JOHN DALTON. 
 
 FEOM AN ENGEAvisra BY C. H. JEEXS. 
 (By permission of Messrs. Macmillan $ Co.} 
 
ISBISTERS' HOME LIBRARY 
 
 THE 
 
 STORY OF CHEMISTRY 
 
 BY HAROLD W. PICTON B.Sc. 
 
 WITH A PREFACE BY SIR HENRY ROSCOE 
 
 M.P., D.C.L., LL.D., F.R.S. 
 
 LONDON 
 ISBISTER AND COMPANY LIMITED 
 
 15 & 16 TAVISTOCK STREET COVENT GARDEN 
 
LONDON t 
 
 PRINTED BY J. S. VIRTUE AND CO., LIMITL'D, 
 CITY ROAD. 
 
TV 
 
 PREFACE. 
 
 AM pleased to be asked to introduce 
 this little book to the notice of the 
 English public. The author has, in 
 my opinion, told his story brightly 
 and truly, and in a way to interest those who 
 have some knowledge of our science, as well as 
 those who wish to gain that knowledge. 
 
 A short and attractive history of Chemistry 
 
PREFACE. 
 
 has long been wanted, and my friend the author 
 seems to have written just such a book as was 
 needed. 
 
 H. E. BOSCOE. 
 
 10, BRAMHAM GARDENS, 
 WETHERBY ROAD, g.W v 
 
 October, 1889. 
 
CONTENTS. 
 
 PREFACE. BY SIR HENRY ROSCOE 
 
 INTRODUCTION 
 
 I. CHEMISTRY BEFORE THE ALCHEMISTS EMPIRICISM 
 
 FIRST PERIOD : ALCHEMICAL MYSTICISM. 
 II. ALCHEMICAL MYSTICISM 
 
 SECOND PERIOD : MEDICAL MYSTICISM. 
 
 III. BASIL VALENTINE . 
 
 IV. PARACELSUS VAN HELMONT 
 
 PAGS 
 
 5 
 
 13 
 23 
 
 37 
 
 55 
 79 
 
 THIRD PERIOD : THE DECLINE OF MYSTICISM. 
 V. GLAUBER 97 
 
 FOURTH PERIOD : THE BEGINNINGS OF SCIENCE. 
 
 VI. THE BEGINNINGS OF SCIENCE 113 
 
 Vir. THE ACKNOWLEDGMENT OF NESCIENCE . . .119 
 VIII. HOOKE MAYOW HALES ..... 137 
 
yiii CONTENTS. 
 
 'FIFTH PERIOD: THE CHILDHOOD OF TRUTH. 
 
 CHAP. PAGE 
 
 IX, CULLEN BLACK 157 
 
 SIXTH PERIOD: THE CONFLICT WITH ERROR. 
 
 X. THE BIRTH OF ERROR 175 
 
 XI. THE FIRST OF AUGUST, 1774 185 
 
 XII. TRUTH IN DISGUISE . . , . . . .211 
 
 SEVENTH PERIOD : THE TRIUMPH OF TRUTH. 
 
 XIII. LAVOISIER 231 
 
 EIGHTH PERIOD : THE ATOMIC THEORY. 
 
 XIV. D ALTON'S IDEA 257 
 
 XV. THE DEVELOPMENT OF DALTON'S IDEA . . .277 
 
 XVI. THE ATOMIC THEORY OF TO-DAY .... 293 
 
 XVII. DAVY AND FARADAY 317 
 
 NINTH PERIOD : THE MODERN SCIENCE. 
 
 XVIII. MODERN INORGANIC CHEMISTRY .... 343 
 XIX. ORGANIC CHEMISTRY TO-DAY 360 
 
 CONCLUSION ......... 382 
 
INTRODUCTION. 
 
 THE ALCHEMIST. 
 
 HE early history of chemistry sounds more 
 like fiction than fact. A romance clings 
 about the stories of the old alchemists 
 which lends them irresistible charm. We 
 may perhaps best get a notion of their 
 character by paying an imaginary visit to 
 an alchemistic laboratory of, say, the fourteenth cen- 
 tury. 
 
 It is a winter's evening and the wind moans melan- 
 choly without. We are in a long gloomy room. 
 Above us age-grimed oak rafters stretch away into 
 the dim shadows of the roof. Smoke and furnace- 
 fumes hang dusky in the air. Glowing eyes seem to 
 gleam at us through chinks in furnace doors. Strange 
 distorted alchemistic vessels stand silently working 
 
i 4 INTRODUCTION. 
 
 out their secret wonders, or lie carelessly neglected 
 on their shelves. Phials filled with deep-coloured 
 liquids stand here and there picturesquely tinged by 
 fitful gleams of fire-light. Open folios lie scattered here 
 and there, the pages covered with mystic writing and 
 cabalistic signs. And there, bending over a heated 
 crucible and watching its contents with grave concern, 
 stands the alchemist himself. 
 
 Beside him an assistant is urging the bellows, and 
 the fire throws a ruddy glow on the face of each. 
 The alchemist is venerable and careworn. His dark 
 eyes look out from under shaggy eyebrows, and just 
 now the forehead is knit in anxious thought. Will 
 his labour succeed ? For years he has sought the 
 true method of preparing the substance at whose 
 touch all metals shall become gold. Now at last the 
 time of successful trial seems at hand. In that small 
 crucible his whole labour is to find its issue, and here 
 and now the great secret is to be won or lost. Two 
 metals are here molten together, and upon them the 
 miracle is to be worked. From their baseness is to 
 come forth pure, lustrous gold. 
 
 The alchemist knits his brows a little closer as the 
 time seems ripe for projection ; he motions his assis- 
 tant to stop the blast, and taking from his breast a 
 small piece of yellow wax enclosing a few red grains 
 dsops it upon the molten mass. A quick bubbling 
 is heard and light puffs of smoke are blown out from 
 the crucible. Presently the bubbling ceases, but the 
 smoke is pouring out faster than ever. It mounts 
 
INTRODUCTION. 15 
 
 in the air and floats in light wreaths round alchemist 
 and servant. It grows denser and obscures the light 
 of the furnace, rolls upwards among the rafters and 
 down into the dark corners, making all darker and 
 mistier and more unreal. Crucibles, folios, alembics, 
 and alchemist are fast vanishing in it, and at length, 
 puff! the whole room, with its workers and their 
 mysteries, has vanished into the dreamland of fancy 
 .from which it sprang. We are back in the nineteenth 
 century again ; but, for all that, we have caught a 
 glimpse of the alchemist at his task. 
 
 Now let us ask who were the alchemists, and 
 what was their work ? The alchemists were a body 
 of men who flourished from the early centuries of 
 the Christian era to the close of the seventeenth 
 century,* and whose main guiding star in their 
 search for knowledge was their belief in the trans- 
 mutation of the baser metals into gold. They 
 sought to prepare the ''philosopher's stone," and 
 it was at the touch of this that transmutation was 
 to occur. Some, it is true, sought in the stone 
 a universal medicine rather than inexhaustible lucre. 
 It was to cure all diseases and ills of flesh. Among 
 such seekers was Geber, perhaps the first alchemist 
 of whom we have record. But Geber seems to have 
 been far more truly scientific than, with very few 
 exceptions, any of his successors for the next six 
 hundred years. 
 
 * Even at the close of the eighteenth century a fefa scattered alche- 
 mists like Peter Woulfe were known. Woulfe died in 1805. 
 
i6 INTRODUCTION. 
 
 It cannot be said then that these men were in the main 
 moved by any very noble ambition. On the whole 
 their object was to find a way to make gold a desire 
 indeed not yet extinct. Still, the alchemist usually 
 had some other interests as well as this which dis- 
 tinguished him from his modern counterpart. Where 
 in his search he chanced to discover other interesting 
 bodies he would not seldom describe them with some 
 care, and in this way made real contributions to 
 science. The alchemists, we may with much proba- 
 bility say, never achieved the main hope of their 
 quest, but in their search for it they achieved much 
 that was far better. Their dreams were not healthy 
 enough to be realised, but the cold realities with 
 which they were disappointed were to fall as cherish- 
 ing snow-flakes above the hidden seeds of truth, 
 which else had withered with the frost. Put in its 
 most matter of fact way they looked for gold, and 
 instead of it they found nitric and sulphuric acids, 
 many other chemicals, and much useful apparatus. 
 
 This may seem somewhat paltry by comparison, 
 but is really not so. It reminds us of an old tale 
 of long ago in which a dying countryman informs his 
 sons that in the farm he is leaving them there lies a 
 hidden treasure. The man has much neglected his 
 farm, and it is thickly grown with weeds ; but among 
 them the treasure must be sought. The sons natu- 
 rally set about digging over the land here and there 
 in their search. But dig where they will the mine 
 of gold and gems they pictured is not found. At 
 
INTRODUCTION. 19 
 
 last every inch is dug over, and they think their 
 father must have been wandering in his mind. But 
 now, things being as they are, they determine to 
 make the best of a bad business, and as the ground 
 is open they proceed to sow and plant. This is done, 
 and in due season, when the crops are growing and 
 the fruit is rounding on the branch, they bethink 
 them once more of the promised treasure. As the 
 money comes in for the immensely increased produce 
 of the farm it strikes them that the treasure their 
 father meant was the unused fruitfulness of the soil; 
 and now, in seeking for the apparently delusive pro- 
 mise, they have found what was much better, the 
 reward of honest industry. 
 
 Having thus briefly seen who were the alchemists 
 and how their work was connected with the chemistry 
 of to-day, we shall in the. next chapter sketch in out- 
 line the chemical knowledge already acquired before 
 their time, the material ready to hand for their use. 
 In the sequel we shall pass briefly in review some of 
 the more renowned and interesting alchemists in 
 chronological order, and endeavour to see more clearly 
 what they actually did for chemistry. 
 
 But before closing this chapter it may be suitable 
 to give one of the many stories of transmutation, which 
 we find related by writers of repute with apparently 
 the sincerest belief in their truth. The story is told 
 by Mangetus, the editor of " Bibliotheca Chemica 
 curiosa ...-." (1702) on the authority of M. Gros, 
 a clergyman of Geneva, said to be of the most unex- 
 
2 o INTRODUCTION. 
 
 ceptionable character, a skilful physician and an expert 
 chemist. About the year 1G50 an unknown Italian 
 came to Geneva and took lodgings at the sign of the 
 Green Cross. Wishing to see what was to be seen 
 at Geneva he requested his landlord, De Luc, to pro- 
 cure him a guide to the to"vvn. De Luc was acquainted 
 with M. Gros, at that time about twenty, and a 
 student of Geneva, and knowing his proficiency in 
 Italian requested him to accompany the stranger 
 about the town. M. Gros at once acceded to this 
 request, and for the space of a fortnight acted the 
 part of guide to the Italian. When this time had 
 elapsed the stranger began to complain of want of 
 money. M. Gros became somewhat alarmed, fearing 
 that he might be asked for a loan, and not being in 
 a position to lose much money without inconvenience. 
 But the Italian only asked to be conducted to a gold- 
 smith who would lend him his blowpipe and utensils 
 for a short space. 
 
 Such a goldsmith was found in the person of 
 M. Bureau, to whom M. Gros conducted his acquaint- 
 ance. M. Bureau courteously placed his workshop 
 at the Italian's disposal, and there left him with 
 M. Gros and a workman, The Italian then at 
 once proceeded, before the astonished gaze of the 
 clergyman, to melt tin in one crucible and heat some 
 quicksilver in another. When the crucibles were 
 hot he poured the mercury upon the molten tin and 
 projected upon it "a red powder enclosed in wax/' 
 A rapid reaction seemed to occur, the mass bccrmo 
 
INTRODUCTION. 21 
 
 agitated, fames were exhaled, and the metals were 
 forthwith converted into pure gold, yielding six heavy 
 ingots. The identity of the product with gold was 
 not allowed to rest upon its appearance alone, for it 
 was submitted to a 1 ! the tests then known and certi 
 fled by the goldsmith to be pure. Furthermore the 
 ingots were taken to the mint, so says the account, 
 and Jhere exchanged for a large sum in Spanish coin. 
 As eome token of his indebtedness, the stranger pre- 
 sented M. Gros with twenty pieces, while fifteen more 
 were given jointly to M. Gros and M. Bureau for their 
 own entertainment. 
 
 And now comes the dramatic climax to the scene. 
 The mysterious Italian proceeded to order for that 
 evening a sumptuous supper for the three with which 
 to celebrate the occasion. He then went out, and as 
 the day passed and the ; evening came they waited in 
 vain for his return. He never came back, and the 
 secret of the transmutation had gone with him. 
 
 This is a very circumstantial account ; but as no 
 detailed directions have ever been given for success- 
 fully performing such transmutation, and as the sub- 
 ject is one where imposture or inaccuracy must be 
 peculiarly liable to creep in, we can only conclude, 
 with a very high degree of probability, that the 
 above is not a case of the actual transmutation of 
 metals into gold. There is no doubt that the alche- 
 mists' ideas gave rise to a vast amount of deliberate 
 deception of others, and still more muddleheaded de- 
 ception of self. A race of jugglers, severely satirised 
 
22 INTRODUCTION. 
 
 in Ben Jonson's Alchemist, arose who traded upon the 
 gullibility of their dupes most successfully and most 
 mercilessly. To these latter they could give easy evi- 
 dence of their power by stirring the mixture in their 
 crucibles with hollow rods containing oxide of gold 
 or silver within and having the lower end closed 
 with wax. In this way by the reduction of the oxide 
 they could obtain particles of metallic gold. 
 
 Another form of imposture, it is said, was to use 
 crucibles having a false fusible bottom, below which 
 oxide of gold or silver was contained. Or nails were 
 dipped into an appropriate liquid and drawn out half 
 converted into gold. The nails consisted of gold 
 soldered to iron, and covered so as to conceal their 
 colour. It was possible also for the alchemist himself to 
 be deceived by such an operation as that of cupelling 
 argentiferous lead* in a crucible of ashes or pulverised 
 bones. The lead then disappears, being oxidised and 
 sinking into the porous crucible, leaving the silver 
 behind. To one having imperfect knowledge of what 
 took place, it might well seem that the lead was con- 
 verted into silver. And so, indeed, the main fabric 
 of alchemy was a fairy palace resting upon the basis of 
 a false dream. Its ruin was sure, but from its shat- 
 tered fragments the workers of to-day are building a 
 fabric which to-morrow will be fairer than the fairest 
 dream. 
 
 * That is lead containing silver. 
 
CHAPTER I. 
 
 CHEMISTRY BEFORE THE ALCHEMISTS. EMPIRICISM. 
 
 JKE GO many other accomplishments of civili- 
 sation chemistry may probably be traced 
 back to an Egyptian origin. In the mys- 
 teries of the Egyptian temples is found 
 the beginning of the sacred art. In the 
 third and fourth centuries the learning of 
 Egypt was the fashion. As the power of Egypt de- 
 clined the art passed thence, and from Greece, about 
 the beginning of the ninth century, into the hands of 
 the Arabians, who produced some of the earliest true 
 men of science. 
 
 The Arabians were certainly real enthusiasts, and in 
 their treaties with the Greeks of Constantinople there 
 occurred repeated stipulations for the surrender of 
 particular manuscripts. To show how strangely in 
 
24 CHEMISTRY BEFORE THE ALCHEMISTS. 
 
 some respects knowledge remained for a long period 
 quiescent we may mention, as a small, though strik- 
 ing instance, that in Part V. of his Opus ALyns 
 Roger Bacon quotes from the Arabian philosopher 
 Alhazen. a description of the anatomy of the eye 
 which, in all essential particulars, is identical with 
 that set forth in modern anatomical text-books. 
 Having got so far, the progress of knowledge for 
 several centuries well-nigh ceased. Indeed, as for 
 chemistry itself, it has only since the opening of the 
 present century thrown off its swaddling clothes. 
 
 Alexander of Aphrodisia invented the term chymike 
 to describe the operations of the laboratory. Hence 
 the word che:nics, a word unknown in the fourth cen- 
 tury, and only popular some centuries later. Later, 
 when men reflected that the old name of Egypt was 
 Cham or Chemia, it flattered the chemists to call their 
 art the art of the ancient Ghemi. Such is the power 
 of words that this false derivation gave fresh impulse 
 to the science. 
 
 We must now give some account of the chemical 
 knowledge acquired, and the chemical notions enter- 
 tained, by the ancients previous to the time of Geber 
 (eighth century), and may in passing point out some 
 of its connections with the knowledge of a later day. 
 Their ideas were of course very vague, and their 
 knowledge had been arrived at by chance and empiri- 
 cally* rather than by intelligent research. Aristotle, the 
 
 * Empiric, empirical, empiricism, are words that need careful 
 definition. They are derived from a Greek word signifying experi- 
 ences. But all knowledge is derived from experience, and, therefore, at 
 
CHEMISTRY BEFORE THE ALCHEMISTS. 25 
 
 great Greek philosopher, looked upon the universe as 
 built up from the four " elements," earth, fire, air, 
 and water, and with such theories science could not 
 progress far. We shall see later on how at the present 
 time we have come to regard an " element " as any 
 substance which we cannot by any known process split 
 up into two or more different things. 
 
 Seven metals were known to the ancients* gold, 
 silver, mercury, copper, tin, lead, and iron. None is 
 more commonplace to us now than the last, but 
 in these early days it was thought very precious 
 indeed, owing to the difficulty of working it. Copper 
 was then more extensively used than any other metal, 
 and generally alloyed with tin to form bronze. This 
 alloy, bronze, was much used for coinage and for 
 statuary. Here is an analysis of three different 
 bronzes for ' comparison. Each gives the amount of 
 copper and other metals in one hundred parts of the 
 
 bronze. 
 
 I. II. in. 
 
 Copper ... 84-53 99'3 8877 
 
 Tin .... 6-82 07 9-25 
 
 Lead .... 8-65 .. 070 
 
 Zinc 1*28 
 
 first sight, it would appear that empiricism must be the right method 
 of acquiring knowledge. The meaning of words, however, depends 
 not only on derivation, but on accidental use, and "empiricism" 
 happens to have been used chiefly of chance experiences occurring 
 irregularly and without any ordered plan of research An instance 
 of empiricism is found in the discovery of glass, described in Chapter 
 II. The researches of Black on lime and magnesia, described in a 
 later chapter, afford an example of ordered research or induction of a 
 high order. 
 
 * Many of the facts in this chapter are obtained from Thomson's 
 History of Chemistry, 
 
26 CHEMISTRY BEFORE THE ALCHEMISTS. 
 
 I. A Roman bronze coin of Justinian. 
 
 If. Bronze statues of horses in the portal of St. Mark's, Venico 
 ( about A.D. 430). 
 III. Thorwaldsen's " Shepherd " (cast in Berlin, 1825). 
 
 In working and casting metals the ancients were 
 very advanced. The bronze statue of Apollo placed in 
 the capitol in the time of Pliny* was forty-five feet in 
 height and cost five hundred talents, equal to about 
 50,000. The statue of the sun at Rhodes (the 
 " Colossus of Rhodes ") was the work of Chares, a 
 disciple of Lysippus. According to one account it 
 was a hundred and five feetf in height, was twelve 
 years in making, and cost three hundred talents 
 (30,000). It bestrode the entrance to the harbour, 
 and ships could pass full sail between its legs. A 
 winding staircase ran to the top, and the shoulders 
 afforded an excellent point of view. For about fifty- 
 six years this tower of bronze stood unhurt and was 
 then overthrown and partly ruined by an earthquake. 
 Money was subscribed to the Rhodians to restore it 
 to its place. This they divided among each other 
 and excused themselves by an oracle from Delphi 
 which forbade them to raise the statue. For nine 
 hundred years it lay on the ground and was at last 
 sold to a merchant who loaded nine hundred camels 
 with its fragments. Iron and steel were used in the 
 time of Pliny, but of the method of working them 
 there is little record. 
 
 Various mineral colouring matters were used, as 
 for instance, minium (red lead), which is an oxide of 
 
 * First century A.D. 
 
 t Thomson gives ninety feet. 
 
CHEMISTRY BEFORE THE ALCHEMISTS. 27 
 
 lead ; cinnaberis (cinnabar) or sulphide of mercury, 
 &c. Some dyes were also prepared, the most impor- 
 tant being the celebrated Tyrrhian purple discovered 
 about 1500 B.C. This colouring matter was extracted 
 from two kinds of shell- fish found in the Mediter- 
 ranean. The ordinary process of calico-printing is to 
 stamp the material at certain parts with "mordants" 
 which fix the colour in its meshes. It is then 
 steeped in the dye, after which the colouring matter 
 may be washed out from the unmordanted portion, 
 leaving the pattern stamped in colour on the material. 
 This process seems to have been known in ancient 
 times in India and the East, and probably to the 
 Egyptians. 
 
 Among the most important chemical products 
 known to the ancients was the invaluable substance, 
 glass. Glass beads are found on Egyptian mummies 
 which date back to some thousands of years B.C. 
 Glass consists mainly of a compound of silica with 
 soda and lime. Silica is a white substance occurring 
 in nearly all rocks and existing almost pure in white 
 sand. The glass is made by fusing soda-ash with 
 sand, the lime being added in various forms such as 
 calc-spar, chalk or limestone, according to circum- 
 stances. Its original discovery as described by Pliny 
 has thus by no means any great improbability. 
 According to his account some Phoenician merchants, 
 in a ship loaded with carbonate of soda from Egypt, 
 stopped and went ashore on the banks of the river 
 Belus. Having nothing to support their kettles 
 they used lumps of carbonate of soda : the fires melted 
 
28 CHEMISTRY BEFORE THE A L CHEMISTS. 
 
 this and fused it into the sand of the river, thus 
 .forming glass. In Pliny's time too, coloured glasses 
 were decolourised by the addition of manganese in 
 the making, just as now. 
 
 Starch was known to the Greeks and its manu- 
 facture is described by Pliny. It was prepared by 
 Avashing wheaten flour by processes similar to those of 
 the present day. It may not be out of place to 
 shortly describe these here. Wheat, maize, rice, and 
 potatoes consist very largely of starch. From these 
 sources it is obtained by rasping or grinding the 
 vegetable structure to pulp and washing the mass 
 upon a sieve, by which the torn cellular tissue of the 
 plant is retained. The starch passes through and 
 settles dwn from the liquid in the form of a fine 
 white powder. Examined by the microscope it is 
 seen to consist of little rounded, concentrically 
 striated particles, the appearance of which differs 
 characteristically in different plants. The chemical 
 constitution of starch is a subject which has given 
 rise to much labour and discussion. We may gain 
 some insight into the amount of labour involved in 
 the thorough study of one apparently commonplace 
 body by noticing that in a recent famous paper upon 
 starch by two chemists, Brown and Heron, the 
 authors in their introduction remark that more than 
 four hundred papers have already appeared on the 
 same subject. 
 
 Porcelain and stoneware are made by heating 
 various clays with a " frit," " flux," or fusible 
 
CHEMISTRY BEFORE THE AL CHEMISTS. 29 
 
 material. Porcelain is obtained when the whole 
 mass is thoroughly permeated by the frit, and is 
 thus semi-transparent or translucent. Earthen- 
 ware is made from a coloured plastic clay which 
 forms a porous mass w 7 hen baked. It is then 
 glazed. The history of porcelain is of no little 
 interest. The first discovery is lost far back in the 
 unrecorded ages of the great Chinese empire. Like 
 much other knowledge which Europeans had pain- 
 fully to rediscover for themselves it lay there totally 
 hidden. To the Romans the art was wholly un- 
 known,* and remained so to the rest of Europe for 
 many centuries, till in 1709 the method of making it 
 was discovered by Eotticher and a manufactory was 
 established at Meissen, in Saxony. This manufacture 
 was kept strictly secret, and the King of Prussia 
 instructed the celebrated chemist Pott to find the 
 secret out. Pott could obtain no details as to the 
 materials actually used. His only plan was to choose 
 those which seemed suitable, to mix them together 
 in varying proportions and see what happened. It is 
 said that Pott's experiments in this w T ay reached the 
 enormous total of thirty thousand. After all he did 
 not discover what he sought, but to his work we owe 
 much valuable information. He was followed in the 
 search by Re'aumur and other French chemists, and 
 finally the lost art was rediscovered, and in 1769 the 
 great Sevres manufactory was founded. It is only 
 
 * The art of pottery, i.e. the opaque ware, of course never became 
 extinct. 
 
30 CHEMISTRY BEFORE THE ALCHEMISTS. 
 
 during the present century that porcelain has become 
 an article of every-day use and is known to us more 
 familiarly as china. The knowledge of earthenware 
 or faience dates back to equally early times, but this 
 did not in the same way suffer extinction. In more 
 recent times it was the renowned Bernard Palissy 
 whose disinterested labours spread abroad a thorough 
 knowledge of this important product. 
 
 We shall next discuss the knowledge which the 
 ancients had attained of a very important article 
 important at least to us moderns. "The quantity 
 of soap," says Liebig, " consumed by a nation would 
 be no inaccurate measure whereby to estimate its 
 wealth and civilisation. Political economists, indeed, 
 will not give it this rank ; but whether we regard it 
 as joke or earnest, it is not the less true, that, of two 
 countries with an equal amount of population, we 
 may declare with positive certainty that the wealthiest 
 and most highly civilised is that which consumes the 
 greatest weight of soap. This consumption does not 
 subserve sensual gratification, nor depend upon 
 fashion, but upon the feeling of the beauty, comfort 
 and welfare attendant upon cleanliness ; and a regard 
 to this feeling is coincident with wealth and civilisa- 
 tion. The rich in the Middle Ages who concealed a 
 want of cleanliness in their clothes and persons under 
 a profusion of costly scents and essences, were more 
 luxurious than we are in eating and drinking, in 
 apparel and horses. But how great is the difference 
 between their days and our own, when a want of 
 
32 CHEMISTRY BEFORE THE ALCHEMISTS. 
 
 cleanliness is equivalent to insupportable misery and 
 misfortune ! " 
 
 Before the time of Pliny soap seems to have been 
 unknown. The word is used in the Old Testament, 
 in one case for the Hebrew word nether, which 
 probably signifies trona or native carbonate of soda, 
 and in the other for borith, meaning the lye or solu- 
 tion obtained from the ash of a plant, arid which 
 contains the same ingredient. In the older Greek 
 period garments were washed with water onh r , and oil 
 was used to soften the skin after bathing. 
 
 Pliny is the first to mention soap. He describes 
 it as made from wood-ashes and tallow, and says it was 
 used as a pomade, and more among men than women. 
 In a work published in the second century soap is 
 stated to be used both as a medicine and for cleansing- 
 purposes. In early times, however, other cleansing 
 agents seem to have been more frequently used. 
 These included native carbonate of soda, the ashes of 
 sea-plants, and putrid urine. Among the many 
 secrets which the buried remains of Pompeii have 
 disclosed is the fact of the use of soap among the 
 Romans, at least in later times, for a complete soap- 
 boiling establishment has there been discovered. At 
 present soap is made from caustic alkalies (soda and 
 potash) and fats. 
 
 The ancients were acquainted with only one acid 
 vinegar, which is merely dilute acetic acid. It is 
 formed when alcoholic drinks turn sour, and is 
 obtained from alcohol by further fermentation. Its 
 
CHEMISTRY BEFORE THE ALCHEMISTS. 33 
 
 solvent properties are said to have been known to 
 Cleopatra when she boasted to Anthony that she 
 would consume an incredible value of food to her own 
 share at one meal. Towards the close of the appointed 
 meal she produced a goblet containing some weak 
 vinegar and dropped into this the two finest pearls 
 then known in the world. They at once dissolved 
 in the acid and in this way her one draught cost ten 
 million sestertii. This story is, however, of very 
 doubtful authenticity, pearls, indeed, being insoluble 
 in weak vinegar. 
 
 Of gases we find in these times really no knowledge 
 at all. Pliny's whole account of the air is that it 
 condenses itself in clouds and rages in storms. So too 
 of that most common body, water, little was known. 
 Its properties were too simple to be explained without 
 much greater progress, and our knowledge of water 
 may be said to commence with Cavendish in 1785. 
 
 Another substance which has acquired a rather 
 questionable importance among us, and which was 
 known to the ancients, is the old English beverage, 
 beer. The story of beer is a very old story indeed, 
 and, as Prof. Huxley says, " among the earliest records 
 of all kinds of men you find a time recorded when 
 they got drunk." The process of fermentation has 
 apparently been made use of from the earliest periods 
 of which we have any records handed down. The 
 question may be asked what is fermentation ? 
 Well, in spite of the long ages it has been in use it is 
 impossible to sny certainly what it is. But the way 
 
 c 
 
34- CHEMISTRY BEFORE THE ALCHEMISTS. 
 
 in which it is brought about is simple enough, and 
 much the same now as in ancient times. Grain 
 barley, for instance is steeped in cold water and 
 spread out, when it begins to sprout. In this 
 process part of its starch is changed into sugar. 
 The grain is now killed by heating it, and in this 
 state is called malt. The crushed malt is run into 
 a large vessel, the " mash tun," where it is mixed 
 with warm water. Here the rest of the starch 
 becomes changed into sugar, and it is this solution 
 of sugar which is fermented by adding common 
 yeast. Yeast is made up of a number 
 of little round bodies which are really 
 small plants. These grow in the li- 
 quid, and by their growth they some- 
 how manage to attack the sugar and 
 YEAST CELLS. form alcohol from it. If beer is being 
 -made the wort or infusion of malt is 
 first boiled with hops before fermenting. This gives 
 its characteristic bitter taste to the beer. 
 
 The Egyptians appear to have prepared beer from 
 malted grain, while wine, prepared by allowing grape- 
 juice to ferment, is mentioned in Homer and the Old 
 Testament. But as the ordinary methods of distil- 
 lation were in those times unknown, ardent spirits 
 and spirits of wine could not be obtained. Thus, 
 although alcohol had been for ages produced as a 
 drink, it was never obtained in anything like purity 
 till probably the time of the alchemist, Raymond 
 Lully, at the close of the thirteenth century, 
 
FIRST PERIOD. 
 
CHAPTER II. 
 
 FIRST PERIOD .- ALCHEMICAL MYSTICISM. 
 
 E shall now pass in review some of the work 
 of- the alchemistic teachers, and see how 
 air-built were their castles, and how they 
 failed to put foundations under them. We 
 shall find out how involved and mysterious 
 were their writings, but also how distinct 
 was their service to knowledge, and how patiently 
 they followed their lode-star even though it proved a 
 will-o'-the-wisp. In this Avay we may seek not in vain 
 among their broken alembics for some grains of a 
 wisdom whose price is more precious than gold or 
 rubies. 
 
 According to Suidas (who flourished in the eleventh 
 century), the art of alchemy was known as early as 
 the Argonautic expedition, the golden fleece being 
 
3 8 ALCHEMICAL MYSTICISM. 
 
 actually a treatise written on skins concerning the 
 making of gold. Such is the subtlety of exegetics. 
 
 Alchemy was also said to have originated with a 
 mysterious Hermes Trismegistus, an Egyptian. In a 
 reputed writing of Albertus Magnus it is said that 
 Alexander the Great discovered the tomb of Hermes, 
 in which were many golden treasures, and, most 
 precious of all, an emerald ta,ble on which was 
 inscribed a description of the preparation of the 
 philosopher's stone capable of curing all diseases. 
 The description is of course unintelligible, and after 
 an immense amount of controversy as to the claims 
 which these directions have to authenticity, it is now 
 almost certain that both they and the tract, attributed 
 to Albertus Magnus, in which they were inserted, are 
 altogether forgeries. The Tractatus Aureus is attri- 
 buted to Herrnes and is of the same type. To pre- 
 pare this mystic philosopher's stone we are directed 
 to " catch the flying bird," by which is meant quick- 
 silver (mercury), " and drown it so that it may fly 
 no more." This is what was afterwards termed the 
 fixation of mercury by uniting it to gold. And so on ; 
 the total result in the end probably being to increase 
 the weight of the gold by addition of impurity. So 
 much for the reputed founder of alchemy ! 
 
 The first alchemist of whom we have probably any 
 authentic record is Geber, an Arabian of the eighth 
 century, also known as Djafar, or in full as Abu Musa 
 Dschabir Ben Haijan Ben Abdallah el-Sufi el-Tarsusi 
 Kufi. If his writings are indeed authentic, they 
 
ALCHEMICAL MYSTICISM. 39 
 
 present us with one of those extraordinary instances 
 of a man born hundreds of years before his time, for 
 which it is difficult on any hypothesis to account. 
 Geber's reputed works are precise and clear to a degree 
 surpassing the best writers in the later alchymical 
 period. Older writings there are none. Subsequent 
 treatises as clear do not appear till far more know- 
 ledge had been acquired. His work stands out alone. 
 There seems indeed to linger in it the after-glow of 
 some previous sunset of knowledge, soon to be plunged 
 in almost starless night.* 
 
 Geber describes a number of metallic compounds, 
 such as green vitriol (a sulphate of iron), saltpetre, 
 corrosive sublimate (a chloride of mercury) . Possibly 
 the accounts given of various acids and salts may 
 have been added to at a later date. But his claims 
 to be considered the first propounder of a chemical 
 theory are probably valid. According to Geber's views 
 
 * Geber is mentioned in the Kitab-al-Fihrist (tenth century), by 
 Ibn Khallickan (thirteenth century) and others. If these references 
 are correct he nourished in the eighth century. His birth-place was 
 probably Tarsus and he resided at Damascus and Kufa, but some 
 have gone the length of altogether questioning his existence. The 
 titles of no less than five hundred of Dschabir's works on chemistry 
 are given in the Fihrist, and have been catalogued by Hammer- 
 Purgstall ; nothing more is known about the majority of them. 
 Arabic manuscripts on alchemy bearing the name of Dschabir Ben 
 Haijan exist in Leyden, Paris, and London. Geber describes many 
 chemical operations, such as filtration, crystallisation, and sublimation, 
 and was able, it seems, to prepare nitric acid, or aquafortis, and from 
 it the mixture aqua regia, a liquid almost fulfilling, at least in its 
 solvent properties, Van Helmont's dreams of the alcahest or universal 
 solvent, and the only acid dissolving gold. It consists of mixed nitric 
 and hydrochloric acids. 
 
40 ALCHEMICAL MYSTICISM. 
 
 all the metals are composed of the same " elements," 
 so that the less perfect may be developed into the 
 more perfect, or as he somewhat fantastically puts it, 
 " Bring me the six lepers, so that I may heal them, 53 
 that is transmute the six imperfect metals into gold. 
 The elements which he considered to be combined in 
 various proportions to produce the different metals 
 are sulphur and mercury. The mercury was supposed 
 to give the body its metallic characteristics. The 
 more mercury the substance contained the more truly 
 metallic it became, and the less readily altered by 
 heat or chemical agents. If much sulphur were 
 present the metal would, said Geber, be less perfectly 
 metallic and would lose its metallic properties in the 
 fire. But this was not all ; the mercury and sulphur 
 could exist in different degrees of purity and of 
 division, and these conditions also affected the cha- 
 racter of the metal so composed. Thus either by 
 changing the proportion of mercury and sulphur, or 
 by altering their condition, or by combining both 
 changes, we might reasonably hope to convert one 
 metal into another, and to convert all metals into 
 gold. Gold and silver were supposed to contain a 
 very pure mercury, combined in the first case with a 
 red, and in the second with a white sulphur. These 
 ideas are, as we shall see, adopted by Roger Bacon in 
 his Mirrour of Alchemy. 
 
 Now what are we to say of such ideas as these ? 
 Are we to treat them scornfully as unscientific and as 
 unworthy of recapitulation ? The suppositions have 
 
ALCHEMICAL MYSTICISM. 41 
 
 been disproved, it is true, but then so have innumer- 
 able hypotheses which were useful in their time. 
 The Copernican system which represented the planets 
 as moving round the sun in circular paths was given 
 up in favour of the view which regarded those paths 
 as an ellipse, but it was only by constructing the 
 first hypothesis and finding that to bo insufficient, 
 that the second could ever have been arrived at. 
 
 Again, the theory according to which matter is built 
 up of multitudinous minute particles called atoms 
 which cannot be divided, when philosophically con- 
 sidered, involves us in absurd inconsistencies. Never- 
 theless it has been an especially useful hypothesis in 
 helping us to a proper classification of chemical facts 
 for purposes of research. It is quite true that it will 
 not suffice in science to set about weaving fancies 
 without reference to fact ; but in trying to explain 
 things we are bound to make guesses at truth, and 
 some of our first guesses are sure to be wrong. The 
 proper way to treat the guesses which we call 
 hypotheses is to think out what logically follows 
 when we assume that they are true. If our deduc- 
 tions are found to coincide with fact the hypothesis 
 is probably valid, if not it is invalid. Thus if we were 
 to assume that the moon is made of green cheese, it 
 would follow from this that the weight of the moon 
 would be for its bulk very small, but this is known 
 not to be the case ; and moreover as many other 
 absurd and impossible or improbable results would 
 follow, such a hypothesis is obviously invalid. New- 
 
42 ALCHEMICAL MYSTICISM. 
 
 ton assumed that the force of gravity varied inversely 
 as the square of the distance, and the validity of this 
 hypothesis was proved by showing that Kepler's laws 
 of planetary motion, which were known to be true, 
 followed naturally from this assumption. 
 
 When we have got a hypothesis which in many 
 cases is workable but in some cases also fails, it may 
 still be of immense service, but we should not 
 hastily describe it as a fact. Of such a hypothesis, 
 for instance, as the atomic theory* we can say that 
 there is between this idea and the actual constitution 
 of matter sufficient analogy to make the former a 
 great help towards the appreciative study of many 
 scientific facts. But we have no right whatever to 
 say that this theory in any form rightly represents 
 what is the constitution of matter. Shortly then 
 the use of any hypothesis is to lead to a more appre- 
 ciative study of facts. One of the first fruits of this 
 study may be the proof that the hypothesis itself was 
 invalid, but that does not destroy its value as a means 
 to progress. In this light Geber's idea was a first 
 guess. It was wrong, but it at least led people to 
 think of the metals together, and as a class ; and was 
 the first step in a series of conjectures as to what 
 were the " elements " or simple substances out of 
 which complex bodies were composed. It was a 
 decided advance on the old Aristotelian notion of the 
 four elements, earth, fire, air, and water ; and it was 
 something to have escaped so early from the thraldom 
 
 * For the atomic theory see p. 257 
 
ALCHEMICAL MYSTICISM. 43 
 
 in which the ideas of Aristotle were destined to hold 
 the world for centuries to come. 
 
 After Geber we seem almost to go back. The 
 writings of his successors, for a long period, are in 
 most cases a farrago of mysterious nonsense broken by 
 rare deviations into sense. Their descriptions of their 
 experiments are among the most wonderful specimens 
 of a falsely metaphorical style on record. These 
 treatises are interesting, however, for the occasional 
 gleams of light they shed on the development of what 
 was to become a science. Some of the alchemists, 
 too, certainly did good work. After all they had few 
 means then of attaining their knowledge, and we can- 
 not justly scoff at those who, while seeking their 
 unsubstantial dreams, w r ere unconsciously preparing 
 the ground for the seed which later generations sowed, 
 seed now, though the sowers have long slept, spring- 
 ing forth into a full harvest of ripe grain. 
 
 Albert Groot, better known as Albertus Magnus 
 (1193 1282), was a German; a universal genius 
 he would probably be termed now, who after being 
 made Bishop of Ratisbon, gave up his bishopric to 
 follow science. He was theologian, physician, astro- 
 loger, and alchemist. In his chemical ideas, he fol- 
 lowed Geber, considering all metals to be composed 
 of sulphur and mercury. He describes various 
 apparatus, such as alembics and aludels, but it is 
 difficult, of course, to say how many of his ideas 
 were original. He is chiefly renowned as the com- 
 mentator of Aristotle. Alembics were used for 
 
44 ALCHEMICAL MYSTICISM. 
 
 distilling liquids. The aludel was used chiefly for 
 distilling solids which vaporise without melting, i.e. 
 for sublimation. 
 
 We next come to a name which, like Geber's, stands 
 out alone, though the bearer of it was greater as a 
 philosopher than as a chemist. Hoger Bacon was 
 a contemporary of Albertus Magnus, though the 
 dates of his birth and death are somewhat uncertain 
 (perhaps 1214 1284). In the course of his life 
 he passed through many vicissitudes. After studying 
 at Oxford, he enrolled himself as a Franciscan friar, 
 probably in order to pursue his meditations in peace. 
 He engaged in experimental research, thereby ac- 
 quiring an unenviable notoriety. One who cared 
 to study God's work, must, it was thought in those 
 days, be in league with the devil. Accordingly Bacon 
 was ordered to Paris, and there confined to his cell, 
 without writing materials, it is said, for ten years. 
 Imagine the torment this insane act of barbarity 
 must have caused to a man whose brain was seething 
 with thoughts struggling to be uttered, and theories 
 waiting to be tested by fact. For ten mortal years 
 to be compelled to silence, when some of the greatest 
 purposes of life could only be fulfilled in speech ; 
 for ten years to be forced into idleness, when a 
 millennium would be all too short to accomplish the 
 work waiting to be done! 
 
 But at length there intervened one whose soul 
 seems, at least, to have been above the superstitious 
 prejudices of his subordinates, Pope Clement IV. wa.s 
 
ALCHEMICAL MYSTICISM. 45 
 
 appealed to, and ordered Bacon forthwith to send him 
 any writings he might prepare. The restrictions as to 
 writing materials were then removed, and Bacon was 
 at work once more. The long pent-up flood of his 
 thoughts seems to have burst forth then in an over- 
 whelming torrent. In the next eighteen months 
 three large treatises were dispatched to the Pope 
 the Opus Majus, Minus, and Tertium the first itself 
 filling a large folio volume of print. In 12GS Bacon 
 returned to Oxford, and characteristically undaunted 
 by the penalties he had suffered, forthwith produced 
 a strongly-worded attack upon the Church, for 
 which he was once more promptly thrown into 
 prison. There it appears he remained for fourteen 
 years, being released in 1282, after which he pub- 
 lished his Campendium Studii Theologies and died 
 probably in. 12 84. 
 
 Condemnation of this treatment could not be ex- 
 pected for a long time after his death. The greater 
 a man is, indeed, the longer period must elapse 
 after his death before he is thought of as even not 
 below the level of the ordinary man. The ordinary 
 man is apt to honour people with reverence in pro- 
 portion as they conform more nearly to his own type, 
 so that a few flashes of diplomatic tact superimposed 
 upon invulnerable mediocrity afford an immediate 
 passport to popularity, though not to lasting fame. 
 Roger Bacon could not be mediocre, nor did he 
 stoop to be diplomatic. He was centuries in advance 
 of his contemporaries, and such presumption W as 
 
46 ALCHEMICAL MFSTICISM. 
 
 reckoned, as it ever is, unpardonable. It is only 
 of late years, indeed, that his position has come to 
 be appreciated, though some indignation had been 
 aroused at a much earlier date. Here is an extract, 
 for instance, from a writer of the seventeenth 
 century. 
 
 <( But such was the stupid ingratitude of Bacon's 
 age that it almost repented this learned man of 
 his knowledge. For his own order would scarce 
 admit his books into their libraries. And great was 
 this poor man's unhappiness : for being accused of 
 magick and heresy, and appealing to Pope Nicholas 
 the Fourth, the Pope liked not his learning, and by 
 his authority kept him close prisoner a great many 
 years." * 
 
 The stories told about Bacon were, of course, of the 
 wildest and most extraordinary kind. The best 
 known of them is embodied in a play of Robert 
 Greene's (1594), entitled The Honourable History 
 of Friar Bacon and Friar Bungay. The story is 
 here told of the famous brazen head, by the enchant- 
 ments of which the whole of England was to have 
 been walled with brass. Bacon sent his servant 
 Miles to watch it while he slept, with exhortations to 
 waken him if the head should speak. The head 
 merely uttered the words " Time is," for which Miles 
 thought it not worth while to waken his master. 
 The second speech, " Time was," did not suffice to rouse 
 
 * Bacon, Roger : His Discoveries of the Miracles of Art, $c. Trans- 
 lated by T. M. (London, 1659). 
 
ALCHEMICAL MYSTICISM. 47 
 
 him, and finally came the fatal words, " Time is past." 
 Then, as they have it in the play, " a lightning 
 flashes forth, and a hand appears that breaks down 
 the head. with a hammer." Miles now roused his 
 master at once, but it was, of course, too late. In 
 The Famous Historic of Fryer Bacon, a chap-book 
 of the year 1527, will be found this and many other 
 amusing stories. There seems no doubt that Koger 
 Bacon was one of the several people incorporated 
 in the old Faust legend. This will be seen by 
 reference to a curious old book, The Surprizing and 
 damnable life of Dr. Faustus.* 
 
 Of Bacon's works, we must make reference to the 
 Opus May us, though this is not strictly chemical, 
 but rather a treatise on the general principles of 
 science, t But as these principles have a bearing upon 
 chemistry as well as upon other sciences, and as, 
 moreover, Bacon insists strenuously upon the value 
 of experiment a doctrine the acceptance of which 
 is peculiarly necessary to the advance of chemical 
 science his work should have interest for every 
 chemist. 
 
 In Part IV. of the Opus Bacon upholds the 
 value of mathematics. Force, according to him, is 
 invariably subject to mathematical laws. If we 
 recollect, and it is certainly difficult to realise it, that 
 such ideas were promulgated in the thirteenth 
 
 * London (1608). 
 
 t Roger Bacon: Opus Majus (London, 1733, folio). See also an 
 interesting paper by Prof. R. Adamson (1876), on The Philosophy of 
 Science in the Middle Ages. 
 
48 ALCHEMICAL MYSTICISM. 
 
 century, while the great Kepler thought the revo- 
 lutions of the planets might be accounted for by 
 guiding spirits, we may be able to appreciate Bacon's 
 pre-eminence. In Part VI., Bacon treats of experi- 
 ment, and in a way more truly philosophical than 
 that of his successor Francis Bacon, who is gene- 
 rally referred to as the founder of the inductive 
 philosophy. Francis Bacon's system rests wholly 
 upon induction ; Roger Bacon grants the validity, 
 indeed, the necessity, of theorising, but the hypothe- 
 sis must be verified by appeal to observation and 
 experiment. As he says in Part VI., "Argument 
 shuts up the question, and makes us shut it up too ; 
 but it gives no proof, nor does it remove doubt, and 
 cause the mind to rest in the conscious possession of 
 truth, unless the truth is discovered by way of 
 experience." 
 
 The strange resemblance in many points between 
 Roger Bacon's ideas and those of his illustrious 
 namesake has been noticed by Hal lam in his 
 History of the Middle Ages. "Whether Lord 
 Bacon," he says, " ever read the Opus Majus, I 
 know not, but it is singular that his favourite quaint 
 expression, prerogatives scientiarum, should be 
 found in that work ; and whoever reads the sixth 
 part of the Opus Mo jus upon experimental science, 
 must be struck by it as the prototype in spirit of 
 the Novum Organum." But we must not further 
 discuss the Opus Majus here. So far as it has 
 bearing upon the general principles of scientific 
 
ALCHEMICAL MYSTICISM. 49 
 
 research, it deserves a prominent place in the history 
 of every science. The practice of spinning wordy 
 cobwebs without appeal to fact w r as the fashion for 
 centuries after Bacon's death, and we all owe rever- 
 ence to the man who so early saw that a theory or 
 hypothesis cannot stand " unless the truth is dis- 
 covered by way of experience." But having thus far 
 glanced at the importance of Bacon's logical work, 
 we must now turn to more strictly chemical matter. 
 
 Bacon has been usually alluded to as the discoverer 
 of gunpowder, at least as far as Europe is concerned. 
 That he was acquainted with it is certain from 
 the following passage in the sixth chapter of his 
 De secretis operibus artis et naturce.* "Mix together 
 saltpetre, luru vopo vir conutiret (sic), and sulphur, and 
 you will make thunder and lightning, if you know 
 the method of mixing them." By the extraordinary 
 term "luru vopo vir conutiret," he presumably refers 
 to charcoal. But it is not certain that he invented this 
 mixture. On the authority of an Arabic writer in 
 the Escurial collection, referred to by Hallam, it 
 seems that gunpowder was introduced by the Sara- 
 cens into Europe before the middle of the fifteenth 
 century. Whether Bacon had gathered his informa- 
 tion at an earlier date from some Eastern source is 
 uncertain and may be doubted. And, whoever first 
 prepared this substance, it is difficult to say whether 
 it has done much credit to its inventor. 
 
 Bacon's Mirrour of Alchimy is written in a style 
 
 * Hamburg (1618). Also a translation by T. M. : London (1659). 
 
 r> 
 
S o ALCHEMICAL MYSTICISM. 
 
 similar to that of other alchemistic writing of his and 
 a later period. In it he adopted Geber's ideas as to 
 the constitution of the metals : " All metals and 
 minerals .... are begotten of Argentvive and 
 sulphur." The book, as a whole, does not seem 
 worthy of its author. 
 
 Raymond Lully's name may perhaps be mentioned 
 in connection with Roger Bacon (1235 1315). 
 He wrote a great deal, but for the most part it 
 was jargon. He had a romantic life, beginning as 
 a lover of the Lady Eleanor of Castello. She 
 cured him of his passion by showing him an ulcer 
 eating away her breast. At her request he con- 
 secrated himself to God and missionised the Mus- 
 sulmans. He died in sight of Minorca after being 
 stoned at Tunis. He was acquainted, it seems, with 
 nitric acid, Avhich he obtained by distilling saltpetre 
 with the lower sulphate of iron, and he knew that on 
 adding potashes to a liquid containing alcohol the 
 alcohol rose to the surface or was salted out. His 
 opinion of alcohol seems to have been high, for he 
 terms it consolatio ultima corporis humani. His 
 missionising propensities notwithstanding, Lully seems 
 to have been somewhat of an impostor, and his 
 chemical opinions are not of much moment. 
 
 Bernard of Trevisa spent his whole life in searching 
 for the secret. In one striking chemical passage he 
 asserts that the alchemists are mistaken in supposing 
 that with acids they obtain solutions of the metals as 
 such, or, as he puts it, as with mercury, for by the 
 
ALCHEMICAL MYSTICISM. 5I 
 
 action of these acids the metals are severed or " de- 
 composed" (aeparalytmtur). The truth, of course, 
 is that the acid is decomposed, the metal forming a 
 soluble salt. When we dissolve copper in nitric acid 
 a chemical change occurs and the metal disappears. 
 We obtain a blue solution, but this is not a solution 
 of copper, it contains a salt of copper, viz. copper 
 nitrate. The writings of this time are romances, and 
 indeed so far did the writers carry their hyperbole 
 and mysticism that we find treatises on alchemy 
 almost unrecognisably disguised in what on the sur- 
 face seems merely a romantic tale. 
 
 But the darkest age of alchemy was now drawing to 
 a close, and although for a long time the alchemists 
 held the field, yet more and more of them were 
 chemists as well. The time of the mere gold- searcher, 
 the mere alchemist, whose desires consumed them- 
 selves like his furnace fires to white profitless ashes 
 which could be rekindled no more, was almost past. 
 
SECOND PERIOD. 
 
CHAPTER III. 
 
 SECOND PERIOD : MEDICAL MYSTICISM. 
 BASIL VALENTINE. 
 
 ^RANDE rather rashly utters a sweeping con- 
 demnation of the history of the alchemists 
 up to the date at which the last chapter 
 closes : "It presents nothing that the 
 mind rests upon with satisfaction ; no- 
 thing that it reverts to with interest or 
 profit." This is certainly going too far ; for Geber 
 and Roger Bacon both afford us interest and profit. 
 But it was a dark age for chemistry to this time. In 
 the present chapter we shall meet with people who 
 directed many experiments to the elucidation of 
 other mysteries than that of the preparation of gold. 
 It is true- their writings are still written in a very 
 inflated and often unintelligible style, but we find 
 a greater tendency to attempt accurate description. 
 
5 6 MEDICAL MYSTICISM. 
 
 Basil Valentine is the first of these new chemists 
 .whom we shall notice. Valentine Avas a native of 
 Erfurth, and wrote towards the close of the fifteenth 
 century. He strangely combines the incoherent jar- 
 gon of the older aViemist with really rational descrip- 
 tions of experiments. The period which opens with 
 Valentine is a new one in more than one characteris- 
 tic. The era of medical chemistry, iatro-chemistry 
 as it is called, was ushered in by Valentine's Tri- 
 umphant Chariot of Antimony, in which the medi- 
 cinal properties of antimony were insisted upon with 
 strenuous vehemence. The search for transmutation 
 was to some extent exchanged for the pursuit of the 
 elixir vitce, which was to cure all the ills of flesh, 
 and by means of which, even so far back as 1130, 
 Artephius was said to have lived to the advanced age 
 of 1,025. The term philosopher's stone has also 
 been applied to this elixir, and probably some 
 thought that the same body was to transmute the 
 metals and prolong life. However, Valentine's pur- 
 pose was in the main medical, and his work in this 
 direction led him to important results. Before con- 
 sidering what services he rendered to science we may 
 quote a passage from him where the alchemistic taint 
 i.i pronounced. 
 
 The following is from The twelve Keys of Brother 
 Basil Valentine, of the Benedictine Order. By which 
 the doors to the ancient stone of our forefathers is 
 opened, and the unfathomable well-spring of all health 
 
THE KINO AND HIS BEIDE. 
 
 From a Woodcut in Die Zivdlf Schlussel 
 (illustrating the quoted passage). 
 
5 8 MEDICAL MYSTICISM. 
 
 is discovered.* " The crown of the king must be of 
 pure gold, and a chaste bride must be given to him 
 in marriage. Therefore if you wish to work through 
 our bodies then take the greedy, grey wolf, so-called 
 because he is subject to the warlike Mars, but who is 
 by birth a child of old Saturn, found in the valleys and 
 hills of the world and possessed by great hunger, and 
 throw to him the body of the king that he may make 
 it his food, and when he has devoured the king make 
 a great fire and throw the wolf into it, that he may 
 be wholly burned, and by this means will the king be 
 again released. When this has happened three times 
 the lion will have conquered the wolf, and will find 
 nothing more of him to consume, and in this way our 
 body is made perfect for the beginning of our work." 
 This is a fair example of the falsely metaphorical 
 style, and it is a similar passage which is chosen for 
 satire by Glauber at a later date. If this is indeed 
 one of the keys to the stone it is itself shut within 
 what at first seems a keyless lock. If we merely read 
 the prescription as it stands it is indeed senseless 
 jargon, but it becomes more intelligible when we make 
 some attempt to interpret these alchemical terms. The 
 king signifies sulphur, the ivolf is antimony, Mars is 
 iron. By thus substituting rational equivalents for 
 this fanciful nomenclature something may be made of 
 it, but, as a rule, lejeu ne vaut pas la chandelle.^ 
 
 * Basilius Valentinug : Chymische Schriften, Hamburg (1677). 
 
 t Not content with these fanciful names they represented the metals 
 by the curious symbols still not entirely obsolete. These symbols are 
 given below ; each of them is enclosed in a square as they occur in 
 
MEDICAL MYSTICISM. 
 
 Valentine's important chemical work is concerned 
 with the metal antimony, and with ni- 
 tric, hydrochloric, and sulphuric acids- 
 Of antimony and its medicinal uses he 
 writes at length in his best-known work, 
 The Triumphant Chariot of Antimony. 
 His other, principal writing is the Halio- 
 graphia, which appeared in 1644 at 
 Bologna. It embodies a mass of in- 
 formation on the mineral, vegetable, 
 and animal salts. It is scattered through 
 this and the former work that his refer- 
 ences to nitric, hydrochloric, and sul- 
 phuric acids will be found. 
 
 Nitric acid is a very old chemical 
 product. The acid was in common use 
 among the early alchemists, but we find 
 in Valentine the first mention of a sim- 
 ple preparation, according to which a 
 mixture of three parts of powdered 
 earthenware with one of nitre is dis- 
 tilled. The method remained in use for 
 a long period. Other methods are given 
 by Valentine and sufficiently clearly 
 
 Glauber's Treatise of the Signature of Salts, Metals, 
 and Plants. The extent to which the symbol 
 touches the enclosing squares is intended, says 
 Glauber, to indicate the relative perfection of the 
 metal. ' ' New if into one of these I put the charac- 
 ter of the sun or gold, viz., a round circle, it touches 
 four parts of the square and filleth it up, signify- 
 ing that among celestial and terrestrial creatures, the snn and gold 
 do excel all other things in their perfection." 
 
6o MEDICAL MYSTICISM. 
 
 described. The method at present in use was 
 not discovered apparently till the time of Glauber. 
 It consists in distilling mixed nitre (saltpetre or nitrate 
 of potash) and sulphuric acid (oil of vitriol), and will be 
 farther mentioned when Glauber's work is considered. 
 Valentine termed it water or acid spirit of nitre. It 
 was afterwards called aquafortis. 
 
 Hydrochloric or muriatic acid was known to the 
 Arabian alchemists, as was its mixture with nitric 
 acid or aqua regia. But it is in Basil Valentine's work 
 that we first find mention of the pure acid under the 
 name spiriius sails, prepared from guter vitriol and 
 sal commune, that is from the green sulphate of iron 
 and common salt. 
 
 Sulphuric acid was apparently known to Geber, but 
 its preparation from green vitriol is first fully described 
 by Valentine. He refers to the product as oil of vitriol 
 in the Ilaliographia, while the directions for pre- 
 paring the green vitriol, or lower sulphate of iron, by 
 dissolving iron filings in dilute oil of vitriol, are also 
 there given. " The solution, " he says, " when put 
 aside in a cool place, soon forms beautiful crystals ; " 
 while elsewhere he states that < this salt is an excel- 
 lent tonic ; that it comforts weak stomachs ; find 
 that externally applied it is an admirable styptic." 
 
 In references like these we see a distinct desire to 
 examine chemical products for their own sake, and 
 not merely because they might lead to the discovery 
 of the philosopher's stone. Further we see in the 
 medical tendency which the science was now assum- 
 
From Die Zwolf Schliissel. 
 
62 MEDICAL MYSTICISM. 
 
 ing the awakening of a conviction that some every- 
 day good might be hoped for from its earnest study. 
 It does not do to love your science any more than to 
 love a person with an entirely abstract and fanciful 
 passion. One must love as well 
 
 " to the level of every day's 
 Most quiet need by sun and candlelight; " 
 
 and the alchemists were only just realising that their 
 science must be an every-day science as well as a 
 beautiful dream. 
 
 As the main facts concerning the preparation of 
 this most important substance, sulphuric acid, were 
 by this time discovered, we may here find an appro- 
 priate place for a general sketch of its history. Val- 
 entine, as just stated, prepared it from ferrous sulphate 
 by heat. The liquid so obtained fumes in the air, 
 and is thus distinguished from the acid as ordinarily 
 prepared by the name of fuming sulphuric acid. It 
 is also now known as Nordhausen sulphuric acid, 
 from the fact that it was prepared at Nordhausen, 
 in the Hartz. It consists really of a solution 
 of sulphur trioxide in sulphuric acid. It is now 
 prepared in Bohemia in the works of J. D. StarcJk. It 
 is a colourless, thick, oily liquid when pure, but is 
 generally coloured slightly brown from the presence 
 of organic matter. The oxide of iron left behind in 
 the retort when the distillation is complete was termed 
 colcothar or caput -mortuum of vitriol. This last term 
 arose from the fanciful practice by which the old 
 chemists symbolised the dregs and last products of 
 
MEDICAL MYSTICISM. 63 
 
 substance by the figure of a death's head and cross- 
 bones. Sulphur trioxide (SO 3 ) is also prepared in 
 large quantities, near London, by Dr. Messel. 
 
