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OSMANIA UNIVERSITY LIBRARY
Call No.
Title
This book should be returned on or before the date
last marked below.
Makers of
CHEMISTRY
OXFORD UMVERSHY PRESS
AMKN Horsr, K.C. 4
LONDON I D I N B U K G H G L A S O O W
L fc. 1 P / I G N E W \ O K K TORONTO
MIMiOUKNL CAI'lilOVVN BOMUAY
CALCUTTA MAOKAS SHANGHAI
HUMPHKKV MIL1-ORJ3
Pl T BLIbHl< K TO 1 1IL
UN1V 1 KS11\
Assyrian tablet dealing with glass-making
Makers of
CHEM ISTR Y
BY
ERIC JOHN HOLMYARD
MEMBRE CORRESPONDANT 1)U CO MITE INTERNATIONAL
D'lIISTOIRE DIiS SCIENCES
OXFORD
AT THE CLARENDON PRESS
PRINTED IN GREAT BRITAIN
TO MY
FATHER AND MOTHER
PREFACE
IN this book I have tried to tell the story of chemistry from its
remote and obscure beginnings up to the establishment of the
modern science by Dalton, Lavoisier, Avogadro and their con-
temporaries. Brief sketches of subsequent developments have
been appended in order that the reader may perceive something
of the wonderful efflorescence of chemical progress in the nine-
teenth and twentieth centuries, though a full treatment of this
progress lay outside the present limits. Like the other volumes
in this series of Makers of Science, Makers of Chemistry is
primarily intended for the general reader, to whom a detailed
account of the chemistry of the last hundred years would
necessarily prove unintelligible unless he were equipped with
more than a little technical knowledge. If my narrative enables
those with no special scientific training to understand how the
great and fascinating science of chemistry slowly took shape,
until at length it was set firmly upon its present fruitful course,
I shall have achieved the object with which I set out.
Though I have had very large recourse to original authorities,
I do not claim to have used no other. Students of the history of
chemistry will recognize my debt to Kopp, Hoefer, Ferguson,
Thomson, Stillman, von Meyer, von Lippmann, Berthelot and
other scholars, which indeed I frankly and gratefully acknow-
ledge. Unfortunately, the new discoveries concerning the works
of Jabir ibn Hayyan, announced a short time ago by Ruska and
his collaborators, came too late for me to make use of them ; but
it is still uncertain what their true import may be.
I have much pleasure in expressing my sincere thanks to the
Delegates of the Clarendon Press and their officers for their
continued encouragement and special assistance in the problems
of illustration and printing; to Mr. R. B. Pilcher, Registrar of
the Institute of Chemistry, who generously gave me the benefit
of his unrivalled knowledge of portraits of chemists and kindly
supplied several prints and photographs for reproduction; to
x Preface
Mr. W. L. Cooper, Librarian of the University of Bristol,
for assistance in procuring journals and works of reference ; to
Messrs. Edward Arnold & Co., who kindly gave me permission
to quote passages from my Inorganic Chemistry in the section
on the structure of the atom; and to Miss Lilian Long, who
prepared the index of names, assisted in the preparation of the
subject-index, made a typescript of the manuscript and read
the proofs.
Several of the illustrations are reproduced from originals in
the Stone Memorial Science Library of Clifton College, which
is fortunate in possessing a large and valuable collection of
alchemical and early chemical books and manuscripts.
E.J. H.
Clifton College,
February 1931.
CONTENTS
SECTION I'AUE
i . Fancy and Fable ....... i
2- Egypt 2
3. Sumer, Assyria, Babylonia . . . . . .10
4. Greece . . . . . . . . 15
5. The Classical Atomic Theory . . . . .21
6. China ......... 24
7. India ......... 26
8. Rome ......... 27
9. The Ley den and Stockholm Papyri .... 29
10. The School of Alexandria . . . . . .32
11. Gnosticism ........ 33
12. Neo-Platonism . . . . . . . -33
13. The Fusion of Practice with Speculation ... 34
14. Zosimos the Panopolitan ...... 35
15. A Retrospect ........ 39
1 6. The Rise of Islam ....... 41
17. The Origins of Alchemy in Islam . . . .43
1 8. Jabir ibn Hayyan ....... 49
19. The Latin Works of Jabir or Geber . . . .60
20. Raxi ......... 63
21. Abu Mansur Muwaffak ...... 67
22. Avicenna ........ 68
23. 'The Sage's Step' ....... 77
24. Later Writers . . . . . . . .81
25. General Review of Muslim Chemistry .... 82
26. The Translators ....... 84
27. Robert of Chester 86
28. Vincent de Beauvais ....... 89
29. Albertus Magnus and Roger Bacon .... 90
30. Popular Books and the Technical Tradition ... 98
31. Paracelsus ........ 106
32. Later latrochemists . . . . . . 115
33. van Helmont . . . . . . . .119
xii Contents
SECTION PAOF
34. Nicolas Lemery . . . . . . .124
35. Review of Chemistry to the Time of Lemery . . 132
36. Robert Boyle . . . . . . . .132
37. Becher and Stahl . . . . . . 143
38. Troublesome Facts . . . . . . .150
39. Mayow . . . . . . . . 154
40. Pneumatic Chemistry . . . . . .158
41. Joseph Black ........ 164
42. Joseph Priestley . . . . . . .169
43. Henry Cavendish . . . . . . .177
44. Karl Wilhelm Scheele 186
45. Guillaume Francois Rouelle . . . . .189
46. Summary . . . . . . . 197
47. Antoine Laurent Lavoisier . . . . . 197
48. The Revision of Nomenclature . . . . .213
49. Sir Isaac Newton . . . . . . .217
50. John Dalton . . . . . . . .221
51. Berzelius ......... 240
52. Avogadro ......... 248
53. Modern Chemistry Established ..... 257
54. The Electrochemical or Dualistic Theory . . . 258
55. The Classification of the Elements .... 263
56. The Rise of Organic Chemistry ..... 273
57. The Rise of Physical Chemistry ..... 284
58. The Structure of the Atom . ..... 290
LIST OF ILLUSTRATIONS
Assyrian tablet dealing with glass-making. British Museum. Frontispiece
An Alchemical Laboratory, from the fresco by Jan Stradanus.
Photograph Alinari . . . . xvi
1. Thoth 3
2. An Egyptian Metallurgist. From Garland and Bannister, Ancient
Egyptian Metallurgy (Charles Griflin Co.) .... 4
3. Metal-workers' workshop in Egypt. From J. II. Breasted, A His-
tory of Egypt, 2nd edition (Charles Scribner's Sons, New York;
Hodder & Stoughton, Ltd., London) ..... 5
4. Egyptian Goldsmiths' workshop in the Pyramid Age. From J. R.
Partington, Everyday (Ihemntry (Macmillan & Co , Ltd.). . 7
5. Clay Crucible found at El Argar. British Museum ... 9
6. The oldest stone weight (Sumerian). Ashmolean Museum. . n
7. Aristotle. Capitolme Museum, Rome. Photograph, Anderson . 17
8. Democntus. Capitolme Museum, Rome. Photograph, Anderson . 23
9. The Iron Pillar of Delhi. From a photograph kindly lent by Sir
Robert I ladneld 26
10. Pliny offering a work to Caesar. From G. Carbonelh, Sulle Fonti
Stonchc dellti (Ihnnna e delV Alcluima in Italia, 1925 (Institute)
Nazionale Medico-Farmacologico, Rome) . . . .28
11. Part of the Stockholm Papyrus. From A. Lagereantz, Papyrus
Graetus Hohniem*is (Otto Harrasowitz, Leipzig) . . .31
12. Figures of late Greek chemical apparatus. From Berthelot, Collec-
tion des anciens alchimiites greis, 1887 (Georges Stemheil, Pans) . 37
13. Cleopatra's system of gold-making. From Berthelot, op. cit. . 40
14. The Ka'ha at Mecca. By permission from a photograph by H.
Campbell .......... 45
15. Page of an Ancient Koran. Bodleian, MS. Marsh 2 . . .47
16. Imaginative portrait of Jabir. Photograph, A. Chelazzi, Florence . 51
17. The Islamic Empire ........ 53
18. Page of one of Jabir's chemical works in arable. Bodleian, MS.
Marsh 70 ..... .... 54
19. Figures of alchemical processes in Arabic manuscript. British
Museum, MS. Add. 25724 ....... 55
20. Early MS. of Geber's Investigation of Perfection. Bodleian, MS.
Cod. Canon, eccles. lat. 53 . . . . . . .62
21. Title-page of A vicenna's Canon of Medicine . 71
22. The Alhambra . . . . % 86
23. The supposed first work on Alchemy in Latin. Bodleian, MS.
Digby 162. . . . . . . . . -87
24. Vincent de Beauvais. Bibliotheque Nationale, MS. Fran9ais 316 . 89
25. Roger Bacon with a pupil. MS. Bodl. 211 . . . -93
26. Roger Bacon's Study. From a drawing in the Bodleian Library . 95
xiv List of Illustrations
27. Incipit page of a fifteenth-century edition of Bartholomew's On the
Properties of Things ........ 99
28. Paracelsus From a painting by Rubens. . . .107
29. Libavius' Chemical House .... .116
30. Plan of Libavius' Chemical House . 117
31. van Ilelmont and his Son ... . . 121
32. Chemical Laboratory of Pieter Breughel, 1558 .... 123
33. Nicolas Lemery. From the collection of Mr. R. B. Pilcher, O.B.E. 124
34. Title-page of Lefebure's Trmte de la Chymie, 1669 . . . 125
35. Apparatus from Lemery 's Course of Chymntry . . . .126
36. Further apparatus from Lemery's Course of Chvmistry . . 127
37. Title-page of Lemery's Course of Chvmistry . . . .129
38. Robert Boyle. From the portrait by F. Kerseboom in the posses-
sion of the Royal Society . . . . . . .135
39. Title-page of The Sceptical Chymist . . ... 139
40. The Old Ashmolean. From a print in the Bodleian Library . . 141
41. Johann Joachim Becher. British Museum .... 144
42. Title-page of Becher's Physica Subterranea .... 145
43. Georg Ernst Stahl. From the collection of Mr. R. B. Pilcher, O.B.E. 147
44. Richard Watson . . . . . . . . .149
45. John Mayow . . . 155
46. Apparatus of Mayow . . . ... 157
47. Jean Bernouilli ....... .158
48. Bernoulli's apparatus . . . . . . . .159
49. The Rev. Stephen Hales. From the painting by T. Hudson in the
National Portrait Gallery . . . . . . .161
50. Stephen Hales' apparatus for collecting gases . . .162
51. Boerhaave ...... . . 163
52. William Cullen ..... .164
53. Joseph Black . . . 165
54. Joseph Priestley ... ..... 170
55. The Birmingham mob wrecking Priestley's House. From T. E.
Thorpe, Joseph Priestley (J. M. Dent & Sons, Ltd.) . . 171
56. Priestley's Apparatus . . . . . . .173
57. Autograph letter of Joseph Priestley. Science Library, Clifton
College ......... 174-5
58. Henry Cavendish ......... 178
59. Cavendish's Eudiometer. Preserved in the Chemical Department,
University of Manchester . . . . . . 179
60. Cavendish's metallic Eudiometer . . . . . .182
61. Cavendish's Apparatus . . . . . . . .183
62. Guillaume Francois Rouelle. From the collection of Mr. R. B.
Pilcher, O.B.E 191
63. MS. of Rouelle 's Lectures. Clifton College Science Library . 192
64. MS. of Rouelle's Lectures. Clifton College Science Library . 193
List of Illustrations xv
65. Le Jardin des Plantes, Paris. Photograph, E.N.A. . . . 195
66. Antoine Laurent Lavoisier . . . . . . .198
67. M. and Mme. Lavoisier in their laboratory. Photograph, Giraudon 199
68. Lavoisier's Apparatus ........ 205
69. C. L Berthollet ......... 213
70. Sir Isaac Newton. From an engraving by S. Freeman after the
painting by Sir Godfrey Kneller . . . . . .218
71. Blake's Newton. From the copy in the possession of Mr. W.
Graham Robertson, R.B.I. . . . . . . .219
72. John Dalton . . . . . . . . .221
73. Dalton 's card. From II. E. Roscoe,jW/w 7)//0/i(Cassell& Co., Ltd.) 223
74. Copy of letter from Dalton to Miss Johns. From Roscoe, op. cit. . 225
75. Some of Dalton 's Apparatus. In the possession of the Manchester
Literary & Philosophical Society ...... 226
76. More of Dalton 's Apparatus. In the possession of the Manchester
Literary & Philosophical Society ...... 227
77. Thomas Thomson ......... 228
78. Title-page of Dalton 's A New System of Chemical Philosophy . 229
79. Johann J. Berzehus. From Seidhtz, Portratzverk, vol. x (F.
Bruckmann, A.-G., Munchen) . . . . . .241
80. Dalton 's Symbols ......... 243
81. Amedeo Avogadro From Opere stelte di Amedeo Avogadro (R.
Accademia delle Scienze di Torino) ..... 249
82. Joseph-Louis Gay-Lussac. From Seidlitz, op. cit. . . .251
83 . Specimen of Avogadro 's handwriting. From Opere scelte di Amedeo
Avogadro (R. Accademia delle Scienze di Torino) . . . 255
84. Sir Humphry Davy. From the painting after Sir T. Lawrence in
the National Portrait Gallery ...... 260
85. Davy's Battery preserved in the Royal Institution . . . 261
86. Stamslao Cannizzaro. From J. R. Partington, Everyday Chemistry
(Macmillan Co., Ltd.) ....... 265
87. Cannizzaro 's autograph. Science Library, Clifton College . . 266
88. Title-page of Newlands' The Discovery of the Periodic Law, 1884
(E. & F. N. Spon). From the copy in the Science Library, Clifton
College .......... 267
89. MendeleefT. Photograph, E.N.A. ...... 269
90. Justus von Liebig. From the collection of Mr. R. B. Pilcher, O.B.E. 277
91. Kekule. From the collection of Mr. R. B. Pilcher, O.B.E. . . 279
92. van't HofT. From the collection of Mr. R. B. Pilcher, O.B.E. . 285
93. Arrhemus. From the collection of Mr. R. B. Pilcher, O.B.E. . 287
94. Crookes' Tube. From E. J. Holmyard, Inorganic Chemistry
(Edward Arnold & Co., Ltd.) ...... 291
95. X-ray Spectrometer. From E. J. Holmyard, op. cit. . . . 293
96. Lattice of potassium chloride. From E. J. Holmyard, op. cit. . 295
97. X-ray Spectra. From M. Siegbahn, The Spectroscopy of X-rays . 299
98. Isotopes and Heterotopes. From E. J. Holmyard, op. cit. . . 301
An Alchemical Laboratory, from the fresco by Jan Stradanus
i . Fancy and Fable
WE read in Genesis that 'the sons of God saw the daughters of
men, that they were fair; and they took them wives of all which
they chose'. From whence it was inferred, says Boerhaave, that
the sons of God were daemons, consisting of a soul, and a
visible, but impalpable body, like the image in a looking-glass;
that they knew all things, fell in love with women, and revealed
secrets. The solemn Tertullian, in a manner worthy of his (pro-
bably apocryphal) credo quia absurdum, gravely assures us that
these wicked angels condemned of God first discovered the art of
painting the eyebrows, that of dyeing, and those alluring things
gold and silver. Such an ingenious exegesis may prepare us for the
clouds of tradition that enwrap the veritable origins of chemistry.
Legends were invented, during the Dark and Middle Ages, to
meet the needs of the moment : Greeks of Alexandria ascribed
the birth of chemistry to Egypt and particularly to the god
Thoth or Hermes ; Muslim chemists vacillated between the Pro-
phet Muhammad and the Caliph Ali on the one hand and Aristotle,
Plato, Pythagoras and Democritus on the other; early Jewish
and Christian writers made the first chemists of scriptural figures ;
and the Chinese asserted that chemistry was an outgrowth of the
venerable system of Tao-ism.
The extent to which the manufacture of mythical history
proceeded may be gauged by a description of a few typical
instances. Thus Moses, from his treatment of the golden calf,
which could not have been accomplished (says the legend)
without a knowledge of the art of chemistry, was elected
a member of this strange chemical society. His sister Miriam
was credited with the invention of the water-bath. Tubal-Cain
was a past master in the science of the chemistry of metals.
Cleopatra, who dissolved pearls in vinegar, was from that very
fact declared to be an adept. The golden fleece, which Jason and
the Argonauts carried over the Pontic Sea to Colchis, was only
a manuscript on parchment, teaching the manner of making
2613-4 B
2 Egypt
gold by chemical art. Hermes wrote 36,000 books on chemistry,
and the inscriptions in the pyramids and tombs of Egypt are
nothing more than pictorial representations of the transmuta-
tion of base metals into gold. A twelfth-century hymn, by
Adam de St. Victor, celebrates St. John the Evangelist's
alchemical skill :
Cum gemmarum paries fractas
Solidasset, has compactas
Tribuit pauperibus.
Inexhaustum fert thesaurum,
Qui de virgis fecit aurum,
Gemmas de lapidibus.
Finally, the Song of Solomon is an alchemical treatise, and
chemistry is so called because it was invented by Noah's son
Shem or Chem!
2. Egypt
LEAVING behind us these bewildering fables, let us turn to the
more solid results of modern archaeological and historical re-
search. Chemistry is a science that deals essentially with the
changes in composition that matter may undergo, and therefore
presupposes, as its necessary foundation, an accumulation of
observational and experimental facts. These facts need not be,
and in point of actual development were not, investigated with
the object of elaborating a distinct scientific philosophy. They
were rather the outcome of the various arts and crafts practised
by the nations of antiquity, and therefore remained a hetero-
geneous collection until informed, centuries if not millennia
later, by the first primitive chemical theories.
So far as our information goes, one of the oldest civilizations
was that of ancient Egypt, which emerges from pre-history into
the period of more or less precise chronological record at a date
perhaps not far removed from 3400 B.C. This highly developed
but in many respects static civilization endured for over 3,000
. years, during which it spread its influence far and wide; some
archaeologists, indeed, claim to see in all other civilizations the
signs of an Egyptian origin. However this may be, it is univer-
Egypt 3
sally agreed that in technical arts Egyptian workers pointed the
way to the rest of the world, and it is to them that we must turn
for the first disco very of those facts that make chemistry possible.
Primitive arts that provide data of a chemical nature are those
of the metallurgist, the
glass-maker, the dyer and
the like, many of which
reached an astonishingly
high level of perfection in
ancient Egypt. Metallurgy
in particular was carried on
with an elaborate technique
and a business organization
not unworthy of the modern
world, while the systematic
exploitation of mines was an
important industry employ-
ing many thousands of
workers. Even as early as
3400 B.C., at the beginning
of the historical period, the
Egyptians had an intimate
knowledge of copper ores
and of processes of extracting the metal. During the fourth
and subsequent dynasties (i.e. from about 2900 B.C. onwards),
metals seem to have been entirely monopolies of the Court,
the management of the mines and quarries being entrusted
to the highest officials and sometimes even to the sons of the
Pharaoh. Whether these exalted personages were themselves
professional metallurgists we do not know, but we may at
least surmise that the details of n^etallurgical practice, being
of extreme importance to the Crown, were carefully guarded
from the vulgar. And when we remember the close association
between the Egyptian royal family and the priestly class we
appreciate the probable truth of the tradition that chemistry
first saw the light in the laboratories of Egyptian priests.
B 2
Fig. i. THOTH
In addition to copper, which was mined in the eastern desert
between the Nile and the Red Sea, iron was known in Egypt
from a very early period and came into general use about
800 B.C. According to Lucas, iron appears to have been an
Asiatic discovery. It was
certainly known in Asia
Minor about 1300 B.C., for
one of the Kings of the
Hittites sent Rameses II,
the celebrated Pharaoh of
the Nineteenth Dynasty,
an iron sword and a promise
of a shipment of the same
metal . The Egyptians called
iron 'the metal of heaven'
or ba-en-pet, which in-
dicates that the first speci-
mens employed were of
meteoric origin. As we
shall see shortly, the Baby-
lonian name has the same
meaning. It was no doubt
on account of its rarity that
iron was prized so highly
by the early Egyptians, while its celestial source would have
added to its fascination. Strange to say, it was not used for
decorative, religious or symbolical purposes, which coupled
with the fact that it rusts so readily may explain why com-
paratively few iron objects of early dynastic age have been
discovered. One which fortunately has survived presents
several points of interest : jt is an iron tool from the masonry
of the Great Pyramid of Khufu at Gizeh, and thus pre-
sumably dates from the time when the Pyramid was being
built, i.e. about 2900 B.C. This tool was subjected to chemical
analysis and was found to contain combined carbon, which
suggests that it may have been composed of steel. Two other
Fig. 2. AN EGYPTIAN METALLURGIST
Egypt 5
specimens of early Egyptian iron, when tested by Garland, also
proved to be steely, one of them being mild steel of good quality.
By 666 B.C, the process of case-hardening was in use for the
edges of iron tools, but the story that the Egyptians had some
secret means of hardening copper and bronze that has since
been lost is probably without foundation. Desch has shown
that a hammered bronze, containing 10*34 P er cen t- f tin, is
Fig. 3. MKTAL-WORKERS' WORKSHOP IN EGYPT
considerably harder than copper and keeps a cutting edge much
better.
Of the other non-precious metals, tin was used in the manu-
facture of bronze, and cobalt has been detected as a colouring
agent in certain specimens of glass and glaze. Neither metal
occurs naturally in Egypt, and it seems probable that supplies of
ore were imported from Persia. Lead, though it never found
extensive application, was among the earliest metals known,
specimens having been found in graves of pre-dynastic times.
Galena (PbS) was mined in Egypt at Gebel Rasas (' Mountain
of Lead'), a few miles from the Red Sea coast; and the supply
must have been fairly good, for wheri the district was re-worked
from 1912 to 1915 it produced more than 18,000 tons of ore.
The vast quantities of gold amassed by the Pharaohs were the
envy of contemporary and later sovereigns. Though much was
imported, received by way of tribute, or captured in warfare,
the Egyptian mines themselves were reasonably productive.
6 Egypt
Over one hundred ancient gold workings have been discovered
in Egypt and the Sudan, though within the limits of Egypt
proper there appear to have been gold mines only in the desert
valleys to the east of the Nile near Koptos, Ombos and Apolli-
nopolis Magna. Of one of these mines possibly near Apolli-
nopolis a plan has been found in a papyrus of the fourteenth
century B.C., and the remains of no fewer than 1,300 houses for
gold-miners are still to be seen in the Wadi Fawakhir, half-way
between Koptos and the Red Sea. In one of the treasure
chambers of the temple of Rameses III, at Medinet-Habu, are
represented eight large bags, seven of which contained gold and
bear the following descriptive labels :
.
Ethiopian gold.
T Gold, 1000 ten.
_, , Gold of the mountain,
iv. P*""*! ^^ ^T T Alluvial gold, 1000 ten.
/WWW WVWA I 1 ^ O
v> p^ 1 n Gold from Apollinopolis Magna.
/WWVA ~"7. ^xl [\>^yl A
vi. P^ fi) tj() ^ Gold from Ombos.
vii. C^^\ 5 J Gold from Koptos.
The Egyptian word for gold is nub y which survives in the
name Nubia, a country that provided a great deal of the precious
metal in ancient days. The symbol for nub, f^H, has given rise
to much speculation and many different interpretations have
been suggested. Champollion regarded it as a kind of crucible,
while Rossellini and Lepsius preferred to see in it a bag or cloth,
with hanging ends, in which the grains of gold were washed
the radiating lines representing the streams of water that ran
through. Crivelli has more recently advanced the theory that
P^O is the conventional sign for a portable furnace used for the
fusion of gold, and that the rays represent the flames, which, 'as
Egypt 7
can be observed in the use of this type of furnace, are unable to
ascend because the wind inclines them horizontally'. In the
later dynasties, the Egyptians themselves forgot the original
signification of the sign and drew it as a necklace with pendent
beads, though Elliot Smith says that this was the primitive form
Fig. 4. EGYPTIAN GOLDSMITHS' WORKSHOP IN THE
PYRAMID AGE
and became the determinative of Hathor, the Egyptian Aphro-
dite, who was the guardian of the Eastern valleys where gold
was found.
The gold mines in Nubia and other parts of the Egyptian
empire seem to have been very efficiently designed and con-
trolled, though with a callous disregard for the human element
employed. This is the picture which is drawn for us by Dio-
dorus Siculus (following Agatharchides of Cnidos) :
In the furthest part of Egypt, on the confines of Arabia and
Ethiopia, there is a place containing many mines of gold, which is
procured by numerous workmen with vast hardship and expense.
J The soil being naturally^ black, and containing many veins and
strata of marble, extremely white, and thus distinguished from the
circumjacent materials, the superintendents set over the mine-
works prosecute the search with a multitude of labourers. For the
kings of Egypt collect those condemned for crimes, captives taken
in war, persons ruined by false accusations, and therefore sen-
8 Egypt
tenced to imprisonment, sometimes alone, sometimes with all their
families, and condemn them to the mines, thereby at once inflict-
ing punishment upon the sentenced, and extracting vast profits out
of their labours. Now these convicts, in great numbers, all in
fetters, are kept at the works, not merely all day, but throughout
the night also, getting no intermission of labour, and carefully
guarded against escaping. For guards are set over them of foreign
soldiers, and speaking a different language, so that it is impossible
for the prisoners to corrupt any of their guards by speech, or by
motives of humanity. The ground containing the gold they first
heat with long-continued fire, and so render full of fissures, before
they apply manual labour to it ; but the rock that is soft and capable
of yielding to moderate labour is cut down with the tools stone-
cutters use by myriads of these poor wretches. The entire opera-
tion is directed by the engineer, who looks out for the proper stone,
and marks it out for the labourers. Of those appointed to this
miserable task, such as are of the strongest break down the marble-
like rock with iron pickaxes, applying no art to their labour, but
mere brute strength, and thus cut galleries, running not in a
straight line, but guided by the direction of the white veins.
These men, in consequence of the crooked course of the galleries,
work in darkness, and therefore carry lamps ingeniously fastened
upon their foreheads; and frequently changing their posture,
according to the arrangement of the veins, they break down and
bring to the floor the fragments of the cut rock, doing this under
the lash and cruelty of an overseer. Meanwhile the boys, creeping
into the passages, throw up, with much toil, the broken mineral as
it falls little by little, and carry it up into the open air at the mine's
mouth. Here those above thirty years old receive from them a
fixed measure of the broken ore, and pound it in stone mortars
with iron pestles, until they reduce it to the size of a vetch. From
these the granulated ore is taken by the women and the older men,
who have many hand-mills set in a row, and, standing two or three
together at the handle, they (grind the measure given to them as fine
as flour.
Last of all the skilled workmen receive the ore ground fine, and
complete the operation. They have a board placed somewhat
sloping, on which they throw a small quantity of the dust, and
pouring water over it they rub it. Then the earthy particles are
Egypt 9
dissolved by the water, and run off, owing to the slope of the board ;
but those containing the gold remain upon it in consequence of
their weight. Repeating this frequently, first of all they rub the
dust gently with their hands, afterwards they press it with coarse
sponges lightly, taking up in this way the loose and earthy part,
until the gold-dust is left behind unmixed. Finally, other work-
men, taking from them the collected dust, according to weight and
Fig. 5. CLAY CRUCIBLE FOUND AT EL ARGAR
measure, place it in earthen crucibles, mixing in a certain propor-
tion of lead-ore and lumps of salt, to which they add a little tin and
barley-bran. Then they fit on the cover of the crucible, luting it
down carefully with clay, and bake it in a furnace five days and
nights continuously. Then taking it out, and leaving it to cool,
they find nothing of the other materials left in the crucible, but get
the gold quite pure, but slightly diminished in weight. The dis-
covery of these mines dates very far back; probably they were
found out by the ancient kings.
Alluvial auriferous sand was also treated, a distinction being
made between the gold obtained in this way and that extracted
from the mines. The latter was called nub-en-set, i.e. 'gold of the
mountain', while alluvial gold was named nub-en-mu, i.e. 'gold
of the river'. Auriferous sand was placed in a bag made of a
io Sumer, Assyria, Babylonia
fleece with the woolly side inwards ; water was then added and
the bag vigorously shaken by two men. When the water was
poured off, the earthy particles were carried away, leaving
the heavier particles of gold adhering to the fleece. There is a
picture of this operation on one of the buildings at Thebes.
Metallurgy was by no means the only art practised with con-
spicuous success by the ancient Egyptian craftsmen. Glass was
almost certainly the invention, not of the Phoenicians, but of the
Egyptians, and was produced on a large scale from a very early
date. Artificial pearls, made of glass, were manufactured in such
numbers that they formed an important article of export trade,
and the old legends of enormous emeralds and other precious
stones are most reasonably explained on the assumption that the
preparation of paste jewelry was widely undertaken. The
earliest glass-works of which the remains have been found date
from the eighteenth dynasty, and the oldest dated glass object
is a large ball bead bearing the cartouche of Amen-Hotep I,
now in the Ashmolean Museum at Oxford. The invention of
glass-blowing, as opposed to the older method of glass-moulding,
is comparatively recent, dating back only to about the beginning
of the Christian Era. Sir Flinders Petrie has shown that the
reliefs at Beni-Hassan, which were formerly supposed to
represent glass-blowers, are more probably to be interpreted as
metal-workers blowing a fire.
The manufacture of soap (from oil and naturally-occurring
sodium sesqui-carbonate or natron), the art of dyeing (including
the use of alum as a mordant), the preparation of enamels,
poisons, perfumes, unguents and cosmetics: such were some of
the minor technical arts that flourished in Egypt. They all
imply an acquaintance with the chemical properties of a very large
number of compounds, an d^the Egyptians thus provided the first
basis for chemistry and established the first chemical industry.
3. Sumer, Assyria, Babylonia
THE banks of the Tigris and Euphrates witnessed the growth
and decay of at least three ancient civilizations, namely those of
Sumer, Assyria, Babylonia n
Sumer, Assyria, and Babylonia. Four or five millennia before
Christ, the southern part of Babylonia was inhabited by a non-
Semitic race known as the Sumerians, who were probably
immigrants from the east and north-east. Professor S. H.
Langdon believes that a great pre-historic civilization spread
from Central Asia to the plateau of Iran (ancient Persia), and to
Syria and Egypt, long before 4000 B.C., and that the Sumerian
Fig. 6. THE OLDEST STONE WEIGHT [SUMERIAN]
people, who were a somewhat later branch of the Central Asian
people, entered Mesopotamia before 5000 B.C.
The earliest archaeological remains of the Sumerians are
found in the mound that represents the ancient town of Susa,
in Elam. They show us that this people brought with them, or
very quickly discovered, the use of metals, for among the articles
discovered are rude copper objects. It seems likely, too, that
to the Sumerians is due the invention of writing, which was
originally pictorial. The use of the clay tablet so characteristic
of ancient Mesopotamian civilization appears to have origi-
nated about a century before the time of the oldest historical ruler
of the town of Lagash (the modern mound Telloh), whose name
was Ur-Nina and who lived about 3100 B.C. The reign of
Entemena, Ur-Nina's great-grandson (c. 3040 B.C.), is of particu-
12 Sumer, Assyria, Babylonia
lar interest to us, because in it were made the two oldest known
stone weights. One of these is preserved in the Ashmolean
Museum at Oxford. It has a unique form, being pear-shaped,
with a deep groove on each side running from the point to the
base, and is highly polished. The top is pierced by a round hole
by which the weight was suspended. The object weighs
680-485 grams (about if Ib.) and carries the following inscrip-
tion in ancient Sumerian characters: 'One mana of wages in
wool. Dudu the High-Priest. ' Dudu, high-priest of the god
Nin-girsu, was a very important official in the city of Lagash
during Entemena's reign. Monuments of this king were, in fact,
frequently dated by the phrase, 'At this time his servant Dudu
was high-priest of the god Nin-girsu'.
Even in the earliest period, anterior to the reign of Ur-Nina,
the Sumerians practised the art of casting in metal, small
foundation-figures having been discovered that were cast in
solid copper. This was the metal most frequently employed by
the Sumerians, who seem to have been unacquainted with
bronze.
After a long period, the Sumerians were overcome by the
Semites, who adopted the culture of their predecessors. The
celebrated Sargon, king of Akkad (the northern portion of Baby-
lonia), about 28728.0., was a great warrior, and among other
conquests in the third year of his reign invaded the West and
may even have penetrated to Cyprus. An inscription on one of
his statues says : 'The god Enlil gave unto him the upper land,
Maer, Yarmuthi and Ibla, as far as the cedar forests and
the silver-mountains/ The latter are probably the Taurus
mountains, and the inscription bears witness to the great age
of silver-mining in Asia Minor.
In the reign of Gudea, ruler of Lagash (c. 2600), gypsum and
asphalt were brought by ship from Magda, while copper was
obtained from the neighbouring city of Rimash (in the foothills
of the Zagros mountains). His gold Gudea procured from
Melukhkha, and his silver from Taurus, while his marble he
quarried in the 'Amorite mountains' (Anti- Lebanon?).
Sumer, Assyria, Babylonia 13
The golden age of Babylon was under Khammurabi (^123-
2081 B.C.), who is well known for his famous Code of Law. In
his time, gold, silver, copper and lead were all mined and were
in common use. The copper- working industry was carried on
at Umma principally, but Dur-gurgurri, near Larsa, 'was
another town where the clangour of coppersmiths at work could
be heard continuously/ In the first volume of the Cambridge
Ancient History, we read that a private letter of the period of the
first Babylonian Dynasty (founded about 2200 B.C.) runs as
follows: 'To Baba say: thus Munaivirum. May Shamash and
Marduk keep thee in good health for ever. I am sending
Lumursha-Marduk ; give him a copper pot. I am out of health :
since thou lovest me truly, send the copper pot/ *It is an
indication that a copper bazaar existed only in the towns, as of
course happens to this day/
During the second millennium B.C., the high-priests of the
northern city of Assur became kings, and so the new kingdom of
Assyria arose. At first, Babylonia exacted tribute from Assyria,
but in 1250 B.C. the Assyrian king Tiglath-Inurta captured
Babylon and ruled it for seven years. He was afterwards driven
out, and subsequently murdered by his own son, but for many
years Assyria was supreme. Not until the time of Nebuchad-
rezzar did Babylonia regain its ancient power. In 668 B.C. the
king of Assyria was Assurbanipal, the Sardanapallos of the
Greeks. He was a generous patron of literature and learning and
possessed an immense library. No fewer than 25,000 tablets
from it have been excavated, and are now in the British Museum.
Among them are several that deal with glass-making from
a severely practical point of view and these are of great
interest to students of the history of chemistry. They have
found a very capable interpreter in t\ie person of Dr. R. Camp-
bell Thompson, who has not only edited and translated the
texts, but has provided us with a remarkably ingenious and
penetrating commentary.
The essentials in all glass-making are silica, an alkali, and
lime or, less frequently, lead oxide. A decolourizing agent, such
14 Sumer, Assyria, Babylonia
as manganese dioxide, is usually added. That all these sub-
stances were used so far back as A.D. 79 is proved by an analysis
of window-glass from Pompeii: silica, 69; soda, 17; lime, 7;
alumina, 3 ; iron oxide, i per cent. ; manganese and copper, traces.
Chemical analysis of ancient glasses has, moreover, revealed the
nature of many of the colouring agents employed in the manu-
facture of tinted glass ; thus Assyrian blue glass has been found
to contain copper, and red glass cuprous oxide. Assyrian white
glass contains tin oxide, while lead antimonate has been dis-
covered in yellow.
From data of this kind it becomes an easier task to identify
the names of the principal constituents of Assyrian glass as
given in the texts. Uhulu, immanakku and namrutu are the basic
substances. The first, uhulu, has long been recognized as
'alkali', and Dr. Thompson is able to show that immanakku
probably represents a pure quartz sand. Since the word for lead
(anaku) does not occur in any of the glass-texts, it is reasonable
to assume that namrutu signifies a form of lime or limestone,
and the evidence shows that it is probably chalk. With the
three main ingredients definitely settled, attention can be devoted
to the rest, and one of the most interesting recipes appears
to describe a rudimentary form of the Purple of Cassius. The
aim of the operation described in this particular recipe is
apparently to produce an artificial pink or red coral. The in-
gredients are given as 7,200 parts of an ordinary glass, 32 parts
of oxide of tin, 20 parts of antimony, an unreadable number of
parts of salt or saltpetre, and i part of gold. The proportion
of gold here stated (0-014 per cent.) is of the usual order of
magnitude in the preparation of ruby glass.
Several of the technical terms are of great interest, such as
guhlu (eye-paint), whence^ the Arabic kuhl and our alcohol',
sindu arqu (yellow paint), whence sandarach; sadanu, whence the
Arabic shadana, haematite. Sapphire is traced back to the
Assyrian sipru, and means 'the scratching stone', a name no
doubt given to it on account of its great hardness (it is next to
the diamond on Moh's scale). Marcasite apparently come from
Greece 1 5
mar hast, which probably means 'pyrites'. It is thrilling also to
find a mineral called kibaltu, though whether there is a con-
nexion between this and cobalt remains for the present
undecided.
The metal mines in the Taurus mountains were being actively
worked by Babylonian firms as early as 2300 B.C. Their
representatives and agents, mostly Assyrian, had business
offices, and their safes were filled with business letters, receipts,
cheques, and so on. At Kara Eyuk in Cappadocia two interest-
ing tablets relating to the metal industry have been excavated.
The first reads roughly as follows: 'Labikum writes as follows:
Askutum and Kurub-Istar say to Ana-Nada: Ana-Samsi has
brought 2 talents 10 manehs and 4 shekels of lead with your
seal. We have packed the lead and have paid 2| manehs of raw
metal and \ maneh 6 shekels of pure metal to the house of the
Garum. The rest of the lead 2 talents 6| manehs and 4 shekels
we have reserved, and we send you silver in payment. In
accordance with your order, Ana-Samsi has brought down the
whole to you.' The second tablet states that 4^ shekels of iron
of the best quality had been dispatched to a customer.
The Semitic word for iron, barzelin Hebrew, parzel in Baby-
lonian, parzillu or barzillu in Assyrian, is written in the second of
the above tablets in Sumerian characters KU-AN, meaning 'metal
of the god' or 'metal of heaven'. The Sumerian name thus corre-
sponds to the Semitic barzi-iliand Egyptian ba-en-pet (p. 4). It
therefore seems likely that the Egyptians derived their name for
iron, and consequently the metal itself, from Asia Minor, as has
already been mentioned. Incidentally, Professor Sayce suggests
that the linguistic evidence just described may perhaps solve
the mystery of the Old Testament Terizzites', who would seem
to have been 'the metal-workers'.
)
4. Greece
WITH two exceptions that are, however, of the first con-
sequence classical antiquity in Greece has little direct interest
1 6 Greece
for the historian of chemistry. Accomplished as the ancient
Greek craftsmen were, they showed small originality in technical
procedure, and it is to the philosophers that we must turn for the
two theories that proved of paramount importance in the
development of chemical thought and practice. The first of
them, in its mature form, was due to Aristotle, and the second
was the composite contribution of the Atomists. It will be con-
venient to deal with each of them in turn.
Aristotle (384-322 B.C.), the tutor and friend of Alexander the
Great, and the most celebrated scientific authority of antiquity,
appears to have been one of the first to insist upon an experi-
mental and observational basis for a knowledge of nature. The
exaggerated reverence, however, with which he came to be
regarded in the Middle Ages, and his semi-official recognition as
the orthodox philosopher of both Islam and early Christianity,
caused much of his true spirit to be obscured; with the result
that a false Aristotelianism proved to be a millstone round the
ineck of chemistry until long after the Renaissance. Aristotle's
theory of the constitution of matter is to be found mainly in the
De Caelo, Books III and IV, in the De generations et corruptions,
and in the Meteor ologica. He supposed that the basis of the
material world was a primitive matter or prima materia, which
had, however, only a potential existence until impressed with
form. Form is that which gives to every body its individuality.
In its simplest manifestation it gives rise to the 'Four Elements',
Fire, Air, Water and Earth, which are distinguished from one
another by their qualities. The four primary qualities are the
fluid, the dry, the hot, and the cold, and each element possesses
two of them. Hot and cold, however, and fluid and dry, are
contraries and cannot be coupled; hence the four possible
combinations of them in pairs are :
Hot and dry, assigned to Fire.
Hot and fluid, assigned to Air.
Cold and fluid, assigned to Water.
Cold and dry, assigned to Earth.
Greece 17
In each element, one quality predominates over the other: in
earth, dryness; in water, cold; in air, fluidity; and in fire, heat.
None of the four elements is unchangeable ; they may pass into
one another through the medium of that quality which they
possess in common; thus
fire can pass into air through
the medium of heat, air into
water through the medium
of fluidity, and so on. Two
elements taken together
may pass into a third by
each parting with one
quality, subject to the limi-
tation that this process must
not leave two identical or
contrary qualities ; thus fire
and water, by dropping the
dry and cold qualities, could
produce air, or by dropping
the hot and fluid qualities
could give rise to earth. In
all these changes it is only
the form that alters; the
matter of which the ele-
ments are made never
changes, however diverse
and manifold the changes Fig. 7. ARISTOTLE
of form may be.
All other substances are composed of all the elements or
'simple' bodies.
For they all contain Earth because e^ery * simple body* is to be
found specially and most abundantly in its own place. And they
all contain Water because (a) the compound must possess a
definite outline and Water, alone of the 'simple' bodies, is readily
adaptable in shape : moreover (b) Earth has no power of cohesion
without the moist. On the contrary, the moist is what holds it
2613-4 C
1 8 Greece
together; for it would fall to pieces if the moist were eliminated
from it completely. They contain Earth and Water, then, for the
reasons we have given: and they contain Air and Fire, because
these are contrary to Earth and Water (Earth being contrary to Air
and Water to Fire, in so far as one Substance can be 'contrary' to
another). Now all compounds presuppose in their coming-to-be
constituents which are contrary to one another: and in all com-
pounds there is contained one set of the contrasted extremes, i.e.
cold-dry (Earth) and cold-fluid (Water). Hence the other set [i.e.
hot-fluid (Air) and hot-dry (Fire)] must be contained in them also,
so that every compound will include all the 'simple' bodies.
It is not altogether easy to follow this argument, in which
Aristotle seeks to prove that Fire, Air, Water and liarth must
each and all necessarily be contained in every other substance.
A little reflection, will, however, enable us to understand its
chief points. Aristotle maintained that each element had a
natural tendency to move to 'its own place'. Conceiving the
universe as a structure of some fifty-nine concentric spheres, he
made earth occupy the innermost, water the next, and air and
fire the third and fourth, though there was no definite line of
demarcation between them, particularly in the case of the last
pair. Since the 'proper place' for Earth is the (planet) Earth,
it follows that all terrestrial substances must, of all the four
elements, contain Earth at least. Secondly, they must all
contain Water, for the two reasons he mentions reasons which
may not satisfy us but are perfectly intelligible. The real
difficulty then arises : what does Aristotle mean by saying that
since all compound substances contain Earth and Water they
must therefore contain Fire and Air as well ? We can begin to
get an answer to this question by referring to a passage which
occurs a little earlier than, that quoted. 'There are differences in
degree in hot and cold. Although, therefore, when either is
fully real without qualification, the other will exist potentially;
yet when neither exists in the full completeness of its being . . .
both by combining destroy one another's excesses, so that there
exist instead a hot which (for a "hot") is cold and a cold which
Greece 19
(for a "cold") is hot.' This seems to imply that a compound of
Earth and Water only would show the qualities of these elements
in an excessive or absolute degree, which is contrary to observa-
tion. The contraries are required to modify this character of
excess and so to explain the actually observed properties of
terrestrial substances.
The proportion in which the various elements occur in
different substances is infinitely variable ; hence the existence of
such an enormous number of distinct compounds. But since
each element can, as we have seen, be transformed into any
other, it follows that any compound can likewise be transformed
into any other by some device that will alter the relative pro-
portions between the elements of which it is composed. Here
we have the germ of all theories of metallic transmutation. If
lead and gold both consist merely of fire, air, water and earth,
all of which are interconvertible, why may the dull and common
metal not be transmuted into the shining, precious one ? Such
was the question with which generation after generation of
alchemists confounded the sceptics and justified their ceaseless
search for the philosopher's stone.
On the more detailed problem of the formation of metals and
minerals as such, Aristotle expresses his views at the end of the
third book of the Meteor ologica. He maintains here that there
are two 'exhalations', one vaporous and the other smoky; the
former is produced when the sun's rays fall upon water, and is
moist and cold, while the smoky exhalation is formed when the
rays fall upon dry land, and is hot and dry. Each exhalation is,
however, mixed with more or less of the other. To the two
exhalations correspond two classes of bodies that originate in
the earth, namely, minerals and metals. The heat of the dry
exhalation is the cause of all minerals, i.e. these substances are
composed mainly of the * smoky' exhalation. Such are the kinds
of stones that cannot be melted, and realgar, ochre, ruddle,
sulphur and other substances of that kind. The 'vaporous'
exhalation is the cause of all metals, those bodies which are
either fusible or malleable, such as iron, copper, gold. All these
ca
2O Greece
originate from the imprisonment of the vaporous exhalation in
the earth, the dryness of which compresses it and finally con-
verts it to metal. Thus, since neither exhalation is entirely free
from the other, metals and minerals, like all other substances,
are composed of each of the four elements, but in metals the
predominating elements are water and air (chiefly water), while
in minerals they are earth and fire (chiefly earth).
We shall find in the sequel that in this theory of metallic
constitution we have the seed of the celebrated or perhaps
notorious Theory of Phlogiston, which can be traced step by
step from Aristotle to its final development at the hands of
Becher and Stahl in the seventeenth and eighteenth centuries.
A striking testimony to Aristotle's scientific acumen is that he
seems to have distinguished very clearly between mechanical
mixture and chemical combination. In strict Aristotelian
terminology, the former is called avvOeais and the latter fut?,
the most common and conspicuous type of combination, viz.
that between liquids, being distinguished by the special term
xpacris. Professor Joachim interprets Aristotle's ideas as follows : T
If two or more bodies are put together without alteration, this is
a avv6cris and the resultant is a mechanical mixture. Suppose that
we first chop up the component bodies into particles too small for
the normal eyesight to discriminate them, and then shuffle them
together: we should still have a mere mechanical mixture,
although relatively to our vision the result would seem to be
a chemical compound. It would not really be a /u^fleV [chemical
compound] : for the component particles still retain their distinctive
natures. They form an aggregate, not a, genuine unity. If we
symbolize the components as A B C D, the resultant is A -f B -f- C -f D.
