m 
 
 i 
 
HEROES OF SCIENCE, 
 
 CHEMISTS. 
 
 BY 
 
 M. M. PATTISON MUIR, M.A., F.R.S.E, 
 
 V* 
 
 FELLOW, AND PRELECTOR IN CHEMISTRY, OF GONVILLE 
 AND CAIUS COLLEGE, CAMBRIDGE. 
 
 PUBLISHED UNDER THE DIRECTION OF THE COMMITTEE 
 
 OF GENERAL LITERATURE AND EDUCATION APPOINTED BY THE 
 
 SOCIETY FOR PROMOTING CHRISTIAN KNOWLEDGE. 
 
 OF THE 
 
 UNIVERSITY 
 
 LONDON: 
 
 SOCIETY FOR PROMOTING CHRISTIAN KNOWLEDGE, 
 NORTHUMBERLAND AVENUE, CHARING CROSS; 
 
 43, QUEEN VICTORIA STREET, E.G. J 
 
 26, ST. GEORGE'S PLACE, HYDE PARK CORNER, s.w. 
 
 BRIGHTON : 135, NORTH STREET. 
 
 NEW YORK: E. & J. B. YOUNG & CO. 
 
 1883. 
 
"The discoveries of great men never leave us; they are immortal; they 
 contain those eternal truths which survive the shock of empires, outlive the 
 struggles of rival creeds, and witness the decay of successive religions." BUCKLE. 
 
 "He who studies Nature has continually the exquisite pleasure of discerning 
 or half discerning and divining laws ; regularities glimmer through an appear- 
 ance of confusion, analogies between phenomena of a different order suggest 
 themselves and set the imagination in motion ; the mind is haunted with the sense 
 of a vast unity not yet discoverable or nameable. There is food for contemplation 
 which never runs short ; you gaze at an object which is always growing clearer, 
 and yet always, in the very act of growing clearer, presenting new mysteries." 
 THE AUTHOR OF " ECCE HOMO." 
 
 "Je langer ich lebe, desto mehr verlern' ich das Gelernte, namlich die 
 Systeme." JEAN PAUL RICHTER. 
 
 
PREFACE. 
 
 I HAVE endeavoured in this book to keep to the 
 lines laid down for me by the Publication Com- 
 mittee of the Society, viz. "to exhibit, by selected 
 biographies, the progress of chemistry from the 
 beginning of the inductive method until the present 
 time." The progress of chemistry has been made 
 the central theme ; around this I have tried to 
 group short accounts of the lives of those who have 
 most assisted this progress by their labours. 
 
 This method of treatment, if properly conducted, 
 exhibits the advances made in science as intimately 
 connected with the lives and characters of those 
 who studied it, and also impresses on the reader 
 the continuity of the progress of natural knowledge. 
 
 
IV PREFACE. 
 
 The lives of a few chemists have been written ; of 
 others there are, however, only scanty notices to be 
 found. The materials for this book have been 
 collected chiefly from the following works : 
 
 Kopp's " Geschichte der Chemie." 
 
 Thomson's " History of Chemistry." 
 
 Ladenburg's " Entwickelungsgeschichte der Chemie." 
 
 Wurtz's " History of the Atomic Theory." 
 
 Watts's " Dictionary of Chemistry." 
 
 Whewell's "History of the Inductive Sciences." 
 
 RodwelPs " Birth of Chemistry ; " " Inquiry into the 
 Hermetic Mystery and Alchemy" (London, 1850) ; " Popular 
 Treatises on Science written during the Middle Ages," 
 edited for the Historical Society of Science by Thomas 
 Wright, M.A. (London, 1841); " Ripley Reviv'd ; or, An 
 Exposition upon Sir George Ripley's Hermetico-Poetical 
 Works," by Eirenaeus Philalethes (London, 1678); "Tripus 
 Aureus, hoc est Tres Tractates Chymici Selectissimi " 
 (Frankfurt, 1618). 
 
 " Alchemy ; " article in " Encyclopaedia Britannica." 
 
 Boyle's " Sceptical Chymist." 
 
 " Biographic Universelle ; " for notices of Berzelius and 
 Lavoisier. 
 
 " English Cyclopaedia ; " for notices of Black, Berzelius 
 and Lavoisier. 
 
 Black's "Lectures," with Memoir : edited by Dr. Robinson. 
 
 Priestley's " Memoirs : " written partly by himself. 
 
 Priestley's works on " Air," etc. 
 
 Lavoisier's " (Euvres." 
 
 Dalton's " Life," by Dr. Henry ; " Life," by Dr. R. Angus 
 Smith ; " New System of Chemical Philosophy." 
 
 Davy's " Collected Works ; " with Life, by his brother ; 
 " Life," by Dr. Paris, 
 
PREFACE. V 
 
 Berzelius's " Lehrbuch," and various dissertations. 
 Wohler's " Jugenderinnerungen eines Chemikers." 
 Graham's " Collected Memoirs." 
 
 Sketch of Graham's life, in Chemical Society's Journal. 
 " Life- Work of Liebig," by A. W. Hofmann. 
 " Dumas," by A. W. Hofmann. 
 
 Various dissertations by Liebig and Dumas in Annalen, 
 and elsewhere. 
 
 My warmest thanks are due to my friend, Mr. 
 Francis Rye, for the great assistance he has given 
 me in correcting the proof-sheets. 
 
 M. M. PATTISON MUIR. 
 
 CAMBRIDGE, April, 1883. 
 
CONTENTS. 
 
 PAGE 
 
 INTRODUCTORY ... ... ... ... ... i 
 
 CHAPTER I. 
 
 ALCHEMY : AND THE DAWN OF CHEMISTRY. 
 
 Beginnings of natural knowledge Chemistry in the Middle 
 
 Ages Alchemy The phlogistic theory ... ... 5 
 
 CHAPTER II. 
 
 ESTABLISHMENT OF CHEMISTRY AS A SCIENCE PERIOD 
 OF BLACK, PRIESTLEY AND LAVOISIER. 
 
 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 Lavoisier, the founder of the science of chemistry 
 He clearly establishes a connection between composition 
 and properties of bodies ... ... ... ... 3 
 
 CHAPTER III. 
 
 ESTABLISHMENT OF GENERAL PRINCIPLES OF CHEMICAL 
 SCIENCE PERIOD OF DALTON. 
 
 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 ... ... ... .... 106 
 
CONTENTS. Vll 
 
 CHAPTER IV. 
 
 ESTABLISHMENT OF GENERAL PRINCIPLES OF CHEMICAL 
 
 SCIENCE (continued} PERIOD OF DAVY AND BERZELIUS. 
 
 PAGE 
 
 Electro chemistry The dualistic theory developed by Berze- 
 lius Davy's work on acids, alkalis, and salts He proves 
 chlorine to be an element His discovery of the safety- 
 lamp ... ... ... ... ... ... 155 
 
 CHAPTER V. 
 
 THE WORK OF GRAHAM. 
 
 Graham traces the movements of molecules He distinguishes 
 
 between colloids and cystalloids Dialysis ... .., 232 
 
 CHAPTER VI. 
 
 RISE AND PROGRESS OF ORGANIC CHEMISTRY PERIOD 
 OF LIEBIG AND DUMAS. 
 
 The barrier between inorganic and organic chemistry begins 
 to be broken down Wohler prepares urea Dumas 
 opposes the dualistic system of Berzelius Liebig's con- 
 ception of compound radicles His work in animal and 
 agricultural chemistry ... ... ... ... 252 
 
 CHAPTER VII. 
 
 MODERN CHEMISTRY. 
 
 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 ... ... ... ... ... ... 294 
 
 CHAPTER VIII. 
 
 SUMMARY AND CONCLUSION ... ... ... ... 316 
 
OF THE 
 
 { UNIVERSITY ) 
 
 OF 
 
 : 
 
 HEROES OF SCIENCE 
 
 INTRODUCTORY. 
 
 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 accu- 
 rate and definite views of Nature. We find that as 
 man's conceptions of natural phenomena become 
 more accurate they also for a time become more 
 limited, but that this limitation is necessary in 
 order that facts may be correctly classified, and so 
 there may be laid the basis for generalizations which, 
 being definite, shall also be capable of expansion. 
 
 At first Nature is strange ; she is full of wonder- 
 ful and fearful appearances. Man is- overwhelmed 
 by the sudden and apparently irregular outbreaks 
 of storms, by the capricious freaks of thunder and 
 lightning, by the awful and unannounced devasta- 
 tions of the volcano or the earthquake ; he believes 
 himself to be surrounded by an invisible array of 
 
 III. B 
 
2 HEROES OF SCIENCE. 
 
 beings more powerful than himself, but, like himself, 
 changeable in their moods and easily provoked to 
 anger. 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 him. 
 
 The huntsman observes that certain kinds of 
 plants always grow where the game which he pursues 
 is chiefly to be found ; 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-boat ; 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 
 time. And thus man comes to believe that natural 
 events follow each other in a fixed order ; there 
 arises a conscious reference on his part of certain 
 effects to certain definite causes. Accurate know- 
 ledge has begun. 
 
 As knowledge of natural appearances advances 
 there comes a time when men devote themselves 
 chiefly to a careful study of some one class of 
 facts ; they try to consider that part of Nature 
 with which they are mostly concerned as separate 
 from all other parts of Nature. Thus the various 
 branches of natural knowledge begin to have each 
 a distinct existence. These branches get more 
 and more subdivided, each division is more accu- 
 rately studied, and so a great number of facts 
 is accumulated in many classes, Then we usually 
 
INTRODUCTORY. 3 
 
 find that a master mind arises, who shows the 
 connection which exists between the different parts 
 of each division of natural knowledge, who takes 
 a wide, far-reaching view of the whole range of the 
 province of knowledge which he studies, and who, 
 at the same time, is able to hold in his vision all 
 the important details of each branch of which that 
 province is composed. 
 
 And thus we again get wide views of Nature. 
 But these are very different from the vague, dim 
 and hesitating notions in which natural knowledge 
 had its beginnings. In this later time men see 
 that Nature is both simple and complex ; that she 
 is more wonderful than their fathers dreamed, 
 but that through all the complexity there runs a 
 definite purpose ; that the apparently separate 
 facts are bound together by definite laws, and that 
 to discover this purpose and these laws is possible 
 for man. 
 
 As we trace this progress in the various branches 
 of natural knowledge we are struck with the fact 
 that each important advance is generally accom- 
 plished by one or two leading men ; we find that 
 it becomes possible to group the history of each 
 period round a few central figures ; 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 man. 
 
 It will be my endeavour in the following pages 
 to give an account of the advance of chemical 
 science, grouping the facts in each stage of pro- 
 
4 HEROES OF SCIENCE. 
 
 gress round the figures of one or two men who 
 were prominent in that period. 
 
 For the purposes of this book it will be necessary 
 that I should sketch only the most important periods 
 in the story of chemical progress, and that in each 
 of these I should fill in the prominent points alone. 
 
 I shall therefore select three periods in the pro- 
 gress of this science, and try to give an account of 
 the main work done in each of these. And the 
 periods will be : 
 
 I. The period wherein, chiefly by the work of 
 Black, Priestley and Lavoisier, the aim of chemical 
 science was defined and the essential characters of 
 the phenomena to be studied were clearly stated. 
 
 II. The period during which, chiefly by the 
 labours of Dalton, Berzelius and Davy, the great 
 central propositions of the science were laid down 
 and were developed into a definite theory. As 
 belonging in great extent to this period, although 
 chronologically later, I shall also consider the work 
 of Graham. 
 
 III. The period when, chiefly owing to advances 
 made in organic chemistry, broader and more far- 
 reaching systems of classification were introduced, 
 and the propositions laid down in the preceding 
 period were modified and strengthened. The 
 workers in this period were very numerous ; I shall 
 chiefly consider these two Liebig and Dumas. 
 
 I shall conclude with a brief sketch of some 
 of the important advances of chemical science 
 in more recent times, and a summary of the cha- 
 racteristics of each of the three periods. 
 
CHAPTER I. 
 ALCHEMY: AND THE DAWN OF CHEMISTRY. 
 
 EARLY chemistry was not a science. The ancient 
 chemists dealt chiefly with what we should now 
 call chemical manufactures ; they made glass, 
 cleaned leather, dyed cloth purple and other colours, 
 extracted metals from their ores, and made alloys 
 of metals. No well-founded explanations of these 
 processes could be expected either from men who 
 simply used the recipes of their predecessors, or 
 from philosophers who studied natural science, not 
 by the help of accurate experiments, but by the 
 unaided light of their own minds. 
 
 At somewhat later times chemistry assumed a 
 very important place in the general schemes pro- 
 pounded by philosophers. 
 
 Change is vividly impressed on all man's sur- 
 roundings : the endeavour to find some resting- 
 place amidst the chaos of circumstances, some 
 unchanging substance beneath the ever-changing 
 
6 HEROES OF SCIENCE. 
 
 appearances of things, has always held a prominent 
 place with those who study the phenomena of the 
 world which surrounds them. In the third and 
 fourth centuries of our era much attention was 
 given to the art which professed to explain the 
 changes of Nature. Religion, philosophy, and 
 what we should now call natural science, were at 
 that time closely intermingled ; the scheme of 
 things which then, and for several centuries after 
 that time, 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 
 universe. 
 
 Thus, in the Emerald Table of Hermes, which 
 was held in much repute in the Middle Ages, we 
 read 
 
 " True, without error, certain and most true : 
 that which is above is as that which is below, 
 and that which is below is as that which is above, 
 for performing the miracles of the One Thing ; and 
 as all things were from one, by the mediation of 
 one, so all things arose from this one thing by 
 adaptation : the father of it is the Sun, the mother 
 of it is the Moon, the wind carried it in its belly, 
 the nurse of it is the Earth. This is the father 
 of all perfection, the consummation of the whole 
 world." 
 
 And again, 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 matter, 
 
ALCHEMY : AND THE DAWN OF CHEMISTRY. 7 
 
 which, being discovered and brought by art to 
 perfection, converts to itself proportionally all im- 
 perfect bodies that it touches." 
 
 To discover this fundamental principle, this One 
 Thing, became the object of all research. Earth 
 and the heavens were supposed to be bound to- 
 gether by the all-pervading presence of the One 
 Thing ; he who should attain to a knowledge of 
 this precious essence would possess all wisdom. 
 To the vision of those who pursued the quest for 
 the One Thing the whole universe was filled by one 
 ever-working spirit, concealed now by this, now by 
 that veil of sense, ever escaping identification in 
 any concrete form, yet certainly capable of being 
 apprehended by the diligent searcher. 
 
 Analogy was the chief guide in this search. If 
 it were granted that all natural appearances were 
 manifestations of the activity of one essential 
 principle, then the vaguest and most far-fetched 
 analogies between the phenomena of nature might, 
 if properly followed up, lead to the apprehension 
 of this hidden but everywhere present essence. 
 
 The history of alchemy teaches, in the most 
 striking manner, the dangers which beset this 
 method of pursuing the study of Nature ; this 
 history teaches us that analogies, unless founded 
 on carefully and accurately determined facts, are 
 generally utterly misleading in natural science. 
 
 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 
 
8 HEROES OF SCIENCE. 
 
 that transmutation of one kind of matter into 
 another is of constant occurrence in Nature. 
 
 The alchemist heated a quantity of water in an 
 open glass vessel ; the water slowly disappeared, 
 and when it was all gone there remained in the 
 vessel a small quantity of a white earthy solid 
 substance. What could this experiment teach 
 save that water was changed into earth and air ? 
 The alchemist then plunged a piece of red-hot iron 
 into water placed under a bell-shaped glass vessel ; 
 some of the water seemed to be changed into 
 air, and a candle, when brought into the bell, caused 
 the air therein to take fire. Therefore, concluded 
 the experimenter, water is proved to be changeable 
 into fire. 
 
 A piece of lead was then strongly heated in the 
 air ; it lost its lustre and became changed into a 
 reddish-white powder, very unlike lead in its pro- 
 perties ; this powder was then heated in a con- 
 venient vessel with a little wheat, whereupon the 
 lead was again produced. Therefore, said the 
 alchemist, lead is destroyed by fire, but it can be 
 reproduced from its ashes by the help of heat and 
 a few grains of corn. 
 
 The experimenter would now proceed to heat 
 a quantity of a mineral containing lead in an open 
 vessel made of pulverized bones ; the lead slowly 
 disappeared, and at the close of the experiment a 
 button of silver remained. Might he not trium- 
 phantly assert that he had transmuted lead into 
 silver ? 
 
ALCHEMY : AND THE DAWN OF CHEMISTRY. Q 
 
 In order that the doctrine of the transmutation 
 of metals might rest on yet surer evidence, the 
 alchemist placed a piece of copper in spirits of 
 nitre (nitric acid) ; the metal disappeared ; into the 
 green liquid thus produced he then placed a piece 
 of iron ; the copper again made its appearance, 
 while the iron was removed. He might now well 
 say that if lead was thus demonstrably changed 
 into silver, and copper into iron, it was, to say the 
 least, extremely probable that any metal might be 
 changed into any other provided the proper means 
 for producing the change could be discovered. 
 
 But the experimental alchemist had a yet 
 stranger transmutation wherewith to convince the 
 most sceptical. He poured mercury in a fine stream 
 on to melted sulphur ; at once the mercury and the 
 sulphur disappeared, and in their place was found 
 a solid substance black as the raven's wing. He 
 then heated this black substance in a closed vessel, 
 when it also disappeared, and in its place there 
 was found, deposited on the cooler part of the 
 vessel, a brilliantly red-coloured solid. This experi- 
 ment taught lessons alike to the alchemist, the 
 philosopher, and the moralist of these times. The 
 alchemist learned that to change one kind of matter 
 into another was an easy task : the philosopher 
 learned that the prevalence of change or trans- 
 mutation is one of the laws of Nature : and the 
 moralist learned that evil is not wholly evil, but 
 contains also some germs of good ; for was not 
 the raven-black substance emblematical of the evil, 
 
IO HEROES OF SCIENCE. 
 
 and the red-coloured matter of the good principle 
 of things ? * 
 
 On such experimental evidence as this the 
 building of alchemy was reared. A close relation- 
 ship was believed to prevail through the whole 
 phenomena of Nature. What more natural then 
 than to regard the changes which occur among the 
 forms of matter on this earth as intimately con- 
 nected with the changes which occur among the 
 heavenly bodies ? 
 
 Man has ever been overawed by the majesty of 
 the stars ; yet he has not failed to notice that the 
 movements of these bodies are apparently capri- 
 cious. The moon has always been to him a type 
 of mutability ; only in the sun has he seemed to 
 find a settled resting-point. Now, when we re- 
 member that in the alchemical scheme of things 
 the material earth and material heavens, the in- 
 tellectual, the moral, and the spiritual world were 
 regarded as one great whole, the parts of which 
 were continuously acting and reacting on each 
 other, we cannot wonder that the alchemist should 
 regard special phenomena which he observed in 
 his laboratory, or special forms of matter which he 
 examined, as being more directly than other pheno- 
 mena or other forms of matter, under the influence 
 of the heavenly bodies. This connection became 
 gradually more apparent to the student of alchemy, 
 
 * I have borrowed these illustrations of the alchemical experi- 
 mental method from M. Hoefer's " Histoire de la Chimie," quoted 
 in the " Encyclopaedia Brittanica," art. " Alchemy." 
 
ALCHEMY : AND THE DAWN OF CHEMISTRY. 1 1 
 
 until at last it was fixed in the language and the 
 symbols which he employed. 
 
 Thus the sun (Sol) was represented by a circle, 
 which likewise became the symbol for gold, as 
 being the most perfect metal. The moon (Luna) 
 was ever changing ; she was represented by a half- 
 circle, which also symbolized the pale metal silver. 
 
 Copper and iron were regarded as belonging to 
 the same class of metals as gold, but their less 
 perfect nature was denoted by the sign -j- or f . 
 Tin and lead belonged to the lunar class, but like 
 copper they were supposed to be ^imperfect metals. 
 Mercury was at once solar and lunar in its pro- 
 perties. 
 
 These suppositions were summed up in such 
 alchemical symbols as are represented below 
 
 Sol. Luna. Venus. Mars. 
 
 o 
 
 Gold. Silver. /% Copper. Iron. 
 
 Jupiter. Saturn. 
 
 Lead. 
 
 Tin. 
 
 Mercury. 
 
 Quicksilver. 
 
12 HEROES OF SCIENCE. 
 
 Many of the alchemical names remain to the 
 present time ; thus in pharmacy the name " lunar 
 caustic " is applied to silver nitrate, and the symp- 
 toms indicative of lead-poisoning are grouped 
 together under the designation of "saturnine 
 cholic." 
 
 But as the times advanced the older and nobler 
 conception of alchemy became degraded. 
 
 If it be true, the later alchemists urged, that all 
 things suffer change, but that a changeless essence 
 or principle underlies all changing things, and that 
 the presence of more or less of this essence confers 
 on each form of matter its special properties, it 
 follows that he who can possess himself of this 
 principle will be able to transmute any metal into 
 any other; he will be able to change any metal 
 into gold. 
 
 Now, as the possession of gold has always carried 
 with it the means of living luxuriously, it is easy 
 to understand how, when this practical aspect of 
 alchemy had taken firm root in men's minds, the 
 pursuit of the art became for all, except a few 
 lofty and noble spirits, synonymous with the pur- 
 suit of wealth. So that we shall not, I think, 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 gold. In one 
 respect this was an advance. In the early days 
 of alchemy there had been too much trusting to 
 the mental powers for the manufacture of natural 
 facts : chemists now actually worked in labora- 
 
ALCHEMY: AND THE DAWN OF CHEMISTRY. 13 
 
 lories ; and very hard did many of these alchemists 
 work. 
 
 Paracelsus says of the alchemists, " They are 
 not given to idleness, nor go in a proud habit, or 
 plush and velvet garments, often showing their 
 rings upon their fingers, or wearing swords with 
 silver hilts by their sides, or fine and gay gloves 
 upon their hands ; but diligently follow their labours, 
 sweating whole days and nights by their furnaces. 
 They do not spend their time abroad for recreation, 
 but take delight in their laboratory. They put 
 their fingers amongst coals, into clay and filth, not 
 into gold rings. They are sooty and black like 
 smiths and miners, and do not pride themselves 
 upon clean and beautiful faces." By thus " taking 
 delight in their laboratories " the later alchemists 
 gathered together many facts ; but their work 
 centred round one idea, viz. that metals might all 
 be changed into gold, and this idea was the result 
 rather of intellectual guessing than of reasoning on 
 established facts of Nature. 
 
 One of the most famous alchemists of the Middle 
 Ages was born at Einsiedeln, in Switzerland, in 
 1493. His name, when paraphrased into Greek, 
 became Paracelsus. This man, some of whose 
 remarks have just been quoted, acquired great fame 
 as a medical practitioner, and also as a lecturer on 
 medicine : he travelled throughout the greater part 
 of Europe, and is supposed to have been taught 
 the use of several new medicines by the Arabian 
 physicians whom he met in Spain. With an over- 
 
14 HEROES OF SCIENCE. 
 
 weening sense of his own powers, with an ardent 
 and intemperate disposition, revolting against all 
 authority in medicine or science, Paracelsus yet 
 did a good work in calling men to the study of 
 Nature as the only means whereby natural science 
 could be advanced. 
 
 "Alchemy has but one aim and object," Para- 
 celsus taught : " to extract the quintessence of 
 things, and to prepare arcana and elixirs which 
 may serve to restore to man the health and sound- 
 ness he has lost." He taught that the visible 
 universe is but an outer shell or covering, that 
 there is a spirit ever at work underneath this veil 
 of phenomena ; but that all is not active : " to 
 separate the active function (the spirit) of this 
 outside shell from the passive " was, he said, the 
 proper province of alchemy. 
 
 Paracelsus strongly insisted on the importance 
 of the changes which occur when a substance 
 burns, and in doing this he prepared the way for 
 Stahl and the phlogistic chemists. 
 
 However we may admire the general conceptions 
 underlying the work of the earlier alchemists, we 
 must admit that the method of study which they 
 adopted could lead to very few results of lasting 
 value ; and I think we may add that, however 
 humble the speculations of these older thinkers 
 might appear, this humility was for the most part 
 only apparent. 
 
 These men were encompassed (as we are) by un- 
 explained appearances : they were every moment 
 
ALCHEMY: AND THE DAWN OF CHEMISTRY. 15 
 
 reminded that man is not "the measure of all 
 things;" and by not peering too anxiously into 
 the mysteries around them, by drawing vague con- 
 clusions from partially examined appearances, they 
 seemed at once to admit their own powerlessness 
 and the greatness of Nature. But I think we 
 shall find, as we proceed with our story, that this 
 is not the true kind of reverence, and that he is the 
 really humble student of Nature who refuses to 
 overlook any fact, however small, because he feels 
 the tremendous significance of every part of the 
 world of wonders which it is his business and his 
 happiness to explore. 
 
 As examples of the kind of explanation given 
 by alchemists of those aspects of Nature which they 
 professed to study, I give two quotations from 
 translations of the writings of Basil Valentine and 
 Paracelsus, who flourished in the first half of the 
 fifteenth and sixteenth centuries respectively. 
 
 " Think most diligently about this ; often bear 
 in mind, observe and comprehend that all minerals 
 and metals together, in the same time, and after 
 the same fashion, and of one and the same prin- 
 cipal matter, are produced and generated. That 
 matter is no other than a mere vapour, which is 
 extracted from the elementary earth by the supe- 
 rior stars, or by a sidereal distillation of the macro- 
 cosm ; which sidereal hot infusion, with an airy 
 sulphureous property, descending upon inferiors, 
 so acts and operates as that there is implanted, 
 spiritually and invisibly, a certain power and virtue 
 
1 6 HEROES OF SCIENCE. 
 
 in those metals and minerals ; which fume, more- 
 over, resolves in the earth into a certain water 
 wherefrom all metals are thenceforth generated 
 and ripened to their perfection, and thence pro- 
 ceeds this or that metal or mineral, according as 
 one of the three principles acquires dominion and 
 they have much or little of sulphur and salt, or 
 an unequal mixture of these ; whence some metals 
 are fixed, that is, constant or stable ; and some 
 are volatile and easily changeable, as is seen in 
 gold, silver, copper, iron, tin and lead." 
 
 " The life of metals is a secret fatness ; of salts, 
 the spirit of aqua fortis ; of pearls, their splendour ; 
 of marcasites and antimony, a tingeing metalline 
 spirit ; of arsenics, a mineral and coagulated 
 poison. The life of all men is nothing else but 
 an astral balsam, a balsamic impression, and a 
 celestial invisible fire, an included air, and a tinge- 
 ing spirit of salt. I cannot name it more plainly, 
 although it is set out by many names." 
 
 When the alchemists gave directions for making 
 the stone which was to turn all it touched into 
 gold, they couched them in such strange and 
 symbolical language as this : " After our serpent 
 has been bound by her chain, penetrated with the 
 blood of our green dragon, and driven nine or ten 
 times through the combustible fire into the elemen- 
 tary air, if you do not find her to be exceeding 
 furious and extremely penetrating, it is a sign that 
 you do not hit our subject, the notion of the 
 homogenea, or their proportion ; if this furious 
 
ALCHEMY: AND THE DAWN OF CHEMISTRY. 17 
 
 serpent does not come over in a cloud and turn 
 into our virgin milk, or argentine water, not corro- 
 sive at all and yet insensibly and invisibly de- 
 vouring everything that comes near it, it is plainly 
 to be seen that you err in the notion of our 
 universal menstruum." Or, again, what could any 
 reasonable man make of this ? " In the green lion's 
 bed the sun and moon are born ; they are married 
 and beget a king. The king feeds on the lion's 
 blood, which is the king's father and mother, 
 who are at the same time his brother and sister. 
 I fear I betray the secret, which I promised 
 my master to conceal in dark speech from any 
 one who knows not how to rule the philosopher's 
 fire." 
 
 Concerning the same lion, another learned author 
 says that " though 'called a lion, it is not an animal 
 substance, but for its transcendant force, and the 
 rawness of its origin, it is called the green lion." 
 But he adds in a moment of confidence : " This 
 horrid beast has so many names, that unless God 
 direct the searcher it is impossible to distinguish 
 him." 
 
 And once more. " Take our two serpents, which 
 are to be found everywhere on the face of the 
 earth : tie them in a love-knot and shut them up 
 in the Arabian caraha. This is the first labour ; 
 but the next is more difficult. Thou must encamp 
 against them with the fire of nature, and be sure 
 thou dost bring thy line round about. Circle them 
 in and stop all avenues that they find no relief. 
 
 III. C 
 
1 8 HEROES OF SCIENCE. 
 
 Continue this siege patiently, and they turn into 
 an ugly venomous black toad, which will be trans- 
 formed to a horrible devouring dragon, creeping 
 and weltering in the bottom of her cave without 
 wings. Touch her not by any means, for there is 
 not on earth such a vehement transcending poison. 
 As thou hast begun so proceed, and this dragon 
 will turn into a swan. Henceforth I will show 
 thee how to fortify thy fire till the phoenix appear : 
 it is a red bird of a most deep colour, with a shining 
 fiery hue. Feed this bird with the fire of his father 
 and the ether of his mother : for the first is meat 
 and the second is drink, and without this last he 
 attains not to his full glory. Be sure to understand 
 this secret," etc., etc. 
 
 The alchemists spoke of twelve gates through 
 which he who would attain to the palace of true 
 art must pass : these twelve gates were to be un- 
 locked by twelve keys, descriptions of which, 
 couched in strange and symbolical language, were 
 given in alchemical treatises. Thus in " Ripley 
 reviv'd"* we read that Canon Ripley, of Bridling- 
 ton, who lived in the time of Edward IV., sang 
 thus of the first gate, which was " Calcination : "- 
 
 " The battle's fought, the conquest won, 
 
 The Lyon dead reviv'd ; 
 The eagle's dead which did him slay> 
 And both of sense depriv'd. 
 
 * " Ripley reviv'd : or an exposition upon Sir George Ripley 's 
 Hermetico-poetical works," by Eirenreus Philalethes. London, 1678. 
 
ALCHEMY : AND THE DAWN OF CHEMISTRY. 19 
 
 The showers cease, the dews which fell 
 
 For six weeks do not rise ; 
 The ugly toad that did so swell 
 
 With swelling bursts and dies." 
 
 And of the third gate, or "Conjunction," we find 
 the Canon saying 
 
 " He was a king, yet dead as dead could be ; 
 
 His sister a queen, 
 
 Who when her brother she did breathless see. 
 The like was never seen, 
 
 She cryes 
 Until her eyes 
 
 With over-weeping were waxed dim 
 So long till her tears 
 Reach'd up to her ears : 
 The queen sunk, but the king did swim." 
 
 In some books these gates and keys are sym- 
 bolically represented in drawings, e.g. in a pamph- 
 let by Paracelsus, called " Tripus Aureus, hoc est 
 Tres Tractates chymici selectissimi." (Frankfurt, 
 1618.) 
 
 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 men ; and, at the same time, 
 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 everything. Granted that a man 
 
20 HEROES OF SCIENCE. 
 
 by "sweating whole days and nights by his fur- 
 naces" can acquire knowledge which gives him 
 great power over his fellows, it necessarily follows 
 that many will be found ready to undergo these 
 days and nights of toil. And when we find that 
 this supposed knowledge is hidden under a mask 
 of strange and mystical signs and language, we 
 may confidently assert that there will be many 
 who learn to repeat these strange terms and use 
 these mystical signs without attempting to pene- 
 trate to the truths which lie behind without, in- 
 deed, believing that the mystical machinery which 
 they use has any real meaning at all. 
 
 We find, as a matter of fact, that the age of 
 the alchemists produced many deceivers, who, by 
 mumbling incantations and performing a few 
 tricks, which any common conjuror would now 
 despise, were able to make crowds of men believe 
 that they possessed a supernatural power to con- 
 trol natural actions, and, under this belief, to make 
 them part with their money and their substance. 
 
 One respectable physician of the Hague, who 
 entertained a peripatetic alchemist, complains that 
 the man entered his " best-furnished room without 
 wiping his shoes, although they were full of snow 
 and dirt." However, the physician was rewarded, 
 as the stranger gave him, " out of his philosophical 
 commiseration, as much as a turnip seed in size " 
 of the much-wished-for stone of wisdom. 
 
 That the alchemist of popular belief was a man 
 who used a jargon of strange and high-sounding 
 
ALCHEMY: AND THE DAWN OF CHEMISTRY. 21 
 
 words, that he might the better deceive those whom 
 he pretended to help, is evident from the literature 
 of the sixteenth and seventeenth centuries. 
 
 In the play of the " Alchymist " Ben Jonson 
 draws the character of Subtle as that of a com- 
 plete scoundrel, whose aim is to get money from 
 the pockets of those who are stupid enough to 
 trust him, and who never hesitates to use the basest 
 means for this end. 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 gold. 
 
 ' ' Subtle. Name the vexations and the martyrizations of metals in 
 the work. 
 
 Face. Sir, putrefaction, 
 Solution, ablution, sublimation, 
 Cohobation, calcination, ceration, and 
 Fixation. 
 
 Snb. And when comes vivification? 
 
 Face. After mortification. 
 
 Sub. What's cohobation ? 
 
 Face. 'Tis the pouring on 
 Your aqua regis, and then drawing him off, 
 To the trine circle of the seven spheres. 
 
 ****** 
 
 Sub. And what's your mercury ? 
 Face. A very fugitive ; he will be gone, sir. 
 Sub. How know you him ? 
 Pace. By his viscosity, 
 His oleosity, and his suscitability. " 
 
 Even in the fourteenth century, Chaucer (in the 
 " Canon's Yeoman's Tale ") depicts the alchemist 
 as a mere cunning knave. A priest is prevailed 
 
22 HEROES OF SCIENCE. 
 
 on to give the alchemist money, and is told that 
 he will be shown the change of base metal into 
 gold. The alchemist busies himself with prepara- 
 tions, and sends the priest to fetch coals. 
 
 " And whil he besy was, this feendly wrecche, 
 This false chanoun (the foule feende him fecche) 
 Out of his bosom took a bechen cole 
 In which ful subtilly was maad an hole, 
 And therein put was of silver lymayle 
 An unce, and stopped was withoute fayle 
 The hole with wex, to keep the lymayle in. 
 And understondith, that this false gyn 
 Was not maad there, but it was maad before." 
 
 This " false gyn " having been put in the crucible 
 and burned with the rest of the ingredients, duly 
 let out its " silver lymayle " (filings), which appeared 
 in the shape of a small button of silver, and so 
 accomplished the " false chanoun's " end of de- 
 ceiving his victim. 
 
 The alchemists accumulated many facts : they 
 gained not a little knowledge concerning the 
 appearances of Nature, but they were dominated 
 by a single idea. Living in the midst of an ex- 
 tremely complex order of things, surrounded by a 
 strange and apparently capricious succession of 
 phenomena, they were convinced that the human 
 intelligence, directed and aided by the teachings 
 of the Church, would guide them through the 
 labyrinth. And so they entered on the study of 
 Nature with preconceived notions and foregone 
 conclusions : enthusiastic and determined to know 
 although many of them were, they nevertheless 
 
ALCHEMY: AND THE DAWN OF CHEMISTRY. 23 
 
 failed because they refused to tread the only path 
 which leads to true advances in natural science 
 the path of unprejudiced accurate experiment, and 
 of careful reasoning on experimentally determined 
 facts. 
 
 And even when they had become convinced that 
 their aims were visionary, they could not break 
 free from the vicious system which bound them. 
 
 " . . . I am broken and trained 
 To my old habits : they are part of me. 
 I know, and none so well, my darling ends 
 Are proved impossible : no less, no less, 
 Even now what humours me, fond fool, as when 
 Their faint ghosts sit with me and flatter me, 
 And send me back content to my dull round." * 
 
 One of the most commonly occurring and most 
 noticeable changes in the properties of matter is 
 that which proceeds when a piece of wood, or a 
 candle, or a quantity of oil burns. The solid wood, 
 or candle, or the liquid oil slowly disappears, and 
 this disappearance is attended with the visible for- 
 mation of flame. Even the heavy fixed metals, tin 
 or lead, may be caused to burn ; light is produced, 
 a part of the metal seems to disappear, and a white 
 (or reddish) solid, very different from the original 
 metal, remains. The process of burning presents 
 all those peculiarities which are fitted to strike an 
 observer of the changes of Nature ; that is, which 
 are fitted to strike a chemist for chemistry has 
 
 * Browning's " Paracelsus," 
 
24 HEROES OF SCIENCE. 
 
 always been recognized as having for its object to 
 explain the changes which matter undergoes. The 
 chemists of the seventeenth and eighteenth cen- 
 turies were chiefly occupied in trying to explain 
 this process of burning or combustion. 
 
 Van Helmbnt (1577-1644), who was a physician 
 and chemist of Brussels, clearly distinguished be- 
 tween common air and other " airs " or gases pro- 
 duced in different ways. Robert Hooke (1635- 
 1703), one of the original Fellows of the Royal 
 Society, in the " Micographia, or Philosophical 
 Description of Minute Bodies," published in 1665, 
 concluded from the results of numerous experiments 
 that there exists in common air a peculiar kind of 
 gas, similar to, or perhaps identical with the gas or 
 air which is got by heating saltpetre ; and he further 
 supposed that when a solid burns, it is dissolved by 
 (or we should now say, it is converted into a gas by 
 combining with) this peculiar constituent of the air. 
 
 John Mayow (1645-1679), a physician of Oxford, 
 experimented on the basis of facts established by 
 Hooke. He showed that when a substance, e.g. a 
 candle, burns in air, the volume of air is thereby 
 lessened. To that portion of the air which had 
 dissolved the burned substance he gave the name 
 of nitre-air, and he argued that this air exists in 
 condensed form in nitre, because sulphur burns 
 when heated with nitre in absence of common air. 
 Mayow added the most important fact a fact 
 , which was forgotten by many later experimenters 
 that the solid substance obtained by burning a metal 
 
ALCHEMY : AND THE DAWN OF CHEMISTRY. 25 
 
 in air weighs more than the metal itself did before 
 burning. He explained this increase in weight 
 by saying that the burning metal absorbs particles 
 of " nitre-air " from the atmosphere. Thus Hooke 
 and Mayow had really established the fact that 
 common air consists of more than one definite kind 
 of matter in other words, that common air is not an 
 element ; but until recent times the term " element " 
 or "elementary principle" was used without any 
 definite meaning. When we say that the ancients 
 and the alchemists recognized four elements 
 earth, air, fire, and water we do not attach to the 
 word " element " the same definite meaning as when 
 we now say, -"Iron is an element." 
 
 From earth, air, fire and water other substances 
 were obtained ; or it might be possible to resolve 
 other substances into one or more of these four. But 
 even to such a word as " substance " or " matter " no 
 very definite meaning could be attached. Although, 
 therefore, the facts set forth by Hooke and Mayow 
 might now justify the assertion that air is not an 
 element, they did not, in the year 1670, necessarily 
 convey this meaning to men's minds. The distinc- 
 tion between element and compound was much more 
 clearly laid down by the Hon. Robert Boyle (1627- 
 1691), whose chemical work was wonderfully accu- 
 rate and thorough, and whose writings are charac- 
 terized by acute scientific reasoning. We shall again 
 return to these terms " element " and " compound." 
 
 But the visible and striking phenomenon in most 
 processes of burning is the production of light and 
 
11 
 
 26 HEROES OF SCIENCE. 
 
 sometimes of flame. The importance of the fact 
 that the burned substance (when a solid) weighs 
 more than the unburned substance was over- 
 shadowed by the apparent importance of the out- 
 ward part of the process, which could scarcely be 
 passed over by any observer. There appears to be 
 an outrush of something from the burning substance. 
 There is an outrush of something, said Becher 
 and Stahl, and this something is the " principle of 
 fire." The principle of fire, they said, is of a very 
 subtle nature ; its particles, which are always in 
 very rapid motion, can penetrate any substance, 
 however dense. When metals burn the argu- 
 ment continued they lose this principle of fire ; 
 when the burned metal or calx as it was usually 
 called is heated with charcoal it regains this 
 "principle," and so the metal is re-formed from 
 the calx. 
 
 Thus arose the famous theory of phlogiston (from 
 Greek, " burned "), which served as a central 
 nucleus round which all chemical facts were grouped 
 for nearly a hundred years. 
 
 John Joachim Becher was born at Speyer in 
 1635, and died in 1682 ; in his chemical works, the 
 most important of which is the " Physica Subter- 
 ranea," he retained the alchemical notion that the 
 metals are composed of three " principles " the 
 nitrifiable, the combustible, and the mercurial and 
 taught that during calcination the combustible 
 and mercurial principles are expelled, while the 
 itrifiable remains in the calx. 
 
ALCHEMY : AND THE DAWN OF CHEMISTRY. 2/ 
 
 George Ernest Stahl born at Anspach in 1660, 
 and died at Berlin in 1734 had regard chiefly to 
 the principles which escape during the calcination 
 of metals, and simplifying, and at the same render- 
 ing more definite the idea of Becher, he conceived 
 and enunciated the theory of phlogiston. 
 
 But if something (name it " phlogiston " or call 
 it by any other name you please) is lost by a 
 metal when the metal is burned, how is it that the 
 loss of this thing is attended with an increase 
 in the weight of the matter which loses it ? Either 
 the theory of phlogiston must be abandoned, or 
 the properties of the thing called phlogiston must 
 be very different from those of any known kind of 
 matter. 
 
 Stahl replied, phlogiston is a " principle of 
 levity ; " the presence of phlogiston in a substance 
 causes that substance to weigh less than it did 
 before it received this phlogiston. 
 
 In criticizing this strange statement, we must 
 remember that in the middle of the seventeenth 
 centuiy philosophers in general were not firmly 
 convinced of the truth that the essential character 
 of matter is that it possesses weight, nor of the 
 truth that it is impossible to destroy or to create 
 any quantity of matter however small. It was not 
 until the experimental work of Lavoisier became 
 generally known that chemists were convinced of 
 these truths. Nevertheless, the opponents of the 
 Stahlian doctrine were justified in asking for further 
 explanations in demanding that some other facts 
 
28 HEROES OF SCIENCE. 
 
 analogous to this supposed fact, viz. that a sub- 
 stance can weigh less than nothing, should be ex- 
 perimentally established. 
 
 The phlogistic theory however maintained its 
 ground ; we shall find that it had a distinct 
 element of truth in it, but we shall also find that 
 it did harm to scientific advance. This theory was 
 a wide and sweeping generalization from a few 
 facts ; it certainly gave a central idea around which 
 some facts might be grouped, and it was not very 
 difficult, by slightly cutting down here and slightly 
 adding there, to bring many new discoveries within 
 the general theory. 
 
 We now know that in order to explain the 
 process of combustion much more accurate know- 
 ledge was required than the chemists of the seven- 
 teenth century possessed ; but we ought to be 
 thankful to these chemists, and notably to Stahl, 
 that they did not hesitate to found a generalization 
 on the knowledge they had. Almost everything 
 propounded in natural science has been modified 
 as man's knowledge of nature has become wider 
 and more accurate ; but it is because the scientific 
 student of nature uses the generalizations of to- 
 day as stepping-stones to the better theories 
 of to-morrow, that science grows " from more to 
 more." 
 
 Looking at the state of chemistry about the 
 middle of the eighteenth century, we find that 
 the experiments, and especially the measurements, 
 .of Hooke and Mayow had laid a firm basis of fact 
 
ALCHEMY : AND THE DAWN OF CHEMISTRY. 2Q 
 
 concerning the process of combustion, but that 
 the phlogistic theory, which appeared to contradict 
 these facts, was supreme ; that the existence of 
 airs, or gases, different from common air was 
 established, but that the properties of these airs 
 were very slightly and very inaccurately known ; 
 that Boyle had distinguished element from com- 
 pound and had given definite meanings to these 
 terms, but that nevertheless the older and vaguer 
 expression, "elementary principle," was generally 
 used ; and lastly, that very few measurements of 
 the masses of the different kinds of matter taking 
 part in chemical changes had yet been made. 
 
CHAPTER II. 
 
 ESTABLISHMENT OF CHEMISTRY AS A SCIENCE 
 PERIOD OF BLACK, PRIESTLEY AND LA- 
 VOISIER. 
 
 Joseph Black, 1728-1799. Joseph Priestley, 1733-1804. Antoinc 
 Laurent Lavoisier, 1743-1794. 
 
 DURING this period of advance, which may be 
 broadly stated as comprising the last half of the 
 eighteenth century, the aim and scope of chemical 
 science were clearly indicated by the labours of 
 Black, Priestley and Lavoisier. The work of these 
 men dealt chiefly with the process of combustion. 
 Black and Priestley finally proved the existence of 
 airs or gases different from common air, and La- 
 voisier applied these discoveries to give a clear ex- 
 planation of what happens when a substance burns. 
 
 JOSEPH BLACK was born near Bordeaux in the 
 year 1728. His father was of Scottish family, but a 
 native of Belfast ; his mother was the daughter of 
 Mr. Gordon, of Hilhead in Aberdeenshire. We 
 
FOUNDERS OF CHEMISTRY BLACK. 31 
 
 are told by Dr. Robison, in his preface to Black's 
 Lectures, that John Black, the father of Joseph, 
 was a man "of most amiable manners, candid 
 and liberal in his sentiments, and of no common 
 information." 
 
 At the age of twelve Black was sent home to a 
 school at Belfast ; after spending six years there 
 he went to the University of Glasgow in the year 
 1746. Little is known of his progress at school or 
 at the university, but judging from his father's 
 letters, which his son preserved, he seems to have 
 devoted himself to study. While at Glasgow he 
 was attracted to the pursuit of physical science, 
 and chose medicine as a profession. Becoming a 
 pupil of Dr. Cullen, he was much impressed 
 with the importance of chemical knowledge to 
 the student of medicine. Dr. Cullen appears to 
 have been one of the first to take large and philo- 
 sophical views of the scope of chemical science, and 
 to attempt to raise chemistry from the rank of a 
 useful art to that of a branch of natural philosophy, 
 Such a man must have been attracted by the young 
 student, whose work was already at once accurate 
 in detail and wide in general scope. 
 
 In the notes of work kept by Black at this time 
 are displayed those qualities of methodical arrange^ 
 ment, perseverance and thoroughness which are 
 so prominent in his published investigations 
 and lectures. In one place we find, says his bio* 
 grapher, many disjointed facts and records of 
 diverse observations, but the next time he refers 
 
32 HEROES OF SCIENCE. 
 
 to the same subjects we generally have analogous 
 facts noted and some conclusions drawn we have 
 the beginnings of knowledge. Having once entered 
 on an investigation Black works it out steadily 
 until he gets definite results. 
 
 His earlier notes are concerned chiefly with heat 
 and cold ; about 1752 he begins to make references 
 to the subject of " fixed air." 
 
 About 1750 Black went to Edinburgh University 
 to complete his medical studies, and here he was 
 again fortunate in finding a really scientific student 
 occupying the chair of natural philosophy. 
 
 The attention of medical men was directed at 
 this time to the action of lime-water as a remedy 
 for stone in the bladder. 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 " (or as we should now call 
 it caustic potash or soda). These caustic medicines 
 were mostly prepared by the action of quicklime on 
 some other substance, and quicklime was generally 
 supposed to derive its caustic, or corrosive pro- 
 perties from the fire which was used in changing 
 ordinary limestone into quicklime. 
 
 When quicklime was heated with " fixed alkalis " 
 (i.e. with potassium or sodium carbonate), it 
 changed these substances into caustic bodies which 
 had a corrosive action on animal matter ; hence it 
 was concluded that the quicklime had derived a 
 " power " or some said had derived " igneous 
 matter " from the fire, and had communicated this 
 
FOUNDERS OF CHEMISTRY BLACK. 33 
 
 to the fixed alkalis, which thereby acquired the 
 property of corroding animal matter. 
 
 Black thought that he might be able to lay hold 
 of this " igneous matter " supposed to be taken by 
 the limestone from the fire ; but he found that lime- 
 stone loses weight when changed into quicklime. 
 He then dissolved limestone (or chalk) in spirits 
 of salt (hydrochloric acid), 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 heated. This investigation led 
 Black to a fuller study of the action of heat on 
 chalk and on "mild magnesia" (or as we now 
 say, magnesium carbonate). 
 
 In order that his experiments might be complete 
 and his conclusions well established, he delayed 
 taking the degree of Doctor of Medicine for three 
 years. He graduated as M.D. in 1 75 5, and presented 
 his thesis on " Magnesia Alba, Quicklime and other 
 Alkaline Substances," which contained the results 
 of what is probably the first accurately quantitative 
 examination of a chemical action which we possess. 
 
 Black prepared mild magnesia (magnesium car- 
 bonate) by boiling together solutions of Epsom 
 salts (magnesium sulphate) and fixed alkali (potas- 
 sium carbonate). He showed that when mild 
 magnesia is heated 
 
 1. It is much decreased in bulk. 
 
 2. It loses weight (twelve parts become five, 
 according to Black). 
 
 3. It does not precipitate lime from solutions 
 III. D 
 
34 HEROES OF SCIENCE. 
 
 of that substance in acids (Black had already 
 shown that mild magnesia does precipitate lime). 
 
 He then strongly heated a weighed quantity of 
 mild magnesia in a retort connected with a 
 receiver ; a few drops of water were obtained in 
 the receiver, but the magnesia lost six or seven 
 times as much weight as the weight of the water 
 produced. Black then recalls the experiments of 
 Hales, wherein airs other than common air had 
 been prepared, and concludes that the loss of 
 weight noticed when mild magnesia is calcined is 
 probably due to expulsion, by the heat, of some 
 kind of air. Dissolving some of his mild magnesia 
 in acid he noticed that effervescence occurred, and 
 from this he concluded that the same air which, 
 according to his hypothesis, is expelled by heat, is 
 also driven out from the mild magnesia by the action 
 of acid. He then proceeded to test this hypothesis. 
 One hundred and twenty grains of mild magnesia 
 were strongly calcined ; the calcined matter, amount- 
 ing to seventy grains, was dissolved in dilute oil of 
 vitriol, and this solution was mixed with common 
 fixed alkali (potassium carbonate). The solid 
 which was thus produced was collected, washed 
 and weighed ; it amounted to a trifle less than one 
 hundred and twenty grains, and possessed all the 
 properties detailed by Black of the original mild 
 magnesia. But this is exactly the result which 
 ought to have occurred according to his hypothesis. 
 
 The next step in the investigation was to collect 
 the peculiar air which Black had proved to be 
 
FOUNDERS OF CHEMISTRY BLACK. 35 
 
 evolved during the calcination of mild magnesia. 
 To this substance he gave the name of " fixed air," 
 because it was fixed or held by magnesia. Black 
 established the existence of this air in the expired 
 breath of animals, and also showed that it was 
 present in the air evolved during vinous fermenta- 
 tion. He demonstrated several of its properties ; 
 among these, the fact that animals die when placed 
 in this air. An air with similar properties was 
 obtained by calcining chalk. 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 heated. Chalk ought therefore to 
 lose weight when calcined ; the residue ought to 
 neutralize an acid without evolution of any gas, 
 and the quantity of acid thus neutralized ought to 
 be the same as would be neutralized by the un- 
 calcined chalk ; lastly, it ought to be possible to 
 recover the uncalcined chalk by adding a fixed 
 alkali to a solution of the calcined chalk or 
 quicklime. 
 
 The actual results which Black obtained were as 
 follows : 
 
 One hundred and twenty grains of chalk were 
 dissolved in dilute muriatic (hydrochloric) acid ; 
 421 grains of the acid were needed to neutralize 
 the chalk, and 48 grains of fixed air were evolved. 
 One hundred and twenty grains of the same 
 specimen of chalk were strongly calcined, and 
 then dissolved in dilute muriatic acid ; 414 grains 
 
36 HEROES OF SCIENCE. 
 
 of the acid were required to neutralize the calcined 
 chalk. The difference between 421 and 414 is very 
 slight ; considering the state of practical chemistry 
 at Black's time, 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 acid. One hundred and twenty 
 grains of the same specimen of chalk were again 
 strongly heated ; the calcined chalk, amounting 
 to 68 grains, was digested with a solution of 
 fixed alkali in water. The substance thus obtained, 
 when washed and dried, weighed 118 grains, and 
 had all the properties of ordinary chalk. There- 
 fore, said Black, it is possible to recover the whole 
 of the chalk originally present before calcination, 
 by adding a fixed alkali to the calcined chalk or 
 quicklime. 
 
 At this time it was known that water dissolves 
 quicklime, but it was generally held that only 
 about one-fourth (or perhaps a little more) of any 
 specimen of quicklime could be dissolved by 'water, 
 however much water was employed. Black's re- 
 searches had led him to regard quicklime as a homo- 
 geneous chemical compound ; he concluded that 
 as water undoubtedly dissolves quicklime to some 
 extent, any specimen of this substance, provided it 
 be pure, must be wholly soluble in water. Carefully 
 conducted experiments proved that Black's con- 
 clusion was correct. Black had thus proved that 
 quicklime is a definite substance, with certain fixed 
 properties which characterize it and mark it off 
 
FOUNDERS OF CHEMISTRY BLACK. 37 
 
 from all other substances ; that by absorbing, or 
 combining with another definite substance (fixed 
 air), quicklime is changed into a third substance, 
 namely chalk, which is also characterized by pro- 
 perties as definite and marked as those of quicklime 
 or fixed air. 
 
 Black, quite as much as the alchemists, recognized 
 the fact that change is continually proceeding in 
 Nature ; but he clearly established the all-impor- 
 tant conclusion that these natural changes proceed 
 in definite order, and that it is possible by careful 
 experiment and just reasoning to acquire a know- 
 ledge of this order. He began the great work of 
 showing that, as in other branches of natural science, 
 so also in chemistry, which is pre-eminently the 
 study of the changes of Nature, " the only dis- 
 tinct meaning of that word " (natural) " is stated, 
 fixed, or settled " (Butler's " Analogy," published 
 1736). 
 
 This research by Black is a model of what scien- 
 tific work ought to be. He begins with a few obser- 
 vations of some natural phenomenon ; these he 
 supplements by careful experiments, and thus 
 establishes a sure basis of fact ; he then builds on 
 this basis a general hypothesis, which he proceeds 
 to test by deducing from it certain necessary con- 
 clusions, and proving, or disproving, these by an 
 appeal to Nature. This is the scientific method ; it 
 is common sense made accurate. 
 
 Very shortly after the publication of the thesis 
 on magnesia and quicklime, a vacancy occurred 
 
38 HEROES OF SCIENCE. 
 
 in the chemical chair in Glasgow University, and 
 Black was appointed Professor of Anatomy and 
 Lecturer on Chemistry. As he did not feel fully 
 qualified to lecture on anatomy, he made an ar- 
 rangement to exchange subjects with the Professor 
 of Medicine, and from this time he delivered 
 lectures on chemistry and on "The Institutes of 
 Medicine." 
 
 Black devoted a great deal of care and time to 
 the teaching duties of his chair. His chemical ex- 
 perimental researches were not much advanced 
 after this time ; but he delivered courses of lectures 
 in which new light was thrown on the whole range 
 of chemical science. 
 
 In the years between 1759 and 1763 Black ex- 
 amined the phenomena of heat and cold, and gave 
 an explanation, founded on accurate experiments, 
 of the thermal changes which accompany the melt- 
 ing of solids and the vaporization of liquids. 
 
 If pieces of wood, lead and ice be taken by the 
 hand from a box in which they have been kept 
 cold, the wood feels cold to the touch, the lead 
 feels colder than the wood, and the ice feels colder 
 than the lead ; hence it was concluded that the 
 hand receives cold from the wood, more cold from 
 the lead, and most cold from the ice. 
 
 Black however showed that the wood really takes 
 away heat from the hand, but that as the wood 
 soon gets warmed, the process stops before long ; 
 that the lead, not being so quickly warmed as the 
 wood, takes away more heat from the hand than 
 
FOUNDERS OF CHEMISTRY BLACK. 39 
 
 the wood does, and that the ice takes away more 
 heat than either wood or lead. 
 
