little particles split into smaller parts1 but as the smaller parts so produced could not exist in this state1 they seized hold of the corresponding very small parts of the other gas1 and thus a particle of a compound gas was produced4 ,a compound gas was pictured by ,avogadro as also built up of small particles1 each exhibiting in miniature the properties of the gas1 and each remaining undecomposed when the gas was subjected only to physical actions2 but when the gas was chemically decomposed1 each little particle split1 but the very small parts thus produced1 being each a particle of an elementary substance1 continued to exist1 and could be recognized by the known properties of that element4 ,to the smallest particle of any substance 7elementary or compound7 which exhibits the properties of that substance1 and which cannot be split into parts without destroying these properties1 we now give the name of molecule4 ,a molecule is itself a structure4 ,it is built up of parts2 each of these parts we now call an atom4 ,the molecule of a compound is1 of course1 composed of the atoms of the elements which form that compound4 ,the molecule may contain two or three or more unlike atoms4 ,the molecule of an element is composed of the atoms of that element1 and all of these atoms are supposed to be alike4 ,we cannot get hold of elementary atoms and examine them1 but we have a large mass of evidence in favour of the view which regards the molecule of an element as composed of parts each weighing less than the molecule itself4 ,the student of physics or chemistry now believes that1 were a very small quantity of a gas 7say ammonia7 or a drop of a liquid 7say water7 magnified to something like the size of the earth1 he should see before him a vast heap of particles of ammonia or of water1 each exhibiting all the properties by the possession of which he now distinguishes ammonia or water from all other kinds of matter4 ,he believes that he should see these particles in motion1 each moving rapidly from place to place1 sometimes knocking against another1 sometimes traversing a considerable space without coming into collision with any other4 ,but the student tries to penetrate yet further into the nature of things4 ,to the vision of the chemist these particles of almost inconceivable minuteness are themselves built up of smaller particles4 ,as there is an architecture of masses1 so is there an architecture of molecules4 ,hydrogen and oxygen are mixed2 the chemist sees the molecules of each in their never-ceasing dance moving here and there among the molecules of the other1 yet each molecule retaining its identity2 an electric spark is passed through the mixture1 and almost instantaneously he sees each hydrogen molecule split into two parts1 and each oxygen molecule split into two parts1 and then he sees these parts of molecules1 these atoms1 combine1 a pair of hydrogen atoms with an atom of oxygen1 to form compound molecules of water4 ,avogadro's hypothesis gave the chemist a definition of molecule2 it also gave him a definition of atom4 ,it is evident that1 however many atoms of a given element there may be in this or in that compound molecule1 no compound of this element can exist containing less than a single atom of the element in question2 therefore an atom of an element is the smallest quantity of that element in the molecule of any compound thereof4 ,and so we have come back to the original hypothesis of ,dalton2 but we have extended and modified that hypothesis--we have distinguished two orders of small particles1 the molecule 7of a compound or of an element7 and the atom 7of an element74 ,the combination of two or more elements is now regarded as being preceded by the decomposition of the molecules of these elements into atoms4 ,we have defined molecule and we have defined atom1 but before we can determine the relative weights of elementary atoms we must have a means of determining the relative weights of compound molecules4 ,the old difficulty still stares us in the face--how can we find the number of elementary atoms in the molecule of a given compound8 ,the same naturalist who enriched chemical science by the discovery of the molecule as distinct from the atom1 placed in the hands of chemists the instrument for determining the relative weights of molecules1 and thus also the relative weights of atoms4 ,the great generalization1 usually known as ,avogadro's law1 runs thus3 ,equal volumes of gases measured at the same temperature and under the same pressure contain equal numbers of molecules4 ,gay-,lussac had concluded that equal volumes of gases contain equal numbers of atoms2 but this conclusion was rejected1 and rightly rejected by ,dalton1 who however at the same time refused to admit that there is a simple relation between the combining volumes of elements4 ,the generalization of ,avogadro has however stood the test of experiment1 and is now accepted as one of the fundamental laws of chemical science4 ,like the atomic theory itself1 ,avogadro's law is an outcome of physical work and of physical reasoning4 ,of late years the great naturalists1 ,clausius1 ,helmholtz1 ,joule1 ,rankine1 ,clerk ,maxwell and ,thomson have developed the physical theory of molecules1 and have shown that ,avogadro's law may be deduced as a necessary consequence from a few simple physical assumptions4 ,this law has thus been raised1 from being a purely empirical generalization1 to the rank of a deduction from a wide1 yet simple physical theory4 ,now1 if equal volumes of gases contain equal numbers of molecules1 it follows that the ratio of the densities of any two gases must also be the ratio of the weights of the molecules which constitute these gases4 ,thus1 a given volume of water vapour weighs nine times more than an equal volume of hydrogen2 therefore the molecule of gaseous water is nine times heavier than the molecule of hydrogen4 ,one has therefore only to adopt a standard of reference for molecular weights1 and ,avogadro's law gives the means of determining the number of times any gaseous molecule is heavier than that of the standard molecule4 ,but consider the combination of a gaseous element with hydrogen2 let us take the case of hydrogen and chlorine1 which unite to form gaseous hydrochloric acid1 and let us determine the volumes of the uniting elements and the volume of the product4 ,here is a statement of the results3 one volume of hydrogen combines with one volume of chlorine to form two volumes of hydrochloric acid4 ,assume any number of molecules we please in the one volume of hydrogen--say ten--there must be1 by ,avogadro's law1 also ten molecules in the one volume of chlorine2 but inasmuch as the volume of hydrochloric acid produced is double that of either the hydrogen or the chlorine which combined to form it1 it follows1 by the same law1 that twenty molecules of hydrochloric acid have been formed by the union of ten molecules of hydrogen with ten molecules of chlorine4 ,the necessary conclusion is that each hydrogen molecule and each chlorine molecule has split into two parts1 and that each half-molecule 7or atom7 of hydrogen has combined with one half-molecule 7or atom7 of chlorine1 to produce one compound molecule of hydrochloric acid4 ,therefore we conclude that the hydrogen molecule is composed of two atoms1 and that the chlorine molecule is also composed of two atoms2 and as hydrogen is to be our standard element1 we say that if the atom of hydrogen weighs one1 the molecule of the same element weighs two4 ,it is now easy to find the molecular weight of any gas2 it is only necessary to find how many times heavier the given gas is than hydrogen1 the weight of the latter being taken as #b4 ,thus1 oxygen is sixteen times heavier than hydrogen1 but #a3 #af #b3 #cb1 therefore the molecule of oxygen is thirty-two times heavier than the molecule of hydrogen4 ,ammonia is eight and a half times heavier than hydrogen1 but #a3 #h-a_/b #b3 #ag1 therefore the molecule of ammonia is seventeen times heavier than the molecule of hydrogen4 ,this is what we more concisely express by saying the molecular weight of oxygen is #cb1 or the molecular weight of ammonia is #ag1 etc41 etc4 ,now1 we wish to determine the atomic weight of oxygen2 that is1 we wish to find how many times the oxygen atom is heavier than the atom of hydrogen4 ,we make use of ,avogadro's law and of the definition of atom which has been deduced from it 7see p4 #adb74 ,we know that eight parts by weight of oxygen combine with one part by weight of hydrogen to form water2 but we do not know whether the molecule of water contains one atom of each element1 or two atoms of hydrogen and one atom of oxygen1 or some other combination of these atoms 7see p4 #aca74 ,but by vaporizing water and weighing the gas so produced1 we find that water vapour is nine times heavier than hydrogen3 now1 #a3 #i #b3 #ah1 therefore the molecular weight of water gas is #ah4 ,analysis tells us that eighteen parts by weight of water gas contain sixteen parts of oxygen and two parts of hydrogen2 that is to say1 we now know that in the molecule of water gas there are two atoms of hydrogen combined with sixteen parts by weight of oxygen4 ,we now proceed to analyze and determine the molecular weights of as many gaseous compounds of oxygen as we can obtain4 ,the outcome of all is that we have as yet failed to obtain any such compound in the molecule of which there are less than sixteen parts by weight of oxygen4 ,in some of these molecules there are sixteen1 in some thirty-two1 in some forty-eight1 in some sixty-four parts by weight of oxygen1 but in none is there less than sixteen parts by weight of this element4 ,therefore we conclude that the atomic weight of oxygen is #af1 because this is the smallest amount1 referred to hydrogen taken as #a1 which has hitherto been found in the molecule of any compound of oxygen4 ,the whole of the work done since the publication of ,dalton's ,new ,system has emphasized the importance of that chemist's remark1 that no safe conclusion can be drawn as to the value of the atomic weight of an element except from a consideration of many compounds of that with other elements4 ,but in ,avogadro's law we have a far more accurate and trustworthy method for determining the molecular weights of compounds than any which ,dalton was able to devise by his study of chemical combinations4 ,we have thus got a clearer conception of atom than was generally possessed by chemists in the days of ,dalton1 and this we have gained by introducing the further conception of molecule as that of a quantity of matter different from1 and yet similar to1 the atom4 ,the task now before us will for the most part consist in tracing the further development of the fundamental conception of ,dalton1 the conception1 viz41 of each chemical substance as built up of small parts possessing all the properties1 other than the mass1 of the whole2 and--what we also owe to ,dalton--the application of this conception to explain the facts of chemical combination4 99 99 99 99 99 ,the circumstances of ,dalton's early life obliged him to trust largely to his own efforts for acquiring knowledge2 and his determination not to accept facts at second hand but to acquire them for himself1 is very marked throughout the whole of his life4 ,in the preface to the second part of the ,new ,system he says1 ,having been in my progress so often misled by taking for granted the results of others1 ,i have determined to write as little as possible but what ,i can attest by my own experience4 ,we should not expect such a man as this to make any great use of books2 one of his friends tells us that he heard him declare on a public occasion that he could carry his library on his back1 and yet had not read half of the books which comprised it4 ,the love of investigation which characterized ,dalton when young would naturally be increased by this course of intellectual life4 ,how strong this desire to examine everything for himself became1 is amusingly illustrated by a story told by his medical adviser1 ,dr4 ,ransome4 ,once when ,dalton was suffering from catarrh ,dr4 ,ransome had prescribed a ,james's powder1 and finding his patient much better next day1 he congratulated himself and ,dalton on the good effects of the medicine4 ,i do not well see how that can be1 said ,dalton1 as ,i kept the powder until ,i could have an opportunity of analyzing it4 ,as ,dalton grew older he became more than ever disinclined to place much trust in the results obtained by other naturalists1 even when these men were acknowledged to be superior to himself in manipulative and experimental skill4 ,thus1 as we have already learned1 he could not be brought to allow the truth of ,gay-,lussac's experimentally established law regarding gaseous combinations2 he preferred to attribute ,gay-,lussac's results to errors of experiment4 ,the truth is1 ,i believe1 that gases do not unite in equal or exact measures in any one instance2 when they appear to do so it is owing to the inaccuracy of our experiments4 ,that ,dalton did not rank high as an experimenter is evident from the many mistakes in matters of fact which are to be found in the second part of his ,new ,system4 ,a marked example of his inaccuracy in purely experimental work is to be found in the supposed proof given by him that charcoal1 after being heated to redness1 does not absorb gases4 ,he strongly heated a quantity of charcoal1 pulverized it1 and placed it in a ,florence flask1 which was connected by means of a stopcock with a bladder filled with carbonic acid3 after a week he found that the flask and its contents had not sensibly increased in weight1 and he concluded that no carbonic acid had been absorbed by the charcoal4 ,but no trustworthy result could be obtained from an experiment in which the charcoal1 having been deprived of air by heating1 was again allowed to absorb air by being pulverized in an open vessel1 and was then placed in a flask filled with air1 communication between the carbonic acid and the external air being prevented merely by a piece of bladder1 a material which is easily permeated by gases4 ,dalton used a method which can only lead to notable results in natural science when employed by a really great thinker2 he acquired a few facts1 and then thought out the meaning of these4 ,almost at the beginning of each investigation he tried to get hold of some definite generalization1 and then he proceeded to amass special facts4 ,the object which he kept before himself in his experimental work was to establish or to disprove this or that hypothesis4 ,every experiment was conducted with a clearly conceived aim4 ,he was even willing to allow a large margin for errors of experiment if he could thereby bring the results within the scope of his hypothesis4 ,that the law of multiple proportions is simply a generalization of facts1 and may be stated apart from the atomic theory1 is now generally admitted4 ,but in ,dalton's mind this law seems to have arisen rather as a deduction from the theory of atoms than to have been gained as a generalization from experiments4 ,he certainly always stated this law in the language of the atomic theory4 ,in one of his walking excursions he explained his theory to a friend1 and after expounding his views regarding atomic combinations1 he said that the examples which he had given showed the necessary existence of the principle of multiple proportions3 ,thou knowest it must be so1 for no man can split an atom4 ,we have seen that carburetted hydrogen was one of the compounds on the results of the analysis of which he built his atomic theory2 yet we find him saying of the constitution of this compound that no correct notion seems to have been formed till the atomic theory was introduced and applied in the investigation4 ,when ,dalton was meditating on the laws of chemical combination1 a ,french chemist1 ,m4 ,proust1 published analyses of metallic oxides1 which proved that when a metal forms two oxides the amount of metal in each is a fixed quantity--that there is a sudden jump1 as it were1 from one oxide to another4 ,we are sometimes told that from these experiments ,proust would have recognized the law of multiple proportions had his analyses only been more accurate2 but we know that ,dalton's analyses were very inaccurate1 and yet he not only recognized the law of multiple proportions1 but propounded and established the atomic theory4 ,something more than a correct system of keeping books and balancing accounts is wanted in natural science4 ,dalton's experimental results would be the despair of a systematic analyst1 but from these ,dalton's genius evolved that splendid theory which has done so much to advance the exact investigation of natural phenomena4 ,probably no greater contrast could be found between methods of work1 both leading to the establishment of scientific 7that is1 accurate and precise7 results1 than that which exists between the method of ,dalton and the method pursued by ,priestley4 ,priestley commenced his experiments with no particular aim in view2 sometimes he wanted to amuse himself1 sometimes he thought he might light upon a discovery of importance1 sometimes his curiosity incited him to experiment4 ,when he got facts he made no profound generalizations2 he was content to interpret his results by the help of the prevailing theory of his time4 ,but each new fact only spurred him on to make fresh incursions into the fields of ,nature4 ,dalton thought much and deeply2 his experimentally established facts were to him symbols of unseen powers4 ,he used facts as ,hobbes says the wise man uses words3 they were his counters only1 not his money4 ,when we ask how it was that ,dalton acquired his great power of penetrating beneath the surface of things and finding general laws1 we must attribute this power in part to the training which he gave himself in physical science4 ,it was from a consideration of physical facts that he gained the conception of ultimate particles of definite weight4 ,his method was essentially dynamical2 that is1 he pictured a gas as a mass of little particles1 each of which acted on and was acted on by1 other particles4 ,the particles were not thrown together anyhow2 definite forces existed between them4 ,each elementary or compound gas was pictured as a system of little particles1 and the properties of that gas were regarded as dependent on the nature and arrangement of these particles4 ,such a conception as this could only be gained by a careful and profound thinker versed in the methods of physical and mathematical science4 ,thus we see that although ,dalton appeared to gain his great chemical results by a method which we are not generally inclined to regard as the method of natural science1 yet it was by virtue of his careful training in a branch of knowledge which deals with facts1 as well as in that science which deduces particular conclusions from general principles1 that he was able to introduce his fruitful conceptions into the science of chemistry4 ,to me it appears that ,dalton was pre-eminently distinguished by the possession of imagination4 ,he formed clear mental images of the phenomena which he studied1 and these images he was able to combine and modify so that there resulted a new image containing in itself all the essential parts of each separate picture which he had previously formed4 ,from his intense devotion to the pursuit of science the development of ,dalton's general character appears to have been somewhat dwarfed4 ,although he possessed imagination1 it was the imagination of a naturalist rather than that of a man of broad culture4 ,perhaps it was a want of broad sympathies which made him trust so implicitly in his own work and so readily distrust the work of others1 and which moreover led him astray in so many of his purely experimental investigations4 99 99 99 99 99 ,dalton began his chemical work about six years after the death of ,lavoisier4 ,unlike that great philosopher he cared nothing for political life4 ,the friends in whose family he spent the greater part of his life in ,manchester were never able to tell whether he was ,whig or ,tory4 ,unlike ,priestley he was content to let metaphysical and theological speculation alone4 ,in his quiet devotion to study he more resembled ,black1 and in his method1 which was more deductive than that usually employed in chemistry1 he also resembled the ,edinburgh professor4 ,trained from his earliest days to depend on himself1 nurtured in the creedless creed of the ,friends1 he entered on his life's work with few prejudices1 if without much profound knowledge of what had been done before him4 ,by the power of his insight into ,nature and the concentration of his thought1 he drew aside the curtain which hung between the seen and the unseen2 and while ,herschel1 sweeping the heavens with his telescope and night by night bringing new worlds within the sphere of knowledge1 was overpowering men's minds by new conceptions of the infinitely great1 ,john ,dalton1 with like imaginative power1 was examining the architecture of the ultimate particles of matter1 and revealing the existence of law and order in the domain of the infinitely small4 ,,footnotes3 #g ,see ,fig4 #b1 which is copied from the original in the ,new ,system of ,chemical ,philosophy1 and illustrates ,dalton's conception of a quantity of carbonic acid gas1 each atom built up of one atom of carbon and two of oxygen2 of nitrous oxide gas1 each atom composed of one atom of nitrogen and one of oxygen2 and of hydrogen gas1 constituted of single atoms4 #h ,more accurate analysis has shown that there are six parts of carbon united respectively with one and with two parts by weight of hydrogen in these compounds4 ,,chapter ,,iv4 ,,establishment ,,of ,,general ,,principles ,,of ,,chemical ,,science 7continued7--,,period ,,of ,,davy ,,and ,,berzelius4 ,humphry ,davy1 #aggh-ahbi4 ,johann ,jacob ,berzelius1 #aggi-ahdh4 ,we may roughly date the period of chemical advance during which the connections between chemistry and other branches of natural knowledge were recognized and studied1 as beginning with the first year of this century1 and as continuing to our own day4 ,the elaboration of the atomic theory was busily carried on during the second and third decades of this century2 to this the labour of the ,swedish chemist ,berzelius largely contributed4 ,that there exist many points of close connection between chemical and electrical science was also demonstrated by the labours of the same chemist1 and by the brilliant and impressive discoveries of ,sir ,humphry ,davy4 ,a system of classification of chemical elements and compounds was established by the same great naturalists1 and many inroads were made into the domain of the chemistry of bodies of animal and vegetable origin4 ,the work of ,berzelius and ,davy1 characterized as it is by thoroughness1 clearness and definiteness1 belongs essentially to the modern era of chemical advance2 but ,i think we shall better preserve the continuity of our story if we devote a chapter to a consideration of the work of these two renowned naturalists before entering on our review of the time immediately preceding the present1 as typical workers in which time ,i have chosen ,liebig and ,dumas4 ,in the last chapter we found that the foundations of the atomic theory had been laid1 and the theory itself had been applied to general problems of chemical synthesis1 by ,dalton4 ,in giving1 in that chapter1 a short sketch of the modern molecular theory1 and in trying to explain the meaning of the term molecule as contrasted with atom1 ,i necessarily carried the reader forward to a time considerably later than the first decade of this century4 ,we must now retrace our steps2 and in perusing the account of the work of ,berzelius and ,davy given in the present chapter1 the reader must endeavour to have in his mind a conception of atom analogous to the mental picture formed by ,dalton 7see pp4 #ace1 #acf72 he must regard the term as applicable to element and compound alike2 he must remember that the work of which he reads is the work of those who are striving towards a clear conception of the atom1 and who are gradually rising to a recognition of the existence of more than one order of small particles1 by the regular putting together of which masses of matter are constituted4 ,no materials1 so far as ,i am aware1 exist from which a life of ,berzelius can be constructed4 ,i must therefore content myself with giving a mere enumeration of the more salient points in his life4 ,of his chemical work abundant details are fortunately to be found in his own ,lehrbuch1 and in the works and papers of himself and his contemporaries4 99 99 99 99 99 ,,johann ,,jacob ,,berzelius was the son of the schoolmaster of ,waefersunda1 a village near ,linkoping1 in ,east ,gothland1 ,sweden4 ,he was born in ,august #aggi--;he was born1 that is1 a few years after ,priestley's discovery of oxygen2 at the time when ,lavoisier had nearly completed his theory of combustion2 when ,dalton was endeavouring to keep the unruly youth of ,eaglesfield in subjection2 and when ,black1 having established the existence of fixed air and the theory of latent heat1 was the central figure in the band of students who were enlarging our knowledge of ,nature in the ,scottish capital4 ,being left an orphan at the age of nine1 the young ,berzelius was brought up by his grandfather1 who appears to have been a man of education and sense4 ,after attending school at ,linkoping1 he entered the ,university of ,upsala as a student of medicine4 ,here he soon began to show a taste for chemistry4 ,it would appear that few or no experiments were then introduced into his lectures by the ,professor of ,chemistry at ,upsala2 little encouragement was given to pursue chemical experiments1 and so ,berzelius had to trust to his own labours for gaining an acquaintance with practical chemistry4 ,having thus made considerable progress in chemistry1 and being on a visit to the mineral baths of ,medevi1 he seized the opportunity to make a very thorough analysis of the waters of this place1 which were renowned in ,sweden for their curative properties4 ,the publication of this analysis marks the first appearance of ,berzelius as an author4 ,he graduated as ,m4,b4 in #ahja1 and a year or two later presented his dissertation1 entitled ,the ,action of ,galvanism on ,organic ,bodies1 as a thesis for the degree of ,doctor of ,medicine4 ,this thesis1 like that of ,black1 published about half a century earlier1 marks an important stage in the history of chemistry4 ,these and other publications made the young doctor famous2 he was called to ,stockholm to be extraordinary 7or assistant7 ,professor of ,chemistry in the medical school of that capital4 ,sometimes practising medicine in order to add to his limited income1 but for the most part engaged in chemical research1 he remained in ,stockholm for nearly fifty years1 during most of which time the laboratory of ,berzelius in the ,swedish capital was regarded as one of the magnetic poles of the chemical world4 ,to this point came many of the great chemists who afterwards enriched the science by their discoveries4 ,woehler1 ,h4 and ,g4 ,rose1 ,magnus1 ,gmelin1 ,mitscherlich and others all studied with ,berzelius4 ,he visited ,england and ,france1 and was on terms of intimacy and in correspondence with ,davy1 ,dalton1 ,gay-,lussac1 ,berthollet and the other men who at that period shed so much lustre on ,english and ,french science4 ,it is said that ,berzelius was so much pleased with the lectures of ,dr4 ,marcet at ,guy's ,hospital1 that on his return from his visit to ,england in #ahab1 he introduced much more liveliness and many more experimental illustrations into his own lectures4 ,at the age of thirty-one1 ,berzelius was chosen ,president of the ,stockholm ,academy of ,sciences2 a few years later he was elected a ,foreign ,fellow of the ,royal ,society1 which society bestowed on him the ,copley ,medal in #ahcf4 ,he was raised to the rank of a baron by the ,king of ,sweden1 being allowed as a special privilege to retain his own name4 ,in the year #ahcb ,berzelius resigned his professorship1 and in the same year he married4 ,during the remainder of his life1 he continued to receive honours of all kinds1 but he never for a moment forsook the paths of science4 ,after the death of ,davy1 in #ahbi1 he was recognized as the leading ,european chemist of his age2 but1 although firm in his own theoretical views1 he was ready to test these views by appealing to ,nature4 ,the very persistency with which he clung to a conception established on some solid experimental basis insured that new light would be thrown on that conception by the researches of those chemists who opposed him4 ,probably no chemist has added to the science so many carefully determined facts as ,berzelius2 he was always at work in the laboratory1 and always worked with the greatest care4 ,yet the appliances at his command were what we should now call poor1 meagre1 and utterly inadequate4 ,professor ,woehler of ,goettingen1 who in the fulness of days and honours has so lately gone from amongst us1 recently gave an account of his visit to ,berzelius in the year #ahbc4 ,woehler had taken his degree as ,doctor of ,medicine at ,heidelberg1 and being anxious to prosecute the study of chemistry he was advised by his friends to spend a winter in the laboratory of the ,swedish professor4 ,having written to ,berzelius and learned that he was willing to allow him working room in his laboratory1 the young student set out for ,stockholm4 ,after a journey to ,luebeck and a few days' passage in a small sailing-vessel1 he arrived in the ,swedish capital4 ,knocking at the door of the house pointed out as that of ,berzelius1 he tells us that his heart beat hard as the door was opened by a tall man of florid complexion4 ,it was ,berzelius himself1 he exclaims4 ,scarcely believing that he was in the very room where so many famous discoveries had been made1 he entered the laboratory4 ,no water1 no gas1 no draught-places1 no ovens were to be seen2 a couple of plain tables1 a blowpipe1 a few shelves with bottles1 a little simple apparatus1 and a large water-barrel whereat ,anna1 the ancient cook of the establishment1 washed the laboratory dishes1 completed the furnishings of this room1 famous throughout ,europe for the work which had been done in it4 ,in the kitchen which adjoined1 and where ,anna cooked1 was a small furnace and a sand bath for heating purposes4 ,in this room many great discoveries were made4 ,among these we may note the separation of the element columbium in #ahae1 and of selenion in #ahah2 the discovery of the new earth thoria in #ahbh2 the elucidation of the properties of yttrium and cerium about #ahbj1 of uranium in #ahbc1 and of the platinum metals in #ahbh2 the accurate determination of the atomic weights of the greater number of the elements2 the discovery of sulphur salts in #ahbf-bg1 and the proof that silica is an acid1 and that most of the stony minerals are compounds of this acid with various bases4 ,but we shall better learn the value of some of these discoveries by taking a general review of the contributions to chemical science of the man who spent most of his life at work in that room in ,stockholm4 ,the ,german chemist ,richter1 in the first or second year of this century1 had drawn attention to the fact that when two neutral compounds1 such as nitrate of potash and chloride of lime1 react chemically1 the substances produced by this reaction are also neutral4 ,all the potash combined with nitric acid in one salt changes places with all the lime combined with muriatic acid in the other salt2 therefore1 said ,richter1 these different quantities of potash and lime are neutralized by the same quantity of nitric acid2 and1 hence1 these amounts of potash and lime are chemically equivalent1 because these are the amounts which perform the same reaction1 viz4 neutralization of a fixed quantity of acid4 ,if then careful analyses were made of a number of such neutral compounds as those named1 the equivalents of all the commoner bases and acids#i might be calculated4 ,richter's own determinations of the equivalents of acids and bases were not very accurate1 but ,berzelius was impressed with the importance of this work4 ,the year before the appearance of ,dalton's ,new ,system 7i4e4 in #ahjg71 he began to prepare and carefully analyze series of neutral salts4 ,as the work was proceeding he became acquainted with the theory of ,dalton1 and at once saw its extreme importance4 ,for some time ,berzelius continued to work on the lines laid down by ,dalton1 and to accumulate data from which the atomic weights of elements might be calculated2 but he soon perceived--as the founder of the theory had perceived from the very outset--that the fundamental conception of each atom of an element as being a distinct mass of matter weighing more or less than the atom of every other element1 and of each atom of a compound as being built up of the atoms of the elements which compose that compound1--,berzelius1 ,i say1 perceived that these conceptions must remain fruitless unless means were found for determining the number of elementary atoms in each compound atom4 ,we have already learned the rules framed by the founder of the atomic theory for his guidance in attempting to solve this problem4 ,berzelius thought those rules insufficient and arbitrary2 he therefore laid down two general rules1 on the lines of which he prosecuted his researches into chemical synthesis4 ,one atom of one element combines with one1 two1 three1 or more atoms of another element4 ,this is practically the same as ,dalton's definitions of binary1 ternary1 etc41 compounds 7p4 #acb74 ,two atoms of one element combine with three and five atoms of another element4 ,berzelius here recognizes the existence of compound atoms of a more complex structure than any of those recognized by ,dalton4 ,berzelius further extended the conception of atom by applying it to groups of elements formed1 according to him1 by the combination of various compound atoms4 ,to his mind every compound atom appeared as built up of two parts2 each of these parts might be an elementary atom1 or might be itself built up of several elementary atoms1 yet in the ,berzelian theory each acted as a definite whole4 ,so far as the building up of the complex atom went1 each of the two parts into which this atom could be divided acted as if it were a simple atom4 ,if we suppose a patch of two shades of red colour to be laid on a smooth surface1 and alongside of this a patch of two shades of yellow colour1 and if we suppose the whole mass of colour to be viewed from a distance such that one patch appears uniformly red and the other uniformly yellow1 we shall have a rough illustration of the ,berzelian compound