If we divide it far enough, we shall reach parts which are A or B
or C or Z), and not (A+B + C+D): i.e. the smallest parts of the
whole are different in character from the whole.
But now suppose that A, B, C and Z>, by acting and reacting on
one another, produce an alteration in one another's qualities.
Suppose further that this reciprocal alteration continues until
a resultant, x, emerges, whose qualities are modifications of the
1 Journal of Philology, xxix. 72-6 (1903).
The Classical Atomic Theory 21
qualities of the components, and yet are different from the
qualities of any (and of all) of them. Suppose further that every
part of x, however far you subdivide it, retains the character of the
whole. And suppose finally that (by appropriate processes of re-
solution) you can recover (or re-create) from x components the
same in character as the original A, B, C and D. If these condi-
tions are fulfilled, x is a yuyftiv or KpaOev [compound], emerging
from the ju,tf is or Kpdcris of the {JLLKTCL [components] A, B, C and D
... A [Liyjdiv is such that (i) its components have really merged
into a unity, instead of forming a mere aggregate by juxtaposition:
and that (2) the components, although contained in the resultant,
are contained there in an altered form. ... It is thus clear that
Aristotle recognizes in principle the modern distinction between
mechanical mixture and chemical combination. But the details of
his theory of combination are quite remote from modern specula-
tion.
5. The Classical Atomic Theory
PERHAPS the greatest legacy bequeathed to chemists by the
philosophers of Greece though its value was not fully realized
till after the lapse of two thousand years was the theory that
matter is composed of atoms. Our detailed knowledge of this
theory is derived almost entirely from the poem of Lucretius
(first century B.C.) called De Rerum Natura, in which the earlier
views of Leucippus and Democritus (fifth century B.C.) and
Epicurus (about 300 B.C.) are logically marshalled and brilliantly
expounded. The chief points of permanent value, in the light of
subsequent developments, are as follow:
1 . There is only one ultimate species of matter.
2. Matter is indestructible and cannot be created.
3. Matter is not continuous, but discrete, i.e. it has a 'grained"
structure.
4. Matter is composed of 'atoms' which are invisible, physically
indivisible, indestructible, eternal, and impenetrable.
5. Between atoms there is simply a void empty space.
6. The atoms of different substances are different in shape, size, and
weight.
22 The Classical Atomic Theory
7. Atoms are in constant motion rectilinear according to Demo-
critus colliding with, and rebounding from, one another
'like motes in a sunbeam".
8. Substances differ in properties according to the nature , number
and arrangement of the atoms of which they are composed.
This arbitrary selection of certain features must not be
allowed to give an entirely erroneous impression of the Greek
atomic theory. As with Aristotle and the idea of chemical
combination, so with the atomists and their theory : superficially
their conceptions were very similar to those which we owe to
Newton, Dalton and others, but in wider ramifications the
divergence is great. There is also a more basic difference
between the ancient and modern theories. While it would be
incorrect to say that the ancient theory was not based upon
observational facts, it is nevertheless true that the number and
quality of these facts were ridiculously inadequate to the grand
scheme erected upon them; whereas the modern theory is
supported by countless thousands of well-established, relevant
facts. Had their theory been based upon, or verified by, ex-
perimental observations, the Greeks might have made incalcu-
lable advance in chemistry ; actually, however, it was no more
than a shrewd and lucky guess (or, if you will, a flash of insight),
and its importance lies in the influence it exerted upon later
thinkers until it finally suffered a drastic metamorphosis into the
atomic theory of John Dalton at the beginning of the nineteenth
century.
It is fatally easy to read into the views of bygone scientists
ideas of a later period, and to credit them with discoveries or
theories or opinions to which, in actual fact, they have no claim
whatever. The superficial resemblance between the classical
and modern atomic theories very largely vanishes in the light of
closer inspection. The classical theory was, indeed, meta-
physical rather than physical, and its features become grotesque
when carefully examined. Lucretius, for instance, assumes that
the atoms slightly deviate from a rectilinear path for no other
The Classical Atomic Theory 23
reason than that he may thereby deduce a theory of free-will!
The service which the Greek atomists rendered to chemistry
was that they familiarized men with the conceptions of atoms
and empty space ; conceptions that remained latent for centuries
afterwards but ultimately
lent themselves to a sys-
tematic and scientific treat-
ment.
The wonderful achieve-
ments of Hellenic thinkers
so dazzle our intellectual
vision that we are apt to re-
gard them as the possessors
of a scientific and rationa-
list attitude that was really
quite foreign to them, or at
least to most of them. Greek
interpretations of Nature
are saturated with supersti-
tion , mythology, astrological
beliefs and even magic.
For Aristotle, the stars were
deities ; Empedocles be-
lieved himself capable of
magic powers ; Plato considered the world to have a soul and, in
his Timaeus, plainly shows his belief in occultism ; he also speaks
of the stars as ' divine animals' ; and Pythagoras, or his followers,
ascribed mystic powers to numbers. While, therefore, the
Greeks must be given full credit for having presented science
with many conceptions that proved invaluable in later times,
we should be doing less than justicp to the great men who
followed if we imagined them merely to have revived Hellenic
knowledge. In the form in which Lucretius left it, the atomic
theory could never have occasioned the wonderful progress of
chemistry witnessed by the nineteenth century: that progress
was rendered possible by the genius of John Dalton, whose
Fig. 8. DEMOCRITUS
24 China
atomic theory, though a direct descendant of that of Lucretius,
bears the same sort of relation to it as a man does to one of his
simian ancestors.
6. China
THE inhabitants of China, with their air of inscrutable wisdom,
have always appeared to the eyes of Western beholders as the
possessors of ancient and mysterioiis lore. In consequence, they
have frequently been credited with the first discovery or in-
vention of many objects, arts and crafts the early history of
which is obscure. Oxygen, gunpowder, china-ware and print-
ing are among the discoveries attributed to the Celestial Empire :
perhaps with reason and perhaps baselessly. The principal
difficulty with which the investigator is faced is the fact that in
many cases it is quite impossible to date the authorities, while
even those whose period is approximately known are often inter-
polated with such skill that criticism is at a loss to distinguish the
original from the added. Until historians have succeeded in
reducing to order this heterogeneous mass of historical and
pseudo-historical records, very little trustworthy knowledge of
Chinese chemistry will be available.
Dr. O. S. Johnson has recently suggested that alchemy was an
indigenous product of China, and that it arose from the philo-
sophy of Tao-ism. According to this philosophy, the entire
universe was identical in substance and was animated and
dominated by a cosmic soul, manifesting itself in the dual forces
of Yin and Yang. All minerals or metals were thus substantially
the same, but differed in qualities in proportion to their relative
infusion with Yin and Yang. Base metals might therefore be
transmuted into precious metals by the dual method of elimi-
nating the more material Yin qualities in their composition, and
by augmenting, or refining, the more spiritual Yang qualities.
The first instance recorded in Chinese history of attempts to
transmute metals by artificial means, says Johnson, we find
during the reign of the famous emperor Wu Ti (140-86 B.C.),
but the principal authority on alchemy in China is Ko Hung, of
the fourth century of our era. He was a devoted Taoist, and
China 25
under the pseudonym Pao Pu Tzu ('Old Sober-sides') he wrote
in A.D. 330 an important treatise on Taoist philosophy and
alchemy. It is divided into two parts, of which the first, called
Nuy peen or 'inner chapters', consists of twenty chapters on the
transmutation of the metals, elixirs of life, ascetic rules for
prolonging life, and methods of attaining immortality. The
account of making yellow and white elixirs for converting base
metals into gold and silver respectively is chiefly contained in
chapters 4, n and 16. Ko Hung states that a man may prolong
his life by taking medicines made from plants, but can only
become immortal by the use of a Divine Elixir made from
minerals and metals. It is difficult to identify the substances
that were to be employed in the preparation of this elixir, but
red and yellow arsenic sulphides, sulphur, cinnabar, alum, salt,
white arsenic, oyster shells, mica, chalk and the resin of the pine
tree were certainly included among them. The resulting elixir,
when thrown on to mercury, or a mixture of lead and tin con-
tained in an iron pot, converted the metal into gold or silver,
while taken as a medicine for 100 days it made a man immortal.
That the Chinese discovered for themselves many properties
of minerals, and that they attempted to prepare medicines
which should confer long life or immortality, is not to be
doubted; but the greatest living historian of chemistry, E. O.
von Lippmann, believes that alchemy proper reached China
from the West in the course of the eighth century A.D., after the
port of Kanton had been opened to foreigners. In A.D. 714 the
first Arab ships dropped anchor at Kanton, and thereafter trade
developed with amazing rapidity. The eminent sinologist
Richthofen reached the conclusion that only from that time and
source did the Chinese acquire a true alchemy, and that sub-
sequently they described it as their own national discovery.
To support the claim they forged' all documents that they
considered necessary, either writing whole books and ascribing
a completely false antiquity to them, or cleverly interlarding
genuine works with spurious passages.
Amid these conflicting views and claims it is not possible to
2b India
arrive at any firm judgement, but there certainly is a close
similarity between Chinese alchemy and that of Islam (see
p. 46), so that it at least seems certain- that the two were derived
either from a common source or one from the other.
7. India
THE Indians are the blood-relations of the European peoples,
and it would be extremely surprising if so ancient a civilization
Fig. 9. THE IRON PILLAR OF DELHI
as that of India had failed to produce chemical facts and theories :
though we should remember that Egyptian chemistry was
'almost completely devoid of serious speculation. Unfortunately,
we know with certainty but little of the history of chemistry in
India, though there is a large medieval literature, in Sanskrit,
in which chemical and medical facts are described. The difficul-
ties of investigation are the same as those encountered in the
case of China, viz. the great uncertainty in the dating of
Rome 27
authorities, and the impossibility of accurately distinguishing
between indigenous and imported knowledge.
It has been suggested that Greek natural philosophy was
largely derived from that of ancient India : and as steadfastly
denied. There is certainly truth in the statement that an early
Indian philosopher named Kanada probably prior to Leu-
cippus supposed matter to be composed of five elements
(earth, water, light, air and 'ether') which were themselves made
up of indestructible and eternal atoms. Possibly this theory
found its way to Greece, though there is no satisfactory evidence
of the fact. In any case, it was the Greek, and definitely not the
Indian, form of the theory that influenced the Western world,
so that in this book we may perhaps leave the matter there.
The question of Indian influence arises again during the
period of Islamic chemistry. Certain Indian chemists, such as
Biwan the Brahman, are occasionally quoted by Muslim authors,
but the balance of evidence goes to show that chemistry was
carried to India by the Muslims rather than to Arabia by the
Indians. Yet it is only proper to repeat the statement that the
history of Indian chemistry and its relation to the outer world
has yet to be written.
8. Rome
IMPERIAL Rome has left us no grand chemical generalizations or
striking chemical discoveries. An eminently practical people,
the Romans were quick to perceive the value of applied science,
and Roman artificers and engineers were unequalled in skill and
ingenuity. The whole of the ancient world experienced their
activity: whether one goes to Constantinople or Frejus, to
Algeria or Spain, or to the nearer Mendips, the traces of the
Roman are obvious. Mining and metallurgy, the quarrying of
stone, dyeing, painting, wine-making all imply more or less
chemical knowledge, and the facts described in Pliny's Natural
History 1 and in the medical works of Galen clearly demonstrate
:he vast body of empirical science at the disposal of the Empire.
1 See Dr. Kenneth Bailey's The Elder Pliny 1 s Chapters on Chemical
Subjects t London, 1929. ,
28 Rome
Yet when the historian of chemistry attempts to lay his finger
on definite advances that the Romans made he finds it an
almost impossible task. Perhaps here and there a recipe is given
Fig. 10. PLINY OFFERING A WORK TO CAESAR
that cannot be paralleled in an earlier age ; here and there is
a process that seems particularly appropriate to special cir-
cumstances ; here and there a new experiment is described ; but
1 hat is all. Roman craftsmen for the most part merely applied
>ld knowledge with new efficiency, and Roman thinkers were
The Leyden and Stockholm Papyri 29
more attracted to law than to the philosophy of nature. So it is
that we must turn to the later developments of Greek thought,
in the city of Alexandria, if we wish to assist at the christening
of the infant chemistry.
9. The Leyden and Stockholm Papyri
THE Egyptian metallurgists and other technical workers doubt-
less worked out very frequently recipes that they considered
worth recording. At the same time, the fact that such informa-
tion was extremely valuable must have made them reluctant to
write the recipes in so clear a manner that, in cases of theft, the
thief would be able to understand and profit by them. More
probably they would resort to a semi-cryptic language, a custom
not unknown even to modern workers- in similar circumstances.
Unluckily, very few Egyptian technical manuscripts have sur-
vived, a misfortune which may be accounted for in part by an
act of the Emperor Diocletian in A.D. 290 or thereabouts. It
seems probable that, in the course of their work, the ancient
metal-workers had occasionally prepared alloys more or less
closely resembling the precious metals gold and silver. Too
shrewd and accomplished to deceive themselves very often, they
yet may have succumbed to the temptation of deceiving others
of less experience, passing off a good imitation of gold as the
genuine metal and thus acquiring an easy though dishonest
wealth. It can readily be imagined that such a delightfully
simple way of solving financial difficulty would rapidly become
popular, and that counterfeiters found a credulous market for
their spurious wares. Historians tell us that this actually
happened, and the nuisance at length became extremely serious.
Diocletian is therefore said to have commanded a diligent
inquiry to be made 'for all the ancient books which treated of
the admirable art of making gold and silver, and without pity
committed them to the flames ; apprehensive, as we are assured,
lest the opulence of the Egyptians should inspire them with
confidence to rebel against the Roman Empire'. But, as Gibbon
(who relates the story) sagely remarks, 'If Diocletian had been
30 The Leyden and Stockholm Papyri
convinced of the reality of that valuable art, far from ex-
tinguishing the memory, he would have converted the operation
of it to the benefit of the public revenue. It is much more likely
that his good sense discovered to him the folly of such magni-
ficent pretensions, and that he was desirous of preserving the
reason and fortunes of his subjects from the mischievous pursuit/
Fortunately, two manuscripts escaped the general massacre.
They appear to be the recipe-books of an Egyptian chemist, of
about the time of Diocletian, and were discovered in a tomb at
Thebes in the early years of the nineteenth century. One of
them is preserved at Leyden, and is therefore generally known
as the Leyden papyrus, while the other, the Stockholm papyrus,
belongs now to the Victoria Museum at Upsala. The Leyden
papyrus was translated and analysed by Berthelot, while in 1913
Lagercrantz translated the Stockholm papyrus and provided it
with a critical commentary. Although both manuscripts date
from the third century of our era, much of the material in them
is undoubtedly far more ancient and goes back to the days when
metallurgy was a secret craft controlled by the Egyptian priest-
lood.
The Leyden papyrus deals mainly with metals, and though
some of its recipes are plainly expressed, others are more
:ryptically worded and give mere hints or suggestion as to the
processes they describe. Of particular interest is the fact that
tfhile many of the recipes deal with the falsification and * pro-
duction' of the precious metals, they are noticeably free from
superstitious and magical theories. Similar remarks apply to the
Stockholm papyrus, which treats mainly of methods of 'pre-
paring' the precious stones, that is, of manufacturing passable
imitations. of them from glass and other materials. There seems,
indeed, little doubt that until the Alexandrian School began to
make its philosophical and mystical influence felt, the technical
workers were almost entirely free from the speculative im-
pulse, and carried on their activities in a purely empirical way
and with a mere utilitarian and practical aim. In the absence of
reliable criteria, they may occasionally have been mistaken as to
if, xi. OF THE
32 The School of Alexandria
the real nature of the metallic alloys they prepared, but it is
more likely that instructions for the 'doubling' of gold were
rarely misinterpreted by the chemist for whom they were
intended. He, at least, would know that 'artificial gold' was but
a technical term, and the Ley den and Stockholm papyri convey
the impression that their writer was too intelligent a man, and
too expert a craftsman, to believe in the actual transmutation of
metals or in the genuineness of the 'precious stones' prepared in
the laboratory.
10. The School of Alexandria
ALEXANDRIA, founded in 332 B.C. by Alexander the Great,
rapidly grew to be the greatest and most important town of
the ancient world. Under succeeding sovereigns, particularly
Ptolemy Soter (323-285), Ptolemy Philadelphus (285-247) and
Ptolemy Kuergetes (247-222) an enormous library was gathered
together Philadelphus even being fortunate enough to buy
Aristotle's library and a museum or university was built to
house the brilliant scholars attracted thither from various parts
of Greece. A mathematical school was founded by the great
Euclid himself, and among its celebrated pupils were Archi-
medes, Hipparchus, Eratosthenes, and Apollonius of Perga.
Grammar, literary criticism, philology, astronomy and medicine
all found learned teachers and enthusiastic disciples, and the
commercial industry of Alexandria was paralleled only by its
intellectual activity.
In the history of chemistry, Alexandria played a part of
fundamental importance. Here, for the first time, Egyptian
practical arts and Greek scientific thought were brought into
effective contact ; but the result was not, as perhaps one would
expect it to have been, the immediate synthesis of a logical
system of chemistry. Chemistry indeed may be said to have
begun in Alexandria, but it was almost stifled at birth through
the influence of two philosophical developments, some know-
ledge of which is essential to a proper understanding of the pro-
gress of the science. They are Gnosticism and Neo-Platonism.
[33]
ii. Gnosticism
THE first philosophico-religious system that profoundly in-
fluenced the childhood of chemistry is that known as Gnosti-
cism. Arising in the early years of the Christian era, it appears
in its full strength about A.D. 120 as a singular mixture of the
most diverse elements. Some parts of it derive from Greek
philosophy, others from Christianity, and still others from
a Persianized form of the old Babylonian religion. Such a com-
posite structure was inevitably confused, and the confusion was
rendered worse by the marked predilection for symbolic expres-
sion shown by the principal Gnostics. Yet Basilides, Valentine,
Marcion and the other exponents of the system had one thing in
common : their belief that they possessed the secret of a sublime
knowledge or gnosis which had been transmitted to them by
ineffable and occult means. This transcendental knowledge had
nothing in common with our science. 'We passionately seek the
truth/ says de Faye, 'that is, the real, whether in the past or in
the phenomena immediately before us. We desire to know that
which is. The Gnostics cared very little for the phenomena of
the sensible world ; the physical explanation of the Cosmos had
no interest whatever for them.' They were much more anxious
to know the invisible world, which they imagined to be peopled
with abstract yet living entities, and of which they described
their ideas in the strange and mysterious language of an in-
volved symbolism. It is significant that one of the earliest
chemical writers, Zosimos, was a Gnostic.
12. Neo-Platonism
NEO-PLATONISM has been described as the last great creation
of Greek philosophy and the noblest product of latter-day
paganism. Essentially it was a logical development of the
Platonic philosophy, combined, however, with ideas taken over
from the Stoics and Aristotle. Its principal creator was the
Egyptian Plotinus (c. 204-270), whose conceptions were ex-
tended and modified by Porphyry (233-304?), lamblichus (died
about 330), and others. The world to a Neo-Platonist was
2613-4 D
34 The Fusion of Practice with Speculation
imbued throughout with a soul, in which even inanimate
objects shared. The ordinary facts of nature, which we account
of paramount importance as the basis of natural science, were
regarded as plastic and variable manifestations of a transcen-
dental spiritual world, and were consequently neglected. More
essential to the Neo-Platonist than the external properties of
substances were their occult or sympathetic properties, by which
they could act upon one another even at a distance. All material
bodies were, like all spiritual entities, in harmony and sympathy
with one another, but matter was the principle of unreality or
evil and the disciple therefore attempted to detach himself from
the things of sense. The universe in part expressed itself through
the figures formed by the movements of the sun, moon, planets
and stars, and the celestial bodies both exerted an influence and
were signs of the future. Magic, as then practised by the Gnostics,
Plotinus denounced, but rather because its contemporary form
was, in his opinion, corrupt than because it was altogether base-
less. Numbers had mystical powers, and divination was a reason-
able art.
Such are the points of Neo-Platonism that immediately
concern us. Put thus baldly, they convey an unworthy idea of
the sublimity of the great system of philosophy in which many
profound thinkers have seen the highest expression of meta-
physical thought; but it was just this detachment from the
material world, and belief in the occult properties of the con-
tents of the universe, that largely defined the course of chemical
theory in its early days. Sympathetic action, action at a distance,
the distinction between occult and manifest properties, the
influence of the stars, the mystical powers of numbers, are all
ideas which permeate chemistry from its beginnings at the time
of Plotinus until the close of the seventeenth century.
13. The Fusion of Practice with Speculation
THE intercourse between Egyptian artificers and the followers
of Neo-Platonism and Gnosticism appears to have led the latter
to apply their mystical theories to the supposed art of gold-
Zosimos the Panopolitan 35
making and the nature and generation of metals and minerals.
Accepting transmutation as a fact, these primitive chemical
philosophers erected amazing structures of fanciful hypothesis
to account for it, discoursed at length upon the explanation of
the changes involved and, to lend dignity to the new science,
maintained that it was of great antiquity and that the god
Hermes or Thoth himself was its founder. When the knowledge
of the hieroglyphic characters was lost, they were claimed by the
chemists as expositions of chemeia, the Art of the Black Land,
Egypt or Khem, and the fabulous treasures of the Pharaohs were
stated to have been amassed through successful transmutations.
|The name chemeia appears for the first time in the writings
Attributed to Zosimos the Panopolitan, whose life and works we
must now consider.
14. Zosimos the Panopolitan
ZOSIMOS of Panopolis, in Upper Egypt, is the most ancient
alchemical author of whom we have genuine writings and whom
we can identify. A contemporary of Plotinus and Porphyry, he
lived towards the end of the third century A.D. or possibly at the
beginning of the fourth, and spent his early youth in Alexandria,
where he studied and wrote. Suidas, who flourished about the
year A.D. 1000, tells us that Zosimos composed an encyclopaedic
work on chemistry in at least twenty-eight books, which he dedi-
cated to his ' mystical sister' in the Art, Theosebeia. A few
treatises attributed to him are still in existence, and have been
published and translated by Berthelot; among them are his
Authentic Memoirs, A Treatise on the Alembic with Three Beaks,
On the Evaporation of the Divine Water that fixes Mercury, The
Book of Virtue: On the Composition of Waters, and a Treatise on
Instruments and Furnaces. These may be partly or mainly
genuine, but probably all contain interpolations of a later date.
They coffer us the most bizarre picture of Gnostic theory inter-
mingled with chemical fact, ecstatic visions, descriptions of
apparatus, and injunctions to the reader to keep the secret of
the Art from the vulgar.
D 2
36 Zosimos the Panopolitan
Zosimos tells us that the chemical arts were practised in Egypt
under royal and priestly control, and that it was illegal to publish
any work on the subject. Only 'Democritus' had dared to in-
fringe this regulation; as for the priests themselves, they had
engraved their secrets on the walls of the temples in hiero-
glyphic characters, so that even if any evilly disposed people
had ventured to brave the darkness of the sanctuaries they would
have found the inscriptions unintelligible. The Jews, however,
had been initiated into the mysteries and afterwards trans-
mitted them to others.
Believing in the possibility of metallic transmutation, Zosimos
describes the theory or rather theories of the process in
symbolic and mystical language of which the following is a
typical example: 1
I fell asleep and saw before me a priest standing upright before
a dome-shaped altar, leading up to which were fifteen steps. The
priest remained standing, and I heard a voice from on high which
said to me: 'I have accomplished the action of descending the
fifteen steps walking toward the darkness, and the action of
ascending the steps going towards the light. The sacrifice renews
me, rejecting the dense nature of the body. Thus necessarily con-
secrated, I become a spirit/ Having heard the voice of him who
stood upright upon the dome-shaped altar, I asked him who he
was. In a weak voice he answered me in these terms: 'I am Ion,
priest of the sanctuaries, and I suffer intolerable violence. Some
one came quickly in the morning, cleaving me with a sword, and
dismembering me according to the rules of the combination. He
removed all the skin from my head with the sword which he held ;
he mixed my bones with my flesh and burned them with the fire
of the treatment. It is thus, by the transformation of the body,
that I have learned to become spirit. . . .'
It is difficult to decide whether language of this kind is in-
tended to portray in symbolic form definite chemical operations,
or whether it merely represents a hypothetical philosophy of
certain chemical changes or whether, indeed, it has any mean-
ing at all. We can, however, in certain passages, discern a more
1 Stillman, The Story of Early Chemistry, London, 1924, p. 163.
Zosimos the Panopolitan 37
prosaic level whence we may extract relics of Zosimos's un-
deniably wide knowledge of practical chemistry. Thus he
mentions the preparation of mercury from cinnabar, and dis-
cusses the question whether or not mercury should be called
a metal (deciding that it is 'a metal and no metal', a 'neutral'
/^. 12. FIGURES OF LATE GREEK CHEMICAL APPARATUS
substance or a 'hermaphrodite'). The 'second mercury', arsenic,
he says can be obtained from sandarach [arsenic sulphide], by
first roasting it to get rid of the sulphur, when the 'Cloud of
Arsenic' [arsenious oxide] will be left. If this is heated with
various [reducing] substances, it yields the second mercury
[metallic arsenic], known as the 'Bird', which can be used to
convert copper into silver [copper arsenide is a white metallic-
looking compound not altogether unlike silver]. White lead may
be obtained by exposing lead to 'vapours' [scil. of acetic acid,
vinegar] ; on heating it yields litharge. If litharge is combined
with vinegar, the product [sugar of lead, lead acetate] has the
38 Zosimos the Panopolitan
remarkable property of being both sweet and salt-like ; on keep-
ing it is transformed into white lead [by the action of atmo-
spheric carbon dioxide, &c.]. Other chemicals mentioned are
realgar, ochre, haematite, natron, and chalkanthos [Fe 2 O 3 ].
Chemical apparatus may consist of pottery or glass, the latter
being particularly convenient on account of its transparency and
impermeability to certain vapours such as that of mercury. The
best glass vessels, Zosimos assures us, come from Askalon in
Syria, an observation of peculiar interest in that a Cairene
chemist of the fourteenth century also makes special mention of
the Askalon vessels. For fixing parts of apparatus together, clay,
fat, wax, gypsum and similar substances may be used. Heat may
be applied by (a) the sun, (b) fermenting manures, (r) sand-baths
or baths of hot ashes, (d) water-baths and (e) furnaces.
Facts and descriptions such as these show quite clearly that
Zosimos had a by no means negligible laboratory experience,
and that he and his like are not to be lightly dismissed as mere
theorizers. Yet they were obsessed with mystical and super-
stitious philosophies current at the time, and appear to have
welcomed the fabulous as much as the true, if not more. We
inevitably find it difficult to understand how a man as well
versed in simple metallurgical and chemical facts as Zosimos
must have been, could accept the following account of the
origin of tin : l
In a place in the far west, where tin is found, there is a spring
which rises from the earth and gives rise to it like water. When the
inhabitants of this region see that it is about to spread beyond its
source, they select a young girl remarkable for her beauty and place
her entirely nude below it, in a hollow of the ground, in order that
it shall be enamoured of the beauty of the young girl. It springs at
her with a bound, seeking to seize her; but she escapes by running
rapidly while the young men keep near her holding axes in their
hands. As soon as they see it approach the girl, they strike and cut
it, and it comes of itself into the hollow and of itself solidifies and
hardens. They cut it into bars and use it.
1 Stillman, op. cit., p. 168.
A Retrospect 39
Yet such descriptions, whether intended to be taken literally
or as merely symbolical, grow more and more frequent and more
and more incomprehensible as we pass to those chemists who
succeeded Zosimos: Pelagius, Synesius, Heliodorus, Olympi-
odorus and others. Speculation and occult theory grow ever
wider apart from experimental fact, and at length we encounter
the conception of a philosopher's stone, a divine elixir, which,
if projected upon 'base' metals in fusion, will convert them into
gold 'better than that of the mines'. When this remarkable idea
was first evolved we have no definite knowledge, but from the
seventh century till the seventeenth it was the object of un-
ceasing search on the part of the great majority of chemists, and
indeed formed the central theme of chemistry for the major
portion of its existence.
15. A Retrospect
EARLY chemistry is somewhat difficult to follow, and we shall
probably find it useful to clear our ideas by taking a bird's-
eye view of the territory we have already traversed, before
entering upon the travels in Arabia that await us. We have
seen that technical arts were highly developed in Egypt and
other nations of antiquity, and that in Egypt in particular the
professional knowledge of metallurgy and similar processes was
practically the monopoly of the priesthood and the Crown. On
the other side of the Mediterranean, the Greeks had burst into
an efflorescence of intellectual effort and had produced two
theories, viz. those of Aristotle on the constitution of the world,
and of the Atomists on the minute structure of matter, which
will emerge again later in our story. Plato also had evolved a
philosophical system which continued to develop after his
death, and reached its culminating point in the Neo-Platonism
of Alexandria in the early centuries of the Christian era.
At Alexandria, Egyptian practice and late Greek speculation
fused, the occultism of the Gnostics and the transcendentalism
of the Neo-Platonists leading to highly imaginative theoretical
explanations of metallurgical processes and mineralogical
4O A Retrospect
observations. The transmutation of metals a superficial inter-
pretation of Egyptian metallurgical facts gained universal
credence, and the philosopher's stone was a means whereby this
Fig. 13. CLEOPATRA'S SYSTEM OF GOLD-MAKING
transmutation could be effected. The new science or art was
called Chemeia, whence in Muslim days the name al-chemy and
later still our chemistry. With the degeneration of Hellenic
culture, chemistry itself became more and more divorced from
The Rise of Islam 41
fact, until in the seventh century A.D. it was almost completely
an occult art. Yet among the Alexandrian chemists there must
have been many capable men, who undoubtedly advanced the
practical side of the subject.
1 6. The Rise of Islam
ON 8 June, A.D. 632, the Prophet Muhammad died, having
accomplished the marvellous task of uniting the tribes of Arabia
into a homogeneous and powerful nation. Exactly a century
later, in A.D. 732, the victorious march of the Muslim armies was
stemmed at Poitiers (France) by Charles the Hammer. In the
interval, Persia, Asia Minor, Syria, Palestine, Egypt, the whole
North African littoral, Gibraltar and Spain had been conquered
by the forces of Islam, and a new civilization had been estab-
lished. 'The stupendous conquests which laid the foundations
of the Arab Empire/ says Sir Thomas Arnold,
were certainly not the outcome of a holy war, waged for the
propagation of Islam, but they were followed by such a vast
defection from the Christian faith that this result has often been
supposed to have been their aim. Thus the sword came to be
looked upon by Christian historians as the instrument of Muslim
propaganda, and in the light of the success attributed to it the
evidences of the genuine missionary activity of Islam were obscured.
But the spirit which animated the invading hosts of Arabs who
poured over the confines of the Byzantine and Persian empires, was
no proselytizing zeal for the conversion of souls. On the contrary,
religious interests appear to have entered hut little into the con-
sciousness of the protagonists of the Arab armies. This expansion
of the Arab race is more rightly envisaged as the migration of
a vigorous and energetic people driven by hunger and want, to
leave their inhospitable deserts and overrun the richer lands of
their more fortunate neighbours.
The Arabs quickly assimilated the culture and knowledge of
the peoples they conquered, while the latter in turn Persians,
Syrians, Copts, Berbers, and others adopted the Arabic
language. The nationality of the Muslim thus became sub-
merged, and the term Arab acquired a linguistic sense rather
42 The Rise of Islam
than a strictly ethnological one. By an 'Arab', indeed in this
book we shall understand an Arabic-writing Muslim of whatever
race, unless definite indication is given that the word is used in
its narrow sense.
As soon as the disturbance of military operations had sub-
sided, the Arabs began to encourage learning of all kinds.
Schools, colleges, libraries, observatories and hospitals were
built throughout the empire, and were adequately staffed and
endowed. Scholars were invited to Damascus and Baghdad
without distinction of nationality or creed. Greek manuscripts
were acquired in large numbers and were studied, translated
and provided with scholarly and illuminating commentaries.
The old learning was thus infused with a new vigour, and the
intellectual freedom of the men of the desert stimulated the
search for knowledge.
The oft-repeated story that the Arabs burnt the library at Alex-
andria is a fable that appears for the first time in the thirteenth
century, some six hundred years after the supposed event. It
carries its own refutation in the circumstantial detail provided to
give 'verisimilitude to an otherwise bald and unconvincing
narrative ' ; we are told that the books were used as fuel in the baths
at Alexandria and that the supply was sufficient for six months.
Now we happen to know that there were 4,000 baths in the town,
and, on a very moderate estimate, to heat them for six months
would have required a library of no fewer than 72,000,000 volumes!
The truth is that the library had been destroyed long before the
Muslim conquest.
In early days jit least, the Muslims were eager seekers after
knowledge, and Baghdad was the intellectual centre of the world.
A celebrated historian has justly remarked that what charac-
terized the school of Baghdad from its inception was its
scientific spirit. Proceeding from the known to the unknown;
taking precise account of phenomena ; accepting nothing as true
which was not confirmed by experience, or established by
experiment such were the fundamental principles taught and
acclaimed by the then masters of the sciences.
L43J
1 7. The Origins of Alchemy in Islam
TRADING operations between Arabia and the countries on its
boundaries, particularly Syria, must have resulted in the in-
filtration of the main doctrines and practices of alchemy even in
thejahiliyya, or 'Time of ignorance', as Muslim writers describe
pre-Islamic days. Yet the knowledge thus gained roused little
general attention and no records of it remain ; the Arabs them-
selves assert that alchemy was first studied in Islam by Khalid
ibn Yazid, though deferential tradition ascribes a knowledge of
the Art to Muhammad and to his cousin and son-in-law the
Caliph Ali.
The Jews came to the Prophet, says the story, and asked him con-
cerning alchemy. He said, 'If I will that the camels from Tihama
come to me laden with gold and silver, it is so : lift ye up the reed
mat. ' They lifted it and saw a large quantity of gold. Then said
the Jews, 'That and the like thereof can the magicians also do/
The Prophet replied, 'If I reveal the Art to you, will ye then accept
Islam?' They answered him, 'Yea'. Thereupon the Prophet said,
'It consists in common gold, lead, bitter salt and ordinary quick-
silver; yet will ye not believe!' We can, perhaps, hardly blame them.
It is evident from stories such as this that the Muslims very
quickly became acquainted with alchemy, and no doubt their
information reached them from very many different sources. It
was, however, through the city of Alexandria that the first real
introduction of the art to Islam took place, if the unanimous
tradition of the Arabs themselves is to be believed. The main
thesis is probable enough Alexandria, as we have already seen,
was a centre of alchemy and other occult arts and sciences but
the details given by native writers are open to doubt. Yet the
story is worth repeating, for it tells us what Muslim chemists
believed about the origin of alchemy in Islam and may well be
based upon some foundation of truth :
There lived in Alexandria a Christian monk named Marianus,
an ascetic and an adept in alchemy. The young Arab prince,
Khalid ibn Yazid (died 704 A.D.), heard of the fame of Marianus
and summoned him to Damascus to expound the science of the
44 The Origins of Alchemy in Islam
transmutation of the metals. After much persuasion, Marianus
came and instructed Khalid in the art of preparing the Elixir ;
whereupon Khalid became so enamoured of alchemy that he
caused numbers of Greek alchemical works to be translated into
Arabic, and seems to have devoted a great deal of time to the
investigation of the subject. There is no statement of the actual
works translated, but we may suspect them to have been books
of Zosimos, 'Democritus', 'Ostanes', and similar writers, their
general characteristics being a love of mystification and a re-
markable reluctance to state any definite facts. None of
Khalid's own writings on alchemy appears to be extant, if we
except certain poetical fragments of doubtful authenticity;
these lead one to the conclusion that the loss is not a serious one,
as they show only too clearly that their author was quite un-
critical and credulous. Khalid's services to chemistry, indeed, if
he ever performed any, lie in the fact that by his enthusiasm and
example he led better men to its study, rather than in any
advance of either a theoretical or a practical nature. This is the
picture given of him in a tenth-century Muslim encyclopaedia :
The first to investigate the books of the ancients upon alchemy was
Khalid ibn Yazid ibn Mu'awiyya. He was an orator, a poet,
eloquent, and full of enthusiasm and judgement. He was the first
to have translated the [ancient] books of medicine, astrology and
alchemy. Of a generous nature, it is said that he replied thus to one
who had reproached him with devoting most of his life to the pur-
suit of alchemy: 'All my researches have for their sole aim the
enrichment of my brethren and companions. I had hoped for the
Caliphate, but it has been taken from me, and I have found no
compensation except in attempting to reach the utmost limits of
the Art. I wish to render every one whom I know, or who has
known me though it were for but a single day independent of
the necessity of soliciting favours from a prince/ It is said (Allah
knows best whether it is true!) that Khalid was successful in his
alchemical undertakings. He wrote on the subject a number of
treatises and tracts and composed much verse on the matter.
From the same encyclopaedia we can also gather some of the
names venerated by alchemists in the early days of Islam. Many
u
u
w
^
h
W
46 The Origins of Alchemy in Islam
are those of historical personages, others are mythical and others
cannot be identified. First comes Hermes (Thoth), followed by
Agathodemon; then come Plato, Zosimos, Democritus, Herac-
lius, Ostanes, Alexander, Mary the Jewess and many more, the
main interest in the list being the indication it affords that
alchemy was widely studied, even if not very intelligently, and
that the habit of falsely attributing works on the Art to any
great man whose authority was considered desirable had already
'become established.
We may be quite certain that, in the main, Muslim alchemy
was derived from the Greek. The frequency with which Greek
authors are quoted, the numerous theories that are common
to both Greek and Arabic alchemy, and the large number
of Arab technical terms clearly taken over from Hellenic
treatises (e.g. hayuli* atisyus, 2 athalia? iksir^ qambarf] prove
beyond doubt the affiliation of Muslim and Greek alchemy.
The transmission was made partly through direct contact in
Egypt, partly through the medium of Syrian Christian trans-
lators, and partly by way of Persia. There are unmistakable
traces of Persian influence, manifested distinctly by linguistic
affinities in technical names and usages and in names of minerals.
These traces are sufficiently well marked to render it probable
that Persia was, indeed, one of the main channels through which
alchemy came to Islam; and it is not without interest to note
that many of the principal Muslim alchemists were Persians.
It has already been observed that Chinese alchemy has so
much in common with Greek and Arabic alchemy as to afford
support to the hypothesis that all three had a common origin ;
and there is some reason to believe that the Chinese practised
a kind of alchemy long before the days of Islam (see p. 25). The
remote origins of Arabic alchemy are therefore still to some
extent uncertain, but there is very little to recommend the
suggestion that the Arabs received any direct introduction to
alchemy from the Chinese. Whatever may be the cause of the
similarity between Chinese, Greek and Muslim alchemical ideas,
4 fijpiov. 5 Ktvvdf}api.
The Origins of Alchemy in Islam 47
Arabic alchemy is for the most part a direct legacy from the
Greek, and to a less extent from Persian, Chaldean and other
sources. A further factor to be considered in this connexion is
the practical knowledge possessed by the craftsmen of the
nations with which the Arabs had at one time or another come
si*L^4^'^-i
V^v; - ;
Fig. 15. PAGE OF AX ANCIENT KORAN
into contact. The skill attained by the technical workers of
ancient Egypt and Assyria has already been described, and it is
noteworthy that many Assyrian mineral and other names are to
be found in Arabic treatises on alchemy. Not the least in-
teresting is the word abaru, meaning the metal extracted from
collyrium, that is, lead or antimony, which occurs very fre-
quently in Arabic alchemy and even passed over into medieval
Latin treatises.
Briefly, it is reasonable to suppose that, although the main
source of alchemy in Islam is certainly Greek, the Greek know-
ledge and theories found awaiting them a fairly extensive
acquaintance with certain practical arts ; and that they were also
admixed sooner or later with fresh material from surrounding
countries and even perhaps from India and China.
48 The Origins ot Alchemy in Islam
In the actual process of transmission of Greek alchemy to
Islam, there is much evidence to show that a good deal of the
work of translation was carried out by Syrian Christians.
Berthelot, indeed, goes so far as to maintain that Syrian scholars
played the chief part in handing on Greek learning to the Arabs.
'They already played an important part', he says, 'as inter-
mediaries between the Persian sovereigns und the Emperors of
Constantinople, but their authority became even greater when
the Arabs had conquered Persia and Syria. The caliphs sought
them particularly on account of their medical skill, but they
played many parts, for we find them as physicians, civil and
military engineers, astrologers, treasury officials, town governors,
etc. The importance they acquired was very favourable to the
development of scientific culture; now all their science came
from the Greeks, and it was through them that Greek doctrine
passed on to the Arabs/
This estimate is probably exaggerated. It seems possible that
even in the eighth century many Muslim scholars could read
Greek, and were thus in a position to study Greek authors in the
original. Moreover, as was stated above, the transmission of
Greek knowledge to Islam by way of Persia was by no means
negligible, and was of special importance in medicine, alchemy
and astrology. The great Academy at Jundi-Shapur in Khuzis-
tan (S.W. Persia) was still flourishing in the days of the 'Abbasid
caliphs, and the Persianized form of Greek philosophy and
medicine taught there had great influence upon the progress of
Muslim learning. Still another channel through which Hellenic
wisdom passed to Islam was the town of Harran in Mesopotamia.
Harran had been a home of Greek culture ever since the days of
Alexander the Great. It was inhabited by Syrian pagans who
later became known to the Arabs as Sabians; they were star-
worshippers and enthusiastic astrologers. As linguists they
possessed unusual skill, and the ease with which they learnt to
speak Arabic put them into an exceptionally favourable position
for teaching their eager neighbours. In spite of their paganism
they found favour at the Court of Baghdad, no doubt on account
Jabir ibn Hayyan 49
of their scholarship, but to ensure their personal safety they dis-
covered it necessary to pay a considerable sum in the way of
bribes to the conscientious Muslim officials. It is probable that
Harran also transmitted much of the old Babylonian lore in
addition to the Hellenic culture.
1 8. Jabir ibn Hayyan
THE greatest chemist of Islam has long been familiar to Western
readers under the name of Geber, which is the medieval render-
ing of the Arabic Jabir. For our knowledge of Jabir 's life, we
now have a not insignificant collection of data, and can recon-
struct his figure with reasonable accuracy. Although much is
conjectural, the following may be taken to represent, in brief,
what we know of him.
In A.D. 638 the Caliph Omar was visited at Medina by a
deputation of Arabs from Al-Meda'in, a town on the Tigris
that they had recently conquered. The Caliph was startled by
their sallow and unwholesome look, and asked the cause. They
replied that the air of the town did not suit the Arab tempera-
ment, and the Caliph therefore ordered inquiry for some more
healthy and congenial spot. A plain on the banks of the
western branch of the Euphrates was finally chosen, and there
the city of Kufa was founded. The new town suited the
Arabs well, and to it they accordingly migrated in great
numbers. But the dwellings were at first made of reeds, and
fires were frequent, so after a particularly disastrous conflagra-
tion the city was rebuilt with less inflammable material, and the
streets were laid out in regular lines. In orderly fashion, be-
fitting a military station, the various Arab tribes were settled in
particular quarters of the town no doubt with a view to the
prevention of civil commotion.
One of the tribes whose members were present at Kufa in
sufficient numbers to be assigned a definite quarter was that
known as Al-Azd, a celebrated tribe of South Arabia. From this
tribe there sprang, towards the end of the seventh century A.D.,
a man named Hayyan, who carried on the business of a druggist
2613-4 E
50 Jabir ibn Hayyan
at Kufa. His life would appear to have been uneventful until
the early years of the eighth century, when we find that he
espoused the cause of the powerful 'Abbasid family, who were
trying to overthrow the reigning Caliph of the house of Umayya
in order to usurp his place. To further their plans, the 'Abbasids
engaged in extensive political propaganda, and Hayyan was sent
as an emissary to Persia on this business. It was while he and his
wife were at the town of Tus, in Khorasan, near the modern
Meshed, that his son Jabir was born, probably in the year
A.D. 721 or 722. Shortly afterwards, Hayyan was arrested by
agents of the Caliph and was subsequently executed.
The now fatherless Jabir ibn [son of] Hayyan was sent to
Arabia, perhaps to his kinsmen of the Azd tribe, to be cared for
until he was old enough to fend for himself. Whilst in Arabia,
he studied the Koran, mathematics and other subjects under
a scholar named Harbi al-Himyari, of whom unfortunately we
have no record. Meanwhile the 'Abbasids, in whose service
Jabir 's father had lost his life, succeeded in achieving their
object. In A.D. 748 they overthrew theUmayyads and themselves
assumed the Caliphate, so that Hayyan had not died in vain. It
was under the 'Abbasid caliphs, the most famous of whom was
Harun al-Rashid, that Islamic civilization reached its zenith.
During the period in which these political changes were
taking place, Jabir appears to have won the friendship of the
Imam Ja'far al-Sadiq, one of whose disciples he became. Ja'far
was a man held in very high esteem by a section of Muslims
known as the Shi'ites, and the Shi'ites themselves had been
active in support of the 'Abbasid cause. These facts, coupled
with the recollection of Hayyan *s activity in the same direction,
enable us to understand how Jabir in middle life came to be
welcomed at the Court of Harun al-Rashid at Baghdad. He does
not seem to have had much personal contact with the sovereign
himself, but he was on intimate terms with the Caliph's all-
powerful ministers the Barmecides, some of whom figure in The
Thousand and One Nights.
On one occasion we find him accompanying his patrons to the
Jabir ibn Hayyan 51
slave-market, to buy handmaids, while on another he describes
a cure he effected in Yahya the Barmecide's household.
Yahya ibn. Khalid [says Jabir] possessed a very valuable hand-
maiden, unequalled in beauty and perfection and deportment and
:
Fig. 16. IMAGINATIVE PORTRAIT OF JAH1K
intelligence and accomplishments. One day she fell ill and though
she drank medicine it failed to cure her, and she rapidly grew
worse and finally became delirious. A messenger came to Yahya
with the news and he asked me what I advised. I had not seen her
and thought she might be poisoned, so I recommended the applica-
tion of cold water. This treatment was of no avail, so I ordered
them to poultice her abdomen with heated salt and to chafe her
feet. As she still grew worse, Yahya at last asked me to go and see
her, and I found her at the point of death from some obscure
2
52 Jabir ibn Hayyan
disease. Now I had a certain elixir with me, so I gave her a draught
of two grains of it in three ounces of oxymel, and, by Allah ! the
sickness departed from the damsel, and in less than half an hour
she was as well as ever. And Yahya fell at my feet and kissed them,
hut I said, 'Do not so, O my brother.' And he asked me about the
uses of the elixir, and I gave him the remainder of it and explained
how it was employed, whereupon he applied himself to the study
of science and persevered until he knew many things; but he was
not so clever as his son Ja'far.