 Black thought that the heat which is taken by 
 melting ice from a warm body remains in the 
 water which is produced ; 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 degree, the source of heat being the same in 
 each case. 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 water. He found that in 
 order to melt one pound of ice without raising its 
 temperature, as much heat had to be added to the 
 ice as sufficed to raise the temperature of one pound 
 of water through about 140 degrees of Fahrenheit's 
 thermometer. But this heat which has been added 
 to the ice to convert it into water is not indicated by 
 the thermometer. Black called this " latent heat? 
 
 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 Glasgow, on April 23, 1762 ; but 
 it appears that Black was accustomed to teach the 
 theory in his ordinary lectures before this date. 
 
 The theory of latent heat ought also to explain 
 the phenomena noticed when liquid water is changed 
 into steam. Black applied his theory generally to 
 this change, but did not fully work out the details 
 and actually measure the quantity of heat which is 
 
40 HEROES OF SCIENCE. 
 
 absorbed by water at the boiling point before it 
 is wholly converted into steam at the same tem- 
 perature, until some years later when he had the 
 assistance of his pupil and friend James Watt. 
 
 Taking a survey of the phenomena of Nature, 
 Black insisted on the importance of these experi- 
 mentally established facts that before ice melts it 
 must absorb a large quantity of heat, and before 
 water is vaporized it must absorb another large 
 quantity of heat, which amounts of heat are restored 
 to surrounding substances when water vapour 
 again becomes liquid water and when liquid water 
 is congealed to ice. He allows his imagination to 
 picture the effects of these properties of water in 
 modifying and ameliorating the climates of tropical 
 and of Northern countries. In his lectures he says, 
 " Here we can also trace another magnificent train 
 of changes which are nicely accommodated to the 
 wants of the inhabitants of this globe. In the 
 equatorial regions, the oppressive heat of the sun 
 is prevented from a destructive accumulation by 
 copious evaporation. The waters, stored with their 
 vaporific heat, are then carried aloft into the atmo- 
 sphere till the rarest of the vapour reaches the very 
 cold regions of the air, which immediately forms a 
 small portion of it into a fleecy cloud. This also 
 further tempers the scorching heat by its opacity, 
 performing the acceptable office of a screen. From 
 thence the clouds are carried to the inland countries, 
 to form the sources in the mountains which are to 
 supply the numberless streams that water the 
 
FOUNDERS OF CHEMISTRY BLACK. 41 
 
 fields. And by the steady operation of causes, 
 which are tolerably uniform, the greater part of 
 the vapours passes on to the circumpolar regions, 
 there to descend in rains and dews ; and by this bene- 
 ficent conversion into rain by the cold of those 
 regions, each particle of steam gives up the heat 
 which was latent in it. This is immediately dif- 
 fused, and softens the rigour of those less comfort- 
 able climates." 
 
 In the year 1766 Black was appointed Professor 
 of Chemistry in the University of Edinburgh, in 
 which position he remained till his death in 1799. 
 During these thirty-three years he devoted himself 
 chiefly to teaching and to encouraging the advance 
 of chemical, science. He was especially careful in the 
 preparation of his elementary lectures, being per- 
 suaded that it was of the utmost importance that 
 his pupils should be well grounded in the principles 
 of chemistry. 
 
 His health had never been robust, and as he 
 grew old he was obliged to use great care in his 
 diet ; his simple and methodical character and 
 habits made it easy for him to live on the plainest 
 food, and to take meals and exercise at stated times 
 and in fixed quantities. 
 
 Black's life closed, as was fitting, in a quiet and 
 honoured old age. He had many friends, but lived 
 pretty much alone he was never married. 
 
 On the 26th of November 1799, " being at table 
 with his usual fare, some bread, a few prunes and 
 a measured quantity of milk diluted with water, 
 
42 HEROES OF SCIENCE. 
 
 and having the cup in his hand when the last stroke 
 of his pulse was to be given, he had set it down on 
 his knees, which were joined together, and kept it 
 steady with his hand, in the manner of a person 
 perfectly at ease ; and in this attitude he expired, 
 without spilling a drop, and without a writhe in his 
 countenance, as if an experiment had been required 
 to show to his friends the facility with which he 
 departed." 
 
 Black was characterized ^by " moderation and 
 sobriety of thought ; " he had a great sense of the 
 fitness of things of what is called by the older 
 writers "propriety." But he was by no means a 
 dull companion ; he enjoyed general society, and 
 was able to bear a part in any kind of conversation. 
 A thorough student of Nature, he none the less did 
 not wish to devote his whole time to laboratory 
 work or to the labours of study ; 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 science. But with his 
 true scientific peers he doubtless appeared at his 
 best. Among his more intimate friends were the 
 famous political economist Adam Smith, and the 
 no less celebrated philosopher David Hume. Dr. 
 Hutton, one of the earliest workers in geology, was 
 a particular friend of Black ; his friendship with 
 James Watt began when Watt was a student in his 
 class, and continued during his life. 
 
 With such men as his friends, and engaged in 
 the study of Nature that boundless subject whicli 
 
FOUNDERS OF CHEMISTRY BLACK. 43 
 
 one can never know to the full, but which one can 
 always know a little more year by year Black's 
 life could not but be happy. His example and his 
 teaching animated his students ; he was what a 
 university professor ought to be, a student among 
 students, but yet a teacher among pupils. His work 
 gained for him a place in the first rank of men 
 of science ; his clearness of mind, his moderation, 
 his gentleness, his readiness to accept the views of 
 others provided these views were well established 
 on a basis of experimentally determined facts, fitted 
 him to be the centre of a circle of scientific students 
 who looked on him as at once their teacher and 
 their friend. 
 
 As a lecturer Black was eminently successful. 
 He endeavoured to make all his lectures plain and 
 intelligible ; he enlivened them by many experi- 
 ments designed simply to illustrate the special 
 point which he had in view. He abhorred osten- 
 tatious display and trickiness in a teacher. 
 
 Black was strongly opposed to the use of hypo- 
 theses in science. Dr. Robison (the editor of his 
 lectures) tells that when a student in Edinburgh 
 he met Black, who became interested in him from 
 hearing him speak somewhat enthusiastically in 
 favour of one of the lecturers in the university. 
 Black impressed on him the necessity of steady 
 experimental work in natural science, gave him a 
 copy of Newton's " Optics " as a model after 
 which scientific work ought to be conducted, and 
 advised him " to reject, even without examination. 
 
44 HEROES OF SCIENCE. 
 
 any hypothetical explanation, as a mere waste of 
 time and ingenuity." But, when we examine 
 Black's own work, we see that by "hypothetical ex- 
 planations " he meant vague guesses. He himself 
 made free use of scientific (i.e. of exact) hypotheses ; 
 indeed the history of science tells us that without 
 hypotheses advance is impossible. Black taught by 
 his own researches that science is not an array of 
 facts, but that the object of the student of Nature is 
 to explain facts. But the method generally in vogue 
 before the time of Black was to gather together a 
 few facts, or what seemed to be facts, and on these 
 to raise a vast superstructure of " vain imaginings." 
 Naturalists had scarcely yet learned that Nature is 
 very complex, and that guessing and reasoning on 
 guesses, with here and there an observation added, 
 was not the method by which progress was to be 
 made in learning the lessons written in this complex 
 book of Nature. 
 
 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 studied. Such an image could be obtained 
 only by beginning with detailed observation and 
 experiment. From a number of definite mental 
 images the student must put together a picture of 
 the whole natural phenomenon under examination ; 
 perceiving that something was wanted here, or that 
 the picture was overcrowded there, he must again 
 go to Nature and gain fresh facts, or sometimes 
 prove that what had been accepted as facts had no 
 
FOUNDERS OF CHEMISTRY BLACK. 45 
 
 real existence, and so at length he would arrive at 
 a true representation of the whole process. 
 
 So anxious was Black to define clearly what he 
 knew and professed to teach, that he preferred to 
 call his lectures " On the Effects of Heat and 
 Mixtures," rather than to announce them as "A 
 Systematic Course on Chemistry." 
 
 His introductory lecture on " Heat in General " 
 is very admirable ; the following quotation will 
 serve to show the clearness of his style and the 
 methodical but yet eminently suggestive manner 
 of his teaching : 
 
 " Of Heat in General. 
 
 "That this extensive subject may be treated in a 
 profitable manner, I propose 
 
 " First. To ascertain what I mean by the word 
 heat in these lectures. 
 
 " Secondly. To explain the meaning of the term 
 cold, and ascertain the real difference between heat 
 and cold. 
 
 "Thirdly. To mention some of the attempts 
 which have been made to discover the nature of 
 heat, or to form an idea of what may be the im- 
 mediate cause of it. 
 
 " Fourthly and lastly. I shall begin to describe 
 sensible effects produced by heat on the bodies to 
 which it is communicated. 
 
 " Any person who reflects on the ideas which we 
 annex to the word heat \\i\\ perceive that this word 
 
46 HEROES OF SCIENCE. 
 
 is used for two meanings, or to express two 
 different things, It either means a sensation ex- 
 cited in our organs, or a certain quality, affection, 
 or condition of the bodies around us, by which 
 they excite in us that sensation. The word is used 
 in the first sense when we say, we feel heat ; in 
 the second, when we say, there is heat in the fire 
 or in a hot stone. There cannot be a sensation of 
 heat in the fire, or in the hot stone, but the matter 
 of the fire, or of the stone, is in a state or condition 
 by which it excites in us the sensation of heat. 
 
 " Now, in beginning to treat of heat and its effects, 
 I propose to use the word in this second sense only ; 
 or as expressing that state, condition, or quality of 
 matter by which it excites in us the sensation of 
 heat. This idea of heat will be modified a little 
 and extended as we proceed, but the meaning of 
 the word will continue at bottom the same, and the 
 reason of the modification will be easily perceived." 
 
 Black's manner of dealing with the phenomenon 
 of combustion illustrates the clearness of the con- 
 ceptions which he formed of natural phenomena, 
 and shows moreover the thoroughly unbiased 
 nature of his mind. As soon as he had convinced 
 himself that the balance of evidence was in favour 
 of the new (antiphlogistic) theory, he gave up 
 those doctrines in which he had been trained, and 
 accepted the teaching of the French chemists ; but 
 he did not as some with less well-balanced minds 
 might do regard the new theory as a final state- 
 ment, but rather as one stage nearer the complete 
 
FOUNDERS OF CHEMISTRYBLACK. 47 
 
 explanation which future experiments and future 
 reasoning would serve to establish. 
 
 In his lectures on combustion Black first of all 
 establishes the facts, that when a body is burned 
 it is changed into a kind (or kinds) of matter which 
 is no longer inflammable ; that the presence of air 
 is needed for combustion to proceed ; that the sub- 
 stance must be heated " to a certain degree " before 
 combustion or inflammation begins; that this degree 
 of heat (or we should now say this degree of 
 temperature) differs for each combustible sub- 
 stance ; that the supply of air must be renewed if 
 the burning is to continue ; and that the process of 
 burning produces a change in the quality of the air 
 supplied to the burning body. 
 
 He then states the phlogistic interpretation of 
 these phenomena : that combustion is caused by 
 the outrush from the burning body of a something 
 called the pr inciple of fire ', or phlogiston. 
 
 Black then proceeds to demonstrate certain 
 other facts : When the substances produced by 
 burning phosphorus or sulphur are heated with 
 carbon (charcoal) the original phosphorus or 
 sulphur is reproduced. This reproduction is due, 
 according to the phlogistic chemists, to the giving 
 back, by carbon, of the phlogiston which had 
 escaped during the burning. Hence carbon con- 
 tains much phlogiston. But as a similar reproduc- 
 tion of phosphorus or sulphur, from the substances 
 obtained by burning these bodies, can be accom- 
 plished by the use of substances other than carbon, 
 
48 HEROES OF SCIENCE. 
 
 it is evident that these other substances also con- 
 tain much phlogiston, and, moreover, that the 
 phlogiston contained in all these substances is 
 one and the same principle. What then, he asks, is 
 this " principle " which can so escape, and be so 
 restored by the action of various substances ? He 
 then proceeds as follows : 
 
 " But when we inquire further, and endeavour to 
 learn what notion was formed of the nature of this 
 principle, and what qualities it was supposed to 
 have in its separate state, we find this part of the 
 subject very obscure and unsatisfactory, and the 
 opinions veiy unsettled. 
 
 " The elder chemists, and the alchemists, con- 
 sidered sulphur as the universal inflammable prin- 
 ciple, or at least they chose to call the inflammable 
 part of all bodies, that are more or less inflammable, 
 by the name of their sulphur. . . . The famous 
 German chemist Becher was, I believe, the first 
 who rejected the notion of sulphur being the prin- 
 ciple of inflammability in bodies. . . . His notion 
 of the nature of the pure principle of inflamma- 
 bility was afterwards more fully explained and 
 supported by Professor Stahl, who, agreeably to 
 the doctrine of Becher, represented the principle of 
 inflammability as a dry substance, or of an earthy 
 nature, the particles of which were exquisitely sub- 
 tile, and were much disposed to be agitated and 
 set in motion with inconceivable velocity. . . . The 
 opinion of Becher and Stahl concerning this 
 terra secunda, or terra inflammabilis, or plilogis- 
 
FOUNDERS OF CHEMISTRY BLACK. 49 
 
 ton, was that the atoms of it are, more than all 
 others, disposed to be affected with an excessively 
 swift whirling motion (inotus vorticillaris}. The 
 particles of other elementary substances are like- 
 wise liable to be affected with the same sort of 
 motion, but not so liable as those of terra secunda ; 
 and when the particles of any body are agitated 
 with this sort of motion, the body exhibits the 
 phenomena of heat, or ignition, or inflammation 
 according to the violence and rapidity of the 
 motion. . . . Becher and Stahl, therefore, did not 
 suppose that heat depended on the abundance of a 
 peculiar matter, such as the matter of heat or fire 
 is now supposed to be, but on a peculiar motion of 
 the particles of matter. . . . 
 
 "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 in- 
 flammable substances, by which they resist the 
 action of water as a solvent. The greater num- 
 ber of the earthy substances are little, or not at all, 
 soluble in water. . . . And when Becher and Stahl 
 found those compounds, which they supposed con- 
 tained phlogiston in the largest quantity, to be 
 insoluble in water, although the other matter, with 
 which the phlogiston was supposed to be united, 
 was, in its separate state, exceedingly soluble in 
 that fluid, they concluded that a dry nature, or an in- 
 capability to be combined with water, was an eminent 
 quality of their phlogiston ; and this was what they 
 meant by calling it an earth or earthy substance. 
 
 III. E 
 
50 HEROES OF SCIENCE, 
 
 . . . But these authors supposed, at the same time, 
 that the particles of this dry and earthy phlogiston 
 were much disposed to be excessively agitated with 
 a whirling motion ; which whirling motion, exerted 
 in all directions from the bodies in which phlogiston 
 is contained, produced the phenomena of inflamma- 
 tion. This appears to have been the notion formed 
 by Becher and Stahl, concerning the nature of the 
 principle of inflammability, or the phlogiston ; a 
 notion which seems the least entitled to the name of 
 explanation of anything we can think of. I presume 
 that few persons can form any clear conception of 
 this whirling motion, or, if they can, are able to 
 explain to themselves how it produces, or can pro- 
 duce, anything like the phenomena of heat or fire." 
 
 Black then gives a clear account of the experi- 
 ments of Priestley and Lavoisier (see pp. 58, 59, 
 and 87-89), which established the presence, in com- 
 mon air, of a peculiar kind of gas which is especially 
 concerned in the processes of combustion ; he em- 
 phasizes the fact that a substance increases in weight 
 when it is burned ; and he gives a simple and clear 
 statement of that explanation of combustion which 
 is now accepted by all, and which does not require 
 that the existence of any principle of fire should be 
 assumed. 
 
 It is important to note that Black clearly con- 
 nects the physical fact that heat is absorbed, or 
 evolved, by a substance during combustion, with 
 the chemical changes which are brought about in 
 the properties of the substance burned. He con- 
 
FOUNDERS OF CHEMISTRY BLACK. 51 
 
 eludes with an admirable contrast between the 
 phlogistic theory and the theory of Lavoisier, 
 which shows how wide, and at the same time how 
 definite, his conceptions were. Black never speaks 
 contemptuously of a theory which he opposes. 
 
 "According to this theory" (i.e. the theory of 
 Lavoisier), "the inflammable bodies, sulphur for 
 example, or phosphorus, are simple substances. 
 The acid into which they are changed by inflam- 
 mation is a compound. The chemists, on the 
 contrary " (i.e. the followers of Stahl), " consider the 
 inflammable bodies as compounds, and the unin- 
 flammable matter as more simple. In the common 
 theory the heat and light are supposed to emanate 
 from, or to be furnished by, the burning body. 
 But, in Mr. Lavoisier's theory, both are held to be 
 furnished by the air, of which they are held to be 
 constituent parts, or ingredients, while in its state of 
 fire-supporting air." 
 
 Black was not a brilliant discoverer, but an 
 eminently sound and at the same time imaginative 
 worker ; whatever he did he did well, but he did 
 not exhaust any field of inquiry. Many of the 
 facts established by him have served as the basis 
 of important work done by those who came after 
 him. The number of new facts added by Black 
 to the data of chemistry was not large ; but by 
 his lectures which are original dissertations of 
 the highest value he did splendid service in ad- 
 vancing the science of chemistry. Black possessed 
 that which has generally distinguished great men 
 
$2 HEROES OF SCIENCE. 
 
 of science, a marked honesty of character ; and to 
 this he added comprehensiveness of mental vision : 
 he saw beyond the limits of the facts which formed 
 the foundations of chemical science in his day. 
 He was not a fact-collector, but a philosopher. 
 
 JOSEPH PRIESTLEY, the son of Jonas Priestley, 
 " a maker and dresser of woollen cloth," was b born 
 at Fieldhead, near Leeds, in the year 1733. His 
 mother, who was the daughter of a farmer near 
 Wakefield, died when he was seven years old. 
 From that time he was brought up by a sister of his 
 father, who was possessed of considerable private 
 means. 
 
 Priestley's surroundings in his young days were 
 decidedly religious, and evidently gave a tone to 
 his whole after life. We shall find that Priestley's 
 work as a man of science can scarcely be separated 
 from his theological and metaphysical work. His 
 cast of mind was decidedly metaphysical ; he was 
 altogether different from Black, who, as we have 
 seen, was a typical student of natural phenomena. 
 
 The house of Priestley's aunt was a resort for all 
 the Dissenting ministers of that part of the county. 
 She herself was strictly Calvinistic in her theological 
 views, but not wholly illiberal. 
 
 Priestley's early schooling was chiefly devoted to 
 learning languages ; he acquired a fair knowledge 
 of Latin, a little Greek, and somewhat later he 
 learned the elements of Hebrew. At one time 
 he thought of going into trade, and therefore, as he 
 
FOUNDERS OF CHEMISTRY PRIESTLEY. $3 
 
 tells us in his " Memoirs," he acquired some know- 
 ledge of French, Italian and High Dutch. With 
 the help of a friend, a Dissenting minister, he 
 learned something of geometry, mathematics and 
 natural philosophy, and also got some smattering 
 of the Chaldee and Syriac tongues. 
 
 At the age of nineteen Priestley went to an 
 "academy" at Daventry. The intellectual atmo- 
 sphere here seems to have been suitable to the 
 rapid development of Priestley's mind. Great 
 freedom of discussion was allowed ; even during 
 the teachers' lectures the students were permitted 
 "to ask whatever questions and to make what- 
 ever remarks " they pleased ; and they did it, 
 Priestley says, " with the greatest, but without any 
 offensive, freedom." 
 
 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' 
 lectures. Theological disputations appear to have 
 been the favourite topics on which the students 
 exercised their ingenuity among themselves. 
 Priestley tells us that he " saw reason to embrace 
 what is generally called the heterodox side of 
 almost every question." 
 
 Leaving this academy, Priestley went, in 1755, 
 as assistant to the Dissenting minister at Needham, 
 in Suffolk. Here he remained for three years, living 
 on a salary of about 30 a year, and getting more 
 and more into bad odour because of his peculiar 
 theological views. 
 
54 HEROES OF SCIENCE. 
 
 From Needham he moved to Nantwich, in 
 Cheshire, where he was more comfortable, and, 
 having plenty of work to do, he had little time for 
 abstruse speculations. School work engaged most 
 of his time at Nantwich ; he also began to collect 
 a few scientific instruments, such as an electrical 
 machine and an air-pump. These he taught his 
 scholars to use and to keep in good order. He 
 gave lectures on natural phenomena, and en- 
 couraged his scholars to make experiments and 
 sometimes to exhibit their experiments before 
 their parents and friends. He thus extended the 
 reputation of his school and implanted in his 
 scholars a love of natural knowledge. 
 
 In the year 1761 Priestley removed to Warrington, 
 to act as tutor in a newly established academy, 
 where he taught languages a somewhat wide 
 subject, as it included lectures on " The Theory of 
 Languages," on " Oratory and Criticism," and on 
 " The History, Laws, and Constitution of England." 
 He says, " It was my province to teach elocution, 
 and also logic and Hebrew. The first of these I 
 retained, but after a year or two I exchanged the 
 two last articles with Dr. Aikin for the civil law, 
 and one year I gave a course of lectures on 
 anatomy." 
 
 During his stay at Warrington, which lasted until 
 1767, Priestley married a daughter of Mr. Isaac 
 Wilkinson, an ironmaster of Wrexham, in Wales. 
 He describes his wife as "a woman of an excellent 
 understanding much improved by reading, of great 
 
FOUNDERS OF CHEMISTRY PRIESTLEY. 55 
 
 fortitude and strength of mind, and of a temper in 
 the highest degree affectionate and generous, feel- 
 ing strongly for others and little for herself, also 
 greatly excelling in everything relating to household 
 affairs." 
 
 About this time Priestley met Dr. Franklin more 
 than once in London. His conversation seems to 
 have incited Priestley to a further study of natural 
 philosophy. He began to examine electrical pheno- 
 mena, and this led to his writing and publishing a 
 " History of Electricity," in the course of which he 
 found it necessary to make new experiments. The 
 publication of the results of these experiments 
 brought him more into notice among scientific 
 men, and led to his election as a Fellow of the 
 Royal Society, and to his obtaining the degree of 
 LL.D. from the University of Edinburgh. In the 
 year 1767 Priestley removed to Leeds, where he 
 spent six years as minister of Millhill Chapel. 
 
 He was able to give freer expression to his theo- 
 logical views in Leeds than could be done in smaller 
 places, such as Needham and Nantwich. During 
 this time he wrote and published many theological 
 and metaphysical treatises. But, what is of more 
 importance to us, he happened to live near a 
 brewery. Now, the accidental circumstances, as we 
 call them, of Priestley's life were frequently of the 
 greatest importance in their effects on his scientific 
 work. Black had established the existence and 
 leading properties of fixed air about twelve or 
 thirteen years before the time when Priestley came 
 
56 HEROES OF SCIENCE. 
 
 to live near the brewery in Leeds. He had shown 
 that this fixed air is produced during alcoholic fer- 
 mentation. Priestley knowing this used to collect 
 the fixed air which came off from the vats in the 
 neighbouring brewery, and amuse himself with ob- 
 serving its properties. But removing from this part 
 of the town his supplies of fixed air were stopped. 
 As however he had become interested in working 
 with airs, he began to make fixed air for himself from 
 chalk, 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 gases, or pneumatic chemistry. 
 Priestley's pneumatic trough is at this day to be 
 found in every laboratory ; it is extremely simple 
 and extremely perfect. A dish of glass, or earthen- 
 ware, or wood is partly filled with water ; a shelf 
 runs across the dish at a little distance beneath 
 the surface of the water ; a wide-mouthed bottle is 
 filled with water and placed, mouth downwards, 
 over a hole in this shelf. The gas which is to be 
 collected in this bottle is generated in a suitable 
 vessel, from which a piece of glass or metal tubing 
 passes under the shelf and stops just where the 
 hole is made. The gas which comes from the ap- 
 paratus bubbles up into the bottle, drives out the 
 water, and fills the bottle. When the bottle is full 
 of gas, it is moved to one side along the shelf, and 
 another bottle filled with water is put in its place. 
 As the mouth of each bottle is under water there 
 is no connection between the gas inside and the 
 
FOUNDERS OF CHEMISTRY PRIESTLEY. 57 
 
 air outside the bottle ; the gas may therefore be 
 kept in the bottle until the experimenter wants it. 
 (See Fig. i. which is reduced from the cut in 
 Priestley's " Air.") 
 
 Fig. i. 
 
 Priestley tells us that at this time he knew very 
 little chemistry, but he thinks that this was a good 
 thing, else he might not have been led to make 
 so many new discoveries as he did aftenvards 
 make. 
 
 Experimenting with fixed air, he found that water 
 could be caused to dissolve some of the gas. In 
 1772 he published a pamphlet on the method of 
 
58 HEROES OF SCIENCE. 
 
 impregnating water with fixed air ; this solution 
 of fixed air in water was employed medicinally, 
 and from this time we date the manufacture of 
 artificial mineral waters. 
 
 The next six years of Priestley's life (1773-1779) 
 are very important in the history of chemistry ; it 
 was during these years that much of his best \vork 
 on various airs was performed. During this 
 time he lived as a kind of literary companion 
 (nominally as librarian) with the Earl of Shelburne 
 (afterwards Marquis of Lansdowne.) His wife and 
 family he had now three children lived at Calne, 
 in Wiltshire, near Lord Shelburne's seat of Bowood. 
 Priestley spent most of the summer months with 
 his family, and the greater part of each winter with 
 Lord Shelburne at his London residence ; during 
 this time he also travelled in Holland and Germany, 
 and visited Paris in 1774. 
 
 In a paper published in November 1772, Priestley 
 says that he examined a specimen of air which 
 he had extracted from saltpetre above a year before 
 this date. This air " had by some means or other 
 become noxious, but," he supposed, " had been re- 
 stored to its former wholesome state, so as to 
 effervesce with nitrous air " (in modern language, 
 to combine with nitric oxide) "and to admit a 
 candle to burn in it, in consequence of agitation 
 with water." He tells us, in his " Observations on 
 Air " (1779), that at this time he was altogether in 
 the dark as to the nature of this air obtained from 
 saltpetre. In August 1774, he was amusing himself 
 
FOUNDERS OF CHEMISTRY PRIESTLEY. 59 
 
 by observing the action of heat on various sub- 
 stances "without any particular view," he says, 
 "except that of extracting air from a variety of 
 substances by means of a burning lens in quicksilver, 
 which was then a new process with me, and which 
 I was very proud of" when he obtained from red 
 precipitate (oxide of mercury) an air in which a 
 candle burned with a " remarkably vigorous flame." 
 The production of this peculiar air " surprised me 
 more than I can well express ;" "I was utterly at a 
 loss how to account for it." At first he thought 
 that the specimen of red precipitate from which the 
 air had been obtained was not a proper prepara- 
 tion, but getting fresh specimens of this salt, he 
 found that they all yielded the same kind of air. 
 Having satisfied himself by experiment that this 
 peculiar air had " all the properties of common air, 
 only in much greater perfection," he gave to it the 
 name of dephlogisticated air. Later experiments 
 taught him that the same air might be obtained 
 from red lead, from manganese oxide, etc., by the 
 action of heat, and from various other salts by the 
 action of acids. 
 
 Priestley evidently regards the new " dephlogisti- 
 cated air " simply as very pure ordinary air ; indeed, 
 he seems to look on all airs, or gases, as easily 
 changeable one into the other. He always inter- 
 prets his experimental results by the help of the 
 theory of phlogiston. One would indeed think from 
 Priestley's papers that the existence of this sub- 
 stance phlogiston was an unquestioned and unques- 
 
60 HEROES OF SCIENCE. 
 
 tionable fact. Thus, he says in the preface to his 
 " Experiments on Air : " " If any opinion in all the 
 modern doctrine concerning air be well founded, it 
 is certainly this, that nitrous air is highly charged 
 with phlogiston, and that from this quality only it 
 renders pure air noxious. ... If I have completely 
 ascertained anything at all relating to air it is 
 this." Priestley thought that "very pure air" 
 would take away phlogiston from some metals 
 without the help of heat or any acid, and thus cause 
 these metals to rust. He therefore placed some clean 
 iron nails in dephlogisticated air standing over mer- 
 cury ; after three months he noticed that about one- 
 tenth of the air in the vessel had disappeared, and 
 he concluded, although no rust appeared, that the 
 dephlogisticated air had as a fact withdrawn phlo- 
 giston from the iron nails. This is the kind of 
 reasoning which Black described to his pupils as 
 " mere waste of time and ingenuity." The experi- 
 ment with the nails was made in 1779 ; at this time, 
 therefore, Priestley had no conception as to what 
 his dephlogisticated air really was. 
 
 Trying a great many experiments, and finding 
 that the new air was obtained by the action of acids 
 on earthy substances, Priestley was inclined to 
 regard this air, and if this then all other airs, as 
 made up of an acid (or acids) and an earthy sub- 
 stance. We now know how completely erroneous 
 this conclusion was, but we must remember that in 
 Priestley's time chemical substances were generally 
 regarded as of no very definite or fixed composition ; 
 
FOUNDERS OF CHEMISTRY PRIESTLEY. 6l 
 
 that almost any substance, it was supposed, might 
 be changed into almost any other ; that no clear 
 meaning was attached to the word "element;" and 
 that few, if any, careful measurements of the quan- 
 tities of different kinds of matter taking part in 
 chemical actions had yet been made. 
 
 But at the same time we cannot forget that the 
 books of Hooke and Mayow had been published 
 years before this time, and that twenty years 
 before Priestley began his work on airs, Black had 
 published his exact, scientific investigation on 
 fixed air. 
 
 Although we may agree with Priestley that, had 
 he made himself acquainted with what others had 
 done before he began his own experiments, he 
 might not have made so many new discoveries as 
 he did, yet one cannot but think that his discoveries, 
 although fewer, would have been more accurate. 
 
 We are told by Priestley that, when he was in 
 Paris in 1774, he exhibited the method of obtain- 
 ing dephlogisticated air from red precipitate to 
 Lavoisier and other French chemists. We shall see 
 hereafter what important results to science followed 
 from this visit to Lavoisier. 
 
 Let us shortly review Priestley's answer to the 
 question, " What happens when a substance burns 
 in air ? " 
 
 Beginning to make chemical experiments when 
 he had no knowledge of chemistry, and being 
 an extremely rapid worker and thinker, he natur- 
 ally adopted the prevalent theory, and as naturally 
 
62 HEROES OF SCIENCE, 
 
 interpreted the facts which he discovered in accord- 
 ance with this theory. 
 
 When a substance burns, phlogiston, it was said, 
 rushes out of it. But why does rapid burning only 
 take place in air ? Because, said Priestley, air has a 
 great affinity for phlogiston, and draws it out of the 
 burning substance. What then becomes of this 
 phlogiston? we next inquire. The answer is, ob- 
 viously it remains in the air around the burning 
 body, and this is proved by the fact that this air 
 soon becomes incapable of supporting the process 
 of burning, it becomes phlogisticated. Now, if phlo- 
 gisticated air cannot support combustion, the greater 
 the quantity of phlogiston in air, the less will it sup- 
 port burning ; but we know that if a substance is 
 burnt in a closed tube containing air, the air which 
 remains when the burning is quite finished at once 
 extinguishes a lighted candle. Priestley also proved 
 that an air can be obtained by heating red preci- 
 pitate, characterized by its power of supporting com- 
 bustion with great vigour. What is this but common 
 air completely deprived of phlogiston ? It is dephlo- 
 gisticated air. Now, if common air draws phlogiston 
 out of substances, surely this dephlogisticated air 
 will even more readily do the same. That it really 
 does this Priestley thought he had proved by his 
 experiment with clean iron nails (see p. 60). 
 
 Water was regarded as a substance which, like 
 air, readily combined with phlogiston ; but Priestley 
 thought that a candle burned less vigorously in 
 dephlogisticated air which had been shaken with 
 
FOUNDERS OF CHEMISTRY PRIESTLEY. 63 
 
 water than in the same air before this treatment ; 
 hence he concluded that phlogiston had been taken 
 from the water. 
 
 After Cavendish had discovered (or rather re- 
 discovered) hydrogen, and had established the 
 fact that this air is extremely inflammable, most 
 chemists began to regard this gas^as pure or 
 nearly pure phlogiston, or, at least, as a substance 
 very highly charged with phlogiston. " Now," said 
 Priestley, "when a metal burns phlogiston rushes out 
 of it ; if I restore this phlogiston to the metallic 
 calx, I shall convert it back into the metal." He 
 then showed by experiment that when calx of iron 
 is heated with hydrogen, the hydrogen disappears 
 and the metal iron is produced. 
 
 He seemed, therefore, to have a large experi- 
 mental basis for his answer to the question, " What 
 happens when a substance burns ? " But at a later 
 time it was proved that iron was also produced by 
 heating the calx of iron with carbon. The antiphlo- 
 gistic chemists regarded fixed air as composed of 
 carbon and dephlogisticated air ; the phlogisteans 
 said it was a substance highly charged with phlo- 
 giston. The antiphlogistic school said that calx of 
 iron is composed of iron and dephlogisticated air ; 
 the phlogisteans said it was iron deprived of its 
 phlogiston. Here was surely an opportunity for a 
 crucial experiment : when calx of iron is heated with 
 carbon, and iron is produced, there must either be 
 a production of fixed air (which is a non-in- 
 flammable gas, and forms a white solid substance 
 
64 HEROES OF SCIENCE. 
 
 when brought into contact with limewater), or 
 there must be an outrush of phlogiston from the 
 carbon. The experiment was tried : a gas was 
 produced which had no action on limewater and 
 which was very inflammable; what could this be 
 but phlogiston, already recognized by this very 
 property of extreme inflammability ? Thus the 
 phlogisteans appeared to triumph. But if we ex- 
 amine these experiments made by Priestley with the 
 light thrown on them by subsequent research, we 
 find that they bear the interpretation which he put 
 on them only because they were not accurate ; thus, 
 two gases are inflammable, but it by no means 
 follows that these gases are one and the same. We 
 must have more accurate knowledge of the pro- 
 perties of these gases. 
 
 The air around a burning body, such as iron, 
 after a time loses the power of supporting com- 
 bustion ; but this is merely a qualitative fact. 
 Accurately to trace the change in the properties 
 of this air, it is absolutely necessary that exact 
 measurements should be made ; when this is done, 
 we find that the volume of air diminishes during 
 the combustion, that the burning body gains weight, 
 and that this gain in weight is just equal to the 
 loss in weight undergone by the air. When the 
 inflammable gas produced by heating calx of iron 
 with carbon was carefully and quantitatively 
 analyzed, it was found to consist of carbon and 
 oxygen (dephlogisticated air), but to contain these 
 substances in a proportion different from that in 
 
FOUNDERS OF CHEMISTRY PRIESTLEY. 65 
 
 which they existed in fixed air. It was a new kind 
 of air or gas ; it was not hydrogen. 
 
 This account of Priestley's experiments and con- 
 clusions regarding combustion shows how easy it is 
 in natural science to interpret experimental results, 
 especially when these results are not very accurate, 
 in accordance with a favourite theory ; and it also 
 illustrates one of the lessons so emphatically taught 
 by all scientific study, viz. the necessity of sus- 
 pending one's judgment until accurate measure- 
 ments have been made, and the great wisdom of 
 then judging cautiously. 
 
 About 1779 Priestley left Lord Shelburne, and 
 went as minister of a chapel to Birmingham, where 
 he remained until 1791. 
 
 During his stay in Birmingham, Priestley had a 
 considerable amount of pecuniary help from his 
 friends. He had from Lord Shelburne, according 
 to an agreement made when he entered his service, 
 an annuity of ^"150 a year for life; some of his 
 friends raised a sum of money annually for him, in 
 order that he might be able to prosecute his re- 
 searches without the necessity of taking pupils. 
 During the ten years or so after he settled in Bir- 
 mingham, Priestley did a great deal of chemical 
 work, and made many discoveries, almost entirely 
 in the field of pneumatic chemistry. 
 
 Besides the discovery of dephlogisticated air 
 (or oxygen) which has been already described, 
 Priestley discovered and gave some account of the 
 properties of nitro2is air (nitric acid), vitriolic acid 
 
 III. F 
 
66 HEROES OF SCIENCE. 
 
 air (sulphur dioxide), muriatic acid air (hydrochloric 
 acid), and alkaline air (ammonia), etc. 
 
 In the course of his researches on the last-named 
 air he showed, that when a succession of electric 
 sparks is passed through this gas a great increase 
 in the volume of the gas occurs. This fact was 
 further examined at a later time by Berthollet, 
 who, by measuring the increase in volume under- 
 gone by a measured quantity of ammonia gas, 
 and determining the nature of the gases produced 
 by the passage of the electric sparks, proved that 
 ammonia is a compound of hydrogen and nitrogen, 
 and that three volumes of the former gas combine 
 with one volume of the latter to produce two 
 volumes of ammonia gas. 
 
 Priestley's experiments on " inflammable air " or 
 hydrogen are important and interesting. The 
 existence of this substance as a definite kind of 
 air had been proved by the accurate researches of 
 Cavendish in 1766. Priestley drew attention to many 
 actions in which this inflammable air is produced, 
 chiefly to those which take place between acids and 
 metals. He showed that inflammable air is not 
 decomposed by electric sparks ; but he thought that 
 it was decomposed by long-continued heating in 
 closed tubes made of lead-glass. Priestley re- 
 garded inflammable air as an air containing much 
 phlogiston. He found that tubes of lead-glass, 
 filled with this air, were blackened when strongly 
 heated for a long time, and he explained this by 
 saying that the lead in the glass had a great 
 
FOUNDERS OF CHEMISTRY PRIESTLEY. 6/ 
 
 affinity for phlogiston, and drew it out of the 
 inflammable air. 
 
 When inflammable air burns in a closed vessel 
 containing common air, the latter after a time loses 
 its property of supporting combustion. Priestley 
 gave what appeared to be a fairly good explanation 
 of this fact, when he said that the inflammable air 
 parted with phlogiston, which, becoming mixed 
 with the ordinary air in the vessel, rendered it un- 
 able to support the burning of a candle. He gave 
 a few measurements in support of this explanation ; 
 but we now know that the method of analysis which 
 he employed was quite untrustworthy. 
 
 Thinking that by measuring the extent to which 
 the phlogistication (we would now say the deoxida- 
 tioii) of common air was carried by mixing measured 
 quantities of common and inflammable airs and 
 exploding this mixture, he might be able to 
 determine the amount of phlogiston in a given 
 volume of inflammable air, he mixed the two airs 
 in glass tubes, through the sides of which he had 
 cemented two pieces of wire, sealed the tubes, and 
 exploded the" mixture by passing electric sparks 
 from wire to wire. The residual air now contained, 
 according to Priestley, more phlogiston, and there- 
 fore relatively less dephlogisticated air than before 
 the explosion. He made various measurements of 
 the quantities of dephlogisticated air in the tubes, 
 but without getting any constant results. He 
 noticed that after the explosions the insides of the 
 tubes were covered with moisture. At a later 
 
68 HEROES OF SCIENCE. 
 
 time he exploded a mixture of dephlogisticated 
 and inflammable airs (oxygen and hydrogen) in a 
 copper globe, and recorded the fact that after the 
 explosion the globe contained a little water. 
 Priestley was here apparently on the eve of a 
 great discovery. " In looking for one thing," says 
 Priestley, " I have generally found another, and 
 sometimes a thing of much more value than that 
 which I was in quest of." Had he performed the 
 experiment of exploding dephlogisticated and in- 
 flammable airs with more care, and had he made 
 sure that the airs used were quite dry before the 
 explosion, he would probably have found a thing 
 of indeed much more value than that of which he 
 was in quest ; 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 Priestley. 
 
 Some very curious observations were made by 
 Priestley regarding the colour of the gas obtained 
 by heating "spirit of nitre" (i.e. nitric acid). He 
 showed that a yellow gas or air is obtained by 
 heating colourless liquid spirit of nitre in a sealed 
 glass tube, and that as the heating is continued 
 the colour of the gas gets darker, until" it is finally 
 very dark orange red. These experiments have 
 found an explanation only in quite recent times. 
 
 Another discovery made by Priestley while in 
 Birmingham, viz. that an acid is formed when 
 electric sparks are passed through ordinary air for 
 some time, led, in the hands of Cavendish an ex- 
 
FOUNDERS OF CHEMISTRY PRIESTLEY. 69 
 
 perimenter who was as careful and deliberate as 
 Priestley was rapid and careless to the demon- 
 stration of the composition of nitric acid. 
 
 Many observations were made by Priestley on the 
 effects of various airs on growing plants and living 
 animals ; indeed, 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 breathing. 
 He grew sprigs of mint in common air, in dephlo- 
 gisticated air (oxygen), and in phlogisticated 
 air (nitrogen, but probably not pure) ; the sprig 
 in the last-named air grew best, while that in the 
 dephlogisticated air soon appeared sickly. He also 
 showed that air which has been rendered "noxious" 
 by the burning of a candle in it, or by respiration 
 or putrefaction, could be restored to its original 
 state by the action of growing plants. He thought 
 that the air was in the first instance rendered 
 noxious by being impregnated with phlogiston, 
 and that the plant restored the air by removing 
 this phlogiston. Thus Priestley distinctly showed 
 that (to use his own words) "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 it, and the putrefaction of such 
 vast masses, both of vegetable and animal sub- 
 stances, exposed to it, is, in part at least, repaired 
 by the vegetable creation." But from want of 
 quantitative experiments he failed to give any just 
 explanation of the process whereby this "repara- 
 tion " is accomplished. 
 
70 HEROES OF SCIENCE. 
 
 During his stay in Birmingham, Priestley was 
 busily engaged, as was his wont during life, in 
 writing metaphysical and theological treatises arid 
 pamphlets. 
 
 At this time the minds of men in England 
 were much excited by the events of the French 
 Revolution, then being enacted before them. 
 Priestley and some of his friends were known to 
 sympathize with the French people in this great 
 struggle, as they had been on the side of the 
 Americans in the War of Independence. Priestley's 
 political opinions had, in fact, always been more 
 advanced than the average opinion of his age ; by 
 some he was regarded as a dangerous character. 
 But if we read what he lays down as a fundamental 
 proposition in the " Essay on the First Principles 
 of Civil Government" (1768), we cannot surely 
 find anything very startling. 
 
 " It must be understood, whether it be expressed 
 or not, that all people live in society for their 
 mutual advantage ; so that the good and happiness 
 of the members, that is the majority of the 
 members of any state, is the great standard by 
 which everything relating to that state must be 
 finally determined. And though it may be sup- 
 posed that a body of people may be bound by a 
 voluntary resignation of all their rights to a single 
 person, or to a few, it can never be supposed that the 
 resignation is obligatory on their posterity, because 
 it is manifestly contrary to the good of the whole 
 that it should be so." 
 
FOUNDERS OF CHEMISTRY PRIESTLEY. 7 1 
 
 Priestley proposed many political reforms, but 
 he was decidedly of opinion that these ought to 
 be brought about gradually. He was in favour of 
 abolishing all religious State establishments, and 
 was a declared enemy to the Church of England. 
 His controversies with the clergy of Birmingham 
 helped to stir up a section of public opinion against 
 him, and to bring about the condemnation of his 
 writings in many parts of the country ; he was also 
 unfortunate in making an enemy of Mr. Burke, 
 who spoke against him and his writings in the 
 House of Commons. 
 
 In the year 1791, the day of the anniversary of 
 the taking of the Bastille was celebrated by some 
 of Priestley's friends in Birmingham. On that day 
 a senseless mob, raising the cry of " Church and 
 King," caused a riot in the town. Finding that 
 they were not checked by those in authority, they 
 after a time attacked and burned Dr. Priestley's 
 meeting-house, and then destroyed his dwelling- 
 house, and the houses of several other Dissenters 
 in the town. One of his sons barely escaped with 
 his life. He himself found it necessary to leave 
 Birmingham for London, as he considered his life 
 to be in danger. Many of his manuscripts, his 
 library, and much of his apparatus were destroyed, 
 and his house was burned. 
 
 A congregation at Hackney had the courage 
 at this time to invite Priestley to become their 
 minister. Here he remained for about three years, 
 ministering to the congregation, and pursuing his 
 
72 HEROES OF SCIENCE. 
 
 chemical and other experiments with the help of 
 apparatus and books which had been supplied by 
 his friends, and by the expenditure of part of the 
 sum, too small to cover his losses, given him by 
 Government in consideration of the damage done 
 to his property in the riots at Birmingham. 
 
 But finding himself more and more isolated and 
 lonely, especially after the departure of his three 
 sons to America, which occurred during these years, 
 he at last resolved to follow them, and spend 
 the remainder of his days in the New World. 
 Although Priestley had been very badly treated 
 by a considerable section of the English people, 
 yet he left his native country "without any resent- 
 ment or ill will." "When the time for reflection," 
 he says, "shall come, my countrymen will, I am 
 confident, do me more justice." He left England 
 in 1/95, and settled at Northumberland, in Penn- 
 sylvania, about a hundred and thirty miles north- 
 west of Philadelphia. By the help of his friends in 
 England he was enabled to build a house and 
 establish a laboratory and a library ; an income 
 was also secured sufficient to maintain him in 
 moderate comfort. 
 
 The chair of chemistry in the University of 
 Philadelphia was offered to him, and he was also 
 invited to the charge of a Unitarian chapel in New 
 York ; but he preferred to remain quietly at work 
 in his laboratory and library, rather than again to 
 enter into the noisy battle of life. In America 
 he published several writings. Of his chemical 
 
FOUNDERS OF CHEMISTRY PRIESTLEY. 73 
 
 discoveries made after leaving England, the most 
 important was that an inflammable gas is obtained 
 by heating metallic calces with carbon. The pro- 
 duction of this gas was regarded by Priestley as 
 an indisputable proof of the justness of the theory 
 of phlogiston (see pp. 63, 64). 
 
 His health began to give way about 1801 ; 
 gradually his strength declined, and in February 
 1804, the end came quietly and peacefully. 
 
 A list of the books and pamphlets published by 
 Priestley on theological, metaphysical, philological, 
 historical, educational and scientific subjects would 
 fill several pages of this book. His industry was 
 immense. To accomplish the vast amount of work 
 which he did required the most careful outlay of 
 time. In his " Memoirs," partly written by himself, 
 he tells us that he inherited from his parents "a 
 happy temperament of body and mind ; " his father 
 especially was always in good spirits, and " could 
 have been happy in a workhouse." His paternal 
 ancestors had, as a race, been healthy and long- 
 lived. He was rot himself robust as a youth, yet 
 he was always able to study : " I have never found 
 myself," he says, "less disposed or less qualified 
 for mental exertion of any kind at one time of the 
 day more than another ; but all seasons have been 
 equal to me, early or late, before dinner or after." 
 
 His peculiar evenness of disposition enabled him 
 quickly to recover from the effects of any un- 
 pleasant occurrence; indeed, he assures us that 
 "the most perfect satisfaction" often came a day 
 
74 HEROES OF SCIENCE. 
 
 or two after "an event that afflicted me the most, 
 and without any change having taken place in the 
 state of things." 
 
 Another circumstance which tended to make 
 life easy to him was his fixed resolution, that in 
 any controversy in which he might be engaged, he 
 would frankly acknowledge every mistake he per- 
 ceived himself to have fallen into. 
 
 Priestley's scientific work is marked by rapidity 
 of execution. The different parts do not hang 
 together well ; we are presented with a brilliant 
 series of discoveries, but we do not see the con- 
 necting strings of thought. We are not then 
 astonished when he tells us that sometimes he 
 forgot that he had made this or that experiment, 
 and repeated what he had done weeks before. He 
 says that he could not work in a hurry, and that 
 he was therefore always methodical ; but he adds 
 that he sometimes blamed himself for "doing to-day 
 what had better have been put off until to-morrow." 
 
 Many of his most startling discoveries were the 
 results of chance operations, " not of themes 
 worked out and applied." He was led to the dis- 
 covery of oxygen, he says, by a succession of 
 extraordinary accidents. But that he was able 
 to take advantage of the chance observations, and 
 from these to advance to definite facts, constitutes 
 the essential difference between him and ordinary 
 plodding investigators. Although he rarely, if 
 ever, saw all the bearings of his own discoveries, 
 although none of his experiments was accurately 
 
FOUNDERS OF CHEMISTRY PRIESTLEY. 75 
 
 worked out to its conclusion, yet he did see, 
 rapidly and as it appeared almost at one glance, 
 something of their meanings, and this something 
 was enough to urge him on to fresh experimental 
 work. 
 
 Although we now condemn Priestley's theories 
 as quite erroneous, yet we must admire his un- 
 daunted devotion to experiment. He was a true 
 student of science in one essential point, viz. 
 Nature was for him the first and the last court 
 of appeal. He theorized and speculated much, he 
 experimented rapidly and not accurately, but he 
 was ever appealing to natural facts ; and in doing 
 this he could not but lay some foundation which 
 should remain. The facts discovered by him are 
 amongst the very corner-stones on which the 
 building of chemical science was afterwards raised. 
 
 So enthusiastic was Priestley in the prosecution 
 of his experiments, that when he began, he tells 
 us, " I spent all the money I could possibly raise, 
 carried on by my ardour in philosophical investi- 
 gation, and entirely regardless of consequences, 
 except so far as never to contract any debts." He 
 seems all through his life to have been perfectly 
 free from anxiety about money affairs. 
 
 Priestley's manner of work shows how kindly 
 and genial he was. He trained himself to talk and 
 think and write with his family by the fireside ; 
 " nothing but reading aloud, or speaking without 
 interruption," was an obstruction to his work. 
 
 Priestley was just the man who was wanted in 
 
76 HEROES OF SCIENCE. 
 
 the early days of chemical science. By the vast 
 number, variety and novelty of his experimental 
 results, he astonished scientific men he forcibly 
 drew attention to the science in which he laboured 
 so hard ; by the brilliancy of some of his experi- 
 ments he obliged chemists to admit that a new 
 field of research was opened before them, and the 
 instruments for the prosecution of this research 
 were placed in their hands ; and even by the un- 
 satisfactoriness of his reasoning he drew attention 
 to the difficulties and contradictions of the theories 
 which then prevailed in chemistry. 
 
 That the work of Priestley should bear full fruit 
 it was necessary that a greater than he should 
 interpret it, and should render definite that which 
 Priestley had but vaguely shown to exist. 
 
 The man who did this, and who in doing it 
 really established chemistry as a science, was 
 Lavoisier. 
 
 But before considering the work of Lavoisier, 
 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 Boyle. In the 
 "Sceptical Chymist," published in 1661, Mr. Boyle 
 had established the fact that air is a material sub- 
 stance possessed of weight, that this air presses on 
 the surface of all things, and that by removing 
 part of the air in an enclosed space the pressure 
 within that space is diminished. He had demon- 
 strated that the boiling point of water is dependent 
 
FOUNDERS OF CHEMISTRYPRIESTLEY. 77 
 
 on the pressure of the air on the surface of the 
 water. Having boiled some water " a pretty while, 
 that by the heat it might be freed from the latitant 
 air," 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 space ; 
 as soon as he began to suck out air from this re- 
 ceiver, the water boiled " as if it had stood over a 
 very quick fire. . . . Once, when the air had been 
 drawn out, the liquor did, upon a single exsuction, 
 boil so long with prodigiously vast bubbles, that 
 the effervescence lasted almost as long as was 
 requisite for the rehearsing of a Pater noster" 
 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 subjected ; he had shown by simple and 
 accurate experiments that " the volume varies in- 
 versely as the pressure." He had established the 
 generalization of so much importance in physical 
 science now known as Boyle's law. 
 
 The work of the Honourable Henry Cavendish 
 will be considered in some detail in the book on 
 "The Physicists" belonging to this series, but I 
 must here briefly allude to the results of his ex- 
 periments on air published in the Philosophical 
 Transactions for 1784 and 1785. 
 
 Cavendish held the ordinary view that when a 
 metal burns in air, the air is thereby phlogis- 
 ticated ; but why is it, he asked, that the volume 
 of air is decreased by this process ? It was very 
 
7 HEROES OF SCIENCE. 
 
 generally said that fixed air was produced during 
 the calcination of metals, and was absorbed by the 
 calx. But Cavendish instituted a series of experi- 
 ments which proved that no fixed air could be ob- 
 tained from metallic calces. In 1766 inflammable 
 air (hydrogen) was discovered by Cavendish ; he 
 now proved that when this air is exploded with 
 dephlogisticated air (oxygen), water is produced. 
 He showed that when these two airs are mixed in 
 about the proportion of two volumes of hydrogen 
 to one volume of oxygen, the greater part, if not 
 the whole of the airs is condensed into water by 
 the action of the electric spark. He then pro- 
 ceeded to prove by experiments that when common 
 air is exploded with inflammable air water is like- 
 wise produced, and phlogisticated air (i.e. nitrogen) 
 remains. 
 
 Priestley and Cavendish had thus distinctly 
 established the existence of three kinds of air, 
 viz. dephlogisticated air, phlogisticated air, and 
 inflammable air. Cavendish had shown that 
 when the last named is exploded with common 
 air water is produced (which is composed of 
 dephlogisticated and inflammable airs), and phlo- 
 gisticated air remains. Common air had thus 
 been proved to consist of these two phlogisticated 
 and dephlogisticated airs (nitrogen and oxygen). 
 Applying these results to the phenomenon of the 
 calcination of metals, Cavendish gave reasons for 
 thinking that the metals act towards common air 
 in a manner analogous to that in which inflam- 
 
FOUNDERS OF CHEMISTRY LAVOISIER. 79 
 
 mable air acts that they withdraw dephlogisti- 
 cated and leave phlogisticated air ; but, as he was 
 a supporter of the phlogistic theory, he rather 
 preferred to say that the burning metals withdraw 
 dephlogisticated air and phlogisticate that which 
 remains ; in other words, while admitting that a 
 metal in the process of burning gains dephlogisti- 
 cated air, he still thought that the metal also loses 
 something^ viz. phlogiston. 
 
 That Cavendish in 1783-84 had proved air to 
 consist of two distinct gases, and water to be pro- 
 duced by the union of two gases, must be remem- 
 bered as we proceed with the story of the discoveries 
 of Lavoisier. 
 
 ANTOINE LAURENT LAVOISIER, born in Paris in 
 1743, was the son of a wealthy merchant, who, 
 judging from his friendship with many of the men 
 of science of that day, was probably of a scientific 
 bent of mind, and who certainly showed that he 
 was a man of sense by giving his son the best 
 education which he could obtain. After studying 
 in the Mazarin College, Lavoisier entered on a 
 course of training in physical, astronomical, botani- 
 cal and chemical science. The effects of this 
 training in the accurate methods of physics are 
 apparent in the chemical researches of Lavoisier. 
 
 At the age of twenty-one Lavoisier wrote a 
 memoir which gained the prize offered by the 
 French Government for the best and most econo- 
 mical method of lighting the streets of a large city. 
 
8O HEROES OF SCIENCE. 
 
 While making experiments, the results of which 
 were detailed in this paper, Lavoisier lived for six 
 weeks in rooms lighted only by artificial light, in 
 order that his eyesight might become accustomed 
 to small differences in the intensities of light from 
 various sources. When he was twenty-five years 
 old Lavoisier was elected a member of the Aca- 
 demy of Sciences. During the next six years 
 (1768-1774) he published various papers, some on 
 chemical, some on geological, and some on mathe- 
 matical subjects. Indeed at this time, although an 
 ardent cultivator of natural science, he appears to 
 have been undecided as to which branch of science 
 he should devote his strength. 
 