 Another and more important method of preparing 
 sulphuric acid is for the first time described by Basil 
 Valentine, and it is a modification of this which is 
 now in general use. It consists in burning a mixture 
 of sulphur and nitre (nitrate of potash), whereby the 
 sulphur is oxidised or burnt up by the oxygen of the 
 nitre, and sulphuric acid is formed. The following 
 are his words : " Take of antimony,* sulphur, salt nitre, 
 of each equal parts, fulminate them under a bell, as oil 
 of sulphur per campanam is made, which way of pre- 
 paring hath long since been known to the ancients ; 
 but you will have a better way if instead of a bell 
 you take an alembic and apply to it a recipient, so 
 you will obtain more oil, which will indeed be of 
 the same colour as that made of common sulphur, 
 but in powers and virtues not a little more excel- 
 lemV'f 
 
 The present method of manulacturing sulphuric 
 acid was, according to some accounts, introduced into 
 England from the Continent by Cornelius Drebbel ; 
 but the first authentic information is that a certain 
 Dr. Ward obtained a patent for its manufacture. He 
 employed glass globes of about forty or fifty gallons 
 capacity. A little water was poured into the globe, 
 
 * The antimony forms a sulphide with the sulphur present and is 
 not essential to the reaction 
 
 *" Triumphant Chariot of Antimony. 
 
6 4 
 
 MEDICAL MYSTICISM. 
 
 a stoneware pot introduced and on this was placed a 
 red-hot iron ladle. A mixture of sulphur and salt- 
 petre was then thrown into this ladle, and the vessel 
 closed to prevent the escape of the copious fumes 
 evolved. The vapours were absorbed by the water 
 
 APPARATUS TO ILLUSTRATE THE MANUFACTURE OF SULPHURIC ACID. 
 
 a, flask for boiling water. 
 
 l>, flask containing copper and sulphuric acid to evolve sulphuric dioxide, 
 c, flask containing copper and nitric acid to evolve nitrous fumes. The other 
 tubes in the large flask are to admit air. 
 
 and sulphuric acid thus formed. To distinguish it 
 from the acid obtained from the iron sulphate it was 
 termed oil of vitriol made by the bell. It was priced 
 
MEDICAL MYSTICISM. 65 
 
 at from Is. 6d. to 2s. Gd. per pound. The next 
 advance was effected by Dr. Roebuck, a physician of 
 Birmingham, who replaced the glass globes by leaden 
 chambers. These chambers were first erected in 
 Birmingham in 1746, and in 1749 at Preston Pans 
 in Scotland. As before, the charge of sulphur and 
 nitre was placed within the chamber, ignited, and 
 the door closed. After the lapse of time sufficient 
 for the absorption of the product by the water in the 
 chamber the doors were opened and the charging 
 repeated. 
 
 The size of the leaden chambers was at first limited 
 to six feet square, and for many years did not exceed ten 
 feet- square. By 1783 Messrs. Kingscote and Walker 
 had erected chambers forty-five feet long and ten feet 
 wide. Berthollet's application of chlorine to the 
 bleaching of cotton goods (1788) gave at once an 
 enormous impulse to the manufacture, and in the fol - 
 lowing way : Hydrochloric acid is largely used in the 
 preparation of chlorine, and sulphuric acid in the pre- 
 paration of hydrochloric. The reaction of the manu- 
 facture of each upon that of the other is thus readily 
 seen. The final improvement, chiefly proposed by 
 Chaptal, resulted in making the process continuous. 
 To this end the sulphur * is burnt separately to form 
 sulphur dioxide, and this is sent into the leaden 
 chambers mixed with steam. Nitre is heated in 
 separate vessels and the nitrous fumes resulting from 
 its decomposition also passed into the chambers. 
 
 * Iron pyrites, a sulphide of iron, is actually used in practice. 
 E 
 
66 
 
 MEDICAL MYSTICISM. 
 
 To show the extent to which the sulphuric acid 
 industry has developed we must recall that in Dr. 
 Ward's time the commercial acid was priced at from 
 Is. 6d. to 2s. 6d. per Ib. It may now be obtained 
 at the price of Id. per Ib., while the annual product 
 in Great Britain cannot fall far short of 1,000,000 
 
 MANUFACTURE OF SULPHURIC ACID. 
 
 Steam passes in from the boiler (i) ; sulphur dioxide and nitrous fumes through 
 the large pipes (a). 
 
 tons. In the South Lancashire district alone the 
 quantity manufactured some years ago amounted to 
 3,000 tons per week. Dyeing, bleaching, and the 
 alkali industry consume enormous quantities of sul- 
 
MEDICAL MYSTICISM. 67 
 
 phuric acid, and there are innumerable manufactures 
 in whick it is more or less employed. Such is the 
 development presented to us by a single chemical 
 industry. The figures are impressive enough, and we 
 are apt to become elated by mere contemplation of a 
 long succession of noughts when anything commercial 
 is concerned. Perhaps it may be well, therefore, to 
 remind ourselves that the mere production of sul- 
 phuric acid, even to the amount of inland seas, is 
 in itself no special boon. Chemistry has so far been 
 applied to manufacture. Good, but how far has 
 the manufacture increased the happiness of life ? 
 
 Having now shown the wider development and 
 application of some ideas known in all their essential 
 details so far back as the time of Basil Valentine, 
 and brought to their present enormous range of ap- 
 plication by only very slight additions and changes, 
 we must return to our alchemist. We have discussed 
 to some extent his position as a chemist, and we need 
 now only treat of -the work upon which he himself 
 most strenuously insisted the elucidation of the 
 properties and virtues of antimony. 
 
 This metal occurs native as stibnite or antimony 
 sulphide, a mineral known in very early times, and 
 employed by women in the East for painting the eye- 
 brows. In St. Jerome's translation of the Hebrew of 
 Ezekiel xxiii., 40, we read " circumlinisti stibio oculos 
 tuos," "thou hast painted thine eyes around with 
 stibnite." 
 
 The word alcohol was originally used to distinguish 
 
6s MEDICAL MYSTICISM. 
 
 this mineral. The Arabic name was " Kohl/' and this 
 word passed as alcool or alkohol into other languages, 
 as, for instance Spanish, where the above biblical 
 passage is rendered "alcoholaste tus ojos." At a 
 later date the term alcohol was applied to any fine 
 powder and, finally, spirits of wine. How this last 
 transition was effected it is difficult to say. We 
 know that strong alcohol was formerly termed vinum 
 alcalisatum (wine strengthened with alcohol), and it 
 has been suggested that by some misunderstanding this 
 came to be written vinum alcoholisatum, and then 
 alcohol vini. At best this is a somewhat doubtful 
 conjecture. Pliny termed the mineral stibium, while 
 in the Latin translation of Geber the word antimo- 
 nium is used. The German name spiessglas is first 
 found in the writings of Basil Valentine.* 
 
 How the word antimony was derived it seems 
 impossible to say. A fanciful story is related to the 
 effect that Valentine, intent upon discovering the 
 medicinal properties of this substance, used his 
 brother monks as " subjects " for his experiments, and 
 administered it in some form to several, some of whom 
 succumbed to its powers. Upon this it is said that 
 Valentine invented for this body the term antimoine, 
 i.e., " hostile to monks." (!) To dispose of this story it 
 is only necessary, apart from its inherent absurdity, to 
 cite Kopp's remark to the effect that this word would 
 have been invented by a Frenchman, while Valentine 
 wrote in German. 
 
 * This account is taken from Eoscoe and Schorlemmcy's Treatise. 
 
MEDICAL MYSTICISM. 69 
 
 Valentine's monograph indicates a really epoch- 
 making advance on previous chemical writings. It 
 is a thoroughly earnest attempt to study in detail the 
 properties of one substance and its derivatives. We 
 find here the first description of the mode of obtaining 
 the metal, though this is not mentioned as a new 
 discovery. Numerous antimonial preparations are 
 described, and special stress is laid upon their 
 medicinal properties. 
 
 The metal antimony, as already stated, is found in 
 nature chiefly as the sulphide. It forms with other 
 metals some important alloys which may here be 
 mentioned. Valentine alludes to the existence of 
 alloys of antimony. English type-metal is an alloy 
 of lead, antimony, and tin. The antimony gives the 
 alloy the property of expanding as it solidifies. From 
 this it results that when used to make a cast of a 
 letter it presses itself into all the interstices, and a 
 very accurate reproduction is obtained. The tin 
 gives the metal toughness and coherence. Three 
 analyses of English type-metal are here given : 
 
 I. II. ill. 
 
 Lead .... 50 55-0 61-3 
 
 Antimony . . .25 22*7 18'8 
 
 Tin . . .25 22-1 20'2 
 
 German type-metal contains about 15 per cent, of 
 antimony. 
 
 Britannia Metal and Pewter. This is a silver- 
 white alloy largely used for spoons, tea-pots, and 
 
other " silver" articles. 
 tin and antimony, 
 
 MEDICAL MYSTICISM. 
 
 It is mainly composed of 
 
 
 Britannia Metal. 
 
 Plate 
 Pewter. 
 
 Ashbury 
 Metal. 
 
 Tin . . 
 
 85-7 
 
 81-9 
 
 89-3 
 
 77-8 
 
 Antimony . . 
 Copper . . . 
 
 10.4 
 1-0 
 
 16-2 
 
 7-1 
 
 1-8 
 
 19-4 
 
 Zinc . . 
 
 2-9 
 
 1-9 
 
 . 
 
 2 8 
 
 Bismuth . . 
 
 
 
 
 
 1-8 
 
 
 
 White or anti-friction metal is used for lining the 
 brasses of various parts of locomotive engines. It is 
 composed of tin, antimony, and copper. The variety 
 of this alloy known as Babbit's metal, also contains 
 a considerable percentage of lead. 
 
 Two processes may be used to extract metallic 
 antimony from the native sulphide. In either case 
 the sulphide is subjected to the -liquation process. In 
 this process the mineral is melted in vertical cylinders, 
 through a hole in the bottom of which it flows out 
 leaving the gangue behind. The sulphide, thus puri- 
 fied, is known as crude antimony. By one process the 
 metal is obtained from it by heating to redness with 
 scrap iron. The iron takes away the sulphur from 
 the antimony sulphide, leaving the metal behind.* 
 The metal is fused with sodium carbonate (pearl-ash) 
 
 * Where Fe stands for iron, Sb for antimony, and S for sulphur we 
 have: 
 
 Sb 2 S 3 + 3 Fe = 3 Fe 8 + Sb 8 . 
 
MEDICAL MYSTICISM. 71 
 
 to purify it from foreign metals, and poured into 
 moulds where it is allowed to cool slowly. During 
 this slow cooling the metal assumes a crystalline 
 
 structure and exhibits on its surface very beautiful 
 fern-leaf markings. It has a white colour and is very 
 brittle. In the second process the purified sulphide 
 is roasted in order to convert it into oxide, and the 
 
72 .MEDICAL MYSTICISM. 
 
 oxide is "reduced" to metal by melting in a large 
 earthen crucible with charcoal or crude tartar. The 
 construction of a common form of liquation furnace 
 is shown in the illustration on the previous page. 
 The ore is placed in the cylinders c. c and the molten 
 sulphide collects in the pots 71, n'. 
 
 Both of the above methods were known to Basil 
 Valentine : " Antimonium is a master in medicine, 
 and from it by means of cream of tartar and salt a 
 king (regulus) is made, steel-iron being added to the 
 spiessglas during fusion. Thus by an artifice a 
 wonderful star is obtained which the learned before 
 my time have termed the philosophical signet star." 
 Again : " Take good Hungarian spiessglas with the 
 same quantity of crude tartar, and half as much 
 saltpetre ; rub these small and let them fuse well in a 
 wind furnace ; afterwards pour out into a mould 
 and allow to cool, when a regulus is found." The 
 preparation of the stellated antimony was asserted 
 by different alchemists to be due to the action of 
 various occult influences. Valentine thought the 
 appearance only resulted when iron was employed in 
 the preparation ; many on the other hand asserted 
 that the stars were in some way answerable for the 
 result, and that it was only during some propitious 
 conjunction that the stellated metal could be ob- 
 tained. We see here once more an indication of the 
 parting of the ways between alchemy and chemis- 
 try. The path of the former, leagued with astrology 
 
MEDICAL MYSTICISM. 73 
 
 and other mystic arts, was to tend ever downwards 
 towards deeper degradation, until it was represented 
 only by a race of ignorant impostors and a few perplexed 
 fanatics. That of the latter was to ascend by ways 
 that were often steep and barren, but became ever 
 more prosperously fruitful, to the lonely Pisgah heights 
 beyond which the land of promise stretched no longer 
 as an unfulfilled dream but as the realisation of 
 unbaffled hope. 
 
 Of Valentine's description of his antimonial pre- 
 parations we may here give some samples. After a 
 very lengthy introduction, the greater part of which 
 is devoted to violent abuse of the doctors of his day, 
 and during the perusal of which we wait with grow- 
 ing impatience for matter which is really to the point, 
 Basil Valentine at last rewards us by describing the 
 preparation of " antimony-glass " which consists of 
 the oxide usually coloured by sulphide. " Take Hun- 
 garian antimony, or any other (the best), grind it upon 
 a marble into most subtile powder, lay this powder 
 thin and sparingly in a plain earthen vessel, round 
 or square, which let be made with rims about the 
 height of t\vo fingers' breadth ; place this vessel on a 
 calcining furnace, administer at first a gentle fire of 
 coals and when the stibium begins to fume, stir it with 
 a little iron rod to and againe, without ceasing, until 
 it ceaseth to emit any vapour ; but if in the calcina- 
 tion the antimony chanceth to melt and run into 
 balls, take off the vessel from the fire and let the 
 
74 MEDICAL MYSTICISM. 
 
 stibium cool, and grind it again, and doe as afore, 
 which must be so often done, until it neither 
 fumes nor runs together any more, but remains in 
 the, form of white ashes, for then is your calcination 
 perfect. 
 
 " Take now this stibium thus calcined, put it into 
 a goldsmith's crucible, place it at a violent fire, that 
 the antimony may flow like pure clear water, and 
 that you may know when the glasse of stibium has 
 attained a perfect and pellucid colour, put into the 
 crucible a long cold iron, and the glasse will stick 
 thereunto, which strike with an hammer, and so sepa- 
 rate it, and hold it up against the light, which if it 
 be transparent 'tis good and perfect glasse."* 
 
 The above quotation is given to show that the 
 alchemist's style is here passing into the clear and 
 accurate language of the chemist. It contrasts 
 strangely indeed with the language used by the same 
 writer in Die Zwblff Schlussel. 
 
 We must lastly refer to the marked medical ten- 
 dencies of Basil Valentine's work. We have already 
 said that with him the era of medical chemistry 
 opened. His naive enthusiasm for the union of 
 chemistry and medicine is often irresistibly amusing, 
 but is at the same time of grave significance. Medi- 
 cine had indeed up to this date been a very unscien- 
 tific affair, and, when we recollect that up to this day 
 we are almost wholly ignorant of the true functions of 
 such a well-known organ as the spleen, this will not 
 
 * Triumphant Chariot of Antimony, London (1661). 
 
MEDICAL MYSTICISM. 75 
 
 surprise us. With regard to the chemical changes 
 which go on in the body we are far more ignorant. 
 The question of the clotting of blood and its pre- 
 cise causes is still sub judice, and the common ideas 
 of yesterday on this matter have been strongly com- 
 bated of late. We know that phosphorus and 
 arsenic are both very poisonous bodies, but ivhy 
 they are so it seems impossible to say. We can 
 conjecture that phosphorus affects the oxidation pro- 
 cesses of the body, but when we have said so much 
 we have not got far and can go no farther. 
 
 The case of arsenic is made doubly mysterious by the 
 fact that people can accustom themselves to take poison 
 ous doses of the substance without harm. Eoscoe has 
 contributed to the -Literary and Philosophical Society 
 of Manchester an interesting paper " On the alleged 
 practice of arsenic-eating in Styria," from which it 
 appears that in one case a wood-cutter was seen by a 
 medical man to eat a piece of arsenious acid (arsenic 
 trioxide) weighing 4-5 grains, and the next day he 
 crushed and swallowed another piece weighing 5 '5 
 grains, and the following morning was in his usual 
 state of health: A dose of one grain is, with those 
 who are not of the cult, very dangerous, while one of 
 two to four grains is almost always fatal. How 
 individuals can thus by practice withstand fatal doses 
 it is at present simply impossible to say. When 
 then on such simple matters we are at the close of the 
 nineteenth century so ignorant, it is startling to find 
 any writer at the close of the fifteenth century who could 
 
76 MEDICAL MYSTICISM. 
 
 discern any relation between chemistry and medicine, 
 or could conceive that the latter was to be dealt with 
 scientifically at all. 
 
 Antimony was the substance above all others whose 
 medicinal properties Valentine was sworn to defend. 
 In The Triumphant Chariot he approaches his 
 subject with almost awed devotion : " He that will 
 write of Antimony needs a great consideration and 
 most ample minde .... in a word one man's life is 
 too short to be perfectly acquainted with all its 
 mysteries. It is to be administered for inward and 
 outward diseases, which to many moles Avill seem 
 incredible." Valentine is not given to compliment 
 those who oppose him. " Whoever, therefore, will 
 be a true antimonial anatomist, let him first consider 
 the division or operation of his body." For the 
 unchemical medicine -man Basil Valentine entertains 
 the loftiest scorn, and upon such men he pours out 
 the vials of his wrath. They do not even know how 
 to prepare their own medicines ; " they know not 
 whether they be hot or dry, black or white, they only 
 know them as written in their books, and seek after 
 nothing but money. Labour is tedious to them, and 
 they commit all to chance ; they have no conscience, 
 and coals are outlandish wares with them ; they write 
 long scrolls of prescriptions, and the apothecary thumps 
 their medicine in his mortar, and health out of the 
 patient." Probably Valentine's denunciations might 
 apply to some medicine men even now, for it is said 
 
MEDICAL MYSTICISM. 77 
 
 that they have been known to mix in a prescription 
 substances which by interaction would lose their 
 characteristic medicinal properties ; " they only know 
 them as written in their books." 
 
 Valentine finds it difficult to repress his wrath 
 against these " moles/' and especially such as refuse 
 to recognise the surpassing value to the human 
 organism of antimony. Thus we find him breaking 
 forth in this strain : " So I know that many trifling 
 wanderers, lazy doctors, empericks, and many other 
 intruders into physick, will clamour out against 
 antimony, crying a crucifige, but yet it will endure, 
 when those ignorant medicasters shall be broken in 
 pieces." Farther on he gives two ways of extracting 
 a poison, first by its contrary, second by its like : 
 "which proudly arrogant medicasters or physicians, by 
 reason of their sluggish and droanish laziness, are 
 unacquainted with." A plain-spoken man is this 
 Basil Valentine. 
 
 Again : " Ah, wretched men, unlearned doctors, 
 unexperienced physicians, who write tedious receipts 
 on a long paper. ye apothecaries that set over 
 the fire great cauldrons sufficient to boil the meat of 
 noblemen's houses, and to hold enough for a hundred 
 persons, Low long will ye be blind ...?... O 
 deplorable, putrid and stinking bag of worms . . . ' 
 
 These vigorous onslaughts are amusing enough now, 
 but they must have called for some courage when 
 they were made, and at least their tendency was in 
 
78 MEDICAL MYSTICISM, 
 
 the right direction. And this must close our account 
 of Valentine. He rendered some sterling services to 
 knowledge by his discoveries, by his advocacy of 
 really scientific aims, by the dauntless courage of his 
 attacks upon an effete empiricism, and by his early 
 inauguration of the union between medicine and 
 chemistry. 
 
CHAPTER IV. 
 
 SECOND PERIOD : MEDICAL MYSTICISM. 
 PARACELSUS : VAN HELMONT, 
 
 >HE scientific sky was now for a moment 
 illuminated by the flash of an erratic 
 meteor, which after some moments of 
 dazzling brilliancy plunged back into 
 cimmerian gloom, and left behind it only 
 the feebly glimmering track of light surviv- 
 ing until now. The name of Paracelsus carries with 
 it a mysterious suggestion of power. But it was 
 power for the most part expended in fitful and 
 unproductive bursts. According to Van Helmont's 
 account Paracelsus came to Constantinople during 
 1521 and received there the philosopher's stone. 
 The adept from whom he received the stone was said 
 to be a certain Solomon Trismosinus, a countryman 
 of Paracelsus. This man appears also to have been 
 
So MEDICAL MYSTICISM. 
 
 in possession of the Universal Panacea and is said to 
 have been seen still alive by a French traveller at 
 the end of the seventeenth century ! * The details 
 left us of his career are all too few, but as we read 
 even these scattered fragments we continually expect 
 some consummation of achievement from so mysteri- 
 ously isolated a man. But we await in vain ; " we 
 have a careless and insolent indication of things that 
 might be not the splendid promise of a grand 
 impatience, but the scrabbled remnant of a scornfully 
 abandoned aim." 
 
 Phillipus Aureolus Theophrastus Bombastus Para- 
 celsus von Hohenheim was by birth Philip Hochener, 
 but he changed his name on commencing his pro- 
 fessional career. He was the son of a physician and 
 born in 1493 at Einsiedeln, a small town in the 
 canton of Schwitz, distant some leagues from Zurich. 
 At an early age he quitted his native country and 
 wandered over Europe, visiting the most important 
 towns. This restless spirit characterizes the whole of 
 his future career, and was one great reason why so 
 much of his influence was dissipated and lost. 
 
 In 1526 he returned to his native land and was 
 recommended by CEcolampadius to the chair of physic 
 at Basle. Here Paracelsus commenced his career by 
 burning publicly in the hall the works of Avicenna 
 and Galen. These two physicians were not together 
 
 * F. Hartmann : Life of Paracelsus and the Substance of his Teachings ; 
 a curious work in which the author professes belief in all the mysteries 
 of alchemy. 
 
MEDICAL MYSTICISM. 8 1 
 
 possessed of so much knowledge, he assured his 
 audience, as were his own shoe-ties ; all the universi- 
 ties and all the writers united were less instructed 
 than the hairs of his beard, and he was to be regarded 
 as the sole monarch of physic. 
 
 After such proceedings Basle soon ceased to be able 
 to contain him. According to some accounts he was 
 obliged to leave the town owing to his dissolute habits 
 and the wild extravagance of his life. On the whole 
 one may fairly incline to doubt some of these worst 
 stories that were told of him. The force of impact 
 with which this strange being met the stormy oppo- 
 sition of his age is sufficient proof of some nobler 
 aims ; and the blindness of his enemies to these leads 
 one to suspect that their condemnation was not un- 
 mingled with spite. Besides, Paracelsus was essentially 
 of an aggressive nature, he wanted to do things in a 
 way of his own, and moreover he wanted people to 
 see that that way of his own was a good one. The 
 mildest-mannered man would be sure to incur some 
 hatred as soon as he suggested that things might be 
 done better than they are, and Paracelsus does not 
 seem by any means to have bee'n mild or bland.* 
 Indeed we may fully expect that such a character 
 would have to take an unusually large share of 
 envenomed hatred and scorn. 
 
 Let us make allowance for the hatred he inspired 
 
 * See his works Opera omnia medico- chemico-chirurgica, Geneva 
 (1658). Some of his chemical writing was translated by R. Turner : 
 London (1657). 
 
 F 
 
82 MEDICAL MYSTICISM. 
 
 and consent, to take him at his best. Another 
 account is given of the reasons which obliged him to 
 leave Basle and it seerns the more probable story. A 
 rich canon, it is said, fell sick and offered a hundred 
 florins to any one who could cure him. Paracelsus, 
 with characteristic daring, at once offered to cope 
 with the disease. He administered three pills and 
 the canon got well. We all know the old rhyme : 
 
 " The devil was ill, 
 
 The devil a monk would be ; 
 The devil got well, 
 
 The devil a monk was he." 
 
 And the Canon of Basle seems to have acted in this 
 . case after the pattern of one who should not have 
 been his patron saint. Being so soon restored he felt 
 too confident to part readily with his money, and he 
 refused to pay the promised sum.* The matter was 
 brought before the judicial powers, who decreed that 
 the physician should only receive his customary fee. 
 Probably, such a decision was capable of being called 
 legal ; it was certainly not just. Incensed at his 
 treatment by the canon, and at the absurd partiality 
 of the judicial decision, Paracelsus retired in high 
 dudgeon, declaring he would leave the inhabitants of 
 Basle to the eternal destruction which they deserved. 
 In 1527, therefore, he quitted Basle for Strasburg, 
 then travelled into Hungary, and after wandering all 
 
 * Testimonials to his cures of cases of elephantiasis placed under his 
 care by the City Council of Nuremberg may be found in the archives 
 of that city. (Hartmann.) 
 
MEDICAL MYSTICISM. 83 
 
 over Europe in restless discontent, returned to Salz- 
 burg to die in poverty in 1541, at forty-eight years of 
 age. 
 
 It is difficult to speak very definitely of the dis- 
 coveries made by Paracelsus. It was, as already hinted, 
 by the impact of his masterful personality that he 
 made the impression that he has left behind. To him 
 was due the growing closeness of union between 
 chemistry and medicine. An alchemist, he yet de- 
 spised the mere search for gold ; a physician, he de- 
 spised the ordinary rote and rule of his profession ; a 
 learned professor, he yet determined, in spite of 
 all precedent, to lecture in the common people's 
 tongue. He aimed at making knowledge at once 
 more useful and more widely known. The hide-bound 
 pedants of his age were all against him, and this the 
 more because, even making all allowance for ex- 
 aggeration, we must admit he was most extrava- 
 gantly aggressive. But, in spite of the pedants, his 
 work produced a resistlessly expansive impression. 
 
 Of the discoveries of Paracelsus as a chemist we 
 may mention that he was the first to prepare hydro- 
 gen gas. That alone is sufficient to lend deep inte- 
 rest to his name. He obtained an inflammable gas by 
 the action of dilute acids on metals ; this gas was 
 certainly hydrogen, though its true nature and its 
 importance lay undiscovered till the time of Caven- 
 dish in 1766. Paracelsus adopted the views taken by 
 Basil Valentine as to the universal constituents of 
 matter, supposing them to be three in number, sul- 
 
84 MEDICAL MFSTICISM. 
 
 phur, mercury, and salt. It appears, however, that 
 these constituents were not regarded as identical with 
 the common substances recognised by these names, 
 but that, for instance, salt was taken in the sense of 
 the principle of saltness, and so on; it was the some- 
 thing which gave rise to the saltness of salt itself. 
 But it is difficult to enter into the subtlety of these 
 views and if we appreciate their general bearing we 
 may be content. 
 
 Paracelsus was the first who included animal and 
 vegetable bodies in the same classification, and, ac- 
 cording to his theories, health was supposed to result 
 from the presence in the organism of the above con- 
 stituents in their normal proportions, while a dis- 
 turbance of these relations led to disease. 
 
 In his desire for the union of chemistry and medi- 
 cine Paracelsus introduced a variety of mercurial pre- 
 parations in certain diseases. The use of mercury 
 for these purposes is strongly maintained at this 
 day. Opium also came into general use as a medicine 
 owing to the influence of Paracelsus. In such ways 
 he took the initiative in establishing the class of chemi- 
 cal-physicians which now arose. 
 
 These men were of course treated as possessed of 
 very questionable powers. It was not " the thing" to 
 administer chemical preparations for medicine ; it was 
 not done ; and what more condemnation could be 
 needed of those who should try to do it ? That mer- 
 cury and antimony should be used as medicines was 
 certainly too heterodox to be allowed. Their fathers 
 
MEDICAL MYSTICISM. 85 
 
 had lived and died without antimony or calomel, and 
 why should these new-fangled faddists think they 
 knew better ? And the superior people among them 
 said it was all very well in theory no doubt ; but in 
 practice ! and they shook their heads silently and 
 with infinite wisdom. 
 
 This made the introduction of chemical prepara- 
 tions by no means easy, and so, when the physicians 
 wanted to administer chemical substances, they dis- 
 guised them under pretty and fanciful names and their 
 patients were quite satisfied and happy. If these sub- 
 terfuges were not resorted to, woe betide the physician. 
 Towards the end of the fifteenth century the use of 
 antimony was prohibited at Paris, and Besnier was 
 expelled from the faculty for having persisted in ad- 
 ministering it. Chemical medicines came into use in 
 England in the reign of Charles I., and shortly after 
 1644 the London College of Surgeons made its appear- 
 ance. We must be ready to recognise the good done by 
 the line of medical chemists. As Brande says, " The 
 foundations of chemical science are to be found in the 
 medical and pharmaceutical writers of the sixteenth 
 century, who rescued it from the hands of the alchemical 
 pretenders, and gave it a place and character of its 
 own." As time went on and the medical sect grew, 
 the alchemists were becoming more and more pre- 
 tenders indeed, and more and more justly typified by 
 the Subtle of Ben Jonson. The finest talent was 
 enlisted in the ranks of the medical chemists to 
 whose work Paracelsus had given such impetus. It 
 
86 MEDICAL MYSTICISM. 
 
 is true that Paracelsus had often raved rather than 
 reasoned, but his ravings, like those of Cassandra, 
 were at least prophetic, and, unlike hers, were never 
 doomed to be impotent.* 
 
 Van Helrnont, a Dutchman, was one of the fol- 
 lowers of Paracelsus, and flourished in the early part 
 of the seventeenth century. He was, it seems, a 
 conscientious enthusiast, but of his additions to 
 knowledge nothing very definite can be said. That 
 the character of the man was of interest is suffi- 
 ciently shown by the following extract from an 
 autobiographical fragment which he left : f 
 
 "In 1594, being then seventeen years of age, I 
 finished rny courses of philosophy, but upon seeing 
 none admitted to examinations at Lou vain who were 
 not in a gown and hood, as though the garment made 
 the man, I was struck with the mockery of taking 
 degrees in arts. I therefore thought it more profit- 
 able, seriously and conscientiously, to examine myself ; 
 and then I perceived that I really knew nothing, or, 
 at least, nothing that was worth knowing. I had, in 
 fact, merely to talk and to wrangle, and therefore 
 refused the title of Master of Arts, finding that no- 
 thing was sound, nothing true, and unwilling to be 
 declared master of the seven arts, when my conscience 
 told me I knew not one. The Jesuits, who then 
 taught philosophy at Louvain, expounded to me the 
 
 * Those who wish for an idealised and poetical sketch of the career 
 ol Paracelsus should of course read Browning's poem, published under 
 that name. 
 
 -f Quoted in Brando's Chemistry (2nd ed., 1821). 
 
MEDICAL MYSTICISM. 87 
 
 disquisitions and secrets of magic but these were 
 empty and unprofitable conceits ; and instead of grain 
 I reaped stubble. In moral philosophy, when I ex- 
 pected to grasp the quintessence of truth, the empty and 
 swollen bubble snapped in my hands. I then turned 
 my thoughts to medicine, and having seriously read 
 Galen and Hippocrates, noted all that seemed certain 
 and incontrovertible ; but was dismayed upon re- 
 vising my notes, when I found that the pains I had 
 bestowed, and the years I had spent, were alto- 
 gether fruitless ; but I learned at least the emptiness 
 of books and formal discourses and promises of the 
 schools. I went abroad and there I found the same 
 sluggishness in study, the same blind obedience to 
 the doctrines of their forefathers, the same deep-rooted 
 ignorance." 
 
 Van Helmont (15771644) adopted neither the 
 Aristotelian nor the Paracelsian doctrine as to the 
 constituents of matter. He admitted that air and 
 water were elements. Yet he was the first to recog- 
 nise the existence of different kinds of " air," and was 
 apparently the inventor of the word " gas." He gave 
 his attention to the " air " which is given off during 
 the process of fermentation, and gave to it the name of 
 gas sikestre, or " the gas that is wild and lives in 
 out-of-the-way places." Later this gas was called 
 fixed air, and is of course carbonic acid gas, carbon 
 dioxide, or the gas which is obtained on burning 
 charcoal in air. Yan Helmont identified this gas 
 with that given off during combustion, with that found 
 
88 MEDICAL MYSTICISM. 
 
 in the " Grotto del Cane," near Naples, and also with 
 that obtained by the action of acids on calcareous sub- 
 stances, such as marble. He mentions a gas pingue 
 which is evolved from dung, and is inflammable. 
 This is probably impure ammonia. Van Helmont 
 also showed that when a metal is dissolved in an 
 acid it is not destroyed, but may be recovered from 
 solution in the metallic state by suitable means. 
 
 Van Helmont was a representative of a different 
 sect of the alchemists from any we have yet discussed. 
 As his ideal and goal he set before himself the dis- 
 covery, not of transmutation nor of the medicinal 
 "philosopher's stone" as usually understood, but 
 of the universal solvent, or alkahest as it was termed, 
 which at the same time was to serve as the cure of 
 all diseases. 
 
 Apart then from his interest as a man of penetrating 
 judgment, sufficiently discernible in the short auto- 
 biographical extract quoted above, Van Helmont's 
 chief merits lie in his discovery of the existence of 
 different kinds of gases, which had hitherto been all 
 generally confused under the one name of " air." 
 This discovery was indeed one of the very first impor- 
 tance, and required at that time great keenness of 
 observation and alertness of attention. If we recall 
 how in all their superficially observable properties 
 atmospheric air and carbon dioxide are exactly 
 similar, we shall be more in a position to appreciate 
 the talents which, in that condition of knowledge, 
 could discern the differences. In the first place one 
 
MEDICAL MYSTICISM. 89 
 
 cannot see air, and in the ordinary sense cannot feel 
 it, cannot take it up and inspect it as one does a 
 mineral ; and these peculiar attributes are characteristic 
 of most gases. This of course makes the discovery 
 of their properties a work of quite peculiar delicacy. 
 
 Then too such bodies are always tending to escape 
 from us. If one takes a handful of carbonic acid gas 
 out of a jar it at once streams away into the surround- 
 ing air. They will not remain, or at least not remain 
 
 PREPARATION OF CARBONIC ACID. 
 
 long, in a vessel which is open at top, as water will 
 do. We cannot pour hydrogen into a basin and then 
 examine it at leisure, as could be done with a liquid. 
 Carbonic acid, however, being a very heavy gas, and 
 thus tending to sink rapidly in the air, will in this 
 respect to some extent behave like water. If marble, 
 which is calcium carbonate (carbonate of lime), is 
 treated with hydrochloric acid, carbon dioxide is 
 given off and we may conduct the gas so evolved out 
 
go MEDICAL MYSTICISM. 
 
 of the evolution flask into a collecting cylinder as 
 shown. The gas being so much heavier than air it 
 will lie in the cylinder, and only be disturbed quickly 
 by a considerable draught. And having got this gas 
 in the cylinder we may indeed pour it out into 
 another, much as we should do with water, though 
 some will certainly be lost in the process. It will 
 stream downwards into the lower cylinder, and by 
 simple tests, such as pouring in a little lime water 
 which will at once be turned milky, we can readily 
 show that it is there. 
 
 Such being the properties of carbonic acid gas it is 
 readily seen that it presents us with fewer difficulties 
 than do other gases ; we can more easily get hold 
 of it and deal with it. And carbonic acid, indeed, 
 was the first gas distinguished from ordinary atmo- 
 spheric air, and this work was accomplished by 
 Van Helmont. In the fermenting vats of breweries 
 this gas is evolved in large quantities. Being heavy 
 and not exposed to rapid air- currents it collects 
 there, and it was there that Van Helmont discovered 
 it. He found that it extinguishes flame and, when 
 inhaled for some minutes, is fatal to animal life.* 
 These properties were at once sufficient to distinguish 
 it from atmospheric air, and this and others were 
 sufficient to identify it with the gas obtained by other 
 processes, such as the action of acid upon marble, and 
 found by Van Helmont in the Grotto del Cane, the 
 
 * It should be noted, however, that this gas taken into the stomach 
 as in aerated drinks is quite harmless and even beneficial. 
 
MEDICAL MYSTICISM. 9I 
 
 mineral waters at Spa, and at other places. Carbon 
 dioxide is formed during combustion, the carbon of 
 the burning body, such as a candle, combining with 
 the oxygen of the air to form the oxide.* It is also 
 given off in large quantity in the breath of animals, 
 being formed by the burning up of the waste products 
 in the tissues. It occurs in chalybeate, and acidulous 
 waters, and in volcanic districts escapes in large 
 volumes from the fumeroles and rents in the ground. 
 The Poison Valley in Java is remarkable for the 
 evolution of this gas in very large quantities. In 
 the Grotto del Cane the gas issues from fissures some 
 two or three feet below the mouth of the cave. Up 
 to this depth the gas, by reason of its great density, 
 collects. The cave is thus fatal to small animals 
 thrown into it, while men breathing the pure air above 
 this level are unaffected. , 
 
 It is interesting to remind ourselves that carbon 
 dioxide has now became a commercial article in eve^- 
 day use. Aerated waters in almost every case hold 
 carbonic acid gas in solution, t The gas is forced in 
 under pressure, and in these circumstances the water 
 will take up more than its usual amount. On opening 
 a bottle, therefore, of one of these aerated waters, and 
 thus releasing the pressure, the gas begins to escape, 
 thereby causing effervescence and the peculiar spark- 
 ling appearance seen in the liquid. The consumption 
 
 * C -\- 62 COz ; or carbon -\- oxygen = carbon dioxide, 
 t The eau oxygene now somewhat in vogue contains oxygen in place 
 of carbonic acid. 
 
92 MEDICAL MYSTICISM. 
 
 of these drinks is now enormous. Forty years ago 
 two hundred thousand bottles of aerated waters were 
 consumed annually in France. Ten years ago two 
 hundred million bottles were scarcely sufficient to 
 satisfy the demand. Some natural waters are aerated, 
 for example, Apollinaris, Carlsbad, and Friedrichshall 
 waters. 
 
 To make the water strongly effervescent the gases 
 which escape from the Apollinaris Brunnen, and which 
 contain more than 99 per cent, of carbonic acid, are 
 condensed into the water by machinery specially 
 erected at the spring. The Apollinaris spring fur- 
 nishes a regular supply of water amounting to G,000 
 quart bottles per hour, or more than forty million 
 (40,000,000) bottles per annum.* 
 
 In manufacturing the artificial water the gas evolved 
 by treating marble with a mineral acid is first passed 
 through water in the purifier, then stored in a gas- 
 holder, and next passed into a machine for mixing it 
 thoroughly with water. The bottling of the water 
 is also effected by machinery, and in bottles now 
 generally used, small glass balls are inserted as a 
 substitute for corks. 
 
 Such then is the importance of carbonic acid gas, 
 which to Yan Helmont was known as the wild or out- 
 of-the-way gas, "gas silvestre." It would have seemed 
 to him strange and even incredible that so subtle and 
 intangible an essence should be bottled every day for 
 the use of thousands of quite ordinary mortals at quite 
 
 * Spon's Encyclopedia. 
 
MEDICAL MYSTICISM. Q3 
 
 ordinary dinner-tables. The wandering, mysterious 
 gas silvestre sparkling before us on our table of an 
 evening in the light shed by the burning of a still 
 more wonderful "gas" than any known to Van 
 Helmont, that is a strange picture to contrast with 
 the knowledge of his day. 
 
 Van Helmont was bitten with the Paracelsian 
 spiritualistic madness and was by this led to form 
 some very curious ideas. The archeus or sentient 
 soul he conceived as having its seat in the stomach, 
 where it directs the first digestion ; other digestions 
 being carried on with the aid of the vital spirits in 
 different parts of the body. There are in all six 
 digestions described by him ; the number seven has 
 been chosen by nature for the state of repose. The 
 mystical tendency of Van Helmont is sufficiently in- 
 dicated by the last clause. It permeated his whole 
 being. He had striven in vain to find any satisfac- 
 tory knowledge till he secured the works of Thomas 
 a Kempis and Jonn Tauler. He then thought he 
 perceived that wisdom is to be obtained only by 
 humility and prayer. Though a gentleman of means 
 and lord of Merode, of Royenbock, of Oorschot, and 
 of Pellines, he gave up all his property to his sister 
 and renounced all the privileges of his birth. After 
 this a genius appeared to him in all important cir- 
 cumstances of life, and in 1633 his own soul ap- 
 peared to him in the form of a resplendent crystal. 
 Having followed the ordinary courses of medicine and 
 discarding their doctrines with disgust, he turned his 
 
94 MEDICAL MYSTICISM. 
 
 attention to Paracelsus, of whom he became in most 
 respects a warm follower. After the year 1599 he 
 travelled for some time, and on his return married a 
 rich Brabantine lady and passed the rest of his life 
 on his estate at Vilvorde. 
 
 Van Helmont achieved for himself immortal fame 
 by his discovery of the gas silvestre, but for a long 
 period his work sank into obscurity and was forgotten. 
 Such strange halts are there in the progress of science 
 that it was left to Dr. Black, in the middle of the 
 eighteenth century, to rediscover infixed air the for- 
 gotten gas of Van Helmont. 
 
THIRD PERIOD, 
 
CHAPTER V. 
 
 THIKD PERIOD : THE DECLINE OF MYSTICISM. 
 GLAUBER. 
 
 , AN HELMONT as a disciple of Paracelsus was 
 mentioned immediately after him, but the 
 name of Agricola, who was a contemporary 
 (1490 1555) of Paracelsus, must not pass 
 unnoticed. He was the author of a re- 
 markable work, De Re Metallica, contain- 
 ing a complete treatise on metallurgy and mining, 
 and most clearly written. Many of the processes 
 described by him are now actually in use. 
 
 The next name of importance is that of Glauber 
 (1G03 1G68), who still shares a somewhat hazy 
 popular fame as the discoverer of " Glauber's salt," 
 or sodium sulphate. This was the piece of work 
 which seems to have been Glauber's favourite, and 
 his admiration for this substance certainly led him to 
 
 o 
 
9 8 THE DECLINE OF MYSTICISM. 
 
 much magnify its value. The hydrated* sodium sul- 
 phate, known as Glauber's salt, is first mentioned in 
 his De Natura Salium published in 1658. His col- 
 lected works were translated into English and pub- 
 lished in a folio volume " for public good, by the 
 labour, care, and charge of Christopher Packe, Philo- 
 Chemico-Medicus, in 1689. In Glauber's works 
 we find the first clear description of the preparation 
 of ammonium sulphate (sulphate of ammonia), for- 
 merly known as sal ammoniacum secretum Glauberi. 
 This salt is now used for the manufacture of other 
 ammonia salts, and is also largely employed as a fer- 
 tiliser in artificial manures. Its conversion into sal 
 ammoniac, f or ammonium chloride, by distillation 
 with common salt (sodium chloride), was also first 
 described by Glauber. Ammonium nitrate, too, was 
 first prepared by him and known as nitrum flam- 
 mans. The production of copper sulphate or blue 
 vitriol by boiling copper with sulphuric acid (oil of 
 vitriol) was first proved by Glauber in 1648. The 
 sulphate is now obtained on the manufacturing scale 
 by roasting the copper ores and digesting with sul- 
 phuric acid. It is largely used in calico-printing, 
 and in preparing copper pigments, such as Scheele's 
 green and emerald green. It is also used in electro- 
 metallurgy. 
 
 The production of vinegar by the distillation of 
 wood is described by Glauber, but not as a new dis- 
 
 * I.e., combined with water. 
 
 f Sal ammoniac, the reader may be reminded, was known to Geber. 
 
THE DECLINE OF MYSTICISM. 99 
 
 covery. He mentions that the acetum lignorum so 
 obtained may, by redistillation, be made as virtuous 
 as the common acetum vini. At a later date his 
 wood vinegar came to be known as pyroligneous acid, 
 a name which is indeed preserved still. The method 
 of preparing this acid and its derivatives is described 
 by Glauber in great detail and, apparently, with ori- 
 ginal improvements. He tells us of the power pos- 
 sessed by wood-tar, or the oily product of the distil- 
 lation, which is less volatile than the acid, of preserv- 
 ing wood. "Any wood exposed to the Rain, or 
 standing in the water, easily rotting, being anointed 
 with this Oil will be preserved so that it will not so 
 easily rot." In closing this portion of his discourse 
 Glauber says : " Nevertheless I easily persuade myself, 
 that this discourse of mine will not be credited by 
 many, which I cannot help. It content eth me that 
 I have written the Truth and lighted a candle to my 
 neighbour." 
 
 But Glauber's chief claim to immortality rests in 
 his being the first to describe the preparation of 
 hydrochloric (muriatic) acid, by distilling common 
 salt with sulphuric acid, and the first to obtain by 
 this same operation the sodium sulphate so long to 
 be known to posterity as <c Glauber's salt." The pre- 
 paration of the hydrochloric acid, or spirit of salt, is 
 described in the first section of the second part of 
 the Miraculum Mundi. Here also is given the 
 method for obtaining the Sal Mirabile, which is, of 
 course, obtained in the same process and the discovery 
 
THE DECLINE OF MYSTICISM. 101 
 
 of which first appeared in Glauber's De Natura 
 Salium in 1658. To the discussion of the spirit of 
 salt Glauber acutely adds : " Plainly after the very 
 same manner as we have taught spirit of salt to be 
 prepared, so may also be made Aquafortis* .... 
 Instead of salt take nitre, and you will have Aqua- 
 fortis" 
 
 The present method of preparing nitric acid from 
 nitre and oil of vitriol (sulphuric acid), would thus 
 appear to have been first used by Glauber, and, 
 indeed, for a long time afterwards the acid thus ob- 
 tained was known as Spiritus nitrifumans Glauberi. 
 Glauber entertained somewhat grandiose ideas as to 
 the uses and virtues of his salt. " Husbandmen, 
 physicians, apothecaries, and chirurgeons are to 
 receive in it a priceless boon." Again, " I believe 
 every Artificer and Trading Man when he can per- 
 form his work with less labour and charge, and 
 acquire his wares for less trouble and cost, will sell 
 his commodities to his neighbours at a cheaper rate 
 than he could before he found the benefit of this 
 salt." He then goes on to enumerate fifty-nine of 
 its uses in Medicine, the Arts, and in Alchemy. 
 
 As a stage in the manufacture of carbonate of soda 
 in the alkali works, the sulphate is now produced on 
 an immense scale. In the year 1876, no less than 
 
 * Nitric Acid. This acid is now prepared on the manufacturing 
 scale from sodium nitrate and oil of vitriol. It is largely employed in 
 the manufacture of coal-tar colours, nitro-glycerine, gun-cotton, sul- 
 phuric acid, and nitrate of silver (now much used for photography). 
 
102 THE DECLINE OF MYSTICISM. 
 
 700,000 tons were in this way prepared in the United 
 Kingdom. The pure sulphate is used in the production 
 of various kinds of glass chiefly bottles ; in certain 
 medicinal preparations, and to some small extent in 
 dyeing and printing. Here again, as in the case of 
 Helmont's gas silvestre, a wonder of the world has 
 become a commonplace. It is, however, none the less 
 wonderful for that. 
 
 Salt was regarded by Glauber as one of the prin- 
 ciples of matter, and he assigns more power to it than 
 to the others. " This known salt I here call (and 
 not injuriously) the universal treasure, and general 
 riches." Again, " It is the beginning and end of all 
 things, and it increases their powers and their virtues." 
 
 Glauber invented and improved chemical apparatus 
 to a large extent, and in his Furni Novi Philosophic 
 many useful and interesting furnaces may be found 
 described. 
 
 We cannot forbear, before closing our comments 
 upon Glauber, to quote the following amusing imita- 
 tion by him of the style adopted by Basil Valentine 
 in a paragraph already quoted. This passage occurs 
 in the discussion on concentrating and amending 
 metals by nitre. " First a man is to be made of iron, 
 having two noses on his head, and on his crown a 
 mouth which may be opened and again close shut. 
 This if it be to be used for the concentration of metals 
 is to be so inserted into another man made of iron or 
 stone, that the inward head only may come forth of 
 the outward man t but the rest of his body or belly 
 
104 THE DECLINE OF MYSTICISM. 
 
 may remain hidden in the belly of the exterior man. 
 And to each nose of the head glass receivers are to be 
 applied, to receive the vapours ascending from the 
 hot stomach. When you use this man you must 
 render him bloody with fire to make him hungry and 
 greedy of food. When he grows extremely hungry 
 he is to be fed with a white swan. When that food 
 shall be given to this iron man, an admirable water 
 will ascend from his fiery stomach into his head, and 
 thence by his two noses flow into the appointed 
 receivers ; a water, I say, which will be a true and 
 efficacious aqua- vita? ; for the iron man consumeth the 
 whole swan by digesting it, and changeth it into a 
 most excellent and profitable food for the king and 
 queen, by which they are corroborated, augmented, 
 and grow. But before the swan yieldeth up her spirit 
 she singe th her swan-like song, which being ended, 
 her breath expireth with a strong wind, and leaveth 
 her roasted body for meat for the king, but her 
 anima or spirit she consecrateth to the gods that thence 
 may be made a salamander, a wholesome medicament 
 for men and women." This is a very good imitation 
 of the style of the older alchemists. It has the advan- 
 tage, too, of being more humorously absurd. The iron 
 man with two noses to which receivers are attached is 
 seen in the illustration which is taken from a woodcut 
 in Packe's edition of Glauber's collected works. 
 
 We may get a further glimpse into the character of 
 our author from the following quotation taken from a 
 paragraph on gunpowder ; 
 
THE DECLINE OF MYSTICISM. 105 
 
 '' Of this mischievous composition and diabolical 
 abuse of gunpowder much might be written ; but 
 because the present world taketh only delight in shed- 
 ding innocent blood, and cannot endure that un- 
 righteous things should be reproved, and good things 
 praised, therefore it is best to be silent, and to let 
 every one answer for himself when the time cometh 
 that we shall give an account of our stewardship, 
 which, perhaps, is not far off ; and then there will be 
 a separation of good and bad by him that trieth the 
 heart, even as gold is refined in the fire from dross. 
 And then it will be seen what Christians we have been. 
 We do all bear the name, but do not approve our- 
 selves to be such by our works. Ever one thinketh 
 himself better than others, and for a word's sake which 
 one understandeth otherwise, or takes in another sense 
 than the other (and though it be no point whereon 
 salvation doth depend), one curseth and condemneth 
 another, and persecuteth another unto death, which 
 Christ never taught us to do, but rather did earnestly 
 command us that we should love one another, reward 
 evil with good and not good with evil as now-a-days 
 everywhere they use to do. Every one standeth upon 
 his own reputation ; but the honour of God and his 
 commands are in no repute, but are trampled under 
 foot, and Lucifer's pride, vain ambition, and phari- 
 saical hypocrisy or show of holiness hath so far got 
 the upper hand with the learned, that none will leave 
 his contumacy or stubbornness or recede a little from 
 his opinion, although the whole world should be turned 
 
106 THE DECLINE OF MYSTICISM. 
 
 upside down thereby. Are not these fine Christians ? 
 By their fruit you shall know them, and not by their 
 words. Wolves are clothed with sheep's skins, so that 
 none of them almost are to be found, and yet the 
 deeds and works of wolves are everywhere extant." 
 
 This is not chemistry, it is true : but we are con- 
 cerned here also with character, and of that the pre- 
 vious passage gives much indication. What a man visi- 
 bly does may not be so important as what he is. As 
 Emerson puts it, " we do not want actions, but men." 
 So in studying the lives of the workers in any tech- 
 nical branch of human labour, the study is generally 
 pleasant in proportion to the space in their hearts 
 which we find unoccupied by technicality. The quaint 
 moralizing of Glauber in the foregoing passage and in 
 other places shows us a man who had a good deal of 
 earnestness in his heart, and it is all the pleasanter on 
 that account to read of his chemical work. 
 
 Glauber was a truly scientific worker and had a 
 fertile mind. We see in his work a distinct advance 
 in method upon that of Basil Valentine. It is cer- 
 tainly more sane, though not so striking, as that of 
 Paracelsus. We are indeed approaching, though 
 sloAvly, to a more quietly scientific age. Mysticism 
 had received some mortal wounds to which, in spite 
 of its intense vitality, it must gradually succumb. 
 Theory was gradually to become more closely insepar- 
 able from observation and experiment. 
 
 An interesting alchemical work may next be re- 
 ferred to The Brief of the Golden Calf: discover- 
 
THE DECLINE OF MYSTICISM. 107 
 
 ing the Rarest Miracle in Nature, how by the smallest 
 portion of the Philosopher s Stone a great Piece of 
 common Lead teas totally transmuted into the purest 
 transplendent Gold, at the Hague in 1C 66. This 
 work is by Joliann F. Helvetius, and contains one of 
 the most celebrated records of transmutation, which, 
 as it is of considerable interest, may be here quoted 
 at some length : " : 
 
 "The 27th day of December, 1666, in the afternoon, 
 came a stranger to my house at the Hague, in a ple- 
 beick habit, of honest gravity and serious authority, 
 of a mean stature and a little long face, black hair and 
 not at all curled, a beardless chin, and about forty -four 
 years (as I guess) of age, and born in ^fcrth Holland. 
 After salutation he beseeched me with great reverence 
 to pardon his rude accesses, for he was a lover of the 
 Pyrotechnian art, and having read my treatise against 
 the sympathetic powder of Sir Kenelm Digby, and 
 observed my doubt about the philosophic mystery, 
 induced him to ask me if I really was a disbeliever as 
 to the existence of a universal medicine which would 
 care all diseases, unless the principal parts were 
 perished or the predestinated time of death come. I 
 replied I never met with an adept, or saw such a 
 medicine, though I had frequently prayed for it. 
 
 " Then I said, ' Surely you are a learned physician.' 
 ' No,' said he, * I am a brass-founder and a lover of 
 
 * The original version is, like most of these documents, exceedingly 
 prolix and abounds in unnecessary details. That here given is from 
 an abridgment in Brande's Chemistry, 
 
icS THE DECLINE OF MYSTICISM. 
 
 chemistry.' He then took from his bosom-pouch a 
 neat ivory box, and out of it three ponderous lumps 
 of stone, each about the bigness of a walnut. I 
 greedily saw and handled for a quarter of an hour this 
 most noble substance, the value of which might be 
 somewhere about twenty tons of gold ; and having 
 drawn from the owner many rare secrets of its admir- 
 able effects, I returned him this treasure of treasures 
 with a most sorrowful mind, humbly beseeching him 
 to bestow a fragment of it upon me in perpetual 
 memory of him, though but the size of a coriander 
 seed. ' No, no/ said he, ' that is not lawful, though 
 thou wouldst give me as many golden ducats as would 
 fill this room ; for it would have particular conse- 
 quences, arid, if fire could be burned of fire, I would 
 at this instant rather cast it all into the fiercest flames.' 
 He then asked if I had a private chamber whose pro- 
 spect was from the public street ; so I presently con- 
 ducted him to my best furnished room backwards, 
 which he entered without wiping his shoes, which 
 were full of snow and dirt. 
 
 " I now expected he would bestow some great 
 secret upon me, but in vain. He asked for a piece 
 of gold, and opening his doublet showed me five 
 pieces of that precious metal which he wore upon 
 a green riband, and which very much excelled mine 
 in flexibility and colour, each being the size of a 
 small trencher. I now earnestly craved a crumb 
 of the stone, and at last, out of his philosophical com- 
 miseration, he gave me a morsel as large as a rape- 
 
THE DECLINE OF MYSTICISM. log 
 
 seed ; ( But/ I said, ' this scant portion will scarcely 
 transmute four grains of lead/ ' Then/ said he, ' de- 
 liver it me back ; ' which I did in hopes of a greater 
 parcel ; but he, cutting off half with his nail, said, 
 ' Even this is sufficient for thee/ ' Sir/ said I, with 
 a dejected countenance, 'what means this?' And he 
 said, 'Even that will transmute half an ounce of lead/ 
 So I gave him great thanks and said I would try, and 
 reveal it to no one. He then took his leave and said 
 he would call again next morning at nine. 
 
 " I then confessed that while the mass of his medicine 
 was in my hand, I had secretly scraped off a bit with my 
 nail which I projected on lead, but it caused no trans- 
 mutation, but the whole flew away in fumes. ' Friend/ 
 said he, ' thou art more dexterous in committing a 
 theft than in applying medicine ; hadst thou wrapped 
 up thy stolen prey in yellow wax, it would have pene- 
 trated and transmuted the lead into gold/ I then 
 asked if the philosophic work cost much or required 
 long time, for philosophers say that nine or ten 
 months are required for it. He answered, ' Their 
 writings are only to be understood by adepts, without 
 whom no student can prepare his magistery. Fling 
 not away, therefore, thy money and goods in hunting 
 out this art, for thou shalt never find it/ To which I 
 replied, ' As thy master showed it thee, so mayest thou 
 perchance discover something thereof to me, who 
 know the rudiments, and therefore it may be easier to 
 add to a foundation than begin anew/ ' In this art/ 
 said he, ' it is quite otherwise ; for unless thou knowest 
 
no THE DECLINE OF MYSTICISM. 
 
 the thing from head to heel, thou canst not break 
 open the glassy seal of Hermes. But enough ; to- 
 morrow at the ninth hour, I will show thee the man- 
 ner of projection.' 
 
 " But Elias never came again ; so my wife, who 
 was curious in the art whereof the worthy man 
 had discoursed, teased me to make the experiment 
 with the little spark of bounty the artist had left 
 me. So I melted half an ounce of lead, upon which 
 my wife put in the said medicine ; it hissed and 
 bubbled, and in a quarter of an hour the mass of lead 
 was transmuted into fine gold, at which we were ex- 
 ceedingly amazed. I took it to the goldsmith, who 
 judged it most excellent, and willingly offered fifty 
 florins for each ounce." 
 
 Comment upon this story is needless. If the events 
 narrated were not very much out-of-the-way we should 
 believe Helvetius at once, but, of such a very extraor- 
 dinary occurrence we should probably feel uncertain 
 on all evidence short of ocular demonstration. 
 
FOURTH PERIOD. 
 
CHAPTER VI. 
 
 FOURTH PERIOD: THE BEGINNINGS OF SCIENCE. 
 
 ,N event of importance belonging to the period 
 with which we have been dealing may 
 here be referred to. The Royal Society 
 was founded by Charles II., and incor- 
 porated by him in 1662, under a Royal 
 Charter, for the improvement of natural 
 knowledge. The first volume of the Philosophical 
 Transactions of that Society bears date 1665. With 
 occasional intermissions the Transactions were pub- 
 lished by the successive secretaries of the Society till 
 the year 1750. At that date the publication was put 
 into the hands of a Committee of Papers, and since 
 1762 a volume has annually appeared. 
 
 In 1666 the Royal Academy of Sciences was in- 
 stituted in Paris under the protection of Louis XIV, 
 
ii4 THE BEGINNINGS OF SCIENCE. 
 
 In its early annals we find the names of Homberg, 
 Geoffrey, and the two Lemerys. Homberg discovered 
 boracic acid, which he prepared by decomposing 
 borax by means of a mineral acid, and termed sal 
 sedativum. Geoffrey made contributions to pharma- 
 ceutical chemistry, and was probably the first com- 
 piler of the " Paris Pharmacopoeia." Of the Lem&rys 
 more will be said in the sequel. 
 
 Ever since its foundation the Eoyal Society of 
 London has been a nucleus round which has clustered 
 the scientific genius of Great. Britain. In the earlier 
 years of its infancy it helped to fan the few glowing 
 sparks of the desire for truth into a broadening blaze. 
 It brought together those who were in sympathy, 
 through their devotion to knowledge, and who in 
 their union found double strength. By the inter- 
 change of their ideas thought was quickened and the 
 advance of science aided. By the publication of 
 original papers new discoveries were placed on record, 
 and thus preserved from being lost, as had too often 
 happened before. The discussion of these papers 
 helped more thoroughly to sift the evidence on which 
 their conclusions were based, and promoted much 
 increased accuracy and simplicity of thought and 
 expression. 
 
 Kesearch, too, was stimulated by the increased 
 definiteness of boundary between the known and the 
 unknown. Before such societies had existed the 
 magic-mongers, who then so frequently took the 
 place of men of science, were accustomed to produce 
 
THE BEGINNINGS OF SCIENCE. 115 
 
 their questionable results in mystical folios, or still 
 stranger manuscripts, the few copies of which became 
 dispersed and too often lost. It was, therefore, al- 
 most impossible to tell what subjects were really 
 uninvestigated, and hence arose much repetition of 
 already accomplished work, and delay in the real 
 advancement of learning. Research was also more 
 directly encouraged by the Royal Society, by award- 
 ing grants of money to defray the expenses of those 
 investigations which seemed worthy of such aid. 
 