Al-Jildaki, a Muslim chemist who lived in the fourteenth
century (see p. 81), tells us that, through the medium of the
vizier Ja'far the Barmecide, Jabir was brought into relation with
the Caliph Harun al-Rashid, 'for whom he wrote a book on the
noble art of alchemy entitled The Book of the Blossom. In it he
described wonderful experiments of a very elegant technique'.
We learn also that it was through the efforts of Jabir that the
second importation of Greek scientific books from Constanti-
nople was made, the first being that which was made under the
auspices of Khalid ibn Yazid some three-quarters of a century
earlier. It was not until the reign of Al-Ma'rnun (A.D. 813- 33)
that the process reached its maximum development ; this Caliph
sent a deputation to the Roman Emperor Leo the Armenian
with a request for Greek books for translation into Arabic, and
built the celebrated 'House of Wisdom' or Baitifl-Hikma at
Baghdad, in which the translators, together with astronomers
and other scientists, were installed.
It seems therefore, that while Jabir's main interests lay in
chemistry, he was a widely-read scholar, and probably had some
knowledge of Greek. His own list of his writings, which has
come down to us at second hand in the Kitab al-Fihrist of Ibn
al-Nadim (about A.D. 1000), shows that, in addition to books on
chemistry, he wrote others on a variety of subjects a fact that
need not surprise us when we remember the vast extent of the
intellectual treasures now becoming available to the Muslims
through their introduction to Greek learning by way of Jundi-
Shapur, Harran, Alexandria and other centres of Hellenic
54 Jabir ibn Hayyan
culture. Thus we find that he wrote a commentary on Euclid
and the Almagest of Ptolemy ; he knew some of the writings or
views of Plato, Socrates, Aristotle, Hippocrates, Empedocles,
Pythagoras and Democri-
tus; he wrote a treatise on
Mirrors, another on Logic,
and another on the art of
Poetry; he interested him-
self in the newly-developed
mystical system of Sufi-ism,
and he studied the ideas of
Apollonius of Tyana. He
was thus a man of culture
and scholarship and not a
petty mystagogue or char-
latan; we can indeed be
certain that the Barme-
cides a pretty shrewd
and level-headed family
would otherwise not long
have tolerated him.
When Jabir first went to
Baghdad to live we do not
know, but for a part of his
life he lived at Kufa. Here
he had a laboratory, which
was rediscovered, about two
Fig. 18. PAGE OF ONE OF JABIR'S centuries after his death,
CHEMICAL WORKS IN ARABIC during ^ demo lition of
some houses in the quarter of the town known as the Damascus
Gate. Among other things brought to light were a mortar and
a large piece of gold, 'of which', says the chronicler slyly, 'the
King's Chamberlain took possession'.
In A.D. 803 Harun al-Rashid finally tired of the Barmecides,
who had .grown so powerful as to be a continual menace to him,
and executed one of them and banished the rest. Jabir, we are
if ",
i>
fe 19 FIGURES OF ALCHEMICAL PROCESSES
IN ARABIC MANUSCRIPT
56 Jabir ibn Hayyan
told, was involved in the disgrace of his patrons, and fled to Kufa,
where he spent the remainder of his life in retirement. The date
of his death is uncertain. According to Al-Jildaki, who was
usually very well informed about the chemists of Islam, Jabir
survived until the days of Al-Ma'mun, who succeeded in
A.D. 813, and the last public act of his life was to help to persuade
the Caliph to nominate as his successor the young Shi'ite Imam
Ali al-Rida, in A.D. 817. We hear nothing of him afterwards, so
we may presume that he died about that time, at the ripe age of
95. It is, of course, possible that the last tradition is mistaken,
but the quality and quantity alike of Jabir 's books are such that
no man who died young would have had time to write them.
The idea that the transmutation of the metals was possible had
the excellent merit of provoking incessant experiment, but un-
fortunately the alchemists were always prone to theorize to an
inordinate extent. Moreover, at Alexandria, the mystical
beliefs of the Gnostics and the Neo-Platonists however
admirable and attractive in themselves had a very detrimental
effect upon experimental science. Alchemy thus became less
and less a matter for experimental research and more and more
the subject of ineffable speculation and superstitious practice,
not to say fraudulent deception.
In such an atmosphere Jabir began his study, and it is not
surprising to find that he never completely shook off the effects.
About a hundred of his books are extant, and many of them seem
to us of the twentieth century to be confused jumbles of puerile
superstition. The peculiar characteristic of Jabir is, however,
that in spite of his leanings to mysticism and superstition, he
more clearly recognized and stated the importance of experiment
than any other early chemist, and made noteworthy advance in
both the theory and practice of chemistry.
One of his chief contributions to the theory of chemistry
lies in his views upon the constitution of the metals. To under-
stand his conceptions properly, we must hark back to Aristotle,
whose philosophy of nature was universally accepted in its main
principles by the scientists of Islam. According to Aristotle, it
Jabir ibn Hayyan 57
will be remembered, all substances are composed of the four
* elements' fire, air, water, and earth, which are themselves inter-
convertible. The immediate constituents of minerals and metals
are two exhalations, one an 'earthy smoke' and the other a
'watery vapour' ; the former consists of small particles of earth
on the way to becoming fire, while the latter consists of small
particles of water on the way to becoming air. Neither exhala-
tion is ever entirely free from some admixture of the other.
Stones and other minerals are formed when the two exhalations
become imprisoned in the earth, the dry or smoky exhalation
predominating ; metals are formed under similar circumstances
if the watery exhalation predominates.
Jabir accepted this theory of the constitution of metals, but
appears to have regarded it as too indefinite to explain observed
facts or to afford a guide to practical methods of transmutation.
He therefore modified it in such a fashion as to make it less
vague, and the theory he suggested survived, with some altera-
tions and additions, until the beginning of modern chemistry in
the eighteenth century. The two exhalations, he believed, when
imprisoned in the bowels of the earth, are not immediately
changed into minerals or metals, but undergo an intermediate
conversion. The dry or smoky exhalation is converted into
sulphur and the watery one into mercury, and it is only by the
subsequent combination of sulphur and mercury that metals
are formed. The reason of the existence of different varieties
of metals is that the sulphur and mercury are not always pure,
and that they do not always combine in the same proportion.
If they are perfectly pure and if, also, they combine in the most
complete natural equilibrium, then the product is the most
perfect of metals, namely gold. Defects in purity or proportion,
or both, result in the formation of silver, lead, tin, iron, or copper,
but since these metals are essentially composed of the same
constituents as gold, the accidents of combination may be
removed by suitable treatment. Such treatment is the object of
alchemy.
To the modern mind it will at once occur that the above
58 Jabir ibn Hayyan
theory might easily have been tested by experimental attempts
to obtain metals by the combination of sulphur and mercury.
We may be quite sure that so obvious a deduction was not
overlooked by Jabir, for in one of his books he describes such an
experiment and states that the product was 'the red stone known
to men of science as cinnabar' the mercuric sulphide of our
text-books of chemistry ^ From observations such as this, Jabir
was forced to the conclusion that the sulphur and mercury of
which metals are composed are not the well-known substances
that go by these names, but hypothetical substances to which
ordinary sulphur and mercury form the closest available
approximations. That this theory has all the bad qualities
which Lavoisier found in the theory of phlogiston several
hundred years later cannot be denied, but it represented a dis-
tinct advance upon any previous theory, and satisfied the
intellectual curiosity of many brilliant scientists for a very
lengthy period. The phlogiston theory itself, which, in spite
of its shortcomings, has been described as 'the lamp and
guide of chemists' during the eighteenth century and 'the time-
honoured and highest generalization of physical chemistry for
over half a century/ was a direct descendant of Jabir's theory of
the constitution of metals, and thus ultimately of Aristotle's
theory of the two exhalations.
On the practical side, Jabir was acquainted with the usual
chemical operations such as crystallization, calcination, solution,
sublimation, reduction, &c., and often describes them. Of more
interest, however, is the fact that he attempts to understand the
changes that go on in these processes, and frequently gives his
opinions as to their aims. His method of reducing calces
[metallic oxides] is illustrated by the following quotation :
Take a pound of litharge and a quarter of a pound of soda and
powder each well. Then mix them together and make them up
into a paste with oil and heat in a descensory. The metal will
descend pure and white.
To calcination, i.e. the conversion of a metal into a powder by
Jabir ibn Hayyan 59
oxidation or otherwise, he devoted a complete book, from which
the passage below is quoted :
Souls and spirits [i.e., volatile substances like sulphur and sal-
ammoniac] will not sustain calcination, since the latter can be
effected only with a very hot fire; now spirits will not sustain
a very hot fire as they are volatile and fly away from it. Moreover,
the aim of calcination is nothing more than the removal of im-
purities from metals and their complete combustion, so that the
metals may be purified and remain unadulterated and unsullied;
in a spirit, however, there is no necessity for the same treatment as
in a metal, and all that is needed is the first process in calcination
[i. e., gentle heating] , when the same effect is produced on the spirit
as [complete] calcination effects on the metals, namely, full
purification. As for the process which is to spirits what calcination
is to metals . . . thou wilt find it to be sublimation.
As I have now made clear the aim of calcination I will next
speak of its various forms, for each metal is calcined in a different
way from the others. This is because among the metals are found
some which are already pure, such as gold ; in this case the object
of calcination is to convert the metal into a fine powder so that it
may be enabled to combine and enter into union with the sublimed
spirits, and also to dissolve. The same applies to silver, but silver
is slightly impure, so that it needs purification as well as conversion
into a fine powder.
As for the rest of the metals, that is excluding the two above-
mentioned, they indeed all require calcination both for purification
and also for converting them into powder ; and the same is true for
those minerals which are infusible, according to their degree of
purity.
The practical applications of chemistry were not neglected.
Jabir describes processes for the preparation of steel and the
refinement of other metals, for dyeing cloth and leather, for
making varnishes to waterproof cloth and to protect iron, for the
preparation of hair-dyes and so on. He gives a recipe for making
an illuminating ink for manuscripts from * golden' marcasite, to
replace the much more expensive one made from gold itself, and
he mentions the use of manganese dioxide in glass-making. He
knew how to concentrate acetic acid by the distillation of
60 Jabir ibn Hayyan
vinegar, and was also acquainted with citric acid and other
organic substances. It is, indeed, abundantly evident that his
experimental work was skilful and extensive; and that he
realized the importance of experiment in chemistry may be
witnessed by the following characteristic remarks :
The first essential in chemistry is that thou shouldest perform
practical work and conduct experiments, for he who performs not
practical work nor makes experiments will never attain to the least
degree of mastery. But thou, O my son, do thou experiment so
that thou mayest acquire knowledge.
Scientists delight not in abundance of material ; they rejoice only
in the excellence of their experimental methods.
Perhaps his most useful discovery was that of nitric acid, the
preparation of which is described for the first time in one of his
books entitled The Chest of Wisdom.
19. The Latin Works of Jabir or Geber
SOME of Jabir 's books, for example, The Book of Seventy and
The Book of Mercy, were translated into Latin in the Middle
Ages, and in the two cases mentioned both the Arabic and Latin
versions are extant. There are, however, certain other Latin
works, entitled The Sum of Perfection, The Investigation of
Perfection, The Invention of Verity, The Book of Furnaces, and
The Testament, which pass under his name but of which no
Arabic original is known. A problem which historians of
chemistry have not yet succeeded in solving is whether these
works are genuine or not. Many scholars have regarded them
as European forgeries of the twelfth or thirteenth centuries,
basing their conclusion upon the following arguments :
1. No Arabic originals have been found.
2. The contents of the books differ from the contents of
Arabic books undoubtedly written by Jabir.
3 . The style of the books is (a) different from that of Jabir
and (b) characteristic of the Schoolmen.
4. The Latin author devotes much space to the refutation of
those who disbelieve in the possibility of transmutation ; now
Jabir ibn Hayyan 61
this disbelief, says one authority, 'appeared only in the twelfth
century'.
We may consider these arguments in order. As to the first,
the fact is undoubted, but the recent discovery of the Arabic text
of The Book of Seventy does much to diminish its weight. As
to the second, it is true that the contents of The Sum of Per-
fection and the books which usually accompany it cannot be
paralleled in any single known Arabic book of Jabir's. But this
fact takes on a different aspect when we read the opening words
of The Sum of Perfection, viz., 'Our whole Science of Chymistry,
which, with a diverse Compilation, out of the Books of the
Ancients, We have abbreviated in our Volumes, We here reduce
into one Sum/ If this passage truly represents the author's
procedure, what we should look for among the extant Arabic
works is not necessarily one which in itself contains all the facts
described in The Sum of Perfection', we should rather examine
the contents of all of them and consider whether The Sum of
Perfection might veritably have been composed of facts scattered
throughout them. Many of Jabir's books still existing have
not yet been studied, but, with a few notable exceptions, no
information is given in The Sum of Perfection^ &c., which is not
to be found in one or other of the Arabic works. It follows
that the second argument is no more conclusive than the first.
The third argument is based upon the contrast in style
between The Sum of Perfection, &c., and genuine Arabic works
of Jabir. That a contrast does exist it would be idle to deny, but
the genius of the Latin language is so different from that of
Arabic that style is inevitably more or less obscured in the process
of translation. Nevertheless, the objection is a weighty one, for
the present writer knows no Arabic book of Jabir's so systematic-
ally arranged as The Sum of Perfection. On the other hand, to
those versed in the writings of the Muslim alchemists, there are
clear traces of an ultimate Arabic origin in The Sum of Perfection
as well as in the other books usually found with it. That the style
of these books is characteristic of the Schoolmen is a statement
that need not be taken too literally ; it is based upon the elaborate
62 Jabir ibn Hayyan
refutation which Geber makes of his opponents, and can be most
conveniently considered in that connexion.
The fourth argument against the authenticity of the Latin
n Wvt-
' "
r<3U> f^
Fig. 20. EARLY MS. OF GEBER'S Investigation of Perfection
books is that Geber formally argues at great length against
those who disbelieve in the possibility of transmutation, first
describing the reasons they advance and then proceeding to
refute them seriatim. This manner is, of course, typical of the
Jabir ibn Hayyan 63
Schoolmen, but it is by no means confined to them and cannot
be regarded as a reliable criterion. In the next place, the state-
ment that disbelief in the possibility of transmutation arose only
in the twelfth century is entirely incorrect, as we shall see later.
In his Arabic works Jabir definitely refers to those who are in-
credulous, and his successor Razi went so far as to write a
book to confound them.
The authenticity of the books under consideration is therefore
still uncertain. It is possible that they are genuine translations
from Arabic books of Jabir ; or that they are genuine translations
from Arabic books of other chemists ; or that they are summaries,
made in medieval Europe, of Jabir's Arabic books; or that they
are medieval European forgeries made by an unknown author
and merely fathered upon Jabir in order to ensure a favourable
reception. Whatever the future may disclose concerning them,
we may safely say that they are not unworthy of Jabir and that
he is worthy of them ; and that we know of no other chemist,
Muslim or Christian, who could for one moment be imagined
to have written them. 1
20. Razi
AFTER the death of Jabir, nearly a century elapsed before Islam
produced a worthy successor. History records a few alchemists
in the interval, but it is only with the Persian chemist and
physician Abu Bakr Muhammad ibn Zakariyya al-Razi (known
to the West as Rhazes) that Jabir's great example is successfully
followed. 2
According to one of his biographers, Razi was born in A.D. 866
at Ray, an ancient town on the southern slopes of the Elburz
Range that skirts the south of the Caspian Sea. In his early
youth he devoted himself to the study of music, literature,
philosophy, manichaeism, magic and alchemy, and it was only
1 It should, however, be stated that the general opinion of those best
qualified to judge is that the Latin works are not authentic. The present
writer is practically alone in believing that they may be.
2 For much in this section, the writer is indebted to the researches of
Principal H. E. Stapleton, of Calcutta.
64 Razi
after his first visit to Baghdad, when he was at least 30 years of
age, that he seriously took up the study of medicine under the
well-known doctor AH ibn Sahl (a Jewish convert to Islam,
belonging to the famous medical school of Tabaristan or
Hyrcania). Razi showed such skill in the subject that he quickly
surpassed his master, and wrote no fewer than a hundred
medical books. He also composed 33 treatises on natural science
(exclusive of alchemy), 1 1 on mathematics and astronomy, and
more than 45 on philosophy, logic and theology. On alchemy,
in addition to his Compendium of Twelve Treatises and Rook of
Secrets, he wrote about a dozen other books, two of which were
refutations of works by other authors in which the possibility of
alchemy had been attacked.
As to the man himself, one of the inhabitants of Ray who
recollected Razi described him as a man with a large square head.
He used to take his seat in the lecture room, with his own pupils
next him, and the pupils of these men behind them, and, behind
these again, other pupils. Whenever any one came with a
question, he used first to ask the back row. If they could answer,
he went away; but, if not, he used to pass on to the others, and
they, in their turn, if they could give a correct answer, tried to
satisfy him ; otherwise Razi would speak on the subject himself.
He was a liberal and generous man, and so compassionate to the
poor and sick that he used to distribute alms to them freely and
even nurse them himself. He was always reading or copying,
and I never visited him (said the narrator) without finding him
at work on either a rough or a fair copy. His eyes were always
watering 'on account of his excessive consumption of beans', and
he became blind towards the end of his life. He died in his
native town on 26 October, A.D. 925, at the age of 60 years and
2 months.
Razi is of exceptional importance in the history of chemistry,
since in his books we find for the first time a systematic classifica-
tion of carefully observed and verified facts regarding chemical
substances, reactions and apparatus, described in language
almost entirely free from mysticism and ambiguity. While he
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66 Razi
perhaps never attained to the genius of Jabir of whom he
speaks with admiration and reverence his clear and orderly
habit of thought and expression made his work easily intel-
ligible and of permanent value. Razi's scheme of classifica-
tion of the substances used in chemistry shows such a sound
chemical insight that it may be reproduced here (page 65).
Razi gives also a list of the apparatus used in chemistry. This
consists of two classes: (i) instruments used for melting metals,
and (ii) those used for the manipulation of substances generally.
In the first class were included the following:
Blacksmith's hearth Tongs
Bellows Shears
Crucible Hammer or Pestle
Descensory File
Ladle Semi-cylindrical iron mould
The second class included :
Cucurbite Flasks Cylindrical stove
Alembic Phials Potter's Kiln
Receiving flask Jars Chafing-dish
Aludel Cauldron Mortar
Beakers Sand-bath Flat stone mortar
Glass cups Water-bath Stone roller
Shallow iron pan Large oven Round mould
Sieve Hair-cloth Glass funnel
Heating-lamps Filter of linen Dish
It will be observed that the list was comprehensive, but Razi
completes the subject by giving details of making composite
pieces of apparatus, and in general provides the same kind of
information as is to be found nowadays in manuals of laboratory
arts.
Like Jabir, Razi was a firm believer in the possibility of
transmutation, and Stapleton describes his scheme of procedure
approximately as follows. The first stage consisted in the
cleansing and purification of the substances employed, by means
of distillation, calcination, amalgamation, sublimation and other
Abu Mansur Muwaffak 67
processes. Having freed the crude materials from their im-
purities, the next step was to reduce them to an easily fusible
condition. This was done by an operation known as ceration,
that resulted in a product which readily melted, without any
evolution of fumes, when dropped upon a heated metal plate.
The next step was to bring the derated ' products to a further
state of disintegration by the process of solution. The solutions
of different substances, suitably chosen in proportion to the
amount of 'bodies', * spirits', &c., they were supposed to possess,
were brought together by the process of combination. Finally,
the combined solutions underwent the process of coagulation or
solidification, the product which it was hoped would result being
the Elixir. This, as previously explained, was a substance of
which a small quantity, when projected upon a larger quantity
of baser metal, would convert the latter into silver or gold.
From a general study of his chemical works, Stapleton says
that henceforward Razi must be accepted as one of the most
remarkable seekers after knowledge that the world has ever
seen not only 'unique in his age and unequalled in his time',
but without a peer until modern science began to dawn in
Europe with Galileo and Robert Boyle. The evidence of his
passion for objective truth that is furnished by his chemical
writings, as well as the genius shown by the wide range of books
he wrote on other subjects, force us to the conclusion that
with the possible exception of his acknowledged master, Jabir
Razi was the most noteworthy intellectual follower of the Greek
philosophers of the seventh to fourth centuries B.C. that mankind
produced for 1900 years after the death of Aristotle. His supreme
merit lay in his rejection of magical and astrological practices,
and adherence to nothing that could not be proved, by experi-
ment and test, to be actual fact.
21. Abu Mansur Muwaffak
THE closing years of the tenth century witnessed the appearance
3f a remarkable book on pharmacology, written by the Persian,
Abu Mansur Muwaffak. It is based upon a comprehensive study
F 2
68 Avicenna
of Greek, Indian, Arabian and Persian medicine, and although
its outlook is primarily that of a physician, it contains much of
interest to the chemist. Thus Abu Mansur is probably the first
to make a clear distinction between sodium carbonate (natruri)
and potassium carbonate, to which he confines the name qali ;
he mentions that the latter is obtained from the ashes of certain
plants, and is a white deliquescent salt of a caustic taste. Quick-
lime he recommends as a depilatory ; for a less vigorous action
milk of lime may be used. He describes arsenious oxide as a
pure white powder, and was acquainted with the silicic acid
(tabashir) obtained from the bamboo. Antimony, he says, is
a substance of dark colour, but a freshly cut surface of it has
a fine metallic lustre. Copper, if left exposed to the air, is often
converted into a green mass similar to malachite; if strongly
heated in air it yields a black substance [CuO] , which may be
used to darken the hair. If taken internally, copper compounds
are poisonous, especially copper vitriol ; so are the compounds of
lead, particularly white lead, the best sort of which comes from
Ispahan. Gypsum when heated yields a sort of Mime' which,
mixed with white of egg, forms a plaster of great service in the
treatment of fractures of bones.
Abu Mansur also mentions the distillation of sea-water (an
operation known to Aristotle or at least to his commentator,
Alexander of Aphrodisias) : 'I have heard that the crew of a ship,
when they have no drinking water, obtain a very serviceable
water, free from saltiness, by the distillation of sea- water/
22. Avicenna
'THE state of the Muslim empire at the end of the tenth century',
says Carra de Vaux, 'may be represented by that of an un-
disciplined and stormy feudality, where, under an enervated and
disorganized central authority, a crowd of vassal powers spring
up one after another, dominate a part of the empire and are then
eclipsed. Races and creeds come into conflict, advancing or
retreating according to the fortunes of the political adventurers
who represent them. In general, the Arab spirit is in decline;
Avicenna 69
the old Persian spirit awakes from time to time, but never quite
succeeds in freeing itself completely from the chaos, hindered
as it is by outbursts of barbarism due chiefly to the Turkish
element. Nevertheless, science pursues its destinies, in the shelter
of the ephemeral protection afforded it here and there by a few
princely personages. It is in such circumstances, whose troubled
and tempestuous character is reflected in his life, that Avicenna
for the first time gave a clear, ordered and complete expression
to that calm and grandiose system which we call scholasticism.'
Abu Ali Ibn Sina, the 'Avicenna' of Europe, who has been
described as the Aristotle of the Arabians and certainly the most
extraordinary man the nation produced, was not, in fact, an
Arab but a Persian. He was born near Bukhara in A.D. 980, and
his father was a native of Balkh. After the birth of Avicenna 's
younger brother, the family moved into Bukhara itself, where
a tutor was engaged to instruct the future philosopher in the
Koran and in Arabic poetry. The boy's progress was so rapid
that auxiliary teaching aids were soon required, and he was
taught arithmetic by a greengrocer, law by an ascetic named
Ibrahim, and Euclid and logic by a wandering scholar named
Natili whom his father lodged in the house for his son's benefit.
Natili seems to have had but a slender stock of knowledge, and
Avicenna, having discovered this, applied himself with energy
and resolution to a course of hard private study. Among many
other subjects he studied medicine, * which', he says, 'is not
difficult,' and by the age of 1 6 he had advanced so far that adult
qualified physicians came to learn from him. From 16 to 17 he
worked at philosophy, which he found very difficult. Every
time he encountered a problem that was too troublesome for
him, he would go to the mosque and spend the day in prayer,
after which he returned to his house, lit the lamp, and set him-
self once more to study. When he became sleepy, he would
drink a glass of wine to stimulate his weary brain and apply
himself to his books again. Even when at last he could remain
awake no longer, he revolved his problems in his dreams and
sometimes solved them in his sleep.
yo Avicenna
Appointed physician to one of the princes of the country at
the tender age of 17, Avicenna held many important posts
in after years, on one occasion being grand vizier or prime
minister ; but he was too fond of the bodily pleasures of life and
died comparatively young in 1036/7. During his brief life,
however, he accomplished an amazing mass of literary, medical,
philosophical and scientific work, and became an almost
legendary hero to his fellow-religionists and even to medieval
Europe.
It is uncertain whether Avicenna ever wrote any books wholly
devoted to chemistry. Several medieval Latin works on alchemy
are known which profess to be translations from Arabic books of
his, but for the most part their authenticity is open to grave doubt.
Recently, however, it was discovered that a well-known Latin
tractate on Minerals, sometimes ascribed to Geber, sometimes
to Aristotle, and sometimes to Avicenna, is partly a direct transla-
tion and partly a resume of sections of a genuine work of Avicenna ,
namely, the Book of the Remedy, which he composed in response
to his friend Al-Juzjani's request that he should write a general
commentary "on "Aristotle's works. He was too busy to write
a formal commentary, but compromised by writing a plain ex-
position of his own views free from any attempt at refutation of
adverse opinions. He had already written the first book of his
great Canon of Medicine, and thereafter worked at the Remedy
and the Canon simultaneously. At this period he was living at
Hamadhan under the protection of a prince named Shams al-
Daula, who died in A.D. 1021, and whose vizier he was. After
the death of Shams al-Daula, Avicenna secretly left Hamadhan
and was honourably received at Ispahan by 'Ala al-Daula, who
annexed Hamadhan in 1023 on the deposition of Shams al-
Daula's son. It was during the time of his stay with 'Ala al-
Daula that the Remedy was finished, and according to Ibn Abi
Usaybi'a, a Muslim chronicler, the chapters which particularly
interest us, namely those on Natural JScience, were composed
after the death of Shams al-Daula in 1021, but before Avicenna
went to Ispahan, probably in 1023 We are thus able to date them
LIBER C'ANONIS > DE MEDICIN1S
1 T CANT 1C A
Cum carti^
Amhc.v AlnoiBcfluncnltshjI'ofolii.K rnc<iu
ctauonc,
'U* i rffrtt ijf'ptut wi<f <xtctjjt runt d> eoJem ft mul
todtcthu
4
nottt* .
Cumprnnlcgn 1 ? Pummt Pontinv-ts,Frani.omm
cnaftis Vcnco.
Fig. 21. TITLE-PAGE OF AVICENNA'S Canon of Medicine
72 Avicenna
very precisely. The Latin translation was made by Alfred the
Englishman about A.D. 1200.
The first part of the section on minerals deals with the forma-
tion of rocks and stones and other geological phenomena, in the
discussion of which Avicenna anticipates in a remarkable way
the conclusions of Leonardo da Vinci and Nicholas Steno. The
second part of the book consists of an account of the properties
of minerals and metals, and is of very considerable interest
and importance. Mineral substances, says Avicenna, may be
roughly divided into four groups, namely, stones, fusible sub-
stances, sulphurs and salts. The basis of this classification is that
some of the mineral bodies are weak in substance and feeble in
composition and union, while others are strong in substance.
Of those which are feeble in substance, some have the nature of
salt and are easily soluble in water, such as alum, vitriol and sal-
ammoniac, while others are oily in nature and are not easily dis-
solved by moisture alone, such as sulphur and realgar and
orpiment. All malleable bodies are fusible, though sometimes
only indirectly, whereas most non-malleable substances cannot
be fused by ordinary methods or even softened except with
difficulty. As regards the stony kinds of naturally occurring
mineral substances, the material of which they are made is
aqueous, but they have not been solidified by the action of cold
alone. Their solidification has, on the contrary, been brought
about by the action of dryness, which has converted the wateri-
ness into earthiness. They do not contain a quick, oily humidity
and so are non-malleable; and because their solidification has
been caused mainly by dryness, the majority of them are in-
fusible unless they are subjected to some physical process that
facilitates fusion.
Alum and sal-ammoniac belong to the family of salts, though
sal-ammoniac possesses a fieriness in excess of its earthiness, and
may therefore be completely sublimed. It consists of water
combined with a hot smoke, very tenuous and excessively fiery,
and has been solidified by dryness. In the case of the sulphurs,
their wateriness has suffered a vigorous leavening with earthi-
Avicenna 73
ness and airiness under the action of heat, so far as to become
oily in nature; subsequently it has been solidified by cold.
The vitriols are composed of a salty principle, a sulphureous
principle, and stone, and contain the virtue of some of the
fusible bodies (that is, metals). Those of them which resemble
yellow and green vitriol are formed from the crude mineral
vitriols by partial solution, the salty constituent alone dissolving,
together with whatever sulphureity there may be. Solidification
follows, after a virtue has been acquired from a metallic ore.
Those which acquire the virtue of iron become red or yellow,
while those which acquire the virtue of copper become green or
blue.
Mercury seems to be water with which a very tenuous and
sulphureous earth has become so intimately mixed that no
surface can be separated from it without something of that
dryness covering it. Consequently it does not cling to the hand
or confine itself closely to the shape of the vessel which contains
it, but remains in no particular shape unless it is 'subdued'.
On the constitution of metals, Avicenna follows Jabir very
closely. He regards the proximate constituents to be mercury
and sulphur, or bodies closely resembling them. If the mercury
is pure, he says, and if it is commingled with the virtue of
a white sulphur which neither induces combustion nor is impure,
but on the contrary is more excellent than that prepared by the
alchemists, then the product is silver. If the sulphur, besides
being pure, is even better than that just described, and whiter,
and if in addition it possesses a tinctorial, fiery, subtle and non-
combustive virtue, it will solidify the mercury into gold. Then
again, if the mercury is of good substance, but the sulphur
that solidifies it is impure, possessing on the contrary a
property of combustibility, the product will be copper. If the
mercury is corrupt, unclean, lacking in cohesion and earthy,
and the sulphur is also impure, the product will be iron. As for
tin, it is probable that its mercury is good but that its sulphur is
corrupt; and that the commingling of the two is not firm, but
has taken place, so to speak, layer by layer, for which reason the
74 Avicenna
metal * shrieks'. This is, of course, a reference to, and an
attempted explanation of, the well-known 'cry of tin', which
modern chemistry ascribes to friction of the crystalline particles.
Lead, says Avicenna, is probably formed from an impure, fetid,
and feeble sulphur, for which reason its solidification has not
been thorough.
Avicenna then proceeds to demolish the alchemists. There is
little doubt, he says, that the alchemists can contrive to make
solids in which the qualities of the metals are perceptible to the
senses, though the alchemical qualities are not identical in
principle or in perfection with the natural ones, but merely bear
a resemblance and relationship to them. As to the claims at
transmutation made by the alchemists, it must be clearly under-
stood that it is not in their power to bring about any true change
of the metallic species. They can, however, produce excellent
imitations, dyeing a red metal white so that it closely resembles
silver, or dyeing it yellow so that it closely resembles gold. They
can, too, dye a white metal in such a way as to make it resemble
gold or copper, and they can free lead and tin from most of their
defects and impurities. Yet in these dyed metals the essential
nature remains unchanged ; they are merely so dominated by
induced qualities that errors may be made concerning their real
nature. 'I do not deny', he proceeds, 'that such a degree of
accuracy in imitation may be reached as to deceive even the
shrewdest, but the possibility of transmutation has never been
clear to me. On the contrary, I regard it as impossible, since
there is no way of splitting up one metallic combination into
another. Those properties that are perceived by the senses
are probably not the differences which distinguish one metallic
species from another, but rather accidents or consequences, the
essential specific differences being unknown. And if a thing is
unknown, how is it possible for any one to endeavour to pro-
duce it or to destroy it ?' It is, indeed, quite clear that Avicenna
was contemptuous of the pretensions of alchemy, for he winds
up by remarking that there was much he might have said on the
subject, but that it would probably have been a sheer waste of
Avicenna 75
time a remark which the Latin translator tactfully omitted
from his version.
As may easily be imagined, scepticism concerning alleged
transmutation had long existed. Some denied the possibility
altogether; others agreed that transmutation might be effected,
but only by magic. Al-Jildaki (p. 81) tells us that in Jabir's time
disbelief in alchemy was very pronounced, while the great Razi
was forced to write a book to confound the sceptics, among
whom was the celebrated Christian scholar and translator Hunain
ibn Ishaq. Avicenna's attack did not go unanswered. His argu-
ments were examined carefully by the vizier Al-Tughra'i, better
known as a skilful poet, and were shown to be inconsistent with
views that Avicenna had himself expressed in other passages in
the same book, and so the controversy went on. It is, indeed, not
unreasonable to maintain that the theory of the possibility of
transmutation was in better accord with observed facts and with
the general philosophic scheme of the time, than the contrary
thesis so vigorously upheld by Avicenna ; and that it was there-
fore temporarily true, in the pragmatic sense. In any case, the
time was not yet ripe, and alchemy was to hold sway for several
centuries to come.
It is not surprising that honest attempts at transmutation
were often brought under suspicion by the knavish tricks which
charlatans employed to deceive the innocent. In the popular
literature, the alchemist is always, or almost always, a rogue, as
in the following typical anecdote :
A Persian charlatan [says Carra de Vaux] , having arrived at Damas-
cus, took 1,000 dinars of good Egyptian gold, filed them up and
mixed the filings with charcoal, various drugs and ordinary flour.
To this mixture he added fish-glue, made the whole into a paste,
and moulded the latter into small pellets which he allowed to dry.
He then clothed himself in the habit of a darwish, and, taking the
pellets to a druggist sold them for a few dirhams under the name of
Tabarmaq of Khurasan. After which, having assumed a rich
cloak, he engaged a slave and went to the mosque, where he
scraped acquaintance with several notable persons. He told them
76 Avicenna
that he was an expert in alchemical science, able to make untold
wealth in a single day. The vizier, hearing of this alchemist,
ordered him to attend and presented him to the Sultan, who ex-
pressed his desire to witness a transmutation. The charlatan
produced a recipe in which, among a large variety of drugs,
Tabarmaq of Khurasan was indicated, to the extent of 100 mith-
qals. All the rest of the drugs were easily obtained, but at first no
trace of Tabarmaq could be discovered. The man insisted upon
its necessity, however, and when the druggists' shops had been well
searched the discovery was at length made of course in the shop
of the druggist to whom the Tabarmaq had been sold a few days
previously, and who stated that he had obtained it from a darwish.
The pellets were bought, and the Persian ordered the ingredients
to be placed in a crucible and strongly heated. When all was
sufficiently hot: 'Take out the crucible/ he said. It was taken out
and turned upside down, when a fine ingot of gold rolled out.
The Sultan, struck with amazement, ordered the Persian to be
rewarded. It was now merely a question of finding more Tabarmaq.
Search failed to reveal any more in Damascus. 'I know a cavern',
said the charlatan, 'in a certain mountain in Khurasan, where a
large quantity is to be found. Send some one to dig it out and bring
back a thousand camel-loads.' 'Go thyself, said the Sultan. The
man, after judicious reluctance, allowed himself to be persuaded,
and accepted the mission. He was furnished with everything
needful for the journey : a tent, a travelling kitchen, sugar, carpets,
stuffs and silks, manufactured objects from Alexandria, and, in
addition, a large sum of money. Thus equipped, he set out and
as might have been expected that was the last that was seen of
him.
In spite of the efforts of Avicenna, belief in the existence of
the Elixir continued, and chemistry became more and more
speculative and more widely divorced from experimental fact.
Such men as Ibn Arfa Ra's (twelfth century), whose alchemical
poem called The Particles of Gold enjoyed the highest reputa-
tion among later Muslim adepts, more closely resemble Thomas
Norton and Philalethes than van Helmont : they were mystical
alchemists rather than practical craftsmen, and the interest of
their writings is for the occultist rather than the historian of
The ' Sage's Step'. 77
scientific chemistry. There are, however, a few notable ex-
ceptions. Mansur al-Kamily, chief chemist at the Egyptian
Mint at Cairo in the thirteenth century, wrote a practical hand-
book on the extraction, purification and assaying of gold, com-
pletely free from the usual alchemical verbosity and theorizing.
It is extremely rare ; there is, indeed, only one copy in existence,
which is preserved in the Library of the King of Egypt. The
contents of the book show that Arab chemists of the thirteenth
century were well acquainted with cupellation, the parting of
^old and silver by means of nitric acid, the extraction of silver by
amalgamation with mercury, and with the quantitative chemical
analysis of gold/silver alloys. The Probierbuechlein and Agri-
cola's De Re Metallica, of the middle of the sixteenth century,
contain scarcely any improvements upon the methods described
by Mansur al-Kamily.
23. The 'Sage's Step'
CONTEMPORARY with, or slightly later than, Avicenna was the
author of a remarkable book entitled The Sage's Step, which is
said to have been composed in 1047-50. For long this book was
thought to have been written by Maslama of Madrid, the most
brilliant of a brilliant group of Spanish Arabs who flourished
ander the Caliph Al-Hakam II (A.D. 961-76). He was the chief
Tnathematician and astronomer of his time, and the lustre of his
lame was increased by his skill in the science of the division of
nheritances. Born at Cordova, he was educated partly in the
Drient, and while there seems to have come into contact with the
:elebrated Encyclopaedists of Islam, the 'Brethren of Purity',
kvhose 'Letters' (which cover a wide range of contemporary
cnowledge) he is believed to have brought back with him to
Europe in a new recension. His authorship of The Sage's Step,
lowever, is very doubtful, as he died about A.D. 1007, and in any
:ase before the outbreak of the civil war in Spain (1009), while
he author of the book plainly states that he composed it on account
)f the lamentable state into which scientific learning had fallen
ince the civil war had spread its ravages throughout the land.
78 The 'Sage's Step 5
The writer, whoever he was, was no armchair chemist but
a man who knew the discipline of the laboratory. Chemistry was
to him a noble science exacting the most a man could give.
Before beginning to study it, the aspirant should undergo a
thorough mathematical training by reading Euclid and the
Almagest of Ptolemy, and should then proceed to the De Caelo
et Mundo, De Generatione et Corruptione, Meteor ologica, and
Physica Auscultatio of Aristotle, or, failing these, the Canon of
Apollonius of Tyana. Having thus acquired a knowledge of the
main theories of natural science, the chemist should practise his
hand in operation, his eye in examination, and his mind in
reflection over chemical substances and reactions. Since
Nature's behaviour is invariable, for she never does the same
thing in different ways, the chemist must strive to follow Nature,
whose servant indeed he is, like the physician. The latter
diagnoses the disease and administers a remedy, but it is Nature
that acts.
In general, the theory of the author of The Sage's Step does not
show any marked advance upon that of Jabir and Razi, whom
he often acknowledges to be his masters (for Jabir, in fact, he
expresses unbounded admiration), but the book serves to show
the progress which had been made in experimental methods and
in empirical knowledge during the hundred and fifty years
or so that had elapsed. One observation is of particular
interest to chemists as in it occurs the first definite description of
a substance which was destined, in the hands of Priestley and
Lavoisier, to play an historic role mercuric oxide: 'I took
natural quivering mercury, free from impurity, and placed it in
a glass vessel shaped like an egg. This I put inside another vessel
like a cooking-pot, and set the whole apparatus over an extremely
gentle fire. The outer pot was tfyen in such a degree of heat that
I could bear my hand upon it. * I heated the apparatus day and
night for forty days, after which I opened it. I found that the
mercury (the original weight of which was Jib.) had been com-
pletely converted into a red powder, soft to the touch, the weight
remaining as it was originally/
The 'Sage's Step' 79
That no gain in weight was observed is not surprising, as some
of the mercury would probably have been lost by volatilization,
while the increase in weight of mercury on oxidation is only
about 8 per cent. The fact, however, that the author attempted
to carry out the experiment quantitatively is in itself important,
as indicating that he paid attention to a fundamental chemical
rule not universally observed until centuries later.
The author's remarks upon Jabir (whom he states to have
lived some 150 years earlier) are worthy of mention. Jabir, he
says, struck out a new line and cut himself off from the old
tradition. He found that most people were sceptical of the
possibility of obtaining the elixir, while those who did believe
were of the most ignorant type. He therefore decided to give
instructions of a more practical kind, and thus improved upon
Khalid ; the latter wrote in an obscure style and wished merely
to show men that he himself was accomplished in alchemy,
whereas Jabir wished to help and instruct others. The great
value of Jabir's works, he continues, lies in this very fact of their
being practical, for if a man reads of a process first and then
carries it out in practice, he will naturally believe in the truth of
the Art. As a matter of fact, all the various operations that
Jabir describes, such as calcination, are in reality transmutations
of one substance into another, so that by performing them the
sceptic may gradually be led to belief. The theory of the Art is,
indeed, difficult, but its practice is easy.
The author then turns to a consideration of sulphur, mercury,
marcasite, tutia, magnesia, talc, lazward, vitriols, alums and
other necessary substances, afterwards giving an account of
the purification of gold and silver, the chief points of which are
as follows :
Silver alloyed with lead may, be separated from the latter by
placing it in a cupel made from bones (called the * dog's head' or
commonly the kuraja ; it is a crucible made from burnt bones)
and fusing it by means of a strong fire. The lead is removed and
absorbed by the cupel and the silver is left pure and free from
base metal. Silver may be separated from copper in the cupel by
8o The 'Sage's Step'
the continual addition of lead ; after a time the silver appears in
a state of purity.
Gold may be purified from silver and copper in two ways.
From copper alone it may be refined by the method used to
purify silver from copper, namely, cupellation with addition of
lead. If it is so desired, sulphur may be added as well ; this burns
the copper and the gold remains pure. Gold may be purified
from lead by the method used to refine silver from lead.
The purification of gold from silver may be carried out in two
ways, one by means of 'stones' and the other by means of salts.
The former method is as follows : the gold alloyed with silver is
beaten out into thin leaves and these are placed on a bed of
haematite and salt and covered with more of the same mixture
followed by a layer of red clay. The whole is then heated in the
oven known to men of science as the 'refining-furnace', when the
silver is absorbed by the earthy matter and the gold leaves are
left pure, containing nothing but the most refined gold.
This operation may also be carried out in a similar way by
using alum and salt or by means of old baked clay. The clay is
finely powdered and mixed with an equal amount of salt and the
two well powdered again. The mixture is then spread in a layer
on a layer of red clay. A gold leaf is next added, followed by
another layer of the mixture of clay and salt, and so on until all
the gold has been added. A covering layer of clay and sand is
then placed on the top and the whole strongly heated, when the
gold is purified and extracted from the silver. The silver may
be recovered merely by the addition of mercury to the earthy
residue. The mercury thickens and coagulates until it becomes
like dough. At this stage it is placed in a crucible over the fire
and the mercury then volatilizes away, leaving the silver.
Gold may also be separated from silver in the same way that it
is separated from copper. The gold-silver alloy is mixed with
a little copper and the mixture fused, with the addition of red
sulphur from time to time. The silver burns away from the gold
and the latter is left pure. The former method, however, is the
more efficient.
Later Writers 81
In the Letters of the Brethren of Purity the Jabirian sulphur-
mercury theory of the constitution of metals is adopted, com-
bined, however, with an astrological theory. There is also an
insistence upon the Aristotelian 'four qualities', and the com-
position of minerals and precious stones is stated in terms of
these qualities with a naive dogmatism.
24. Later Writers
No account of chemistry in Islam would be even approximately
complete which omitted to mention Abu'l-Qasim of Iraq and
Aidamir al-Jildaki. The first of these men lived in the thirteenth
century, probably at Cairo, and has left us several books which,
apart from their intrinsic interest, serve to indicate the trend of
alchemical thought and practice in Islam after the process of
transmission to Europe (see pp. 84-106) had been in action for
some considerable time. It is very obvious that in Abu'l-
Qasim's time the reaction of European scientific thought upon
Islam had not yet begun, and the contrast between the two
intellectual worlds could not be better exemplified than in the
persons of Abu'l-Qasim and his contemporary Roger Bacon
(p. 92). The driving force of Islam was beginning to grow weak,
while the new stimulus that Arabic learning had given to
Europe had resulted in a scientific renaissance which was to
reach its full development not long afterwards. Abu'l-Qasim 's
outlook is that of his predecessors of three or four centuries
earlier, and although there was unquestionably some advance in
empirical practical chemistry, the theoretical views expressed
are supported by quotations not merely from Jabir but from the
still earlier alchemists of the Alexandrian school. Abu'l-Qasim
himself seems to have been a good experimentalist and a com-
paratively logical thinker, but his general views often represent
a retrograde movement upon those of Jabir.
Aidamir al-Jildaki, who also lived for part of his life at Cairo,
is of importance chiefly on account of his extensive and deep
knowledge of Muslim chemical literature. He apparently spent
the major portion of his existence in collecting and explaining
2613-4 O
82 General Review of Muslim Chemistry
all the books upon alchemy that he could discover, and his
labours are now beginning to receive their reward; for his
writings form an indispensable source of a great deal of our
knowledge of chemistry and chemists in Islam . In a few instances
it is possible to observe that he must have carried out experi-
mental work himself, but for the most part his books are com-
mentaries upon the works of earlier writers. Thus his great
End of the Search is a commentary upon Abu'l-Qasim's Book of
Knowledge Acquired concerning the Cultivation of Gold, and
although his explanations are not seldom more obscure than the
passages they are designed to illuminate, he had the admirable
habit of making innumerable and lengthy quotations from
Khalid, Jabir, Razi and many other authors, and his books are
thus a rich storehouse of information upon Muslim chemistry.
It is therefore necessary to inquire into the question whether his
quotations and historical facts are authentic, and whether his
reliability is to be accepted or doubted. Fortunately, it often
happens that a book from which he quotes is extant, and his
quotations in such cases can of course be checked. A test con-
ducted on these lines has shown that Jildaki was conscientious,
and although he does not always come through unscathed, his
general trustworthiness can be safely assumed. He thus
deserves the warmest thanks of all who are interested in the
history of chemistry.
25. General Review of Muslim Chemistry
BEFORE passing on to the next period of the development of the
science, it will be useful to review the salient features shown by
the chemistry. of Islam; for we shall then the better be able to
appreciate both its defects and its merits. And since, as we shall
shortly find, early European chemistry is almost wholly a legacy
from Islam, it is impossible to understand medieval Latin
alchemy without a clear idea of the work of the Arabs.