 The accuracy and thoroughness of Lavoisier's 
 work, and the acuteness of his reasoning powers, 
 are admirably illustrated in two papers, published 
 in the Memoirs of the Academy for 1770, on the 
 alleged conversion of water into earth. 
 
 When water is boiled for a long time in a glass 
 vessel a considerable quantity of white siliceous 
 earth is found in the vessel. This apparent con- 
 version or transmutation of water into earthy 
 matter was quite in keeping with the doctrines 
 which had been handed down from the times of 
 the alchemists ; the experiment was generally 
 regarded as conclusively proving the possibility of 
 changing water into earth. Lavoisier found that 
 after heating water for a hundred and one days in 
 a closed and iveighed glass vessel, there was no 
 change in the total weight of the vessel and its 
 
FOUNDERS OF CHEMISTRYLAVOISIER, 8 1 
 
 contents ; when he poured out the water and 
 evaporated it to dryness, he obtained 20*4 grains 
 of solid earthy matter ; but he also found, what 
 had been before overlooked, that the glass vessel 
 had lost weight. The actual loss amounted to 
 17*4 grains. The difference between this and 
 the weight of the earthy matter in the water, 
 viz. three grains, was set down (and as we now 
 know justly set down) by Lavoisier to errors 
 of experiment. Lavoisier therefore concluded that 
 water, when boiled, is not changed into earth, 
 but that a portion of the earthy matter of which 
 glass is composed is dissolved by the water. This 
 conclusion was afterwards confirmed by the Swe- 
 dish chemist Scheele, who proved that the com- 
 position of the earthy matter found in the water 
 is identical with that of some of the constituents 
 of glass. 
 
 By this experiment Lavoisier proved the old 
 alchemical notion of transmutation to be erroneous ; 
 he showed that water is not transmuted into earth, 
 but that each of these substances is possessed of 
 definite properties which belong to it and to it 
 only. He established the all-important generaliza- 
 tion which subsequent research has more amply 
 confirmed, 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 altera- 
 tion in the total mass of matter taking part in that 
 change. The glass vessel in which Lavoisier 
 boiled water for so many days lost weight ; but 
 
 ill. G 
 
82 HEROES OF SCIENCE, 
 
 the matter lost by the glass was found dissolved 
 in the water. 
 
 We know that this generalization holds good in 
 all chemical changes. Solid sulphur may be con- 
 verted into liquid oil of vitriol, but it is only by the 
 sulphur combining with other kinds of matter ; the 
 weight of oil of vitriol produced is always exactly 
 equal to the sum of the weights of the sulphur, 
 hydrogen and oxygen which have combined to form 
 it. The colourless gases, hydrogen and oxygen, 
 combine, and the limpid liquid water is the result ; 
 but the weight of the water produced is equal to 
 the sum of the weights of hydrogen and oxygen 
 which combined together. It is impossible to 
 overrate the importance of the principle of the 
 conservation of mass, "first definitely established by 
 Lavoisier. 
 
 Some time about the year 1770 Lavoisier turned 
 his attention seriously to chemical phenomena. In 
 1774 he published a volume entitled "Essays 
 Physical and Chemical," wherein he gave an his- 
 torical account of all that had been done on the 
 subject of airs from the time of Paracelsus to 
 the year 1774, and added an account of his own 
 experiments, in which he had established the facts 
 that a metal in burning absorbs air, and that when 
 the metallic calx is reduced to metal by heating 
 with charcoal, an air is produced of the same nature 
 as the fixed air of Dr. Black. 
 
 In November 1772 Lavoisier deposited a sealed 
 note in the hands of the Secretary to the Academy 
 
FOUNDERS OF CHEMISTRY LAVOISIER. 83 
 
 of Sciences. This note was opened on the ist of 
 May 1773, and found to run as follows* : 
 
 " About eight days ago I discovered that sulphur 
 in burning, far from losing, augments in weight ; 
 that is to say, that from one pound of sulphur 
 much more than one pound of vitriolic acid is 
 obtained, without reckoning the humidity of the 
 air. Phosphorus presents the same phenomenon. 
 This augmentation of weight arises from a great 
 quantity of air which becomes fixed during the 
 combustion, and which combines with the vapours. 
 
 "This discovery, confirmed by experiments 
 which I regard as decisive, 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 com- 
 bustion and calcination ; and I was persuaded that 
 the augmentation of weight in the calces of 
 
 proceeded from the same cause. The experiment 
 fully confirmed my conjectures. 
 
 " I operated the reduction of litharge in closed 
 vessels with Hale's apparatus, and I observed that 
 at the moment of the passage of the calx into the 
 metallic state, there was a disengagement of air 
 in considerable quantity, and that this air formed 
 a volume at least one thousand times greater than 
 that of the litharge employed. 
 
 " As this discovery appears to me one of the most 
 interesting which has been made since Stahl, I 
 
 * The translation is taken from Thomson's " History of 
 Chemistry." 
 
84 HEROES OF SCIENCE. 
 
 thought it expedient to secure to myself the pro- 
 perty, by depositing the present note in the hands 
 of the Secretary of the Academy, to remain secret 
 till the period when I shall publish my experiments, 
 
 " LAVOISIER, 
 
 "Paris, nth November 1772." 
 
 In his paper " On the Calcination of Tin in 
 Closed Vessels, and on the Cause of Increase of 
 Weight acquired by the Metal during this Process " 
 (published in 1774), we see and admire Lavoisier's 
 manner of working. A weighed quantity (about 
 half a pound) of tin was heated to melting in a 
 glass retort, the beak of which was drawn out to 
 a very small opening ; the air within the retort 
 having expanded, the opening was closed by melt- 
 ing the glass before the blowpipe. The weight of 
 retort and tin was now noted ; the tin was again 
 heated to its melting point, and kept at this tem- 
 perature as long as the process of calcination 
 appeared to proceed ; the retort and its contents 
 were then allowed to cool and again weighed. No 
 change was caused by the heating process in the 
 i total weight of the whole apparatus. The end of 
 the retort beak was now broken off; air rushed in 
 with a hissing sound. The retort and contents were 
 again weighed, and the increase over the weight 
 at the moment of sealing the retort was noted. 
 The calcined tin in the retort was now collected 
 and weighed. It was found that the increase in the 
 weight of the tin was equal to the weight of the air 
 
FOUNDERS OF CHEMISTRY LAVOISIER. 85 
 
 which rushed into the retort. Hence Lavoisier con- 
 cluded that the calcination of tin was accompanied 
 by an absorption of air, and that the difference be- 
 tween the weights of the tin and the calx of tin 
 was equal to the weight of air absorbed ; but he 
 states that probably only a part of the air had com- 
 bined with the tin, and that hence air is not a 
 simple substance, but is composed of two or more 
 constituents. 
 
 Between the date of this publication and that of 
 Lavoisier's next paper on combustion we know 
 that Priestley visited Paris. In his last work, " The 
 Doctrine of Phlogiston established " (published in 
 1800), Priestley says, "Having made the discovery 
 of dephlogisticated air some time before I was 
 in Paris in 1774, I mentioned it at the table of Mr. 
 Lavoisier, when most of the philosophical people 
 in the city were present ; saying that it was a kind 
 of air in which a candle burned much better than in 
 common air, but I had not then given it any name. 
 At this all the company, and Mr. and Mrs. 
 Lavoisier as much as any, expressed great surprise. 
 I told them that I had got it from precipitatum per 
 se, and also from red lead" 
 
 In 1775 Lavoisier's paper, " On the Nature of the 
 Principle which combines with the Metals during 
 their Calcination, and which augments their 
 Weight," was read before the Academy. The pre- 
 paration and properties of an air obtained, in 
 November 1774, from red precipitate are described, 
 but Priestley's name is not mentioned. It seems 
 
86 HEROES OF SCIENCE. 
 
 probable, however, that Lavoisier learned the exist- 
 ence and the mode of preparation of this air from 
 Priestley ; * but we have seen that even in 1779 
 Priestley was quite in the dark as to the true nature 
 of the air discovered by him (p. 60). 
 
 In papers published in the next three or four 
 years Lavoisier gradually defined and more tho- 
 roughly explained the phenomenon of combustion. 
 He burned phosphorus in a confined volume 
 of air, and found that about one-fourth of the air 
 disappeared, that the residual portion of air was 
 unable to support combustion or to sustain animal 
 life, that the phosphorus was converted into a white 
 substance deposited on the sides of the vessel in 
 which the experiment was performed, and that for 
 each grain of phosphorus . used about two and a 
 half grains of this white solid were obtained. He 
 further described the properties of the substance 
 produced by burning phosphorus, gave it the 
 name of phosphoric acid, and described some of the 
 substances formed by combining it with various 
 bases. 
 
 The burning of candles in air was about this 
 time studied by Lavoisier. He regarded his experi- 
 ments as proving that the air which remained after 
 burning a candle, and in which animal life could 
 not be sustained, was really present before the 
 burning ; that common air consisted of about one- 
 fourth part of dcphlogisticated air and three- 
 
 * Nevertheless, in other places Lavoisier most readily acknow- 
 ledges the merits of Priestley. 
 
FOUNDERS OF CHEMISTRYLAVOISIER, 8/ 
 
 fourths of azotic air (i.e. air incapable of sustaining 
 life) ; and that the burning candle simply com- 
 bined with, and so removed the former of these, 
 and at the same time produced more or less fixed 
 air. 
 
 In his treatise on chemistry Lavoisier describes 
 more fully his proof that the calcination of a metal 
 consists in the removal, by the metal, of dephlogis- 
 ticated air (or oxygen) from the atmosphere, and 
 that the metallic calx is simply a compound of metal 
 and oxygen. The experiments are sfrictly quantita- 
 tive and are thoroughly conclusive. iHe placed four 
 ounces of pure mercury in a glass balloon, the neck 
 of which dipped beneath the surface of mercury in 
 a glass dish, and then passed a little way up into a 
 jar containing fifty cubic inches of air, and standing 
 in the mercury in the dish. There was thus free 
 communication between the air in the balloon and 
 that in the glass jar, but no communication be- 
 tween the air inside and that outside the whole 
 apparatus. The mercury in the balloon was 
 heated nearly to its boiling point for twelve days, 
 during which time red-coloured specks gradually 
 formed on the surface of the metal ; at the end of 
 this time it was found that the air in the glass jar 
 measured between forty-two and forty-three cubic 
 inches. The red specks when collected amounted 
 to forty-five grains ; they were heated in a very 
 small retort connected with a graduated glass 
 cylinder containing mercury. Between seven and 
 eight cubic inches of pure dephlogisticated air 
 
HEROES OF SCIENCE. 
 
 (oxygen) were obtained in this cylinder, and forty- 
 one and a half grains of metallic mercury remained 
 when the decomposition of the red substance was 
 completed. 
 
 The conclusion drawn by Lavoisier from these 
 experiments was that mercury, when heated nearly 
 to boiling in contact with air, withdraws oxygen 
 from the air and combines with this gas to form red 
 precipitate ', and that when the red precipitate which 
 has been thus formed is strongly heated, it parts 
 with the whole of its oxygen, and is changed back 
 again into metallic mercury. 
 
 Lavoisier had now (17/7-78) proved that the 
 calces of mercury, tin and lead are compounds 
 of these metals with oxygen ; and that the oxygen 
 is obtained from the atmosphere when the metal 
 burns. But the phlogistic chemistry was not yet 
 overthrown. We have seen that the upholders 
 of phlogiston believed that in the inflammable air 
 of Cavendish they had at last succeeded in obtain- 
 ing the long-sought-for phlogiston. Now they 
 triumphantly asked, Why, when metals dissolve in 
 diluted vitriolic or muriatic acid with evolution of in- 
 flammable air, are calces of these metals produced ? 
 And they answered as triumphantly, Because 
 these metals lose phlogiston by this process, and 
 we know that a calx is a metal deprived of its 
 phlogiston. 
 
 Lavoisier contented himself with observing that 
 a metallic calx always weighed more than the 
 metal from which it was produced ; and that as 
 
j 
 
 FOUNDERS OF CHEMISTRY LAVOISIER. 89 
 
 inflammable air, although much lighter than com- 
 mon air, was distinctly possessed of weight, it was 
 not possible that a metallic calx could be metal 
 deprived of inflammable air. He had given a 
 simple explanation of the process of calcination, 
 and had proved, by accurate experiments, that this 
 explanation was certainly true in some cases. 
 Although all the known facts about solution of 
 metals in acids could not as yet be brought within 
 his explanation, yet none of these facts was abso- 
 lutely contradictory of that explanation. He was 
 content to wait for further knowledge. And to 
 gain this further knowledge he set about devising 
 and performing new experiments. The upholders 
 of the theory of phlogiston laid considerable stress 
 on the fact that metals are produced by heating 
 metallic calces in inflammable air; the air is ab- 
 sorbed, they said, and so the metal is reproduced. 
 It was obviously of the utmost importance that 
 Lavoisier should learn more about this inflammable 
 air, and especially that he should know exactly 
 what happened when this air was burned. He 
 therefore prepared to burn a large quantity of 
 inflammable air, arranging the experiment so that 
 he should be able to collect and examine the 
 product of this burning, whatever should be 
 the nature of that product. But at this time 
 the news was brought to Paris that Cavendish 
 had obtained water by burning mixtures of in- 
 flammable and dephlogisticated airs. This must 
 have been a most exciting announcement to 
 
90 HEROES OF SCIENCE. 
 
 Lavoisier; he saw how much depended on the 
 accuracy of this statement, and as a true student of 
 Nature, he at once set about to prove or disprove it. 
 On the 24th of June 1783, in the presence of the 
 King and several notabilities (including Sir Charles 
 Blagden, Secretary of the Royal Society, who had 
 told Lavoisier of the experiments of Cavendish), 
 Lavoisier and Laplace burned inflammable and 
 dephlogisticated airs, and obtained water. As the 
 result of these experiments they determined that 
 one volume of dephlogisticated air combines with 
 i '9 1 volumes of inflammable air to form water. 
 
 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 hot, inflammable air is evolved and calx 
 of iron remains in the tube. 
 
 Lavoisier could now explain the conversion of a 
 metallic calx into metal by the action of inflam- 
 mable air ; this air decomposes the calx that is, 
 the metallic oxide combines with its oxygen to 
 form water, and so the metal is produced. 
 
 When a metal is dissolved in diluted vitriolic or 
 muriatic acid a calx is formed, because, according 
 to Lavoisier, the water present is decomposed by 
 the metal, inflammable air is evolved, and the 
 dephlogisticated air of the water combines with 
 the metal forming a calx, which then dissolves in 
 the acid. 
 
 Lavoisier now studied the properties of the com- 
 pounds produced by burning phosphorus, sulphur 
 
FOUNDERS OF CHEMISTRY LAVOISIER. gi 
 
 and carbon in dephlogisticated air. He found that 
 solutions of these compounds in water had a more 
 or less sour taste and turned certain blue colouring 
 matters red ; but these were the properties regarded 
 as especially belonging to acids. These products of 
 combustion in dephlogisticated air were therefore 
 acids ; but as phosphorus, carbon and sulphur were 
 not themselves acids, the acid character of the sub- 
 stances obtained by burning these bodies in dephlo- 
 gisticated air must be due to the presence in them 
 of this air. Hence Lavoisier concluded that this 
 air is the substance the presence of which in a 
 compound confers acid properties on that com- 
 pound. This view of the action of dephlogisticated 
 air he perpetuated in the name "oxygen" (from 
 Greek, = acid-producer], which he gave to dephlo- 
 gisticated air, and by which name this gas has ever 
 since been known. 
 
 Priestley was of opinion that the atmosphere is 
 rendered noxious by the breathing of animals, be- 
 cause it is thereby much phlogisticated, and he 
 thought that his experiments rendered it very pro- 
 bable that plants are able to purify this noxious air 
 by taking away phlogiston from it (see p. 69). But 
 Lavoisier was now able to give a much more definite 
 account of the effects on the atmosphere of animal 
 and vegetable life. He had already shown that or- 
 dinary air contains oxygen and azote (nitrogen), and 
 that the former is alone concerned in the process of 
 combustion. He was now able to show that animals 
 during respiration draw in air into their lungs ; that 
 
92 HEROES OF SCIENCE. 
 
 a portion of the oxygen is there combined with 
 carbon to form carbonic acid gas (as the fixed air 
 of Black was now generally called), which is again 
 expired along with unaltered azote. Respiration 
 was' thus proved to .be a process chemically analo- 
 gous to that of calcination. 
 
 Thus, about the year 1784-85, the theory of 
 phlogiston appeared to be quite overthrown. The 
 arguments of its upholders, after this time, were 
 not founded on facts ; they consisted of fanciful 
 interpretations of crudely performed experiments. 
 Cavendish was the only opponent to be dreaded 
 by the supporters of the new chemistry. . But we 
 have seen that although Cavendish retained the 
 language of the phlogistic theory (see pp. 78, 79) as 
 in his opinion equally applicable to the facts of com- 
 bustion with that of the new or Lavoisierian theory, 
 he nevertheless practically admitted the essential 
 point of the latter, viz. that calces are compounds 
 of metal and oxygen (or dephlogisticated air). 
 Although Cavendish was the first to show that 
 water is produced when the two gases hydrogen 
 and oxygen are exploded together, it would yet 
 appear that he did not fully grasp the fact that 
 - water is a compound of these two gases ; it was 
 left to Lavoisier to give a clear statement of this 
 all-important fact, and thus to remove the last prop 
 from under the now tottering, but once stately 
 edifice built by Stahl and his successors. 
 
 The explanation given by Lavoisier of com- 
 bustion was to a great extent based on a concep- 
 
FOUNDERS OF CHEMISTRY LAVOISIER. 93 
 
 tion of element and compound very different from 
 that of the older chemists. In the " Sceptical 
 Chymist " (1661) Boyle had argued strongly against 
 the doctrine of the four "elementary principles," 
 earth, air, fire and water, as held by the " vulgar 
 chymists." The existence of these principles, or 
 some of them, in every compound substance was 
 firmly held by most chemists in Boyle's time. They 
 argued thus : when a piece of green wood burns, the 
 existence in the wood of the principle of fire is 
 made evident by the flame, of the principle of air 
 by the smoke which ascends, of that of water by 
 the hissing and boiling sound, and of the principle 
 of earth by the ashes which remain when the burn- 
 ing is finished.* 
 
 Boyle combated the inference that because a 
 flame is visible round the burning wood, and a light 
 air or smoke ascends from it, therefore these prin- 
 ciples were contained in the wood before combustion 
 began. He tried to prove by experiments that one 
 substance may be obtained from another in which 
 the first substance did not already exist ; thus, he 
 heated water for a year in a closed glass vessel, and 
 obtained solid particles heavier than, and as he 
 supposed formed from, the water. We have already 
 
 * A similar method of reasoning was employed so far back as the 
 tenth century : thus, in an Anglo-Saxon " Manual of Astronomy" 
 we read, " There is no corporeal thing which has not in it the four 
 elements, that is, air and fire, earth and water. . . . Take a stick 
 and rub it on something, it becomes hot directly with the fire which 
 lurks in it ; burn one end, then goeth the moisture out at the other 
 end with the smoke." 
 
94 HEROES OF SCIENCE. 
 
 learned the true interpretation of this experiment 
 from the work of Lavoisier. Boyle grew various 
 vegetables in water only, and thought that he had 
 thus changed water into solid vegetable matter. 
 He tells travellers' tales of the growth of pieces of 
 iron and other metals in the earth or while kept in 
 underground cellars. 
 
 We now know how erroneous in most points this 
 reasoning was, but we must admit that Boyle es- 
 tablished one point most satisfactorily, viz. that 
 because earth, or air, or fire, or water is obtained 
 by heating or otherwise decomposing a substance, 
 it does not necessarily follow that the earth, or air, 
 or fire, or water existed as such in the original sub- 
 stance. He overthrew the doctrine of elementary 
 principles held by the "vulgar chymists." De- 
 fining elements as "certain primitive and simple 
 bodies which, not being made of any other bodies, 
 or of one another, are the ingredients of which all 
 those called perfectly mixt bodies are immediately 
 compounded, and into which they are ultimately 
 resolved," Boyle admitted the possible existence, 
 but thought that the facts known at his time did 
 not warrant the assertion of the certain existence, 
 of such "elements." The work of Hooke and 
 Mayow on combustion tended to strengthen this 
 definition of " element " given by Boyle. 
 
 Black, as we have seen, clearly proved that certain 
 chemical substances were possessed of definite and 
 unvarying composition and properties ; and Lavoi- 
 sier, indirectly by his explanation of combustion, 
 
FOUNDERS OF CHEMISTRY LAVOISIER. 95 
 
 and directly in his " Treatise on Chemistry," laid 
 down the definition of " element " which is now 
 universally adopted. 
 
 An element is a substance from which no simpler 
 forms of matter that is, no forms of matter each 
 weighing less than the original substance have as 
 yet been obtained. 
 
 In the decade 1774-1784 chemical science was 
 thus established on a sure foundation by Lavoisier. 
 Like most great builders, whether of physical or 
 mental structures, he used the materials gathered 
 by those who came before him, but the merit of 
 arranging these materials into a well-laid founda- 
 tion, on which the future building might firmly 
 rest, is due to him alone. 
 
 The value of Lavoisier's work now began to 
 be recognized by his fellow-chemists in France. 
 In 1785 Berthollet, one of the most rising of the 
 younger French chemists, declared himself a con- 
 vert to the views of Lavoisier on combustion. 
 Fourcroy, another member of the Academy, soon 
 followed the example of Berthollet. Fourcroy, 
 knowing the weakness of his countrymen, saw that 
 if the new views could be made to appear as espe- 
 cially the views of Frenchmen, the victory would 
 be won ; he therefore gave to the theory of Lavoisier 
 the name"Z# cJdmie Fran$aise" Although this 
 name was obviously unfair to Lavoisier, it never- 
 theless caused the antiphlogistic theory to be iden- 
 tified with the French chemists, and succeeded in 
 impressing the French public generally with the 
 
96 HEROES OF SCIENCE. 
 
 idea that to hold to the old theory was to be a traitor 
 to the glory of one's country. M. de Morveau, 
 who held a prominent place both in politics and 
 science, was invited to Paris, and before long was 
 persuaded to embrace the new theory. This conver- 
 sion for " the whole matter was managed as if it 
 had been a political intrigue rather than a philo- 
 sophical inquiry" was of great importance to 
 Lavoisier and his friends. M. de Morveau was 
 editor of the chemical part of the " Encyclopedic 
 Methodique ; " in that part of this work which had 
 appeared before 1784 De Morveau had skilfully 
 opposed the opinions of Lavoisier, but in the second 
 part of the work he introduced an advertisement 
 announcing the change in his opinions on the sub- 
 ject of combustion, and giving his reasons for this 
 change. 
 
 The importance of having a definite language in 
 every science is apparent at each step of advance. 
 Lavoisier found great difficulty in making his 
 opinions clear because he was obliged to use a lan- 
 guage which had been introduced by the phlogistic 
 chemists, and which bore the impress of that theory 
 on most of its terms. About the years 1785-1787, 
 Lavoisier, Berthollet, Fourcroy and De Morveau 
 drew up a new system of chemical nomenclature. 
 The fundamental principles of that system have 
 remained as those of every nomenclature since pro- 
 posed. They are briefly these : 
 
 An element is a substance from which no form of 
 matter simpler than itself has as yet been obtained. 
 
FOUNDERS OF CHEMISTRY -LAVOISIER. 9; 
 
 Every substance is to be regarded as an element 
 until it is proved to be otherwise. 
 
 The name of every compound is to tell of what 
 elements the substance is composed, and it is to 
 express as far as possible the relative amounts of 
 the elements which go to form the compound. 
 
 Thus the compounds of oxygen with any other 
 element were called oxides, e.g. iron oxide, mercury 
 oxide, tin oxide, etc. When two oxides of iron 
 came to be known, one containing more oxygen 
 relatively to the amount of iron present than the 
 other, that with the greater quantity of oxygen 
 was called iron peroxide, and that with the smaller 
 quantity iron protoxide. 
 
 We now generally prefer to use the name of the 
 element other than oxygen in adjectival form, and 
 to indicate the relatively smaller or greater quantity 
 of oxygen present by modifications in the termina- 
 tion of this adjective. Thus iron protoxide is now 
 generally known as ferrous oxide, and iron per- 
 oxide as fernV oxide. But the principles laid 
 down by the four French chemists in 1785-1787 
 remain as the groundwork of our present system of 
 nomenclature. 
 
 The antiphlogistic theory was soon adopted by 
 all French chemists of note. We have already seen 
 that Black, with his usual candour and openness to 
 conviction, adopted and taught this theory, and we 
 are assured by Dr. Thomas Thomson that when he 
 attended Black's classes, nine years after the pub- 
 lication of the French system of nomenclature, that 
 ' in. II 
 
98 HEROES OF SCIENCE. 
 
 system was in general use among the chemical 
 students of the university. The older theory was 
 naturally upheld by the countrymen of the distin- 
 guished Stahl after it had been given up in France. 
 In the year 1792 Klaproth, who was then Professor 
 of Chemistry in Berlin, proposed to the Berlin 
 Academy of Sciences to repeat the more important 
 experiments on which the Lavoisierian theory 
 rested, before the Academy. His offer was ac- 
 cepted, and from that time most of the Berlin 
 chemists declared themselves in favour of the new 
 theory. 
 
 By the close of last century the teaching 01 
 Lavoisier regarding combustion found almost uni- 
 versal assent among chemists. But this teaching 
 carried with it, as necessary parts, the fundamental 
 distinction between element and compound ; the de- 
 nial of the existence of "principles" or "essences ;" 
 the recognition of the study of actually occurring 
 reactions between substances as the basis on which 
 all true chemical knowledge was to be built ; and 
 the full acknowledgment of the fact that matter is 
 neither created nor destroyed, but only changed as 
 to its form, in any chemical reaction. 
 
 Of Lavoisier's other work I can only mention 
 the paper on " Specific Heats " contributed by La- 
 place and Lavoisier to the Memoirs of the Academy 
 for 1780. In this paper is described the ice calori- 
 meter, whereby the amount of heat given out by a 
 substance in cooling from one definite temperature 
 to another is determined, by measuring the amount 
 
FOUNDERS OF CHEMISTRY LAVOISIER. 99 
 
 of ice converted into water by the heated substance 
 in cooling through the stated interval of tempera- 
 ture. The specific heats of various substances, e.g. 
 iron, glass, mercury, quicklime, etc., were deter- 
 mined by the help of this instrument. 
 
 As we read the record of work done by Lavoisier 
 during the years between 1774 and 1794 work 
 which must have involved a great amount of con- 
 centrated 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 time. 
 
 In the earlier days of the French Revolution, 
 and in the time immediately preceding that move- 
 ment, many minds had been stirred to see the 
 importance of the study of Nature ; but it was 
 impossible that natural science should continue to 
 flourish when the tyrant Robespierre had begun 
 the Reign of Terror. 
 
 The roll of those who perished during this time 
 contains no more illustrious name than that of 
 Antoine Laurent Lavoisier. In the year 1794 
 Lavoisier, who had for some time acted as a.fer- 
 mier-general under the Government, was accused 
 of mixing with the tobacco " water and other in- 
 gredients hurtful to the health of the citizens." 
 On this pretext he and some of his colleagues were 
 condemned to death. For some days Lavoisier 
 found a hiding-place among his friends, but hearing 
 that his colleagues had been arrested, he delivered 
 
I GO HEROES OF SCIENCE. 
 
 himself up to the authorities, only asking that the 
 death sentence should not be executed until he had 
 completed the research in which he was engaged ; 
 " not " that he was " unwilling to part with life," 
 but because he thought the results would be " for 
 the good of humanity." 
 
 " The Republic has no need of chemists ; the 
 course of justice cannot be suspended," was the 
 reply. 
 
 On the 8th of May 1794, the guillotine did its 
 work ; and in his fifty-first year Lavoisier "joined 
 the majority." 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 science, 
 braving the wrath of Robespierre, penetrated to 
 the dungeons of the prison and placed a wreath on 
 the grave of their comrade. 
 
 The period of the infancy of chemical science 
 which I have now briefly described is broadly con- 
 temporaneous with the second half of the eighteenth 
 century. 
 
 At this time the minds of men were greatly 
 stirred. Opinions and beliefs consecrated by the 
 assent of generations of men were questioned or 
 denied ; the pretensions of civil and ecclesiastical 
 authorities were withstood; assertions however 
 strongly made, and by whatever authority sup- 
 ported, were met by demands for reasons. In 
 France this revolt against mere authority was 
 especially marked. Led by the great thinker 
 
FOUNDERS OF CHEMISTRY. IOI 
 
 Voltaire, the French philosophers attacked the 
 generally accepted views in moral, theological 
 and historical matters. A little later they began 
 to turn with eager attention and hope to the facts 
 of external Nature. Physical science was cultivated 
 with wonderful vigour and with surprising success. 
 
 In the sciences of heat and light we have at this 
 time the all-important works of Fourier, Prevost 
 and Fresnel ; in geology and natural history we 
 have Buffon and Cuvier ; the name of Bichat marks 
 the beginning of biological science, and chemistry 
 takes rank as a science only from the time of 
 Lavoisier. 
 
 From the philosophers an interest in natural 
 science spread through the mass of the people. 
 About the year 1870 the lecture-rooms of the 
 great teachers of chemistry, astronomy, electricity, 
 and even anatomy were crowded with ladies and 
 gentlemen of fashion in the French capital. A 
 similar state of matters was noticeable in this 
 country. Dr. Black's lecture theatre was filled by 
 an audience which comprised many young men of 
 good position. To know something of chemistry 
 became an essential part of the training of all who 
 desired to be liberally educated. 
 
 The secrets of Nature were now rapidly ex- 
 plored ; astonishing advances were made, and as a 
 matter of course much opposition was raised. 
 
 In this active, inquiring atmosphere the young 
 science of chemistry grew towards maturity. 
 
 Priestley, ever seeking for new facts, announcing 
 
102 HEROES OF SCIENCE, 
 
 discovery after discovery, attacking popular belief 
 in most matters, yet satisfied to interpret his scien- 
 tific discoveries in terms of the hypothesis with 
 which he was most familiar, was the pioneer of the 
 advancing science. 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 body : his w r ork was not to level the rough 
 parts of the way, or to fill in the miry places with 
 well-laid metal, but rather rapidly to make a road 
 as far into the heart of the country as possible. 
 
 And we have seen how well he did the work. 
 In his discovery of various kinds of airs, notably 
 of oxygen, he laid the basis of the great generali- 
 zations of Lavoisier, and, what was perhaps of even 
 more importance, he introduced a new method into 
 chemistry. He showed the existence of a new and 
 unexplored region. Before his time, Hooke and 
 Mayow had proved the existence of more than one 
 kind of air, but the chemistry of gases arose with 
 the discoveries of Priestley. 
 
 Although Black's chief research, on fixed air and 
 on latent heat, was completed fifteen or twenty 
 years before Priestley's discovery of oxygen, yet 
 the kind of work done by Black, and its influence 
 on chemical science, mark him as coming after 
 Priestley in order of development. We have seen 
 that the work of Black was characterized by 
 thoroughness and suggestiveness. The largeness 
 of scope, the breadth of view, of this great philo- 
 sopher are best illustrated in his discourses on 
 
FOUNDERS OF CHEMISTRY, 103 
 
 heat ; he there leads us with him in his survey of 
 the domain of Nature, and although he tells us 
 that hypotheses are a "mere waste of time," 
 we find that it is by the strength of his imagi- 
 nation that he commands assent. But he never 
 allows the imagination to degenerate into fanciful 
 guesses ; he vigorously tests the fundamental facts 
 of his theory, and then he uses the imagination in 
 developing the necessary consequences of these facts. 
 
 To Black we owe not only the first rigorously 
 accurate chemical investigation, but also the estab- 
 lishment of just ideas concerning the nature of heat. 
 
 But Lavoisier came before us as a greater than 
 either Priestley or Black. To great accuracy and 
 great breadth of view he added wonderful power 
 of generalizing ; with these, aided by marked 
 mental activity and, on the whole, favourable 
 external circumstances, he was able finally to over- 
 throw the loose opinions regarding combustion and 
 elementary principles which prevailed before his 
 time, and so to establish chemistry as one of the 
 natural sciences. 
 
 At the close of the first period of advance we 
 find that the sphere of chemistry has been defined ; 
 that the object of the science has been laid down, 
 as being to find an explanation of the remarkable 
 changes noticed in the properties of bodies ; that 
 as a first step towards the wished-for explanation, 
 all material substances have been divided by the 
 chemist into elements and compounds ; that an 
 element has been defined as any kind of matter 
 
104 HEROES OF SCIENCE. 
 
 from a given weight of which no simpler forms of 
 matter that is, no kinds of matter each weighing 
 less than the original matter have as yet been 
 obtained ; that the great principle of the inde- 
 structibility of matter has been established, viz. 
 that however the properties of matter may be 
 altered, yet the total mass (or quantity) remains 
 unchanged ; and lastly, we find that an explanation 
 of one important class of chemical changes those 
 changes which occur when substances burn has 
 been found. 
 
 And we have also learned that the method by 
 which these results were obtained was this to 
 go to Nature, to observe and experiment accurately, 
 to consider carefully the results of these experi- 
 ments, and so to form a general hypothesis ; by the 
 use of the mental powers, and notably by the use 
 of the imagination, to develop the necessary deduc- 
 tions from this hypothesis ; and finally, to try these 
 deductions by again inquiring from Nature " whether 
 these things were so." 
 
 Before the time which we have been considering 
 the paths of chemical science had scarcely yet 
 been trodden. Each discovery was full of promise, 
 each advance displayed the possibility of further 
 progress; the atmosphere was filled as with "a 
 mighty rushing wind " ready to sweep away the 
 old order of things. The age was an age of doubt 
 and of freedom from the trammels of authority ; 
 it was a time eminently suited for making advances 
 in natural knowledge, 
 
FOUNDERS OF CHEMISTRY. 105 
 
 In the unceasing activity of Priestley and Lavoi- 
 sier we may trace the influence of the restlessness 
 of the age ; but in the quietness and strength of 
 the best work of these men, and notably in the 
 work of Black ; in the calmness with which 
 Priestley bore his misfortunes at Birmingham ; in 
 the noble words of Lavoisier, " I am not unwilling 
 to part with life, but I ask time to finish my ex- 
 periments, because the results will, I believe, 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 her," 
 
CHAPTER III, 
 
 ESTABLISHMENT OF GENERAL PRINCIPLES OF 
 CHEMICAL SCIENCE PERIOD OF DALTON. 
 
 John Dalton, 1766-1844. 
 
 THE progress of chemical knowledge became so 
 rapid in the early years of the present century, 
 that although I have in this chapter called the 
 time immediately succeeding that of Lavoisier 
 " the period of John Dalton," and although I shall 
 attempt to describe the advances made by this 
 philosopher without considering those of his con- 
 temporaries Davy and Berzelius, yet I must insist 
 on the facts that this arrangement is made purely 
 for the sake of convenience, and that many of the 
 discoveries of Davy, Berzelius and others came 
 in order of time before, or followed close upon the 
 publication of Dalton's atomic theory. 
 
 Nevertheless, as the work of these men belongs 
 in its essence to the modern period, and as the 
 promulgation of the atomic theory by Dalton 
 
CHEMICAL PRINCIPLES ESTABLISHED. IO/ 
 
 marks the beginning of this period, 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 successors. 
 
 JOHN DALTON, the second of three children of 
 Joseph and Deborah Dalton, was born at Eagles- 
 field, a village near Cockermouth, in Cumberland, 
 on the 5th of September 1766. One of the first 
 meeting-houses established by the Society of 
 Friends is to be found in Eaglesfield. 
 
 The Dalton family had been settled for several 
 generations on a small copyhold estate in this 
 village. The first of them to join the Friends was 
 the grandfather of John Dalton ; his descendants 
 remained faithful adherents of this society. 
 
 Dalton attended the village schools of Eagles- 
 field and the neighbourhood until he was eleven 
 years old, by which time, in addition to learning 
 reading, writing and arithmetic, he had "gone 
 through a course of mensuration, surveying, navi- 
 gation, etc." At the age of ten his taste for 
 measurements and calculations began to be re- 
 marked by those around him ; this taste was en- 
 couraged by Mr. Robinson, a relative of Dalton, 
 who recognizing the indomitable perseverance of 
 the boy appears to have taken some care about 
 this time in directing his mathematical studies. 
 
 At the early age of twelve Dalton affixed to the 
 door of his father's house a large sheet of paper 
 
IOS HEROES OF SCIENCE. 
 
 whereon he announced that he had opened a 
 school for youth of both sexes ; also that " paper, 
 pens and ink " were sold within. The boy-teacher 
 had little authority over his pupils, who challenged 
 their master to fight in the graveyard, and broke 
 the windows of the room into which they had 
 been locked till their tasks should be learned. 
 
 When he was fifteen years old Dalton removed 
 to Kendal, where he continued for eleven or twelve 
 years, at first as assistant-master, and then, along 
 with his elder brother Jonathan, as principal of a 
 boarding school for boys. 
 
 It was announced by the brothers that in this 
 school " youth will be carefully instructed in 
 English, Latin, Greek and French ; also writing, 
 arithmetic, merchants' accounts and the mathe- 
 matics." The school was not very successful. 
 Both brothers were hard, inflexible, and ungainly 
 in their habits, and neither was fitted to become 
 a successful teacher of boys : of the two, John had 
 the gentler disposition, and was preferred by the 
 boys ; " besides, his mind was so occupied by 
 mathematics that their faults escaped his notice." 
 
 During this time Dalton employed his leisure in 
 learning Latin, Greek and French, and in pursuing 
 his studies in mathematics and natural philosophy. 
 He became a frequent contributor to the Gentle- 
 men's Diary, a paper which received problems of 
 various kinds chiefly mathematical and pre- 
 sented prizes for their successful solution. 
 
 Besides setting and answering mathematical 
 
CHEMICAL PRINCIPLES ESTABLISHED. 109 
 
 problems in this journal, and also in the Ladies' 
 Diary, Dalton sometimes ventured into the wider 
 fields of mental phenomena. It seems strange to 
 read that, even at the age of twenty-six, Dalton 
 should occupy his leisure time composing answers 
 to such queries as these : 
 
 " Whether, to a generous mind, is the conferring 
 or receiving an obligation, the greater pleasure ? " 
 
 " Is it possible for a person of sensibility and 
 virtue, who has once felt the passion of love in the 
 fullest extent that the human heart is capable of 
 receiving it (being by death or some other cir- 
 cumstance for ever deprived of the object of its 
 wishes), ever to feel an equal passion for any other 
 object ? " 
 
 In his answer to the second of these queries, 
 Dalton carefully framed two hypotheses, and as 
 carefully drew conclusions from each. The 
 question in the Diary was by " Mira ;" if " Mira" 
 were a " rapturous maiden " she would not derive 
 much comfort from the cold and mathematical 
 answer by " Mr. John Dalton of Kendal." 
 
 At Kendal Dalton made the acquaintance of Mr. 
 Gough, who was about eight years older than Dal- 
 ton, and had been blind from the age of two. Mr. 
 Gough, we are assured by Dalton, was "a perfect 
 master of the Latin, Greek and French tongues ; " 
 he understood "well all the different branches of 
 mathematics ; " there was " no branch of natural 
 philosophy but what he was well acquainted with ; " 
 he knew "by the touch, taste and smell, almost 
 
110 HEROES OF SCIENCE. 
 
 every plant within twenty miles of Kendal." To 
 the friendship of this remarkable man Dalton owed 
 much ; with his help he acquired a fair knowledge 
 of the classical languages, and he it was who set 
 Dalton the example of keeping a regular record 
 of weather observations. 
 
 On the 24th of March 1787 Dalton made his 
 first entry in a book which he entitled " Obser- 
 vations on the Weather, etc. ; " the last entry in this 
 book he made fifty-seven years later on the evening 
 preceding his death. The importance of Dalton's 
 meteorological observations, as leading him to the 
 conception of the atomic theory, will be noticed 
 as we proceed. 
 
 In the year 1793 Dalton, who was now twenty- 
 seven years of age, was invited to Manchester to 
 become tutor in the mathematical and natural 
 philosophy department of a college recently 
 established by influential Dissenters in that town. 
 Eighty pounds for the session of ten months was 
 guaranteed him ; and he was provided with "rooms 
 and commons " in the college at a charge of 
 27 los. per session. 
 
 He held this appointment for six years, when he 
 retired, and continuing to live in Manchester de- 
 voted himself to researches in natural philosophy, 
 gaining a living by giving private lessons in mathe- 
 matics and physical science at a charge of 2s. 6d. 
 per hour, or is. 6d. each if more than two pupils 
 attended at the same time. 
 
 Dalton was elected a Fellow of the Literary 
 
CHEMICAL PRINCIPLES ESTABLISHED. Ill 
 
 and Philosophical Society of Manchester in the 
 year 1/94 ; 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 Street, in 
 studying and teaching. The fifty years thus spent 
 are marked by few outward events. The history 
 of Dalton's life from this time is the history of the 
 development of his intellect, and the record of his 
 scientific discoveries. 
 
 On one occasion during Dalton's stay at Kendal, 
 as he was about to make a visit to his native 
 village, he bethought himself that the present of a 
 pair of silken hose would be acceptable to his 
 mother. He accordingly purchased a pair marked 
 "newest fashion;" but his mother's remark, 
 " Thou hast brought me a pair of grand hose, John ; 
 but what made thee fancy so light a colour ? I 
 can never show myself at meeting in them," 
 rather disconcerted him, as to his eyes the hose 
 were of the orthodox drab colour. His mother 
 insisted that the stockings were " as red as a 
 cherry." John's brother upheld the "drab" side 
 of the dispute ; so the neighbours were called in, 
 and gave their decision that the hose were " varra 
 fine stuff, but uncommon scarlety." 
 
 From this time Dalton made observations on the 
 peculiarities of his own vision and that of others, 
 and in his first paper read before the Literary and 
 Philosophical Society in 1794, he described these 
 peculiarities, He says, " Since the year 1790 the 
 
112 HEROES OF SCIENCE. 
 
 occasional study of botany obliged me to attend 
 more to colour than before. With respect to 
 colours that were white, yellow, or green, I readily 
 assented to the appropriate term ; blue, purple, 
 pink and crimson appeared rather less distinguish- 
 able, being, according to my idea, all referable to 
 blue. I have often seriously asked a person 
 whether a flower was blue or pink, but was gene- 
 rally considered to be in jest." Dalton's colour- 
 blindness was amusingly illustrated at a later time, 
 when having been created D.C.L. by the University 
 of Oxford he continued to wear the red robes of his 
 degree for some days ; and when his attention was 
 drawn to the somewhat strange phenomenon, even 
 in a university town, of an elderly gentleman in 
 the dress of a Quaker perambulating the town day 
 after day in a scarlet robe, he remarked that to 
 him the gown appeared to be of the same colour 
 as the green trees. 
 
 Dalton's work during the next six or eight years 
 dealt chiefly with problems suggested by his 
 meteorological observations ; he published a 
 volume on " Meteorological Observations and 
 Essays," chiefly occupied with descriptions of the 
 instruments employed, more especially of the ther- 
 mometer and barometer, and an instrument for de- 
 termining the dew-point of air. By this time he had 
 established the existence of a connection of some 
 kind between magnetism and the aurora, and had 
 thus laid the foundations of a most important 
 branch of meteorology. 
 
CHEMICAL PRINCIPLES ESTABLISHED. 113 
 
 In 1799, in a note to a paper on rain and dew, 
 he begins his work on aqueous vapour in the atmo- 
 sphere by proving- that water vapour exists as 
 such in the air. This paper is quickly followed by 
 another on the conducting power of water for heat. 
 
 A very important paper was published in 1801, 
 on the " Constitution of Mixed Gases, etc.," 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 gas ; in 
 other words, 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 
 mixture. In a paper published much later (1826), 
 when his views and experiments on this subject 
 were matured, he writes : " It appears to me as 
 completely demonstrated as any physical principle, 
 that whenever two or more . . . gases or vapours 
 . . . are put together, either into a limited or un- 
 limited space, they will finally be arranged each as 
 if it occupied the whole space, and the others were 
 not present ; the nature of the fluids and gravita- 
 tion being the only efficacious agents." 
 
 This conclusion was followed out and extended 
 in a paper published in 1803, on the absorption of 
 gases by water and other liquids, 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 mixture, the 
 other gases exerting no influence in this respect. 
 
 Dalton now considered the variation in the 
 
 III. I 
 
114 HEROES OF SCIENCE. 
 
 pressures of various gases caused by increasing or 
 decreasing temperature, and then proceeded to 
 discuss the relations which exist between the 
 volumes of gases and the temperature at which 
 these volumes are measured. He concluded that 
 " all elastic fluids " under the same pressure ex- 
 pand equally by heat : and he adds the very im- 
 portant remark, " It seems, therefore, 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 Dalton. 
 
 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 
 air, that is, the temperature at which the de- 
 position of water in the liquid form begins. The 
 introduction of this method for finding the humidity 
 of air marks an important advance in the history 
 of meteorology. 
 
 In this series of papers published within the 
 first three years of the present century Dalton evi- 
 dently had before his mind's eye a picture of a gas 
 as a quantity of matter built up of small but 
 independent particles ; he constantly speaks ol 
 pressures between the small particles of elastic 
 
CHEMICAL PRINCIPLES ESTABLISHED. 115 
 
 fluids, of these particles as repelling'each other, etc. 
 In his " New System" he says, "A vessel full of any 
 pure elastic fluid presents to the imagination a 
 picture like one full of small shot." 
 
 It is very important to notice that Dalton makes 
 use of this conception of small particles to explain 
 purely physical experiments and operations. 
 Although we know that during these years he 
 was thinking much of "chemical combinations," 
 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 small, 
 equally heavy particles. A consideration of these 
 papers by Dalton on the constitution of mixed 
 gases shows us the method which he pursued in 
 his investigations. " The progress of philosophical 
 knowledge," he says, " is advanced by the discovery 
 of new and important facts ; but much more when 
 these facts lead to the establishment of general 
 laws." Dalton always strove to attain to general 
 laws. The facts which he describes are frequently 
 inaccurate ; he was singularly deficient in manipula- 
 tion, and he cannot claim a high place as a careful 
 experimenter. He was however able to draw 
 general conclusions of wide applicability. He 
 seems sometimes to have stated a generalization 
 in definite form before he had obtained any ex- 
 perimental verification of it. 
 
 In the year 1802 Dalton conducted an examina- 
 tion of air from various localities, and concluded 
 
Il6 HEROES OF SCIENCE. 
 
 that one hundred volumes of air are composed of 
 twenty-one volumes of oxygen and seventy-nine 
 volumes of nitrogen. This appears to have been 
 his first piece of purely chemical work. But in the 
 next year he again returns to physical phenomena. 
 In the paper already referred to, on the absorption 
 of gases by water and other liquids, published in 
 this year, he had stated that " All gases that enter 
 into water and other liquids by means of pressure, 
 and are wholly disengaged again by the removal of 
 that pressure, are mechanically mixed with the 
 liquid, and not chemically combined with it." But 
 if this be so, why, he asked, does not water me- 
 chanically dissolve the same bulk of every kind of 
 gas ? The answer which he gives to this question 
 is found at the close of the paper ; to the student of 
 chemistry it is very important : 
 
 "This question I have duly considered, and 
 though I am not yet able to satisfy myself com- 
 pletely, I am nearly persuaded that the circumstance 
 depends upon the weight and number of the 
 ultimate particles of the several gases, those whose 
 particles are lightest and single being least absorb- 
 able, and the others more, accordingly as they 
 increase in weight and complexity. An inquiry 
 into the relative weights of the ultimate particles 
 of bodies is a subject, as far as I know, entirely 
 new. I have lately been prosecuting this inquiry 
 with remarkable success. The principle cannot be 
 entered upon in this paper ; but I shall just sub- 
 join the results, as far as they appear to be 
 
CHEMICAL PRINCIPLES ESTABLISHED. 1 1/ 
 
 ascertained by my experiments." Then follows a 
 " Table of the relative 10 eights of the ultimate 
 particles of gaseous and other bodies" The follow- 
 ing numbers, among others, are given : 
 
 Hydrogen I Sulphur 14*4 
 
 Oxygen 5-5 Alcohol I5'I 
 
 Azote 4*2 Nitrous oxide 137 
 
 Phosphorus 7 "z Ether 9-6 
 
 Here is the beginning of the atomic theory ; and 
 yet Dalton's strictly chemical experimental work 
 lies in the future. The scope of the theory is 
 defined in that sentence "An inquiry into the rela- 
 tive weights of the ultimate particles of bodies" His 
 paper on mixed gases is illustrated by a plate,* 
 which shows how vividly Dalton at this time pic- 
 tured to himself a quantity of gas as composed of 
 many little particles, and how clearly he recognized 
 the necessity of regarding all the particles of each 
 elementary gas as alike, but as differing from those 
 of every other elementary gas. 
 
 In 1804 Dalton was invited to deliver a course 
 of lectures in the Royal Institution of London, on 
 heat, mixed gases and similar subjects. In these 
 lectures he expounded his views on the constitu- 
 tion of gases, on absorption of gases by liquids, etc. 
 These views drew much attention in this and other 
 
 * See Fig. 2, which is copied from the original in the "New 
 System of Chemical Philosophy," and illustrates Dalton's concep- 
 tion of a quantity of carbonic acid gas, each atom built up of one 
 atom of carbon and two of oxygen ; of nitrous oxide gas, each atom 
 composed of one atom of nitrogen and one of oxygen ; and of hydro- 
 gen gas, constituted of single atom?. 
 
nS 
 
 HEROES OF SCIENCE. 
 
 countries. 
 
 
 ' 
 
 " They are busy with them," he writes 
 in 1804, "at London, 
 Edinburgh, Paris and 
 in various parts of 
 Germany, some main- 
 taining one side and 
 some another. The 
 truth will surely out 
 at last." 
 
 Dalton's love of 
 numerical calculations 
 is noticeable in a 
 trivial circumstance 
 which he mentions in 
 a letter from London 
 to his brother. He 
 tried to count the 
 number of coaches 
 which he met in going 
 to the Friends' morn- 
 ing meeting : this he 
 assures his brother he 
 "effected with toler- 
 able precision. The 
 number was one hun- 
 dred and four." 
 
 During vacation 
 time Dalton usually 
 made a walking ex- 
 cursion in the Lake 
 district. He was ex- 
 
CHEMICAL PRINCIPLES ESTABLISHED. IIQ 
 
 tremely fond of mountain scenery, but generally 
 combined the pursuit of science with that of 
 pleasure ; he carried his meteorological instruments 
 with him, determined the dew-point at various 
 altitudes, and measured mountain heights by the 
 aid of his barometer. Sometimes however he 
 refused to have anything to do with science. A 
 companion in one of these excursions says that he 
 was "like a schoolboy enjoying a holiday, mocking 
 the cuckoos, putting up and chasing the hares, stop- 
 ping from time to time to point out some beautiful 
 view, or loitering to chat with passing pedestrians." 
 
 This side of Dalton's nature was not often 
 apparent. In him the quiet, hard-working student 
 generally appeared prominently marked ; but on the 
 half-holiday which he allowed himself on each 
 Thursday afternoon, in order to enjoy the society 
 of a few friends and to engage in his favourite 
 amusement of a game at bowls, he laid aside 
 something of the quietness, regularity and decorum 
 which usually characterized him. " When it came 
 to his turn to bowl he threw his whole soul into 
 the game, . . . and it was not a little amusing 
 to spectators to see him running after the ball 
 across the green, stooping down as if talking to it, 
 and waving his hands from one side to the other 
 exactly as he wished the line of the ball to be, and 
 manifesting the most intense interest in its coming 
 near to the point at which he aimed." 
 
 From the year 1803-4 Dalton becomes more 
 and more a worker in chemistry. The establish- 
 
120 HEROES OF SCIENCE. 
 
 ment of the atomic theory now engaged most of 
 his time and attention. The results of his investiga- 
 tion of " the primary laws which seem to obtain in 
 regard to heat and to chemical combinations" 
 appeared in his " New System of Chemical 
 Philosophy," Part I. of which, " On Heat, on the 
 Constitution of Bodies and on Chemical Synthe- 
 sis," was published in 1808. 
 
 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 world ; 
 but I think we shall do better to postpone our con- 
 sideration of this great inquiry until we have com- 
 pleted our review of the chief events in the life of 
 Dalton, other than this the greatest event of all. 
 
 Dalton did not look for rewards he desired only 
 the just fame of one who sought for natural truths ; 
 but after the publication of the " New System " re- 
 wards began to come to him. In 1817 he was 
 elected a corresponding member of the French 
 Academy of Sciences. 
 
 In 1822, when his fame as a philosophical chemist 
 was fully established, Dalton visited Paris. This 
 visit gave him great pleasure. He was constantly 
 in the society of the great men who then so nobly 
 represented the dignity of natural science in France ; 
 Laplace, Cuvier, Biot, Arago, Gay-Lussac, Milne- 
 Edwards and others were his friends. For some 
 time after this visit he was more vivacious and 
 communicative than usual, and we are told by one 
 
CHEMICAL PRINCIPLES ESTABLISHED. 1 21 
 
 who lived in the same house as he, " We frequently 
 bantered him with having become half a French- 
 man." Dalton especially valued the friendship of 
 Clementine Cuvier, daughter of the great naturalist, 
 with whom he became acquainted during his visit 
 to Paris. All through life he greatly delighted in 
 the society of cultivated women, and his warmest 
 friendships were with gentlewomen. At one time, 
 shortly after going to Manchester, he was much 
 taken by a widow lady who combined great per- 
 sonal charms with considerable mental culture. 
 " During my captivity" he writes to a friend, 
 "which lasted about a week, I lost my appetite, 
 and had other symptoms of bondage about me, as 
 incoherent discourse, etc., but have now happily 
 regained my freedom." The society of men who 
 like himself were actively engaged in the investi- 
 gation of natural science was also a source of much 
 pleasure to Dalton. Such men used to visit him in 
 Manchester, so that in the house of the Rev. Mr. 
 Johns, in whose family he lived, " there were found 
 from time to time some of the greatest philo- 
 sophers in Europe." 
 
 Dalton was elected a Fellow of the Royal 
 Society in 1822, and four years later he became 
 the first recipient of one of the Royal Medals, 
 then founded by the King (George IV.). In 1830 
 he was elected one of the eight foreign Asso- 
 ciates of the French Academy, an honour which 
 is generally regarded as the highest that can be 
 bestowed on any man of science. 
 
122 HEROES OF SCIENCE. 
 
 Dalton was one of the original members of the 
 British Association for the Advancement of Science, 
 and he attended most of the meetings from the 
 first held in York in 1831 to that held in Man- 
 chester two years before his death. At the Oxford 
 meeting of 1832 he was created D.C.L. by the 
 University, and two years later the University of 
 Edinburgh honoured herself by enrolling his name 
 on the list of her doctors of law. 
 
 About this time some of Dalton's scientific friends, 
 who considered his work of great national import- 
 ance, endeavoured to obtain a pension for him from 
 the civil list. At the meeting of the British Asso- 
 ciation held at Cambridge in 1833, the president, 
 Professor Sedgwick, was able to announce that 
 " His Majesty, willing to manifest his attachment 
 to science, and his regard for a character like that of 
 Dr. Dalton, had graciously conferred on him, out of 
 the funds of the civil list, a substantial mark of his 
 royal favour." The "substantial mark of royal 
 favour," the announcement of which Dalton re- 
 ceived "with his customary quietness and sim- 
 plicity of manner," consisted of a pension of i$o 
 per annum, which was increased three years later 
 to 300. 
 
 The second part of Volume I. of his "New 
 System" was published by Dalton in 1810, and the 
 second volume of the same work in 1827. In 1844 
 a paper by him was read before the British Asso- 
 ciation, in which he announced some important 
 discoveries with regard to the water in crystallizable 
 
CHEMICAL PRINCIPLES ESTABLISHED. 123 
 
 salts, and thus brought a new class of facts within 
 the range of the atomic theory. 
 