 Having now left Glauber behind us, we are enter- 
 ing upon a new epoch once more, the period with 
 which the names of Boyle, Hooke, and Mayow are 
 indissolubly connected. 
 
 But, before passing on to consider Boyle and his 
 assistant, Hooke, mention must be made of a chemist 
 whose work, though not of so great importance, is yefc 
 of considerable interest. Nicholas Lemery (1645 
 1715) was the well-known author of the GOUTS de 
 CTiymie (1675). This book embodied his ideas and 
 teachings, and, being translated into Latin and most 
 modern languages, enjoyed a wide popularity and 
 produced great effects upon the progress of the 
 science. He still retained the belief in salt, mercury 
 (or spirit), sulphur (or oil), as elements, but to these 
 were added water (or phlegm), and earth. The for- 
 mer set were the active, the latter the passive ele- 
 ments. As already stated these terms when thus 
 used did not necessarily signify only the bodies more 
 specially known by those Dames. " Sulphur," although 
 
1 1 6 THE BEGINNINGS OF SCIENCE. 
 
 used for brimstone, was also more generally applied 
 to oils (perhaps from their usually having a yellow 
 colour), and hence we also find the plural " sulphurs" 
 in use. The substances included under one of these 
 names were also supposed to share the same essential 
 nature exhibited under different forms. It is difficult 
 to state clearly what these ideas were ; the fact being 
 that the ideas themselves were not clear. But if we 
 bear this in mind we shall be able to appreciate the 
 advances made as the theoretical notions of the 
 chemists become more intelligible. 
 
 Lemery, in his work, defines the aim of chemistry 
 to be a knowledge of the various substances " qui se 
 rencontrent dans un mixte " (which meet in a com- 
 pound), understanding by this term natural products 
 in general. He classifies the products as mineral, 
 vegetable, and animal, placing among the first, 
 metals, minerals, earths, and stones ; among the 
 second, plants, resins, gums, fungi, fruits, acids, juices, 
 flowers, mosses, manna, and honey ; and among 
 the third, the various parts of the animal organism. 
 Lemery thus established the distinction, now become 
 so broadly defined, between inorganic and organic 
 chemistry. The difference between the two realms 
 of the science was for long a subject of dispute. It 
 became gradually evident that the chemistry of mine- 
 rals or unorganized structures obeys certain well- 
 defined and never abrogated laws. A true inorganic 
 chemical compound, say, for instance, mercuric oxide, 
 is found on analysis to have always the same compo- 
 
THE BEGINNINGS OF SCIENCE. 117 
 
 sition ; in this case, 100 parts of mercuric oxide 
 always contain 92 4 6 parts of mercury to 7'4 parts of 
 oxygen. Now, owing to the difficulty of purifying 
 substances found in the vegetable and animal king- 
 doms, it was for a long time considered that these 
 bodies did not obey those and other laws of com- 
 bination. 
 
 :' As discovery advanced, however, substances, un- 
 mistakably organic, were found which distinctly 
 obeyed these laws'; and when finally it was found 
 possible artificially to prepare compounds previously 
 known only as existing in the organized structure of 
 plant or animal, the gulf, hitherto separating the 
 organic and inorganic realms of the science, was at 
 last bridged, and the universal reign of consistency 
 and law became apparent. 
 
 But the gulf although -bridged did not cease to 
 exist, although it has been subsequently narrowed. 
 Broadly, the distinction is now between compounds 
 of carbon, and compounds of not-carbon. The ele- 
 ment carbon is sharply distinguished from the other 
 elements by the immense number and complexity of 
 its compounds, while among these compounds nearly 
 all the substances playing an active part in the life 
 and decay of an organized structure are to be found. 
 Becher, in 1669, argued that the same elements occur 
 in the three natural kingdoms, but more simply 
 combined in the mineral than in the vegetable or 
 animal. Stahl, in 1702, asserted that- in vegetable 
 as well as animal substances a larger proportion of 
 
n8 THE BEGINNINGS OF SCIENCE. 
 
 watery and combustible principles is to be found ; a 
 view in which he was perfectly at one with the more 
 exact science of a later day, for hydrogen and carbon 
 are as a rule the main and characteristic constituents 
 of organic bodies. Van Helinont had held before 
 Stahl that organic substances can be resolved by 
 heat into their constituent elements, aqueous and 
 combustible principles, or water and fire. This idea 
 was, as we shall see, controverted by Robert Boyle 
 in his " Sceptical Chemist " (1661). He pointed out 
 that heat leads to different results under different 
 conditions. As an example of how near the light 
 truth may rest hidden for long periods before being 
 discovered, it is interesting to note that, in spite of 
 these suggestive discussions regarding the composition 
 of organic bodies, it was not till 1784 that the exis- 
 tence of carbon and hydrogen hi alcohol was a proven 
 fact. 
 
CHAPTER VII. 
 
 FOURTH PERIOD. THE BEGINNINGS OF SCIENCE. 
 THE ACKNOWLEDGMENT OF NESCIENCE.* 
 
 t 
 
 >E have already observed that the progress of 
 chemistry was once more carrying it into 
 a new era far more nearly allied to the 
 present. Like the dawn of much new 
 knowledge which the world slowly wins 
 from darkness, the first brightening touch 
 on the horizon was to creep upwards in a tremulous 
 twilight of doubt. It is ever difficult to unsay what 
 is said, or to combat an error that has become a 
 habit of thought. Old instincts and old superstitions 
 when they have ceased to be openly loud in their 
 insistence, fall back upon whispering persuasion, to 
 which, because we are often unconscious of its 
 seductive suggestion, we easily fall a prey, and before 
 
 * The term nescience is a convenient one to signify the negation or 
 absence of knowledge. 
 
izo THE BEGINNINGS OF SCIENCE. 
 
 we can dare to openly defy a principle which has 
 lived long in our hearts, we pass through a time of 
 half-timid wonderment, and doubt if, after all, it 
 be infallibly true. Then, after a long period of 
 lingering doubt, our mind is made up, and we 
 combat the false thought until we think that we 
 have slain it. But a false confidence in our victory 
 often deludes us, and the day comes when we 
 discover in some fresh bias our old enemy in a new 
 disguise. 
 
 A parallel to this frequent course of progress in 
 the individual human mind is found in the changes 
 passed through by the science we are considering. 
 Alchemy and mysticism had ruled the older chemists, 
 the latter partially crystallizing in the form of fan- 
 tastical notions concerning the fundamental principles 
 of matter. Slowly but surely uncertainty and doubt 
 was creeping into the minds of the workers as to the 
 so-called truths of transmutation. For some time 
 yet the doubt was not to become open denial, and 
 the idea was to spring up again and again even until 
 the present century, at the commencement of which 
 Peter Woulfe lived. The curious mysticism em- 
 bodied in the notions entertained about the elements 
 was to prove a phantom even less easily exorcised, 
 and more powerful to do harm. The period of doubt 
 was beginning, as will be seen in the discussion of 
 Robert Boyle, and true ideas concerning the nature 
 of an " element," and hence of combustion and otlier 
 important natural phenomena, seemed about to spring 
 
THE BEGINNINGS OF SCIENCE. 121 
 
 up. But soon after this the apparently-slain demon 
 was to be resuscitated as a giant of invulnerable 
 strength. The phlogistic theory was started, and, as 
 we shall see, for half a century it held chemistry in 
 thrall, and caused men of remarkable brilliancy and 
 power to grope blindly in the darkness for truths 
 which, except for the baleful shadow that en- 
 shrouded them, would have been as clear as day. 
 Chemistry had to wait for the steady lustre of 
 Lavoisier's talents to dispel the gloom. 
 
 In entering upon this period of doubt, we shall 
 discuss the three chemists, Boyle, Hooke, and Mayow ; 
 and first of all let us take the man who is most 
 fitly representative of this era Robert Boyle. 
 
 Robert Boyle (1627 1691) was the seventh son 
 and fourteenth child of Richard, Earl of Cork. He 
 was born at Lismore, in Munster. At eight years of 
 age he was sent to Eton, where, says he, a perusal of 
 " Quintus Curtins" "conjured up in me that un- 
 satisfied appetite for knowledge that is yet as greedy 
 as when it was first raised." It is related that while 
 recovering from a fever at Eton he was induced to 
 read "Amadis de Gaul" and other romantic books. 
 The effect of the romance of that period upon him 
 was to produce an intolerable restlessness and unset- 
 tlement in his mind, which he determined to end. 
 To counteract these tendencies, he, therefore, set 
 himself, .being then ten years old, to extracting 
 square and cube roots and other laborious and 
 uninteresting calculations, in order to calm his brain. 
 
122 THE BEGINNINGS OF SCIENCE. 
 
 Such strength of mind in one so young was perhaps 
 to be condemned as dangerously prophetic of too 
 great austerity. As a matter of fact, however, he 
 seems through life to have kept his heart readily 
 open to human sympathies and to have been quite 
 free from the cynical reserve which has characterized 
 a few intellectual workers. While at Eton his life 
 was greatly endangered by the fall of the room in 
 which he was sleeping, and had he not, with striking 
 presence of mind, wrapped the sheet of the bed round 
 his face he would probably have been suffocated with 
 the dust. 
 
 After about four years at Eton, Boyle went to his 
 father's seat in Dorset, and afterwards travelled 
 abroad with his brother Francis and tutor. He took 
 a view of those wild mountains where Bruno, the 
 first founder of the Carthusian monks, lived in 
 solitude, and where the first and chief of the 
 Carthusian abbeys was built. Boyle relates that " the 
 devil, taking advantage of that deep, raving melan- 
 choly, so sad a place, his own humour, which was 
 naturally grave and serious, and the strange stories 
 and pictures he found there of Bruno, suggested 
 such strange and distracting doubts of some of the 
 fundamentals of Christianity that, though his looks 
 did little betray his thoughts, nothing but the for- 
 biddenness of self-despatch hindered his acting it."* 
 He shortly after became fully converted to Christi- 
 anity, though "the fleeting clouds of doubt and 
 
 hic Britannica. 
 
THE BEGINNINGS OF SCIENCE. 123 
 
 disbelief did .never after cease to now and then 
 darken the serenity of his quiet." Boyle was in 
 Marseilles in 1641 at the outbreak of the Irish 
 Rebellion. His father transmitted his brother 250, 
 but it never reached them, and they were left almost 
 penniless. They made their way to Marcombes, and 
 then to Geneva, where they lived for two years on 
 credit, and at length, by the sale of some jewels, got 
 together enough money to bring them home. They 
 reached England in the summer of 1644. Their 
 father was dead, and so confused was the state of the 
 country that for nearly four months Boyle could not 
 make his way to the manor of Stalbridge, which he 
 had inherited. 
 
 But through all this turmoil the scientific men were 
 steadily, though secretly, at work. Through all the 
 din of conflicting faction and disputed power they 
 held calmly on towards the goal which to them was 
 highest and best. There is something perhaps rather 
 coldly grand about their impenetrable patience, but 
 grand it certainly is. The " Philosophical Society," or, 
 as Boyle preferred to call it, the " Invisible Society," 
 met secretly in London in 1645, and from these 
 meetings he derived fresh impulse. " Vulcan has so 
 transported and bewitched me," he wrote from Stal- 
 bridge to his sister, Lady Ranelagh (1649), "as to 
 make me fancy my laboratory a kind of Elysium." 
 In 1652 3 he visited his Irish estates, and on his 
 return in 1654 settled at Oxford in the society of 
 some of his early philosophical associates. Meetings 
 
124 
 
 THE BEGINNINGS OF SCIENCE. 
 
 were held amongst them and experiments performed 
 and discussed. 
 
 In 1659 Boyle perfected his air-pump, and in 
 1660, amongst other results, he published "Boyle's 
 Law," confirmed by Mariotte in 1676. This well- 
 known law asserts that the volume* of a gas varies 
 
 inversely as the pressure. For instance, if a certain 
 volume of air be contained in the closed end of 
 the U-shaped tube shown in the illustration, let 
 us call this volume 1, and the pressure to which it is 
 at first subjected 1. If we double the pressure we 
 shall halve the volume. The volume 1 under pres- 
 sure 1 becomes the volume J under pressure 2, the 
 
 * " Volume " means the amount of cubic space occupied by any 
 substance. 
 
THE BEGINNINGS OF SCIENCE. , 25 
 
 volume I under pressure 4, and so on. Similarly 
 the volume 1 under pressure 1 becomes the volume 
 2 under a pressure J, the volume 4 under pressure 
 i &c. Of the two cases shown in the illustration the 
 first shows the gas at the ordinary pressure of the 
 atmosphere, the mercury standing at the same height 
 in each limb of the tube. Now the ordinary pressure 
 
 SIMPLEST FORM OF THE BAROMETER. 
 
 of the atmosphere, as recorded by the barometer, is 
 sufficient to support a column of mercury 760 milli- 
 metres high. If therefore we pour mercury into the 
 long limb of the bent tube till the height of the 
 column in it is 760 millimetres higher than the 
 height of the column in the short limb, the gas 
 enclosed behind the mercury which was formerly at 
 
126 THE BEGINNINGS OF SCIENCE. 
 
 the ordinary atmospheric pressure will now have 
 to sustain twice that pressure, and its volume is 
 accordingly halved, as is seen in the second illustra- 
 tion. This law, though not exactly true for all degrees 
 of pressure, has yet been of very great service. 
 
 It may be objected that this is a question of physics 
 rather than of chemistry. But it is a law, which 
 is in every-day use by the chemist in calculating 
 the amount of a gas the volume of which is not 
 observed under the normal pressure of 760 mm. A 
 further complication arises from the fact that these 
 gases are observed at various temperatures and not 
 often at the normal temperature, which is taken as 
 the melting point of ice, or centigrade. Now 
 gases expand on heating, and it was Gay-Lussac who 
 at a much later date discovered the laws of their 
 expansion. Each gas expands for one degree centi- 
 grade Y -f T of its volume at C. Thus 273jolumes 
 of gas at C. become at 1 equal to 274 volumes, 
 and so on. From these laws we can readily reduce 
 the volume of a gas observed at any given tempera- 
 ture and pressure to the volume the same weight of 
 gas would occupy at C. and 760 mm. pressure. 
 Once this is known the weight of the gas may be very 
 simply deduced. In this way, if in analysing a 
 nitrogenous organic body a certain volume of nitrogen 
 is obtained, the weight of nitrogen contained in the 
 body is readily calculated. 
 
 In 1668 Boyle came to London and was a pro- 
 minent member of the then newly constituted Royal 
 
THE BEGINNINGS OF SCIENCE. 127 
 
 Society. He was elected president in 1680, but 
 refused to act, owing to a scruple he entertained as to 
 taking oaths. In 1689 his health began to fail and 
 he issued an advertisement restricting the visits of 
 his acquaintances. He also had a board put up out- 
 side his house announcing when he received visits. 
 Boyle's health had never been good ; from the age 
 of twenty-one he suffered from stone, and much feared 
 that if it forced him to take to his bed the pain of it 
 would become insupportable. He died, however, 
 without pain, and almost without serious illness. 
 
 Boyle developed talent early, and at twenty-one he 
 had already written on ethics and published several 
 moral and religious essays. In 1 6 6 5 he published his 
 " Occasional Reflection upon Several Subjects," which 
 procured him the satire of Swift in " A pious Medita- 
 tion upon a Broomstick, in the style of the Honourable 
 Mr. Boyle." 
 
 Personally Robert Boyle is described as pale, 
 emaciated, and very delicate, so " that he had divers 
 sorts of cloaks to put on when he went abroad, 
 according to the temperature of the air, and in this 
 he governed himself by his thermometer .... For 
 almost forty years he laboured under such a feeble- 
 ness of body and lowness of strength and spirits that 
 it was astonishing how he could read, meditate, try 
 experiments and write as he did." To these dis- 
 abilities was added that of a memory by his own 
 account so treacherous that he was often tempted to 
 abandon study in despair. 
 
iz8 THE BEGINNINGS OF SCIENCE. 
 
 He " wore the white flower of a blameless life." 
 Naturally choleric he controlled himself to mildness; he 
 was unostentatiously liberal, unselfish, and unambitious. 
 He refused to take orders, excusing himself on the 
 ground of not having an inner call, though this involved 
 refusing the provostship of Eton. He also repeatedly 
 declined a peerage. There is something very attrac- 
 tively quiet and simple about such a nature. It is 
 an example of a man who worked quietly and peace- 
 fully at the problems toward which his nature felt 
 drawn, undisturbed by feverish unrealities of ambi- 
 tion and unsullied by the desire of worldly fame. 
 His work never led him into the bitter controversies 
 in which others have sometimes too readily engaged, 
 it did not lead him to forget the claims of human 
 sympathy and sorrow, or to doubt the existence of 
 knowledge beyond his own. The work itself has 
 proved of lasting and notable service, and perhaps 
 even more serviceable when we read of it, was the 
 calm, unsullied purity of his soul. 
 
 Boyle's principal chemical work was published in 
 1661, under the title of The Sceptical Chymist ; or 
 Chemico-physical Doubts and Paradoxes, touching the 
 Experiments whereby vulgar Spagyrists are wont to 
 endeavour to evince their Salt, Sulphur, and Mercury 
 to be the true Principles of Things. We see here 
 the beginning of the time of doubt. It is in this work 
 that the first rational notion of an element, and of the 
 difference between an element and a compound, is con- 
 tained. The book is written in the form of a discus- 
 
THE BEGINNINGS OF SCIENCE. 129 
 
 sion between a party of learned gentlemen, of whom 
 one, Carneades, plays the part of the Sceptical Chymist. 
 The earlier portions of the book are devoted to a 
 demolition of the Aristotelian doctrine of the elements, 
 which is amusingly and interestingly defended by one 
 speaker in the following passage : 
 
 " I speak thus, Eleutherius (adds Themistius), only 
 to do right to reason, and not out of diffidence of the 
 experimental proof I am to allege. For though I shall 
 name but one, yet it is such a one as will make all 
 other appear as needless, as itself will be found satis- 
 factory. For if you but consider a piece of green wood 
 burning in a- chimney, you will readily discern in the 
 disbanded parts of it the four elements of which we 
 teach it and other mixed bodies to be composed. The 
 fire discovers itself in the flame of its own light ; the 
 smoke by ascending to the top of the chimney and 
 there readily vanishing into air like a river losing itself 
 in the sea, sufficiently manifests to what element it 
 belongs and gladly returns. The water in its own 
 form boiling and rising at the ends of the burning 
 wood betrays itself to more than one of our senses ; 
 and the ashes by their weight, their firiness, and their 
 dry ness put it past doubt that they belong to the ele- 
 ment of earth. If I spoke (continues Themistius) to 
 less knowing persons I would perhaps make some ex- 
 cuse for building upon such an obvious and easy 
 analysis, but 'twould be I fear injurious not to think 
 such an apology needless to you, who are too judi- 
 pious either to think it necessary that experiments to 
 
 I 
 
130 THE BEGINNINGS OF SCIENCE. 
 
 prove obvious truths should be far-fetched, or to 
 wonder that among so many mixed bodies that are 
 compounded of the four elements some should, upon 
 a slight analysis, manifestly exhibit the ingredients they 
 consist of." There is a delicious naivete about the 
 concluding portion of this speech, a blind simplicity 
 that is almost charming. The absurdity of the sup- 
 positions implied in the experiment are so quietly put 
 aside, that we become aware of the figure of Boyle 
 behind Themistius with a satirical smile upon his 
 face. 
 
 Carneades, after some preamble, replies thus : " To 
 begin then with his experiment of the burning wood, 
 it seems to me to be obnoxious to not a few consid- 
 erable exceptions. And first, if I would now deal 
 rightly with my adversary, I might here make a great 
 question of the very way of probation which he and 
 others employ without the least scruple to evince 
 that the bodies commonly called mixed are made up 
 of earth, air, water, and fire, which they are pleased 
 also to call elements ; namely, that upon the supposed 
 analysis made by fire of the former sort of concretes, 
 there are wont to emerge bodies resembling those 
 which they take for the elements. For . . . . i-f I 
 were disposed to wrangle I might allege that by The- 
 mistius, his experiments, it would appear rather that 
 those he calls elements are made up of those he calls 
 mixed bodies, than mixed bodies of the elements ; 
 .... it appears .... that which he takes for ele- 
 mentary fire and water are made out of the concrete, 
 
THE BEGINNINGS OF SCIENCE. 131 
 
 but it appears not that the concrete was made up of 
 fire and water. Nor has .... he .... yet proved 
 that nothing can be obtained from a body by the fire 
 that was not pre-existent in it." 
 
 There is some very shrewd reasoning here. How, 
 indeed, are we to know that heat thus applied splits 
 a body up into its constituent elements ? Besides, the 
 absurdity of describing the smoke as air when; as Car- 
 neades points out, the main portion of it descends 
 as soot, what an odd piece of reasoning it is which 
 makes the appearance of flame during the combus- 
 tion prove that fire is one of the principles of the 
 wood. 
 
 In the succeeding discourses Carneades proceeds to 
 apply his judgment to the other theories of the elements 
 as well. He states that the so-called elements obtained 
 by the chemists are not even pure. He is told that 
 later Aristotelians have undertaken to further purify 
 these supposed elements (salt, sulphur, and mercury). 
 Very well, that does not alter the truth of what he 
 has said as to the ordinary operations. " And as to 
 the thing itself, I shall freely acknowledge to you that 
 I love not to be forward in determining things to 
 be impossible, till I know and have considered the 
 means by which they are proposed to be effected. 
 And therefore I shall not peremptorily deny either 
 the possibility of what these artists promise, or my 
 assent to any just inference, however destructive to 
 my conjectures, that may be drawn from their per- 
 formance. But give me leave to tell you withal, 
 
132 THE BEGINNINGS OF SCIENCE. 
 
 that, because such promises are wont (as experience 
 has more than once informed me) to be much more 
 easily made than made good by chemists, I must with- 
 hold my belief from their assertion till their experiments 
 exact it, and must not be so easy as to expect before- 
 hand an unlikely thing upon no stronger inducements 
 than are yet given me." 
 
 The extreme and almost amusing caution of Car- 
 neades is sufficiently evident from the above quota- 
 tions. He has begun to distrust the old theories and 
 beliefs, but he is not prepared to dogmatically assert 
 a new creed of his own. But in the course of the dis- 
 cussion it becomes more and more clear what defini- 
 tion of the "element" Carneades is inclined to favour. 
 The modem view is here for the first time suggested, 
 that an element is a body which by no -known process 
 can be split up into two or more different substances. 
 It is a simple body. It is a whole made up of similar 
 parts. If we find that we can, by some new analytical 
 process, split up an apparently simple body, we cease 
 to regard it as an element ; and it is by no means 
 improbable that we may in this way cease to regard 
 as elements many of the substances now so-called. 
 
 Boyle was quite aware of the variability of the 
 number of apparently elemental principles. He thinks 
 " that it may as yet be doubted whether or no there 
 be any determinate number of elements ; or, if you 
 please, whether or no all compound bodies do consist 
 of the same number of elementary ingredients or 
 material principles." Finally, in a sequel added to the 
 
THE BEGINNINGS OF SCIENCE. 133 
 
 discourses proper to the Sceptical Cliymist, Carneades 
 goes so far as to say : "I am content .... 
 to tell you that .... though it may seem extrava- 
 gant, yet it is not absurd, to doubt whether, for ought 
 has been proved, there be a necessity to admit any 
 elements or Hypostatical principles at all." Boyle 
 had certainly penetrated far into the period of 
 doubt/" 
 
 From these details we see the great credit due to 
 Boyle for first openly distrusting the curiously vague 
 and mystical notions, concerning the constitution of 
 the various kinds of matter, which for so long had 
 held in bondage the infant science. It was a strangely 
 deep insight which led him to view the number of so- 
 called elements as variable, and it may even be that 
 his suggestion that, after all, there may be no such 
 thing as a true element, may become the most accepta- 
 ble hypothesis. Or it may be thought that all the 
 elements enumerated in our tables are modifications 
 and combinations of modifications of one primordial 
 element. Oxygen, hydrogen, nitrogen, iron, copper, 
 are well-known examples of substances now regarded 
 as elements. It may well, however, be that, by spec- 
 troscopical or other mode of research, these substances 
 may; be found to be made up of still simpler bodies, 
 
 * See also the interesting Appendix to the Sceptical Chymist, on the 
 Produciblcncss of Chemical Principles. In this Boyle discusses the want 
 of uniformity among bodies supposed to be part of the same principle. 
 Thus some oils, spirits, and brimstone, were all termed sulphurs, 
 because inflammable. Boyle looks with disfavour upon so loose a 
 notion, and thinks it more probable that "sulphur " itself is made up 
 of the same universal matter as other bodies. 
 
134 THE BEGINNINGS OF SCIENCE. 
 
 though of this at present not much can be said. We 
 have even had suggestions as to the possible ways in 
 which the elementary bodies may have come into 
 existence and how also they may cease to be."* At 
 present much of the work in this region must consist 
 in speculation, but speculation is ever the forerunner 
 of discovery. 
 
 Besides his really remarkable observations upon the 
 nature of the elementary bodies, Boyle was the author 
 of some pregnant work upon that great puzzle of 
 chemists up to the time of Lavoisier, the phenomenon 
 of combustion. We all of us now know that what 
 happens when a candle burns, is that its carbon and 
 hydrogen combine with the oxygen of the air thus 
 forming carbonic acid gas and water vapour. But 
 at the time of Boyle vague notions, such as that 
 described by Themistius in the Sceptical Chymist 
 were in vogue. The first step towards clearing up 
 the difficulty was to find out whether the air had 
 anything to do with the burning of combustible 
 materials, and accordingly Boyle experimented with a 
 view to finding whether they would burn under the 
 exhausted receiver of his air-pump. There being 
 under these conditions very little air present Boyle 
 found that such combustibles as a candle, charcoal, 
 sulphur, etc., would not light. 
 
 On the other hand gunpowder, if strongly heated 
 under the receiver by means of a burning-glass, 
 
 * See the suggestive paper by Prof, Crookes in his presidential 
 address to the Chemical Society (1888). 
 
THE BEGINNINGS OF SCIENCE. 135 
 
 exploded, and from this it was concluded that the 
 nitre in the gunpowder gave up something capable of 
 acting as a substitute for air. Nitre, we now know, 
 contains oxygen and readily parts with it to other 
 combustible bodies. Boyle's conclusion was therefore 
 perfectly correct. But in spite of such advance Boyle 
 still believed in the material nature of flame, and, 
 owing to bias of this kind, though he was aware that 
 many metals when heated in air are altered with gain 
 of weight, he ignored the true explanation. It seems 
 strange that it should not have occurred to him that 
 the metals had absorbed a ponderable constituent 
 (oxygen) of the atmosphere. Instead of this he sup- 
 posed them to weigh heavier, owing to addition of 
 11 igneous corpuscles." 
 
 To sum up Boyle's work, his discussion of the 
 qualities proper to an element led to the views con- 
 cerning those bodies at present entertained ; he was 
 the first to distinguish definitely between an element 
 and a compound, and between a compound and a 
 mixture ; his work upon combustion was accompanied 
 by very suggestive experiments; he seems to have 
 introduced vegetable colour tests to distinguish acid 
 and alkali,* and he developed the law of the compres- 
 sion of gases now so familiar by his name and so 
 serviceable alike to chemists and physicists. 
 
 His style of writing, as may have been suggested 
 by the quotations given, though quaintly interesting, 
 
 * The every-day test now in use is that of litmus, which is turned red 
 by acid and blue by alkali. 
 
I 3 6 
 
 THE BEGINNINGS OF SCIENCE. 
 
 is intolerably prolix, a characteristic in those days 
 not uncommon.* But we readily forgive his defects 
 when we find how earnestly painstaking he was. 
 
 * The Life and Works of the Honourable Robert Boyle were brought out 
 in five volumes folio by Thomas Birch in 1744. A curious pamphlet, 
 by Boyle, -An Historical Account of a Degradation of Gold made by an 
 Anti-elixir, not mentioned in the text, gives a description of the con- 
 version of gold into a baser metal. 
 
CHAPTER VIII. 
 
 FOURTH PERIOD : THE BEGINNINGS OF SCIENCE. 
 HOOKE: MAYOW: HALES. 
 
 HE next of those to be considered in this 
 period is Robert Hooke (16351702). 
 Hooke is naturally associated with Boyle, 
 as he was for a considerable time his 
 assistant and aided him in some im- 
 portant work. But his character is very 
 much less attractive than that of his employer ; he 
 wanted the unambitious earnestness which had always 
 characterized Robert Boyle. 
 
 Robert Hooke was born in the Isle of Wight and 
 was originally intended for the Church, but he was 
 of a weakly constitution, and much subject to head- 
 ache, and owing to these causes the idea was finally 
 abandoned. His leanings were first shown in a con- 
 siderable aptitude, as a boy, for constructing mechan- 
 
138 THE BEGINNINGS OF SCIENCE. 
 
 ical toys. After his father's death Dr. Busby took 
 him into his house and supported him while at West- 
 minster School. After leaving school he went to 
 Christ Church, Oxford, and, in 1G55, he was intro- 
 duced to the Philosophical Society. Here his talents 
 were speedily discovered and he was employed to 
 assist first Dr. Willis and then Mr. Boyle. In 1662 
 he was made curator of experiments to the Eoyal 
 Society, and when this body was established by 
 charter he was one of the first nominated to fellow- 
 ship. He obtained several professional posts and in 
 1665 he published in folio his Micrographia, or 
 some physiological descriptions of minute bodies made 
 by magnifying glasses, with observations and inquiries 
 thereupon. The work was dedicated to Charles II. 
 After the great fire of London Hooke was appointed 
 one of the city surveyors, and in this capacity seems 
 to have amassed a considerable sum of money which, 
 after his death, was found locked up and untouched 
 in a large iron chest. He seems to have had an 
 ungovernable tendency to believe that all new dis- 
 coveries had been anticipated by himself, and when 
 Newton, in 1686, published his Principia Hooke 
 claimed priority in the idea of gravitation. There 
 was enough truth in this to cause Newton to allow 
 the claim, but the fact is that the idea of gravitation 
 is a very old one, and Newton's honour was to have 
 made it a workable theory. When Hooke laid claim 
 to having originated Newton's views as to gravitation 
 Newton wrote to Dr. Hal ley : "I intended in this 
 
THE BEGINNINGS OF SCIENCE. 139 
 
 letter to let you understand the case fully, but, it 
 being a frivolous business I shall content myself with 
 giving you the heads of it." In a postscript he adds, 
 " Since my writing this letter I am told by one who 
 had it from another lately present at one of your 
 meetings how Mr. Hooke should make a great stir, 
 pretending that I had all from him .... This 
 carriage towards me is very strange and undeserved 
 . . . . he has published Borell's hypothesis in his 
 own name .... Borell did something and wrote 
 modestly. He has done nothing and yet written in 
 such a way as if he knew and had sufficiently hinted 
 all but what remained to be determined by the 
 drudgery of calculation and observations ....." 
 
 But here Hooke was somewhat maligned by report. 
 The facts were that at a meeting of the Royal Society 
 a member remarked that Newton had done the work 
 so thoroughly that no more was to be added. Sir 
 John Hoskins, the Vice- President, was in the chair, 
 and replied that the book was the more to be prized ; 
 the theory was both invented and perfected at the 
 same time. This gave Hooke offence, " upon which," 
 writes Halley, "they two who till then were the 
 most inseparable cronies have since scarcely seen one 
 another and are utterly fallen out." A spirit such 
 as this would cause us to reluctantly withdraw 
 our reverence from a worker of even the highest 
 intellectual predominance. Hooke lived the life 
 of a cynic and recluse, and on the death in 1687 
 of his niece, Mrs. Grace Hooke, with whom he 
 
140 THE BEGINNINGS OF SCIENCE. 
 
 lived, he became more cynical than ever. The tradi- 
 tion runs that for the two or three last years of 
 his life he sat night and day at a table engrossed 
 with his inventions and studies, and never went to 
 bed or undressed. Wasted and emaciated by his 
 strange mode of life, and by the denial to himself 
 of comforts he could readily have gained, he died 
 in 1702 and was buried in St. Helen's Church, 
 Bishopsgate Street. He is described as penurious, 
 melancholy, mistrustful, and jealous. We could more 
 readily pity his melancholy had it not been so self- 
 imposed. We must, however, admire his keen in- 
 sight and penetrative power. 
 
 The main interest of Hooke's work centres in his 
 Micrographia and probably the most remarkable 
 words he ever uttered are contained, almost paren- 
 thetically, in a work where, from its title, we should 
 have no expectation of finding the subject they deal 
 with treated of at all.'"" 
 
 Hooke seems in the quietest and most unbiassed 
 way to have set about observing the facts of combus- 
 tion, and waited for these facts to work out in his 
 
 * To understand Hooke's work thoroughly, the pregnant preface to 
 the Micrographia should be read. First of all Hooke implores the 
 reader to observe great caution in accepting the conclusions there set 
 forth. Caution is naturally the key-note of the period of doubt. But 
 an over -caution often produces a tendency to cling to a hypothesis 
 once accepted and an over -reluctance to accept the plunge into the 
 stream of new ideas. Hooke avoids both Scylla and Chary The 
 
 door of the senses, he says, must always be left open. The under- 
 standing "must watch the irregularities of the senses, but it must not 
 go before them or prevent their information." 
 
THE BEGINNINGS OF SCIENCE. 141 
 
 mind their natural conclusion. He arrives at the 
 opinion that the combustion of a combustible, or, as 
 he calls it, " sulphureous," body, for instance, char- 
 coal, is due to the combination of part of it with a 
 substance contained in the air, and also in saltpetre. 
 This resulting body is volatile and flies off, and, of 
 course, corresponds to carbonic acid gas, together with 
 water vapour. Another portion of the body uniting 
 with part of the air is supposed to form an unvolatile 
 " coagulum " extrac table from soot. Part of the 
 combustible will often not combine with the air and 
 is left behind as the ashes. The air is spoken of as 
 the solvent of inflammable bodies, by a somewhat in- 
 accurate analogy, so that when charcoal burns, it is 
 viewed as an analogous action to that of dissolving a 
 solid in alcohol. The air is viewed as containing but 
 a little of the true solvent ; a view quite correct, as 
 four-fifths of the atmosphere consist of nitrogen ; and 
 the solvent is therefore easily exhausted. Thus, for 
 instance, air must be continually admitted into a 
 vessel in which we are burning a large piece of char- 
 coal, or the charcoal will cease to burn. Just as heat 
 is sometimes generated by dissolving substances in a 
 liquid, so, says Hooke, heat is produced during the 
 solution or combustion of a body in air, and this heat 
 shows itself as flame, and is not an element, but a 
 phenomenon resulting from the violent agitation of 
 the particles of the burning body. Saltpetre contains 
 more of this supporter of combustion and hence burns 
 more rapidly. Altogether, this is a very wonder- 
 
H2 THE BEGINNINGS OF SCIENCE. 
 
 ful anticipation of the present ideas about combus- 
 tion. So far as it goes it is accurate, and if it 
 could have been followed up farther in the same 
 spirit, chemistry might have advanced more rapidly 
 than it did. The passage from Micrographia above 
 described is so interesting and deals with so immensely 
 important a subject that we shall not hesitate here 
 to quote at some length therefrom : 
 
 " Thirdly, from the experiment of the charring of 
 coals (whereby we see that notwithstanding the great 
 heat, and the duration of it % the solid parts of the 
 wood remain, whilst they are preserved from the free 
 access of air, undissipated), we may learn that which 
 has not, that I know of, been published or hinted, 
 nay, not so much as thought of, by any ; and that, in 
 short, is this. 
 
 <( First, that the Air in which we live, move, and 
 breathe, and which encompasses very many^ and 
 cherishes most bodies it encompasses, that this Air 
 is the menstruum, or universal dissolvent of all sul- 
 phureous bodies. 
 
 " Secondly, that this action it performs not till the 
 body be sufficiently heated, as we find requisite also 
 to the dissolution of many other bodies by several 
 other menstruums. 
 
 " Thirdly, that this action of dissolution produces or 
 generates a very great heat, and that which we call 
 fire ; and this is common also to many dissolutions 
 of other bodies, made by menstruums, of which I 
 could give multitudes of instances. 
 
THE BEGINNINGS OF SCIENCE. 143 
 
 "Fourthly, that this action is performed with so 
 great a violence and does so minutely act, and 
 rapidly agitate the smallest parts of the combustible 
 matter, that it produces in the diaphanous medium 
 of the air the action or pulse of light, which what it 
 is I have elsewhere already shown. 
 
 "Fifthly, that the dissolution of sulphureous bodies 
 is made by a substance inherent and mixed with the 
 air, that is like, if not the very same with that which 
 is fixed in saltpetre,* which by multitudes of experi- 
 ments that may be made with saltpetre, will, I think, 
 most evidently be demonstrated. 
 
 " Sixthly, that in this dissolution of bodies by the 
 air a certain part is united and mixed, or dissolved 
 and turned into ike air and made to fly up and down 
 with it* in the same manner as a metalline or other 
 body dissolved in any menstruum does follow the 
 motions and progresses of that menstruum till it be 
 precipitated. 
 
 " Seventhly, that as there is one part that is dis- 
 soluble by the air, so are there other parts with 
 which the parts of the air uniting do make a coagulum 
 or precipitation, as one may call it, which causes it 
 to be separated from the air, but this precipitate is 
 so light and in so small and rarefied or porous clusters 
 that it is very voluble and is easily carried up by the 
 motion of the air, though afterwards, Avhen the heat 
 and agitation that kept it rarefied ceases, it easily 
 condenses and, commixt with other indissoluble 
 
 * Italics not in the original. 
 
H4 THE BEGINNINGS OF SCIENCE. 
 
 parts, it sticks and adheres to the next bodies it 
 meets withal, and this is a certain salt that may be 
 extracted out of soot. 
 
 " Eighthly, that many indissoluble parts being very 
 apt and prompt to be rarefied and so, whilst they 
 continue in that heat and agitation, are lighter than the 
 ambient air, are thereby thrust and carried upwards 
 with great violence and, by that means, carry along 
 with them not only the saline concrete I mentioned 
 before, but many terrestrial or indissoluble and irrare- 
 fiable parts, nay many parts also which are dissoluble 
 but are not suffered to stay long enough in a suffi- 
 cient heat to mate them prompt and apt for that 
 action. And therefore we find in soot, not only 
 a part that being continued longer in a competent 
 heat will be dissolved by the air or take fire and 
 burn, but a part also which is fixed, terrestrial and 
 irrarefiable. 
 
 " Ninthly, that as there are these several parts that 
 will rarefy and fly or be driven up by the heat, so 
 are there many others that, as they are indissoluble 
 by the aerial menstruum, so are they of such sluggish 
 and gross parts that they are not easily rarefied by 
 heat and therefore cannot be raised by it ; the 
 volubility or fixtness of a body seeming to consist 
 only in this, that the one is of a texture or has 
 component parts that will be easily rarefied into the 
 form of air, and the other that it has such as will not 
 without much ado be brought to such a constitution ; 
 and this is that part which remains behind in a white 
 
THE BEGINNINGS OF SCIENCE. 145 
 
 body called ashes, which contains a substance or salt 
 which chemists call alkali. What the particular 
 nature of each of these bodies is I shall not here 
 examine, intending it in another place, but shall 
 rather add that this hypothesis does so exactly agree 
 with alf phenomena of fire and so genuinely explicate 
 each particular circumstance that I have hitherto 
 observed that it is more than probable that this 
 cause which I have assigned is the true, adequate, 
 real and only cause of those phenomena, and there- 
 fore I shall proceed a little further to show the 
 nature and use of the air. 
 
 " Tenthly, therefore, the dissolving parts of the air 
 are but few, that is it seems of the nature of those 
 saline menstruums or spirits that have very much 
 phlegm mixed with the spirit, and therefore a small 
 parcel of it is quickly glutted, and will dissolve no 
 more ; and therefore unless some fresh part of this 
 menstruum be applied to the body to be dissolved 
 the action ceases and the body leaves to be dissolved 
 and to shine, which is the indication of it, though 
 placed or kept in the greatest heat; whereas, salt- 
 petre is a menstruum, when melted and red hot, that 
 abounds more with those dissolvent particles, and 
 therefore as a small quantity of it will dissolve a 
 great sulphureous body, so will the dissolution be 
 very quick and violent. 
 
 " Therefore, in the eleventh place, ifc is observable 
 that, as in other solutions, if a copious and quick 
 supply of fresh menstruum, though but weak, be 
 
 K 
 
1 4 6 THE BEGINNINGS OF SCIENCE. 
 
 poured on or applied to the dissoluble body, it 
 quickly consumes it : so this menstruum of the air, 
 if by bellows or any such contrivance it be copiously 
 applied to the shining body, is found to dissolve it 
 as soon and as violently as the more strong men- 
 struum of dissolved nitre. 
 
 "Therefore, twelfthly, it seems reasonable to think 
 that there is no such iliing as an Element of fire that 
 should attract or draw up the flame, or towards 
 which the flame should endeavour to ascend out of a 
 desire or appetite of uniting with that as its homo- 
 geneal, primitive and generating Element ; but that 
 that shining transient body, which we call flame, is 
 nothing but a mixture of air and volatile sulphureous 
 parts of dissoluble or combustible bodies which are 
 acting upon each other whilst they ascend ; that is 
 flame seems to be a mixture of air and the combustible 
 volatile parts of any body, which parts the encom- 
 passing air does dissolve or work upon, which, action, 
 as it does intend the heat of the aerial parts of the 
 dissolvent, so does it thereby further rarefy those 
 parts that are acting or that are very near them, 
 whereby they, growing much lighter than the heavy 
 parts of that menstruum that are more remote, are 
 thereby protruded and driven upward ; and this may 
 bo easily observed also in dissolutions made by any 
 other menstruum, especially such as either create heat 
 or bubbles. Now this action of the menstruum or air 
 on the dissoluble part is made with such violence or 
 is such that it imparts such a motion or pulse to the 
 
THE BEGINNINGS OF SCIENCE. 147 
 
 diaphonous parts of the air as I have elsewhere shown 
 is requisite to produce light." 
 
 This hypothesis, Hooke says, is the result of " an 
 infinite of observations and experiments." He holds 
 out the prospect of a much larger discourse on the 
 same subject, " the air being a subject which (although 
 all the world have hitherto lived and breathed in 
 and been conversant about) has yet been so little 
 truly examined or explained that a diligent inquirer 
 will be able to find but very little information from 
 what has been (till of late) written of it." 
 
 John Mayow (1645 1679) was born in Cornwall 
 and became a student of medicine. He practised 
 chiefly at Bath in the summer. 
 
 Mayow carried on investigations into the nature 
 of combustion, published in 1674 in his Tracts on 
 various Philosophical Subjects* which, apparently 
 unknown to himself, had been to some extent antici- 
 pated in Hooke's Micrographia (1665). He burned 
 a candle under a bell-glass over water, observed 
 that the air diminished in volume, and that the 
 gas left was a little lighter than air and had no 
 longer the power of supporting combustion or life. 
 This gas was, of course, nitrogen, the other constituent 
 of the atmosphere. The carbonic acid gas formed 
 had been slowly absorbed by the water. He recog- 
 nised that the portion of the air necessary to com- 
 bustion and to life (i.e. oxygen) was contained also 
 
 * Mayow's first paper, however, De Sale Nitro et Spiritu Nitro- 
 aereo, was published ia 1669, 
 
i 4 8 THE BEGINNINGS OF SCIENCE. 
 
 in saltpetre (potassium nitrate, KNO 3 ). The nitre 
 or saltpetre he said contains fire-air (oxygen) and no 
 sulphureous (combustible) particles. For combustion 
 he asserted that fire-air and sulphureous particles 
 were needed. 
 
 Mayow seems to have been the first to use the 
 pneumatic trough for collecting gases, and the use of 
 this alone makes possible the examination of most 
 gases. An example of it is given farther on in the 
 sketch of Priestley's apparatus. 
 
 In the course of his investigations Mayow was, by 
 his medical leanings, induced to consider the chemical 
 meaning of breathing. He ascertained, as already 
 stated, that one part only of the atmosphere is the 
 supporter of life, but he did not wish to stop there. 
 The idea of his time was that respiration cooled the 
 blood. Mayow, on the other hand, seeing the part 
 played by these " nitre-aerial particles" or oxygen in 
 combustion, concluded that this gas was connected 
 with the heating of the blood.* He showed the 
 existence of gases in the blood by subjecting it to 
 the action of the air-pump, which extracts them. 
 Mayow was quite right in thinking that the " fire- 
 air" had to do with supplying the heat of the 
 blood. 
 
 On the subject of chemical affinity Mayow made 
 remarks of some moment. It may be as well to 
 explain here shortly what the term chemical affinity 
 is supposed to convey. There is no doubt that 
 
 * ChemischpJiysiologisclteSchriftcn. Jena (1799), 
 
THE BEGINNINGS OF SCIENCE. 149 
 
 strictly speaking affinity should mean similarity to or 
 relation to ; but the word has been diverted from 
 its proper significance and is now generally, used 
 to denote the tendency exhibited by substances to 
 combine with each other. Thus we say that phos- 
 phorus has a great affinity for oxygen, thereby 
 intending to convey the fact that phosphorus and 
 oxygen have a strong tendency to combine to- 
 gether. This is brought home to us by observing 
 that phosphorus when exposed at ordinary tempe- 
 ratures to the air burns slowly away, without a dis- 
 tinct flame, but giving off light fumes of phosphorus 
 pentoxide (anhydrous phosphoric acid) and emitting 
 a pale glow when observed in the dark. If slightly 
 heated, as, for instance, by the sudden pressure of a 
 blow, the phosphorus at once bursts into flame. Again, 
 if sufficiently finely divided the phosphorus will in- 
 flame, as we say, spontaneously and without applica- 
 tion of heat. Thus if a small piece of white phosphorus 
 be dissolved in some carbon disulphide (a highly 
 refracting liquid usually possessing an atrocious smell) 
 and a little of the solution be poured upon blotting 
 paper, the volatile carbon disulphide v r ery rapidly 
 evaporates and leaves the phosphorus on the paper 
 in a very fine state of division. Directly the paper 
 has become thoroughly dry the outer edges of the 
 phosphorus disc left by the carbon disulphide begin 
 to fume strongly, the heat developed by the combina- 
 tion rapidly increases, the paper begins to char, and 
 the next instant the whole mass bursts into flame. 
 
I5 o THE BEGINNINGS OF SCIENCE. 
 
 Such facts as these teach us that phosphorus and 
 oxygen are very eager to become united, and we 
 express the general result of our observations in the 
 statement that phosphorus and oxygen have a strong 
 affinity for each other. 
 
 The cause of the luminosity of phosphorus when 
 exposed to the air was not for some time decided. 
 The obvious suggestion would be that the light arose 
 from combination with the oxygen of the air. On 
 the other hand it was stated that phosphorus became 
 luminous when exposed in an atmosphere upon which 
 it would exert no chemical action, for instance, hydro- 
 gen or nitrogen gas. The luminosity in these cases 
 was, however, found to be due to the presence of 
 traces of oxygen gas, and it seems at last decided 
 that these phenomena of phosphorescence are to be 
 seen only in the presence of oxygen gas. From these 
 facts we should naturally expect phosphorus to be 
 more luminous in pure oxygen than in air. But now 
 comes a curious surprise for our expectations ; in 
 pure oxygen phosphorus exhibits no luminosity at all. 
 If the temperature be raised or the gas be rarefied, 
 the phenomenon of phosphorescence is observed, but 
 below 20 C., and at atmospheric pressure, phos- 
 phorus may be preserved for many weeks in this 
 gas without undergoing the slightest oxidation. If 
 the oxygen be diluted with an indifferent gas, as 
 hydrogen, or be rarefied, the luminosity is once more 
 seen. If a stick of phosphorus be introduced into a 
 tube filled with oxygen, closed above and connected 
 
THE BEGINNINGS OF SCIENCE, 151 
 
 below with a mercury reservoir, by raising or lower- 
 ing the latter we may alternately increase or lower the 
 pressure in the tube, and at the same time extinguish 
 or revive the phosphorescence. Certain gases and 
 vapours such as sulphuretted hydrogen, ether, turpen- 
 tine, permanently put out the luminosity. 
 
 Kobert Boyle had made some remarks upon these 
 tendencies of bodies to combination, and held that 
 combination consists of an approximation, a bringing 
 close together of the smallest particles of matter. 
 Previous to this time it was thought that the sub- 
 stances entering into a compound were annihilated by 
 the act of combination. Mayow strongly combated 
 this error. The views advocated by him would lead 
 us to say that when phosphorus and oxygen combine, 
 both bodies are still present in the compound, and 
 could by suitable means be obtained from it. Mayow 
 supported his argument by a somewhat ambiguous 
 example ; that of the combination between hydro- 
 chloric acid and ammonia. For although it may in 
 a certain way be said that hydrochloric acid and 
 ammonia exist together in sal-ammoniac, yet it by no 
 means follows that each of them exists as suck, 
 Hydrochloric acid consists of hydrogen and chlorine 
 combined togetber in a certain way ; it is perfectly 
 true that the hydrogen and the chlorine occur in the 
 sal-ammoniac but probably not combined in the same 
 way ; there may, in the sal-ammoniac, be a re-arrange - 
 nient of the constituents of the gas. 
 
 The phenomena of double decomposition were also 
 
1 52 THE BEGINNINGS OF SCIENCE. 
 
 studied by Mayow. We may illustrate these by the 
 action of sulphuric acid upon potassium nitrate (nitre) 
 from which result nitric acid and potassium sulphate. 
 In this case the group of elements attached to the 
 hydrogen of the sulphuric acid exchange this bondage 
 for a union with the potassium of the nitre, the group 
 attached to the potassium combining at the same time 
 with the hydrogen to form nitric acid. In chemical 
 symbols this is expressed thus : 
 
 2 KNO :i -f H 3 S0 4 = K 2 S0 4 + 2 HNO 3 . 
 Nitre -f- sulphuric potassium -j- nitric acid 
 acid sulphate. 
 
 Mayow's comments upon this reaction correctly express 
 this exchange, though their explanation of why it 
 occurs is somewhat erroneous. 
 
 Mayow, like the medical chemists of an earlier 
 school, offers a timely warning to the physicians who 
 may be ignorant of the mutual affinities and decom- 
 positions of bodies. He reminds them that the dif- 
 ferent substances in their prescriptions may act upon 
 each other with surprising results ; " one substance 
 may destroy the efficacy of another, and something 
 perfectly different from the original may result." 
 
 Mayow's work was almost wholly forgotten, as was 
 the fate of so much other work previous to this time. 
 At the close of the eighteenth century his fame was 
 revived chiefly through the agency of Drs. Beddoes* 
 and Yeats. There was indeed then a tendency to 
 overrate his discoveries in the spirit of those who 
 
 * Chemical Experiments, $c., from Mayow. Edited by Beddoes. 
 Oxford (1790). 
 
THE BEGINNINGS OF SCIENCE. I53 
 
 are fond of exclaiming that there is nothing new 
 under the sun. Beddoes attributed to Mayow the 
 discovery of, " if not the whole, certainly many of those 
 splendid truths which adorn the writings of Priestley, 
 Scheele, Lavoisier, Crawford, Goodwin, and other 
 philosophers." 
 
 Certainly Mayow was remarkably lucid and far- 
 sighted in some of his expositions, but it must be 
 allowed that such judgment as that quoted much 
 overrates his achievements. 
 
 Before leaving this period of the science, mention 
 may be made of Dr. Stephen Hales (1677 -1761), 
 an ingenious and able experimenter, though one 
 who was too much engrossed in the details of 
 his experiments to consider sufficiently their pur- 
 pose. 
 
 He was the grandson of Sir Kobert Hales, and, 
 after leaving Cambridge, resided till the time of 
 his death at Teddington. Offered a canonry at 
 Windsor, he showed unusual wisdom by refusing 
 it, preferring to continue to devote himself to the 
 parochial duties and scientific pursuits engaged in 
 which he felt perfectly content. He published in 
 1727 his Statical Essays .... also a Specimen 
 of an Attempt to analyse the Air, ly a great variety 
 of Chymico- Statical Experiments. Hales made a 
 number of experiments on the "air" produced by 
 heating bodies, by fermentation, etc. He collected 
 his gases in ingeniously-devised apparatus, but think- 
 ing they were all modifications of common air he 
 
i 5 4 THE BEGINNINGS OF SCIENCE, 
 
 appears never to have examined them systematically, 
 and thus a whole series of discoveries eluded his 
 grasp. He obtained "air" by distilling wood, and 
 found it fatal to animals (carbonic acid), from nitre 
 (oxygen), etc., and he details the amount of air ob- 
 tained by distilling hogs' blood, tallow, sal-ammoniac, 
 Indian wheat, peas, mustard seed, amber, tobacco, 
 sugar, by fermenting sheeps' blood, by the action of 
 vinegar on oyster shells, &c., but with the mass of 
 undigested facts so obtained he seemed content. He 
 found that iron filings and strong sulphuric acid pro- 
 duced scarcely any air, he observed that on adding 
 water a gas is abundantly evolved. This gas was 
 hydrogen, but including all gases as "air" he did not 
 stop to examine it. 
 
 Dr. Hales also made a number of investigations 
 into the movement of sap in vegetables. In his 
 experiments, directed to ascertain the force with 
 which trees imbibe moisture, he obtained some strik- 
 ing results. Thus, after cutting across the root of a 
 pear-tree, the section being half an inch diameter, he 
 cemented this into a tube, twenty-six inches long, 
 filled with water, and dipping at its lower end into 
 mercury. So vigorously was the water absorbed that 
 in six minutes the mercury rose eight inches in the 
 tube. The experiment was made in August. Eight 
 inches of mercury would be about equal to 109 inches 
 or about nine feet of water. Thus the absorption of 
 the root would be sufficiently powerful to raise or sup- 
 port a column of water nine feet high. 
 
FIFTH PERIOD. 
 
CHAPTER IX. 
 
 FIFTH PERIOD: THE CHILDHOOD OF TRUTH. 
 CULLEN, BLACK. 
 
 ,Y those readers acquainted with some of the 
 chief characteristics of modern science it 
 will have been observed that up to the 
 date we have now reached very little 
 notice had been taken of the quantitative 
 aspect -of phenomena. Weight Avas not 
 yet considered an all-important factor in chemical 
 investigations ; and, indeed, it could not be so until, 
 at least to some extent, the fact of the indestructibi- 
 lity of matter was recognised. It is true that in the 
 directions given by such men as Basil Valentine and 
 Glauber, for the preparation of various bodies, men- 
 tion is often made of the quantities of the different 
 ingredients intended to be mixed together. But 
 there is no precise attempt to connect the quantity of 
 the product with the quantities of the substances em- 
 ployed to produce it, nor to elucidate in this way its 
 composition, 
 
158 THE CHILDHOOD OF TRUTH. 
 
 When we reflect how often a portion at least of 
 the product of a reaction is gaseous and would there- 
 fore seem to be destroyed, we shall not wonder 
 that the value of weight in chemical science was lost 
 sight of. When a candle burns, all that we are 
 directly aware of is that light is given out and the 
 candle slowly disappears ; and what more natural 
 than to conclude that where there is disappearance 
 there is destruction ? As a matter of fact we now 
 know that in this process no particle of the candle 
 has ceased to exist ; all the matter that composed it 
 is there, but the candle is no longer there as such. 
 But so long as chemists could not collect the carbon 
 dioxide and measure or weigh it, what could they 
 suggest, but that matter was now and again in the 
 habit of evanescing, or, so to say, " going to coloured 
 cob-web " and becoming inappreciable. While these 
 views prevailed no great depths could be reached by 
 science ; it was held back, as it were, by the want of 
 weight. 
 
 But we are now entering upon the period when 
 quantitative chemistry really begins. It is true that 
 many of the experiments of Dr. Hales included mea- 
 surement of gases ; but he was not sufficiently aware 
 of any definite purpose in what he did. It has, in- 
 deed, been very shrewdly remarked that Hales had 
 learnt how to question Nature, but not how to cross- 
 examine her.* The cross-examination was to be con^ 
 ducted, in part, by the well-known chemist, Dr. 
 
 * F. H. Butler, Encye. rit. Art. Chemistry. 
 
THE CHILDHOOD OF TRUTH. 159 
 
 Black, and it has been continued with increasing 
 skill and penetration to this day. 
 
 Before, however, we proceed to sketch Black's life 
 and work it is only just that some reference should 
 be made to his instructor, Dr. Cullen, of Edinburgh. 
 Dr. Cullen was a man who engaged in remarkably 
 little original work, and yet such was the charm of 
 his character, and so wide-spread was the elevating 
 influence of his enthusiasm, that, after we have got to 
 know his life, we are almost glad that the brilliance 
 of original achievement should not be there to distract 
 us from the calm of his energy and the loving-kind- 
 ness of his toil. Cullen* was essentially a man who 
 influenced others. Not striving after his own fame 
 he was content that others should reap the benefits 
 of his knowledge, and that to them should pass the 
 glory of penetrating those problems which his con- 
 scientious enthusiasm as. a teacher left him no time 
 to solve. He was an example of the few teachers 
 who follow closely the mental unfolding of their 
 pupils, and of the still fewer who aim at influence 
 upon character as well as upon brain. He was 
 uniformly attentive to his students, while his cordiality 
 and warmth of heart took them by storm. 
 
 He made himself personally known to all his pupils. 
 He used to invite them to his house, two, three, 
 and sometimes four at a time, and he would place 
 himself on terms of the easiest intimacy with those 
 
 * William Cullen, M.D., born at Hamilton in Scotland (1710 
 1790\ 
 
160 THE CHILDHOOD OF TRUTH. 
 
 of whose character he formed high opinion. He 
 would talk with them upon any topic to which they 
 chose to refer, and by the complete confidence with 
 which he spoke to them would win from them con- 
 fession as to all their plans and difficulties in life. 
 He became their friend, and by the individuality of 
 his contact with them won a high place in their hearts. 
 Caring little for the emoluments of office he succeeded 
 by the most delicate tact in evading payment for his 
 courses where he thought his students pecuniarily 
 unable to afford it. In such a case, for instance, he 
 might invite the student to attend certain lectures, as 
 he would be glad of his opinion on certain parts of 
 the course. Or, again, he would press books from 
 his own library upon them. As persons in such 
 positions are often peculiarly sensitive he was. here 
 again obliged to resort to little schemes in order to 
 make the offer agreeable. He would point out some 
 particular passage of importance in the book that he 
 wished the student to borrow, and use his professional 
 authority to desire him to take the book home at 
 once and study this passage as a matter of immediate 
 importance. 
 
 By such winning generosity and insight Cullen 
 acquired a quite exceptional popularity with his 
 pupils, and as a result a quite exceptional bitter- 
 ness of jealousy on the part of his colleagues. But 
 to this jealousy he gave no heed, and went on his way 
 without appearing to hear the sneers uttered at his 
 expense. As an instance of his deserved popularity 
 
THE CHILDHOOD OF TRUTH. 161 
 
 it may be mentioned that when the professor of 
 Materia Medica, Dr. Alston, died in 1763, Cullen was 
 invited to continue his course. Alston had opened 
 the lectures with ten students. When Cullen con- 
 sented to continue them one hundred new students 
 instantly enrolled themselves. That is sufficiently 
 indicative of the position he had attained. 
 
 Among those thus taught by him was one pupil 
 whose name was to be remembered for many long 
 years as a true son of science, Dr. Joseph Black. It 
 was well for Black to have obtained his instruction at 
 the hands of such a man, for Cullen saw chemistry, 
 not as a curious and useful art, but as a division of 
 the vast science of nature. 
 