Until the time of Jabir, chemistry was 'without form and void'.
The solid technical knowledge of the craftsmen was lost in the
vapourings of occultists, and if there were any men with a more
General Review of Muslim Chemistry 83
reasonable view of chemical science, its aims, its objects and its
methods, we find no record of them. By the efforts of Jabir and
Razi, the two Muslim chemical geniuses, much of the vast
accretion of unbridled speculation was cleared away, and
chemistry first began to take shape as a true science. Experi-
mental fact was at last informed with the beginnings of reason-
able theory, while on the practical side a workmanlike scheme of
classification was evolved and a wide range of substances was
carefully investigated and systematically characterized. The
common laboratory methods of distillation, sublimation, cal-
cination, reduction, solution and crystallization were improved
and their general purposes well understood. The refinement of
metals, by cupellation and in other ways, was brought to a high
degree of perfection, and the careful assay of gold and silver was
accompanied by extraordinary accuracy in methods of weighing
and in the determination of specific gravities.
On the theoretical side, the idea that 'base' metals could be
transmuted into gold or silver overshadowed every other. The
generally accepted belief was that elixirs could be prepared
which, by an action we should now describe as catalytic, would
convert practically unlimited amounts of lead, mercury, tin,
copper, or even iron into silver first and then into gold. There
were alternative theories as to the means whereby transmutation
could be effected, but as we may more conveniently study these
in their later developments a mere reference to them in passing
may be sufficient at the moment. The philosophical justification
for the almost universal credence in the possibility of trans-
mutation is to be found ultimately in the Aristotelian conception
of the Four Elements and proximately in Jabir J s theory that all
metals are composed of sulphur and mercury. Its practical
justification lay in the elegant manner in which it explained
numerous phenomena and stimulated unceasing research.
As with all other branches of natural science, alchemy was
often permeated with magical and astrological superstitions,
particularly in the later years of the period. The rationalistic
temper of Razi and Avicenna had not completely extirpated
G2
84 The Translators
the weeds of occultism, and unfortunately Jabir, the hero of
Muslim chemists, had so frequently allowed his mystical reflec-
tions to colour his chemical writings that his books afforded
excellent material for those who practised alchemy as an esoteric
cult rather than as a reasonable branch of the philosophy of
Nature. Yet, on the whole, the scientists of Islam were the first
to apply scientific methods to the study of chemical phenomena ;
and the tongue of the infant science of chemistry is that of the
Koran.
26. The Translators
WHILE medieval Europe was, of course, by no means destitute
of skilful dyers, painters, glass-makers, practical metallurgists,
and other craftsmen, there seems to be no doubt that chemistry
as a science was a definite importation from the civilization of
Islam. The role which Islam played as the transmitter of Greek
learning to late medieval Christendom is so well known that it
need not be emphasized here; but its particular importance in
the history of science, especially chemistry, has not always been
fully realized. As Professor C. H. Haskins has recently reminded
us, practically the only contact between Islam and Christian
Europe until the twelfth century was through the Crusades,
which were clearly not favourable to the transmission of learning.
Soon after A.D. noo, however, European scholars began to dis-
cover that the Saracens were possessed of much knowledge and
ancient wisdom, and the bolder spirits began to travel in Muslim
lands in search of learning and enlightenment. Sicily, an
appanage of Islam from 902-1091, was taken by the Normans
in the latter year, but Muslim physicians and other scientists
were retained at the Norman court, and the island thus became
a centre of diffusion of Arabian learning. It was, however, in
Spain that the greatest activity prevailed. Christian students
were welcomed to the Muslim colleges and libraries at Pamplona^
Segovia, Barcelona, Toledo and other Spanish towns, and study
was soon followed by translation.
Some of the chief translators were Adelard of Bath, Gerard of
Fig. 22. THE ALHAMBRA
86 Robert of Chester
Cremona, Robert of Chester, Alfred the Englishman, Plato of
Tivoli and Hermann of Carinthia : men diverse in nationality
and taste but alike in their passionate desire to open the treasuries
of Saracen knowledge to Latin Christianity. Besides original
Arabic treatises, many Greek works thus became available to
medieval Europe for the first time, together with commentaries
and expositions which did much to direct the future progress of
European thought.
This is not all: with the Arabs^and Jews of the Middle Ages,
scientific knowledge was a thing of supreme importance, and this
spirit of devotion to science passed to the Latins who came in
contact with their learning. With interest came method: a ration-
alistic habit of mind and an experimental temper. These, of course,
could have been found among the ancient Greeks and were in-
herent in their writings, but they had been fostered and kept alive
in the Mohammedan countries, and it was chiefly from these that
they passed to Western Christendom. 1
27. Robert of Chester
ON ii February in the year 1144 the Englishman, Robert of
Chester, finished the first translation from the Arabic of a book
on chemistry, the Book of the Composition of Alchemy. In the
preface to his translation he says, * Since what Alchymia is, and
what its composition is, your Latin world does not yet know,
I will explain in the present book/ If this story is to be believed
but there is some reason to suspect it the introduction of
chemistry into Europe is an honour of our native land ; so no
English history of chemistry can dismiss Robert of Chester with
a mere word in passing.
Of Robert's early life we know nothing beyond the facts that
he may have been a native of Ketton in Rutland and that he was
doubtless educated in the well-known school at Chester. In
1141, he and his friend Hermann the Dalmatian were living in
Spain near the Ebro, studying the arts of astrology. In that
year Peter the Venerable found them and persuaded them to
translate the Koran, a task which they finished in 1143. Robert
1 C. H. Haskins, The Renaissance of the Twelfth Century, London, 1928.
Robert of Chester 87
must then have returned to his beloved sciences, for the Com-
position of Alchemy, as we have seen, was finished early in the
following year. For some time, Robert was Archdeacon of
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F/>. 23. THE SUPPOSED FIRST WORK ON ALCHEMY IN LATIN
Pampeluna, in northern Spain, but he returned to London in
1 147 and again in 1 150. In addition to his services to chemistry,
Robert translated the Algebra of the celebrated Muslim mathe-
matician Al-Khwarizmi and thus introduced into Latin Europe
88 Robert of Chester
both a new science and a new branch of mathematics. He also
calculated a set of astronomical tables for the meridian of London
(1149/50) and wrote a treatise on the astrolabe (London, 1147).'
Robert's pioneer work was followed by many other transla-
tions in rapid succession. By the middle of the thirteenth
century, in spite of some ecclesiastical opposition (which was,
however, much less than has sometimes been asserted), there
was a vigorous scientific renaissance, and the chief books of the
Muslim chemists and of Aristotle and other Greek philosophers
had been translated from the Arabic and diligently studied.
Our knowledge of this transition period is, however, unfortu-
nately inadequate, in spite of the fact that there is abundant
material available for study. When the manuscripts preserved
in our libraries, and recently catalogued for us in a most admir-
able way by (Mrs.) Dorothea Waley Singer, are systematically
examined, much that is now difficult and obscure will become
clear. There can be no doubt that many Latin works which
profess to be translations from the Arabic are spurious, written
by Europeans and fathered upon the great names of Greek and
Islamic chemistry. Nevertheless, recent research has shown
that among the mass of extant Arabic manuscripts are several
that appear to be originals of works hitherto known only in
Latin dress, and further investigation would doubtless reveal
many more similar cases. It seems, therefore, that we should not
be too hasty in dismissing as falsifications early Latin works
which profess to be translations from the Arabic ; in any event
there can be no doubt that the translations which were made in
the twelfth and thirteenth centuries by men like Robert of
Chester, Hermann of Carinthia, Gerard of Cremona and
Adelard of Bath formed the foundation upon which European
chemistry was built.
At first, progress in the new subject was slow (though by 1350
a monk of Bologna possessed no fewer than 72 alchemical works),
and the books of the period are, at bottom, little more than
compilations of excerpts from earlier writers. The galaxy of
brilliant men who busied themselves with science in the
Vincent de Beauvais 89
thirteenth century, men whose names are familiar to students of
the Middle Ages Vincent de Beauvais (c. 1190-1264), Albertus
Magnus (1193-1282), Roger Bacon (1214-1292), Raymond
Lully (1225 or 1235-1315), and Arnold of Villanova (1240-1313)
Ptg. 24.
made little real advance in chemistry, as we shall see by taking
a glance at their works.
28. Vincent de Beauvais
VINCENT DE BEAUVAIS, a Dominican monk, for some years
'reader' in the Cistercian monastery at Royaumont, and tutor tfe
the two sons of Louis IX, divides minerals into four classes:
90 Albertus Magnus and Roger Bacon
metals, stones, sulphureous bodies, and salts. Each metal is
considered separately, and appropriate quotations are made
from Razi, Avicenna and others. The generation of metals is
considered, and Avicenna 's doubts as to the possibility of
transmutation are reproduced. Finally, a good deal of material
of a practical nature is included. Vincent de Beauvais notices the
theory that metals are composed of sulphur and mercury, which,
as we have seen, was first clearly stated by Jabir, and expresses
his firm belief that 'by the art of chemistry mineral bodies,
especially metals, may be transmuted from their own species
into others'.
29. Albertus Magnus and Roger Bacon
ALBERTUS MAGNUS, Count of Bollstadt, was born at Lauingen
in Suabia, probably in the year 1193, though some say 1206.
Joining the Dominican Order at Padua in 1223 he rapidly
became a miracle of learning and was popularly known as
the Doctor Universalis though his detractors contemptuously
nicknamed him 'the Ape of Aristotle'. From 1228 to 1245 he
taught in Cologne and other German cities, while from 1245 to
1248 he lectured in Paris and began the publication of his great
philosophical encyclopaedia. From 1254 to 1262 he occupied
important ecclesiastical offices in Germany, but in the latter
year he retired to a cloister at Cologne to spend the remainder
of his life in study. He is said to have died at Cologne on
1 5 November 1280. A genuinely pious man, he conformed strictly
to the rules of his order, even walking barefoot on his official
journeys through the parts of Germany under his supervision.
His fame as a teacher was so great that the young Thomas
Aquinas made the long journey from Italy to Cologne to become
his pupil.
Albertus whom tradition describes as a man of exceedingly
small stature was a widely-read scholar, and although his
reputation rests mainly upon his philosophical works, he had an
extensive and unusually accurate knowledge of contemporary
science, which he describes in his Book on Minerals and else-
Albertus Magnus and Roger Bacon 91
where. Although he yielded to none in his admiration of
Aristotle, he would not agree that the great philosopher was
either infallible or omniscient, and held that the development
of science was not closed by his death. Albertus felt a keen
'desire for concrete, specific, detailed, accurate knowledge con-
cerning everything in nature ', and maintained that, in the study
of natural phenomena, one should not merely transcribe an
ancient statement but observe with his own eyes and mind. Yet
he does not appear to have appreciated the extreme scientific
importance of experiment, as distinct from observation, and
though he tested the genuineness of alchemical gold, and offered
bits of iron to ostriches to ascertain whether the old story was
true, these were exceptional cases and find few parallels in his
writings. Like all his contemporaries, he believed in magic and
astrology, and, in spite of his own canon of criticism, is often
quite ready to admit the fabulous.
Albertus was not an Arabic scholar, but was well acquainted
with Latin translations of Avicenna, Averroes and other Muslim
writers. In his De Miner alibus he moulds his views upon
alchemy very largely in accordance with Avicenna's opinions
expressed in the chapters from The Remedy translated about
1 200 by Alfred the Englishman. Thus he believes that most
alchemists merely succeed in dyeing metals so that they resemble
gold or silver, the actual metallic species remaining unaltered.
'Alchemy', he says, 'cannot change species but only imitate
them. ... I myself have tested alchemical gold and found that
after six or seven ignitions it was converted into powder/
Perhaps, however, in this passage of his Miner alia he is referring
only to the generality of the alchemists, for in another book,
entitled Libellus de Alchimia, he relates that he was given a
knowledge of alchemy by the grace of God. It is true that the
authenticity of the Libellus is not definitely established, but it
was ascribed to Albertus before 1350. The author recounts the
errors of his predecessors, and promises to describe nothing but
what he has actually seen. Next he states eight rules to be
observed by the alchemist, much in the style of an admonition
92 Albertus Magnus and Roger Bacon
made five centuries earlier by Jabir. He then proceeds to discuss
the various operations and pieces of apparatus employed in
chemistry, and describes the common chemical substances and
experiments that may be carried out with them. Finally,
recipes are given for the production of gold and silver. The
belief is expressed 'that metals can be produced by alchemy
which are the equal of natural metals in almost all their qualities
and effects ', except that alchemical iron does not possess magnetic
properties and that alchemical gold lacks certain curative powers
supposed to inhere in the natural metal.
In general, Albert's chemical theory and practice show no
advance upon Arabic knowledge of the ninth and tenth centuries.
Avicenna's scepticism influences him at one time, while at
another he seems to accept every alchemical commonplace.
His undoubted zeal for an observational basis for the investiga-
tion of natural phenomena was not entirely successful in
emancipating him from belief in the occult, and in this respect
he is typical of many minds of the thirteenth century. He
nevertheless did much to popularize the study of science, and
his influence was at least as great as that of the Doctor Admira-
bilis, Roger Bacon.
Roger Bacon, so far as our records go, was the first English-
man, after Robert of Chester, to interest himself in chemistry.
He was born at Ilchester in Somerset, probably in 1214, and
' appears to have belonged to a wealthy family, which, sub-
sequently, in the struggle between Henry III and the Barons
(1258-65), sacrificed their fortunes in the cause of the King'.
Bacon went to Oxford at an early age and took his M.A. degree
some years later. Under the influence of the celebrated Grosse-
tete he undertook the study of Greek, and it was doubtless
Grossetete who persuaded him to join the Franciscan Order
about 1247. From 1234-50 he studied and lectured at the
University of Paris, choosing as his master 'one of the most
modest and most learned men of the time, one who had devoted
himself to the study of chemistry and mathematics and astro-
nomy, and, above all, to those practical applications of experi-
Albertus Magnus and Roger Bacon 93
mental science which prompted his enthusiastic pupil to call him
"the Master of Experiments" ', to wit, Petrus Peregrinus of
Maricourt, the author of one of the first treatises on the Magnet.
Between 1250 and 1257 h e probably spent most of his time at
Oxford, but in the latter year, having fallen under the suspicions
Fig. 25. ROGER BACON WITH A PUPIL
of the authorities of the Franciscan Order, he was sent to Paris
and kept under a close watch until 1267. In 1268, probably
owing to Papal intervention, he was permitted to return to
Oxford; but his criticism of authority and independence of
thought once again brought him into conflict with his superiors
in the Order, and it is generally supposed that he was imprisoned
again at Paris for fourteen years (1277-91). In 1292, once
more at liberty, he returned to Oxford; but his freedom was
short-lived, for 'the noble doctor Roger Bacon was buried at
the Grey Friars [church of the Franciscans, long demolished],
in Oxford, A.D. 1292, on the Feast of St. Barnabas the Apostle'
[June 1 1] . A tower, traditionally known as 'Friar Bacon's Study',
stood until 1779 on Folly Bridge, on the south side of Oxford.
94 Albertus Magnus and Roger Bacon
In 1267, Bacon writes, in his Opus Tertium,
I have laboured from my youth in the sciences and languages, and
for the furtherance of study, getting together much that is useful.
I sought the friendship of all wise men among the Latins, and
caused youth to be instructed in languages and geometric figures,
in numbers and tables and instruments, and many needful matters.
I examined everything useful to the purpose, and I know how to
proceed, and with what means, and what are the impediments:
but I cannot go on for lack of the necessary funds. Through the
twenty years in which I laboured specially in the study of wisdom,
careless of the crowd's opinion, I spent more than two thousand
livres [about 10,000] in these pursuits on occult books (libros
secretos) and various experiments, and languages and instruments,
and tables and other things.
Bacon was, indeed, 'a devotee of tangible knowledge', and
emphasized the fundamental importance of experience and ex-
periment in reaching the truth. His exact position in the history
of science is, however, difficult to determine; and we may be
sure that the tendency, observable in some quarters, to regard
him as a lone figure, heralding the dawn of modern science amid
the gloom of the thirteenth century, is very much to be depre-
cated. It is clear that such a large question lies outside the scope
of the present book, in which we need merely to ascertain
Bacon's services, if any, to the progress of chemistry. For this
purpose we must first obtain a rough idea of his general intel-
lectual outlook.
In the first place, Bacon in common with all other Christians
of his age believed that the Bible contained, either explicitly or
implicitly, the whole realm of knowledge. On the other hand,
to understand the Bible thoroughly every art and science is
necessary though the patriarchs and prophets had full know-
ledge of all sciences, magic and astrology included. The queen
of sciences is, therefore, Theology, and all other branches of
learning are her handmaids. Round this central theme Bacon's
whole system often very tactlessly expressed continually re-
volves, and we cannot properly understand his attitude towards
Fig. 26. ROGER BACON'S STUDY
96 Albertus Magnus and Roger Bacon
natural science if we forget this cardinal fact. His advocacy of
the experimental method 'nothing can be certainly known but
by experience' was therefore primarily concerned not with the
search for objective truth, but with the exposition of scriptural
scientific knowledge, and it is only within these limits that it
must be envisaged. Bacon, in short, must be judged against the
intellectual background of his day, and must not be gratuitously
endowed with a mental outlook that, in actual fact, arose only
very much later. Moreover, by experience, Bacon meant more
than mere observation and experiment; for him, 'experience'
included the illumination of faith, spiritual intuition and divine
inspiration, and this esoteric experience was 'much better' than
the 'experience of philosophy' or science.
' Bacon's view of natural science was thus very different from
our own. Yet, if we discount his broad philosophy and confine
ourselves to his more detailed opinions on the advance of positive
knowledge, we shall find that he always endeavoured to live up
to his famous adage: sine experientia nihil sufficienter sciripotest.
He applied this canon to all branches of science, including
alchemy, of which he distinguished two kinds, viz. 'speculative'
and 'practical'. Practical alchemy he regarded as more impor-
tant than the other sciences, as more productive of material
advantages than they. Speculative alchemy 1
treats of the generation of things from the elements and of all
inanimate things and of simple and composite humours, of
common stones, gems, marbles, of gold and other metals, of
sulphurs and salts and pigments, of lapis lazuli and minium and
other colours, of oils and burning bitumens and other things with-
out limit, concerning which we have nothing in the books of
Aristotle. Nor do the natural philosophers know of these, nor the
whole assembly of Latin writers. And because this science is not
known to the generality of students it necessarily follows that they
are ignorant of all that depends upon it concerning natural things,
namely of the generation of animate things, of plants, and animals
and men, for being ignorant of what comes before they are
necessarily ignorant of what follows. . . .
1 Stillman, The Story of Early Chemistry, London, 1924.
Albertus Magnus and Roger Bacon 97
But there is another alchemy, operative and practical, which
teaches how to make the noble metals, and colours and many other
things better or more abundantly by art than they are made in
Nature. And the science of this kind is greater than all those pre-
ceding because it produces greater utilities. For not only can it
yield wealth and very many other things for the public good, but it
also teaches how to discover such things as are capable of pro-
longing human life for much longer periods than can be accom-
plished by Nature. ... It confirms theoretical alchemy through its
works and therefore confirms natural philosophy and medicine,
and this is plain from the books of the physicians. For these authors
teach how to sublime, distil and resolve their medicines, and by
many other methods according to the operations of that science,
as is clear in health-giving waters, oils and many other things.
Bacon was thus one of the first to distinguish between the
study of chemistry for its own sake and the study of chemistry
on account of its valuable technical and practical applications.
Except, however, for the fact tbat he minimized the importance
of the Aristotelian 'prime matter' and made fuller use of the
theory of the Four Elements, he differs very little from the other
alchemists in his conception of alchemical theory and practice.
He accepts the sulphur-mercury theory, which he appears to
have taken over bodily from Avicenna, and is quite as credulous
on the subject of transmutation as any of his contemporaries.
He clearly had a wide knowledge of the Arabian authors, whom
He read in the original Arabic, and he seems to have perceived
that in chemistry must be sought the science which should fill
the gap between Aristotelian physics and the biological sciences.
As to actual discoveries in chemistry, there is no evidence that
he made any; and the famous 'cipher' in which he was supposed
to describe the preparation of gunpowder has recently been
shown to be a copyist's blunder.
Bacon's services to chemistry were roughly these : he gave an
accurate picture of contemporary alchemical thought, explained
its methods and aims with lucidity, saw that it had a great future
as an experimental science, and appreciated (within the limits
noted) the importance of an experimental basis for natural
2613-4 H
98 Popular Books and the Technical Tradition
science. But it is rather as the epitome of his age than as a
thinker in advance of his age that we ought to regard him.
Of Raymond Lully and Arnold of Villanova there is little that
need be said. Many chemical works are ascribed to Lully
the celebrated missionary to the Moors but Mrs. Singer has
recently shown that they are all spurious and probably of a much
later date. Arnold of Villanova's voluminous works are chiefly
concerned with medical subjects, and chemistry is dealt with
only incidentally; still, Arnold was widely read and was familiar
with the books of the chief Muslim chemists, and a study of his
chemical ideas would doubtless be a very useful piece of re-
search. On the whole, the twelfth and thirteenth centuries may
be regarded as a time of assimilation, when the chemical know-
ledge of Islam was being absorbed into Europe : it is only much
later that a fresh efflorescence occurred.
30. Popular Books and the Technical Tradition
TURNING aside from the work of the great men of the period, let
us now pass in review one of the many popular books written for
the instruction of the laity and the less well educated among the
clergy. Such books were generally in the form of an encyclo-
paedia, giving a conspectus of the whole realm of contemporary
knowledge. One of the most famous of them was Bartholomew
the Englishman's book On the Properties of Things, written by an
English Franciscan about 1260. The great popularity it attained
shows that there was a keen public demand for learning ; and its
success was by no means confined to England. The Emperor
Charles V, in 1372, ordered it to be translated into French,
while Spanish and Dutch translations quickly followed. Ori-
ginally written in Latin, it appeared in English in 1397, and as
many as seventeen editions of the various versions were pub-
lished in the course of the fifteenth century.
Two extracts from Mr. Robert Steele's edition of the English
text will serve to show us the kind of chemistry current, in the
thirteenth century, among educated men like Bartholomew.
The first describes the 'discovery' of glass, reproducing a very
Be
f m ft*
^ m
:* ^
no s^
'oa <P* ft* I'
rep
fit
It ftii
Ifttfi* 0* tt?0 g ^
r qu Pirft t pit
jMte ffit ft Ptttt to
cris t f ^ *ft^t a!
tt *
Mb* tt 1 t
to tftl qui i:
li ttit ft
te f ftti * r *.
tl
. Sfe
fit m i^c p
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Fig. 27. INCIPIT PAGE OF A FIFTEENTH-CENTURY EDITION OF
BARTHOLOMEW'S OAT THE PROPERTIES OF THINGS
H 2
ioo Popular Books and the Technical Tradition
old story, and the second discusses the nature of quicksilver and
the constitution of the metals.
Glass, as Avicen saith, is among stones as a fool among men, for it
taketh all manner of colour and painting. Glass was first found
beside Ptolomeida in the cliff beside the river that is called Vellus,
that springcth out of the foot of Mount Carmel, at which shipmen
arrived. For upon the gravel of that river shipmen made fire of
clods medlied with bright gravel, and thereof ran streams of new
liquor, that was the beginning of glass. It is so pliant that it taketh
anon divers and contrary shapes by blast of the glazier, and is
sometimes beaten, and sometimes graven as silver. And no matter
is more apt to make mirrors than is glass, or to receive painting;
and if it be broken it may not be amended without melting again.
But long time past, there was one that made glass pliant, which
might be amended and wrought with an hammer, and brought
a vial made of such glass before Tiberius the Emperor, and threw
it down on the ground, and it was not broken but bent and folded.
And he made it right and amended it with a hammer. Then the
emperor commanded to smite off his head anon, lest that his craft
were known. For then gold should be no better than fen, and all
other metal should be of little worth, for certain if glass vessels
were*not brittle, they should be accounted of more value than
vessels of gold.
Quicksilver is a watery substance medlied strongly with subtle
earthly things, and may not be dissolved and that is for great dry-
ness of earth that melteth not on a plain thing. Therefore it
cleaveth not to thing that it toucheth, as doth the thing that is
watery. The substance thereof is white : and that is for clearness of
clear water, and for whiteness of subtle earth that is well digested.
Also it hath whiteness of medlying of air with the aforesaid things.
Also quicksilver hath the property that it curdeth not by itself
kindly without brimstone: but with brimstone, and with sub-
stance of lead it is congealed and fastened together. And therefore
it is said, that quicksilver and brimstone is the element, that is to
wit matter, of which all melting metal is made. Quicksilver is
matter of all metal, and therefore in respect of them it is a simple
element. Isidore saith it is fleeting, for it runneth and is specially
found in silver forges as it were drops of silver molten. And it is
oft found in old dirt of sinks, and in slime of pits. And also it is
Popular Books and the Technical Tradition 101
made of minium done in caverns of iron, and a patent or a shell
done thereunder; and the vessel that is anointed therewith, shall
be beclipped with burning coals, and then the quicksilver shall
drop. Without this silver nor gold nor latten nor copper may be
overgilt. And it is of so great virtue and strength, that though
thou do a stone of an hundred pound weight upon quicksilver of
the weight of two pounds, the quicksilver anon withstandeth the
weight. And if thou doest thereon a scruple of gold, it ravisheth
unto itself the lightness thereof. And so it appeareth it is not
weight, but nature to which it obeyeth. It is best kept in glass vessels,
for it pierceth, boreth, and fretteth other matters.
We see that the critical faculty of our author is not very
active, and that he is content to accept as true any information
for which he can find authority. The section on quicksilver
plainly betrays its Arabic origin, and goes back ultimately to
Jabir by way of Avicenna. There is nothing new no original
contribution by European scientists, no fresh theory by Euro-
pean philosophers. The new science was still in process of be-
coming naturalized, and the extent of the borrowing from Islam
may be estimated not only by the numerous translations and
quotations but by the scores of Arabic chemical terms taken over
bodily into Latin alchemy. The following examples, chosen at
random, are typical, and serve incidentally to demonstrate how
impossible it is to understand medieval European alchemy
without a previous knowledge of Muslim work :
Abicum, Arabic, al-anbiq, alembic.
Abric, A. al-kibrit, sulphur.
Alcalai, A. al-qali, alkali.
Alcazdir, A. al-qasdir, tin.
Alchitram, A. al-qitran, pitch.
Alchohol, A. al-kuhl, kohl (stibium, Sb 2 S 3 , or galena, PbS).
Aliocab, A. al-'uqab, 'the eagle' (sal-ammoniac).
Almizadir, A. al-nushadhir, sal-ammoniac.
Anticar, A. al-tinkar, borax.
Appebriock, A. al-kibrit, sulphur.
Asabon, A. al-sabun, soap.
IO2 Popular Books and the Technical Tradition
Ased, A. asad, lion.
Athanor, A. al-tannur, furnace.
Azarnet, A. al-zarnikh, arsenic [sulphides].
Baul, A. haul, urine.
Bayda, A. al-baida, egg [name of a piece of apparatus].
Daeb, A. dhahab, gold.
Danic, A. daniq, a certain weight.
Dem, A. damm, blood.
Faulex, A. fulad, steel.
Fom, A. fum, month.
lladid, A. hadid, iron.
Hager, A. hajar, stone.
Kald y A. khall, vinegar.
Kamar, A. qamar, silver moon.
Khamir, A. kharnir, ferment.
Luban, A. luban, gum, resin.
Lubanjawa, gum of Java, was corrupted into Benjawin, or
benzoin, whence our 'benzene'.
Malek, A. milh, salt.
Martach, A. martak, litharge or massicot.
Merdasingi, A. mardasanj, litharge.
Misadir, A. nushadhir, sal-ammoniac.
Nar, A. nar, fire.
Noas, A. nuhas, copper.
Nora, A. nura, lime.
Obelchera, A. abu'l-qar'a, large cucurbite.
Ocob, A. uqab, eagle [sal-ammoniac].
Rusatagi, A. rusakhtaj, black oxide of copper.
Tain, A. tin, clay.
Usifur, A. zanjifar, cinnabar.
Zaibar, A. zaibaq, mercury.
Zaibuch, A. zaibaq, mercury.
Ziniar, A. zinjar, verdigris.
In considering the rise of chemistry in Europe, one should not
forget the technical tradition, carried on by humble craftsmen
Popular Books and the Technical Tradition 103
and artisans, and more or less continuous throughout the ages.
Most of these technical workers are nameless and the records of
their work are, as would be expected, but scanty. At least three
books of importance have, however, survived the vicissitudes of
time and remain to bear witness to the vast amount of laborious
practical investigation that was carried on in what some are
pleased to call the Dark Ages. These three books are known as
the Compositiones ad tingenda, the Mappae Clavicula and the
Liber ignium ad comburendos hostes.
The Compositiones ad tingenda is known in a manuscript that
dates from the time of Charlemagne (r. 742-814). It is not a
systematic treatise but a collection of recipes, probably gathered
together by some technical worker for his own use in the arts.
It deals with such varied subjects as the dyeing of skins, the pre-
paration of coloured glass, methods of writing in letters of gold,
the gilding of copper and other metals, and a description of the
various metals, minerals, earths and herbs that found technical
application. It is believed that many of the recipes are of
Byzantine origin, while some are still more ancient, having been
found in the famous Ley den papyrus. The work, as a whole, is
noticeable for the complete absence of superstition in it. We
here meet, too, for the first time with the names vitriol (given
to an impure sulphate of iron obtained by the weathering of
pyrites), and bronze, which has been derived probably by a
false etymology from Brundisium (Brindisi), where the alloy
has been stated to have been prepared on a large scale.
The Mappae Clavicula (the earliest known manuscript is of
the tenth century and is at Schlestadt) includes practically all
the recipes of the Compositiones ad tingenda, and adds a great
many more. It is noteworthy that a large number of the new
recipes deal with transmutation, a subject which is scarcely
mentioned in the earlier work. A later manuscript of this work,
written in the twelfth century, contains the earliest account of
the preparation of alcohol, expressed in the following sentence:
De commixtione puri et fortissimi xkok cum HI qbsuf tbmkt cocta
in ejus negocii vasts fit aqua quae accensa flammam incumbustam
104 Popular Books and the Technical Tradition
servat materiam. The riddle of the three words in cipher was
solved by Berthelot, who showed that each letter stood for that
which precedes it in the alphabet. Thus xkok is vini y qbsuf is
parte, and tbmkt is salts \ the passage may then be translated as
follows : 'On mixing a pure and very strong wine with a third of
a part of salt, and heating it in vessels suitable for the purpose,
an inflammable water is obtained which burns away without
consuming the material [on which it is poured]. *
The third book, the Liber ignium ad comburendos hostes, of
'Marcus Graecus', appears to be a translation from the Arabic.
No Arabic original is known, however, nor is anything known of
its author. The earliest manuscript is of the early fourteenth
century (perhaps, indeed, of the year 1300). Its recipes may be
divided into four groups: those for (i) incendiary substances,
(2) phosphorescent substances, (3) 'Greek fires', and (4) ex-
plosives containing saltpetre. Among them is one for the pre-
paration of gunpowder: 'Take i Ib. of live sulphur, 2 Ib. of
charcoal from the lime or willow, 6 Ib. of saltpetre. Let the
three substances be very finely powdered upon a marble slab
[and then mixed together].' This is one of the earliest mentions
of gunpowder, although Roger Bacon, in his Opus Tertium,
says that at that time (1267) it was already in common use for
children's fireworks.
Two further examples may suffice to illustrate the practical
chemical knowledge of the time. The first of them is taken from
an English work (hopefully ascribed to Hermes) called The Book
of Quintessence. It describes very lucidly how to convert gold
into a powder or calx and also how to 'part' silver from gold :
The science to brynge gold into calx. Take fyn gold and make it
into small lymayl. take a crusible with a good quantity of Mercuric,
and sette it to a litil fier so that it vapoure not, and putte therinne
thi lymail of gold, and stire it weel togidere and aftirward withinne
a litil tyme ye schal se al the gold withinne the Mercuric turned
into erthe as sotil as flour, thanne yeue it a good fier that the
Mercuric arise and go his wey, or ellis and ye wole ye may distille
and gadere it, putty nge therupon a lembike and in the corusible ye
Popular Books and the Technical Tradition 105
schal fynde the gold calcyned and reducid into erthe. And if ye
wole not make lymayl of gold, thanne make therof a sotil thinne
plate, as ye kan, and putte withinne the Mercuric al warm, and ye
schal haue youre desier. And in this same maner ye may worche
with siluir. Thanne take the calx of these two bodies, and here
hem openly with you. and ther schal noman knowe what thei ben.
. . . Now I wole teche you the maistrie of departynge of gold fro
siluir whanne thei be meyngid togidere. Forsothe ye woot weel
that ther be manye werkis in the whiche gold and siluir be meyngid,
as in giltynge of vessel and lewellis therfore whanne ye wole drawe
the toon from that othir. putte ai that mixture into a strong watir
maad of vitriol and of sal petre. and the silyur wole be dissolued,
and not the gold, thanne ye haue that oon departid fro the tothir.
And if ye wole dissolue ye gold to watir. putte thanne yn the watir
corosyve. Sal armoniac. and that watir withoute doute wole
dissolue gold into watir.
The second extract is taken from a painter's recipe-book of
the thirteenth century and serves very well to illustrate the
empirical chemistry of the medieval craftsman :
On making verdigris. If you wish to make verdigris, take a new pot,
or any other hollow vessel, and put into the vessel some very strong
vinegar, and arrange sheets of the purest copper over the vinegar, in
such a way that they may not come into contact with the vinegar.
And so cover it up, and seal it, and put it in a warm place, or
underground, and set it aside for six months. And then you must
open the vessel, and scrape off into a very clean dish the material
which you find in it, and set it in the sun to dry. Furthermore, if
you wish to make Rouen-green, take some sheets of very pure
copper, and smear them all over with the best soap, and put these
sheets into a clean vessel, made for the purpose, and fill it with
pure vinegar. But arrange the sheets above it, in such a way that
they may not come into contact with the vinegar. And when you
have covered the vessel, seal it doubly ; and at the end of one month
open it, and scrape what you find on the copper sheets into a dish,
and dry it.
The following are the instructions for making vermilion or
cinnabar :
On making vermilion. If you wish to make the finest vermilion,
106 Paracelsus
take a glass jar and lute it outside with the finest clay, three times ;
and then take one weight of quicksilver and two weights of white
or yellow sulphur, so that there will be two parts of sulphur and
a third of quicksilver. And put in the above-mentioned in-
gredients in such a way that part of the sulphur, finely divided,
may be on the bottom, and part of the quicksilver above, so that it
may reach right up to the neck of the jar. Put the jar upon four
stones, and then build up a charcoal fire around the jar, but let it
be a very moderate one. And so cover the mouth of the jar with
a little tile or piece of stone. And when you see that the smoke is
blue or yellow-coloured, as it comes off, put on the cover; and
when you see that the smoke is almost as red as vermilion, take it
from the fire, and you will have in the jar the finest vermilion.
It is interesting to compare this last recipe with Jabir's in-
structions for the preparation of the same substance, as given in
a British Museum manuscript of his Great Book of Properties :
To convert mercury into a red solid. Take a round glass vessel,
and pour a convenient quantity of mercury into it. Then take
a Syrian earthenware pot and into it put a little powdered yellow
sulphur. Place the glass vessel on the sulphur and pack it round
with more sulphur up to the brim. Place the apparatus in the
furnace for a night, over a gentle fire . . . after having closed the
mouth of the earthenware pot. Now take it out and you will find
that the mercury has been converted into a hard red stone of the
colour of blood. . . . This is the substance which men of science
call cinnabar.
31. Paracelsus
THE impulse that deflected many chemists from their alchemi-
cal pursuits and, in the sequel, did much to make chemistry
once more a self-respecting science, came from that curious
personality known as Paracelsus. Philippus Aureolus Theo-
phrastus Bombastes von Hohenheim, or Paracelsus, was the
son of a Swiss physician and was born at the village of Ein-
siedeln, near Zurich, on 17 December 1493. As a boy, he
was given elementary instruction in alchemy, astrology, medi-
cine and surgery by his father, and at the age of sixteen entered
the University of Basel. Some time later he proceeded to
Fig. 28.5 PARACELSUS
io8 Paracelsus
Wiirzburg, to study under a celebrated expert in magic, alchemy
and astrology, Hans von Trittenheim, generally known as
Trithemius. It was doubtless during the time of his association
with Trithemius an authority on the Kabbala and a follower of
the Neo-Platonists that he became enamoured of occultism in
general and of alchemy in particular. At the age of 22 he
went to the mining school of Sigismund Fugger, in the Tyrol,
where he worked for a year and was able to glean much valuable
technical information concerning the precious metals and also
to broaden his knowledge of alchemy proper, for Fugger was
widely known as an expert alchemist.
Of a restless disposition, Paracelsus seems to have been
constitutionally incapable of remaining long in any one place.
After learning all that Fugger could teach him, he set off on
a rambling journey through Germany, Italy, France, the Nether-
lands, Denmark, Sweden and Russia, and, according to some,
may even have visited India. For a time he served as an army
surgeon in the Danish wars, and managed to secure the degree
of Doctor of Medicine though at what university remains
undecided. During his travels he associated with physicians,
alchemists, astrologers, apothecaries, miners, gipsies and adepts
of occult science, returning to Germany in 1526 with a stock of
curious knowledge such as few men can ever have possessed. At
that time the celebrated book-publisher of Basel, Johannes
Frobenius or Froben, was seriously ill, and hearing that Para-
celsus was at Strasburg he sent to ask him to come and treat him.
* Froben 's house in Basel was frequented by a number of
scholarly persons, notably by Erasmus, who at that time lived
in Froben 's house, and by Oecolampadius, then professor of
theology in the University of Basel, both prominent in the
reformation movement in Switzerland. Impressed by the per-
sonality and medical skill of the new physician, these men and
particularly, it is said, Oecolampadius prevailed on the city
authorities (Stadtrath) to offer the then vacant position of city
physician to Paracelsus, an offer which was at once accepted.'
Frobenius appears to have been cured, for when Erasmus him-
Paracelsus 109
self was taken ill some time afterwards he wrote Paracelsus as
follows : 'I cannot offer thee a reward equal to thy art and know-
ledge I surely offer thee a grateful soul. Thou hast recalled
from the shades Frobenius who is my other half: if thou
restorest me also thou restorest each through the other. May
fortune favour that thou remain in Basel/ l
A man more unstated to hold public office than 'marvellous
Paracelsus, always drunk and always lucid, like the heroes of
Rabelais', can hardly be imagined. With a great conceit of his
own powers and views and little regard for the opinions and
feelings of others, he signalized his appointment as City
Physician by publicly burning (in a brass pan, with sulphur and
nitre) the works of Avicenna and Galen, to show his contempt of
orthodox medicine and to emphasize the fact that his doctrines
were essentially his own. 'If your physicians,' he said,
only knew that their prince Galen they call none like him was
sticking in hell, from whence he has sent letters to me, they would
make the sign of the cross upon themselves with a fox's tail. In the
same way your Avicenna sits in the vestibule of the infernal portal ;
and I have disputed with him about his aunim potabile, his
Tincture of the Philosophers, his Quintessence, and Philosopher's
stone, his Mcthridatic, his Theriac, and all the rest. O, you
hypocrites, who despise the truths taught you by a great physician,
who is himself instructed by Nature, and is a son of God himself!
Come, then, and listen, impostors who prevail only by the authority
of your high positions! After my death, my disciples will burst
forth and drag you to the light, and shall expose your dirty drugs,
wherewith up to this time you have compassed the death of princes,
and the most invincible magnates of the Christian world. Woe for
your necks in the day of judgement! I know that the monarchy
will be mine. Mine, too, will be the honour and glory. Not that I
praise myself: Nature praises me. Of her I am born; her I follow.
She knows me, and I know her. The light which is in her I have
beheld in her; outside, too, I have proved the same in the figure of
the microcosm, and found it in that universe.
As may easily be imagined, such conduct did not increase the
1 Stillman, Paracelsus, London, 1920.
no Paracelsus
popularity of this bizarre medical officer of health. But his
vituperation did not confine itself to general attacks on the
whole body of physicians : individual members as well felt the
venom of his tongue. To one who had ventured to disagree with
him he replied in the following terms :
So then, you wormy and lousy Sophist, since you deem the
monarch of arcana a mere ignorant, fatuous, and prodigal quack,
now, in this mid age, I determine in my present treatise to disclose
the honourable course of procedure in these matters, the virtues
and preparation of the celebrated Tincture of the Philosophers for
the use and honour of all who love the truth, and in order that all
who despise the true arts may be reduced to poverty. By this
arcanum the last age shall be illuminated clearly and compensated
for all its losses by the gift of grace and the reward of the spirit of
truth, so that since the beginning of the world no similar germina-
tion of the intelligence and of wisdom shall ever have been heard of.
In the meantime, vice will not be able to suppress the good, nor
will the resources of those vicious persons, many though they be,
cause any loss to the upright.
Before long Paracelsus became an object of hatred to all the
druggists and apothecaries in the town, as well as to his brother
physicians. At length matters were brought to a crisis. A pro-
minent citizen of Basel had offered 100 guldens to any physician
who would cure him. Paracelsus accepted the offer and cured
his patient, who thereupon refused to pay the fee that had been
agreed upon. Paracelsus sued him, but as might have been
expected lost his case, a result which so infuriated the hot-
tempered physician that he abused the judges in the roundest
terms, and with a typically Paracelsan collection of libellous
epithets. Warned that he had thus laid himself open to severe
punishment, he left Basel secretly and hurriedly, setting out
once more upon a life of wandering. In succeeding years we
find him in many towns of Germany and Switzerland, but at
last he was invited to Salzburg by the Prince Palatine, Duke
Ernst of Bavaria, himself a keen student of the occult arts.
Here he seems to have found a restful and congenial atmosphere,
Paracelsus 1 1 1
but he was destined to enjoy it for only a short time. On
24 September 1541 he died, at the early age of 48 years a
comparatively young man yet physically worn out by the restless
and strenuous life he had led. His epitaph read:
Here lies buried Philippus Theophrastus, distinguished Doctor of
Medicine, who with wonderful art cured dire wounds, leprosy,
gout, dropsy and other contagious diseases of the body, and who
gave to the poor the goods which he obtained and accumulated.
In the year of our Lord 1541 , the 24th of September, he exchanged
life for death.
We are told by a contemporary that Paracelsus was most
laborious, and that he would often throw himself, fully dressed,
booted and spurred, upon his bed and write ceaselessly for
hours. He has, in fact, left us a large number of books upon
medicine and chemistry, most of which are extremely difficult
to understand on account of the unsystematic way in which
their matter is arranged, and also on account of the * execrable
style' which Paracelsus adopted. As Thomson bitterly exclaims,
'how can we look for a regular system of opinions from a man
who generally dictated his works when in a state of intoxication,
and thus laboured under an almost constant deprivation of
reason?' It is consequently a somewhat exasperating task to
attempt to ascertain exactly what definite advances in knowledge
Paracelsus actually made. That he was an accomplished ex-
perimenter is certain, and among other items of chemical infor-
mation scattered throughout his books are references to zinc,
* cobalt* and bismuth (though he himself did not discover any of
these metals), to the fact that a gas is given off when iron is dis-
solved in dilute sulphuric acid, to the bleaching action of sulphur
dioxide, and to several further observations that bear witness
to his laboratory experience. He showed, too, that the alums
differ from the vitriols, since the latter are derived from a metal
but the former from an 'earth', i.e. a metallic oxide which at
that time could not be reduced to metal. It was Paracelsus who
first gave the name alcohol to spirit of wine. Originally signify-
ing the black eye-paint used by Eastern women, al-kuhlor al-kohol
ii2 Paracelsus
had gradually acquired the meaning of any very finely divided
powder ; thence by a natural transference it came to mean 'the
best or finest part' of a substance. Possibly Paracelsus regarded
spirit of wine as the 'best part' of wine, and therefore named it
alcohol of wine or simply alcohol. This usage of the word has of
course persisted, and the older meaning is now entirely obsolete.
If, then, Paracelsus 's actual discoveries were but meagre, why
is he to be included among the great 'makers of chemistry'?
The answer to this query lies in his emphatic opinion as to the
aim of chemistry. Alchemy, defined as the art of transmuting
the metals, he certainly believed to be possible; yet he regarded
the efforts of the alchemists as a waste of energy which might be
better employed. Like the great Razi, he considered that one
of the chief objects of chemistry should be the preparation and
purification of chemical substances for use as drugs, and urged
chemists, apothecaries and physicians alike to devote themselves
to experiments with this object. We must remember that the
apothecaries of that time usually had no knowledge of chemistry,
preparing their medicines from roots, leaves, fruits, syrups and
the like in the fashion of a village housewife. The physicians
were in no better case. 'They think it suffices', says Paracelsus,
'if, like apothecaries, they jumble a lot of things together and say
"Fiat unguentum". . . . Yet if medicine were handled by artists
[i.e. chemists], a far more healthy system would be set on foot.'
For the few apothecaries and physicians who were enlightened
enough to study chemistry and brave enough to apply chemical
remedies, he had the warmest praise:
I praise the spagyric chemical physicians, for they do not consort
with loafers or go about gorgeous in satins, silks and velvets, gold
rings on their fingers, silver daggers hanging at their sides, and
white gloves on their hands, but they tend their work at the fire
patiently day and night. They do not go promenading, but seek
their recreation in the laboratory, wear plain leathern dress and
aprons of hide upon which to wipe their hands, thrust their fingers
amongst the coals, into dirt and rubbish and not into golden rings.
They are sooty and dirty like the smiths and charcoal-burners, and
Paracelsus 113
hence make little show, make not many words and gossip with
their patients, do not highly praise their own remedies, for they
well know that the work must praise the master, not the master his
work. They well know that words and chatter do not help the sick
nor cure them. . . . Therefore they let such things alone and busy
themselves with working with their fires and learning the steps of
alchemy. These are distillation, solution, putrefaction, extraction,
calcination, reverberation, sublimation, fixation, separation, re-
duction, coagulation, tinction, &c.