 He was seized with paralysis in 1837, but re- 
 covered to a great extent ; a second attack in 1844 
 however completely prostrated him. On the i6th 
 of July in that year he made the last entry in his 
 book of "Observations on the Weather" "Little 
 rain;" next morning he became insensible and 
 quietly passed away. , 
 
 It is as the founder of the chemical atomic 
 theory that Dalton must ever be remembered by 
 all students of physical and chemical science. 
 
 To the Greek philosophers Leucippus and Demo- 
 critus (flourished about 440-400 B.C.) we owe the 
 conception that ." The bodies which we see and 
 handle, which we can set in motion or leave at 
 rest, which we can break in pieces and destroy, are 
 composed of smaller bodies, which we cannot see 
 or handle, which are always in motion, and which 
 can neither be stopped, nor broken in pieces, nor 
 in any way destroyed or deprived of the least of 
 their properties" (Clerk Maxwell). The heavier 
 among these small indivisible bodies or atoms were 
 regarded as always moving downwards. By colli- 
 sions between these and the lighter ascending atoms 
 lateral movements arose. By virtue of the natural 
 law (as they said) that things of like weight and 
 shape must come to the same place, the atoms 
 of the various elements came together ; thus 
 larger masses of matter were formed ; these again 
 
124 HEROES OF SCIENCE. 
 
 coalesced, and so finally worlds came into 
 existence. 
 
 This doctrine was extended by Epicurus (340- 
 270 B.C.), whose teaching is preserved for us in the 
 poem of Lucretius (95-52 B.C.), "De Rerum Natura;" 
 he ascribed to the atoms the power of deviating 
 from a straight line in their descending motion. 
 On this hypothesis Epicurus built a general theory 
 to explain all material and spiritual phenomena. 
 
 The ceaseless change and decay in everything 
 around them was doubtless one of the causes 
 which led men to this conception of atoms as 
 indivisible, indestructible substances which could 
 never wear out and could never be changed. But 
 even here rest could not be found ; the mind was 
 obliged to regard these atoms as always in motion. 
 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 
 agitated. In his dream as told by Tennyson 
 
 ' ' A void was made in Nature : all her bonds 
 Cracked : and I saw the flaring atom-streams 
 And torrents of her myriad universe, 
 Ruining along the illimitable inane, 
 Fly on to clash together again, and make 
 Another and another frame of things 
 For ever." 
 
 The central quest of the physicist, from the days 
 of Democritus to the present time, 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 
 
CHEMICAL PRINCIPLES ESTABLISHED. 12$ 
 
 on the properties of those things which cannot be 
 seen, but which yet exist For two thousand years 
 he has been trying to penetrate beneath the ever- 
 changing appearances of Nature, and to find some 
 surer resting-place whence he may survey these 
 shifting pictures as they pass before his mental 
 vision. The older atomists thought to find this 
 resting-place, not in the atoms themselves, but in 
 the wide spaces which they supposed to exist 
 between the worlds : 
 
 " The lucid interspace of world and world 
 Where never creeps a cloud, or moves a wind, 
 Nor ever falls the least white star of snow, 
 Nor ever lowest roll of thunder moans, 
 Nor sound of human sorrow mounts to mar 
 Their sacred everlasting calm." 
 
 To the modern student of science the idea of 
 absolute rest appears unthinkable ; 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 
 universe." 
 
 Newton conceived the atom as a "solid, massy, 
 hard, impenetrable, movable particle." To the mind 
 of D. 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 consisted. 
 
 Atomic motion was the leading idea in the ex- 
 planation of heat given by Rtimford and Davy, 
 and now universally accepted ; and, as we have 
 seen, Dalton was himself accustomed to regard all 
 
126 HEROES OF SCIENCE. 
 
 " elastic fluids " (i.e. gases) as consisting of vast 
 numbers of atoms. 
 
 But in the year 1802 or so, Dalton thought that 
 by the study of chemical combinations it would be 
 possible to determine the relative weights of atoms. 
 Assume that any elementary gas is composed of 
 small, indivisible, equally heavy parts ; assume that 
 the weight of an atom of one element is different 
 from that of the atom of any other element ; and, 
 lastly, assume that when elements combine the 
 atom of the compound so produced is built up of 
 the atoms of the various elements. Make these 
 assumptions, 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 elements. 
 
 We know that the fixity of composition of 
 chemical compounds had been established before 
 this time, largely by the labours of Black and 
 Lavoisier. Fixity of composition had however been 
 called in question by Berthollet, who held that 
 elements combine together in very varying quan- 
 tities ; that, in fact, in place of there being two or 
 three, or a few definite compounds of, say, iron and 
 oxygen, there exists a graduated series of such 
 bodies ; and that the amount of iron which com- 
 bines with oxygen depends chiefly on such physical 
 conditions as the temperature, the pressure, etc., 
 under which the chemical action occurs. But by 
 the date of the publication of the first part of 
 Dalton's " New System," the long dispute between 
 
CHEMICAL PRINCIPLES ESTABLISHED. 12; 
 
 Berthollet and Proust regarding fixity of com- 
 position of compounds had nearly closed in 
 favour of the latter chemist, who strongly upheld 
 the affirmative side of the argument. But if 
 Dalton's assumptions are correct, it is evident that 
 when two elements form more than one compound, 
 the quantity of element A in one of these must be 
 a simple multiple of the quantity in the other of 
 these compounds ; because there must be a greater 
 number of atoms of element A in the atom of 
 one compound than in that of the other com- 
 pound, and an elementary atom is assumed to be 
 indivisible. Hence it follows that if one element 
 be taken as a standard, 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 
 element ; and this number shall also represent how 
 many times the atom of the given element is heavier 
 than the atom of the standard element, the weight 
 of which has been taken to be one. If this element 
 forms two compounds with the standard element, 
 the amount of this element in the second compound 
 must be expressed by a simple multiple of the 
 number assigned to this element, because it is not 
 possible, according to the fundamental assumptions 
 of the theory, to form a compound by the com- 
 bination of fractions of elementary atoms. 
 
 By pondering on the facts regarding chemical 
 combinations which had been established by various 
 workers previous to the year 1802, Dalton had 
 
128 HEROES OF SCIENCE. 
 
 apparently come to such conclusions as those now 
 indicated. 
 
 In his paper on the properties of the gases 
 constituting the atmosphere, read to the Man- 
 chester Society on November 12, 1802, 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 nitrogen, 
 but with seventy-two measures of the same gas in 
 a wide vessel to produce another oxide of nitrogen. 
 These facts, he says, " clearly point out the theory of 
 the process : the elements of oxygen may combine 
 with a certain portion of nitrous gas, or with twice 
 that portion, but with no intermediate quantity." 
 
 In the concluding paragraph of his paper on 
 absorption of gases by liquids, read on October 
 21, 1803, we found (see p. 116) 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 weights. About this time 
 Dalton made analyses of two gaseous compounds 
 of carbon- olefiant gas and carburetted hydrogen 
 or marsh-gas. He found that both are compounds 
 of carbon and hydrogen ; that in one 4-3 parts by 
 weight of carbon are combined with one part by 
 weight of hydrogen, and in the other the same 
 amount (4-3) of carbon is combined with two parts 
 by weight of hydrogen.* 
 
 * 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 compounds. 
 
CHEMICAL PRINCIPLES ESTABLISHED. I2Q 
 
 This was a striking confirmation of his views 
 regarding combination in multiple proportions, which 
 views followed as a necessary deduction from the 
 atomic hypothesis. From this time he continued 
 to develop and extend this hypothesis, and in the 
 year 1808 he published his "New System of Che- 
 mical Philosophy." 
 
 The first detailed account of the atomic theory 
 was however given to the chemical world the year 
 before Dalton's book appeared. During a conver- 
 sation with Dalton in the autumn of 1804 Dr, 
 Thomas Thomson learned the fundamental points 
 of the new theory, and in the third edition of his 
 "System of Chemistry," published in 1807, he gave 
 an account of Dalton's views regarding the, com- 
 position of bodies. 
 
 In the same year a paper by Thomson appeared 
 in the Philosophical Transactions, wherein it was 
 experimentally proved that oxalic acid combines 
 with strontia to form two distinct compounds, one 
 of which contains twice as much oxalic acid as the 
 other, the amount of strontia being the same in 
 both. Analyses of the oxalates of potash, pub- 
 lished about the same time by Wollaston, afforded 
 another illustration of the law of multiple propor- 
 tions, and drew the attention of chemists to 
 Dalton's theory. But the new theory was opposed 
 by several very eminent chemists, notably by Sir 
 Humphry Davy. In the autumn of 1807 Wollas- 
 ton, Thomson and Davy were present at the dinner 
 of the Royal Society Club, at the Crown and 
 III. K 
 
130 HEROES OF SCIENCE. 
 
 Anchor, in the Strand. After dinner, these three 
 chemists discussed the new theory for an hour 
 and a half, Wollaston and Thomson trying to 
 convince Davy of the truth of Dalton's theory ; 
 but " so far from being convinced, he went away, if 
 possible, more prejudiced against it than ever." 
 
 Soon after this Wollaston succeeded in convincing 
 Mr. Davis Gilbert (afterwards President of the 
 Royal Society) of the justness of the atomic theory, 
 and he in turn so placed the facts and the reason- 
 ing before Davy, that from this time he became a 
 supporter of the new theory. 
 
 In order that the atomic theory should be fruitful 
 of results, it was now necessary that the values of 
 the atomic weights of many elements should be 
 carefully determined. 
 
 Let us consider what knowledge must be acquired 
 before the value to be assigned to the atomic weight 
 of an element can be found. 
 
 Hydrogen was the element chosen as a standard 
 by Dalton. He assumed that the atom of hydrogen 
 weighs I ; 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 hydrogen, Thus, when Dalton said the atomic 
 weight of oxygen is 8, he meant that the atom 
 of oxygen is eight times heavier than that of 
 hydrogen. How was this number obtained ? 
 
 Accurate analyses of water show that in this 
 liquid one part by weight of hydrogen is combined 
 with eight parts by weight of oxygen ; but (it is 
 
CHEMICAL PRINCIPLES ESTABLISHED. 131 
 
 said) as the atom of hydrogen weighs I, the atom 
 of oxygen must weigh 8. In drawing ^this con- 
 clusion it is assumed that the atom, or smallest 
 particle, of water is built up of one atom of hydrogen 
 and one atom of oxygen. Let it be assumed that 
 the atom of water contains two atoms of hydrogen 
 and one of oxygen, then the latter atom must weigh 
 sixteen times as much as each atom of hydrogen ; 
 let it be assumed that three atoms of hydrogen 
 combine with one atom of oxygen to form an 
 atom of water, then the weight of the oxygen atom 
 must be twenty-four times that of the hydrogen 
 atom. Any one of these assumptions will equally 
 satisfy the figures obtained by analyzing water 
 (i : 8 = 2 : 16 = 3: 24). Now, 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 correct, and there- 
 fore to determine the atomic weight of oxygen. 
 Hence, before the atomic weight of an element can 
 be determined, there must be found some method 
 for determining the atomic weights of compounds 
 of that element. Unless this can be done the 
 atomic theory is of little avail in chemistry. 
 
 I conceive it to be one of the signal merits of 
 Dalton that he so clearly lays down rules, the best 
 which could be devised at his time, for determin- 
 ing the atomic weights of compounds, or, what is 
 the same thing, for determining the number of 
 elementary atoms in one atom of any compound. 
 
132 HEROES OF SCIENCE. 
 
 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 com- 
 pound bodies, the number of simple elementary 
 particles which constitute one compound particle, 
 and the number of less compound particles which 
 enter into the formation of one more compound 
 particle." 
 
 Considering compounds of two elements, he 
 divides these into binary, ternary, quaternary, etc., 
 according as the compound atom contains two, 
 three, four, etc., atoms of the elements. He then 
 proceeds thus 
 
 " The following general rules may be adopted as 
 guides in all our investigations respecting chemical 
 synthesis : 
 
 " ist. When only one combination of two bodies 
 . can be obtained, it must be presumed to be a binary 
 one, unless some cause appear to the contrary. 
 
 " 2nd. When two combinations arc observed, they 
 must be presumed to be a binary and a ternary. 
 
 "3rd. When three combinations are obtained, we 
 may expect one to be binary and the other two 
 ternary. 
 
 " 4th. When four combinations are observed, we 
 should expect one binary, two ternary, and one 
 quaternary!' etc. 
 
 Only one compound of hydrogen and oxygen 
 was then known ; hence it was presumed to be a 
 binary compound, i.e. a compound the smallest 
 particle of which consisted of one atom of hydrogen 
 
CHEMICAL PRINCIPLES ESTABLISHED, 133 
 
 and one atom of oxygen ; and hence, from the data 
 already given on page 130, it followed that the 
 atomic weight of oxygen was 8. Two com- 
 pounds of carbon and oxygen were known, each 
 containing six parts by weight of carbon, in one 
 case united with eight, and in the other case with 
 sixteen parts by weight of oxygen. From Dalton's 
 rules one of these was a binary, and the other a 
 ternary compound ; but as the atomic weight of 
 oxygen had already been determined to be 8, 
 that compound of carbon and oxygen containing 
 eight of oxygen combined with six of carbon was 
 decided to be binary, and that containing sixteen 
 of oxygen (i.e. two atoms) to be ternary ; and 
 hence the atomic weight of carbon was determined 
 to be 6. 
 
 In the second part of the " New System " Dalton, 
 guided by these rules, determined experimentally 
 the atomic weights of a great many substances ; 
 but this was not the kind of work suited to Dal- 
 ton's genius. His analytical determinations were 
 generally inaccurate ; nevertheless, he clearly showed 
 how the values of the atomic weights of elements 
 ought to be established, and he obtained results 
 sufficiently accurate to confirm his general theory. 
 To make accurate determinations of the relative 
 weights of elementary atoms was one of the tasks 
 reserved for the great Swedish chemist Berzelius (see 
 pp. 162-170). When we examine Dalton's rules we 
 must confess that they appear somewhat arbitrary. 
 He does not give reasons for his assertion that 
 
134 HEROES OF SCIENCE, 
 
 " when only one combination of two bodies can be 
 obtained, it must be presumed to be a binary one." 
 Why may it not be ternary or quaternary ? Why 
 must the atom of water be built up of one atom of 
 hydrogen combined with one atom of oxygen ? Or, 
 when two compounds are known containing the same 
 pair of elements, why must one be binary and the 
 other ternary ? 
 
 Or, even assuming that this must be justified by 
 facts, does it follow that Dalton's interpretation of 
 the atomic structure of the two oxides of carbon 
 is necessarily correct ? These oxides contain 6 of 
 carbon + 8 of oxygen, and 6 of carbon + 1 6 of 
 oxygen, respectively. 
 
 Take the second, 6 : 16 = 3:8; assume this 
 to be a binary compound of one atom of oxygen 
 (weighing 8) with one atom of carbon (weighing 3), 
 then the other will be a ternary compound contain- 
 ing one atom of oxygen (8) and two atoms of 
 carbon (6). 
 
 Hence it appears that Dalton's rules were 
 too arbitrary, and that they were insufficient to 
 determine with certainty the atomic weights of 
 some of the elements. Nevertheless, without some 
 such rules as those of Dalton, no great advances 
 could have been made in applying the atomic 
 theory to the facts of chemical combination ; and 
 Dalton's rules were undoubtedly founded on wide 
 considerations. In the appendix to Volume II. of 
 his " New System " he expressly states that before 
 the number of atoms of two elements present in the 
 
CHEMICAL PRINCIPLES ESTABLISHED. 135 
 
 atom of a compound can be determined, it is neces- 
 sary that many combinations should be examined, 
 not only of these elements with each other, but also 
 of each of these with other elements ; 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 theory. 
 
 When we find that Dalton applied the term 
 " atom " to the small particles of compound bodies, 
 we at once see that by atom he could not always 
 mean " that which cannot be cut ; " he simply 
 meant the smallest particle of a substance which 
 exhibits the properties of that substance. 
 
 A mass of water vapour was conceived by Dalton 
 as " like a mass of small shot." Each shot exhibited 
 the characteristic chemical properties of water 
 vapour ; it differed 'from the large quantity of vapour 
 only in mass ; but if one of these little pieces of 
 shot were divided as Dalton, of course, knew it 
 could be divided smaller pieces of matter would 
 be produced. But these would no longer be water ; 
 they would be new kinds of matter. They are called 
 oxygen and hydrogen. 
 
 As aids towards gaining a clear conception of 
 the " atom " of a compound as a definite building, 
 Dalton made diagrammatic representations of the 
 hypothetical structures of some of these atoms : 
 the following plate is copied from the "New 
 System : " A represents an atom of alum ; B, an 
 atom of nitrate of alumina ; C, of barium chloride ; 
 
1 3 6 
 
 HEROES OF SCIENCE. 
 
 D, of barium nitrate ; E, of calcium chloride ; F, of 
 calcium nitrate ; G, of calcium sulphate ; H, of 
 
 B I A 
 
 c UT 
 
CHEMICAL PRINCIPLES ESTABLISHED, 137 
 
 potassium carbonate ; I, of potash ; and K, an 
 atom of soda. 
 
 But I think if we consider this application of the 
 term " atom " to elements and compounds alike, we 
 shall see objections to it. When an atom of a 
 compound is divided the smaller particles so pro- 
 duced are each very different in chemical properties 
 from the atom which has just been divided. We 
 may, if we choose, assume that the atom of an 
 element could in like manner be divided, and that 
 the products of this division would be different 
 from the elementary atoms ; but such a division of 
 an elementary atom has not as a matter of fact 
 been yet accomplished, unless we class among ele- 
 ments substances such as potash and soda, which 
 for many years were universally regarded as ele- 
 ments, and rightly so regarded because they had 
 not been decomposed. In Dalton's nomenclature 
 then, the term " atom " is applied alike to a small 
 particle with definite properties known to be divi- 
 sible into smaller particles, each with properties 
 different from those of the undivided particle, and 
 to a small particle which, so far as our knowledge 
 goes, cannot be divided into any particle smaller 
 than or different from itself. 
 
 Nevertheless, if the atomic theory was to be vic- 
 torious, it was necessary that it should be applied 
 to elements and compounds alike. Until a clear 
 conception should be obtained, and expressed in 
 accurate language, of the differences in structure of 
 the ultimate particles of compounds and of elements, 
 
138 HEROES OF SCIENCE, 
 
 it was perhaps better to apply the term " atom " 
 to both alike. 
 
 These two difficulties (i) the difficulty of at- 
 taching to the term " atom " a precise meaning 
 applicable to elements and compounds alike, and 
 (2) the difficulty of determining the number of 
 elementary atoms in the atom of a given compound, 
 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 theory. 
 
 The very great difficulty of clearly comprehend- 
 ing the full meaning of Dalton's proposed theory 
 becomes apparent when we learn that within three 
 years from the publication of Part I. of the " New 
 System," facts were made known by the French 
 chemist Gay-Lussac, and the true interpretation 
 of these facts was announced by the Italian chemist 
 Avogadro, which facts and interpretation were 
 sufficient to clear away both the difficulties I have 
 just mentioned ; 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 recognized. 
 
 In 1809 Gay-Lussac, in a memoir on the 
 combination of gaseous bodies, proved that gases 
 combine chemically in simple proportions by 
 volume, and that the volume of the product always 
 bears a simple relation to the volumes of the com- 
 bining gases. Thus, he showed that two* volumes 
 
CHEMICAL PRINCIPLES ESTABLISHED, 139 
 
 of hydrogen combine with one volume of oxygen 
 to form two volumes of w r ater vapour ; that one 
 volume of nitrogen combines with three volumes of 
 hydrogen to form two volumes of ammonia gas, 
 and so on. Now, as elements combine atom with 
 atom, the weights of these combining Volumes of 
 elements must represent the relative weights of the 
 atoms of the same elements. 
 
 In 1811 Avogadro distinguished between the 
 ultimate particles of compounds and elements. 
 Let a gaseous element, A, combine with another 
 gaseous element, B, to form a gaseous compound, 
 C ; then Avogadro supposed that the little particles 
 of A and the little particles of B (Dalton's atoms) 
 split up, each into two or more smaller particles, 
 and that these smaller particles then combine 
 together to form particles of the compound C. 
 The smaller particles produced by splitting a Dal- 
 tonian elementary atom were regarded by Avo- 
 gadro as all identical in properties, but these very 
 small particles could not exist uncombined either 
 with each other or with very small particles of some 
 other element. When the atom of a compound 
 is decomposed, Avogadro pictured this atom as 
 splitting into smaller particles of two or three or 
 more different kinds, according as\he compound 
 had contained two or three or mb* different 
 elements. 
 
 To Avogadro's mental vision an elementary gas 
 appeared as built up of a great many little particles, 
 each exhibiting in miniature all the properties of 
 
140 HEROES OF SCIENCE. 
 
 the gas. The gas might be heated, or cooled, or 
 otherwise physically altered, but each of the little 
 particles remained intact ; the moment however 
 that this gas was mixed with another on which 
 it could chemically react, these little particles 
 split into smaller parts, but as the smaller parts so 
 produced could not exist in this state, they seized 
 hold of the corresponding very small parts of the 
 other gas, and thus a particle of a compound gas 
 was produced. 
 
 A compound gas was pictured by Avogadro as 
 also built up of small particles, each exhibiting in 
 miniature the properties of the gas, and each re- 
 maining undecomposed when the gas was subjected 
 only to physical actions ; but when the gas was 
 chemically decomposed, each little particle split, 
 but the very small parts thus produced, being each 
 a particle of an elementary substance, continued to 
 exist, and could be recognized by the known pro- 
 perties of that element. 
 
 To the smallest particle of any substance (ele- 
 mentary or compound) which exhibits the proper- 
 ties of that substance, and which cannot be split 
 into parts without destroying these properties, we 
 now give the name of molecule. 
 
 A molecule is itself a structure. It is built up 
 of parts ; each of these parts we now call an atom. 
 The molecule of a compound is, of course, composed 
 of the atoms of the elements which form that com- 
 pound. The molecule may contain two or three or 
 more unlike atoms. The molecule of an element is 
 
CHEMICAL PRINCIPLES ESTABLISHED. 141 
 
 composed of the atoms of that element, and all of 
 these atoms are supposed to be alike. We cannot 
 get hold of elementary atoms and examine them, 
 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 itself. 
 
 The student of physics or chemistry now believes 
 that, were a very small quantity of a gas (say am- 
 monia) or a drop of a liquid (say water) magnified 
 to something like the size of the earth, he should 
 see before him a vast heap of particles of ammonia 
 or of water, each exhibiting all the properties by 
 the possession of which he now distinguishes am- 
 monia or water from all other kinds of matter. He 
 believes that he should see these particles in 
 motion, each moving rapidly from place to place, 
 sometimes knocking against another, sometimes 
 traversing a considerable space without coming 
 into collision with any other. But the student 
 tries to penetrate yet further into the nature of 
 things. To the vision of the chemist these particles 
 of almost inconceivable minuteness are themselves 
 built up of smaller particles. As there is an archi- 
 tecture of masses, so is there an architecture of 
 molecules. Hydrogen and oxygen are mixed ; the 
 chemist sees the molecules of each in their never- 
 ceasing dance moving here and there among the 
 molecules of the other, yet each molecule retaining 
 its identity ; an electric spark is passed through 
 the mixture, and almost instantaneously he sees 
 
142 HEROES OF SCIENCE. 
 
 each hydrogen molecule split into two parts, and 
 each oxygen molecule split into two parts, and then 
 he sees these parts of molecules, these atoms, com- 
 bine, a pair of hydrogen atoms with an atom of 
 oxygen, to form compound molecules of water. 
 
 Avogadro's hypothesis gave the chemist a defi- 
 nition of " molecule ; " it also gave him a definition 
 of " atom." 
 
 It is evident that, however many atoms of a 
 given element there may be in this or in that 
 compound molecule, no compound of this element 
 can exist containing less than a single atom of the 
 clement in question ; therefore an atom of an ele- 
 ment is the smallest quantity of that element in 
 the molecule of any compound thereof. 
 
 And so we have come back to the original 
 hypothesis of Dalton ; but we have extended and 
 modified that hypothesis we have distinguished 
 two orders of small particles, the molecule (of a 
 compound or of an element) and the atom (of an 
 clement). The combination of two or more elements 
 is now regarded as being preceded by the decom- 
 position of the molecules of these elements into 
 atoms. We have defined molecule and we have 
 defined atom, but before we can determine the 
 relative weights of elementary atoms we must have 
 a means of determining the relative weights of 
 compound molecules. The old difficulty still stares 
 us in the face how can we find the number of 
 elementary atoms in the molecule of a given 
 compound ? 
 
CHEMICAL PRINCIPLES ESTABLISHED. 143 
 
 The same naturalist who enriched chemical 
 science by the discovery of the molecule as dis- 
 tinct from the atom, placed in the hands of 
 chemists the instrument for determining the rela- 
 tive weights of molecules, and thus also the relative 
 weights of atoms. 
 
 The great generalization, usually known as Avo- 
 gadro's laiv, runs thus : " Equal volumes of gases 
 measured at the same temperature and under the 
 same pressure contain equal numbers of molecules" 
 
 Gay-Lussac had concluded that " equal volumes 
 of gases contain equal numbers of atoms ; " but 
 this conclusion was rejected, and rightly rejected 
 by Dalton, who however at the same time refused 
 to admit that there is a simple relation between 
 the combining volumes of elements. The gene- 
 ralization of Avogadro has however stood the test 
 of experiment, and is now accepted as one of the 
 fundamental " laws " of chemical science. 
 
 Like the atomic theory itself, Avogadro's law 
 is an outcome of physical work and of physical 
 reasoning. Of late years the great naturalists, 
 Clausius, Helmholtz, Joule, Rankine, Clerk Max- 
 well and Thomson have developed the physical 
 theory of molecules, and have shown that Avo- 
 gadro's law may be deduced as a necessary 
 consequence from a few simple physical assump- 
 tions. This law has thus been raised, from being 
 a purely empirical generalization, to the rank of a 
 deduction from a wide, yet simple physical theory. 
 
 Now, if "equal volumes of gases contain equal 
 
144 HEROES OF SCIENCE. 
 
 numbers of molecules," it follows that the ratio ot 
 the densities of any two gases must also be the 
 ratio of the weights of the molecules which con- 
 stitute these gases. Thus, a given volume of water 
 vapour weighs nine times more than an equal 
 volume of hydrogen ; therefore the molecule of 
 gaseous water is nine times heavier than the mole- 
 cule of hydrogen. One has therefore only to 
 adopt a standard of reference for molecular 
 weights, and Avogadro's law gives the means 
 of determining the number of times any gaseous 
 molecule is heavier than that of the standard 
 molecule. 
 
 But consider the combination of a gaseous 
 element with hydrogen ; let us take the case of 
 hydrogen and chlorine, which unite to form gaseous 
 hydrochloric acid, and let us determine the volumes 
 of the uniting elements and the volume of the 
 product. Here is a statement~of the results : one 
 volume of hydrogen combines with one volume of 
 chlorine to form two volumes of hydrochloric acid. 
 Assume any number of molecules we please in the 
 one volume of hydrogenJ||ay ten there must be, 
 by Avogadro's law, alscj^Ri molecules in the one 
 volume of chlorine ; buj^fcsmuch as the volume of 
 hydrochloric acid prod^^Bis double that of either 
 the hydrogen or the c^ronne which combined to 
 form it, it follows, by the same law, that twenty 
 molecules of hydrochloric acid have been formed 
 by the union of ten molecules of hydrogen with 
 ten molecules of chlorine. The necessary conclu- 
 
UNIVERSITY 
 
 FO 
 CHEMICAL PRINCIPLES ESABLISHED. 145 
 
 sion is that each hydrogen molecule and each chlo- 
 rine molecule has split into two parts, and that each 
 half-molecule (or atom) of hydrogen has combined 
 with one half-molecule (or atom) of chlorine, to pro- 
 duce one compound molecule of hydrochloric acid. 
 
 Therefore we conclude that the hydrogen mole- 
 cule is composed of two atoms, and that the chlorine 
 molecule is also composed of two atoms ; and as 
 hydrogen is to be our standard element, we say 
 that if the atom of hydrogen weighs one, the mole- 
 cule of the same element weighs two. 
 
 It is now easy to find the molecular weight i any 
 gas ; it is only necessary to find how many times 
 heavier the given gas is than hydrogen, the weight 
 of the latter being taken as 2. Thus, oxygen is six- 
 teen times heavier than hydrogen, but 1:16=2:32, 
 therefore the molecule of oxygen is thirty-two 
 times heavier than the molecule of hydrogen. Am- 
 monia is eight and a half times heavier than hydro- 
 gen, but i : 8 J =r 2 : 17, therefore the molecule of 
 ammonia is seventeen times heavier than the mole- 
 cule of hydrogen. This is what we more concisely 
 express by saying " the molecular weight of oxygen 
 is 32," or "the molecular weight of ammonia is 
 17," etc., etc. 
 
 Now, we wish to determine the atomic weight of 
 oxygen ; that is, we wish to find how many times 
 the oxygen atom is heavier than the atom of 
 hydrogen. We make use of Avogadro's law and 
 of the definition of " atom " which has been deduced 
 from it (see p. 142). 
 
146 HEROES OF SCIENCE. 
 
 We know that eight parts by weight of oxygen 
 combine with one part by weight of hydrogen to 
 form water ; but we do not know whether the 
 molecule of water contains one atom of each 
 element, or two atoms of hydrogen and one atom of 
 oxygen, or some other combination of these atoms 
 (see p. 131). But by vaporizing water and weighing 
 the gas so produced, we find that water vapour is nine 
 times heavier than hydrogen : now, I 19 = 2 : 18, 
 therefore the molecular weight of water gas is 18. 
 Analysis tells us that eighteen parts by weight of 
 water gas contain sixteen parts of oxygen and 
 two parts of hydrogen ; that is to say, we now 
 know that in the molecule of water gas there are 
 two atoms of hydrogen combined with sixteen 
 parts by weight of oxygen. We now proceed to 
 analyze and determine the molecular weights of as 
 many gaseous compounds of oxygen as we can 
 obtain. 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 oxygen. In some of these molecules 
 there are sixteen, in some thirty-two, in some forty- 
 eight, in some sixty-four parts by weight of oxygen, 
 but in none is there less than sixteen parts by 
 weight of this element. Therefore we conclude 
 that the atomic weight of oxygen is 16, because 
 this is the smallest amount, referred to hydrogen 
 taken as i, which has hitherto been found in the 
 molecule of any compound of oxygen. 
 
 The whole of the work done since the publica- 
 
CHEMICAL PRINCIPLES ESTABLISHED. 147 
 
 tion of Dalton's " New System " has emphasized 
 the importance of that chemist's remark, that no 
 safe conclusion can be drawn as to the value of 
 the atomic weight of an element except from a con- 
 sideration of many compounds of that with other 
 elements. But in Avogadro's law we have a far 
 more accurate and trustworthy method for deter- 
 mining the molecular weights of compounds than 
 any which Dalton was able to devise by his study 
 of chemical combinations. 
 
 We have thus got a clearer conception of " atom " 
 than was generally possessed by chemists in the 
 days of Dalton, and this we have gained by intro- 
 ducing the further conception of " molecule " as that 
 of a quantity of matter different from, and yet 
 similar to, the atom. 
 
 The task now before us will for the most part 
 consist in tracing the further development of the 
 fundamental conception of Dalton, the conception, 
 viz., of each chemical substance as built up of 
 small parts possessing all the properties, other than 
 the mass, of the whole ; and what we also owe 
 to Dalton -the application of this conception to 
 explain the facts of chemical combination. 
 
 The circumstances of Dalton's early life obliged 
 him to trust largely to his own efforts for acquiring 
 knowledge ; and his determination not to accept facts 
 at second hand but to acquire them for himself, is 
 very marked throughout the whole of his life. In the 
 preface to the second part of the " New System " 
 
148 HEROES OF SCIENCE, 
 
 he says, " Having been' in my progress so often 
 misled by taking for granted the results of others, 
 I have determined to write as little as possible but 
 what I can attest by my own experience." 
 
 We should not expect such a man as this to 
 make any great use of books ; one of his friends tells 
 us that he heard him declare on a public occasion 
 that he could carry his library on his back, and yet 
 had not read half of the books which comprised it. 
 
 The love of investigation which characterized 
 Dalton when young would naturally be increased 
 by this course of intellectual life. How strong this 
 desire to examine everything for himself became, 
 is amusingly illustrated by a story told by his 
 medical adviser, Dr. Ransome. Once when Dalton 
 was suffering from catarrh Dr. Ransome had pre- 
 scribed a James's powder, and finding his patient 
 much better next day, he congratulated himself and 
 Dalton on the good effects of the medicine. " I 
 do not well see how that can be," said Dalton, " as 
 I kept the powder until I could have an oppor- 
 tunity of analyzing it." 
 
 As Dalton grew older he became more than 
 ever disinclined to place much trust in the results 
 obtained by other naturalists, even when these men 
 were acknowledged to be superior to himself in 
 manipulative and experimental skill. Thus, as we 
 have already learned, he could not be brought to 
 allow the truth of Gay-Lussac's experimentally 
 established law regarding gaseous combinations ; 
 he preferred to attribute Gay-Lussac's results to 
 
CHEMICAL PRINCIPLES ESTABLISHED. 149 
 
 errors of experiment. " The truth is, I believe, 
 that gases do not unite in equal or exact measures 
 in any one instance ; when they appear to do so 
 it is owing to the inaccuracy of our experiments." 
 
 That Dalton did not rank high as an experi- 
 menter is evident from the many mistakes in 
 matters of fact which are to be found in the second 
 part of his " New System." A marked example of 
 his inaccuracy in purely experimental work is to 
 be found in the supposed proof given by him that 
 charcoal, after being heated to redness, does not 
 absorb gases. He strongly heated a quantity of 
 charcoal, pulverized it, and placed it in a Florence 
 flask, which was connected by means of a stopcock 
 with a bladder filled with carbonic acid : after a 
 week he found that the flask and its contents had 
 not sensibly increased in weight, and he concluded 
 that no carbonic acid had been absorbed by the 
 charcoal. But no trustworthy result could be ob- 
 tained from an experiment in which the char- 
 coal, having been deprived of air by heating, was 
 again allowed to absorb air by being pulverized 
 in an open vessel, and was then placed in a flask 
 filled with air, communication between the car- 
 bonic acid and the external air being prevented 
 merely by a piece of bladder, a material which is 
 easily permeated by gases. 
 
 Dalton used a method which can only lead to 
 notable results in natural science when employed 
 by a really great thinker ; he acquired a few facts, 
 and then thought out the meaning of these, 
 
150 HEROES OF SCIENCE. 
 
 Almost at the beginning of each investigation he 
 tried to get hold of some definite generalization, 
 and then he proceeded to amass special facts. 
 The object which he kept before himself in his 
 experimental work was to establish or to dis- 
 prove this or that hypothesis. Every experiment 
 was conducted with a clearly conceived aim. 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 hypothesis. 
 
 That the laiv of multiple proportions is simply a 
 generalization of facts, and may be stated apart 
 from the atomic theory, is now generally admitted. 
 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 
 experiments. He certainly always stated this law 
 in the language of the atomic theory. In one 
 of his walking excursions he explained his theory 
 to a friend, and after expounding his views re- 
 garding atomic combinations, he said that the 
 examples which he had given showed the necessary 
 existence of the principle of multiple proportions : 
 "Thou knowest it must be so, for no man can 
 split an atom." We have seen that carburetted 
 hydrogen was one of the compounds on the results 
 of the analysis of which he built his atomic theory ; 
 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 investigation." 
 
CHEMICAL PRINCIPLES ESTABLISHED. I$I 
 
 When Dalton was meditating on the laws of 
 chemical combination, a French chemist, M. Proust, 
 published analyses of metallic oxides, which proved 
 that when a metal forms two oxides the amount 
 of metal in each is a fixed quantity that there 
 is a sudden jump, as it were, from one oxide to 
 another. We are sometimes told that from these 
 experiments Proust would have recognized the 
 law of multiple proportions had his analyses only 
 been more accurate; but we know that Dalton's 
 analyses were very inaccurate, and yet he not only 
 recognized the law of multiple proportions, but 
 propounded and established the atomic theory. 
 Something more than a correct system of keeping 
 books and balancing accounts is wanted in natural 
 science. Dalton's experimental results would be 
 the despair of a systematic analyst, but from these 
 Dalton's genius evolved that splendid theory which 
 has done so much to advance the exact investiga- 
 tion of natural phenomena. 
 
 Probably no greater contrast could be found 
 between methods of work, both leading to the 
 establishment of scientific (that is, accurate and 
 precise) results, than that which exists between 
 the method of Dalton and the method pursued by 
 Priestley. 
 
 Priestley commenced his experiments with no 
 particular aim in view ; sometimes he wanted to 
 amuse himself, sometimes he thought he might 
 light upon a discovery of importance, sometimes 
 his curiosity incited him to experiment. When he 
 
152 HEROES OF SCIENCE. 
 
 got facts he made no profound generalizations ; 
 he was content to interpret his results by the help 
 of the prevailing theory of his time. But each new 
 fact only spurred him on to make fresh incursions 
 into the fields of Nature. Dalton thought much and 
 deeply ; his experimentally established facts were 
 to him symbols of unseen powers. He used facts 
 as Hobbes says the wise man uses words : they 
 were his counters only, not his money. 
 
 When we ask how it was that Dalton acquired his 
 great power of penetrating beneath the surface 
 of things and finding general laws, we must 
 attribute this power in part to the training which 
 he gave himself in physical science. It was from a 
 consideration of physical facts that he gained the 
 conception of ultimate particles of definite weight. 
 His method was essentially dynamical ; that is, he 
 pictured a gas as a mass of little particles, each 
 of which acted on and was acted on by, other 
 particles. The particles were not thrown together 
 anyhow ; definite forces existed between them. 
 Each elementary or compound gas was pictured 
 as a system of little particles, and the properties 
 of that gas were regarded as dependent on the 
 nature and arrangement of these particles. Such 
 a conception as this could only be gained by a 
 careful and profound thinker versed in the methods 
 of physical and mathematical science. 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 
 
CHEMICAL PRINCIPLES ESTABLISHED. 153 
 
 of natural science, yet it was by virtue of his 
 careful training in a branch of knowledge which 
 deals with facts, as well as in that science which 
 deduces particular conclusions from general prin- 
 ciples, that he was able to introduce his fruitful 
 conceptions into the science of chemistry. 
 
 To me it appears that Dalton was pre-eminently 
 distinguished by the possession of imagination. 
 He formed clear mental images of the phenomena 
 which he studied, 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 
 formed. 
 
 From his intense devotion to the pursuit of 
 science the development of Dalton's general cha- 
 racter appears to have been somewhat dwarfed, 
 Although he possessed imagination, it was the 
 imagination of a naturalist rather than that of a 
 man of broad culture. Perhaps it was a want of 
 broad sympathies which made him trust so im- 
 plicitly in his own work and so readily distrust 
 the work of others, and which moreover led him 
 astray in so many of his purely experimental in- 
 vestigations. 
 
 Dalton began his chemical work about six years 
 after the death of Lavoisier. Unlike that great 
 philosopher he cared nothing for political life. 
 The friends in whose family he spent the greater 
 part of his life in Manchester were never able 
 
154 HEROES OF SCIENCE. 
 
 to tell whether he was Whig or Tory. Unlike 
 Priestley he was content to let metaphysical and 
 theological speculation alone. In his quiet devo- 
 tion to study he more resembled Black, and in his 
 method, which was more deductive than that usually 
 employed in chemistry, he also resembled the 
 Edinburgh professor. Trained from his earliest 
 days to depend on himself, nurtured in the creed- 
 less creed of the Friends, he entered on his life's 
 work with few prejudices, if without much profound 
 knowledge of what had been done before him. 
 By the power of his insight into Nature and the 
 concentration of his thought, he drew aside the 
 curtain which hung between the seen and the un- 
 seen ; and while Herschel, sweeping the heavens 
 with his telescope and night by night bringing 
 new worlds within the sphere of knowledge, was 
 overpowering men's minds by new conceptions 
 of the infinitely great, John Dalton, with like 
 imaginative power, was examining the architec- 
 ture of the ultimate particles of matter, and re- 
 vealing the existence of law and order in the 
 domain of the infinitely small. 
 
CHAPTER IV. 
 
 ESTABLISHMENT OF GENERAL PRINCIPLES OF 
 CHEMICAL SCIENCE (continued} PERIOD OF 
 DAVY AND BERZELIUS. 
 
 Humphry Davy > 1778-1829. Johann Jacob Berzelius, 1779-1848. 
 
 WE may roughly date the period of chemical 
 advance during which the connections between 
 chemistry and other branches of natural knowledge 
 were recognized and studied, as beginning with the 
 first year of this century, and as continuing to our 
 own day. 
 
 The elaboration of the atomic theory was busily 
 carried on during the second and third decades 
 of this century ; to this the labour of the Swedish 
 chemist Berzelius largely contributed. 
 
 That there exist many points of close connection 
 between chemical and electrical science was also 
 demonstrated by the labours of the same chemist, 
 and by the brilliant and impressive discoveries of 
 Sir Humphry Davy. 
 
156 HEROES OF SCIENCE. 
 
 A system of classification of chemical elements 
 and compounds was established by the same great 
 naturalists, and many inroads were made into the 
 domain of the chemistry of bodies of animal and 
 vegetable origin. 
 
 The work of Berzelius and Davy, characterized 
 as it is by thoroughness, clearness and defmiteness, 
 belongs essentially to the modern era of chemical 
 advance ; 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 present, as typical 
 workers in which time I have chosen Liebig and 
 Dumas. 
 
 In the last chapter we found that the founda- 
 tions of the atomic theory had been laid, and the 
 theory itself had been applied to general problems 
 of chemical synthesis, by Dalton. In giving, in 
 that chapter, a short sketch of the modern mole- 
 cular theory, and in trying to explain the meaning 
 of the term "molecule " as contrasted with "atom," 
 I necessarily carried the reader forward to a time 
 considerably later than the first decade of this 
 century. We must now retrace our steps ; and 
 in perusing the account of the work of Berzelius 
 and Davy given in the present chapter, the reader 
 must endeavour to have in his mind a conception 
 of atom analogous to the mental picture formed by 
 Dalton (see pp. 135, 136) ; he must regard the term 
 as applicable to element and compound alike ; 
 
WORK OF DAVY AND BERZELIUS. 157 
 
 he must remember that the work of which he 
 reads is the work of those who are striving to- 
 wards a clear conception of the atom, and who 
 are gradually rising to a recognition of the exist- 
 ence of more than one order of small particles, by 
 the regular putting together of which masses of 
 matter are constituted. 
 
 No materials, so far as I am aware, exist from 
 which a life of Berzelius can be constructed. I 
 must therefore content myself with giving a mere 
 enumeration of the more salient points in his life. 
 Of his chemical work abundant details are for- 
 tunately to be found in his own " Lehrbuch," and 
 in the works and papers of himself and his con- 
 temporaries. 
 
 JOHANN JACOB BERZELIUS was the son of the 
 schoolmaster of Wafersunda, a village near Lin- 
 koping, in East Gothland, Sweden. He was born 
 in August 1779 he was born, that is, a few years 
 after Priestley's discovery of oxygen ; at the time 
 when Lavoisier had nearly completed his theory 
 of combustion ; when Dalton was endeavouring to 
 keep the unruly youth of Eaglesfield in subjection ; 
 and when Black, having established the existence 
 of fixed air and the theory of latent heat, was the 
 central figure in the band of students who were 
 enlarging our knowledge of Nature in the Scottish 
 capital. 
 
 Being left an orphan at the age of nine, the 
 young Berzelius was brought up by his grandfather, 
 
158 HEROES OF SCIENCE. 
 
 who appears to have been a man of education and 
 sense. After attending school at Linkoping, he 
 entered the University of Upsala as a student of 
 medicine. Here he soon began to show a taste 
 for chemistry. It would appear that few or no 
 experiments were then introduced into his lectures 
 by the Professor of Chemistry at Upsala ; little 
 encouragement was given to pursue chemical ex- 
 periments, and so Berzelius had to trust to his own 
 labours for gaining an acquaintance with practical 
 chemistry. Having thus made considerable pro- 
 gress in chemistry, and being on a visit to the 
 mineral baths of Medevi, he seized the opportunity 
 to make a very thorough analysis of the waters of 
 this place, which were renowned in Sweden for their 
 curative properties. The publication of this analysis 
 marks the first appearance of Berzelius as an author. 
 
 He graduated as M.B. in 1801, and a year or two 
 later presented his dissertation, entitled "The Action 
 of Galvanism on Organic Bodies," as a thesis for 
 the degree of Doctor of Medicine. This thesis, like 
 that of Black, published about half a century 
 earlier, marks an important stage in the history 
 of chemistry. These and other publications made 
 the young doctor famous ; he was called to Stock- 
 holm to be extraordinary (or assistant) Professor of 
 Chemistry in the medical school of that capital. 
 
 Sometimes practising medicine in order to add 
 to his limited income, but for the most part engaged 
 in chemical research, he remained in Stockholm 
 for nearly fifty years, during most of which time 
 
WORK OF DAVY AND BERZELIUS. 159 
 
 the laboratory of Berzelius in the Swedish capital 
 was regarded as one of the magnetic poles of the 
 chemical world. To this point came many of 
 the great chemists who afterwards enriched the 
 science by their discoveries. Wohler, H. and G. 
 Rose, Magnus, Gmelin, Mitscherlich and others 
 all studied with Berzelius. He visited England 
 and France, and was on terms of intimacy and in 
 correspondence with Davy, Dalton, Gay-Lussac, 
 Berthollet and the other men who at that period 
 shed so much lustre on English and French science. 
 
 It is said that Berzelius was so much pleased 
 with the lectures of Dr. Marcet at Guy's Hospital, 
 that on his return from his visit to England in 
 1812, he introduced much more liveliness and 
 many more experimental illustrations into his own 
 lectures. 
 
 At the age of thirty-one, Berzelius was chosen 
 President of the Stockholm Academy of Sciences ; 
 a few years later he was elected a Foreign Fellow 
 of the Royal Society, which society bestowed on 
 him the Copley Medal in 1836. He was raised to 
 the rank of a barcn by the King of Sweden, being 
 allowed as a special privilege to retain his own 
 name, 
 
 In the year 1832 Berzelius resigned his profes- 
 sorship, and in the same year he married. During 
 the remainder of his life, he continued to receive 
 honours of all kinds, but he never for a moment 
 forsook the paths of science. After the death of 
 Davy, in 1829, he was recognized as the leading 
 
160 HEROES OF SCIENCE. 
 
 European chemist of his age ; but, although firm in 
 his own theoretical views, he was ready to test 
 these views by appealing to Nature. 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 
 ogposed him. 
 
 Probably no chemist has added to the science 
 so many carefully determined facts as Berzelius ; 
 he was always at work in the laboratory, and always 
 worked with the greatest care. Yet the appliances 
 at his command were what we should now call 
 poor, meagre^ and utterly inadequate. Professor 
 Wb'hler of Gottingen, who in the fulness of days 
 and honours has so lately gone from amongst us, 
 recently gave an account of his visit to Berzelius in 
 the year 1823. Wohler had taken his degree as 
 Doctor of Medicine at Heidelberg, 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 professor. Having 
 written to Berzelius and learned that he was will- 
 ing to allow him working room in his laboratory, 
 the young student set out for Stockholm. After 
 a journey to Liibeck and a few days' passage in 
 a small sailing-vessel, he arrived in the Swedish 
 capital. 
 
 " Knocking at the door of the house pointed out 
 as that of Berzelius, he tells us that his heart beat 
 hard as the door was opened by a tall man of 
 
WORK OF DAVY AND BERZELIUS. l6l 
 
 florid complexion. " It was Berzelius himself," he 
 exclaims. Scarcely believing that he was in the 
 very room where so many famous discoveries had 
 been made, he entered the laboratory. No water, 
 no gas, no draught-places, no ovens were to be 
 seen ; a couple of plain tables, a blowpipe, a few 
 shelves with bottles, a little simple apparatus, and 
 a large water-barrel whereat Anna, the ancient 
 cook of the establishment, washed the laboratory 
 dishes, completed the furnishings of this room, 
 famous throughout Europe for the work which had 
 been done in it. In the kitchen which adjoined, 
 and where Anna cooked, was a small furnace and a 
 sand bath for heating purposes. 
 
 In this room many great discoveries were made. 
 Among these we may note the separation of the 
 element columbium in 1815, and of selenion in 
 1818 ; the discovery of the new earth thoria in 1828 ; 
 the elucidation of the properties of yttrium and 
 cerium about 1820, of uranium in 1823, and of the 
 platinum metals in 1828 ; the accurate determina- 
 tion of the atomic weights of the greater number 
 of the elements ; the discovery of " sulphur salts " 
 in 1826-27, an d the proof that silica is an acid, 
 and that most of the " stony " minerals are com- 
 pounds of this acid with various bases. 
 
 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 
 Stockholm. 
 
 in. M 
 
1 62 HEROES OF SCIENCE. 
 
 The German chemist Richter, in the first or 
 second year of this century, had drawn attention 
 to the fact that when two neutral compounds, such 
 as nitrate of potash and chloride of lime, react 
 chemically, the substances produced by this reaction 
 are also neutral. All the potash combined with 
 nitric acid in one salt changes places with all the 
 lime combined with muriatic acid in the other 
 salt ; therefore, said Richter, these different quan- 
 tities of potash and lime are neutralized by the 
 same quantity of nitric acid ; and, hence, these 
 amounts of potash and lime are chemically equiva- 
 lent, because these are the amounts which perform 
 the same reaction, viz. neutralization of a fixed 
 quantity of acid. If then careful analyses were 
 made of a number of such neutral compounds as 
 those named, the equivalents of all the commoner 
 " bases " and " acids " * might be calculated. 
 
 Richter's own determinations of the equivalents 
 of acids and bases were not very accurate, but 
 Berzelius was impressed with the importance of 
 this work. The year before the appearance of 
 Dalton's "New System" (i.e. in 1807), he began to 
 prepare and carefully analyze series of neutral 
 salts. As the work was proceeding he became 
 acquainted with the theory of Dalton, and at once 
 saw its extreme importance. For some time Ber- 
 zelius continued to work on the lines laid down by 
 Dalton, and to accumulate data from which the 
 
 * The history and meaning of these terms is considered on p, 171, 
 ft sc, 
 
WORK OF DAVY AND BERZELIUS. 163 
 
 atomic weights of elements might be calculated ; 
 but he soon perceived as the founder of the theory 
 had perceived from the very outset that the fun- 
 damental conception of each atom of an element 
 as being a distinct mass of matter weighing more 
 or less than the atom of every other element, and 
 of each atom of a compound as being built up of 
 the atoms of the elements which compose that 
 compound, Berzelius, I say, perceived that these 
 conceptions must remain fruitless unless means 
 were found for determining the number of elemen- 
 tary atoms in each compound atom. We have 
 already learned the rules framed by the founder of 
 the atomic theory for his guidance in attempting to 
 solve this problem. Berzelius thought those rules 
 insufficient and arbitrary ; he therefore laid down 
 two general rules, on the lines of which he prose- 
 cuted his researches into chemical synthesis. 
 
 " One atom of one element combines with one, 
 two, three, or more atoms of another element." 
 This is practically the same as Dalton's defini- 
 tions of binary, ternary, etc., compounds (p. 132). 
 "Two atoms of one element combine with three 
 and five atoms of another element." Berzelius here 
 recognizes the existence of compound atoms of a 
 more complex structure than any of those recog- 
 nized by Dalton. 
 
 Berzelius further extended the conception of 
 atom by applying it to groups of elements formed, 
 according to him, by the combination of various 
 compound atoms. To his mind every compound 
 
1 64 HEROES OF SCIENCE. 
 
 atom appeared as built up of two parts ; each of 
 these parts might be an elementary atom, or might 
 be itself built up of several elementary atoms, yet in 
 the Berzelian theory each acted as a definite whole. 
 So far as the building up of the complex atom 
 went, each of the two parts into which this atom 
 could be divided acted as if it were a simple atom. 
 If we suppose a patch of two shades of red 
 colour to be laid on a smooth surface, and alongside 
 of this a patch of two shades of yellow colour, 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 yellow, we 
 shall have a rough illustration of the Berzelian 
 compound atom. To the observer the whole mass 
 of colour appears to consist of two distinct patches 
 of contrasted colours ; but let him approach 
 nearer, 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 
 yellow. The whole mass of colour represents the 
 compound atom ; broadly it consists of two parts 
 the red colour represents one of the constituent 
 ... atoms, the yellow colour represents the other con- 
 stituent atom ; but on closer examination the red 
 atom, 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 atom. 
 
 We shall have to consider in more detail the 
 reasoning whereby Berzelius arrived at this concep- 
 
WORK OF DAVY AND BERZELIUS. 165 
 
 tion of every compound atom as a dual structure 
 (see pp. 209-212). 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 Dal- 
 tonian theory. I wish to insist on the fact that the! 
 atomic theory could not advance without methods 
 being found for determining the number of elemen- 
 tary atoms in a compound atom, without clear 
 conceptions being gained of every compound atom 
 as a structure, and without at least attempts being 
 made to learn the laws in accordance with which 
 that structure was built. 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 known ; otherwise 
 all that could be stated was, the atomic weight of 
 oxygen is a simple multiple of 8. Berzelius did 
 much to advance chemical science by the introduc- 
 tion and application of a few simple rules whereby 
 he determined the number of elementary atoms in 
 various compound atoms. But as the science ad- 
 vanced, and as more facts came to be known, the 
 Berzelian rules were found to be too narrow and too 
 arbitrary ; chemists sought for some surer and more 
 generally applicable method than that which Berze- 
 lius had introduced, and the imperious demand for 
 this method at last forced them to recognize the 
 importance of the great generalization of the Italian 
 naturalist Avogadro, which they had possessed 
 since the year 181 1, but the meaning of which they 
 had so long failed to understand. 
 
1 66 HEROES OF SCIENCE. 
 
 Berzelius made one great step in the direction of 
 recognizing Avogadro's distinction between atom 
 and molecule when he accepted Gay-Lussac's gene- 
 ralization that "equal volumes of gases contain 
 equal numbers of atoms : " but he refused to apply 
 this to other than elementary gases. The weights 
 of the volumes of elementary gases which com- 
 bined were, for Berzelius, also the weights of the 
 atoms of these elements. Thus, let the weight of 
 one volume of hydrogen be called i, then two 
 volumes of hydrogen, weighing 2, combine with 
 one volume of oxygen, weighing 16, to form 
 two volumes of water vapour ; therefore, said Ber- 
 zelius, the atom of water consists of two atoms 
 of hydrogen and one atom of oxygen, and the 
 atom of the latter element is sixteen times heavier 
 than the atom of the former. Three volumes of 
 hydrogen, weighing 3, combine with one volume 
 of nitrogen, weighing 14, to form two volumes 
 of ammonia ; therefore, said Berzelius, the atom of 
 ammonia consists of three atoms of hydrogen com- 
 bined with one atom of nitrogen, and the nitrogen 
 atom is fourteen times heavier than the atom of 
 hydrogen. 
 
 While Berzelius was applying these rules to the 
 determination of the atomic weights of the ele- 
 ments, and was conducting the most important 
 series of analyses known in the annals of the 
 science, two great physico-chemical discoveries were 
 announced. 
 
 In the year 1818 the " law of isomorphism^ 
 
WORK OF DAVY AND BERZELIUS. 
 
 was stated by Mitscherlich : " Compounds the 
 atoms of which contain equal numbers of elemen- 
 tary atoms, similarly arranged, have the same 
 crystalline form." As thus stated, the law of 
 isomorphism affirms that if two compounds crystal- 
 lize in the same form, the atoms of these com- 
 pounds 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 arranged. 
 This statement was soon found to be too absolute, 
 and was accordingly modified ; but to go into the 
 history of the law of isomorphism would lead us 
 too far from the great main path of chemical 
 advance, the course of which we are seeking to 
 trace. 
 