 Dr. Black* had, as a man, about him much of the 
 charm that attached to Cullen. There is a quiet and 
 dignified simplicity about his character that clings 
 round his name to this day. He was so gentle, so 
 unassuming, and so sincere, that it is reassuring to find 
 that in this brawling world his voice could yet be 
 heard above the tumult. Black obtained the chemical 
 chair at Glasgow. Thomson says of him that he 
 " constituted the most complete model of a chemical 
 lecturer that I ever had an opportunity of witnessing." 
 He was not a mere chemist but a cultivated man. 
 He had considerable aesthetic taste, as shown in his 
 love of music and painting. Even a retort or cruci- 
 ble was to his eye an example of beauty or deformity. 
 He was also warm-hearted and affectionate, and with 
 
 * Joseph Black, 17281799. 
 L 
 
1 62 THE CHILDHOOD OF TRUTH. 
 
 Dr. Hutton he formed an unusually close friendship, 
 imparting to him every one of his speculations and 
 receiving the same confidence in return. The two 
 friends were seldom asunder for two days together. 
 
 Black always suffered from delicate health, and 
 towards the end of his life this became so pronounced 
 that he had to give up all professional work. He 
 did not attempt to achieve what his strength would 
 not allow : " he spun his thread of life to the very 
 last fibre." Careless of his own fame he did not 
 torment himself by restlessness or eagerness, but 
 happily resigned work which he felt himself unable 
 to fulfil. Thus his life was always tranquil and at 
 peace. The manner of his death was curiously sudden 
 and calm. He was sitting alone at table with some 
 bread, primes, and milk before him. It seems that 
 he had the cup of milk raised to his lips when, feel- 
 ing some sensation of approaching weakness, he set 
 it down on his knees and held it there between his 
 two hands ; and so, without a single tremor or 
 struggle, he died. It might almost have been an 
 experiment designed by him to show how quietly he 
 could pass away, for the cup was not displaced nor 
 was a drop of the milk spilt. His servant, coming 
 in and seeing him sitting still in so easy an attitude, 
 thought he had dropped into a doze. When the man 
 had left the room, however, he had some unaccount- 
 able misgivings and went gently back into the room 
 once more. Still, however, the pose seemed so easy 
 and natural that he went out reassured. Coming 
 
THE CHILDHOOD OF TRUTH. 163 
 
 back a third time, and finding Dr. Black still seated 
 in the same posture, he at last went up to waken 
 him and found him dead. 
 
 The two great pieces of work for which Black is 
 renowned are his investigation of the alkalies and 
 his discovery of latent heat. The former is con- 
 tained in his Experiments on Magnesia Alba,* of 
 which some account must now be given. The reader 
 may here be reminded of the chemical reactions, 
 called double decompositions, examined by Mayow. 
 One of the first experiments that strike us in Black's 
 paper has an interesting bearing on these reactions. 
 He distilled together in a retort magnesium car- 
 bonate, ammonium chloride, and water, and found 
 some magnesium chloride left behind in the retort. 
 Magnesium chloride is, of course, made up out of the 
 metal magnesium and the "negative" element chlorine, 
 or, as it was then less accurately expressed, it con- 
 contains a base and acid for its constituents. "When 
 ammonium hydratef is added to its solution the 
 ammonium combines with the chlorine to form am- 
 monium chloride, whilst magnesium hydrate separates 
 out as a white precipitate. This Black expressed by 
 saying that " the attraction of the volatile alkali 
 (ammonia) for acids is stronger than that of mag- 
 nesia." 
 
 But the reaction observed by him in the experi- 
 
 *- Edinburgh (1777). 
 
 t Ammonium hydrate is tho ordinary ammonia solution expressed 
 as a derivative of the metallic radical ammonium. The formula for 
 the hydrate isNH 4 (OH), the NH 4 group being ammonium. 
 
j6 4 THE CHILDHOOD OF TRUTH. 
 
 ment first referred to is the very reverse of this. The 
 ammonia is already combined with the strong hydro- 
 chloric acid to form, ammonium chloride, yet it gives 
 up its " negative," or " acid," element which becomes 
 combined with the magnesium. Thus Black re- 
 marks : " But it also appears that a gentle heat is 
 capable of overcoming this superiority of attraction," 
 The truth was beginning to appear that the final 
 arrangement of the elements in a mixture of various 
 bodies is not simply dependent upon superiority of 
 attraction ; for under different circumstances totally 
 different arrangements will result. The view now 
 generally held is that in a mixed solution all possible 
 combinations of the negative and positive elements 
 occur. Thus, suppose we have a mixture in solution 
 of sodium carbonate and magnesium chloride. Then 
 the following bodies will all actually at first occur : 
 sodium carbonate, magnesium chloride, sodium chlo- 
 ride, and magnesium carbonate. But magnesium 
 carbonate (the "magnesia alba" of Black) is insoluble, 
 and hence is precipitated at once. Being thus with- 
 drawn from solution it is at the same time withdrawn 
 from the sphere of action of the other ingredients. 
 Those ingredients now consist of sodium carbonate, 
 magnesium chloride, and sodium chloride, and there 
 being one possible combination now absent more mag- 
 nesium carbonate is at once formed. This again goes 
 out of solution, and so on until there is left in the 
 solution sodium chloride, and the precipitate con- 
 sists of magnesium carbonate. It is not that the 
 
THE CHILDHOOD OF TRUTH. 165 
 
 magnesia has a superior attraction for carbonic acid, 
 but it is simply the fact of the insolubility of the 
 magnesium carbonate which brings about the re- 
 action. Other considerations enter into the study of 
 chemical reactions which we cannot go into now. 
 
 Before Black's time it was known that ordinary 
 lime is quickened by heat. Black experimented with 
 a view to finding out whether magnesia would form 
 " a quicklime." An ounce of magnesia alba was 
 heated for an hour to the melting point of copper. 
 When it came out of the furnace it had lost seven- 
 twelfths of its weight. After being thus treated 
 Black found it would still dissolve in acids to form 
 salts, but laid stress on the fact that it did so " with- 
 out any the least degree of effervescence." 
 
 The question was, what had happened to the mag- 
 nesia alba (magnesium carbonate) in this process of 
 quickening? To elucidate this he distilled magnesia* 
 in a retort, and, as it was evident from the previous 
 experiment, that the magnesia lost something while 
 being quickened, he expected to condense this vola- 
 tile body in his receiver. To his surprise, however, 
 all he could condense was a little water (a substance 
 only present as an impurity in this reaction) the 
 weight of which was not nearly equivalent to the loss 
 of weight sustained by the magnesia. Now this use 
 of weight to assist in unravelling the knots of the 
 problem is exceedingly important. It might have 
 
 * In the course of this passage the terra magnesia is used, as it was 
 used by Black, to signify magnesia alba. 
 
i66 THE CHILDHOOD OF TRUTH. 
 
 been thought that some matter had merely been de- 
 stroyed in the reaction, but it does not seem to have 
 occurred to Black to accept such a view of the matter 
 as rational. His conclusion therefore was that some- 
 thing had gone off in a non-visible form, and the 
 question now was what ? 
 
 His view was that the volatile matter lost in cal- 
 cination was mostly air. He next calcined two 
 drams of magnesia alba, dissolved the resulting 
 quick magnesia in dilute sulphuric acid and reprecipi- 
 tated the magnesia alba from this solution by means 
 of a " mild " alkali. The weight of substance thus 
 obtained was one dram fifty grains, from which it is 
 seen that the magnesia had in this process very 
 nearly recovered its original weight. Obviously part 
 of the addition must be "air," that is gaseous matter, 
 for it could be again driven off as " air " by heat. 
 Furthermore this " air " must have come from the 
 mild alkali by means of which the magnesia alba 
 was reproduced. 
 
 Further Black's argument is this : Stephen Hales 
 had already shown that the mild alkalies contain a large 
 quantity of air which they emit when joined to an 
 acid. Thus if ordinary washing soda be treated with 
 hydrochloric acid there is copious effervescence and 
 evolution of gas. In the case before us, when the 
 quick magnesia dissolved by acids is reprecipitated as 
 magnesia alba by alkali, the alkali, Black argues, 
 really becomes joined to the acid to form a salt, but 
 without visible emission of air. Yet the air is not 
 
THE CHILDHOOD OF TRUTH. 167 
 
 retained by the alkali, for the alkaline salt obtained 
 is the same in quantity as if pure add and not mag- 
 nesium salt had been used to obtain it. That is to 
 say, the weight'of sodium sulphate obtained by adding 
 one ounce of sodium carbonate to magnesium sulphate 
 is the same as that resulting from the solution of one 
 ounce of sodium carbonate in sulphuric acid, no "air" 
 having attached itself to the sodium sulphate in either 
 case. What then has become of this air which was 
 in the mild alkali to start with, and is there no 
 longer ? 
 
 Obviously, concludes Black, forced from the alkali 
 by the acid this air has lodged itself in the magnesia, 
 and it is the presence of this air that distinguishes 
 magnesia alba from quick or calcined magnesia. 
 In our way of stating it the first is magnesium car- 
 bonate, the second is magnesium oxide. Carbonic 
 acid added to the latter produces the former. 
 
 The whole course of this inductive reasoning as 
 pursued by Black is peculiarly thorough and scien- 
 tific, and in itself would make him well worthy of 
 the place he has won. He went on to apply these 
 views to the calcareous earths (such as chalk) and the 
 mild alkalies in general. They are distinguished from 
 the calcined earths and the caustic alkalies by the pre- 
 sence of this air, which the latter tend to reabsorb. * 
 Previously to his time the causticity of quicklime was 
 supposed to be occasioned by its combination with 
 igneous particles. 
 
 * That is, in modern language, they are carbonates. 
 
168 THE CHILDHOOD OF TRUTH. 
 
 Black collected the gas evolved by treating mag- 
 nesia alba with acid, and distinguished it from atmo- 
 spheric and other " airs." In this he was repeating 
 the discovery made by Van Helmont more than a 
 century before, but then entirely forgotten. He dis- 
 tinguished this peculiar body by the name ^i fixed 
 air. 
 
 Black's researches upon these subjects afford a very 
 instructive example of work conducted in a truly 
 scientific spirit. Certain phenomena afforded interest- 
 ing matter for investigation, and Black proceeded by 
 endeavouring first of all to multiply facts. The 
 quickening of lime by heat was already known. 
 Would other analogous bodies, such as magnesia alba, 
 give similar results ? These were found to occur, and 
 the next point was to observe accurately and in detail 
 what took place during the calcination. The observed 
 facts were loss of weight and loss of power of efferves- 
 cence with acid. Could these losses be restored ? By 
 the processes above described he found that they 
 could, use being made of mild alkali which in the 
 reaction lost its "air." In regaining its weight and 
 power of effervescence the magnesia then has taken 
 up " fixed air/' a definite gas found to be common 
 to the calcareous earths and the mild alkalies, and 
 conspicuous by its absence from the calcined earths 
 and the caustic alkalies. In these steps Black aimed 
 consistently at the cross-examination of nature. He 
 did not allow himself to be led astray by any precon- 
 ceived theory or to be turned aside by any apparent 
 
THE CHILDHOOD OF TRUTH. 169 
 
 improbability. This case is only illustrative of the 
 singularly unbiassed character of Black's mind, for he 
 was the only chemist of his day who, in the great 
 phlogiston controversy which will be dealt with in 
 the next chapter, definitely avowed his conversion to 
 the Lavoisierian doctrine of combustion. 
 
 The other research of Black's, which must be briefly 
 sketched in order to appreciate the later development 
 of the science, was his discovery of latent heat. 
 
 It may not be out of place to here refer first to 
 the construction of the ordinary thermometer. It 
 consists of a glass tube of fine bore, having a bulb at 
 one end. This bulb and part of the stem is filled 
 \vith mercury, and before the fine end of the tube is 
 sealed oft" all air is expelled by boiling the mercury. 
 When the end is closed the mercury, as its tempera- 
 ture is lowered, falls in the table. To graduate the 
 thermometer the bulb is plunged into melting ice 
 when the mercury becomes stationary at a definite 
 point, which is then marked by the scratch of a 
 file on the glass. This " freezing-point " is in the 
 centigrade scale and 32 in Fahrenheit's scale. The 
 next operation is to immerse the bulb and stem in 
 steam at the boiling point of water. The mercury, 
 of course, rises, and this time another mark is made 
 where it becomes stationary. Two fixed points are 
 thus obtained, and all that remains is to divide the 
 interval into the required number of degrees. On 
 the centigrade scale the melting point will be and 
 the boiling point 100. On the Fahrenheit scale the 
 
1 7 o THE CHILDHOOD OF TRUTH. 
 
 melting point will be 32 and the boiling point 
 212. 
 
 Now, the ascertainment of these points is only made 
 possible by the fact that ice while melting and water 
 while boiling remain at a uniform temperature. If 
 some pounded ice be placed in a basin and a centi- 
 grade thermometer immersed therein it will be found 
 to indicate a temperature of 0. As time passes the 
 ice gradually melts and a good deal of water collects 
 in the basin, but the mercury still stands at 0. 
 Later on only a few pieces of ice are left floating on 
 the water, but the thermometer still marks the melt- 
 ing point of ice. Moreover, suppose we apply heat 
 to the vessel containing it ; the ice melts faster but 
 it does not grow any warmer ; the temperature is still 
 zero (32 F.). In the same way if water be boiled in 
 an open vessel, the more heat is applied the faster 
 the water boils, but its temperature remains at 100 C. 
 (212R). 
 
 It was these phenomena which led Black to con- 
 clude that an amount of heat was used up or rendered 
 latent in converting the ice into water and the water 
 into steam. Thus, if we start with a vessel full of 
 hard frozen ice at a temperature below the freezing 
 point, and apply heat by means of a small flame, the 
 mercury of a centigrade thermometer immersed in 
 the ice will gradually rise up to arid then will 
 come to a standstill. The first quantity of heat 
 raises the temperature of the ice ; when that has 
 reached its melting point the whole of the rest of the 
 
THE CHILDHOOD OF TRUTH. 171 
 
 heat is used in melting the ice. When the whole of 
 the ice is melted the water so formed begins to rise 
 in temperature once more till the boiling point is 
 reached, when again the mercury becomes stationary. 
 At this stage all the heat is used in converting the 
 water into steam. The steam may be superheated to 
 any desired temperature. 
 
 Black determined the latent heat of water to be 
 7 9 '4 4, and in order to explain how this is done we 
 must use some very simple mathematics. A certain 
 weight of ice M at 0, is immersed in a weight of 
 water m at a temperature t more than sufficient to 
 melt the ice. As soon as the ice has melted the 
 final temperature is noted, say 6. In cooling from 
 t to the water has parted with a quantity of heat, 
 QII (t 0). If x be the latent heat of ice it absorbs 
 in liquefying heat M#, but besides this the water 
 formed from the ice has risen to 6 and has thus 
 absorbed the heat M0. We have : 
 
 = w* (t-9). 
 
 from which x t the latent heat of water, is deduced. It 
 is about 79-2. 
 
 The latent heat of steam, arrived at in a very 
 similar way, is about 538, that is to say, a pound of 
 water at 100 C. absorbs during vaporisation enough 
 heat to raise the temperature of 538 Ibs. of water by 
 1 centigrade. 
 
SIXTH PERIOD. 
 
CHAPTER X. 
 
 SIXTH PERIOD : THE CONFLICT WITH ERROR. 
 THE BIRTH OF ERROR. 
 
 is now time to discuss the development 
 and meaning of a theory which for many 
 long years was the object of blind idolatry 
 to the chemists of the time. In pre- 
 vious pages some examples have been 
 given of the attempts made to conjecture 
 (for it was little more than conjecture) the nature of 
 the fundamental principles of matter. We have seen 
 how salt, sulphur, and mercury had their turn with 
 air, earth, water and fire, and how in the advanced 
 writings of Robert Boyle all dogmatism regarding the 
 elements was eyed askance. Among subsequent 
 theories only two need be mentioned. The first was 
 propounded by a German chemist, Becher (1635 
 1682), who held that the primary ingredients of 
 
176 THE CONFLICT WITH ERROR. 
 
 matter were water and earth, and that from these 
 were produced three earths the fusible or strong, 
 the fatty, and the fluid earths improperly called salt, 
 sulphur, and mercury. The second was the phlogiston 
 theory of Stahl. 
 
 George Ernest Stahl was born at Anspach in 1660, 
 and studied medicine at Jena.* In 1694 he was 
 named second professor of medicine to the University 
 of Halle to which post he was helped by Frederick 
 Hoffmann. In 1716 he was made physician to the 
 King of Prussia, and went to Berlin, where he died in 
 1734. In his medical views Stahl to some extent 
 followed Van Helmont. "The body as such has 
 no power to move itself, and it must always be put 
 in motion by immaterial spirits ; all movement is a 
 spiritual act." His dissertations, pamphlets, etc., 
 number four or five hundred. His theory of the 
 elements lasted half a century. 
 
 Stahl developed the doctrines of Becher and 
 enumerated four elements, viz : water, acid, earth, and 
 phlogiston. Metals on heating for the most part 
 become oxidised, and this calcination was explained 
 by Becher on the supposition that they consisted of 
 an earth and something of -which they became 
 deprived on ignition ; the burning of brimstone 
 (sulphur) was, in like manner, thought to be its 
 
 * Some account of Stahl is given in the Biographic Universette, where 
 his unbounded arrogance is commented, upon. ' ' La lecture atten- 
 tive de ses ecrits prouve une grande disposition a la melancolie, un 
 orgueil sans bornes, et un profond mepris pour tous ceux qui ne 
 pensaient pas comme lui." 
 
THE CONFLICT WITH ERROR. 177 
 
 resolution into an acid and a true sulphur, or that 
 combustible part which was dispelled by heat. It 
 was this supposed combustible body to which Stahl 
 gave the name of phlogiston (cfrXoyiarov, combustible). 
 The " phlogiston " of Stahl is in many ways analogous 
 to the souls and spirits assigned to metals and salts 
 by the alchyrnists, or to what Geber called the 
 " humidity " and Cardan the " celestial heat " of 
 metals. 
 
 To illustrate this curious theory let us take the 
 simple case of the burning of a piece of coal. The 
 question is, what is happening while the coal 
 burns ? We have seen how Hooke would have 
 answered this question more than a hundred years 
 before the overthrow of the Stahlian views. Accord- 
 ing to him a certain part of the coal unites with a 
 part of the air and is "made to fly up and down 
 with it," and moreover the part of the air causing 
 this action is contained, ''fixed," in saltpetre. This 
 comes very near to an account of the production of 
 carbonic acid during combustion, but owing to his 
 unfortunate analogy between the action of the 
 "substance inherent and mixed with the air" and 
 the action of a liquid solvent there was a loophole of 
 escape. Had his ideas been only a little more 
 matured the victory of phlogiston might have been 
 averted. His facts were good, so far as they went, 
 and he did not allow his creeds to outrun his facts 
 The Stahlians, on the contrary, took a different 
 method with the undeniable gaps in the ranks of 
 
 M 
 
178 THE CONFLICT WITH ERROR. 
 
 their facts. They filled up the vacancies with fictions. 
 Their fictions were the creations of clever minds 
 whose facile ingenuity only led them farther astray. 
 
 To the problem above propounded viz., what 
 is happening while coal burns the Stahlian answer 
 was that the combustion of the coal was due to 
 the loss of phlogiston which was given up to the 
 air. The more perfectly combustible a body was the 
 greater the amount of phlogiston it contained, so that 
 charcoal and lamp-black, and other reducing agents, 
 came in time to be regarded as nearly pure phlogiston. 
 When by carbon a metallic calx was reduced, or a 
 compound containing sulphur was obtained from fused 
 sodium sulphate, phlogiston was supposed to be 
 absorbs 1 from the charcoal. Incombustible bodies 
 were upposed to have already parted with their 
 phlogiston. As most combustible bodies were insol- 
 uble phlogiston itself came to be regarded as a dry and 
 earthy body, capable of receiving a motion of great 
 velocity the motus rcrticittaris manifested when 
 ignition or flame was produced.* 
 
 Mayow had stated that the "nitre air" of the 
 atmosphere caused fermentation and souring of wines, 
 produced sulphuric acid from sulphur, and effected 
 the calcination of metals. 
 
 As early as 1630, John Key had noticed that 
 metals grew heavier when calcined, as he thought, 
 by the absorption of " thickened air," but they 
 had given no general theory of combustion, nor 
 
 * Encyc. Eritannica. ait. "Stahl," 
 
THE CONFLICT WITH ERROR. 179 
 
 explained why some bodies grow lighter on heating. 
 Boyle, also, had observed the increase in weight of 
 metals, but attributed it to combination with heat 
 particles or "igneous corpuscles."* The bearing of 
 these observations upon the hypothesis of phlogiston 
 was quickly perceived. If calcination results in the 
 loss of a material principle, phlogiston, how, at the 
 same time, can it be accompanied by a gain in weight ? 
 This was the apparently unanswerable paradox. But 
 with exquisite ingenuity the Stahlians surmounted 
 the difficulty and retorted that phlogiston was the 
 principle of levity or of negative weight. Such slippery 
 opponents could readily elude one's grasp. 
 
 Frederick Hoffmann (1660 1742), who contri- 
 buted to analytical chemistry in Germany, held with 
 Stahl that sulphur consisted of acid and phlogiston, 
 and that combustible bodies contained a principle 
 describable as phlogiston ; but he thought it possible 
 that the calces of metals were formed, not by the 
 subtraction of phlogiston, but by the combination of 
 the metals with an acid material. Boerhaave, too, 
 cast doubt on the assumption of the existence of an 
 earth and a combustible principle in metals. Neu- 
 mann (16831737), J. H. Pott (16921777), 
 Marggraf (1709 1782), and Macquer (17181784), 
 the discoverer of arsenic acid, supported Stahl, and fur 
 many years his doctrine held its ground against all 
 opponents. 
 
 Let us now examine a few chemical facts 1/y the 
 
 * See ante, p. 135. 
 
i8o THE CONFLICT WITH ERROR. 
 
 light of the phlogistic hypothesis and see what is the 
 explanation it affords us. 
 
 When lead is heated it undergoes characteristic 
 changes of colour, becoming first yellow and then red. 
 What is happening to it ? It is losing more and more 
 phlogiston. The yellow substance (massicot) is the 
 partially dephlogisticated calx of lead. When the 
 metal is wholly deprived of phlogiston it is converted 
 into the red substance (red lead). But the yellow sub- 
 stance weighs more than the metal. That is because 
 the metal has been losing "the principle of levity." 
 And the red substance weighs more than the yellow 
 from which it is obtained. That, too, is because 
 the yellow substance has been losing more of " the 
 principle of levity." 
 
 But here is another fact for the Stahlians to explain. 
 Some charcoal is mixed with a little massicot and 
 the mixture heated. A malleable globule of metallic 
 lead is formed. What has occurred ? The charcoal 
 has given up phlogiston to the partially phlogisticated 
 calx, and this, by complete phlogistication has become 
 converted into metal. So too red lead may be 
 reduced to the metallic state, only more phlogiston 
 is needed. 
 
 An interesting phenomenon observable in this 
 experiment if carried on in a closed vessel is the evolu- 
 tion of a considerable amount of an incombustible 
 gas. Does not this suggest that the calx has been 
 losing something during reduction ? So far tho 
 ingenuity of the Stahlians is fairly successful. But 
 
THE CONFLICT WITH ERROR, 181 
 
 next let us ask them, how is it that lamp-black, consist- 
 ing of very nearly pure phlogiston, weighs anything 
 at all ? Or at least, why is it not lighter than air ? 
 Probably they would reply that it does not contain 
 enough phlogiston for that. There is no need to 
 dwell on this trifle, so we will next point out an 
 interesting experiment. 
 
 Here is a small porcelain crucible. The cru- 
 cible on trial does not alter in weight after heating. 
 A small piece of charcoal is placed in it, and crucible 
 and charcoal are heated over a Bunsen burner. 
 The charcoal enters upon a \igorous combustion. 
 On withdrawing the flame the mass is seen to be 
 losing its dense black colour, and presently there 
 is left in the bottom of the crucible only a little 
 grey ash. The charcoal has been in combustion ; it 
 has therefore been losing phlogiston ; phlogiston is 
 the principle of levit} T , therefore obviously the char- 
 coal, since it contained so large a proportion of this 
 principle, should now weigh far more than before it was 
 burnt. Surely that is a correct Stahlian argument. 
 Now let us weigh the crucible with the ash in it. To 
 our astonishment it weighs much Jess. This loss is 
 not due to the crucible, for that, we have already 
 shown, is unchanged by heat, and if now cleaned and 
 weighed will be found to have undergone no altera- 
 tion. The loss, then, is due to the charcoal, and 
 amounts to considerably more than 90 per cent, of its 
 weight. How would the Stahlians answer that ? 
 
 But it would be very easy to puzzle the Stahlians 
 
1 82 THE CONFLICT WITH ERROR. 
 
 with an examination of this kind, and perhaps it 
 would be hardly fair to make use of our increased 
 knowledge to do so. 
 
 The ideas of Scheele upon this subject illustrate 
 the confusion of mind produced by these doctrines. 
 He found that when air was phlogisticated by com- 
 bustion the residual gas (nitrogen) occupied less bulk. 
 Thinking it to be a compound of phlogiston with air 
 he expected it to be heavier than common air. To 
 his surprise he found it to be actually lighter. He 
 concluded that one constituent of the air remained 
 while another, united to phlogiston in some way, 
 disappeared. In his endeavours to find out what 
 had become of it, he finally came to the conclusion 
 that the compound of air with phlogiston was heat or 
 fire, which escaped through the glass. With these 
 views present to his mind he heated nitre in a retort 
 over a charcoal fire with sulphuric acid. In addition 
 to a fuming acid he obtained a colourless air (oxygen). 
 His explanation was that the charcoal in burning 
 united with fire-air (oxygen) to form heat. This heat 
 passed into the retort and was there decomposed, 
 giving rise to red nitrous fumes and pure fire air.* 
 
 When Priestley discovered oxygen gas he tried to 
 suit it to the phlogiston hypothesis. It supported 
 combustion more readily than common air, that is 
 it could take up more phlogiston. Thus in his 
 opinion it contained less phlogiston than common 
 air. It was therefore termed dephlogisticated air. 
 
 * Roscoe and Schorlemmer, Treatise, Hist. Introduction. 
 
THE CONFLICT WITH ERROR. 183 
 
 Nitrogen, not supporting combustion, was on the 
 other hand termed phlogisticated air. It was already 
 saturated with phlogiston and could not take up more. 
 Hydrogen was looked upon as either pure phlogiston 
 or phlogisticated water. 
 
 When we see such a man as Scheele drawn into 
 fanciful assertions of the kind described above we can 
 the better estimate the havoc played by the hypothesis 
 of Stahl in the minds of his followers. 
 
 But it is inexpressibly strange to find such men as 
 Priestley and Cavendish, the one clinging to this idea 
 as though it were the soul of science, and the other 
 unwilling to recognise its absurdity. That they might 
 have been blinded to the meaning of their own dis- 
 coveries we can to some extent understand, but that 
 when this meaning was pointed out they should still 
 have refused to see it, would be incredible were not 
 the facts so certain. Priestley insisted that the effect 
 of combustion was to load dephlogisticated air (oxygen) 
 with the combustible principle phlogiston, in spite of 
 Lavoisier's proof that the only product of the reaction 
 was the incombustible gas fixed air. Cavendish, more 
 unaccountably still, in spite of his own accurate ex- 
 periments, regarded it as most probable that inflam- 
 mable air (hydrogen) was "phlogisticated water." 
 
 Harmful, however, as we cannot but think that the 
 Stahlian hypothesis was, we must recognise that it 
 contained in it at least an element of truth. The 
 supposed loss of phlogiston was really a loss of poten- 
 tial energy. The attraction of oxygen for another 
 
i8 4 
 
 THE CONFLICT WITH ERROR. 
 
 element, so long as they are not combined, is capable 
 of being converted into a certain amount of work or 
 heat. Once the combination takes place the heat is 
 evolved and the capacity for work is destroyed. The 
 acting forces have been brought to a state of equi- 
 librium. The potential energy is lost. 
 
CHAPTER XL 
 
 SIXTH PERIOD : THE CONFLICT WITH ERROR. 
 THE FIRST OF AUGUST, 1774. 
 
 ITH this apparatus, after a variety of other 
 experiments, an account of which will be 
 found in its proper place, on the 1st of 
 August, 1774, I endeavoured to extract 
 air from mercurius calcinatus pev se * ; 
 and I presently found that by means of 
 this lens, air was expelled from it very readily. 
 Having got about three or four times as much as the 
 bulk of my materials I admitted water to it and found 
 it was not imbibed by it". But what surprised me more 
 than I can well express, was that a candle burned in 
 this air with a remarkably vigorous flame, very much 
 
 * I,e. mercuric oxide (HgO) obtained by heating- mercury in presence 
 
186 THE CONFLICT WITH ERROR. 
 
 like that enlarged flame with which a candle burns 
 in nitrous air, exposed to iron or liver of sulphur ; 
 .... I was utterly at a loss to account for it." 
 
 In these words Priestley announces his discovery of 
 oxygen gas. It may be said without qualification 
 that here was the most important chemical fact 
 discovered up to that time. 
 
 The rare cheerfulness which characterized Priestley's 
 temperament had very serious difficulties to contend 
 with in his early days. His father, Joseph Priestley, 
 was a cloth-dresser by trade, living in Birstall, near 
 Leeds. His son Joseph, the subject of this chapter, 
 was born in 1733. As a boy, Priestley was of a 
 weakly and consumptive habit, and his early educa- 
 tion was, in consequence, somewhat desultory. His 
 mother died early, and the strict Calvinism in which 
 he was brought up by his aunt, Mrs. Keighley, of 
 whom he speaks with much affection, threw an occa- 
 sional deep gloom over his boyish life. " I felt occa- 
 sionally such distress of mind as it is not in my power 
 to describe, and which I still look back upon with 
 horror." It must indeed have been a deep mental 
 distress to be so vividly recalled in after life. His 
 continued ill-health interfered for some time with 
 his purpose of entering the ministry. But so inclined 
 was Priestley to look at the bright side of all things 
 that of these drawbacks he wrote : " I even think it 
 an advantage to me, and I am truly thankful for it, 
 that my health received the check that it did when I 
 was young ; since a muscular habit from high health 
 
THE CONFLICT WITH ERROR. 187 
 
 and strong spirits are not, I think, in general, 
 accompanied with that sensibility of mind which is 
 both favourable to piety and to speculative pursuits." 
 Eventually he went to the Dissenting Academy at 
 Daventry and studied under Dr. Doddridge. 
 
 Priestley's first charge on leaving Daventry was 
 Needham Market, in Surrey. He had a marked 
 defect in his speech, and his stuttering manner not 
 suiting his congregation they left him almost penni- 
 less. After resorting to many unsuccessful experi- 
 ments for the purpose of earning his bread and cheese 
 he was finally obliged to leave. Years after he came 
 down to preach at the same chapel when better 
 known. His delivery was much the same and the 
 same congregation attended the chapel; but this time 
 they flocked to hear him, and pretended to admire 
 the utterance they had formerly despised. After 
 other vicissitudes Priestley went, in 1761, to War- 
 rington as " tutor in the languages " to a dissenting 
 academy. Here he taught Latin, Greek, Hebrew, 
 French, and Italian, and lectured on Logic, on Elocu- 
 tion, on the Theory of Language and Universal 
 Grammar, on Oratory and Criticism, on History and 
 General Policy, on Civil Law, and on Anatomy.* 
 
 Here also he found time to marry a daughter of 
 Mr. Isaac Wilkinson, an ironmaster near Wrexham, 
 in Wales. At Warrington, too, he got to know 
 
 * For a view of Priestley's versatility see the catalogue of his books 
 published in 1794. An interesting lecture on Piiestley was delivered 
 at Manchester by Professor Thorpe, Science Lectures (Series 6). 
 
i88 THE CONFLICT WITH ERROR. 
 
 Benjamin Franklin, but for whose influence most of 
 Priestley's scientific work might have been left un- 
 done. It was about this time that he gave some 
 attention to the study of Electricity and, in spite of 
 all his other business, brought out a history of the 
 subject, which was very favourably received. At the 
 Academy he and the tutors lived together in unusual 
 harmony. " \Ye drank tea together every Saturday, and 
 our conversation was equally instructive and pleasing." 
 In 1767 Priestley removed to Leeds. " At Leeds I 
 continued six. years very happy, with a liberal, friendly, 
 and harmonious congregation." Here he made ex- 
 periments on impregnating water with " fixed air " 
 to prevent scurvy, and was to have accompanied an 
 expedition, then sailing, as chaplain, but that his 
 heretical tendencies were discovered in time. But 
 the event at Leeds, of which he speaks with most 
 warmth, is his meeting Thomas Lindsay, then of 
 Catterick. " A correspondence and intimacy com- 
 menced, which has been the source of more real satis- 
 faction to me than any other circumstance in my 
 whole life."* His theological writings were never 
 published without Lindsay's advice and approval. 
 With Lindsay he kept up a very frequent and con- 
 stant correspondence, while with other friends he 
 corresponded very freely, though, as he remarks in a 
 letter to Lindsay, his literary labours often obliged 
 him to write till he could hardly hold the pen. 
 
 * In a much later letter to the same he says, " If I have been any 
 use in the world you are the cause of it," 
 
STATUE OF PSIE3TLEY, AT BIRMINGHAM. 
 
THE CONFLICT WITH ERROR. 191 
 
 From Leeds Priestley went into the family of the 
 Earl of Shelburne, afterwards Marquis of Lansdowne, 
 who had his country seat at Bowood, in Wiltshire. 
 His office was nominally that of librarian, for which 
 he received a house and 250 a year, with a certain 
 annuity for life. He had little employment, he says, 
 attaching to his post, and was thus free to prosecute 
 his own inquiries. When he went to his lordship he 
 had materials for his volume, Experiments and 
 Observations on different Kinds of Air, which he soon 
 afterwards published. 
 
 In his winter residence in London, while with 
 Shelburne, he saw much of Lindsay and of Franklin. 
 This was just before the American war; and their con- 
 versation was chiefly of a political nature. Franklin 
 was very pacifically inclined. He thought that if 
 war broke out it would last ten years, and was sure 
 that America would be finally victorious. As a fact 
 the war lasted eight years, and she was victorious. In 
 March, 1775, Franklin left England ; his last day in 
 the country he and Priestley spent together alone. 
 They read some accounts of the reception of the 
 Boston Port Bill in America, " and as he read the 
 addresses to the inhabitants of Boston from the places 
 in the neighbourhood the tears trickled iloun his 
 cheeks." 
 
 With Shelburne Priestley continued for seven 
 years, when a coolness sprang up between them, which ; 
 however, at a later date passed away. He was not 
 very greatly pleased with this mode of life, and does 
 
-i 9 3 THE CONFLICT WITH ERROR. 
 
 not seem to have envied persons in high station. 
 He believed much more happiness was to he found 
 in the life of the middle classes. But he adds that 
 wealth may be of immense value when in the hands 
 of a good man, and that when a person is born to 
 affluence and not hurt by it, "it produces a godlike 
 character unattainable otherwise." After leaving Lord 
 Shelburne he settled in Birmingham. Here, on 14th 
 of July, 1791, riots in favour of " Church and King " 
 broke out in consequence of a meeting to celebrate 
 the anniversary of the French Eevolution. Priestley's 
 opinions being considered heretical and violent, the 
 mob marched upon his house, where he was unsus- 
 pectingly sitting with his wife and family. Friends 
 hastened to warn him ; at first their news seemed to 
 him incredible, but finally he consented to regard his 
 own safety and left the house. He retired to Mr. 
 Hawkes's in the neighbourhood, and from there saw 
 his house, with library, manuscripts, and philosophical 
 instruments, burnt to the ground. At this destruc- 
 tion of his property and labour he looked on with 
 perfect calm, and afterwards fled in disguise to 
 Worcester and thence to London. " Persons in the 
 habit of gentlemen" were found secreting his papers 
 with a view to discover incriminating details.* He 
 was appointed successor to his friend Dr. Price at 
 the dissenting meeting in Hackney, but still suspicion 
 pursued him. His political opinions gave offence to 
 
 * Curry, Life of Joseph Priestley, a pamphlet. Birmingham 
 (1804). 
 
THE CONFLICT WITH ERROR. 1 93 
 
 men in power, and he was finally obliged to quit the 
 country. 
 
 .-.; He embarked in 1794, a victim to popular igno- 
 rance and ingratitude. Before leaving Priestley placed 
 on record the following remarkable words : "I can- 
 not refrain from repeating again that I leave my 
 native country with real regret, never expecting to 
 find anywhere else society so suited to my disposition 
 and habit, such friends as I have here (whose attach- 
 ment has been more than an even balance to all the 
 abuse I have met with from others), and especially 
 to replace one particular Christian friend, in whose 
 absence I shall, for some time at least, find all the 
 
 world a blank I can, however, truly say that 
 
 I leave without resentment or ill-will. On the con- 
 trary, I sincerely wish my countrymen all happiness, 
 and when the time for the reflection (which my 
 absence may accelerate) shall come, they will, I am 
 confident, do me more justice." It is hardly possible 
 to do justice after a victim's death, but, so far as 
 slow growth of somewhat wider views is equivalent 
 to repentance for past narrowness, to that extent 
 justice has tardily been done to Priestley, among 
 others whose heroism was then considered no mitiga- 
 tion of their heresy. Heresy, not merely in religion 
 but in political views and in social life, has ever been 
 to the ordinary man the one unpardonable sin. 
 
 Priestley settled near his sons on the Susquehanna, 
 and there died. His end was very calm. His mind 
 was perfectly clear and tranquil. He dictated some 
 
 N 
 
194 THE CONFLICT WITH ERROR. 
 
 last words, and then had the manuscript read to him. 
 After making some needful corrections he said quietly, 
 " That is right ; I have done," and after a few hours 
 he passed away. 
 
 He had reason, he said, to be thankful for a happy 
 temperament of body and mind, and certainly a more 
 cheerful mortal it is difficult to conceive of. His 
 constitution had been far from robust, but with ex- 
 quisite felicity he remarks, " excellently adapted to 
 that studious life which has fallen to my lot." He 
 always slept well, and, when fatigued, could sit down 
 and sleep ; " and whatever cause of anxiety I have had, 
 I have almost always lost sight of it when I have got 
 to bed, and I have generally fallen asleep as soon as I 
 have been warm." His spirits after momentary depres- 
 sion always recovered their level, and, indeed, he had 
 found that after trouble they would rise beyond their 
 former height without any change in the circum- 
 stances. 
 
 He spoke of having a very failing memory which 
 made his old writings, when re-read, seem perfectly 
 new to him. One instance is mentioned by him 
 in his autobiographical sketch, where his loss of 
 memory went so far that he had serious fears of his 
 mental powers totally failing. * In writing a prefatory 
 dissertation to one of his books he had occasion to 
 refer to some point (he forgets what) connected with 
 the Jewish passover. He had to consult and com- 
 pare several writers, and he digested the results in a 
 few paragraphs. For a fortnight his attention was 
 
THE CONFLICT WITH ERROR. 195 
 
 drawn to other things, and at the end of this time it 
 suddenly occurred to him that he had still to examine 
 the point of the Jewish passover. Without any 
 recollection that he had already done the work he 
 proceeded to consult the same authorities, and to 
 write out the opinions thus arrived at. He would 
 never have remembered the former paper but that he 
 accidentally discovered the manuscript, " which," says 
 he, " I viewed with a degree of terror." Yet even 
 this defect of memory he thought was, on the whole, 
 probably a boon, being very likely compensated by 
 greater inventive power.* 
 
 Priestley's manner of work was quiet and methodical. 
 He could do nothing if hurried, but could work 
 quickly if he felt that he had ample time. He wrote 
 in the presence of wife and children, occasionally 
 speaking to them ; but could not write during read- 
 ing aloud or uninterrupted conversation. 
 Certainly few characters afford us more varied 
 and interesting material for study. Essentially, and 
 from first to last, Priestley was a brilliant man, a 
 man of splendid talents, wonderfully acute, and quick 
 in perception, inventive and industrious. But his 
 work was not that of a genius, it had hardly its ease 
 or its accuracy. His versatility was amazing, but it 
 was more the outcome of patience than of power, and 
 to some extent he lacked the expansive capacity of 
 a really great mind. In the latter part of his life, at 
 least, he found it difficult to accommodate himself to 
 
 * $. T. Butt, Priestley's Life and Correspondence (1831). 
 
196 THE CONFLICT WITH ERROR. 
 
 new ideas, and although his own discoveries were in 
 themselves ruinous to the phlogistic theory yet he 
 never could be got to see it. His last publication 
 was The Theory of Phlogiston Established. We 
 may say then that Priestley was a man of exceptional 
 acuteness and versatility who made full use of his 
 powers. 
 
 Such an estimate will fairly account for the work 
 accomplished by his life. It is not necessary to say 
 that he was a genius. Indeed, remarkably few 
 scientific men would be worthy of such a title. The 
 career has not as yet attracted many representa- 
 tives of the highest order of mind. At the same time 
 it will not do to lay too much stress upon Priest- 
 ley's blunders over the phlogistic theory. We must 
 bear in mind the great ascendency it had obtained 
 over the minds of all chemists, and we must remem- 
 ber that only in rare cases is the scientific mind free 
 from bias. Priestley's in this case was certainly not. 
 The honour of acknowledging conversion belongs to 
 Dr. Black, as we have already remarked. But the 
 honour of a brilliant and eminently useful career, a 
 life full of wide sympathies and noble unselfishness, 
 a fame unsullied by jealousy or ambition, and a heart 
 cheerfully hopeful through all misfortune belong to 
 Joseph Priestley, whom the English people drove 
 from their shores as their only tribute to his zeal. 
 
 The phlogiston theory is rather fully exemplified 
 in some of the work undertaken by Priestley. When 
 he found that a candle confined in a close vessel ig 
 
igS THE CONFLICT WITH ERROR. 
 
 after a while extinguished, he concluded that this 
 was due to the limited amount of air becoming satu- 
 rated with phlogiston. The candle burned while it 
 could give off phlogiston, but the impulse to this 
 evolution of phlogiston was to be found in the capacity 
 the atmosphere had for combining with or absorbing 
 phlogiston. As soon as this capacity was exhausted 
 and the air could take up no more phlogiston the 
 burning of the candle ceased. 
 
 Priestley experimented upon the action of hydrogen 
 (rediscovered by his contemporary, Cavendish) on 
 metallic calxes (oxides) heated by a burning-glass. 
 The method was to heat the oxides in a cylinder of 
 hydrogen inverted over water or mercury. In this 
 way it was found that the hydrogen was absorbed and 
 the calx converted into metal. We now know that 
 what occurs in such a case is simply that the hydro- 
 gen abstracts the oxygen from the metallic oxide or 
 "calx," combines with this oxygen to form water, 
 and leaves the metal in a free state reduced from its 
 oxide. Now Priestley observed that a small quantity 
 of water was formed in these experiments, but he was 
 bent upon explaining all things by means of phlogis- 
 ton. He therefore neglected this item in the account 
 and concluded that phlogiston was the same thing as 
 inflammable air and existed in a combined state in 
 metals ; just as fixed air was contained in chalk and 
 other calcareous substances, both being equally ca- 
 pable of being expelled again in the form of air. 
 Priestley seems to have been the first to substitute 
 
THE CONFLICT WITH ERROR. 199 
 
 mercury for water in the pneumatic trough, and thus 
 succeeded in obtaining gases, the collection of which 
 had baffled the endeavours of previous experimenters. 
 Cavendish had tried to get " inflammable air " from 
 a mixture of copper and " spirits of salt" (hydrochloric 
 acid). He obtained an air that "lost its elasticity," 
 that is, was absorbed on contact with water. Priestley 
 was " exceedingly desirous " of becoming further ac- 
 quainted with this gas. He therefore began the experi- 
 ment, replacing the water by quicksilver, as, he says, he 
 never failed to do where he suspected that a gas would 
 be in any way affected by water. He in this way 
 collected a gas which, he went on to show, was 
 derived entirely from the acid, and might be equally 
 well obtained by merely boiling common "spirit of 
 salt " per sc. In short Priestley obtained the true 
 hydrochloric acid, which is a gas and had not before 
 been isolated. Ordinary aqueous hydrochloric acid is 
 merely a solution of this gas in water.* 
 
 This method of using quicksilver was of great 
 service to Priestley ; for by means of it too he showed 
 that ordinary " spirits of hartshorn," or spirit its 
 volatilis salts ammoniaci, is a solution of ammonia gas 
 in water. Stephen Hales, in 1727, had heated lime 
 with sal-ammoniac in a vessel closed by water, and he 
 observed that no air was given out, but that, on the 
 contrary, water was drawn into the apparatus. 
 Using a mercury trough Priestley, by this same old 
 method, obtained ammonia gas and showed that the 
 
 * Observations on different Kinds of Air, 1772. 
 
200 THE CONFLICT WITH ERROR. 
 
 ordinary aqueous ammonia, or " volatile spirit of sal- 
 ammoniac/' is a solution of this gas in water.* 
 (1774.) 
 
 Priestley followed up these discoveries by endeavour- 
 ing to obtain an "air" from oil of vitriol (sulphuric 
 acid). He heated the acid for a long period without 
 any result beyond the production of some white 
 fumes which condensed in the upper part of his flask. 
 The tube leading from the flask of course dipped 
 under mercury. The end of this experiment is worth 
 giving in his own words. " Despairing to get any air 
 from the longer application of my candles I with- 
 drew them ; but before I could disengage the phial 
 from the vessel of quicksilver a little of it passed 
 through the tube into the hot acid ;t when, instantly 
 it was all filled with dense white fumes, a prodigious 
 quantity of air was generated, the tube through 
 which it was transmitted was broken into many 
 pieces (I suppose by the heat that was suddenly 
 produced), and part of the hot acid being spilled 
 upon my hand, burned it terribly, so that the effect 
 of it is visible to this day. The inside of the phial 
 was coated with a white substance, and the smell 
 that issued from it was extremely suffocating." In 
 this way Priestley found out (1775) how to prepare 
 pure sulphur dioxide. Stahl had shown that the 
 fumes of burning sulphur are altogether different 
 from sulphuric acid and are only partially on the 
 
 * Observations on different Kinds of Air, 1772. 
 f Being sucked up by the condensation, 
 
THE CONFLICT WITH ERROR. 201 
 
 way to it, but it was Priestley who first isolated tho 
 gas. 
 
 The next passage is characteristic both of Priestley's 
 good spirits and of his obstinacy : " This accident 
 taught me what I am surprised I should not have 
 suspected before, viz. : that some metals will part 
 with their phlogiston to hot oil of vitriol and thereby 
 convert it into a permanent elastic air, producing the 
 very same effect with oil, charcoal, or any other 
 substance." The reaction may be most simply stated 
 as follows : taking copper, which is the metal 
 usually employed, in place of mercury. First, the 
 sulphuric acid is a compound of hydrogen, sulphur, 
 and oxygen hydrogen sulphate. The copper dis- 
 places the hydrogen of the acid, forming copper- 
 sulphate and free hydrogen. This hydrogen is of 
 course liberated in the presence of another portion of 
 sulphuric acid which we may for convenience repre- 
 sent as composed of water and sulphur trioxide. 
 The free hydrogen takes away a third of the oxygen 
 from the trioxide, forming more water and sulphur 
 dioxide, which is evolved as a gas.* Priestley was 
 successful in producing this gas with copper, mercury, 
 silver, iron, and sulphuric acid, the reaction being 
 similar in the different cases. When carbon is used 
 
 * After reading the discussion of chemical symbols the reader may 
 be able to appreciate this reaction when expressed in the more 
 mathematical form of chemical equations : 
 
 (i.) Cu -f H-SO Cu SO 4 + H 2 . 
 (ii.) H 2 SO 3 -f H 2 = 2H 2 + SO 2 , 
 
202 THE CONFLICT WITH ERROR. 
 
 carbon dioxide (the fixed air of Priestley and Black) 
 is evolved. * Sulphur itself may be heated with 
 sulphuric acid, the products in this case being only 
 sulphur dioxide and water, j- Priestley found that 
 gold and sulphuric acid gave no result. 
 
 Sulphur dioxide is a colourless gas of suffocating 
 odour like that of burning sulphur, and during this 
 combustion it is formed. It will not support the 
 combustion of a candle any more than will carbon 
 dioxide. It combines with metallic oxides to form 
 the salts termed sulphites. The moist gas bleaches 
 vegetable colouring matter, such as litmus. The gas 
 is readily soluble in water and its solution is known 
 as sulphurous acid. The dry gas may be condensed 
 to a liquid by being passed through a spiral tube 
 surrounded by a freezing mixture. 
 
 Lastly we come to Priestley's supreme discovery, 
 that of oxygen, or, as he termed it, dephlogisttcated 
 air. To some extent we may attribute such a dis- 
 covery to chance ; but chance as a rule will only assist 
 men of rare intelligence and insight. Opportunities 
 for good work of one kind or another occur con- 
 tinually to all, but the large majority of us are too 
 blind to see them. Most good work is too near us 
 for us to think it worth doing. All honour to those 
 who have lent us their spectacles and shown us how 
 easy their discoveries were! 
 
 Priestley was by no means definitely in search of 
 
 * C + 2 H 2 SO 2 H 2 -{- CO 3 -f 2 SO 2 . 
 f S -f 2 H 2 S0 4 = 3 SO 2 -}- 2 H 2 0. 
 
THE CONFLICT WITH ERROR. 203 
 
 oxygen when he found it. The conditions of scien- 
 tific work then did not admit of such an attitude. 
 Chemistry was not far enough on her uphill path to 
 see the tracts of country crossed by her future 
 advance. We can predict now what compounds and 
 even what elements ought to occur in nature and can 
 often tell how to search for them. If we do not 
 always find them that is because either we or nature 
 are not what we ought to be. In Priestley's time 
 prediction in science, to have any chance of fulfilment, 
 must be as vague as utterances of the Delphic sibyl. 
 In most cases the only course was to " prospect 
 around " and see what turned up. After showing, 
 as he did by experiments with a candle similar to 
 those employed by Mayow, that air would support 
 only a limited amount of combustion, Priestley went 
 on to prove that it could be renovated and made fit 
 once more for respiration by the action of growing 
 plants. Thus on the 17th of August, 1771, he first 
 burned out a wax candle in a confined portion of air 
 and then introduced into it a sprig of mint. On the 
 27th of the same month he found that another 
 candle burned perfectly well in it. The mint had 
 restored to the air its original virtues. To make 
 assurance doubly sure he divided the used-up air 
 into two parts. One he left standing alone over 
 water ; into the other he put the sprig of mint. 
 After some days had elapsed he always found that a 
 candle would burn in the latter but not in the 
 former. 
 
204 THE CONFLICT WITH ERROR. 
 
 The true explanation of these phenomena is that 
 the carbon dioxide formed by the combustion is 
 absorbed by the plant and, in the presence of chloro- 
 phyll and sunlight, split up into carbon and oxygen, 
 the plant retaining the carbon and giving the oxygen 
 back to the air. Priestley did not recognise the full 
 bearing of his discovery on the composition of the 
 atmosphere. In 1772, however, Dr. Rutherford, 
 Professor of Botany in the University of Edinburgh, 
 showed definitely that common or atmospheric air 
 contains a gas differing from fixed air, and yet, like it, 
 incapable of supporting combustion. This he showed 
 by treating air in which animals had breathed with 
 caustic potash. The potash in this case absorbed the 
 fixed air (forming the mild alkali or carbonate), yet 
 when this absorption was complete a residual gas 
 still remained and in this a candle would not burn. 
 It was nitrogen gas. 
 
 In the same year Priestley found that combustion 
 in a bell-glass over water gave rise to fixed air absorb- 
 able by milk of lime. The residual (phlogiscated) 
 air, he found, would not support combustion, but he 
 did not then consider it as a constituent of the at- 
 mosphere.* He showed that " nitrous gas " (nitrogen 
 dioxide) when mixed with " phlogisticated air" 
 
 * At the time of the 1790 edition of his Experiments and Observation, 
 Priestley seems to have been rather doubtful as to the correct way of 
 regarding the composition of the air. He was inclined to reg-ard air 
 as a simple gas in a certain state of phlogistication, but the same 
 nomenclature, he says, will suffice if it be regarded as composed of 
 two distinct gases. 
 
TffE CONFLICT WITH ERROR. $05 
 
 (nitrogen), occasioned no diminution in volume. If 
 mixed with dephlogisticated air (oxygen), on the other 
 hand, in due proportion, the whole of the resultant 
 mixture was absorbed over water. This, indeed, 
 was the method used by Priestley for the analysis of 
 air, or of ascertaining what was termed the good- 
 ness of atmospheric air. The results of these analyses 
 varied, and thus suggested the notion that the com- 
 position of the air varied, but this idea was exploded 
 by Cavendish. 
 
 Interested as he became in his researches on gas- 
 eous bodies in general, Priestley proceeded somewhat 
 as Hales had done before him, but with much more 
 alertness of observation, to investigate the air obtain- 
 able from different bodies. In the course of these 
 labours mercuriits cakinatus per se, or mercuric oxide 
 (red precipitate), was one of the bodies experimented 
 on. From the important paper on this subject we 
 may quote his own words : " For my own part I will 
 frankly acknowledge that, at the commencement of 
 the experiments recited in this section I was so far 
 from having formed any hypothesis that led to the 
 discoveries I made in pursuing them, that they would 
 have appeared very improbable to me had I been 
 told of them ; and when the decisive facts did at 
 length obtrude themselves upon my notice it was 
 very slowly, and with great hesitation, that I yielded 
 to the evidence of my senses. And yet, when I con- 
 sider the matter, and compare my last discoveries 
 relating to the constitution of the atmosphere with 
 
206 THE CONFLICT WITH ERROR, 
 
 the first, I see the closest and easiest connection in 
 the world between them, so as to wonder that I 
 should not have been immediately led from the one to 
 the other. That this was not the case I attribute to 
 the force of prejudice, which, unknown to ourselves, 
 biases, not only our judgments, properly so-called, 
 but even the perceptions of our senses : for we may 
 take a maxim so strongly for granted that the plain- 
 est evidence of sense will not entirely change, and 
 often hardly modify, our persuasions ; and the more 
 ingenious a man is the more effectually he is en- 
 tangled in his errors ; his ingenuity only helping 
 him to deceive himself by evading the force of 
 truth." 
 
 How pointedly these latter remarks applied to 
 Priestley himself it is scarcely necessary to say. 
 Having discovered the supporter of combustion in 
 oxygen gas, having seen its relation to combustion very 
 fully discussed by others, how could he, except at the 
 impulse of bias, continue fixed in his belief that com- 
 bustion essentially means loss of phlogiston. He was 
 aware that metals gained in weight by calcination, 
 but still held to the idea that this gain was consis- 
 tent with the loss of a constituent element. Lavoisier 
 showed him that the only product resulting from 
 combustion in dephlogisticated air was fixed air, 
 but still Priestley held that the result of combus- 
 tion was to load the air with phlogiston. And so, 
 whatever difficulties and inconsistencies grew out of 
 the Stahlian hypothesis, Priestley defended it, im- 
 
THE CONFLICT WITH ERROR, 207 
 
 pervious to sense and reason. Yet the grim tyranny 
 of a false idea is ever in the end overcome. " No- 
 thing," said the old chemist, Glauber, " can extin- 
 quish truth it may be prest, but cannot be overcome ; 
 like the sun's light it may be hidden, but not extin- 
 guished ; " and when we see the distorting power of 
 bias we need his faith to believe in the final van- 
 quishing of error. 
 
 In the pursuit of his inquiries Priestley ( ' proceeded 
 to examine by the help of a burning-glass what kind 
 of air a great variety of substances, natural and facti- 
 tious, would yield, putting them in vessels filled 
 with quicksilver and kept inverted in a basin of the 
 same 
 
 " With this apparatus, .... on the 1st of August, 
 I endeavoured to extract air from mercurius calci- 
 natus per se : and I presently found that, by means of 
 this lens, air was expelled from it very readily." 
 With true caution Priestley suspected that this result 
 might be due to some peculiarity or impurity in his 
 individual specimen of mercuric oxide. But other 
 specimens obtained by him gave precisely similar 
 results. He proceeded to test this gas with " nitrous 
 air" (nitrogen dioxide), and, to his astonishment, 
 found that it was better than common air, that is to 
 say, the product was more completely absorbed by 
 water. Now the nitrous air test is, according to 
 Priestley's ideas, the fitness of air for respiration, 
 and he naturally next experimented directly upon the 
 respirability of the new gas, Placing a mouse in a 
 
208 THE CONFLICT WITH ERROR. 
 
 jar of the dephlogisticated air he found that it would 
 live for an hour. In the same bulk of atmospheric 
 
 air it lived only a fourth of the time. L.^ 
 breathed it himself. " The feeling of it to my lungs 
 was not sensibly different from that of common air ; 
 
THE CONFLICT WITH ERROR. 209 
 
 but I fancied that my heart felt peculiarly light and 
 easy for some time afterwards. Who can tell but that 
 in time this pure air may become a fashionable article 
 of luxury ? Hitherto, only two mice and myself have 
 had the privilege of breathing it."* 
 
 The conclusion deducible from the experiments 
 related in the paper from which several extracts 
 
 COMBUSTION OF PHOSPHORUS IN OXYGEN. 
 
 above are made is, that the atmosphere is, on an 
 average, made up of four volumes of phlogisticated 
 air (nitrogen) to one volume of this new gas, de- 
 phlogisticated air, or, as Lavoisier termed it, oxygen, 
 Priestley, however, did not directly assert these con- 
 clusions himself, though we may so interpret his 
 experiments. The analyses made by him and others of 
 air gave somewhat varying results, and it was thought 
 
 * Experiments and Observations on different Kinds of Air. London 
 (1774-75), 2 vols. Another edition in 3 vols. was published at Bir- 
 mingham in 1790. 
 
 O 
 
210 THE CONFLICT WITH ERROR. 
 
 that the proportion of the two chief constituent gases 
 was actually different at different places and seasons. 
 It was left to Cavendish to show that this was not 
 the case, but that the proportion of these consti- 
 tuents was, on the other hand, remarkably constant. 
 We have glanced rapidly at the more striking of 
 Priestley's discoveries, and we can readily see that 
 they were interesting and important. He had an 
 admirable knack of finding out new things ; but he 
 hardly ever followed up sufficiently the discoveries he 
 had made. Others had to show the bearing of his 
 work upon the general theory of chemistry and to 
 draw from his experiments conclusions he would 
 not stop to deduce. Happily there was at least 
 one man then living fit for the task, pre-eminent in 
 the power of combining scattered ideas into an 
 orderly whole, a man in intellectual power and grip 
 surpassing any chemist before his time. That man 
 was the great French chemist, Lavoisier. Before pro- 
 ceeding to the discussion of his work we must say 
 something about the accurate and acute English 
 worker, Cavendish. Next we shall pass on to Lavoi- 
 sier, and with him the dawn of modern chemistry 
 begins. 
 
CHAPTER XII 
 
 SIXTH PERIOD : THE CONFLICT WITH ERROR. 
 TRUTH IN DISGUISE. 
 
 FTER Priestley's work the material, at least, 
 for the solution of great chemical problems 
 was at hand. The solution of one of the 
 principal of these was afforded by Caven- 
 dish, whose other work also threw much 
 light upon the path of chemical progress, 
 though his eyes were too blinded by the dust of the 
 phlogiston theory to fully discern what lay before 
 him. 
 
 As a man Cavendish was certainly one of the most 
 extraordinary of the chemists with whom we have 
 had to deal. In fact, in no real or full significance 
 of the word, was Cavendish a man at all. He was a 
 well-arranged intellectual machine, a thing without 
 enthusiasm, sympathy, or happiness. The questions 
 
212 THE CONFLICT WITH ERROR. 
 
 coming before him were apparently answered with 
 absence of emotion as complete as that of the logical 
 machine invented by Professor Jevons when it draws 
 conclusions from data which are given it. To irse 
 this machine a key is pressed for each term of the 
 propositions forming the data from which conclusions 
 are to be drawn. The proper series of keys having 
 been pressed the correct deductions from those data 
 are at once presented to view. This is apparently 
 representative of the action of Cavendish's mind. 
 Various facts struck different keys in his mind, and 
 in consequence of its internal mechanical construction 
 these facts were at once sorted out and arranged so 
 as to make evident the conclusions derivable from 
 them. He was more wonderful than the machine, in 
 that he was able to vary the relations of external 
 facts ; he was less wonderful than it, in that his 
 conclusions were not wholly accurate. Mechanical 
 as he was, he was not free from bias. 
 