atom4 ,to the observer the whole mass of colour appears to consist of two distinct patches of contrasted colours2 but let him approach nearer1 and he perceives that what appeared to be a uniform surface of red or yellow really consists of two patches of unlike shades of red or of yellow4 ,the whole mass of colour represents the compound atom2 broadly it consists of two parts--the red colour represents one of the constituent atoms1 the yellow colour represents the other constituent atom2 but on closer examination the red atom1 so to speak--and likewise the yellow atom--is found to consist of parts which are less unlike each other than the whole red atom is unlike the whole yellow atom4 ,we shall have to consider in more detail the reasoning whereby ,berzelius arrived at this conception of every compound atom as a dual structure 7see pp4 #bji-bab74 ,at present ,i wish to notice this conception as lying at the root of most of the work which he did in extending and applying the ,daltonian theory4 ,i wish to insist on the fact that the atomic theory could not advance without methods being found for determining the number of elementary atoms in a compound atom1 without clear conceptions being gained of every compound atom as a structure1 and without at least attempts being made to learn the laws in accordance with which that structure was built4 ,before the atomic weight of oxygen could be determined it was necessary that the number of oxygen and of hydrogen atoms in the atom of water should be known2 otherwise all that could be stated was1 the atomic weight of oxygen is a simple multiple of #h4 ,berzelius did much to advance chemical science by the introduction and application of a few simple rules whereby he determined the number of elementary atoms in various compound atoms4 ,but as the science advanced1 and as more facts came to be known1 the ,berzelian rules were found to be too narrow and too arbitrary2 chemists sought for some surer and more generally applicable method than that which ,berzelius had introduced1 and the imperious demand for this method at last forced them to recognize the importance of the great generalization of the ,italian naturalist ,avogadro1 which they had possessed since the year #ahaa1 but the meaning of which they had so long failed to understand4 ,berzelius made one great step in the direction of recognizing ,avogadro's distinction between atom and molecule when he accepted ,gay-,lussac's generalization that equal volumes of gases contain equal numbers of atoms3 but he refused to apply this to other than elementary gases4 ,the weights of the volumes of elementary gases which combined were1 for ,berzelius1 also the weights of the atoms of these elements4 ,thus1 let the weight of one volume of hydrogen be called #a1 then two volumes of hydrogen1 weighing #b1 combine with one volume of oxygen1 weighing #af1 to form two volumes of water vapour2 therefore1 said ,berzelius1 the atom of water consists of two atoms of hydrogen and one atom of oxygen1 and the atom of the latter element is sixteen times heavier than the atom of the former4 ,three volumes of hydrogen1 weighing #c1 combine with one volume of nitrogen1 weighing #ad1 to form two volumes of ammonia2 therefore1 said ,berzelius1 the atom of ammonia consists of three atoms of hydrogen combined with one atom of nitrogen1 and the nitrogen atom is fourteen times heavier than the atom of hydrogen4 ,while ,berzelius was applying these rules to the determination of the atomic weights of the elements1 and was conducting the most important series of analyses known in the annals of the science1 two great physico-chemical discoveries were announced4 ,in the year #ahah the law of isomorphism was stated by ,mitscherlich3 ,compounds the atoms of which contain equal numbers of elementary atoms1 similarly arranged1 have the same crystalline form4 ,as thus stated1 the law of isomorphism affirms that if two compounds crystallize in the same form1 the atoms of these compounds are built up of the same number of elementary atoms--however different may be the nature of the elements in the compounds--and that these elementary atoms are similarly arranged4 ,this statement was soon found to be too absolute1 and was accordingly modified2 but to go into the history of the law of isomorphism would lead us too far from the great main path of chemical advance1 the course of which we are seeking to trace4 ,berzelius at once accepted ,mitscherlich's law1 as an aid in his researches on atomic weights4 ,the help to be derived from this law may be illustrated thus3 let us assume that two compounds have been obtained exhibiting identity of crystalline form2 let it be further assumed that the number of elementary atoms in the atom of one of these compounds is known2 it follows1 by the law of isomorphism1 that the number of elementary atoms in the atom of the other is known also4 ,let the two compounds be sulphate of potash and chromate of potash2 let it be assumed that the atom of the first named is known to consist of two atoms of potassium1 one atom of sulphur1 and four atoms of oxygen2 and that the second substance is known to be a compound of the elements potassium1 chromium and oxygen2 then the atom of the second compound contains1 by ,mitscherlich's law1 two atoms of potassium1 one atom of chromium and four atoms of oxygen3 hence the relative weight of the atom of chromate of potash can be determined1 and hence the relative weight of the atom of chromium can also be determined4 ,a year after the announcement of ,mitscherlich's law1 the following generalization was stated to hold good1 by two ,french naturalists1 ,dulong and ,petit3--,the atoms of all solid elements have the same capacity for heat4 ,if the amount of heat required to raise the temperature of one grain of water through one degree be called one unit of heat1 then the capacity for heat of any body other than water is the number of units of heat required to raise the temperature of one grain of that substance through one degree4 ,each chemical substance1 elementary and compound1 has its own capacity for heat2 but1 instead of comparing the capacities for heat of equal weights1 ,dulong and ,petit compared the capacities for heat of weights representing the weights of the atoms of various elements4 ,thus1 equal amounts of heat are required to raise1 through the same interval of temperature1 fifty-six grains of iron1 one hundred and eight grains of silver1 and sixty-three and a half grains of copper2 but the weights of the atoms of these three elements are in the proportion of #ef3ajh3fc-a_/b4 ,dulong and ,petit based their generalization on measurements of the capacities for heat of thirteen elements2 further research has shown that their statement most probably holds good for all the solid elements4 ,here then was a most important instrument put into the hands of the chemist4 ,it is only necessary that the atomic weight of one solid element should be certainly known1 and that the amount of heat required to raise through one degree the number of grains of that element expressed by its atomic weight should also be known2 then the number which expresses the weight1 in grains1 of any other solid element which is raised through one degree by the same amount of heat1 likewise expresses the relative weight of the atom of that element4 ,thus1 suppose that the atomic weight of silver is known to be #ajh1 and suppose that six units of heat are required to raise the temperature of one hundred and eight grains of this metal through one degree2 then suppose it is found by experiment that six units of heat suffice to raise the temperature of two hundred and ten grains of bismuth through one degree1 it follows--according to the law of ,dulong and ,petit--that #baj is the atomic weight of bismuth4 ,the modified generalization of ,gay-,lussac--,equal volumes of elementary gases contain equal numbers of atoms2 the laws of isomorphism and of atomic heat2 and the two empirical rules stated on p4 #afc2--these were the guides used by ,berzelius in interpreting the analytical results which he and his pupils obtained in that memorable series of researches1 whereby the conceptions of ,dalton were shown to be applicable to a wide range of chemical phenomena4 ,the fixity of composition of chemical compounds has now been established2 a definite meaning has been given to the term element2 the conception of atom has been gained1 but much remains to be done in the way of rendering this conception precise2 and fairly good1 but not altogether satisfactory methods have been introduced by which the relative weights of the atoms of elements and compounds may be determined4 ,at this time chemists are busy preparing and describing new compounds1 and many new elements are also being discovered2 the need of classification begins to be felt more and more4 ,in the days of ,berzelius and ,davy strenuous efforts were made to obtain some generalizations by the application of which the many known elements and compounds might be divided into groups4 ,it was felt that a classification might be founded on the composition of compounds1 or perhaps on the properties of the same compounds4 ,these two general principles served as guides in most of the researches then instituted2 answers were sought to these two questions3 ,of what elements is this compound composed8 and1 ,what can this compound do2 how does it react towards other bodies8 ,lavoisier1 as we know1 regarded oxygen as the characteristic element of all acids4 ,this term acid implies the possession1 by all the substances denoted by it1 of some common property2 let us shortly trace the history of this word in chemistry4 ,vinegar was known to the ,greeks and ,romans1 and the names which they gave this substance tell us that sourness was to them its characteristic property4 ,they knew that vinegar effervesced when brought into contact with chalky earths1 and that it was able to dissolve many substances--witness the story of ,cleopatra's draught of the pearl dissolved in vinegar4 ,other substances possessed of these properties--for instance oil of vitriol and spirits of salt--as they became known1 were classed along with vinegar2 but no attempts were made to clearly define the properties of these bodies till comparatively recent times4 ,the characteristics of an acid substance enumerated by ,boyle are--solvent power1 which is exerted unequally on different bodies2 power of turning many vegetable blues to red1 and of restoring many vegetable colours which had been destroyed by alkalis2 power of precipitating solid sulphur from solutions of this substance in alkalis1 and the power of acting on alkalis to produce substances without the properties of either acid or alkali4 ,but what1 one may ask1 is an alkali1 of which mention is so often made by ,boyle8 ,from very early times it had been noticed that the ashes which remained when certain plants were burned1 and the liquid obtained by dissolving those ashes in water1 had great cleansing powers2 that they removed oily matter1 fat and dirt from cloth and other fabrics4 ,the fact that an aqueous solution of these ashes affects the coloured parts of many plants was also noticed in early times4 ,as progress was made in chemical knowledge observers began to contrast the properties of this plant-ash with the properties of acids4 ,the former had no marked taste1 the latter were always very sour2 the former turned some vegetable reds to blue1 the latter turned the blues to red2 a solution of plant-ash had no great solvent action on ordinary mineral matter1 whereas this matter was generally dissolved by an acid4 ,in the time of the alchemists1 who were always seeking for the principles or essences of things1 these properties of acids were attributed to a principle of acidity1 while the properties of plant-ash and substances resembling plant-ash were attributed to a principle of alkalinity 7from ,arabic alkali1 or the ash74 ,in the seventeenth century the distinction between acid and alkali was made the basis of a system of chemical medicine4 ,the two principles of acidity and alkalinity were regarded as engaged in an active and never-ending warfare4 ,every disease was traced to an undue preponderance of one or other of these principles2 to keep these unruly principles in quietness became the aim of the physician1 and of course it was necessary that the physician should be a chemist1 in order that he might know the nature and habits of the principles which gave him so much trouble4 ,up to this time the term alkali had been applied to almost any substance having the properties which ,i have just enumerated2 but this group of substances was divided by ,van ,helmont and his successors into fixed alkali and volatile alkali1 and fixed alkali was further subdivided into mineral alkali 7what we now call soda7 and vegetable alkali 7potash74 ,about the same time acids were likewise divided into three groups2 vegetable1 animal1 and mineral acids4 ,to the properties by which alkali was distinguished1 viz4 cleansing power and action on vegetable colouring matters1 ,stahl 7the founder of the phlogistic theory7 added that of combining with acids4 ,when an acid 7that is1 a sour-tasting substance which dissolves most earthy matters and turns vegetable blues to red7 is added to an alkali 7that is1 a substance which feels soap-like to the touch1 which does not dissolve many earthy matters1 and which turns many vegetable reds to blue7 the properties of both acid and alkali disappear1 and a new substance is produced which is not characterized by the properties of either constituent4 ,the new substance1 as a rule1 is without action on earthy matters or on vegetable colours2 it is not sour1 nor is it soapy to the touch like alkali2 it is neutral4 ,it is a salt4 ,but1 although ,stahl stated that an alkali is a substance which combines with an acid1 it was not until a century later that these three--alkali1 acid1 salt--were clearly distinguished4 ,but the knowledge that a certain group of bodies are sour and dissolve minerals1 etc41 and that a certain other group of bodies are nearly tasteless and do not dissolve minerals1 etc41 was evidently a knowledge of only the outlying properties of the bodies2 it simply enabled a term to be applied to a group of bodies1 which term had a definite connotation4 ,why are acids acid1 and why are alkalis alkaline8 ,acids are acid1 said ,becher 7latter part of seventeenth century71 because they all contain the same principle1 viz4 the primordial acid4 ,this primordial acid is more or less mixed with earthy matter in all actual acids2 it is very pure in spirits of salt4 ,alkalis are alkaline1 said ,basil ,valentine 7beginning of the sixteenth century71 because they contain a special kind of matter1 the matter of fire4 ,according to other chemists 7e4g4 ,j4 ,f4 ,meyer1 #agfd71 acids owe their acidity to the presence of a sharp or biting principle got from fire4 ,acids1 alkalis and salts all contain1 according to ,stahl 7beginning of the eighteenth century71 more or less primordial acid4 ,the more of this a substance contains1 the more acid it is2 the less of this it contains1 the more alkaline it is4 ,all these attempted explanations recognize that similar properties are to be traced to similarity of composition2 but the assertion of the existence of a primordial acid1 or of the matter of fire1 although undoubtedly a step in advance1 was not sufficiently definite 7unless it was supplemented by a distinct account of the properties of these principles7 to be accepted when chemical knowledge became accurate4 ,the same general consideration1 founded on a large accumulation of facts1 viz4 that similarity of properties is due to similarity of composition1 guided ,lavoisier in his work on acids4 ,he found the primordial acid of ,stahl1 and the biting principle of ,meyer1 in the element oxygen4 ,i have already 7p4 #ia7 shortly traced the reasoning whereby ,lavoisier arrived at the conclusion that oxygen is the acid-producer2 here ,i would insist on the difference between his method and that of ,basil ,valentine1 ,stahl and the older chemists4 ,they carried into the domain of natural science conceptions obtained from1 and essentially belonging to the domain of metaphysical or extra-physical speculation2 he said that oxygen is the acidifier1 because all the compounds of this element which he actually examined were possessed of the properties included under the name acid4 ,we know that ,lavoisier's conclusion was erroneous1 that it was not founded on a sufficiently broad basis of facts4 ,the conception of an acidifying principle1 although that principle was identified with a known element1 was still tainted with the vices of the alchemical school4 ,we shall see immediately how much harm was done by the assertion of ,lavoisier1 ,all acids contain oxygen4 ,in ,chapter ,,ii4 7pp4 #cb-cg7 we traced the progress of knowledge regarding alkalis from the time when the properties of these bodies were said to be due to the existence in them of matter of fire1 to the time when ,black had clearly distinguished and defined caustic alkali and carbonated alkali4 ,the truly philosophical character1 and at the same time the want of enthusiasm1 of ,black become apparent if we contrast his work on alkali with that of ,lavoisier on acid4 ,black did not hamper the advance of chemistry by finding a principle of alkalinity2 but neither did he give a full explanation of the fact that certain bodies are alkaline while others are not4 ,he set himself the problem of accurately determining the differences in composition between burnt 7or caustic7 and unburnt 7or mild7 alkali1 and he solved the problem most successfully4 ,he showed that the properties of mild alkalis differ from those of caustic alkalis1 because the composition of the former differs from that of the latter2 and he showed exactly wherein this difference of composition consists1 viz4 in the possession or non-possession of fixed air4 ,strange we may say that this discovery did not induce ,black to prosecute the study of caustic alkalis3 surely he would have anticipated ,davy1 and have been known as the discoverer of potassium and sodium4 ,in the time of ,stahl the name salt was applied1 as we have learned1 to the substance produced by the union of an acid with an alkali2 but the same word was used by the alchemists with an altogether different signification4 ,originally applied to the solid matter obtained by boiling down sea-water1 and then extended to include all substances which1 like this solid matter1 are very easily dissolved by water and can be recovered by boiling down this solution1 salt was1 in the sixteenth and seventeenth centuries1 the name given to one of the hypothetical principles or elements4 ,many kinds of matter were known to be easily dissolved by water2 the common possession of these properties was sought to be accounted for by saying that all these substances contained the same principle1 namely1 the principle of salt4 ,i have already tried to indicate the reasoning whereby ,boyle did so much to overthrow this conception of salt4 ,he also extended our knowledge of special substances which are now classed as salts4 ,the chemists who came after ,boyle gradually reverted to the older meaning of the term salt1 adopting as the characteristics of all substances placed in this class1 ready solubility in water1 fusibility1 or sometimes volatility1 and the possession of a taste more or less like that of sea-salt4 ,substances which resembled salts in general appearance1 but were insoluble in water1 and very fixed in the fire1 were called earths2 and1 as was generally done in those days1 the existence of a primordial earth was assumed1 more or less of which was supposed to be present in actual earths4 ,this recognition of the possibility of more or less of the primordial earth being present in actually occurring earths1 of course necessitated the existence of various kinds of earth4 ,the earths were gradually distinguished from each other2 lime was recognized as a substance distinct from baryta1 baryta as distinct from alumina1 etc4 ,stahl taught that one essential property of an earth was fusibility by fire1 with production of a substance more or less like glass4 ,this property was possessed in a remarkable degree by quartz or silica4 ,hence silica was regarded as the typical earth1 until ,berzelius1 in #ahae1 proved it to be an acid4 ,but the earths resembled alkalis1 inasmuch as they too combined with1 and so neutralized1 acids4 ,there is an alkali hidden in every earth1 said some chemists4 ,an alkali is an earth refined by the presence of acid and combustible matter1 said others4 ,earths thus came to be included in the term alkali1 when that term was used in its widest acceptation4 ,but a little later it was found that some of the earths were thrown down in the solid form from their solutions in acids by the addition of alkalis2 this led to a threefold division1 thus-- ,earths ---- ,alkaline earths ---- ,alkalis ,insoluble ,somewhat soluble ,very soluble in in water4 in water4 water4 ,the distinction at first drawn between earth and alkali was too absolute2 the intermediate group of alkaline earths served to bridge over the gap between the extreme groups4 ,in ,nature1 says ,wordsworth1 everything is distinct1 but nothing defined into absolute independent singleness4 ,at this stage of advance1 then1 an earth is regarded as differing from an alkali in being insoluble1 or nearly insoluble in water2 in not being soapy to the touch1 and not turning vegetable reds to blue3 but as resembling an alkali1 in that it combines with and neutralizes an acid2 and the product of this neutralization1 whether accomplished by an alkali or by an earth1 is called a salt4 ,to the earth or alkali1 as being the foundation on which the salt is built1 by the addition of acid1 the name of base was given by ,rouelle in #agdd4 ,but running through every conception which was formed of these substances--acid1 alkali1 earth1 salt--we find a tendency1 sometimes forcibly marked1 sometimes feebly indicated1 but always present1 to consider salt as a term of much wider acceptation than any of the others4 ,an acid and an alkali1 or an acid and an earth1 combine to form a salt2 but the salt could not have been thus produced unless the acid1 the alkali and the earth had contained in themselves some properties which1 when combined1 form the properties of the salt4 ,the acid1 the alkali1 the earth1 each is1 in a sense1 a salt4 ,the perfect salt is produced by the coalescence of the saltness of the acid with the saltness of the alkali4 ,this conception finds full utterance in the names1 once in common use1 of sal acidum for acid1 sal alkali for alkali1 and sal salsum or sal neutrum for salt4 ,all are salts2 at one extreme comes that salt which is marked by properties called acid properties1 at the other extreme comes the salt distinguished by alkaline properties1 and between these1 and formed by the union of these1 comes the middle or neutral salt4 ,it is thus that the nomenclature of chemistry marks the advances made in the science4 ,what's in a name8 ,to the historical student of science1 almost everything4 ,we shall find how different is the meaning attached in modern chemistry to these terms1 acid salt1 alkaline salt1 neutral salt1 from that which our predecessors gave to their sal acidum1 sal alkali1 and sal neutrum4 ,we must note the appearance of the term vitriol1 applied to the solid salt-like bodies obtained from acids and characterized by a glassy lustre4 ,by the middle of last century the vitriols were recognized as all derived from1 or compounded of1 sulphuric acid 7oil of vitriol7 and metals2 this led to a subdivision of the large class of neutral salts into 7#a7 metallic salts produced by the action of sulphuric acid on metals1 and 7#b7 neutral salts produced by the action of earths or alkalis on acids generally4 ,to ,rouelle1 a predecessor of ,lavoisier1 who died four years before the discovery of oxygen1 we owe many accurate and suggestive remarks and experiments bearing on the term salt4 ,i have already mentioned that it was he who applied the word base to the alkali or earth1 or it might be metal1 from which1 by the action of acid1 a salt is built up4 ,he also ceased to speak of an acid as sal acidum1 or of an alkali as sal alkali1 and applied the term salt exclusively to those substances which are produced by the action of acids on bases4 ,when the product of such an action was neutral--that is1 had no sour taste1 no soapy feeling to the touch1 no action on vegetable colours1 and no action on acids or bases--he called that product a neutral salt2 when the product still exhibited some of the properties of acid1 e4g4 sourness of taste1 he called it an acid salt2 and when the product continued to exhibit some of the properties of alkali1 e4g4 turned vegetable reds to blue1 he called it an alkaline salt4 ,rouelle also proved experimentally that an acid salt contains more acid--relatively to the same amount of base--than a neutral salt1 and that an alkaline salt contains more base--relatively to the same amount of acid--than a neutral salt2 and he proved that this excess of acid1 or of base1 is chemically united to the rest of the salt--is1 in other words1 an essential part of the salt1 from which it cannot be removed without changing the properties of the whole4 ,but we have not as yet got to know why certain qualities connoted by the term acid can be affirmed to belong to a group of bodies1 why certain other1 alkaline1 properties belong to another group1 nor why a third group can be distinguished from both of these by the possession of properties which we sum up in the term earthy4 ,surely there must be some peculiarity in the composition of these substances1 common to all1 by virtue of which all are acid4 ,the atom of an acid is surely composed of certain elements which are never found in the atom of an alkali or an earth2 or perhaps the difference lies in the number1 rather than in the nature of the elements in the acid atoms1 or even in the arrangement of the elementary atoms in the compound atom of acid1 of alkali1 and of earth4 ,i think that our knowledge of salt is now more complete than our knowledge of either acid1 alkali1 or earth4 ,we know that a salt is formed by the union of an acid and an alkali or earth2 if1 then1 we get to know the composition of acids and bases 7i4e4 alkalis and earths71 we shall be well on the way towards knowing the composition of salts4 ,and now we must resume our story where we left it at p4 #agf4 ,lavoisier had recognized oxygen as the acidifier2 ,black had proved that a caustic alkali does not contain carbonic acid4 ,up to this time metallic calces1 and for the most part alkalis and earths also1 had been regarded as elementary substances4 ,lavoisier however proved calces to be compounds of metals and oxygen2 but as some of those calces had all the properties which characterized earths1 it seemed probable that all earths are metallic oxides1 and if all earths1 most likely all alkalis also4 ,many attempts were made to decompose earths and alkalis1 and to obtain the metal1 the oxide of which the earth or the alkali was supposed to be4 ,one chemist thought he had obtained a metal by heating the earth baryta with charcoal1 but from the properties of his metal we know that he had not worked with a pure specimen of baryta1 and that his supposed metallic base of baryta was simply a little iron or other metal1 previously present in the baryta1 or charcoal1 or crucible which he employed4 ,but if ,lavoisier's view were correct--if all bases contained oxygen--it followed that all salts are oxygen compounds4 ,acids all contain oxygen1 said ,lavoisier2 this was soon regarded as one of the fundamental facts of chemistry4 ,earths and alkalis are probably oxides of metals2 this before long became an article of faith with all orthodox chemists4 ,salts are produced by the union of acids and bases1 therefore all salts contain oxygen3 the conclusion was readily adopted by almost every one4 ,when the controversy between ,lavoisier and the phlogistic chemists was at its height1 the followers of ,stahl had taunted ,lavoisier with being unable to explain the production of hydrogen 7or phlogiston as they thought7 during the solution of metals in acids2 but when ,lavoisier learned the composition of water1 he had an answer sufficient to quell these taunts4 ,the metal1 said ,lavoisier1 decomposes the water which is always present along with the acid1 hydrogen is thus evolved1 and the metallic calx or oxide so produced dissolves in the acid and forms a salt4 ,if this explanation were correct--and there was an immense mass of evidence in its favour and apparently none against it--then all the salts produced by the action of acids on metals necessarily contained oxygen4 ,the ,lavoisierian view of a salt1 as a compound of a metallic oxide--or base--with a non-metallic oxide--or acid--seemed the only explanation which could be accepted by any reasonable chemist3 in the early years of this century it reigned supreme4 ,but even during the lifetime of its founder this theory was opposed and opposed by the logic of facts4 ,in #aghg ,berthollet published an account of experiments on prussic acid1--the existence and preparation 7from ,prussian blue7 of which acid had been demonstrated three or four years before by the ,swedish chemist ,scheele--which led him to conclude this compound to be a true acid1 but free from oxygen4 ,in #agif the same chemist studied the composition and properties of sulphuretted hydrogen1 and pronounced this body to be an acid containing no oxygen4 ,but the experiments and reasoning of ,berthollet were hidden by the masses of facts and the cogency of argument of the ,lavoisierian chemists4 ,the prevalent views regarding acids and bases were greatly strengthened by the earlier researches of ,sir ,humphry ,davy1 in which he employed the voltaic battery as an instrument in chemical investigation4 ,let us now consider some of the electro-chemical work of this brilliant chemist4 ,in the spring of the year #ahjj the electrical battery1 which had recently been discovered by ,volta1 was applied by ,nicholson and ,carlisle to effect the decomposition of water4 ,the experiments of these naturalists were repeated and confirmed by ,davy1 then resident at ,bristol1 who followed up this application of electricity to effect chemical changes by a series of experiments extending from #ahjj to #ahjf1 and culminating in the ,bakerian ,lecture delivered before the ,royal ,society in the latter year4 ,the history of ,davy's life during these years1 years rich in results of the utmost importance to chemical science1 will be traced in the sequel2 meanwhile we are concerned only with the results of his chemical work4 ,the first ,bakerian ,lecture of ,humphry ,davy1 ,on some ,chemical ,agencies of ,electricity1 deserves the careful study of all who are interested in the methods of natural science2 it is a brilliant example of the disentanglement of a complex natural problem4 ,volta and others had subjected water to the action of a current of electricity1 and had noticed the appearance of acid and alkali at the oppositely electrified metallic surfaces4 ,according to some experimenters1 the acid was nitrous1 according to others1 muriatic acid4 ,one chemist asserted the production of a new and peculiar body which he called the electric acid4 ,the alkali was generally said to be ammonia4 ,when ,davy passed an electric current through distilled water contained in glass vessels1 connected by pieces of moist bladder1 cotton fibre1 or other vegetable matters1 he found that nitric and hydrochloric acids were formed in the water surrounding the positively electrified plate or pole1 and soda around the negatively electrified pole1 of the battery4 ,when the same piece of cotton fibre was repeatedly used for making connection between the glass vessels1 and was washed each time in dilute nitric acid1 ,davy found that the production of muriatic acid gradually ceased2 hence he traced the formation of this acid to the presence of the animal or vegetable substance used in the experiments4 ,finding that the glass vessels were somewhat corroded1 and that the greater the amount of corrosion the greater was the amount of soda making its appearance around the negative pole1 he concluded that the soda was probably a product of the decomposition of the glass by the electric current2 he therefore modified the experiment4 ,he passed an electric current through distilled water contained in small cups of agate1 previously cleaned by boiling in distilled water for several hours1 and connected by threads of the mineral asbestos1 chosen as being quite free from vegetable matter2 alkali and acid were still produced4 ,the experiment was repeated several times with the same apparatus2 acid and alkali were still produced1 but the alkali decreased each time4 ,the only conclusion to be drawn was that the alkali came from the water employed4 ,two small cups of gold were now used to contain the water2 a very small amount of alkali appeared at the negative pole1 and a little nitric acid at the positive pole4 ,the quantity of acid slowly increased as the experiment continued1 whereas the quantity of alkali remained the same as after a few minutes' action of the electric current4 ,the production of alkali is probably due1 said ,davy1 to the presence in the water of some substance which is not removed by distillation in a glass retort4 ,by boiling down in a silver dish a quantity of the water he had used1 a very small amount of solid matter was obtained1 which after being heated was distinctly alkaline4 ,moreover when a little of this solid matter was added to the water contained in the two golden cups1 there was a sudden and marked increase in the amount of alkali formed around the negative pole4 ,another quantity of the water which he had used was again distilled in a silver retort1 and a little of the distillate was subjected to electrolysis as before4 ,no alkali appeared4 ,a little piece of glass was placed in the water2 alkali quickly began to form4 ,davy thus conclusively proved that the alkali produced during the electrolysis 7i4e4 decomposition by the electric current7 of water is not derived from the water itself1 but from mineral impurities contained in the water1 or in the vessel in which the water is placed during the experiment4 ,but the production of nitric acid around the positive pole was yet to be accounted for4 ,before further experiments could be made it was necessary that ,davy should form an hypothesis--that he should mentally connect the appearance of the nitric acid with some other phenomenon sufficient to produce this appearance2 he could then devise experiments which would determine whether the connection supposed