 Berzelius at once accepted Mitscherlich's law, 
 as an aid in his researches on atomic weights. 
 The help to be derived from this law may be 
 illustrated thus : let us assume that two compounds 
 have been obtained exhibiting identity of crystal- 
 line form ; let it be further assumed that the 
 number of elementary atoms in the atom of 
 one of these compounds is known ; it follows, by 
 the law of isomorphism, that the number of ele- 
 mentary atoms in the atom of the other is 
 known also. Let the two compounds be sulphate 
 of potash and chr ornate of potash ; let it be assumed 
 that the atom of the first named is known to 
 consist of two atoms of potassium, one atom of 
 sulphur, and four atoms of oxygen ; and that the 
 
1 68 HEROES OF SCIENCE. 
 
 second substance is known to be a compound of the 
 elements potassium, chromium and oxygen ; then 
 the atom of the second compound contains, by 
 Mitscherlich's law, two atoms of potassium, one 
 atom of chromium and four atoms of oxygen : hence 
 the relative weight of the atom of chromate of 
 potash can be determined, and hence the relative 
 weight of the atom of chromium can also be 
 determined. 
 
 A year after the announcement of Mitscherlich's 
 law, the following generalization was stated to hold 
 good, by two French naturalists, Dulong and Petit : 
 " The atoms of all solid elements have the same 
 capacity for heat." 
 
 If the amount of heat required to raise the tem- 
 perature of one grain of water through one degree 
 be called one unit of heat, 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 degree. 
 Each chemical substance, elementary and com- 
 pound, has its own capacity for heat ; but, instead 
 of comparing the capacities for heat of equal 
 weights, Dulong and Petit compared the capacities 
 for heat of weights representing the weights of the 
 atoms of various elements. Thus, equal amounts of 
 heat are required to raise, through the same interval 
 of temperature, fifty-six grains of iron, one hundred 
 and eight grains of silver, and sixty-three and a half 
 grains of copper ; but the weights of the atoms of 
 these three elements are in the proportion of 56 ; 
 
WORK OF DAVY AND BERZELIUS. 169 
 
 1 08 : 63!-. Dulongand Petit based their generaliza- 
 tion on measurements of the capacities for heat of 
 thirteen elements ; further research has shown that 
 their statement most probably holds good for all 
 the solid elements. Here then was a most impor- 
 tant instrument put into the hands of the chemist. 
 
 It is only necessary that the atomic weight of 
 one solid element should be certainly known, 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 
 known ; then the number which expresses the 
 weight, in grains, of any other solid element which 
 is raised through one degree by the same amount 
 of heat, likewise expresses the relative weight of 
 the atom of that element. Thus, suppose that 
 the atomic weight of silver is known to be 108, 
 and suppose that six units of heat are required 
 to raise the temperature of one hundred and 
 eight grains of this metal through one degree ; 
 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 degree, it follows according to the law of 
 Dulong and Petit that 210 is the atomic weight 
 of bismuth. 
 
 The modified generalization of Gay-Lussac 
 " Equal volumes of elementary gases contain equal 
 numbers of atoms;" the laws of " isomorphism " 
 and of " atomic heat ; " and the two empirical rules 
 stated on p. 163 ; these were the guides used by 
 
I/O HEROES OF SCIENCE. 
 
 Berzelius in interpreting the analytical results 
 which he and his pupils obtained in that memor- 
 able series of researches, whereby the conceptions 
 of Dalton were shown to be applicable to a wide 
 range of chemical phenomena. 
 
 The fixity of composition of chemical com- 
 pounds has now been established ; a definite mean- 
 ing has been given to the term " element ; " the 
 conception of " atom " has been gained, but much 
 remains to be done in the way of rendering this 
 conception precise ; and fairly good, but not alto- 
 gether satisfactory methods have been introduced 
 by which the relative weights of the atoms of 
 elements and compounds may be determined. 
 At this time chemists are busy preparing and 
 describing new compounds, and many new ele- 
 ments are also being discovered ; the need of 
 classification begins to be felt more and more. 
 
 In the days of Berzelius and Davy strenuous 
 efforts were made to obtain some generalizations 
 by the application of which the many known ele- 
 ments and compounds might be divided into 
 groups. It was felt that a classification might be 
 founded on the composition of compounds, or per- 
 haps on the properties of the same compounds. 
 These two general principles served as guides in 
 most of the researches then instituted ; answers 
 were sought to these two questions : Of what ele- 
 ments is this compound composed ? and, What can 
 this compound do ; how does it react towards 
 other bodies ? 
 
WORK OF DAVY AND BERZELIUS. I/ 1 
 
 Lavoisier, as we know, regarded oxygen as the 
 characteristic element of all acids. This term acid 
 implies the possession, by all the substances de- 
 noted by it, of some common property ; let us 
 shortly trace the history of this word in chemistry. 
 
 Vinegar was known to the Greeks and Romans, 
 and the names which they gave this substance tell 
 us that sourness was to them its characteristic pro- 
 perty. They knew that vinegar effervesced when 
 brought into contact with chalky earths, and that 
 it was able to dissolve many substances witness 
 the story of Cleopatra's draught of the pearl dis- 
 solved in vinegar. Other substances possessed of 
 these properties for instance oil of vitriol and 
 spirits of salt as they became known, were classed 
 along with vinegar ; but no attempts were made 
 to clearly define the properties of these bodies till 
 comparatively recent times. 
 
 The characteristics of an acid substance enume- 
 rated by Boyle are solvent power, which is exerted 
 unequally on different bodies ; power of turning 
 many vegetable blues to red, and of restoring 
 many vegetable colours which had been destroyed 
 by alkalis ; power of precipitating solid sulphur 
 from solutions of this substance in alkalis, and the 
 power of acting on alkalis to produce substances 
 without the properties of either acid or alkali. 
 
 But what, one may ask, is an alkali, of which 
 mention is so often made by Boyle ? 
 
 From very early times it had been noticed that 
 the ashes which remained when certain plants were 
 
HEROES OF SCIENCE. 
 
 burned, and the liquid obtained by dissolving those 
 ashes in water, had great cleansing powers ; that 
 they removed oily matter, fat and dirt from cloth 
 and other fabrics. The fact that an aqueous 
 solution of these ashes affects the coloured parts of 
 many plants was also noticed in early times. As 
 progress was made in chemical knowledge observers 
 began to contrast the properties of this plant-ash 
 with the properties of acids. The former had no 
 marked taste, the latter were always very sour ; 
 the former turned some vegetable reds to blue, the 
 latter turned the blues to red ; a solution of plant- 
 ash had no great solvent action on ordinary mineral 
 matter, whereas this matter was generally dissolved 
 by an acid. In the time of the alchemists, who 
 were always seeking for the principles or essences 
 of things, these properties of acids were attributed 
 to a principle of acidity, while the properties of 
 plant-ash and substances resembling plant-ash 
 were attributed to a principle of alkalinity (from 
 Arabic alkali, or the ask). 
 
 In the seventeenth century the distinction be- 
 tween acid and alkali was made the basis of a 
 system of chemical medicine. The two principles 
 of acidity and alkalinity were regarded as engaged 
 in an active and never-ending warfare. Every 
 disease was traced to an undue preponderance of 
 one or other of these principles ; to keep these 
 unruly principles in quietness became the aim of 
 the physician, and of course it was necessary that 
 the physician should be a chemist, in order that he 
 
WORK OF DAVY AND BERZELIUS. 1/3 
 
 might know the nature and habits of the principles 
 which gave him so much trouble. 
 
 Up to this time the term " alkali " had been ap- 
 plied to almost any substance having the properties 
 which I have just enumerated ; but this group of 
 substances was divided by Van Helmont and his 
 successors into fixed alkali and volatile alkali^ 
 and fixed alkali was further subdivided into mineral 
 alkali (what we now call soda) and vegetable alkali 
 (potash). About the same time acids were like- 
 wise divided into three groups; vegetable, animal > 
 and mineral acids. To the properties by which 
 alkali was distinguished, viz. cleansing power 
 and action on vegetable colouring matters, Stahl 
 (the founder of the phlogistic theory) added that 
 of combining with acids. When an acid (that is, a 
 sour-tasting substance which dissolves most earthy 
 matters and turns vegetable blues to red) is 
 added to an alkali (that is, a substance which feels 
 soap-like to the touch, which does not dissolve 
 many earthy matters, and which turns many vege- 
 table reds to blue) the properties of both acid and 
 alkali disappear, and a new substance is produced 
 which is not characterized by the properties of 
 either constituent. The new substance, as a rule, is 
 without action on earthy matters or on vegetable 
 colours ; it is not sour, nor is it soapy to the touch 
 like alkali ; it is neutral. It is a salt. But, although 
 Stahl stated that an alkali is a substance which 
 combines with an acid, it was not until a century 
 later that these three alkali, acid, salt were clearly 
 distinguished. 
 
174 HEROES OF SCIENCE. 
 
 But the knowledge that a certain group of bodies 
 are sour and dissolve minerals, etc., and that a 
 certain other group of bodies are nearly tasteless 
 and do not dissolve minerals, etc., was evidently 
 a knowledge of- only the outlying properties of the 
 bodies ; it simply enabled a term to be applied to 
 a group of bodies, which term had a definite conno- 
 tation. 
 
 Why are acids acid, and why are alkalis alkaline ? 
 
 Acids are acid, said Becher (latter part of seven- 
 teenth century), because they all contain the same 
 principle, viz. the primordial acid. This primor- 
 dial acid is more or less mixed with earthy matter 
 in all actual acids ; it is very pure in spirits of salt. 
 
 Alkalis are alkaline, said Basil Valentine (begin- 
 ning of the sixteenth century), because they contain 
 a special kind of matter, " the matter of fire." 
 
 According to other chemists (e.g. J. F. Meyer, 
 1764), acids owe their acidity to the presence of a 
 sharp or biting principle got from fire. 
 
 Acids, alkalis and salts all contain, according to 
 Stahl (beginning of the eighteenth century), more 
 or less primordial acid. The more of this a sub- 
 stance contains, the more acid it is ; the less of this 
 it contains, the more alkaline it is. 
 
 All these attempted explanations recognize that 
 similar properties are to be traced to similarity of 
 composition ; but the assertion of the existence of 
 a " primordial acid," or of " the matter of fire," 
 although undoubtedly a step in advance, was not 
 sufficiently definite (unless it was supplemented 
 
WORK OF DAVY AND BERZELIUS. 1/5 
 
 by a distinct account of the properties of these 
 principles) to be accepted when chemical know- 
 ledge became accurate. 
 
 The same general consideration, founded on a 
 large accumulation of facts, viz-, that similarity 
 of properties is due to similarity of composition, 
 guided Lavoisier in his work on acids. He found 
 the " primordial acid " of Stahl, and the a biting 
 principle " of Meyer, in the element oxygen. 
 
 I have already (p. 91) shortly traced the reason- 
 ing whereby Lavoisier arrived at the conclusion 
 that oxygen is the acid-producer ; here I would 
 insist on the difference between his method and 
 that of Basil Valentine, Stahl and the older 
 chemists. They carried into the domain of natural 
 science conceptions obtained from, and essentially 
 belonging to the domain of metaphysical or 
 extra-physical speculation ; he said that oxygen 
 is the acidifier, because all the compounds of 
 this element which he actually examined were pos- 
 sessed of the properties included under the name 
 acid. We know that Lavoisier's conclusion was 
 erroneous, that it was not founded on a sufficiently 
 broad basis of facts. The conception of an acidifying 
 principle, although that principle was identified 
 with a known element, was still tainted with the 
 vices of the alchemical school. We shall see im- 
 mediately how much harm was done by the 
 assertion of Lavoisier, " All acids contain oxygen." 
 
 In Chapter II. (pp. 32-37) we traced the progress 
 of knowledge regarding alkalis from the time when 
 
1/6 HEROES OF SCIENCE. 
 
 the properties of these bodies were said to be due 
 to the existence in them of " matter of fire," to the 
 time when Black had clearly distinguished and 
 defined caustic alkali and carbonated alkali. 
 
 The truly philosophical character, and at the 
 same time the want of enthusiasm, of Black become 
 apparent if we contrast his work on alkali with 
 that of Lavoisier on acid. Black did not hamper 
 the advance of chemistry by finding a " principle 
 of alkalinity;" but neither did he give a full ex- 
 planation of the fact that certain bodies are alkaline 
 while others are not. He set himself the pro- 
 blem of accurately determining the differences in 
 composition between burnt (or caustic) and unburnt 
 (or mild) alkali, and he solved the problem most 
 successfully. He showed that the properties of 
 mild alkalis differ from those of caustic alkalis, 
 because the composition of the former differs from 
 that of the latter ; and he showed exactly wherein 
 this difference of composition consists, viz. in the 
 possession or non-possession of fixed air. 
 
 Strange we may say that this discovery did not 
 induce Black to prosecute the study of caustic 
 alkalis : surely he would have anticipated Davy, 
 and have been known as the discoverer of potassium 
 and sodium. 
 
 In the time of Stahl the name "salt" was 
 applied, as we have learned, to the substance pro- 
 duced by the union of an acid with an alkali ; but 
 the same word was used by the alchemists with 
 an altogether different signification. Originally 
 
WORK OF DAVY AND BERZELIUS. 1 77 
 
 applied to the solid matter obtained by boiling 
 down sea-water, and then extended to include all 
 substances which, like this solid matter, are very 
 easily dissolved by water and can be recovered 
 by boiling down this solution, "salt" was, in the 
 sixteenth and seventeenth centuries, the name given 
 to one of the hypothetical principles or elements. 
 Many kinds of matter were known to be easily 
 dissolved by water; the common possession of 
 these properties was sought to be accounted for by 
 saying that all these substances contained the 
 same principle, namely, the principle of salt. I have 
 already tried to indicate the reasoning whereby 
 Boyle did so much to overthrow this conception of 
 salt. He also extended our knowledge of special 
 substances which are now classed as salts. The 
 chemists who came after Boyle gradually reverted to 
 the older meaning of the term " salt," adopting as 
 the characteristics of all substances placed in this 
 class, ready solubility in water, fusibility, or some- 
 times volatility, and the possession of a taste more 
 or less like that of sea-salt. 
 
 Substances which resembled salts in general 
 appearance, but were insoluble in water, and very 
 fixed in the fire, were called " earths " ; and, as was 
 generally done in those days, the existence of a 
 primordial earth was assumed, more or less of which 
 was supposed to be present in actual earths. This 
 recognition of the possibility of more or less of the 
 primordial earth being present in actually occurring 
 earths, of course necessitated the existence of 
 
 III. N 
 
i;8 HEROES OF SCIENCE. 
 
 various kinds of earth. The earths were gradually 
 distinguished from each other ; lime was recog- 
 nized as a substance distinct from baryta, baryta 
 as distinct from alumina, etc. 
 
 Stahl taught that one essential property of an 
 earth was fusibility by fire, with production of a 
 substance more or less like glass. This property 
 was possessed in a remarkable degree by quartz 
 or silica. Hence silica was regarded as the typical 
 earth, until Berzelius, in 1815, proved it to be an 
 acid. But the earths resembled alkalis, inasmuch as 
 they too combined with, and so neutralized, acids. 
 
 There is an alkali hidden in every earth, said 
 some chemists. 
 
 An alkali is an earth refined by the presence of 
 acid and combustible matter, said others. 
 
 Earths thus came to be included in the term 
 "alkali," when that term was used in its widest 
 acceptation. 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 alkalis ; this led to a threefold division, thus 
 
 Earths < > Alkaline earths < > Alkalis 
 
 Insoluble in water. Somewhat soluble in Very soluble in 
 water. water. 
 
 The distinction at first drawn between " earth " 
 and " alkali " was too absolute ; the intermediate 
 group of " alkaline earths " served to bridge over 
 the gap between the extreme groups. 
 
 " In Nature," says Wordsworth, " everything is 
 
WORK OF DAVY AND BERZELIUS, 1 79 
 
 distinct, but nothing defined into absolute inde- 
 pendent singleness." 
 
 At this stage of advance, then, an earth is re- 
 garded as differing from an alkali in being in- 
 soluble, or nearly insoluble in water ; in not being 
 soapy to the touch, and not turning vegetable reds 
 to blue : but as resembling an alkali, in that it 
 combines with and neutralizes an acid ; and the 
 product of this neutralization, whether accomplished 
 by an alkali or by an earth, is called a salt. To 
 the earth or alkali, as being the foundation on 
 which the salt is built, by the addition of acid, 
 the name of base was given by Rouelle in 1744. 
 
 But running through every conception which was 
 formed of these substances acid, alkali, earth, salt 
 we find a tendency, sometimes forcibly marked, 
 sometimes feebly indicated, but always present, to 
 consider salt as a term of much wider acceptation 
 than any of the others. An acid and an alkali, or 
 an acid and an earth, combine to form a salt ; but 
 the salt could not have been thus produced unless 
 the acid, the alkali and the earth had contained 
 in themselves some properties which, when com- 
 bined, form the properties of the salt. 
 
 The acid, the alkali, the earth, each is, in a 
 sense, a salt. The perfect salt is produced by the 
 coalescence of the saltness of the acid with the 
 saltness of the alkali. This conception finds full 
 utterance in the names, once in common use, of sal 
 acidiim for acid, sal alkali for alkali, and sal salsum 
 or sal neiitrnm for salt. All are salts ; at one extreme 
 
I SO HEROES OF SCIENCE, 
 
 comes that salt which is marked by properties called 
 acid properties, at the other extreme comes the salt 
 distinguished by alkaline properties, and between 
 these, and formed by the union of these, comes the 
 middle or neutral salt. 
 
 It is thus that the nomenclature of chemistry 
 marks the advances made in the science. " What's 
 in a name ? " To the historical student of science, 
 almost everything. 
 
 We shall find how different is the meaning 
 attached in modern chemistry to these terms, acid 
 salt, alkaline salt, neutral salt, from that which our 
 predecessors gave to their sal acidnm, sal alkali, and 
 salneutrunt. 
 
 We must note the appearance of the term vitriol, 
 applied to the solid salt-like bodies obtained from 
 acids and characterized by a glassy lustre. By the 
 middle of last century the vitriols were recognized 
 as all derived from, or compounded of, sulphuric 
 acid (oil of vitriol) and metals ; this led to a sub- 
 division of the large class of neutral salts into 
 (i) metallic salts produced by the action of sul- 
 phuric acid on metals, and (2) neutral salts pro- 
 duced by the action of earths or alkalis on acids 
 generally. 
 
 To Rouelle, a predecessor of Lavoisier, who died 
 four years before the discovery of oxygen, we owe 
 many accurate and suggestive remarks and experi- 
 ments bearing on the term " salt." I have already 
 mentioned that it was he who applied the word 
 " base " to the alkali or earth, or it might be metal, 
 
WORK OF DAVY AND BERZELIUS. l8l 
 
 from which, by the action of acid, a salt is built up. 
 He also ceased to speak of an acid as sal acidtim, 
 or of an alkali as sal alkali, and applied the term 
 " salt " exclusively to those substances which are 
 produced by the action of acids on bases. When 
 the product of such an action was neutral that is, 
 had no sour taste, no soapy feeling to the touch, no 
 action on vegetable colours, and no action on acids 
 or bases he called that product a neutral salt ; 
 when the product still exhibited some of the pro- 
 perties of acid, e.g. sourness of taste, he called it 
 an acid salt ; and when the product continued to 
 exhibit some of the properties of alkali, e.g. turned 
 vegetable reds to blue, he called it aii alkaline salt. 
 
 Rouelle also proved experimentally that an acid 
 salt contains more acid relatively to the same 
 amount of base than a neutral salt, and that an 
 alkaline salt contains more base relatively to the 
 same amount of acid than a neutral salt ; and 
 he proved that this excess of acid, or of base, is 
 chemically united to the rest of the salt is, in other 
 words, an essential part of the salt, from which it 
 cannot be removed without changing the properties 
 of the whole. 
 
 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 bodies, why cer- 
 tain other, " alkaline," properties belong to another 
 group, nor why a third group can be distinguished 
 from both of these by the possession of properties 
 which we sum up in the term " earthy." Surely 
 
1 82 HEROES OF SCIENCE. 
 
 there must be some peculiarity in the composition 
 of these substances, common to all, by virtue of 
 which all are acid. The atom of an acid is 
 surely composed of certain elements which are 
 never found in the atom of an alkali or an earth ; 
 or perhaps the difference lies in the number, rather 
 than in the nature of the elements in the acid 
 atoms, or even in the arrangement of the elemen- 
 tary atoms in the compound atom of acid, of 
 alkali, and of earth. 
 
 I think that our knowledge of salt is now more 
 complete than our knowledge of either acid, alkali, 
 or earth. We know that a salt is formed by the 
 union of an acid and an alkali or earth ; if, then, 
 we get to know the composition of acids and bases 
 (i.e. alkalis and earths), we shall be well on the way 
 towards knowing the composition of salts. 
 
 And now we must resume our story where we 
 left it at p. 176. Lavoisier had recognized oxygen 
 as the acidifier ; Black had proved that a caustic 
 alkali does not contain carbonic acid. 
 
 Up to this time metallic calces, and for the most 
 part alkalis and earths also, had been regarded as 
 elementary substances. Lavoisier however proved 
 calces to be compounds of metals and oxygen ; 
 but as some of those calces had all the properties 
 which characterized earths, it seemed probable that 
 all earths are metallic oxides, and if all earths, 
 most likely all alkalis also. Many attempts were 
 made to decompose earths and alkalis, and to 
 obtain the metal, the oxide of which the earth or 
 
WORK OF DAVY AND BERZELIUS. 183 
 
 the alkali was supposed to be. One chemist 
 thought he had obtained a metal by heating the 
 earth baryta with charcoal, but from the properties 
 of his metal we know that he had not worked 
 with a pure specimen of baryta, and that his sup- 
 posed metallic base of baryta was simply a little 
 iron or other metal, previously present in the baryta, 
 or charcoal, or crucible which he employed. 
 
 But if Lavoisier's view were correct if all bases 
 contained oxygen it followed that all salts are 
 oxygen compounds. Acids all contain oxygen, 
 said Lavoisier ; this was soon regarded as one of 
 the fundamental facts of chemistry. Earths and 
 alkalis are probably oxides of metals; this before 
 long became an article of faith with all orthodox 
 chemists. Salts are produced by the union of acids 
 and bases, therefore all salts contain oxygen : the 
 conclusion was readily adopted by almost every one. 
 
 When the controversy between Lavoisier and the 
 phlogistic chemists was at its height, the followers 
 of Stahl had taunted Lavoisier with being unable 
 to explain the production of hydrogen (or phlogis- 
 ton as they thought) during the solution of metals 
 in acids ; but when Lavoisier learned the compo- 
 sition of water, he had an answer sufficient to quell 
 these taunts. The metal, said Lavoisier, decom- 
 poses the water which is always present along with 
 the acid, hydrogen is thus evolved, and the metallic 
 calx or oxide so produced dissolves in the acid and 
 forms a salt. If this explanation were correct 
 and there was an immense mass of evidence in its 
 
1 84 HEROES OF SCIENCE. 
 
 favour and apparently none against it then all 
 the salts produced by the action of acids on metals 
 necessarily contained oxygen. 
 
 The Lavoisierian view of a salt, 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 chemist : in 
 the early years of this century it reigned supreme. 
 
 But even during the lifetime of its founder this 
 theory was opposed and opposed by the logic of 
 -facts. In 1787 Berthollet published an account of 
 experiments on prussic acid, the existence and 
 preparation (from Prussian blue) of which acid had 
 been demonstrated three or four years before by the 
 Swedish chemist Scheele which led him to con- 
 clude this compound to be a true acid, but free from 
 oxygen. In 1796 the same chemist studied the 
 composition and properties of sulphuretted hydro- 
 gen, and pronounced this body to be an acid 
 containing no oxygen. 
 
 But the experiments and reasoning of Berthollet 
 were hidden by the masses of facts and the cogency 
 of argument of the Lavoisierian chemists. 
 
 The prevalent views regarding acids and bases 
 were greatly strengthened by the earlier researches 
 of Sir Humphry Davy, in which he employed the 
 voltaic battery as an instrument in chemical inves- 
 tigation. Let us now consider some of the electro- 
 chemical work of this brilliant chemist. 
 
 In the spring of the year 1800 the electrical 
 battery, which had recently been discovered by 
 
WORK OF DAVY AND BERZELIUS. 185 
 
 Volta, was applied by Nicholson and Carlisle to 
 effect the decomposition of water. The experi- 
 ments of these naturalists were repeated and con- 
 firmed by Davy, then resident at Bristol, who 
 followed up this application of electricity to effect 
 chemical changes by a series of experiments 
 extending from 1800 to 1806, and culminating in 
 the Bakerian Lecture delivered before the Royal 
 Society in the latter year. 
 
 The history of Davy's life during these years, 
 years rich in results of the utmost importance to 
 chemical science, will be traced in the sequel ; mean- 
 while we are concerned only with the results of his 
 chemical work. 
 
 The first Bakerian Lecture of Humphry Davy, 
 " On some Chemical Agencies of Electricity," de- 
 serves the careful study of all who are interested 
 in the methods of natural science ; it is a brilliant 
 example of the disentanglement of a complex 
 natural problem. 
 
 Volta and others had subjected water to the 
 action of a current of electricity, and had noticed 
 the appearance of acid and alkali at the oppositely 
 electrified metallic surfaces. According to some 
 experimenters, the acid was nitrous, according to 
 others, muriatic acid. One chemist asserted the 
 production of a new and peculiar body which he 
 called the electric acid. The alkali was generally 
 said to be ammonia. 
 
 When Davy passed an electric current through 
 distilled water contained in glass vessels, connected 
 
1 86 HEROES OF SCIENCE. 
 
 by pieces of moist bladder, cotton fibre, or other 
 vegetable matters, he found that nitric and hydro- 
 chloric acids were formed in the water surrounding 
 the positively electrified plate or pole, and soda 
 around the negatively electrified pole, of the 
 battery. 
 
 When the same piece of cotton fibre was re- 
 peatedly used for making connection between the 
 glass vessels, and was washed each time in dilute 
 nitric acid, Davy found that the production of 
 muriatic acid gradually ceased ; hence he traced the 
 formation of this acid to the presence of the animal 
 or vegetable substance used in the experiments. 
 
 Finding that the glass vessels were somewhat 
 corroded, and that the greater the amount of cor- 
 rosion the greater was the amount of soda making 
 its appearance around the negative pole, he con- 
 cluded that the soda was probably a product of the 
 decomposition of the glass by the electric current ; 
 he therefore modified the experiment. He passed 
 an electric current through distilled water contained 
 in small cups of agate, previously cleaned by boil- 
 ing in distilled water for several hours, and con- 
 nected by threads of the mineral asbestos, chosen 
 as being quite free from vegetable matter ; alkali 
 and acid were still produced. The experiment was 
 repeated several times with the same apparatus ; 
 acid and alkali were still produced, but the alkali 
 decreased each time. The only conclusion to be 
 drawn was that the alkali came from the water 
 employed. Two small cups of gold were now used 
 
WORK OF DAVY AND BERZELIUS. l8/ 
 
 to contain the water ; a very small amount of alkali 
 appeared at the negative pole, and a little nitric 
 acid at the positive pole. The quantity of acid 
 slowly increased as the experiment continued, 
 whereas the quantity of alkali remained the same 
 as after a few minutes' action of the electric current. 
 The production of alkali is probably due, said 
 Davy, to the presence in the water of some sub- 
 stance which is not removed by distillation in a 
 glass retort. By boiling down in a silver dish a 
 quantity of the water he had used, a very small 
 amount of solid matter was obtained, which after 
 being heated was distinctly alkaline, Moreover 
 when a little of this solid matter w r as added to the 
 water contained in the two golden cups, there was 
 a sudden and marked increase in the amount of 
 alkali formed around the negative pole. Another 
 quantity of the water which he had used was again 
 distilled in a silver retort, and a little of the dis- 
 tillate was subjected to electrolysis as before. No 
 alkali appeared. A little piece of glass was placed 
 in the water ; alkali quickly began to form. Davy 
 thus conclusively proved that the alkali produced 
 during the electrolysis (i.e. decomposition by the 
 electric current) of water is not derived from the 
 water itself, but from mineral impurities contained 
 in the water, or in the vessel in which the water is 
 placed during the experiment. But the production 
 of nitric acid around the positive pole was yet to 
 be accounted for. 
 
 Before further experiments could be made it was 
 
1 88 HEROES OF SCIENCE. 
 
 necessary that Davy should form an hypothesis 
 that he should mentally connect the appearance of 
 the nitric acid with some other phenomenon suffi- 
 cient to produce this appearance; he could then 
 devise experiments which would determine whether 
 the connection supposed to exist between the two 
 phenomena really did exist or not. 
 
 Now, of the constituents of nitric acid nitrogen, 
 hydrogen and oxygen all except the first named 
 are present in pure water ; nitrogen is present in 
 large quantity in the ordinary atmosphere. 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 water, 
 and the continual production of nitric acid during 
 the whole process of electrolysis was explained. 
 
 But how was this assumption to be proved or dis- 
 proved ? Davy adopted a method frequently made 
 use of in scientific investigations : remove the 
 assumed cause of a phenomenon ; if the phenomenon 
 ceases to be produced, the assumed cause is pro- 
 bably the real cause. Davy surrounded the little 
 gold cups containing the water to be electro- 
 lysed with a glass jar which he connected with an 
 air-pump ; he exhausted most of the air from the 
 jar and then passed the electric current through 
 the water. Very little nitric acid appeared. He 
 now again took out most of the air from the glass 
 jar, admitted some hydrogen to supply its place, 
 and again pumped this out. This process he re- 
 
WORK OF DAVY AND BERZELIUS, 189 
 
 peated two or three times and then passed the 
 electric current. No acid appeared in the water. He 
 admitted air into the glass vessel ; nitric acid began 
 to be produced. Thus he proved that whenever 
 air was present in contact with the water being 
 electrolysed, nitric acid made its appearance, and 
 when the air was wholly removed the acid ceased 
 to be produced. As he had previously shown that 
 the production of this acid was not to be traced to 
 impurities in the water, to the nature of the vessel 
 used to contain the water, or to the nature of the 
 material of which the poles of the battery were 
 composed, the conclusion was forced upon him that 
 the production of nitric acid in the water, and the 
 presence of ordinary air around the water invariably 
 existed together ; that if one of these conditions 
 was present, the other was also present in other 
 words, that one was the cause of the other. 
 
 The result of this exhaustive and brilliant piece 
 of work is summed up by Davy in these words : 
 " It seems evident then that water, chemically pure, 
 is decomposed by electricity into gaseous matter 
 alone, into oxygen and hydrogen." 
 
 From the effects of the electric current on glass, 
 Davy argued that other earthy compounds would 
 probably undergo change under similar conditions. 
 He therefore had little cups of gypsum made, in 
 which he placed pure water, and passed an electric 
 current through the liquid. Lime was formed 
 around the negative, and sulphuric acid around the 
 positive pole. Using similar apparatus, he proved 
 
1 90 HEROES OF SCIENCE. 
 
 that the electric current decomposes very many 
 minerals into an earthy or alkaline base and an 
 acid. 
 
 Picturing to himself the little particles of a salt 
 as being split by the electric current each into two 
 smaller particles, one possessed of acid and the 
 other of alkaline properties, Davy thought it might 
 be possible to intercept the progress of these smaller 
 particles, which he saw ever travelling towards the 
 positive and negative poles of the battery. He 
 accordingly connected these small glass vessels by 
 threads of washed asbestos ; in one of the outer 
 vessels he placed pure water, in the other an aqueous 
 solution of sulphate of potash, and in the central 
 vessel he placed ammonia. The negative pole of 
 the battery being immersed in the sulphate of 
 potash, and the positive pole in the water, it was 
 necessary for the particles of sulphuric acid pro- 
 duced 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 pole. Now, ammonia and sulphuric 
 acid cannot exist in contact they instantly combine 
 to form sulphate of ammonia ; the sulphuric acid 
 particles ought therefore to be arrested by the 
 ammonia. But the sulphuric acid made its appear- 
 ance at the positive pole just as if the central 
 vessel had contained water. It seemed that the 
 mutual attraction ordinarily exerted between sul- 
 phuric acid and ammonia was overcome by the 
 action of the electric current. Ammonia would 
 
WORK OF DAVY AND BERZELIUS. IQI 
 
 generally present an insuperable barrier to the pro- 
 gress of sulphuric acid, but the electrical energy ap- 
 peared to force the acid particles over this barrier ; 
 they passed towards their goal as if nothing stood in 
 their way. 
 
 Experiments are now multiplied by Davy, and 
 the general conclusion drawn is that " Hydrogen, 
 the alkaline substances, the metals and certain 
 metallic oxides are attracted by negatively elec- 
 trified metallic surfaces, and repelled by positively 
 electrified metallic surfaces ; and contrariwise, that 
 oxygen and acid substances are attracted by posi- 
 tively electrified metallic surfaces, and repelled by 
 negatively electrified metallic surfaces ; and these 
 attractive and repulsive forces are sufficiently ener- 
 getic to destroy or suspend the usual operation of 
 chemical affinity." * 
 
 To account for this apparent suspension of the 
 ordinary chemical laws, Davy supposes that che- 
 mical compounds are continually decomposed and 
 re-formed throughout the liquid which is subjected 
 to the electrical action. Thus, in the experiment 
 with water, ammonia and sulphate of potash, he 
 supposes that the sulphuric acid and ammonia do 
 combine in the central vessel to form sulphate of 
 ammonia, but that this compound is again decom- 
 posed, by the electrical energy, into sulphuric acid 
 which passes on towards the positive pole and 
 ammonia which remains in the central vessel 
 
 * For an explanation of this expression, "chemical affinity," see 
 p.' 206, et seq. 
 
192 HEROES OF SCIENCE. 
 
 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 water. 
 
 The eye of the philosopher had pierced beneath 
 the apparent stability of the chemical systems 
 which he studied. To his vision there appeared in 
 those few drops of water and ammonia and sul- 
 phate of potash a never-ceasing conflict of contend- 
 ing forces ; there appeared a continual shattering 
 and rebuilding of the particles of which the masses 
 were composed. The whole was at rest, the parts 
 were in motion ; the whole was constant in che- 
 mical composition, the composition of each particle 
 was changed a thousand times in the minutest 
 portion of every second. To the mind of Davy, 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 
 reaction." 
 
 Each step made in chemical science since Davy's 
 time has but served to emphasize the universality 
 of this principle of action and reaction, a principle 
 which has been too much overlooked in the che- 
 mical text-books, but the importance of which 
 recent researches are beginning to impress on the 
 minds of chemists. 
 
 It is the privilege of the philosophic student of 
 Nature to penetrate the veil with which she con- 
 ceals her secrets from the vulgar gaze. To him 
 are shown sights which " eye hath not seen/' and 
 
WORK OF DAVY AND BERZELIUS. IQ3 
 
 by him are perceived sounds which " ear hath not 
 heard." Each drop of water is seen by him not 
 only to be built up of myriads of small parts, 
 but each particle is seen to be in motion ; many 
 particles are being decomposed into still smaller 
 particles of matter, different in properties from 
 the original particles, but as the original par- 
 ticles are at the same time being reproduced, 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 forces. 
 He knows that rest and permanence are gained, not 
 by the cessation of action, but by the continuance 
 of conflict ; he knows that in the realm of natural 
 phenomena, stable equilibrium is the resultant of 
 the action of opposite forces, and that complete 
 decomposition occurs only when one force becomes 
 too powerful or another becomes too weak. 
 
 Pursuing the train of thought initiated by the 
 experiments which I have described, Davy entered 
 upon a series of researches which led him to con- 
 sider every chemical substance as possessing defi- 
 nite electrical relations towards every other sub- 
 stance. "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 is, by bringing it into a 
 state similar to the other so it may be increased 
 by exalting its natural energy." Thus zinc, a metal 
 easily oxidized, does not combine with oxygen 
 when negatively electrified, whereas silver, a metal 
 
 III. O 
 
194 HEROES OF SCIENCE. 
 
 oxidized with difficulty, readily combines with 
 oxygen when positively electrified. 
 
 Substances in opposite electrical states appear 
 to combine chemically, and the greater the elec- 
 trical difference the greater the readiness with 
 which chemical combination is effected, Electrical 
 energy and chemical attraction or affinity are 
 evidently closely connected ; perhaps, said Davy, 
 they are both results of the same cause. 
 
 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 forces ; by increasing either of 
 these a change is necessarily produced in the 
 other. Under certain electrical conditions the 
 bodies will exert no chemical action on one 
 another, but such action may be started by 
 changing these electrical conditions, or, on the 
 other hand, by changes in the chemical relations of 
 the bodies a change in the electrical relations may 
 be induced. Thus Davy found that if plates of 
 copper and sulphur are heated, the copper exhibits 
 a positive and the sulphur a negative electrical 
 condition ; that these electrical states become more 
 marked as temperature rises, until the melting point 
 of sulphur is reached, when the copper and sulphur 
 combine together chemically and produce sulphide 
 of copper. 
 
 When water is electrolysed, Davy looked on the 
 oppositely electrified metallic plates in the battery 
 as striving to attain a state of equilibrium ; the 
 
WORK OF DAVY AND BERZELIUS. 195 
 
 negatively electrified zinc strives to gain positive 
 electricity from the copper, which strives to gain 
 negative electricity from the zinc. The water he 
 regarded as the carrier of these electricities, the one 
 in this direction, the other in that. In thus acting 
 as a carrier, the water is itself chemically decom- 
 posed, with production of hydrogen and oxygen ; 
 but this chemical rearrangement of some of the 
 substances which composed the original system (of 
 battery and water) involves a fresh disturbance of 
 electrical energy, 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 
 battery. If the water were not chemically decom- 
 posed, Davy thought that the zinc and copper in 
 the battery would quickly attain the state of elec- 
 trical equilibrium towards which they continually 
 strive, and that the current would therefore quickly 
 cease. 
 
 Davy thought that " however strong the natural 
 electrical energies of the elements of bodies may 
 be, yet there is every probability of a limit to their 
 strength ; whereas the powers of our artificial in- 
 struments seem capable of indefinite increase." By 
 making use of a very powerful battery, he hoped to 
 be able to decompose substances generally regarded 
 as simple bodies. 
 
 Taking a wide survey of natural phenomena, he 
 sees these two forces, which we call chemical and 
 electrical, everywhere at work, and by their mutual 
 actions upholding the material universe in equili- 
 
IQ6 HEROES OF SCIENCE. 
 
 brium. In the outbreaks of volcanoes he sees the 
 disturbance of this equilibrium by the undue pre- 
 ponderance of electrical force ; and in the forma- 
 tion of complex minerals beneath the surface of 
 the earth, he traces the action of those chemical 
 attractions which are ever ready to bring about 
 the combination of elements, if they are not held 
 in check by the opposing influence of electrical 
 energy. 
 
 We shall see how the great and philosophical 
 conception of Davy was used by Berzelius, and 
 how, while undoubtedly gaining in precision, it lost 
 much in breadth in being made the basis of a 
 rigid system of chemical classification. 
 
 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 realized. A year after 
 the lecture " On some Chemical Agencies of Elec- 
 tricity," Davy was again the reader of the Bakerian 
 Lecture ; this year (1807) it was entitled, "On some 
 New Phenomena of Chemical Change produced by 
 Electricity, particularly the Decomposition of the 
 Fixed Alkalis ; and the Exhibition of the New 
 Substances which constitute their Bases ; and on 
 the General Nature of Alkaline Bodies." 
 
 In his first experiments on the effect of the 
 electrical current on potash and soda, Davy used 
 strong aqueous solutions of these alkalis, with 
 the result that hydrogen and oxygen only were 
 evolved. He then passed the current through melted 
 
WORK OF DAVY AND BERZELIUS. 197 
 
 potash kept liquid during the operation by the 
 use of a spirit-lamp, the flame of which was fed 
 with oxygen. Much light was evolved, and a great 
 flame appeared at the negative pole ; on changing 
 the direction of the current, "aeriform globules, 
 which inflamed in the air, rose through the potash." 
 
 On the 6th of October 1807, a piece of potash 
 was placed on a disc of platinum, which was made 
 the negative pole of a very powerful battery; 
 a platinum wire brought into contact with the 
 upper surface of the potash served as the positive 
 pole. When the current was passed, the potash 
 became hot and soon melted ; gas was evolved at 
 the upper surface, and at the lower (negative) side 
 " there was no liberation of elastic fluid, but small 
 globules, having a high metallic lustre, and being 
 precisely similar in visible characters to quicksilver 
 appeared, some of which burst with explosion and 
 bright flame as soon as they were formed, and 
 others remained, and were merely tarnished, 
 and finally covered by a white film which formed 
 on their surfaces." 
 
 When Davy saw these metallic globules burst 
 through the crust of fusing potash, we are told by 
 one of his biographers, " he could not contain his 
 joy, he actually bounded about the room in ecstatic 
 delight ; and some little time was required for him 
 to compose himself sufficiently to continue the 
 experiment." 
 
 This was the culminating point of the researches 
 in which he had been continuously engaged for 
 
198 HEROES OF SCIENCE. 
 
 about six years. His interest and excitement were 
 intense ; the Bakerian Lecture was written " on the 
 spur of the occasion, before the excitement of the 
 mind had subsided," yet, says his biographer and 
 we may well agree with him " yet it bears proof 
 only of the maturest judgment ; the greater part 
 of it is as remarkable for experimental accuracy 
 as for logical precision." But " to every action there 
 is an equal and opposite reaction : " immediately 
 after the delivery of the lecture, Davy was pro- 
 strated by a severe attack of illness, which confined 
 him to bed for nine weeks, and was very nearly 
 proving fatal. 
 
 That the phenomenon just described was really 
 the decomposition of potash, and the production of 
 the metal of which this substance is an oxygenized 
 compound, was proved by obtaining similar results 
 whether plates of silver, copper, or gold, or vessels 
 of plumbago, or even charcoal, were used to contain 
 the potash, or whether the experiment was con- 
 ducted in the air, or in a glass vessel from which 
 air had been exhausted, or in glass tubes wherein 
 the potash was confined by mercury. The decom- 
 position of potash was followed within a few days by 
 that of soda, from which substance metallic globules 
 were obtained which took fire when exposed to 
 the air. 
 
 But the analysis of potash and soda was not 
 sufficient for Davy ; he determined to accomplish 
 the synthesis of these substances. For this purpose 
 he collected small quantities of the newly discovered 
 
WORK OF DAVY AND BERZELIUS. 1 99 
 
 metals, by conducting the electrolysis of potash 
 and soda under experimental conditions such that 
 the metals, as soon as produced, were plunged 
 under the surface of naphtha, a liquid which does 
 not contain oxygen, and which protected them 
 from the action of the surrounding air. 
 
 A weighed quantity of each metal was then 
 heated in a stream of pure dry oxygen, the pro- 
 ducts were collected and weighed, and it was 
 found that solutions of these products in water 
 possessed all the properties of aqueous solutions 
 of potash and soda. 
 
 The new metals were now obtained in larger 
 quantity by Davy, and their properties carefully 
 determined by him ; they were named potassium 
 and sodium respectively. They were shown to 
 possess all those properties which were generally 
 accepted as characteristic of metal, except that of 
 being heavy. The new metals were extremely 
 light, lighter than water. For some time it was 
 difficult to convince all chemists that a metal 
 could be a very light substance. We are assured 
 that a friend of Davy, who was shown potassium 
 for the first time, and was asked what kind of 
 substance he supposed it to be, replied, " It is 
 metallic, to be sure ; " " and then, balancing it on 
 his finger, he added in a tone of confidence, ' Bless 
 me, how heavy it is ! " 
 
 Davy argued that since the alkalis, potash and 
 soda, were found to be oxygen compounds of 
 metals, the earths would probably also be found 
 
20O HEROES OF SCIENCE. 
 
 to be metallic oxides. In the year 1808 he suc- 
 ceeded in decomposing the three earths, lime, 
 baryta and strontia, and in obtaining the metals 
 calcium, barium and strontium, but not in a perfectly 
 pure condition, or in any quantity. He also got 
 evidence of the decomposition of the earths silica, 
 alumina, zirconia and beryllia, by the action of 
 powerful electric currents, but he did not succeed 
 in obtaining the supposed metallic bases of these 
 substances. 
 
 So far Davy's discoveries had all tended to 
 confirm the generally accepted view which regarded 
 alkalis and earths as metallic oxides. But we 
 found that the outcome of these views was to 
 regard all salts and among these, of course, com- 
 mon salt as oxygen compounds.* Acids were 
 oxygen compounds, bases were oxygen compounds, 
 and as salts were produced by the union of acids 
 with bases, they, too, must necessarily be oxygen 
 compounds. 
 
 Berthollet had thrown doubt on the universality 
 of Lavoisier's name " oxygen," the acidifier, but he 
 had not conclusively proved the existence of any 
 acid which did not contain oxygen. 
 
 The researches of Davy naturally led him to 
 consider the prevalent views regarding acids, bases 
 and salts. 
 
 Muriatic (or as we now call it hydrochloric) acid 
 had long been a stumbling-block to the thorough- 
 going Lavoisierian chemists. Oxygen could not 
 
 * These views have been already explained on pp. 182, 183. 
 
WORK OF DAVY AND BERZELIUS. 2OI 
 
 be detected in it, yet it ought to contain oxygen, 
 because oxygen is the acidifier. Of course, if 
 muriatic acid contains oxygen, the salts muriates 
 produced by the action of this acid on alkalis and 
 earths must also contain oxygen. 'Many years 
 before this time the action of muriatic acid on 
 manganese ore had been studied by the Swedish 
 chemist Scheele, who had thus obtained a yellow- 
 coloured gas with a very strong smell. Berthollet 
 had shown that when a solution of this gas in 
 water is exposed to sunlight, oxygen is evolved 
 and muriatic acid is produced. The yellow gas 
 was therefore supposed to be, and was called, 
 " oxidized muriatic acid," and muriatic acid was 
 itself regarded as composed of oxygen and an 
 unknown substance or radicle. 
 
 In 1809 Gay-Lussac and Thenard found that one 
 volume of hydrogen united with one volume of the 
 so-called oxidized muriatic acid to form muriatic 
 acid ; the presence of hydrogen in this acid was 
 therefore proved. 
 
 When Davy began (1810-11) to turn his at- 
 tention specially to the study of salts, he adopted 
 the generally accepted view that muriatic acid is 
 a compound of oxygen and an unknown radicle, 
 and that by the addition of oxygen to this com- 
 pound oxidized muriatic acid is produced. 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 substance. He tried to obtain direct evidence 
 
202 HEROES OF SCIENCE. 
 
 of the presence of oxygen, but failed. 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 
 substances. He showed that salt-like compounds 
 were produced by the action of oxidized muriatic 
 acid either on metals or on the oxides of these 
 metals, oxygen being evolved in the latter cases ; 
 and that the same compounds and water were pro- 
 duced by the action of muriatic acid on the same 
 metallic oxides. 
 
 These results were most easily and readily ex- 
 plained by assuming the so-called oxidized muriatic 
 acid to be an elementary substance, and muriatic 
 acid to be a compound of this element with hydro- 
 gen. To the new element thus discovered for he 
 who establishes the elementary nature of a sub- 
 stance may almost be regarded as its discoverer 
 Davy gave the name of chlorine, suggested by the 
 yellow colour of the gas (from Greek, = yellow). 
 He at once began to study the analogies of chlorine, 
 to find by experiment which elements it resembled, 
 and so to classify it. Many metals, he found, com- 
 bined readily with chlorine, with evolution of heat 
 and light. It acted, like oxygen, as a supporter of 
 combustion ; it was, like oxygen, attracted towards 
 the negative pole of the voltaic battery ; its com- 
 pound with hydrogen was an acid ; hence said 
 Davy chlorine, like oxygen, is a supporter of com- 
 bustion and also an acidifier. 
 
 But it was very hard to get chemists to adopt 
 
WORK OF DAVY AND BERZELIUS. 
 
 these views. As Bacon says, "If false facts in 
 Nature be once on foot, what through neglect of 
 examination, the countenance of antiquity, and the 
 use made of them in discourse, they are scarce ever 
 retracted." 
 
 Chemists had long been accustomed to systems 
 which pretended to explain all chemical facts. The 
 phlogistic theory, which had tyrannized over 
 chemistry, had been succeeded by the Lavoisierian 
 chemistry, which recognized one acidifier, and this 
 also the one supporter of combustion. To ascribe 
 these properties to any element other than oxygen 
 appeared almost profane. 
 
 But when Davy spoke of chlorine as an acidifier, 
 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 acids ; he simply meant to ex- 
 press the fact that a compound containing chlorine 
 as one of its constituents, but not containing oxygen, 
 was a true acid. When Gay-Lussac attempted to 
 prove that hydrogen is an alkalizing principle, 
 Davy said, "This is an attempt to introduce into 
 chemistry a doctrine of occult qualities, and to refer 
 to some mysterious and inexplicable energy what 
 must depend upon a peculiar corpuscular arrange- 
 ment." And with regard to Gay-Lussac's strained 
 use of analogies between hydrogen compounds and 
 alkalis, he says, "The substitution of analogy for 
 fact is the bane of chemical philosophy ; the legiti- 
 mate use of analogy is to connect facts together, 
 and to guide to new experiments." 
 
2O4 HEROES OF SCIENCE. 
 
 But Davy's facts were so well established, and 
 his experiments so convincing, that before two or 
 three years had passed, most chemists were per- 
 suaded that chlorine was an element i.e. a sub- 
 stance which had never been decomposed and 
 that muriatic acid was a compound of this element 
 with hydrogen. 
 
 Berzelius was among the last to adopt the new 
 view. Wohler tells us that in the winter of 1823, 
 when he was working in the laboratory of Berzelius, 
 Anna, while washing some basins, remarked that 
 they smelt strongly of oxidized muriatic acid : 
 " Now," said Berzelius, " listen to me, Anna. Thou 
 must no longer say ' oxidized muriatic acid/ but 
 ( chlorine ; ' that is better." 
 
 This work on chlorine was followed up, in 1813, 
 by the proof that the class of acidifiers and sup- 
 porters of combustion contains a third elementary 
 substance, viz. iodine. As Davy's views regard- 
 ing acids and salts became developed, he seems 
 to have more and more opposed the assumption 
 that any one element is especially to be regarded 
 as the acidifying element ; but at the same time 
 he seems to admit that most, if not all, acids con- 
 tain hydrogen. Such oxides as sulphur trioxide, 
 nitrogen pentoxide, etc., do not possess acid pro- 
 perties except in combination with water. But he 
 of course did not say that all hydrogen compounds 
 are acids ; he rather regarded the possession by a 
 substance of acid properties as dependent, to a 
 great extent, on the nature of the elements other 
 
WORK OF DAVY AND BERZELIUS. 2O5 
 
 than hydrogen which it contained, or perhaps on 
 the arrangement of all the elements in the particles 
 of the acid. He regarded the hydrogen in an 
 acid as capable of replacement by a metal, and to 
 the metallic derivative as it might be called of 
 the acid, thus produced, he gave the name of " salt." 
 An acid might therefore be a compound of hydro- 
 gen with one other element such were hydrochloric, 
 hydriodic, hydrofluoric acids or it might be a 
 compound of hydrogen with two or more elements, 
 of which one might or might not be oxygen such 
 were hydrocyanic acid and chloric or nitric acid. 
 If the hydrogen in any of these acids were replaced 
 by a metal a salt would be produced. A salt might 
 therefore contain no oxygen, e.g. chloride or iodide 
 of potassium ; but in most cases salts did contain 
 oxygen, e.g. chlorate or nitrate of potassium. 
 
 Acids were thus divided into oxyacids (or acids 
 which contain oxygen) and acids containing no 
 oxygen ; the former class including most of the 
 known acids. The old view of salts as being com- 
 pounds of acids (i.e. oxides of the non-metallic 
 elements) and bases (i.e. oxides of metals) was 
 overthrown, and salts came to be regarded as 
 metallic derivatives of acids. 
 
 From this time, these terms acids, salts, bases 
 become of less importance than they formerly 
 were in the history of chemical advance. 
 
 In trying to explain Davy's electro-chemical 
 theory I have applied the word affinity to the 
 mutual action and reaction between two substances 
 
2O6 HEROES OF SCIENCE. 
 
 which combine together to form a chemical com- 
 pound. It is now necessary that we should look 
 a little more closely into the history of this word 
 affinity. 
 
 Oil and water do not mix together, but oil and 
 potash solution do ; the former may be said not 
 to have, and the latter to have, an affinity one 
 for the other. When sulphur is heated, the yellow 
 odourless solid, seizing upon oxygen in the air, 
 combines with it to produce a colourless strongly 
 smelling gas. Sulphur and oxygen are said to 
 have strong affinity for each other. 
 
 If equal weights of lime and magnesia be thrown 
 into diluted nitric acid, after a time it is found that 
 some of the lime, but very little of the magnesia, is 
 dissolved. If an aqueous solution of lime be added 
 to a solution of magnesia in nitric acid, the mag- 
 nesia is precipitated in the form of an insoluble 
 powder, while the lime remains dissolved in the 
 acid. It is said that lime has a stronger affinity for 
 nitric acid than magnesia has. Such reactions as 
 these used to be cited as examples of single elective 
 affinity single, because one substance combined 
 with one other, and elective, because a substance 
 seemed to choose between two others presented to 
 it, and to combine with one to the exclusion of the 
 other. 
 
 But if a neutral solution of magnesia in sulphuric 
 acid is added to a neutral solution of lime in nitric 
 acid, sulphate of lime and nitrate of magnesia are 
 produced. The lime, it was said, leaves the nitric 
 
WORK OF DAVY AND BERZELIUS. 2O/ 
 
 and goes to the sulphuric acid, which, having been 
 deserted by the magnesia, is ready to receive it ; at 
 the same time the nitric acid from which the lime 
 has departed combines with the magnesia formerly 
 held by the sulphuric acid. Such a reaction was 
 said to be an instance of double affinities. The 
 chemical changes were caused, it was said, by 
 the simultaneous affinity of lime for sulphuric acid, 
 which was greater than its affinity for nitric acid, 
 and the affinity of magnesia for nitric acid, which 
 was greater than its affinity for sulphuric acid. 
 
 If a number of salts were mixed, each base sup- 
 posing the foregoing statements to be correct 
 would form a compound with that acid for which 
 it had the greatest affinity. It should then be 
 possible to draw up tables of affinity. Such tables 
 were indeed prepared. Here is an example : 
 
 Snip/in He Acid. 
 
 Baryta. Lime. 
 
 Strontia. Ammonia, 
 
 Potash. Magnesia. 
 
 Soda. 
 
 This table tells us that the affinity of baryta for 
 sulphuric acid is greater than that of strontia for 
 the same acid, that of strontia greater than that of 
 potash, and so on. It also tells that potash will 
 decompose a compound of sulphuric acid and soda, 
 just as soda will decompose a compound of the 
 same acid with lime, or strontia will decompose a 
 compound with potash, etc. 
 
 But Berthollet showed in the early years of this 
 
2O8 HEROES OF SCIENCE. 
 
 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 affinity. He 
 showed, that is, that the formation or non-forma- 
 tion of a compound is dependent not only on the 
 so-called affinities between the constituents, but also 
 on the relative quantities of these constituents. 
 Berthollet and other chemists also showed that 
 affinity is much conditioned by temperature ; that 
 is, that two substances which show no tendency 
 towards chemical union at a low temperature may 
 combine when the temperature is raised. He, and 
 they, also proved that the formation or non-forma- 
 tion of a compound is much influenced by its 
 physical properties. Thus, if two substances are 
 mixed in solution, and if by their mutual action a 
 substance can be produced which is insoluble in 
 the liquids present, that substance is generally pro- 
 duced whether the affinity between the original 
 pair of substances be strong or weak. 
 