 Cavendish's family traces back its origin to Sir 
 John Cavendish, Lord Chief Justice of the King's 
 Bench in the reign of Edward III., while other 
 genealogists have carried it back to Robert de Gernon, 
 a famous Norman who assisted William the Conqueror 
 in his invasion. The Honourable Henry Cavendish, 
 son of Lord Charles Cavendish, -was born at Nice, on 
 the 10th of October, 1731. His mother died when he 
 was about two years old, and of his early years 
 nothing is known. In 1749 he went to Cambridge 
 and remained there till 1753) but did not graduate. 
 
THE CONFLICT WITH ERROR. 213 
 
 For the next ten years his history is a blank. His 
 intellect was gathering strength. His first contribu- 
 tion to the Koyal Society was made in 1766, On 
 Factitious Airs. Cavendish had training in many 
 sciences, electricity, geology, chemistry and mathe- 
 matics. His chief work was purely chemical. He 
 was not at all eager to publish his researches. Two 
 lengthy investigations, Experiments on Arsenic 
 and Experiments on Heat, were written before 
 1766 and discovered for the first time after his 
 death. They were apparently written out for some 
 friend whose name never transpired, and the reason 
 of their remaining unpublished Avas never known. 
 His Experiments on Air were published in the 
 Philosophical Transactions for 1784. 
 
 His father, Lord Charles Cavendish, allowed his 
 son 500 a year during his lifetime, and it was 
 argued, but with not much appearance of truth, that 
 the smallness of this allowance led Cavendish into 
 the too economical habits afterwards characteristic of 
 him. Cuvier states that Cavendish was left a very 
 large fortune by his uncle about the year 1773. At 
 his father's death, in 1783, he also had a fortune 
 left him. The details as to how he came by his 
 wealth are somewhat contradictory, but however that 
 may be, he died in 1810, leaving 700,000 in the 
 funds and a landed estate producing an income of 
 6,000 a year. None of this great wealth went to 
 the help of science. 
 
 Cavendish's London residence was close to the 
 
2i4 THE CONFLICT WITH ERROR, 
 
 British Museum, at the corner of Montague Place 
 and Gower Street. Those who passed its portals 
 reported that books and apparatus were its chief 
 furniture. Latterly he had a separate house for 
 books in Dean Street, Soho. It is one of the few 
 indications that he might have been capable of 
 interest in human affairs that he allowed books from 
 this library to be lent to scientific men on recom- 
 mendation. It is characteristic also of the extremes 
 to which he carried his methodical habits that when 
 he thus took a book from his own library he entered 
 his name as an ordinary borrower. His favourite 
 residence was a suburban house at Clapham, after- 
 wards known as Cavendish House, the draAving-room 
 of which was converted into a laboratory. 
 
 Many stories are told illustrative of Cavendish's 
 extreme reserve, and his apparent freedom from all 
 human sympathy.* He constantly attended the 
 meetings of the Royal Society, and as a rule avoided 
 all conversation. An F.R.S. wrote : " We used to 
 dine at the Crown and Anchor and Cavendish often 
 dined with us. He came slouching in, one hand 
 behind his back, and, taking off his hat (which by- 
 the-bye he always hung up on one particular peg) 
 he sat down without taking notice of anybody. If 
 you attempted to draw him into conversation he 
 always fought shy. Dr. Wollaston's directions I 
 found to succeed best. He said, ' The way to talk to 
 Cavendish is never to look at him, but to talk as it 
 
 * See G. Wilson : Life of the Honourable H. C. Cavendish (1848). 
 
.THE CONFLICT WITH ERROR, 215 
 
 were into vacancy, and then it is not unlikely but 
 you may set him going.'" T. G. Children relates 
 how, when he first became a member of the Crown 
 and Anchor club he saw Cavendish talking very 
 earnestly to Marsden, Davy and Hatchett. Children 
 went up and joined the group. His eye caught that 
 of Cavendish and the latter instantly became silent 
 and would not say another word. He had seen a 
 strange face. 
 
 Lord Brougham remarks : " He entered diffidently 
 into any conversation and then seemed to dislike 
 being spoken to. He would often leave the place 
 when he was addressed, and leave it abruptly with a 
 kind of cry or ejaculation, as if scared and disturbed." 
 On one occasion, it is related, Cavendish was present 
 at some reception when a foreigner was introduced to 
 him. The latter began expatiating upon his talents 
 to Cavendish's great annoyance. Growing more 
 and more embarrassed he at length darted from the 
 room and left the house. 
 
 His horror of females was extreme. He ordered 
 his dinner by a note left on the hall table, and would 
 not allow any maidservant to show herself on pain of 
 instant dismissal. The person whom he had made 
 his heir he saw only once a year, and then for about 
 ten minutes. He lived by himself and no one was 
 known to be his friend. One single letter written to 
 him, and discovered after his death, signed " Your 
 most affectionate," brings Cavendish nearer to ordinary 
 human sympathies than anything else in his career. 
 
216 THE CONFLICT WITH ERROR. 
 
 In the journals kept by him of his travels about the 
 country there is, except in one solitary spot, no 
 reference to the beauties of scenery passed through, 
 no suggestion that he was capable of being cheered 
 by nature's brightness or made pensive by her 
 gloom. In the one exceptional passage referred to 
 he does mention the bald fact that from a certain 
 place a fine view of the surrounding country is to be 
 obtained. Otherwise the pages are untinged, in their 
 dreary preciseness, by the warmth of a single emotion. 
 It should, however, be stated that according to the 
 journal recording his visit to his rival Watt at 
 Birmingham in 1785, he seems to have felt quite a 
 considerable interest in his inventions, if not in the 
 man. Numerous references occur to the explanations 
 Watt had given him, 
 
 For scientific purposes Cavendish would very occa- 
 sionally invite Fellows of the Eoyal Society to his 
 house, and his few guests were always treated to a leg 
 of mutton. An F.R.S. is responsible for the follow- 
 ing statement : " Cavendish seldom has company at 
 his house ; but, on one occasion, three or four scientific 
 men were to dine with him, and when his house- 
 keeper came to ask what was to be got for dinner 
 he said ' a leg of mutton.' ' Sir, that will not be 
 enough for five.' 'Well, then, get two,' was the 
 reply." 
 
 In spite of his wealth Cavendish hardly over gave 
 pecuniary aid to science. It is amusing to find him, 
 when an enlarged voltaic battery was desired at the 
 
THE CONFLICT WITH ERROR. 217 
 
 Royal Institution, joining in the complaints of illibe- 
 rality in the patrons and himself doing nothing. He 
 had apparently an objection to be considered liberal, 
 or rather, perhaps, he was not sufficiently awake to 
 the ordinary affairs of life to recollect that a liberal 
 course was open to him. On one occasion he was 
 induced to allow a gentleman of small means and 
 considerable talents to reside in his London library in 
 order to rearrange it. The man finished this work 
 and left London. Some time after, when Cavendish 
 was dining at the Royal Society's Club, the gentle- 
 man's name was mentioned. "Ah! poor fellow," 
 said Cavendish, " how does he do, how does he get 
 on ? " "I fear very indifferently." " I am sorry for 
 it." " We had hoped you would have done some- 
 thing for him, sir." " Me, me, me ? what could I 
 do ? " "A little annuity for his life ; he is not in 
 the best of health." " Well, well, well, a cheque for 
 ten thousand pounds, would that do ? " " Oh, sir, 
 more than sufficient, more than sufficient." And the 
 cheque was accordingly written. 
 
 In person Cavendish was tall and rather thin, his 
 face in the portrait prefixed to his life looking wizened 
 and pinched. His dress was old-fashioned and some- 
 times a little neglected. 
 
 This is almost all that can be said of Cavendish 
 apart from his scientific work. Occasional gleams 
 of wider sympathy suggest that his nature held 
 within it possibilities of a far higher order ; there 
 was a spark of fire buried deep in the ice. But no 
 
218 THE CONFLICT WITH ERROR. 
 
 influence he encountered had power to develop the 
 possibilities, or break down the ice-barriers. And so 
 at last he became what we have seen him to be, a 
 passively selfish cynic, aware only of monotonous 
 existence, not of life, ignorant of laughter and of 
 tears. Morally his character was a blank. There 
 was not apparently a human soul with which he had 
 relations other than those of business and science. 
 He was interested in no one and in nothing outside 
 his scientific work. His life was, in regard to all 
 human sympathy, one of the most sadly wasted that 
 history records. Through it all he was alone. For 
 him no human face was rich in the beauty of affec- 
 tion, no voice was welcomed with gladness, no caress 
 could soothe pain. To him was unknown the power 
 of unselfish sympathy, the joy of helpful pity, or 
 exultation in the redress of wrong. To him life 
 brought only its morning of labour and its night of 
 sleep, work without happiness, quiescence without 
 rest. To him sky and earth were silent, and heaven 
 was without hope. He understood the voices neither 
 of joy nor sorrow. Life to him was an ashen desert 
 of speculation and proof. Through it all he was 
 loveless and alone. It is a saddening life to con- 
 template, and still sadder is it to think of what 
 can have induced so chilling a frost. Whether defi- 
 nite sorrow and disappointment, or only absence of 
 surrounding warmth of sympathy was its cause, it 
 will now never be possible to say. With his sorrows, 
 if his heart ever felt human pain, and with his errors, 
 
THE CONFLICT WITH ERROR, 219 
 
 his life has passed out into the darkness, and of him. 
 there is left with us the best that he could leave us, 
 the germ of nobleness that was in him, the work, in 
 these latter days, so full in fruit. 
 
 The work done by Cavendish was small in amount, 
 but what remains of it is excellent. Considering the 
 power shown in what he did accomplish and the 
 advantages he possessed it is only surprising that he 
 did not do more. We are tempted to wonder how 
 his time was employed. But when we recollect how 
 withdrawn he was from the impulse of every-day con- 
 tact with other men, a stimulus quickening and in- 
 vigorating alike to heart and brain, we can readily 
 believe that much of his intellectual life must have 
 lain dormant and never wakened into activity of 
 thought. 
 
 The first communication made by Cavendish to the 
 Royal Society was, as already mentioned, in 1766, 
 under the title of Factitious Airs. The research 
 is divided into four papers and deals with hydrogen, 
 carbon dioxide, and the gases evolved by fermenta- 
 tion, putrefaction, and destructive distillation. It is 
 true that hydrogen had been obtained so far back as 
 the time of Paracelsus, that Mayo\v had collected it, 
 and that Hales had shown it to be combustible ; but 
 the phenomena of its production and its properties 
 were first distinctly studied and clearly set forth by 
 Cavendish. He showed that different metals yield 
 different quantities of the gas, but that the same 
 weight of the same metal evolved a like amount of 
 
220 THE CONFLICT WITH ERROR, 
 
 gas from different acids.* He observed that, though 
 itself inflammable, hydrogen extinguished flame and 
 also destroyed life. He also proved it to be lighter 
 than air, and as a result of this the gas was subse- 
 quently used in balloons instead of heated air. 
 
 In the same papers referred to above Cavendish 
 
 COMBUSTION OF HYDEOGEN. 
 
 6* vessel in which the water vapour formed is condensed. 
 S, dish to receive the water. 
 
 discussed the properties of carbon dioxide, or fixed 
 air, more fully than had previously been done, and 
 showed the fixed air obtained from marble to be 
 identical with the air produced during fermentation. 
 His next paper (1767) consists merely of an analysis 
 of the water in Rathbone Place. It is interesting as 
 showing the results obtainable at that time. In the 
 same paper he seems to have been the first to notice 
 
 * The suggest! ven ess of this discovery will appear in the sequel, 
 when we see that a certain weight of any metal is equivalent to a 
 definite quantity of hydrogen, and will therefore always replace and 
 set free the same amount of it in any acid. 
 
THE CONFLICT WITH ERROR. 221 
 
 that the liine, existing in water as carbonate, is, 
 though insoluble in pure water, held in solution by 
 the excess of free carbon dioxide present. This 
 carbonic acid can be removed by boiling the water, 
 whereupon the calcium carbonate is deposited as the 
 fur lining kettles and boilers. 
 
 In 1781 Cavendish accurately investigated by 
 Priestley's method the composition of atmospheric 
 air. Contrary to previous ideas he showed it to be 
 of unvarying composition. 
 
 The paper, Experiments on Air, in the Philo- 
 sophical Transactions for 1784,* con tains his greatest 
 work. He here relates experiments made on explod- 
 ing together air and hydrogen " to find out what 
 becomes of the air lost by phlogistication." Accord- 
 ing to some observations of Priestley's friend, Waltire, 
 it appeared that this explosion was accompanied by 
 loss of weight. Cavendish repeated these experiments 
 with the result that in most cases there was no loss 
 of weight and it never exceeded the fifth of a grain, 
 an amount ascribable to errors of experiment. Wal- 
 tire and Priestley had observed the production of 
 water during the experiment, but, just as Priestley 
 had done before in the case of the reduction of 
 metallic calxes, they neglected it, and it was leffe for 
 Cavendish to discover its meaning. 
 
 In his paper, Experiments on Air, in the Philo- 
 sophical Transactions for 1784, we find the follow- 
 ing epoch-making passage. 
 
 * Philosophical Transactions, 1784, p. 719. 
 
222 THE CONFLICT WITH ERROR. 
 
 "From the fourth experiment it appears that 423 
 measures of inflammable air are nearly sufficient to 
 completely phlogisticate 1,000 of common air, and 
 that the bulk of the air remaining after the explosion 
 is then very little more than four-fifths of the common 
 air employed, so that, as common air cannot be 
 reduced to a much less bulk than that by any method 
 of phlogistication, we may safely conclude that when 
 they are mixed in this proportion and exploded, 
 almost all the inflammable air and about one-fifth 
 part of the common air lose their elasticity and 
 are condensed into the deiv ivhich lines the 
 glass." 
 
 Now, 1,000 volumes of air actually contain 210 
 volumes of oxygen, and these need 420 volumes of 
 hydrogen to combine with them. Cavendish's ex- 
 periments, therefore, for that date, were remarkably 
 exact. 
 
 The next point was to ascertain without doubt 
 what was the nature of the " dew " so obtained. To 
 this end he led oxygen and hydrogen gases into a 
 long cylinder measuring eight feet by three-quarters 
 of an inch, and there burnt them together. The 
 dew condensed in the further part of the tube. " By 
 this means upwards of 135 grains of water were 
 condensed in the cylinder, which had no taste nor 
 smell, and which left no sensible sediment when 
 evaporated to dryness, neither did it yield any pungent 
 smell during the evaporation ; in short, it seemed pure 
 water." 
 
THE CONFLICT WITH ERROR, 223 
 
 His conclusions are set forth in the following 
 sentence : 
 
 . " By the experiments with the globe it appeared 
 that when inflammable and common air are exploded 
 in a proportion, almost all the inflammable air, and near 
 one-fifth of the common air, lose their elasticity and 
 are condensed into dew. And by this experiment it 
 appears that this dew is plain water, and, conse- 
 quently that almost all the inflammable air, and about 
 one-fifth of the common air, are turned into pure 
 water." 
 
 In another experiment Cavendish admitted the gases 
 mixed in proper proportion into a vacuous globe, 
 exploded them and found that the condensation was 
 complete, so that repeated charges were admitted into 
 the globe without any need for re- exhaustion. 
 
 The paper appearing in 1785 is also of great 
 importance as containing the first account of the 
 composition of nitric acid. Priestley had observed 
 that some nitric acid was always present in the water 
 obtained by the union of its constituent gases. Caven- 
 dish made a long and very careful series of experi- 
 ments with the object of explaining the occurrence 
 of this acid. After much trouble he was able to 
 show that pure dephlogisticated air (oxygen), when 
 combined with pure inflammable air (hydrogen), 
 formed only pure water. He found that the addition 
 of phlogisticated air (nitrogen) increased the amount 
 of nitric acid formed, and finally concluded that its 
 formation in ordinary cases was due to the presence 
 
224 THE CONFLICT WITH ERROR. 
 
 of traces of atmospheric air, the phlogisticated air 
 (nitrogen) of which went to form the acid. 
 
 In spite of the prolonged and accurate attention 
 given by Cavendish to the composition of water he 
 seems to have never clearly conceived that it was a 
 compound of dephlogisticated and inflammable airs. 
 It is strange, considering how obvious and simple a 
 solution this afforded of the phenomenon that the 
 two gases when exploded together produce water, 
 that this plain notion should never have found favour 
 with him. James Watt, the engineer, had already, 
 in 1783, in a letter to Black thrown out the sugges- 
 tion that " water is composed of dephlogisticated and 
 inflammable air." In this opinion he anticipated and 
 made a distinct advance upon Cavendish, and much 
 has been written as to their rival claims to be con- 
 sidered as discoverers of the composition of water. 
 Cavendish certainly first established the facts proving 
 its composition, although he was so blind to their 
 meaning as to write in 1784 the following words : 
 
 " From what has been said there seems the utmost 
 reason to think that dephlogisticated air is only water 
 deprived of its phlogiston, and that inflammable air, 
 as was before said, is either phlogisticated water or else 
 pure phlogiston, but in all probability the former." 
 
 But although Cavendish remained to the last a 
 believer in phlogiston, and was thus, like Priestley, 
 precluded from seeing the full importance of his own 
 work, yet he was by no means so bigoted in his 
 partisanship as the latter chemist. He recognised 
 
THE CONFLICT WITH ERROR. 225 
 
 in a passage net sufficiently noticed that many facts 
 could be explained as well by the Lavoisierian method,* 
 and although he never became a convert he was not 
 an ungracious opponent. His aberration on the 
 subject of phlogiston should not detract much from 
 our opinion of his intellectual power, when we recog- 
 nise how universal a sway that notion possessed over 
 the minds of men. It is indeed an annoyance to find 
 his acute and accurate papers reduced sometimes by 
 its means, like all the work of his day, to an incohe- 
 rence not unworthy of the jargon of the early alche- 
 mists; but our appreciation of his merit becomes 
 more unalloyed as we become accustomed to the 
 peculiar intellectual atmosphere in which he lived. 
 And considering the power of one false idea over the 
 minds of that day we gain an increased appreciation 
 of the singular fairness and freedom from bias of Dr. 
 Joseph Black, the one chemist who was converted to 
 truth. But though Cavendish could not discern the 
 widening dawn, his. work did much to produce its 
 light. 
 
 Two Swiss chemists of renown, Bergman and Scheele, 
 were at work about this time. Bergman (1735 
 1784) was one of the pioneers of analytical chemistry, 
 but of his work it is impossible to speak here in 
 detail. Scheele (1742 178G) is famous as the dis- 
 coverer of chlorine and as one of the first workers in 
 the field of organic chemistry. Another discovery 
 redounds much to his credit, though in it he had 
 
 * See p 246., 
 P 
 
226 THE CONFLICT WITH ERROR. 
 
 probably been anticipated by Priestley the discovery 
 of oxygen. Scheele obtained the gas by the decom- 
 position of nitric acid by heat, and gave it the name 
 of empyreal air. His discovery of chlorine gas was 
 made in 1774, and this element was termed by him 
 dephlogisticated marine acid gas.'"" He prepared it 
 
 TREPANATION OF CHLORINE, 
 w, wash-bottle containing water. 
 
 by the action of hydrochloric acid upon manganese 
 dioxide. On mixing the black oxide with the acid 
 a greenish mass is obtained which rapidly begins to 
 evolve chlorine. The first part of the operation may 
 be conducted at the ordinary temperature of the air, 
 unless the weather is very cold, but heat is needed 
 to drive off the latter portions of the gas. This is 
 passed through a small wash-bottle containing water 
 to remove hydrochloric acid, and if needed dry is 
 
 * Marine acid = muriatic acid = hydrochloric acid. 
 
THE CONFLICT WITH ERROR. 227 
 
 further passed through sulphuric acid or other re- 
 agent capable of absorbing its water. 
 
 It seems also that Scheele was the first to carefully 
 investigate sulphuretted hydrogen, a gas invaluable 
 to the analytical chemist, as by its means different 
 metals are under different conditions thrown out of 
 solution as insoluble sulphides by the action of the 
 gas. Furthermore it was Scheele's announcement of 
 the existence of calcium phosphate in bones (a dis- 
 covery made first by Gahn in 1769), which led to 
 the manufacture of phosphorus from bone-ash, a 
 source from which all the phosphorus of commerce is 
 still obtained.* 
 
 Scheele's investigations of Prussian blue led him to 
 the discovery of prussic acid which he made in 1782. 
 This substance if? still prepared by his process of 
 acting on potassium ferrocyanide (yellow prussiate of 
 potash) with sulphuric acid. The pure acid is a 
 mobile liquid and one of the most powerful of known 
 poisons. A few drops produce death in a dog in 
 thirty seconds. 
 
 He first showed baryta to be a distinct earth, 
 and proved the separate existence of molybdic and 
 tungstic acids. 
 
 Some of Scheele's best-known discoveries lay in the 
 domain of organic chemistry. A number of organic 
 acids tartaric, oxalic, citric, malic, gallic, uric, lactic, 
 and mucic were either first prepared or first identi- 
 
 * Phosphorus was probably first prepared by the alchemist Brand, 
 of Hamburg, in the 17th century, 
 
228 THE CONFLICT WITH ERROR. 
 
 fied by him. But even this does not complete the 
 long list of his discoveries, for he was the first to 
 obtain the valuable substance glycerine, to which he 
 gave the name of " the sweet principle of fats," and 
 which afterwards bore the name of Scheele's sweet 
 principle or oil-sugar. Scheele obtained his glycerine 
 by the action of litharge on olive oil. Oils and fats 
 contain glycerine or, more strictly, " glyceryl," com- 
 bined with acids. If these be heated with potash or 
 litharge the metal takes the acid and glycerine is 
 set free. The name glycerine was first given to the 
 body by Chevreul in his " Recherches sur les Corps 
 gras," etc. He also determined its composition. 
 Many workers were engaged upon this body before 
 an accurate knowledge of its constitution was obtained, 
 and these include Pelouze, Berzelius, Liebig, Berthelot, 
 De Luca, and Wurtz. 
 
 The number of Scheele's discoveries is surprising, 
 and he was the first to pay any accurate attention to 
 the phenomena of organic chemistry. He, too, was 
 blinded by his bias on the phlogiston theory, but his 
 work contributed greatly to the building up of the 
 modern science.* 
 
 * Some of Scheele's papers are translated by Beddoes under the title 
 of Scheele's Chemical Essay* (1786)4 
 
SEVENTH PERIOD. 
 
CHAPTER XIIL 
 
 SEVENTH PERIOD: THE TRIUMPH OF TRUTH. 
 LAVOISIER, 
 
 HE greater chemists of this period repre- 
 sented three different types of mind ; 
 Priestley, brilliant and rapid in discovery, 
 but somewhat inaccurate in experiment, 
 and insufficient in theoretical grasp ; Ca- 
 vendish, slow but thorough in discovery, 
 accurate and painstaking in experiment, but not 
 directly influencing the theoretical ideas of his time : 
 Lavoisier, who discovered no new fact, but was ori- 
 ginal and exact in his experiments, and exerted, by 
 his marvellous intellectual grasp, incalculable in- 
 fluence upon the theoretical progress of his science. 
 He was not one who dealt with isolated facts, his 
 mind had something of the philosopher's taste for 
 classification and general principles. There is, perhaps, 
 
232 THE TRIUMPH OF TRUTH, 
 
 come tendency in experimental work to arrest the 
 imagination, to deter from speculation, to dull the 
 worker's appreciation of what is not presentable to 
 sense. But this tendency is indulged at the peril of 
 the worker and his science. It produces a conserva- 
 tism often delaying scientific advance. The conser- 
 vative tendency was strong in Lavoisier's time, 
 but he escaped it and rescued his science from its 
 grasp. 
 
 Antoine Laurent Lavoisier (1743 1794) was born 
 at Paris in 1743. His father, a wealthy tradesman, 
 educated him at the College Mazarin, and encouraged 
 him in his scientific tendencies. Lavoisier was re- 
 lieved from the necessity of earning his bread, and 
 was thus able to devote his time and energy to science. 
 On leaving college he worked with extraordinary 
 ardour, and a devotion greater than most would have 
 exhibited had their work been forced upon them by 
 want. His latter work was for the most part devoted 
 to science for its own sake, but among his early ex- 
 periments were some made in the hope of a prize 
 offered for the best mode of lighting the streets of 
 Paris. He experimented with various lamps, and it 
 is indicative of the depth of his enthusiasm that, to 
 increase the sensitiveness of his eyes while thus en- 
 gaged, he lived for six weeks in a room deprived of 
 all light and hung with black. Not long after this 
 he refuted the belief, entertained by many, that water 
 by distillation could be converted into earth. 
 
 Lavoisier availed himself, as much as possible, of 
 
THE TRIUMPH OF TRUTH. 233 
 
 the benefits of discussion and criticism. One day a 
 week he threw open his laboratory to a select company 
 of friends, communicated his results, and invited 
 comment or criticism. 
 
 In 1772 he recorded the results of his experiments 
 on the calcination of metals. These led him to aban- 
 don the theories of the phlogiston school. In 1778 
 he broached his theory that oxygen was the uni- 
 versal acidifying or oxygenizing principle. In 1783 
 he completed the proof of the composition of water. 
 In 1792 the Lavoisierian doctrines received recogni- 
 tion in Berlin, and in 1789 he published his remark- 
 able Traite elemental de Chimie. 
 
 Lavoisier's abandonment of the old chemical creed 
 brought upon him much obloquy and odium. At the 
 height of his unpopularity he was burnt in effigy at 
 Berlin on account of his antiphlogistic ideas ; yet 
 Berlin only a few years later was converted to his 
 views. But it was not his independence as a chemist 
 which was to cause his ruin. His overflowing energy 
 had engaged him also in political work. He was a pro- 
 minent member of the body of" Farmers-General " of 
 the revenue, and in this administrative capacity is 
 said to have done some good work. " Lavoisier," 
 said Lalande, " was to be found everywhere."* 
 
 '' Francois de Fourcroy speaks indignantly of Lavoisier's fate. 
 " L'homme qui auroit illustre son siecle par ses talens, qui auroit 
 repandu ses lumieres sur la societe, dont les travaux auroicnt eu pour 
 but d'instruire, de rend re meilleurs et plus heureux les homines, seroii 
 place dans un meme tombeau avec celui qui en auroit fait le tourment 
 ou qui en auroit etc la honte ! " Notice sur la vie de Lavoisier. Paris 
 (1796). Lalande's notice is given by Scherer in his Nachtrage. 
 
234 THE TRIUMPH OF TRUTH, 
 
 But in May, 1792, the year 2 of the Republic 
 and at the height of the revolution, the arrest of all 
 the Farmers-General was ordered. All were to give 
 account of their moneys and incomings, and die " for 
 putting water in the tobacco they sold." The charges 
 were brought against the whole body on the 2nd of 
 May by Dupin, a member of the Convention. Lavoi- 
 sier found a hiding-place in the deserted rooms of the 
 Academy. Hearing, however, that his action would 
 tend to prejudice his colleagues he gave himself up 
 and awaited his fate. He expected the confiscation 
 of his property, and announced his intention if this 
 sentence was passed of earning his bread as an 
 apothecary, the trade most nearly suited to his tastes. 
 But on the 6th of May he, with twenty-seven others, 
 was condemned to the guillotine. 
 
 The death of a man of such peaceful eminence did 
 not pass without some protest. Petitions for commu- 
 tation of the sentence, in consideration of his high 
 services to knowledge and the state, were presented in 
 vain. He himself looked on calmly, and might have 
 met his death without a word had he not been inter- 
 rupted in some investigations. But to be snatched away 
 just before an interesting research was completed, just 
 when nature was in a mood to bring him more confi- 
 dences that, at its best, was annoying. So he peti- 
 tioned for a fortnight's delay to get done with his expe- 
 riments ; then he would be at their service. But the 
 petitions were all alike refused. The Republic had "no 
 need of savants." And on the 4th of May, with the 
 
THE TRIUMPH OF TRUTH. 235 
 
 experiments unfinished, the guillotine reeeiv in him 
 one of her most illustrious victims. We can only be 
 thankful that his doom did not descend in time to 
 rob us of the work, the results of which we are still 
 permitted to inherit. 
 
 It is a very unfortunate circumstance that our 
 admiration for Lavoisier is to some extent restricted 
 by the too clearly proved fact that he laid claim to 
 discoveries to which he had no right. His Opus- 
 cules Physiques et Ghymiques contain discoveries of 
 Joseph Black, put forward as if they were his own, 
 while his claim to the simultaneous discovery of 
 oxygen has been the occasion of many disputes, 
 finally ending by an invalidation of the claim. It is 
 much to be regretted that our warm admiration 
 for the splendid talents and services of so great 
 a worker should have to encounter the chill of dis- 
 appointment we must experience in the character of 
 the man. 
 
 Lavoisier claims our attention chiefly on account of 
 his being the first to distinctly and clearly enunciate 
 the great principle of the indestructibility of matter* 
 The belief in this pervades, and indeed alone makes 
 possible, the whole of his work. He showed that 
 chemistry could not exist without the chemical 
 balance. 
 
 It is true that quantitative experiments in the 
 
 * As a philosophic principle this had been taught ages before : e.g. 
 by Lucretius, who followed Greek masters. But as a scientific truth 
 it had never been proved, and indeed was not generally held. . 
 
236 THE TRIUMPH OF TRUTH. 
 
 science had already been performed, and that Black 
 and Cavendish had raised these to a high degree of 
 exactitude. There was necessarily in these experi- 
 ments a tacit assumption that at least in the case 
 under investigation matter was not expected to be 
 destroyed. If he had expected the destruction of 
 matter how could Black have inferred that because 
 magnesia alba lost weight on heating some thing was 
 given off, and when he found out that the thing could 
 not be condensed, further concluded that it was a 
 gas ? Or how could Cavendish have determined the 
 relative amounts of oxygen and hydrogen condensing 
 to form water, had he thought that during the ex- 
 plosion some of either gas might cease to exist ? 
 Clearly these experiments had an underlying disbelief 
 in the destruction of matter in the course of these 
 particular experiments. But such vague previsions 
 were widely different from any assertion of a general 
 law. It is the difference between the unscientific 
 industry of his contemporaries and the far-sighted 
 precision of Lavoisier. According to him every 
 chemical change is accompanied only by transfer and 
 exchange of matter, not by destruction. His doc- 
 trine is, " Rien ne se cree, rien ne se perde de la 
 nature." The total weight of the reacting bodies 
 remains the same from beginning to end of the 
 reaction. We see here the first attempt at a chemical 
 equation. 
 
 The theory was propounded in regard to fermenta- 
 tion, Lavoisier having tried to make out what became of 
 
THE TRIUMPH OF TRUTH. 237 
 
 the sugar during the process. After investigating the 
 matter he came to the conclusion that, starting with 
 a certain weight of sugar, there were obtained as a 
 result of the fermentation certain weights of alcohol 
 and carbonic acid gas, which together were equal to 
 the weight of sugar present when the reaction began. 
 N othing, said Lavoisier, is lost ; but instead of our 
 sugar we have an equivalent quantity of carbonic acid 
 and alcohol. 
 
 Strangely enough this argument, forming one of 
 the bases of "the great theory, was founded upon an 
 experimental error. The carbonic acid and alcohol 
 produced by the fermentation are not together equal 
 in weight to the sugar made use of. What then is 
 the final conclusion ? Not that matter has been 
 destroyed, but that, as shown by the eminent French- 
 man, Pasteur, other substances besides alcohol and 
 carbonic acid are formed. What Lavoisier said was 
 quite true for about 95 per cent, of the sugar used, 
 but the remaining 5 per cent., or thereabouts, is con- 
 verted partly into glycerine and succinic acid, and 
 partly used up for developing the growth of the 
 ferment. But even this is not a full list of the pro- 
 ducts which include other " alcohols " differing from 
 common alcohol (higher homologues of it, as they are 
 called), organic acids of the fatty series and ethereal 
 salts, from which the spirit derives a peculiar smell. 
 All these bodies have a higher boiling point than 
 common alcohol, and are classed together under the 
 name of fusel-oil. The fusel-oil is got rid of by rectifi- 
 
2 3 8 THE TRIUMPH OF TRUTH. 
 
 cation, and if present forms a very deleterious im- 
 purity.* 
 
 Lavoisier then was not quite accurate in the 
 example most immediately connected with his bril- 
 liant thought. But the theory need happily never 
 be wanting in support. All the thousands of opera- 
 tions carried on daily in the laboratories eastward 
 from San Francisco to Pekin are so many confirma- 
 tions of its truth. The balance is the first requisite 
 of the laboratory, and did we not believe in the 
 indestructibility of matter the use of the balance 
 would be meaningless and absurd. 
 
 It may be as well here to illustrate from every- 
 day life the full force and truth of this great idea. 
 When a candle has burnt out what has become of 
 it? This is the chemist's riddle, and like most 
 riddles we must give it up and ask our questioner 
 for the answer. First of all the riddle was asked by 
 nature and the chemist had to find out the answer 
 for himself ; for nature is not so lenient as the chemist, 
 and would not allow us to give it up. The chemist 
 knows her principles in these matters well, so that 
 he at once sets to work to puzzle the matter out, 
 and, as the result of his puzzling, this is what lie 
 would tell us to do, to find out what has happened to 
 the candle. 
 
 We have already been introduced to many of the 
 
 * The reader wishing to follow the interesting subject of fermenta- 
 tion in more detail should consult Schiitzenberger's admirable book On, 
 Fermentation, Intern. Scientific Series. 
 
THE TRIUMPH OF TRUTH. 239 
 
 facts destined to overthrow the Stahlian hypothesis, 
 and need not therefore start from the beginning in 
 our reasoning. Suppose we burn a candle under a 
 glass jar* as Priestley did long ago. Its flame is soon 
 extinguished, and after any fumes may have subsided 
 a clear gas is left in the bell-jar not differing in sight 
 from ordinary atmospheric air. Now let us light 
 another candle and plunge it, as the chemists say, 
 into this innocent-looking gas. The flame at once 
 goes out, and if we were cruel enough to put a 
 mouse into the jar the flame of its life would go 
 out too. Evidently something is now in the air 
 which was not there before. 
 
 If our gas-jar is appropriately constructed, open at 
 both ends with the lower end placed in water and 
 the neck closed by a wide glass stopper, we may do 
 something further with the gas we have got. If we 
 introduce some caustic potash into the water in 
 which the jar is standing we shall soon have evidence 
 that the potash is taking up or absorbing some of the 
 gas in the jar, for the level of the water in it will rise. 
 Repeating this experiment with the potash with a jar 
 of air in which a candle has not been burnt we shall 
 obtain no alteration of level ; there is nothing here 
 absorbable by the potash, f Evidently the combus- 
 tion of the candle has produced a gas absorbable by 
 potash. 
 
 * Any common glass bottle with a neck wide enough to admit a 
 candle may serve for this purpose. 
 
 t Of course a little carbonic acid gas is present in ordinary air, "but 
 it will be very much too little to be, in this way, perceived, 
 
2 4 o THE TRIUMPH OF TRUTH. 
 
 If we repeat these experiments with a jar filled 
 with pure oxygen instead of air we should obtain 
 the following results. With the unaltered gas 
 potash would effect no absorption. After the com- 
 bustion of a candle therein potash would effect far 
 more absorption than in the same circumstances 
 with common air. Any gas left after absorption will 
 be either nitrogen, an impurity derived from atmo- 
 spheric air, or unused oxygen gas further reducible 
 by repeated combustion. From these experiments we 
 may conclude that part of the candle (its carbon) 
 combines with part of the air (its oxygen) to form 
 a gas (carbon dioxide) not supporting combustion 
 and absorbable by caustic potash. The presence of 
 carbon dioxide may be readily and simply shown by 
 merely pouring a little clear limewater into a glass 
 bottle in which a candle has been burnt. The lime- 
 water is at once turned milky. This phenomenon 
 will not occur with ordinary air and is characteristic 
 of carbon dioxide, the " fixed air " of Black. 
 
 One product of the combustion, then, is carbon 
 dioxide. That another product results may be 
 very readily shown by merely holding a common 
 tumbler over a burning candle. A misty appearance 
 is at once seen on the interior of the glass, soon 
 gathering into drops of dew. If instead of using 
 such primitive apparatus we suck the products of 
 combustion through a cooled tube or condenser, we 
 may collect enough of the drops formed to find out 
 that they are pure water, Wo should find that it 
 
THE TRIUMPH OF TRUTH. 241 
 
 was tasteless, boiled at 100 C,, and evaporated with- 
 out leaving any residue. 
 
 The products of the combustion of a candle then 
 are carbonic acid and water. The carbonic acid is 
 derived from the carbon contained in a combined 
 form in the candle. We may obtain the same gas 
 by the combustion of charcoal, and, as Lavoisier 
 showed, by the combustion of the diamond. The 
 water must be obtained from the hydrogen of the 
 candle, for as the facts of Cavendish showed, water is 
 composed of hydrogen and oxygen. The matter of 
 the candle has not, then, been wholly destroyed as 
 appearances would at first suggest. By appropriate 
 arrangements we may show that the products of 
 combustion actually weigh more than did the candle 
 itself or the part of it that has been burnt away. 
 
 A wide tube is suspended from one arm of a balance. 
 A cork having a candle fixed upon its upper surface 
 and pierced with holes to admit of the passage of a 
 current of air, is fitted into the lower end of the 
 tube. Its upper end is connected by a piece of 
 caoutchouc tubing with a second glass tube bent 
 into the form of a U. The bent tube is filled with 
 fragments of solid caustic potash, a substance, as we 
 just now learned, capable of absorbing carbonic acid 
 gas, and at the same time very hygroscopic, or taking 
 up water with great activity. The two tubes having 
 been exactly counterpoised on the balance, are con- 
 nected finally with an aspirator. By allowing the 
 water to flow out from this last a current of air is 
 
242 
 
 THE TRIUMPH OF TRUTH. 
 
 drawn through the whole apparatus. The candle 
 being lighted the aspirator is set to work, care being 
 taken that the current is not too rapid, lest some 
 carbonic acid or water vapour should be drawn past 
 the caustic potash unabsorbed. When an appreciable 
 amount of the candle has been burnt the apparatus 
 is disconnected from the aspirator and the balance 
 once more allowed to vibrate freely. It will now be 
 found that the index point oscillates farther on the 
 side of the counterpoise than on the side of the tubes. 
 
 XT-TUBE. 
 
 The tubes now weigh more than the counterpoise. 
 But when the experiment began the tubes and their 
 counterpoise were equivalent. They have therefore 
 gained in weight. Thus in spite of the apparent 
 disappearance of some of the matter composing the 
 candle, not only has none of it been destroyed but 
 it has actually gained in weight, owing to the addition 
 to it of oxygen from the air during the process of 
 combustion. 
 
 We have thus been able to catch the invisible 
 
THE TRIUMPH OF TRUTH. 243 
 
 products of the combustion and render their existence 
 evident to the eye. We may further show that the 
 amount of carbon and hydrogen in the products is 
 just the same amount as that contained in the burnt 
 portion of the candle, but the inquiry here would be 
 somewhat more complicated. We know the propor- 
 tions of hydrogen and oxygen in water, we know also 
 the proportions of oxygen and carbon in carbonic 
 acid, we know lastly, from individual experiments 
 and by reason of the law of constant proportions first 
 definitely recognised by Lavoisier, that the composi- 
 tion of these compounds is constant. If then we 
 knew the amount of water and carbonic acid generated 
 we could calculate the amount of carbon and hydrogen 
 in the candle. But to do this we must collect the 
 water and carbonic acid separately. 
 
 Let us make use of a pure paraffin candle contain- 
 ing nothing but hydrogen and carbon. Let us pass 
 its products of combustion first through a U tube, 
 containing fragments of pumice soaked in sulphuric 
 acid. This will absorb the water. The carbonic 
 acid escaping from this tube may then be collected 
 by passing the gases through bulbs containing 
 caustic potash solution. We have thus got the 
 means of collecting the two products separately. But, 
 if we are to be at all accurate, we must make further 
 provision against error ; for water vapour and car- 
 bonic acid are present in the common air used to 
 burn our candle, and will, of course, add their weight 
 to the result, To obviate this, we may first pass the 
 
244 THE TRIUMPH OF TRUTH. 
 
 air through soda-lime and sulphuric acid to free it from 
 carbonic acid and water, and then over the burning 
 candle. If we were to weigh the tube containing the 
 candle before and after the experiment, the loss of 
 weight would give us the weight of candle burnt. 
 The gain in weight of the U tube containing sul- 
 phuric acid, would give us the weight of water 
 formed, while the gain in the potash bulbs would 
 represent the carbonic acid evolved. Knowing the 
 composition of water and carbonic acid, we could 
 calculate the weight of hydrogen and carbon these 
 gains respectively represented. Added together, we 
 should find these very nearly the same as the weight 
 of candle burnt. None of the matter composing it 
 is lost during combustion. We might thus account 
 for the matter composing the candle, and determine 
 its composition. 
 
 The method is not quite the same as that at 
 present in use for determinations of carbon and 
 hydrogen in organic bodies, but it is substantially 
 that used by Lavoisier in some of his attempts at 
 organic analysis made by him just before his exe- 
 cution. We may refer to these experiments again 
 in a chapter on the development of organic chemis- 
 try, a subject which can only, in a work of this kind, 
 be very briefly sketched, and is more conveniently 
 treated separately. 
 
 Finally, we must remember that the doctrine of 
 the indestructibility of matter includes also a dis- 
 belief of its creatability. Just as it cannot be 
 
THE TRIUMPH OF TRUTH. 245 
 
 destroyed, so neither can it be created. The products 
 of a reaction contain the same amount of matter as 
 the substances taking part in it. They do not 
 contain less, and they do not contain more. This 
 belief is distinctly contained in Lavoisier's own 
 words on the subject of fermentation : " We may 
 consider the substances submitted to fermentation 
 and the products resulting from that operation as 
 forming an algebraic equation, and, by successively 
 supposing each of the elements in this equation 
 unknown, we can calculate their values in succession, 
 and then verify our experiments by calculation, and 
 our calculations by experiment, reciprocally. I 
 have often successfully employed this method for 
 correcting the first results of my experiments, and so 
 to direct me in the proper road for repeating them 
 with advantage."* 
 
 Lavoisier, in his mission of evolving order from 
 incoherence, was also the first to openly acknowledge 
 the law of combination in constant proportions. 
 Bergman (1735 1784) tacitly acknowledged the 
 truth in his numerous analytical researches. For 
 what is the use of analysing a compound, if different 
 specimens of it have varying composition ? How can 
 its composition be stated if it be indefinite ? But 
 this is not the first time in the history of science in 
 which a great principle has been acted on before it 
 was realised. Lavoisier distinctly stated that in 
 
 * Lavoisier: Elements of Chemistry (1787). Kerr's Translation, 
 p. 197. 
 
246 THE TRIUMPH OF TRUTH, 
 
 every oxide and every acid, the relation of oxygen to 
 the metal is constant. He also refers to the different 
 oxides of nitrogen exhibiting different, but in each 
 individual compound definite, degrees of oxidation. 
 He had, indeed, only just escaped discovering the 
 law of multiple proportions. Had not his execution 
 terminated his career, he might have followed up 
 this among several others of his uncompleted trains 
 of thought. 
 
 His first important research (1770) depended 
 upon the use of the balance, and thus early indicated 
 the tendency of his mind. In it he refuted the 
 notion, at the time a moot point, that water, by being 
 heated, may be converted into earth. He found 
 that previous observers had been deceived by the 
 use of impure water, or by the water having taken 
 up some matter from the vessel in which it was 
 heated. 
 
 Lavoisier's work on combustion and his combat 
 with the Stahlian hypothesis began with some 
 experiments first recorded in 1772, and not pub- 
 lished till 1774, on the calcinations of the metals. 
 His open rejection of phlogiston was not announced 
 till 1777, and it is interesting to note that before 
 this date, at least one other worker had seen reason 
 to distrust the theory. Bayen, in 1774, had 
 supposed calcination due to the absorption of an 
 aerial fluid. He had found that calx of mercury 
 (mercuric oxide) on heating loses weight, evolving 
 a gas equal in weight to what is lost. From this he 
 
THE TRIUMPH OF TRUTH. 247 
 
 concluded that either the phlogiston theory was in- 
 correct, or that this particular calx could be reduced 
 without addition of phlogiston. But the phlogistians 
 with their principles of levity and the like, were well 
 capable of preventing these simple facts from dis- 
 pelling the clouds which befogged the minds of the 
 chemists in 1774. 
 
 Lavoisier's conclusions on the subject of the cal- 
 cination of metals were first placed in the hands of the 
 French Academy as a sealed paper in 1772, the final 
 publication not taking place till 1774. His reason for 
 first depositing the inquiry in its unfinished state in 
 the hands of the Academy, was the desire to have 
 proof of priority should another worker anticipate 
 him before his investigation was complete. "I was 
 young, I had just entered upon the career of science, 
 I was eager for glory, and I believed I ought to take 
 some care to protect the. ownership of my discovery." 
 In his first work on the subject Lavoisier finds that 
 sulphur and phosphorus not only do not lose but 
 actually gain in weight. His attention is thus 
 directed to the calcination of metals with the idea 
 that the combustion has in the previous cases been 
 accompanied by an absorption of air, and that similar 
 results may be expected from calcination. To eluci- 
 date his point he reduces the calx of lead or litharge 
 with charcoal, and finds that a large quantity of gas 
 is liberated. We see at once the point at which this 
 meets the phlogistic theory. According to this last 
 the addition of phlogiston to the calx was alone 
 
2 48 THE TRIUMPH OF TRUTH. 
 
 needed to produce the metal. But Lavoisier did not 
 grasp these relations at once, though he saw that the 
 discovery was important. " Experience has entirely 
 justified my suspicions ; I have effected the reduction 
 of litharge in closed vessels with the apparatus of 
 Hales, and I have observed that at the moment of 
 the transition of calx into metal a large quantity of 
 air was set free, and that this air had a volume at 
 least a thousand times that of the litharge used. This 
 discovery appears to me one of the most interesting 
 made since Stahl, and I have thought it right to 
 secure my property in it." 
 
 In 1774 Lavoisier made experiments on the calci- 
 nation of lead and tin. These metals he, like Boyle, 
 heated in closed glass globes. The globes did not alter 
 in weight, proving that the amount of air absorbed 
 was the same as that taken up by the metal. When 
 the globes were opened air rushed in and the weight 
 increased. In a paper on calcination, first read before 
 the Academy in 1775, occurs his first reference to 
 oxygen gas under the name of Vair pur or Vair vital. 
 In 1777 Lavoisier combated Priestley's assertion that 
 combustion loaded air with phlogiston. He showed 
 that air, after the combustion of a candle in it, con- 
 tained " fixed air," and, moreover, that if for common 
 atmospheric air dephlogisticated air (oxygen) were 
 substituted, the gas left after combustion was almost 
 wholly composed of fixed air. The phlogiston war 
 was now raging, and in 1778 he broached his theory 
 that oxygen (as he now called the gas : 6i;?, sour, and 
 
THE TRIUMPH OF TRUTH. 249 
 
 aw, I produce) was the universal acidifying or 
 oxygenizing principle. 
 
 Two memoirs contain the chief portion of Lavoi- 
 sier's views on combustion, one read before the 
 Academy in 1775, Sur la Combustion en general, 
 and another, Reflexions sur le Phlogistique, published 
 by the Academy in 1783. The second paper con- 
 tains the full development of his theory, and in it 
 he denies the existence of phlogiston, upholds the 
 elementary character of the metals and such substances 
 as carbon, sulphur, etc., and states emphatically that 
 when these bodies are burnt all that occurs is their 
 combination with oxygen.* The simple truth of these 
 views was possessed of a resistless force which in the 
 end carried all before it. 
 
 After Cavendish's experiments in 1783 Lavoisier 
 completed the proof that water was a compound of 
 oxygen and hydrogen. He repeated, in conjunction 
 with Laplace, the experiments of Cavendish and added 
 a further confirmation of his own. In this case water 
 was allowed to drop slowly into a gun-barrel heated 
 to redness in a furnace. Here part of the water was 
 decomposed, any that escaped being condensed in a 
 worm through which the gases passed after leaving 
 the furnace. The oxygen combined with the metallic 
 iron in the gun-barrel, and the gas finally collected 
 under the bell-jar was found to be pure hydrogen. 
 This completed the proof now resting upon both 
 
 * Lavoisier was thus the first to ascertain the composition of " fixed 
 air " or carbonic acid, as also of sulphur dioxide, 
 
250 
 
 THE TRIUMPH OF TRUTH. 
 
 analytical and synthetical foundations. The exact 
 composition of water has since been most accurately 
 determined both by endiometric synthesis or explosion 
 of the mixed gases in a carefully graduated tube, and 
 by gravimetric synthesis by passing perfectly pure 
 hydrogen over a known weight of copper oxide. 
 
 Lavoisier was not slow to appreciate the full im- 
 port of these discoveries. Kopp has concisely set 
 
 LAVOISIER'S APPARATUS FOE THE ANALYSIS OF WATER. 
 
 forth the steps leading to a clear knowledge of the 
 composition of water ; Cavendish first ascertained 
 the facts; Watt first argued from them as to the com- 
 pound nature of water ; Lavoisier first clearly recog- 
 nised its compound nature and the nature and 
 amounts of its components. 
 
 Before closing the account of Lavoisier's work 
 mention must be made of his very remarkable Traite 
 El&nentaire de Chimie. It is a work remarkable 
 
THE TRIUMPH OF TRUTH. 251 
 
 for its arrangement and lucidity, for scientific accu- 
 racy, and for the originality of the ideas it contains. 
 
 "It is a very constant principle, and one of which 
 the general application is well recognised in mathe- 
 matics as in all kinds of sciences, that we can, for our 
 instruction, proceed only from the known to the un- 
 known When we enter for the first time 
 
 upon the study of a science we are, with regard to 
 this science, in a state very similar to that in which 
 children are, and the course that we have to follow is 
 precisely that which nature follows in the formation 
 of their ideas. Just as in the child the idea is the 
 result of sensation, and it is sensation which causes 
 the idea, in the same way too, for him who begins to 
 devote himself to the study of the physical sciences, 
 ideas should only be a consequence, an immediate 
 result of an experiment or of an observation." * 
 
 It is in his " Traite" that he gives the very clear 
 proof devised by him of the presence of oxygen in 
 the air. He heated mercury in a retort connected 
 by its bent neck with air confined under a bell glass 
 over mercury. After heating for twelve days the air 
 had been reduced from 50 to 42 or 43 cubic inches, 
 while red particles appeared on the surface of the 
 mercury. These last, which consisted of mercuric 
 oxide, were carefully collected, and on heating yielded 
 411 grains of mercury, and 7 to 8 cubic inches of 
 pure oxygen. The whole of the oxygen was thus 
 recovered from the mercury. 
 
 * (Etivres da Lavoisier (1862), torn. i. Introduction to the Trails. 
 
2 5 2 THE TRIUMPH OF TRUTH. 
 
 He gives a table of thirty-three simple substances, 
 among which he still includes heat or caloric and 
 light. He also gives tables of the combinations of 
 the various elements, and in these he looks upon the 
 gaseous elements as combinations of a ponderable 
 substance, the true element, with heat. Thus the 
 combination of " 1'hydrogene avec le calorique = gas 
 hydrogens."* So too the combination of sulphur 
 with caloric gives rise to sulphur gas. After all, 
 though incorrect, these views only veil a great truth, 
 for in these gases heat is rendered latent. Black, the 
 discoverer of latent heat, had himself regarded the 
 phenomenon as an act of combination. Of combus- 
 tion Lavoisier here remarks,! " Combustion is nothing 
 but the decomposition of oxygen gas acted upon by 
 a combustible body. The oxygen which forms the 
 base of this gas is absorbed, the caloric and light 
 become free and are liberated (deviennent libres ei se 
 degagent). All combustion then carries with it the 
 idea of oxygenation. . . ' 
 
 The view of combustion here set forth is now, 
 perhaps, somewhat modified, and combustion is 
 regarded as " an act of chemical union accompanied 
 by the evolution of light and heat." 
 
 This same work contains a prediction of the com- 
 pound nature of the alkaline earths (soda and potash) 
 previously thought to be simple bodies. From their 
 ready combination with acids he concludes that 
 "they may very possibly be metallic oxides with 
 
 * (Eui-res, torn. i. f (Em-res, i. 338. -, 
 
THE TRIUMPH OF TRUTH. 253 
 
 which oxygen has a stronger affinity than with 
 carbon, and consequently are not reducible by any 
 known means." This was a prediction of Sir 
 Humphrey Davy's discoveries on this point. 
 
 Quite enough has been said to account for the 
 enormous and resistless influence exerted by Lavoisier 
 on the progress of the science, but one more achieve- 
 ment must be recorded of him, and that is, that he 
 entirely revised its nomenclature. He devised the 
 term oxide for those combinations of oxygen which 
 
 SPECIMEN OF DIAMOND. THE KOH-I-NOOB. 
 
 were not acids. When more than one oxide or acid 
 was known the one containing less oxygen was dis- 
 tinguished by the termination ons, as nitrous oxide, 
 the one containing more by ic, as nitric oxide. He 
 devised the term hydrogen (vcwp, water ; <yevvcua> I 
 produce) in place of inflammable air, and carbonic 
 acid as a substitute for fixed air. The meaning of 
 the term acid has somewhat changed since Lavoisier's 
 day, and it is now used for substances containing 
 hydrogen replaceable by a metal. Lavoisier was the 
 first to show that the combustion of diamond gives 
 
254. THE TRIUMPH OF TRUTH. 
 
 rise to carbonic acid, and thus to show the identity 
 of the diamond with common charcoal. The diamond 
 may readily be burnt when heated in air or oxygen. 
 The formation of carbonic acid in the process may be 
 readily shown by igniting a diamond, encircled in 
 platinum wire, by means of an electric current from 
 a few Grove's cells. A little lime-water contained in 
 the jar will, after the combustion, become turbid. 
 
 It is difficult to over-estimate the influence of 
 Lavoisier, and after seeing for ourselves what he did, 
 and what precision and simplicity he introduced 
 where so much before was only inaccuracy and 
 incoherence, time would be wasted in panegyric. 
 
 Liebig's summary of his achievements is as follows : 
 " He discovered no new body, no new property, no 
 new natural phenomenon previously unknown ; but 
 all the facts established by him were the necessary 
 consequences of the labours of those who preceded 
 him. His merit, his immortal glory, consisted in 
 this that he infused into the body of science a 
 new spirit."* 
 
 * Letters on Chemistry, ii= 
 
EIGHTH PERIOD. 
 
CHAPTER XIV. 
 
 EIGHTH TElilOD : THE ATOMIC THEORY. 
 DALTON'S IDEA. 
 
 ,Y the atomic theory the older chemistry has 
 been transformed into the modern science. 
 It will be our business in the two succeed- 
 ing chapters to trace its growth. Lavoisier 
 had asserted the law of constant propor- 
 tions. He recognised that, for example, a 
 given weight of mercuric oxide always contained the 
 same weights of mercury and of oxygen. This was a 
 great advance upon the older ideas of chemical com- 
 binations. But so simple and true a doctrine was 
 not to remain uncontested. It was assailed by Ber- 
 thollet, a pupil of Lavoisier's, in a memoir read before 
 the Egyptian Institute at Cairo. Berthollet ascribed 
 the composition of compounds to physical causes. 
 
 ll 
 
2 5 8 THE ATOMIC THEORY. 
 
 He showed that varying results could be obtained in 
 the neutralisation of an acid by a base. S. L. Proust 
 enlisted himself on the side of the Lavoisierian theory, 
 and the battle was converted into a duel between 
 these two opponents. The contest was continued for 
 a period of seven years with varying fortune, but 
 Proust finally came off victor. He had rendered a 
 lasting service to science. " The discussion," says 
 Wurtz, " was maintained on both sides with a power 
 of reasoning, and a respect for truth and propriety, 
 which have never been surpassed."* 
 
 Proust found that on dissolving carbonate of copper 
 in acid and reprecipitating by alkaline carbonate, the 
 same weight of carbonate as that originally dissolved 
 was obtained. This is an example of his work, and 
 by it he was led to conclude that copper carbonate 
 Avas of unvarying composition. Subsequent work led 
 to similar conclusions about other compounds. The 
 varying composition attributed by Berthollet to salts 
 was explained by showing that although two or more 
 salts may be formed by different quantitative combi- 
 nations between a given acid and given base, yet for 
 these salts the proportions are constant. Thus mercury 
 forms two different chlorides, one containing twice as 
 much chlorine as the other. There is only a differ- 
 ence in the proportion of chlorine present, yet the 
 properties of the two substances are wholly distinct, 
 
 * The Atomic Theory (International Scientific Series) ; to which book 
 is owing much of the material of these chapters. Those who wish to 
 follow more closely the development of the theory cannot do better 
 than consult this very ably and lucidly written work. 
 
THE ATOMIC THEORY. 259 
 
 and for each of the two salts the composition is con- 
 stant. The lower chloride, mercurous chloride (Hg 2 
 Cl 2 ), is a white insoluble powder, used as a non-poi- 
 sonous medicine, and, in this capacity, known as 
 calomel* 
 
 The next step was the discovery of the law of defi- 
 nite proportions by the German chemist, J. D. Bichter, 
 of Berlin. He was much possessed with the idea of 
 applying mathematics to chemistry. He followed 
 his hobby too far, and by many ingenious manoeuvres 
 attempted to show that the quantities of bases satu- 
 rating a given weight of acid represent the terms of 
 an arithmetical progression, while the quantities of 
 acids combining with a given weight of base, form the 
 terms of a geometrical progression. His reasoning 
 on these points broke down, but he did succeed in 
 showingf that definite, but different, amounts of 
 bases are needed to saturate and neutralise a given 
 weight of a given acid. The weights of bases saturat- 
 ing a given amount of a given acid bear to each other 
 a definite ratio. Thus 60 grammes of acetic acid 
 are saturated by 40 grammes of caustic soda, and by 
 56 grammes of caustic potash, the proportions being 
 as 5 to 7. Further, a certain weight, 3 6 '5 grammes, 
 of hydrochloric acid will be neutralised by exactly 
 these same weights of soda and potash, they have 
 the same relative capability of saturating the two 
 
 * From KaXo/xtXac, a fine black colour, because it turns black when 
 acted upon by an alkali. 
 
 . t -Anfanpsffrunds der Stiichiometrie, oder Hesskunst chemlscher Ele- 
 mente. 
 
260 
 
 THE ATOMIC THEORY. 
 
 different acids. Considerations such as these led 
 Bichter to draw up a table showing the equivalent 
 quantities of different bases saturating 1000 parts of 
 different acids. The numbers, though of course in- 
 accurate, contained a great truth more clearly ex- 
 hibited by G. E. Fischer, in a note to his translation 
 of Berthollet's Chemical Statics. 
 
 The following is part of Fischer's table, and it shows 
 at a glance the equivalent quantities of bases and 
 acids. Thus it states that 859 parts of soda are 
 equivalent in neutralising power to 1,605 parts of 
 potash; further, that 712 parts of muriatic acid 
 (hydrochloric) are equivalent to 1,480 parts of acetic 
 acid. It also contains the assertion that 859 parts 
 of soda will neutralise 712 parts of muriatic acid, or 
 1,480 parts of acetic acid, and that 1,605 parts 
 of potash, the equivalent of the foregoing amount 
 of soda, will neutralize the same weights of these 
 acids. 
 
 BASES. 
 
 Alumina . 
 