The relentless war that Paracelsus waged against contem-
porary medicine had the effect of making chemistry, for the
future, an indispensable part of a medical training. Physicians
were set free from slavish deference to authority, and chemistry,
presented with a new aim, was released from the trammels of
degenerate alchemy. After this time, 'the art of chemistry was
cultivated by medical men in general it became a necessary part
of their education, and began to be taught in colleges and medical
schools. The object of chemistry came to be, not to discover the
philosopher's stone, but to prepare medicines; and a great
number of new medicines, from both the mineral and vegetable
kingdoms some of more, some of less, consequence, soon issued
from the laboratories of the chemical physicians/ The im-
portance of the new valuation of chemistry can scarcely be
exaggerated. As long as alchemy and chemistry were synony-
mous terms, the exponents of the Art (or science) were living
under a growing cloud of suspicion and contempt. Quickly
hardening into a rigid mould, alchemy was practised on stereo-
typed lines and on its theoretical side was fast becoming a chaos
of superstitious verbiage. Paracelsus's vigorous onslaught on
orthodox medicine and his call to the chemists to prepare drugs
provided a much-needed stimulus. The honourable task of the
age of iatrochemistry, or medical chemistry, that he inaugurated,
was to make the way clear for a reasonable medicine ; but it did
more it made the way clear also for a reasonable chemistry.
Before leaving Paracelsus for his successors, we may take a
brief glance at his chemical theory, in so far as it may be
2613-4 j
ii4 Paracelsus
disentangled from the cabbalistic ideas everywhere intertwined
with it. Like the Neo-Platonists (of whose teachings there was
a revival at this time), Paracelsus believed that the universe as
a whole and all the objects in it were endowed with life. Inter-
mediate between the material and immaterial were beings con-
sisting of a body and spirit but no soul ; such were the sylphs of
the air, the nymphs of water and the salamanders of fire which
will be familiar to many from the alchemist in La Rotisserie de la
Reine Pedauque. As to material substances, these are ultimately
composed of the four Aristotelian elements, but immediately of
three primary bodies, tria prima, viz. salt (body), sulphur (spirit)
and mercury (soul). Paracelsus was thus taking over a previously
existing modification of the old sulphur-mercury theory of
metals, extended so as to apply to all substances whether metallic
or not. Salt was the principle of incombustibility and non-
volatility; mercury was the principle of fusibility and volatility;
while sulphur was the principle in virtue of which substances are
inflammable. This theory is, of course, not to be taken literally :
the 'sulphur' in wood, for instance, is not the same as the
'sulphur' in lead, and neither of them is to be conceived as very
closely resembling ordinary sulphur. These tria prima are,
indeed, nothing more than abstractions of qualities, and there-
fore differ essentially in character from the elements of modern
chemistry. Paracelsus himself says :
You should know all seven metals originate from three materials,
namely, from mercury, sulphur, and salt, though with different
colours. Therefore Hermes has said not incorrectly that all seven
metals are born and composed from three substances, similarly
also the tinctures and philosopher's stone. He calls these three
substances spirit, soul and body. But he has not indicated how
this is to be understood nor what he means by it. Although he may
perhaps have known, yet he has not thought (to say) it. I therefore
do not say that he has erred, but only kept silent. But that it be
rightly understood what the three different substances are that he
calls spirit, soul and body, you should know that they mean not
other than the three principia, that is mercury, sulphur and salt,
Later latrochemists 115
out of which all seven metals originate. Mercury is the spirit,
sulphur is the soul, salt the body.
[But] as many as there are kinds of fruits so many kinds there
are of sulphur, salt, and so many of mercury. A different sulphur is
in gold, another in silver, another in lead, another in iron, tin, &c.
Also a different one in sapphire, another in the emerald, another
in the ruby, chrysolite, amethyst, magnets, &c. Also another in
stones, flint, salts, springwaters, &c. And not only so many kinds of
sulphur but also as many kinds of salt, different ones in metals,
different ones in gems, stones, others in salts, in vitriol, in alum.
Similarly with mercuries, a different one in the metals, another in
gems, and as often as there is a species there is a different mercury.
Of one nature is sulphur, of one nature salt, of one nature mercury.
And further they are still more divided, as there is not merely one
kind of gold but many kinds of gold, just as there is not merely one
kind of pear or apple but many kinds. Therefore there are just as
many different kinds of sulphurs of gold, salts of gold, mercuries of
gold.
The views on chemical philosophy peculiar to Paracelsus need
j not unduly delay us, however, for they soon became obsolete and
of themselves bore but little fruit. We may, in fact, legitimately
suspect that even their author was not always certain of what he
\ meant by his emphatically dogmatic statements on chemical
theory. Their most valuable feature was their revolutionary
character, and the worlds of medicine and alchemy, rudely
awakened by Paracelsus 's vitriolic tongue, never afterwards
relapsed into their former state of undignified but self-satisfied
somnolence. Study Nature, said Paracelsus, for 'in her mysteries
you will have enough to last you all your life . . . without re-
ferring to paper books ' . ' This has been my Academy, not Athens ,
or Paris, or Toulouse.'
32. Later latrochemists
AFTER the death of Paracelsus, a bitter strife broke out between
his followers and the supporters of the old methods of pharmacy
and medicine. Many of the Paracelsan school were even more
unrestrained than their master, and administered extraordinary
not to say dangerously poisonous drugs to their unfortunate
I 2
n6 Later latrochemists
patients. Whatever may be said in depreciation of the 'Galenical
liquors' their 'Maukish, Spiritless, Dull, Flat Posset-drink,
Small-beer, Early- water, loathsome Decoctions of cooling crude
Herbs, Pippin Liquors, and the like, which starve the Vital
Fig. 29. LIBAVIUS'S CHEMICAL HOUSE
Spirit, bringing a numness upon it', it is hard to believe that the
following iatrochemical suggestions were any more efficacious :
Cinnabar, to scatter 'those black Clouds arising from the horrid
Spectrums of the Appoplexie, Epilepsie, introducing instead
thereof a brightness and splendour in the Spirit' ; zinc sulphate
for the eyes, to cause 'the Species of Objects to be seen more
Later latrochemists 117
plain' ; mercury, to destroy 'all sorts of Worms' ; lead acetate, to
'Clarifie the Spleen, Reforming it's peccant Idea's'; and iron
sulphide to cure diabetes.
Such excesses were vigorously opposed by several chemists,
OCCAJV.T.
Fi^. 3 o. PLAN OF LIBAVIUS'S CHEMICAL HOUSE
notably Andreas Libavius (1540-1616). Born at Halle, Libavius
practised for some years as a doctor, but in 1588 went to Jena
as professor of history in the university there. Later he taught at
the Gymnasium at Rothenburg on the Tauber, and from 1607
till his death he was director of the Gymnasium at Coburg.
Though not an extreme reactionary, Libavius had little sympathy
n8 Later latrochemists
with Paracelsan views, and carried on controversies with many
of the wilder iatrochemists. He was ready to admit the value of
chemical remedies, but sought to establish clearly a distinction
between experimental truth and imaginative hypothesis. In
chemical theory he has no claim to originality ; at times he seems
to support the Paracelsan theory of the triaprima y salt, sulphur
and mercury, and at others he reverts to the older Arabian
sulphur-mercury theory. It is rather on the practical side that
Libavius attracts our attention. In 1595 he published his great
work Alchymia, which was for many years the chief chemical
text-book. It is a comprehensive survey of contemporary
chemical knowledge and has earned its author an undying fame.
The keynote throughout is one of system and plain exposition,
and though it is mainly a compilation it contains much that is
new. Libavius was, for instance, the first to show that sulphuric
acid can be made by burning sulphur with saltpetre, and proved
that the acid so obtained was identical with that prepared by
distilling green vitriol or alum; he discovered stannic chloride,
which he prepared by heating tin with mercuric chloride; he
first described ' glass of antimony' and the blue colour given by
ammonia with copper salts; and he developed a rudimentary
system of chemical analysis.
Libavius also devoted much thought to the design and equip-
ment of chemical laboratories. Figures 29 and 30 show respec-
tively the elevation and ground-floor plan of his ideal 'chemical
house', containing, besides the main laboratory, a store-room
for chemicals, a preparation room, a room for the laboratory
assistants, a room for crystallization and freezing, a room for
sand and water baths, a fuel room and, not least among the
amenities, a wine cellar a delightful feature unhappily over-
looked by the modern architect of chemical laboratories ! In the
main room, apparatus was arranged round the walls ; it included
a great variety of furnaces, descensories, sublimatories, dis-
tillation apparatus, crucibles, mortars and phials. Very sig-
nificant is the absence of a balance-room : chemistry was not yet
a quantitative science. As a whole, Libavius 's chemical house,
van Helmont 119
in its workmanlike design and orderly plan, contrasts very
strongly with the usual alchemical laboratory of the time, of
which we can get a good impression from the pictures drawn by
Peter Breughel (c. 1525-69), John Stradanus (c. 1530-1605),
J. Pinas (c. 1600), David Teniers the younger (1610-90) and
John Steen (1626-79). Libavius may, in fact, be said to have
planned the first chemical, as opposed to alchemical, laboratory.
33. van Helmont
ONE of the last and certainly the greatest of the iatrochemists
proper was Johann Baptista van Helmont, born at Brussels in
1577 of a noble and wealthy Brabant family. By the age of
seventeen he had completed an Arts course at the University of
Lou vain, but he declined to take a degree on the grounds that he
was dissatisfied with what he had been taught. Turning to
science, mathematics and philosophy, he found them equally
unsatisfactory, and after dallying with mysticism for some time
he took up the study of medicine. Here he found his true bent,
and when he graduated at Louvain in 1599 he astonished his
examiners by the extent of his learning. Falling ill a short time
later, he was attended by a Galenist physician, whose treatment
unfortunately proved a failure, van Helmont consequently
determined to exert himself to overthrow what was left of the
orthodox system of medicine, and joined the ranks of the Para-
celsan school; he was, however, too original and independent
a thinker to follow Paracelsus blindly and had no hesitation in
differing from 'the immortal Theophrastus' when he thought fit.
After an extended tour throughout Europe he returned to the
Netherlands deeply impressed with the importance of chemistry.
Having married a rich Brabant lady, Marguerite van Ranst, he
settled at Vilvorde, near Brussels, and for the rest of his life shut
himself up in his laboratory pursuing chemical investigations
and writing scientific books. His fame became so great that he
received many flattering offers from German princes to accept
an official position at their Courts, but he could not be induced
to leave his beloved laboratory. He died at Vilvorde on 30
I2O van Helmont
December 1644. His writings were gathered together after his
death by his son, under the title Ortus medicinae, and published
by the famous house of Elzevir at Leyden. An English transla-
tion, by John Chandler, appeared in 1662.
van Helmont resembled Paracelsus in his intense inclination
to the supernatural, his trenchant style and his bitter contempt
of the Galenists ; but in disposition and character the two were
very different. Modest and unassuming, van Helmont found
his pleasure in the patient investigation of scientific subjects
rather than in the meretricious splendour of a princely court.
For chemistry, the choice was a happy one.
In chemical theory, van Helmont was more reactionary than
Libavius, and, neglecting both the Aristotelian elements and the
iatrochemical tria prima, he harks back to an ancient Greek
theory (due to Thales) that water is the true principle of all
things. Mercury, salt and sulphur, he says, which the chemists
call the three primary bodies, are not in reality principles, i.e.
elements, since (a) there are bodies in which they do not exist,
(b) they are themselves formed from water, and (c) they can be
reconverted into water. His belief that water is the essential
principle of all things was not a mere imaginative flight; he
adduced both observation and experiment in support of it.
Thus he draws attention to the fact that an enormous number of
both organic and inorganic substances yield water when strongly
heated, and described the following experiment, which may well
have appeared quite conclusive :
He took 200 pounds of earth dried in an oven, and having put it
into an earthen vessel and moistened it with rain water, he planted
in it the trunk of a willow tree of five pounds weight; this he
watered, as need required, with rain or distilled water ; and to keep
the neighbouring earth from getting into the vessel, he employed
a plate of iron tinned over and perforated with many holes. Five
years having elapsed, he took out the tree and weighed it, and (in-
cluding the weight of the leaves that fell during the four autumns)
he found it to weigh 169 pounds 3 ounces. And having again dried
the earth it grew in, he found it only about 2 ounces short of its
van Helmont 121
former weight of 200 pounds; so that 164 pounds of the roots,
leaves, wood, and bark, which constituted the tree appeared to
have sprung from the water alone.
We know now that the source of the increase in weight was not
merely the water, but also the carbon dioxide of the air, but we
can readily admit that, in the absence of any knowledge of the
constitution of the atmo-
sphere and the relation be-
tween atmospheric gases and
plant life, van Helmont's
experiment must have ap-
peared to him to provide irre-
futable evidence of the truth
of his theory. In this con-
nexion, it is interesting to
find that van Helmont was
the founder of pneumatic
chemistry; it is, indeed, by
his work on gases that he will Fi s-
be chiefly remembered. He
was not successful in collecting them, although he made many
attempts to do so, but he it was who first realized that here was
a new and important class of substances, and who, in fact,
actually invented the word gas (from * chaos') by which to
designate them. It is unnecessary to point out the incalculable
results of van Helmont's observations one has only to re-
member that the development of the atomic and molecular
theories by Dalton, Gay-Lussac and Avogadro was based very
largely upon work on gases to realize that van Helmont opened
the way to one of the most fruitful fields of chemistry. He had
not the good fortune to hit upon the beautifully simple idea of
the pneumatic trough so obvious to us, but in its discovery
a mark of genius and broke innumerable vessels in vain
attempts to isolate the 'wild invisible spirits, which will not be
pent up'. As Hoefer remarks: 'Que de vaisseaux brises avant
que Ton parvint a recueiller les fluides elastiquesF It is pleasant
VAN IIELMONT AND HIS SON
122 van Helmont
to think that the solution of this tremendous problem is mainly
the honour of the Englishmen, Hales and Priestley, though
Boyle too had used a method of collecting gases over water.
van Helmont's gas silvestre was carbon dioxide. He showed
that it was formed when charcoal was burnt, and when beer and
wine were fermented, and he also detected it in the air of the
Grotto del Cane (Naples). He discovered its presence in the
mineral waters of Spa, and prepared it by the action of acetic
acid upon a carbonate. He believed, too, that the same gas was
evolved when silver was dissolved in nitric acid, since his only
test was to find whether the gas would extinguish a flame or
whether it would itself burn. An inflammable gas obtained from
the intestines and by the fermentation of dung he called gas
pingue. In short, van Helmont showed that gases were distinct
substances, with definite properties, but, owing to his inability
to collect them, he was able to distinguish only two kinds,
namely, inflammable (gas pingue) and those which would not
support combustion (gas silvestre).
A last point of interest in connexion with van Helmont is that
he clearly recognized the law of the conservation of matter, at
least in particular cases, and realized that substances continue
to exist even after undergoing chemical change. Thus he
showed that if a certain weight of silica is converted into water-
glass and the latter then treated with acid, the precipitated silicic
acid will on ignition yield the same weight of silica as that
originally taken. Yet in spite of his keen scientific insight and
his powers as an experimentalist, he retained a firm belief in the
possibility of the transmutation of the metals, and one of the
most circumstantial of all accounts of supposed transmutation is
vouched for by him.
In 1618, van Helmont received at his laboratory at Vilvorde, from
an unknown source, about a quarter of a grain of the philosophers'
stone. He projected it upon 8 ounces of mercury, which was
transformed into fine gold. From that day he became a warm
partisan of alchemy, and even christened his new-born son with
the name Mercurius. 'Mercurius van Helmont did not belie his
124 Nicolas Lemery
alchemical baptism, for he converted Leibniz to this way of
thinking ; during the whole of his life the latter sought the philo-
sophers' stone, dying without having found it, it is true, but as
a fervent disciple/
34. Nicolas Lemery
BEFORE leaving the iatrochemists for Boyle and the beginnings
of modern chemistry, we may take a passing glance at a succes-
Fig. 33. NICOLAS LEMERY
sion of accomplished French chemists who flourished in the
seventeenth and early eighteenth centuries at Paris. The work
of all of them was on similar lines, largely coloured by iatro-
chemical practice, and in itself it had little immediate effect upon
chemical philosophy. We can, therefore, in a book of this size,
conveniently consider it as a whole and so avoid the necessity of
interrupting the main thread of our story in later pages.
In 1606 chemistry received official recognition in France by
the establishment of a Demonstratorship, and some years after-
TRAITE
DE LA
CHYMIE-
TOME PREMIER.
QVI SERVIRA D'INSTRVCTION ET
d'introdudion y tant pour rintclligcncc dcs Au-
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en general : Quepour faciliter Ics moycns dc faire
amftement & methodicjueinem Ics operations
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catre ordinaire A^T(oj d'*4nglcterrt &de fa Mtttfo> O*
Mcmlre <le Vdicademic'Royale deLowlres.
de Edition, revcuc, corrigcc &dc bcaucoiip
augmentcc de bon nombre d'excellcns
remedes , par 1'Authcur.
A PARIS,
thez THOMAS IOLLY , au Palais, en la Salle dcs
Merciers,au coin de la Gallcrie dcs Prifonniers,
a la Palme , & aux Armes d'Hollande.
MT D C. TX I X.
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Fig- 34
Fig. 35. APPARATUS FROM LEMERY'S COURSE
OF CHYMISTRY
Fig. 36. APPARATUS FROM LEMKRY'S COURSE
OF CHYMISTRY
ia8 Nicolas Lemery
wards it became part of the duty of the First Physician to the
King to give public lectures on chemistry at the laboratories in
the Jar din du Roi or Jar din des Plantes : a garden founded in
1627 by Guy de la Brosse, Mathematician to the King, as a site
for the cultivation of medicinal plants. The first demonstrator
was the eminent Scottish doctor, William Davidson or
d'Avisonne, as he preferred to call himself. He was succeeded
by Jean Beguin, the author of a popular treatise entitled Les
Clemens de Chymie, and by Nicolas Lefebure, who frankly stated
that he drew from Paracelsus, van Helmont and others, and laid
no claim to originality. According to Lefebure, there are three
kinds of chemistry: (a) philosophical, i.e. scientific or contem-
plative, which reflects upon nature and natural effects; (b) iatro-
chemical, which is essentially practical but is inspired by the
philosophical; and (c) pharmaceutical, which is merely operative,
since the apothecaries must work only according to the direc-
tions of the iatrochemists 'of whom', says Lefebure with
a flourish, 'we have a veritable model in the person of M. Vallot,
chosen by His Very Christian Majesty for his First Physician*.
Shortly after the foundation of the Royal Society, Charles II
summoned Lefebure to London, where he spent the rest of his
life at the Court of St. James's. His post in Paris was filled by
Christopher Glaser, who was afterwards forced to leave the
country through becoming involved in the notorious poisoning
case known as the affaire Brinvilliers : he was suspected of having
supplied the amiable Marquise with the arsenic she employed
to murder her father and brother.
One of Glaser 's pupils was Nicolas Lemery, who, like many of
the seventeenth-century chemists of France, belongs rather to
the history of pharmacy than to that of chemistry. Yet his text-
book entitled Cours de Chymie (first published in 1675) enjoyed
an unparalleled success, going through eleven editions in France
alone and being translated into English, Latin, German, Italian
and Spanish. It consequently exerted a deep influence upon
contemporary chemical thought and incidentally brought its
author a handsome fortune by way of royalties. The chief
C O UR SE
O F
Chymiftry.
CONTAINING
The Eafleft Manner of perv
formirig thofe Operations that are in
life in PHTSICK.
ILLUSTRATED
With many Curious Remarks and
Ufeful Difcourfes upon each
OPERATION.
Writ in FRENCH by Monfieur
NICHOLAS LEMERT.
TranHated by W A L T E R II A R R 1 S,
Doftor of PHTSICK.
L O 2^ 1> O
Printed for Walter Kettilfy at the
Head in.St. Caul's Church- Yard , 1677.
Fig. 37
K
130 Nicolas Lemery
characteristics of Lemery were his rational outlook and his firm
resolve to abolish completely the enigmatical and mystificatory
language in which chemists still too often chose to enwrap their
knowledge. In his preface he states explicitly that he will endeavour
to render himself intelligible and to avoid the obscure expressions
of previous authors : now this had been a common gambit since
the days of Zosimos, but Lemery actually did what he promised,
and his book can be read and understood with ease and certainty.
Lemery admits the convenience of assuming that there are five
chemical 'principles' of natural things, viz. Water, Spirit, Oil,
Salt and Earth, but cautiously remarks that the word principle in
chemistry must not be undersood in too rigid a sense: for the
substances so called are only ' principles' in so far as our weak
imperfect chemical analysis fails to divide them further. Now
chemistry is an Art that demonstrates what it does (he says), so it
recognizes as fundamental only such things as are palpable and
demonstrable. 'The fond conceits of other Philosophers, con-
cerning natural principles, do only puff up the Mind with Grand
Idea's, but they prove or demonstrate nothing.' Instead of con-
tenting ourselves with metaphysical conceptions, like that of a
Universal Matter, 'it will be fit to establish some sensible ones'.
The Cours de Chymte, a book of some 500 closely printed
pages, describes in completely unequivocal language the prac-
tical chemical knowledge of the time, including much that is due
to Lemery himself. The descriptions are accompanied by
shrewd observations, and the general impression left on the
mind of a modern reader is that Lemery must have been one of
the most acute and skilful experimenters France has ever pro-
duced. Not the least interesting passage is that which describes
the explosion of a mixture of air and hydrogen. It is true that
Lemery did not properly appreciate the reaction, or the nature
of the inflammable substance, and that the real 'discovery' of
hydrogen was made only a century later, by Cavendish ; but the
passage is worth quoting :
If 3 Ounces of the Oil of Vitriol be put into a middle-sized Phial,
with a long Neck, and to it 12 Ounces of Water; when the Mixture
Nicolas Lemery 131
grows warm, if an Ounce, or an Ounce and half of Iron File-Dust
be thrown into it at several Times, there will arise an Ebullition,
and a Solution of the Iron, which will produce white Vapours, that
will rise and fill the Neck of the Phial. If one puts to the Aperture
a lighted wax Candle, the Vapour will immediately take Fire, and
at the same Time occasion a violent and a cracking Noise, and then
go out. ... It also often happens that the Vapour will keep lighted
like a Torch, at the Top of the Neck of the Phial, above a quarter of
an Hour. . . . The Sulphur of the File-Dust being disengaged and
rarified by the Oil of Vitriol, exalts itself in a Vapour very sus-
ceptible of Fire. . . . Aquafortis, or the Spirit of Saltpeter, does not
excite a Detonation.
Lemery also describes the preparation of fulminating gold by
the addition of aqueous ammonia to a solution of gold in aqua
regia. lie explains the formation and properties of the substance
as follows. When the gold is dissolved in the aqua regia it be-
comes divided into extremely fine particles, which are kept in
suspension [solution] by the sharp points of the acid particles,
just as a piece of metal may be made to float if it is attached to
wood. On the addition of ammonia, the acid points are weakened
and the gold particles are thus precipitated; they are, however,
impregnated with some part of the dissolvent, viz. 'the sharpest
part* of the acid edges. On heating the fulminating powder, the
'spirits' locked up in it 'violently divide the most compact Body
of Gold to get out quickly'.
However inadequate we may think the theories expressed in
these two extracts, we must admit that they are reasonable and
scientific in spirit, free from the taint of the occult. They are
definitely an attempt to explain observed facts on rational
grounds and as such must win our approval. The scientific
attitude was, indeed, once again beginning to make its appearance
in chemistry, and if we now leave Paris for Oxford we shall find
its most celebrated protagonist in the person of Robert Boyle.
During the journey, which is essentially a passage from the old
to the new chemistry, we may spend our time in a brief review
of the country we have already traversed.
K 2
132 Robert Boyle
35. Review of Chemistry to the Time of Lemery
IN this first part of the book we have seen how chemistry arose
in an empirical way from the observations of ancient craftsmen.
Particularly in Egypt metallurgical knowledge was of vital im-
portance to the Crown, and metallurgy was therefore largely
practised as a secret art under the control of priests and other
Crown officials. In Greece and Alexandria philosophical
schemes of the universe were elaborated, tending in later
classical times to an involved mysticism. During the first three
or four centuries of our era Gnostic and Neo-Platonist thinkers
applied their doctrines to the supposed art of transmuting base
metals into gold, and so a practical craft became a false science.
It is in Islam that we at length meet with real chemists, in the
modern sense of the word. Men like Jabir and Razi systema-
tized chemical knowledge, evolved definite chemical theories,
and established chemistry as a true science. Later chemists of
Islam on the whole failed to maintain the standard set them, and
magic and superstition again vitiated the young science.
From Islam chemistry was transmitted bodily to Europe in
the twelfth to fourteenth centuries, but unfortunately the
alchemical aspect received most attention, and alchemy, rather
than chemistry, was cultivated for two or three hundred years.
Then, about 1500, Paracelsus reorientated chemistry and en-
gaged it in the service of medicine. Though alchemy continued
to flourish, the more reasonable chemists turned to the prepara-
tion of drugs and thus the extent of practical chemical knowledge
was increased by leaps and bounds. With extended knowledge
came a more scientific spirit, exemplified by men like Libavius,
van Helmont and Lemery. Men felt that weighty events por-
tended and that chemistry was on the eve of great advances.
How well that feeling was justified the remaining sections of
this book will show.
36. Robert Boyle
UNTIL the declining years of the seventeenth century, the
ultimate background of chemical theory was the Aristotelian
Robert Boyle 133
system of the Four Elements. For almost exactly two thousand
years this system reigned supreme and unchallenged; it was
modified, additions were made to it, it occasionally receded into
a temporary obscurity, but it was always there and always
formed the philosophical basis of theoretical chemistry and the
justification of practice. But with the vastly increased number of
experimental facts brought to light by the alchemists and,
particularly, iatrochemists, the Aristotelian or 'peripatetic'
theory was perceived to be growing less and less adequate as
a scientific explanation of phenomena ; and many chemists gave
it lip-service rather than a genuine belief. It was at length felt,
in general unconsciously perhaps, that Fire, Air, Earth and
Water could be regarded as the elements of material bodies in
only a metaphysical sense: hence the three 'hypostatical prin-
ciples' or triaprima of the iatrochemists, and the salt, spirit, oil,
water and earth favoured by Lemery. After a long and useful
life the ancient Greek theory was becoming unequal to the
strain of advancing with the march of knowledge, and soon we
shall find it written, 'a new king reigned in his stead'.
It was the Irishman Boyle who first remorselessly exposed the
deficiencies of the old 'principles' and thus, in effect, founded
the modern science of chemistry. The Hon. Robert Boyle was
born in 1627 at Lismore Castle in Munster. At seventeen years
of age he went to Oxford, where he began the study of natural
philosophy, which was to occupy him till his death in 1691. By
the reckoning of time he was a contemporary of Lemery, but
Lemery was among the last of the old school while Boyle was
the first of the new. It is with another contemporary, namely
Sir Isaac Newton, that Boyle may more properly be compared;
for although his work did not receive the immediate support
accorded to that of Newton he nevertheless provided the philo-
sophical system that has ever since guided the path of
chemistry. His scientific writings cover a wide range and were
by no means confined to chemistry, although it is in the latter
province that the effect of his genius was most beneficially felt.
Greatest, perhaps, in constructive work as a physicist, his con-
134 Robert Boyle
tributions to chemistry were a searching and relentless criticism
of prevailing theories and a rigorous insistence upon the prin-
ciples of scientific method formulated, a few years previously,
by Francis Bacon. His most famous discovery was that of the
law which describes the behaviour of gases under varying
pressures, and which still bears his name. Boyle's style is virile
and precise, and reflects his mental attributes of clear thinking
and logical deduction. He is seen at his best in his demolition
of the Aristotelian ' elements' and the Paracelsan * principles', in
place of which he substituted that definition of an element which
is now universally adopted. Let us hear him first on the defects
of the Paracelsans and their 'salt, sulphur, and mercury':
I might begin [he says] with taking notice of the Obscurity of
those Principles [i.e. sulphur, mercury, and salt] which is no small
defect in Notions whose proper office it should be to conduce to the
illustration of others. For, how can that facilitate the understand-
ing of an obscure Quality or Phaenomenon which is itself scarcely
intelligible, or at least needs almost as much explanation as the
thing 'tis designed and pretended to explicate ? Now a man need
not be very conversant in the writings of Chymists to observe, in
how Laxe, Indefinite, and almost Arbitrary Senses they employ the
Terms of Salt, Sulphur and Mercury ; of which I could never find
that they were agreed upon any certain Definitions or settled
Notions; not onely differing Authors, but not unfrequently one
and the same, and perhaps in the same Book, employing them in
very differing senses. But I will not give the Chymists any rise to
pretend, that the chief fault that I find with their Hypothesis is,
but verbal ; though that itself may not a little blemish any Hypo-
thesis, one of the first of whose Requisites ought to be Clearness.
. . . Methinks a Chymist, who by the help of his Tria Prima, takes
upon him to interpret that Book of Nature of which the Qualities
of bodies make a great part, acts at but a little better rate than he,
that seeing a great book written in a Cypher, whereof he were
acquainted but with three Letters, should undertake to decypher
the whole piece. ... I must not forget to take notice, that some
learned modern Chymists would be thought to explicate divers of
the changes that happen to Bodies in point of Odours, Colours, etc.
by saying that in such alterations the Sulphur or other Hypostatical
Robert Boyle 135
Principle is introverted or extraverted, or, as others speak, inverted,
But I confess, to me these seem to be rather new terms than real
explications. . . .
Thus, dear Pyrophilus, I have laid before you some of the chiei
Imperfections I have observed in the vulgar Chymists' Doctrine oJ
Qualities. . . . And as my objections are not taken from the
Scholastical subleties nor the doubtful speculations of the Peri-
Fig. 38. ROBERT BOYLE
pateticks or other Adversaries of the Hermetick Philosophy, bu
from the nature of things and from Chymical experiments them-
selves ; so I hope, if any of your Spagyrical friends have a minde tc
convince me, he will attempt to doe it by the most proper way
which is, by actually giving us clear and particular explications.
The supporters of the Aristotelian elements fare no better ai
his hands ; in fact, all the older chemists, he says, in their searches
after truth, are not unlike the navigators of Solomon's Tarshisl:
fleet, who brought home from their long and tedious voyage*
not only gold, and silver, and ivory, but apes and peacocks too
for some of the chemical theories either, like peacocks' feathers
make a great show but are neither solid nor useful, or else, like
apes, if they have some appearance of being rational, an
blemished with some absurdity or other, that, when they an
attentively considered, make them appear ridiculous.
136 Robert Boyle
Boyle tells us that after he had gone through the common
operations of chemistry and had begun to make some serious
reflections upon them, he thought it was a pity that instruments
that might prove so serviceable to the advancement of natural
philosophy should not be more studiously and skilfully made
use of to so good a purpose. Chemistry, he felt, ought not to be
a mere handmaid to medicine (as the iatrochemists maintained)
or a slave to the search after transmutation (as the alchemists
averred), but a natural philosophy, a systematic investigation of
nature with the object of the advancement of knowledge.
I saw, indeed, that divers of the Chymists had by a diligent and
laudable employment of their pains and industry, obtained divers
Productions, and lighted on several Phaenomena considerable in
their kind, and indeed more numerous, than, the narrowness and
sterility of their Principles considered, could be well expected. But
I observed too, that the generality of those that busie themselves
about Chymical Operations; some because they practise Physick;
and others because they either much wanted, or greedily coveted
money, aimed in their Trials but at the Preparation of good
Medicines for the humane body, or to discover the ways of curing
the Diseases or Imperfections of Metals, without referring their
Trials to the advancement of Natural Philosophy in general; of
which most of the Alchymists seem to have been so incurious;
that not onely they did not institute Experiments for that purpose,
but overlookt and despis'd those undesign'd ones that occur 'd to
them whilst they were prosecuting to preparation of a Medicine,
or a Transmutation of Metals. The sense I had of this too general
omission of the Chymists, tempted me sometimes to try, whether
I could do any thing towards the repairing of it by handling
Chymistry, not as a Physician, or an Alchymist, but as a meer
Naturalist, and so by applying Chymical Operations to Philosophical
purposes. And in pursuance of these thoughts, I remember I drew
up a Scheme of what I ventured to call a Chymia Philosophica, not
out of any affectation of a splendid Title, but to intimate, that the
Chymical Operations, there treated of, were not directed to the usual
scopes of Physicians, or Transmuters of Metals, but partly to illus-
trate or confirm some Philosophical Theories by such Operations ;
and partly to explicate those Operations by the help of such Theories.
Robert Boyle 137
Boyle's masterpiece was his great work The Sceptical Chymist,
first published at London in 1661. Here, in the form of a
dialogue between Themistius, who represents the older view, and
Carneades, the spokesman of Boyle himself, the modern con-
ception of an element is clearly expressed while previous ones
are exploded. Themistius is allowed to give a very fair and just
exposition of the theories of the peripatetics and Paracelsans,
but Carneades seizes on their weak points with unerring acumen
and demonstrates with cold logic how profoundly unsatisfactory
Themistius 's arguments prove to be when closely examined.
The chemists' typical 'proof that substances consist of fire, air,
earth and water lay in pointing out the fact that when a piece of
wood is burnt (a) fire appears, (6) water boils and hisses from
the ends of the burning wood, (c) smoke ascends into the air,
where it vanishes, thus showing itself to be of the same nature,
and (d) an earthy ash is left. Boyle pertinently inquires what
proof there is that the fire, air, earth and water really are present
in wood before combustion, and also demands evidence for
assuming that the four 'elements' are actually 'simpler' than the
original wood. Obtaining no convincing answer he sums up as
follows :
Since, in the first place, it may justly be doubted whether or no the
fire be, as chymists suppose it, the genuine and universal resolver
of mixt compound bodies ;
Since we may doubt, in the next place, whether or no all the
distinct substances that may be obtained from a mixt body by the
fire were pre-existent there in the formes in which they were
separated from it ;
Since also, though we should grant the substances separable
from mixt bodies by the fire to have been their component in-
gredients, yet the number of such substances does not appear the
same in all mixt bodies; some of them being resoluble into more
differing substances than three; and others not being resoluble
into so many as three ;
And since, lastly, those very substances that are thus separated
are not for the most part pure elementary bodies, but new kinds of
mixts ;
138 Robert Boyle
Since, I say, these things are so, I hope you will allow me to
inferr, that the vulgar experiments (I might perchance have added,
the arguments too) wont to be alledged by chy mists to prove, that
their three hypostatical principles do adequately compose all mixt
bodies, are not so demonstrative as to induce a wary person to
acquiesce in their doctrine, which, till' they explain and prove it
better, will by its perplexing darkness be more apt to puzzle than
satisfy considering men, and will to them appear incumbered with
no small difficulties.
There is, he says, no valid reason for limiting the number of
the elements to four, as the Aristotelians do, or to three, like the
Paracelsans, or indeed to any particular, preconceived number:
And if according to this notion we allow a considerable number of
differing elements, I -may add, that it seems very possible, that to
the constitution of one sort of mixt bodies two kinds of elementary
ones may suffice (as I lately exemplified to you, in that most durable
concrete, glass), another sort of mixts may be composed of three
elements, another of four, another of five, and another perhaps of
many more. So that according to this notion, there can be no
determinate number assigned, as that of the elements, of all sorts
of compound bodies whatsoever, it being very probable that some
concretes consist of fewer, some of more elements. Nay, it does not
seem impossible, according to these principles, but that there may
be two sorts of mixts, whereof the one has not any of all the same
elements as the other consists of; as we oftentimes see two words,
whereof the one has not any of the letters to be met with in the
other.
Finally, having accomplished his destruction of the Four
Elements and the tria prima, he completes his work by stating
his own view of an element as it should be conceived in chemistry :
I mean by elements, as those chymists that speak plainest do by
their Principles, certain primitive and simple, or perfectly 'un-
mingled bodies; which not being made of any other bodies, or of
one another, are the ingredients of which all those called perfectly
mixt bodies are immediately compounded, and into which they are
ultimately resolved. ... I must not look upon any body as a true
principle or element, which is not perfectly homogeneous, but is
further resolvable into any number of distinct substances.
SCEPTICAL CHYMIST:
OR
CHYMI CO-PHYSICAL
Doubts & Paradoxes ,
Touching the
SPACYRIST'S PRINCIPLES
Commonly call'd
HYPOSTATICAL,
I
As they, are wont to be Propos'd and
Defended by the Generality of
ALCHYMISTS.
!Whereunto is prsmis'dPart of another Difcourfc
relating to the fame Subject.
B Y
The Honourable ROBERT tOTLE, Efqj
LONDON,
printed by J* Cattvell for J* Crookt, and are to be
Sold at the Ship in St JtAvfr Church-Yard*
D Cl. -JT /.
Fig. 39
140 Robert Boyle
In other words, chemists should regard as elementary all those
substances that they have not yet been able to split up into two
or more constituents, and should not limit themselves by any
preconceived notions of the number of these elements. If a sub-
stance is undecomposable it is to be considered an element, and
it will retain that title for just so long as it withstands the efforts
of chemists to decompose it. It will be seen that Boyle's defini-
tion of an element was purely empirical, and that instead of
postulating any definite number of elements he is content to
investigate the subject experimentally and so to find out how
many there actually are. This attitude is so much our own that
we find it difficult to realize the revolutionary character that it
presented to Boyle's contemporaries. It made, indeed, little
immediate progress ; Boyle himself afterwards complained :
I thought the rousing stile I sometimes wrote in, might prove no
unhopefull way to procure somewhat considerable from those
great Masters, and orders of Chymicall Arcana, that must be
provok'd before they will come out with them ; as the sea is observ'd
not to give us one of its preciousest treasures, Ambergreece; till it
have been agitated by winds and storms.
He was disappointed at the lack of controversy and discussion
that he had hoped to arouse, but, on looking back, we can see
that from the date of the publication of The Sceptical Chymist
the Aristotelian elements became obsolete. One reason, at least,
for the lack of discussion was the impossibility of answering
Boyle's arguments.
Boyle himself was unable to evolve experimental methods of
deciding whether or not a given substance is to be considered an
element; that advance was left for the great Lavoisier, whose
acquaintance we shall soon make. It is, however, interesting
to compare Lavoisier's own statement on the nature of the
chemical elements, made in 1789, with that which Boyle had
expressed a century earlier. Lavoisier says :
It is very remarkable, notwithstanding the number of philosophical
chemists who have supported the doctrine of the four elements,
that there is not one who has not been led by the evidence of facts
Robert Boyle 141
to admit a greater number of elements into their theory. The first
chemical authors, after the revival of letters, considered sulphur
and salt as elementary substances entering into the composition of
a great number of substances ; hence instead of four, they admitted
the existence of six elements. Becher assumes the existence of
three kinds of earth; from the combination of which, in different
Fig. 40. THE OLD ASHMOLEAN, OXFORD (FIRST UNIVERSITY
CHEMICAL LABORATORY)
proportions, he supposed all the varieties of metallic substances to
be produced. Stahl gave a new modification to this system; and
succeeding chemists have taken the liberty to make or to imagine
changes and additions of a similar nature. All these chemists were
carried along by the genius of the age in which they lived, being
satisfied with assertions instead of proofs; or, at least, often
admitting as proofs the slightest degrees of probability, unsup-
ported by that strictly rigorous analysis which is required by
modern philosophy.
All that can be said upon the number and nature of elements is,
in my opinion, confined to discussions entirely of a metaphysical
nature. The subject only furnishes us with indefinite problems,
142 Robert Boyle
which may be solved in a thousand different ways, not one of which,
in all probability, is consistent with nature. I shall, therefore, only
add upon this subject, that if, by the term elements, we mean to
express those simple and indivisible atoms of which matter is
composed, it is extremely probable that we know nothing at all
about them; but, if we apply the term elements or principles of
bodies, to express our ideas of the last point which analysis is
capable of reaching, we must admit, as elements, all the sub-
stances into which we are able to reduce bodies by decomposition.
Not that we are entitled to affirm, that these substances which we
consider as simple, may not themselves be compounded of two, or
even of a greater number of more simple principles; but since
these principles cannot be separated, or rather since we have not
hitherto discovered the means of separating them, they act with
regard to us as simple substances, and we ought never to suppose
them compounded until experiment and observation has proved
them to be so.
And lastly, to show how much alive Boyle's idea still is, we
may quote the following words from J. W. Mellor's Compre-
hensive Treatise on Inorganic and Theoretical Chemistry (1922) :
The definition of an element is not founded upon any intrinsic
property of the elements, but rather upon the limited resources of
the chemist. To find if a given substance is an element or com-
pound, it is usual to assume that it is a compound and then to
apply all known methods for resolving compounds into simple
substances. If the methods fail to effect a decomposition, the
substance is said to be an element. ... In fine, element is a con-
ventional term employed to represent the limit of present-day
methods of analysis or decomposition. We may, therefore,
summarize these ideas in the definition : An element is a substance
which, so far as we know, contains only one kind of matter. To say
the substances we call elements cannot be decomposed may be
regarded as an unwarranted reflection on the powers of our
successors.
We have not yet bidden farewell to Boyle, whom we shall meet
again in succeeding pages ; but in this place it may be recalled
that he it was who introduced into Oxford the first regular
teacher of practical chemistry, viz. 'the noted chemist and Rosi-
Becher and Stahl 143
crucian, Peter Sthael of Strasburgh in Royal Prussia, a Lutheran,
a great hater of women, and a very useful man'. Boyle engaged
Sthael as his assistant, but allowed him to have pupils, among
whom was the philosopher John Locke. Locke, we are told,
was 'a man of turbulent spirit, clamorous and never contented.
The club [class] wrote and took notes from the mouth of their
master, who sat at the upper end of a table ; but the said J. Lock
scorned to do it ; so that while every man besides of the club
were writing, he would be prating and troublesome.' However,
says Dr. Gunther, a few years later we find him writing to Boyle,
'I find my fingers still itch to be at it' (experiments in chemistry).
37. Becher and Stahl
IT has already been mentioned that Boyle's work evoked little
immediate response, coming to full fruition only a century later.
The explanation must be sought mainly in the fact that chemists
became deeply engrossed in a theory of combustion, which
occupied the attention of practically all the best minds of the
eighteenth century to the virtual exclusion of everything else.
Comprehensive theories are very seldom perhaps never the
work of one man, as we shall have many opportunities to realize.
A suggestion here, another there, a casual remark, an old hypo-
thesis, such are the materials that the genius takes and moulds
into a new and better form. Nowhere do we find this more
clearly demonstrated than in the history of theories of combus-
tion. For centuries combustion was regarded as a decomposition
of the burning substance into its constituents, so that only com-
pound bodies could be combustible. On the sulphur-mercury
theory of metals, elaborated by Jabir, the combustion of a metal
was explained by supposing the loss of its sulphureous constituent.
Advancing knowledge soon rendered this primitive theory un-
tenable, and even among the chemists of Islam, as well as in the
thirteenth and fourteenth centuries in Europe, the combusti-
bility of a substance was assigned to the presence in it of an oily
constituent. Sulphur, from its greasy feel and from its oily
appearance when molten, was believed to contain a high per-
144 Becher and Stahl
centage of this oil, and one of the Latin works ascribed to Jabir
goes so far as to say that sulphur is merely 'an oily fatness of the
earth'. A metal, therefore, containing sulphur as an essential
constituent, would, ipso facto, be combustible. The residue left
after the calcination or burning of a metal was regarded as the
Fig. 41. JOHANN JOACHIM BECHER
mercurial constituent contaminated with more or less earthy
impurity.
This vague theory of combustion, with various modifications
in detail, persisted up to the middle of the seventeenth century.
The theory favoured by Paracelsus, that there was a third, saline,
constituent of bodies, did not essentially change ideas of com-
bustion it remained the generally accepted belief that any-
thing which would burn contained an oily, sulphureous prin-
ciple : ubi ignis et color ibi sulphur. Such was the state of affairs
when Johann Joachim Becher (1635-82) in 1669 published his
Acta Laboratorii Chymici Monacensis, seu Physica Subterranea,
A6lorum Laboratori'i
Chyraici Monaccnfis,
Sett
PHYSICS
SUBTERRANE^E
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JOANNES JOACHIMUS
BECHERUS,SP1RENS1S,
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riw , nee non SercniJJtmi B#vari* ElcHorif
AuU Medic'tt.
FRANCOFURTI,
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ANNO M. DC LX1X.
Fig. 42
2613 4
146 Becher and Stahl
in which he promulgated the theory that in the hands of his
pupil, Stahl, finally assumed such imposing dimensions.
According to Becher, all minerals were composed of three
constituents, in varying proportions terra pinguis, terra mercu-
rialis, and terra lapida. The first two obviously correspond to
the old sulphur and mercury, while the third is parallel with
the saline constituent. Every combustible substance Becher
believed to contain terra pinguis y which was lost on com-
bustion. * Metals', he says, * contain an inflammable principle
which by the action of fire goes off into the air ; a metal calx is
left', that is, its terra lapida and terra mercurialis. Combustion
is therefore a disintegration of the burning body and the loss of
its more volatile constituent.
It will be seen that Becher 's theory was only a re-expression
of older ideas in language a little less vague. His terra pinguis is
the inflammable earth, the fiery oil, and the burning sulphur of
the ancients. Nevertheless, his arguments and illustrations were
so forcible that they carried conviction where before there had
been doubt, and, when elaborated and extended by Georg
Ernst Stahl (1660-1734), Becher's form of the theory won the
allegiance of practically all chemists.
Stahl re-edited the Physica Subterranea in 1702, and added
a work of his own, the Specimen Becherianum, in which he ex-
pressed his views of combustion. The materia ignis of com-
bustible bodies he called phlogiston ('burnt', from </>Aoyiiv to
inflame), thus giving his theory the name by which it has
been known ever since. Stahl did not regard phlogiston as
fire itself, but rather as the material of fire materia out prin-
cipium ignis, non ipse ignis. It is contained in all combustible
bodies as an essential constituent, and is given up to the air on
combustion. It becomes appreciable to our senses only when it
leaves the body with which it was combined, and appears in the
form of fire with its accompaniments of light and heat. The
richer a substance is in phlogiston, the more easily it may be
burnt, and the more ready it will be to give up phlogiston to
substances that do not already possess it, or possess it only in
Becher and Stahl 147
small quantity. As for the actual process of combustion, this is
merely a liberation of phlogiston from the body that is being
burnt.
Now practically all metals may be converted into an ash by
means of heat, even though they may not be inflammable in the
ordinary sense of the word ; the metallic ashes were known as the
Fig. 43. GEORG ERNST STAHL
calces of the metals and the process was called calcination.
According to Stahl, the calcination or burning of a metal was to
be explained in the same way as the combustion of any other
combustible body, namely, as a loss of phlogiston. Metals, in
short, were to be considered as compound bodies, each com-
posed of two constituents : phlogiston and calx. Different metals
naturally have different calces, but the dual composition is
common to all metals. Oil, charcoal, fats, &c., which burn away
almost completely and leave little residue, are, from that very
property, extremely rich in phlogiston. Hence, if a metallic calx
L 2
148 Becher and Stahl
is heated with charcoal, for instance, one might expect the
charcoal to give up some of its phlogiston to the calx, thus re-
converting the latter into the metal. The fact that metallic
calces can thus be 'reduced' to metal by heating with charcoal
had, of course, been known for centuries, and at length a reason-
able hypothesis was advanced to explain it.