 The outcome of Berthollet's work was that 
 tables of affinity became almost valueless. To say 
 that the affinity of this body for that was greater 
 than its affinity for a third body was going beyond 
 the facts, because the formation of this or that com- 
 pound depended on many conditions much more 
 complex than those connoted by the term " affinity." 
 Yet the conception of affinity remained, although 
 it could not be applied in so rigorous a way as had 
 been done by the earlier chemists. If an element. 
 
WORK OF DAVY AND BERZELIUS. 2OQ 
 
 A, readily combines with another element, B, under 
 certain physical conditions, but does not, under the 
 same conditions, combine with a third element, C, 
 it may still be said that A and B have, and A and 
 C have not, an affinity for each other. 
 
 This general conception of affinity was applied 
 by Berzelius to the atoms of elements. Affinity, 
 said Berzelius, acts between unlike atoms, and 
 causes them to unite to form a compound atom, 
 unlike either of the original atoms ; cohesion, on 
 the other hand, acts between like atoms, causing 
 them to hold together without producing any 
 change in their properties. Affinity varies in dif- 
 ferent elements. Thus the affinity of gold for oxygen 
 is very small ; hence it is that gold is found in the 
 earth in the metallic state, while iron, having a 
 great affinity for oxygen, soon rusts when exposed 
 to air, or when buried in the earth. Potassium and 
 sodium have great affinities for oxygen, chlorine, 
 etc. ; yet the atoms of potassium and sodium do 
 not themselves combine. The more any elements 
 are alike chemically the smaller is their affinity for 
 each other ; the more any elements are chemically 
 unlike the greater is their mutual affinity ; but this 
 affinity is modified by circumstances. Thus, said 
 Berzelius, if equal numbers of atoms of A and B, 
 having equal or nearly equal affinity for C, mutually 
 react, compound atoms, AC and BC, will be pro- 
 duced, but atoms of A and B will remain. The 
 amounts of AC and BC produced will be influenced 
 by the greater or less affinity of A and B for C ; 
 
 III. p 
 
210 HEROES OF SCIENCE. 
 
 but if there be a greater number of A than of B 
 atoms, a greater amount of AC than of BC will be 
 produced. In these cases all the reacting sub- 
 stances and the products of the actions are sup- 
 posed to be liquids ; but BC, if a solid substance, 
 will be produced even if the affinity of A for C is 
 greater than that of B for C. 
 
 In some elements, Berzelius taught, affinity slum- 
 bers, and can be awakened only by raising the 
 temperature. Thus carbon in the form of coal has 
 no affinity for oxygen at ordinary temperatures ; it 
 has remained for ages in the earth without under- 
 going oxidation ; but when coal is heated the affini- 
 ties of carbon are awakened, combination with 
 oxygen occurs, and heat is produced. 
 
 But why is it that certain elementary atoms 
 exhibit affinity for certain others ? It depends, 
 said Berzelius, on the 'electrical states of these atoms. 
 According to the Berzelian theory, every elemen- 
 tary atom has attached to it a certain quantity of 
 electricity, part of which is positive and part nega- 
 tive. This electricity is accumulated at two points 
 on each atom, called respectively the positive pole 
 and the negative pole ; 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 body. 
 When two atoms combine chemically the positive 
 electricity in one neutralizes the negative elec- 
 tricity in the other. As we know that similar 
 electricities repel, and opposite electricities attract 
 
WORK OF DAVY AND BERZELIUS, 211 
 
 each other, it follows that a markedly positive atom 
 will exhibit strong affinity for a markedly negative 
 atom, less strong affinity for a feebly negative, and 
 little or no affinity for a positively electrified atom ; 
 but two similarly electrified atoms may exhibit 
 affinity, because in every positive atom there is 
 some negative electricity, as in every negative 
 atom there is some positive electricity. Thus, 
 in the atoms of copper and zinc positive elec- 
 tricity predominates, said Berzelius, but the zinc 
 atoms are more positive than those of copper ; 
 hence, when the metals are brought into contact 
 the negative electricity of the copper atoms is 
 attracted and neutralized by the positive electri- 
 city of the zinc atoms, combination takes place, 
 and the compound atom is still characterized by a 
 predominance of positive electricity. 
 
 Hence Berzelius identified " electrical polarity " 
 with chemical affinity. Every atom was regarded 
 by him as both positively and negatively electrified ; 
 but as one of these electricities was always much 
 stronger than the other, every atom regarded as 
 a whole appeared to be either positively or nega- 
 tively electrified. Positive atoms showed affinity 
 for negative atoms, and vice versa. As a positive 
 atom might become more positive by increasing 
 the temperature of the atom, so might the affinity 
 of this atom for that be more marked at high than 
 at low temperatures. 
 
 Now, if two elementary atoms unite, the com- 
 pound atom must according to the Berzelian 
 
212 HEROES OF SCIENCE, 
 
 views be characterized either by positive or 
 negative electricity. This compound atom, if 
 positive, will exhibit affinity for other compound 
 atoms in which negative electricity predominates ; 
 if negative, it will exhibit affinity for other posi- 
 tively electrified compound atoms. If two com- 
 pound atoms unite chemically, the complex atom 
 so produced will, again, be characterized by one or 
 other of the two electricities, and as it is positive 
 or negative, so will it exhibit affinity for positively 
 or negatively electrified complex atoms. Thus 
 Berzelius and his followers regarded every com- 
 pound atom, however complex, as essentially built 
 up of two parts, one of which was positively and 
 the other negatively electrified, and which were held 
 together chemically by virtue of the mutual attrac- 
 tions of these electricities ; they regarded every 
 compound atom as a dual structure. The classifi- 
 cation adopted by Berzelius was essentially a dual- 
 istic classification. His system has always been 
 known in chemistry as dualism. 
 
 Berzelius divided compound atoms (we should 
 now say molecules) into three groups or orders 
 
 Compound atoms of the first order, formed by the 
 immediate combination of atoms of two, or in or- 
 ganic compounds of three, elementary substances. 
 
 Compound atoms of the second order > formed by 
 the combination of atoms of an element with atoms 
 of the first order, or by the combination of two or 
 more atoms of the first order. 
 
 Compound atoms of the third order, formed by 
 
WORK OF DAVY AND BERZELIUS. 213 
 
 combination of two or more atoms of the second 
 order. 
 
 When an atom of the third order was decom- 
 posed by an electric current, it split up, accord- 
 ing to the Berzelian teaching, into atoms of the 
 second order some positively, others negatively 
 electrified. When an atom of the second order 
 was submitted to electrolysis, it decomposed into 
 atoms of the first order some positively, others 
 negatively electrified. 
 
 Berzelius said that a base is an electro-positive 
 oxide, and an acid is an electro-negative oxide. 
 The more markedly positive an oxide is, the more 
 basic it is ; the more negative it is, the more is it 
 characterized by acid properties. 
 
 One outcome of this teaching regarding acids 
 and bases was to overthrow the Lavoisierian con- 
 ception of oxygen as the acidifying element. Some 
 oxides are positive, others negative, said Berzelius ; 
 but acids are characterized by negative electricity, 
 therefore the presence of oxygen in a compound 
 does not always confer on that compound acid 
 properties. 
 
 We have already seen that silica was regarded 
 by most chemists as a typical earth ; but Berzelius 
 found that in the electrolysis of compounds of 
 silica, this substance appeared at the positive pole 
 of the battery that is, the atom of silica belonged 
 to the negatively electrified order of atoms. Silica 
 was almost certainly an oxide ; but electro-negative 
 oxides are, as a class, acids ; therefore silica was 
 
214 HEROES OF SCIENCE. 
 
 probably an acid. The supposition of the acid 
 character of silica was amply confirmed by the 
 mineralogical analyses and experiments of Ber- 
 zelius. He showed that most of the earthy minerals 
 are compounds of silica with electro-positive metal- 
 lic oxides, and that silica plays the part of an acid 
 in these minerals ; and in 1823 he obtained the 
 element silicon, the oxide of which is silica. On 
 this basis Berzelius reared a system of classifi- 
 cation in mineralogy which much aided the advance 
 of that branch of natural science. 
 
 By the work of Berzelius and Davy the Lavoi- 
 sierian conception of acid has now been much 
 modified and extended ; it has been rendered less 
 rigid, and is therefore more likely than before to be 
 a guide to fresh discoveries. 
 
 The older view of acid and alkali was based, for 
 the most part, on a qualitative study of the reac- 
 tions of chemical substances : bodies were placed 
 in the same class because they were all sour, or 
 all turned vegetable blues to red, etc. This was 
 followed by a closer study of the composition of 
 substances, and by attempts to connect the proper- 
 ties of these substances with their composition ; 
 but when this attempt resulted in the promulgation 
 of the dictum that " oxygen is the acidifying prin- 
 ciple," 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 substances. This larger basis 
 was laid by the two chemists whose work we have 
 
WORK OF DAVY AND BERZELIUS. 215 
 
 now reviewed. Of the life of one of these men I 
 have already given such a sketch as I can from 
 the materials available to me ; of the life of the 
 other we happily possess ample knowledge. Let 
 us now consider the main features of this life. 
 
 HUMPHRY DAVY, the eldest son of Robert and 
 Grace Davy, was born at Penzance, in Corn- 
 wall, on December 17, 1778, eight months that is 
 before the birth of Berzelius. His parents resided 
 on a small property which had belonged to their 
 ancestors for several generations. Surrounded by 
 many kind friends by whom he was much thought 
 of, the boy appears to have passed a very happy 
 childhood. Even at the age of five his quickness 
 and penetration were marked by those around him, 
 and at school these continued to be his predominant 
 characteristics. Nurtured from his infancy in the 
 midst of beautiful and romantic scenery, and en- 
 dowed with great observing power and a lively 
 imagination, young Davy seemed destined to be 
 one of those from whose lips is " poured the death- 
 less singing ; " all through life he was characterized 
 by a strongly marked poetic temperament. 
 
 Humphry Davy was held in much esteem by his 
 school friends as a composer of valentines and love 
 letters, as a daring and entertaining teller of stories, 
 and as a successful fireworks manufacturer. Such a 
 combination of qualities would much endear him to 
 his boy-companions. We are told that at the age 
 of eight he used to mount on an empty cart, around 
 
2l6 HEROES OF SCIENCE. 
 
 which a circle of boys would collect to be enter- 
 tained by the wonderful tales of the youthful 
 narrator. 
 
 Finishing his school education at the age of 
 fifteen, he now began his own education of himself. 
 In 1795 he was apprenticed to a surgeon and 
 apothecary (afterwards a physician), in Penzancc, 
 with whom he learned the elements of medical 
 science ; but his time during the years which he 
 spent under Mr. Borlase was much occupied in 
 shooting, fishing, searching for minerals and geo- 
 logical specimens, composing poetry, and pursuing 
 metaphysical speculations. He was now, as through 
 life, an enthusiastic lover of Nature ; his mind was 
 extremely active, ranging over the most diverse 
 subjects ; he was full of imagination, and seemed 
 certain to distinguish himself in any pursuit to 
 which he should turn his attention. During the 
 next three or four years Davy indulged freely in 
 speculations in all manner of subjects ; he started, 
 as people generally do when young, from general 
 principles and followed these out to many conclu- 
 sions. Even in his study of physiology and other 
 branches of science, he appears at this time to 
 have adopted the speculative rather than the ex- 
 perimental method ; but unlike most youthful 
 metaphysicians he was ready to give up an opinion 
 whenever it appeared to him incorrect. By the 
 time he reached the age of twenty he had dis- 
 carded this method of seeking for truth, and was 
 ever afterwards distinguished by his careful work- 
 
\VORK OF DAVY AND BERZELIUS. 2I/ 
 
 ing out of facts as the foundation for all his bril- 
 liant theories. 
 
 Davy appears to have begun the study of 
 chemistry about 1798 by reading Lavoisier's 
 " Elements of Chemistry," the teachings of which 
 he freely criticized. About this time Mr. Gre- 
 gory Watt came to live at Penzance as a lodger 
 with Davy's mother, and with him the young philo- 
 sopher had much talk on chemical and other scien- 
 tific subjects. He also became acquainted with Mr. 
 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 studies. 
 
 It was during these years ^that Davy made ex- 
 periments on heat, which were published some 
 years later, 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 bodies. 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 plate ; the 
 plates were covered by a glass jar, from which he 
 exhausted the air by means of a simple syringe of 
 his own contrivance ; the machine being placed on 
 blocks of ice the plates were caused to revolve. The 
 ice inside the jar soon melted ; Davy concluded 
 that the heat required to melt this ice could only 
 be produced by the friction of the ice and brass, 
 and that therefore heat could not be any form 
 of ponderable matter. 
 
21 8 HEROES OF SCIENCE. 
 
 In the year 1798 Davy was asked to go to 
 Bristol as superintendent of the laboratory of a new 
 Pneumatic Institution started by Dr. Beddoes for 
 the application of gases to the treatment of dis- 
 eases. Davy had corresponded with Beddoes before 
 this time regarding his experiments on heat, and 
 the latter seems to have been struck with his great 
 abilities and to have been anxious to secure him 
 as experimenter for his institution. Davy was 
 released from his engagements with Mr. Borlase, 
 and, now about twenty years of age, set out for his 
 new home, having made as he says all the experi- 
 ments he could at Penzance, and eagerly looking 
 forward to the better appliances and incitements 
 to research which he hoped to find at Bristol. 
 
 The Pneumatic Institution was supported by 
 subscriptions, for the most part from scientific men. 
 It was started on a scientific basis. Researches were 
 to be made on gases of various kinds with the view 
 of applying these as remedies in the alleviation of 
 disease. An hospital for patients, a laboratory for 
 experimental research, and a lecture theatre were 
 provided. 
 
 At this time many men of literary and intellectual 
 eminence resided in Bristol ; among these were 
 Coleridge and Southey. Most of these men were 
 visitors at the house of Dr. Beddoes, and many 
 distinguished men came from various parts of the 
 county to visit the institution. Davy thus entered 
 on a sphere of labour eminently suited for the 
 development of his genius. With ample mechanical 
 
WORK OF DAVY AND BERZELIUS. 2IQ 
 
 appliances for research, with plenty of time at his 
 disposal, surrounded by an atmosphere of inquiry 
 and by men who would welcome any additions he 
 could make to the knowledge of Nature, and being 
 at the same time not without poetic and imaginative 
 surroundings, by which he was ever spurred onwards 
 in the pursuit of truth placed in these circum- 
 stances, such an enthusiastic and diligent student of 
 science as Davy could not but obtain results of 
 value to his fellows. The state of chemical science 
 at this time was evidently such as to incite the 
 youthful worker. The chains with which Stahl and 
 his successors had so long bound the limbs of the 
 young science had been broken by Lavoisier ; and 
 although the French school of chemistry was at 
 this time dominant, and not disinclined to treat as 
 ignorant any persons who might differ from its 
 teaching, yet there was plenty of life in the culti- 
 vators of chemistry. The controversy between 
 Berthollet and Proust was about to begin ; the La- 
 voisierian views regarding acids and salts were not 
 altogether accepted by Gay-Lussac, Thenard and 
 others ; 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 Sweden. The voltaic 
 battery had been discovered, and had opened up a 
 region of possibilities in chemistry. 
 
 Davy began his researches at the institution by 
 experiments with nitrous oxide, a gas supposed by 
 some people at that time to be capable of produc- 
 
220 HEROES OF SCIENCE. 
 
 ing most harmful effects on the animal system. He 
 had to make many experiments before he found 
 a method for preparing the pure gas, and in the 
 course of these experiments he added much to the 
 stock of chemical knowledge regarding the com- 
 pounds of nitrogen and oxygen. Having obtained 
 fairly pure nitrous oxide, he breathed it from a silk 
 bag ; he experienced a " sensation analogous to 
 gentle pressure on all the muscles; . . . the objects 
 around me became dazzling and my hearing more 
 acute ; ... at last an irresistible propensity to 
 action was indulged in. ... I recollect but indis- 
 tinctly what followed ; I know that my motions 
 were various and violent." Southey and Coleridge 
 breathed the gas ; the poets only laughed a little. 
 Encouraged by the results of these experiments, 
 Davy proceeded to prepare and breathe nitric 
 oxide whereby he was rendered very ill and 
 then carburetted hydrogen which nearly killed 
 him. 
 
 In his chemical note-book about this time, Davy 
 says, "The perfection of chemical philosophy, or 
 the laws of corpuscular motion, must depend on 
 the knowledge of all the simple substances, their 
 mutual attractions, and the ratio in which the 
 attractions increase or diminish with increase or 
 diminution of temperature. . . . The first step to- 
 wards these laws will be the decomposition of those 
 bodies which are at present undecompounded." 
 And in the same note-book he suggests methods 
 which he thinks might effect the decomposition of 
 
WORK OF DAVY AND BERZELIUS. 221 
 
 muriatic and boric acids, the alkalis and earths, 
 Here are the germs of his future work. 
 
 After about eight months' work at Bristol he 
 published a volume of " Researches," which con- 
 tained a great many new facts, and was charac- 
 terized by vigour and novelty of conception. These 
 researches had been carried out with intense 
 application ; each was struck off at a red heat. 
 His mind during this time was filled with vast 
 scientific conceptions, and he began also to think 
 of fame. "An active mind, a deep ideal feeling 
 of good, and a look towards future greatness," he 
 tells us, sustained him. 
 
 Count Rumford, the founder of the Royal Institu- 
 tion in London, was anxious to obtain a lecturer on 
 chemistry for the Institution. Davy was strongly 
 recommended, and after a little arrangement con- 
 cerning which Davy says in a letter, " I will accept 
 of no appointment except on the sacred terms of 
 independence" he was appointed Assistant Lec- 
 turer on Chemistry and Director of the Labora- 
 tory. About a year later his official designation 
 was changed to Professor of Chemistry. This ap- 
 pointment opened up a great sphere of research ; 
 " the sole and uncontrolled use of the apparatus of 
 the institution for private experiments " was to be 
 granted him, and he was promised " any apparatus 
 he might need for new experiments." 
 
 He had now the command of a good laboratory ; 
 he had not to undergo the drudgery of systematic 
 teaching, but was only required to give lectures 
 
222 HEROES OF SCIENCE. 
 
 to a general audience. Before leaving Bristol 
 he had commenced experiments on the chemical 
 applications of the voltaic battery ; these he at 
 once followed up with the better apparatus now 
 at his command. The results of this research, 
 and his subsequent work on the alkalis and on 
 muriatic acid and chlorine, have been already de- 
 scribed. The circumstances of Davy's life had 
 hitherto been most favourable ; how nobly he had 
 availed himself of these circumstances was testified 
 by the work done by him. 
 
 His first lecture was delivered in the spring of 
 1801, and at once he became famous. A friend of 
 Davy says, "The sensation created by his first 
 course of lectures at the Institution, and the enthu- 
 siastic admiration which they obtained, is scarcely 
 to be imagined. Men of the first rank and talent, 
 the literary and the scientific, the practical and the 
 theoretical, blue-stockings and women of fashion, the 
 old and the young all crowded, eagerly crowded 
 the lecture-room. His youth, his simplicity, his 
 natural eloquence, his chemical knowledge, his 
 happy illustrations and well-conducted experi- 
 ments, excited universal attention and unbounded 
 applause. Compliments, invitations and presents 
 were showered upon him in abundance from all 
 quarters ; his society was courted by all, and all 
 appeared proud of his acquaintance." One of his 
 biographers says of these lectures, " He was always 
 in earnest, and when he amused most, amusement 
 appeared most foreign to his object. His great and 
 
WORK OF DAVY AND BERZELIUS. 223 
 
 first object was to instruct, and in conjunction with 
 this, maintain the importance and dignity of science ; 
 indeed, the latter, and the kindling a taste for scien- 
 tific pursuits, might rather be considered his main 
 object, and the conveying instruction a secondary 
 one." 
 
 The greatest pains were taken by Davy in the 
 composition and rehearsal of his lectures, and in 
 the arrangement of experiments, that everything 
 should tend towards the enlightenment of his 
 audience. Surrounded by a brilliant society, in- 
 vited to every fashionable entertainment, flattered 
 by admirers, tempted by hopes of making money, 
 Davy remained a faithful and enthusiastic student 
 of Nature. " I am a lover of Nature," he writes at 
 this time to a friend, " with an ungratified imagi- 
 nation. I shall continue to search for untasted 
 charms, for hidden beauties. My real, my waking 
 existence, is amongst the objects of scientific re- 
 search. Common amusements and enjoyments are 
 necessary to me only as dreams to interrupt the 
 flow of thoughts too nearly analogous to enlighten 
 and vivify." 
 
 During these years (i.e. from 1802 to 1812) he 
 worked for the greater part of each day in the 
 laboratory. Every week, almost every day, saw 
 some fresh discovery of importance. He advanced 
 from discovery to discovery. His work was 
 characterized by that [vast industry and extreme 
 rapidity which belong only to the efforts of genius. 
 Never, before or since, has chemical science made 
 such strides in this country. 
 
224 HEROES OF SCIENCE. 
 
 In 1 803 Davy was elected a Fellow, and in 1 807 
 one of the secretaries of the Royal Society. In 
 1812 he retired from the professorship of chemistry 
 at the Royal Institution ; in the same year he was 
 made a knight. 
 
 The next two or three years were mostly spent 
 in travelling abroad with his wife he had married 
 a widow lady, Mrs. Apreece, in 1812. During his 
 visit to Paris he made several experiments on the 
 then recently discovered iodine, and proved this 
 substance to be an element. 
 
 The work which Davy had accomplished in the 
 seventeen years that had now elapsed since he 
 began the study of chemistry, whether we consider 
 it simply as a contribution to chemical science, or 
 in the light of the influence it exerted on the re- 
 searches of others, was of first-rate importance ; 
 but a fresh field now began to open before him, 
 from which he was destined to reap the richest 
 fruits. In the autumn of 1815 his attention was 
 drawn to the subject of fire-damp in coal-mines. 
 As he passed through Newcastle, on his return from 
 a holiday spent in the Scottish Highlands, he 
 examined various coal-mines and collected samples 
 of fire-damp ; in December of the same year his 
 safety-lamp was perfected, and soon after this it 
 was in the hands of the miner. 
 
 The steps in the discovery of this valuable in- 
 strument were briefly these. Davy established the 
 fact that fire-damp is a compound of carbon and 
 hydrogen ; he found that this gas must be mixed 
 
WORK OF DAVY AND BERZELIUS. 22$ 
 
 with a large quantity of ordinary air before the 
 mixture becomes explosive, that the temperature 
 at which this explosion occurs is a high one, 
 and that but little heat is produced during the 
 explosion ; he found that the explosive mixture 
 could not be fired in narrow metallic tubes, and 
 also that it was rendered non-explosive by addi- 
 tion of carbonic acid or nitrogen. He reasoned 
 on these facts thus : " It occurred to me, as a 
 considerable heat was required for the inflamma- 
 tion of the fire-damp, and as it produced in 
 burning a comparatively small degree of heat, 
 that the effect of carbonic acid and azote, and 
 of the surfaces of small tubes, in preventing its 
 explosion, depended on their cooling powers 
 upon their lowering the temperature of the ex- 
 ploding mixture so much that it was no longer 
 sufficient for its continuous inflammation." 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 attained, 
 and which therefore, while burning, might be filled 
 with this mixture without any danger of an ex- 
 plosion. He surrounded the flame of an oil-lamp 
 with a cylinder of fine wire-gauze ; this lamp when 
 brought into an atmosphere containing fire-damp 
 and air could not cause an explosion, because 
 although small explosions might occur in the 
 interior of the wire cylinder, so much heat was 
 conducted away by the large metallic surface that 
 the temperature of the explosive atmosphere out- 
 Ill. Q 
 
226 HEROES OF SCIENCE. 
 
 side the lamp could not attain that point at 
 which explosion would occur. 
 
 In 1818 Sir Humphry Davy was made a 
 baronet, in recognition of his great services as the 
 inventor of the safety-lamp; and in 1820 he was 
 elected to the most honourable position which can 
 be held by a man of science in this country, he 
 became the President of the Royal Society. 
 
 For seven years he was annually re-elected 
 president, and during that time he was the central 
 figure in the scientific society of England. During 
 these years he continued his investigations chiefly 
 on electro-chemical subjects and on various branches 
 of applied science. In 1826 his health began to 
 fail. An attack of paralysis in that year obliged 
 him to relinquish most of his work. He went abroad 
 and travelled in Italy and the Tyrol, sometimes 
 strong enough to shoot or fish a little, or even to 
 carry on electrical experiments ; sometimes con- 
 fined to his room, or to gentle exercise only. He 
 resigned the presidentship of the Royal Society in 
 1827. In 1828 he visited Rome, where he was 
 again attacked by paralysis, and thought himself 
 dying, but he recovered sufficiently to attempt 
 the journey homeward. At Geneva he became 
 very ill, and expired in that city on the 2Qth of 
 May 1829. 
 
 During these later years of illness and suffering, 
 his intense love of and delight in Nature were very 
 apparent ; he returned again to the simple tastes 
 and pleasures of his early days, His intimate 
 
WORK OF DAVY AND BERZELIUS. 22/ 
 
 knowledge of natural appearances and of the sights 
 and sounds of country life is conspicuous in the 
 " Salmonia, or Days of Fly-fishing," written during 
 his later years. 
 
 Sir Humphry Davy was emphatically a genius. 
 He was full of eager desire to know the secrets of 
 the world in which he lived ; he looked around him 
 with wonder and delight, ever conscious of the 
 vastness of the appearances which met his gaze ; 
 an exuberance of life and energy marked his 
 actions ; difficulties were encountered by him only 
 to be overcome ; he was depressed by no mis- 
 fortunes, deterred by no obstacles, led aside from 
 his object by no temptations, and held in bondage 
 by no false analogies. 
 
 His work must ever remain as a model to the 
 student of science. A thorough and careful founda- 
 tion of fact is laid ; on this, hypotheses are raised, 
 to be tested first by reasoning and argument, then 
 by the tests of the laboratory, which alone are final. 
 Analogies are seized ; hints are eagerly taken up, 
 examined, and acted on or dismissed. As he 
 works in the laboratory, we see his mind ranging 
 over the whole field of chemical knowledge, finding 
 a solution of a difficulty here, or guessing at a so- 
 lution there ; combining apparently most diverse 
 facts ; examining phenomena which appear to have 
 no connection ; never dwelling too long on an 
 hypothesis which cannot yield some clue to the 
 object of research, but quickly discovering the road 
 which will lead to the wished-for solution. 
 
228 HEROES OF SCIENCE. 
 
 Like so many great experimenters Davy ac- 
 complished wonders with little apparatus. When 
 he went abroad for the first time he took with him 
 two small boxes, one twenty, and the other twelve 
 inches long, by about seven inches wide and four 
 deep. With the apparatus contained in these boxes 
 he established the elementary nature of iodine, 
 and made a rough estimation of its atomic weight ; 
 he determined many of its analogies with chlorine, 
 proving that, like chlorine, it is markedly electro- 
 negative, and that its compounds are decomposed 
 by chlorine ; he accomplished the synthesis of 
 hydriodic acid, and approximately determined the 
 composition of iodide of nitrogen. But when it was 
 necessary to employ delicate or powerful apparatus, 
 he was able by the use of that also to obtain results 
 of primary importance. The decomposition of 
 potash, soda, baryta, lime and strontia could not 
 have been effected had he not had at his com- 
 mand the resources of a well-furnished laboratory. 
 
 Davy has had no successor in England. Much 
 useful and some brilliant work has been done by 
 English chemists since his day, but we still look 
 back to the first quarter of the century as the 
 golden age of chemistry in this country. On the 
 roll wherein are written the names of England's 
 greatest sons, there is inscribed but a single 
 chemist Humphry Davy. 
 
 I carried on the account of the work of Davy's 
 great contemporary, Berzelius, to the time when he 
 
WORK OF DAVY AND BERZELIUS. 22Q 
 
 had fairly established dualistic views of the 
 structure of chemical compounds, and when, by 
 the application of a few simple rules regarding the 
 combinations of elementary atoms, he had largely 
 extended the bounds of the atomic theory of 
 Dalton. 
 
 Berzelius also did important work in the domain 
 of organic chemistry. By numerous analyses of 
 compounds of animal and vegetable origin, he 
 clearly established the fact that the same laws of 
 combination, the same fixity of composition, and 
 the same general features of atomic structure pre- 
 vail among the so-called organic as among the 
 inorganic compounds. In doing this he broke 
 down the artificial barrier which had been raised 
 between the two branches of the science, and so 
 prepared the way for modern chemistry, which has 
 won its chief triumphs in the examination of organic 
 compounds. 
 
 By the many and great improvements which he 
 introduced into analytical chemistry, and by the 
 publication of his " Textbook of Chemistry," which 
 went through several editions in French and Ger- 
 man, and also of his yearly report on the advance 
 of chemistry, Berzelius exerted a great influence 
 on the progress of his favourite science. Wohler 
 tells us that when the spring of the year came, 
 at which time his annual report had to be prepared, 
 Berzelius shut himself up in his study, surrounded 
 himself with books, and did not stir from the 
 writing-table until the work was done. 
 
230 HEROES OF SCIENCE. 
 
 In his later days Berzelius was much engaged 
 in controversy with the leaders of the new school, 
 the rise and progress of which will be traced in the 
 next chapter, but throughout this controversy he 
 found time to add many fresh facts to those already 
 known. He continued his researches until his death 
 in 1848. 
 
 The work of the great Swedish chemist is charac- 
 terized by thoroughness in all its parts : to him 
 every fact appeared to be of importance ; although 
 now perhaps only an isolated fact, he saw that 
 some day it would find a place in a general scheme 
 of classification. He worked in great measure on 
 the lines laid down by Dalton and Davy ; the enor- 
 mous number and accuracy of his analyses estab- 
 lished the law of multiple proportions on a sure 
 basis, and his attempts to determine the constitu- 
 tion of compound atoms, while advancing the 
 atomic theory of Dalton, drew attention to the all- 
 important distinction between atom and molecule, 
 and so prepared chemists for the acceptance of the 
 generalization of Avogadro. The electro-chemical 
 conceptions of Davy were modified by Berzelius ; 
 they were shorn of something of their elasticity, 
 but were rendered more suited to be the basis of a 
 rigid theory. 
 
 At the close of this transition period from the 
 Lavoisierian to the modern chemistry, we find 
 analytical chemistry established as an art ; we find 
 the atomic theory generally accepted, but we notice 
 
WORK OF DAVY AND BERZELIUS. 231 
 
 the existence of much confusion which has arisen 
 from the non-acceptance of the distinction made 
 by Avogadro between atom and molecule ; we find 
 the analogies between chemical affinity and electri- 
 cal energy made the basis of a system of classifi- 
 cation which regards every compound atom (or 
 molecule) as built up of two parts, in one of which 
 positive, and in the other negative electricity pre- 
 dominates; and accompanying this system of 
 classification we find that an acid is no longer 
 regarded as necessarily an oxygen compound, but 
 rather as a compound possessed of certain proper- 
 ties which are probably due to the arrangement 
 of the elementary atoms, among which hydrogen 
 appears generally to find a place ; we find that salts 
 are for the most part regarded as metallic deriva- 
 tives of acids ; and we find that by the decom- 
 position of the supposed elementary substances, 
 potash, soda, lime, etc., the number of the elements 
 has been extended, the application of a new instru- 
 ment of research has been brilliantly rewarded, and 
 the Lavoisierian description of " element " as the 
 " attained, not the attainable, limit of research " 
 has been emphasized. 
 
CHAPTER V. 
 
 THE WORK OF GRAHAM, 
 
 Thomas Graham, 1805-1869. 
 
 THE work of Graham, concerned as it mostly was 
 with the development of the conception of atoms, 
 connects the time of Dalton with that in which we 
 are now living. I have therefore judged it advisable 
 to devote a short chapter to a consideration of 
 the life-work of this chemist, before proceeding to 
 the third period of chemical advance, that, namely, 
 which witnessed the development of organic 
 chemistry through the labours of men who were 
 Graham's contemporaries. 
 
 The printed materials which exist for framing 
 the story of Graham's life are very meagre, but as 
 he appears, from the accounts of his friends, to have 
 devoted himself entirely to scientific researches, we 
 cannot go far wrong in regarding the history of his 
 various discoveries as also the history of his life. 
 
 THOMAS GRAHAM was born in Glasgow, on 
 
THE WORK OF GRAHAM. 233 
 
 December 21, 1805. His father, James Graham, 
 a successful manufacturer, was in a position to give 
 his son a good education. After some years spent 
 in the ordinary school training, Graham entered 
 Glasgow University at the early age of fourteen, 
 and graduated as M.A. five years later. It was the 
 intention of Graham's father that his son should 
 enter the Scottish Church ; but under the teach- 
 ing of Dr. Thomas Thomson and others the lad 
 imbibed so strong a love of natural science, that 
 rather than relinquish the pursuit of his favourite 
 study, he determined to be independent of his 
 father and make a living for himself. His father 
 was much annoyed at the determination of his son 
 to pursue science, and vainly attempted to force 
 him into the clerical profession. The quarrel be- 
 tween father and son increased in bitterness, 
 and notwithstanding the intervention of friends 
 the father refused to make his son any allowance 
 for his maintenance ; and although many years 
 after a reconcilement was effected, yet at the 
 time when Graham most needed his father's help 
 he was left to struggle alone. Graham went to 
 Edinburgh, where he pursued his studies under 
 Hope and Leslie, professors of chemistry and 
 physics respectively men whose names were famous 
 wherever natural science was studied. Graham's 
 mother, for whom he had always the greatest 
 respect and warmest love, and his sister Margaret 
 helped him as best they could during this trying 
 time, 
 
234 HEROES OF SCIENCE. 
 
 The young student found some literary occu- 
 pation and a little teaching in Edinburgh, and 
 sometimes he was asked to make investigations in 
 subjects connected with applied chemistry. Thus 
 he struggled on for four or five years, during which 
 time he began to publish papers on chemico-physical 
 subjects. In the year 1829 he was appointed Lec- 
 turer on Chemistry at the Mechanics' Institution in 
 Glasgow, and next year he was removed to the 
 more important position of lecturer on the same 
 science at the Andersonian Institution in that city. 
 This position he occupied for seven years, when he 
 was elected Professor of Chemistry in the Univer- 
 sity of London (now University College) : he had 
 been elected to the Fellowship of the Royal Society 
 in the preceding year. During his stay at the 
 Andersonian Institution Graham had established 
 his fame as a physical chemist ; he had begun his 
 work on acids and salts, and had established the 
 fundamental facts concerning gaseous diffusion. 
 These researches he continued in London, and 
 from 1837 to 1854 he enriched chemical science 
 with a series of papers concerned for the most part 
 with attempts to trace the movements of the atoms 
 of matter. 
 
 In 1854 Graham succeeded Sir John Herschel in 
 the important and honourable position of Master of 
 the Mint. For some years after his appointment he 
 was much engaged with the duties of his office, but 
 about 1860 he again returned to his atomic studies, 
 and in his papers on "Transpiration of Liquids" 
 
THE WORK OF GRAHAM. 235 
 
 and on " Dialysis" he did much in the application of 
 physical methods to solve chemical problems, and 
 opened up new paths, by travelling on which his 
 successors greatly advanced the limits of the science 
 of chemistry. Graham was almost always at work ; 
 his holidays were " few and far between." By the 
 year 1868 or so his general health began to grow 
 feeble ; in the autumn of 1 869, during a visit to 
 Malvern where he sought repose and invigorating 
 air, he caught cold, which developed into inflam- 
 mation of the lungs. On his return to London the 
 disease was overcome by medical remedies, but he 
 continued very weak, and gradually sank, till the 
 end came on the i6th of September 1869. 
 
 I have said that the seven years during which 
 Graham held the lectureship on chemistry in the 
 Andersonian Institution, Glasgow, witnessed the 
 beginning alike of his work on salts and of that 
 on gaseous diffusion. He showed that there exists 
 a series of compounds of various salts, e.g. chloride 
 of calcium, chloride of zinc, etc., with alcohol. He 
 compared the alcohol in these salts, which he called 
 alcoates, to the water in ordinary crystallized salts, 
 and thus drew the attention of chemists to the 
 important part played by water in determining the 
 properties of many substances. Three years later 
 (1833) appeared one of his most important papers, 
 bearing on the general conception of acids : " Re- 
 searches on the Arseniates, Phosphates, and Modi- 
 fications of Phosphoric Acid." Chemists at this 
 time knew that phosphoric acid that is, the sub- 
 
336 HEROES OF SCIENCE. 
 
 stance obtained by adding water to pentoxide of 
 phosphorus exhibited many peculiarities, but they 
 were for the most part content to leave these un- 
 explained. Graham, following up the analogy 
 which he had already established between water 
 and bases, prepared and carefully determined the 
 composition of a series of phosphates, and con- 
 cluded that pentoxide of phosphorus is able to 
 combine with a base say soda in three different 
 proportions, and thus to produce three different 
 phosphates of soda. But as Graham accepted that 
 view which regards a salt as a metallic derivative of 
 an acid, he supposed that three different phosphoric 
 acids ought to exist ; these acids he found in the 
 substances produced by the action of water on 
 the oxide of phosphorus. He showed that just as 
 the oxide combines with a base in three propor- 
 tions, so does it combine with water in three pro- 
 portions. This water he regarded as chemically 
 analogous to the base in the three salts, one atom 
 (we should now rather say molecule) of base could 
 be replaced by one atom of water, two atoms of 
 base by two atoms of water) or three atoms of base 
 by three atoms of water. Phosphoric acid was 
 therefore regarded by Graham as a compound of 
 pentoxide of phosphorus and water, the latter being 
 as essentially a part of the acid as the former. 
 He distinguished between monobasic, dibasic, and 
 tribasic phosphoric acids : by the action of a base 
 on the tmmobasic acid, one, and only one salt was 
 produced ; the dibasic acid could ' furnish two salts, 
 
THE WORK OF GRAHAM. 237 
 
 containing different proportions (or a different 
 number of atoms) of the same base : and from 
 the tribasic acid three salts, containing the same 
 base but in different proportions, could be obtained. 
 
 Davy's view of an acid as a compound of water 
 with a negative oxide was thus confirmed, and 
 there was added to chemical science the conception 
 of acids of different basicity. 
 
 In 1836 Graham's paper on " Water as a Consti- 
 tuent of Salts " was published in the " Transactions 
 of the Royal Society of Edinburgh." In this paper 
 he inquires whether the water in crystalline salts 
 can or cannot be removed without destroying the 
 chemical individuality of the salts. He finds that 
 in some crystalline salts part of the water can be 
 easily removed by the application of heat, but the 
 remainder only at very high temperatures. He dis- 
 tinguishes between those atoms of water which 
 essentially belong to the compound atom of the 
 salt, and those atoms which can be readily removed 
 therefrom, which are as it were added on to, or built 
 up around the exterior of the atom of salt. In this 
 paper Graham began to distinguish what is now 
 called water of crystallization from water of consti- 
 tution^ a distinction pointed to by some of Davy's 
 researches, but a distinction which has remained 
 too much a mere matter of nomenclature since the 
 days of Graham. 
 
 In these researches Graham emphasized the neces- 
 sity of the presence of hydrogen in all true acids ; 
 as he had drawn an analogy between water and 
 
238 HEROES OF SCIENCE. 
 
 bases, so now he saw in the hydrogen of acids the 
 analogue of the metal of salts. He regarded the 
 structure of the compound atom of an acid as 
 similar to that of the compound atom of a salt ; the 
 hydrogen atom, or atoms, in the acid was replaced 
 by a metallic atom, or atoms, and so a compound 
 atom of the salt was produced. 
 
 Davy and Berzelius had proved that hydrogen is 
 markedly electro-positive ; hydrogen appeared to 
 Graham to belong to the class of metals. In 
 making this bold hypothesis Graham necessarily 
 paid little heed to those properties of metals which 
 appeal to the senses of the observer. Metals, as 
 a class, are lustrous, heavy, malleable substances ; 
 hydrogen is a colourless, inodourless, invisible, 
 very light gas : how then can hydrogen be said 
 to be metallic ? 
 
 I have again and again insisted on the need of 
 imagination for the successful study of natural 
 science. Although in science we deal with pheno- 
 mena which we wish to measure and weigh and 
 record in definite and precise language, yet he only 
 is the successful student of science who can pene- 
 trate beneath the surface of things, who can form 
 mental pictures different from those which appear 
 before his bodily eye, and so can discern the intri- 
 cate and apparently irregular analogies which 
 explain the phenomena he is set to study. 
 
 Graham was not as far as we can learn endowed, 
 like Davy, with the sensitive nature of a poet, 
 yet his work on hydrogen proves him to have 
 
THE WORK OF GRAHAM. 239 
 
 possessed a large share of the gift of imagination. 
 Picturing to himself the hydrogen atom as essen- 
 tially similar in its chemical functions to the atom 
 of a metal, he tracked this light invisible gas 
 through many tortuous courses : he showed how it 
 is absorbed and retained (occluded as he said) by 
 many metals ; he found it in meteors which had 
 come from far-away regions of space ; and at last, 
 the year before he died he prepared an alloy of 
 palladium *and the metal hydrogen, from which a 
 few medals were struck, bearing the legend " Palla- 
 dium-Hydrogenium 1869." 
 
 Within the last few years hydrogen has been 
 liquified and, it is said, solidified. Solid hydrogen 
 is described as a steel-grey substance which fell 
 upon the table with a sound like the ring of a 
 metal. 
 
 But Graham's most important work was con- 
 cerned with the motion of the ultimate particles of 
 bodies. 
 
 He uses the word " atom " pretty much as Dalton 
 did. He does not make a distinction between the 
 atom of an element and the atom of a compound, 
 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 substance. As Graham was chiefly con- 
 cerned with the physical properties of chemical 
 substances, or with those properties which are 
 studied alike by chemistry and physics, the distinc- 
 tion between atom and molecule, so all-important 
 
240 HEROES OF SCIENCE. 
 
 ill pure chemistry, might be, and to a great ex- 
 tent was, overlooked by him. 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 chemistry, a sense 
 which has been already discussed (see pp. 139-143). 
 
 Many years before Graham began his work a 
 curious fact had been recorded but not explained. 
 In 1823 Dobereiner filled a glass jar with hydro- 
 gen and allowed the jar to stand over water : 
 on returning after twelve hours he found that the 
 water had risen about an inch and a half into the 
 jar. Close examination of the jar showed the pre- 
 sence of a small crack in the glass. Many jars, 
 tubes and flasks, all with small cracks in the glass, 
 were filled with hydrogen and allowed to stand 
 over water ; in every case the water rose in the 
 vessel. No rise of the water was however notice- 
 able if the vessels were filled with ordinary air, 
 nitrogen or oxygen. 
 
 In 1831 Graham began the investigation of the 
 peculiar phenomenon observed by Dobereiner. 
 Repeating Dobereiner's experiments, Graham found 
 that a portion of the hydrogen in the cracked 
 vessels passed outwards through the small fissures, 
 and a little air passed inwards : the water there- 
 fore rose in the jar, tube or flask, because there 
 was a greater pressure on the surface of the water 
 outside than upon that inside the vessel. Any gas 
 lighter than air behaved like hydrogen ; when gases 
 heavier than air were employed the level of the 
 
THE WORK OF GRAHAM. 241 
 
 water inside the vessel was slightly lowered after 
 some hours. 
 
 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 Paris, than by using vessels with 
 small fissures- in the glass. 
 
 The difftision-tube used by Graham generally 
 consisted of a piece of glass tubing, graduated in 
 fractions of a cubic inch and having a bulb blown 
 near one end ; the short end was closed by a thin 
 plug of dry plaster of Paris (gypsum), the tube was 
 filled with the gas to be examined, and the open 
 end was immediately immersed in water. The water 
 was allowed to rise until it had attained a constant 
 level, when it was found that the whole of the gas 
 originally in the tube had passed outwards through 
 the porous plug, and air had passed inwards. The 
 volume of gas originally in the tube being known, 
 and the volume of air in the tube at the close of 
 the experiment being measured, it was only neces- 
 sary 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 inwards ; in other words to obtain 
 the rate of diffusion compared with air of the gas 
 under examination. 
 
 Graham's results were gathered together in the 
 statement, "The diffusion-rates of any two gases 
 are inversely as the square roots of their densities." 
 
 III. R 
 
242 HEROES OF SCIENCE. 
 
 Thus, take oxygen and hydrogen : oxygen is sixteen 
 times heavier than hydrogen, therefore hydrogen 
 diffuses four times more rapidly than oxygen. 
 Take hydrogen and air : the specific gravity of 
 hydrogen is 0^0694, air being I ; the square root of 
 0*0694 is 0^2635, therefore hydrogen will diffuse 
 more rapidly than air in the ratio of 0*2635 : i. 
 
 In the years 1846-1849 Graham resumed this 
 inquiry ; he now distinguished between diffusion, 
 or the passage of gases through porous plates, and 
 transpiration, or the passage of gases through 
 capillary tubes. He showed that if a sufficiently 
 large capillary tube be employed the rate of 
 transpiration of a gas becomes constant, but that 
 it is altogether different from the rate of diffusion 
 of the same gas. He established the fact that there 
 is a connection of some kind between the transpi- 
 ration-rates and the chemical composition of gases, 
 and in doing this he opened up a field of inquiry 
 by cultivating which many important results have 
 been gained within the last few years, and which 
 is surely destined to yield more valuable fruit in 
 the future. 
 
 Returning to the diffusion of gases, Graham, after 
 nearly thirty years' more or less constant labour, 
 begins to speculate a little on the causes of the 
 phenomena he had so studiously and perseveringly 
 been examining. In his paper on " The Molecular 
 Mobility of Gases," read to the Royal Society in 
 1 863, after describing a new diffusion-tube wherein 
 thin plates of artificial graphite were used in place 
 
THE WORK OF GRAHAM. 243 
 
 of plaster of Paris, Graham says, "The pores of 
 artificial graphite appear to be really so minute 
 that a gas in mass cannot penetrate the plate at 
 all. It seems that molecules only can pass ; and 
 they may be supposed to pass wholly unimpeded 
 by friction, 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 
 body." He then shortly describes the molecular 
 theory of matter, and shows how this theory a 
 sketch of which so far as it concerns us in this 
 book has been given on pp. 123-125 explains the 
 results which he has obtained. When a gas passed 
 through a porous plate into a vacuum, or when 
 one gas passed in one direction and another in the 
 opposite direction through the same plate, Graham 
 saw the molecules of each gas rushing through the 
 " tunnels " of graphite or stucco. The average rate 
 at which the molecules of a gas rushed along was 
 the diffusion-rate of that gas. The lighter the gas 
 the more rapid was the motion of its molecules. 
 If a mixture of two gases, one much lighter than 
 the other, were allowed to flow through a porous 
 plate, the lighter gas would pass so much more 
 quickly than the heavier gas that a partial sepa- 
 ration of the two might probably be effected. 
 Graham accomplished such a separation of oxygen 
 and hydrogen, and of oxygen and nitrogen ; and 
 he described a simple instrument whereby this 
 process of dtmolysis, as he called it, might be 
 effected, 
 
244 HEROES OF SCIENCE, 
 
 Graham's tube dtmolyser consisted of a long 
 tobacco-pipe stem placed inside a rather shorter 
 and considerably wider tube of glass ; the pipe 
 stem was fixed by passing through two corks, one 
 at each end of the glass tube ; through one of these 
 corks there also passed a short piece of glass tubing. 
 When the instrument was employed, the piece of 
 short glass tubing was connected with an air-pump, 
 and one end of the pipe stem with the gaseous mix- 
 ture say ordinary air. The air-pump being set in 
 motion, the gaseous mixture was allowed to flow 
 slowly through the pipe stem ; the lighter ingre- 
 dient of the mixture passed outwards through the 
 pipe stem into the wide glass tube more rapidly 
 than the heavier ingredient, and was swept away 
 to the air-pump ; the heavier ingredient could be 
 collected, mixed with only a small quantity of the 
 lighter, at the other end of the pipe stem. As 
 Graham most graphically expressed it, " The stream 
 of gas diminishes as it proceeds, like a river flowing 
 over a pervious bed." 
 
 Graham then contrived a very simple experi- 
 ment whereby he was able to measure the rate 
 of motion of the molecules of carbonic acid. Pie 
 introduced a little carbonic acid into the lower part 
 of a tall cylindrical jar, 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 
 jar. Knowing the height of the jar, he now knew 
 the distance through which a small portion of 
 
THE WORK OF GRAHAM. 245 
 
 carbonic acid passed in a stated time, and regard- 
 ing this small portion as consisting of a great many 
 molecules, all moving at about equal rates, he had 
 determined the average velocity of the molecules 
 of carbonic acid. A similar experiment was per- 
 formed with hydrogen. The general results were 
 that the molecules of carbonic acid move about 
 in still air with a velocity equal to seventy-three 
 millimetres per minute, and that under the same 
 conditions the molecules of hydrogen move with a 
 velocity equal to about one-third of a metre per 
 minute.* 
 
 The Bakerian Lecture for 1849, read by Graham 
 before the Royal Society, was entitled " On the 
 Diffusion of Liquids." 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 diffuses, or passes upwards into 
 a layer of pure water above it, the salt solution 
 and the water not being separated by any inter- 
 vening medium. Graham's method of procedure^ 
 consisted in completely filling a small bottle with 
 a salt solution of known strength, placing this 
 bottle in a larger graduated vessel, and carefully 
 filling the latter with water. Measured portions of 
 the water in the larger vessel were withdrawn at 
 stated intervals, and the quantity of salt in each 
 portion was determined. Graham found that 
 under these conditions salts diffused with very 
 
 * A metre is equal to about thirty-nine inches ; a millimetre is the 
 one-thousandth part of a metre. 
 
246 HEROES OF SCIENCE. 
 
 varying velocities. Groups of salts showed equal 
 rates of diffusion. There appeared to be no 
 definite connection between the molecular weights 
 of the salts and their diffusion-rates ; but as 
 Graham constantly regarded diffusion, whether of 
 gases or liquids, as essentially due to the move- 
 ments of minute particles, 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 
 words, Graham recognized various orders of small 
 particles. As the atom was supposed to have a 
 simpler structure than the molecule (if indeed it 
 had a structure at all), so there probably existed 
 groups of molecules which, under certain condi- 
 tions, behaved as individual particles with definite 
 properties. 
 
 As Graham applied the diffusion of gases to the 
 separation of two gases of unequal densities, so he 
 applied the diffusion of liquids to the separation 
 of various salts in solution. He showed also that 
 some complex salts, such as the alums, were par- 
 tially separated into their constituents during the 
 process of diffusion. 
 
 The prosecution of these researches led to most 
 important results, which were gathered together in 
 a paper on " Liquid Diffusion applied to Analysis," 
 read to the Royal Society in 1861. 
 
 Graham divided substances into those which dif- 
 fused easily and quickly into water, and those 
 which diffused very slowly ; he showed that the 
 
THE WORK OF GRAHAM. 247 
 
 former were all crystallizable substances, while 
 the latter were non-crystallizable jelly-like bodies. 
 Graham called these jelly-like substances colloids ; 
 the easily diffusible substances he called crystal- 
 loids. He proved that a colloidal substance acts 
 towards a crystalloid much as water does ; that 
 the crystalloid rapidly diffuses through the colloid, 
 but that colloids are not themselves capable of 
 diffusing through other colloids. On this fact was 
 founded Graham's process of dialysis. As colloid 
 he employed a sheet of parchment paper, which 
 he stretched on a ring of wood or caoutchouc, 
 and floated the apparatus so constructed the 
 dialyser on the surface of pure water in a glass 
 dish ; he then poured into the dialyser the mixture 
 of substances which it was desired to separate. 
 Let us suppose that this mixture contained sugar 
 and gum ; the crystalloidal sugar soon passed 
 through the parchment paper, and was found in 
 the water outside, but the colloidal gum remained 
 in the dialyser. 
 
 If the mixture in the dialyser contained two 
 crystalloids, 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 diffusible ; 
 a partial separation was thus effected. 
 
 This method of dialysis was applied by Graham 
 to separate and obtain in the pure state many 
 colloidal modifications of chemical compounds, 
 such as aluminium and tin hydrates, etc. By his 
 study of these peculiar substances Graham intro- 
 
248 HEROES OF SCIENCE. 
 
 duced into chemistry a new class of bodies, and 
 opened up great fields of research. 
 
 Matter in the colloidal state appears to be en- 
 dowed with properties which are quite absent, or 
 are hidden, when it is in the ordinary crystalloidal 
 condition. Colloids are readily affected by the 
 smallest changes in external conditions ; they 
 are eminently unstable bodies ; they are, Graham 
 said, always on the verge of an impending change, 
 and minute disturbances in the surrounding 
 conditions may precipitate this change at any 
 moment. Crystalloids, on the other hand, arc 
 stable ; they have definite properties, which are 
 not changed without simultaneous large changes 
 in surrounding conditions. But although, to use 
 Graham's words, these classes of bodies "appear 
 like different worlds of matter," there is yet no 
 marked separating line between them. Ice is a 
 substance which under ordinary conditions exhibits 
 all the properties of crystalloids, but ice formed in 
 contact with water just at the freezing point is not 
 unlike a mass of partly dried gum ; it shows no 
 crystalline structure, but it may be rent and split 
 l&e a lump of glue, and, like glue, the broken 
 pieces may be pressed together again and caused 
 to adhere into one mass. 
 
 " Can any facts," asks Graham, " more strikingly 
 illustrate the maxim that in Nature there are no 
 abrupt transitions, and that distinctions of class are 
 never absolute ? " 
 
 In the properties of colloids and crystalloids 
 
THE WORK OF GRAHAM. 249 
 
 Graham saw an index of diversity of molecular 
 structure. The smallest individual particle of a 
 colloid appeared to him to be a much more com- 
 plex structure than the smallest particle of a 
 crystalloid. The colloidal molecule appeared to 
 be formed by the gathering together of several 
 crystalloidal molecules ; such a complex structure 
 might be expected readily to undergo change, 
 whereas the simpler molecule of a crystalloid would 
 probably present more definite and less readily 
 altered properties. 
 
 In this research Graham had again, as so often 
 before, arrived at the conception of various orders 
 of small particles. In the early days of the 
 Daltonian theory it seemed that the recognition 
 of atoms as ultimate particles, by the placing 
 together of which masses of this or that kind of 
 matter are produced, would suffice to explain all 
 the facts of chemical combinations ; but Dalton's 
 application of the term " atom " to elements and 
 compounds alike implied that an atom might 
 itself have parts, and that one atom might be more 
 complex than another. The way was thus already 
 prepared for the recognition of more than one order 
 of atoms, a recognition which was formulated three 
 years after the appearance of Dalton's "New System " 
 in the statement of Avogadro, " Equal volumes of 
 gases contain equal numbers of molecules ; " for we 
 have seen that the application of this statement to 
 actually occurring reactions between gases obliges 
 us to admit that the molecules of hydrogen, oxygen 
 
250 HEROES OF SCIENCE. 
 
 and many other elementary gases are composed 
 of two distinct parts or atoms. 
 
 Berzelius it is true did not formally accept the 
 generalization of Avogadro ; but we have seen how 
 the conception of atom which runs through his 
 work is not that of an indivisible particle, but 
 rather that of a little individual part of matter 
 with definite properties, from which the mass of 
 matter recognizable by our senses is constructed, 
 just as the wall is built up of individual bricks. 
 And as the bricks are themselves constructed of 
 clay, which in turn is composed of silica and 
 alumina, so may each of these little parts of matter 
 be constructed of smaller parts ; only as clay is not 
 brick, and neither silica nor alumina is clay, so the 
 properties of the parts of the atom if it has parts 
 are not the properties of the atom, and a mass 
 of matter constructed of these parts would not 
 have the same properties as a mass of matter con- 
 structed of the atoms themselves. 
 