 Magnesia 
 
 Ammonia 
 
 Lime 
 
 Soda 
 
 Strontia 
 
 Potash 
 
 Baryta 
 
 525 
 
 Fluoric aci 
 
 A 
 
 a 
 
 415 
 
 Carbonic 
 
 
 572 
 
 Muriatic 
 
 
 793 
 
 Oxalic 
 
 
 859 
 
 Phosphoric 
 
 
 1,329 
 
 Sulphuric 
 
 
 1,605 
 
 Nitric 
 
 
 2,222 
 
 Acetic 
 
 i 
 
 
 Citric , 
 
 > 
 
 AdD9. 
 
 427 
 
 577 
 
 712 
 
 755 
 
 979 
 
 1,000 
 
 1,405 
 
 1,480 
 
 1,583 
 
 The precise bearing of these results upon the atomic 
 theory will be presently seen. Had the weights here 
 given been those of elements, instead of acids and 
 
THE ATOMIC THEORY. 261 
 
 bases, they would be analogous to the chemical equi- 
 valents of a later date. 
 
 We have said that with Lavoisier came the triumph 
 of truth over fanciful error. But it was a hard-won 
 fight, and her fit weapons had yet to be forged. The 
 evil power had been driven from her own land, but 
 she. had need of added strength before attempting the 
 conquest of his kingdom. Her trustiest sword was 
 to be forged by John Dalton and tempered by the 
 workers that came after him. 
 
 John Dalton was born in 1766, at Eaglesfield, two 
 miles and three-quarters south-west of Cockermouth, 
 in Cumberland. 
 
 " The township of Eaglesfield, situated on the undu- 
 lating limestone formation of West Cumberland, pre- 
 -vious to the enclosure of the waste lands and the in- 
 troduction of good husbandry, about half a century 
 ago, would offer little more than herbage for rough 
 kine, and hard lines of life to the scattered inhabi- 
 tants. Bucolic life of the boorish* sort prevailed in 
 the hamlet, in which farmers of small holdings, their 
 clodhopping service, and common craftsmen, laboured 
 for a subsistence of a vegetative or earthy sort. The 
 village consisted, and its features are not much altered 
 to-day, of old-fashioned grey-stone dwellings, regular 
 in their irregularity of position, and in structure 
 dilapidated ; straggling manure heaps, a bit of dirty 
 common or village green, and dirtier duck-pond, backed 
 
 * Boorish is perhaps an unfortunate word. The race that produced 
 Dalton can hardly have been boorish. 
 
262 THE ATOMIC THEORY. 
 
 by a dingy ' smiddy/ to which the loungers with 
 their gossip and tittle-tattle daily gravitated to dis- 
 cuss the news of the district Eaglesfield 
 
 folk were a stiff race of countrymen, presenting stal- 
 wart forms in a coarse woollen garb of home-make, 
 and the horny hands and sweating brows of labour, 
 rejoicing in hamlet isolation, and heedless of the con- 
 tentions and turmoil of the world."* 
 i This vivid description helps us to clearly realise the 
 surroundings of Dalton' s early life. The one light of 
 the village was quakerism, and this the Daltons well 
 represented. 
 
 " The house in which Dalton was born has been 
 altered and much improved since his days ; its low 
 thatched roof has been raised and slated ; the par- 
 tially boarded loft converted into upper rooms ; its 
 small leaden windows displaced by large panes of 
 glass ; and the grey-stone facing of the building white- 
 washed. Still the general features of the interior of 
 the humble dwelling remain pretty much as when 
 occupied by weaver Joseph Dalton and his active 
 spouse Deborah." 
 
 "By a small porch, showing quaint recesses for pots 
 and pans, you enter the kitchen or general sitting and 
 business room of the family, where probably, Joseph 
 had his loom placed ; from this apartment, by a 
 narrow passage, you reach a smaller room immedi- 
 ately adjacent, in height and width six feet, and in 
 length fifteen feet. The recess to the left of the 
 
 * Lonsdale's Life of Dalton [Cumberland Worthies]. 
 
THE ATOMIC THEORY. 263 
 
 doorway was occupied by a chaff bed, upon which 
 Joseph and Deborah slept, and there John Dalton, 
 the chemist, first saw the light of day, on or about 
 September 6th, 1766." When Dalton afterwards 
 showed friends his birthplace he used to point with a 
 smile to the corner cupboard, where, in his early 
 boyhood, the sweets were kept. Having a great 
 longing for these, when his mother was one day out, 
 he tried to reach the door-handle, but was too small. 
 To effect his purpose he, regardless of consequences, 
 kicked a hole in the plaster of the wall below the 
 cupboard, and in this way gained a footing. Detec- 
 tion was, alas, inevitably certain, and his feat was 
 followed by an interview with an angry mother ter- 
 minated by a sound whipping. 
 
 All Dal ton's ancestors were real " sons of toil," 
 but some of them must surely have had latent intel- 
 lectual power, or else whence did his wonderful in- 
 sight arise. His father, Joseph, showed no special 
 ability, or at least none is recorded of him. He 
 earned small wages by his shuttle, and had six chil- 
 dren, three of whom, Jonathan, Mary, and John, 
 grew to maturity. No record occurs of John's birth, 
 and the date of it is a matter of hearsay and guess- 
 work. He was sent to Pardshaw Hall school, two 
 and a half miles off, and placed under Mr. John 
 Fletcher. John was by no means a quick boy, either 
 at work or play. But he was steady-going and 
 thoughtful, and fond of his books. At ten or eleven 
 years old, Dalton delivered his first lecture to some 
 
264 THE ATOMIC THEORY. 
 
 of his schoolfellows from the top of a hedge. The 
 audience was enthusiastic, and received his demon- 
 strations with loud applause. Mr. Fletcher was wise 
 enough to discern the boy's latent power, and led him 
 to begin the study of mathematics. Later on, Elihu 
 Eobinson, a Quaker gentleman of the neighbourhood, 
 helped him in his studies. Another youth, Alderson, 
 and he would puzzle together over a problem. Al- 
 derson was more ready to seek Robinson's help than 
 was Dalton. " Yan med deu't,"* John would say. 
 Such a dialogue as the following would sometimes take 
 place between Eobinson and Dalton : 
 . "Well, John, hast thou done that question ? " 
 
 " No ; yan med deu't," and then later, t( I can't 
 deu't to-neet, but mebby to-morn I will." 
 
 In 1785 he, with his cousin and brother, became 
 joint-managers of a school at Kendal. The school 
 was not a great success. He continued at Kendal till 
 1793, when he obtained a post of teacher of mathe- 
 matics and natural philosophy at New College, Mosley 
 Street, Manchester. In 1792 he made his first visit 
 to London, (( a surprising place," but " the most dis- 
 agreeable place on earth for one of a contemplative 
 turn of mind." In 1794 he first described colour- 
 blindness, being himself an instance of it. His dis- 
 covery of his own defect arose through the purchase 
 of a pair of stockings as a present for his mother. 
 His mother was somewhat startled by their appear- 
 ance, their colour being a brilliant red, unfit for any 
 
 * (Me might do it." 
 
THE ATOMIC THEORY. 265 
 
 Quaker to wear. To Dalton they seemed a bluish 
 dark drab. 
 
 New College was removed in 1799 to York and, 
 unwilling to leave Manchester, where he evidently 
 formed close associations, Dalton became a private 
 tutor. In 1805 he took up his abode with the Kev. 
 \V. Johns, and lived with him in a very delightful 
 harmony. The way in which it came about was 
 characteristic of Dalton' s childlike simplicity. Johns' 
 wife met Dalton one morning : 
 
 " Mr. Dalton, how is it that you so seldom come 
 to see us ? " 
 
 " Why, I don't know, but I have a mind to come 
 and live with you." 
 
 At first the wife doubted whether he was serious, 
 but finding that he was so, she consulted with her 
 husband who had a true attachment for Dalton, and 
 the arrangements were made. Dalton came and 
 remained with them for the following twenty-six 
 years. " During the long period," says Johns' 
 daughter, " he and my father never, on any occasion, 
 exchanged one angry word." 
 
 Dalton was robust and muscular, and of a simple 
 and open countenance, his profile in old age striking 
 us with a certain strange beauty of enduring patience. 
 He stooped slightly, his height being about five feet 
 seven inches. His health, compared with that of 
 most of the chemists of whom we have spoken, was 
 exceptionally good. It is related that on one occasion, 
 when he had an attack of catarrh, his physician pre- 
 
266 THE ATOMIC THEORY. 
 
 scribed James's powder. Next day, finding Dalton 
 better, he naturally put the cure down to his medi- 
 cine. "I do not well see how that can be," said 
 Dalton, "as I kept the powder until I could have an 
 opportunity of analysing it." In general company 
 Dalton was silent, and on religious topics extremely 
 reticent. He was fond of tobacco, and of Davy he 
 said, " the principal failing in his character as a 
 philosopher is that he does not smoke." He did not 
 marry ; he had never, he said, had time. The truth 
 of this statement may be doubted, but possibly the 
 smallness of his pecuniary resources may have helped 
 to prevent it. With growing age his capacity to 
 receive new truths seems to have become somewhat 
 narrowed, but he always preserved the genuine sim- 
 plicity of heart which lends an added charm to his 
 name. 
 
 It was in 1802 that Dalton conceived his theory. 
 The facts influencing him were such as these. He 
 noticed that nitric oxide would combine with two 
 different amounts of oxygen to form two distinct 
 more highly oxygenated compounds. These two 
 distinct compounds could be formed by combining 
 the nitric oxide (or nitrous air, as it was still called) 
 with a lesser or greater amount of oxygen. But 
 between these no definite compound could be ob- 
 tained. A compound of nitric oxide with either one 
 volume or two volumes of oxygen gas could be 
 got, but not between nitric oxide and one and a half 
 volumes of oxygen or one and three-quarters. 
 
THE ATOMIC THEORY. 267 
 
 Again Dalton observed that marsh gas* contains 
 just double as much hydrogen as olefiant gas.t It 
 was these facts, as we learn from Thomson in his 
 History of Chemistry, which formed the foundations 
 of Dalton's theory. Meditating upon such facts as 
 these, Dalton asked himself why nitrogen will com- 
 bine with oxygen only in quantities which are simple 
 multiples of a certain number ? or why carbon will 
 similarly combine with hydrogen only in like definite 
 proportions ? Then came the brilliant hypothesis won 
 from this apparently barren fact. 
 
 It had been supposed by others long before Dal- 
 ton's time, by Democritus, Epicurus, and Lucretius, 
 that matter is made up of minute indivisible particles 
 or atoms. Just before Dalton's hypothesis was de- 
 veloped, Kirwan (1783) and Higgins (1789) had 
 suggested that chemical combination is due to the 
 approximation of these unlike particles. Higgins 
 represented certain compounds as formed by the 
 union of particles or atoms of the same weight, but 
 united in different proportions. So far had specula- 
 tion gone before Dalton's turn came, and so far spe- 
 culation was barren. 
 
 In spite of the efforts of other workers the concep- 
 tion remained until Dalton's time, wanting in cohe- 
 
 * Marsh gas is a hydrocarbon given off, as its name implies, in 
 marshes and forming the fire-damp of mines. It is evolved with 
 petroleum in petroleum springs, and the gas of the mud volcanoes at 
 Bulganak, in the Crimea, consists, according to Bunsen, of pure 
 marsh gas or methane. It exists in large quantities in coal gas. 
 
 t Bicarburetted hydrogen, olefiant gas, or ethylene, is formed by the 
 action of sulphuric acid on common alcohol. 
 
2 63 THE A TOM 1C THEORY, 
 
 rence and consistency. But Dalton's keen intuitive 
 insight readily saw where the error lay. The hypo- 
 thesis was reasonable enough, but one fatal mistake 
 deprived it of influence upon science. The atoms or 
 different elements are not of equal weight, and Dai- 
 ton set about weighing them. It is not certain how 
 in some cases his results were arrived at. His first 
 table of atomic weights is introduced casually at the 
 close of a paper read before the Manchester Literary 
 and Philosophical Society, October 23rd, 1803, on 
 the absorption of gases by liquids. He applies his 
 theory, and wrongly, to the particular subject in 
 hand. 
 
 " The inquiry," he says, " into the relative weights 
 of the ultimate particles of bodies is a subject, as far 
 as I know, entirely new ; I have lately been prosecu- 
 cuting this inquiry with remarkable success. The 
 principle cannot be entered upon in this paper, but I 
 shall subjoin the results, as far as they appear, ascer- 
 tained by my experiments." He then gives a table of 
 the relative weights of atoms, starting with hydrogen 
 as unity. It is of special interest as being the first 
 table of atomic weights ; but as a table given at a later 
 date is less inaccurate, we shall quote that instead. 
 
 Before, however, proceeding farther we must notice 
 that three distinct ideas lie embedded in this atomic 
 theory of Dalton's. It includes the law of constant 
 proportions of Lavoisier and Proust, the law of de- 
 finite proportions of Richter* and others, and the law 
 
 * Wurtz terms Richter's law the law of proportionality. 
 
THE ATOMIC THEORY. 269 
 
 of multiple proportions of Thomson, Wollaston, and 
 Dalton himself. Let us briefly consider what each of 
 these laws states. 
 
 The law of constant proportions asserts that in 
 every individual compound there is a fixed relation 
 between the weights of the elements composing it. 
 Thus. 216 grammes of mercuric oxide always contains 
 200 grammes of mercury and 1G grammes of oxygen. 
 It has a constant composition. 
 
 The law of definite proportions asserts something- 
 more than this. It asserts that there is a definable 
 relation between the proportions in which different 
 bodies unite. It is really a law of equivalence. 
 As an illustration we may take the following facts : 
 
 One part by weight of hydrogen combines with 35-5 parts of chlorine, 
 with 80 parts of bromine with l'26'o of iodine, or with 19 parts of 
 fluorine.* 
 
 Now 39 parts of potassium combine with 3 5 '5 
 parts of chlorine to form potassium chloride. 39 
 parts of potassium therefore combine with the same 
 amount of chlorine as does 1 part of hydrogen. We 
 naturally inquire farther, with how many parts of 
 the other elements just named will this quantity of 
 potassium combine ? 
 
 We find that 
 
 39 parts by weight of potassium combine with 35 5 parts of chlorine, 
 with 80 parts of bromine, with 126-5 parts of iodine, and with 19 parts 
 of fluorine. 
 
 39 parts of potassium therefore combine with the same amount of 
 chlorine, bromine, iodine, or fluorine, as does 1 part of hydrogen. 
 
 * To form the corresponding acids, hydrochloric, hydrobromic acids, 
 &o. 
 
2 70 THE ATOMIC THEORY. 
 
 This is a striking relation. From these state- 
 ments it appears that 39 parts of potassium are 
 equivalent to 1 part of hydrogen. If we suppose the 
 compounds formed to be, in Dalton's nomenclature, 
 binary compounds, containing one atom of each ele- 
 ment, one of hydrogen to one of chlorine, one of 
 potassium to one of chlorine, and so on, we must 
 conclude that the atom of potassium is equivalent in 
 combining power to the atom of hydrogen, but weighs 
 39 times as much As a matter of fact the modern 
 atomic weight of potassium is approximately 39. 
 
 The law of multiple proportions contains an addi- 
 tional truth. It asserts that in a series of compounds 
 of the same elements, these are always combined 
 together in the proportion of simple multiples of 
 certain definite weights, the combining weights of the 
 elements combined. Thus, to take an example in the 
 series of hydro-carbons known as the paraffins, we 
 observe the following relations : 
 
 In the first of the series methane or marsh gas 
 
 12 parts of carbon are combined with 4x1 = 4 parts of hydrogen. 
 
 In the second, ethane 
 
 2 x 12 = 24 parts of carbon are combined with 6x1=6 parts of 
 hydrogen. 
 
 In the third, propane 
 
 3 x 12 = 36 parts of carbon are combined with 8x1=8 parts of 
 hydrogen. 
 
 In the fourth, butane 
 
 4 x 12 = 48 parts of carbon are combined with 10 x 1 =*10 parts 
 of hydrogen. 
 
 Starting with 1 6 parts of methane we cannot add 
 
THE ATOMIC THEORY. 271 
 
 less than 12 parts of carbon* to get the next higher 
 compound. We could not, for instance, obtain a 
 compound containing 20 parts of carbon to 5 J parts 
 of hydrogen. 
 
 Again, in the case of the nitrogen oxides, already 
 united, we have a series of five compounds 
 
 The first containing 28 parts of nitrogen to 16 of oxygen (nitrous 
 oxide). 
 
 The second containing 28 parts of nitrogen to 2 x 16 = 32 of oxy- 
 gen (nitric oxide). 
 
 The third containing 28 parts of nitrogen to3x 16 = 48 of oxygen 
 (nitrogen trioxide). 
 
 The fourth containing 28 parts of nitrogen to 4 x 16 = 64 of oxygen 
 (nitric peroxide). 
 
 The fifth containing 28 parts of nitrogen to 5x16 = 80 of oxygen 
 (nitrogen pentoxide).f 
 
 Now, if we consider these facts in the light of the 
 atomic theory how can we explain them ? Very 
 simply ; thus : we cannot add less than 1 2 parts of 
 carbon at a time, because we cannot add less than 
 one atom of carbon at a time. The atom of carbon 
 we have reason to believe weighs twelve times as much 
 as the atom of hydrogen. In the first compound 
 one atom of carbon weighing 12 combines with four 
 atoms of hydrogen, weighing altogether 4, to form a 
 molecule of methane. The composition of the whole 
 volume of the gas is of course the same as the com- 
 position of each molecule, 1 2 parts of carbon to 4 of 
 h} 7 drogen. To get the next higher compound we add 
 
 * The reader must understand that the addition of carbon cannot be 
 made directly ; all that is meant is that no intermediate compound is 
 obtainable. 
 
 t The older formulae for these gases are, for present convenience 
 adopted. 
 
272 THE ATOMIC THEORY. 
 
 one atom of carbon to each molecule of methane, and 
 the atom being indivisible we cannot add less. We 
 also add two atoms of hydrogen. Each molecule of 
 the gas (ethane) will now contain two atoms of car- 
 bon to six atoms of hydrogen, that is 24 parts by 
 weight of carbon to 6 of hydrogen, and the gas as 
 a whole, possessing the composition of each of its 
 own molcules, contains 24 parts of carbon to G of 
 hydrogen. In the case of the nitrogen oxides we may 
 picture the relation as simpler still, one atom of oxy- 
 gen being added at each step. Unfortunately, how- 
 ever, matters are here somewhat complicated by other 
 changes. 
 
 The law of combination in multiple proportions 
 may now be more shortly stated thus : The elements 
 unite in the proportion of simple multiples of certain 
 definite ^veights, called their combining weights. 
 
 It is easy to see how readily these laws fall into 
 their places under the atomic theory. Indeed, it 
 would be impossible to fully express them without 
 its aid. In the cruder form assumed by them in 
 Dalton's day, they led him to his great conception. 
 He conceived of each element as made up of minute 
 indivisible particles or atoms. These atoms for each 
 element had a definite weight of their own. How 
 did he arrive at this weight? To answer this question 
 we must form some idea of the different kinds of 
 combination possible among these atoms. In Dal- 
 ton's New System of Chemical Philosophy we find the 
 following : - 
 
THE ATOMIC THEORY. 273 
 
 " If there are two bodies, A and B, which are dis- 
 posed to combine, the following is the order in which 
 the combinations may take place, beginning with the 
 most simple, namely : 
 
 1 atom of A + 1 atom of B = 1 atom of c, binary.* 
 
 1 ,, -f 2 ,, =1 ,, D, ternary. 
 
 2 ,, +1 , b =1 ,, B, ternary. 
 
 1 ,, + 3 ,, = 1 ,, F, quaternary." 
 
 arid so on. The left hand side of the equation re- 
 presents the elements combining, the right hand side 
 the compound formed. Dal ton applied the term 
 atom to the smallest particles of the resulting com- 
 bination where we now should use the word molecule. 
 Having formed this conception of the possible com- 
 binations, Dalton was further guided by the following 
 set of arbitrary rules. f 
 
 " 1st. 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 are observed they must be pre- 
 sumed to be a Unary and a ternary. 
 
 " 3rd. When three combinations are obtained we may expect one 
 to be a binary and the other two ternary. 
 
 "4th. When four combinations are observed we should expect 
 one binary, two ternary, and one quarternary. 
 
 " 5th. A binary compound should be specifically heavier than the 
 mere mixture of its two ingredients. 
 
 " 6th. A ternary compound should be specifically heavier than the 
 mixture of a binary, and a simple, which would, if combined, con- 
 stitute it. 
 
 " 7th. The above rules and observations equally apply when two 
 bodies, such as c and D, D and E, &c., are combined." 
 
 * That is, containing 1 one atom of each element ; a ternary com- 
 pound contains two atoms of one element, one of the other, 
 f New System of Chemieal Philosophy, pt. i. 
 
274 THE ATOMIC THEORY. 
 
 From rule 1, Dalton deduced that water was a 
 binary compound. Water thus contained, according 
 to Dalton, one atom of hydrogen to every atom of 
 oxygen. Further, it contained, by weight, he said, 1 
 part of hydrogen to 7 parts of oxygen. Taking the 
 hydrogen atom as the unit of weight this meant that 
 the oxygen atom weighed seven times as much as the 
 lydrogen atom, the atomic iveight of oxygen was 7. 
 In his assumption that water was a binary compound 
 Dalton was wrong, but it was the best possible as- 
 sumption under the circumstances. Moreover, the 
 proportion of oxygen to hydrogen is not 7 to 1, but 
 very nearly 8 to 1 ; but this inaccuracy was necessary 
 to the determinations of that time. Ammonia, Dal- 
 ton also supposed to be binary, containing one atom 
 of nitrogen to every atom of hydrogen. By weight it 
 consisted, according to him, of 1 part of hydrogen to 
 5 of nitrogen. This meant that the nitrogen atom 
 weighed five times as much as the hydrogen atom, 
 the atomic weight of nitrogen was 5. " Nitrous gas" 
 (nitric oxide) he considered to be binary, containing 
 one atom of nitrogen to one of oxygen, 5 parts by 
 weight of nitrogen to 7 of oxygen, in accordance with 
 the atomic weights. 
 
 By steps such as these Dalton arrived at his table 
 of the atomic weights of the elements. Moreover, he 
 adopted a characteristic symbol for the atom of each 
 element, and combined these to symbolise the "atom" 
 of compounds. A few of his atomic weights are here 
 given. Had his determinations been correct they 
 
THE ATOMIC THEORY. 
 
 2 75 
 
 should have been simple submultiples of the weights 
 now in use. The numbers he would have obtained 
 by accurate experiment appear in the second column. 
 
 Elements. 
 
 Dalton's atomic 
 weights. 
 
 Corrected 
 numbers. 
 
 Symbol. 
 
 Hydrogen 
 
 1 
 
 1 
 
 o 
 
 Nitrogen 
 
 
 
 4-66 
 
 CD 
 
 Carbon .... 
 
 5 
 
 6 
 
 
 
 Oxygen .... 
 
 7 
 
 8 
 
 O 
 
 Iron 
 
 38 
 
 28 
 
 O 
 
 Silver .... 
 
 100 
 
 108 
 
 
 
 OF COMPOUNDS. 
 
 Compound. 
 
 Dalton's atomic 
 weights. 
 
 Corrected 
 numbers. 
 
 Symbol. 
 
 Water .... 
 
 8 
 
 9 
 
 00 
 
 Carbonic oxide 
 
 12 
 
 14 
 
 00 
 
 Carbon dioxide 
 
 19 
 
 22 
 
 O0O 
 
 In Dalton's first table there are some curious inac- 
 curacies which it is difficult to explain. Thus the 
 " atomic " weight of nitric oxide should be the sum 
 of the weights of nitrogen and oxygen ; these in the 
 first table, are 4'2 and 5'5, giving 97. But 9'3 is the 
 number in the table. These discrepancies are difficult 
 of explanation.* 
 
 The symbols adopted at a somewhat later date 
 were analogous to those now in use, For these in 
 
 * See Roscoe on Dalton's first table of atomic weights, Nature, 
 
 1874. 
 
27 6 THE ATOMIC THEORY. 
 
 most cases the first letter of the name of the element 
 is taken to represent the atom. Thus on the Dal- 
 tonian hypothesis that water is a binary compound, 
 containing one atom of hydrogen to one of oxygen, its 
 symbol will be HO, H representing the hydrogen 
 atom and the oxygen atom. Ammonia will be NH, 
 sulphuretted hydrogen HS, olefiant gas HC, carbonic 
 oxide CO, and carbonic acid CO 2 . 
 
 One word more must be said before closing this 
 account of Dalton's work. The fact of the inaccuracy 
 of his determinations should not be allowed to detract 
 from the grandeur of his conception. It should 
 rather enhance and elevate our admiration for his 
 talent, that with means so imperfect he could achieve 
 so much. It is easy from our modern laboratories to 
 lock back with a smile upon the crude methods in 
 use at Dalton's time. It is easy to suggest that 
 determinations so inaccurate could never alone have 
 given the atomic weights their true value and posi- 
 tion in ihe science. That may be, but it was Dalton's 
 intuitive penetration and patient thought which trans- 
 formed the old atomic theory from a baseless fancy 
 into ij resistless truth.* 
 
 * It is legitimate to term the atomic theory a truth, and one of a 
 high order, so long as we regard it as only expressing an analogy 
 between the actual constitution of matter and our conception of it. It 
 was by sifting the truth of the conception from the falsehood that 
 fche theory became capable of serving its science. 
 
CHAPTER XV. 
 
 EIGHTH PERIOD: THE ATOMIC THEOEY. 
 THE DEVELOPMENT OF D ALTON'S IDEA. 
 
 HEN we wish to estimate the quantity of 
 anything we describe it in measures of 
 weight or of volume. Dalton described 
 the quantity of his individual atoms by 
 weight. The introduction of their mea- 
 sure by volume was to complete the 
 power of the atomic theory as a weapon 
 of science. 
 
 Gay-Lussac found that the relations existing 
 between the volume of one gas and that of another 
 with which it will combine, and that of the com- 
 pound formed, are very simple. The starting- 
 point was the determination of the volumetric com- 
 position of water by Gay-Lussac and Humboldt in 
 1805. 
 
 2 volumes of hydrogen unite with 1 volume of 
 oxygen to form 2 volumes of aqueous vapour, 
 
278 THE ATOMIC THEORY. 
 
 2 volumes of nitrogen unite with one volume of 
 oxygen to form 2 volumes of nitrogen protoxide. 
 
 1 volume of chlorine unites with 1 volume of 
 hydrogen to form 2 volumes of hydrochloric acid. 
 
 1 volume of nitrogen unites with 3 volumes of 
 hydrogen to form 2 volumes of ammonia. 
 
 1 volume of carbonic oxide unites with 2 volumes 
 of chlorine to form 2 volumes of carbonyl chloride.* 
 
 Carbonic oxide is a compound gas, and therefore 
 not on quite the same footing as the rest of the 
 bodies mentioned in this table. 
 
 In 1808 Gay-Lussac stated his general law of gas- 
 eous volumes : The iveights of the combining volumes 
 of the gaseous elements bear a simple ratio to their 
 atomic weights. He suggested that the relative 
 weights of the gaseous volumes entering into combi- 
 nation exactly represent the relative weight of the 
 atoms. The specific gravities of the elementary 
 gases, i.e. their weight in terms of the weight of an 
 equal volume of hydrogen as unity, are therefore the 
 same as their atomic weights. Thus, taking the 
 unit volume of hydrogen to weigh 1, we find that 
 the unit volume of nitrogen weighs fourteen times as 
 much ;f the specific gravity of nitrogen is 14 and its 
 atomic weight is 1 4. This is the outcome of Gay- 
 Lussac' s theory, and establishes an intimate relation 
 between the volumes of the elementary gases and 
 their atomic weights. 
 
 t According to modern determinations. 
 
THE ATOMIC THEORY. 279 
 
 The Italian chemist, Amedeo Avogadro, in 1811, 
 explained the relation between the volumes and the 
 combining weights by the supposition of a simple 
 relation between the volumes of gases and the number 
 of ultimate particles they contain. The hypothesis 
 put forward by Avogadro was that equal volumes of 
 all gases contain always equal numbers of these ulti- 
 mate particles.* 
 
 Let us consider the case of a compound, and, to 
 choose a simple case, take water. The volume of the 
 atom is necessarily taken as the unit volume. Now, 
 to use the language of the chemists of Gay-Lussac's 
 time : 2 volumes of hydrogen, i.e. 2 atoms of hydrogen, 
 unite with 1 volume of oxygen, i.e. 1 atom of oxygen, 
 to form 2 volumes of water, i.e. two atoms of water. 
 2 volumes of water thus contain 2 volumes of hydro- 
 gen and 1 volume of oxygen. Then comes the 
 difficulty, for it follows from this that 1 volume of 
 water, i.e. I atom of water, must contain 1 volume of 
 hydrogen, i.e. I atom of hydrogen and \ volume of 
 oxygen, i.e. \ atom of oxygen. T>y similar reasoning 
 we should find that 1 atom of hydrochloric acid gas 
 contains J atom of hydrogen and J atom of chlorine. 
 Obviously as we have started with the atom as the 
 ultimate particle and the indivisible unit, it is a con- 
 tradiction of our own theory to introduce J atoms 
 into it. 
 
 This difficulty was seen by Avogadro, and it seemed 
 
 * What these ultimate particles are will appear in the sequel. 
 Also see p. 271. 
 
280 THE ATOMIC THEORY. 
 
 likely to invalidate his hypothesis about the relation 
 between the number of the ultimate particles and the 
 volumes of the gases. If the atom of water vapour 
 occupied twice the volume occupied by the atom 
 of oxygen the relation became less simple. But 
 Avogadro brought a subtle and, the same time, essen- 
 tial distinction to the aid of the theory. The ulti- 
 mate particle of water occupies the same volume as 
 two atoms of oxygen or of hydrogen, &c. The ulti- 
 mate particle of water consists of more than one 
 atom. It becomes in the end most simple to assume 
 that there similarly exists an ultimate particle of 
 oxygen gas made up of more than one atom. This it 
 is which occupies the same volume as the smallest 
 particle of water, and in modern language we call it a 
 molecule. But the molecule of water occupies the 
 same volume as two atoms of oxygen. 
 
 The molecule of oxygen is thus composed of two 
 atoms. 
 
 The chemical definition of an atom is : 
 
 An atom is the smallest portion of matter which 
 can enter into a chemical compound. 
 
 A molecule is the smallest quantity of an element 
 or of a compound which can exist in the free 
 state. 
 
 To illustrate these definitions, the smallest portion 
 of oxygen, represented by the symbol 0, can be trans- 
 ferred from one compound to another, but cannot 
 exist alone. Directly the atom is set free it tends to 
 combine with another atom either of its own kind 
 
THE ATOMIC THEORY. 28 1 
 
 or not. The molecule of oxygen, consisting of two 
 atoms, and represented by the symbol 2 , can exist 
 free. 
 
 In the production of water by the combination of 
 oxygen and hydrogen, each molecule of oxygen is 
 acted on by two molecules of hydrogen. We may 
 represent this as an equation by the use of chemical 
 symbols. The first letter of the name is taken to 
 represent the atom, of the element, thus represents 
 an atom of oxygen occupying 1 volume and weighing 
 16.* To represent two atoms a small numeral is 
 placed below or above the symbol, 2 . The molecule 
 of water composed of two atoms of hydrogen to one 
 atom of oxygen, or of two volumes of hydrogen to 
 one volume of oxygen, or of two parts by weight of 
 hydrogen to 16 parts by weight of oxygen, is repre- 
 sented by the symbol H 2 ; two molecules of water 
 will be represented by 2H 2 0. Now we are ready to 
 express symbolically the formation of two molecules 
 of water from one molecule of oxygen and two mole- 
 cules of hydrogen. 
 
 2 + 2H 2 = 2H 2 0. 
 
 In this reaction the molecule of oxygen is separated 
 into its two constituent atoms, one of which goes to 
 each molecule of water. The atom of oxygen can 
 exist in the compound, water, but cannot exist by 
 itself. 
 
 Having now got some idea of what is the chemist's 
 
 * That ia 16 times the weight of an atom of hydrogen, the atom 
 of hydrogen, the lightest element known, being always taken as unity. 
 
282 THE ATOMIC THEORY. 
 
 conception of atom and molecule we can give a clear 
 and concise statement of Avogadro's law :* 
 
 Equal volumes of gases and vapours at equal 
 temperature and under the same pressure, contain 
 the same number of molecules, and consequently the 
 relative weights of these molecules are proportional fo 
 the densities of the gases or vapours. 
 
 This is often termed the law of Avogadro and Am- 
 pere, for the latter, in 1814, propounded ideas similar 
 to those of the Italian chemist. He drew a distinction 
 between particles and molecules, the molecule pf Am- 
 pere corresponding to the modern atom. According 
 to Ampere the distances between the individual (< par- 
 ticles " of gases, or, as we should say, their molecules, 
 ''depends entire upon the heat to which the gas is 
 subjected." Under equal pressure and temperature 
 the molecules of all gases are equidistant from each 
 other. From these suppositions the fact, already 
 noticed, of the equal expansibility of all gasesby equal 
 rise of temperature or fall of pressure follows as a 
 simple deduction. The fact that all gases have- the 
 same co-efficient of expansion as air was first dis- 
 covered by Charles. This co-efficient is independent 
 of pressure. These two laws were arrived at indepen- 
 dently by Dalton and Gay-Lussac, and it was the 
 latter chemist who first accurately determined the 
 co-efficient of expansion of gases. They are in 
 complete harmony with the hypothesis of Avogadro 
 and Ampere. 
 
 * Journal de Physique, xxxiii. 58. 
 
THE ATOMIC THEORY. 283 
 
 The great achievement of Avogadro and Ampere 
 was not, however, well received by chemists. Its 
 simplifying power was not acknowledged, and other 
 and more confused ideas were for many years pre- 
 ferred to it. This is only one of the many instances 
 of a great scientific truth being ignored by the men 
 of science themselves. Contradictions were found to 
 occur in the rigorous application of the hypothesis, 
 a*hd it was too readily concluded that a speculation 
 not immediately and in every detail commendable to 
 the average scientific mind must for ever remain 
 barren. The simplicity and truth of Avogadro's 
 hypothesis were indeed too far in advance of the time. 
 
 The great Swedish chemist, Berzelius, attempted a 
 union between the atomic hypothesis and the law of 
 volumes. His views were first stated in 1813, but 
 were more perfectly presented in 1818. He con- 
 ceived that equal volumes of the simple gases contain 
 not only, as Avogadro and Ampere had stated, equal 
 numbers of molecules, but equal numbers of atoms, so 
 that to compare densities was to determine not merely 
 the relative weights of the molecules but the relative 
 weights of the atoms. Thus if we find that a litre of 
 chlorine weighs 35*5 times as much as a litre of 
 hydrogen, we may, according to Avogadro, conclude 
 that the molecule of chlorine is 3 5 '5 times as heavy 
 as the molecule of hydrogen. But if the molecules 
 of hydrogen and of chlorine may contain any numbers 
 of atoms, this tells us nothing about the atomic 
 weight. Now if we suppose that each molecule of 
 
284 THE ATOMIC THEORY. 
 
 hydrogen contains two atoms, and each molecule of 
 chlorine the same number, the comparison of mole- 
 cules comes to the same thing as the comparison of 
 atoms. 3 5 '5 may now be taken as the atomic weight 
 of chlorine. 
 
 This was the view taken by Berzelius. In general 
 it holds good, but in some cases there are marked 
 exceptions. Thus the vapours of liquids at a tem- 
 perature not far removed from their boiling points 
 often exhibit very anomalous densities. Taking the 
 atomic weight of sulphur as 32, its vapour density, 90, 
 not far above its boiling point, shows that the mole- 
 cule at that temperature must consist of six atoms.""" 
 Above 860 its vapour density (32) corresponds to 
 its atomic weight. The molecule of six atoms is 
 broken up into 3 molecules of two atoms each. 
 
 The hypothesis of Prout was set forth about this 
 time (1816), to the effect that the atomic weights of 
 the elements were integral multiples of that of hy- 
 drogen. One of the advantages claimed for such a 
 system of weights was that it would enable us to con- 
 ceive of hydrogen as the primordial element, from 
 which the others were formed by successive con- 
 densations. The J or J of the atomic weight of 
 hydrogen has been suggested as the atomic weight of 
 this fundamental element, but even then the weights 
 cannot be reduced to integral multiples of it. The 
 
 * Sulphur boils, according to Regnault, under normal pressure at 
 44S-4 centigrade, its vapour density being, according- to Dumas, 35-55 
 at 524. 
 
THE ATOMIC THEORY. 285 
 
 suggested hypothesis of a single primordial element 
 is not, however, to be lightly set aside. It is a pro- 
 found speculation, and viewed rightly, may afford 
 valuable guidance to future research. 
 
 Two important principles were at this time formu- 
 lated and incorporated by Berzelius in his table of 
 atomic weights. The first was the law of specific 
 heats of Dulong and Petit. We must first offer some 
 explanation of what is to be understood by the term 
 specific heat. Shortly, then, it is found that equal 
 weights of different bodies require different amounts 
 of heat to raise them through the same number of 
 degrees of temperature. The unit of heat or thermal 
 unit may be taken as the quantity of heat necessary 
 to raise 1 gram of water through 1 centigrade. It 
 takes less heat to raise a gram of nickel one degree 
 than to raise a gram of water through the same 
 temperature. 
 
 Now a body will give out on cooling through 
 a certain number of degrees the same amount of heat 
 as would be needed to raise it through the same 
 number of degrees. To find how much is needed 
 we may therefore mix a certain weight of the heated 
 substance with a certain weight of cold water. Thus 
 suppose we mix 100 grams of metallic nickel at 
 100C. with 100 grams of water at 10C. When 
 the heat of the nickel has become equally diffused 
 through the water we find the temperature to have 
 risen to 18*9. The nickel has cooled through 
 81-1, and has in so doing heated an equal weight of 
 
286 THE ATOMIC THEORY. 
 
 water through 8 -9. 100 grams of nickel thus re- 
 quires 890 units of heat to raise it through 8 1-1. 
 But 100 grams of water requires 8110 units of heat 
 to raise it through 81 '1, since 1 gram needs 1 unit 
 to raise it through 1. Thus the 100 grams of nickel 
 takes g-WV times as much heat to raise it through a 
 given temperature as does the same quantity of 
 of water. Its specific heat is -g- 8 T 9 T o- = '1097. 
 The quantity of heat which would raise the tempera- 
 ture of a given weight of nickel through 1 C. would 
 raise the temperature of a given weight of water 
 through only "1097 C. In actual experiments of the 
 kind just described, the specific heat of the calori- 
 meter or vessel in which the water is contained must 
 be taken into account. It of course becomes heated 
 at the same time as the water, but to understand 
 the bearing of Dulong and Petit's law, it is unneces- 
 sary here to enter into further detail. 
 
 In 1819 these chemists gave the specific heats of 
 many solid bodies, particularly metals, and made the 
 observation that in most cases they were inversely 
 proportional to the atomic weights. The specific 
 heat gives the capacity of each gram of the substance 
 for heat. If we multiply this number therefore by 
 the atomic weights we shall get the capacities of the 
 atoms for heat, or, as it is termed, the atomic heat of 
 the elements. On performing this multiplication we 
 see that with the greater number of the solid elements 
 the atomic heat is a nearly constant quantity. The 
 atomic heats of most of the elements are found to lie 
 
THE ATOMIC THEORY. 
 
 287 
 
 near 6*4. Dulong and Petit's law then states that 
 the atomic heat of the elements is a constant quantity ; 
 or that the atoms of all simple bodies have precisely 
 the same capacity for heat* 
 
 It is readily seen that this generalisation must be 
 of great service in controlling the atomic weights. 
 In the case of these metals a very close adherence to 
 the law is observed, so that Dulong and Petit corrected 
 by its means the atomic weights of zinc, iron, nickel, 
 copper, lead, tin, and gold. In the case of these 
 metals the atomic weight attributed by Berzelius had 
 been just double that which was in accordance with 
 the law of specific heats. Their weight was therefore 
 halved and the formulae of the oxides changed from 
 Zn0 2 , Fe0 2 , Ni0 2J Cu0 2> &c., to ZnO, FeO, NiO, 
 CuO, &c.t 
 
 A few of the specific and atomic heats are given 
 below : 
 
 Element. 
 
 Specific heat. 
 
 Temperature of 
 observation. 
 
 Atomic 
 weight. 
 
 Atomic heat. 
 
 Zinc . 
 
 0-0955 
 
 + 55 
 
 64-9 
 
 62 
 
 Cadmium 
 
 0-0567 
 
 + 55 
 
 111-6 
 
 6-3 
 
 Lead . 
 
 0-0315 
 
 + 34 
 
 206-4 
 
 6-5 
 
 Mercury 
 
 0-0319 
 
 59 
 
 199-8 6-4 
 
 Iron 
 
 0-1140 
 
 + 58 
 
 55-9 6-4 
 
 Among the non-metals carbon has an atomic heat 
 which is far too low. In the form of diamond its 
 atomic heat at 45 is 1*8. It is found, however, that 
 
 * Annalcsde Chimie, 1819. 
 
 t Fe iron (ferrum), Cu copper (cuprum), Zn zinc. 
 
2 88 THE ATOMIC THEORY. 
 
 its atomic heat rises with the temperature and at 
 985 is 5-51. 
 
 Another generalisation destined to exercise consi- 
 derable influence upon the development of the atomic 
 theory was the law of isomorphism made known 
 by the German chemist, Mitscherlich, in December,, 
 1819. Mitscherlich observed that similarity of con- 
 stitution in salts tended to produce similarity of 
 crystalline form. Thus potassium chloride is isomor- 
 phous with sodium chloride ; magnesium sulphate is 
 isomorphous* with the sulphate of zinc and nickel. 
 Ordinary sodium phosphate is isomorphous with the 
 corresponding sodium arsenate. The similarity of 
 constitution is exhibited in the following formulae, 
 the water of crystallization being united by a plus 
 sign to the formula of the salt. Ordinary sodium 
 phosphate is phosphoric acid, H 3 P0 4 , in which 2 
 atoms of hydrogen are replaced by sodium, Na 2 HP0 4 ; 
 and it crystallizes with 12 molecules of water, 
 Na 2 HP0 4 + 12H 2 0. The corresponding arsenate is 
 similarly derived from arsenic acid, H 3 As0 4 , and is 
 thus represented by the formula Na 2 HAs0 4 + 
 12H 2 0.f As a last instance we may take the case 
 of sodium nitrate isomorphous with calc-spar (calcium 
 carbonate), the formulae being respectively NaNO 3 and 
 CaCO 3 . Upon the older view of the constitution of me- 
 tallic salts, the view held down to the time of Gerhardt, 
 
 * i.e. built up or constructed on the same lines ; from isos, equal ; 
 and morphe, shape. 
 
 t For explanation of any of these symbols see the table of modern 
 atomic weights given below. 
 
THE ATOMIC THEORY. 289 
 
 that they were formed by the union of an acid with 
 a basic oxide, the formulas of these salts would be- 
 come N 2 5 + Na 2 and CO 2 + CaO ; the similarity 
 of constitution would be obscured and the fact of 
 their isomorphism remain unexplained. 
 
 Mitscherlich's law of isomorphism was stated by 
 him as follows : The same number of elementary 
 atoms, combined in the same manner, produce the 
 same crystalline form, and this form is independent of 
 the chemical nature of the atoms, and determined 
 solely by their number and arrangement. The 
 statement so made is somewhat too wide, and impor- 
 tant restrictions and exceptions have to be allowed. 
 Nevertheless, the law is an important one, and had 
 considerable influence with Berzelius in his deter- 
 mination of atomic weights. Chromium oxide being 
 Cr 2 3 the isomorphism of chrome alum and iron 
 alum led to the adoption of Fe 2 3 as formula for 
 ferric oxide and FeO for ferrous oxide. The adoption 
 of the last formula led, by chemical analogy and 
 isomorphism, to similar formulas for lime (calcium 
 oxide), magnesia (magnesium oxide), and zinc oxide. 
 Thus this law as well as the law of specific heats 
 could only be recognised by halving the atomic 
 weights of a number of metals, and the weights were 
 accordingly halved. 
 
 Guided by these considerations Berzelius adopted 
 the atomic weights given by him in 1826. His 
 weights are referred to oxygen as 100. On calcula- 
 ting them for the atomic weight of hydrogen as the 
 
 T 
 
290 
 
 THE ATOMIC THEORY. 
 
 unit we are struck by the very remarkable accuracy 
 of the results lie had arrived at. All the accurate 
 appliances of modern chemistry and the labour of 
 "workers of unexampled patience and skill have only 
 in the more important cases succeeded in effecting 
 alterations in the decimal places of his atomic 
 weights. A few examples from his table may here 
 be given. 
 
 Element. 
 
 Symbol. 
 
 Atomic weights 
 referred to 
 Oxygen as 100. 
 
 Atomic weights 
 referred to 
 Hydrogen as 1. 
 
 Modern 
 atomic weights. 
 
 Oxygen 
 Carbon 
 
 
 
 c 
 
 100 
 76-44 
 
 16-02 
 12-26 
 
 15-96 
 
 Phosphorus 
 Sulphur 
 Selenium 
 
 p 
 
 s 
 
 Se 
 
 196-14 
 201-17 
 494-58 
 
 31-44 
 32-24 
 79-26 
 
 30-96 
 31-98 
 79-0 
 
 Iodine 
 
 I 
 
 789-75 
 
 126-56 
 
 126-53 
 
 Chlorine 
 
 Cl 
 
 221-33 
 
 35-48 
 
 35-37 
 
 Calcium 
 
 Ca 
 
 256-02 
 
 41-04 
 
 39-9 
 
 Aluminium 
 
 Al 
 
 171-17 
 
 27-44 
 
 27-3 
 
 Zinc 
 
 Zn 
 
 403-23 
 
 64-62 
 
 64-9 
 
 Up to this point the atomic theory had progressed 
 rapidly, but the chemists began to repent of their 
 rapid adoption of the new ideas. Atomic weights 
 had at their first start been regarded as expressive of 
 what quantities of the different elements were equi- 
 valent to each other. Upon this idea the theory had 
 been founded, it was difficult to change its foundations, 
 it was difficult to admit that additional facts must be 
 contained in the formulae adopted. Gay-Lussac, 
 Wollaston, and Gmelin used their influence in favour 
 of atomic weights founded only upon equivalence, and 
 
THE ATOMIC THEORY. 291 
 
 Berzelius was obliged in some points to give way. 
 He did not, however, readily yield, and, driven back 
 to the older formula), he adopted HO, H6i and H 3 ^, 
 as formulae for water, hydrochloric acid and ammonia, 
 regarding H as a double atom of hydrogen represent- 
 ing the equivalent of other chemists. 
 
 Any inaccuracies in the conceptions of Berzelius 
 now came rapidly to light. We have seen how he 
 considered the vapour densities of the elements, 
 where obtainable, as identical with their atomic 
 weight. Avogadro had stated that equal volumes of 
 gases or vapours contained equal numbers of molecules. 
 Berzelius, in the case of the elements at least, held 
 that they contained equal numbers of atoms. In 
 some cases this idea proved to be erroneous. Thus 
 we are obliged to adopt 200 as the atomic weight of 
 mercury. The laws of Dulong and Petit, the vapour 
 densities of its volatile compounds, and purely 
 chemical considerations necessitate the adoption of 
 this weight. But, as first pointed out by the French 
 chemist Dumas, the vapour density of mercury 
 vapour compared with that of hydrogen is very 
 nearly 100. It is only half what, according to the 
 ideas of Berzelius, it should be. There is not the 
 same number of atoms in a litre of hydrogen and of 
 mercury vapour. The atom of mercury occupies 
 twice the space that the atom of hydrogen does. If 
 the molecule of hydrogen consists of two atoms, 
 the molecule of mercury vapour consists of one. 
 Anomalous vapour densities were also found by 
 
292 THE ATOMIC THEORY. 
 
 Dumas, in 1832, in the cases of phosphorus and 
 sulphur. In the case of sulphur the molecule is 
 disintegrated at a high temperature, but phosphorus 
 preserves a four-atom molecule at 1040 (Deville and 
 Troost), Avhile the molecule of arsenic consists of four 
 atoms at 860 (Deville and Troost). 
 
 In consequence of this and other actual or 
 supposed flaws in the theory of Berzelius the system 
 of chemical equivalents, as distinguished from the 
 true atomic weights, gradually gained ground. The 
 attempt to represent as equivalent molecules not 
 really comparable led to great complication and 
 difficulty. Into this labyrinth it is unnecessary here 
 to attempt to follow chemical theory. An emergence 
 began with the work of Laurent and Gerhardt* but 
 the influence of these chemists like that of A.vogadro 
 was unrecognised and unrewarded till they passed 
 beyond gratitude or condemnation. 
 
 * For the work of these two chemists Laurent's Chemical Method 
 (Cavendish Society) may be consulted. 
 
CHAPTER XVI. 
 
 EIGHTH PERIOD: THE ATOMIC THEORY. 
 THE ATOMIC THEORY OF TO-DAY. 
 
 ,HERE are a number of reactions in organic 
 chemistry as a result of which carbonic 
 acid, water, or ammonia is produced. 
 Gerhard t noticed a curious point with 
 regard to these reactions when written out 
 as equations in the formula in use in his 
 day. The equations were observed never to con- 
 tain formula} for single molecules of water or car- 
 bonic acid, while they did contain single molecules 
 of ammonia. The acute mind of Gerhardt sought 
 for a cause of this strange fact. Representing the 
 molecules of carbonic acid and water by CO 2 and HO, 
 never less than two molecules of either occurred in the 
 representation of these reactions. It appeared to Ger- 
 hardt an unwarrantable supposition to conclude that 
 these substances were never liberated in less than two 
 
294 THE ATOMIC THEORY . 
 
 molecules at a time. For example, let us take oxida- 
 tion of alcohol to aldehyde. On the old system of 
 atomic weights this is formulated : 
 
 <7*# 6 o 2 -f o 3 = 2HO -f CWCP 
 alcohol + oxygen = water + aldehyde. 
 Again, take the action of any acid upon alcohol : 
 
 CH*(P -f HCl = C*H*Cl -f 2HO. 
 
 We here see two molecules of water always liberated, 
 and on this system it was possible always to represent 
 the water taking part in a reaction as a whole multi- 
 ple of H 2 2 . The use of the formula HO seemed to 
 Gerhardt to be therefore in a large measure gone. So 
 too with the formula CO 2 , and both were accordingly 
 doubled, becoming H 2 2 and C 2 4 . These formulae 
 were the true equivalents of the formulas then in use 
 for ammonia, NH 3 . So too S 2 4 and C 2 2 represented, 
 according to Gerhardt's equivalents of sulphur, dioxide 
 and carbonic oxide.* The same equivalent, might, 
 however, be obtained by simpler means, and instead 
 of using these double formulae, Gerhardt concluded 
 that the atomic weights of carbon, sulphur, and 
 oxygen should be doubled. The school of equivalent 
 chemists had assigned to these elements the weights 
 6, 16, and 8 ; Gerhardt adopted the atomic weights 
 12, 32, and 16. C 2 , representing two atoms of car- 
 bon weighing 1 2 times as much as the atom hydrogen, 
 is thus replaced by C representing one atom weighing 
 the same amount. In this way the double formulae 
 are halved and become CO 2 , H 2 0, SO 2 , and CO. These 
 
 * The molecules represented by these formulae would occupy four 
 volumes, if the molecule of hydrogen, H 2 , be taken as occupying two. 
 
THE ATOMIC THEORY, 295 
 
 formulae possess the great advantage of being in ac- 
 cordance with Avagadro's law of volumes. The older 
 formulae were not comparable in this respect. Thus the 
 molecule of ether vapour, C 4 H 5 0, would occupy two 
 volumes, while that of alcohol vapour, C 4 H 6 2 , would 
 occupy four. Williamson showed, by purely chemical 
 reasoning, that the old formula of ether must be 
 doubled. It then becomes simpler to use the new 
 atomic weights, and the molecular formulae of ether 
 and alcohol then become C 4 H 10 and C 2 H 6 0, each 
 occupying two volumes. 
 
 After adopting the new atomic weights, Gerhardt 
 saw that it would be necessary to halve the organic 
 formulae so obtained, if single molecules of water or 
 carbonic acid were to appear in the equations, and if 
 the formulae were to be brought into accordance with 
 the law of volumes. But here he was met by a diffi- 
 culty. Silver acetate under his new system had the 
 formula C 4 H 6 Ag0 4 . How could this be halved, seeing 
 that it contained only one atom of silver ? Gerhardt 
 solved this problem by halving the atomic weight of 
 silver. The formula then became G 4 H 6 Ag 2 4 , and 
 when halved, C 2 H 3 2 Ag. Oxide of silver then became 
 Ag 2 0, analogous to water H 2 0. In following out his 
 analogy, Gerhardt halved the atomic weights of a 
 number of metals. He went too far, but in many 
 cases the idea was a correct one. 
 
 The reforms of Gerhardt necessitated a change in 
 the conception of the constitution of salts. Previously 
 salts were considered as combinations of an acid oxide 
 with a basic oxide. Silver nitrate was, for instance, 
 
29 6 THE ATOMIC THEORY. 
 
 regarded as a combination of silver oxide with nitrogen 
 pentoxide, AgO.NO 5 . Under the new regime such 
 formulae became simplified, and silver nitrate became 
 Ag 2 N 2 6 and thus AgNO 3 . The old ideas as to the 
 constitution of salts thus became untenable, and we 
 now define a salt as an acid having the whole or part 
 of its hydrogen replaced by a metal. 
 
 Laurent adopted and extended the notions of Ger- 
 hardt. He pointed out that the hydrates cannot be 
 considered as compounds of oxide and water, any 
 more than the salts could be considered as compounds 
 of oxide with oxide. A hydrate, said Laurent, is an 
 intermediate stage between water and oxide. 
 
 Water is H 2 0; when one hydrogen atom is re- 
 placed by potassium it becomes KHO, caustic potash ; 
 when two atoms are replaced it becomes K 2 0, potas- 
 sium oxide. There is a close analogy here between 
 the organic and inorganic compounds. Replacing 
 one hydrogen atom by the organic radical ethyl 
 (C 2 II 5 ) we obtain ordinary alcohol. Replacing both 
 hydrogen atoms we obtain ordinary ether. 
 
 H 2 0, water. H 2 0, water. 
 
 KHO, potassium hydrate. (C 2 H 5 ) HO, alcohol. 
 
 K 2 0, potassium oxide. (C 2 H 5 ) 2 0, ether. 
 
 Cannizzaro (1858) doubled the atomic weight of a 
 number of metals once more in accordance with the 
 law of specific heats, and by a series of gradually 
 narrowing oscillations the opinions of chemists at 
 length gravitated to an almost stationary point, and 
 the table of atomic weights and system of formulae 
 now adopted is the result of their agreement. 
 
THE ATOMIC THEORY. 
 
 297 
 
 The following is a table of the atomic weights now 
 in use.* 
 
 Element. 
 
 Atomic 
 Weight. 
 
 Sym- 
 bol. 
 
 Element. 
 
 Atomic 
 Weight. 
 
 Sym- 
 bol. 
 
 Aluminium . . 
 
 27-3 
 
 Al 
 
 Molybdenum 
 
 95-8 
 
 Mo 
 
 Antimony . . 
 
 120-0 
 
 Sb 
 
 Nickel. . . . 
 
 58-6 
 
 Ni 
 
 Arsenic . . . 
 
 74-9 
 
 As 
 
 Niobium . . . 
 
 94-0 
 
 Nb 
 
 Barium . . . 
 
 136-8 
 
 Ba 
 
 Nitrogen . . . 
 
 14-01 
 
 N 
 
 Beryllium . . 
 
 9-2 
 
 Be 
 
 Osmium . . . 
 
 198-6 
 
 Os 
 
 Bismuth . . 
 
 210-0 
 
 Bi 
 
 Oxygen . . . 
 
 15-96 
 
 
 
 Boron .... 
 
 11-0 
 
 B 
 
 Palladium . . 
 
 106-2 
 
 Pd 
 
 Bromine % . 
 
 79.75 
 
 Br 
 
 Phosphorus . . 
 
 30-96 
 
 P 
 
 Cadmium . . 
 
 111-6 
 
 Cd 
 
 Platinum . . . 
 
 196-7 
 
 Pfc 
 
 Caesium . . . 
 
 132-5 
 
 Cs 
 
 Potassium . . 
 
 39-04 
 
 K 
 
 Calcium . . \ 
 
 39-9 
 
 Ca 
 
 Rhodium . . . 
 
 104-1 
 
 Rh 
 
 Carbon . . . 
 
 11-97 
 
 C 
 
 Rubidium . . 
 
 85-2 
 
 Rb 
 
 Chlorine . . 
 
 35-37 
 
 Cl 
 
 Ruthenium . . 
 
 103-5 
 
 Ru 
 
 Cerium . . . 
 
 141-2 
 
 Ce 
 
 Scandium . . 
 
 44-0 
 
 So 
 
 Chromium 
 
 52-4 
 
 Cr 
 
 Selenium . 
 
 79-0 
 
 Se 
 
 Cobalt. . . . 
 
 58-6 
 
 Co 
 
 Silver .... 
 
 107-66 
 
 Ag 
 
 Copper . . . 
 
 63-1 
 
 Cu 
 
 Silicon .... 
 
 28-0 
 
 Si 
 
 Didymium . . 
 
 147-0 
 
 Di 
 
 Sodium . . . 
 
 22-99 
 
 Na 
 
 Erbium . . . 
 
 169-0 
 
 Er 
 
 Strontium . . 
 
 87-2 
 
 Sr 
 
 Fluorine . 
 
 19-1 
 
 F. 
 
 Sulphur . 
 
 31-98 
 
 S 
 
 Gallium . . . 
 
 69.8 
 
 Ga 
 
 Tantalum . . 
 
 182-0 
 
 Ta 
 
 Gold .... 
 
 196-2 
 
 Au 
 
 Tellurium . . . 
 
 128-0 
 
 Te 
 
 Hydrogtn . . . 
 
 1-0 
 
 II 
 
 Terbium . . . 
 
 148-5 
 
 Tr 
 
 Indium . . . 
 
 113-4 
 
 In 
 
 Thallium . . . 
 
 203-6 
 
 Tl 
 
 Iodine .... 
 
 126-53 
 
 I 
 
 Thorium . . 
 
 231-5 
 
 Th 
 
 Iridium . . . 
 
 192-7 
 
 Ir 
 
 Tin 
 
 117-8 
 
 Sn 
 
 Iron .... 
 
 55-9 
 
 Fe 
 
 Titanium . . . 
 
 48-0 
 
 Ti 
 
 Lanthanum . . 
 
 139-0 
 
 La 
 
 Tungsten . . . 
 
 183-5 
 
 W 
 
 Lead .... 
 
 206-4 
 
 Pb 
 
 Uranium . . . 
 
 240-0 
 
 u 
 
 Lithium . . . 
 
 7-01 
 
 Li 
 
 Vanadium . . 
 
 51-2 
 
 V 
 
 Magnesium . 
 
 23-94 
 
 Mg 
 
 Yttrium . . . 
 
 92-5 
 
 Y 
 
 Manganese . . 
 
 54-8 
 
 Mn 
 
 Zinc .... 
 
 64-9 
 
 Zn 
 
 Mercury . . . 
 