to exist between the two phenomena really did exist or not4 ,now1 of the constituents of nitric acid--nitrogen1 hydrogen and oxygen--all except the first named are present in pure water2 nitrogen is present in large quantity in the ordinary atmosphere4 ,it was only necessary to assume that some of the hydrogen and oxygen produced during the electrolysis of water seized on and combined with some of the nitrogen in the air which surrounded that water1 and the continual production of nitric acid during the whole process of electrolysis was explained4 ,but how was this assumption to be proved or disproved8 ,davy adopted a method frequently made use of in scientific investigations3--remove the assumed cause of a phenomenon2 if the phenomenon ceases to be produced1 the assumed cause is probably the real cause4 ,davy surrounded the little gold cups containing the water to be electrolysed with a glass jar which he connected with an air-pump2 he exhausted most of the air from the jar and then passed the electric current through the water4 ,very little nitric acid appeared4 ,he now again took out most of the air from the glass jar1 admitted some hydrogen to supply its place1 and again pumped this out4 ,this process he repeated two or three times and then passed the electric current4 ,no acid appeared in the water4 ,he admitted air into the glass vessel2 nitric acid began to be produced4 ,thus he proved that whenever air was present in contact with the water being electrolysed1 nitric acid made its appearance1 and when the air was wholly removed the acid ceased to be produced4 ,as he had previously shown that the production of this acid was not to be traced to impurities in the water1 to the nature of the vessel used to contain the water1 or to the nature of the material of which the poles of the battery were composed1 the conclusion was forced upon him that the production of nitric acid in the water1 and the presence of ordinary air around the water invariably existed together2 that if one of these conditions was present1 the other was also present--in other words1 that one was the cause of the other4 ,the result of this exhaustive and brilliant piece of work is summed up by ,davy in these words3 ,it seems evident then that water1 chemically pure1 is decomposed by electricity into gaseous matter alone1 into oxygen and hydrogen4 ,from the effects of the electric current on glass1 ,davy argued that other earthy compounds would probably undergo change under similar conditions4 ,he therefore had little cups of gypsum made1 in which he placed pure water1 and passed an electric current through the liquid4 ,lime was formed around the negative1 and sulphuric acid around the positive pole4 ,using similar apparatus1 he proved that the electric current decomposes very many minerals into an earthy or alkaline base and an acid4 ,picturing to himself the little particles of a salt as being split by the electric current each into two smaller particles1 one possessed of acid and the other of alkaline properties1 ,davy thought it might be possible to intercept the progress of these smaller particles1 which he saw ever travelling towards the positive and negative poles of the battery4 ,he accordingly connected these small glass vessels by threads of washed asbestos2 in one of the outer vessels he placed pure water1 in the other an aqueous solution of sulphate of potash1 and in the central vessel he placed ammonia4 ,the negative pole of the battery being immersed in the sulphate of potash1 and the positive pole in the water1 it was necessary for the particles of sulphuric acid--produced by the decomposition of the sulphate of potash--to travel through the ammonia in the central vessel before they could find their way to the positive pole4 ,now1 ammonia and sulphuric acid cannot exist in contact--they instantly combine to form sulphate of ammonia2 the sulphuric acid particles ought therefore to be arrested by the ammonia4 ,but the sulphuric acid made its appearance at the positive pole just as if the central vessel had contained water4 ,it seemed that the mutual attraction ordinarily exerted between sulphuric acid and ammonia was overcome by the action of the electric current4 ,ammonia would generally present an insuperable barrier to the progress of sulphuric acid1 but the electrical energy appeared to force the acid particles over this barrier2 they passed towards their goal as if nothing stood in their way4 ,experiments are now multiplied by ,davy1 and the general conclusion drawn is that ,hydrogen1 the alkaline substances1 the metals and certain metallic oxides are attracted by negatively electrified metallic surfaces1 and repelled by positively electrified metallic surfaces2 and contrariwise1 that oxygen and acid substances are attracted by positively electrified metallic surfaces1 and repelled by negatively electrified metallic surfaces2 and these attractive and repulsive forces are sufficiently energetic to destroy or suspend the usual operation of chemical affinity4#aj ,to account for this apparent suspension of the ordinary chemical laws1 ,davy supposes that chemical compounds are continually decomposed and re-formed throughout the liquid which is subjected to the electrical action4 ,thus1 in the experiment with water1 ammonia and sulphate of potash1 he supposes that the sulphuric acid and ammonia do combine in the central vessel to form sulphate of ammonia1 but that this compound is again decomposed1 by the electrical energy1 into sulphuric acid--which passes on towards the positive pole--and ammonia--which remains in the central vessel--ready to combine with more sulphuric acid as that comes travelling onwards from its source in the vessel containing sulphate of potash to its goal in the vessel containing water4 ,the eye of the philosopher had pierced beneath the apparent stability of the chemical systems which he studied4 ,to his vision there appeared in those few drops of water and ammonia and sulphate of potash a never-ceasing conflict of contending forces2 there appeared a continual shattering and rebuilding of the particles of which the masses were composed4 ,the whole was at rest1 the parts were in motion2 the whole was constant in chemical composition1 the composition of each particle was changed a thousand times in the minutest portion of every second4 ,to the mind of ,davy1 the electrolysis of every chemical compound was a new application of the great law established by ,newton--,to every action there is an equal and opposite reaction4 ,each step made in chemical science since ,davy's time has but served to emphasize the universality of this principle of action and reaction1 a principle which has been too much overlooked in the chemical text-books1 but the importance of which recent researches are beginning to impress on the minds of chemists4 ,it is the privilege of the philosophic student of ,nature to penetrate the veil with which she conceals her secrets from the vulgar gaze4 ,to him are shown sights which eye hath not seen1 and by him are perceived sounds which ear hath not heard4 ,each drop of water is seen by him not only to be built up of myriads of small parts1 but each particle is seen to be in motion2 many particles are being decomposed into still smaller particles of matter1 different in properties from the original particles1 but as the original particles are at the same time being reproduced1 the continued existence of the drop of water with the properties of water is to him the result of the mutual action and reaction of contending forces4 ,he knows that rest and permanence are gained1 not by the cessation of action1 but by the continuance of conflict2 he knows that in the realm of natural phenomena1 stable equilibrium is the resultant of the action of opposite forces1 and that complete decomposition occurs only when one force becomes too powerful or another becomes too weak4 ,pursuing the train of thought initiated by the experiments which ,i have described1 ,davy entered upon a series of researches which led him to consider every chemical substance as possessing definite electrical relations towards every other substance4 ,as chemical attraction between two bodies seems to be destroyed by giving one of them an electrical state different from that which it naturally possessed--that is1 by bringing it into a state similar to the other--so it may be increased by exalting its natural energy4 ,thus zinc1 a metal easily oxidized1 does not combine with oxygen when negatively electrified1 whereas silver1 a metal oxidized with difficulty1 readily combines with oxygen when positively electrified4 ,substances in opposite electrical states appear to combine chemically1 and the greater the electrical difference the greater the readiness with which chemical combination is effected4 ,electrical energy and chemical attraction or affinity are evidently closely connected2 perhaps1 said ,davy1 they are both results of the same cause4 ,thus ,davy arrived at the conception of a system of bodies as maintained in equilibrium by the mutual actions and reactions of both chemical and electrical forces2 by increasing either of these a change is necessarily produced in the other4 ,under certain electrical conditions the bodies will exert no chemical action on one another1 but such action may be started by changing these electrical conditions1 or1 on the other hand1 by changes in the chemical relations of the bodies a change in the electrical relations may be induced4 ,thus ,davy found that if plates of copper and sulphur are heated1 the copper exhibits a positive and the sulphur a negative electrical condition2 that these electrical states become more marked as temperature rises1 until the melting point of sulphur is reached1 when the copper and sulphur combine together chemically and produce sulphide of copper4 ,when water is electrolysed1 ,davy looked on the oppositely electrified metallic plates in the battery as striving to attain a state of equilibrium2 the negatively electrified zinc strives to gain positive electricity from the copper1 which strives to gain negative electricity from the zinc4 ,the water he regarded as the carrier of these electricities1 the one in this direction1 the other in that4 ,in thus acting as a carrier1 the water is itself chemically decomposed1 with production of hydrogen and oxygen2 but this chemical rearrangement of some of the substances which composed the original system 7of battery and water7 involves a fresh disturbance of electrical energy1 and so the process proceeds until the whole of the water is decomposed or the whole of the copper or zinc plate is dissolved in the battery4 ,if the water were not chemically decomposed1 ,davy thought that the zinc and copper in the battery would quickly attain the state of electrical equilibrium towards which they continually strive1 and that the current would therefore quickly cease4 ,davy thought that however strong the natural electrical energies of the elements of bodies may be1 yet there is every probability of a limit to their strength2 whereas the powers of our artificial instruments seem capable of indefinite increase4 ,by making use of a very powerful battery1 he hoped to be able to decompose substances generally regarded as simple bodies4 ,taking a wide survey of natural phenomena1 he sees these two forces1 which we call chemical and electrical1 everywhere at work1 and by their mutual actions upholding the material universe in equilibrium4 ,in the outbreaks of volcanoes he sees the disturbance of this equilibrium by the undue preponderance of electrical force2 and in the formation of complex minerals beneath the surface of the earth1 he traces the action of those chemical attractions which are ever ready to bring about the combination of elements1 if they are not held in check by the opposing influence of electrical energy4 ,we shall see how the great and philosophical conception of ,davy was used by ,berzelius1 and how1 while undoubtedly gaining in precision1 it lost much in breadth in being made the basis of a rigid system of chemical classification4 ,davy's hope that the new instrument of research placed in the hands of chemists by ,volta would be used in the decomposition of supposed simple substances was soon to be realized4 ,a year after the lecture ,on some ,chemical ,agencies of ,electricity1 ,davy was again the reader of the ,bakerian ,lecture2 this year 7#ahjg7 it was entitled1 ,on some ,new ,phenomena of ,chemical ,change produced by ,electricity1 particularly the ,decomposition of the ,fixed ,alkalis2 and the ,exhibition of the ,new ,substances which constitute their ,bases2 and on the ,general ,nature of ,alkaline ,bodies4 ,in his first experiments on the effect of the electrical current on potash and soda1 ,davy used strong aqueous solutions of these alkalis1 with the result that hydrogen and oxygen only were evolved4 ,he then passed the current through melted potash kept liquid during the operation by the use of a spirit-lamp1 the flame of which was fed with oxygen4 ,much light was evolved1 and a great flame appeared at the negative pole2 on changing the direction of the current1 aeriform globules1 which inflamed in the air1 rose through the potash4 ,on the #fth of ,october #ahjg1 a piece of potash was placed on a disc of platinum1 which was made the negative pole of a very powerful battery2 a platinum wire brought into contact with the upper surface of the potash served as the positive pole4 ,when the current was passed1 the potash became hot and soon melted2 gas was evolved at the upper surface1 and at the lower 7negative7 side there was no liberation of elastic fluid1 but small globules1 having a high metallic lustre1 and being precisely similar in visible characters to quicksilver appeared1 some of which burst with explosion and bright flame as soon as they were formed1 and others remained1 and were merely tarnished1 and finally covered by a white film which formed on their surfaces4 ,when ,davy saw these metallic globules burst through the crust of fusing potash1 we are told by one of his biographers1 he could not contain his joy1 he actually bounded about the room in ecstatic delight2 and some little time was required for him to compose himself sufficiently to continue the experiment4 ,this was the culminating point of the researches in which he had been continuously engaged for about six years4 ,his interest and excitement were intense2 the ,bakerian ,lecture was written on the spur of the occasion1 before the excitement of the mind had subsided1 yet1 says his biographer--and we may well agree with him--yet it bears proof only of the maturest judgment2 the greater part of it is as remarkable for experimental accuracy as for logical precision4 ,but to every action there is an equal and opposite reaction3 immediately after the delivery of the lecture1 ,davy was prostrated by a severe attack of illness1 which confined him to bed for nine weeks1 and was very nearly proving fatal4 ,that the phenomenon just described was really the decomposition of potash1 and the production of the metal of which this substance is an oxygenized compound1 was proved by obtaining similar results whether plates of silver1 copper1 or gold1 or vessels of plumbago1 or even charcoal1 were used to contain the potash1 or whether the experiment was conducted in the air1 or in a glass vessel from which air had been exhausted1 or in glass tubes wherein the potash was confined by mercury4 ,the decomposition of potash was followed within a few days by that of soda1 from which substance metallic globules were obtained which took fire when exposed to the air4 ,but the analysis of potash and soda was not sufficient for ,davy2 he determined to accomplish the synthesis of these substances4 ,for this purpose he collected small quantities of the newly discovered metals1 by conducting the electrolysis of potash and soda under experimental conditions such that the metals1 as soon as produced1 were plunged under the surface of naphtha1 a liquid which does not contain oxygen1 and which protected them from the action of the surrounding air4 ,a weighed quantity of each metal was then heated in a stream of pure dry oxygen1 the products were collected and weighed1 and it was found that solutions of these products in water possessed all the properties of aqueous solutions of potash and soda4 ,the new metals were now obtained in larger quantity by ,davy1 and their properties carefully determined by him2 they were named potassium and sodium respectively4 ,they were shown to possess all those properties which were generally accepted as characteristic of metal1 except that of being heavy4 ,the new metals were extremely light1 lighter than water4 ,for some time it was difficult to convince all chemists that a metal could be a very light substance4 ,we are assured that a friend of ,davy1 who was shown potassium for the first time1 and was asked what kind of substance he supposed it to be1 replied1 ,it is metallic1 to be sure2 and then1 balancing it on his finger1 he added in a tone of confidence1 ',bless me1 how heavy it is6' ,davy argued that since the alkalis1 potash and soda1 were found to be oxygen compounds of metals1 the earths would probably also be found to be metallic oxides4 ,in the year #ahjh he succeeded in decomposing the three earths1 lime1 baryta and strontia1 and in obtaining the metals calcium1 barium and strontium1 but not in a perfectly pure condition1 or in any quantity4 ,he also got evidence of the decomposition of the earths silica1 alumina1 zirconia and beryllia1 by the action of powerful electric currents1 but he did not succeed in obtaining the supposed metallic bases of these substances4 ,so far ,davy's discoveries had all tended to confirm the generally accepted view which regarded alkalis and earths as metallic oxides4 ,but we found that the outcome of these views was to regard all salts--and among these1 of course1 common salt--as oxygen compounds4#aa ,acids were oxygen compounds1 bases were oxygen compounds1 and as salts were produced by the union of acids with bases1 they1 too1 must necessarily be oxygen compounds4 ,berthollet had thrown doubt on the universality of ,lavoisier's name oxygen1 the acidifier1 but he had not conclusively proved the existence of any acid which did not contain oxygen4 ,the researches of ,davy naturally led him to consider the prevalent views regarding acids1 bases and salts4 ,muriatic 7or as we now call it hydrochloric7 acid had long been a stumbling-block to the thorough-going ,lavoisierian chemists4 ,oxygen could not be detected in it1 yet it ought to contain oxygen1 because oxygen is the acidifier4 ,of course1 if muriatic acid contains oxygen1 the salts--muriates--produced by the action of this acid on alkalis and earths must also contain oxygen4 ,many years before this time the action of muriatic acid on manganese ore had been studied by the ,swedish chemist ,scheele1 who had thus obtained a yellow-coloured gas with a very strong smell4 ,berthollet had shown that when a solution of this gas in water is exposed to sunlight1 oxygen is evolved and muriatic acid is produced4 ,the yellow gas was therefore supposed to be1 and was called1 oxidized muriatic acid1 and muriatic acid was itself regarded as composed of oxygen and an unknown substance or radicle4 ,in #ahji ,gay-,lussac and ,thenard found that one volume of hydrogen united with one volume of the so-called oxidized muriatic acid to form muriatic acid2 the presence of hydrogen in this acid was therefore proved4 ,when ,davy began 7#ahaj-aa7 to turn his attention specially to the study of salts1 he adopted the generally accepted view that muriatic acid is a compound of oxygen and an unknown radicle1 and that by the addition of oxygen to this compound oxidized muriatic acid is produced4 ,but unless ,davy could prove the presence of oxygen in muriatic acid he could not long hold the opinion that oxygen was really a constituent of this substance4 ,he tried to obtain direct evidence of the presence of oxygen1 but failed4 ,he then set about comparing the action of muriatic acid on metals and metallic oxides with the action of the so-called oxidized muriatic acid on the same substances4 ,he showed that salt-like compounds were produced by the action of oxidized muriatic acid either on metals or on the oxides of these metals1 oxygen being evolved in the latter cases2 and that the same compounds and water were produced by the action of muriatic acid on the same metallic oxides4 ,these results were most easily and readily explained by assuming the so-called oxidized muriatic acid to be an elementary substance1 and muriatic acid to be a compound of this element with hydrogen4 ,to the new element thus discovered--for he who establishes the elementary nature of a substance may almost be regarded as its discoverer--,davy gave the name of chlorine1 suggested by the yellow colour of the gas 7from ,greek1 yellow74 ,he at once began to study the analogies of chlorine1 to find by experiment which elements it resembled1 and so to classify it4 ,many metals1 he found1 combined readily with chlorine1 with evolution of heat and light4 ,it acted1 like oxygen1 as a supporter of combustion2 it was1 like oxygen1 attracted towards the negative pole of the voltaic battery2 its compound with hydrogen was an acid2 hence said ,davy chlorine1 like oxygen1 is a supporter of combustion and also an acidifier4 ,but it was very hard to get chemists to adopt these views4 ,as ,bacon says1 ,if false facts in ,nature be once on foot1 what through neglect of examination1 the countenance of antiquity1 and the use made of them in discourse1 they are scarce ever retracted4 ,chemists had long been accustomed to systems which pretended to explain all chemical facts4 ,the phlogistic theory1 which had tyrannized over chemistry1 had been succeeded by the ,lavoisierian chemistry1 which recognized one acidifier1 and this also the one supporter of combustion4 ,to ascribe these properties to any element other than oxygen appeared almost profane4 ,but when ,davy spoke of chlorine as an acidifier1 he did not use this word in the same sense as that in which it was employed by the upholders of the oxygen theory of acids2 he simply meant to express the fact that a compound containing chlorine as one of its constituents1 but not containing oxygen1 was a true acid4 ,when ,gay-,lussac attempted to prove that hydrogen is an alkalizing principle1 ,davy said1 ,this is an attempt to introduce into chemistry a doctrine of occult qualities1 and to refer to some mysterious and inexplicable energy what must depend upon a peculiar corpuscular arrangement4 ,and with regard to ,gay-,lussac's strained use of analogies between hydrogen compounds and alkalis1 he says1 ,the substitution of analogy for fact is the bane of chemical philosophy2 the legitimate use of analogy is to connect facts together1 and to guide to new experiments4 ,but ,davy's facts were so well established1 and his experiments so convincing1 that before two or three years had passed1 most chemists were persuaded that chlorine was an element--i4e4 a substance which had never been decomposed--and that muriatic acid was a compound of this element with hydrogen4 ,berzelius was among the last to adopt the new view4 ,woehler tells us that in the winter of #ahbc1 when he was working in the laboratory of ,berzelius1 ,anna1 while washing some basins1 remarked that they smelt strongly of oxidized muriatic acid3 ,now1 said ,berzelius1 listen to me1 ,anna4 ,thou must no longer say 'oxidized muriatic acid1' but 'chlorine2' that is better4 ,this work on chlorine was followed up1 in #ahac1 by the proof that the class of acidifiers and supporters of combustion contains a third elementary substance1 viz4 iodine4 ,as ,davy's views regarding acids and salts became developed1 he seems to have more and more opposed the assumption that any one element is especially to be regarded as the acidifying element2 but at the same time he seems to admit that most1 if not all1 acids contain hydrogen4 ,such oxides as sulphur trioxide1 nitrogen pentoxide1 etc41 do not possess acid properties except in combination with water4 ,but he of course did not say that all hydrogen compounds are acids2 he rather regarded the possession by a substance of acid properties as dependent1 to a great extent1 on the nature of the elements other than hydrogen which it contained1 or perhaps on the arrangement of all the elements in the particles of the acid4 ,he regarded the hydrogen in an acid as capable of replacement by a metal1 and to the metallic derivative--as it might be called--of the acid1 thus produced1 he gave the name of salt4 ,an acid might therefore be a compound of hydrogen with one other element--such were hydrochloric1 hydriodic1 hydrofluoric acids--or it might be a compound of hydrogen with two or more elements1 of which one might or might not be oxygen--such were hydrocyanic acid and chloric or nitric acid4 ,if the hydrogen in any of these acids were replaced by a metal a salt would be produced4 ,a salt might therefore contain no oxygen1 e4g4 chloride or iodide of potassium2 but in most cases salts did contain oxygen1 e4g4 chlorate or nitrate of potassium4 ,acids were thus divided into oxyacids 7or acids which contain oxygen7 and acids containing no oxygen2 the former class including most of the known acids4 ,the old view of salts as being compounds of acids 7i4e4 oxides of the non-metallic elements7 and bases 7i4e4 oxides of metals7 was overthrown1 and salts came to be regarded as metallic derivatives of acids4 ,from this time1 these terms--acids1 salts1 bases--become of less importance than they formerly were in the history of chemical advance4 ,in trying to explain ,davy's electro-chemical theory ,i have applied the word affinity to the mutual action and reaction between two substances which combine together to form a chemical compound4 ,it is now necessary that we should look a little more closely into the history of this word affinity4 ,oil and water do not mix together1 but oil and potash solution do2 the former may be said not to have1 and the latter to have1 an affinity one for the other4 ,when sulphur is heated1 the yellow odourless solid1 seizing upon oxygen in the air1 combines with it to produce a colourless strongly smelling gas4 ,sulphur and oxygen are said to have strong affinity for each other4 ,if equal weights of lime and magnesia be thrown into diluted nitric acid1 after a time it is found that some of the lime1 but very little of the magnesia1 is dissolved4 ,if an aqueous solution of lime be added to a solution of magnesia in nitric acid1 the magnesia is precipitated in the form of an insoluble powder1 while the lime remains dissolved in the acid4 ,it is said that lime has a stronger affinity for nitric acid than magnesia has4 ,such reactions as these used to be cited as examples of single elective affinity--single1 because one substance combined with one other1 and elective1 because a substance seemed to choose between two others presented to it1 and to combine with one to the exclusion of the other4 ,but if a neutral solution of magnesia in sulphuric acid is added to a neutral solution of lime in nitric acid1 sulphate of lime and nitrate of magnesia are produced4 ,the lime1 it was said1 leaves the nitric and goes to the sulphuric acid1 which1 having been deserted by the magnesia1 is ready to receive it2 at the same time the nitric acid from which the lime has departed combines with the magnesia formerly held by the sulphuric acid4 ,such a reaction was said to be an instance of double affinities4 ,the chemical changes were caused1 it was said1 by the simultaneous affinity of lime for sulphuric acid1 which was greater than its affinity for nitric acid1 and the affinity of magnesia for nitric acid1 which was greater than its affinity for sulphuric acid4 ,if a number of salts were mixed1 each base--supposing the foregoing statements to be correct--would form a compound with that acid for which it had the greatest affinity4 ,it should then be possible to draw up tables of affinity4 ,such tables were indeed prepared4 ,here is an example3-- ,sulphuric ,acid4 ,baryta4 ,lime4 ,strontia4 ,ammonia4 ,potash4 ,magnesia4 ,soda4 ,this table tells us that the affinity of baryta for sulphuric acid is greater than that of strontia for the same acid1 that of strontia greater than that of potash1 and so on4 ,it also tells that potash will decompose a compound of sulphuric acid and soda1 just as soda will decompose a compound of the same acid with lime1 or strontia will decompose a compound with potash1 etc4 ,but ,berthollet showed in the early years of this century that a large quantity of a body having a weak affinity for another will suffice to decompose a small quantity of a compound of this other with a third body for which it has a strong affinity4 ,he showed1 that is1 that the formation or non-formation of a compound is dependent not only on the so-called affinities between the constituents1 but also on the relative quantities of these constituents4 ,berthollet and other chemists also showed that affinity is much conditioned by temperature2 that is1 that two substances which show no tendency towards chemical union at a low temperature may combine when the temperature is raised4 ,he1 and they1 also proved that the formation or non-formation of a compound is much influenced by its physical properties4 ,thus1 if two substances are mixed in solution1 and if by their mutual action a substance can be produced which is insoluble in the liquids present1 that substance is generally produced whether the affinity between the original pair of substances be strong or weak4 ,the outcome of ,berthollet's work was that tables of affinity became almost valueless4 ,to say that the affinity of this body for that was greater than its affinity for a third body was going beyond the facts1 because the formation of this or that compound depended on many conditions much more complex than those connoted by the term affinity4 ,yet the conception of affinity remained1 although it could not be applied in so rigorous a way as had been done by the earlier chemists4 ,if an element1 ,a1 readily combines with another element1 ,b1 under certain physical conditions1 but does not1 under the same conditions1 combine with a third element1 ,c1 it may still be said that ,a and ,b have1 and ,a and ,c have not1 an affinity for each other4 ,this general conception of affinity was applied by ,berzelius to the atoms of elements4 ,affinity1 said ,berzelius1 acts between unlike atoms1 and causes them to unite to form a compound atom1 unlike either of the original atoms2 cohesion1 on the other hand1 acts between like atoms1 causing them to hold together without producing any change in their properties4 ,affinity varies in different elements4 ,thus the affinity of gold for oxygen is very small2 hence it is that gold is found in the earth in the metallic state1 while iron1 having a great affinity for oxygen1 soon rusts when exposed to air1 or when buried in the earth4 ,potassium and sodium have great affinities for oxygen1 chlorine1 etc42 yet the atoms of potassium and sodium do not themselves combine4 ,the more any elements are alike chemically the smaller is their affinity for each other2 the more any elements are chemically unlike the greater is their mutual affinity2 but this affinity is modified by circumstances4 ,thus1 said ,berzelius1 if equal numbers of atoms of ,a and ,b1 having equal or nearly equal affinity for ,c1 mutually react1 compound atoms1 ,,ac and ,,bc1 will be produced1 but atoms of ,a and ,b will remain4 ,the amounts of ,,ac and ,,bc produced will be influenced by the greater or less affinity of ,a and ,b for ,c2 but if there be a greater number of ,a than of ,b atoms1 a greater amount of ,,ac than of ,,bc will be produced4 ,in these cases all the reacting substances and the products of the actions are supposed to be liquids2 but ,,bc1 if a solid substance1 will be produced even if the affinity of ,a for ,c is greater than that of ,b for ,c4 ,in some elements1 ,berzelius taught1 affinity slumbers1 and can be awakened only by raising the temperature4 ,thus carbon in the form of coal has no affinity for oxygen at ordinary temperatures2 it has remained for ages in the earth without undergoing oxidation2 but when coal is heated the affinities of carbon are awakened1 combination with oxygen occurs1 and heat is produced4 ,but why is it that certain elementary atoms exhibit affinity for certain others8 ,it depends1 said ,berzelius1 on the electrical states of these atoms4 ,according to the ,berzelian theory1 every elementary atom has attached to it a certain quantity of electricity1 part of which is positive and part negative4 ,this electricity is accumulated at two points on each atom1 called respectively the positive pole and the negative pole2 but in each atom one of these electricities so much preponderates over the other as to give the whole atom the character of either a positively or a negatively electrified body4 ,when two atoms combine chemically the positive electricity in one neutralizes the negative electricity in the other4 ,as we know that similar electricities repel1 and opposite electricities attract each other1 it follows that a markedly positive atom will exhibit strong affinity for a markedly negative atom1 less strong affinity for a feebly negative1 and little or no affinity for a positively electrified atom2 but two similarly electrified atoms may exhibit affinity1 because in every positive atom there is some negative electricity1 as in every negative atom there is some positive electricity4 ,thus1 in the atoms of copper and zinc positive electricity predominates1 said ,berzelius1 but the zinc atoms are more positive than those of copper2 hence1 when the metals are brought into contact the negative electricity of the copper atoms is attracted and neutralized by the positive electricity of the zinc atoms1 combination takes place1 and the compound atom is still characterized by a predominance of positive electricity4 ,hence ,berzelius identified electrical polarity with chemical affinity4 ,every atom was regarded by him as both positively and negatively electrified2 but as one of these electricities was always much stronger than the other1 every atom regarded as a whole appeared to be either positively or negatively electrified4 ,positive atoms showed affinity for negative atoms1 and vice versa4 ,as a positive atom might become more positive by increasing the temperature of the atom1 so might the affinity of this atom for that be more marked at high than at low temperatures4 ,now1 if two elementary atoms unite1 the compound atom must--according to the ,berzelian views--be characterized either by positive or negative electricity4 ,this compound atom1 if positive1 