Let us take a definite example of the phenomenon and hear
how it was explained by R. Watson, Professor of Divinity (!) in
the University of Cambridge :
Lead, it has been observed, when melted in a strong fire, burns
away like rotten wood ; all its properties as a metal are destroyed
and it is reduced to ashes. If you expose the ashes of lead to
a strong fire, they will melt; but the melted substance will not be
a metal ; it will be a yellow or orange coloured glass [litharge] . If you
pound this glass and mix it with charcoal dust, or if you mix the
ashes of the lead with charcoal dust, and expose either mixture to
a melting heat, you will obtain, not a. glass, but a metal, in weight,
colour, consistency, and every other property the same as lead. . . .
The ashes of lead melted without charcoal become glass ; the ashes
of lead melted with charcoal become a metal \ the charcoal then
must have communicated something to the ashes of lead, by which
they are changed from a glass to a metal ; charcoal consists but of
two things, of ashes, and of phlogiston ; the ashes of charcoal, though
united with the ashes of lead, would only produce glass; it must
therefore be the other constituent part of charcoal, or phlogiston,
which is communicated to the ashes of lead, and by an union with
which the ashes are restored to their metallic form. The ashes of
lead can never be reduced to their metallic form, without their
being united with some matter containing phlogiston, and they
may be reduced to their metallic form, by being united with any
substance containing phlogiston in a proper state.
The phlogiston theory, then, offered a rational explanation of
the formation of metallic calces and of the reduction of the latter
to metals : but it did more. Like every scientific theory worthy
of the name it soon proved to be applicable to facts with which
at first it seemed completely unconnected, and by bringing them
all to a common denominator it achieved the earliest great
Becher and Stahl 149
synthesis of chemical philosophy. Thus the experimental facts
(a) that when sulphur is burnt under suitable conditions it yields
sulphuric acid, and (b) that by the action of charcoal upon
sulphuric acid sulphur can be regenerated, were simply and con-
Fig. 44. RICHARD WATSON
sistently explained by assuming that sulphur is composed of
sulphuric acid and phlogiston. Upon burning sulphur the
phlogiston is lost and the acid remains, but when the acid is
heated with charcoal a substance rich in phlogiston it once
more combines with phlogiston to form sulphur. Again, if zinc
is dissolved in dilute sulphuric acid a colourless inflammable
gas [hydrogen] is evolved and a solution of white vitriol remains.
The inflammable gas was regarded as practically pure phlogis-
150 Troublesome Facts
ton, and the reaction was explained by supposing that the acid
split up the zinc into 'phlogiston' (which was evolved) and zinc
calx, the latter dissolving in the acid to form the white vitriol.
A logical deduction from this hypothesis was that if zinc were
first burnt, so removing its phlogiston, the residual zinc calx
should dissolve in dilute sulphuric acid, to yield a solution of
white vitriol without evolution of the inflammable gas. Experi-
ment shows that this deduction is correct, for the reaction takes
place exactly as indicated.
Further, it follows from the phlogiston theory that if a metallic
calx is heated in the above-mentioned inflammable gas, the
metal ought to be regenerated : a deduction which once more is
in perfect agreement with the experimentally established fact.
And lastly, the facts that a combustible substance will not burn
in a vacuum, and that its flame is soon extinguished in a limited
supply of air, were explained by assuming that a medium is
necessary to absorb phlogiston, just as a sponge absorbs water.
To the original hypothesis of Becher and Stahl addition after
addition was made, until a large and complex theoretical system
was constructed and practically every known type of chemical
reaction found a more or less satisfactory explanation. The chief
protagonist of the adult theory was the French chemist Macquer,
who devoted a lengthy article to phlogiston in his Dictionnaire
de Chimie (second edition, 1778). There is, however, no need for
us to follow all the intricacies of his exposition, the main points
of the theory having remained unchanged from the time of their
formulation by Stahl. It will be more profitable for us to turn
next to some of the difficulties that the phlogistians had to face
and to witness the growth of those intractable facts that after-
wards led to a revolution in chemical theory.
38. Troublesome Facts
' NOTWITHSTANDING all that perhaps can be said upon the
subject/ admits Watson, 'I am sensible the reader will be still
ready to ask what is phlogiston!' Replying to this question he
says, 'You do not surely expect that chemistry should be able to
Troublesome Facts 151
present you with a handful of phlogiston, separated from an
inflammable body ; you may just as reasonably demand a handful
of magnetism, gravity, or electricity to be extracted from
a magnetic, weighty, or electric body ; there are powers in nature,
which cannot otherwise become the objects of sense, than by the
effects they produce, and of this kind is phlogiston.' It may be
doubted whether this explanation satisfied all of Watson's
readers, or whether, even, it would have satisfied Stahl himself;
the latter, indeed, definitely regarded phlogiston as a material
substance though of a very subtle nature, invisible, in constant
and rapid spiral motion and capable of penetrating the densest
substances. We begin to see that the question, 'What is phlogis-
ton?' was a very pertinent one, and that the reply given was
rather an evasion than an answer.
A more serious difficulty was that during calcination metals
undergo an increase in weight. This fact had been known for
a great many years, for it is mentioned by Jabir in the eighth
century, by Eck de Sultzbach in 1489, and by Cardanus in 1553.
Attention had been specifically directed to it by Jean Rey in
1630, who remarks in his Essays that some eminent personages
had observed with astonishment that tin and lead increase in
weight when they are calcined, and that he had been asked by
the Sieur Brun, Master Apothecary in Bergerac, to furnish him
with an explanation of this phenomenon. Brun had placed 2 Ib.
6 oz. of fine English tin in an iron vessel and heated it strongly
on an open furnace for the space of six hours with continual
agitation and without adding anything to it. At the close of the
operation he recovered 2 Ib. 13 oz. of a white calx, which filled
him with amazement and with a desire to know whence the 7 oz.
of surplus had come. Rey considered carefully all the conflicting
hypotheses that had been advanced in explanation, and showed
that they were untenable. He then attempted to show that
the only hypothesis in accordance with the observed facts
was 'that this increase in weight comes from the air, which in
the vessel had been rendered denser, heavier, and in some
measure adhesive, by the vehement and long-continued heat of
152 Troublesome Facts
the furnace : which air mixes with the calx (frequent agitation
aiding) and becomes attached to its most minute particles'.
Rey meets the objection that, the amount of air available being
practically unlimited, there should be no limit to the increase in
weight of a metal upon calcination, by saying that Nature is
scrupulous to stop at the bounds she has once prescribed her-
self. The calx is in this condition : the condensed air becomes
attached to it, and adheres little by little to the smallest of its
particles: thus its weight increases from the beginning to the
end, but when all is saturated it can take up no more. 'Do not
continue your calcination in this hope: you would lose your
labour/ He concludes with
another objection which might be raised. Why do not all other
calces and ashes made by the force of fire increase in weight as well
as the calx of tin and of lead ? What privileges have these over the
others? I answer that the things calcined or incinerated are of
different nature. Some have much exhalable and evaporable
matter, or much sulphur and mercury, which the fire expels to the
end. Here there is much diminution and little ash, which cannot
attach to itself as much of the air condensed by fire as even to make
up for the decrease. Others have little exhalable and evaporable
matter, or little sulphur and mercury : consequently there is little
diminution, and much ash . . . which attracts so much of the
condensed air, that not only is the diminution made good, but the
weight increases largely in addition.
Lemery was equally puzzled by the increase in weight that
occurs during the calcination of a metal. 'In the calcination of
lead and of several other substances/ he says in his Cours de
Chymie (1675), * there occurs an effect which well deserves that
some attention should be paid to it ; it is that although by the
action of the fire the sulphureous or volatile parts of the lead are
dissipated, which should make it decrease in weight, neverthe-
less after a long calcination it is found that instead of weighing
less than it did, it weighs more/
This was indeed an awkward fact for the Theory of Phlogis-
ton. Surely, one might argue, if phlogiston is lost when a metal
Troublesome Facts 153
is calcined, the calx ought to weigh less than the original metal.
The actual fact was widely known Stahl himself knew it and
it had been established beyond dispute. To us, it would have
rendered the phlogiston theory untenable from the very start,
but the phlogistians were wholly unperturbed. Some of them
followed Stahl's lead in regarding an alteration in weight during
a chemical change as an unimportant detail that might be
neglected ; a course of action which may serve to remind us that
the quantitative age of chemistry had not yet arrived. In those
days, moreover, the distinction between weight and density was
not so clear as it afterwards became, so that, taking a sympathetic
view, we can perhaps understand Stahl's attitude. Other
chemists adopted the standpoint that the fact was admittedly
inexplicable, but that the phlogiston theory explained so many
other facts, and explained them so well, that the solution of the
matter might safely be left to the future. Still others, such as
Venel and Guyton de Morveau, sought escape from the diffi-
culty by ascribing to phlogiston a negative weight. 'Phlogiston,'
said Venel in his course of chemistry at Montpellier, 'is not
attracted towards the centre of the earth, but tends to rise;
thence comes the increase in weight in the formation of metallic
calces and the diminution in weight in their reduction'! Com-
ment upon this over-ingenious suggestion is unnecessary.
Boyle himself had been attracted to the problem of the nature
of the changes that occur during the calcination of metals.
He calcined weighed quantities of copper, lead, tin and other
metals, and noted that in every case there was an increase in
weight. In one experiment,
two ounces of filings of tin were carefully weighed and put into
a little retort, whose neck was afterwards drawn slender to a very
small apex ; then the glass was placed on kindled coals, which drove
out fumes at a small orifice of the neck, for a pretty while. After-
wards the glass, being sealed at the apex, was kept in the fire for
above two hours, and then being taken off, was broken at the same
apex: whereupon I heard the external air rush in, because, when
the retort was sealed the air within it was highly rarefied. Then
1 54 Mayow
the body of the glass being broken, the tin was taken out, consisting
of a lump, about which there appeared some grey calx, and some
very small globules, which seem to have been filings melted into
that form. The whole weighed two ounces and twelve grains.
Boyle explained the increase in weight by assuming that the
metal had absorbed heat, which he imagined to be a material
substance possessing weight. It has been erroneously stated
that Boyle's explanation of calcination formed the basis of the
phlogiston theory, but that this statement is incorrect is obvious
in view of the facts that (i) the phlogiston theory is merely
i development of more ancient views on combustion, and (2) on
the phlogiston theory combustion was a decomposition, whereas
according to Boyle it was a combination: Boyle, for example,
:onsidered lead calx to be lead plus heat, while Becher and
Stahl regarded it as lead minus phlogiston.
We must now consider a further difficulty that confronted
:he phlogistians, viz. the necessity of air for combustion. The
solution which they offered, it will be remembered, was that the
iir provided a medium in which the phlogiston could be
ibsorbed ; in the absence of such a medium phlogiston could not
3e given off from a combustible body, which would consequently
3e unable to burn. Similarly, when a given quantity of air was
saturated with phlogiston it would naturally be unable to
support combustion. One of the facts that these suggestions
were intended to explain had been known from time immemorial,
lamely, that substances will not burn indefinitely in a limited
volume of air, while the other that substances will not burn in
i vacuum had been established by Boyle and was now common
3roperty. The hypothesis advanced by the phlogistians was not
he only one put forward, and as the others are of importance
,hey may be briefly described.
39. Mayow
WE saw that Rey had supposed the increase in weight on calcina-
ion of a metal to be caused by the condensation of air upon the
^articles of calx, an idea which at first sight appears to fore-
Mayow 155
shadow the theory we now hold. Reflection will, however, show
us that Rey imagined the calx to be formed first, in some way
that he does not explain, and only afterwards to absorb the
condensed air. There is thus a vital difference between his
hypothesis and the modern theory. A like remark applies to the
Pig- 45
work of Robert Hooke (1635-1703), who suggested that the
combustion of a substance when heated with saltpetre is similar
in essentials to its combustion in air : he regarded combustion as
a loss of the sulphureous principle which was taken up by the air
in the one case and by the saltpetre in the other.
The researches of John Mayow deserve closer attention, since
this remarkable man has been held to have 'anticipated the work
of Lavoisier (1775) by more than a century'. Mayow was born
in London in 1643, went to Wadham College, Oxford, in 1658,
156 Mayow
and became a Fellow of All Souls in 1660. In 1675 he settled in
Bath as a practising physician, devoting his leisure hours to
scientific research, on the results of which he was elected a Fellow
of the Royal Society in 1678. A few months later, on a visit to
London, he died 'in an apothecarie's house bearing the sign of
the Anker in York Street, Covent Garden, having a little before
been married not altogether to his content'.
Like Hooke, Mayow emphasized the similarity between com-
bustion in air and combustion in saltpetre, but suggested that
probably air and saltpetre contain a common 'spirit* necessary
to combustion; this he called the nitro-aerial spirit. He remarks
that it has
to be admitted that something aerial, whatever it may be, is
necessary to the production of any flame a fact which the ex-
periments of Boyle have placed beyond doubt, since it is established
by these experiments that a lighted lamp goes out much sooner in
a glass that contains no air than it does in the same when filled with
air a clear proof that the flame goes out . . . because it is deprived
of its aerial food. ... In the second place, it would be reasonable to
suppose that the igneous particles of air necessary to the support of
all flame reside in sal nitrum and constitute its more active and
fiery part, for it is to be noted that nitre mixed with sulphur
deflagrates readily enough in a glass which does not contain air.
Mayow also observed the increase in weight during calcina-
tion and the decrease in volume which a limited quantity of air
undergoes when a candle is burnt in it. The former observation
he explains by assuming that the metal unites with nitro-aerial
particles, and the latter by the loss of nitro-aerial particles from
the air. Superficially, these explanations seem astonishingly like
our own, if we substitute 'oxygen* for 'nitro-aerial particles';
and Mayow has thus been credited with the great discovery
usually attributed to Lavoisier.
Professor J. B. Cohen, however, in 1901 pointed out that
Mayow's nitro-aerial spirit differs essentially from the modern
oxygen, in that (a) although nitro-aerial particles are present in
the air they are not a part of it ; (b) the sun's rays are imagined
Fig. 46. APPARATUS OF MAYOW
158 Pneumatic Chemistry
to be a chaos of nitro-aerial particles; (c) metallic iron, which
forms sparks when struck, therefore contains nitro-aerial
particles ; (d) the latter can be annihilated ; (e) they give rise to
heat if set in motion ; (/) they appear to be confused with the red
fumes given off when nitric acid is heated. The conclusion to be
drawn is that although Mayow appreciated the necessity of air
Fi//. 47. HHKNOUILLI
for combustion, and the similarity between combustion in air
and deflagration in nitre, he had no real conception of the true
nature of burning or of the composition of the air. The solution
of these problems is the honour of Lavoisier and of Lavoisier
alone.
40. Pneumatic Chemistry
THE age of phlogiston might equally well be called the age of
pneumatic chemistry, for it was during the period in which the
brilliant theory of Stahl reached its zenith, that many of the
common gases were first discovered, collected and investigated.
One of the most familiar objects of a modern chemical laboratory
Pneumatic Chemistry 159
is the pneumatic trough, at which gases are collected by the
displacement of water or, less frequently, mercury. So simple is
the device that, having once seen it in use, we are apt to take it
purely as a matter of course and rarely regard it as a supreme
achievement of the inventive genius. Perhaps this indifference
is only natural, but what an immensity of labour lies behind the
Fig. 48. BERNOUILLI'S APPARATUS
trite instruction of the text-book: 'Collect the gas over water at
the pneumatic trough'! Indifference before even the dullest
chemical experiment cannot survive a knowledge of the work
which made that experiment possible. Every chemical we use,
every piece of apparatus we take, and every experiment we per-
form, hide a romance. Who, for instance, automatically selecting
a cork to stopper his flask, gives a thought to the origin of that
admirably effective contrivance ? It comes as a surprise to find
that the use of corks for closing bottles is not yet 300 years old ;
it is said to have been introduced by the Benedictine monk Dom
Perignon about 1680. Perignon was born in 1638 and became
Cellarer of the monastery of Hautvillers, not far from Reims.
As the result of much long and patient observation, he invented
the wine now universally known as champagne, but was faced
160 Pneumatic Chemistry
with the difficulty of preserving its effervescent nature. He finally
hit upon the idea of closing the bottles with pieces of cork, and
such was the superiority of this method over all which had gone
before that the whole world rapidly adopted it. Let us toast
Dom Perignon's service to chemistry in a glass of his own wine!
We have already heard of van Helmont's new name, gas, for
those 'wild, untamable' varieties of matter that resist imprison-
ment, and of his failure to devise a means of collecting them.
Boyle was more ingenious. He took a glass flask with a long neck
and completely filled it with dilute sulphuric acid . He then dropped
in six iron nails and inverted the flask in a vessel containing
more of the dilute acid. Bubbles of gas [hydrogen] were formed
and rose to the top of the apparatus, displacing the acid and soon
filling the flask. Here was the germ of the pneumatic trough.
Mayow made a further advance, showing that a gas could be
transferred from one vessel to another by filling the latter with
water, inverting it in a trough of water, and bringing the mouth
of the first vessel, containing the gas, under the mouth of the
other ; 'care being taken [as he says] that the mouth of neither of
the glasses is raised above the surface of the water'. He further
emphasized the importance, in quantitative work, of levelling
the water inside and outside ajar containing gas, in order to get
the latter at atmospheric pressure. This he accomplished by
means of a siphon-tube.
A few years later Jean Bernouilli (1667-1748) used the
apparatus illustrated in fig. 48 to demonstrate experimentally the
fact that the propulsive force of gunpowder is due to the pro-
duction of gases that, when liberated, occupy a much greater
space than the powder from which they are formed.
Another skilful manipulator of gases chiefly air was the
French physician Moitrel d 'Element, who dwelt in a wretched
garret in the Rue Saint-Hyacinthe, Paris, towards the beginning
of the eighteenth century. To relieve his poverty, he gave a
public course of experiments on air, in which he 'measured air by
pints', transferring it from one vessel to another in the way
suggested by Mayow.
Pneumatic Chemistry 161
The next improvement was made by the Englishman Stephen
Hales (1677-1761). In 1724 Hales undertook a comprehensive
research upon the physiology of plants, and in 1727 published
his results in a book entitled Vegetable Staticks. Having
Fig. 49. THE REV. STEPHEN HALES
occasion to conduct many experiments with gases in connexion
with his botanical work, Hales devoted himself to the elabora-
tion of a suitable technique. He devised several forms of
apparatus for the purpose, but the most interesting is shown in
fig. 50 ; it will be at once recognized as our modern pneumatic
trough in an unusual shape.
Further development was mainly a matter of detail, though it
should be mentioned that Boerhaave (1668-1738) measured the
2613-4
M
Fig. 50. STEPHEN HALES' APPARATUS FOR
COLLECTING GASES
Pneumatic Chemistry 163
volume of a gas evolved in a particular reaction by conducting
the reaction in vacua ^ noting the change in pressure, and correct-
ing by the then newly-discovered Boyle's Law. With Priestley
(p. i69)we find the trough in its present-day shape, but Priestley
Fig. 51. BOERHAAVE
had the happy inspiration of substituting, on occasion, mer-
cury for water, and so made the discovery of several gases
which, since they are soluble in water, had previously been
overlooked.
With the recognition of gases as definite species of matter or
rather as different varieties of 'air* and with the establishment
of methods of collecting and measuring them, the way was open
for great progress. Of the five 'makers of chemistry' we are
are about to meet, four owe their fame chiefly to their work on
gases.
M 2
[i6 4 ]
41. Joseph Black
AMONG the chemists of the middle of the eighteenth century,
five men tower high above the rest : Guillaume Francois Rouelle
(1703-70), Joseph Black (1728-99), the Hon. Henry Cavendish
Fig. 52. WILLIAM CULLEN
(1731-1810), Karl Wilhelm Scheele (1742-86), and Joseph
Priestley (1733-1804). Of these men the last three were stead-
fast adherents of the phlogiston theory, while Black and Rouelle
were largely indifferent, devoting themselves to their researches
and placing their own interpretations upon the results.
Joseph Black, the son of a Scottish wine-merchant residing at
Bordeaux, was born in France in 1728. At the age of 1 8 he went
to Glasgow University, where he had the good fortune to begin
the study of chemistry under Dr. William Cullen. Cullen,
though not a great investigator, saw chemistry as a Vast depart-
ment of the science of nature' rather than as a 'curious and useful
art', and the lectures he gave on the subject are inspired through-
Joseph Black 165
out with the true spirit of scientific method. These lectures
were never published, but a lucky chance has preserved a
manuscript copv made by one of Cullen's pupils, 1 from which
Fig. 53. JOSEPH BLACK
the following passage may be quoted as an example of the
splendid teaching the young Black received :
In all our reasonings we are apter to be led into error by assuming
false premises, than by drawing fallacious conclusions when the
premises are just. We must therefore in our Chymical Enquiries
be remarkably accurate in collecting Facts, as it is from these alone
that a proper System can be deduced. In particular we must guard
against many Facts that are related in Books of chymistry, as many
of them are false through a Design to cheat (at least of those that
we find in the Books of the old Alchymists) and others, where that
is not the case, Erroneous through Inaccuracy. As an Instance of
the latter kind Lime water was always said to be strong in propor-
1 Dr. William Falconer. The manuscript is in the Science Library at
Clifton College.
1 66 Joseph Black
tion to the quantity of Lime that was put into a given quantity of
water, but Dr. Alston has shewn that one Pound of Limestone
[i.e. 'burnt limestone' or quicklime] Impregnates 40 of Water as
strongly as it does 10.
Those facts that are merely deduced from Theory without the
Concurrence of Experiment ought not to be admitted : Macquer
in this way tells us that a Salt is formed of the combination of
Water and Earth.
Only such Experiments ought to be depended on, as have been
often repeated, for there are many which vary remarkably every
time they are performed either from some difference in the opera-
tion or the Difficulty we find in subjecting them to the observation
of our senses, by which means some of the most remarkable
Phaenomena escape us. This was long the case in making Aether.
In relating Facts every concurrent Circumstance ought to be
taken notice of in order to render them as complete as possible.
This is a thing of the utmost consequence and in general very little
attended to.
In 1756 Cullen was called to Edinburgh and Black succeeded
to the Glasgow professorship. Ten years later Cullen resigned
the chair of chemistry at Edinburgh, and again Black followed
him. At Edinburgh he remained until his death in 1799. Great
as a teacher, Black was no less eminent as an experimenter, and
although he published only three papers on chemical subjects,
these were models of accuracy and logic, and may still be read
with profit. The most important of the three is entitled Experi-
ments upon Magnesia Alba, Quicklime, and some other Alcaline
Substances, published in 1756. A modern reprint of it was made
by the Alembic Club, with a short preface in which it is well
remarked that
the paper constitutes a highly important step in the laying of the
foundations of chemistry as an exact science, and furnishes a model
of carefully planned experimental investigation, and of clear
reasoning upon the results of experiment. . . . Attention may be
particularly called to Black's tacit adoption of the quantitative
method in a large number of his experiments, and to the way in
which he bases many of his conclusions upon the results obtained
in these experiments.
Joseph Black 167
The problem that Black set out to solve was the nature
of the changes that occur when quicklime is added to the
'mild' alkalis (potassium and sodium carbonates) to render
them caustic, that is, in modern terms, to convert them into
potassium and sodium hydroxides. The caustic nature of the
quicklime formed when chalk is strongly heated was explained
on the phlogiston theory by assuming that the chalk had taken
up phlogiston from the fire. Black, however, observed (i) that
a loss in weight occurs when chalk is converted into quicklime,
and (2) that this loss in weight is due to the fact that a g&s, fixed
air [carbon dioxide], is evolved in the reaction. He found, more-
over, that magnesia alba [a carbonate of magnesium] underwent
a similar change when strongly heated, but that heat had no
effect upon the fixed 'mild' alkalis.
It is sufficiently clear [he says] that the calcarious earths in their
native state, and that the alkalis and magnesia in their ordinary
condition, contain a large quantity of fixed air, and this air cer-
tainly adheres to them with considerable force, since a strong fire is
necessary to separate it from magnesia, and the strongest is not
sufficient to expel it entirely from fixed alkalis, or take away their
power of effervescing with acids. . . . Crude lime [limestone] was
therefore considered as a peculiar acrid earth rendered mild by its
union with fixed air: and quicklime as the same earth, in which, by
having separated the air, we discover that acrimony or attraction
for water, for animal, vegetable, and for inflammable substances.
With remarkable insight he goes on to explain the reaction
between slaked lime and carbon dioxide :
A calcarious earth deprived of its [fixed] air, or in the state of quick-
lime, greedily absorbs a considerable quantity of water, becomes
soluble in that fluid, and is then said to be slaked ; but as soon as it
meets with fixed air, it is supposed to quit the water and join itself
to the air, for which it has a superior attraction, and is therefore
restored to its first state of mildness and insolubility in water.
When slaked lime is mixed with water, the fixed air dissolved in
the water is attracted by the lime, and saturates a small portion of
it, which then becomes again incapable of dissolution, but part of
the remaining slaked lime is dissolved and composes lime-water.
1 68 Joseph Black
If this fluid be exposed to the open air, the particles of quicklime
which are nearest the surface gradually attract the particles of fixed
air which float in the atmosphere. But at the same time that
a particle of lime is thus saturated with air, it is also restored to its
native state of mildness and insolubility; and as the whole of this
change must happen at the surface, the whole of the lime is
successively collected there under its original form of an insipid
calcarious earth, called the cream or crusts of lime-water.
Black had thus arrived at an astonishingly accurate con-
ception of the constitution of limestone and of magnesia alba,
and was now in a position to bring his knowledge to bear upon
the original problem, namely, to explain the reaction that
occurs between quicklime and the 'mild' alkalis. In the first
place he knew that both limestone and the mild alkalis effer-
vesced when treated with dilute acids. He reasonably supposed
that the gas evolved in the former case was fixed air, and he
obtained a proof of this assumption by experiments in which he
found (a) that no gas 'is separated from quicklime by an acid,
and that chalk saturates nearly the same quantity of an acid after
it is converted into quicklime as before', and (b) that two drams
of chalk lost the same weight of 'air' when treated with a dilute
acid as when heated strongly in a furnace.
He next showed that if a definite weight of chalk was taken
and converted into quicklime, the latter could be reconverted
into chalk by treatment with a solution of a mild alkali, and that
the weight of the chalk thus formed was equal to that of the
original specimen. The lime therefore had been 'saturated with
fixed air which must have been furnished by the alkali'.
On exposing a solution of caustic alkali to the air for some
time, Black found that 'the alkali lost the whole of its causticity,
and seemed entirely restored to the state of an ordinary fixed
alkali', and this he explained by assuming that the caustic alkali
had absorbed fixed air from the atmosphere.
From this remarkable series of experiments he had thus
obtained results that enabled him to explain satisfactorily the
whole problem. Limestone was a compound of quicklime with
Joseph Priestley 169
fixed air; when heated it lost the fixed air, quicklime being left.
The mild alkalis were compounds of fixed air with substances
resembling quicklime, but much more soluble in water. When
a solution of a mild alkali was treated with quicklime, the latter
absorbed the fixed air of the former, with production of insoluble
chalk or limestone ; the filtrate was therefore a solution of caustic
alkali. In all essentials, Black's explanation is identical with our
own, and the careful logic of his procedure makes his mono-
graph conspicuous at once among the multitudes of useful re-
searches that were now beginning to bear witness to the new
spirit in chemistry. His only other important discovery was that
of the bicarbonates, but he is nevertheless correctly regarded as
one of the greatest chemists of one of the most fruitful periods of
chemistry, and his fame rests upon impregnable foundations.
42. Joseph Priestley
THE phlogiston theory of combustion found its most ardent
supporter in the person of Joseph Priestley, who was born about
six miles from Leeds, in 1733, and at the age of twenty-two
became a Unitarian pastor. To supplement his meagre income
he undertook teaching work in addition, and showed such ability
that in 1761 he was appointed to the chair of languages and
literature at the Warrington Academy. Further promotion
came in 1767, when he became pastor of a large congregation in
Leeds. Six years later his reputation as a scientist and philo-
sopher was thoroughly established, and he accepted an invita-
tion from Lord Shelburne (the first Marquis of Lansdowne) to
fill the post of his lordship's companion and librarian at Bowood
(Wiltshire). Here he had ample time for the scientific researches
that were his principal delight, and the eight years during
which the association lasted were among the most fruitful of his
life. In 1780 he was elected junior minister of the New Meeting,
Birmingham, and resigned his post with Lord Shelburne, who,
however, presented him with an annuity of 150.
During the unsettled period of the French Revolution,
Priestley openly expressed sympathy with the revolutionaries,
1 70 Joseph Priestley
and was indeed one of their warmest advocates in this country.
He particularly provoked the great Burke by his reply to the
latter's book on the Revolution, and also drew upon himself the
animosity of the orthodox clergy by his attacks on the Estab-
lished Church. The feeling of the country was roused against
#'tg. 54. JUbJt^rt
him, and on 14 July 1791, the anniversary of the fall of the
Bastille, the Birmingham mob wrecked his house and made
a bonfire of his furniture and books. He himself made a hurried
escape to London, travelling on the stage-coach under an
assumed name. Matters were not mended by the action of the
French Assembly which, in September 1792, made him a
citizen of France, and finally he thought it wise to emigrate to
America, whither his three sons had preceded him. He set sail
for New York in April 1794, and was well received in scientific
and religious circles; but he refused to become a naturalized
Joseph Priestley 171
American and also declined the offer of the professorship of
chemistry at Philadelphia. After a short time he established
himself in Pennsylvania, and spent the remaining years of his
life in honoured retirement. He died in 1804.
Passionately devoted to the study of gases, the 'father of
Fig. 55- THE BIRMINGHAM MOB WRECKING PRIESTLEY'S HOUSE
pneumatic chemistry' seems to have had no definite working
plan but to have strayed whither his fancy took him. This
fortunate trait was directly responsible for his most celebrated
discovery, for on i August 1774 it led him to investigate the
effect of heat upon the red calx of mercury. A moment's
reflection will show us that had Priestley, as a staunch phlogis-
tian, stopped to consider the experiment he was about to per-
form, he would probably have changed his mind. "This calx',
he would have said, 'is only mercury from which the phlogiston
has been removed. Now it is just this removal of phlogiston
that is the characteristic effect of heat upon a metal, a mere
172 Joseph Priestley
calx being left. Why waste time in heating a substance upon
which heat has already performed its action?'
However, one's mental activities are not as a rule at their best
on a warm Sunday afternoon in summer, and, moreover,
Priestley had just become the happy possessor of a fine new
burning-glass or convex lens. Tradition says that this lens had
formerly belonged to the Grand-Duke Cosmo III of Tuscany,
who had amused himself by burning his subjects' diamonds
with it. Whether this is true or not we need not stay to inquire :
it is sufficient to know that Priestley was highly delighted with
his splendid new instrument, and 'proceeded with great alacrity
to examine, by the help of it, what kind of air a great variety
of substances, natural and factitious [artificial], would yield, put-
ting them into . . . vessels . . . which I filled with quicksilver, and
kept inverted in a bason of the same'. Among the substances
chosen was the red calx of mercury, a choice which, as we have
seen, was merely a fortunate accident. Priestley himself, on
looking back, frankly remarks that it was a matter of chance :
The contents of this section will furnish a very striking illustration
of the truth of a remark, which I have more than once made in my
philosophical writings, and which can hardly be too often repeated,
as it tends greatly to encourage philosophical investigations; viz.
that more is owing to what we call chance, that is, philosophically
speaking, to the observation of events arising from unknown causes,
than to any proper design, or preconceived theory in this business.
. . . For my own part, I will frankly acknowledge, that, at the com-
mencement 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.
When the mercury calx was heated, Priestley saw with amaze-
ment that mercury was formed and that a colourless 'air' was
expelled. 'But what surprised me more than I can well express,
was that a candle burned in this air with a remarkably brilliant
flame.' In general properties the gas resembled ordinary air,
Joseph Priestley 173
but it would support combustion very much better, and a mouse
was able to live in it for nearly twice as long as it could have lived
in the same volume of air. We may well sympathize with
Priestley's surprise. No result could have been more unexpected,
Fig. 56. PRIESTLEY'S APPARATUS
and Priestley's difficulty in explaining it can be imagined. It
did not occur to him that the phlogiston theory was inadequate
to account for these new and astonishing phenomena; the
problem as he saw it was to reconcile the theory with the observa-
tions he had made. This he proceeded to do, unmindful of the
warning he had himself expressed:
We may take a maxim so strongly for granted that the plainest
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 entangled in his errors, his ingenuity only helping
him to deceive himself by evading the force of truth.
^ l^^ f~*'f -*~* J^*^ /"//*-* <~y;.
*4? >+^6(*?
4u~ "
&~s j~-
. ^,
Fig. 57. AUTOGRAPH LETTER OF JOSEPH PRIESTLEY
Priestley obviously experienced the utmost difficulty in
arriving at a clear conclusion on the nature of the changes he
had observed. His train of thought is confused and inconsistent,
but two points at length emerge distinctly. They are (a) that
ordinary air must contain phlogiston, and (b) that his new gas
represented air which had been deprived of its phlogiston ; he
therefore called it dephlogisticated air. As to point (a), it is plain
that since phlogiston is considered to be evolved from all burn-
ing substances, the air must contain a good deal of it. Moreover,
Priestley had shown the close connexion that exists between
combustion and respiration, and in the latter process there was
clearly a second source of atmospheric phlogiston. On respira-
tion and putrefaction he remarks that they 'affect common air
in the same manner in which all noxious processes diminish air
and make it noxious and which agree in nothing but the emission
of phlogiston. If this be the case it should seem that the phlogis-
ton which we take in with our aliment, after having discharged
its proper function in the animal system, is discharged as
effete by the lungs into the great common menstruum, the
atmosphere*.
There was, then, no difficulty in assuming that the atmo-
sphere, in its normal condition, is charged with a certain pro-
portion of phlogiston. Now the capability of air of supporting
176 Joseph Priestley
combustion was considered to be a function of its power of
absorbing phlogiston. Air, therefore, deprived of its phlogiston
can naturally absorb more than could the same volume of
ordinary air; dephlogisticated air is air of this kind and its
properties are thus explained. Such, in short, was Priestley's
reasoning, and it fitted the facts moderately well.
But there was still the difficulty of explaining why mercury
calx, which presumably is simply the earthy residue of mercury,
should be able to yield dephlogisticated air when heated, and it
is here that Priestley floundered in a morass of involved hypo-
theses. To trace his steps closely lies outside the province of
this book, but he seems to have argued as follows. When
mercury is calcined, it is true that its phlogiston is liberated
from combination with the calx, but instead of going off into the
air it absorbs pure air, i.e. air minus phlogiston, or dephlogisti-
cated air, and the phlogisticated air thus produced remains fixed
in a mechanical way in the particles of calx. Upon heating the
calx, the phlogisticated air is split up, its phlogiston combining
with the calx to re-form metallic mercury while its dephlogisti-
cated air is evolved. It is, however, impossible to give a definite
account of Priestley's views, since they were themselves never
clearly outlined : his own statement may be reproduced in order
to give the reader an opportunity of arriving at an independent
interpretation :
The phlogiston belonging to the metal unites with that air [pure
or dephlogisticated air] so as together to form fixed air [which is not,
in this case, carbon dioxide as with Black], and therefore the calx
may be said to be the metal united to fixed air. Then, in a greater
degree of heat than that in which the union was formed, this
factitious fixed air is again decomposed; the phlogiston in it
reviving the metal, while the pure air is set loose. Consequently
the precipitate mercury calx actually contains within itself all the
phlogiston that is necessary to the revival of the mercury.
In October 1774 Priestley accompanied Lord Shelburne to
Paris. Here he was invited to dine with the French chemist
Lavoisier, and the meeting, which was fraught with tremendous
Henry Cavendish 177
consequences for chemistry, may be described in Priestley's own
words : 'Having made the discovery of dephlogisticated air some
time before I was in Paris, in the year 1774, 1 mentioned it at the
table of Mr. Lavoisier, when most of the philosophical people of
the city were present, saying that it was a kind of air in which
a candle burnt much better than in common air, but I had not
then given it any name. At this all the company, and Mr. and
Mrs. Lavoisier as much as any, expressed great surprise. I told
them I had gotten it horn precipitate per se [calx of mercury] and
also from red lead. Speaking French very imperfectly, and being
little acquainted with the terms of chemistry, I saidplombe rouge,
which was not understood till Mr. Macquer said I must mean
minium. 9
In a short time we shall see the results of this historic meeting,
but in the meanwhile we must leave Priestley in order to form
the acquaintance of 'the richest of the learned and the most
learned of the rich', the Hon. Henry Cavendish.
43. Henry Cavendish
CAVENDISH was a member of the family of the Duke of Devon-
shire, and was born at Nice in 1731. His appearance Mid not
much prepossess strangers in his favour; he was somewhat
above the middle size, his body rather thick, and his neck rather
short. He stuttered a little in his speech, which gave him an air
of awkwardness : his countenance was not strongly marked, so
as to indicate the profound abilities which he possessed'. Of
a quiet and retiring disposition, he shunned publicity of all kinds,
and carried out his experiments solely for his own satisfaction.
Caring little for worldly pleasures, he made but small inroads
into his money, although he provided a library for the use of the
scientific public and was even generous enough to give ^10,000
to one of the temporary librarians who fell ill.
'He was shy and bashful to a degree bordering on disease; he
could not bear to have any person introduced to him, or to be
pointed out in any way as a remarkable man. One Sunday
evening he was standing at Sir Joseph Banks 's in a crowded
178 Henry Cavendish
room, conversing with Mr. Hatchett, when Dr. Ingenhousz,
who had a good deal of pomposity of manner, came up with an
Austrian gentleman in his hand, and introduced him formally
to Mr. Cavendish. He mentioned the titles and qualifications of
his friend at great length,
and said that he had been
peculiarly anxious to be in-
troduced to a philosopher so
profound and so universally
known and celebrated as
Mr. Cavendish. As soon as
Dr.Ingenhouszhadfinished,
the Austrian gentleman be-
gan , and assured Mr. Caven-
dish that his principal rea-
son for coming to London
was to see and converse with
one of the greatest orna-
ments of the age, and one
of the most illustrious philo-
sophers that ever existed.
To all these high-flown
speeches Mr. Cavendish
answered not a word, but
stood with his eyes cast
down quite abashed and
confounded . At last , spying
an opening in the crowd, he
darted through it with all
the speed of which he was master; nor did he stop till he
reached his carriage, which drove him directly home.'
Cavendish's chief contributions to chemistry were his work on
gases and his discovery of the composition of water and of nitric
acid. In 1766 he published in the Philosophical Transactions of
the Royal Society three papers, entitled 'Experiments on
Factitious Air'. In these he described the preparation of an
r/X /) /
\s* L "fl f
18 '
Henry Cavendish 179
inflammable air [hydrogen] by the action of dilute sulphuric or
hydrochloric acid upon zinc, iron, or tin.
Zinc [he says] dissolves with great rapidity in both these acids;
and, unless they are very much diluted, generates considerable
heat. One ounce of zinc produces about 356
ounce measures of air: the quantity seems just
the same whichever of these acids it is dissolved
in. Iron dissolves readily in the diluted vitriolic
[sulphuric] acid, but not near so readily as zinc.
One ounce of iron wire produces about 412
ounce measures of air: the quantity was just the
same, whether the oil of vitriol was diluted with
i^, or 7 times its weight of water: so that the
quantity of air seems not at all to depend on the
strength of the acid. I know of only three
metallic substances, namely, zinc, iron, and tin,
that generate inflammable air by solution in
acids; and those only by solution in the diluted
vitriolic acid, or spirit of salt.
He determined the density of the gas (al-
though the value he obtained was very in-
accurate), and discovered its chief chemical
properties, from a study of which he concluded
that the gas was practically pure phlogiston and
was derived from the metals, not from the acids.
The action of nitric acid on metals was found
to yield an incombustible air, generally nitric
oxide, a result that he explained by assuming
that the phlogiston had reacted with the acid.
Cavendish also conducted experiments on
Black's 'fixed air' [carbon dioxide], measuring
its density and determining its solubility in water. In this
connexion it is interesting to note that Cavendish, making use
of an observation of Boerhaave's, was the first to introduce a
method of drying a gas, which he did by passing it through dry
potassium carbonate or pearl-ashes. He also invented the
method of storing gases over mercury, an idea that inspired
N 2
Fig- 59-
CAVENDISH'S
EUDIOMETER
180 Henry Cavendish
Priestley to use mercury instead of water in the pneumatic
trough. It is, however, for his work on the composition of water
and of nitric acid that he is chiefly remembered, and to an
account of these experiments we must now proceed.
In 1781, Priestley and his friend Warltire had both noticed
that on firing a mixture of common and inflammable airs in a
clean and dry glass vessel, by means of an electric spark, 'the
inside of the glass . . . immediately became dewy'. This experi-
ment was repeated by Cavendish, who published his results in
the Philosophical Transactions of the year 1784. He found that
In all the experiments the inside of the glass globe became dewy,
as observed by Mr. Warltire ; but not the least sooty matter could
be perceived. Care was taken in all of them to find how much the
air was diminished by the explosion. . . . The result is as follows:
the bulk of the inflammable air being expressed in decimals of the
common air.
Inflammable Air remaining
Common Air. Air. Diminution. after the Explosion.
1-241 0686 i'555
i 055 o 642 1-413
o 706 o 647 1-059
0-423 o 612 o 811
0-331 0476 0855
0-206 o 294 0-912
. . . 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 ex-
ploded, almost all the inflammable air, and about one-fifth part of
the common air, lose their elasticity, and are condensed into the
dew which lines the glass.
The better to examine the nature of this dew, 500,000 grain
measures of inflammable air were burnt with about 2\ times that
quantity of common air, and the burnt air made to pass through
a glass cylinder eight feet long and three-quarters of an inch in
diameter, in order to deposit the dew. The two airs were con-
Henry Cavendish 181
veyed slowly into this cylinder by separate copper pipes, passing
through a brass plate which stopped up the end of the cylinder;
and as neither inflammable nor common air can burn by themselves,
there was no danger of the flame spreading into the magazines
from which they were conveyed. Each of these magazines con-
sisted of a large tin vessel, inverted into another vessel just big
enough to receive it. The inner vessel communicated with the
copper pipe, and the air was forced out of it by pouring water into
the outer vessel ; and in order that the quantity of common air
expelled should be 2\ times that of the inflammable, the water was
let into the outer vessel by two holes in the bottom of the same tin
pan, the hole which conveyed the water into that vessel in which the
common air was confined being 2\ times as big as the other.
In trying the experiment, the magazines being first filled with
their respective airs, the glass cylinder was taken off, and water let,
by the two holes, into the outer vessels, till the airs began to issue
from the ends of the copper pipes ; they were then set on fire by
a candle, and the cylinder put on again in its place. 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.
In my first experiment, the cylinder near that part where the air
was fixed was a little tinged with sooty matter, but very slightly so ;
and that little seemed to proceed from the putty with which the
apparatus was luted, and which was heated by the flame; for in
another experiment, in which it was contrived so that the luting
should not be much heated, scarce any sooty tinge could be
perceived.
By the experiments with the globe it appeared, that when in-
flammable and common air are exploded in a proper 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 con-
sequently that almost all the inflammable air, and about one-fifth
of the common air, are turned into pure water.
Cavendish had thus shown that water, instead of being an
element, was a compound of inflammable air [hydrogen] with
1 82 Henry Cavendish
a part of common or atmospheric air a part which appeared to
form one-fifth of the whole. Knowing of the astonishing power
of supporting combustion possessed by Priestley's dephlogisti-
cated air, Cavendish was anxious to find out what happened
when inflammable air and dephlogisticated air were exploded
Fig. bo. CAVliJN LUSH'S METALLIC liULUUMliTEK
together, and carried out experiments with this aim immediately
after those just described. He says:
In order to examine the nature of the matter condensed on firing
a mixture of dephlogisticated and inflammable air, I took a glass
globe, holding 8,800 grain measures, furnished with a brass cock
and an apparatus for firing air by electricity. This globe was well
exhausted by an air-pump, and then filled with a mixture of in-
flammable and dephlogisticated air, by shutting the cock, fastening
a bent glass tube to its mouth, and letting up the end of it into
a glass jar inverted into water, and containing a mixture of 19,500
grain measures of dephlogisticated air, and 37,000 of inflammable ;
so that, upon opening the cock, some of this mixed air rushed
through the bent tube, and filled the globe. (In order to prevent
any water from getting into this tube, while dipped under water to
let it up into the glass jar, a bit of wax was stuck upon the end of it,
which was rubbed off when raised above the surface of the water.)
The cock was then shut, and the included air fired by electricity,
by which means almost all of it lost its elasticity. The cock was
then again opened, so as to let in more of the same air, to supply
Henry Cavendish 183
the place of that destroyed by the explosion, which was again fired,
and the operation continued till almost the whole of the mixture
was let into the globe and exploded. By this means, though the globe
held not more than the sixth part of the mixture, almost the whole
of it was exploded therein, without any fresh exhaustion of the globe.
F-gE
F lf >.6i. CAVENDISH'S APPARATUS
As a result of this experiment, Cavendish obtained about
thirty grains of water, and concluded 'that dephlogisticated air
is in reality nothing but dephlogisticated water, or water de-
prived of its phlogiston; or, in other words, that water consists
of dephlogisticated air united to phlogiston ; and that inflam-
mable air is either pure phlogiston, as Dr. Priestley and Mr.
Kirwan suppose, or else water united to phlogiston'. The
Richard Kirwan (1733-1812) here referred to was an Irish savant
who had settled down in London, devoting himself to experi-
mental chemistry.
Cavendish had thus accurately determined the composition of
water, and had shown that it was quite definitely not an element,
thus driving the last nail into the coffin of Aristotelian chemical
theory, and affording more valuable material for elaboration by
Lavoisier. Cavendish mentions that a friend of his gave an
account of the foregoing experiments to 'M. Lavoisier, as well as
of the conclusion drawn from them, that dephlogisticated air is
only water deprived of phlogiston ; but at that time so far was
M. Lavoisier from thinking any such opinion warranted, that,
184 Henry Cavendish
till he was prevailed upon to repeat the experiment himself, he
found some difficulty in believing that nearly the whole of the
two airs could be converted into water'.