 199-8 
 
 Hg 
 
 Zirconium 
 
 90-0 
 
 Zr 
 
 * Some of the symbols are derived from the Latin names of the 
 elements, e.g., Potassium, K (Kalium] ; Silver, Ag (Argentum) ; 
 Sodium, Na (Natrium], ; Mercury, Hg (Hydrargyrum], &c, 
 
298 THE ATOMIC THEORY, 
 
 In the above table the non-metallic elements are 
 printed in italics. The distinction between metals 
 and non-metals is a convenient one, but the two 
 classes are not sharply separated from each other. 
 It is in Geber's writing that the first definition of a 
 metal occurs: "Metallumest corpus miscibile, fusibile, 
 et sub malleo ex omni dimensione extendibile."* The 
 discovery of the brittle metals (antimony, bismuth, 
 and zinc) destroyed the completeness of this defini- 
 tion. There is no attempt now at a sharply drawn 
 distinction, but the metals are, as a rule, distinguished 
 by their peculiar lustre. The metals are also cha- 
 racterized by the formation of basic oxides. These 
 basic oxides unite with acid oxides, the oxides of the 
 non-metallic elements, to form salts. Thus copper 
 oxide, CuO, unites with sulphur trioxide, S0 3 , to 
 form copper sulphate, CuSO 4 . If now an electric 
 current be passed through a solution of this salt it is 
 decomposed, and the copper is deposited at the nega- 
 tive pole. Copper is thus positive as compared with 
 the other group SO 4 , and its oxide is termed positive 
 or basic. The non-metals have a special tendency 
 to form negative oxides. Thus sulphur forms two 
 oxides, S0 2 and S0 3 ; both are negative, and com- 
 bined with water form respectively sulphurous and 
 sulphuric acids, H 2 S0 3 and H 2 S0 4 . The hydrogen 
 in these acids may be replaced by a metal to form a 
 salt, and, indeed, the acids themselves may be re- 
 
 * " A metal is a fusible body susceptible to combination, and wbich 
 may be extended in all directions under the hammer." 
 
THE ATOMIC THEORY. 299 
 
 gar Jed as hydrogen salts (hydrogen sulphite and sul- 
 phate), and hydrogen itself considered as a metal 
 owing to its numerous chemical resemblances to that 
 class of bodies. We already know a liquid metal, 
 and there is no a priori objection to the existence of 
 one which is gaseous at ordinary temperatures. On 
 January 10th, 1878, Raoul Pictet, of Geneva, suc- 
 ceeded in liquefying hydrogen under a pressure of G 5 
 atmospheres and at a temperature of -140. When 
 the stopcock was opened a steel-blue coloured, opaque 
 jet of liquid hydrogen rushed out, and particles of 
 solid hydrogen fell with a rattle upon the floor. If 
 this solid hydrogen could be examined it would per- 
 haps agree with ordinary ideas of a metal. 
 
 This table of the atomic weights is based upon the 
 great laws of the atomic theory already discussed. 
 It is founded on the laws of constant, definite, 
 and multiple proportions. Its supporting pillars 
 are the laws of volume, of specific heat, and of 
 isomorphism. 
 
 Take the symbol of any individual element and 
 ask what does it tell us ? is the symbol for the 
 atom of oxygen weighing 15 '9 6 and occupying one 
 volume. Further, as in most cases the density of a 
 gaseous element corresponds with its atomic weight, 
 we learn that the density of oxygen as compared 
 with hydrogen at the same temperature and pressure 
 is about 16. But this is not all; if we express the 
 atomic weight in grams instead of in hydrogen units 
 15*96 grams of oxygen occupy 11 -2 litres, aod in 
 
300 THE ATOMIC THEORY. 
 
 the same way 1 gram of hydrogen occupies 11*2 litres, 
 All this is contained in the symbol 0. 
 
 Take now the symbol of a metal, lead, Pb. This 
 represents an atom of lead weighing 20 6 '4, and if 
 this atomic weight be correct we must assume that 
 this amount of lead in the gaseous state would occupy 
 one volume. We also know that the atomic weight 
 multiplied by the specific heat of lead must give a 
 result approximating to 6 '4, and we can thus calcu- 
 late the approximate specific heat of the metal. 
 
 Let us now pass to the case of compounds. What 
 do we learn from the symbol CO 2 ? It represents 
 one molecule of carbon dioxide containing 1 atom of 
 carbon and 2 atoms of oxygen, that is 12 parts of 
 carbon* and 2 X 16 32 parts of oxygen. This 
 molecule we know will occupy 2 volumes, and con- 
 tains its own volume of oxygen. It occupies the 
 same volume as 2 atoms of hydrogen, weighing 2. 
 Its density compared with hydrogen is therefore 
 
 32 -1-12 
 
 = 22, or half its molecular weight. If the 
 
 molecular weight of carbon dioxide were unknown we 
 could deduce it from its density. The molecular 
 weight of a gaseous compound is always equal to twice 
 its specific gravity compared with hydrogen. If the 
 molecular weight of carbon dioxide be expressed in 
 grams we see that 44 grams of the gas occupy 2 2 '4 
 litres (i.e. 2X11 -2), and contain 2 2 '4 litres of oxygen. 
 
 * In ordinary use decimal places in the atomic weights smaller or 
 greater than '5 may be disregarded. 
 
THE ATOMIC THEORY. 301 
 
 When a substance, as ordinary quick-lime (calcium 
 oxide), CaO, cannot be volatilised, we cannot defi- 
 nitely say that the true molecular formula has been 
 determined. Indeed, it is probable that in the solid 
 state most bodies have complicated molecules consist- 
 ing of aggregations of many molecules of the same 
 substance when gaseous. 
 
 Lastly, let us see what is contained in an ordinary 
 chemical equation, 
 
 2 Ho -f 2 2H 2 0. 
 
 Interpreted, this means that two molecules of hydro- 
 gen, weighing 4 and occupying 4 volumes, combine 
 with one molecule of oxygen, weighing 32 and occu- 
 pying 2 volumes, to form two molecules of water 
 weighing 2 x 18 = 36 and occupying 4 volumes. 
 Also we see that 4 grams of hydrogen, occupying 
 4 X 11-2 = 44-8 litres, combine with 2 X 16 = 32 
 grams of oxygen, occupying 22*4 litres, to form 36 
 grams of water vapour occupying 2 2 '4 litres. 
 
 Other equations representing interchanges may be 
 similarly interpreted, though in many cases the volume 
 relations cannot be so fully given. As a case take 
 the following: 
 
 Bad 2 -f- CuSO 4 = BaSO 4 + CuCi 2 . 
 
 * If we add a solution of barium chloride to one of 
 copper sulphate a precipitate of baric sulphate is 
 obtained, and cupric chloride remains in solution. 
 The chlorine is here transferred from the barium to 
 the copper, and the SO 4 group from the copper to the 
 qarium. By consulting the table of atomic weights 
 
302 THE ATOMIC THEORY. 
 
 the reader may follow out this reaction quantita- 
 tively. 
 
 It will not be difficult now to sec the immense 
 advantage conferred upon chemistry by this concise 
 and accurate method of recording and generalising its 
 facts. The coping-stone has yet, however, to be put 
 in place. This is the idea of valency or atomicity 
 developed by the aid of .a large number of workers, 
 among whom were Dumas, Williamson, Odling, Kekule', 
 and many others. We have seen that a certain school 
 of chemists, disdaining the use of Avogadro's hypo- 
 thesis or Dulong and Pe tit's law, wished to restrict 
 chemical symbols to a representation of the equivalent 
 weights of the elements, or those quantities which were 
 of the same value. When the real atomic weights 
 came to be adopted it was, however, seen that the 
 true atoms of the elements were not really equivalent 
 to each other, they had not all the same capacity for 
 combination. Some elements would combine together 
 only in single atoms, one with one ; they were termed 
 monads, and said to be monovalent. Other elements 
 could combine with two atoms of a monad element, 
 and were thus termed diads, or said to be divalent or 
 diatomic. As an illustration, hydrogen, chlorine, 
 bromine, iodine, fluorine, potassium, sodium, are taken 
 to be monovalent. Their atoms combine together in 
 pairs, one atom of hydrogen with one of chlorine, 
 forming a molecule of hydrochloric acid, and so on. 
 The fact that the molecule of hydrogen consists of 
 two atoms explains why the molecular weight of a 
 
THE ATOMIC THEORY. 303 
 
 compound is equal to tivice its vapour density com- 
 pared with hydrogen. Taking hydrogen, fluorine, 
 chlorine, bromine, iodine, as monovalent, we gain 
 insight into the valency of other elements from a 
 survey of the following compounds : 
 
 HgCl 2 , Hgl 2 ; OH 2 , OC1 2 ; SH? ; SeH? ; ZnCl 2 ; NH 3 ; PCI 3 ; 
 AsH 3 , AsCl 3 , Asl 3 ; CH 4 , CC1* ; SiF 1 ; PF* ; NbCl 3 ; WCP ; WC1 6 . 
 
 Oxygen is here seen to be divalent (OH 2 ), arsenic 
 trivalent (AsH 3 ), and carbon tretravalent (CH 4 ).* The 
 valency of an element was formerly regarded as defi- 
 nitely fixed. As a matter of fact, however, many 
 elements are capable of exhibiting different valencies 
 in different compounds. Thus, phosphorus is triva- 
 lent in the trichloride, PCI 3 , and pentavalent in the 
 pentafluoride, PF 5 . 
 
 Combining power runs parallel to replacing power. 
 An element capable of combining with two monovalent 
 atoms will be capable of replacing two also. Each 
 zinc atom combines with two chlorine atoms in the 
 chloride, ZnCl 2 ; each zinc atom replaces two hydro- 
 gen atoms of sulphuric acid, H 2 S0 4 , in the sulphate, 
 ZnSO 4 . 
 
 Valency or " atomicity " is variable, but the con- 
 ception does not on this account lose its significance. 
 In some elements it is much more strictly marked 
 than in others, and the very variability of it is char- 
 acteristic of certain elements (e.g. tungsten) and there- 
 fore useful. What has yet to be done is to find out 
 
 * The prefixes mono, di, tri, tetra, penta, sex, hepta, octo, must be 
 understood to stand respectively for one, two, three, four, five, six, 
 seven, eight. 
 
304 THE ATOMIC THEORY. . . 
 
 the laws of the variation of valency, to determine the 
 conditions under which it varies. 
 
 While upon the subject of valency a word must be 
 said with regard to the structural formulae of com- 
 pounds, a subject now of the highest importance. 
 Can we tell in what manner the atoms are combined 
 together in the molecule ? Take such a simple case 
 as water, H 2 0. How are the atoms combined together ? 
 In the molecule of free hydrogen, H 2 , we must suppose 
 each hydrogen atom directly united to the other, and, 
 representing direct union by a straight line, our 
 structural formula becomes H H. Similarly the 
 molecule of hydrochloric acid, where monovalent 
 hydrogen is combined with monovalent chlorine, is 
 H Cl, and the most natural conclusion is that the 
 structural formula for the molecule of water, where 
 monovalent hydrogen is combined with divalent oxy- 
 gen, is H H. This formula is entirely supported 
 by chemical facts. The two hydrogen atoms in this 
 molecule being similarly united to the oxygen atom 
 would be expected to play a similar role, and this is 
 actually found to be the case. The compound 
 obtained by replacing one hydrogen atom by potas- 
 sium is always the same substance. But if the two 
 hydrogen atoms were differently combined we should 
 expect them to play different parts, and to give rise 
 to two distinct compounds according as one or the 
 other was replaced by potassium or other metal. 
 Furthermore both atoms may be so replaced, a common 
 property further accentuating their similarity. In 
 
THE ATOMIC THEORY. 305 
 
 the same way either or both atoms may be replaced 
 by an organic radical, as in alcohol C 2 H 5 OH and ether 
 C 2 H 5 .O.C 2 H 5 , and we thus become convinced of the 
 similarity of the two hydrogen atoms in water which 
 we consider as each directly united to the oxygen 
 atom. Other and far more complicated structural 
 formulae are built up by similar reasoning. It is 
 obvious that in building up such formulae considera- 
 tions of valency will often be useful, enabling us to 
 detect which arrangement is in accordance with the 
 prevalent valency of the elements, and therefore which 
 arrangement is most probable. 
 
 It may be asked what purpose do such structural 
 formulae serve ? They enable us, in the first place, to 
 express the internal molecular structure of a com- 
 pound, so that we may see at a glance what are its 
 chief observed chemical properties and relationships, 
 what is the way of obtaining it, and how it may be 
 named ; in the ' second place, they enable us to 
 predict what will be the chemical properties which 
 have not yet been observed. In most cases we may 
 condense these structural formula^ writing together 
 the atoms forming a group or radical which acts as a 
 
 whole. Thus the full structural formula of sulphuric 
 
 O\ /O H 
 
 acid may be written I s I but this may be advan- 
 o/ \0^-H, 
 
 tageously condensed to SO 2 ^^ The use of structural 
 formulae is at present most markedly evident in the 
 region of organic chemistry* but as an inorganic 
 
 * See p. 369. 
 V 
 
306 THE ATOMIC THEORY. 
 
 example of it we may take the formula of pyrophos- 
 phoric acid, H 4 P 2 7 . From this empirical formula 
 we learn very little. We cannot even tell how many 
 hydrogen atoms of the acid are replaceable by a 
 metal, for usually in oxygen acids only those hydrogens 
 occurring as hydroxyl (OH) can be so replaced. But 
 if we expand the formula the properties and relation- 
 ships of the acid appear at once. So expanded the 
 /OH H0\ 
 
 formula becomes o=P OH HO_P=O ; and we see that 
 
 the acid contains four hydroxylic hydrogens, that is 
 four hydrogen atoms replaceable by a metal, and 
 
 further that it is obviously obtained from orthophos- 
 
 /OH 
 phoric acid o=P OH by the withdrawal of water from 
 
 \OH 
 
 two of its molecules thus : 
 
 /OH H0\ /OH R\ 
 
 O=P OH + HO P=0 = H*0 4- O~P OH HO P=O. 
 \OH HO/ \0^ 
 
 Two molecules of phosphoric acid rr water -f- one molecule of 
 pyrophosphoric acid. 
 
 In these formula phosphorus is represented as 
 pentavalent, the union with the divalent oxygen 
 atom being represented by a double line. This is 
 merely a convention, and is not to be taken as 
 implying a stronger union. The two " units of 
 saturation" of the oxygen atom are supposed to be 
 satisfied by the two " units of saturation" of the 
 phosphorus atom.* 
 
 * W. Lossen would do away with these double bonds and any 
 adherence to the idea of distinct valencies for each element. He 
 regards the valency of an element in any particular compound as 
 represented by the number of atoms with which each atom of the 
 
THE ATOMIC THEORY. 
 
 3<>7 
 
 The following table gives the valency of a number 
 of elements : 
 
 Monovalent. 
 
 Divalent. 
 
 Trivalent. 
 
 Tetravalent. 
 
 I 
 Pentavalent. 
 
 Hexava- 
 lent. 
 
 Bromine 
 
 Barium 
 
 Antimony 
 
 Carbon 
 
 Antimony 
 
 Platinum 
 
 Chlorine 
 
 Calcium 
 
 Arsenic 
 
 Chro- 
 
 Arsenic 
 
 Tung- 
 
 Gold 
 
 Carbon 
 
 Bismuth 
 
 mium 
 
 Bismuth 
 
 sten 
 
 Hydrogen 
 
 Chromium 
 
 Gold 
 
 Iron 
 
 Molybde- 
 
 
 Iodine 
 
 Iron 
 
 Nitrogen 
 
 Molybde- 
 
 num 
 
 
 Lithium 
 
 Magnesium 
 
 Phospho- 
 
 num 
 
 Nitrogen 
 
 
 Potassium 
 Silver 
 
 Manganese 
 Molybde- 
 
 rus 
 Potassium 
 
 Platinum 
 Selenium 
 
 Phosphorus 
 Tungsten 
 
 
 Sodium 
 
 num 
 
 Silver 
 
 Silicon 
 
 
 
 Thallium 
 
 Oxygen 
 
 Sodium 
 
 Sulphur 
 
 
 
 
 Platinum 
 
 Thallium 
 
 Tellurium 
 
 
 
 
 Selenium 
 
 
 Tin 
 
 
 
 
 Sulphur 
 
 
 Titanium 
 
 
 
 
 Tellurium 
 
 
 Tungsten 
 
 
 
 
 Tin 
 
 
 Zirconium 
 
 
 
 
 Titanium 
 
 
 
 
 
 
 Tungsten 
 
 
 
 
 
 
 Zinc 
 
 
 
 
 
 
 Zirconium 
 
 
 
 
 
 element is in. that compound combined. Thus he "would regard 
 carbon in carbonic oxide, CO, as monovalent [C-O] and in carbon 
 dioxide, C02, as divalent, being combined with two oxygen atoms 
 
 [0-C-O or O-C-0]. There is direct action and reaction between the 
 carbon atom and one oxygen atom in the first case, and between the 
 carbon atom and two oxygen atoms in the second. Lossen's views 
 are the outcome of an attempt to give greater precision to our 
 conceptions of valency. The desirability of such an attempt cannot 
 be exaggerated, and Lossen's ideas are important and suggestive. It 
 must, however, be remembered that, in the present state of our 
 knowledge the conceptions of valency cannot by any ingenuity be 
 made very precise, and that theories in a state of unperfected evolu- 
 tion must lose their possibilities of development with loss of mobility. 
 ( Ueber die Ycrllieihuuj der d. tome in der Molekel ; Annalcn dsr chonie, 
 cciv. 265.) His reasoning is'.followel and adopted by Pattison Muir 
 in his Principles of Chemistry (1884). 
 
3 o8 THE ATOMIC THEORY. 
 
 The question as to whether the valency of chlorine, 
 bromine, and iodine varies has yet to be solved. 
 Thus, one of the compounds discovered by Prinvault, 
 
 Cl\ / Cl wliprp 
 
 PC1 6 I, may be represented as P i=CP 
 
 Cl/ \ci 
 
 phosphorus is pentavalent and iodine trivalent. 
 Platinum must be supposed to be octovalent in the 
 double chloride (KCl) 2 PtCl 4 , unless WQ allow that 
 this is a molecular as distinguished from an atomic 
 compound. 
 
 The present system of atomic weights has received 
 much confirmation from the views developed by 
 Newlands and Mendelejeff. These chemists found 
 that the elements may be arranged in periods accord- 
 ing to their atomic weight, each period repeating the 
 gradation of properties observed in each of them to 
 accompany the rise of their atomic weights. This 
 generalisation was first made by Newlands, and 
 independently originated by the Kussian chemist, 
 Mendelejeff, who more developed the theory which is 
 known as the periodic law. 
 
 That there is a relation between atomic weight and 
 chemical properties is readily seen by a study of the 
 following table. It gives some of the principal pro- 
 perties of the Nitrogen family of the fifth natural 
 group of the elements. 
 
THE ATOMIC THEORY. 
 
 39 
 
 N=14-01 
 
 P=30-96 
 
 As = 74-9 
 
 Sb = 122 
 
 Bi=210 
 
 Physical State 
 
 
 
 
 
 gas 
 
 M.P.*44-3. 
 
 Sublimes 
 
 M.P. 425 
 
 M.P. 270B. 
 
 
 B.P. 290. 
 
 abt. 180. 
 
 
 white heat. 
 
 Specific gra- 
 
 
 
 
 
 vity of Solid 
 
 
 
 
 
 ? 
 
 1-83 
 
 673 
 
 6-75 
 
 9-82 
 
 Atomic 
 
 
 
 
 
 Volume 
 
 
 
 
 
 ? 
 
 16-92 
 
 13-07 
 
 18-07 
 
 21-38 
 
 Metallic 
 
 
 
 
 
 Properties 
 
 
 
 
 
 umnetallic 
 
 unmetallic 
 
 feebly me- 
 
 decidedly 
 
 very per- 
 
 
 
 tallic 
 
 metallic 
 
 fect metal. 
 
 
 
 brittle 
 
 brittle 
 
 brittle 
 
 brittle. 
 
 Hydrogen 
 
 
 
 
 
 Compounds 
 
 
 
 
 
 NH 3 
 
 PH 3 
 
 AsH 3 
 
 SbH 3 
 
 
 
 NH 3 , am- 
 
 PH 3 ,phos- 
 
 AsH 3 , ar- 
 
 Antimoni- 
 
 BiH 3 is un- 
 
 monia, is a 
 
 phuretted 
 
 seniuretted 
 
 uretted hy- 
 
 known. 
 
 very stable 
 
 hydrogen, is 
 
 hydrogen, is 
 
 drogen de- 
 
 
 body. It is 
 
 stable, but 
 
 readily de- 
 
 composes 
 
 
 only with 
 
 more read- 
 
 composedby 
 
 with great 
 
 
 great diffi- 
 
 ily decom- 
 
 heat. Is al- 
 
 ease. Is only 
 
 
 culty decom- 
 posed by 
 
 posed by the 
 electric 
 
 w a y s o b- 
 tainedmixed 
 
 obtained 
 mixed with 
 
 
 heat. 
 
 spark. 
 
 with hydro- 
 gen- 
 
 96 per cent, 
 of H. 
 
 
 It has 
 
 Less strong- 
 
 No basic 
 
 - 
 
 
 strongly 
 
 ly basic. 
 
 properties. 
 
 
 
 basic pro- 
 
 
 
 
 
 perties. 
 
 
 
 
 
 It burns 
 
 Burns above 
 
 Readily in- 
 
 Very read- 
 
 
 with diffi- 
 
 100. 
 
 flammable. 
 
 ily inflam- 
 
 
 culty. 
 
 
 
 mable. 
 
 
 Oxygen Com- 
 
 
 
 
 
 pounds 
 
 
 
 
 
 N 2 is the 
 
 P 2 3 and 
 
 As 8 3 and 
 
 Sb'O 3 has 
 
 BisO 3 is 
 
 most stable. 
 
 P 2 5 are 
 
 As 2 5 are 
 
 very feeble 
 
 strongly 
 
 NaO 3 is un- 
 stable, as is 
 
 very stable 
 and for well- 
 
 both stable. 
 As^O 3 is 
 
 acid proper- 
 ties. It is 
 
 basic. 
 Bi 2 5 is 
 
 N*0 5 . 
 
 defined phos- 
 
 less acid than 
 
 also basic. 
 
 very u n- 
 
 Both N 2 3 
 
 phorous and 
 
 P 2 3 but 
 
 Sb 2 5 is 
 
 stable and 
 
 and N*0 5 
 
 phosphoric 
 
 As*0 5 is 
 
 somewhat 
 
 only very 
 
 have strong- 
 
 acids. 
 
 strongly 
 
 more strong- 
 
 feebly acid. 
 
 ly acid pro- 
 
 
 acid. 
 
 ly acid. 
 
 
 preties. 
 
 
 
 
 
 * M.P. = melting point ; B.P. = boiling point. 
 
3io 77/# ATOMIC THEORY, 
 
 In the above table we see a very well-marked 
 gradation of properties as the atomic weights of the 
 elements rise. Beginning with unmetallic nitrogen, 
 we end with perfectly metallic bismuth ; and begin- 
 ning with very stable and strongly basic ammonia, 
 we end with very unstable and non-basic antimoni- 
 uretted hydrogen, and finally with the unknown 
 bismuthamine. There is also much similarity among 
 the different members of the family, as is shown by 
 the formation of analogous hydrides and oxides. 
 
 The following is Mendelejeff's table. The vertical 
 column (Roman numerals) constitutes a group, each 
 group corresponding, for the most part, with a 
 natural family. The horizontal column (Arabic 
 numerals) constitutes a series. In the groups the 
 members present striking similarities, in the series 
 they present still more striking gradations. The 
 properties of any member of a series may be taken 
 as standing between those of the members imme- 
 diately preceding and succeeding it. 
 
THE ATOMIC THEORY. 
 
 rt 
 
 fjl 
 
 .... 10 VQ ^ 
 
 d 
 
 6 
 
 1 
 
 1 1 
 
 P4 
 
 " 
 
 , 
 
 l 
 
 
 - OD OJ O r-i 
 
3i2 THE ATOMIC THEORY. 
 
 In the horizontal series of the elements thus 
 arranged we observe periodical gradations of pro- 
 perties. The periodicity may be shown by reference 
 to the densities of third series of elements which 
 increase towards the centre of the series and diminish 
 towards the ends. The atomic volume, on the con- 
 trary, that is, the specific gravity divided by atomic 
 weight, diminishes towards the centre and increases 
 towards the ends. 
 
 Xa Mg Al Si P S Cl 
 
 Densities .... 0-97 1'75 2-67 2'42 1-84 2'06 1-38 
 Atomic Volumes . . 24 14 10 11 16 16 27 
 
 The capacity of combination with monovalent ele- 
 ments or the valency also undergoes modification. 
 Thus, taking the first two series we have : 
 
 LiCl BeCi 3 BOP CC1 4 ; CH 4 NIP OH 2 FH 
 NaCl MgCP A1CP SiCl 4 ; SiH* PH* SH 3 C1H 
 
 What we now observe is that the second series 
 repeats the changes observed in the first, so that the 
 elements in the vertical groups are closely connected 
 in their properties. 
 
 When we come to the fourth series a certain change 
 in this arrangement, so far as physical properties are 
 concerned, is observed. From potassium the specific 
 gravity increases steadily up to nickel and decreases 
 again down to rubidium, the oscillation in this case 
 including two groups. The atomic volume, on the 
 contrary, decreases down to nickel and rises again up 
 to rubidium. If we arrange the elements upon a 
 curve which rises and falls according to increase and 
 
THE ATOMIC THEORY. 313 
 
 decrease of atomic volume, as was done by Lothar 
 Meyer, lithium, sodium, potassium, and rubidium 
 occupy summits on this curve. The properties of 
 the elements are found to be characteristically different 
 according as they occupy portions on the descending, 
 ascending, or lowest portions of these curves. 
 
 We cannot examine more closely here into the 
 interesting relations between properties and combin- 
 ing weights. But the most interesting point of all 
 still remains to be touched upon. In a first glance 
 at MendelejefF's table we cannot but be struck by the 
 fact that gaps occur in it in which no element is 
 placed. These places have yet to be filled. They 
 represent the elements remaining to be discovered 
 in the future. How far the gaps may be filled it is 
 impossible to say, but that many of the absent ele- 
 ments will yet be found we cannot doubt. By means 
 of this table Mendelejeff has been able to prophesy 
 the discovery of unknown elements, and even to 
 describe with exactness their chief properties. In 
 three remarkable cases his prophesies have already 
 been fulfilled. Before 1875 the place now filled by 
 gallium in the fifth series was vacant. Mendelejeff 
 suggested that the place belonged to a hypothetical 
 element, eka-aluminium, the properties of which he 
 proceeded to define. In the year 1875 Lecoq de Bois- 
 baudran announced the discovery of a new element 
 by means of spectrum analysis, termed by him gallium. 
 On comparison of their properties it became clear 
 that Lecoq de Boisbaudran's gallium and Mendelej eft's 
 
THE ATOMIC THEORY. 
 
 eka-aluminium were one and the same element. The 
 following is the comparison of the predicted and 
 actual properties : 
 
 [Eka-aluminium. Gallium. 
 
 Readily obtained by reduction. 
 
 Melting point low. Sp. gr. 
 
 5-9. 
 Not acted on by air. 
 
 Will decompose water at red 
 heat ; slowly attacked by acids 
 or alkalis. 
 
 Will form a potassium alum. 
 Oxide, EFO 3 . Chloride, EFC1 6 . 
 Atomic weight about 69. 
 
 Readily obtained by electrolysing 
 
 alkaline solutions. 
 M.P. = 30-15. Sp. gr. = 5-93. 
 
 Non-volatile and but superficially 
 acted on by air at bright red 
 heat. 
 
 Decomposes water at high tem- 
 peratures. Soluble in hot hy- 
 drochloric acid, scarcely at- 
 tacked by cold nitric acid ; 
 soluble in caustic potash. 
 
 Forms a well-defined alum. 
 
 Chloride, Ga 2 Cl 6 . Oxide, Ga 2 3 . 
 
 Atomic weight 69 '7. 
 
 So, too, the metal scandium discovered by Nilson 
 in 1870 is identical with the hypothetical eka-boron 
 of Mendelejeff with atomic weight about 44. Lastly, 
 the germanium of Winkler (1885) is identical with 
 the eka-silicon of Mendelejeff with atomic weight 72. 
 
 The greatness of a generalisation enabling us to 
 predict what elements will be discovered in the future, 
 and what their chief properties will be, as well as to 
 systematise the varying properties of the elements 
 now known, needs no discussion to make its impor- 
 tance evident. Since Mendelejeff 's discovery chemistry 
 has seen no greater generalisation. 
 
DAVY. 
 
CHAPTER XVII 
 
 DAVY AND FARADAY. 
 
 ;HE foundations of the science have now been 
 laid, and we must next glance at what the 
 workers of to-day have built upon those 
 foundations. 
 
 Sir Humphry Davy's work comes next 
 in order. His name has become almost a 
 household word, and there are very few who have 
 never heard of Davy's safety lamp. Davy* came of 
 an old but not wealthy family. After the death of 
 his father he was apprenticed to a trade, and was 
 soon regarded as rather an idle fellow. He used to 
 be continually occasioning explosions and other dis- 
 turbing phenomena in the house of the gentleman 
 
 * Dr. J. A. Paris: Life of Sir Humphry Davy (1831). Dr. J. 
 Davy : Works of Sir H. Davy (1839), Born at Penzance in Cornwall, 
 31778. Died at Geneva, 1829. 
 
3 1 8 DAVY AND FARAD A Y. 
 
 who helped him after his father's death, and who had 
 not quite the keenness of sight necessary to see what 
 the boy might become. But his talents were not to 
 be cheated of their destiny, and in good time he be- 
 came the great original worker, immortal as the dis- 
 coverer of the alkali metals and cf the safety lamp, 
 and the great lecturer of whom Coleridge said, " I 
 attend Davy's lectures to increase my stock of meta- 
 phors." 
 
 In 1799 Davy discovered the anesthetic properties 
 of nitrous oxide (N 2 0). This gas is usually prepared 
 by decomposing ammonium nitrate by heat. 
 
 (NH 4 )N0 3 = N 2 -f- 2H 2 0. 
 
 It is a colourless gas which, like oxygen, supports 
 ordinary combustion. A red-hot splinter of wood 
 rekindles when brought into the gas just as it would 
 do in oxygen. In these reactions the nitrogen of the 
 gas is set free ; 4N 2 + C 2 = 2C0 2 + 4N 2 .* But 
 the most remarkable property of nitrous oxide is its 
 effect upon animal life. If nitrous oxide be inhaled 
 by the human subject the first effects are singing in 
 the ears. Insensibility then follows and, if the gas 
 be persistently inhaled, death through suffocation. 
 If air be allowed to enter the lungs when the phase 
 of insensibility has set in, the effects pass off and no 
 evil result follows. A certain amount of excitement 
 
 * The reason for not halving this and other equations is that so 
 manipulated they would contain expressions for single atoms (as, in 
 this instance, C), which have already been defined as not existing 
 separately. 
 
320 DA VY AND FARADAY. 
 
 is sometimes observed after inhalation, whence has 
 arisen the popular name of laughing gas. 
 
 The great discovery of the compound nature of the 
 alkalis "was made by Davy in 1808."* His method 
 was to place a small piece of pure potash "upon a disc 
 of platinum, connecting this with the negative pole of 
 a galvanic battery, while the upper surface was joined 
 by a platinum wire to the positive pole. Small 
 lustrous metallic globules collected on the lower sur- 
 face of the potash, some of which burnt off while 
 others became tarnished, and so preserved from further 
 action of the air. The globules were metallic potas- 
 sium. At the same time that the metal was being 
 liberated a violent effervescence, due to liberation of 
 gases from the caustic potash, occurred at the positive 
 pole. Davy was unable to obtain the metal in large 
 quantities but he succeeded in demonstrating its chief 
 properties. It rapidly absorbs oxygen, t being con- 
 verted into the oxide (K 2 0), and the oxide is extremely 
 hygroscopic, and when combined with water forms, as 
 Davy showed, ordinary caustic potash. Represented 
 by modern equations these reactions become : 
 2K 3 + O 3 = 2K 2 0. K?0 + H 2 = 2KOH. 
 
 Davy found that when thrown upon water metallic 
 potassium swam upon its surface, exciting a violent 
 reaction, and dissolved with formation of caustic potash. 
 
 * "On some new phenomena of chemical changes produced by 
 electricity, particularly the decomposition of the fixed alkalies," c. 
 Philosophical Transactions of the Royal Society (1808). 
 
 f In perfectly dry and pure air potassium, at the ordinary tempe- 
 rature, remains unchanged. 
 
DAVY AND FARADAY. 321 
 
 In this reaction he found that hydrogen was evolved 
 and, at the high temperature produced, burst into 
 flame. 
 
 K 2 + 2H 2 = 2KHO + H 2 . 
 
 The compounds of sodium had been of importance 
 earlier than those of potash. We have already, in 
 the second chapter, seen that sodium carbonate was 
 known to the ancients. The " nitre " mentioned in 
 Proverbs xxv. 20,* is native carbonate of soda, and is 
 given as a translation of the Hebrew nether, the same 
 substance being known as v^rpov in Greek, and nitrum 
 in Latin. 
 
 The discovery of metallic sodium is announced by 
 Davy in the same memoir, and it was obtained by him 
 by exactly the same process. Davy observed the for- 
 mation of the oxide (Na 2 0), and the action of the metal 
 upon water, and further stated erroneously that sodium 
 took fire in chlorine gas. 
 
 Some of the knowledge relating to these elements 
 obtained since Davy's discovery may here be briefly 
 sketched. Gay-Lussac t and Thenard heated iron 
 turnings in a gun-barrel, and allowed melted caustic 
 potash to flow slowly on to the hot iron. The iron 
 took the oxygen of the hydrate while hydrogen gas 
 was evolved, and metallic potassium distilled over and 
 was collected in a bent copper tube. The method at 
 present in use was proposed by Curadau and has been 
 
 * " As he that taketh away a garment in cold weather, and as vinegar 
 upon nitre, so is he that singeth songs to an heavy heart." 
 t Louis Joseph Gay-Lussac (1778-1850). 
 
 X 
 
322 DAVY AND FARADAY. 
 
 improved by Brunner, Wohler, and especially by 
 Donny and Mareska. It consists in the reduction, 
 at a white heat, of potassium carbonate by carbon : 
 
 K 2 C0 3 4- 20 = K 3 -f 3CO. 
 
 The ignition of crude tartar (hydrogen potassium 
 tartrate) provides us with an intimate mixture of 
 charcoal and potassium carbonate. The mixture is 
 heated in iron cylinders coated with clay, and the 
 metal collected in the flat iron condensers suggested 
 by Donny and Mareska. The rapid cooling of the 
 vapour insured by these flat and shallow condensers 
 prevents the formation of the explosive compound, 
 K 6 C 6 6 5 produced by the union of the potassium va- 
 pour with carbon monoxide (CO). 
 
 The specific gravity of potassium at 13C. com- 
 pared with water is 0'875 (Baumhauer). The only 
 metal lighter than potassium unless hydrogen be 
 included is lithium. At the ordinary temperature 
 the metal is soft and may easily be cut with a knife. 
 The fresh surfaces rapidly oxidise and the metal 
 should be kept under naphtha. Potassium melts at 
 6 2 4 5 (Bunsen). It boils at a red heat* and the 
 vapour density suggests a molecule composed of two 
 atoms. 
 
 One or two of its compounds may be mentioned. 
 Potassium hydrate or caustic potash, KOH, may be 
 obtained pure by the action of the metal on water, 
 
 * E. P. Perman {Journal of the Chemical Society, vol. lv., p. 326, 
 (1889)] lias quite recently determined the boiling- points of potassium 
 and sodium. That of potassium he finds to be about 667 C., that of 
 eoJium 742" C. 
 
DA VY AND FAR AD A Y. 323 
 
 It is usually prepared by decomposing potassium 
 carbonate with slaked lime, Ca(OH) 2 (calcium hy- 
 drate). 
 
 Ca(OH) 3 -f K 2 C0 3 = 2KOH + CaCO 3 . 
 
 If the solution be too concentrated the reverse 
 action sets in and potassium carbonate is produced. 
 This is an interesting example of the fact that 
 chemical reactions depend upon other conditions 
 besides that of the simple affinity of one element for 
 another. 
 
 Potassium hydrate is a hard, Avhite, brittle sub- 
 stance. It is used for absorbing carbonic acid in 
 analysis, for surgical purposes, and in the manufacture 
 of soft soap. The last-named article consists of the 
 potassium salts of organic acids. 
 
 Potassium chloride is found in the Stassfurt potash 
 beds, and is used in artificial manures, while the 
 bromide and iodide are extensively used in medicine. 
 The tri-iodide KI 3 is a somewhat inexplicable com- 
 pound on the ordinary ideas of valency.* Oxygen 
 is usually prepared by heating potassium chlorate, 
 KC10 3 . It decomposes, leaving a residue of chlo- 
 ride. 
 
 2KC10 3 = 2KC1 + 30 3 . 
 
 The salt is used in the manufacture of lucifer 
 matches, for pyrotechnic purposes, and as a medicine. 
 
 * It may, however, be regarded as a molecular compound of KI 
 with P, but the usefulness of any distinction between molecular and 
 atomic compounds is at present a moot point. 
 
3 2 4 DAVY AND FARAD A T. 
 
 Potassium nitrato (saltpetre), KNO 3 , occurs as an 
 efflorescence on the soil in various hot countries. 
 It is used in medicine, but most largely in the manu- 
 facture of gunpowder. Gunpowder consists of a mix- 
 ture of charcoal, sulphur, and nitre, the proportion 
 being, approximately, 75 per cent, of saltpetre (nitre), 
 15 per cent, of charcoal, and 10 per cent, of sulphur, 
 The simplest expression for the reaction occurring when 
 gunpowder is fired js : * 
 
 2KNO 3 + S -f 30 = K 2 S + N 2 + 3C0 3 . 
 Nitre + Sulphur + carbon = P$-tam + nitrogen + d ^ 
 
 This simple expression cannot, however, be taken 
 as accurately representing what occurs. The first 
 thorough investigation of the decompositions taking 
 place was made by Bunsen and Schischkoff. Abel and 
 Noble have, more recently (1874), published an ela- 
 borate series of results on the same subject. Among 
 other results they find that the tension produced on 
 firing powder in a space which it completely fills 
 amounts to 6,400 atmospheres, or 42 tons per square 
 inch. The temperature of the] explosion is about 
 2,200 C. 
 
 Potassium carbonate is obtained by extracting with 
 water, or lixiviating as it is termed, the ashes of 
 wood. The name potashes arose from this extraction 
 being made in pots. By dissolving it in appropriate 
 
 * For the sake of simplicity many equations may be written with 
 single atoms. But the reader must not take this as implying the 
 separate existence of single atoms, 
 
DAVY AND FARADAY. 325 
 
 acids the other potassium salts may be formed. It> 
 is used in the manufacture of soft soap. 
 
 Sodium was obtained by Gay-Lussac and The'nard 
 by heating caustic soda with metallic iron. At the 
 present time it is manufactured in considerable quan- 
 tities by heating to whiteness a mixture of caustic 
 soda, slack, or small coal, and chalk. Sodium is of 
 more commercial importance than potassium, being 
 used in the manufacture of aluminium. When me- 
 tallic sodium is thrown into water it evolves hydro- 
 gen, but the heat is insufficient to ignite the gas. 
 Caustic soda may be formed similarly to the potas- 
 sium compound. 
 
 Sodium chloride, or common salt, is an article of 
 great commercial importance. The total salt pro- 
 duced in England amounted in 187G to 1,676,000 
 tons, of which 1,500,000 tons were obtained by 
 evaporating brine and 176,000 were raised as rock- 
 salt. 
 
 Sodium carbonate is an article of great commercial 
 importance. It is obtained from common salt by first 
 converting into sulphate by means of sulphuric acid 
 and then acting upon this with coal and chalk. Na 2 S0 4 
 + 40= Na 2 S + 4CO : Na 2 S = +CaC0 3 = Na 2 C0 3 
 -f CaS. This is Leblanc's process (1 794). To him we 
 owe cheap soap and cheap glass. He died in a French 
 asylum for paupers. The ammonia soda process con- 
 sists in passing carbonic acid into an ammoniacal solu- 
 tion of common salt. 
 
 The importance of Davy's discovery becomes very 
 
3-26 DAVY AND FARADAY. 
 
 apparent when we thus see the extensive use to which 
 the compounds of these nietals are put. From these 
 researches Davy concludes : " Oxygen then may be 
 considered as existing in, and as forming an element 
 in all the true alkalies ; and the principle of acidity 
 of the French nomenclature might now likewise be 
 called the principle of alkalescence."* From analogy 
 alone Davy thinks it reasonable to expect that the 
 alkaline earths (lime, baryta, &c.,) are similarly com- 
 posed of metallic bases united to oxygen. " I have 
 tried some experiments upon barytes and strontites, 
 and they go far towards proving that this must be 
 the case." 
 
 His first attempts to electrolyse barytaf (BaO), 
 i.e. to analyse it by electricity, were not very success- 
 ful. Berzelius and Pontin obtained the metal by 
 electrolysis in presence of mercury, whereby an 
 amalgam of the metal with mercury was formed. 
 The amalgam was then heated in absence of air 
 when the mercury distilled off. Berzelius and 
 Pontin communicated their results to Davy, who 
 repeated their experiments and electrolysed baryta, 
 barium chloride (Bad 2 ) and other barium salts. 
 
 * Phil Trans. (1808), 
 
 f The compound of barium first observed was the natural sulphate, 
 heavy spar (BaSO 4 ). It was examined in 1G02 by a Bolognese shoe- 
 maker, V. Casciorolus. For a long time it baffled analysis. The 
 presence of a new earth was detected by Scheele in an ore of mangan- 
 ese and Gahn recognised it ae the basis of heavy-spar. Guyton de 
 Morveau, a disciple of Lavoisier, proposed in 1779 to name this earth 
 barote (/3apvs, heavy) and this name was altered by Lavoisier to 
 baryta. 
 
DAVY AND FARADAY. 327 
 
 The metal is best obtained by electrolysis of the 
 fused chloride. 
 
 Calcium was obtained by Davy and by Berzelius and 
 Pontin by electrolysis of calcium chloride. Matthies- 
 sen first prepared it as a coherent metallic mass in 
 1856. Calcium plays an important part in nature. 
 The carbonate occurs in enormous quantities in its 
 various forms of calc-spar, arragonite, chalk, marble, 
 limestone, coral, &c., and united with magnesium 
 carbonate as magnesium limestone or dolomite. 
 Quicklime is the oxide, CaO ; slaked lime the hy- 
 droxide, Ca(OH) 2 . Bleaching powder is formed by 
 the action of chlorine on dry slaked lime. Calcium 
 sulphate in different states is known as gypsum, 
 alabaster, and plaster of Paris. 
 
 Strontium was first obtained by Davy in the 
 same year (1808) by electrolysis of the moistened 
 hydroxide and of the chloride. It is a yellow metal. 
 It occurs in nature as the sulphate (SrSO 4 , celes- 
 tine) isomorphous with heavy-spar and the carbo- 
 nate (SrCO 3 , strontianite isomorphous) with arrago- 
 nite. 
 
 The discovery of metallic magnesium was an- 
 nounced by Davy in the same paper. It was first 
 obtained as a coherent metal by Bussy. The method 
 proposed by Caron and Deville for its manufacture 
 is now used on the large scale. The method consists 
 essentially in decomposing the anhydrous chloride by 
 metallic sodium, Magnesium is a silver-white metal. 
 The ribbon, in which form it is usually seen, burns 
 
$23 DAV AND FARADAY. 
 
 when lit by a flame with a light of dazzling brilliancy. 
 It has been observed at sea at a distance of twenty- 
 eight miles. Bunsen and Roscoe have shown that 
 this light is rich in chemically active rays, and have 
 determined its chemical value compared with the 
 light of the sun. 
 
 DAVY S SAFETY LAMP. 
 
 Davy attempted unsuccessfully to decompose alu- 
 mina (APO 3 ), silica (SiO 2 ) and zirconia (ZrO 2 ). In 
 1809 he published his important paper on chlorine.* 
 This gas was not then recognised to be an element, 
 
 * Phil. Trans. (1809): "Researches on the oxymurlatic acid," &c. 
 
DA VY AND FARADAY. 329 
 
 but was known as oxymuriatic acid, and supposed 
 to contain oxygen. Davy heated the gas with carbon, 
 and obtaining no action was led to doubt the pre- 
 sence of oxygen in it. Tin he found to absorb 
 the gas but the body so formed did not contain 
 oxygen. By a number of negative proofs of this kind 
 Davy established the elementary nature of chlorine.* 
 
 In 1815 Davy invented his safety -lamp, and it is 
 to his credit that he took out no patent for it, 
 preferring to make the discovery a free gift. The 
 principle of the lamp depends upon the fact that 
 flame will not pass through fine wire gauze, owing to 
 the rapid conduction of the heat away from the 
 point of contact and the consequent cooling down the 
 gases below their ignition point. 
 
 The work of Davy has enriched his science with a 
 number of brilliant discoveries, but the best of them 
 all, as he himself said, was his discovery of Faraday. 
 
 Michael Faraday Avas born in Newington Butts on 
 September 22nd, 1791. t His father was a journey- 
 man blacksmith, and the family afterwards lived in 
 Jacob's Well Mews, near Manchester Square. Fara- 
 day himself became errand boy at a bookseller's shop 
 and \vas afterwards taken on as apprentice. During 
 
 * The following 1 passage in this paper is worth quoting : * ' The 
 vivid combustion of bodies in oxymuriatic acid gas at first view 
 appears a reason why oxygene should be admitted in it, but heat and 
 light are merely results of the intense agency of combination." Cf t 
 HooJcc. 
 
 t Michael Faraday : a Biography. By J. H. Gladstone (1872). See 
 also Tyndall's Faraday as a Discoverer (1870). 
 
330 DA Vr AND FARAD A Y. 
 
 his apprenticeship he was sometimes engaged in 
 book-binding, and books bound by him are now 
 preserved at the Royal Institution, The first chemical 
 lectures he attended were paid for by his brother 
 Robert, who was thus doing more than he could have 
 been conscious of in aid of science. From his shop 
 Faraday was taken to hear Davy lecture at the Royal 
 Institution. Afterwards he was introduced to Davy, 
 and when the latter was injured in the eyes by his 
 investigations of nitrogen chloride he became for a 
 short time his amanuensis. " My desire," says 
 Faraday, " to escape from trade, which I thought 
 vicious and selfish, and to enter into the service of 
 a science which I imagined made its pursuers amia- 
 ble and liberal, induced me at last to take the bold 
 step of writing to Sir H. Davy expressing my wishes." 
 Davy soon after made him his laboratory assistant, 
 but not till he had earnestly tried to dissuade him 
 from following a scientific career. It would mean 
 poverty, ingratitude, and unrewarded toil. But 
 Faraday was not to be dissuaded. 
 
 Faraday married in 1821, though from his posi- 
 tion at the Royal Institution he obtained up to 1833 
 besides a house, coal and candles, only 100 per 
 annum. He had no children. If he had a family 
 he would probably have been deprived of much of 
 his work, for it did not pay. He presents us with 
 the spectacle of a man giving up all for his devotion 
 to pure, as distinguished from applied, science. In 
 his earlier years he undertook, commercial analyses 
 
FARADAY. 
 
DA VY AND FARAD A F. 3 3 3 
 
 which paid him far better, and in 1830 he made 
 XI, 000 by these means, and in 1831 considerably 
 more. But his researches in pure science multiplied 
 around him, and he at last found that he must 
 choose between making money and adding to know- 
 ledge. He did not hesitate in his choice, he did not 
 try to combine both. He deliberately chose to 
 abandon treasure for truth. In the following year, 
 (1832), his total income amounted to 155 Os. 
 Ever after it was even less than that. 
 
 Faraday gave up all in order to follow the 
 particular work that he felt he was meant to do. 
 His mind was essentially cast for that of an explorer 
 into the undiscovered countries of knowledge, and he 
 determined to be only what he was. In pursuit of 
 this he refused all other invitations. Thus he was 
 offered the professorship of chemistry at the London 
 University (now University College), but tke offer 
 was declined. 
 
 The picture drawn of him by Dr. Gladstone, work- 
 ing quietly in his laboratory in the morning with 
 his little niece beside him, never forgetting to please 
 her by conversation or amuse her with some pretty 
 experiment, and all the while engaged upon work of 
 the gravest moment, is charming indeed. If some 
 one called in and his work was interrupted he was 
 never put out or otherwise than pleased to see his 
 visitor. At half-past two he dined, and the after- 
 noon was spent in writing to friends, of whom he had 
 many. Then perhaps he would attend a council 
 
3 3 1 DA VY AND FARAD A Y. 
 
 meeting, come back for a short time to his laboratory 
 and then spend the evening very happily at home, 
 probably reading aloud to his wife or some intimate 
 friends. 
 
 In religion Faraday belonged to the small sect of 
 the Sandemanians, and at their meetings on Sunday 
 he sometimes preached. As he approached his 
 seventieth year the strain of his work became too 
 great for him, and in 1861 he resigned part of his 
 duties at the Koyal Institution. His energies slowly 
 waned, and on August 25th, 1867 he passed away. 
 
 Faraday's character took the hearts of all who 
 knew him with joy. He was so simple and gentle 
 and self-less, and yet beneath his gentleness lay 
 hidden a cavern of volcanic fire, ready to blaze out 
 at sight of injustice or cruelty. He had a fund of 
 playful, boyish humour which lent added charm to 
 his presence. Thus Gladstone relates how Faraday 
 came down unexpectedly to visit him at Hastings 
 and knocked at the door while he was dressing. 
 " Who's there ? " cried Gladstone, but the only reply 
 Faraday would volunteer Avas " Guess," and the 
 discomfited chemist was forced to go through a 
 long list of names containing all but the right one 
 before Faraday would reveal himself, His kindliness 
 is exemplified by the fact that he would listen with 
 great interest to the chemical lectures of a boy friend 
 of his, aged 13, and applauded the experiments 
 heartily. 
 
 As a lecturer Faraday's equal could with difficulty 
 
DA VY AND FARADAY. 335 
 
 be found. He contrived by his own earnestness and 
 enthusiasm to bring out new beauties in the most 
 commonplace facts. In his enthusiasm over facts of 
 singular beauty he forgot everything except his own 
 delight in the knowledge. He was raised into a 
 state almost of ecstasy, by force of which lie and his 
 audience were alike carried away. 
 
 The most prominent results achieved by Faraday 
 were electrical, and of these his demonstrations of 
 the theory of electrical induction are the chief. But 
 we cannot discuss this part of his work here, and 
 must pass on to consider his chemical discoveries, 
 also of great importance. In conjunction with Davy, 
 Faraday experimented upon the very dangerous com- 
 pound chloride of nitrogen. This body is formed by 
 the action of chlorine upon a solution of sal-ammoniac. 
 It collects as a yellowish oil, the composition of which 
 has only recently been determined.* 
 
 Faraday was the first to effect the union between 
 carbon and chlorine. Ethylene, or olefiant gas 
 (C 2 H 4 ), is obtained by treating alcohol with sul- 
 
 * This substance was discovered by Dulong in 1811, who continued 
 his work upon it after it had caused him the loss of three fingers and 
 one eye. During Faraday's and Davy's investigation it repeatedly 
 exploded without warning, and sometimes with such violence as to 
 stun the operators. Dr. Gattermann, of Gottingen, has recently 
 (1888) continued the investigation of this subsiance. He finds that it 
 consists of the trichloride (NCI 3 ) together with other chlorides. By 
 allowing the chlorine to act for some time, washing the resulting oil 
 free of sal-ammoniac, and again chlorinating, he has obtained per- 
 fectly pure NCI 3 . He finds that light is a powerful cause of the 
 explosions of this substance. Dr. Gattermann unfortunately states 
 that his eyes and nerves have been so affected as to oblige him to tem- 
 porarily abandon work on the subject. 
 
33b DA VY AND FARADAY. 
 
 phuric acid. This gas treated with great excess of 
 chlorine in presence of light gave rise to a white 
 solid termed by Faraday perchloride of carbon. 
 Expressed according to our present equations this 
 reaction becomes : C 2 H 4 + 5C1 2 = C 2 C1 6 + 4HC1. 
 When this body was passed through a red-hot tube 
 Faraday found that it lost chlorine and formed pro- 
 tochloride of carbon. The reaction may be expressed 
 thus : * C 2 C1 6 = C 2 C1 4 + Cl 2 . The chloride so 
 obtained is a liquid. Faraday also combined iodine 
 with carbon by acting with iodine upon ethylene 
 (carburetted hydrogen) in sunlight. Ethylene dio- 
 elide, (C 2 H 4 I 2 ) is thus obtained. 
 
 In 1823 Faraday analysed the hydrate of chlorine 
 (Cl 2 + 10H 2 0) obtained by the action of ice-cold 
 water upon chlorine, and by use of this compound he 
 liquefied chlorine gas. 
 
 In 1825, Faraday discovered benzene in the oil 
 obtained from portable gas prepared by Taylor in 
 1815 by strongly heating fats. His analysis of the 
 new liquid led him to name it bicarburet of hydro- 
 gen, its empirical formula being taken as C 2 H where 
 C = 6. Adopting modern weights (C = 12) this 
 becomes CH, The vapour density of the body is, 
 however, six times what this formula would allow and 
 furthermore the hydrogen of the compound can be 
 replaced by chlorine in six stages, so that it must be 
 supposed to contain at least six atoms of hydrogen 
 
 * These expressions were, of course, not made use of by Faraday. 
 They are the interpretations now given of his facts. 
 
DAVY AND FARADAY. 337 
 
 in the molecule. Taking this evidence into account 
 the formula becomes C 6 H 6 . At the present day this 
 hydrocarbon is obtained by the distillation of coal- 
 tar. The numberless multitude of the aromatic 
 compounds (as they are called) are all derivatives 
 of this body. The department of aromatic chemistry 
 now far exceeds in area the other combined provinces 
 of the science. It is difficult to realise that in 1821 
 at the publication of the second edition of Brande's 
 Manual of Chemistry, benzene was yet undiscovered. 
 In the same liquid Faraday obtained a new gaseous 
 hydrocarbon butylene (C 4 H 8 ). 
 
 Some of Faraday's chief chemical work was con- 
 cerned with condensation of the gases. His experi- 
 ments established the high probability that the ordi- 
 nary gases were only liquids with a very low boiling 
 point. To appreciate this we may recall that liquids 
 tend to give off vapour at all temperatures. If a 
 little water be introduced into a barometer tube with 
 the mercury standing at 760 mm. and at the ordinary 
 temperature the column is instantly depressed a cer- 
 tain distance. At a certain temperature this depres- 
 sion will amount to half the barometric height. 
 The vapour tension of the water now amounts to 
 half an atmosphere, or 380 mm. of mercury. If the 
 temperature of the water in the tube be at last raised 
 to its boiling point (100 C.) the mercury will be 
 driven down to the same level as that outside the 
 tube. The vapour tension now amounts to one 
 atmosphere. In other words a liquid boils when its 
 
 Y 
 
338 DAVY AND FARADAY. 
 
 vapour tension is equal to the superincumbent atmos- 
 pheric pressure. If the pressure upon it be increased 
 its boiling point will be raised. This at once 
 suggests a method for liquefying the gases by 
 pressure. Supposing them to be liquids with low 
 boiling points their boiling points will thus be raised 
 and as the pressure increases will ultimately rise 
 above the temperature at which the experiment is 
 being performed. The gas will then condense to a 
 liquid. 
 
 The subject was fully investigated by Faraday,* 
 who succeeded in liquefying a number of gases, t 
 By sealing up chlorine hydrate in a strong bent glass 
 tube, warming the compound, and placing the other 
 limb of the tube in a freezing mixture, Faraday 
 obtained liquid chlorine which condensed in the cold 
 limb. The tubes used for these purposes must be 
 prepared with care and, properly 
 made, withstand an internal pres- 
 sure of many tons per square inch. 
 The application by these means of 
 FARADAY'S TUBE. pressure and cold succeeded with a 
 number of gases. Thus, in the case 
 of sulphuretted hydrogen (hydrogen sulphide, H 2 S), 
 Faraday brought the material, iron sulphide (FeS) 
 and sulphuric acid, J into the closed limb of the tube, 
 the former being separated from the latter by plati- 
 
 * Phil. Trans. 1823, p. 160. Ibid, 1823, p. 189. 
 
 f The first gas liquefied was chlorine by Northmore in 1806. 
 
 J H a SO* 4- FeS = IPS -f- FeSO*. 
 
\ DAVY AND FARADAY. 339 
 
 num foil. The open end of the tube was then 
 sealed and the sulphide shaken down into the 
 acid. The gas then condensed as the pressure 
 increased. The gases liquefied by Faraday include : 
 sulphur dioxide (SO 2 ), carbon dioxide (CO 2 ), nitrous 
 oxide (N 2 0), cyanogen (CN), ammonia (NH 3 ), hydro- 
 chloric acid (HC1), hydrobromic acid (HBr), and 
 hydriodic acid (HI), besides those already mentioned. 
 Other gases, the so-called permanent gases, resisted 
 his attempts. He endeavoured in vain to liquefy 
 hydrogen, oxygen, nitrogen, nitric oxide, marsh-gas, 
 and carbon monoxide. Natterer and Andrews 
 though employing very high pressures both failed 
 in the same attempts, but in 1877 Cailletet and 
 Pictet * succeeded in liquefying oxygen, carbon 
 monoxide, and hydrogen. Oxygen liquefies under 
 a pressure of 475 atmospheres at - 140 C., hydrogen 
 at 650 atmospheres. Cailletet liquefied ethylene 
 (C 2 H 4 ), acetylene (C 2 H 2 ), nitric oxide (NO), and 
 marsh gas (CH 4 ). 
 
 Before concluding, mention must be made of Fara- 
 day's important discovery of the electro-chemical 
 equivalents of the elements. The same strength of 
 current, he found, would in equal times liberate 
 equivalent quantities of the elements. Thus if a 
 current passing for a given time through a solution 
 of copper sulphate liberated 63 grains of copper, it 
 would, under similar conditions, liberate 65 grains 
 of zinc, 63 and 65 being the respective atomic 
 
 * See page 299. 
 
340 
 
 DA VY AND FARAD A F. 
 
 weights of these metals. It would similarly liberate 
 216 grains of silver, or twice its atomic weight ; the 
 equivalent weight of silver, compared with zinc and 
 copper, being twice its atomic weight, owing to the 
 fact that silver is monovalent, while zinc and copper 
 are divalent. 
 
NINTH PERIOD. 
 
r 
 
 CHAPTER XVIII, 
 
 NINTH PERIOD : THE MODERN SCIENCE. 
 MODERN INORGANIC CHEMISTRY, 
 
 N treating of Davy, Faraday, and Dalton, 
 the later developments of their greater 
 discoveries have been shortly discussed. 
 It has seemed clearer and more intelli- 
 gible to observe strictly chronological 
 order only in the case of the main and 
 fundamental discoveries of the science and those 
 associated with great and illustrious names. In most 
 cases, therefore, the later development has been 
 treated together with the main idea. The chief part 
 of what remains in this chapter will therefore consist 
 in briefly summarizing any omitted results of modern 
 research. 
 
 The following table contains the names of elements 
 discovered since the close of last century. The name 
 
344 
 
 THE MODERN SCIENCE. 
 
 of the observer by whom the element was first isolated 
 is printed in ITALICISED CAPITALS. In many cases, 
 however, compounds were recognised as containing 
 a new element before the element was obtained 
 in a free and uncombined state. Names of workers 
 Observing and recognising such compounds are printed 
 in italics. The name of the principal worker upon 
 an element, other than its discoverer, is printed in 
 CAPITALS, and any other workers in ordinary type. 
 
 
 SGregor .... 
 
 1789 
 
 Titanium . . 
 
 Klaproth. ... 
 
 1795 
 
 
 BERZELIUS . 
 
 1825 
 
 Uranium . . 
 
 (Klaproth. ... 
 ( PELIGOT ... 
 
 1789 
 1842 
 
 Chromium . . 
 
 VAUQUELIN . 
 
 1797 
 
 Tellurium . . 
 
 KLAPROTH 
 
 1798 
 
 Tantalum . . 
 