will exhibit affinity for other compound atoms in which negative electricity predominates2 if negative1 it will exhibit affinity for other positively electrified compound atoms4 ,if two compound atoms unite chemically1 the complex atom so produced will1 again1 be characterized by one or other of the two electricities1 and as it is positive or negative1 so will it exhibit affinity for positively or negatively electrified complex atoms4 ,thus ,berzelius and his followers regarded every compound atom1 however complex1 as essentially built up of two parts1 one of which was positively and the other negatively electrified1 and which were held together chemically by virtue of the mutual attractions of these electricities2 they regarded every compound atom as a dual structure4 ,the classification adopted by ,berzelius was essentially a dualistic classification4 ,his system has always been known in chemistry as dualism4 ,berzelius divided compound atoms 7we should now say molecules7 into three groups or orders-- ,compound atoms of the first order1 formed by the immediate combination of atoms of two1 or in organic compounds of three1 elementary substances4 ,compound atoms of the second order1 formed by the combination of atoms of an element with atoms of the first order1 or by the combination of two or more atoms of the first order4 ,compound atoms of the third order1 formed by combination of two or more atoms of the second order4 ,when an atom of the third order was decomposed by an electric current1 it split up1 according to the ,berzelian teaching1 into atoms of the second order--some positively1 others negatively electrified4 ,when an atom of the second order was submitted to electrolysis1 it decomposed into atoms of the first order--some positively1 others negatively electrified4 ,berzelius said that a base is an electro-positive oxide1 and an acid is an electro-negative oxide4 ,the more markedly positive an oxide is1 the more basic it is2 the more negative it is1 the more is it characterized by acid properties4 ,one outcome of this teaching regarding acids and bases was to overthrow the ,lavoisierian conception of oxygen as the acidifying element4 ,some oxides are positive1 others negative1 said ,berzelius2 but acids are characterized by negative electricity1 therefore the presence of oxygen in a compound does not always confer on that compound acid properties4 ,we have already seen that silica was regarded by most chemists as a typical earth2 but ,berzelius found that in the electrolysis of compounds of silica1 this substance appeared at the positive pole of the battery--that is1 the atom of silica belonged to the negatively electrified order of atoms4 ,silica was almost certainly an oxide2 but electro-negative oxides are1 as a class1 acids2 therefore silica was probably an acid4 ,the supposition of the acid character of silica was amply confirmed by the mineralogical analyses and experiments of ,berzelius4 ,he showed that most of the earthy minerals are compounds of silica with electro-positive metallic oxides1 and that silica plays the part of an acid in these minerals2 and in #ahbc he obtained the element silicon1 the oxide of which is silica4 ,on this basis ,berzelius reared a system of classification in mineralogy which much aided the advance of that branch of natural science4 ,by the work of ,berzelius and ,davy the ,lavoisierian conception of acid has now been much modified and extended2 it has been rendered less rigid1 and is therefore more likely than before to be a guide to fresh discoveries4 ,the older view of acid and alkali was based1 for the most part1 on a qualitative study of the reactions of chemical substances3 bodies were placed in the same class because they were all sour1 or all turned vegetable blues to red1 etc4 ,this was followed by a closer study of the composition of substances1 and by attempts to connect the properties of these substances with their composition2 but when this attempt resulted in the promulgation of the dictum that oxygen is the acidifying principle1 it began to be perceived that a larger basis of fact must be laid before just conclusions could be drawn as to the connections between properties and composition of substances4 ,this larger basis was laid by the two chemists whose work we have now reviewed4 ,of the life of one of these men ,i have already given such a sketch as ,i can from the materials available to me2 of the life of the other we happily possess ample knowledge4 ,let us now consider the main features of this life4 99 99 99 99 99 ,,humphry ,,davy1 the eldest son of ,robert and ,grace ,davy1 was born at ,penzance1 in ,cornwall1 on ,december #ag1 #aggh1 eight months that is before the birth of ,berzelius4 ,his parents resided on a small property which had belonged to their ancestors for several generations4 ,surrounded by many kind friends by whom he was much thought of1 the boy appears to have passed a very happy childhood4 ,even at the age of five his quickness and penetration were marked by those around him1 and at school these continued to be his predominant characteristics4 ,nurtured from his infancy in the midst of beautiful and romantic scenery1 and endowed with great observing power and a lively imagination1 young ,davy seemed destined to be one of those from whose lips is poured the deathless singing2 all through life he was characterized by a strongly marked poetic temperament4 ,humphry ,davy was held in much esteem by his school friends as a composer of valentines and love letters1 as a daring and entertaining teller of stories1 and as a successful fireworks manufacturer4 ,such a combination of qualities would much endear him to his boy-companions4 ,we are told that at the age of eight he used to mount on an empty cart1 around which a circle of boys would collect to be entertained by the wonderful tales of the youthful narrator4 ,finishing his school education at the age of fifteen1 he now began his own education of himself4 ,in #agie he was apprenticed to a surgeon and apothecary 7afterwards a physician71 in ,penzance1 with whom he learned the elements of medical science2 but his time during the years which he spent under ,mr4 ,borlase was much occupied in shooting1 fishing1 searching for minerals and geological specimens1 composing poetry1 and pursuing metaphysical speculations4 ,he was now1 as through life1 an enthusiastic lover of ,nature2 his mind was extremely active1 ranging over the most diverse subjects2 he was full of imagination1 and seemed certain to distinguish himself in any pursuit to which he should turn his attention4 ,during the next three or four years ,davy indulged freely in speculations in all manner of subjects2 he started1 as people generally do when young1 from general principles and followed these out to many conclusions4 ,even in his study of physiology and other branches of science1 he appears at this time to have adopted the speculative rather than the experimental method2 but unlike most youthful metaphysicians he was ready to give up an opinion whenever it appeared to him incorrect4 ,by the time he reached the age of twenty he had discarded this method of seeking for truth1 and was ever afterwards distinguished by his careful working out of facts as the foundation for all his brilliant theories4 ,davy appears to have begun the study of chemistry about #agih by reading ,lavoisier's ,elements of ,chemistry1 the teachings of which he freely criticized4 ,about this time ,mr4 ,gregory ,watt came to live at ,penzance as a lodger with ,davy's mother1 and with him the young philosopher had much talk on chemical and other scientific subjects4 ,he also became acquainted with ,mr4 ,davies ,gilbert--who was destined to succeed ,davy as ,president of the ,royal ,society--and from him he borrowed books and received assistance of various kinds in his studies4 ,it was during these years that ,davy made experiments on heat1 which were published some years later1 and which are now regarded as laying the foundations of the modern theory according to which heat is due to the motions of the small parts of bodies4 ,he arranged two brass plates so that one should carry a block of ice which might be caused to revolve in contact with the other plate2 the plates were covered by a glass jar1 from which he exhausted the air by means of a simple syringe of his own contrivance2 the machine being placed on blocks of ice the plates were caused to revolve4 ,the ice inside the jar soon melted2 ,davy concluded that the heat required to melt this ice could only be produced by the friction of the ice and brass1 and that therefore heat could not be any form of ponderable matter4 ,in the year #agih ,davy was asked to go to ,bristol as superintendent of the laboratory of a new ,pneumatic ,institution started by ,dr4 ,beddoes for the application of gases to the treatment of diseases4 ,davy had corresponded with ,beddoes before this time regarding his experiments on heat1 and the latter seems to have been struck with his great abilities and to have been anxious to secure him as experimenter for his institution4 ,davy was released from his engagements with ,mr4 ,borlase1 and1 now about twenty years of age1 set out for his new home1 having made as he says all the experiments he could at ,penzance1 and eagerly looking forward to the better appliances and incitements to research which he hoped to find at ,bristol4 ,the ,pneumatic ,institution was supported by subscriptions1 for the most part from scientific men4 ,it was started on a scientific basis4 ,researches were to be made on gases of various kinds with the view of applying these as remedies in the alleviation of disease4 ,an hospital for patients1 a laboratory for experimental research1 and a lecture theatre were provided4 ,at this time many men of literary and intellectual eminence resided in ,bristol2 among these were ,coleridge and ,southey4 ,most of these men were visitors at the house of ,dr4 ,beddoes1 and many distinguished men came from various parts of the county to visit the institution4 ,davy thus entered on a sphere of labour eminently suited for the development of his genius4 ,with ample mechanical appliances for research1 with plenty of time at his disposal1 surrounded by an atmosphere of inquiry and by men who would welcome any additions he could make to the knowledge of ,nature1 and being at the same time not without poetic and imaginative surroundings1 by which he was ever spurred onwards in the pursuit of truth--placed in these circumstances1 such an enthusiastic and diligent student of science as ,davy could not but obtain results of value to his fellows4 ,the state of chemical science at this time was evidently such as to incite the youthful worker4 ,the chains with which ,stahl and his successors had so long bound the limbs of the young science had been broken by ,lavoisier2 and although the ,french school of chemistry was at this time dominant1 and not disinclined to treat as ignorant any persons who might differ from its teaching1 yet there was plenty of life in the cultivators of chemistry4 ,the controversy between ,berthollet and ,proust was about to begin2 the ,lavoisierian views regarding acids and salts were not altogether accepted by ,gay-,lussac1 ,thenard and others2 and from the laboratory of ,berzelius there was soon to issue the first of those numerous researches which drew the attention of every chemist to the capital of ,sweden4 ,the voltaic battery had been discovered1 and had opened up a region of possibilities in chemistry4 ,davy began his researches at the institution by experiments with nitrous oxide1 a gas supposed by some people at that time to be capable of producing most harmful effects on the animal system4 ,he had to make many experiments before he found a method for preparing the pure gas1 and in the course of these experiments he added much to the stock of chemical knowledge regarding the compounds of nitrogen and oxygen4 ,having obtained fairly pure nitrous oxide1 he breathed it from a silk bag2 he experienced a sensation analogous to gentle pressure on all the muscles2444 the objects around me became dazzling and my hearing more acute2444 at last an irresistible propensity to action was indulged in4444 ,i recollect but indistinctly what followed2 ,i know that my motions were various and violent4 ,southey and ,coleridge breathed the gas2 the poets only laughed a little4 ,encouraged by the results of these experiments1 ,davy proceeded to prepare and breathe nitric oxide--whereby he was rendered very ill--and then carburetted hydrogen--which nearly killed him4 ,in his chemical note-book about this time1 ,davy says1 ,the perfection of chemical philosophy1 or the laws of corpuscular motion1 must depend on the knowledge of all the simple substances1 their mutual attractions1 and the ratio in which the attractions increase or diminish with increase or diminution of temperature4444 ,the first step towards these laws will be the decomposition of those bodies which are at present undecompounded4 ,and in the same note-book he suggests methods which he thinks might effect the decomposition of muriatic and boric acids1 the alkalis and earths4 ,here are the germs of his future work4 ,after about eight months' work at ,bristol he published a volume of ,researches1 which contained a great many new facts1 and was characterized by vigour and novelty of conception4 ,these researches had been carried out with intense application2 each was struck off at a red heat4 ,his mind during this time was filled with vast scientific conceptions1 and he began also to think of fame4 ,an active mind1 a deep ideal feeling of good1 and a look towards future greatness1 he tells us1 sustained him4 ,count ,rumford1 the founder of the ,royal ,institution in ,london1 was anxious to obtain a lecturer on chemistry for the ,institution4 ,davy was strongly recommended1 and after a little arrangement--concerning which ,davy says in a letter1 ,i will accept of no appointment except on the sacred terms of independence--he was appointed ,assistant ,lecturer on ,chemistry and ,director of the ,laboratory4 ,about a year later his official designation was changed to ,professor of ,chemistry4 ,this appointment opened up a great sphere of research2 the sole and uncontrolled use of the apparatus of the institution for private experiments was to be granted him1 and he was promised any apparatus he might need for new experiments4 ,he had now the command of a good laboratory2 he had not to undergo the drudgery of systematic teaching1 but was only required to give lectures to a general audience4 ,before leaving ,bristol he had commenced experiments on the chemical applications of the voltaic battery2 these he at once followed up with the better apparatus now at his command4 ,the results of this research1 and his subsequent work on the alkalis and on muriatic acid and chlorine1 have been already described4 ,the circumstances of ,davy's life had hitherto been most favourable2 how nobly he had availed himself of these circumstances was testified by the work done by him4 ,his first lecture was delivered in the spring of #ahja1 and at once he became famous4 ,a friend of ,davy says1 ,the sensation created by his first course of lectures at the ,institution1 and the enthusiastic admiration which they obtained1 is scarcely to be imagined4 ,men of the first rank and talent1 the literary and the scientific1 the practical and the theoretical1 blue-stockings and women of fashion1 the old and the young--all crowded1 eagerly crowded the lecture-room4 ,his youth1 his simplicity1 his natural eloquence1 his chemical knowledge1 his happy illustrations and well-conducted experiments1 excited universal attention and unbounded applause4 ,compliments1 invitations and presents were showered upon him in abundance from all quarters2 his society was courted by all1 and all appeared proud of his acquaintance4 ,one of his biographers says of these lectures1 ,he was always in earnest1 and when he amused most1 amusement appeared most foreign to his object4 ,his great and first object was to instruct1 and in conjunction with this1 maintain the importance and dignity of science2 indeed1 the latter1 and the kindling a taste for scientific pursuits1 might rather be considered his main object1 and the conveying instruction a secondary one4 ,the greatest pains were taken by ,davy in the composition and rehearsal of his lectures1 and in the arrangement of experiments1 that everything should tend towards the enlightenment of his audience4 ,surrounded by a brilliant society1 invited to every fashionable entertainment1 flattered by admirers1 tempted by hopes of making money1 ,davy remained a faithful and enthusiastic student of ,nature4 ,i am a lover of ,nature1 he writes at this time to a friend1 with an ungratified imagination4 ,i shall continue to search for untasted charms1 for hidden beauties4 ,my real1 my waking existence1 is amongst the objects of scientific research4 ,common amusements and enjoyments are necessary to me only as dreams to interrupt the flow of thoughts too nearly analogous to enlighten and vivify4 ,during these years 7i4e4 from #ahjb to #ahab7 he worked for the greater part of each day in the laboratory4 ,every week1 almost every day1 saw some fresh discovery of importance4 ,he advanced from discovery to discovery4 ,his work was characterized by that vast industry and extreme rapidity which belong only to the efforts of genius4 ,never1 before or since1 has chemical science made such strides in this country4 ,in #ahjc ,davy was elected a ,fellow1 and in #ahjg one of the secretaries of the ,royal ,society4 ,in #ahab he retired from the professorship of chemistry at the ,royal ,institution2 in the same year he was made a knight4 ,the next two or three years were mostly spent in travelling abroad with his wife--he had married a widow lady1 ,mrs4 ,apreece1 in #ahab4 ,during his visit to ,paris he made several experiments on the then recently discovered iodine1 and proved this substance to be an element4 ,the work which ,davy had accomplished in the seventeen years that had now elapsed since he began the study of chemistry1 whether we consider it simply as a contribution to chemical science1 or in the light of the influence it exerted on the researches of others1 was of first-rate importance2 but a fresh field now began to open before him1 from which he was destined to reap the richest fruits4 ,in the autumn of #ahae his attention was drawn to the subject of fire-damp in coal-mines4 ,as he passed through ,newcastle1 on his return from a holiday spent in the ,scottish ,highlands1 he examined various coal-mines and collected samples of fire-damp2 in ,december of the same year his safety-lamp was perfected1 and soon after this it was in the hands of the miner4 ,the steps in the discovery of this valuable instrument were briefly these4 ,davy established the fact that fire-damp is a compound of carbon and hydrogen2 he found that this gas must be mixed with a large quantity of ordinary air before the mixture becomes explosive1 that the temperature at which this explosion occurs is a high one1 and that but little heat is produced during the explosion2 he found that the explosive mixture could not be fired in narrow metallic tubes1 and also that it was rendered non-explosive by addition of carbonic acid or nitrogen4 ,he reasoned on these facts thus3 ,it occurred to me1 as a considerable heat was required for the inflammation of the fire-damp1 and as it produced in burning a comparatively small degree of heat1 that the effect of carbonic acid and azote1 and of the surfaces of small tubes1 in preventing its explosion1 depended on their cooling powers--upon their lowering the temperature of the exploding mixture so much that it was no longer sufficient for its continuous inflammation4 ,he at once set about constructing a lamp in which it should be impossible for the temperature of ignition of a mixture of fire-damp and air to be attained1 and which therefore1 while burning1 might be filled with this mixture without any danger of an explosion4 ,he surrounded the flame of an oil-lamp with a cylinder of fine wire-gauze2 this lamp when brought into an atmosphere containing fire-damp and air could not cause an explosion1 because although small explosions might occur in the interior of the wire cylinder1 so much heat was conducted away by the large metallic surface that the temperature of the explosive atmosphere outside the lamp could not attain that point at which explosion would occur4 ,in #ahah ,sir ,humphry ,davy was made a baronet1 in recognition of his great services as the inventor of the safety-lamp2 and in #ahbj he was elected to the most honourable position which can be held by a man of science in this country1 he became the ,president of the ,royal ,society4 ,for seven years he was annually re-elected president1 and during that time he was the central figure in the scientific society of ,england4 ,during these years he continued his investigations chiefly on electro-chemical subjects and on various branches of applied science4 ,in #ahbf his health began to fail4 ,an attack of paralysis in that year obliged him to relinquish most of his work4 ,he went abroad and travelled in ,italy and the ,tyrol1 sometimes strong enough to shoot or fish a little1 or even to carry on electrical experiments2 sometimes confined to his room1 or to gentle exercise only4 ,he resigned the presidentship of the ,royal ,society in #ahbg4 ,in #ahbh he visited ,rome1 where he was again attacked by paralysis1 and thought himself dying1 but he recovered sufficiently to attempt the journey homeward4 ,at ,geneva he became very ill1 and expired in that city on the #bith of ,may #ahbi4 ,during these later years of illness and suffering1 his intense love of and delight in ,nature were very apparent2 he returned again to the simple tastes and pleasures of his early days4 ,his intimate knowledge of natural appearances and of the sights and sounds of country life is conspicuous in the ,salmonia1 or ,days of ,fly-fishing1 written during his later years4 ,sir ,humphry ,davy was emphatically a genius4 ,he was full of eager desire to know the secrets of the world in which he lived2 he looked around him with wonder and delight1 ever conscious of the vastness of the appearances which met his gaze2 an exuberance of life and energy marked his actions2 difficulties were encountered by him only to be overcome2 he was depressed by no misfortunes1 deterred by no obstacles1 led aside from his object by no temptations1 and held in bondage by no false analogies4 ,his work must ever remain as a model to the student of science4 ,a thorough and careful foundation of fact is laid2 on this1 hypotheses are raised1 to be tested first by reasoning and argument1 then by the tests of the laboratory1 which alone are final4 ,analogies are seized2 hints are eagerly taken up1 examined1 and acted on or dismissed4 ,as he works in the laboratory1 we see his mind ranging over the whole field of chemical knowledge1 finding a solution of a difficulty here1 or guessing at a solution there2 combining apparently most diverse facts2 examining phenomena which appear to have no connection2 never dwelling too long on an hypothesis which cannot yield some clue to the object of research1 but quickly discovering the road which will lead to the wished-for solution4 ,like so many great experimenters ,davy accomplished wonders with little apparatus4 ,when he went abroad for the first time he took with him two small boxes1 one twenty1 and the other twelve inches long1 by about seven inches wide and four deep4 ,with the apparatus contained in these boxes he established the elementary nature of iodine1 and made a rough estimation of its atomic weight2 he determined many of its analogies with chlorine1 proving that1 like chlorine1 it is markedly electro-negative1 and that its compounds are decomposed by chlorine2 he accomplished the synthesis of hydriodic acid1 and approximately determined the composition of iodide of nitrogen4 ,but when it was necessary to employ delicate or powerful apparatus1 he was able by the use of that also to obtain results of primary importance4 ,the decomposition of potash1 soda1 baryta1 lime and strontia could not have been effected had he not had at his command the resources of a well-furnished laboratory4 ,davy has had no successor in ,england4 ,much useful and some brilliant work has been done by ,english chemists since his day1 but we still look back to the first quarter of the century as the golden age of chemistry in this country4 ,on the roll wherein are written the names of ,england's greatest sons1 there is inscribed but a single chemist--,humphry ,davy4 99 99 99 99 99 ,i carried on the account of the work of ,davy's great contemporary1 ,berzelius1 to the time when he had fairly established dualistic views of the structure of chemical compounds1 and when1 by the application of a few simple rules regarding the combinations of elementary atoms1 he had largely extended the bounds of the atomic theory of ,dalton4 ,berzelius also did important work in the domain of organic chemistry4 ,by numerous analyses of compounds of animal and vegetable origin1 he clearly established the fact that the same laws of combination1 the same fixity of composition1 and the same general features of atomic structure prevail among the so-called organic as among the inorganic compounds4 ,in doing this he broke down the artificial barrier which had been raised between the two branches of the science1 and so prepared the way for modern chemistry1 which has won its chief triumphs in the examination of organic compounds4 ,by the many and great improvements which he introduced into analytical chemistry1 and by the publication of his ,textbook of ,chemistry1 which went through several editions in ,french and ,german1 and also of his yearly report on the advance of chemistry1 ,berzelius exerted a great influence on the progress of his favourite science4 ,woehler tells us that when the spring of the year came1 at which time his annual report had to be prepared1 ,berzelius shut himself up in his study1 surrounded himself with books1 and did not stir from the writing-table until the work was done4 ,in his later days ,berzelius was much engaged in controversy with the leaders of the new school1 the rise and progress of which will be traced in the next chapter1 but throughout this controversy he found time to add many fresh facts to those already known4 ,he continued his researches until his death in #ahdh4 ,the work of the great ,swedish chemist is characterized by thoroughness in all its parts3 to him every fact appeared to be of importance2 although now perhaps only an isolated fact1 he saw that some day it would find a place in a general scheme of classification4 ,he worked in great measure on the lines laid down by ,dalton and ,davy2 the enormous number and accuracy of his analyses established the law of multiple proportions on a sure basis1 and his attempts to determine the constitution of compound atoms1 while advancing the atomic theory of ,dalton1 drew attention to the all-important distinction between atom and molecule1 and so prepared chemists for the acceptance of the generalization of ,avogadro4 ,the electro-chemical conceptions of ,davy were modified by ,berzelius2 they were shorn of something of their elasticity1 but were rendered more suited to be the basis of a rigid theory4 99 99 99 99 99 ,at the close of this transition period from the ,lavoisierian to the modern chemistry1 we find analytical chemistry established as an art2 we find the atomic theory generally accepted1 but we notice the existence of much confusion which has arisen from the non-acceptance of the distinction made by ,avogadro between atom and molecule2 we find the analogies between chemical affinity and electrical energy made the basis of a system of classification which regards every compound atom 7or molecule7 as built up of two parts1 in one of which positive1 and in the other negative electricity predominates2 and accompanying this system of classification we find that an acid is no longer regarded as necessarily an oxygen compound1 but rather as a compound possessed of certain properties which are probably due to the arrangement of the elementary atoms1 among which hydrogen appears generally to find a place2 we find that salts are for the most part regarded as metallic derivatives of acids2 and we find that by the decomposition of the supposed elementary substances1 potash1 soda1 lime1 etc41 the number of the elements has been extended1 the application of a new instrument of research has been brilliantly rewarded1 and the ,lavoisierian description of element as the attained1 not the attainable1 limit of research has been emphasized4 ,,footnotes3 #i ,the history and meaning of these terms is considered on p4 #aga1 et seq4 #aj ,for an explanation of this expression1 chemical affinity1 see p4 #bjf1 et seq4 #aa ,these views have been already explained on pp4 #ahb1 #ahc4 ,,chapter ,v4 ,,the ,,work ,,of ,,graham4 ,thomas ,graham1 #ahje-ahfi4 ,the work of ,graham1 concerned as it mostly was with the development of the conception of atoms1 connects the time of ,dalton with that in which we are now living4 ,i have therefore judged it advisable to devote a short chapter to a consideration of the life-work of this chemist1 before proceeding to the third period of chemical advance1 that1 namely1 which witnessed the development of organic chemistry through the labours of men who were ,graham's contemporaries4 ,the printed materials which exist for framing the story of ,graham's life are very meagre1 but as he appears1 from the accounts of his friends1 to have devoted himself entirely to scientific researches1 we cannot go far wrong in regarding the history of his various discoveries as also the history of his life4 99 99 99 99 99 ,,thomas ,,graham was born in ,glasgow1 on ,december #ba1 #ahje4 ,his father1 ,james ,graham1 a successful manufacturer1 was in a position to give his son a good education4 ,after some years spent in the ordinary school training1 ,graham entered ,glasgow ,university at the early age of fourteen1 and graduated as ,m4 ,a4 five years later4 ,it was the intention of ,graham's father that his son should enter the ,scottish ,church2 but under the teaching of ,dr4 ,thomas ,thomson and others the lad imbibed so strong a love of natural science1 that rather than relinquish the pursuit of his favourite study1 he determined to be independent of his father and make a living for himself4 ,his father was much annoyed at the determination of his son to pursue science1 and vainly attempted to force him into the clerical profession4 ,the quarrel between father and son increased in bitterness1 and notwithstanding the intervention of friends the father refused to make his son any allowance for his maintenance2 and although many years after a reconcilement was effected1 yet at the time when ,graham most needed his father's help he was left to struggle alone4 ,graham went to ,edinburgh1 where he pursued his studies under ,hope and ,leslie1 professors of chemistry and physics respectively--men whose names were famous wherever natural science was studied4 ,graham's mother1 for whom he had always the greatest respect and warmest love1 and his sister ,margaret helped him as best they could during this trying time4 ,the young student found some literary occupation and a little teaching in ,edinburgh1 and sometimes he was asked to make investigations in subjects connected with applied chemistry4 ,thus he struggled on for four or five years1 during which time he began to publish papers on chemico-physical subjects4 ,in the year #ahbi he was appointed ,lecturer on ,chemistry at the ,mechanics' ,institution in ,glasgow1 and next year he was removed to the more important position of lecturer on the same science at the ,andersonian ,institution in that city4 ,this position he occupied for seven years1 when he was elected ,professor of ,chemistry in the ,university of ,london 7now ,university ,college73 he had been elected to the ,fellowship of the ,royal ,society in the preceding year4 ,during his stay at the ,andersonian ,institution ,graham had established his fame as a physical chemist2 he had begun his work on acids and salts1 and had established the fundamental facts concerning gaseous diffusion4 ,these researches he continued in ,london1 and from #ahcg to #ahed he enriched chemical science with a series of papers concerned for the most part with attempts to trace the movements of the atoms of matter4 ,in #ahed ,graham succeeded ,sir ,john ,herschel in the important and honourable position of ,master of the ,mint4 ,for some years after his appointment he was much engaged with the duties of his office1 but about #ahfj he again returned to his atomic studies1 and in his papers on ,transpiration of ,liquids and on ,dialysis he did much in the application of physical methods to solve chemical problems1 and opened up new paths1 by travelling on which his successors greatly advanced the limits of the science of chemistry4 ,graham was almost always at work2 his holidays were few and far between4 ,by the year #ahfh or so his general health began to grow feeble2 in the autumn of #ahfi1 during a visit to ,malvern where he sought repose and invigorating air1 he caught cold1 which developed into inflammation of the lungs4 ,on his return to ,london the disease was overcome by medical remedies1 but he continued very weak1 and gradually sank1 till the end came on the #afth of ,september #ahfi4 ,i have said that the seven years during which ,graham held the lectureship on chemistry in the ,andersonian ,institution1 ,glasgow1 witnessed the beginning alike of his work on salts and of that on gaseous diffusion4 ,he showed that there exists a series of compounds of various salts1 e4g4 chloride of calcium1 chloride of zinc1 etc41 with alcohol4 ,he compared the alcohol in these salts1 which he called alcoates1 to the water in ordinary crystallized salts1 and thus drew the attention of chemists to the important part played by water in determining the properties of many substances4 ,three years later 7#ahcc7 appeared one of his most important papers1 bearing on the general conception of acids3 ,researches on the ,arseniates1 ,phosphates1 and ,modifications of ,phosphoric ,acid4 ,chemists at this time knew that phosphoric acid--that is1 the substance obtained by adding water to pentoxide of phosphorus--exhibited many peculiarities1 but they were for the most part content to leave these unexplained4 ,graham1 following up the analogy which he had already established between water and bases1 prepared and carefully determined the composition of a series of phosphates1 and concluded that pentoxide of phosphorus is able to combine with a