The glass globe in which Cavendish's historic experiment was
made may (Fig. 59) still be seen in a case in one of the corridors of
the Chemistry Department of the University of Manchester ; there
seems little doubt of the authenticity of the exhibit, as Professor
Partington tells us that its pedigree can be traced fairly com-
pletely.
Cavendish's investigation of the composition of nitric acid was
of almost equal importance with his researches on water. Nitric
acid has been known for centuries, and its preparation by heating
a mixture of alum, vitriol, and saltpetre is described by Jabir
(see p. 60). It was known also to other Arab chemists, who used
it for separating the silver from the gold in a gold-silver alloy.
Glauber (1604-68) prepared it by heating a mixture of saltpetre
and sulphuric acid, and by the middle of the eighteenth century
it was obtainable in quantity from the chemical manufacturers.
In 1784 Cavendish conducted a series of experiments on the
effect of sparking a mixture of moist dephlogisticated air
[oxygen] and phlogisticated air [nitrogen]. The apparatus he
employed is shown in Fig. 61.
The air through which the spark was intended to be passed [he says]
was confined in a glass tube Af, bent to an angle (p. 183), which,
after being filled with quicksilver, was inverted into two glasses of
the same fluid, as in the figure. The air to be tried was then intro-
duced by means of a small tube, such as is used for thermometers,
bent in the manner represented by ABC (Fig. 61), the bent end of
which, after being previously filled with quicksilver, was intro-
duced, as in the figure, under the glass DBF, inverted into water,
and filled with the proper kind of air, the end C of the tube being
kept stopped by the finger; then, on removing the finger from C,
the quicksilver in the tube descended in the leg BC, and its place
was supplied with air from the glass DEF. Having thus got the
proper quantity of air into the tube ABC, it was held with the end
C uppermost, and stopped with the finger; and the end A y made
smaller for that purpose, being introduced into one end of the
Henry Cavendish 185
bent tube M (Fig. 61), the air, on removing the finger from C, was
forced into that tube by the pressure of the quicksilver in the leg
BC. By these means I was enabled to introduce the exact quantity
I pleased of any kind of air into the tube M ; and, by the same
means, I could let up any quantity of soap-lees, or any other
liquor which I wanted to be in contact with the air. . . .
I now proceed to the experiments. When the electric spark was
made to pass through common air, included between short
columns of a solution of litmus, the solution acquired a red colour,
and the air was diminished, conformably to what was observed by
Dr. Priestley. . . . When the air is confined by soap-lees, the
diminution proceeds rather faster than when it is confined by
lime-water.
It must be considered, that common air consists of one part of
dephlogisticated air, mixed with four of phlogisticated ; so that
a mixture of five parts of pure dephlogisticated air, and three of
common air, is the same thing as a mixture of seven parts of
dephlogisticated air with three of phlogisticated.
I introduced into the tube a little soap-lees, and then let up
some dephlogisticated and common air, mixed in the above-
mentioned proportions, which rising to the top of the tube M,
divided the soap-lees into its two legs. As fast as the air was
diminished by the electric spark, I continued adding more of the
same kind, till no further diminution took place : after which a little
pure dephlogisticated air, and after that a little common air, were
added, in order to see whether the cessation of diminution was not
owing to some imperfection in the proportion of the two kinds of
air to each other; but without effect. The soap-lees being then
poured out of the tube, and separated from the quicksilver,
seemed to be perfectly neutralized, as they did not at all discolour
paper tinged with the juice of blue flowers. Being evaporated to
dryness, they left a small quantity of salt, which was evidently
nitre, as appeared by the manner in which paper, impregnated
with a solution of it, burned.
From these experiments it was clear that 'phlogisticated air'
is a constituent of nitre and of nitric acid, and the first stage in
the elucidation of the constitution of the acid had therefore been
established. It was left to later chemists to complete the solution
1 86 Karl Wilhelm Scheele
of the problem, notably the brilliant French scientist Gay-
Lussac.
In the course of the experiments that have just been de-
scribed, Cavendish made an observation of much interest an
observation, however, the importance of which was not appre-
ciated until over a century later. In 1784 he 'diminished a mix-
ture of dephlogisticated and common air [by means of the
electric spark] in the same manner as before, till it was reduced
to a small part of its original bulk'. Then, he says:
In order to decompound as much as I could of the phlogisticated
air which remained in the tube, I added some dephlogisticated air
to it, and continued the spark till no further diminution took place.
Having by these means condensed as much as I could of the
phlogisticated air, I let up some solution of liver of sulphur to
absorb the dephlogisticated air ; after which only a small bubble of
air remained unabsorbed, which certainly was not more than -^
of the bulk of the phlogisticated air let up into the tube ; so that if
there is any part of the phlogisticated air of our atmosphere which
differs from the rest, and cannot be reduced to nitrous acid, i.e.
converted into nitric acid, we may safely conclude that it is not
more than j| 5 part of the whole.
In 1895 Lord Rayleigh and Professor (later Sir) William
Ramsay showed that this bubble of intractable gas contained an
extremely unreactive element, to which they gave the name of
argon, and a short time afterwards the presence of other in-
active gases mixed with the argon was demonstrated. No more
striking testimony to the skill and accuracy of Cavendish's
work could be desired.
44. Karl Wilhelm Scheele
PRIESTLEY and Cavendish, brilliant experimenters as they were,
fell short in this respect of a poor Swedish apothecary named
Karl Wilhelm Scheele. Scheele was one of those men who have
an instinctive flair for experimental work every teacher of
chemistry must have experienced the phenomenon among his
pupils but Scheele possessed the instinct in a superlative
Karl Wilhelm Scheele 187
degree. It is not necessarily accompanied by a capacity for pro-
found scientific thought ; on the contrary, the brilliant experi-
menter and investigator is often but a mediocre thinker, as
witness Priestley and Lemery. Scheele himself was no theorist
and accepted the phlogiston system unquestioningly, but as
a discoverer of chemical facts he has few, if any, equals.
Scheele was born at Stralsund, in Swedish Pomerania, on
19 December 1742. At 14 years of age he was apprenticed to
Bauch, an apothecary of Gothenburg, with whom he remained
for eight years. In 1765 he went to Malmo, in 1767 to Stock-
holm, and in 1773 to Upsala, in each town holding a post as an
apothecary 's assistant and in his spare time throwing himself
enthusiastically into researches on experimental chemistry. In
1775 he was placed in charge of an apothecary's shop at Koping,
on Lake Maelar, to run the business on behalf of the deceased
proprietor's widow. Two years later he bought the shop, and in
1786 married his predecessor's widow, only to die within forty-
eight hours.
Brief as his life was, he found time to make a series of dis-
coveries of incalculable importance. Sir Edward Thorpe, in his
excellent little History of Chemistry (London, 1909), summarizes
them as follows :
Scheele 'first isolated chlorine, and determined the in-
dividuality of manganese and baryta. He was an independent
discoverer of oxygen, ammonia, and hydrogen chloride. He
discovered also hydrofluoric, nitro-sulphonic,molybdic,tungstic
and arsenic, among the inorganic acids ; and lactic, gallic, pyro-
gallic, oxalic, citric, tartaric, malic, mucic and uric acids among
the organic acids. He isolated glycerine and milk-sugar; deter-
mined the nature of microcosmic salt, borax, and Prussian blue,
and prepared hydrocyanic [prussic] acid. He demonstrated that
graphite is a form of carbon. He discovered the chemical nature
of sulphuretted hydrogen, arseniuretted hydrogen, and the green
arsenical pigment known by his name. He invented new pro-
cesses for preparing ether, powder of algaroth, phosphorus,
calomel, and magnesia alba. He first prepared ferrous ammonium
1 88 Karl Wilhelm Scheele
sulphate ; showed how iron may be analytically separated from
manganese ; and described the method of breaking up mineral
silicates by fusion with alkaline carbonates'. Can a like array of
discoveries be claimed by any other chemist except, perhaps,
Emil Fischer?
A year or more before Priestley performed his celebrated
experiment on calx of mercury, Scheele had obtained a gas which
he called Feuerluft or fire-air by the action of heat upon (a) a
mixture of saltpetre and oil of vitriol, (b) red calx of mercury,
(r) saltpetre alone, (d) pyrolusite [manganese dioxide], and other
substances. This, of course, is identical with dephlogisticated
air, but Scheele 's publishers were slow, and his results were not
made public until 1777, so t ^ at priority in the discovery is
usually assigned to Priestley. Scheele, however, definitely con-
cluded that ordinary air consists of 'two kinds of elastic fluid' or
gas, noticed that part of the air was lost in combustion, and
observed that the residual air was relatively lighter than the
original air. The part of the air which was lost during com-
bustion he was unable to find again. He remarks that it might be
suggested that 'the lost air still remains in the residual air which
can no more unite with phlogiston ; for, since I have found that
it is lighter than ordinary air, it might be believed that the
phlogiston united with this air makes it lighter, as appears to be
known already from other experiments. But since phlogiston is
a substance, which always presupposes some weight, I much
doubt whether such hypothesis has any foundation'. How near
Scheele was to a supreme discovery !
During the course of an investigation of pyrolusite, a black
mineral found in Spain, Asia Minor and certain other localities,
Scheele heated the substance with spirit of salt or marine acid
[hydrochloric acid] and observed the formation of a greenish-
yellow gas [chlorine]. He explained the reaction by assuming
that the pyrolusite had dephlogisticated the marine acid, i.e.
removed phlogiston from it, and therefore called the new gas
dephlogisticated marine acid. He noticed that the gas attacked
organic matter, that it would bleach litmus and coloured flowers,
Guillaume Francois Rouelle 189
that its solution on standing became converted into a solution of
marine acid, that it attacked metals, that it formed a white cloud
with ammonia, that it was poisonous, and that it would not
support ordinary combustion. The proof of the elementary
nature of Scheele's 'dephlogisticated marine acid', and its later
name chlorine, are both due to Sir Humphry Davy (p. 260).
Scheele's devotion to chemistry cost him his life, for it was
doubtless exposure to cold in the unheated shop and the inhalation
of fumes from his experiments, not to mention the enormous
demands he made upon his physical strength in managing
a business as well as performing ceaseless research, that caused
the breakdown in his health and brought him to an early grave.
He refused honours that were offered him, preferring, like van
Ilelmont, to remain in peaceful obscurity. 'Avec cle petites
ressources, il fit de grandes choses', says a chronicler, and it
would be difficult to find more appropriate words.
45. Guillaume Franfois Rouelle
THE eccentric personality of Cavendish finds its counterpart
across the Channel in Guillaume Franois Rouelle, one of the
greatest teachers of chemistry that France, or indeed the world,
has ever produced. Rouelle was born in 1703, at the village of
Mathieu, in Normandy, and after preliminary education at the
College of Caen he went to Paris. Here he studied chemistry
and pharmacy with such success that, about the middle of the
century (1742), he was appointed Demonstrator of chemistry at
the Jardin du Rot. The courses in chemistry at the Jardin were
open to the public, and were conducted concurrently by a pro-
fessor of theory and a demonstrator of practice. The arrange-
ment is humorously described by Hoefer, the historian of
chemistry, whose books are written in a delightful style that
hides the wide scholarship beneath :
The interminable contention [says Hoefer] between theory and
practice was later personified by the Professor and the Demon-
strator, charged, under Louis XIV and Louis XV, with the teach-
ing of chemistry at the Jardin du Roi. The Professor, soaring in
190 Guillaume Frai^ois Rouelle
the realms of abstract principle, regarded it beneath his dignity to
descend to the details of the laboratory and to soil his fingers with
charcoal dust. He, indeed, was Theory: a role which was filled by
the First Physician of the King. After the Professor had finished
lecturing the Demonstrator arrived. His duty was to support the
speculative views of the Professor by experimental facts : he was ,
in fact, Practice.
It was Rouelle (1703-70) who, under Louis XV, fulfilled the
functions of Demonstrator at the Jar din du Roi\ Bourdelain
occupied the chair of chemistry there. The Professor, who was
received coldly, invariably finished his lecture with the words
1 Such, gentlemen, are the principles and the theory of this opera-
tion, as the Demonstrator is about to prove to you by his experi-
ments/ Rouelle made his appearance immediately afterwards
amidst the plaudits of the audience, but, nearly always, M. le
Demonstrates upset, by his experiments, the theories of M. le
Professeur.
Rouelle was a very original man; he had in him something of
Paracelsus and Bernard Palissy. He used to come into the lecture-
room elegantly attired : velvet coat, powdered wig, and a little hat
under his arm. Collected enough at the beginning of his lecture,
he gradually became more animated. If his train of thought became
obscure, he lost patience; he would put his hat on a retort, take off
his wig and untie his cravat. Then, talking all the while, he would
unbutton his coat and waistcoat and take them off one after the other.
Rouelle was helped in his experiments by one of his nephews,
but as tfeis help was not always to be found close at hand he used
to call with an ear-splitting shout, 'Nephew! O that eternal
nephew!' and the eternal nephew not appearing he would himself
depart into the back regions of his laboratory to find the object he
needed. Meanwhile he used to continue his lecture as though he
were still in the presence of his audience. When he returned he
had generally finished the demonstration which he had begun, and
would come in again saying, ' There, gentlemen, that is what I had
to tell you'. Then he was begged to begin again, which he always
did with the best grace in the world, in the conviction that he had
merely been badly understood.
In his habitual absent-mindedness, Rouelle would often de-
scribe processes that he wished to keep secret. In the warmth
Guillaume Francois Rouelle 191
of his discourse he would say, "This is one of my secrets which
I will never tell any one', having just revealed it to everybody!
Grimm relates that one day, when Rouelle was in a mixed
company and talking with his usual vivacity, he untied his
garter, pulled down his stocking, scratched his leg with both
Fig. 62. GUILLAUME FRANCOIS ROUELLE
hands, replaced his stocking and garter, and continued his con-
versation quite unconscious of what he had been doing. His
favourite term for his opponents, or for any one of whom he dis-
approved, was plagiarist. At the Jar din du Roi on one occasion
the conversation turned on a recent defeat of the French army ;
Rouelle called the French commander, the Prince de Soubise,
a fool, a criminal and a plagiarist. 'But', said Buffon, 'it isn't
a plagiarism to get beaten by the Prussians ; on the contrary it is
an entirely new invention of M. de Soubise!' 'Don't defend
him', said Rouelle, 'he 's a low animal, a horned mule, a one-
192 Guillaume Francois Rouelle
eyed pig! I am sure there is something vicious in his con-
formation.'
In spite of these peculiarities, Rouelle was much esteemed as
a man and honoured as a great chemist. In 1750 he was made
a member of the Royal Academy of Stockholm and also of that
Fig. 63. MS. OF ROUELLE'S LECTURES
of Emfurt. Two years later he was elected an associate of the
Academy of Sciences at Paris. Unfortunately, his health began
to give way, and in 1768 he resigned his post at thejardin. For
some months he lingered on at his house at Passy, but death
claimed him on 3 August 1770.
Although, like Black, Rouelle published few researches, these
are of great importance. Yet Rouelle's chief service to chemistry
lay in his public lectures, which were followed with eagerness
and enthusiasm by a vast number of students, among them the
great Lavoisier. The lectures were carefully taken down by the
pupils, and some of their copies are still in existence: the
Bibliotheque nationals has several examples and there is a very
good one in the Science Library at Clifton College. The last is
of special interest since it was transcribed from a copy belonging
to d'Arcet, Rouelle's son-in-law, and is therefore probably very
accurate. Its original owner, however, bitterly complains that
/
en
,
O^Vt / /Y ?
f '*
'faln<j
f-7 *
n
-<
Fig. 64. MS. OF ROUELLE'S LECTURES
2613.4
194 Guillaume Franois Rouelle
though he paid his scribe 'cinq Louis d'or', numerous mistakes
were made, 'que j'ai toutes corrigees de ma main de sorte que ce
manuscrit peut passer pour tres exact et tres sur et fait un
ouvrage tres precieux'. From the manuscript, we can gather
that Rouelle J s course was divided into four sections. The first
section was introductory, and gave an account of the nature,
history, uses and principles of chemistry, from the point of view
of a follower, but a critical follower, of Stahl. The second
section consisted of lectures on plant life, essential oils, fixed
alkalis, fermentation, &c., illustrated by some fifty-six experi-
ments describing in detail the decomposition of vegetable sub-
stances by careful distillation, extraction with solvents, and so on.
A brief treatment of animal substances, with ten experiments,
followed in section three. It is clear from the manuscript that
animal chemistry offered great difficulties, and the writer says,
'The connexion between the various phenomena presented by
the animal kingdom has not been discovered or developed by
any one, and is still the object of M. Rouelle 's researches'.
The main portion of the course dealt with the mineral kingdom.
Here Rouelle gave a full account of the chemistry of the acids,
salts, metals and semi-metals then known, performing no fewer
than 159 experiments in demonstration of the facts he described.
Long dissertations on geology, alchemy and mineralogy were
interspersed at appropriate intervals, and the course as a whole
affords striking evidence of the versatility and originality of *le
chef d'une ecole dont le souvenir honora son siecle et sa patrie'.
Rouelle was the first to define clearly the nature of a salt and
to give a systematic classification of this important class of com-
pounds. Previous chemists had been unable to settle upon any
definite conception of a salt, but Rouelle, with characteristic
insight, saw directly to the heart of the problem. 'Most
chemists', he says, 'give the name neutral, middle or "salty" salt
to only a small number of salts ; there are even some who have
given it to vitriolated tartar [normal potassium sulphate] alone,
requiring as the characteristic of these salts that the acid and
alkali which form them should be so firmly united as to resist all
Guillaume Francis Rouelle 195
attempts at decomposition. Others have admitted, in addition
to vitriolated tartar, the two neutral salts formed by the union of
the acids of sea-salt [NaCl] and nitre with alkaline fixed bases
[Na 2 CO 3 , K 2 CO 3 ]; such are sea salt and nitre. Others add
three more salts formed by the union of the three acids with
Fig. 65. LE JARDIN DES PLANTES, PARIS
a volatile alkali [ammonium carbonate], viz. Glauber's secret
ammoniacal salt or vitriolic ammoniacal salt [(NH 4 ) 2 SO 4 ],
ordinary sal ammoniac [NH 4 C1], and nitrous ammoniacal salt
[NH 4 NO 3 ]. Other chemists have added several more saline
substances to the number of these neutral salts. I give to the
family of neutral salts all the extension of which it is capable ;
I call a neutral, middle, or salty salt, every salt formed by the
combination of whatever acid, whether mineral or vegetable,
with a fixed alkali, a volatile alkali, an absorbent earth [e.g. MgO,
CaO], a metallic substance, or an oil.'
Rouelle 's 'neutral' salts were, then, our present 'salts' without
qualification. He did not leave the matter there, however, but
went on to divide neutral salts into (a) perfect salts, correspond-
ing to our 'normal' salts, (b) acid salts and (c) salts with the
minimum possible acid in them. Perfect salts he defines as
o 2
196 Guillaume Franois Rouelle
those whose point of saturation is exact, and which have the
exact quantity of acid in them. They do not alter the colour of
syrup of violets (a contemporary indicator like litmus). Acid
salts are those which, in addition to the exact quantity of acid
necessary to give them perfect neutrality, contain a further
amount. 'And this excess of acid', he says, 'must not be merely
mixed with the neutral salt ; it must be joined to and combined
with the other parts, and there must be an exact quantity of it :
this excess acid itself has its point of saturation/
It will be observed that Rouelle had arrived at a scientifically
sound conclusion as to the formation and classification of salts,
and that he made our modern distinction between normal (or
'perfect') and acid salts. He did not quite succeed in defining
our 'basic' salts, for his third class included such substances as
silver chloride and calomel, which we now regard as normal
salts. Rouelle classified them separately on account of their
sparing solubility; but it was a great advance to recognize that
they were salts a fact that no one had previously admitted.
Rouelle was also one of the first to use the word 'base' in
a sense essentially similar to that which it now bears. Thus he
says that a salt is to be defined as a substance formed by the
union of an acid with any substance which serves it as a base and
gives it a concrete or solid form.
That his views on the formation and classification of salts
were established on a firm experimental basis may be gathered
from the descriptions he gives of properties and preparations.
He notes, for instance, that acid salts are usually more soluble
than the corresponding normal salts, and that many of them are
deliquescent ; that they turn tincture of violets red ; and that
they cause effervescence with fixed alkalis [K 2 CO 3 and Na 2 CO 3 ]
and volatile alkali [(NH 4 ) 2 CO 3 ]. Acid potassium sulphate he
prepared by heating potassium sulphate with sulphuric acid and
then driving off the excess of acid at a higher temperature.
Rouelle 's work on salts was not immediately accepted, but
was revived later by Lavoisier and his school and thus lies at the
root of our own system.
[197]
46. Summary
CHEMISTRY under phlogiston was almost entirely qualitative,
Black's quantitative research upon magnesia alba standing
nearly alone. The period was one of intense activity, resulting
in the discovery of scores of new compounds, in the improve-
ment of laboratory technique, and in the gradual evolution of
more systematic schemes of classification. The greatest pro-
gress was, as we have seen, in the chemistry of gases, where
Priestley, Cavendish and Scheele were daily enlarging the
hounds of knowledge at a bewildering speed. The phlogiston
theory throve unchecked, explaining much but leaving many
things unexplained. No voice was raised against it and it
numbered among its adherents all the greatest chemists of the
time. For over half a century it had been 'the lamp and guide of
chemists', and no one could have foreseen the stirring events
that were about to happen.
47. Antoine Laurent Lavoisier
THE stage is now set for the most dramatic episode in the whole
story of chemistry: a single-handed, impetuous and determined
attack on the citadel of phlogiston, ending in its complete over-
throw and final destruction. Confident in their fancied security,
the phlogistians at first derided the onslaught, and when at
length they awoke to the gravity of the position it was already too
late. Some of them went over to the enemy, but many contested
the ground inch by inch and fought to the last ditch, but in vain.
Then, with a gesture of Greek tragedy, Fate ordained the
political murder of the victor in the very hour of his triumph.
History offers us few more moving spectacles than that of
8 May 1794, when the greatest chemist of all time calmly
awaited death on the guillotine at the hands of the unwashed
rabble of revolutionary France.
Antoine Laurent Lavoisier was born of a good family at Paris,
on 26 August 1743. He and his sister Marie Marguerite Emilie
were brought up by their maternal grandmother, Madame
Punctis, for their mother died when the boy was only five years
198 Antoine Laurent Lavoisier
old. The Punctis were a wealthy family, and as Lavoisier very
quickly gave evidence of an unusually high intelligence, they
lavished money on his education. At the age of 21 he was a
fully-qualified lawyer, attached to the Parlement, and his relatives
doubtless foresaw a brilliant legal career for him. Their hopes
Fig. 66. ANTOINE LAURENT LAVOISIER
were realized, though not in the sense they expected: Lavoisier
indeed became a great legislator, but the laws he formulated
were the laws of chemistry.
In his hours of leisure, Lavoisier was attracted to the Jardin
du Roi, where Rouelle J s lectures had inspired Parisian society
with a passion for chemistry. Every man and woman of fashion
made a point of attending the laboratory at the Jardin when
Rouelle was to lecture, and Lavoisier was among their number.
Another regular auditor was the encyclopaedist Diderot, who
attended for three years; he was industrious enough to take
down the lecturer's words and to work them up into a correct
'edition'. A manuscript copy of Diderot's notes enabled
Lavoisier to give his full attention to Rouelle and the experi-
ments, undistracted by the necessity of transferring his impres-
Antoine Laurent Lavoisier 199
sions to paper. So was awakened in the young lawyer a deter-
mination to leave the dust of the law for the study of the
problems of chemistry: a conversion that was not the least of
Rouelle's achievements.
Lavoisier's first chemical paper was published when its
Fig. 67. M. AND MME LAVOISIER IN THEIR LABORATORY
author was 22. Other researches followed in rapid succession,
and after a few years he was elected to membership of the
Academic des Sciences. At about the same time, he became one
ofihefermiers-gene'rauxywho were responsible for the collection
of taxes and who, owing to the rapacity and extortion of many
of their number, were the object of deep-rooted popular hatred.
There were, of course, honest and conscientious members of the
ferme, among them Lavoisier, who strove to lessen the cost of
collecting the taxes and to diminish the severity of the imposts.
It speaks much for his character that when at length he fell into
the hands of the revolutionists the only charge they could prefer
against him was that 'of adding to tobacco water and other in-
gredients detrimental to the health of the citizens'.
Before the troublous days of the Revolution, Lavoisier had
2OO Antoine Laurent Lavoisier
turned his scientific genius and administrative skill to the benefit
of his country in several ways. As a member of a Committee of
Agriculture he worked hard to improve the lot of the French
agricultural labourer and attempted to introduce scientific
method into agricultural practice. He was also appointed, by
Turgot, one of four Commissioners to be directly responsible to
the State for the manufacture and supply of gunpowder.
On 1 6 December 1771, Lavoisier married Marie- Anne-
Pierrette Paulze, a woman who added high intellectual powers
to a great personal charm. She was able to assist her husband in
the laboratory, translated the memoirs of Priestley and Caven-
dish into French, and engraved several plates for a Treatise on
Chemistry that Lavoisier published in I789. 1
After Lavoisier had been nominated Commissioner of Powder
in 1775, he and his wife went to live at the Arsenal, where the
great discoveries about to be described were made. The labora-
tory in the Arsenal soon became a rendezvous for French, and
even foreign, scientists; one might meet there the chemists
Berthollet, Darcet, Macquer and Guyton de Morveau; the
mathematicians Laplace and Lagrange; Blagden, permanent
secretary of the Royal Society ; Benjamin Franklin ; James Watt,
and the Rev. Joseph Priestley. They were attracted not only by
the delightful dinners given by M. and Mme Lavoisier, but more
especially by the 'new and bold' views on the nature of com-
bustion which their host was now beginning to promulgate.
About 1770, Lavoisier began an investigation into the
problems of combustion, and soon discovered that on burning
sulphur and phosphorus an increase in weight occurs, ac-
companied by the absorption of much air. Thus when a piece of
phosphorus was placed under a bell-jar inverted in a trough of
mercury, and ignited by means of a burning-glass, the following
observations were made : (i) a limited volume of air will not burn
an unlimited weight of phosphorus; (2) when an excess of
phosphorus is used the flame is extinguished after a time, before
1 After Lavoisier's death, his widow married the American physicist
Count Rumford.
Antoine Laurent Lavoisier 201
the complete combustion of the phosphorus ; (3) to relight the
residual phosphorus, or to burn a fresh piece, the addition oi
more air is necessary; (4) a white powder, solid phosphoric acid
is formed during the combustion ; (5) after the completion of the
reaction the residual air occupies about four-fifths of the origina!
volume; (6) the weight of 'phosphoric acid' produced is about
two and a half times that of the phosphorus taken ; and (7) the
residual air is slightly lighter than ordinary air, and will nc
longer support combustion or life.
Lavoisier followed up this line of experiment by further re-
searches on the calcination of tin and lead. It will be remembered
that the increase in weight that occurs when tin and lead are
burnt had already been observed many times, and was now
common knowledge. The only explanation that Lavoisier re-
garded as at all satisfactory was that advanced by Boyle, who
supposed that heat which he considered a material substance
had passed through the vessel from the fire to the metal, thus
causing the increase in weight. Reflection showed, however,
that this hypothesis was easily susceptible of experimental proof
or disproof, as Lavoisier most lucidly explains :
'If, he says, 'the increase in weight of metals calcined in
closed vessels is due, as Boyle thought, to the addition of the
matter of flame and fire which penetrates the pores of the glass
and combines with the metal, it follows that if, after having
introduced a known quantity of metal into a glass vessel, and
having sealed it hermetically, one determines its weight exactly;
and that if one then proceeds to the calcination in a charcoal fire,
as Boyle did ; and lastly that if one then re weighs the same vessel
after the calcination, before opening it, its weight ought to be
found to have increased by the whole of the quantity of the
matter of fire which entered during the calcination.
'If, on the contrary . . . the increase in weight of the metallic
calx is not due to the combination of the matter of fire nor to any
exterior matter whatever, but to the fixation of a portion of the
air contained in the space of the vessel, the vessel ought not to
weigh more after the calcination than before, it ought merely to
2O2 Antoine Laurent Lavoisier
be found partly empty of air, and the increase in weight of the
vessel should take place only at the moment when the missing
portion of air is allowed to enter/
Lavoisier then proceeded to put his views to the test of
experiment. He took a weighed glass flask, introduced a
weighed quantity of tin, sealed the flask hermetically and then
heated it for an hour or two until no further calcination appeared
to be taking place inside. He now allowed the flask to cool, after
which he weighed it. There was no change in weight. Upon
opening the flask, air was heard to rush in, and when the
apparatus was weighed once more, an increase in weight was
found. The actual figures obtained in the experiment are as
follows :
Onces Gros Grains
Weight of flask . . . . . 12 6 5175
Weight of flask plus tin . . . .20 6
/. Weight of tin . . . . . 8 o
5175
o-oo
After calcination but before opening:
Weight of whole apparatus, unchanged.
After calcination and opening:
Onces Gros Grains
Weight of whole apparatus . . . 20 6 61-81
/. Increase in weight on calcination o o 10*06
Lavoisier next removed the tin calx and residual tin from the
flask and weighed them separately :
Gros Grains
Tin calx ......
Tin
Onces
2
5
8
8
7
i
o
o
275
7*25
lO'OO
o-oo
Total weight after calcination
But total weight before calcination
/. Increase in weight on calcination .
These results showed clearly that the increase in weight was
due, not to the absorption of a hypothetical * matter of fire' as
10-00
Antoine Laurent Lavoisier 203
Boyle had supposed, but to an absorption of air, the increase in
weight of the metal being almost exactly equal to the weight of
air that rushed in when the flask was opened.
Further experiments on the same lines led him to conclude :
First, that one cannot calcine an unlimited quantity of tin in
a given quantity of air ;
Second, that the quantity of metal calcined is greater in a large
vessel than in a small one, although it cannot yet be affirmed that
the quantity of metal calcined is exactly proportional to the
capacity of the vessels.
Third, that the hermetically sealed vessels, weighed before and
after the calcination of the portion of tin they contain, show no
difference in weight, which clearly proves that the increase in
weight of the metal comes neither from the material of the fire nor
from any matter exterior to the vessel.
Fourth, that in every calcination of tin, the increase in weight of
the metal is, fairly exactly, equal to the weight of the quantity of
air absorbed, which proves that the portion of the air which com-
bines with the metal during the calcination, has a specific gravity
nearly equal to that of atmospheric air.
I may add that, from certain considerations drawn from actual
experiments made upon the calcination of metals in closed vessels,
considerations which it would be difficult for me to explain to the
reader without going into too great detail, I am led to believe that
the portion of the air which combines with the metals is slightly
heavier than atmospheric air, and that that which remains after the
calcination is, on the contrary, rather lighter. Atmospheric air, on
this assumption, would form, relatively to the specific gravity,
a mean result between these two airs.
His experimental figures enabled him to deduce that the air
must consist of at least two gases, only one of which is concerned
in calcination. By a measurement of the capacity of the flask, he
was able to calculate the weight of air it originally contained.
This was considerably greater than the weight of air that
entered when the flask was opened, the deduction therefore
being that only a part of the air had been used. Now, since
there was an excess of tin, the cessation of calcination before the
204 Antoine Laurent Lavoisier
whole of the air had been consumed could be explained only on
the assumption that the air consists of a mixture of gases, of
which one can effect calcination while the other or others cannot.
At this point occurred the pregnant meeting with Priestley,
who described his amazing experiment with mercury calx.
Lavoisier immediately appreciated the importance of Priestley's
discovery, and at once became convinced that 'dephlogisticated
air' was in reality the active constituent of the atmosphere
that constituent absorbed by metals on calcination. During the
winter of 1774-5 ne repeated and extended Priestley's experi-
ments, and described his results to the Academic des Sciences
early in the latter year.
He first showed that by heating red calx of mercury with
carbon one obtained mercury and 'fixed air', and secondly, that
by heating the red calx alone Priestley's 'dephlogisticated air'
was evolved. From one ounce of the calx he obtained 78 cubic
inches of the latter gas, and showed that it did not turn lime-
water milky (as fixed air does), that it would not combine with
alkalis, that it was able to bring about the calcination of metals,
and that it supported life and combustion very well 'tous les
corps combustibles en general s'y consommaient avec une eton-
nante rapidite'. It is evident that his observations were practically
those of Priestley, but his conclusions were very different:
It thus appears to be proved that the principle which combines
with metals during their calcination, and which increases their
weight, is nothing else than the purest portion of the very air which
surrounds us, which we breathe, and which passes, during this
operation [i.e. calcination], fromt he gaseous state to the solid state;
if, therefore, one obtains it in the form of fixed air in all metallic
reductions where carbon is used, this effect is due to the combina-
tion of the carbon with the pure portion of the air. It is, indeed,
very probable that all metallic calces would, like that of mercury,
give nothing but l eminently respirable air' if one could reduce
them all without the addition of any other substance, as one
reduces red precipitate of mercury per se.
His crucial experiment, however that which has come to be
Antoine Laurent Lavoisier
205
known as 'Lavoisier's Experiment 'par excellence we may allow
him to relate in his own words :
I took a matrass [A, Fig. 68] of about 36 cubical inches capacity,
having a long neck BCDE, of six or seven lines internal diameter,
and having bent the neck as in [Fig. 68], to allow of its being
placed in the furnace MM/V7V, in such a manner that the extremity
Fig. 68. LAVOISIER'S APPARATUS
of its neck E might be inserted under a bell-glass /*'G, placed in
a trough of quicksilver RRSS\ I introduced four ounces of pure
mercury into the matrass, and, by means of a syphon, exhausted
the air in the receiver FG, so as to raise the quicksilver to /,/,, and
I carefully marked the height at which it stood, by pasting on a slip
of paper. Having accurately noted the height of the thermometer
and barometer, I lighted a fire in the furnace MMNN, which
I kept up almost continually during twelve days, so as to keep the
quicksilver always very near its boiling-point. Nothing remarkable
took place during the first day: the mercury, though not boiling,
was continually evaporating, and covered the interior surface of the
vessel with small drops, at first very minute, which gradually
augmenting to a sufficient size, fell back into the mass at the bottom
of the vessel. On the second day, small red particles began to
appear on the surface of the mercury; these, during the four or five
following days, gradually increased in size and number, after which
they ceased to increase in either respect. At the end of twelve days,
seeing that the calcination of the mercury did not at all increase,
I extinguished the fire, and allowed the vessels to cool. The bulk
206 Antoine Laurent Lavoisier
of air in the body and neck of the matrass, and in the bell-glass,
reduced to a medium of 28 inches of the barometer and 54-5 of the
thermometer, at the commencement of the experiment was about
50 cubical inches. At the end of the experiment the remaining air,
reduced to the same medium pressure and temperature, was only
between 42 and 43 cubical inches; consequently it had lost about
J of its bulk. Afterwards, having collected all the red particles,
formed during the experiment, from the running mercury in which
they floated, I found these to amount to 45 grains.
I was obliged to repeat this experiment several times, as it is
difficult in one experiment both to preserve the whole air upon
which we operate, and to collect the whole of the red particles, or
calx of mercury, which is formed during the calcination. It will
often happen in the sequel, that 1 shall, in this manner, give in one
detail the results of two or three experiments of the same nature.
The air which remained after the calcination of the mercury in
this experiment, and which was reduced to of its former bulk,
was no longer fit either for respiration or for combustion; animals
being introduced into it were suffocated in a few seconds, and when
a taper was plunged into it, it was extinguished as if it had been
immersed in water.
In the next place I took 45 grains of red matter formed during
this experiment, which I put into a small glass retort, having
a proper apparatus for receiving such liquid, or gaseous product,
as might be extracted. Having applied a fire to the retort in the
furnace, I observed that, in proportion as the red matter became
heated, the intensity of its colour augmented. When the retort was
almost red hot, the red matter began gradually to decrease in bulk,
and in a few minutes after it disappeared altogether; at the same
time 41 J grains of running mercury were collected in the recipient,
and 7 or 8 cubical inches of elastic fluid, greatly more capable of
supporting both respiration and combustion than atmospherical
air, were collected in the bell-glass.
A part of this air being put into a glass tube of about an inch
diameter, showed the following properties: A taper burned in it
with a dazzling splendour, and charcoal, instead of consuming
quietly as it does in common air, burnt with a flame, attended with
a decrepitating noise, like phosphorus, and threw out such a
brilliant light that the eyes could hardly endure it. This species
Antoine Laurent Lavoisier 207
of air was discovered almost at the same time by Dr. Priestley,
Mr. Sheele, and myself. Dr. Priestley gave it the name of de-
phlogisticated air, Mr. Sheele called it empyreal air ; at first I named
it highly respirable air y to which has since been substituted the term
of vital air. We shall presently see what we ought to think of these
denominations.
In reflecting upon the circumstances of this experiment, we
readily perceive, that the mercury, during its calcination, absorbs
the salubrious and respirable part of the air, or, to speak more
strictly, the base of this respirable part ; that the remaining air is
a species of mephitis, incapable of supporting combustion or
respiration ; and consequently that atmospheric air is composed of
two elastic fluids of different and opposite qualities. As a proof of
this important truth, if we recombine these two elastic fluids,
which we have separately obtained in the above experiment, viz.
the 42 cubical inches of mephitis, with the 8 cubical inches of
respirable air, we reproduce an air precisely similar to that of the
atmosphere, and possessing nearly the same power of supporting
combustion and respiration, and of contributing to the calcination
of metals.
Lavoisier had thus by now begun to elaborate an entirely new
theory of combustion, and had shown (i) that air consists of at
least two gases, one of which, 'air eminemment respirable'
(Priestley's dephlogisticated air), combined with metals on cal-
cination and thus caused the increase in weight, (2) that the
same air was the active agent in combustion, (3) that 'fixed air'
(carbon dioxide) was a compound of charcoal with this air, and
(4) that metallic calces were not elements, as had previously been
thought, but compounds of the metals with 'eminently respir-
able air'. His position was therefore incompatible with the
phlogiston theory, and in 1783 he attacked the theory in his
Reflexions sur Phlogistique. In the intervening years he had
continued his researches and had discovered that the combin-
ation of moist 'eminently respirable air' with sulphur yielded
sulphuric acid, with phosphorus phosphoric acid, with nitrogen
nitric acid, and with carbon carbonic acid. Hence, he says,
'I shall for the future call dephlogisticated air or eminently
208 Antoine Laurent Lavoisier
respirable air by the name of the acidifying principle, or, if the
same meaning is preferred in a Greek word, by that of the
oxygine principle', thus bestowing upon the gas its modern
name, oxygen.
'In designing the word Oxygen ', says Professor H. E. Arm-
strong, ' Lavoisier rose to the greatest height of his unparalleled
genius. Not only is the word a monument to his astounding
insight into chemical phenomena, to his philosophic power; it is
also proof of a deep philological feeling and acumen, as well as of
his sense of the beauty of words. Think of the astounding step
he took, after his instant appreciation of Priestley's discovery, in
translating the old nonconformist's ponderous reminder of the
doubtful past of our science conveyed in the name Dephlogisti-
cated Air into an all-significant word of the aural and lingual
perfection of Oxygen . . . think of him as the pioneer who not
only sought to put system into the souls of chemists but also
tipped their tongues with harmony.'
Meanwhile the phlogistians were beginning to pass from
amusement to alarm. Lavoisier's audacity in casting a doubt
upon the theory of phlogiston had at first provoked sarcasm
and heavy humour. The Grand Master of French phlogistian
chemistry, Macquer (professor at t\\ejardin du Roi), refers with
scorn to 'a certain person who wishes to meddle in higher
chemistry without understanding anything of the science', and
in 1778 writes as follows to Guy ton de Morveau:
M. Lavoisier has been terrifying me for some time by a great dis-
covery, which ke kept in petto and which was going to do no less
than to overthrow the theory of phlogiston ; his confident air nearly
made me die of fright. Where should we have been, with our old
chemistry, if we had had to build an entirely different edifice ? For
my own part, I don't mind admitting I should have given up the
game. However, M. Lavoisier has just published this discovery
of his, and I can tell you that since that time I have had a great
weight removed from my chest.
Scheele was equally sceptical. * Would it be so difficult', he
wrote to the chemist Bergman in 1784, 'to convince Lavoisier
Antoine Laurent Lavoisier 209
that his system of acids [i. e. that they are compounds of oxygen]
is not to everybody's taste ? Nitric acid composed of pure air
and nitrous air [NO 2 ], aerial acid [CO 2 ] of carbon and pure air,
sulphuric acid of sulphur and pure air! ... Is it credible ? . . .
Observation.
1. Calcination.
2. Constitution of calx.
3. Increase in weight on
calcination.
4. Mercury calx yields
'pure air' when
heated.
5. Calx heated with
charcoal yields
metal and fixed air.
6. Phlogiston cannot be
isolated.
Water can be made
by exploding a
mixture of 'dephlo-
gisticated' and 'in-
flammable' airs.
A flame in a limited
volume of air is
soon extinguished.
Why does not air
saturated with
phlogiston become
inflammable ? In
point of fact it is
not inflammable.
| Phlogistian Explanation. \ Lavoisier's Explanation.
Gain of oxygen.
Metal -f oxygen.
Due to weight of oxygen
taken up.
Oxygen is liberated from
the metallic oxide.
Loss of phlogiston.
Metal phlogiston.
Pnlogiston has nega-
tive weight.
(See p. 176.)
Charcoal yields phlo-
giston to calx.
Heat, light, and mag-
netism and electri-
city cannot be iso-
lated.
Dephlogisticated air
is water deprived of
phlogiston.
The air becomes satu-
rated with phlogis-
ton.
No explanation offer-
ed.
Charcoal combines with
oxygen in calx, forming
'carbonic acid gas' and
leaving the metal.
It does not exist.
Water is a compound of
oxygen and inflam-
mable air [hydrogen].
The oxygen in the air is
all consumed. See
no. 9.
'Air saturated with phlo-
giston' is merely air
that has lost its
oxygen but is other-
wise unchanged ; there
is therefore no reason
why it should become
inflammable.
I will rather place my faith in what the English say [i.e. Priestley,
Cavendish, and others].'
Cavendish, on the contrary, was cautious, and admits that his
own experiments, as well as 'most other phaenomena of nature,
seem explicable as well, or nearly as well, upon Lavoisier's
2613-4 P
2i o Antoine Laurent Lavoisier
theory as upon the commonly believed principle of phlogiston'.
Priestley, however, was adamant in his refusal to see any
blemishes in the phlogiston theory or any good points in that of
Lavoisier, and the general situation began to change in favour of
Lavoisier only in 1785. Yet if we compare the explanations of
certain common phenomena given by the phlogiston theory and
the oxygen theory respectively, we shall not be surprised to find
that defection from the former, once started, soon became
general, except for one or two older men such as Priestley. For
the sake of clearness, the facts and their interpretations may be
tabulated (see previous page).
Heedless of his initial lack of success, Lavoisier renewed the
attack, armed with clear ideas and incontestable facts; his on-
slaught soon became irresistible.
It is time [he says] to recall chemistry to a more rigorous method
of reasoning; to strip the facts with which this science is enriched
every day from that which reasoning and prejudices add thereto;
to distinguish fact and observation from that which is systematic
and hypothetical; finally, to mark the limit, so to speak, to which
chemical knowledge has arrived, in order that those who follow us
may set out with confidence from this point to advance the science.
Chemists have made of phlogiston a vague principle which is
not rigorously defined, and which consequently adapts itself to all
explanations into which it may be brought. Sometimes this
principle is heavy, and sometimes it is not ; sometimes it is free fire,
sometimes it is fire combined with the earthy element ; sometimes
it passes through the pores of vessels, and sometimes they are
impenetrable for it. It explains at once causticity and non-
causticity, transparency and opacity, colours and the absence of
colours. It is a veritable Proteus which changes its form at every
instant.
He proceeds to demonstrate, with sure logic, how the oxgyen
theory satisfactorily explains the known facts of combustion, and
how the phlogiston theory fails. Phlogiston is 'an imaginary
entity', and the relevant facts can be explained much more
simply without it than with it. Yet Lavoisier realized the great
Antoine Laurent Lavoisier 211
hold that the phlogiston theory had on the minds of men, and
concludes his memoir by saying:
I do not expect that my ideas will he adopted all at once; the
human mind adjusts itself to a certain point of view, and those who
have looked at nature from one standpoint, during a portion of
their life, adopt new ideas only with difficulty; it is, then, for time
to confirm or to reject the opinions which I have brought forward.
Meanwhile, I see with a great satisfaction that young people who
begin to study the science without prejudice, that mathematicians
and physicists who come fresh to chemical truths, no longer believe
in phlogiston in the way in which Stahl presented it, and look upon
the whole of this doctrine as a scaffolding more embarrassing than
useful for the continuance of the structure of chemical science.
Lavoisier was, however, too pessimistic about the attitude of
contemporary chemists, for on 6 August 1785, Berthollet swore
allegiance to the new theory ; de la Metherie, Monge, Guyton de
Morveau and Fourcroy soon followed ; and in 1791 Kirwan, one
of the staunchest English protagonists of phlogiston, wrote : 'At
last I am laying down my arms and abandoning phlogiston.
I see clearly that there is no authentic experiment in which the
production of fixed air from pure inflammable air has been
demonstrated, and that being so, it is impossible to maintain the
system of phlogiston. ... I myself will give a refutation of my
own essay on phlogiston/
Priestley alone remained obdurate. One of the last acts of his
life (he died in 1804) was to issue a Defence of Phlogiston, in
which he reiterates his faith in the system of Stahl, and remarks
that it appears 'not a little extraordinary, that a theory so new,
and of such importance, overturning everything that was thought
to be best established in chemistry, should rest on so very
narrow and precarious a foundation; the experiments adduced
in support of it being not only ambiguous, or explicable on
either hypothesis, but exceedingly few. . . . Tho' the title of this
work expresses perfect confidence in the principles for which
I contend, I shall still be ready publicly to adopt those of my
opponents, if it appears to me that they are able to support them.
P2
212 Antoine Laurent Lavoisier
Nay, the more satisfied I am at present with the doctrine of
phlogiston, the more honourable shall I think it to give it up
upon conviction of its fallacy : following the noble example of
Mr. Kirwan, who has acquired more honour by this conduct
than he could have done by the most brilliant discoveries that he
could have made/
As Priestley's splendid but lonely figure disappears over the
horizon, the old theory vanishes for ever. It was a great and
brilliant theory and served chemistry well : the reader will there-
fore feel a peculiar pleasure in learning that the victors always
spoke of it with respect. One of them truly remarked that 'it
made chemistry a new science by the precision of its luminous
ideas', and that its simple and easy principles had long been
a compass to guide the path of each and every chemist.