 ( Hatchett . . 
 \Ekeberg .... 
 
 1801 
 1802 
 
 
 [Del Rio .... 
 
 1801 
 
 Vanadium . . 
 
 ) Selfstrom 
 JBERZELIUS .... 
 
 1830 
 1831 
 
 
 \ROSCOE . 
 
 1867 
 
 Cerium . . . 
 
 (Klaproth 
 \MOSANDER 
 
 1803 
 1839 
 
 Palladium . 
 
 WOLLASTON .... 
 
 1803 
 
 Potassium . . 
 
 / Stahl 
 \DAVY 
 
 1736 
 1808 
 
 Sodium . . . 
 
 f Stahl 
 \DAVY 
 
 1736 
 1808 
 
 Barium . . . 
 
 ( BERZELIUS % PONTIN . 
 \DAVY 
 
 1808 
 1808 
 
 
 (DAVY 
 
 1808 
 
 Boron . . . 
 
 \ GAY-LUS. $ THENAED . 
 
 1808 
 
 
 (DAVY 
 
 1808 
 
 Calcium . . 
 
 BEBZELIUS $ PONTIN . 
 
 1808 
 
 
 ( Matthiessen 
 
 1856 
 
 Magnesium 
 
 DAVY 
 
 1808 
 
 Strontium . . 
 
 DAVY 
 
 1808 
 
 Chlorine . . 
 
 ( SCHEELE 
 (DAVY 
 
 1774 
 1810 
 
 Iodine . 
 
 COI7RTOIS 
 
 1811 
 
 Lithium . . 
 
 / Arfvedson ..... 
 t B UNSEN 4- MA TTHIESSEN 
 
 1817 
 1855 
 
THE MODERN SCIENCE. 
 
 345 
 
 Selenium . . 
 
 BERZELIUS 
 
 1817 
 
 Cadmium . . 
 
 ( Hermann 
 \STROMEYER .... 
 
 1817 
 1818 
 
 Silicon . . . 
 
 BERZELIUS 
 
 1823 
 
 Bromine . . 
 
 BALARD 
 
 1826 
 
 Aluminium 
 
 ( Marggraf ..... 
 \ W(EKLER 
 
 1754 
 
 1827 
 
 Beryllium . . 
 
 j Vauquelin 
 \ WCEHLER 
 
 1798 
 1828 
 
 Thorium . . 
 
 BERZELIUS 
 
 1828 
 
 
 
 1794 
 
 Yttrium. . . 
 
 J Eckeberg 
 
 1797 
 
 
 (MOSANDER 
 
 1839 
 
 Didymium . . 
 
 ( Mosander ..... 
 \MARIGNAC 
 
 1841 
 1853 
 
 Lanthanum . 
 
 MOSANDER 
 
 1841 
 
 Erbium . . . 
 
 ( Mosander ..... 
 ( CLEVE & HOEGLUND . 
 
 1843 
 1872 
 
 
 (Rose 
 
 1844 
 
 Niobium . . 
 
 < Blomstrand ..... 
 
 1866 
 
 
 (ROSCOE 
 
 1879 
 
 Ruthenium . 
 
 CLA US 
 
 1844 
 
 Caesium . . 
 
 Xirchhoff $ Bunsen .... 
 
 1860 
 
 Rubidium . . 
 
 BUNSEN 
 
 1861 
 
 Thallium . . 
 
 ( CROOKES 
 \LAMY 
 
 1861 
 1862 
 
 Indium . . . 
 
 Reich $ Richter .... 
 
 1863 
 
 Gallium. . . 
 
 LECOQ de BOISBA UDRAN 
 
 1875 
 
 
 {Scheele . . . 
 
 1771 
 
 Fluorine . . 
 
 AMPERE 
 Gore 
 
 1810 
 1870 
 
 
 MOISSAN 
 
 1887 
 
 
 ( Mosander ..... 
 
 1843 
 
 Terbium . 
 
 \ DELAEONTAINE & MARIGNAC 
 
 1878 
 
 Ytterbium 
 
 Marignac 
 
 1878 
 
 Decipium 
 Philippium 
 
 Delafontaine ..... 
 Delafontaine 
 
 1878 
 1878 
 
 Scandium 
 
 Nilson 
 
 1879 
 
 Samarium 
 
 Lecoq de Boisbaudran 
 
 1879 
 
 Thulium . 
 
 Cleve 
 
 1879 
 
 Germanium 
 
 Winlcler 
 
 1885 
 
 
 
 i 
 
 The existence of others is as yet somewhat doubt- 
 ful, such as the Yttrium a and Yttrium /? of Marignac 
 (1879). Ytterbium to Thulium inclusive were all dis- 
 covered by spectrum analysis. 
 
 Of one or two of these bodies some further mention 
 
346 THE MODERN SCIENCE. 
 
 must be made. Metallic iodides are found in the ash 
 of sea-weed, and by treatment with sulphuric acid and 
 manganese dioxide (MnO 2 ) free iodine is obtained from 
 this source. Bromine may be obtained from the same 
 source. It was first discovered by Balard in the salts 
 obtained by the evaporation of sea-water. Cadmium 
 occurs as an impurity in most ores of zinc. Silicon 
 
 QTJAETZ CEYSTAL9. 
 
 is, next to oxygen, the chief constituent of the earth's 
 solid crust. It occurs always as the dioxide, SiO 2 . 
 This combined with the metallic oxides gives rise to 
 the large class of silicates, compounds which play a 
 very prominent part in geological formations. Clays 
 consist largely of aluminium silicate. Emerald is a 
 silicate of aluminium and beryllium. Felspar is a 
 potassium aluminium silicate. Talc is a magnesium 
 
THE MODERN SCIENCE. 347 
 
 silicate. Serpentine, mica, topaz, &c., are complicated 
 silicates. Pure silica (SiO 2 ) occurs in crystals as quartz 
 and tridymite. The amorphous * varieties include 
 opal, flint, sand, &c. Davy's discoveries led to the 
 suggestion that silica, like baryta and lime, was the 
 oxide of an unisolated element. Berzelius,f whose 
 immense services to chemistry are but feebly indicated 
 by his prominence in the foregoing table, first isolated 
 the element in 1810, and obtained it in a pure state 
 in 1823. % It forms a dark brown powder. 
 
 The interesting metal aluminium is next to oxy- 
 gen and silicon in importance as a constituent of the 
 earth's crust. Its presence in clay and felspar has 
 been referred to. Felspar forms the chief constituent 
 of granite, gneiss, porphyry, &c. The oxide, A1 2 3 , 
 occurs as the mineral corundum. Of this mineral 
 the ruby and sapphire are varieties. Wohler obtained 
 the metal by acting on the chloride with sodium. 
 The mineral bauxite, a hydroxide of aluminium and 
 iron, is the usual source of the element. From this 
 mineral pure aluminium hydrate is prepared. The 
 dried powder is mixed with common salt and char- 
 coal and made up into balls. These are heated 
 and a stream of dry chlorine led over them. A 
 double chloride of aluminium and sodium distils off 
 
 * That is, having no regular rorm. 
 
 f 17791848. 
 
 % The process used by Berzelius was to treat potassium silicofluoride, 
 a compound of potassium, silicon, and fluorine, K 2 SiF 6 with metallic 
 potassium. Potassium fluoride (KF) is formed and silicon liberated. 
 K 2 SiF 6 -f 4K = 6KF -f Si. 
 
3 48 THE MODERN SCIENCE. 
 
 and is condensed in a receiver. The double chloride 
 is then treated with sodium. The metal is thus 
 separated, fused, and cast into moulds. 
 
 Aluminium is now prepared in this way on a large 
 scale. Its lightness, malleability, ductility, and fusi- 
 bility render it highly serviceable. Its white colour, 
 its susceptibility to high polish, and its unsuscepti- 
 bility to aerial action enhance its value and render it 
 an almost ideal metal. Its tensile strength is high, 
 much higher than that of cast iron, and it is exceed- 
 ingly sonorous. In spite of these manifold advan- 
 tages and its universal occurrence it has proved im- 
 possible to prepare aluminium at a rate enabling it to 
 compete with other metals. Improvements have, 
 however, lately been effected which promise to bring 
 it more into the market. * 
 
 Caesium and Kubidium were discovered by Bun- 
 sen by means of spectrum analysis, a subject to which 
 we shall briefly refer in the sequel. The spectrum of 
 the salts of Diirkheim water contained two splendid 
 blue lines not before observed. They proved to 
 belong to a new element, the first discovered by 
 spectrum analysis. The delicacy of the spectroscopic 
 test is indicated by the fact that it was necessary to 
 evaporate forty tons of the water to obtain enough 
 caesium for investigation. Rubidium was similarly 
 discovered in the mineral lepidolite. 
 
 Scheele observed that fluor-spar (CaF 2 ) was the salt 
 
 * See a recent discourse of Sir Henry Roscoe's " On Aluminium; " 
 Nature, 1889. 
 
SIB, HEXRY ROSCOE. 
 
350 THE MODERN SCIENCE, 
 
 of a new acid. Ampere in 1810 determined the con- 
 stitution of, this acid, HF. But the element itself re- 
 sisted all attempts at isolation. Davy tried the action 
 of chlorine on silver fluoride (AgF). He expected the 
 chlorine to replace the fluorine thus : AgF + Cl =s 
 AgCl -I- F. This reaction actually occurred, but the 
 fluorine as soon as liberated attacked the vessels in 
 which the experiments were carried on, and formed 
 fresh compounds. It appeared incapable of remain- 
 ing free in the presence of any other element. In 
 1887 the French chemist, Moissan* succeeded by the 
 electrolysis of hydrofluoric acid containing potassium 
 fluoride in obtaining a colourless gas, attacking metals 
 and other substances with formation of fluorides and 
 proved to be elementary fluorine. Owing to its ex- 
 tremely energetic properties it was at first impossible 
 to collect the gas, but more recently it has been col- 
 lected and its specific gravity ascertained. 
 
 Some points of importance still remain to be 
 noticed. By modern observation Cavendish's deter- 
 mination of the composition of atmospheric air has 
 been confirmed. Approximately one-fifth is oxygen 
 and four-fifths nitrogen. This may be illustrated by 
 a simple experiment. A tube closed at one end and 
 graduated is inverted over water, and a certain volume 
 of air enclosed within it. A piece of ordinary phos- 
 phorus is now pushed up into the tube on the end of 
 a wire. If left for some time this will gradually 
 absorb the oxygen of the air, and nitrogen will be left 
 
 * An. de Chim. 
 
THE MODERN SCIENCE. 35 1 
 
 behind. If the air measured originally 20 divisions 
 from the top it will now measure 16. One-fifth, or 
 the amount occupying the space between 4 divisions 
 of the tube, has been absorbed by the phosphorus. 
 The actual method of analysis used by modern che- 
 mists is the eudiometric one discussed below. 
 
 Besides nitrogen and oxygen air contains traces 
 of other gases, notably carbonic acid and ammonia. 
 The normal amount of the former gas is 4 volumes 
 in 10,000 volumes of air. 
 
 The analysis of the air by weight was conducted in 
 1841 by Dumas and Boussingault. They found 
 2 2- 9 2 per cent, oxygen to 77*08 per cent, nitrogen. 
 
 The analysis of water has been frequently repeated 
 since Cavendish's time.* According to the volumetric 
 method a graduated tube is filled with mercury and 
 inverted over a mercury trough. The tube used for 
 such a purpose is termed an eudiometer.^ Some pure 
 oxygen gas is next passed up into the tube and its vol- 
 ume carefully measured. The height of the mercurial 
 column in the tube above the mercurial surface in the 
 trough must also be noted, as this by its downward 
 tendency diminishes the pressure upon the gas. The 
 height of the thermometer and barometer must also be 
 carefully observed. A large excess of hydrogen is next 
 admitted, but the total quantity of both gases must not 
 
 * Nicholson and Carlisle, in 1800, first decomposed water by elec- 
 tricity. 
 
 t From evdia, clear weather, and ptrpov, a measure, i.e. a measure 
 of the purity of air, or of the quantity of oxygen which it contains. 
 
3 S 2 THE MODERN SCIENCE. 
 
 be more than sufficient to fill about one-sixth of the 
 tube. The tube is now pressed securely down upon 
 a plate of caoutchouc (india-rubber) placed under the 
 mercury, and by means of two platinum wires passing 
 through the glass in the upper part of the tube a spark 
 is sent through the mixed gases. A flame is seen to 
 pass through the gases and combination occurs, the 
 water forming, as Cavendish observed, a dew upon the 
 side of the tube. On releasing the eudiometer from the 
 caoutchouc pad the mercury rises and the volume is 
 found to be considerably diminished. The residual gas 
 is carefully measured, and the observation of the 
 mercury column, thermometer and barometer repeated. 
 The volumes of the gas before and after the explosion 
 must next be reduced by calculation to what they 
 would be at identical pressure and temperature.* 
 The customary pressure and temperature are 760 
 millimetres of mercury and 0C. The following 
 numbers are those of an actual experiment; f the 
 volumes being reduced to and a barometric height 
 of one metre. 
 
 Volume of oxygen 95*45 
 
 V" Volume of oxygen + hydrogen . . . 55 7 '26 
 Volume after explosion 271 '06 
 
 Thus with the explosion 286 - 2 volumes J dis- 
 appeared. 
 
 * See ante p. 126. 
 
 t As given in Roscoe and Schorlemmer's Treatise. 
 
 J The volumes here spoken of may be taken as cubic centimetres, 
 cubic inches, or multiples of any other unit. The actual graduations 
 of the tube are usually in millimetres (measures of length] and their 
 
THE MODERN SCIENCE. 353 
 
 As a large excess of hydrogen was present we 
 know that the whole of the oxygen will have been 
 used in the production of water. Thus of the 286*2 
 volumes 95*45 are oxygen; the rest, 286*2 95*45 
 = 190*75, consists therefore of hydrogen. Now the 
 cause of the disappearance of these 286*2 volumes is 
 their condensation to form a very small bulk of water.* 
 Thus we must conclude that 95*45 volumes of oxygen 
 combine with 19075 volumes of hydrogen to form 
 water, or that 1 volume of oxygen combines with 
 1*9963, i.e. very nearly 2 volumes of hydrogen to 
 form water. The relations of the volumes are thus, 
 
 1 : 2, as expressed in the formula OH 2 . By explod- 
 ing his gases in a eudiometer, heated by the vapour 
 of arnyl alcohol, Gay-Lussac showed that the volume 
 of steam formed was identical with the volume of 
 hydrogen used. In accordance with Avogadro's law 
 
 2 volumes of hydrogen combine with 1 volume of 
 oxygen to form 2 volumes of water vapour. 
 
 II 2 -f = IPO. 
 
 2 vols. -f- 1 vol. = 2 vols. 
 
 Careful gravimetric analyses, or analyses by weight, 
 of water were carried out first by Berzelius and 
 Dulong, and afterwards in 1843 by Dumas and Stas. 
 The method adopted was to pass hydrogen over 
 
 capacity will thus depend on the "width of the tube. This in no way 
 affects the proportions between them. The numbers refer to divisions 
 of the tube. 
 
 * In very accurate experiments allowance must be made for the 
 volume occupied by the condensed water, but compared with the 
 volume of the gases it is a negligeable amount. 
 
 Z 
 
354 THE MODERN SCIENCE. 
 
 heated copper oxide and collect the water formed by 
 its reduction. The experiments of the two latter 
 chemists were conducted with very many precautions. 
 The hydrogen was passed through a series of 8 U 
 tubes containing substances which freed it from every 
 trace of impurity and moisture. It then passed over 
 a weighed quantity of copper oxide and the water 
 formed was condensed in a small weighed bulb, the 
 last traces being absorbed by hygroscopic substances 
 in weighed tubes. The loss of weight of the copper 
 oxide gives the weight of oxygen used, the gain in 
 weight of the second bulb and tube gives the weight 
 of water formed. The difference between the two 
 weights gives the weight of hydrogen in that quantity 
 of water. From these experiments it was found that 
 two parts by weight of hydrogen combine with 15*9608 
 parts of oxygen. The composition by weight deduced 
 by calculation from the composition by volume coin- 
 cides with these results.* 
 
 The properties of water it is unnecessary to enu- 
 merate. It may, however, be well to remind the 
 reader that the density of water increases with a 
 cold till the point of 4 is reached on the Centigrade 
 scale. Water below 4 is lighter than that at 4 and 
 therefore floats upon the warmer water, as does the 
 ice formed from it. In this way the rapid circulation 
 of the water as it cools is stopped, and our lakes and 
 
 * The exact composition of water and hence the exact atomic weight 
 of oxygen is still the subject of experiment. Thomsen, Scott, Cooke 
 and Richards, Keiser and Rayleigh are the recent workers in this 
 field. 
 
B. VT. BTTN'SEN', 
 
356 THE MODERN SCIENCE. 
 
 rivers prevented from becoming a mass of ice. Other 
 substances, such as grey cast-iron, expand similarly 
 on solidification. The beautiful forms assumed by 
 water during crystallisation are sufficiently well known 
 in the phenonema of snow-crystals. 
 
 Lastly, we must refer to the great invention of the 
 spectroscope, an instrument of increasing importance 
 to the chemist. Roscoe says, " The spectroscope, 
 next to the balance, is the most useful and important 
 instrument which the chemist possesses." Crookes 
 has remarked, "If I name the spectroscope as the 
 most important scientific invention of the latter half 
 of this century I shall not fear to be accused of exag- 
 geration," The very importance of the subject pre- 
 vents us from entering into any long discussion of it 
 here. It has come to form a distinct branch of 
 chemical science. In the hands of men like Bunsen 
 and Crookes it has explored the recesses of the rocks 
 for minute traces of hidden treasures, while with it 
 workers like Miller, Huggins, and Lockyer have 
 fathomed the abysses of space and determined the 
 constitution of the stars. 
 
 It was first observed by Newton that white light 
 when passed through a prism is split up into coloured 
 rays. Some of the rays are bent more sharply out 
 of their course by the prism than others, and thus 
 if these be received upon a screen they form a band 
 or spectrum in which the colours follow the order : 
 violet, indigo, blue, green, yellow, orange, red. Using 
 the light of the sun we obtain in this way the solar 
 
THE MODERN SCIENCE. 357 
 
 spectrum. Dark lines in the solar spectrum were 
 first observed by Wollaston in 1802 and mapped by 
 Fraunhofer, an optician of Munich. Herschel and 
 Talbot observed that bright lines in the spectrum 
 might be obtained by heating certain substances in 
 the flame, but it is to Kirchhoff and Bunsen that the 
 
 BOLAE SPECTEUM. 
 
 interpretation and utilisation of the phenomena of the 
 spectrum are due. Different substances when volati- 
 lised in a colourless flame colour it in various ways. 
 Thus, if a little common salt be held in the flame of 
 a spirit lamp it colours it an intense yellow. The 
 sodium compound is capable when thus heated of 
 emitting light rays of a particular refrangibility. 
 The spectrum obtained from this flame is very dif- 
 
358 
 
 THE MODERN SCIENCE. 
 
 ferent from the continuous spectrum described above. 
 It consists of two bright yellow lines. Moreover, if 
 pure white light (lime-light, for instance) be made to 
 pass through such a sodium flame before being ana- 
 lysed it will be found that its continuous spectrum is 
 interrupted by a double black line occupying a definite 
 position in the yellow. 
 
 Kirchhoff and-Bunsen invented their spectroscope 
 
 SPECTEOSCOPE. 
 
 for observing these phenomena. The light is received 
 through a very fine slit and by an arrangement of 
 lenses the rays are rendered parallel before reaching 
 the prism where the light is split up. It then enters 
 the observing telescope where, by means of another 
 lens, an image of the spectrum is obtained, and this 
 is observed through a magnifying glass. An incan- 
 
THE MODERN SCIENCE. 359 
 
 descent solid or liquid gives only a continuous spec- 
 trum, but where the substance is capable of being 
 ever so slightly volatilised it is found that each 
 element gives a spectrum of characteristic bright 
 lines. So delicate is the test that u o~owo~o ^ a m ^^~ 
 gram of sodium salt can be detected with certainty. 
 
 The dark lines in the solar spectrum are due to 
 the absorption of certain portions of the solar light 
 by upper incandescent vapours. Each vapour absorbs 
 in this way the same light that it emits. Thus the 
 sodium line is in the sun represented by a black line 
 in the yellow. But the interesting facts of spectro- 
 scopy and stellar chemistry cannot be gone into here. 
 These few words have only been inserted to remind 
 readers that these discoveries are among the most im- 
 portant of the modern science. 
 
I 
 
 CHAPTER XIX, 
 
 NINTH PERIOD : THE MODERN SCIENCE, 
 ORGANIC CHEMISTRY TO-DAY. 
 
 OME short reference must now be made to 
 the immense strides made by organic 
 chemistry since the time of Scheele. 
 Lavoisier was the first to attempt the 
 ultimate analysis of organic bodies. In 
 his later form of apparatus for the deter- 
 mination of carbon and hydrogen in these bodies, 
 Lavoisier burnt his oil or other organic substance in 
 a stream of oxygen and collected the water and car- 
 bonic acid formed, employing eight or nine absorp- 
 tion bulbs for the latter purpose. The substantial 
 features of this method have already been described. 
 From his analyses he drew the correct conclusion 
 that vegetable bodies are composed mainly of carbon, 
 hydrogen, and oxygen, while animal bodies contain 
 in addition nitrogen and sometimes phosphorus. 
 Guyton de Morveau, one of Lavoisier's disciples, 
 
THE MODERN SCIENCE. 361 
 
 suggested the term of la base or le radical for that 
 portion of a substance which combines with oxygen. 
 This radical might be either elementary as carbon, 
 or compound as the radical of tartaric acid. The 
 radicals of the vegetable and animal kingdom La- 
 voisier regarded as usually complex. His researches 
 on fermentation have been referred to. He did not 
 make any wide distinction between inorganic and 
 organic chemistry, but he was an illustrious pioneer 
 in the latter branch of the science. 
 
 Berzelius, in 1814, began important investigations 
 into the composition of organic bodies. His method 
 of analysis for carbon and hydrogen depended upon 
 treating the substance with potassium chlorate and 
 collecting the water and carbonic acid formed. Ber- 
 zelius followed Lavoisier in a belief in the existence 
 of compound radicals. In 1815 Gay-Lussac dis- 
 covered cyanogen gas (CN). 
 
 The belief prevailed at this time that organic 
 bodies could not be artificially prepared. This was 
 the view adopted by the German chemist, Gmelin, in 
 his great Handbuch. But the belief in mysterious 
 vital forces alone capable of giving rise to organic 
 products was rudely shaken by the synthesis of urea 
 effected by Wohler in 1828. Urea is a highly 
 important animal product and is excreted regularly 
 in the urine.* Ammonium cyanate is an artificial 
 
 * The quantity excreted by an adult man amounts to from 30 to 
 40 grams daily (a little over 1 oz.). The formation of the various 
 constituents of the urine forms one of the most interesting chapters in 
 physiological chemistry. 
 
362 THE MODERN SCIENCE. 
 
 product of the laboratory and may be obtained by 
 
 acting with an ammo- 
 nium salt upon potassium 
 cyanate. Now, this salt 
 when heated to 100 C. 
 becomes rapidly converted 
 into urea. Here, then, is 
 the first case of an organic 
 j product synthesised from 
 oj J inorganic sources. 
 
 In 1823 the great Ger- 
 ,J man chemist, Liebig,* be- 
 & gan to perfect the me- 
 | I thods of organic analysis. 
 I | His labours on this point 
 S | culminated in the develop- 
 
 *rh CJ 
 
 8 | ment of the process actu- 
 * I ally in use at the present 
 * day for determining the 
 carbon and hydrogen in or- 
 ganic bodies. His method 
 consists essentially in heat- 
 ing a mixture of the car- 
 bon compound with copper 
 oxide in a long glass tube. 
 The carbon and hydrogen of 
 the substance are oxidised; the water formed is absorbed 
 
 * Justus Liebig (18031873) was born at Darmstadt. He was 
 made professor at Giessen, and founded its laboratory. He remained 
 at Giessen for twenty-six years, during which time he published 200 
 
THE MODERN SCIENCE. 363 
 
 in a tube filled either with calcium chloride or with 
 pumice moistened with sulphuric acid, while the carbon 
 dioxide is absorbed by potash solu- 
 tion contained in the bulbs devised 
 byLiebig. The method customarily 
 in use at the present day differs 
 from that of Liebig in only a few 
 particulars. The combustion is now 
 usually carried on in a current of 
 oxygen gas, the substance analysed POTASH 
 being placed in a porcelain boat 
 behind a long column of copper oxide. * Gas has 
 replaced charcoal as a .means of heating the combus- 
 tion tube. The perfection of this method of ana- 
 lysis took Liebig many years to accomplish, but the 
 results of its use amply rewarded the labour bestowed 
 upon it. 
 
 In 1832 Liebig and Wohler published their cele- 
 brated research upon the radical of benzoic acid- 
 These chemists found that bitter almond oil, benzoio 
 acid and their derivatives all contained a particular 
 group of atoms, or compound radical, involving 
 oxygen as well as carbon and hydrogen, and termed 
 
 papers, 20 of them joint works chiefly with Wohler. He also pub- 
 lished works on organic analysis, organic chemistry, physiological 
 and agricultural chemistry, his chemical letters, &c., and edited several 
 journals. His discoveries include those of aldehyde, chloral, and, 
 simultaneously with Souberain, chloroform. 
 
 * To estimate nitrogen in nitrogenous bodies with this apparatus all 
 that is necessary is to mix the substance with copper oxide and substi- 
 tute, a current of carbon dioxide for one of oxygen. The nitrogen of 
 the substance escapes as such and is collected over potash solution. 
 
THE MODERN SCIENCE. 365 
 
 by them benzoy.l* (C 7 H 6 0). Liebig gave great sup- 
 port to the radical theory by the development of 
 his true idea that both ether and common alcohol 
 contain the same radical ethyl, the former being the 
 oxide (O i H 5 0), while the latter is its hydrate f 
 (C*H*0, HO). The work of Liebig, Berzelius, and 
 Dumas further developed this theory, the central 
 idea of which is that the elements of inorganic 
 chemistry are represented in organic chemistry by 
 combinations of elements, or compound radicals, 
 which play the part of elementary bodies. We 
 term cyanogen a radical, says Liebig, 1, because it 
 is an unchanging constituent in a series of com- 
 pounds ; 2, because it may be replaced in these 
 compounds by simple bodies ; and, 3, because in its 
 compounds with elementary bodies these latter can 
 be set free and replaced by their equivalents of 
 other simple bodies. At least two of these condi- 
 tions must be fulfilled if the radical is to be con- 
 sidered a true one. 
 
 The work of Dumas and Laurent led to the 
 publication, in 1839, of Dumas's theory of chemical 
 types. Dumas observed that the elements of a 
 compound could often be replaced by their equi- 
 valents of other elements or compound radicals. 
 Laurent added the observation that when such 
 substitution was made the compound still retained 
 
 * " Yl " from the Greek v\?i, matter. 
 
 f In our present formulae the relation between the compounds is 
 expressed by ether (C 2 H 5 ) 2 O. alcohol C 2 H 5 OH. 
 
366 THE MODERN SCIENCE. 
 
 its essential chemical properties or its^ehemical type. 
 As an example we may take the case of acetic acid, 
 C 2 H 4 2 . By the action of chlorine one of the atoms 
 of hydrogen may be replaced, and we obtain mono- 
 chloracetic acid, C 2 H 3 C10 2 , in which the chlorine 
 plays the part of the hydrogen replaced. The views 
 of Dumas and Laurent were strongly combated, but 
 they held their ground. The observation of reverse 
 substitution in the conversion of a chlorinated body 
 back again into its hydrogen derivative much 
 strengthened their position (Melsens, 1842). The 
 facts of replacement had an interesting bearing upon 
 the development of the atomic theory. The fact 
 that in these substitutions never less than two atoms 
 of chlorine react was one of those which led Lau- 
 rent to the conclusion that the molecule of chlorine 
 must consist of two atoms.* 
 
 The older radical theory was modified by Gerhardt 
 (1839) and assimilated to the theory of chemical 
 types. The older theory regarded the radicals as 
 closed groups of atoms, while Gerhardt, though not 
 abandoning the belief in a cc residue," which was the 
 equivalent of the radical, regarded the whole com- 
 pound as forming the chemical unit. Thus, accord- 
 ing to Laurent and Gerhardt j* alcohol is represented 
 
 * As examples take the action of chlorine upon acetic acid above 
 mentioned : 
 
 Cl 2 -f C 2 H 4 2 = HC1 -f C 2 H 3 C10 3 
 or upon marsh gas : 
 
 CH* -f CF = CH 3 C1 + HC1, 
 t See ante p. 296. 
 
THE MODERN SCIENCE. 367 
 
 by the formula C 2 H 5 OH, containing the residue OH. 
 The action of hydrochloric acid upon alcohol will be 
 represented as C 2 H 5 OH + HC1 = C 2 H 5 C1 + HOH, 
 or C 2 H 5 |OH H| Cl, forming ethyl chloride, C 2 H 5 C1, 
 a body first prepared by Basil Valentine and known 
 as sweet spirit of salt. 
 
 The classical researches of Bunsen upon the caco- 
 dyl compounds were of weighty service to the true 
 radical theory. The source of these interesting com- 
 pounds is Cadet's fuming liquid obtained by distilling 
 arsenious acid (As 2 3 ) with potassium acetate. In a 
 series of researches which are models of penetration 
 and skill, Bunsen investigated the composition of 
 this liquid and its derivatives. " If we examine this 
 group of bodies," says he, " we recognise in them an 
 unchangeable member (Glied), the composition of 
 which is represented by the formula C 4 H 12 As 2 "* 
 [C 2 H 6 As]. To this radical Bunsen gives the name 
 cacodyl (ATCU- &>?/?, stinking), from the frightful smell 
 possessed by most of its compounds. Bunsen finally 
 succeeded in preparing the free radical by the action 
 of zinc on cacodyl chloride [(CH 3 ) 2 AsjCl. Taking 
 the group (CH 3 ) 2 As, as analogous to the atom of an 
 element, the molecule of free cacodyl contains tivo 
 such atoms (CH 3 ) 2 As As (CH 3 ) 2 , and it has there- 
 fore been termed dicacodyl. Soon after this Kolbe 
 and Frankland succeeded in similarly isolating the 
 radicals of the alcohol series. 
 
 * Annalen xxxvii. 1. (1841), 
 
3 68 THE MODERN SCIENCE. 
 
 In 1849 Wurtz discovered the compound ammonias, 
 the existence of which was predicted by Liebig. They 
 consist of ammonia, NH 3 , in which one or more of the 
 hydrogen atoms is replaced by an organic radical. 
 Thus if the radical ethyl, C 2 H 5 , be substituted for one 
 hydrogen atom, the compound NH 2 C 2 H 5 termed ethy- 
 lamine is obtained. The replacement of two atoms 
 produces diethylamine NH(C 2 H 5 ) 2 , and so on. The 
 new theory of types initiated by Laurent and whix;h 
 regarded organic compounds as formed upon the type 
 of the simple inorganic ones, was much aided by these 
 discoveries. The compound ammonias may be con- 
 ceived as built upon the ammonia type. Again, 
 Williamson's classical research on etherification in 
 1850 proved that the alcohols and ethers must be 
 considered as built up on the water type. We thus 
 have 
 
 Water ^ J ethyl alcohol G ^ J ethyl ether ^HS } O 
 
 Substituting the hydrogen atoms of water by other 
 radicals we obtain other alcohols and ethers, as for 
 instance, 
 
 Propyl alcohol C3 ^ ? j O propyl ether ^^j j and mixed ethers as 
 
 P2TT9 *) 
 
 ethyl propyl ether 3jj 7 j O 
 
 and so on. 
 
 The subsequent discoveries of Williamson and others 
 did much to develop the new theory. The theory must 
 not be pressed too far, the same substance can be 
 arranged on a variety of types, and the formulae are 
 less advanced than true structural formula?, inasmuch 
 
THE MODERN SCIENCE. 369 
 
 as they only suggest a certain number of reactions of 
 the compound. -%/ 
 
 Since 1850 the researches of innumerable workers 
 have completely transformed the science, and the best 
 course to adopt in closing this chapter seems to be to 
 sketch, in what must of necessity be very bare outline, 
 the system of organic chemistry to-day. 
 
 First, let us define the range of organic chemistry.* 
 The simplest and truest way of stating the pro- 
 vince of organic chemistry is to say that it is the 
 chemistry of the hydrocarbons and their derivatives. 
 Let us also start with the assumption that carbon is 
 tetravalent (a fact first pointed out by the great 
 German chemist Kekule'). The primary hydrocarbon 
 thus becomes marsh gas or methane CH 4 . Its struc- 
 tural formula is 
 
 H 
 H-C H 
 
 A . 
 
 all the hydrogen atoms playing a chemically similar 
 part. By the action of chlorine upon this substance 
 we can replace the hydrogen atom by atom, obtaining 
 successively CH 4 , methane ; CH 3 Cl,f methyl chloride ; 
 CH 2 C1 2 , dichloromethane ; CHOP, chloroform J or 
 
 * For- a discussion of the distinction between the organic an! 
 inorganic departments of the science vide Chapter VI., p. 116. 
 
 t CH 3 is an organic radical termed methyl ; see p. 365. 
 
 J This invaluable compound was first introduced into medicine by 
 Sir James Simpson of Edinburgh in 1848. 
 
 A A 
 
37 o THE MODERN SCIENCE. 
 
 trichloromethane ; CC1 4 , tetrachloromethane or car- 
 bon tetrachloride. In a similar way we can replace 
 the hydrogen atoms of the hydrocarbon by bromine 
 and iodine, obtaining corresponding compounds as, for 
 instance, CH 3 I, methyl iodide. The action of caustic 
 potash upon methyl chloride gives rise to methyl 
 alcohol } the term alcohol being applied to hydrocarbons 
 having one or more of their hydrogen atoms replaced 
 by hydroxyl (OH) : 
 
 CH 3 C1 + KOH = CH 3 OH -f KC1. 
 
 Methyl alcohol is a convenient source of a number of 
 methyl compounds. The first action of sulphuric acid 
 gives us hydrogen methyl sulphate CH 8 HS0 4 . The 
 remaining hydrogen atom of sulphuric acid may be 
 replaced by a metal. By various other means, such 
 as the action of an acid on the alcohol or of a metallic 
 salt on an haloid ether (CH 3 I, Br or Cl), many other 
 methyl salts may be obtained, as the nitrate, nitrite 
 sulphide, sulphite, silicate, &c. Where an acid is 
 dibasic, as sulphuric acid, we may obtain two salts, 
 for instance CH 3 HS0 4 and (CH 3 ) 2 S0 4 according as one 
 or both hydrogens are replaced. On oxidising methyl 
 alcohol the first product is termed formic aldehyde. 
 
 H H 
 
 H-C OH + = H 2 -f H C=Q* 
 
 OHO being 1 the characteristic aldehyde group. 
 
THE MODERN SCIENCE. 371 
 
 Further oxidation converts it into formic acid, 
 H OH 
 
 H C = + = H C = 0. 
 
 OH 
 The group c or, as it is shortly written C0 2 H, 
 
 ^o 
 
 is termed carboxyl, and is characteristic of the organic 
 acids. 
 
 It has already been observed that the first product 
 of the action of sulphuric acid upon methyl alcohol is 
 methyl hydrogen sulphate, CH 3 HS0 4 ; another product 
 formed under suitable conditions is methyl oxide, or 
 
 CH 3 ^ 
 dimethyl ether, /- 
 
 CH 3// 
 
 When methyl iodide (CH 3 I), is treated with silver 
 nitrite (AgNO 2 ), nitromethane (CH 3 N0 2 ) is obtained, 
 being methane (CH 4 ) in which one hydrogen atom is 
 replaced by the group NO 2 . 
 
 H H 
 
 I ^ I / 
 
 H-C I + AgN ! = Agl + H-C-N | 
 I M) I X 
 
 H H 
 
 By appropriate means we can replace further hydro- 
 gen atoms in methane by the nitroxyl group (NO 2 ), 
 obtaining, for instance, trinitromethane or nitroform 
 CH (NO 2 ) 3 . Furthermore we can, as might be expected, 
 replace different hydrogen atoms at one and the same 
 time by different groups, obtaining, for instance, bromo- 
 trinitromethane, C(N0 2 ) 3 Br, and so on. It is obvious 
 therefore, that from the single hydrocarbon methane 
 
372 THE MODERN SCIENCE. 
 
 a large number of direct derivatives may be obtained, 
 for there is no theoretical reason why we should not 
 introduce into the molecule of methane these various 
 substituting groups in every kind of combination. 
 
 Some important classes of bodies still remain to be 
 mentioned. If we reduce nitromethane by nascent 
 hydrogen the nitroxyl group becomes converted into 
 amidogen NH 2 
 
 CH 3 N0 2 -f 3H 2 ^CI1 3 NH 2 -f- 2H 3 0. 
 
 The substance so formed may indeed be regarded as 
 ammonia, NH 3 , in which one hydrogen atom has 
 been replaced by methyl, CH 3 . It is termed methy- 
 lamine. The two remaining hydrogen atoms of 
 ammonia may be similarly replaced with production 
 of di- and tri- methylamine ((CH 3 ) 2 NH & (CH 3 ) 3 N). 
 Here again we may effect a double substitution, obtain- 
 ing, for instance, di-iodomethylamine CH 3 NI 2 , where 
 one hydrogen atom of ammonia, NH 3 , is replaced by 
 methyl and the two others by iodine. Bodies of a 
 similar nature may be derived from arseniuretted 
 hydrogen, AsH 3 , giving respectively monomethyl, 
 dimethyl, and trimethyl arsine, &c. So too from 
 phosphuretted hydrogen, PH 3 , analogous phosphines 
 are obtainable. Amines, arsines, and phosphines 
 are all of them basic bodies, and, like ammonia, 
 combine with acids to form a variety of salts. By a 
 very superficial glance we are thus able to see how 
 rapidly the number of compounds derivable from 
 even one hydrocarbon swells. But if we take methyl 
 
THE MODERN SCIENCE. 373 
 
 iodide and heat it with zinc the following reaction 
 
 occurs 
 
 CH 3 1 1 1 1 CH 3 
 
 I Zn I 
 that is to say, the zinc takes away the iodine from 
 
 two molecules forming zinc iodide, Znl 2 , and the two 
 methyl groups are left. They cannot exist separately ; 
 each carbon being combined with only three hydrogen 
 atoms has yet power of combining with another 
 atom. The two carbons thus become directly united 
 and H 3 C CH 3 , or ethane, is the result. It is 
 methane in which one hydrogen atom is replaced by 
 the methyl group, CH 3 . Graphically its formula is 
 
 H H 
 
 H-b C-H, and from it a whole series of compounds 
 H H 
 
 analogous to those obtainable from methane may be 
 produced. The only difference is that there being 
 more hydrogen atoms to replace, the number of 
 derivatives is considerably larger in number. Thus 
 we may obtain two hydroxyl derivatives ; the first, 
 CH 3 .CH 2 OH, is common alcohol, or ethyl alcohol, 
 as it is distinctly termed, the group, CH 3 .CH 2 
 or C 2 H 5 , constituting the radical ethyl. The 
 second is CH 2 OH.CH 2 OH, having one hydroxyl 
 in each methyl (CH 3 ) group* and known as ethylene 
 
 * At first sight it would seem that we might obtain a body 
 H 
 I 
 CH 3 .C OH containing its two hydroxyls attached to the same 
 
 OH 
 
 carbon atom. Such bodies, however, cannot be obtained, losing 
 water at once and becoming monohydroxylic. 
 
374 THE MODERN SCIENCE. 
 
 glycol.* The acid corresponding to ethyl alcohol is 
 of course acetic acid, CH 3 .C0 2 H, Mono-, di- and 
 tri-ehloroacetic acids (CH 2 C1.C0 2 H : CHC1 2 .C0 2 H : 
 CCP. C0 2 H) and other such derivations are known. 
 Acetic aldehyde is CH 3 .CHO. Trichloracetaldehyde, 
 CCP.CHO, is usually known as chloral. 
 
 The hydrocarbon next above ethane, C 2 H 6 , is 
 propane C 3 H 8 . These hydrocarbons are said to form 
 a homologous series, the higher being obtained from 
 the next lower one by the addition of CH 2 . Their 
 derivatives are also homologous. 
 
 From propane, C 3 H 8 , analogous derivatives may be 
 obtained, but here some complications occur. Writ- 
 ing out the formula of propane more fully we have 
 CH 3 .CH 2 .CH 3 . Now it makes all the difference 
 whether we substitute a hydrogen atom in the 
 methyl (CH 3 ) groups at the end of the chain or an 
 atom in the CH 2 group at the centre. Suppose, for 
 instance, that we introduce iodine into the methyl 
 group. The formula becomes CH 3 .CH 2 .CH 2 I. The 
 carbon atom with which the iodine is combined is 
 attached to one other carbon atom and two hydrogen 
 atoms. It moreover plays a certain part in respect 
 to the rest o the molecule. The introduction of the 
 iodine atom alters its relation to the rest of the 
 molecule. But now suppose the iodine atom in 
 the central group. The formula becomes CH 3 . 
 CHI.CH 3 . The carbon atom with which the 
 
 * Dibasic acids, &c., can of course be obtained, corresponding to 
 the alcohols. 
 
THE MODERN SCIENCE. 375 
 
 iodine is now combined is attached to two other 
 carbon atoms and one hydrogen atom. It plays 
 a part in the molecular whole quite distinct from 
 that of the terminal carbon atoms. The intro- 
 duction of the iodine atom now alters its relation to 
 the rest of the molecule. The change produced in 
 the molecule by the introduction of the Jodine atom 
 in the one case is therefore quite distinct from that 
 produced in the other. The two compounds are 
 therefore quite distinct. The first is termed primary, 
 the second, secondary propyl iodide.* It may be 
 well to observe that the two terminal carbon atoms 
 play an exactly similar part in the molecule and that 
 therefore the compound CH 3 .CH 2 .CH 2 I is identical 
 with the compound CH 2 LCH 2 .CH 3 ; indeed these 
 formulas must never be taken as representing the 
 relation of the atoms in space but merely as indicat- 
 ing which atoms are directly united to each other. 
 Obviously these modes of substitution in the propane 
 molecule may be repeated with other substituting 
 groups, giving us, for instance, CH 3 .CH 2 .CH 2 OH, 
 primary propyl alcohol (C 3 H 5 .OH) and CH 3 .CHOH, 
 CH 3 , secondary propyl alcohol (C 3 H 5 OH). It is 
 noticeable that the empirical formulae (C 3 H 6 0) of the 
 secondary and primary derivatives are identical. 
 The substances are only distinguishable when their 
 rational or structural formulae are given. Bodies thus 
 
 * When there is a long chain a large number of isomers may be 
 obtained as CHICHI. CH 2 .CH 3 . CH 2 . CH 3 ; CH 3 . CH 2 . CHI. (CH 2 ) 2 . 
 CH 3 and so on. 
 
376 THE MODERN SCIENCE. 
 
 containing in their molecules the same number of 
 the same molecules are said to be isomeric* From 
 propane, then, we may not only obtain a series of 
 derivatives strictly analogous to those obtainable 
 from, ethane, but the number of derivatives is also 
 much increased by the possibility of forming such 
 isomeric bodies. Proceeding up the series of hydro- 
 carbons we have 
 
 4 , C 2 H 6 , C 3 H 8 , C 4 H 10 . 
 
 The last hydrocarbon, butane, has not yet been 
 mentioned. In this case the hydrocarbon itself may 
 exist in two isomeric modifications and each of these 
 gives rise to a long series of derivatives. 
 
 The first modification where all the carbon atoms 
 may be written out in a chain is termed normal 
 butane, CH 3 .CH 2 .CH 2 .CH 3 , the second, isobutane, 
 CH 3 CH(g3 or trimethyl methane. Each of these is 
 capable of forming two mono-substitution products. 
 The alcohol, CH 3 COH(gis, is termed a tertiary al- 
 cohol, the substituting group being in primary com- 
 pounds united to CH 2 , in secondary compounds to 
 CH, and in tertiary compounds to C. The primary 
 alcohols when oxidised give rise to acids as we have 
 seen. The secondary alcohols on the other hand form 
 a new class of bodies termed ketones. Thus with 
 secondary propyl alcohol, 
 
 CIF.CIP.CHOH.CH3 + O = CH 3 .CH 2 .CO.CH3 + H 2 O, 
 the product being known as ethylmethyl ketone. 
 
 * Tliis name was given by Berzelius (taog, equal ; ftepof, a share)* 
 
THE MODERN SCIENCE. 377 
 
 Tertiary alcohols split up on oxidation. We have 
 then 
 
 CH 3 .CH 2 .CH 2 .CH* 
 CH 3 .CH 2 .CHOH.CH 3 CIP.CH 2 .CH 2 .CH 2 OH. 
 
 /CB? 
 CH3.CH 7 
 
 X CH3 
 
 , CH 3 , CH 3 
 
 CIF.COH' CH 2 OH.CH / 
 
 and by introducing various substituting groups we 
 may theoretically obtain chlorine substitution pro- 
 ducts, alcohols, aldehydes, ethers, acids, ketones, 
 amines, and so forth, in almost any number. 
 
 Butane exists in two modifications ; of the next 
 higher paraffin, C 5 H 12 , there are three modifications ; 
 of the next, C 6 H U , five are possible and four known ; 
 of the next, C 7 H 16 , nine are possible, and when we 
 reach the hydrocarbon, C 13 H 28 , it has been calculated 
 by Professor Cayley that no less than 799 modifica- 
 tions should exist. Each of these modifications should 
 give rise to several complete series of derivatives of its 
 own. 
 
 But this is by no means the only series of hydro- 
 carbons known to the chemist. Another series 
 begins with the term C 2 H 4 , ethylene, and like the 
 other proceeds upwards by increments of CH 2 . The 
 structural formula of ethylene is 
 
 CH 3 
 
 (U 
 
 where we see that two of the units of saturation of 
 carbon are engaged with each other. The series of 
 
378 THE MODERN SCIENCE. 
 
 the defines, as they are termed, is characterised by 
 this constitution. Its members tend to combine 
 directly with chlorine and other elements. Thus 
 ethylene produces the dichloride, CH 2 C1.CH 2 C1, which 
 is identical with symmetrical dichloroethane. We can 
 also substitute hydrogen in ethylene, obtaining for 
 instance, monochlorethylene, CH 2 :CHC1. and so on. 
 The hydrocarbons form the series C 2 H 4 , C 3 H 6 , C 4 H 8 , 
 C 5 H 10 , and so on. We may obtain from them a large 
 number of derivatives similar to those obtained from 
 the paraffins, except for the peculiar union of two 
 of the carbon atoms and the unsaturated character or 
 proneness to combination resulting from that union. 
 An example of this group is afforded by the following 
 compounds : 
 
 CH 2 : CH.CH 3 , CH 2 : CH.CH 2 OH, CH 2 : CH.C0 2 H, 
 
 CH 2 : CH.CH 2 !. 
 
 Another important series of hydrocarbons is the 
 acetylene series commencing with the term ClfeCH, 
 a gas capable of combining with four atoms of chlo- 
 rine to form CHCP.CHCl 2 . Far fewer compounds 
 of this series are, however, known. 
 
 Other series of hydrocarbons are known, but need 
 not be referred to here with the exception of one, 
 which has become of greater importance than all the 
 rest, the benzene series. All the hydrogen atoms of 
 benzene (C 6 H 6 ) are proved to be of equal value in 
 the molecule, and the only way of representing this 
 structurally is by the ring formula proposed by 
 Kekule: 
 
THE MODERN SCIENCE. 379 
 
 iic CH 
 
 or, perhaps preferably Ladenburg's modification. 
 
 We may obtain from it substitution products much 
 in the same way as from other hydrocarbons. But 
 there are special laws regulating this substitution. 
 Representing the benzene molecule as is commonly 
 done by a simple hexagon we see that we can obtain 
 only one monosubstitution product, all the hydrogens 
 being similar, and three disubstitution products, e.g. 
 
 ci 
 
 V 
 
 \J 
 
 Fara- 
 
 known as ortho-, meta-, and para-dichlorobenzene. 
 C 6 H 4 C1 2 1 : 6 is identical with C 6 H 4 C1 2 1 : 2, the 
 chlorine in both cases being combined with adjacent 
 carbon atoms. Where three hydrogen atoms are re- 
 placed by the same element three isomeric modifica- 
 tions may be obtained, but where there is more than 
 one substituting element there is a larger number 
 of isomers. 
 
 We may thus replace hydrogen in the benzene ring 
 by a variety of groups just as in the case of the 
 paraffins, and may produce higher hydrocarbons by 
 
380 THE MODERN SCIENCE. 
 
 introducing alkyl radicals, as, for instance, CH 3 . We 
 thus obtain C 6 H 5 .CH 3 where CH 3 is termed a side 
 chain. On oxidising such derivatives the side chain 
 becomes converted into carboxyl and thus we here 
 obtain C 6 H 5 .C0 2 H, benzoic acid. Where there are 
 two side chains as in C 6 H 4 (cJp[J), orthoxylene, oxida- 
 tion produces a dibasic acid as C G H 4 (co*H[Jj, ortho- 
 phthalic acid. By substitutions of this kind we may 
 obtain an enormous number of benzene derivatives, and 
 the reader may at will construct large numbers on paper 
 for himself. It is easy with the constitutional formula 
 now in use to predict the existence of numerous 
 compounds as yet undiscovered, and to describe their 
 chief properties, for these undergo a gradual modifica- 
 tion of properties as we pass up a homologous series 
 just as properties of the elements become modified 
 with rise of atomic weight. 
 
 In many compounds two or three benzene rings 
 may be combined, either indirectly, as in rosaniline, 
 or directly, as in naphthalene 
 
 I II I 
 
 which body is again the source of a large series of 
 compounds. We cannot do more here than thus 
 indicate how in the modern system of organic chernis- 
 
THE MODERN SCIENCE. 381 
 
 try the vast numbers of its compounds diverge from 
 a few simple hydrocarbons like the branches of an 
 enormous genealogical tree. The system is so far 
 perfected that the character of the undiscovered com- 
 pouuds is in many cases as plain to the chemists as 
 the character of the elements destined to fill the 
 blanks in Mendelejeff's table. Modifications of pro- 
 perties occur along with rise of molecular weight and 
 change of structure. Thus, as an instance of the 
 former truth, boiling points rise, and often very regu- 
 larly, as we pass up a homologous series. As an 
 instance of the latter normal compounds have a higher 
 boiling-point than iso-compound. Similarity of struc- 
 ture on the other hand always goes hand in hand 
 with similarity of properties, and thus it happens that 
 all the paraffin hydrocarbons have great chemical 
 similarity, for instance, in allowing their hydrogen to 
 be replaced by chlorine, and that all the primary 
 alcohols form acids on oxidation. It is these strictly 
 defined relations which make it possible to direct 
 research in this department upon such definite lines 
 and make organic chemistry so perfect a science. 
 
CONCLUSION. 
 
 may seem to some that science becomes 
 less interesting and less beautiful as it 
 advances. This, however, is but a one- 
 sided view to take. The mere facts of 
 science may be dry enough, but the facts 
 have to be interpreted, and so arise deep 
 truths through which we seem to peer 
 into the great heart of nature. There is a poetical 
 side to this, and the poetry of it becomes more obvious 
 as the truths become more deep. Again, the truths 
 which Ave are able to see and the conjectures we are able 
 to frame only bring us more closely into contact with 
 the vast regions of mystery where knowledge fades 
 into speculation, and speculation into awe. We need 
 fear no loss of the mysterious by the achievements of 
 
THE MODERN SCIENCE. 3 S 3 
 
 science, though, we exchange a lesser mystery for a 
 greater. The wonder with which in ignorance we 
 look up through the branches of a forest beech and see 
 the giant boughs spread upwards in moveless strength 
 and the floating tresses of sunlit leaves curved back 
 towards us, the wonder with which we watch in its 
 cool nooks the softness of the shadow, or through 
 its recesses the changeful play of palpitating light 
 this wonder is great. But that is still greater and 
 of more enduring worth with which, by higher know- 
 ledge, we watch the same wondrous beauty and see 
 beyond it how, through the myriad cells of leaf and 
 branch and trunk, minute by minute, the life cur- 
 rents of protoplasm ebb and flow, making the green 
 grace of the tree possible by their swift mysterious 
 power : or again, how the gleaming spears of sun- 
 light that shiver into soft glow of colour upon 
 those tiny wind-lifted shields have sped unstayed in 
 their few moments of dazzling life through depths of 
 space, so vast and desolate that before them the mind 
 of man can only wonder in impotence, or recoil in 
 dread, to be stayed at last and fall in fragments at 
 the light touch of one trembling leaf. No need is 
 here to complain that science will leave us with 
 nothing to wonder at. It is only morbid conceit which 
 can forget the great truth uttered by a man who com- 
 bined the keen observance of science with the lofty 
 insight of the poet " Poetry is the impassioned ex- 
 pression which is in the face of all science." 
 
 In our review of the progress of our science we have 
 
384 THE HfODERN SCIENCE. 
 
 soon it at first advancing slowly through the darkness 
 of ignorance and error. In this darkness it was 
 difficult to go forward, but it was more difficult to 
 go back. After a while the darkness hero and there 
 lightened a little, but the first gleams of brightness 
 were too often alluring marsh-lights beckoning to 
 impenetrable morass ; the false guides were more 
 treacherous than the night. But as the twilight of 
 doubt broadened into the day of knowledge it re- 
 vealed ever wider and wider tracts of hill and hollow 
 for us to explore. At last the daylight has flooded 
 mountain rock, and valley mist, and we stand in 
 wonderment before the vision of the newly revealed 
 realm as it stretches before us, from the gold of the 
 sunrise to where hastening night has dropped his 
 purple mantle on the hills. It is a splendid kingdom, 
 but great is the task of mastering it, and great our 
 responsibility if we err. We must have regard to its 
 beauty and not merely to its wealth. We must 
 not forget the beauty of its mountains in our search 
 for the treasure of its mines. Wo must see the 
 countenance but not forget its expression. 
 
INDEX; 
 
 Acid, Acetic, 98, .374 
 
 Hydrochloric, CO, 99, 199 
 
 Nitric, 39, 59, 00, 101, 
 W.I 
 
 Organic, 227, 371 
 
 PniBBic, 227 
 
 Sulphuric, 00, 02 
 Affinity, 148, 163 
 Agricola, 1)7 
 
 AlbertuB Magnus, 38, 43 
 Alcohol, 33, 118, 237 
 Alkalies, 105, 252, 320 
 Aluminium, 328, 347 
 Ammonia, 88, 199 
 Ampere, 282 
 Antimony, 07, 85 
 Aquafortis, 00 
 Aqua regia, 39 
 
 Atmosphere, 33, 203, 209, 221, 
 
 251, 351 
 
 Atomic theory, 257 
 Avogadro, 279 
 
 Bacon, It., 24, 40 
 
 Barium, 227, :'2 
 
 Bayen, 240 
 
 Bechcr, 117, 175 
 
 Benzene, 330, 378 
 
 Bergman, 225, 245 
 
 Bernard of Trevimi, 50 
 
 Berth elot, 228 
 
 Berthollet, 257 
 
 BerzdiuH, 228, 283, 289, 326, 
 
 353, 301 
 
 lilack, Dr., 94, 101 
 Boerhaavc, 179 
 
 U 
 
INDEX. 
 
 Boyle, 121,151, 179,243. 
 Bunsen, 348, 358, 367 
 
 Calcium, 327 
 
 Carbonate, 89, 167 
 Carbon dioxide, 89, 141, 219, 
 
 241 
 
 Cavendish, 33,83, 183, 211 
 Chaptal, 65 
 Chevreul, 228 
 
 Chlorine, 225, 328, 336, 338 
 Chloroform, 369 
 Combustion, . 134, 140, 147, 
 
 246, 252 
 
 Condensation, 337 
 Constant proportions, 245, 257, 
 
 269 
 
 Copper sulphate, 98 
 Crookes, 134, 345, 356 
 Cullen, 159 
 
 Dalton, 261 
 Davy, 317 
 
 Dulong and Petit, 285 
 Dumas, 351, 353, 365 
 
 Electro-chemical equivalents, 
 
 339 
 Elements, 40, 50, 83, 87, 102, 
 
 115, 128, 146, 176, 252, 297, 
 
 344 
 
 Faraday, 320 
 Fats, 228 
 
 Fermentation, 34, 287 
 Fusel-oil, 237 
 
 Gas, 87 
 
 Gay-Lussac, 278, 325, 353, 361 
 
 Geber, 15, 38, 298 
 
 Geoffrey, 114 
 
 Gerliarclt, 293 
 
 Glass, 27 
 
 Glauber, 58, 97 
 
 Glycerine, 228 
 
 Gunpowder, 49, 105, 134 
 
 Hales, 153, 199 
 Helmont, Van, 86 
 Hermes Trismegistus, 38 
 Higgins, 267 
 Hoffmann, F., 179 
 Hooke, 137 
 Hydrogen, 83, 89, 219 
 
 Sulphide, 227 
 
 Indestructibility, 157,235 
 Iron sulphate, 39, 50, 60 
 Isomers, 374 
 Isomorphism, 289 
 
 Latent heat, 169 
 Laurent, 296 
 Lavoisier, 183, 231, 360 
 
INDEX. 
 
 Lead oxides, 180 
 
 Lemery, 114 
 
 Liebig, 30, 228, 254, 362, 368 
 
 Lessen, 306 
 
 Lully, Raymond, 34, 50 
 
 Macquer, 179 
 Magnesium, 327 
 Marsh gas, 267 
 Mayow, 147, 178 
 Mendelejeff, 308 
 Metals and non-metals, 298 
 Metals known to ancients, 25 
 Molybdenum 227 
 
 Newlands, 308 
 Newton, 138, 356 
 Nitrogen, 204 
 Nomenclature, 253 
 Northmore, 338 
 
 Olefiant gas, 267 
 
 Opium, 84 
 
 Organic chemistry, 116, 225, 
 
 360 
 Oxygen, 147, 185, 202, 226, 
 
 248 
 
 Palissy, Bernard, 30 
 Paracelsus, 79, 94 
 Phlogiston, 169, 176, 206 
 
 Phosphorus, 150, 227 
 Pliny, 27, 32, 68 . 
 Pneumatic trough, 143, 198 
 Porcelain, 29 
 Pott, 29, 179 
 Priestley, 182, 1C5 
 Proust, 258 
 Prout, 284 
 
 Radical, 361, 363 
 Reactions, 163 
 Reaumur, 30 
 Rey, John, 178 
 Richter, 259 
 Roscoe, 75, 276, 344 
 Royal Society, 113 
 Rutherford, 204 
 
 Sal-ammoniac, 98 
 
 Salt-petre, 49, 101, 131, 145 
 
 Salts, 50, 151, 295 
 
 Scheele, 182, 225, 326 
 
 Silicon, 27, 346 
 
 Soap, 30 
 
 Sodium sulphate, 98 
 
 Spectroscope, 356 
 
 Stahl, 117, 176,200 
 
 Starch, 28 
 
 Stas, 353 
 
 Strontium, 326 
 
 Structural formula?, 304 
 
 Suidas, 37 
 
 Sulphur dioxide, 200 
 
 
Sulphurs, 116 
 Symbols, 59, 275, 299 
 
 INDEX. 
 
 Valentine, 55, 83, 367 
 
 Tractatus A.ureus, 40 
 Transmutation, 19, 40, 107 
 Tungsten, 227 
 
 Valency, 302 
 
 Ward, 63 
 
 Water, 33, 221, 233, 246, 351 
 
 Watt, 224 
 
 Williamson, 268, 302 
 
 Wohler, 361 
 
 Wood tar, 99 
 
 Wurtz, 228, 368 
 
 THE END. 
 
 PRINTED BY J. 8. VIRTUE AND CO., LIMITED, CITY ROAD, LONDON. 
 
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