base--say soda--in three different proportions1 and thus to produce three different phosphates of soda4 ,but as ,graham accepted that view which regards a salt as a metallic derivative of an acid1 he supposed that three different phosphoric acids ought to exist2 these acids he found in the substances produced by the action of water on the oxide of phosphorus4 ,he showed that just as the oxide combines with a base in three proportions1 so does it combine with water in three proportions4 ,this water he regarded as chemically analogous to the base in the three salts1 one atom 7we should now rather say molecule7 of base could be replaced by one atom of water1 two atoms of base by two atoms of water1 or three atoms of base by three atoms of water4 ,phosphoric acid was therefore regarded by ,graham as a compound of pentoxide of phosphorus and water1 the latter being as essentially a part of the acid as the former4 ,he distinguished between monobasic1 dibasic1 and tribasic phosphoric acids3 by the action of a base on the monobasic acid1 one1 and only one salt was produced2 the dibasic acid could furnish two salts1 containing different proportions 7or a different number of atoms7 of the same base3 and from the tribasic acid three salts1 containing the same base but in different proportions1 could be obtained4 ,davy's view of an acid as a compound of water with a negative oxide was thus confirmed1 and there was added to chemical science the conception of acids of different basicity4 ,in #ahcf ,graham's paper on ,water as a ,constituent of ,salts was published in the ,transactions of the ,royal ,society of ,edinburgh4 ,in this paper he inquires whether the water in crystalline salts can or cannot be removed without destroying the chemical individuality of the salts4 ,he finds that in some crystalline salts part of the water can be easily removed by the application of heat1 but the remainder only at very high temperatures4 ,he distinguishes between those atoms of water which essentially belong to the compound atom of the salt1 and those atoms which can be readily removed therefrom1 which are as it were added on to1 or built up around the exterior of the atom of salt4 ,in this paper ,graham began to distinguish what is now called water of crystallization from water of constitution1 a distinction pointed to by some of ,davy's researches1 but a distinction which has remained too much a mere matter of nomenclature since the days of ,graham4 ,in these researches ,graham emphasized the necessity of the presence of hydrogen in all true acids2 as he had drawn an analogy between water and bases1 so now he saw in the hydrogen of acids the analogue of the metal of salts4 ,he regarded the structure of the compound atom of an acid as similar to that of the compound atom of a salt2 the hydrogen atom1 or atoms1 in the acid was replaced by a metallic atom1 or atoms1 and so a compound atom of the salt was produced4 ,davy and ,berzelius had proved that hydrogen is markedly electro-positive2 hydrogen appeared to ,graham to belong to the class of metals4 ,in making this bold hypothesis ,graham necessarily paid little heed to those properties of metals which appeal to the senses of the observer4 ,metals1 as a class1 are lustrous1 heavy1 malleable substances2 hydrogen is a colourless1 inodourless1 invisible1 very light gas3 how then can hydrogen be said to be metallic8 ,i have again and again insisted on the need of imagination for the successful study of natural science4 ,although in science we deal with phenomena which we wish to measure and weigh and record in definite and precise language1 yet he only is the successful student of science who can penetrate beneath the surface of things1 who can form mental pictures different from those which appear before his bodily eye1 and so can discern the intricate and apparently irregular analogies which explain the phenomena he is set to study4 ,graham was not as far as we can learn endowed1 like ,davy1 with the sensitive nature of a poet1 yet his work on hydrogen proves him to have possessed a large share of the gift of imagination4 ,picturing to himself the hydrogen atom as essentially similar in its chemical functions to the atom of a metal1 he tracked this light invisible gas through many tortuous courses3 he showed how it is absorbed and retained 7occluded as he said7 by many metals2 he found it in meteors which had come from far-away regions of space2 and at last1 the year before he died he prepared an alloy of palladium and the metal hydrogen1 from which a few medals were struck1 bearing the legend ,palladium-,hydrogenium #ahfi4 ,within the last few years hydrogen has been liquified and1 it is said1 solidified4 ,solid hydrogen is described as a steel-grey substance which fell upon the table with a sound like the ring of a metal4 ,but ,graham's most important work was concerned with the motion of the ultimate particles of bodies4 ,he uses the word atom pretty much as ,dalton did4 ,he does not make a distinction between the atom of an element and the atom of a compound1 but apparently uses the term as a convenient one to express the smallest undivided particle of any chemical substance which exhibits the properties of that substance4 ,as ,graham was chiefly concerned with the physical properties of chemical substances1 or with those properties which are studied alike by chemistry and physics1 the distinction between atom and molecule1 so all-important in pure chemistry1 might be1 and to a great extent was1 overlooked by him4 ,in considering his work we shall however do well to use the terms atom and molecule in the sense in which they are now always used in chemistry1 a sense which has been already discussed 7see pp4 #aci-adc74 ,many years before ,graham began his work a curious fact had been recorded but not explained4 ,in #ahbc ,doebereiner filled a glass jar with hydrogen and allowed the jar to stand over water3 on returning after twelve hours he found that the water had risen about an inch and a half into the jar4 ,close examination of the jar showed the presence of a small crack in the glass4 ,many jars1 tubes and flasks1 all with small cracks in the glass1 were filled with hydrogen and allowed to stand over water2 in every case the water rose in the vessel4 ,no rise of the water was however noticeable if the vessels were filled with ordinary air1 nitrogen or oxygen4 ,in #ahca ,graham began the investigation of the peculiar phenomenon observed by ,doebereiner4 ,repeating ,doebereiner's experiments1 ,graham found that a portion of the hydrogen in the cracked vessels passed outwards through the small fissures1 and a little air passed inwards3 the water therefore rose in the jar1 tube or flask1 because there was a greater pressure on the surface of the water outside than upon that inside the vessel4 ,any gas lighter than air behaved like hydrogen2 when gases heavier than air were employed the level of the water inside the vessel was slightly lowered after some hours4 ,graham found that the passage of gases through minute openings could be much more accurately studied by placing the gas to be examined in a glass tube one end of which was closed by a plug of dry plaster of ,paris1 than by using vessels with small fissures in the glass4 ,the diffusion-tube used by ,graham generally consisted of a piece of glass tubing1 graduated in fractions of a cubic inch and having a bulb blown near one end2 the short end was closed by a thin plug of dry plaster of ,paris 7gypsum71 the tube was filled with the gas to be examined1 and the open end was immediately immersed in water4 ,the water was allowed to rise until it had attained a constant level1 when it was found that the whole of the gas originally in the tube had passed outwards through the porous plug1 and air had passed inwards4 ,the volume of gas originally in the tube being known1 and the volume of air in the tube at the close of the experiment being measured1 it was only necessary to divide the former by the latter number in order to obtain the number of volumes of gas which had passed outwards for each one volume of air which had passed inwards2 in other words to obtain the rate of diffusion compared with air of the gas under examination4 ,graham's results were gathered together in the statement1 ,the diffusion-rates of any two gases are inversely as the square roots of their densities4 ,thus1 take oxygen and hydrogen3 oxygen is sixteen times heavier than hydrogen1 therefore hydrogen diffuses four times more rapidly than oxygen4 ,take hydrogen and air3 the specific gravity of hydrogen is #j4jfid1 air being #a2 the square root of #j4jfid is #j4bfce1 therefore hydrogen will diffuse more rapidly than air in the ratio of #j4bfce3a4 ,in the years #ahdf-ahdi ,graham resumed this inquiry2 he now distinguished between diffusion1 or the passage of gases through porous plates1 and transpiration1 or the passage of gases through capillary tubes4 ,he showed that if a sufficiently large capillary tube be employed the rate of transpiration of a gas becomes constant1 but that it is altogether different from the rate of diffusion of the same gas4 ,he established the fact that there is a connection of some kind between the transpiration-rates and the chemical composition of gases1 and in doing this he opened up a field of inquiry by cultivating which many important results have been gained within the last few years1 and which is surely destined to yield more valuable fruit in the future4 ,returning to the diffusion of gases1 ,graham1 after nearly thirty years' more or less constant labour1 begins to speculate a little on the causes of the phenomena he had so studiously and perseveringly been examining4 ,in his paper on ,the ,molecular ,mobility of ,gases1 read to the ,royal ,society in #ahfc1 after describing a new diffusion-tube wherein thin plates of artificial graphite were used in place of plaster of ,paris1 ,graham says1 ,the pores of artificial graphite appear to be really so minute that a gas in mass cannot penetrate the plate at all4 ,it seems that molecules only can pass2 and they may be supposed to pass wholly unimpeded by friction1 for the smallest pores that can be imagined to exist in the graphite must be tunnels in magnitude to the ultimate atom of a gaseous body4 ,he then shortly describes the molecular theory of matter1 and shows how this theory--a sketch of which so far as it concerns us in this book has been given on pp4 #abc-abe--;explains the results which he has obtained4 ,when a gas passed through a porous plate into a vacuum1 or when one gas passed in one direction and another in the opposite direction through the same plate1 ,graham saw the molecules of each gas rushing through the tunnels of graphite or stucco4 ,the average rate at which the molecules of a gas rushed along was the diffusion-rate of that gas4 ,the lighter the gas the more rapid was the motion of its molecules4 ,if a mixture of two gases1 one much lighter than the other1 were allowed to flow through a porous plate1 the lighter gas would pass so much more quickly than the heavier gas that a partial separation of the two might probably be effected4 ,graham accomplished such a separation of oxygen and hydrogen1 and of oxygen and nitrogen2 and he described a simple instrument whereby this process of atmolysis1 as he called it1 might be effected4 ,graham's tube atmolyser consisted of a long tobacco-pipe stem placed inside a rather shorter and considerably wider tube of glass2 the pipe stem was fixed by passing through two corks1 one at each end of the glass tube2 through one of these corks there also passed a short piece of glass tubing4 ,when the instrument was employed1 the piece of short glass tubing was connected with an air-pump1 and one end of the pipe stem with the gaseous mixture--say ordinary air4 ,the air-pump being set in motion1 the gaseous mixture was allowed to flow slowly through the pipe stem2 the lighter ingredient of the mixture passed outwards through the pipe stem into the wide glass tube more rapidly than the heavier ingredient1 and was swept away to the air-pump2 the heavier ingredient could be collected1 mixed with only a small quantity of the lighter1 at the other end of the pipe stem4 ,as ,graham most graphically expressed it1 ,the stream of gas diminishes as it proceeds1 like a river flowing over a pervious bed4 ,graham then contrived a very simple experiment whereby he was able to measure the rate of motion of the molecules of carbonic acid4 ,he introduced a little carbonic acid into the lower part of a tall cylindrical jar1 and at the close of certain fixed periods of time he determined the amount of carbonic acid which had diffused upwards through the air into the uppermost layer of the jar4 ,knowing the height of the jar1 he now knew the distance through which a small portion of carbonic acid passed in a stated time1 and regarding this small portion as consisting of a great many molecules1 all moving at about equal rates1 he had determined the average velocity of the molecules of carbonic acid4 ,a similar experiment was performed with hydrogen4 ,the general results were that the molecules of carbonic acid move about in still air with a velocity equal to seventy-three millimetres per minute1 and that under the same conditions the molecules of hydrogen move with a velocity equal to about one-third of a metre per minute4#ab ,the ,bakerian ,lecture for #ahdi1 read by ,graham before the ,royal ,society1 was entitled ,on the ,diffusion of ,liquids4 ,in this paper he describes a very large number of experiments made with a view to determine the rate at which a salt in aqueous solution diffuses1 or passes upwards into a layer of pure water above it1 the salt solution and the water not being separated by any intervening medium4 ,graham's method of procedure consisted in completely filling a small bottle with a salt solution of known strength1 placing this bottle in a larger graduated vessel1 and carefully filling the latter with water4 ,measured portions of the water in the larger vessel were withdrawn at stated intervals1 and the quantity of salt in each portion was determined4 ,graham found that under these conditions salts diffused with very varying velocities4 ,groups of salts showed equal rates of diffusion4 ,there appeared to be no definite connection between the molecular weights of the salts and their diffusion-rates2 but as ,graham constantly regarded diffusion1 whether of gases or liquids1 as essentially due to the movements of minute particles1 he thought that the particles which moved about as wholes during diffusion probably consisted of groups of what might be called chemical molecules--in other words1 ,graham recognized various orders of small particles4 ,as the atom was supposed to have a simpler structure than the molecule 7if indeed it had a structure at all71 so there probably existed groups of molecules which1 under certain conditions1 behaved as individual particles with definite properties4 ,as ,graham applied the diffusion of gases to the separation of two gases of unequal densities1 so he applied the diffusion of liquids to the separation of various salts in solution4 ,he showed also that some complex salts1 such as the alums1 were partially separated into their constituents during the process of diffusion4 ,the prosecution of these researches led to most important results1 which were gathered together in a paper on ,liquid ,diffusion applied to ,analysis1 read to the ,royal ,society in #ahfa4 ,graham divided substances into those which diffused easily and quickly into water1 and those which diffused very slowly2 he showed that the former were all crystallizable substances1 while the latter were non-crystallizable jelly-like bodies4 ,graham called these jelly-like substances colloids2 the easily diffusible substances he called crystalloids4 ,he proved that a colloidal substance acts towards a crystalloid much as water does2 that the crystalloid rapidly diffuses through the colloid1 but that colloids are not themselves capable of diffusing through other colloids4 ,on this fact was founded ,graham's process of dialysis4 ,as colloid he employed a sheet of parchment paper1 which he stretched on a ring of wood or caoutchouc1 and floated the apparatus so constructed--the dialyser--on the surface of pure water in a glass dish2 he then poured into the dialyser the mixture of substances which it was desired to separate4 ,let us suppose that this mixture contained sugar and gum2 the crystalloidal sugar soon passed through the parchment paper1 and was found in the water outside1 but the colloidal gum remained in the dialyser4 ,if the mixture in the dialyser contained two crystalloids1 the greater part of the more diffusible of these passed through the parchment in a short time along with only a little of the less diffusible2 a partial separation was thus effected4 ,this method of dialysis was applied by ,graham to separate and obtain in the pure state many colloidal modifications of chemical compounds1 such as aluminium and tin hydrates1 etc4 ,by his study of these peculiar substances ,graham introduced into chemistry a new class of bodies1 and opened up great fields of research4 ,matter in the colloidal state appears to be endowed with properties which are quite absent1 or are hidden1 when it is in the ordinary crystalloidal condition4 ,colloids are readily affected by the smallest changes in external conditions2 they are eminently unstable bodies2 they are1 ,graham said1 always on the verge of an impending change1 and minute disturbances in the surrounding conditions may precipitate this change at any moment4 ,crystalloids1 on the other hand1 are stable2 they have definite properties1 which are not changed without simultaneous large changes in surrounding conditions4 ,but although1 to use ,graham's words1 these classes of bodies appear like different worlds of matter1 there is yet no marked separating line between them4 ,ice is a substance which under ordinary conditions exhibits all the properties of crystalloids1 but ice formed in contact with water just at the freezing point is not unlike a mass of partly dried gum2 it shows no crystalline structure1 but it may be rent and split like a lump of glue1 and1 like glue1 the broken pieces may be pressed together again and caused to adhere into one mass4 ,can any facts1 asks ,graham1 more strikingly illustrate the maxim that in ,nature there are no abrupt transitions1 and that distinctions of class are never absolute8 ,in the properties of colloids and crystalloids ,graham saw an index of diversity of molecular structure4 ,the smallest individual particle of a colloid appeared to him to be a much more complex structure than the smallest particle of a crystalloid4 ,the colloidal molecule appeared to be formed by the gathering together of several crystalloidal molecules2 such a complex structure might be expected readily to undergo change1 whereas the simpler molecule of a crystalloid would probably present more definite and less readily altered properties4 ,in this research ,graham had again1 as so often before1 arrived at the conception of various orders of small particles4 ,in the early days of the ,daltonian theory it seemed that the recognition of atoms as ultimate particles1 by the placing together of which masses of this or that kind of matter are produced1 would suffice to explain all the facts of chemical combinations2 but ,dalton's application of the term atom to elements and compounds alike implied that an atom might itself have parts1 and that one atom might be more complex than another4 ,the way was thus already prepared for the recognition of more than one order of atoms1 a recognition which was formulated three years after the appearance of ,dalton's ,new ,system in the statement of ,avogadro1 ,equal volumes of gases contain equal numbers of molecules2 for we have seen that the application of this statement to actually occurring reactions between gases obliges us to admit that the molecules of hydrogen1 oxygen and many other elementary gases are composed of two distinct parts or atoms4 ,berzelius it is true did not formally accept the generalization of ,avogadro2 but we have seen how the conception of atom which runs through his work is not that of an indivisible particle1 but rather that of a little individual part of matter with definite properties1 from which the mass of matter recognizable by our senses is constructed1 just as the wall is built up of individual bricks4 ,and as the bricks are themselves constructed of clay1 which in turn is composed of silica and alumina1 so may each of these little parts of matter be constructed of smaller parts2 only as clay is not brick1 and neither silica nor alumina is clay1 so the properties of the parts of the atom--if it has parts--are not the properties of the atom1 and a mass of matter constructed of these parts would not have the same properties as a mass of matter constructed of the atoms themselves4 ,another feature of ,graham's work is found in the prominence which he gives to that view of a chemical compound which regards it as the resultant of the action and reaction of the parts of the compound4 ,as the apparent stability of chemical compounds was seen by ,davy to be the result of an equilibrium of contending forces1 so did the seemingly changeless character of any chemical substance appear to ,graham as due to the orderly changes which are continually proceeding among the molecules of which the substance is constructed4 ,a piece of lime1 or a drop of water1 was to the mind of ,graham the scene of a continual strife1 for that minute portion of matter appeared to him to be constructed of almost innumerable myriads of little parts1 each in more or less rapid motion1 one now striking against another and now moving free for a little space4 ,interfere with those movements1 alter the mutual action of those minute particles1 and the whole building would fall to pieces4 ,for more than thirty years ,graham was content to trace the movements of molecules4 ,during that time he devoted himself1 with an intense and single-minded devotion1 to the study of molecular science4 ,undaunted in early youth by the withdrawal of his father's support2 unseduced in his middle age by the temptations of technical chemistry1 by yielding to which he would soon have secured a fortune2 undazzled in his later days by the honours of the position to which he had attained2 ,graham dedicated his life to the nobler object of advancing the bounds of natural knowledge1 and so adding to those truths which must ever remain for the good and furtherance of humanity4 ,,footnotes3 #ab ,a metre is equal to about thirty-nine inches2 a millimetre is the one-thousandth part of a metre4 ,,chapter ,,vi4 ,,rise ,,and ,,progress ,,of ,,organic ,,chemistry--,,period ,,of ,,liebig ,,and ,,dumas4 ,justus ,liebig1 #ahjc-ahgc4 ,jean ,baptiste ,andre ,dumas1 born in #ahjj4 ,i have as yet said almost nothing with regard to the progress of organic chemistry1 considered as a special branch of the science4 ,it is however in this department that the greatest triumphs which mark the third period of chemical advance have been won4 ,we must therefore now turn our attention to the work which has been done here4 ,the ancients drew no such distinction between portions of their chemical knowledge1 limited as it was1 as is implied by the modern terms organic and inorganic chemistry4 ,an organic acid--acetic--was one of the earliest known substances belonging to the class of acids2 many processes of chemical handicraft practised in the olden times dealt with the manufacture of substances1 such as soap1 leather or gum1 which we should now call organic substances4 ,nor did the early alchemists1 although working chiefly with mineral or inorganic substances1 draw any strict division between the two branches of chemistry4 ,the medical chemists of the sixteenth century dealt much with substances derived from plants and animals1 such as benzoic and succinic acids1 spirit of wine1 oils1 etc4 ,but neither in their nomenclature nor in their practice did they sharply distinguish inorganic from organic compounds4 ,they spoke of the quintessence of arsenic and the quintessence of alcohol2 they applied the term oil alike to the products of the action of acids on metallic salts and to substances obtained from vegetables4 ,but towards the end of the seventeenth century1 at the time that is when the phlogistic theory began to gain pre-eminence1 we find gradually springing up a division of chemical substances into mineral1 animal and vegetable substances--a division which was based rather on a consideration of the sources whence the substances were derived than on the properties of the substances themselves1 and therefore a division which was essentially a non-chemical one4 ,about a century after this1 systematic attempts began to be made to trace some peculiarity of composition as belonging to all compounds of organic1 that is1 of animal or vegetable1 origin4 ,as very many of the substances then known belonging to this class were more or less oil-like in their properties--oils1 fats1 balsams1 gums1 sugar1 etc4--organic substances generally were said to be characterized by the presence in them of the principle of oil4 ,such a statement as this1 although suited to the conceptions of that time1 could not be received when ,lavoisier had shown chemists how ,nature ought be examined4 ,with the definite conception of element introduced by the new chemistry1 came an attempt to prove that organic compounds were built up of elements which were rarely found together in any one compound of inorganic origin4 ,substances of vegetable origin were said by ,lavoisier to be composed of carbon1 hydrogen and oxygen1 while phosphorus and nitrogen1 in addition to those three elements1 entered into the composition of substances derived from animals4 ,but neither could this definition of organic compounds be upheld in the face of facts4 ,wax and many oils contained only carbon and hydrogen1 yet they were undoubtedly substances of vegetable or animal origin4 ,if the presence of any two of the three elements1 carbon1 hydrogen and oxygen1 were to be regarded as a sufficient criterion for the classification of a compound1 then it was necessary that carbonic acid--obtained by the action of a mineral acid on chalk--should be called an organic compound4 ,to ,berzelius belongs the honour of being the chemist who first applied the general laws of chemical combination to all compounds alike1 whether derived from minerals1 animals1 or vegetables4 ,the ultimate particles1 or molecules1 of every compound were regarded by ,berzelius as built up of two parts1 each of which might itself be an elementary atom1 or a group of elementary atoms4 ,one of these parts1 he said1 was characterized by positive1 the other by negative electricity4 ,every compound molecule1 whatever was the nature or number of the elementary atoms composing it1 was a dual structure 7see p4 #afd74 ,organic chemistry came again to be a term somewhat loosely applied to the compounds derived from animals or vegetables1 or in the formation of which the agency of living things was necessary4 ,most1 if not all of these compounds contained carbon and some other element or elements1 especially hydrogen1 oxygen and nitrogen4 ,but the progress of this branch of chemistry was impeded by the want of any trustworthy methods for analysing compounds containing carbon1 oxygen and hydrogen4 ,this want was to be supplied1 and the science of organic chemistry1 and so of chemistry in general1 was to be immensely advanced by the labours of a new school of chemists1 chief among whom were ,liebig and ,dumas4 ,let us shortly trace the work of these two renowned naturalists4 ,the life-work of the first is finished2 ,i write this story of the progress of his favourite science on the eighty-second birthday of the second of these great men1 who is still with us a veteran crowned with glory1 a true soldier in the battle against ignorance and so against want and crime4 99 99 99 99 99 ,,justus ,,liebig was born at ,darmstadt1 on the #abth of ,may #ahjc4 ,the main facts which mark his life regarded apart from his work as a chemist are soon told4 ,showing a taste for making experiments he was apprenticed by his father to an apothecary4 ,fortunately for science he did not long remain as a concoctor of drugs1 but was allowed to enter the ,university of ,bonn as a student of medicine4 ,from ,bonn he went to ,erlangen1 at which university he graduated in #ahba4 ,a year or two before this time ,liebig had begun his career as an investigator of ,nature1 and he had already made such progress that the ,grand ,duke of ,hesse-,darmstadt was prevailed on to grant him a small pension and allow him to prosecute his researches at ,paris1 which was then almost the only place where he could hope to find the conditions of success for the study of scientific chemistry4 ,to ,paris accordingly he went in #ahbc4 ,he was so fortunate--thanks to the good graces of the renowned naturalist ,alexander von ,humboldt--as to be allowed to enter the laboratory of ,gay-,lussac1 where he continued the research on a class of explosive compounds1 called fulminates1 which he had begun before leaving ,darmstadt4 ,a year later ,liebig was invited to return to his native country as ,professor of ,chemistry in the small ,university of ,giessen--a name soon to be known wherever chemistry was studied1 and now held dear by many eminent chemists who there learned what is meant by the scientific study of ,nature4 ,the year before ,liebig entered the laboratory of ,gay-,lussac there came to ,paris a young and enthusiastic student who had already made himself known in the scientific world by his physiological researches1 and who was now about to begin his career as a chemist4 ,in that southern part of ,france which is rich in memories of the ,roman occupation1 not far from the remains of the great aqueduct which spans the valley of the ,gardon1 at no great distance from the famous cities of ,arles and ,nimes1 was born1 in the town of ,alais1 on the #adth of ,july #ahjj1 ,,jean ,,baptiste ,,andre ,,dumas4 ,the father of ,dumas was a man of considerable culture2 he gave his son as good an education as could be obtained in the little town of his birth4 ,at the age of fourteen young ,dumas was a good classical scholar1 and had acquired a fair knowledge of natural science4 ,but for his deficiency in mathematics he would probably have entered for the examination which admitted those who passed it to join the ,french navy4 ,but before he had made good his mathematical deficiencies the troublous nature of the times 7#ahad-ae7 obliged his parents to think of some other profession for their son which would entail less sacrifice on their part4 ,like his great fellow-worker in after life he was apprenticed to an apothecary1 and like him also1 he soon forsook this sphere of usefulness4 ,desirous of better opportunities for the study of science1 and overpowered by the miseries which war had brought upon the district of his birth1 ,dumas persuaded his father to allow him to go to ,geneva4 ,at ,geneva ,dumas found an atmosphere more suited to his scientific progress2 chemistry1 physics1 botany1 and other branches of natural science were taught by men whose names were everywhere known4 ,he began experiments in chemistry with the crudest and most limited apparatus1 but even with these he made discoveries which afterwards led to important work on the volumes occupied by the atoms of elementary substances4 ,about the year #ahah ,dumas became acquainted with ,dr4 ,j4 ,l4 ,prevost1 who had returned from studying in many of the most famous medical schools of ,europe4 ,invited by ,prevost to join in an investigation requiring medical1 botanical and chemical knowledge1 ,dumas now began a series of researches which soon passed into the domain of animal physiology1 and by the prosecution of which under many difficulties he laid the foundations of his future fame4 ,but along with his physiological work ,dumas carried on a research into the expansion of various ethers4 ,this necessitated the preparation of a series of ethers in a state of purity2 but so difficult did ,dumas find this to be1 so much time did he consume in this preliminary work1 and so interested did he become in the chemical part of the investigation1 that he abandoned the experiments on expansion1 and set himself to solve some of the problems presented by the composition and chemical properties of the ethers4 ,dumas would probably have remained in ,geneva had he not had a morning visit paid him in the year #ahbb4 ,when at work in his laboratory one day1 some one knocked and was bidden come in4 ,i was surprised to find myself face to face with a gentleman in a light-blue coat with metal buttons1 a white waistcoat1 nankeen breeches1 and top-boots4444 ,the wearer of this costume1 his head somewhat bent1 his eyes deep-set but keen1 advanced with a pleasant smile1 saying1 ',monsieur ,dumas4' ',the same1 sir2 but excuse me4' ',i am ,m4 de ,humboldt1 and did not wish to pass through ,geneva without having had the pleasure of seeing you4'444 ,i had only one chair4 ,my visitor was pleased to accept it1 whilst ,i resumed my elevated perch on the drawing stool4444 ',i intend1' said ,m4 de ,humboldt1 'to spend some days in ,geneva1 to see old friends and to make new ones1 and more especially to become acquainted with young people who are beginning their career4 ,will you act as my cicerone8 ,i warn you however that my rambles begin early and end late4 ,now1 could you be at my disposal1 say from six in the morning till midnight8' ,after some days spent as ,humboldt had indicated the great naturalist left ,geneva4 ,dumas tells us that the town seemed empty to him4 ,i felt as if spell-bound4 ,the memorable hours ,i had spent with that irresistible enchanter had opened a new world to my mind4 ,dumas felt that he must go to ,paris--that there he would have more scope and more opportunities for prosecuting science4 ,a few kind words1 a little genuine sympathy1 and a little help from ,humboldt were thus the means of fairly launching in their career of scientific inquiry these two young men1 ,liebig and ,dumas4 ,in ,paris1 whither he went in #ahbc1 ,dumas found a welcome4 ,he soon made the acquaintance and gained the friendship of the great men who then made natural science so much esteemed in the ,french capital4 ,when the year #ahbf came1 it saw him ,professor of ,chemistry at the ,athenaeum1 and married to the lady whom he loved1 and who has ever since fought the battle of life by his side4 ,liebig left ,paris in #ahbd4 ,by the year #ahcj he had perfected and applied that method for the analysis of organic compounds which is now in constant use wherever organic chemistry is studied2 by the same