 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 compound. As the apparent stability of 
 chemical compounds was seen by Davy to be the 
 result of an equilibrium of contending forces, so 
 did the seemingly changeless character of any 
 chemical substance appear to Graham as due 
 to the orderly changes which are continually pro- 
 ceeding among the molecules of which the sub- 
 stance is constructed. 
 
THE WORK OF GRAHAM. 25! 
 
 A piece of lime, or a drop of water, was to the 
 mind of Graham the scene of a continual strife, 
 for that minute portion of matter appeared to him 
 to be constructed of almost innumerable myriads 
 of little parts, each in more or less rapid motion, 
 one now striking against another and now moving 
 free for a little space. Interfere with those move- 
 ments, alter the mutual action of those minute 
 particles, and the whole building would fall to 
 pieces. 
 
 For more than thirty years Graham was content 
 to trace the movements of molecules. During that 
 time he devoted himself, with an intense and 
 single-minded devotion, to the study of molecular 
 science. Undaunted in early youth by the with- 
 drawal of his father's support ; unseduced in his 
 middle age by the temptations of technical che- 
 mistry, by yielding to which he would soon have 
 secured a fortune ; undazzled in his later days by 
 the honours of the position to which he had 
 attained ; Graham dedicated his life to the nobler 
 object of advancing the bounds of natural know- 
 ledge, and so adding to those truths which must 
 ever remain for the good and furtherance of 
 humanity. 
 
CHAPTER VI. 
 
 RISE AND PROGRESS OF ORGANIC CHEMISTRY 
 PERIOD OF LIEBIG AND DUMAS. 
 
 Justus L icbig, 1 803-1 873. Jean Baptiste A ndrt Dumas, 
 born in 1800. 
 
 I HAVE as yet said almost nothing with regard to 
 the progress of organic chemistry, considered as a 
 special branch of the science. It is however in 
 this department that the greatest triumphs which 
 mark . the third period of chemical advance have 
 been won. We musFtKerefore now turn our atten- 
 tion to the work which has been done here. 
 
 The ancients drew no such distinction between 
 portions of their chemical knowledge, limited as it 
 was, as is implied by the modern terms " organic " 
 and " inorganic chemistry." An organic acid acetic 
 was one of the earliest known substances belong- 
 ing to the class of acids ; many processes of chemical 
 handicraft practised in the olden times dealt with 
 the manufacture of substances, such as soap, 
 
ORGANIC CHEMISTRY LIEBIG AND DUMAS. 253 
 
 leather or gum, which we should now call organic 
 substances. Nor did the early alchemists, although 
 working chiefly with mineral or inorganic substances, 
 draw any strict division between the two branches of 
 chemistry. The medical chemists of the sixteenth 
 century dealt much with substances derived from 
 plants and animals, such as benzoic and succinic 
 acids, spirit of wine, oils, etc. But neither in their 
 nomenclature nor in their practice did they sharply 
 distinguish inorganic from organic compounds. 
 They spoke of the quintessence of arsenic and the 
 quintessence of alcohol ; they applied the term " oil " 
 alike to the products of the action of acids on 
 metallic salts and to substances obtained from ve- 
 getables. But towards the end of the seventeenth 
 century, at the time that is wjjfn the phlogistic 
 4heory began to gain pre-eminence, we find 
 gradually springing up a division of chemical 
 substances into mineral, 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 themselves, and therefore a 
 division which was essentially a non-chemical 
 one. 
 
 About a century after this, systematic attempts 
 began to be made to trace some peculiarity of 
 composition as belonging to all compounds of 
 organic, that is, of animal or vegetable, origin. As 
 very many of the substances then known belonging 
 to this class were more or less oil-like in their 
 
254 HEROES OF SCIENCE. 
 
 properties oils, fats, balsams, gums, sugar, etc. 
 organic substances generally were said to be 
 characterized by the presence in them of the 
 principle of oil. 
 
 I Such a statement as this, although suited to the 
 / conceptions of that time, could not be received 
 / when Lavoisier had shown chemists how Nature 
 / ought be examined. With the definite conception 
 of element introduced by the new chemistry, came 
 an attempt to prove that organic compounds were 
 built up of elements which were rarely found 
 together in any one compound of inorganic origin. 
 Substances of vegetable origin were said by La- 
 voisier to be composed of carbon, hydrogen and 
 oxygen, while phosphorus and nitrogen, in addition 
 to those three elements, entered into the com- 
 position of substances derived from animals. But 
 neither could this definition of organic compounds 
 be upheld in the face of facts. Wax and many oils 
 contained only carbon and hydrogen, yet they 
 were undoubtedly substances of vegetable or animal 
 origin. If the presence of any two of the three 
 elements, carbon, hydrogen and oxygen, were to be 
 regarded as a sufficient criterion for the classifica- 
 tion of a compound, then it was necessary that 
 carbonic acid obtained by the action of a mineral 
 acid on chalk should be called an organic com- 
 pound. 
 
 To Berzelius belongs the honour of being the 
 chemist who first applied the general laws of 
 chemical combination to all compounds alike, 
 
ORGANIC CHEMISTRY LIEBIG AND DUMAS. 255 
 
 whether derived from minerals, animals, or vege- 
 tables. The ultimate particles, or molecules, of 
 every compound were regarded by Berzelius as 
 built up of two parts, each of which might itself be 
 an elementary atom, or a group of elementary 
 atoms. One of these parts, he said, was charac- 
 terized by positive, the other by negative electricity. 
 Every compound molecule, whatever was the 
 nature or number of the elementary atoms com- 
 posing it, was a dual structure (see p. 164). 
 Organic chemistry came again to be a term some- 
 what loosely applied to the compounds derived 
 from animals or vegetables, or in the formation 
 of which the agency of living things was necessary. 
 Most, if not all of these compounds contained 
 carbon and some other element or elements, espe- 
 cially hydrogen, oxygen and nitrogen. 
 
 But the progress of this branch of chemistry was 
 impeded by the want of any trustworthy methods 
 for analysing compounds containing carbon, oxygen 
 and hydrogen. This want was to be supplied, and 
 the science of organic chemistry, and so of chemistry 
 in general, was to be immensely advanced by the 
 labours of a new school of chemists, chief among 
 whom were Liebig and Dumas. 
 
 Let us shortly trace the work of these two 
 renowned naturalists. The life-work of the first is 
 finished ; I write this story of the progress of his 
 favourite science on the eighty-second birthday of 
 the second of these great men, who is still with us 
 a veteran crowned with glory, a true soldier in the 
 
256 HEROES OF SCIENCE. 
 
 battle against ignorance and so against want and 
 crime, 
 
 JUSTUS LIEBIG was born at Darmstadt, on the 
 1 2th of May 1803. The main facts which mark 
 his life regarded apart from his work as a chemist 
 are soon told. Showing a taste for making ex- 
 periments he was apprenticed by his father to an 
 apothecary. Fortunately for science he did not 
 long remain as a concoctor of drugs, but , was 
 allowed to enter the University of Bonn as a student 
 of medicine. From Bonn he went to Erlangen, at 
 which university he graduated in 1821. A year or 
 two before this time Liebig had begun his career 
 as an investigator of Nature, 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 Paris, which was then almost the only place 
 where he could hope to find the conditions of 
 success for the study of scientific chemistry. To 
 Paris accordingly he went in 1823. He was so 
 fortunate thanks to the good graces of the re- 
 nowned naturalist Alexander von Humboldt as 
 to be allowed to enter the laboratory of Gay-Lussac, 
 where he continued the research on a class of ex- 
 plosive compounds, called fulminates y which he had 
 begun before leaving Darmstadt. 
 
 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 
 
ORGANIC CHEMISTRY LIEBIG AND DUMAS. 257 
 
 be known wherever chemistry was studied, and 
 now held dear by many eminent chemists who 
 there learned what is meant by the scientific study 
 of Nature. 
 
 The year before Liebig entered the laboratory of 1 
 Gay-Lussac there came to Paris a young and I 
 enthusiastic student who had already made himself V 
 known in the scientific world by his physiological 
 researches, and who was now about to begin his 
 career as a chemist. 
 
 In that southern part of France which is rich in 
 memories of the Roman occupation, not far from 
 the remains of the great aqueduct which spans the 
 valley of the Garden, at no great distance from 
 the famous cities of Aries and Nimes, was born, 
 in the town of Alais, on the I4th of July 1800, 
 JEAN BAPTISTS ANDRE DUMAS. 
 
 The father of Dumas was a man of considerable 
 culture ; he gave his son as good an education as 
 could be obtained in the little town of his birth. 
 At the age of fourteen young Dumas was a good 
 classical scholar, and had acquired a fair knowledge 
 of natural science. But for his deficiency in mathe- 
 matics he would probably have entered for the 
 examination which admitted those who passed it 
 to join the French navy. But before he had made 
 good his mathematical deficiencies the troublous 
 nature of the times (1814-15) obliged his parents 
 to think of some other profession for their son 
 which would entail less sacrifice on their part. 
 
 Like his great fellow-worker in after life he was 
 
 III. S 
 
2$8. HEROES OF SCIENCE. 
 
 apprenticed to an apothecary, and like him also, 
 he soon forsook this sphere of usefulness. 
 
 Desirous of better opportunities for the study of 
 science, and overpowered by the miseries which 
 war had brought upon the district of his birth, 
 Dumas persuaded his father to allow him to go to 
 Geneva. At Geneva Dumas found an atmosphere 
 more suited to his scientific progress ; chemistry, 
 physics, botany, and other branches of natural 
 science were taught by men whose names were 
 everywhere known. He began experiments in 
 chemistry with the crudest and most limited appa- 
 ratus, but even with these he made discoveries 
 which afterwards led to important work on the 
 volumes occupied by the atoms of elementary 
 substances. 
 
 About the year 1818 Dumas became acquainted 
 dth Dr. J. L. Prevost, who had returned from 
 studying in many of the most famous medical 
 schools of Europe. Invited by Prevost to join in 
 an investigation requiring medical, botanical and 
 chemical knowledge, Dumas now began a series of 
 researches which soon passed into the domain of 
 animal physiology, and by the prosecution of which 
 under many difficulties he laid the foundations of 
 his future fame. 
 
 But along with his physiological work Dumas 
 carried on a research into the expansion of various 
 ethers. This necessitated the preparation of a 
 series of ethers in a state of purity ; but so difficult 
 did Dumas find this to be, so much time did he 
 
ORGANIC CHEMISTRY LIEBIG AND DUMAS. 259 
 
 consume in this preliminary work, and so interested 
 did he become in the chemical part of the investi- 
 gation, that he abandoned the experiments on 
 expansion, and set himself to solve some of the 
 problems presented by the composition and che- 
 mical properties of the ethers. 
 
 Dumas would probably have remained in Geneva 
 had he not had a morning visit paid him in the 
 year 1822. When at work in his laboratory o 
 day, some one knocked and was bidden come in. 
 u I was surprised to find myself face to face with a 
 gentleman in a light-blue coat with metal buttons, 
 a white waistcoat, nankeen breeches, and top-boots. 
 . . . The wearer of this costume, his head some- 
 what bent, his eyes deep-set but keen, advanced 
 with a pleasant smile, saying, ' Monsieur Dumas.' 
 ' The same, sir ; but excuse me.' 'I am M. de 
 Humboldt, and did not wish to pass through 
 Geneva without having had the pleasure of seeing 
 you.' ... I had only one chair. My visitor was 
 pleased to accept it, whilst I resumed my elevated 
 perch on the drawing stool. . . . ' I intend,' said 
 M. de Humboldt, ' to spend some days in Geneva, 
 to see old friends and to make new ones, and more 
 especially to become acquainted with young people 
 who are beginning their career. Will you act as 
 my^cicerone ? I warn you however that my 
 rambles begin early and end late. Now, could you 
 be at my disposal, say from six in the morning till 
 midnight ? ' " After some days spent as Humboldt 
 had indicated the great naturalist left Geneva. 
 
2(k> HEROES OF SCIENCE. 
 
 Dumas tells us that the town seemed empty to 
 him. "I felt as if spell-bound. The memorable 
 hours I had spent with that irresistible enchanter 
 had opened a new world to my mind." Dumas 
 felt that he must go to Paris that there he would 
 have more scope and more opportunities for prose- 
 cuting science. A few kind words, a little genuine 
 sympathy, and a little help from Humboldt were 
 thus the means of fairly launching in their career 
 of scientific inquiry these two young men, Liebig 
 and Dumas. 
 
 In Paris, whither he went in 1823, Dumas found 
 a welcome. He soon made the acquaintance and 
 gained the friendship of the great men who then 
 made natural science so much esteemed in the 
 French capital. When the year 1826 came, it saw 
 him Professor of Chemistry at the Athenaeum, and 
 married to the lady whom he loved, and who has 
 ever since fought the battle of life by his side. 
 
 Liebig left Paris in 1824. By the year 1830 he 
 had perfected and applied that method for the 
 analysis of organic compounds which is now in 
 constant use wherever organic chemistry is studied ; 
 by the same year Dumas had given the first warn- 
 ing of the attack which he was about to make on 
 the great structure of dualism raised by Berzelius. 
 In a paper, "On Some Points of the Atomic Theory," 
 published in 1826, Dumas adopted the distinction 
 made by Avogadro between molecules and atoms, 
 or between the small particles of substances which 
 remain undivided during physical actions, and the 
 
ORGANIC CHEMISTRY LIEBIG AND DUMAS. 26 1 
 
 particles, smaller than these, which are undivided 
 during chemical actions. But, unfortunately, Dumas 
 did not mark these two conceptions by names suffi- 
 ciently definite to enable the readers of his memoir 
 to bear the distinction clearly in mind. The terms 
 " atom " and " molecule " were not introduced into 
 chemistry with the precise meanings now attached 
 to them until some time after 1826. 
 
 Although the idea of two orders of small particles 
 underlies all the experimental work described by- 
 Dumas in this paper, yet the numbers which he 
 obtained as representing the actual atomic weights 
 of several elements e.g. phosphorus, arsenic, tin, 
 silicon show that he had not himself carried out 
 Avogadro's hypothesis to its legitimate conclusions. 
 
 Two years after this Dumas employed the reac- 
 tion wherein two volumes of gaseous hydrochloric 
 acid are produced by the union of one volume of 
 hydrogen with one volume of chlorine, as an argu- 
 ment which obliged him to conclude that, if Avo- 
 gadro's physical hypothesis be accepted, the mole- 
 cules of hydrogen and chlorine split, each into two 
 parts, when these gases combine chemically. But 
 Dumas did not at this time conclude that the 
 molecular weight of hydrogen must be taken as 
 twice its atomic weight, and that hydrogen being 
 the standard substance the molecular weights of 
 all gases must be represented by the specific gravi- 
 ties of these gases, referred to hydrogen as 2. 
 
 I have already shortly discussed the method for 
 finding the relative weights of elementary atoms 
 
262 HEROES OF SCIENCE. 
 
 which is founded on Avogadro's hypothesis, and, I 
 think, 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 (see p. 142). 
 
 This deduction from Avogadro's law is now 
 a part and parcel of our general chemical know- 
 ledge. We wonder why it was not made by Dumas ; 
 but we must remember that a great mass of facts 
 has been accumulated since 1826, and that this 
 definition of " atom " has been gradually forced on 
 chemists by the cumulative evidence of those 
 facts. 
 
 One thing Dumas did do, for which the thanks 
 of every chemist ought to be given him ; he saw 
 the need of a convenient method for determining 
 the densities of compounds in the gaseous state, and 
 he supplied this need by that simple, elegant and 
 trustworthy method, still in constant use, known as 
 Dumas 's vapour density process. 
 
 While Dumas was working out the details of 
 this analytical method, which was destined to be so 
 powerful an instrument of research, Liebig was 
 engaged in similar work ; 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 science. 
 The processes in use during the first quarter of 
 this century for determining the amounts of carbon, 
 hydrogen, and oxygen in compounds of those 
 elements, were difficult to conduct and gave im- 
 
ORGANIC CHEMISTRY LIEBIG AND DUMAS. 263 
 
 trustworthy results. Liebig adopted the principle 
 of the method used by Lavoisier, viz. that the 
 carbon in a compound can be oxidized, or burnt, 
 to carbonic\acid, and the hydrogen to water. 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 weighed. Liebig's apparatus remains 
 now essentially as it was presented to the chemical 
 world in 1830. Various improvements in details 
 have been made ; the introduction of gas in place 
 of charcoal as a laboratory fuel has given the 
 chemist a great command over the process of 
 combustion, 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 hand. A 
 weighed quantity of the substance to be analyzed 
 is heated with oxide of copper in a tube of 
 hard glass ; the carbon is burnt to carbonic acid 
 and the hydrogen to water at the expense of the 
 oxygen of the copper oxide. Attached to the com- 
 bustion tube is a weighed tube containing chloride 
 of calcium, a substance which greedily combines 
 with water, and this tube is succeeded by a set of 
 three or more small bulbs, blown in one piece of 
 glass, and containing an aqueous solution of caustic 
 potash, a substance with which carbonic acid 
 readily enters into combination. The chloride of 
 calcium tube and the potash bulbs are weighed 
 before and after the experiment ; the increase in 
 weight of the former represents the amount of 
 
264 HEROES OF SCIENCE, 
 
 water, and the increase in weight of the latter the 
 amount of carbonic acid obtained by burning a 
 given weight of the compound under examination. 
 As the composition of carbonic acid and of water 
 is known, the amounts of carbon and of hydrogen 
 in one hundred parts of the compound are easily 
 found ; the difference between the sum of these and 
 one hundred represents the amount of oxygen in 
 one hundred parts of the compound. If the com- 
 pound should contain elements other than these 
 three, those other elements are determined by 
 special processes, the oxygen being always found 
 by difference. 
 
 Soon after his settlement at Giessen Liebig 
 turned his attention to a class of organic com- 
 pounds known as the cyanates ; but Wohler who, 
 while Liebig was in Paris in the laboratory of Gay- 
 Lussac, was engaged in studying the intricacies of 
 mineral chemistry under the guidance of Berzelius 
 had already entered on this field of research. 
 The two young chemists compared notes, re- 
 cognized each other's powers, and became friends ; 
 this friendship strengthened as life advanced, and 
 some of the most important papers which enriched 
 chemical science during the next thirty years bore 
 the joint signatures of Liebig and Wohler. 
 
 I have already mentioned that when it was found 
 necessary to abandon the Lavoisierian definition of 
 organic chemistry as the chemistry of compounds 
 containing carbon, hydrogen and oxygen, and 
 sometimes also phosphorus or nitrogen, a defini- 
 
ORGANIC CHEMISTRY LIEBIG AND DUMAS. 265 
 
 tion 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 organism. But the 
 discovery made in 1828 by Wohler, that %trea 
 a substance specially characterized by its produc- 
 tion in the animal economy, and in that economy 
 only could be built up from mineral materials, 
 rendered this definition of organic chemistry im- 
 possible, and broke down the artificial barrier 
 whereby naturalists attempted to separate two 
 fields of study between which Nature made no 
 division. 
 
 We have here another illustration of the truth of 
 the conception which underlies so many of the 
 recent advances of science, which is the central 
 thought of the noble structure reared by the 
 greatest naturalist of our time, and which is ex- 
 pressed 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 " Lyri- 
 cal Ballads," "In Nature everything is distinct, 
 but nothing defined into absolute independent 
 singleness." 
 
 From this time the progress of organic chemistry 
 became rapid. Dumas continued the researches 
 upon ethers which he had commenced at Geneva, 
 and by the year 1829 or so he had established the 
 relations which exist between ethers and alcohols 
 on the one hand, and ethers and acids on the other. 
 This research, a description of the details of which 
 
266 HEROES OF SCIENCE. 
 
 I cannot introduce here as it would involve the 
 use of many technical terms and assume the 
 possession by the reader of much technical know- 
 ledge, was followed by others, whereby Dumas 
 established the existence of a series of compounds 
 all possessed of the chemical properties of alcohol, 
 all containing carbon, hydrogen and oxygen, but 
 differing from one another by a constant amount of 
 carbon and hydrogen. This discovery of a series 
 of alcohols, distinguished by the possession of 
 certain definite properties whereby they were 
 marked off from all other so-called organic com- 
 pounds, was as the appearance of a landmark to the 
 traveller in a country where he is without a guide. 
 The introduction of the comparative method of 
 study into organic chemistry the method, that is, 
 which bases classification on a comparison of large 
 groups of compounds, and which seeks to gather 
 together those substances which are like and to 
 separate those which are unlike soon began to 
 bear fruit. This method suggested to the expe- 
 rimenter new points of view from which to regard 
 groups of bodies ; analogies which were hidden 
 when a few substances only were considered, 
 became prominent as the range of view was 
 widened. What the gentle Elia calls "fragments 
 and scattered pieces of truth," " hints and glimpses, 
 germs, and crude essays at a system,", became im- 
 portant. There was work to be done, not only by 
 the master spirits who, looking at things from a 
 central position of vantage, saw the relative im- 
 
ORGANIC CHEMISTRY LIEBIG AND DUMAS. 267 
 
 portance of the various detailed facts, but also by 
 those who could only "beat up a little game 
 peradventure, and leave it to knottier heads, more 
 robust constitutions, to run it down." 
 
 Twenty years before the time of which we are 
 now speaking Davy had decomposed the alkalis 
 potash and soda ; as he found these substances to 
 be metallic oxides, he thought it very probable 
 that the other well-known alkali, ammonia, would 
 also turn out to be the oxide of a metal. By the 
 electrolysis of salts formed by the action of ammonia 
 on acids, using mercury as one of the poles of the 
 battery, Davy obtained a strange-looking spongy 
 substance which he was inclined to regard as an 
 alloy of the metallic base of ammonia with mercury. 
 From the results of experiments by himself and 
 others, Davy adopted a view of this alloy which 
 regarded it as containing a compound radicle, or 
 group of elementary atoms which in certain definite 
 chemical changes behaved like a single elementary 
 atom. 
 
 To this compound radicle he gave the name 
 of ammonium. 
 
 As an aqueous solution of potash or soda was 
 regarded as a compound of water and oxide of 
 potassium or sodium, so an aqueous solution of 
 ammonia was regarded as a compound of water 
 and oxide of ammonium. 
 
 When the composition of this substance, am- 
 monium, came to be more accurately determined, 
 it was found that it might be best represented as a 
 
268 HEROES OF SCIENCE. 
 
 compound atom built up of one atom of nitrogen 
 and four atoms of hydrogen. The observed pro- 
 perties of many compounds obtained from ammonia, 
 and the analogies observed between these and 
 similar compounds obtained from potash and soda, 
 could be explained by assuming in the compound 
 atom (or better, in the molecule) of the ammonia 
 salt, the existence of this group of atoms, acting as 
 one atom, called ammonium. 
 
 The reader will not fail to observe how essentially 
 atomic is this conception of compound radicle. 
 The ultimate particle, the molecule, of a compound 
 has now come to be regarded as a structure built 
 up of parts called atoms, just as a house is a 
 structure built up of parts called stones and bricks, 
 mortar and wood, etc. But there may be a closer 
 relationship between some of the atoms in this 
 molecule than between the other atoms. It may be 
 possible to remove a group of atoms, and put 
 another group or perhaps another single atom 
 in the place of the group removed, without causing 
 the whole atomic structure to fall to pieces ; just as 
 it may be possible to remove some of the bricks 
 from the wall of a house, or a large wooden beam 
 from beneath the lintels, and replace these by 
 other bricks or by a single stone, or replace the 
 large wooden beam by a smaller iron one, without 
 involving the downfall of the entire house. The 
 group of atoms thus removable the compound 
 radicle may exist in a series of compounds. As 
 we have an oxide, a sulphide, a chloride, a nitrate, 
 
ORGANIC CHEMISTRY LIEBIG AND DUMAS. 269 
 
 etc., of sodium, so we may have an oxide, a sulphide, 
 a chloride, a nitrate, etc., of ammonium. The com- 
 pounds of sodium are possessed of many properties 
 in common ; this is partly explained by saying that 
 they all contain one or more atoms of the element 
 sodium. The compounds of ammonium possess 
 many properties in common, and this is partly ex- 
 plained if we assume that they all contain one or 
 more atoms of the compound radicle ammonium. 
 
 The conception of compound radicle was carried 
 by Berzelius to its utmost limits. We have learned 
 that the Swedish chemist regarded every molecule 
 as composed of two parts ; in very many cases each 
 of these parts was itself made up of more than one 
 kind of atom it was a compound radicle. But the 
 Berzelian system tended to become too artificial : 
 it drifted further and further away from facts. Of 
 the two parts composing the dual molecular 
 structure, one was of necessity positively, and the 
 other negatively electrified. The greater number 
 of the so-called organic compounds contained 
 oxygen ; oxygen was the most electro-negative 
 element known ; hence most organic compounds 
 were regarded as formed by the coming together of 
 one, two, or more atoms of oxygen, forming the 
 negative part of the molecule, with one, two, or 
 more atoms of a compound radicle, which formed 
 the positive part of the molecule. 
 
 From this dualistic view of the molecule there 
 naturally arose a disposition to regard the com- 
 pound radicles of organic chemistry as the non- 
 
2/0 HEROES OF SCIENCE. 
 
 oxygenated parts of the molecules of organic 
 compounds. An organic compound came gradually 
 to be regarded as a compound of oxygen with 
 some other elements, which were all lumped to- 
 gether under the name of a compound radicle, and 
 organic chemistry was for a time defined as the 
 chemistry of compound radicles. 
 
 From what has been said on p. 268, I think it will 
 be evident that the idea of substitution is a neces- 
 sary part of the original conception of compound 
 radicle ; a group of atoms in a molecule may, it 
 is said, be removed, and another group, or another 
 atom, substituted for that which is removed. Berze- 
 lius adopted this idea, but he made it too rigid ; he 
 taught that an electro -negative atom, or compound 
 radicle, could be replaced or substituted only by 
 another electro-negative atom or group of atoms, 
 and a positively electrified atom or group of atoms, 
 only by another electro-positive atom or com- 
 pound radicle. Thus oxygen could perhaps be re- 
 placed by chlorine, but certainly not by hydrogen ; 
 while hydrogen might be replaced by a positively 
 electrified atom, but certainly not by chlorine. 
 
 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 field. 
 
 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 
 
ORGANIC CHEMISTRY LIEBtG AND DUMAS. 
 
 to illuminate the apartments ; Dumas was asked 
 to examine the candles and find the reason of their 
 peculiar behaviour. He found that the manufac- 
 turer had used chlorine to bleach the wax, that 
 some of this chlorine remained in the candles, and 
 that the irritating vapours which had annoyed the 
 guests of Charles X. contained hydrochloric acid, 
 produced by the union of chlorine with part of the 
 hydrogen of the wax. Candles bleached by some 
 other means than chlorine were in future used in 
 the royal palaces ; and the unitary theory, which 
 was to overthrow the dualism of Berzelius, began 
 to arise in the mind of Dumas. 
 
 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 impurity. Dumas thoroughly investigated 
 the action of chlorine on wax and other organic 
 compounds; and in 1834 he announced that 
 hydrogen in organic compounds can be exchanged 
 for chlorine, every volume of hydrogen given up by 
 the original compound being replaced by an equa. 
 volume of chlorine. 
 
 Liebig and Wohler made use of a similar con- 
 ception to explain the results which they had 
 obtained about this time in their study of the oil 
 of bitter almonds, a study which will be referred to 
 immediately. 
 
 The progress of this bold innovation made by 
 Dumas was much advanced by the experiments 
 and reasonings of two French chemists, whose 
 
2?2 HEROES OF SCIENCE. 
 
 names ought always to be reverenced by students 
 of chemistry as the names of a pair of brilliant 
 naturalists to whom modern chemistry owes much. 
 Gerhdrdt was distinguished by clearness of vision 
 and expression ; Laurent by originality, breadth of 
 mind and power of speculation. 
 
 Laurent appears to have been the first who 
 made a clear statement of the fundamental con- 
 ception of the unitary theory : " Many organic 
 compounds, when treated with chlorine lose a 
 certain number of equivalents of hydrogen, which 
 passes off as hydrochloric acid. An equal num- 
 ber of equivalents of chlorine takes the place of 
 the hydrogen so eliminated ; thus the physical 
 and chemical properties of the original sub- 
 stance are not profoundly changed. The chlorine 
 occupies the place left vacant by the hydrogen ; 
 the chlorine plays in the new compound the same 
 part as was played by the hydrogen in the original 
 compound." 
 
 The replacement of electro-positive hydrogen by 
 electro-negative chlorine was against every canon 
 of the dualistic chemistry ; and to say that the 
 physical and chemical properties of the original 
 compound were not profoundly modified by this 
 replacement, 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 age. 
 
 But facts accumulated, By the action of 
 
ORGANIC CHEMISTRY LIEBIG AND DUMAS. 273 
 
 chlorine on alcohol Liebig obtained chloroform 
 and chloral, substances which have since been 
 so largely applied to the alleviation of human 
 suffering ; but it was Dumas who correctly deter- 
 mined the composition of these two compounds, 
 and showed how they are related to alcohol and 
 to one another. 
 
 Liebig's reception of the corrections made by 
 Dumas in his work furnishes a striking example of 
 the true scientific spirit. " As an excellent illustra- 
 tion," said Liebig, "of the mode in which errors 
 should be corrected, the investigation of chloral 
 by Dumas may fitly be introduced. It carried 
 conviction to myself, as I think to everybody else, 
 not by the copious number of analytical data 
 opposed to the not less numerous results which I 
 had published, but because these data gave a 
 simpler explanation both of the formation and of 
 the changes of the substances in question." 
 
 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 (1833), wherein 
 he proved that the product of this action, viz. tri- 
 chloracetic acid, is related to the parent substance by 
 containing three atoms of chlorine in place of three 
 atoms of hydrogen in the molecule ; that the new 
 substance is, like the parent substance, a monobasic] 
 acid ; that its salts are very analogous in properties 
 to the salts of acetic acid ; that the action oj 
 the same reagents on the two substances is similai 
 and finally, that the existence of many derivatives 
 
 III. T 
 
2/4 HEROES OF SCIENCE. 
 
 of these compounds could be foretold by the help 
 of the new hypothesis, which derivatives ought not 
 to exist according to the dualistic theory, but which, 
 unfortunately for that theory, were prepared and 
 analyzed by Dumas. W\ 
 
 I have alluded to a* research by Liebig and 
 Wohler on oil of bitter almonds as marking an 
 important stage in the advance of the anti-dualistic 
 views. The paper alluded to was published in 
 1832. At that time it was known that benzole acid 
 is formed by exposure of bitter-almond oil to the 
 air. Liebig and Wohler made many analyses of 
 these two substances, and many experiments on the 
 mutual relations of their properties, 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 com- 
 pound radicle itself a compound of carbon, hydro- 
 gen and oxygen to which they gave the name of 
 benzoyl* Benzoic acid they regarded as a com- 
 pound of the same radicle with another radicle, 
 consisting of equal numbers of oxygen and hydro- 
 gen atoms. By the action of chlorine and other 
 reagents on bitter-almond oil these chemists ob- 
 tained substances which were carefully analyzed 
 and studied, and the properties of which they 
 
 * " In reviewing once more the facts elicited by our inquiry, we 
 find them arranged around a common centre, a group of atoms pre- 
 serving intact its nature, amid the most varied associations with 
 other elements. This stability, this analogy, pervading all the phe- 
 nomena, has induced us to consider this group as a sort of compound 
 element, and to designate it by the special name of bcnzoyl"- 
 Liebig and Wohler, 1832. 
 
ORGANIC CHEMISTRY LIEBIG AND DUMAS. 2/5 
 
 showed could be simply explained by regarding 
 them all as compounds of the radicle benzoyl with 
 chlorine and other atoms or groups of atoms. But 
 this view, if adopted, necessitated the belief that 
 chlorine atoms could replace oxygen atoms ; and, 
 generally, that the substitution of an electro-posi- 
 tive by a negative atom or group of atoms did not 
 necessarily cause any great alteration in the pro- 
 perties of the molecule. 
 
 Thus it was that the rigid conceptions of dualism 
 were shown to be too rigid ; that the possibility 
 of an electro-positive radicle, or atom, replacing 
 another of opposite electricity was recognized ; and 
 thus the view which regarded a compound mole- 
 cule as one structure atoms in which might be 
 replaced by other atoms irrespective of the mutual 
 electrical relations of these atoms began to gain 
 ground. 
 
 From this time the molecule of a compound has 
 been generally regarded as a unitary structure, as 
 one whole, and the properties of the molecule as 
 determined by the nature, number, and arrange- 
 ment of all the atoms which together compose it. 
 
 The unitary conception of a compound molecule 
 appeared at first to be altogether opposed to the 
 system of Berzelius ; but as time went on, and as 
 fresh facts came to be known, it was seen that the 
 new view conserved at least one, and that perhaps 
 the most important, of the thoughts which formed 
 the basis of the Berzelian classification. 
 
 Underlying the dualism of Berzelius was the con- 
 
2/5 HEROES OF SCIENCE, 
 
 ception of the molecule as an atomic structure ; 
 this was retained in the unitary system of Dumas, 
 Gerhardt and Laurent. 
 
 Berzelius had insisted that every molecule is a 
 dual structure. This is taking too narrow a view 
 of the possibilities of Nature, said the upholders of 
 the new school. This molecule may have a dual 
 structure ; that may be built up of three parts. The 
 structure of this molecule or of that can be deter- 
 mined only by a careful study of its relations with 
 other molecules. 
 
 For a time it seemed also as if the new chemistry 
 could do without the compound radicle which had 
 been so much used by Berzelius ; but the pressure 
 of facts soon drove the unitary chemists to recog- 
 nize 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 structures. As a house is not simply 
 a putting together of so many bricks, so much 
 mortar, so many doors and windows, so many 
 leaden pipes, etc., but rather a definite structure 
 composed of parts, many of which are themselves 
 also definite structures, such as the window and its 
 accessory parts, the door with its lintel and handle, 
 etc., so to the unitary chemists did the molecule 
 appear to be built up of parts, some of which, 
 themselves composed of yet smaller parts, dis- 
 charged a particular function in the molecular 
 economy. 
 
ORGANIC CHEMISTRY LIEBIG AND DUMAS. 
 
 A general division of a plant might describe 
 it as a structure consisting of a stem, a root, 
 and leaves. Each of the parts, directly by its 
 individual action and indirectly by the mutual 
 action between it and all the other parts, contributes 
 to the growth of the whole plant ; but if the stem, 
 or root, or leaves be further analyzed, each is found 
 to consist of many parts, of fibres and cells and 
 tissue, etc. We may liken the plant to the molecule 
 of an organic compound ; the root, the stem and 
 the leaves to the compound radicles of which this 
 molecule is built up, and the tissue, fibres, etc., to 
 the elementary atoms which compose these com- 
 pound radicles. The molecule is one whole, pos- 
 sessed of definite structure and performing a definite 
 function by virtue of the nature and the arrange- 
 ment of its parts. 
 
 Many years elapsed after the publication of the 
 researches of Dumas, and of Liebig and Wohler, 
 before such a conception of the molecule as this 
 was widely accepted by chemists. The opposition 
 of the older school, headed by their doughty cham- 
 pion Berzelius, had to be overcome ; the infallibility 
 of some of the younger members of the new school 
 had to be checked ; facts had to be accumulated, 
 difficulties explained, weak analogies abandoned 
 and strong ones rendered stronger by research ; 
 special views of the structure of this or that mole- 
 cule, deduced from a single investigation, had to be 
 supplemented and modified by wider views gained 
 by the researches of many workers. It was not 
 
2/8 HEROES OF SCIENCE. 
 
 till 1867 that Liebig, when asked by Dumas at a 
 dinner given during the French Exhibition to the 
 foreign chemists, why he had abandoned organic 
 chemistry, replied that " now, with the theory of 
 substitution as a foundation, the edifice may be 
 built up by workmen : masters are no longer 
 needed," 
 
 Laurent and Gerhardt did noble work in advancing 
 the unitary theory ; to them is largely due the 
 fruitful conception of types, an outcome of Dumas's 
 work, which owed its origin to the flickerjng of the 
 wax candles in the Tuileries during the royal soiree. 
 
 Chlorine can be substituted for hydrogen in acetic 
 acid, and the product is ^closely related in its pro- 
 perties to the parent substance ; various atoms or 
 groups of atoms can be substituted by other groups 
 in the derivatives of oil of bitter almonds, but a 
 "close analogy in properties runs through all these 
 compounds : these facts might be more shortly 
 expressed by saying that acetic and trichloracetic 
 acids belong to the same type, and that the deriva- 
 tives of bitter-almond oil likewise belong to one 
 type. 
 
 Laurent carried this conception into inorganic 
 chemistry. Water and potash did not seem to have 
 much in common, but Laurent said potash is not a 
 compound of oxide of potassium and water, it is 
 rather a derivative of water. The molecule of potash 
 is derived from that of water by replacing one atom 
 of hydrogen in the latter by one atom of potassium ; 
 water and potash belong to the same type. 
 
ORGANIC CHEMISTRY LIEBlG ANt) DUMAS. 2/6 
 
 Thus there was constituted the water type. 
 
 Light was at once thrown on many facts in 
 organic chemistry. The analogies between alcohol 
 and water, some of which were first pointed out by 
 Graham (see p. 235), seemed to follow as a neces- 
 sary consequence when the molecule of alcohol was 
 regarded as built on the water type. In place of 
 two atoms of hydrogen combined with one of 
 oxygen, there was in the alcohol molecule one 
 atom of the compound radicle ethyl (itself composed 
 of carbon and hydrogen), one atom of oxygen and 
 one of hydrogen. Alcohol was water with one 
 hydrogen atom substituted by one ethyl atom ; the 
 hydrogen atom was the atom of what we call an 
 element, the ethyl was tne atom of what we call a 
 compound radicle. 
 
 Gerhardt sought to refer all organic compounds to 
 one or other of three types the water type, the? 
 hydrochloric acid type, and the ammonia type. 
 As new compounds were prepared and examined, 
 other types had to be introduced. To follow the 
 history of this conception would lead us into too 
 many details ; suffice it to say that the theory of 
 types was gradually merged in the wider theory of 
 equivalency, about which I shall have a little to 
 say in the next chapter. 
 
 One result of the introduction of types into 
 chemical science, associated as it was with the 
 unitary view of compound radicles, was to over- 
 throw that definition of organic chemistry which 
 had for some time prevailed, and which stated that 
 
280 HEROES OF SCIENCE. 
 
 organic chemistry is " the chemistry of compound 
 radicles." Compound radicles, it is true, were more 
 used in explaining the composition and properties 
 of substances obtained from animals and vegetables 
 than of mineral substances, but a definition of one 
 branch of a science which practically included the 
 other branch, from which the first was to be defined, 
 could not be retained. Chemists became gradually 
 convinced that a definition of organic chemistry was 
 not required ; that there was no distinction between 
 so-called organic and inorganic compounds ; and 
 they have consented, but I scarcely think will 
 much longer consent, to retain the terms " organic " 
 and " inorganic," only because these terms have been 
 so long in use. The known compounds of the ele- 
 ment carbon are so numerous, and they have been 
 so much studied and so well classified, that it has 
 become more convenient for the student of chemistry 
 to consider them as a group, to a great extent 
 apart from the compounds of the other elements ; 
 to this group he still often gives the name of 
 " organic compounds." 
 
 Liebig continued to hold the chair of Chemistry 
 in the University of Giessen until the year 1852, 
 when he was induced by the King of Bavaria to 
 accept the professorship of the same science in the 
 University of Munich. During the second quarter 
 of this century Giessen was much resorted to by 
 students of chemistry from all parts of the world, 
 more especially from England. Many men who 
 
ORGANIC CHEMISTRY LIEBIG AND >UMAS. 28 1 
 
 afterwards made their mark in chemical discovery 
 worked under the guidance of the professor oi 
 Stockholm, but Giessen has the honour of being 
 the place where a well-appointed chemical labora- 
 tory for scientific research was first started as 
 distinctly educational institution. The fame of 
 Liebig as a discoverer and as a teacher soon filled 
 the new institution with students, who were stirred 
 to enthusiasm as they listened to his lectures, or 
 saw him at work in his laboratory. " Liebig was 
 not exactly what is called a fluent speaker," says 
 Professor Hofmann, of Berlin, "but there was an 
 earnestness, an enthusiasm in all he said, which 
 irresistibly carried away the hearer. Nor was it so 
 much the actual knowledge he imparted which 
 produced this effect, as the wonderful manner in 
 which he called forth the reflective powers of even 
 the least gifted of his pupils. And what a boon 
 was it, after having been stifled by an oppressive 
 load of facts, to drink the pure breath of science 
 such as it flowed from Liebig's lips ! what a delight, 
 after having perhaps received from others a sack full 
 of dry leaves, suddenly in Liebig's lectures to see 
 the living, growing tree ! . . . We felt then, we feel 
 still, and never while we live shall we forget, Liebig's 
 marvellous influence over us ; and if anything could 
 be more astonishing than the amount of work he 
 did with his own hands, it was probably the moun- 
 tain of chemical toil which he got us to go through. 
 Each word of his carried instruction, every intona- 
 tion of his voice bespoke regard ; his approval was 
 
282 HEROES OF SCIENCE. 
 
 a mark of honour, and of whatever else we might 
 be proud, our greatest pride of all was having him 
 for our master. ... Of our young winnings in the 
 noble playground of philosophical honour, more 
 than half were free gifts to us from Liebig, and to 
 his generous nature no triumphs of his own brought 
 more sincere delight than that which he took in 
 seeing his pupils' success, and in assisting, while he 
 watched, their upward struggle." 
 
 Liebig had many friends in England. He fre- 
 quently visited this country, and was present at 
 several meetings of the British Association. At the 
 meeting of 1837 he was asked to draw up a report 
 on the progress of organic chemistry ; he complied, 
 and in 1840 presented the world with a book which 
 marks a distinct epoch in the applications of science 
 to industrial pursuits " Chemistry in its Appli- 
 cations to Agriculture and Physiology." 
 
 In this book, and in his subsequent researches 
 and works,* 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 crops ; he suggested that manure rich 
 in the salts which are needed by plants might be 
 artificially manufactured, and by doing this he laid 
 the foundation of a vast industry which has arisen 
 during the last two decades. He strongly and suc- 
 cessfully attacked the conception which prevailed 
 
 * "Animal Chemistry, or Chemistry in its Applications to Phy- 
 siology 'and Pathology," 1842. " Researches on the Chemistry of 
 Food," 1847. " The Natural Laws of Husbandry," 1862. 
 
ORGANIC CHEMISTRY LIEBIG AND DUMAS. 283 
 
 among most students of physiology at that time, 
 that chemical and physical generalizations could not 
 be applied to explain the phenomena presented by 
 the growth of living organisms. He was among the 
 first to establish, as an induction from the results of 
 many and varied experiments, the canon which has 
 since guided all teachers of the science of life, that 
 a true knowledge of biology must be based on a 
 knowledge of chemistry and physics. 
 
 But Liebig was not content to establish broad 
 generalizations and to leave the working out of 
 them to others ; he descended from the heights of 
 philosophical inquiry, and taught the housewife to 
 make soup wherein the greatest amount of nourish- 
 ment was conveyed to the invalid in the most 
 easily digestible form ; and has he not, 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 
 Australia, made his name, in every English home, 
 familiar as a household word ? 
 
 On the death of Berzelius in 1848, it was to 
 Liebig that every chemist looked for a continuation 
 of the annual Report on the progress of chemistry, 
 which had now become the central magazine of 
 facts, whither each worker in the science could 
 resort to make himself acquainted with what had 
 been done by others on any subject which he pro- 
 posed to investigate. From that time to the 
 present day Liebig's Annalen has been the leading 
 chemical journal of the world. 
 
284 IIEROES OF SCIENCE. 
 
 Of the other literary work of Liebig of his essays, 
 his celebrated " Chemical Letters," his many reports, 
 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 researches, I have not time, nor would this be 
 the place, to speak. 
 
 Honoured by every scientific society of any note 
 in the world, crowned with the highest reward 
 which England and France can offer to the man 
 of science who is not an Englishman or a French- 
 man the Copley Medal and the associateship of 
 the Institute honoured and respected by every 
 student of science, loved by each of the band of 
 ardent natures whom he had trained and sent forth 
 to battle for the good of their race, and, best of all, 
 working himself to the last in explaining the 
 wonders of Nature, he " passed into the silent land " 
 on the 1 8th of April 1873, leaving the memory of 
 a life nobly devoted to the service of humanity, and 
 the imperishable record of many truths added to 
 the common stock of the race. 
 
 The life-work of Dumas, other than that which 
 
 I have already sketched, is so manifold and so 
 
 varied, 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 
 
 I book. In one of his earliest papers Dumas adopted 
 
 \the atomic theory as the corner-stone of his 
 
 Chemical system ; he was thus led to an experi- 
 
ORGANIC CHEMISTRY LIEBIG AND DUMAS. 285 
 
 mental revision of the values generally accepted 
 for the atomic weights of some of the elements. 
 Among these revisions, that of the atomic weight of 
 carbon holds a most important place, partly be- 
 cause of the excellency of the work, but more 
 because of the other inquiries to which this work 
 gave rise. 
 
 Dumas's experiments were summed up in the 
 statement that the atom of carbon is twelve times 
 heavier than the atom of hydrogen. The experi- 
 mental methods and the calculations used in this 
 determination involved a knowledge of the atomic 
 weight of oxygen ; in order accurately to deter- 
 mine the value to be assigned to this constant, 
 Dumas, in conjunction with Boussingault, under- 
 took a series of experiments on the synthesis of 
 water, which forms one of the classical researches of 
 chemistry, and wherein the number 16 was estab- 
 lished as representing the atomic weight of oxygen. 
 Stas, from experiments conducted at a later time 
 with the utmost care and under conditions emi- 
 nently fitted to gain accurate results, obtained 
 the number 15*96, in place of 16, for the atomic 
 weight of oxygen ; but in a paper recently pub- 
 lished by the veteran Dumas, a source of error 
 is pointed out which Stas had overlooked in his 
 experiments, and it is shown that this error would 
 tend slightly to increase the number obtained by 
 Stas. 
 
 As the values assigned to the atomic weights of 
 the elements are the very fundamental data of 
 
286 HEROES OF SCIENCE, 
 
 chemistry, 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 atoms, we can scarcely lay too much 
 stress on such work as this done by Dumas and 
 Stas. Not many years after the publication of 
 Dalton's " New System," the hypothesis was sug- 
 gested 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 two, three, four, or more 
 atoms of hydrogen, and that consequently there 
 exists but a single elementary form of matter. 
 Among the upholders of this hypothesis Dumas 
 has held an important place. He modified the 
 original statement of Prout, and suggested that all 
 atomic weights are whole multiples of half of that 
 of hydrogen (that is, are whole multiples of J). The 
 experiments of Stas seemed to negative this view, 
 but later work more especially the important 
 critical revision of the results obtained by all the 
 most trustworthy workers, conducted by Professor 
 Clarke of Cincinnati, and published by the Smith- 
 sonian Institution as part of their series of " Con- 
 stants of Nature" has shown that we are in no 
 wise warranted by facts in rejecting Prout's hypo- 
 thesis as modified by Dumas, but that the balance 
 of evidence is at present rather in its favour. 
 
 It would be altogether out of place to discuss 
 
! %28}> 
 
 ORGANIC CHEMISTRY LIEBIG AXI) DUMAS. 287 
 
 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 indulge. 
 I mention it only because it illustrates the far- 
 reaching nature of the researches of the chemist 
 whose work we are now considering, and also be- 
 cause 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 and, 
 as they say, trivial question as whether the num- 
 ber 15*96 or the number 16 is to be preferred as 
 representing the atomic weight of oxygen ; " for in 
 every speck of dust that falls lie hid the laws of 
 the^ universe, and there is not an hour that passes 
 in which you do not hold the infinite in your 
 hand." 
 
 Another and very different subject, which has 
 been placed on a firm basis by the researches of 
 Dumas, is the chemistry of fermentation. By his 
 work on the action of beer-yeast on saccharine 
 liquids, Dumas proved Liebig's view to be unten- 
 able according to which the conversion of sugar 
 into alcohol is brought about by the influence of 
 chemical changes proceeding in the ferment ; also 
 that the view of Berzelius, who regarded alcoholic 
 fermentation as due simply to the contact of the 
 ferment with the sugar, was opposed to many facts ; 
 and lastly, 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 
 
288 HEROES OF SCIENCE. 
 
 other purely chemical changes, but as a change 
 brought about, so far as our present knowledge 
 goes, only by the agency of a growing organism 
 of low form, such as yeast. 
 
 In 1832 Dumas established at his own expense 
 a laboratory for chemical research. When the 
 Revolution of 1848 broke out Dumas's means were 
 much diminished, and he could no longer afford to 
 maintain his laboratory. The closing of this place, 
 where so much sound work had been done, was 
 generally regarded as a calamity to science. About 
 this time Dumas received a visit from a person of 
 unprepossessing appearance, who accosted him 
 thus : " They assert that you have shut up your 
 laboratory, but you have no right to do so. If you 
 are in need of money, there," throwing a roll of 
 bank-notes on the table, " take what you want. Do 
 not stint yourself; I am rich, a bachelor, and have 
 but a short time to live." Dumas's visitor turned 
 out to be Dr. Jecker. He assured Dumas that 
 he was now only paying a debt, since he had made 
 a fortune by what he had learnt in the medical 
 schools of Paris. Dumas could not however in 
 those troublous times turn his mind continuously to 
 experimental research, and therefore declined Dr. 
 Jecker's offer with many protestations of good will 
 and esteem. 
 
 New work now began to press upon Dumas ; 
 his energy and his administrative powers were 
 demanded by the State. Elected a member of the 
 National Assembly in 1848, he was soon called by 
 
ORGANIC CHEMISTRY LIEBIG AND DUMAS. 289 
 
 the President of the Republic to office as Minister of 
 Agriculture and Commerce. He was made a senator 
 under the second empire. He entered the municipal 
 council of Paris about 1854, and was soon elected 
 to the presidency. Under his presidency the great 
 scheme for providing Paris with spring-water carried 
 by aqueducts and tunnels was successfully accom- 
 plished ; many improvements were made in the 
 drainage of the city ; the cost of gas was decreased, 
 while the quality was improved, the constancy of 
 the supply insured, and the appliances for burning 
 the gas in the streets were altered and rendered 
 more effective. 
 
 Nominated to succeed Pelouze as Master of the 
 Mint in 1868, Dumas held this honourable and 
 important position only until the Franco-German 
 war of 1870. Since that date he has relinquished 
 political life ; but as Permanent Secretary of the 
 Academy Dumas now fills the foremost place in 
 all affairs connected with science, whether pure or 
 applied, in the French capital. 
 
 In the work of these two chemists, Liebig and 
 Dumas, we find admirable illustrations of the 
 scientific method of examining natural appearances. 
 
 In the broad general views which they both 
 take of the phenomena to be studied, and the 
 patient and persevering working out of details, we 
 have shown us the combination of powers which 
 are generally found in separate individuals. 
 
 Dumas has always insisted on the need of com- 
 paring properties and reactions of groups of bodies, 
 
 III. U 
 
290 HEROES OF SCIENCE. 
 
 before any just knowledge can be gained as to the 
 position of a single substance in the series studied 
 by the chemist. It has been his aim as a teacher, 
 we are assured by his friend, Professor Hofmann, 
 never to present to his students " an isolated phe- 
 nomenon, or a notion not logically linked with 
 others." To him each chemical compound is one 
 in a series which connects it directly with many 
 other similar compounds, and indirectly with other 
 more or less dissimilar compounds. 
 
 Amid the overwhelming mass of facts which 
 threaten nowadays to bury the science of che- 
 mistry, and crush the life out of it by their 
 weight, Dumas tracks his way by the aid of general 
 principles ; but these principles are themselves 
 generalized from the facts, and are not the offspring 
 of his own fancy. 
 
 We have, I think, found that throughout the 
 progress of chemical science two dangers have 
 beset the student. He has been often tempted to 
 accumulate facts, to amass analytical details, 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 science ; on the other 
 hand, he has been sometimes allured from the path 
 of experiment by his own day-dreams. The dis- 
 coveries of science have been so wonderful, and 
 the conceptions of some of those who have success- 
 fully prosecuted science have been so grand, that 
 the student has not unfrequently been tempted to 
 rest in the prevailing theories of the day, and, 
 
ORGANIC CHEMISTRY LIEBIG AND DUMAS. 291 
 
 forgetting that these ought only " to afford peace- 
 ful lodgings to the intellect for the time," he has 
 rather allowed them to circumscribe it, until at 
 last the mind "finds difficulty in breaking down 
 the walls of what has become its prison, instead of 
 its home." 
 
 We may think that Dumas fell perhaps slightly 
 into the former of these errors, when he did not 
 allow his imagination a little more scope in dealing 
 with the conception of " atom " and " molecule," the 
 difference between which he had apprehended but 
 not sufficiently marked by the year 1826 (see 
 p. 261). 
 
 We know, from his own testimony, that Liebig 
 once fell into the latter error and that the con- 
 sequences were disastrous. "I know a chemist" 
 meaning himself "who . . . undertook an investi- 
 gation of the liquor from the salt-works. He found 
 iodine in it, and observed, moreover, that the iodide 
 of starch turned a fiery yellow by standing over- 
 night. The phenomenon struck him ; he saturated 
 a large quantity of the liquor with chlorine, and 
 obtained from this, by distillation, a considerable 
 quantity of a liquid which coloured starch yellow, 
 and externally resembled chloride of iodine, but 
 differed from this compound in many properties. 
 He explained, however, every discrepancy with 
 satisfaction to himself; he contrived for himself a 
 theory. Several months later, he received a paper of 
 M. Balard's," announcing the discovery of bromine, 
 " and on that same day he was able to publish the 
 
2Q2 HEROES OF SCIENCE. 
 
 results of experiments on the behaviour of bromine 
 with iron, platinum, and carbon ; for Balard's 
 bromine stood in his laboratory, labelled liquid 
 chloride of iodine. Since that time he makes no 
 more theories unless they are supported and con- 
 firmed by trustworthy experiments ; and I can 
 positively assert that he has not fared badly by 
 so doing." 
 
 Another point which we notice in the life-work of 
 these two chemists is their untiring labour. They 
 were always at work ; wherever they might be, 
 they were ready to notice passing events or natural 
 phenomena, and to draw suggestions from these. 
 As Davy proved the elementary character of 
 iodine and established many of the properties of 
 this substance during a visit to Paris, so we find 
 Dumas making many discoveries during brief visits 
 paid to his friends' laboratories when on excursions 
 away from Paris. During a visit to Aix-les-Bains, 
 he noticed that the walls of the bath-room were 
 covered with small crystals of sulphate of lime. 
 The waters of the bath, he knew, were charged with 
 sulphuretted hydrogen, but they contained no 
 sulphuric acid, nor could that acid be detected in 
 the air of the bath-rooms. This observation was 
 followed up by experiments which proved that 
 a porous material, such as a curtain or an ordinary 
 plastered wall, is able to bring about the union 
 of oxygen with sulphuretted hydrogen, provided 
 moisture be present and a somewhat high tempera- 
 ture be maintained. 
 
ORGANIC CHEMISTRY LIEBIG AND DUMAS. 293 
 
 Again, we find Liebig and Dumas characterized 
 by great mental honesty. " There is no harm in a 
 man committing mistakes," said Liebig, " but great 
 harm indeed in his committing none, for he is sure 
 not to have worked. . . . An error you have 
 become cognizant of, do not keep in your house 
 from night till morning." 
 
 Students of science, more than any other men, 
 ought to be ready to acknowledge and correct the 
 errors into which they fall. It is not difficult for 
 them to do this : they have only to be continually 
 going to Nature ; for there they have a court of 
 appeal always ready to hear their case, and to 
 give an absolutely unbiased judgment : they have 
 but to bring their theories and guesses to this judge 
 to have them appraised at their true value. 
 