year ,dumas had given the first warning of the attack which he was about to make on the great structure of dualism raised by ,berzelius4 ,in a paper1 ,on ,some ,points of the ,atomic ,theory1 published in #ahbf1 ,dumas adopted the distinction made by ,avogadro between molecules and atoms1 or between the small particles of substances which remain undivided during physical actions1 and the particles1 smaller than these1 which are undivided during chemical actions4 ,but1 unfortunately1 ,dumas did not mark these two conceptions by names sufficiently definite to enable the readers of his memoir to bear the distinction clearly in mind4 ,the terms atom and molecule were not introduced into chemistry with the precise meanings now attached to them until some time after #ahbf4 ,although the idea of two orders of small particles underlies all the experimental work described by ,dumas in this paper1 yet the numbers which he obtained as representing the actual atomic weights of several elements--e4g4 phosphorus1 arsenic1 tin1 silicon--show that he had not himself carried out ,avogadro's hypothesis to its legitimate conclusions4 ,two years after this ,dumas employed the reaction wherein two volumes of gaseous hydrochloric acid are produced by the union of one volume of hydrogen with one volume of chlorine1 as an argument which obliged him to conclude that1 if ,avogadro's physical hypothesis be accepted1 the molecules of hydrogen and chlorine split1 each into two parts1 when these gases combine chemically4 ,but ,dumas did not at this time conclude that the molecular weight of hydrogen must be taken as twice its atomic weight1 and that--hydrogen being the standard substance--the molecular weights of all gases must be represented by the specific gravities of these gases1 referred to hydrogen as #b4 ,i have already shortly discussed the method for finding the relative weights of elementary atoms which is founded on ,avogadro's hypothesis1 and1 ,i think1 have shown that this hypothesis leads to the definition of atom as the smallest amount of an element in one molecule of any compound of that element 7see p4 #adb74 ,this deduction from ,avogadro's law is now a part and parcel of our general chemical knowledge4 ,we wonder why it was not made by ,dumas2 but we must remember that a great mass of facts has been accumulated since #ahbf1 and that this definition of atom has been gradually forced on chemists by the cumulative evidence of those facts4 ,one thing ,dumas did do1 for which the thanks of every chemist ought to be given him2 he saw the need of a convenient method for determining the densities of compounds in the gaseous state1 and he supplied this need by that simple1 elegant and trustworthy method1 still in constant use1 known as ,dumas's vapour density process4 ,while ,dumas was working out the details of this analytical method1 which was destined to be so powerful an instrument of research1 ,liebig was engaged in similar work2 he was perfecting that process for the analysis of organic compounds which has since played so important a part in the advancement of this branch of chemical science4 ,the processes in use during the first quarter of this century for determining the amounts of carbon1 hydrogen1 and oxygen in compounds of those elements1 were difficult to conduct and gave untrustworthy results4 ,liebig adopted the principle of the method used by ,lavoisier1 viz4 that the carbon in a compound can be oxidized1 or burnt1 to carbonic acid1 and the hydrogen to water4 ,he contrived a very simple apparatus wherein this burning might be effected and the products of the burning--carbonic acid and water--might be arrested and weighed4 ,liebig's apparatus remains now essentially as it was presented to the chemical world in #ahcj4 ,various improvements in details have been made2 the introduction of gas in place of charcoal as a laboratory fuel has given the chemist a great command over the process of combustion1 but in every part of the apparatus to-day made use of in the laboratory is to be traced the impress of the master's hand4 ,a weighed quantity of the substance to be analyzed is heated with oxide of copper in a tube of hard glass2 the carbon is burnt to carbonic acid and the hydrogen to water at the expense of the oxygen of the copper oxide4 ,attached to the combustion tube is a weighed tube containing chloride of calcium1 a substance which greedily combines with water1 and this tube is succeeded by a set of three or more small bulbs1 blown in one piece of glass1 and containing an aqueous solution of caustic potash1 a substance with which carbonic acid readily enters into combination4 ,the chloride of calcium tube and the potash bulbs are weighed before and after the experiment2 the increase in weight of the former represents the amount of water1 and the increase in weight of the latter the amount of carbonic acid obtained by burning a given weight of the compound under examination4 ,as the composition of carbonic acid and of water is known1 the amounts of carbon and of hydrogen in one hundred parts of the compound are easily found2 the difference between the sum of these and one hundred represents the amount of oxygen in one hundred parts of the compound4 ,if the compound should contain elements other than these three1 those other elements are determined by special processes1 the oxygen being always found by difference4 ,soon after his settlement at ,giessen ,liebig turned his attention to a class of organic compounds known as the cyanates2 but ,woehler--who1 while ,liebig was in ,paris in the laboratory of ,gay-,lussac1 was engaged in studying the intricacies of mineral chemistry under the guidance of ,berzelius--had already entered on this field of research4 ,the two young chemists compared notes1 recognized each other's powers1 and became friends2 this friendship strengthened as life advanced1 and some of the most important papers which enriched chemical science during the next thirty years bore the joint signatures of ,liebig and ,woehler4 ,i have already mentioned that when it was found necessary to abandon the ,lavoisierian definition of organic chemistry as the chemistry of compounds containing carbon1 hydrogen and oxygen1 and sometimes also phosphorus or nitrogen1 a definition was attempted to be based on the supposed fact that the formation of the compounds obtained from animals and plants could be accomplished only by the agency of a living organism4 ,but the discovery made in #ahbh by ,woehler1 that urea--a substance specially characterized by its production in the animal economy1 and in that economy only--could be built up from mineral materials1 rendered this definition of organic chemistry impossible1 and broke down the artificial barrier whereby naturalists attempted to separate two fields of study between which ,nature made no division4 ,we have here another illustration of the truth of the conception which underlies so many of the recent advances of science1 which is the central thought of the noble structure reared by the greatest naturalist of our time1 and which is expressed by one of the profoundest students of ,nature that this age has seen in the words ,i have already quoted from the preface to the ,lyrical ,ballads1 ,in ,nature everything is distinct1 but nothing defined into absolute independent singleness4 ,from this time the progress of organic chemistry became rapid4 ,dumas continued the researches upon ethers which he had commenced at ,geneva1 and by the year #ahbi or so he had established the relations which exist between ethers and alcohols on the one hand1 and ethers and acids on the other4 ,this research1 a description of the details of which ,i cannot introduce here as it would involve the use of many technical terms and assume the possession by the reader of much technical knowledge1 was followed by others1 whereby ,dumas established the existence of a series of compounds all possessed of the chemical properties of alcohol1 all containing carbon1 hydrogen and oxygen1 but differing from one another by a constant amount of carbon and hydrogen4 ,this discovery of a series of alcohols1 distinguished by the possession of certain definite properties whereby they were marked off from all other so-called organic compounds1 was as the appearance of a landmark to the traveller in a country where he is without a guide4 ,the introduction of the comparative method of study into organic chemistry--the method1 that is1 which bases classification on a comparison of large groups of compounds1 and which seeks to gather together those substances which are like and to separate those which are unlike--soon began to bear fruit4 ,this method suggested to the experimenter new points of view from which to regard groups of bodies2 analogies which were hidden when a few substances only were considered1 became prominent as the range of view was widened4 ,what the gentle ,elia calls fragments and scattered pieces of truth1 hints and glimpses1 germs1 and crude essays at a system1 became important4 ,there was work to be done1 not only by the master spirits who1 looking at things from a central position of vantage1 saw the relative importance of the various detailed facts1 but also by those who could only beat up a little game peradventure1 and leave it to knottier heads1 more robust constitutions1 to run it down4 ,twenty years before the time of which we are now speaking ,davy had decomposed the alkalis potash and soda2 as he found these substances to be metallic oxides1 he thought it very probable that the other well-known alkali1 ammonia1 would also turn out to be the oxide of a metal4 ,by the electrolysis of salts formed by the action of ammonia on acids1 using mercury as one of the poles of the battery1 ,davy obtained a strange-looking spongy substance which he was inclined to regard as an alloy of the metallic base of ammonia with mercury4 ,from the results of experiments by himself and others1 ,davy adopted a view of this alloy which regarded it as containing a compound radicle1 or group of elementary atoms which in certain definite chemical changes behaved like a single elementary atom4 ,to this compound radicle he gave the name of ammonium4 ,as an aqueous solution of potash or soda was regarded as a compound of water and oxide of potassium or sodium1 so an aqueous solution of ammonia was regarded as a compound of water and oxide of ammonium4 ,when the composition of this substance1 ammonium1 came to be more accurately determined1 it was found that it might be best represented as a compound atom built up of one atom of nitrogen and four atoms of hydrogen4 ,the observed properties of many compounds obtained from ammonia1 and the analogies observed between these and similar compounds obtained from potash and soda1 could be explained by assuming in the compound atom 7or better1 in the molecule7 of the ammonia salt1 the existence of this group of atoms1 acting as one atom1 called ammonium4 ,the reader will not fail to observe how essentially atomic is this conception of compound radicle4 ,the ultimate particle1 the molecule1 of a compound has now come to be regarded as a structure built up of parts called atoms1 just as a house is a structure built up of parts called stones and bricks1 mortar and wood1 etc4 ,but there may be a closer relationship between some of the atoms in this molecule than between the other atoms4 ,it may be possible to remove a group of atoms1 and put another group--or perhaps another single atom--in the place of the group removed1 without causing the whole atomic structure to fall to pieces2 just as it may be possible to remove some of the bricks from the wall of a house1 or a large wooden beam from beneath the lintels1 and replace these by other bricks or by a single stone1 or replace the large wooden beam by a smaller iron one1 without involving the downfall of the entire house4 ,the group of atoms thus removable--the compound radicle--may exist in a series of compounds4 ,as we have an oxide1 a sulphide1 a chloride1 a nitrate1 etc41 of sodium1 so we may have an oxide1 a sulphide1 a chloride1 a nitrate1 etc41 of ammonium4 ,the compounds of sodium are possessed of many properties in common2 this is partly explained by saying that they all contain one or more atoms of the element sodium4 ,the compounds of ammonium possess many properties in common1 and this is partly explained if we assume that they all contain one or more atoms of the compound radicle ammonium4 ,the conception of compound radicle was carried by ,berzelius to its utmost limits4 ,we have learned that the ,swedish chemist regarded every molecule as composed of two parts2 in very many cases each of these parts was itself made up of more than one kind of atom--it was a compound radicle4 ,but the ,berzelian system tended to become too artificial3 it drifted further and further away from facts4 ,of the two parts composing the dual molecular structure1 one was of necessity positively1 and the other negatively electrified4 ,the greater number of the so-called organic compounds contained oxygen2 oxygen was the most electro-negative element known2 hence most organic compounds were regarded as formed by the coming together of one1 two1 or more atoms of oxygen1 forming the negative part of the molecule1 with one1 two1 or more atoms of a compound radicle1 which formed the positive part of the molecule4 ,from this dualistic view of the molecule there naturally arose a disposition to regard the compound radicles of organic chemistry as the non-oxygenated parts of the molecules of organic compounds4 ,an organic compound came gradually to be regarded as a compound of oxygen with some other elements1 which were all lumped together under the name of a compound radicle1 and organic chemistry was for a time defined as the chemistry of compound radicles4 ,from what has been said on p4 #bfh1 ,i think it will be evident that the idea of substitution is a necessary part of the original conception of compound radicle2 a group of atoms in a molecule may1 it is said1 be removed1 and another group1 or another atom1 substituted for that which is removed4 ,berzelius adopted this idea1 but he made it too rigid2 he taught that an electro-negative atom1 or compound radicle1 could be replaced or substituted only by another electro-negative atom or group of atoms1 and a positively electrified atom or group of atoms1 only by another electro-positive atom or compound radicle4 ,thus oxygen could perhaps be replaced by chlorine1 but certainly not by hydrogen2 while hydrogen might be replaced by a positively electrified atom1 but certainly not by chlorine4 ,the conceptions of compound radicles and of substitution held some such position in organic chemistry as that which ,i have now attempted to indicate when ,dumas and ,liebig began their work in this field4 ,the visitors at one of the royal soirees at the ,tuileries were much annoyed by the irritating vapours which came from the wax candles used to illuminate the apartments2 ,dumas was asked to examine the candles and find the reason of their peculiar behaviour4 ,he found that the manufacturer had used chlorine to bleach the wax1 that some of this chlorine remained in the candles1 and that the irritating vapours which had annoyed the guests of ,charles ,x4 contained hydrochloric acid1 produced by the union of chlorine with part of the hydrogen of the wax4 ,candles bleached by some other means than chlorine were in future used in the royal palaces2 and the unitary theory1 which was to overthrow the dualism of ,berzelius1 began to arise in the mind of ,dumas4 ,the retention of a large quantity of chlorine by wax could scarcely be explained by assuming that the chlorine was present only as a mechanically held impurity4 ,dumas thoroughly investigated the action of chlorine on wax and other organic compounds2 and in #ahcd he announced that hydrogen in organic compounds can be exchanged for chlorine1 every volume of hydrogen given up by the original compound being replaced by an equal volume of chlorine4 ,liebig and ,woehler made use of a similar conception to explain the results which they had obtained about this time in their study of the oil of bitter almonds1 a study which will be referred to immediately4 ,the progress of this bold innovation made by ,dumas was much advanced by the experiments and reasonings of two ,french chemists1 whose names ought always to be reverenced by students of chemistry as the names of a pair of brilliant naturalists to whom modern chemistry owes much4 ,gerhardt was distinguished by clearness of vision and expression2 ,laurent by originality1 breadth of mind and power of speculation4 ,laurent appears to have been the first who made a clear statement of the fundamental conception of the unitary theory3 ,many organic compounds1 when treated with chlorine lose a certain number of equivalents of hydrogen1 which passes off as hydrochloric acid4 ,an equal number of equivalents of chlorine takes the place of the hydrogen so eliminated2 thus the physical and chemical properties of the original substance are not profoundly changed4 ,the chlorine occupies the place left vacant by the hydrogen2 the chlorine plays in the new compound the same part as was played by the hydrogen in the original compound4 ,the replacement of electro-positive hydrogen by electro-negative chlorine was against every canon of the dualistic chemistry2 and to say that the physical and chemical properties of the original compound were not profoundly modified by this replacement1 seemed to be to call in question the validity of the whole structure raised by the labours during a quarter of a century of one universally admitted to be among the foremost chemists of his age4 ,but facts accumulated4 ,by the action of chlorine on alcohol ,liebig obtained chloroform and chloral1 substances which have since been so largely applied to the alleviation of human suffering2 but it was ,dumas who correctly determined the composition of these two compounds1 and showed how they are related to alcohol and to one another4 ,liebig's reception of the corrections made by ,dumas in his work furnishes a striking example of the true scientific spirit4 ,as an excellent illustration1 said ,liebig1 of the mode in which errors should be corrected1 the investigation of chloral by ,dumas may fitly be introduced4 ,it carried conviction to myself1 as ,i think to everybody else1 not by the copious number of analytical data opposed to the not less numerous results which ,i had published1 but because these data gave a simpler explanation both of the formation and of the changes of the substances in question4 ,one of the most important contributions to the new views was made by ,dumas in his paper on the action of chlorine on acetic acid 7#ahcc71 wherein he proved that the product of this action1 viz4 trichloracetic acid1 is related to the parent substance by containing three atoms of chlorine in place of three atoms of hydrogen in the molecule2 that the new substance is1 like the parent substance1 a monobasic acid2 that its salts are very analogous in properties to the salts of acetic acid2 that the action of the same reagents on the two substances is similar2 and finally1 that the existence of many derivatives of these compounds could be foretold by the help of the new hypothesis1 which derivatives ought not to exist according to the dualistic theory1 but which1 unfortunately for that theory1 were prepared and analyzed by ,dumas4 ,i have alluded to a research by ,liebig and ,woehler on oil of bitter almonds as marking an important stage in the advance of the anti-dualistic views4 ,the paper alluded to was published in #ahcb4 ,at that time it was known that benzoic acid is formed by exposure of bitter-almond oil to the air4 ,liebig and ,woehler made many analyses of these two substances1 and many experiments on the mutual relations of their properties1 whereby they were led to regard the molecules of the oil as built up each of an atom of hydrogen and an atom of a compound radicle--itself a compound of carbon1 hydrogen and oxygen--to which they gave the name of benzoyl4#ac ,benzoic acid they regarded as a compound of the same radicle with another radicle1 consisting of equal numbers of oxygen and hydrogen atoms4 ,by the action of chlorine and other reagents on bitter-almond oil these chemists obtained substances which were carefully analyzed and studied1 and the properties of which they showed could be simply explained by regarding them all as compounds of the radicle benzoyl with chlorine and other atoms or groups of atoms4 ,but this view1 if adopted1 necessitated the belief that chlorine atoms could replace oxygen atoms2 and1 generally1 that the substitution of an electro-positive by a negative atom or group of atoms did not necessarily cause any great alteration in the properties of the molecule4 ,thus it was that the rigid conceptions of dualism were shown to be too rigid2 that the possibility of an electro-positive radicle1 or atom1 replacing another of opposite electricity was recognized2 and thus the view which regarded a compound molecule as one structure--atoms in which might be replaced by other atoms irrespective of the mutual electrical relations of these atoms--began to gain ground4 ,from this time the molecule of a compound has been generally regarded as a unitary structure1 as one whole1 and the properties of the molecule as determined by the nature1 number1 and arrangement of all the atoms which together compose it4 ,the unitary conception of a compound molecule appeared at first to be altogether opposed to the system of ,berzelius2 but as time went on1 and as fresh facts came to be known1 it was seen that the new view conserved at least one1 and that perhaps the most important1 of the thoughts which formed the basis of the ,berzelian classification4 ,underlying the dualism of ,berzelius was the conception of the molecule as an atomic structure2 this was retained in the unitary system of ,dumas1 ,gerhardt and ,laurent4 ,berzelius had insisted that every molecule is a dual structure4 ,this is taking too narrow a view of the possibilities of ,nature1 said the upholders of the new school4 ,this molecule may have a dual structure2 that may be built up of three parts4 ,the structure of this molecule or of that can be determined only by a careful study of its relations with other molecules4 ,for a time it seemed also as if the new chemistry could do without the compound radicle which had been so much used by ,berzelius2 but the pressure of facts soon drove the unitary chemists to recognize the value of that hypothesis which looked on parts of the molecule as sometimes more closely associated than other parts--which recognized the existence of atomic structures within the larger molecular structures4 ,as a house is not simply a putting together of so many bricks1 so much mortar1 so many doors and windows1 so many leaden pipes1 etc41 but rather a definite structure composed of parts1 many of which are themselves also definite structures1 such as the window and its accessory parts1 the door with its lintel and handle1 etc41 so to the unitary chemists did the molecule appear to be built up of parts1 some of which1 themselves composed of yet smaller parts1 discharged a particular function in the molecular economy4 ,a general division of a plant might describe it as a structure consisting of a stem1 a root1 and leaves4 ,each of the parts1 directly by its individual action and indirectly by the mutual action between it and all the other parts1 contributes to the growth of the whole plant2 but if the stem1 or root1 or leaves be further analyzed1 each is found to consist of many parts1 of fibres and cells and tissue1 etc4 ,we may liken the plant to the molecule of an organic compound2 the root1 the stem and the leaves to the compound radicles of which this molecule is built up1 and the tissue1 fibres1 etc41 to the elementary atoms which compose these compound radicles4 ,the molecule is one whole1 possessed of definite structure and performing a definite function by virtue of the nature and the arrangement of its parts4 ,many years elapsed after the publication of the researches of ,dumas1 and of ,liebig and ,woehler1 before such a conception of the molecule as this was widely accepted by chemists4 ,the opposition of the older school1 headed by their doughty champion ,berzelius1 had to be overcome2 the infallibility of some of the younger members of the new school had to be checked2 facts had to be accumulated1 difficulties explained1 weak analogies abandoned and strong ones rendered stronger by research2 special views of the structure of this or that molecule1 deduced from a single investigation1 had to be supplemented and modified by wider views gained by the researches of many workers4 ,it was not till #ahfg that ,liebig1 when asked by ,dumas at a dinner given during the ,french ,exhibition to the foreign chemists1 why he had abandoned organic chemistry1 replied that now1 with the theory of substitution as a foundation1 the edifice may be built up by workmen3 masters are no longer needed4 ,laurent and ,gerhardt did noble work in advancing the unitary theory2 to them is largely due the fruitful conception of types1 an outcome of ,dumas's work1 which owed its origin to the flickering of the wax candles in the ,tuileries during the royal soiree4 ,chlorine can be substituted for hydrogen in acetic acid1 and the product is closely related in its properties to the parent substance2 various atoms or groups of atoms can be substituted by other groups in the derivatives of oil of bitter almonds1 but a close analogy in properties runs through all these compounds3 these facts might be more shortly expressed by saying that acetic and trichloracetic acids belong to the same type1 and that the derivatives of bitter-almond oil likewise belong to one type4 ,laurent carried this conception into inorganic chemistry4 ,water and potash did not seem to have much in common1 but ,laurent said potash is not a compound of oxide of potassium and water1 it is rather a derivative of water4 ,the molecule of potash is derived from that of water by replacing one atom of hydrogen in the latter by one atom of potassium2 water and potash belong to the same type4 ,thus there was constituted the water type4 ,light was at once thrown on many facts in organic chemistry4 ,the analogies between alcohol and water1 some of which were first pointed out by ,graham 7see p4 #bce71 seemed to follow as a necessary consequence when the molecule of alcohol was regarded as built on the water type4 ,in place of two atoms of hydrogen combined with one of oxygen1 there was in the alcohol molecule one atom of the compound radicle ethyl 7itself composed of carbon and hydrogen71 one atom of oxygen and one of hydrogen4 ,alcohol was water with one hydrogen atom substituted by one ethyl atom2 the hydrogen atom was the atom of what we call an element1 the ethyl was the atom of what we call a compound radicle4 ,gerhardt sought to refer all organic compounds to one or other of three types--the water type1 the hydrochloric acid type1 and the ammonia type4 ,as new compounds were prepared and examined1 other types had to be introduced4 ,to follow the history of this conception would lead us into too many details2 suffice it to say that the theory of types was gradually merged in the wider theory of equivalency1 about which ,i shall have a little to say in the next chapter4 ,one result of the introduction of types into chemical science1 associated as it was with the unitary view of compound radicles1 was to overthrow that definition of organic chemistry which had for some time prevailed1 and which stated that organic chemistry is the chemistry of compound radicles4 ,compound radicles1 it is true1 were more used in explaining the composition and properties of substances obtained from animals and vegetables than of mineral substances1 but a definition of one branch of a science which practically included the other branch1 from which the first was to be defined1 could not be retained4 ,chemists became gradually convinced that a definition of organic chemistry was not required2 that there was no distinction between so-called organic and inorganic compounds2 and they have consented1 but ,i scarcely think will much longer consent1 to retain the terms organic and inorganic1 only because these terms have been so long in use4 ,the known compounds of the element carbon are so numerous1 and they have been so much studied and so well classified1 that it has become more convenient for the student of chemistry to consider them as a group1 to a great extent apart from the compounds of the other elements2 to this group he still often gives the name of organic compounds4 99 99 99 99 99 ,liebig continued to hold the chair of ,chemistry in the ,university of ,giessen until the year #aheb1 when he was induced by the ,king of ,bavaria to accept the professorship of the same science in the ,university of ,munich4 ,during the second quarter of this century ,giessen was much resorted to by students of chemistry from all parts of the world1 more especially from ,england4 ,many men who afterwards made their mark in chemical discovery worked under the guidance of the professor of ,stockholm1 but ,giessen has the honour of being the place where a well-appointed chemical laboratory for scientific research was first started as a distinctly educational institution4 ,the fame of ,liebig as a discoverer and as a teacher soon filled the new institution with students1 who were stirred to enthusiasm as they listened to his lectures1 or saw him at work in his laboratory4 ,liebig was not exactly what is called a fluent speaker1 says ,professor ,hofmann1 of ,berlin1 but there was an earnestness1 an enthusiasm in all he said1 which irresistibly carried away the hearer4 ,nor was it so much the actual knowledge he imparted which produced this effect1 as the wonderful manner in which he called forth the reflective powers of even the least gifted of his pupils4 ,and what a boon was it1 after having been stifled by an oppressive load of facts1 to drink the pure breath of science such as it flowed from ,liebig's lips6 what a delight1 after having perhaps received from others a sack full of dry leaves1 suddenly in ,liebig's lectures to see the living1 growing tree6444 ,we felt then1 we feel still1 and never while we live shall we forget1 ,liebig's marvellous influence over us2 and if anything could be more astonishing than the amount of work he did with his own hands1 it was probably the mountain of chemical toil which he got us to go through4 ,each word of his carried instruction1 every intonation of his voice bespoke regard2 his approval was a mark of honour1 and of whatever else we might be proud1 our greatest pride of all was having him for our master4444 ,of our young winnings in the noble playground of philosophical honour1 more than half were free gifts to us from ,liebig1 and to his generous nature no triumphs of his own brought more sincere delight than that which he took in seeing his pupils' success1 and in assisting1 while he watched1 their upward struggle4 ,liebig had many friends in ,england4 ,he frequently visited this country1 and was present at several meetings of the ,british ,association4 ,at the meeting of #ahcg he was asked to draw up a report on the progress of organic chemistry2 he complied1 and in #ahdj presented the world with a book which marks a distinct epoch in the applications of science to industrial pursuits--,chemistry in its ,applications to ,agriculture and ,physiology4 ,in this book1 and in his subsequent researches and works1#ad ,liebig established and enforced the necessity which exists for returning to the soil the nourishing materials which are taken from it by the growth of crops2 he suggested that manure rich in the salts which are needed by plants might be artificially manufactured1 and by doing this he laid the foundation of a vast industry which has arisen during the last two decades4 ,he strongly and successfully attacked the conception which prevailed among most students of physiology at that time1 that chemical and physical generalizations could not be applied to explain the phenomena presented by the growth of living organisms4 ,he was among the first to establish1 as an induction from the results of many and varied experiments1 the canon which has since guided all teachers of the science of life1 that a true knowledge of biology must be based on a knowledge of chemistry and physics4 ,but ,liebig was not content to establish broad generalizations and to leave the working out of them to others2 he descended from the heights of philosophical inquiry1 and taught the housewife to make soup wherein the greatest amount of nourishment was conveyed to the invalid in the most easily digestible form2 and has he not1 by bringing within the reach of every one a portion of the animal nourishment which else had run to waste in the pampas of ,south ,america or the sheep-runs of ,australia1 made his name1 in every ,english home1 familiar as a household word8 ,on the death of ,berzelius in #ahdh1 it was to ,liebig that every chemist looked for a continuation of the annual ,report on the progress of chemistry1 which had now become the central magazine of facts1 whither each worker in the science could resort to make himself acquainted with what had been done by others on any subject which he proposed to investigate4 ,from that time to the present day ,liebig's ,annalen has been the leading chemical journal of the world4 ,of the other literary work of ,liebig--of his essays1 his celebrated ,chemical ,letters1 his many reports1 his severe and sometimes harsh criticisms of the work of others--of the details of the three hundred original papers wherein he embodied the results of his researches1 ,i have not time1 nor would this be the place1 to speak4 ,honoured by every scientific society of any note in the world1 crowned with the highest reward which ,england and ,france can offer to the man of science who is not an ,englishman or a ,frenchman--the ,copley ,medal and the associateship of the ,institute--honoured and respected by every student of science1 loved by each of the band of ardent natures whom he had trained and sent forth to battle for the good of their race1 and1 best of all1 working himself to the last in explaining the wonders of ,nature1 he passed into the silent land on the #ahth of ,april #ahgc1 leaving the memory of a life nobly devoted to the service of humanity1 and the imperishable record of many truths added to the common stock of the race4 99 99 99 99 99 ,the life-work of ,dumas1 other than that which ,i have already sketched1 is so manifold and so varied1 that to do more than refer to one or two leading points would carry us far beyond the limits within which ,i have tried to keep throughout this book4 ,in one of his earliest papers ,dumas adopted the atomic theory as the corner-stone of his chemical system2 he was thus led to an experimental revision of the values generally accepted for the atomic weights of some of the elements4 ,among these revisions1 that of the atomic weight of carbon holds a most important place1 partly because of the excellency of the work1 but more because of the other inquiries to which this work gave rise4 ,dumas's experiments were summed up in the statement that the atom of carbon is twelve times heavier than the atom of hydrogen4 ,the experimental methods and the calculations used in this determination involved a knowledge of the atomic weight of oxygen2 in order accurately to determine the value to be assigned to this constant1 ,dumas1 in conjunction with ,boussingault1 undertook a series of experiments on the synthesis of water1 which forms one of the classical researches of chemistry1 and wherein the number #af was established as representing the atomic weight of oxygen4 ,stas1 from experiments conducted at a later time with the utmost care and under conditions eminently fitted to gain accurate results1 obtained the number #ae4if1 in place of #af1 for the atomic weight of oxygen2 but in a paper recently published by the veteran ,dumas1 a source of error is pointed out which ,stas had overlooked in his experiments1 and it is shown that this error would tend slightly to increase the number obtained by ,stas4 ,as the values assigned to the atomic weights of the elements are the very fundamental data of chemistry1 and as we are every day more clearly perceiving that the mutual relations between the properties of elements and compounds are closely connected with the relative weights of the elementary atoms1 we can scarcely lay too much stress on such work as this done by ,dumas and ,stas4 ,not many years after the publication of ,dalton's ,new ,system1 the hypothesis was suggested by ,prout that the atomic weights of all the elements are represented by whole numbers--that of hydrogen being taken as unity--that the atom of each element is probably formed by the putting together of two1 three1 four1 or more atoms of hydrogen1 and that consequently there exists but a single elementary form of matter4 ,among the upholders of this hypothesis ,dumas has held an important place4 ,he modified the original statement of ,prout1 and suggested that all atomic weights are whole multiples of half of that of hydrogen 7that is1 are whole multiples of #a_/b74 ,the experiments of ,stas seemed to negative this view1 but later work--more especially the important critical revision of the results obtained by all the most trustworthy workers1 conducted by ,professor ,clarke of ,cincinnati1 and published by the ,smithsonian ,institution as part of their series of ,constants of ,nature--has shown that we are in no wise warranted by facts in rejecting ,prout's hypothesis as modified by ,dumas1 but that the balance of evidence is at present rather in its favour4 ,it would be altogether out of place to discuss here an hypothesis which leads to some of the most abstruse speculations as to the nature of matter in which chemists have as yet ventured to indulge4 ,i mention it only because it illustrates the far-reaching nature of the researches of the chemist whose work we are now considering1 and also because it shows the shallowness of the scoffs in which some partly educated people indulge when they see scientific men occupying themselves for years with attempts to solve such a minute and1 as they say1 trivial question as whether the number #ae4if or the number #af is to be preferred as representing the atomic weight of oxygen2 for in every speck of dust that falls lie hid the laws of the universe1 and there is not an hour that passes in which you do not hold the infinite in your hand4 ,another and very different subject1 which has been placed on a firm basis by the researches of ,dumas1 is the chemistry of fermentation4 ,by his work on the action of beer-yeast on saccharine liquids1 ,dumas proved ,liebig's view to be untenable--according to which the conversion of sugar into alcohol is brought about by the influence of chemical changes proceeding in the ferment2 also that the view of ,berzelius1 who regarded alcoholic fermentation as due simply to the contact of the ferment with the sugar1 was opposed to many facts2 and lastly1 ,dumas showed that the facts were best explained by the view which regarded the change of sugar into alcohol as in no way different from other purely chemical changes1 but as a change brought about1 so far as our present knowledge goes1 only by the agency of a growing organism of low form1 such as yeast4 ,in #ahcb ,dumas established at his own expense a laboratory for chemical research4 ,when the ,revolution of #ahdh broke out ,dumas's means were much diminished1 and he could no longer afford to maintain his laboratory4 ,the closing of this place1 where so much sound work had been done1 was generally regarded as a calamity to science4 ,about this time ,dumas received a visit from a person of unprepossessing appearance1 who accosted him thus3 ,they assert that you have shut up your laboratory1 but you have no right to do so4 ,if you are in need of money1 there1 throwing a roll of bank-notes on the table1 take what you want4 ,do not stint yourself2 ,i am rich1 a bachelor1 and have but a short time to live4 ,dumas's visitor turned out to be ,dr4 ,jecker4 ,he assured ,dumas that he was now only paying a debt1 since he had made a fortune by what he had learnt in the medical schools of ,paris4 ,dumas could not however in those troublous times turn his mind continuously to experimental research1 and therefore declined ,dr4 ,jecker's offer with many protestations of good will and esteem4 ,new work now began to press upon ,dumas2 his energy and his administrative powers were demanded by the ,state4 ,elected a member of the ,national ,assembly in #ahdh1 he was soon called by the ,president of the ,republic to office as ,minister of ,agriculture and ,commerce4 ,he was made a senator under the second empire4 ,he entered the municipal council of ,paris about #ahed1 and was soon elected to the presidency4 ,under his presidency the great scheme for providing ,paris with spring-water carried by aqueducts and tunnels was successfully accomplished2 many improvements were made in the drainage of the city2 the cost of gas was decreased1 while the quality was improved1 the constancy of the supply insured1 and the appliances for burning the gas in the streets were altered and rendered more effective4 ,nominated to succeed ,pelouze as ,master of the ,mint in #ahfh1 ,dumas held this honourable and important position only until the ,franco-,german war of #ahgj4 ,since that date he has relinquished political life2 but as ,permanent ,secretary of the ,academy ,dumas now fills the foremost place in all affairs connected with science1 whether pure or applied1 in the ,french capital4 ,in the work of these two chemists1 ,liebig and ,dumas1 we find admirable illustrations of the scientific method of examining natural appearances4 ,in the broad general views which they both take of the phenomena to be studied1 and the patient and persevering working out of details1 we have shown us the combination of powers which are generally found in separate individuals4 ,dumas has always insisted on the need of comparing properties and reactions of groups of bodies1 before any just knowledge can be gained as to the position of a single substance in the series studied by the chemist4 ,it has been his aim as a teacher1 we are assured by his friend1 ,professor ,hofmann1 never to present to his students an isolated phenomenon1 or a notion not logically linked with others4 ,to him each chemical compound is one in a series which connects it directly with many other similar compounds1 and indirectly with other more or less dissimilar compounds4 ,amid the overwhelming mass of facts which threaten nowadays to bury the science of chemistry1 and crush the life out of it by their weight1 ,dumas tracks his way by the aid of general principles2 but these principles are themselves generalized from the facts1 and are not the offspring of his own fancy4 ,we have1 ,i think1 found that throughout the progress of chemical science two dangers have beset the student4 ,he has been often tempted to accumulate facts1 to amass analytical details1 to forget that he is a chemist in his desire to perfect the instrument of analysis by the use of which he raises the scaffolding of his science2 on the other hand1 he has been sometimes allured from the path of experiment by his own day-dreams4 ,the discoveries of science have been so wonderful1 and the conceptions of some of those who have successfully prosecuted science have been so grand1 that the student has not unfrequently been tempted to rest in the prevailing theories of the day1 and1 forgetting that these ought only to afford peaceful lodgings to the intellect for the time1 he has rather allowed them to circumscribe it1 until at last the mind finds difficulty in breaking down the walls of what has become its prison1 instead of its home4 ,we may think that ,dumas fell perhaps slightly into the former of these errors1 when he did not allow his imagination a little more scope in dealing with the conception of atom and molecule1 the difference between which he had apprehended but not sufficiently marked by the year #ahbf 7see p4 #bfa74 ,we know1 from his own testimony1 that ,liebig once fell into the latter error and that the consequences were disastrous4 ,i know a chemist--meaning himself--who 444 undertook an investigation of the liquor from the salt-works4 ,he found iodine in it1 and observed1 moreover1 that the iodide of starch turned a fiery yellow by standing over-night4 ,the phenomenon struck him2 he saturated a large quantity of the liquor with chlorine1 and obtained from this1 by distillation1 a considerable quantity of a liquid which coloured starch yellow1 and externally resembled chloride of iodine1 but differed from this compound in many properties4 ,he explained1 however1 every discrepancy with satisfaction to himself2 he contrived for himself a theory4 ,several months later1 he received a paper of ,m4 ,balard's1 announcing the discovery of bromine1 and on that same day he was able to publish the results of experiments on the behaviour of bromine with iron1 platinum1 and carbon2 for ,balard's bromine stood in his laboratory1 labelled liquid chloride of iodine4 ,since that time he makes no more theories unless they are supported and confirmed by trustworthy experiments2 and ,i can positively assert that he has not fared badly by so doing4 ,another point which we notice in the life-work of these two chemists is their untiring labour4 ,they were always at work2 wherever they might be1 they were ready to notice passing events or natural phenomena1 and to draw suggestions from these4 ,as ,davy proved the elementary character of iodine and established many of the properties of this substance during a visit to ,paris1 so we find ,dumas making many discoveries during brief visits paid to his friends' laboratories when on excursions away from ,paris4 ,during a visit to ,aix-les-,bains1 he noticed that the walls of the bath-room were covered with small crystals of sulphate of lime4 ,the waters of the bath1 he knew1 were charged with sulphuretted hydrogen1 but they contained no sulphuric acid1 nor could that acid be detected in the air of the bath-rooms4 ,this observation was followed up by experiments which proved that a porous material1 such as a curtain or an ordinary plastered wall1 is able to bring about the union of oxygen with sulphuretted hydrogen1 provided moisture be present and a somewhat high temperature be maintained4 ,again1 we find ,liebig and ,dumas characterized by great mental honesty4 ,there is no harm in a man committing mistakes1 said ,liebig1 but great harm indeed in his committing none1 for he is sure not to have worked4444 ,an error you have become cognizant of1 do not keep in your house from night till morning4 ,students of science1 more than any other men1 ought to be ready to acknowledge and correct the errors into which they fall4 ,it is not difficult for them to do this3 they have only to be continually going to ,nature2 for there they have a court of appeal always ready to hear their case1 and to give an absolutely unbiased judgment3 they have but to bring their theories and guesses to this judge to have them appraised at their true value4 ,,footnotes3 #ac ,in reviewing once more the facts elicited by our inquiry1 we find them arranged around a common centre1 a group of atoms preserving intact its nature1 amid the most varied associations with other elements4 ,this stability1 this analogy1 pervading all the phenomena1 has induced us to consider this group as a sort of compound element1 and to designate it by the special name of benzoyl4--,liebig and ,woehler1 #ahcb4 #ad ,animal ,chemistry1 or ,chemistry in its ,applications to ,physiology and ,pathology1 #ahdb4 ,researches on the ,chemistry of ,food1 #ahdg4 ,the ,natural ,laws of ,husbandry1 #ahfb4 ,,chapter ,,vii4 ,,modern ,,chemistry4 ,on p4 #afb ,i referred to the work of the ,german chemist ,richter1 by which the equivalents of certain acids and bases were established4 ,those quantities of various acids which severally neutralized one and the same quantity of a given base1 or those quantities of various bases which severally neutralized one and the same quantity of a given acid1 were said to be equivalent4 ,these were the quantities capable of performing a certain definite action4 ,in considering the development of ,dumas's substitution theory1 we found that ,laurent retained this conception of equivalency when he spoke of an equivalent of hydrogen being replaced by an equivalent of chlorine 7see p4 #bgb74 ,a certain weight of chlorine was able to take the place and play the part of a certain weight of hydrogen in a compound2 these weights1 of hydrogen and chlorine1 were therefore equivalent4 ,this conception has been much used since ,laurent's time1 but it has for the most part been applied to the atoms of the elements4 ,hydrogen being taken as the standard substance1 the elements have been divided into groups1 in accordance with the number of hydrogen atoms with which one atom of each element is found to combine4 ,thus certain elements combine with hydrogen only in the proportion of one atom with one atom2 others combine in the proportion of one atom with two atoms of hydrogen2 others in the proportion of one atom with three atoms of hydrogen1 and so on4 ,the adjective monovalent1 divalent1 trivalent1 etc41 is prefixed to an element to denote that the atom of this element combines with one1 or two1 or three1 etc41 atoms of hydrogen to form a compound molecule4 ,let us consider what is implied in this statement--,the nitrogen atom is trivalent4 ,this statement1 if amplified1 would run thus3 ,one atom of nitrogen combines with three atoms of hydrogen to form a compound molecule4 ,now1 this implies 7#a7 that the atomic weight of nitrogen is known1 and 7#b7 that the molecular weight1 and the number of nitrogen and hydrogen atoms in the molecule1 of a compound of nitrogen and hydrogen are also known4 ,but before the atomic weight of an element can be determined1 it is necessary 7as we found on p4 #adf7 to obtain1 analyze1 and take the specific gravities of a series of gaseous compounds of that element4 ,the smallest amount of the element 7referred to hydrogen as unity7 in the molecule of any one of these gases will then be the atomic weight of the element4 ,when it is said that the molecular weight1 and the number of nitrogen and hydrogen atoms in the molecule1 of a compound of nitrogen and hydrogen are known1 the statement implies that the compound in question has been obtained in a pure state1 has been analyzed carefully1 has been gasefied1 and that a known volume of the gas has been weighed4 ,when therefore we say that the nitrogen atom is trivalent1 we sum up a large amount of knowledge which has been gained by laborious experiment4 ,this classification of the elements into groups of equivalent atoms--which we owe to ,frankland1 ,williamson1 ,odling1 and especially to ,kekule--has been of much service especially in advancing the systematic study of the compounds of carbon4 ,it helps to render more precise the conception which has so long been gaining ground of the molecule as a definite structure4 ,a monovalent element is regarded as one the atom of which acts on and is acted on by only one atom of hydrogen in a molecule2 a divalent as one1 the atom of which acts on and is acted on by two atoms of hydrogen--or other monovalent element--in a molecule2 a trivalent element as one1 the atom of which acts on and is acted on by three atoms of hydrogen--or other monovalent element--in a molecule2 and so on4 ,the fact that there often exist several compounds of carbon1 the molecules of which are composed of the same numbers of the same atoms1 finds a partial explanation by the aid of this conception of the elementary atom as a little particle of matter capable of binding to itself a certain limited number of other atoms to form a compound molecule4 ,for if the observed properties of a compound are associated with a certain definite arrangement of the elementary atoms within the molecules of that compound1 it would seem that any alteration in this arrangement ought to be accompanied by an alteration in the properties of the compound2 in other words1 the existence of more than one compound of the same elements united in the same proportions becomes possible and probable4 ,i have said that such compounds exist3 let me give a few examples4 ,the alchemists poured a stream of mercury on to molten sulphur1 and obtained a black substance1 which was changed by heat into a brilliantly red-coloured body4 ,we now know that the black and the red compounds alike contain only mercury and sulphur1 and contain these elements united in the same proportions4 ,hydrogen1 carbon1 nitrogen and oxygen unite in certain proportions to produce a mobile1 colourless1 strongly acid liquid1 which acts violently on the skin1 causing blisters and producing great pain3 if this liquid is allowed to stand for a little time in the air it becomes turbid1 begins to boil1 gets thicker1 and at last explodes1 throwing a white pasty substance about in all directions4 ,this white solid is inodorous1 is scarcely acid to the taste1 and does not affect the skin2 yet it contains the same elements1 united in the same proportions1 as were present in the strongly acid1 limpid liquid from which it was produced4 ,two substances are known each containing carbon and hydrogen united in the same proportions3 one is a gas with strong and irritating odour1 and exerting a most disagreeable action on the eyes2 the other is a clear1 limpid1 pleasant-smelling liquid4 ,phosphorus is a very poisonous substance3 it readily takes fire in the air at ordinary temperatures1 so that it must be kept under water2 but a modification of phosphorus is known1 containing no form of matter other than phosphorus1 which is non-poisonous1 does not take fire easily1 and may be handled with safety4 ,once more1 there is a compound of nitrogen and oxygen which presents the appearance of a deep-red1 almost black gas2 there is also a compound of nitrogen and oxygen which is a clear1 colourless gas2 yet both contain the same elements united in the same proportions4 ,but a detailed consideration of isomerism1 i4e4 the existence of more than one compound built up of the same amounts of the same elements yet possessing different properties1 would lead us too far from the main path of chemical advance which we wish to trace4 ,the chemist is to-day continually seeking to connect the properties of the bodies he studies with the molecular structures of these bodies2 the former he can observe1 a knowledge of the latter he must gain by reasoning on the results of operations and experiments4 ,his guide--the guide of ,lavoisier and his successors--is this3 ,similarity of properties is associated with similarity of composition--by composition he generally means molecular composition4 ,many facts have been amassed of late years which illustrate the general statement that the properties of bodies are connected with the composition of those bodies4 ,thus a distinct connection has been traced between the tinctorial power and the molecular composition of certain dye-stuffs2 in some cases it has even become possible to predict how a good dye-stuff may be made--to say that1 inasmuch as this or that chemical reaction will probably give rise to the production of this or that compound1 the atoms in the molecule of which we believe to have a certain arrangement relatively to one another1 so this reaction or that will probably produce a dye possessed of strong tinctorial powers4 ,the compound to the presence of which madder chiefly owes its dyeing powers is called alizarine2 to determine the nature of the molecular structure of this compound was1 for many years1 the object of the researches of chemists2 at last1 thanks especially to the painstaking zeal of two ,german chemists1 it became fairly clear that alizarine and a compound of carbon and hydrogen1 called anthracene1 were closely related in structure4 ,anthracene was obtained from alizarine1 and1 after much labour1 alizarine was prepared from anthracene4 ,anthracene is contained in large quantities in the thick pitch which remains when coal-tar is distilled2 this pitch was formerly of little or no value1 but as soon as the chemical manufacturer found that in this black objectionable mass there lay hidden enormous stores of alizarine1 he no longer threw away his coal-tar pitch1 but sold it to the alizarine manufacturer for a large sum4 ,thus it has come to pass that little or no madder is now cultivated2 madder-dyeing is now done by means of alizarine made from coal-tar3 large tracts of ground1 formerly used for growing the madder plant1 are thus set free for the growth of wheat and other cereals4 ,this discovery of a method for preparing alizarine artificially stimulated chemists to make researches into the chemical composition1 and if possible to get to know something about the molecular structure of indigo4 ,those researches have very recently resulted in the knowledge of a series of reactions whereby this highly valuable and costly dye-stuff may be prepared from certain carbon compounds which1 like anthracene1 are found in coal-tar4 ,these examples1 while illustrating the connection that exists between the composition and the properties of bodies1 also illustrate the need there is for giving a scientific chemical training to the man who is to devote his life to chemical manufactures4 ,pure and applied science are closely connected2 he who would succeed well in the latter must have a competent and a practical knowledge of the former4 ,that composition--molecular composition--and properties are closely related is generally assumed1 almost as an axiom1 in chemical researches nowadays4 ,lavoisier defined acids as substances containing oxygen2 ,davy regarded an acid as a compound the properties of which were conditioned by the nature and by the arrangement of all the elements which it contained2 ,liebig spoke of acids as substances containing replaceable hydrogen2 the student of the chemistry of the carbon compounds now recognizes in an organic acid a compound containing hydrogen1 but also carbon and oxygen1 and he thinks that the atoms of hydrogen 7or some of these atoms7 in the molecule of such a compound are1 in some way1 closely related to atoms of oxygen and less closely to atoms of carbon1 within that molecule1--in other words1 the chemist now recognizes that1 for carbon compounds at any rate1 acids are acid not only because they contain hydrogen1 but also because that hydrogen is related in a definite manner within the molecule to other elementary atoms2 he recognizes that the acid or non-acid properties of a compound are conditioned1 not only by the nature of the elements which together form that compound1 but also by the arrangement of these elements4 ,davy's view of the nature of acids is thus confirmed and at the same time rendered more definite by the results of recent researches4 ,the physical student is content to go no further than the molecule2 the properties of bodies which he studies are regarded1 for the most part1 as depending on the size1 the nature1 and perhaps the grouping together of molecules4 ,but the chemist seeks to go deeper than this4 ,the molecule is too large a piece of matter for him2 the properties which he studies are conceived by him to be principally conditioned by the nature1 the number1 and the arrangement of the parts of the molecule--of the atoms which together build up the molecule4 ,in these elementary atoms he has1 for the present1 found the materials of which the heavens and the earth are made2 but facts are being slowly gained which render it probable that these atoms are themselves structures--that they are built up of yet smaller parts1 of yet simpler kinds of matter4 ,to gather evidence for or against this supposition1 the chemist has been obliged to go from the earth to the heavens1 he has been obliged to form a new science1 the science of spectroscopic analysis4 ,this subject has been considered in ,the ,astronomers1 belonging to this series of books2 but the point of view from which the matter is there regarded is astronomical rather than chemical4 ,i should like briefly to recall to the reader the fundamental facts of this branch of science4 ,illustration3 ,fig4 #d4 ,when a ray of light is allowed to pass through a glass prism and then fall on to a white surface1 the image produced on this surface consists of a many-coloured band of light4 ,the blue or violet part of this band is more bent away from the plane of the entering ray than the orange part1 and the latter more than the red part of the band4 ,this is roughly represented in ,fig4 #d1 where r is the ray of light passing through the prism ,p1 and emerging as a sevenfold band of coloured lights1 of which the violet1 ,v1 is most1 and the red band1 ,r1 is least bent away from the plane of the ray r4 ,if the surface--say a white screen--on which the many-coloured band of light1 or spectrum1 falls1 is punctured by a small hole1 so as to admit the passage of the violet1 or blue1 or orange1 or red light only1 and if this violet1 etc41 light is then passed through a second prism1 no further breaking up of that light takes place4 ,this state of matters is represented in the part of the figure towards the right hand1 where the red ray1 ,r1 is shown as passing through the screen1 and falling on to a second prism1 ,p'3 the red ray is slightly bent out of its direct course1 but is not subdivided2 it falls on the second screen as a ray of red light1 ,r'4 ,but if a quantity of the metal sodium is vaporized in a hot non-luminous flame1 and if the yellow light thus produced is passed through a prism1 a spectrum is obtained consisting of a single yellow line 7on a dark background71 situated on that part of the screen where the orange-yellow band occurred when the ray of sunlight was split up by the action of the prism4 ,in ,fig4 #e the yellow light from a flame containing sodium is represented by the line ,y4 ,the light emitted by the glowing sodium vapour is said to be monochromatic4 ,illustration3 ,fig4 #e ,lastly1 if the experiment is arranged so that a ray of sunlight or of light from an electric lamp passes through a layer of comparatively cool sodium vapour before reaching the prism1 a spectrum is produced corresponding to the solar spectrum except that a black line appears in the position where the yellow line1 characteristic of sodium1 was noticed in the second experiment4 ,illustration3 ,fig4 #f4 ,fig4 #f represents the result of this experiment3 the ray of sunlight or electric light1 r1 passes through a quantity of sodium vapour1 and is then decomposed by the prism2 the spectrum produced is marked by the absence of light 7or by a dark line7 where the yellow line1 ,y1 was before noticed4 ,these are the fundamental facts of spectroscopic analysis3 sunlight is decomposable into a band of many colours1 that is1 into a spectrum2 light emitted by a glowing vapour is characterized by the presence of coloured lines1 each of which occupies a definite position with reference to the various parts of the solar spectrum2 sunlight--or the electric light--when allowed to pass through a mass of vapour1 furnishes a spectrum characterized by the absence of those bright lines1 the presence of which marked the spectrum of the light obtained by strongly heating the vapour through which the sunlight has passed4 ,the spectrum obtained by decomposing the light emitted by glowing vapour of potassium is characterized by the presence of certain lines--call them ,a and ,b lines4 ,we are asked what element 7or elements7 is present in a certain gas presented to us3 we pass a beam of white light through this gas and then through a prism1 and we obtain a continuous spectrum 7i4e4 a spectrum of many colours like the solar spectrum7 with two dark lines in the same positions as those occupied by the lines ,a and ,b4 ,we therefore conclude that the gas in question contains vapour of potassium4 ,the solar spectrum1 when carefully examined1 is found to be crossed by a very large number of fine black lines2 the exact positions of many hundreds of these lines have been carefully determined1 and1 in most cases1 they are found to correspond to the positions of various bright lines noticed in the spectra of the lights emitted by hot vapours of various elementary bodies4 ,assume that the sun consists1 broadly speaking1 of an intensely hot and luminous central mass1 formed to a large extent of the elementary substances which build up this earth1 and that this central mass is surrounded by a cooler 7but yet very hot7 gaseous envelope of the same elements1--and we have a tolerably satisfactory explanation of the principal phenomena revealed by the spectroscopic study of the sun's light4 ,on this assumption the central mass of glowing iron1 chromium1 magnesium1 nickel1 cobalt1 hydrogen1 etc41 is sending out light2 a portion of the light emitted by the glowing iron is quenched as it passes through a cloud of cooler iron vapour outside the central mass1 a portion of the light emitted by the glowing chromium is quenched as it passes through a cloud of cooler chromium vapour1 and so on2 the black lines in the spectrum are the records of these various quenchings of this and that light4 ,so far then the study of the solar spectrum appears to be tolerably simple1 and this study generally confirms the proposition that the material of which the sun is composed is1 broadly1 identical with those forms of matter which we1 on this earth1 call the chemical elements4 ,but whatever be the composition of the sun1 it is1 ,i think1 evident that in dealing with a ray of light coming therefrom1 we are dealing with a very complex phenomenon4 ,according to the hypothesis which is now guiding us1 the solar light which passes into our spectroscope has probably had its beginning in some central part of the sun1 and has passed through very thick layers of hot metallic clouds1 agitated perhaps by solar cyclones4 ,could we examine the light coming from some defined part of the sun1 we should probably obtain valuable information4 ,during a solar eclipse red prominences are seen projecting beyond the dark shadow of the moon1 which covers the sun's disc4 ,analysis of the light emitted by these prominences has shown that they are phenomena essentially belonging to the sun itself1 and that they consist of vast masses of intensely hot1 glowing gaseous substances1 among which hydrogen is present in large quantities4 ,that these prominences are very hot1 hotter than the average temperature of the ordinary solar atmosphere1 is proved by the fact that the spectrum of the light coming from them is characterized by bright lines4 ,by special arrangements which need not be discussed here1 but which have been partly explained in ,the ,astronomers 7see pp4 #ccd1 #cce of that book71 it has been shown that these prominences are in rapid motion3 at one moment they shoot up to heights of many thousand miles1 at another they recede towards the centre of the sun4 ,we thus arrive at a picture of the solar atmosphere as consisting of layers of very hot gases1 which are continually changing their relative positions and forms2 sometimes ejections of intensely hot1 glowing gases occur1--we call these prominences2 sometimes down-rushes of gaseous matter occur1--we call these spots4 ,among the substances which compose the gaseous layers we recognize hydrogen1 iron1 magnesium1 sodium1 nickel1 chromium1 etc41 but we also find substances which can at present be distinguished only by means of the wave-lengths of the light which they emit2 thus we have #adgd stuff1 #ejag stuff1 #ecfi stuff1 etc4 ,let us now turn to another part of this subject4 ,by a special arrangement of apparatus it is possible to observe the spectrum of the light emitted by a glowing vapour1 parts of which are hotter than other parts1 and to compare the lines in the spectrum of the light coming from the hottest parts with the lines in the spectrum of the light coming from the cooler parts of the vapour4 ,if this is done for sodium vapour1 certain lines are apparent in all the spectra1 others only in the spectrum of the light coming from the hottest parts of the sodium vapour3 the former lines are called long lines1 the latter short lines4 ,a rough representation of the long and short lines of sodium is given in ,fig4 #g4 ,illustration3 ,fig4 #g4--,long and short lines of sodium4 ,now1 suppose that the lines in the spectrum of the light emitted by glowing manganese vapour have been carefully mapped1 and classed as long and short lines3 suppose that the same thing has been done for the iron lines3 now let a little manganese be mixed with much iron1 let the mixture be vaporized1 and let the light which is emitted be decomposed by the prism of a spectroscope1 it will be found that the long lines of manganese alone make their appearance2 let a little more manganese be added to the mixture1 and now some of the shorter lines due to manganese begin to appear in the spectrum4 ,hence it has been concluded by ,lockyer that if the spectrum of the light emitted by the glowing vapour of any element--call it ,a--is free from the long lines of any other element--say element ,b--this second element is not present as an impurity in the specimen of element ,a which is being examined4 ,lockyer has applied this conclusion to purify various elementary spectra4 ,the spectrum of element ,a is carefully mapped1 and the lines are divided into long and short lines1 according as they are noticed in the spectrum of the light coming from all parts of the glowing vapour of ,a1 or only in the spectrum of the light which comes from the hotter parts of that vapour4 ,the spectra of elements ,b and ,c are similarly mapped and classified3 then the three spectra are compared2 the longest line in the spectrum of ,b is noted1 if this line is found in the spectrum of ,a1 it is marked with a negative sign--this means that so far as the evidence of this line goes ,b is present as an impurity in ,a2 the next longest ,b line is searched for in the spectrum of ,a--if present it also is marked with a negative sign2 a similar process of comparison and elimination is conducted with the spectra of ,a and ,c4 ,in this way a purified spectrum of the light from ,a is obtained--a spectrum1 that is1 from which1 according to ,lockyer1 all lines due to the presence of small quantities of ,b and ,c as impurities in ,a have been eliminated4 ,illustration3 ,fig4 #h4 ,fig4 #h is given in order to make this purifying process more clearly understood4 ,but when this process has been completed there remain1 in many cases1 a few short lines common to two or more elementary spectra3 such lines are called by ,lockyer basic lines4 ,he supposes that these lines are due to light emitted by forms of matter simpler than our elements2 he thinks that at very high temperatures some of the elements are decomposed1 and that the bases of these elements are produced and give out light1 which light is analyzed by the spectroscope4 ,such short basic lines are marked in the spectra represented in ,fig4 #h with a positive sign4 ,now1 if the assumption made by ,lockyer be admitted1 viz4 that the short lines1 or some of the short lines1 which are coincident in the purified spectra of various elements1 are really due to light emitted by forms of matter into which our so-called elements are decomposed at very high temperatures1 it follows that such lines should become more prominent in the spectra of the light emitted by elements the higher the temperature to which these elements are raised4 ,but we know 7see p4 #cjh7 that the prominences around the sun's disc are hotter than the average temperature of the solar atmosphere2 hence the spectrum of the light coming from these prominences ought to be specially rich in basic lines3 this supposition is confirmed by experiment4 ,lockyer has also shown that it is the basic1 and not the long lines1 which are especially affected in the spectra of light coming from those parts of the solar atmosphere which are subjected to the action of cyclones1 i4e4 which are at abnormally high temperatures4 ,and finally1 a very marked analogy has been established between the changes in the spectrum of the light emitted by a compound substance as the temperature is raised1 and the substance is gradually decomposed into its elements1 and the spectrum of the light emitted by a so-called elementary substance as the temperature of that substance is increased4 ,but it may be urged that ,lockyer's method of purifying a spectrum is not satisfactory2 that1 although all the longer lines common to two spectra are eliminated1 the coincident short lines which remain are due simply to very minute quantities of one element present as an impurity in the larger quantity of the other4 ,further1 it has been shown that several of the so-called basic lines are resolved1 by spectroscopes of great dispersive power1 into groups of two or more lines1 which lines are not coincident in different spectra4 ,and moreover it is possible to give a fairly satisfactory explanation of the phenomena of solar chemistry without the aid of the hypothesis that our elements are decomposed in the sun into simpler forms of matter4 ,nevertheless this hypothesis has a certain amount of experimental evidence in its favour2 it may be a true hypothesis4 ,i do not think we are justified at present either in accepting it as the best guide to further research1 or in wholly rejecting it4 ,the researches to which this hypothesis has given rise have certainly thrown much light on the constitution of the sun and stars1 and they have also been instrumental in forcing new views regarding the nature of the elements on the attention of chemists1 and so of awakening them out of the slumber into which every class of men is so ready to fall4 ,the tale told by the rays of light which travel to this earth from the sun and stars has not yet been fully read1 but the parts which the chemist has spelt out seem to say that1 although the forms of matter of which the earth is made are also those which compose the sun and stars1 yet in the sun and stars some of the earthly elements are decomposed1 and some of the earthly atoms are split into simpler forms4 ,the tale1 ,i say1 told by the rays of light seems to bear this interpretation1 but it is written in a language strange to the children of this earth1 who can read it as yet but slowly2 for the name given to the new science was ,ge-,urania1 because its production was of earth and heaven4 ,and it could not taste of death1 by reason of its adoption into immortal palaces2 but it was to know weakness1 and reliance1 and the shadow of human imbecility2 and it went with a lame gait2 but in its going it exceeded all mortal children in grace and swiftness4 ,there are certain little particles so minute that at least sixty millions of them are required to compose the smallest portion of matter which can be seen by the help of a good microscope4 ,some of these particles are vibrating around the edge of an orb a million times larger than the earth1 but at a distance of about ninety millions of miles away4 ,the student of science is told to search around the edge of the orb till he finds these particles1 and having found them1 to measure the rates of their vibrations2 and as an instrument with which to do this he is given--a glass prism6 ,but he has accomplished the task2 he has found the minute particles1 and he has measured their vibration-periods4 ,chemistry is no longer confined to this earth3 the chemist claims the visible universe as his laboratory1 and the sunbeams as his servants4 ,davy decomposed soda and potash by using the powerful instrument given him by ,volta2 but the chemist to-day has thrown the element he is seeking to decompose into a crucible1 which is a sun or a star1 and awaits the result4 ,the alchemists were right4 ,there is a philosopher's stone2 but that stone is itself a compound of labour1 perseverance1 and genius1 and the gold which it produces is the gold of true knowledge1 which shall never grow dim or fade away4 ,,chapter ,,viii4 ,,summary ,,and ,,conclusion4 ,we have thus traced some of the main paths along which ,chemistry has advanced since the day when1 ceasing to be guided by the dreams of men who toiled with but a single idea in the midst of a world of strange and complex phenomena1 she began to recognize that ,nature is complex but orderly1 and so began to be a branch of true knowledge4 ,in this review we have1 ,i think1 found that the remark made at the beginning of the introductory chapter is1 on the whole1 a just one4 ,that the views of the alchemists1 although sometimes very noble1 were vague and fanciful is surely borne out by the quotations from their writings given in the first chapter4 ,this period was followed by that wherein the accurate1 but necessarily somewhat narrow conception of the ,lavoisierian chemistry prevailed4 ,founded for the most part on the careful1 painstaking1 and quantitative study of one phenomenon--a very wide and far-reaching phenomenon1 it is true--it was impossible that the classification introduced by the father of chemical science should be broad enough to include all the discoveries of those who came after him4 ,but although this classification had of necessity to be revised and recast1 the genius of ,lavoisier enunciated certain truths which have remained the common possession of every chemical system4 ,by proving that however the forms of matter may be changed the mass remains unaltered1 he for the first time made a science of chemistry possible4 ,he defined element once for all1 and thus swept away the fabric of dreams raised by the alchemists on the visionary foundation of earth1 air1 fire and water1 or of mercury1 sulphur and salt4 ,by his example1 he taught that weighings and measurements must be made before accurate knowledge of chemical reactions can be hoped for2 and by his teaching about oxygen being the acidifier--although we know that this teaching was erroneous in many details--he showed the possibility of a system of classification of chemical substances being founded on the actually observed properties and composition of those substances4 ,lavoisier gained these most important results by concentrating his attention on a few subjects of inquiry4 ,that chemistry might become broad it was necessary that it should first of all become narrower4 ,the period when the objects of the science were defined and some of its fundamental facts and conceptions were established1 was succeeded1 as we saw in our sketch1 by that in which ,dalton departed somewhat from the method of investigation adopted by most masters in science1 and by concentrating his great mental powers on facts belonging to one branch of natural knowledge1 elaborated a simple but very comprehensive theory1 which he applied to explain the facts belonging to another branch of science4 ,chemistry was thus endowed with a grand and far-reaching conception1 which has been developed and applied by successive generations of investigators3 but we must not forget that it was the thorough1 detailed work of ,black and ,lavoisier which made possible the great theory of ,dalton4 ,at the time when ,dalton was thinking out his theory of atoms1 ,davy was advancing as a conqueror through the rich domain which the discovery of ,volta had opened to chemistry4 ,dalton1 trained to rely on himself1 surrounded from his youth by an atmosphere in which sweetness and light did not predominate1 thrown on the world at an early age1 and obliged to support himself by the drudgery of teaching when he would fain have been engaged in research1 and at the same time--if we may judge from his life as recorded by his biographers--without the sustaining presence of such an ideal as could support the emotional part of his nature during this time of struggle1--,dalton1 we found1 withdrew in great part from contact with other scientific workers1 and communing only with himself1 developed a theory which1 while it showed him to be one in the chain of thinkers that begins in ,democritus and ,leucippus1 was nevertheless stamped with the undeniable marks of his own individuality and genius1 and at the same time was untouched by any of the hopes or fears1 and unaffected by any of the passions1 of our common humanity4 ,davy1 on the other hand1 was surrounded from childhood by scenes of great natural beauty and variety1 by contact with which he was incited to eager desire for knowledge1 while at the same time his emotions remained fresh and sensitive to outward impressions4 ,entering on the study of natural science when there was a pause in the march of discovery1 but a pause presageful of fresh advances1 he found outward circumstances singularly favourable to his success2 seizing these favourable circumstances he made rapid advances4 ,like ,lavoisier1 he began his work by proving that there is no such thing in ,nature as transmutation1 in the alchemical meaning of the term2 as ,lavoisier had proved that water is not changed into earth1 so did ,davy prove that acid and alkali are not produced by the action of the electric current on pure water4 ,we have shortly traced the development of the electro-chemical theory which ,davy raised on the basis of experiment2 we have seen how facts obliged him to doubt the accepted view of the composition of hydrochloric acid and chlorine1 and how by the work he did on these subjects chemists have been finally convinced that an element is not a substance which cannot be1 but a substance which has not been decomposed1 and how from this work has also arisen the modern theory of acids1 bases and salts4 ,we found that1 by the labours of the great ,swede ,j4 ,j4 ,berzelius1 the ,daltonian theory was confirmed by a vast series of accurate analyses1 and1 in conjunction with a modification of the electro-chemical theory of ,davy1 was made the basis of a system of classification which endeavoured to include all chemical substances within its scope4 ,the atom was the starting-point of the ,berzelian system1 but that chemist viewed the atom as a dual structure the parts of which held together by reason of their opposite electrical polarities4 ,berzelius1 we saw1 greatly improved the methods whereby atomic weights could be determined1 and he recognized the importance of physical generalizations as aids in finding the atomic weights of chemical substances4 ,but ,berzelius came to believe too implicitly in his own view of ,nature's working2 his theory became too imperious4 ,chemists found it easier to accept than to doubt an interpretation of facts which was in great part undeniably true1 and which formed a central luminous conception1 shedding light on the whole mass of details which1 without it1 seemed confused and without meaning4 ,if the dualistic stronghold was to be carried1 the attack should be impetuous1 and should be led by men1 not only of valour1 but also of discretion4 ,we found that two champions appeared1 and that1 aided by others who were scarcely inferior soldiers to themselves1 they made the attack1 and made it with success4 ,but when the heat of the battle was over and the bitterness of the strife forgotten1 it was found that1 although many pinnacles of the dualistic castle had been shattered1 the foundation and great part of the walls remained2 and1 strange to say1 the men who led the attack were content that these should remain4 ,the atom could no longer be regarded as always composed of two parts1 but must be looked on rather as one whole1 the properties of which are defined by the properties and arrangements of all its parts2 but the conception of the atom as a structure1 and the assurance that something could be inferred regarding that structure from a knowledge of the reactions and general properties of the whole1 remained when ,dumas and ,liebig had replaced the dualism of ,berzelius by the unitary theory of modern chemistry2 and these conceptions have remained to the present day1 and are now ranked among the leading principles of chemical science2 only we now speak of the molecule where ,berzelius spoke of the atom4 ,along with these advances made by ,dumas1 ,liebig and others in rendering more accurate the general conception of atomic structure1 we found that the recognition of the existence of more than one order of small particles was daily gaining ground in the minds of chemists4 ,the distinction between what we now call atoms and molecules had been clearly stated by ,avogadro in #ahaa2 but the times were not ripe4 ,the mental surroundings of the chemists of that age did not allow them fully to appreciate the work of ,avogadro4 ,the seed however was sown1 and the harvest1 although late1 was plentiful4 ,we saw that ,dumas accepted1 with some hesitation1 the distinction drawn by ,avogadro1 but that failing to carry it to its legitimate conclusion1 he did not reap the full benefit of his acceptance of the principle that the smallest particle of a substance which takes part in a physical change divides into smaller particles in those changes which we call chemical4 ,to ,gerhardt and ,laurent we owe the full recognition1 and acceptance as the foundation of chemical classification1 of the atom as a particle of matter distinct from the molecule2 they first distinctly placed the law of ,avogadro--,equal volumes of gases contain equal numbers of molecules--in its true position as a law1 which1 resting on physical evidence and dynamical reasoning1 is to be accepted by the chemist as the basis of his atomic theory4 ,to the same chemists we are indebted for the formal introduction into chemical science of the conception of types1 which1 as we found1 was developed by ,frankland1 ,kekule1 and others1 into the modern doctrine of equivalency of groups of elementary atoms4 ,we saw that1 in the use which he made of the laws of ,mitscherlich1 and of ,dulong and ,petit1 ,berzelius recognized the importance of the aid given by physical methods towards solving the atomic problems of chemistry2 but among those who have most thoroughly availed themselves of such aids ,graham must always hold a foremost place4 ,graham devoted the energies of his life to tracking the movements of atoms and molecules4 ,he proved that gases pass through walls of solid materials1 as they pass through spaces already occupied by other gases2 and by measuring the rapidities of these movements he showed how it was possible to determine the rate of motion of a particle of gas so minute that a group of a hundred millions of them would be invisible to the unassisted vision4 ,graham followed the molecules as in their journeyings they came into contact with animal and vegetable membranes2 he found that these membranes presented an insuperable barrier to the passage of some molecules1 while others passed easily through4 ,he thus arrived at a division of matter into colloidal and crystalloidal4 ,he showed what important applications of this division might be made in practical chemistry1 he discussed some of the bearings of this division on the general theory of the molecular constitution of matter1 and thus he opened the way which leads into a new territory rich in promise to him who is able to follow the footsteps of its discoverer4 ,other investigators have followed on the general lines laid down by ,graham2 connections1 more or less precise1 have been established between chemical and physical properties of various groups of compounds4 ,it has been shown that the boiling points1 melting points1 expansibilities by heat1 amounts of heat evolved during combustion1 in some cases tinctorial powers of dye-stuffs1 and other physical constants of groups of compounds1 vary with variations in the nature1 number and arrangements of the atoms in the molecules of these compounds4 ,but although much good work has been done in this direction1 our ignorance far exceeds our knowledge regarding the phenomena which lie on the borderlands between chemistry and physics4 ,it is probably here that chemists look most for fresh discoveries of importance4 ,as each branch of natural science becomes more subdivided1 and as the quantity of facts to be stored in the mind becomes daily more crushing1 the student finds an ever-increasing difficulty in passing beyond the range of his own subject1 and in gaining a broad view of the relative importance of the facts and the theories which to him appear so essential4 ,in the days when the foundation of chemistry was laid by ,black1 ,priestley1 ,lavoisier and ,dalton1 and when the walls began to be raised by ,berzelius and ,davy1 it was possible for one man to hold in his mental grasp the whole range of subjects which he studied4 ,even when ,liebig and ,dumas built the fabric of organic chemistry the mass of facts to be considered was not so overpowering as it is now4 ,but we have in great measure ourselves to blame2 we have of late years too much fulfilled ,liebig's words1 when he said1 that for rearing the structure of organic chemistry masters were no longer required--workmen would suffice4 ,and ,i think we have sometimes fallen into another error also4 ,most of the builders of our science--notably ,lavoisier and ,davy1 ,liebig and ,dumas--were men of wide general culture4 ,chemistry was for them a branch of natural science2 of late years it has too much tended to degenerate into a handicraft4 ,these men had lofty aims2 they recognized--,davy perhaps more than any--the nobility of their calling4 ,the laboratory was to them not merely a place where curious mixtures were made and strange substances obtained1 or where elegant apparatus was exhibited and carefully prepared specimens were treasured2 it was rather the entrance into the temple of ,nature1 the place where day by day they sought for truth1 where1 amid much that was unpleasant and much that was necessary mechanical detail1 glimpses were sometimes given them of the order1 harmony and law which reign throughout the material universe4 ,it was a place where1 stopping in the work which to the outsider appeared so dull and even so trivial1 they sometimes1 listening with attentive ear1 might catch the boom of the mighty waters rolling evermore1 and so might return refreshed to work again4 ,chemistry was more poetical1 more imaginative then than now2 but without imagination no great work has been accomplished in science4 ,when a student of science forgets that the particular branch of natural knowledge which he cultivates is part of a living and growing organism1 and attempts to study it merely as a collection of facts1 he has already ,esau-like sold his birthright for a mess of pottage2 for is it not the privilege of the scientific student of ,nature always to work in the presence of something which he can never know to the full1 but which he is always going on to know--to be ever encompassed about by the greatness of the subject which he seeks to know8 ,does he not recognize that1 although some of the greatest minds have made this study the object of their lives1 the sum of what is known is yet but as a drop in the ocean8 and has he not also been taught that every honest effort made to extend the boundaries of natural knowledge must advance that knowledge a little way8 ,it is not easy to remember the greatness of the issues which depend on scientific work1 when that work is carried on1 as it too often is1 solely with the desire to gain a formal and definite answer to some question of petty detail4 ,that low man seeks a little thing to do1 ,sees it and does it3 ,this high man1 with a great thing to pursue1 ,dies ere he knows it4 ,that low man goes on adding one to one1 ,his hundred's soon hit3 ,this high man1 aiming at a million1 ,misses a unit4 ,,index4 ,a ,acids1 connected by ,lavoisier with oxygen1 #ia2 ,boyle's and other early definitions1 #aga2 opposed in early medicine to alkalis1 #agb2 grouped1 #agc2 salts1 #agc2 the primordial acid1 #agd2 oxygen not a necessary constituent1 #ahd2 new division of acids by ,davy1 #bje2 acids of different basicity1 #bcg2 modern conception of acids1 #cja4 ,affinity1 chemical1 apparently suspended by electricity1 #aia2 history of term affinity1 #bjf2 tables of1 #bjg2 dependent on electric states1 #baj4 ,air1 composition of1 determined by ,cavendish1 #gi2 ,dalton's investigations1 #aaf4 ,alchemy1 #e2 alchemical symbols of metals1 #aa2 quotations from alchemists1 #ae1 #ag2 alchemical poetry1 #ah4 ,alcoates1 #bce4 ,alkalis1 #aga2 fixed and volatile1 #agc2 mild and caustic1 examined by ,black1 #agf2 connection with earths1 #agh2 name of base given by ,rouelle1 #agi2 ,gay-,lussac's alkalizing principle1 #bjc4 ,ammonia1 discovered by ,priestley1 #ff4 ,atmolysis1 #bdc4 ,atomic theory1 dawn of1 #aag2 early views of ,greek philosophers1 #abc2 of ,epicurus and ,lucretius1 #abd2 of ,newton and ,bernoulli1 #abe2 ,dalton's new views--combination in simple multiples1 #abg1 et seq42 the theory made known by ,dr4 ,thomson1 #abi2 it is opposed at first by ,davy1 #acj2 ,dalton's rules for arriving at atomic weights1 #acb2 more accurately applied by ,berzelius1 #acc1 #afb2 diagrams of atoms1 #aah1 #acf2 the theory as carried out by ,gay-,lussac and ,avogadro1 #ach1 et seq42 conception of the molecule1 #adj2 molecular and atomic weight1 #ade2 ,graham's work on molecular reactions1 #bdi2 ,berzelius's dualistic views1 #bab2 they are attacked by ,dumas1 #bfj2 conception of the compound radicle1 #bfg2 ,laurent's unitary theory1 #bgb2 modern conception of molecule1 #bge2 revision of atomic weights1 #bhe2 equivalency of atoms1 #bie4 ,avogadro1 his elucidation of the atomic theory1 #ach1 et seq42 introduces the idea of molecules1 #adj2 law known as ,avogadro's law1 #adc4 ,b ,base 7of salts71 #agi2 basic lines in spectrum1 #caa4 ,becher1 ,john ,j41 born at ,speyer1 #bf2 his three principles of metals1 #bf2 his principle of inflammability1 #dh2 his views on acids1 #agd4 ,berthollet1 analyzes ammonia1 #ff2 adheres to the ,lavoisierian theory of combustion1 #ie2 questions doctrine of fixity of composition1 #abf2 and necessary presence of oxygen in acids1 #ahd2 shows variable nature of affinities1 #bjh4 ,berzelius1 ,johann ,j41 #ajf2 determines weights of elementary atoms1 #acc2 his birth and education1 #aeg2 works at ,stockholm1 #aei2 his slight appliances and large discoveries1 #afa2 he reviews ,dalton's atomic theory1 #afb2 his views superseded by ,avogadro's generalization1 #afe2 he accepts law of isomorphism1 #aff2 and ,davy's discovery of chlorine1 #bjd2 his views on affinity of atoms1 #bji2 his dual classification1 #bab2 works at organic chemistry1 #bbj2 his dualism attacked by ,dumas1 #bfj4 ,black1 ,joseph1 born at ,bordeaux1 #cj2 his education1 #ca2 his thesis on magnesia and discovery of fixed air1 #cc1 et seq42 inquiries into latent heat1 #ci2 professor at ,edinburgh1 #da2 his death and character1 #da1 et seq42 resume of his work1 #ajb2 his examination of alkalis1 #agf4 ,boyle1 ,hon4 ,robert1 #be2 his ,sceptical ,chymist1 #gf2 law known as ,boyle's law1 #gg2 opposes doctrine of elementary principles1 #ic2 his definition of an acid1 #aga2 extends the knowledge of salts1 #agg4 ,bromine1 discovered by ,balard1 #bia4 ,c ,carbonic acid gas1 or fixed air1 studied by ,black1 #ce2 by ,priestley1 #eg1 #fi4 ,cavendish1 ,hon4 ,henry1 rediscovers hydrogen1 #fc1 #gh2 and composition of water and air1 #gh4 ,chloral1 produced by ,liebig1 composition determined by ,dumas1 #bgc4 ,chloroform1 ,chlorine1 discovered by ,davy1 #bjb2 replaces hydrogen in organic compounds1 #bga4 ,colloids1 #bdg4 ,combination in multiple proportions1 #abg4 ,combustion1 studied by early chemists1 #bd 7vide ,phlogistic theory72 studied by ,black1 #dg2 his views of ,lavoisier's theory1 #ea2 ,priestley's views of combustion1 #fb2 ,lavoisier's experiments1 #hc1 et seq42 ,liebig's combustion-tube1 #bfc4 ,compound radicle1 #bfg2 the idea of substitution1 #bgj1 #bgf4 ,conservation of mass1 doctrine of1 #hb4 ,crystallization1 water of1 #bcg4 ,crystalloids1 #bdg4 ,d ,dalton1 ,john1 his birth and education1 #ajg2 answers to correspondents1 #aji2 his meteorological observations1 #aaj2 teaches at ,manchester1 #aaj2 colour-blind1 #aaa2 pressures of gaseous mixtures1 #aac2 strives after general laws1 #aae2 first view of atomic theory1 #aag2 visits ,paris1 #abj2 honours conferred on him1 #aba1 #abb2 dies1 #abc2 consideration of atomic theory 7which see71 #abc1 et seq42 his ,new ,system of ,chemical ,philosophy1 #abi2 fixes atomic weight of hydrogen1 #acj2 small use he makes of books1 #adh2 inaccurate as an experimenter1 #adi2 his method compared with ,priestley's1 #aea4 ,davy1 ,sir ,humphry1 #ajf2 opposes the atomic theory1 #abi2 accepts same1 #acj2 studies the chemical aspects of electricity1 #ahe2 experiments on the acid and alkali said to be produced by electrolyzing water1 #ahf2 apparent suspension of chemical affinities by action of electricity1 #aia2 discovers potassium1 #aig2 and sodium1 #aih2 the metallic bases of earths1 #bjj2 proves the elementary nature of chlorine1 #bjb2 ,davy's birth and youth1 #bae2 experiments on heat1 #bag2 his work at ,bristol1 #bah2 inhales gases1 #bbj2 lectures at the ,royal ,institution1 #bbb2 discovers iodine and invents safety-lamp1 #bbd2 dies1 #bbf4 ,dialysis1 #bdg4 ,diffusion-rates of gases1 #bda2 distinguished from transpiration-rates1 #bdb2 diffusion-rates of liquids1 #bde4 ,dulong1 his law of atomic heat1 #afh4 ,dumas1 ,jean ,b4 ,a41 birth and education1 #beg2 physiological studies1 #beh2 meets ,von ,humboldt1 #bei2 attacks the dualism of ,berzelius1 #bfj2 ,dumas's vapour density process1 #bfb2 ethers and alcohols1 #bfe2 chlorine in connection with organic compounds1 #bga2 determines composition of chloral and chloroform1 #bgc2 studies fermentation1 #bhg2 member of the ,national ,assembly1 #bhh2 takes office1 #bhi4 ,e ,earths1 #agg2 ,stahl's views1 #agh2 the connection between earths and alkalis1 #agh2 their metallic bases1 #ahb1 #bjj4 ,economy of waste materials1 #cjj4 ,electric affinity1 #aia1 #baj4 ,electricity1 ,volta's battery1 #ahe2 used to decompose water1 #ahe2 new metals discovered by its help1 #aig4 ,elements3 old doctrine of elementary principles opposed by ,boyle1 #ic2 modern definition of element1 #ie 7vide ,spectroscopic analysis--basic lines1 #caa74 ,equivalency1 conception of1 #bid4 ,f ,fermentation1 studied by ,dumas1 #bhg4 ,fourcroy1 calls ,lavoisier's views ,la chimie ,francaise11 #ie ,g ,gay-,lussac1 #ach1 #adc1 #bja1 #bjc1 #beg4 ,gerhardt1 #bgb1 #bgi4 ,graham1 ,thomas1 early life1 #bcc2 made ,master of the ,mint1 #bcd2 his death1 #bce2 studies alcoates1 #bce2 formulates conception of acids of different basicity1 #bcg2 considers hydrogen a metal1 #bch2 investigates phenomena observed by ,doebereiner1 #bdj2 diffusion-rates of gases1 #bda2 of liquids1 #bde2 his atmolyzer1 #bdc2 his dialyzer1 #bdg2 studies movements and reactions of molecules1 #bdi4 ,h ,hales's experiments on gases1 #cd4 ,heat1 ,black's study of latent heat1 #ci2 specific heat1 #ih2 ,dalton lectures on1 #aag2 law of capacity for heat1 #afh2 heat as produced by friction1 #bag4 ,helmholtz1 #adc2 vortex atoms1 #abe4 ,hooke1 ,robert1 his ,micographia1 #bd2 studies combustion1 #cd4 ,humboldt1 ,alexander von1 assists ,liebig1 #bef2 and ,dumas1 #bei4 ,hydrochloric acid discovered by ,priestley1 #ff2 a stumbling-block to ,lavoisierian chemists1 #bjj2 studied by ,davy1 #bja4 ,hydrogen1 rediscovered by ,cavendish1 #fc2 experimented on by ,priestley1 #ff2 its atomic weight decided by ,dalton1 #acj2 ,graham considers it a metal1 #bch4 ,i ,iodine1 discovered by ,davy1 #bbd4 ,isomerism1 #big4 ,isomorphism1 law of1 #afg4 ,l ,laplace1 assists ,lavoisier1 #ij4 ,latent heat1 ,black's theory of1 #ci4 ,laurent1 his unitary theory1 #bgb1 #bgh4 ,lavoisier1 ,antoine ,l41 born at ,paris1 #gi2 confutes idea of transmutation1 #ha2 paper on calcination of tin1 #hd2 meets ,priestley1 #fa1 #he2 his theory of combustion1 #ea1 #hf2 his chemical nomenclature1 #if2 he is guillotined1 #ii2 resume of his work1 #ajc2 his views on salts1 #ahc1 #ahd4 ,liebig1 ,justus1 birth1 #bef2 ,humboldt and ,gay-,lussac1 #beg2 his improved combustion-tube1 #bfc2 studies the cyanates1 #bfd2 distinction between organic and inorganic chemistry effaced1 #bfe2 produces chloroform and chloral1 #bgc2 benzoyl1 #bgd2 he leaves ,giessen for ,munich1 #bhj2 his practical and economic discoveries1 #bhc2 death1 #bhd2 his failure to discover bromine1 #bia4 ,lockyer1 his work with spectroscope1 #caj 7and vide ,spectroscopic analysis74 ,m ,mayow1 ,john1 studies combustion1 #bd4 ,metals1 new1 discovered by ,berzelius1 #aja2 by ,davy1 #aig2 hydrogen a metal1 #bch4 ,meyer1 his views on acids1 #agd4 ,mitscherlich's law of isomorphism1 #afg4 ,molecule1 conception of1 #adj2 molecular weight1 #ade2 molecular mobility of gases1 #bdb2 movements and reactions of molecules1 #bdi2 modern conception of1 #bge4 ,morveau1 ,de1 embraces ,lavoisier's views1 #if4 ,muriatic acid 7vide ,hydrochloric acid17 #aai4 ,n ,nitric acid1 discovered by ,priestley1 #fe2 produced by electrolysis1 #ahh4 ,nomenclature1 ,lavoisier's system of1 #if4 ,o ,oil1 principle of1 #bed4 ,organic chemistry1 worked at by ,berzelius1 #bbi2 attempts to define it1 #bec2 loose application of the term1 #bee2 ,woehler's manufacture of urea abolishes distinction of organic and inorganic chemistry1 #bfe4 ,oxygen discovered by ,priestley1 #ei2 ,lavoisier's experiments1 #hg2 it is viewed by him as an acidifier1 #ia1 #age2 ,berthollet shows it not a necessary constituent of acids1 #ahd 7vide ,acids74 ,p ,paracelsus1 #ac2 his pamphlet1 ,tripus ,aureus1 etc41 #ai4 ,petit1 #afh4 ,phlogistic theory1 #bf2 enunciated by ,stahl1 #bg2 abandoned by ,black1 #df2 phlogiston described as a kind of motion1 #di2 discovery of dephlogisticated air1 #ei2 the theory overthrown by ,lavoisier1 #ib4 ,phosphoric acid1 #hf4 ,pneumatic trough1 invented by ,priestley1 #eg4 ,potassium1 discovered by ,davy1 #aig4 ,prussic acid1 discovered by ,berthollet1 #ahd4 ,priestley1 ,joseph1 born1 #eb2 bred for the ministry1 #ec2 writes on electricity1 #ee2 his pneumatic trough1 #eg2 discovers oxygen1 #ei2 meets ,lavoisier1 #fa1 #he2 goes to ,birmingham1 #fe2 his experiments on hydrogen1 #ff2 his house burnt by rioters1 #ga2 emigrates to ,america1 #gb2 dies there1 #gc2 resume of his work1 #ajb2 his method compared with that of ,dalton1 #aea4 ,q ,quantitative analysis neglected by early chemists1 #bi2 first accurately employed by ,black1 #cc2 used by ,lavoisier1 #hg4 ,r ,respiration explained by ,lavoisier1 #ia4 ,revolution1 ,french1 its effect on ,priestley1 #gj2 ,lavoisier guillotined1 #ii4 ,richter's equivalents of acids and bases1 #afb4 ,ripley1 ,canon1 an alchemist1 his poems1 #ah4 ,rouelle1 invents term base1 #agi2 his studies on salts1 #aha4 ,s ,salts1 #agc2 principle of salt opposed by ,boyle1 #agg2 earth or alkali the base of salts1 #agi2 ,rouelle's inquiries1 #aha2 ,lavoisier's definition1 #ahd2 considered as metallic derivatives of acids1 #bje2 alcoholic salts1 #bce4 ,sceptical ,chymist1 ,the1 by ,hon4 ,robert ,boyle1 #gf-ic4 ,shelburne1 ,earl of1 patron of ,priestley1 #eh2 to whom he grants an annuity1 #fe4 ,spectroscopic analysis1 #cjb2 lines in solar spectrum1 #cjf2 the solar atmosphere1 #cjh2 ,lockyer's mapping of the lines1 #caj2 basic lines1 #caa2 objections to his hypothesis1 #cac4 ,stahl1 ,george ,ernest1 born at ,anspach1 #bg2 enunciates the phlogistic theory1 #bg1 #dh2 his primordial acid1 #agd2 his essential property of earths1 #agh4 ,sulphur dioxide1 discovered by ,priestley1 #ff4 ,sulphur salts1 discovered by ,berzelius1 #afa4 ,t ,transmutation1 confuted by ,lavoisier1 #ha4 ,transpiration of gases1 #bdb4 ,types1 #bgi4 ,v ,valentine1 ,basil1 an alchemist1 #ae2 his views on alkalis1 #agd4 ,van ,helmont1 #bd4 ,vitriols1 #ahj4 ,volta's electric pile1 #ahd4 ,w ,water1 its composition discovered by ,cavendish1 #fh-gh2 nearly discovered by ,priestley1 #fh2 confirmed by ,lavoisier1 #ij2 decomposed by electricity1 #ahe4 ,weight of ultimate particles1 #aag1 #acb2 molecular and atomic1 #ade2 revision of atomic weights1 #bhe4 ,woehler1 his account of visit to ,berzelius1 #afj1 #bjd1 #bbi2 studies cyanates with ,liebig1 #bfd2 results of his discovery as to urea1 #bfe4 ,wollaston1 supports atomic theory1 #acj4 ,,printed ,,by ,,william ,,clowes ,,and ,,sons1 ,,limited1 ,,london ,,and ,,beccles4