CHAPTER VII. 
 
 MODERN CHEMISTRY. 
 
 ON p. 162 I referred to the work of the German 
 chemist Richter, by which the equivalents of certain 
 acids and bases were established. Those quantities 
 of various acids which severally neutralized one 
 and the same quantity of a given base, or those 
 quantities of various bases which severally neutral- 
 ized one and the same quantity of a given acid, were 
 said to be equivalent. These were the quantities 
 capable of performing a certain definite action. 
 
 In considering the development of Dumas's sub- 
 stitution theory, we found that Laurent retained 
 this conception of equivalency when he spoke of 
 an equivalent of hydrogen being replaced by an 
 equivalent of chlorine (see p. 272). A certain 
 weight of chlorine was able to take the place and 
 play the part of a certain weight of hydrogen in a 
 compound ; these weights, of hydrogen and chlorine, 
 were therefore equivalent. 
 
MODERN CHEMISTRY. 2Q5 
 
 This conception has been much used since 
 Laurent's time, but it has for the most part been 
 applied to the atoms of the elements. 
 
 Hydrogen being taken as the standard substance, 
 the elements have been divided into groups, in 
 accordance with the number of hydrogen atoms 
 with which one atom of each element is found to 
 combine. Thus certain elements combine with 
 hydrogen only in the proportion of one atom with 
 one atom ; others combine in the proportion of one 
 atom with two atoms of hydrogen ; others in the 
 proportion of one atom with three atoms of hydro- 
 gen, and so on. 
 
 The adjective monovalent, divalent, trivalent^ 
 etc., is prefixed to an element to denote that the 
 atom of this element combines with one, or two, or 
 three, etc., atoms of hydrogen to form a compound 
 molecule. 
 
 Let us consider what is implied in this state- 
 ment "The nitrogen atom is trivalent." This state- 
 ment, if amplified, would run thus : "One atom of 
 nitrogen combines with three atoms of hydrogen 
 to form a compound molecule." Now, this im- 
 plies (i) that the atomic weight of nitrogen is 
 known, and (2) that the molecular weight, and the 
 number of nitrogen and hydrogem atoms in the 
 molecule, of a compound of nitrogen and hydrogen 
 are also known. 
 
 But before the atomic weight of an element can be 
 determined, it is necessary (as we found on p. 146) 
 to obtain, analyze, and take the specific gravities 
 
296 HEROES OF SCIENCE. 
 
 of a series of gaseous compounds of that element. 
 The smallest amount of the element (referred to 
 hydrogen as unity) in the molecule of any one of 
 these gases will then be the atomic weight of the 
 element. 
 
 When it is said that " the molecular weight, and 
 the number of nitrogen and hydrogen atoms in the 
 molecule, of a compound of nitrogen and hydrogen 
 are known," the statement implies that the com- 
 pound in question has been obtained in a pure state, 
 has been analyzed carefully, has been gasefied, and 
 that a known volume of the gas has been weighed. 
 When therefore we say that " the nitrogen atom is 
 trivalent," we sum up a large amount of knowledge 
 which has been gained by laborious experiment. 
 
 This classification of the elements into groups of 
 equivalent atoms which we owe to Frankland, 
 Williamson, Odling, and especially to Kekule has 
 been of much service especially in advancing the 
 systematic study of the compounds of carbon. It 
 helps to render more precise the conception which 
 has so long been gaining ground of the molecule 
 as a definite structure. 
 
 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 molecule ; a divalent as 
 one, the atom of which acts on and is acted on by 
 two atoms of hydrogen or other monovalent ele- 
 ment in a molecule; a trivalent element as one, 
 the atom of which acts on and is acted on by three 
 atoms of hydrogen or other monovalent element 
 in a molecule ; and so on. 
 
MODERN CHEMISTRY. 297 
 
 The fact that there often exist several compounds 
 of carbon, the molecules of which are composed 
 of the same numbers of the same atoms, finds a par- 
 tial 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 num- 
 ber of other atoms to form a compound molecule. 
 For if the observed properties of a compound are 
 associated with a certain definite arrangement of 
 the elementary atoms within the molecules of that 
 compound, it would seem that any alteration in 
 this arrangement ought to be accompanied by an 
 alteration in the properties of the compound ; in 
 other words, the existence of more than one com- 
 pound of the same elements united in the same 
 proportions becomes possible and probable. 
 
 I have said that such compounds exist : let me 
 give a few examples. 
 
 The alchemists poured a stream of mercury on 
 to molten sulphur, and obtained a black substance, 
 which was changed by heat into a brilliantly red- 
 coloured body. We now know that the black and 
 the red compounds alike contain only mercury 
 and sulphur, and contain these elements united in 
 the same proportions. 
 
 Hydrogen, carbon, nitrogen and oxygen unite 
 in certain proportions to produce a mobile, colour- 
 less, strongly acid liquid, which acts violently on the 
 skin, causing blisters and producing great pain : if 
 this liquid is allowed to stand for a little time in the 
 air it becomes turbid, begins to boil, gets thicker, 
 
298 HEROES OF SCIENCE. 
 
 and at last explodes, throwing a white pasty sub- 
 stance about in all directions. This white solid is 
 inodorous, is scarcely acid to the taste, and does 
 not affect the skin ; yet it contains the same ele- 
 ments, united in the same proportions, as were pre- 
 sent in the strongly acid, limpid liquid from which 
 it was produced. 
 
 Two substances are known each containing 
 carbon and hydrogen united in the same propor- 
 tions : one is a gas with strong and irritating odour, 
 and exerting a most disagreeable action on the eyes ; 
 the other is a clear, limpid, pleasant-smelling liquid. 
 
 Phosphorus is a very poisonous substance : it 
 readily takes fire in the air at ordinary temperatures, 
 so that it must be kept under water ; but a modifi- 
 cation of phosphorus is known, containing no form 
 of matter other than phosphorus, which is non- 
 poisonous, does not take fire easily, and may be 
 handled with safety. 
 
 Once more, there is a compound of nitrogen and 
 oxygen which presents the appearance of a deep- 
 red, almost black gas ; there is also a compound 
 of nitrogen and oxygen which is a clear, colourless 
 gas ; yet both contain the same elements united 
 in the same proportions. 
 
 But a detailed consideration of isomerism, i.e. 
 the existence of more than one compound built up 
 of the same amounts of the same elements yet 
 possessing different properties, would lead us too 
 far from the main path of chemical advance which 
 we wish to trace, 
 
MODERN CHEMISTRY. 299 
 
 The chemist is to-day continually seeking to 
 connect the properties of the bodies he studies 
 with the molecular structures of these bodies ; the 
 former he can observe, a knowledge of the latter 
 he must gain by reasoning on the results of opera- 
 tions and experiments. His guide the guide of 
 Lavoisier and his successors is this : " Similarity 
 of properties is associated with similarity of com- 
 position" by "composition" he generally means 
 molecular composition. 
 
 Many facts have been amassed of late years 
 which illustrate the general statement that the 
 properties of bodies are connected with the com- 
 position of those bodies. Thus a distinct connec- 
 tion has been traced between the tinctorial power 
 and the molecular composition of certain dye-stuffs ; 
 in some cases it has even become possible to pre- 
 dict how a good dye-stuff may be made to say 
 that, inasmuch as this or that chemical reaction 
 will probably give rise to the production of this or 
 that compound, the atoms in the molecule of which 
 we believe to have a certain arrangement relatively 
 to one another, so this reaction or that will pro- 
 bably produce a dye possessed of strong tinctorial 
 powers. 
 
 The compound to the presence of which madder 
 chiefly owes its dyeing powers is called alizarine ; 
 to determine the nature of the molecular structure 
 of this compound was, for many years, the object 
 of the researches of chemists ; at last, thanks 
 especially to the painstaking zeal of two German 
 
3OO HEROES OF SCIENCE. 
 
 chemists, it became fairly clear that alizarine and 
 a compound of carbon and hydrogen, called anthra- 
 cene, were closely related in structure. Anthracene 
 was obtained from alizarine, and, after much labour, 
 alizarine was prepared from anthracene. Anthra- 
 cene is contained in large quantities in the thick 
 pitch which remains when coal-tar is distilled ; 
 this pitch was formerly of little or no value, but as 
 soon as the chemical manufacturer found that in 
 this black objectionable mass there lay hidden 
 enormous stores of alizarine, he no longer threw 
 away his coal-tar pitch, but sold it to the alizarine 
 manufacturer for a large sum. Thus it has come 
 to pass that little or no madder is now cultivated ; 
 madder-dyeing is now done by means of alizarine 
 made from coal-tar : large tracts of ground, for- 
 merly used for growing the madder plant, are thus 
 set free for the growth of wheat and other cereals. 
 
 This discovery of a method for preparing alizarine 
 artificially stimulated chemists to make researches 
 into the chemical composition, and if possible to 
 get to know something about the molecular struc- 
 ture of indigo. 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 
 which, like anthracene, are found in coal-tar. 
 
 These examples, while illustrating the connection 
 that exists between the composition and the pro- 
 perties of bodies, also illustrate the need there 
 is for giving a scientific chemical training to the 
 
MODERN CHEMISTRY. 3OI 
 
 man who is to devote his life to chemical manu- 
 factures. Pure and applied science are closely 
 connected ; he who would succeed well in the latter 
 must have a competent and a practical knowledge 
 of the former. 
 
 That composition molecular] composition and 
 properties are closely related is generally assumed, 
 almost as an axiom, in chemical researches nowa- 
 days. 
 
 Lavoisier defined acids as substances containing 
 oxygen ; 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 contained ; Liebig spoke of acids as substances 
 containing "replaceable" hydrogen; the student 
 of the chemistry of the carbon compounds now 
 recognizes in an organic acid a compound contain- 
 ing hydrogen, but also carbon and oxygen, and he 
 thinks that the atoms of hydrogen (or some of 
 these atoms) in the molecule of such a compound 
 are, in some way, closely related to atoms of oxygen 
 and less closely to atoms of carbon, within that 
 molecule, in other words, the chemist now recog- 
 nizes that, for carbon compounds at any rate, acids 
 are acid not only because they contain hydrogen, 
 but also because that hydrogen is related in a 
 definite manner within the molecule to other ele- 
 mentary atoms ; he recognizes that the acid or non- 
 acid properties of a compound are conditioned, not 
 only by the nature of the elements which together 
 form that compound, but also by the arrangement 
 
302 HEROES OF SCIENCE. 
 
 of these elements. Davy's view of the nature of 
 acids is thus confirmed and at the same time 
 rendered more definite by the results of recent 
 researches. 
 
 The physical student is content to go no further 
 than the molecule ; the properties of bodies which 
 he studies are regarded, for the most part, as de- 
 pending on the size, the nature, and perhaps the 
 grouping together of molecules. But the chemist 
 seeks to go deeper than this. The molecule is too 
 large a piece of matter for him ; the properties 
 which he studies are conceived by him to be prin- 
 cipally conditioned by the nature, the number, and 
 the arrangement of the parts of the molecule of 
 the atoms which together build up the molecule. 
 
 In these elementary atoms he has, for the present, 
 found the materials of which the heavens and the 
 earth are made ; but facts are being slowly gained 
 which render it probable that these atoms are 
 themselves structures that they are built up of 
 yet smaller parts, of yet simpler kinds of matter. 
 To gather evidence for or against this supposition, 
 the chemist has been obliged to go from the earth 
 to the heavens, he has been obliged to form a new 
 science, the science of spectroscopic analysis. 
 
 This subject has been considered in "The As- 
 tronomers," belonging to this series of books ; but 
 the point of view from which the matter is there 
 regarded is astronomical rather than chemical. I 
 should like briefly to recall to the reader the funda- 
 mental facts of this branch of science. 
 
MODERN CHEMISTRY. 
 
 303 
 
 When a ray of light is allowed to pass through a 
 glass prism and then fall on to a white surface, the 
 image produced on this surface consists of a many- 
 coloured band of light. The blue or violet part of 
 this band is more bent away from the plane of the 
 entering ray than the orange part, and the latter 
 more than the red part of the band. This is roughly 
 represented in Fig. 4, where r is the ray of light 
 
 Fig. 4. 
 
 passing through the prism P, and emerging as a 
 sevenfold band of coloured lights, of which the 
 violet, V, is most, and the red band, R, is least bent 
 away from the plane of the ray r. If the surface 
 say a white screen on which the many-coloured 
 band of light, or spectrum^ falls, is punctured by a 
 small hole, so as to admit the passage of the violet, 
 or blue, or orange, or red light only, and if this 
 violet, etc., light is then passed through a second 
 prism, no further breaking up of that light takes 
 place. This state of matters is represented in the part 
 
304 
 
 HEROES OF SCIENCE. 
 
 of the figure towards the right hand, where the red 
 ray, R, is shown as passing through the screen, and 
 falling on to a second prism, P' : the red ray is 
 slightly bent out of its direct course, but is not sub- 
 divided ; it falls on the second screen as a ray of red 
 light, R'. But if a quantity of the metal sodium is 
 vaporized in a hot non-luminous flame, and if the 
 yellow light thus produced is passed through a 
 prism, a spectrum is obtained consisting of a single 
 yellow line (on a dark background), 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 prism. In Fig. 5 the 
 yellow light from a flame containing sodium is 
 
 Sodium 
 
 represented by the line Y. The light emitted by 
 the glowing sodium vapour is said to be mono- 
 chromatic. 
 
 Lastly, 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 prism, a spectrum is 
 
MODERN CHEMISTRY. 
 
 305 
 
 produced corresponding to the solar spectrum ex- 
 cept that a black line appears in the position where 
 the yellow line, characteristic of sodium, was 
 noticed in the second experiment. 
 
 Fig. 6 represents the result of this experiment : 
 
 V M 
 
 - *5 
 
 V/.-O -. 
 
 rr -.." 
 
 I 
 
 V Fig. 6. 
 
 the ray of sunlight or electric light, r, passes 
 through a quantity of sodium vapour, and is then 
 decomposed by the prism ; the spectrum produced 
 is marked by the absence of light (or by a dark line) 
 where the yellow line, Y, was before noticed. 
 
 These are the fundamental facts of spectroscopic 
 analysis : sunlight is decomposable into a band of 
 many colours, that is, into a spectrum ; light 
 emitted by a glowing vapour is characterized by 
 the presence of coloured lines, each of which occu- 
 pies a definite position with reference to the various 
 parts of the solar spectrum ; sunlight or the elec- 
 
 III. X 
 
306 HEROES OF SCIENCE. 
 
 trie light when allowed to pass through a mass of 
 vapour, furnishes a spectrum characterized by the 
 absence of those bright lines, the presence of which 
 marked the spectrum of the light obtained by 
 strongly heating the vapour through which the 
 sunlight has passed. 
 
 The spectrum obtained by decomposing the light 
 emitted by glowing vapour of potassium is charac- 
 terized by the presence of certain lines call them 
 A and B lines. We are asked what element (or 
 elements) is present in a certain gas presented to 
 us : we pass a beam of white light through this gas 
 and then through a prism, and we obtain a con- 
 tinuous spectrum (i.e. a spectrum of many colours 
 like the solar spectrum) with two dark lines in the 
 same positions as those occupied by the lines A 
 and B. We therefore conclude that the gas in 
 question contains vapour of potassium. 
 
 The solar spectrum, when carefully examined, is 
 found to be crossed by a very large number of fine 
 black lines ; the exact positions of many hundreds 
 of these lines have been carefully determined, and, 
 in most cases, 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 bodies. 
 
 Assume that the sun consists, broadly speaking, of 
 an intensely hot and luminous central mass, formed 
 to a large extent of the elementary substances which 
 build up this earth, and that this central mass is 
 surrounded by a cooler (but yet very hot) gaseous 
 
MODERN CHEMISTRY, 3O/ 
 
 envelope of the same elements, and we have a 
 tolerably satisfactory explanation of the principal 
 phenomena revealed by the spectroscopic study of 
 the sun's light. 
 
 On this assumption the central mass of glowing 
 iron, chromium, magnesium, nickel, cobalt, hydro- 
 gen, etc., is sending out light ; a portion of the 
 light emitted by the glowing iron is quenched as it 
 passes through a cloud of cooler iron vapour out- 
 side the central mass, a portion of the light emitted 
 by the glowing chromium is quenched as it passes 
 through a cloud of cooler chromium vapour, and so 
 on ; the black lines in the spectrum are the records 
 of these various quenchings of this and that light. 
 
 So far then the study of the solar spectrum 
 appears to be tolerably simple, and this study 
 generally confirms the proposition that the material 
 of which the sun is composed is, broadly, identical 
 with those forms of matter which we, on this earth, 
 call the chemical elements. 
 
 But whatever be the composition of the sun, it is, 
 I think, evident that in dealing with a ray of light 
 coming therefrom, we are dealing with a very com- 
 plex phenomenon. 
 
 According to the hypothesis which is now guiding 
 us, the solar light which passes into our spectroscope 
 has probably had its beginning in some central 
 part of the sun, and has passed through very thick 
 layers of hot metallic clouds, agitated perhaps by 
 solar cyclones. Could we examine the light coming 
 from some defined part of the sun, we should pro- 
 
308 HEROES OF SCIENCE. 
 
 bably obtain valuable information. During a solar 
 eclipse red prominences are seen projecting beyond 
 the dark shadow of the moon, which covers the sun's 
 disc. Analysis of the light emitted by these pro- 
 minences has shown that they are phenomena 
 essentially belonging to the sun itself, and that they 
 consist of vast masses of intensely hot, glowing 
 gaseous substances, among which hydrogen is pre- 
 sent in large quantities. That these prominences are 
 very hot, hotter than the average temperature of 
 the ordinary solar atmosphere, is proved by the fact 
 that the spectrum of the light coming from them is 
 characterized by bright lines. By special arrange- 
 ments which need not be discussed here, but which 
 have been partly explained in " The Astronomers " 
 (see pp. 334, 335 of that book), it has been shown 
 that these prominences are in rapid motion : at 
 one moment they shoot up to heights of many 
 thousand miles, at another they recede towards the 
 centre of the sun. 
 
 We thus arrive at a picture of the solar atmo- 
 sphere as consisting of layers of very hot gases, 
 which are continually changing their relative posi- 
 tions and forms ; sometimes ejections of intensely 
 hot, glowing gases occur, we call these promin- 
 ences ; sometimes down-rushes of gaseous matter 
 occur, we call these spots. Among the substances 
 which compose the gaseous layers we recognize 
 hydrogen, iron, magnesium, sodium, nickel, chro- 
 mium, etc., but we also find substances which can 
 at present be distinguished only by means of the 
 
MODERN CHEMISTRY. 
 
 309 
 
 wave-lengths of the light which they emit ; thus we 
 
 have 1474 stuff, 5017 stuff, 5369 stuff, etc. 
 
 Let us now turn to another part of this subject. 
 
 By a special arrangement of apparatus it is possible 
 
 to observe the spectrum of the light emitted by a 
 
 glowing vapour, parts of which are hotter than 
 
 other parts, 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 vapour. If this is done for 
 
 sodium vapour, certain lines are 
 
 apparent in all the spectra, 
 
 others only in the spectrum of 
 
 the light coming from the hottest 
 
 parts of the sodium vapour : the 
 former lines are called "long 
 lines," the latter "short lines." 
 A rough representation of the 
 long and short lines of sodium 
 is given in Fig. 7. 
 
 Now, suppose that the lines in the spectrum of 
 the light emitted by glowing manganese vapour 
 have been carefully mapped, and classed as long 
 and short lines : suppose that the same thing has 
 been done for the iron lines : now let a little man- 
 ganese be mixed with much iron, let the mixture 
 be vaporized, and let the light which is emitted 
 be decomposed by the prism of a spectroscope, 
 
 Fig. 7. Long and 
 short lines of sodium. 
 
3IO HEROES OF SCIENCE. 
 
 it will be found that the long lines of manganese 
 alone make their appearance ; let a little more 
 manganese be added to the mixture, and now some 
 of the shorter lines due to manganese begin to 
 appear in the spectrum. Hence it has been con- 
 cluded 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 examined. Lockyer 
 has applied this conclusion to "purify" various 
 elementary spectra. 
 
 The spectrum of element A is carefully mapped, 
 and the lines are divided into long and short lines, 
 according as they are noticed in the spectrum of 
 the light coming from all parts of the glowing 
 vapour of A, or only in the spectrum of the light 
 which comes from the hotter parts of that vapour. 
 The spectra of elements B and C are similarly 
 mapped and classified : then the three spectra are 
 compared ; the longest line in the spectrum of B is 
 noted, if this line is found in the spectrum of A, 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 A ; the next longest B line is 
 searched for in the spectrum of A if present it 
 also is marked with a negative sign ; a similar 
 process of comparison and elimination is conducted 
 with the spectra of A and C. In this way a " puri- 
 fied " spectrum of the light from A is obtained a 
 
MODERN CHEMISTRY. 311 
 
 spectrum, that is, from which, according to Lockyer, 
 all lines due to the presence of small quantities of 
 B and C as impurities in A have been eliminated. 
 Fig. 8 is given in order to make this "purify- 
 
 A 
 
 ,1 
 
 1 
 
 
 1 1 
 
 1 
 
 Fig. 8. 
 
 ing" process more clearly understood. But when 
 this process has been completed there remain, in 
 many cases, a few short lines common to two or 
 more elementary spectra : such lines are called 
 by Lockyer basic lines. He supposes that these 
 lines are due to light emitted by forms of matter 
 simpler than our elements ; he thinks that at very 
 high temperatures some of the elements are decom- 
 posed, and that the bases of these elements are pro- 
 duced and give out light, which light is analyzed 
 
312 HEROES OF SCIENCE. 
 
 by the spectroscope. Such short basic lines are 
 marked in the spectra represented in Fig. 8 with a 
 positive sign. 
 
 Now, if the assumption made by Lockyer be 
 admitted, viz. that the short lines, or some of the 
 short lines, which are coincident in the " purified " 
 spectra of various elements, are really due to light 
 emitted by forms of matter into which our so-called 
 elements are decomposed at very high temperatures, 
 it follows that such lines should become more pro- 
 minent in the spectra of the light emitted by ele- 
 ments the higher the temperature to which these 
 elements are raised. But we know (see p. 308) that 
 the prominences around the sun's disc are hotter 
 than the average temperature of the solar atmo- 
 sphere ; hence the spectrum of the light coming from 
 these prominences ought to be specially rich in 
 " basic " lines : this supposition is confirmed by 
 experiment. Lockyer has also shown that it is the 
 "basic," and not the long lines, which are espe- 
 cially affected in the spectra of light coming from 
 those parts of the solar atmosphere which are 
 subjected to the action of cyclones, i.e. which are 
 at abnormally high temperatures. And finally, 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 raised, 
 and the substance is gradually decomposed into its 
 elements, and the spectrum of the light emitted by 
 a so-called elementary substance as the temperature 
 of that substance is increased. 
 
MODERN CHEMISTRY. 313 
 
 But it may be urged that Lockyer's method of 
 " purifying '\ a spectrum is not satisfactory ; that, 
 although all the longer lines common to two spectra 
 are eliminated, 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 other. Further, it has been shown 
 that several of the so-called " basic " lines are re- 
 solved, by spectroscopes of great dispersive power, 
 into groups of two or more lines, which lines are 
 not coincident in different spectra. 
 
 And moreover it is possible to give a fairly satis- 
 factory 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 matter. Nevertheless this hypothesis has 
 a certain amount of experimental evidence in its 
 favour ; it may be a true hypothesis. I do not think 
 we are justified at present either in accepting it as 
 the best guide to further research, or in wholly 
 rejecting it. 
 
 The researches to which this hypothesis has 
 given rise have certainly thrown much light on the 
 constitution of the sun and stars, and they have 
 also been instrumental in forcing new views regard- 
 ing the nature of the elements on the attention of 
 chemists, and so of awakening them out of the 
 slumber into which every class of men is so ready 
 to fall. 
 
 The tale told by the rays of light which travel 
 to this earth from the sun and stars has not yet 
 
3 14 HEROES OF SCIENCE. 
 
 been fully read, but the parts which the chemist has 
 spelt out seem to say that, although the forms of 
 matter of which the earth is made are also those 
 which compose the sun and stars, yet in the sun and 
 stars some of the earthly elements are decomposed, 
 and some of the earthly atoms are split into simpler 
 forms. The tale, I say, told by the rays of light 
 seems to bear this interpretation, but it is written 
 in a language strange to the children of this earth, 
 who can read it as yet but slowly ; for the name 
 given to the new science was " Ge- Urania, because 
 its production was of earth and heaven. And it 
 could not taste of death, by reason of its adoption 
 into immortal palaces ; but it was to know weak- 
 ness, and reliance, and the shadow of human im- 
 becility ; and it went with a lame gait ; but in its 
 going it exceeded all mortal children in grace and 
 swiftness." 
 
 There are certain little particles so minute that 
 at least sixty millions of them are required to com- 
 pose the smallest portion of matter which can be 
 seen by the help of a good microscope. Some of 
 these particles are vibrating around the edge of an 
 orb a million times larger than the earth, but at a 
 distance of about ninety millions of miles away. 
 The student of science is told to search around the 
 edge of the orb till he finds these particles, and 
 having found them, to measure the rates of their 
 vibrations ; and as an instrument with which to do 
 this he is given a glass prism ! But he has accom- 
 plished the task ; he has found the minute particles, 
 and he has measured their vibration-periods. 
 
MODERN CHEMISTRY. 315 
 
 Chemistry is no longer confined to this earth : 
 the chemist claims the visible universe as his labo- 
 ratory, and the sunbeams as his servants. 
 
 Davy decomposed soda and potash by using the 
 powerful instrument given him by Volta ; but the 
 chemist to-day has thrown the element he is seek- 
 ing to decompose into a crucible, which is a sun or 
 a star, and awaits the result. 
 
 The alchemists were right. There is a philoso- 
 pher's stone ; but that stone is itself a compound 
 of labour, perseverance, and genius, and the gold 
 which it produces is the gold of true knowledge, 
 which shall never grow dim or fade away. 
 
 
CHAPTER VIII. 
 
 SUMMARY AND CONCLUSION. 
 
 WE have thus traced some of the main paths 
 along which Chemistry has advanced since the day 
 when, 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 phenomena, she 
 began to recognize that Nature is complex but 
 orderly, and so began to be a branch of true know- 
 ledge. 
 
 In this review we have, I think, found that the 
 remark made at the beginning of the introductory 
 chapter is, on the whole, a just one. That the 
 views of the alchemists, although sometimes very 
 noble, were " vague and fanciful " is surely borne 
 out by the quotations from their writings given 
 in the first chapter. This period was followed 
 by that wherein the accurate, but necessarily 
 somewhat narrow conception of the Lavoisierian 
 chemistry prevailed. Founded for the most part 
 
SUMMARY AND CONCLUSION. 317 
 
 on the careful, painstaking, and quantitative study 
 of one phenomenon a very wide and far-reach- 
 ing phenomenon, 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 
 him. But although this classification had of neces- 
 sity to be revised and recast, the genius of Lavoisier 
 enunciated certain truths which have remained the 
 common possession of every chemical system. By 
 proving that however the forms of matter may be 
 changed the mass remains unaltered, he for the first 
 time made a science of chemistry possible. He de- 
 fined " element " once for all, and thus swept away 
 the fabric of dreams raised by the alchemists on the 
 visionary foundation of earth, air ; fire and water, or 
 of mercury, sulphur and salt. By his example, 
 he taught that weighings and measurements must 
 be made before accurate knowledge of chemical 
 reactions can be hoped for; 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 substances. 
 
 Lavoisier gained these most important results 
 by concentrating his attention on a few subjects 
 of inquiry. That chemistry might become broad 
 it was necessary that it should first of all become 
 narrower, 
 
318 HEROES OF SCIENCE. 
 
 The period when the objects of the science were 
 defined and some of its fundamental facts and 
 conceptions were established, was succeeded, as 
 we saw in our sketch, by that in which Dalton 
 departed somewhat from the method of investiga- 
 tion adopted by most masters in science, and by 
 concentrating his great mental powers on facts 
 belonging to one branch of natural knowledge, 
 elaborated a simple but very comprehensive theory, 
 which he applied to explain the facts belonging to 
 another branch of science. 
 
 Chemistry was thus endowed with a grand and 
 far-reaching conception, which has been developed 
 and applied by successive generations of investi- 
 gators : but we must not forget that it was the 
 thorough, detailed work of Black and Lavoisier 
 which made possible the great theory of Dalton. 
 
 At the time when Dalton was thinking out his 
 theory of atoms, Davy was advancing as a con- 
 queror through the rich domain which the dis- 
 covery of Volta had opened to chemistry. Dalton, 
 trained to rely on himself, surrounded from his 
 youth by an atmosphere in which " sweetness and 
 light " did not predominate, thrown on the world 
 at an early age, and obliged to support himself by 
 the drudgery of teaching when he would fain have 
 been engaged in research, 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 struggle, Dalton, 
 
SUMMARY AND CONCLUSION. 319 
 
 we found, withdrew in great part from contact with 
 other scientific workers, and communing only with 
 himself, developed a theory which, while it showed 
 him to be one in the chain of thinkers that begins 
 in Democritus and Leucippus, was nevertheless 
 stamped with the undeniable marks of his own 
 individuality and genius, and at the same time was 
 untouched by any of the hopes or fears, and un- 
 affected by any of the passions, of our common 
 humanity. 
 
 Davy, on the other hand, was surrounded from 
 childhood by scenes of great natural beauty and 
 variety, by contact with which he was incited 
 to eager desire for knowledge, while at the same 
 time his emotions remained fresh and sensitive to 
 outward impressions. Entering on the study of 
 natural science when there was a pause in the 
 march of discovery, but a pause presageful of fresh 
 advances, he found outward circumstances singularly 
 favourable to his success ; seizing these favourable 
 circumstances he made rapid advances. Like 
 Lavoisier, he began his work by proving that there 
 is no such thing in Nature as transmutation, in the 
 alchemical meaning of the term ; as Lavoisier had 
 proved that water is not changed into earth, so did 
 Davy prove that acid and alkali are not produced 
 by the action of the electric current on pure water. 
 We have shortly traced the development of the 
 electro-chemical theory which Davy raised on the 
 basis of experiment ; we have seen how facts 
 obliged him to doubt the accepted view of the 
 
320 HEROES OF SCIENCE. 
 
 composition of hydrochloric acid and chlorine, and 
 how by the work he did on these subjects chemists 
 have been finally convinced that an element is not 
 a substance which cannot be, but a substance which 
 has not been decomposed, and how from this work 
 has also arisen the modern theory of acids, bases 
 and salts. 
 
 We found that, by the labours of the great 
 Swede J. J. Berzelius, the Daltonian theory was 
 confirmed by a vast series of accurate analyses, and, 
 in conjunction with a modification of the electro- 
 chemical theory of Davy, was made the basis of a 
 system of classification which endeavoured to in- 
 clude all chemical substances within its scope. 
 The atom was the starting-point of the Berzelian 
 system, but that chemist viewed the atom as a dual 
 structure the parts of which held together by reason 
 of their opposite electrical polarities. Berzelius, we 
 saw, greatly improved the methods whereby atomic 
 weights could be determined, and he recognized 
 the importance of physical generalizations as aids in 
 finding the atomic weights of chemical substances. 
 
 But Berzelius came to believe too implicitly in 
 his own view of Nature's working ; his theory 
 became too imperious. Chemists found it easier 
 to accept than to doubt an interpretation of facts 
 which was in great part undeniably true, and which 
 formed a central luminous conception, shedding 
 light on the whole mass of details which, without it, 
 seemed confused and without meaning. 
 
 If the dualistic stronghold was to be carried, the 
 
SUMMARY AND CONCLUSION. 321 
 
 attack should be impetuous, and should be led by 
 men, not only of valour, but also of discretion. We 
 found that two champions appeared, and that, aided 
 by others who were scarcely inferior soldiers to 
 themselves, they made the attack, and made it with 
 success. 
 
 But when the heat of the battle was over and 
 the bitterness of the strife forgotten, it was found 
 that, although many pinnacles of the dualistic 
 castle had been shattered, the foundation and great 
 part of the walls remained ; and, strange to say, 
 the men who led the attack were content that these 
 should remain. 
 
 The atom could no longer be regarded as always 
 composed of two parts, but must be looked on 
 rather as one whole, the properties of which are 
 defined by the properties and arrangements of all 
 its parts ; but the conception of the atom as a 
 structure, and the assurance that something could 
 be inferred regarding that structure from a know- 
 ledge of the reactions and general properties of the 
 whole, remained when Dumas and Liebig had 
 replaced the dualism of Berzelius by the unitary 
 theory of modern chemistry ; and these concep- 
 tions have remained to the present day, and are 
 now ranked among the leading principles of 
 chemical science ; only we now speak of the " mole- 
 cule " where Berzelius spoke of the " atom." 
 
 Along with these advances made by Dumas, 
 Liebig and others in rendering more accurate the 
 general conception of atomic structure, we found 
 
 III. Y 
 
322 HEROES OF SCIENCE. 
 
 that the recognition of the existence of more than 
 one order of small particles was daily gaining 
 ground in the minds of chemists. 
 
 The distinction between what we now call atoms 
 and molecules had been clearly stated by Avogadro 
 in 1811 ; but the times were not ripe. The mental 
 surroundings of the chemists of that age did not 
 allow them fully to appreciate the work of Avo- 
 gadro. The seed however was sown, and the 
 harvest, although late, was plentiful. 
 
 We saw that Dumas accepted, with some hesita- 
 tion, the distinction drawn by Avogadro, but that 
 failing to carry it to its legitimate conclusion, he 
 did not reap the full benefit of his acceptance of 
 the principle that the smallest particle of a sub- 
 stance which takes part in a physical change divides 
 into smaller particles in those changes which we 
 call chemical. 
 
 To Gerhardt and Laurent we owe the full recog- 
 nition, and acceptance as the foundation of chemical 
 classification, of the atom as a particle of matter 
 distinct from the molecule ; they first distinctly 
 placed the law of Avogadro "Equal volumes of 
 gases contain equal numbers of molecules " in its 
 true position as a law, which, resting on physical 
 evidence and dynamical reasoning, is to be accepted 
 by the chemist as the basis of his atomic theory. 
 To the same chemists we are indebted for the formal 
 introduction into chemical science of the conception 
 of types, which, as we found, was developed by 
 Frankland, Kekule, and others, into the modern 
 
 
SUMMARY AND CONCLUSION. 323 
 
 doctrine of equivalency of groups of elementary 
 atoms. 
 
 We saw that, in the use which he made of the 
 laws of Mitscherlich, and of Dulong and Petit, 
 Berzelius recognized the importance of the aid 
 given by physical methods towards solving the 
 atomic problems of chemistry ; but among those 
 who have most thoroughly availed themselves of 
 such aids Graham must always hold a foremost 
 place. 
 
 Graham devoted the energies of his life to track- 
 ing the movements of atoms and molecules. He 
 proved that gases pass through walls of solid 
 materials, as they pass through spaces already 
 occupied by other gases ; 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 unas- 
 sisted vision. Graham followed the molecules as in 
 their journey ings they came into contact with animal 
 and vegetable membranes ; he found that these 
 membranes presented an insuperable barrier to the 
 passage of some molecules, while others passed 
 easily through. He thus arrived at a division of 
 matter into colloidal and crystalloidal. He showed 
 what important applications of this division might 
 be made in practical chemistry, he discussed some of 
 the bearings of this division on the general theory 
 of the molecular constitution of matter, and thus 
 he opened the way which leads into a new terri- 
 
324 HEROES OF SCIENCE. 
 
 tory rich in promise to him who is able to follow the 
 footsteps of its discoverer. 
 
 Other investigators have followed on the general 
 lines laid down by Graham ; connections, more or 
 less precise, have been established between chemical 
 and physical properties of various groups of com- 
 pounds. It has been shown that the boiling points, 
 melting points, expansibilities by heat, amounts of 
 heat evolved during combustion, in some cases 
 tinctorial powers of dye-stuffs, and other physical 
 constants of groups of compounds, vary with 
 variations in the nature, number and arrange- 
 ments of the atoms in the molecules of these 
 compounds. 
 
 But although much good work has been done in 
 this direction, our ignorance far exceeds our know- 
 ledge regarding the phenomena which lie on the 
 borderlands between chemistry and physics. It is 
 probably here that chemists look most for fresh 
 discoveries of importance. 
 
 As each branch of natural science becomes more 
 subdivided, and as the quantity of facts to be 
 stored in the mind becomes daily more crush- 
 ing, the student finds an ever-increasing difficulty 
 in passing beyond the range of his own subject, 
 and in gaining a broad view of the relative im- 
 portance of the facts and the theories which to him 
 appear so essential. 
 
 In the days when the foundation of chemistry 
 was laid by Black, Priestley, Lavoisier and Dalton, 
 and when the walls began to be raised by Berzelius 
 
SUMMARY AND CONCLUSION. 325 
 
 and Davy, it was possible for one man to hold in his 
 mental grasp the whole range of subjects which he 
 studied. 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 now. But 
 we have in great measure ourselves to blame ; we 
 have of late years too much fulfilled Liebig's words, 
 when he said, that for rearing the structure of or- 
 ganic chemistry masters were no longer required 
 workmen would suffice. 
 
 And I think we have sometimes fallen into 
 another error also. Most of the builders of our 
 science notably Lavoisier and Davy, Liebig and 
 Dumas were men of wide general culture. Che- 
 mistry was for them a branch of natural science ; 
 of late years it has too much tended to degenerate 
 into a handicraft. These men had lofty aims ; 
 they recognized Davy perhaps more than any 
 the nobility of their calling. The laboratory 
 was to them not merely a place where curious 
 mixtures were made and strange substances ob- 
 tained, or where elegant apparatus was exhibited 
 and carefully prepared specimens were treasured ; 
 it was rather the entrance into the temple of 
 Nature, the place where day by day they sought 
 for truth, where, amid much that was unpleasant 
 and much that was necessary mechanical detail, 
 glimpses were sometimes given them of the order, 
 harmony and law which reign throughout the 
 material universe. It was a place where, stop- 
 ping in the work which to the outsider appeared so 
 
 Y3 
 
326 HEROES OF SCIENCE. 
 
 dull and even so trivial, they sometimes, listening 
 with attentive ear, might catch the boom of the 
 " mighty waters rolling evermore," and so might 
 return refreshed to work again. 
 
 Chemistry was more poetical, more imaginative 
 then than now ; but without imagination no great 
 work has been accomplished in science. 
 
 When a student of science forgets that the par- 
 ticular branch of natural knowledge which he 
 cultivates is part of a living and growing organism, 
 and attempts to study it merely as a collection of 
 facts, he has already Esau-like sold his birthright 
 for a mess of pottage ; 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 full, but which he is always going on 
 to know " to be ever encompassed about by the 
 greatness of the subject which he seeks to know ? 
 Does he not recognize that, although some of the 
 greatest minds have made this study the object of 
 their lives, the sum of what is known is yet but 
 as a drop in the ocean ? 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 way ? 
 
 It is not easy to remember the greatness of the 
 issues which depend on scientific work, when that 
 work is carried on, as it too often is, solely with 
 the desire to gain a formal and definite answer to 
 some question of petty detail. 
 
SUMMARY AND CONCLUSION. 327 
 
 " That low man seeks a little thing to do, 
 
 Sees it and does it : 
 
 This high man, with a great thing to pursue, 
 Dies ere he knows it. 
 
 " That lojv man goes on adding one to one, 
 
 His hundred's soon hit : 
 This high man, aiming at a million, 
 Misses a unit." 
 
INDEX. 
 
 Acids, connected by Lavoisier with 
 oxygen, 91 ; Boyle's and other early 
 definitions, 171 ; opposed in early 
 medicine to alkalis, 172 ; grouped, 
 173 ; salts, 173 ; " the primordial 
 acid," 174 ; oxygen not a necessary 
 constituent, 184 ; new division of 
 acids by Davy, 205 ; acids of different 
 basicity, 237 ; modern conception of 
 acids, 301. 
 
 Affinity, chemical, apparently suspended 
 by electricity, 191 ; history of term 
 "affinity," 206; tables of, 207; 
 dependent on electric states, 210. 
 
 Air, composition of, determined by 
 Cavendish, 79 ; Dalton's investiga- 
 tions, 116. 
 
 Alchemy, 5 ; alchemical symbols of 
 metals, n ; quotations from alchemists, 
 15, 17 ; alchemical poetry, 18. 
 
 Alcoates, 235. 
 
 Alkalis, 171 ; fixed and volatile, 173 ; mild 
 and caustic, examined by Black, 176 ; 
 their connection with earths, 178 ; 
 name of " base " given by Rouelle, 
 179 ; Gay-Lussac's alkalizing principle, 
 203. 
 
 Ammonia, discovered by Priestley, 66. 
 
 Atmolysis, 243. 
 
 Atomic theory, dawn of, 117 ; early views 
 of Greek philosophers, 123 ; of 
 Epicurus and Lucretius, 124 ; of 
 Newton and Bernouilli, ijy, ; Dalton's 
 new views combination in simple 
 multiples, 127, et seq. ; the theory 
 made known by Dr. Thomson, 129 ; 
 it is opposed at first by Davy, 130 ; 
 Dalton's rules for arriving at atomic 
 weights, 132 ;, more accurately applied 
 by Berzelius, 03. 162 ; diagrams of 
 atoms, 118, i36;the theory as carried 
 out by Gay-Lussacjyid A vogadro, 138, 
 et seq. ; conception pf the molecule, 
 
 140; molecular and atomic weight, 
 145 ; Graham's work on molecular 
 reactions, 249 ; B^erzelius's dualistic 
 views, 21*2 ; they are attacked by 
 Dumas, 260 ; conception of the com- 
 pound radicle, 267 ; Laurent's unitary 
 theory, 272 { modern conception of 
 molecule, 275 ; revision of atomic 
 weights, 285 ; equivalency of atoms, 
 
 2 95- 
 
 Avogadro, his elucidation of the atomic 
 theory, 138, etseq. ; introduces the idea 
 of molecules, 140; law known as 
 Avogadro's law, 143. 
 
 B 
 
 Base (of salts), 179 ; basic lines in spec- 
 trum, 311. 
 
 Becher, John J. , born at Speyer, 26 ; his 
 three principles of metals, 26 ; his 
 principle of inflammability, 48 ; his 
 views on acids, 174. 
 
 Berthollet, analyzes ammonia, 66 ; 
 adheres to the Lavoisierian theory 
 of combustion, 95 ; questions doctrine 
 of fixity of composition, 126 ; and 
 necessary presence of oxygen in acids, 
 184 ; shows variable nature of affini- 
 ties, 208. 
 
 Berzelius, JohannJ., 106; determines 
 weights of elementary atoms, 133 ; 
 his birth and education, 157 ; works 
 at Stockholm, 159 ; his slight appli- 
 ances and large discoveries, 161 ; he 
 reviews Dalton's atomic theory, 162 ; 
 his views superseded by Avogadro's 
 generalization, 165 ; he accepts law 
 
 cation, 212; wocks at organic che- 
 mistry, 2g ; his dualism attacked by 
 Dumas 260* 
 
330 
 
 INDEX. 
 
 Slack, Joseph, born at Bordeaux, 30 ; 
 his education, 31 ; his thesis on 
 magnesia and discovery of " fixed 
 air," 33 et seq.] inquiries into latent 
 heat, 39 ; professor at Edinburgh, 41 ; 
 his death and character, 41, et seq. ; 
 resume of his work, 102 ; his examina- 
 tion of alkalis, 176. 
 
 Boyle, Hon. Robert, 25 ; his " Sceptical 
 Chymist," 76 ; law known as " Boyle's 
 law," 77 ; opposes doctrine of elemen- 
 tary principles, 93; his definition of 
 an acid, 171 ; extends the knowledge 
 of salts, 177. 
 
 Bromine, discovered by Balard, 291. 
 
 Carbonic acid gas, or " fixed air," studied 
 by Black, 35 ; by Priestley, 57, 69. 
 
 Cavendish, Hon. Henry, rediscovers 
 hydrogen, 63, 78 ; and composition of 
 water and air, 78. 
 
 Chloral, ) produced by Liebig, corn- 
 Chloroform, f position determined by 
 Dumas, 273. 
 
 Chlorine, discovered by Davy, 202 ; re- 
 places hydrogen in organic com- 
 pounds, 271. 
 
 Colloids, 247. 
 
 Combination in multiple proportions, 127. 
 
 Combustion, studied by early chemists, 
 24 (vide 11 Phlogistic theory") ; studied 
 by Black, 47 ; his views of Lavoisier's 
 theory, 51 ; Priestley's views of com- 
 bustion, 62 ; Lavoisier's experiments, 
 83, et seq. ; Liebig's combustion-tube, 
 263. 
 
 Compound radicle, 267 ; the idea of sub- 
 stitution, 270, 276. 
 
 Conservation of mass, doctrine of, 82. 
 
 Crystallization, water of, 237. 
 
 Crystalloids, 247. 
 
 Dalton, John, his birth and education, 
 107 ; " answers to correspondents," 
 109 ; his meteorological observations, 
 no; teaches at Manchester, no; 
 colour-blind, in ; pressures of gaseous 
 mixtures, 113 ; strives after general 
 laws, 115 ; first view of atomic theory, 
 117; visits Paris, 120; honours con- 
 ferred on him, 121, 122 ; dies, 123 ; 
 consideration of atomic theory (which 
 see), 123, et seq.; his "New System 
 of Chemical Philosophy," 129; fixes 
 atomic weight of hydrogen, 130 ; 
 small use he makes of books, 148 ; 
 
 inaccurate as an experimenter, 149 ; 
 his method compared with Priestley's, 
 151. 
 
 Davy, Sir Humphry, 106 ; opposes 
 the atomic theory, 129; accepts same, 
 130; studies the chemical aspects of 
 electricity, 185 ; experiments on the 
 acid and alkali said to be produced 
 by electrolyzing water, 186; apparent 
 suspension of chemical affinities by 
 action of electricity, 191 ; discovers 
 potassium, 197 ; and sodium, 198 ; 
 the metallic bases of earths, 200 ; 
 proves the elementary nature of 
 chlorine, 202 ; Davy's birth and 
 youth, 215 ; experiments on heat, 
 217 ; his work at Bristol, 218 ; inhales 
 gases, 220; lectures at the Royal 
 InstitutionV"222 ; discovers iodine and 
 invents safety-lamp, 224 ; dies, 226. 
 
 Dialysis, 247. 
 
 Diffusion-rates of gases, 241 ; distin- 
 guished from transpiration-rates, 
 242 ; diffusion-rates of liquids, 245. 
 
 Dulong, his law of atomic heat, 168. 
 
 Dumas, Jean B. A., birth and educa- 
 tion, 257 ; physiological studies, 258 ; 
 meets Von Humboldt, 259 ; attacks 
 the dualism of Berzelius, 260 ; Du- 
 mas's vapour density process, 262 ; 
 ethers and alcohols, 265 ; chlorine in 
 connection with organic compounds, 
 271 ; determines composition of chloral 
 and chloroform, 273 ; studies fermen- 
 tation, 287 ; member of the National 
 Assembly, 288 ; takes office, 289. 
 
 Earths, 177 ; Stahl's views, 178 ; the 
 connection between earths and alkalis, 
 178 ; their metallic bases, 182, 200. 
 
 Economy of waste materials, 300. 
 
 Electric affinity, 191, 210. 
 
 Electricity, Volta's battery, 185 ; used 
 to decompose water, 185 ; new metals 
 discovered by its help, 197. 
 
 Elements : old doctrine of elementary 
 principles opposed by Boyle, 93 ; 
 modern definition of element, 95 
 (vide " Spectroscopic analysis" basic 
 lines, 311). 
 
 Equivalency, conception of, 294. 
 
 Fermentation, studied by Dumas, 287. 
 Fourcroy, calls Lavoisier's views " La 
 chimie Franchise," 95 
 
INDEX. 
 
 331 
 
 Gay-Lussac, 138, 143, 201, 203, 257. 
 
 Gerhardt, 272, 279. 
 
 Graham, Thomas, early life, 233; 
 made Master of the Mint, 234 ; his 
 death, 235 ; studies alcoates, 235 ; 
 formulates conception of acids of 
 different basicity, 237 ; considers 
 hydrogen a metal, 238 ; investigates 
 phenomena observed by Dobereiner, 
 240 ; diffusion-rates of gases, 241 ; 
 of liquids, 245 ; his atmolyzer, 243 ; 
 his dialyzer, 247 ; studies movements 
 and reactions of molecules, 249. 
 
 H 
 
 Hales's experiments on gases, 34. 
 
 Heat, Black's study of latent heat, 39 ; 
 specific heat, 98 ; Dalton lectures on, 
 117; law of capacity for heat, 168 j 
 heat as produced by friction, 217. 
 
 Helmholtz, 143 ; vortex atoms, 125. 
 
 Hooke, Robert, his " Micographia," 24 ; 
 studies combustion, 34. 
 
 Humboldt, Alexander von, assists 
 Liebig, 256 ; and Dumas, 259. 
 
 Hydrochloric acid discovered by Priest- 
 ley, 66 ; a stumbling-block to La- 
 voisierian chemists, 200 j studied by 
 Davy, 201. 
 
 Hydrogen, rediscovered by Cavendish, 
 63 ; experimented on by Priestley, 
 66 ; its atomic weight decided by 
 Dalton, 130; Graham considers it a 
 metal, 238. 
 
 Iodine, discovered by Davy, 224. 
 Isomerism, 297. 
 Isomorphism, law of, 167. 
 
 Laplace, assists Lavoisie r , 90. 
 
 Latent heat, Black's theory of, 39. 
 
 Laurent, his unitary theory, 272, 278. 
 
 Lavoisier, Antoine L., born at Paris, 
 79 ; confutes idea of transmutation, 
 81 ; paper on calcination of tin, 84 ; 
 meets Priestley, 61, 85 ; his theory 
 of combustion, 51, 86 ; his chemical 
 nomenclature, 96 ; he is guillotined, 
 99 ; resume of his work, 103 ; his 
 views on salts, 183, 184. 
 ebig 1 , Justus, birth, 256 ; Humboldt 
 nnd Gay-Lnssnc, 257 ; his imoroved 
 combustion-tube, 263 ; studies the 
 cyanates, 264 ; distinction between 
 
 organic and inorganic chemistry 
 effaced, 265 ; produces chloroform 
 and chloral, 273 ; benzoyl, 274 ; he 
 leaves Giessen for Munich, 280 ; his 
 practical and economic discoveries, 
 283 ; death, 284 ; his failure to dis- 
 cover bromine, 291. 
 
 Lockyer. his work with spectroscope, 
 310 (and vide " Spectroscopic ana- 
 lysis H 
 
 M 
 
 Mayow, John, studies combustion, 24. 
 
 Metals, new, discovered by Berzehus, 
 101 ; by Davy, 197 ; hydrogen a 
 metal, 238. 
 
 Meyer, his views on acids, 174. 
 
 Mitscherlich's law of isomorphism, 167. 
 
 Molecule, conception of, 140 ; molecular 
 weight, 145 ; molecular mobility of 
 gases, 242 ; movements and reactions 
 of molecules, 249 ; modern concep- 
 tion of, 275. 
 
 Moryeau, De, embraces Lavoisier's 
 views, 96. 
 
 Muriatic acid (vide " Hydrochloric 
 acid,") 119. 
 
 N 
 
 Nitric acid, discovered by Priestley, 65 ; 
 
 produced by electrolysis, 188. 
 Nomenclature, Lavoisier's system of, 96. 
 
 Oil, principle of, 254. 
 
 Organic chemistry, worked at by Berze- 
 lius, 229 ; attempts to define it, 253 ; 
 loose application of the term, 255; 
 Wohler's manufacture of urea 
 abolishes distinction of organic and 
 inorganic chemistry, 265. 
 
 Oxygen discovered by Priestley, 59 ; 
 Lavoisier's experiments, 87 ; it is 
 viewed by him as an acidifier, 91, 
 175 , Berthollet shows it not a neces- 
 sary constituent of acids, 184 (vide 
 "Acids"). 
 
 P 
 
 Paracelsus, 13; his pamphlet, "Tripus 
 Aureus," etc., 19. 
 
 Petit, 168. 
 
 Phlogistic theory, 26; enunciated by 
 Stahl, 27 ; abandoned by Black, 46 ; 
 phlogiston described as a kind of 
 motion. 49 ; discovery of dephlogisti- 
 cated air, 59 ; the theory overthrown 
 by Lavoisier, 92. 
 
332 
 
 INDEX. 
 
 Phosphoric acid, 86. 
 
 Pneumatic trough, invented by Priestley, 
 
 Potassium, discovered by Davy, 197. 
 
 Prussic acid, discovered by Berthollet, 
 184. 
 
 Priestley, Joseph, born, 52; bred 
 for the ministry, 53 ; writes on elec- 
 tricity, 55 ; his pneumatic trough, 
 57 ; discovers oxygen, 59 ; meets 
 Lavoisier, 61, 85 ; goes to Birming- 
 ham, 65 ; his experiments on hydrogen, 
 66 ; his house burnt by rioters, 71 ; 
 emigrates to America, 72 ; dies there, 
 73 ; resume of his work, 102 ; his 
 method compared with that of Dalton, 
 
 Shelburne, Earl of, patron of Priestley, 
 58 ; to whom he grants an annuity, 
 65. 
 
 Spectroscopic analysis, 302 ; lines in 
 solar spectrum, 306; the solar atmo- 
 sphere, 308 ; Lockyer's mapping of 
 the lines, 310 ; basic lines, 311 ; 
 objections to his hypothesis, 313. 
 
 Stahl, George Ernest, born at Anspach, 
 27 ; enunciates the phlogistic theory, 
 27, 48 ; his " primordial acid," 174 ; 
 his essential property of earths, 178. 
 
 Sulphur dioxide, discovered by Priestley, 
 66. 
 
 Sulphur salts, discovered by Berzelius, 
 161. 
 
 Quantitative analysis neglected by early 
 chemists, 29 ; first accurately em- 
 ployed by Black, 33 ; used by Lavoi- 
 sier, 87. 
 
 Transmutation, confuted by Lavoisier, 
 
 81. 
 
 Transpiration of gases, 242. 
 Types, 279. 
 
 Respiration explained by Lavoisier, 91. 
 Revolution, French, its effect on Priest- 
 
 ley, 70 ; Lavoisier guillotined, 99. 
 Richter's equivalents of acids and bases, 
 
 162 
 
 . 
 Ripley, Canon, an alchemist, his poems, 
 
 18. 
 Rouelle, invents term " base," 179 ; his 
 
 studies on salts, 181. 
 
 Salts, 173 ; "principle of salt" opposed 
 by Boyle, 177 ; earth or alkali the 
 base of salts, 179 ; Rouelle's inquiries, 
 181 ; Lavoisier's definition, 184 ; con- 
 sidered as metallic derivatives of 
 acids, 205 ; alcoholic salts, 235. 
 
 "Sceptical Chymist, The," by Hon. 
 Robert Boyle, 76-93. 
 
 Valentine, Basil, an alchemist, 15 ; his 
 
 views on alkalis, 174. 
 Van Helmont, 24. 
 Vitriols, 1 80. 
 Volta's electric pile, 184. 
 
 W 
 
 Water, its composition discovered by 
 Cavendish, 68-78 ; nearly discovered 
 by Priestley, 68 ; confirmed by La- 
 voisier, 90 ; decomposed by electricity, 
 185. 
 
 Weight of ultimate particles, 117, 132 ; 
 molecular and atomic, 145 ; revision 
 of atomic weights, 285. 
 
 Wohler, his account of visit to Berzelius, 
 160, 204, 229 ; studies cyanates with 
 Liebig, 264 ; results of his discovery 
 as to urea, 265. 
 
 Wollaston, supports atomic theory, 130. 
 
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