The new theory was firmly established by 1792. Lavoisier
fully appreciated the value of his own work. Although he was
not altogether scrupulous in assigning due credit to others, he is
at pains to have it clearly understood that to him and to him
alone is due the honour of founding the oxygen theory.
This theory is not, as I have heard it called, the theory of the
French chemists in general, it is mine, and it is a possession to
which I lay claim before my contemporaries and before posterity.
Others, no doubt, have given it new degrees of perfection, but
I hope that one will not be able to deny to me the whole theory of
oxidation and combustion; the analysis and decomposition of air
by metals and combustible bodies ; the theory of the formation of
acids; more exact knowledge of a great number of acids, notably
vegetable acids; the first ideas on the composition of plant and
animal substances, and the theory of respiration.
This claim may be fully admitted, and it is pleasant to know
that Lavoisier was spared for a short time to enjoy his triumph.
But Fate had already marked him down, and on 8 May 1794 the
usher of the revolutionary tribunal handed in the following report :
I have been to the prison of the tribunal for the execution of the
judgement pronounced to-day against Lavoisier, condemning him
to death, after which I handed him over to the responsible official
The Revision of Nomenclature 213
and to the gendarmerie, who took him to the Place de la Revolution
[now Place de la Concorde'], where, upon a scaffold erected upon
the said Place, the aforesaid Lavoisier, in my presence, suffered the
pain of death.
La Republique ria pas besoin de savants, said the cynical
Fig. 69. C. L. BERTHOLLET
Coffinhal, president of the tribunal. But Lagrange, with
saddened insight, voiced the later feelings of the whole French
people when he said, // ne leur a fallu quun moment pour fairs
tomber cette tete, et cent annees peut-etre ne suffiront pas pour en
reproduire une semblable.
48. The Revision of Nomenclature
THE complete revolution in fundamental chemical principles
effected by Lavoisier made the old system or rather lack of
system of nomenclature obsolete. A new scheme, in con-
sonance with the oxygen theory, was urgently necessary if the
progress of chemistry was to be unhindered by relics of its
'doubtful past*. Lavoisier realized this fact very clearly, and, in
conjunction with three of his disciples, Guyton de Morveau,
214 The Revision of Nomenclature
Berthollet and Fourcroy, he undertook the elaboration of a
nomenclature based upon scientific principles. Guy ton de Mor-
veau had already before his conversion to the oxygen theory
attempted to reform the old nomenclature, and was thus in
a position to realize its main defects. He pointed out (a) that
a chemical name should not be a phrase, (b) that it ought not to
require circumlocutions to become definite, (r) that it ought to
recall the constituents of a compound body, (d) that it should
not be of the type 'Glauber's salt', which conveys nothing about
the composition of the substance, (e) that in the absence of
knowledge concerning the constitution of a substance, the name
should be non-committal, (/) that new names should preferably
be coined from Latin or Greek, so that their signification could
the more widely and easily be understood, and (g) that the form
of such words should be assimilated to the genius of the language
in which they are to be used. De Morveau's advice and ex-
perience must have proved extremely valuable to Lavoisier and
the other two members of the committee of nomenclature.
The results of prolonged conferences between this committee
and other scientists whose advice they sought were published in
1787 under the title Methode de Nomenclature Chimique. In a
prefatory memoir, Lavoisier observes that there are three things
to distinguish in every physical science : the series of facts that
constitute the science, the ideas that recall the facts, and the
words that express them. The word must evoke the idea, the
idea must depict the fact : they are but three impressions of the
same seal. The perfect chemical nomenclature would render
ideas and facts in their exact verity, without suppression and
more particularly without addition ; it ought to be nothing more
than a faithful mirror. It is obvious, he says, that the language of
chemistry as it then existed had not been formed on those
principles; indeed, it could not have been. Moreover, some
chemical expressions were introduced by the alchemists, and
bore one meaning for the adept but another for the vulgar ; thus,
'a pelican' represented an apparatus for distillation, while caput
mortuum signified the residue from a distillation. 'Oil', ' mercury ',
The Revision of Nomenclature 215
and even ' water' were not oil, mercury, and water in the sense in
which we employ the words; and so on.
Equally objectionable, he maintains, are such names as powder
ofAlgaroth, salAlembroth, turbith mineral, colcothar, and aethiops,
which make excessive demands upon the memory and give no
information about the substances for which they are employed.
More ridiculous still are 'oil of vitriol 5 , 'oil of tartar by delique-
scence', 'butter of arsenic', 'flowers of zinc', 'liver of sulphur',
'sugar of lead', &c., which actually give rise to wrong impres-
sions and (as Dumas remarked later) make one think that the
chemists have borrowed their language from the kitchen.
Guy ton de Morveau followed Lavoisier's memoir with another
in which he showed how the principles laid down could be
applied. The system suggested is essentially that which we now
employ, and it is therefore unnecessary for us to consider it in
detail. Our present purpose will be served by a consideration of
a typical example. Sulphur, says de Morveau, in combining
with oxygen produces an acid. It is evident that, to conserve the
idea of this origin and to express clearly the first degree of com-
position, the name of this acid ought to be a derivative of the
name of its basis ; but this acid exists in two states of saturation,
and shows different properties in each. In order not to confuse
them, each state must be given a name which, while conserving
the primitive root, nevertheless marks this difference. Lastly, it
is necessary to consider sulphur in other direct combinations,
e.g. with alkalis, earths and metals. Five different terminations,
adapted to the same root, in the manner which has appeared
most convenient by the judgement of the ear, distinguish the
five states of one principle :
Sulphuric acid will express sulphur saturated with oxygen as
far as it can be; i.e. what is called vitriolic acid.
Sulphurous acid will express sulphur united to a less quantity
of oxygen; i.e. what is called volatile sulphurous vitriolic
acid.
Sulphate will be the generic name of all salts formed from
sulphuric acid.
2i6 The Revision of Nomenclature
Sulphite will be the name of salts formed from sulphurous
acid.
Sulphide will denote all compounds of sulphur not carried to
the state of an acid, and will thus replace, in a uniform
manner, the improper and varying names of 'liver of
sulphur', 'hepar', 'pyrites', &c.
He adds with justice that 'no one will fail to perceive, at the first
glance, all the advantages of such a nomenclature, which, while
indicating various substances, at the same time defines them,
recalls their constituent parts, classes them in their order of
composition, and to a certain extent draws attention to the
proportions that cause the variation in their properties'.
The work of the committee was completed by a dictionary
giving the new and old names of about 700 substances, in which
we find for the first time many very familiar words sulphuretted
hydrogen, copper nitrate, ammonium molybdate, zinc sulphate,
and so on. The enormous improvement of the new system over
the old may be gathered from a single instance : that of the sub-
stance which Lavoisier and his collaborators proposed to call
carbonate of potash. Previously, this compound had rejoiced in
no fewer than eight aliases, viz. sal fixe de tartre, alkali fixe
vegetal, alkali fixe vegetal aere, tartre crayeux, tartre mephitique,
mephite de potasse, nitre fixe par lui-meme, alkaest de Vanhel-
mont! 'Potassium carbonate' may not be as picturesque as 'nitre
fixed by itself or 'van Helmont's alcahest', but few chemists
will be inclined to regret the passing of the old nomenclature.
As an appendix to the Methode de Nomenclature Chimique,
Hassenfratz and Adet wrote a memoir on a proposed system of
symbols for use in chemistry, to replace the old alchemical and
pharmaceutical ones. Non-metallic elements were to be repre-
sented by straight lines and semicircles, while the symbols for
metals were to be circles enclosing the initial letters of their
names. Symbols for compounds were to be formed by putting
together the symbols of their components . While this system had
its advantages, it was too complicated to win general approval
and was never widely adopted. We shall find shortly that the
Sir Isaac Newton 217
whole question of chemical symbolism was about to be placed
on an entirely new footing by the development of the Atomic
Theory. It is to this theory, with all its tremendous con-
sequences, that we must now turn.
49. Sir Isaac Newton
IT is a significant coincidence that the year 1804, which witnessed
the death of the last supporter of the Aristotelian Elements the
chemist Baume should also have seen the first effective use in
chemistry of the Greek theory of atoms . In the eighteen hundred
years that had elapsed since the days of Lucretius, the atomic
conception of matter underwent little development and re-
mained a subject for the speculation of philosophers rather than
a tool for the advancement of science. Towards the close of the
period, indeed, it seems to have been almost entirely neglected,
when attention was once more focused on it by the celebrated
dispute between Descartes (1596-1650) and Gassendi (1592-
1655). Gassendi stoutly supported the atomic theory of
Epicurus, while Descartes, though not an extreme anti-atomist,
argued against the classical form of the theory with an eloquent
lucidity. It is unnecessary to observe that discussions of this
kind, however great their subsequent influence on the general
philosophic scheme, have very little direct value to a particular
science. Nothing more was known about the structure of matter
when Gassendi and Descartes had concluded their controversy
than before it had begun ; and the historian of science is bound
to feel a sympathy with the caustic words of Omar Khayyam
himself a mathematician and astronomer
Myself when young did eagerly frequent
Doctor and saint, and heard great argument
About it and about: but evermore
Came out by the same door as in I went.
Yet we should guard against the easy assumption that pure
philosophy may be regarded as of little worth from the point of
view of pure science ; nothing could be farther from the truth.
Mr. Cyril Bailey has said with justice that 'it was the Greeks
2i 8 Sir Isaac Newton
who put the questions which modern science is still endeavour-
ing to answer', and one may extend this thesis : philosophy in
general puts the grand questions and suggests possible answers.
It is for the scientist to decide what questions are susceptible of
complete or partial solution by the methods at his disposal. The
Fig. 70. SIR ISAAC NEWTON
important conclusion that emerges from this digression is that
the theories of science are the products of the scientist, and that
we must neither belittle philosophy for failing to do what lies
outside its province, nor give the scientist less than justice in
regarding his theories as mere plagiarisms.
The immediate service that Descartes and Gassendi rendered
to chemistry was that they brought the atomic hypothesis into
such prominence that no chemist could remain in ignorance
of it. We find evidence of this fact in the writings of Boyle,
who refers to the 'corpuscular theory' in a way which implies
that it was perfectly familiar to his contemporaries; and it
gained further consideration from scientists when Sir Isaac
Newton (1642-1727) declared his allegiance. Newton's support
was of particular importance, for although his fame rests mainly
upon his physical and mathematical discoveries, he was a keen
student of chemical phenomena and theories. He had a
laboratory at Cambridge, in 'the space between the road and the
Sir Isaac Newton 219
college on the right-hand side on entering the Great Gate at
Trinity College', and we are told that for 'about 6 weeks at
spring and 6 at ye fall, ye fire in the elaboratory scarcely went
out, which was well furnished with chymical materials as bodyes,
receivers, heads, crucibles, &c., which was made very little use
Fig. 71. BLAKE'S NEWTON
of, ye crucibles excepted, in which he fused his metals ; he would
sometimes, tho' very seldom, look into an old mouldy book
which lay in his elaboratory. I think it was titled Agricola de
Metallis y the transmuting of metals being his chief design*.
His library contained a large number of books on chemistry, and
he corresponded on chemical subjects with Boyle and Locke and
with the former's assistant, Hooke.
In his Opticks, Newton says: 'It seems probable to me that
God in the beginning formed matter in solid, massy, hard, im-
penetrable, moveable particles, of such sizes and figures, as most
conduced to the end for which He formed them ; and that these
22O Sir Isaac Newton
primitive particles , being solids , are incompara bly harder than any
porous bodies compounded of them ; even so very hard as never
to wear or break in pieces, no ordinary power being able to
divide what God Himself made one in the first creation. . . . God
is able to create particles of matter of several sizes and figures,
and in several proportions to the space they occupy, and perhaps
of different densities and forces. . . . Now, by the help of these
principles, all material things seem to have been composed of the
hard and solid particles above mentioned variously associated
in the first creation, by the counsel of an intelligent agent/
This passage is very reminiscent of Lucretius, but Newton
was a scientist and applied his hypothesis to experimental fact.
Boyle had recently discovered his 'Law', and Newton offered
a theoretical explanation of the phenomenon in 'the first
quantitative conclusion ever formed about atoms'. He proved in
the Principia that 'if the density of a fluid gas which is made up
of mutually repulsive particles is proportional to the pressure,
the forces between the particles are reciprocally proportional to
the distances between their centres. And vice versa, mutually
repulsive particles, the forces between which are reciprocally
proportional to the distances between their centres, will make
up an elastic fluid, the density of which is proportional to the
pressure/ Newton goes on: 'Whether elastic fluids do really
consist of particles so repelling one another, is a physical
question. We have here demonstrated mathematically the pro-
perties of fluids consisting of this kind, that hence philosophers
may take occasion to discuss that question/
What strikes us immediately is the great difference in attitude
towards the atomic theory, between the scientists as exemplified
by Newton and the general body of atomic philosophers. It
is perfectly true to say that the atomic theory can be traced, in
unbroken historical continuity, from Leucippus to Newton, but
Newton's position is this: 'Let us suppose that these are atoms
and see what may be deduced therefrom in accordance with ex-
perimental fact', and therein lies the vital difference between
a scientific theory and a philosophic speculation.
John Dalton 221
Newton's suggestion that a gas may be composed of particles
that repel one another in a perfectly definite way was the
immediate cause of the formulation of the chemical atomic
theory a century later.
Fig. 72. JOHN DALTON
5- John Dalton
IN the Introductory Discourse to his Dictionary of Chemistry,
the French chemist Wurtz exclaimed with pardonable pride,
Chemistry is a French science. It was founded by Lavoisier, of
immortal memory. An Englishman may yield to none in his
admiration of Lavoisier's work, but will claim that the great
Frenchman found an equal in the humble Quaker schoolmaster
John Dalton. Dalton was the son of a weaver, and was born at
Eaglesfield in Cumberland about 6 September 1766. As his
parents were poorly off, he had to begin to earn his own living at
the early age of 12, and in 1785 he and his brother Jonathan
222 John Dalton
opened a school at Kendal, where, says the prospectus, 'Youth
will be carefully instructed in English, Latin, Greek, French;
also Writing, Arithmetic, Merchants' Accompts, and the Mathe-
matics'. The school was not generally popular, 'owing to the
uncouth manners of the young masters, who did not seem to
have had much intercourse with society; but John's natural dis-
position being gentler, he was more passable'. The boys in
particular preferred John, because he was so absorbed in his
mathematics that their faults escaped notice.
In 1793 Dalton was appointed tutor in mathematics and
natural philosophy at the Manchester Academy, a continuation
of the similar establishment at Warrington, with which, it will
be remembered, Priestley had been connected for some time.
Dalton remained at the Academy for six years, after which he
resigned his post and became a private tutor, devoting all his
leisure hours to scientific research. Modest in his requirements,
and simple and regular in his habits, Dalton lived a quiet and
unassuming life even when in after years he had acquired a
European reputation. Sir Henry Roscoe relates that in 1826,
when the fame of the Quaker scientist was at its height,
*M. Pelletier, a well-known Parisian savant , came to Manchester
with the express purpose of visiting the illustrious author of the
Atomic Theory. Doubtless, he expected to find the philosopher
well known and appreciated by his fellow citizens probably
occupying an official dwelling in a large national building
devoted to the prosecution of science, resembling, possibly, his
own College de France or Sorbonne. There he would expect to
find the great chemist lecturing to a large and appreciative
audience of advanced students. What was the surprise of the
Frenchman to find, on his arrival in Cottonopolis, that the
whereabouts of Dalton could only be found after diligent search ;
and that, when at last he discovered the Manchester philosopher,
he found him in a small room of a house in a back street, engaged
looking over the shoulders of a small boy who was working his
"cyphering" on a slate. "Est-ce que j'ai Thonneur de m'ad-
dresser a M. Dalton?" for he could hardly believe his eyes that
John Dalton 223
this was the chemist of European fame, teaching a boy his first
four rules. "Yes," said the matter-of-fact Quaker. "Wilt thou
sit down whilst I put this lad right about his arithmetic?" '
Through a fondness for meteorology, Dalton was led to a
study of the properties and composition of the atmosphere and
JONATHAN and JOHN DALTON,
Rcfpc&fufly inform their Friends, and the Public in genera), that they intend to continue
the SCHOOL lately feogbt by
GEORGE BEWLEY,
Where Youth will be carefully inftru&ed in
Englifh, Latin, Greek, and French J
A I 8 O
Writing, Arithmetic Merchants Accompts,
And the MATHEMATICS.
The School to be opened on the 28th of March, 1785
N. B. Youth boarded in the Matter** Houfe on reafonable
Terms.
Fig. 73. DALTON'S CARD
thence to an investigation of 'elastic fluids' or gases in general.
Steeped in the works of Newton, he habitually thought in terms
of atoms, and the atomic theory seems to have first taken shape
in his mind as a physical theory to explain the properties of gases.
'Having long been accustomed to make meteorological observa-
tions/ he said, 'and to speculate upon the nature and constitu-
tion of the atmosphere, it often struck me how a compound
atmosphere, or a mixture of two or more elastic fluids, should
constitute apparently a homogeneous mass, or one in all
mechanical relations agreeing with a simple atmosphere.
Newton had demonstrated clearly in the 23rd. Prop, of Book II
224 John Dalton
of the Principia that an elastic fluid is constituted of small
particles or atoms of matter which repel each other by a force
increasing in proportion as their distance diminishes.'
Applying Newtonian principles to the problem of mixed gases,
he was able to account for a phenomenon he had observed in
1 80 1, viz. that the pressure in a mixture of gases is the sum of
the partial pressures, or that in such a mixture each gas exerts
the same pressure as it would if it were separately enclosed in
the volume occupied by the whole mixture. This he explained
by assuming that when two gases, 'denoted by A and 5, are
mixed together, there is no mutual repulsion amongst their
particles, that is, the particles of A do not repel those of B, as
they do one another'. Although this explanation is no longer
held, it shows that Dalton was already employing an atomic
hypothesis, and that he was profoundly influenced by the ideas
of Newton. Two years later, Dalton was able to publish his Law
of Partial Pressures, which states that if a mixture of gases is
exposed to a liquid, each gas dissolves in the liquid according to
its partial pressure.
The further sequence of events which led to the enunciation of
the chemical atomic theory is not clear, owing to contradictory
accounts given by Dalton himself, his friend Thomas Thomson,
and the various notebooks and other documents preserved in
Dalton's laboratory at 36, George Street, Manchester. However,
on 26 August 1804, Dalton gave an account of his views on the
composition of matter to Thomson, who incorporated them in
the third edition of his System of Chemistry (1807). Thomson
took notes at the time, and the reproduction of them he gives in
his History of Chemistry is quoted here. The views they contain
were afterwards amplified by Dalton and published in his New
System of Chemical Philosophy, to which we shall return later.
The ultimate particles of all simple bodies are atoms incapable of
further division. These atoms . . . are all spheres, and are each of
them possessed of particular weights, which may be denoted by
numbers. For the greater clearness Mr. Dalton represented the
atoms of the simple bodies [elements] by symbols. The following
Ai^S^co l^ff-rt^^f^->^-<^ ^^v~-4-s
CH \~4t**^fS-.-
F. 74. COPY OF LETTER FROM DAT-TON TO MISS JOHNS
2613-4
226 John Dalton
are his symbols for four simple bodies, together with the numbers
attached to them by him in 1804:
Oxygen
Hydrogen
Carbon
Azote [nitrogen]
Relative Weights
O 6-5
O i-o
S'O
CD 5-o
SOME OF D ALTON'S APPARATUS
The following symbols represent the way in which he thought
these atoms were combined to form certain binary compounds,
with the weight of an integrant particle of each compound :
Weights
GO Water ....... 7-5
0O Nitrous gas [nitric oxide] . . . * 11-5
00 Olefiant gas [ethylene] . . . . 6-0
O Ammonia ...... 6-0
O0 Carbonic oxide [carbon monoxide] . . 11-5
The following were the symbols by which he represented the
composition of certain tertiary compounds :
O0O Carbonic acid [carbon dioxide]
(DO Nitrous oxide
O0 O Carburetted hydrogen [methane]
OCDO Nitric acid [nitrogen peroxide]
Weights
18-0
16-5
7-0
18-0
John Dalton 227
Thomson was very much attracted by Dalton's scheme, and
lost no time in drawing the attention of other chemists to it.
There were, however, some of our most eminent chemists who
were very hostile to the atomic theory. The most conspicuous of
these was Sir Humphry Davy. In the autumn of 1807 I had a long
conversation with him at the Royal Institution, but could not con-
Fig. 76. MORE OF DALTON'S APPARATUS
vince him that there was any truth in the hypothesis. A few days
after, I dined with him at the Royal Society Club, at the Crown and
Anchor, in the Strand. Dr. Wollaston was present at the dinner.
After dinner every member of the club left the tavern, except
Dr. Wollaston, Mr. Davy, and myself, who staid behind and had
tea. We sat about an hour and a half together, and our whole con-
versation was about the atomic theory. Dr. Wollaston was a con-
vert as well as myself; and we tried to convince Davy of the in-
accuracy of his opinions; but, so far from being convinced, he
went away, if possible, more prejudiced against it than ever. Soon
after, Davy met Mr. Davis Gilbert, the late distinguished president
of the Royal Society; and he amused him with a caricature de-
scription of the atomic theory, which he exhibited in so ridiculous
a light, that Mr. Gilbert was astonished how any man of sense or
Q2
228 John Dalton
science could be taken in with such a tissue of absurdities.
Mr. Gilbert called on Dr. Wollaston (probably to discover what
could have induced a man of Dr. Wollaston's sagacity and caution
to adopt such opinions), and was not sparing in laying the
absurdities of the theory, such as they had been represented to him
by Davy, in the broadest point of view. Dr. Wollaston begged
Fig. 77- THOMAS THOMSON
Mr. Gilbert to sit down, and listen to a few facts which he would
state to him. He then went over all the principal facts at that time
known respecting the salts ; mentioned the alkaline carbonates and
bicarbonates, the oxalate, binoxalate, and quadroxalate of potash,
carbonic oxide and carbonic acid, olefiant gas and carburetted
hydrogen; and doubtless many other similar compounds, in which
the proportion of one of the constituents increases in a regular
ratio. Mr. Gilbert went away a convert to the truth of the atomic
theory ; and he had the merit of convincing Davy that his former
opinions on the subject were wrong. What arguments he employed
I do not know ; but they must have been convincing ones, for Davy
ever after became a strenuous supporter of the atomic theory.
NEW SYSTEM
CHEMICAL PHILOSOPHY.
PART I.
BY
JOHN DALTON.
Printed by S. Russell, isj, Deansgatc,
FOR
ft. BICKERSTAFF, STRAND, LONDON.
180S.
Fig. 78
230 John Dalton
While the theory was taking shape, Dalton obtained much
assistance in clarifying his views by an investigation of the con-
stitution of olefiant gas [ethylene] and carburetted hydrogen
[methane].
It was obvious from the experiments which he made upon them,
that the constituents of both were carbon and hydrogen, and
nothing else. lie found further, that if we reckon the carbon in
each the same, the carburetted hydrogen gas contains exactly
twice as much hydrogen as olefiant gas- docs. This determined him
to state the ratios of these constituents in numbers, and to con-
sider the olefiant gas as a compound of one atom of carbon and one
atom of hydrogen; and carburetted hydrogen of one atom of
carbon and two atoms of hydrogen. The idea thus conceived was
applied to carbonic oxide, water, ammonia, etc. ; and numbers
representing the atomic weights of oxygen, azote, etc., deduced
from the best analytical experiments which chemistry then
possessed.
By 1808 his ideas had become quite precise, and in that year
he published the first part of his great book A New System of
Chemical Philosophy. Throughout this work the atomic theory
is constantly used, and the main points in it are emphasized.
These may be shortly stated as follows :
1. All matter is composed of a great number of extremely
small particles or atoms. To attempt to conceive the number of
particles is like attempting to conceive the number of stars in the
universe ; we are confounded by the thought. But if we limit the
subject, by taking a given volume of a gas, we seem persuaded
that, let the divisions be ever so minute, the number of particles
must be finite ; just as in a given space of the universe, the number
of stars and planets cannot be infinite.
2. Chemical analysis and synthesis go no farther than to the
separation of particles one from another, and to their reunion.
In other words, atoms are indestructible and cannot be created,
whence may be deduced the Law of the Conservation of Matter,
viz. matter can neither be created nor destroyed. 'No new
creation or destruction of matter is within the reach of chemical
agency. We might as well attempt to introduce a new planet
John Dalton 231
into the solar system, or to annihilate one already in existence,
as to create or destroy a particle of hydrogen. All the changes
we can produce consist in separating particles that are in a state
of cohesion or combination, and joining those that were pre-
viously at a distance.'
3. Each element has its own distinctive kind of atom, and
similarly each compound has its own distinctive kind of 'com-
pound atom' or ultimate mechanical particle. Thus, any one
atom of iron exactly resembles any other atom of iron, but is
different from the atoms of all other elements ; and all 'com-
pound atoms' of water exactly resemble one another but differ
from the 'compound atoms' of all other compounds.
4. It is important, and possible, to ascertain the relative weights
of different atoms. 'In all chemical investigations, it has justly
been considered an important object to ascertain the relative
weights of the simples [elements] which constitute a compound.
But unfortunately the inquiry has terminated here; whereas,
from the relative weights, the relative weights of the ultimate
particles or atoms of the bodies might have been inferred, from
which their number and weight in various other compounds
would appear, in order to assist and to guide future investiga-
tions, and to correct their results. Now it is one great object of
this work, to show the importance and advantage of ascertaining
the relative weights of the ultimate particles, both of simple and
compound bodies, the number of simple elementary particles
which constitute one compound particle, and the number of less
compound particles which enter into the formation of one more
compound particle.'
5. When elements combine to form compounds, the ultimate
particles of the compounds consist of small whole numbers of
the atoms of the elements concerned. Thus if there are two
elements A and B, which are disposed to combine, the following
is the order in which the combinations may take place, beginning
with the most simple :
i atom of A + 1 atom of B = i ultimate particle of C, a binary
compound.
232 John Dalton
1 atom of A +2 atoms of B = i ultimate particle of D, a
ternary compound.
2 atoms of A + i atom of B i ultimate particle of E, a
ternary compound.
i atom of ^[+3 atoms of B --- i ultimate particle of F, a
quaternary compound.
3 atoms of A-\-i atom of B =- i ultimate particle of G y a
quaternary compound.
At this stage Dalton had no means of determining the actual
numbers of atoms in the ultimate particles of compounds, so
that he had to fall back on assumptions. The main assumptions
that he made were these :
i st. When only one combination [compound] of two elementary
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
presumed to be a binary 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 quaternary, etc.
7th. The above rules and observations apply, when two com-
pound bodies, such as C and D, D and E, etc., are combined.
These postulates were obviously the most suitable ones to
make, since they were the most readily tested by quantitative
experimental work; they could easily be modified in particular
cases if the results of analysis so required.
Dalton next proceeded to put his principles into practice, and
showed how the relative weights of the atoms of different
elements might be determined. His method may be illustrated
by the following examples :
i . Water. At that time only one compound of hydrogen and
oxygen was known, namely water. Analysis showed that in
water eight parts by weight of oxygen were combined with one
of hydrogen. But since no other compound of hydrogen and
John Dalton 233
oxygen was known, water was considered to be a binary compound,
that is, to be composed of one atom of each element. Hence
the oxygen atom must be eight times as heavy as that of hydrogen.
2. Ammonia. This was the sole compound of nitrogen and
hydrogen known to Dalton, who therefore regarded it as a
binary compound, composed of one atom of each element. By
analysis it was found that the relative weights of hydrogen and
nitrogen in ammonia were as i is to about 5, hence the nitrogen
atom must weigh about five times as much as that of hydrogen.
3. Carbon oxides. Dalton knew of two oxides of carbon,
carbonic oxide [carbon monoxide] and carbonic acid [carbon di-
oxide] ; the former he considered to be a binary compound of one
atom of carbon and one of oxygen, and the other a ternary com-
pound of one atom of carbon and two of oxygen. By quantita-
tive analysis it was therefore easy to arrive at the relative weights
of the oxygen and carbon atoms.
Working in this way Dalton was able to construct a table of
atomic weights of the elements, that is, their relative weights
taking the weight of the hydrogen atom as unity. The following
are the numbers he gives in one place :
Atomic Atomic
Element Weight Element Weight
Hydrogen i Zinc .... 56
Azote [nitrogen) . . 5 Copper . . . .56
Carbon .... 5 Lead 95
Oxygen .... 7 Silver .... 100
Phosphorus ... 9 Platinum . . 100
Sulphur . . .13 Gold .... 140
Iron . . . .38 Mercury . . .167
In the same way he was able to discover the relative weights,
compared to the hydrogen atom, of ultimate particles of com-
pounds, e.g. : Weight of iji timate
Compound Particle
Magnesia
Lime
Soda
Potash
Strontia
Baryta
23
28
42
46
68
234 John Dalton
A glance at the above tables will show that Dalton 's values are
in many cases very different from those accepted at the present
day. This is partly due to inaccurate analysis, but a little con-
sideration will make it apparent that the real difficulty lay in the
fact that Dalton had no conclusive means of arriving at the
number of atoms in the ultimate particle of any compound.
Thus he assumed, in the absence of evidence to the contrary,
that the ultimate particle of water contains only i atom of
hydrogen and i of oxygen, and hence obtained, by deduction
from the data supplied by quantitative analysis, the number 8
for the atomic weight of oxygen. It is, however, obvious that if
the ultimate particle of water consists of 2 atoms of hydrogen and
i of oxygen, then the atomic weight of the latter will be 16,
while if it consists of 3, 4, 5, &c., atoms of hydrogen and i of
oxygen, the atomic weight of oxygen must be 24, 32, 40, &c.
In the same way, by regarding the ultimate particle of
ammonia to consist of i atom of hydrogen and i of nitrogen,
Dalton obtained * about 5' for the atomic weight of nitrogen,
instead of the modern value 14 which is based upon the
fact that i molecule or ultimate particle of ammonia consists
of i atom of nitrogen combined with not i but 3 atoms of
hydrogen.
This lack of knowledge of the number of atoms in the ultimate
particle of a compound was a serious hindrance to the develop-
ment of the theory. Dalton himself was fully alive to the
difficulty, and even as late as 1827 expresses himself as quite
frankly dissatisfied with the position. 'The second object of the
atomic theory/ he writes, 'namely, that of investigating the
number of atoms in the respective compounds, appears to me to
have been little understood, even by some who have undertaken
to expound the principles of the theory.'
When two bodies, A and J5, combine in multiple proportions;
for instance, 10 parts of A combined with 7 of B to form one
compound, and with 14 to form another, we are directed by some
authors to take the smallest combining proportion of one body as
representative of the elementary particle or atom of that body.
John Dalton 235
Now it must be obvious to anyone of common reflection, that such
a rule will be more frequently wrong than right. For, by the above
rule, we must consider the first of the combinations as containing
i atom of B and the second as containing 2 atoms of B, with
1 atom or more of A ; whereas it is equally probable by the same
rule that the compounds may be 2 atoms of A to i of B y and i
atom of A to i of B respectively; for, the proportions being 10 A
toy B (or, which is the same ratio, 20 A to 14 B) and 10 A to 14 B,
it is clear by the rule, that when the numbers are thus stated, we
must consider the former combination as composed of 2 atoms of
A, and the latter of i atom of A, united to i or more of B. Thus
there would be an equal chance for right or wrong. But it is
possible that 10 of A, and 7 of B, may correspond to i atom ^4,and
2 atoms B ; and then 10 of A, and 14 of B, must represent i atom
A y and 4 atoms B. Thus it appears the rule will be more
frequently wrong than right. It is necessary not only to consider
the combination of A with B y but also those of A with C\ D,E> ,
before we can have good reason to be satisfied with our determina-
tions as to the number of atoms which enter into the various com-
pounds. Elements [compounds] formed of azote [nitrogen] and
oxygen appear to contain portions of oxygen, as the numbers 1,2,
3, 4, 5 successively, so as to make it highly improbable that the
combinations can be effected in any other than one of two ways.
But in deciding which of those two we ought to adopt, we have to
examine not only the compositions and decompositions of the
several compounds of these two elements, but also compounds
which each of them forms with other bodies. I have spent much
time and labour upon these compounds, and upon others of the
primary elements, carbon, hydrogen, oxygen, and azote, which
appear to me to be of the greatest importance in the atomic
system; but it will be seen that I am not satisfied on this head,
either by my own labour or that of others, chiefly through want of
an accurate knowledge of combining proportions.
How the difficulty was at length overcome we shall see in
succeeding pages. Meanwhile, we may turn to some of the
deductions that can be made from Dalton's atomic theory and
learn of their fate in the crucible of experiment. The chief of
these deductions are familiar to every student of chemistry
236 John Dalton
under the title of the Laws of The Conservation of Matter,
Constant Composition, Multiple Proportions and Reciprocal
Proportions.
The Law of the Conservation of Matter states that matter can
neither be created nor destroyed. When early chemists thought
about this problem, which was seldom, they seem to have
assumed the impossibility of creating or destroying matter ; but
it was only with the gradual introduction of quantitative method
during the eighteenth century, by men like Black, Lavoisier and
others, that the question really became urgent. By that time,
however, the rational habit of thought had so far taken possession
of chemists that the conservation of matter was never seriously
doubted ; Lavoisier tacitly assumes it in all his experiments but
never troubles to give formal expression to such an obvious
truism. It will be at once apparent that the Law of the Con-
servation of Matter is a corollary of the atomic theory, for if
atoms are uncreatable and indestructible, matter composed of
them must possess the same characteristics. In ordinary
chemical reactions, the most accurate quantitative analysis has
never been able to detect any exceptions to this law.
The Law of Constant Composition states that any particular
compound has an invariable composition. This directly follows
from the atomic theory, since if all the ultimate particles of a
compound are identical, as Dalton postulated, they must contain
the same numbers of the same kinds of atoms, and all the atoms
of the same element are , ex hypothesi, identical . Lavoisier appears
to have taken this law, like that of the Conservation of Matter,
as axiomatic; but his fellow-countryman Berthollet, in a book
entitled Essai de Statique Chimique, maintained that variable
composition is the rule and constant composition the exception.
He urged that only in particular cases and under special condi-
tions do elements and compounds combine in fixed proportions.
Berthollet was opposed by Proust (1755-1826), who was able to
prove, by exact quantitative analysis, that numerous compounds
obeyed the law with extreme accuracy, and that Berthollet had
confused true chemical compounds with mixtures or solutions
John Dalton 237
of which the composition may be continuously variable within
certain limits.
According to my view [said Proust], a compound is a privileged
product to which nature has assigned a fixed composition. Nature
never produces a compound even through the agency of man,
other than balance in hand, ponder e et mensura. Between pole and
pole compounds are identical in composition. Their appearance
may vary owing to their mode of aggregation, hut their properties
never. No differences have yet been observed between the oxides
of iron from the South and those from the North ; the cinnabar of
Japan has the same composition as the cinnabar of Spain; silver
chloride is identically the same whether obtained from Peru or
from Siberia; in all the world there is but one sodium chloride;
one saltpetre; one calcium sulphate; and one barium sulphate.
Analysis confirms these facts at every step.
The second deduction from the atomic theory was thus found
to be in accordance with experimental fact ; and subsequent re-
search has supplied overwhelming confirmation of its truth.
The Law of Multiple Proportions states that when two elements
combine together to form more than one compound, then the
weights of one of those elements which combine with a fixed
weight of the other are in a simple ratio to one another. Like
the two preceding laws, this third law is a logical inference from
the atomic theory. Suppose, for example, that the elements A
and B unite together to form two different compounds. The
simplest imaginable case will be when in one of the compounds
the ultimate particle consists of one atom of A and one of 5, and
in the other compound the ultimate particle consists of one
atom of A and two of B. Since, in one ultimate particle of each
of these two compounds there is one atom of A, it follows that
the weight of A is constant in the two particles. The weights of
B, on the other hand, will be in the ratio of the numbers of
atoms of B respectively present in the particles; in this instance,
1:2. This is a simple ratio, and if compounds are always com-
posed of small numbers of atoms, the ratio will always be a ratio
of small numbers and therefore a simple one.
Although Dalton never gave this law formal expression, there
238 John Dalton
is no doubt whatever that he thoroughly understood it. Indeed,
from the table given on p. 226, which dates from 1804, we can
gather that he already knew of several instances in which the law
held good, viz., carbonic oxide (CO) and carbon dioxide (CO 2 ) ;
olefiant gas (C 2 H 4 ) and carburetted hydrogen (CH 4 ); and
nitrous gas (NO), nitrous oxide (N O) and 'nitric acid' (NO 2 ).
Further confirmation was forthcoming in 1808, when Thomson
analysed the two oxalates of potassium (KHC 2 O 4 and K 2 C 2 O 4 )
and showed that one contains 'just double the proportion of
base' contained in the other. In the same year, Wollaston
pointed out that similar relations held in the cases of the car-
bonates and bicarbonates, and sulphates and bisulphates, adding
that all the facts he had observed were 'but particular instances
of the more general observation of Mr. Dalton, that in all cases
the simple elements of bodies are disposed to unite atom to
atom singly, or if either is in excess, it exceeds by a ratio to be
expressed by some simple multiple of the number of its atoms'.
With sudden insight, he foreshadows an important later develop-
ment of chemical theory: 'I am further inclined to think, that
when our views are sufficiently extended to enable us to reason
with precision concerning the proportions of elementary atoms,
we shall find the arithmetical relation alone will not be sufficient
to explain their mutual action, and that we shall be obliged to
acquire a geometrical conception of their relative arrangement
in all the three dimensions of solid extension.' Wollaston's
prophecy was fulfilled in 1875, when van't Hoff initiated the
study of the arrangement of atoms in space.
The complete establishment of the Law of Multiple Propor-
tions was effected by the Swedish chemist Johann Jacob Berze-
lius (1779-1848) who, in the years 1808-12, analysed with ad-
mirable accuracy a vast number of salts and other compounds.
His analytical figures were such that he was enabled to write to
Dalton: 'You are right in this, that the theory of multiple pro-
portions is a mystery without the atomic hypothesis : and as far
as I have been able to see, all the results gained hitherto con-
tribute to justify this hypothesis/
John Dalton 239
The Law of Reciprocal Proportions, also a logical deduction
from the theory, states that if an element A combines with an
element B and also, separately, with an element C, then if B and
C also combine together, the proportion by weight in which they
do so will be simply related to the ratio of the weights of B and
C which combine, separately of course, with a constant weight
of A. The necessity of this relation will be obvious when it is
remembered that Dalton postulated (a) that combination takes
place between small numbers of atoms, to form the ultimate
particles of compounds, and (b) that all the atoms of the same
element are of exactly the same weight. Particular instances of
the law were observed by Richter (1762-1807), but it was again
Berzelius who thoroughly established it.
All the principal deductions from Dalton 's theory were thus
found to be in perfect agreement with experimental evidence,
and general acceptance of the theory quickly followed. The
scientific world hastened to shower honours upon its illustrious
author. In 1822 he was elected a Fellow of the Royal Society;
in 1830 the French Academy of Sciences made him a Foreign
Associate, 'the highest station it has to bestow, and universally
regarded as the crowning distinction in European science'. At
the meeting of the British Association at Oxford in 1832, the
honorary degree of D.C.L. was conferred upon him, and the
story goes that he proudly wore his scarlet gown (the colour of
which he could not appreciate, as he was colour-blind) through
the streets. In 1833 the Government conferred upon Dalton
a Civil List pension of 150, afterwards raised to 300, and the
next year he had the honour of being presented to the King. In
1837 his health began to fail, and he was seized with a slight
attack of paralysis, from which he never completely recovered.
A further attack gave warning of its approach on 26 July 1844;
on the following day 'his housekeeper found him in a state of
insensibility, and before medical attendance could be procured,
though it was immediately sent for, he expired, passing away
without a struggle or a groan, and imperceptibly, as an infant
sinks into sleep*.
240 Jbterzelms
So died 'the framer of a theory with respect to the mode of
combination between bodies, which stands foremost among the
discoveries of the present age for the universality of its applica-
tions and the importance of its practical results, holding the
same kind of relation to the science of chemistry which the
Newtonian system does to that of mechanics; and throwing
light, not only upon all the ordinary subjects of chemical in-
vestigation, but even upon those more speculative questions,
with respect to the constitution of matter, which seemed to lie
beyond the reach of experimental inquiry'.
51. Berzelius
THOUGH Dalton enunciated the Atomic Theory, it was Berzelius
who did more than any other chemist to provide it with a sound
basis of accurate experimental fact. Two of his services to the
theory we have just learnt, but that which is perhaps the greatest
has yet to be described. Let us, however, first satisfy our natural
curiosity as to the personality of this great ' Maker of Chemistry',
who for many years ruled the chemical world with a rod of iron :
as, indeed, well he might, for the name Berzelius means 'the man
of iron', or so the etymologists suggest.
Berzelius was born at Wafnersunda, in Sweden, on 20 August
1779. His father was head-master of a school in the neighbour-
ing town of Linkoeping. At the local Gymnasium, Berzelius
appears to have shown but little promise, for his leaving certifi-
cate remarked that he 'justified only doubtful hopes'; and his
examiners at Upsala, where he studied medicine, were totally
unimpressed by his chemical ability. In 1802, however, he
sprang at once into fame, on the publication of some brilliant
chemical researches, and was immediately appointed assistant
professor of chemistry and pharmacy in the medical school at
Stockholm: a new post that was actually created for him.
Five years later he was made full professor, retaining this office
for a quarter of a century. In 1818, King Karl Johann raised
him to the rank of nobleman, and on the occasion of his marriage,
in 1835, he was made a baron.
Berzelius 241
Berzelius 's private laboratory at Stockholm soon became the
goal of young chemists ; to work with the great master was their
highest ambition. One of them, Wohler, who himself afterwards
became famous, has left us a vivid picture of his first impressions :
Fig. 79. JOHANN J. BERZELIUS
As he [Berzelius] led me [said Wohler] into his laboratory I was,
as it were, in a dream, doubting whether it was really true that I
was in this famous place. Adjoining the living-room, the labora-
tory consisted of two ordinary chambers with the simplest fittings ;
there was neither oven nor fume chamber, neither water nor gas
supply. In one room stood two ordinary work-tables of deal ; at
one of these Berzelius had his working-place, the other was assigned
to me. On the walls were several cupboards with reagents which,
however, were not provided very liberally, for when I wanted
prussiate for my experiments I had to get it from Liibeck. In the
middle of the room stood the mercury trough and glass-blower's
table, the latter under one of the chimney-places provided with
2613-4 R
242 Berzelius
a curtain of oiled silk. The washing place consisted of a stone
cistern having a tap with a pot under it. In the other room were the
balances and other instruments, besides a small work-bench and
lathe. In the kitchen, where the food was prepared by the severe
old Anna, cook and factotum of the master who was still a bachelor,
stood a small furnace and the ever-heated sandbath.
Anna's dual responsibilities, as cook and laboratory assistant,
must have proved heavy especially as Berzelius seems to have
insisted upon keeping her chemistry up-to-date. On one
occasion, after Davy had shown that the gas hitherto called
oxymuriatic acid, and supposed to be a compound, was really an
element to which he gave the name chlorine, Berzelius overheard
Anna grumbling about the smell of 'oxymuriatic acid' in a flask
she was washing. 'Hearest thou, Anna 7 ; he reproved her, 'thou
must no longer speak of oxidised muriatic acid ; thou must call it
chlorine: that is better!'
As an experimental chemist, Berzelius was nearly, if not quite,
the equal of his fellow-countryman Scheele. His work, however,
lay on different lines, and was chiefly concerned with the develop-
ment of comprehensive and accurate schemes of qualitative and
quantitative analysis. Having established the schemes, he
employed them to test the accuracy of the laws of chemical com-
bination and more particularly to determine atomic weights.
The results he obtained are in many cases astonishingly close
to those now accepted, and offer a striking illustration of his
experimental skill. Berzelius 's figures did more than anything
else to ensure the universal adoption of the atomic theory;
but his supreme achievement was the establishment of the
present system of chemical notation. If we reflect for a moment
upon the convenience of our symbols, formulae and equations,
upon the continual use we make of them, and upon the concise,
definite information they contain, we shall realize how vitally
important they are, and how difficult chemistry would be with-
out them. Essential as they are at the present day, their impor-
tance in the early days of the atomic theory was even more
fundamental, for they enabled the rank and file of the army of
Berzelius 243
chemists to think in terms of atoms. Great philosophic minds
might perhaps have applied the atomic theory to chemical
problems without the assistance of literal symbols ; but we are
not all cast in this heroic mould. The conceptions of the theory
are, at bottom, highly abstruse, and the triumph of Berzelius is
n. B M E N T S
O O
9 in II 13 U I*
<D> <fl> O O
H 18 19 00.
O
GO GXD (DO O
(DO CXDO OO O*O
Fig. 80. DALTON'S SYMBOLS
that he rendered those conceptions intelligible to every one of us
through his scheme of symbolic representation.
The story of chemical symbolism is a long one, reaching back
to the very origins of chemistry itself. Sometimes the symbols
were used to convey information, sometimes to conceal it except
from the initiated ; sometimes they were purely practical, and at
others they served to express mystical ideas in alchemical terms.
R 2
244 Berzelius
Until the end of the eighteenth century, however, there was no
serious attempt at the construction of a systematic and uniform
scheme which should serve the sole purpose of a concise expres-
sion of chemical facts. Hassenfratz and Adet and others then
attacked the problem in a careful and logical fashion, but the
matter was soon afterwards raised to a higher plane by the
arrival of the atomic theory.
The first scheme of atomic notation was introduced by Dalton
himself, who used circles with lines and dots as symbols for the
atoms of elements, and appropriate groupings of these elemen-
tary symbols as formulae for the ultimate particles of compounds.
A list of some of Dalton 's symbols and formulae is given in
Fig. 80. The important difference between Dalton J s symbols and
those which had been used in earlier times is this : that whereas
the old sign $, for instance, had signified copper in any quantity ,
Dalton 's symbol Q stood for one atom of copper, and thus
possessed a definite quantitative significance completely absent
from the sign 5. The formulae of compounds conveyed even
more information; thus that of carbon dioxide, O0O, showed
that, in the opinion of those who adopted it, i ultimate particle
of carbon dioxide contains i atom of carbon and 2 of oxygen ;
and since (according to Dalton) the atomic weight of oxygen is
6-5 and that of carbon 5, the formula implicitly states that the
composition by weight of carbon dioxide is carbon : oxygen as
5 ' 13-
Dalton's formulae were adopted by those few chemists who
fully appreciated their tremendous import, but for the chemical
world in general the system proved much too cumbersome.
Fortunately, about 1814 or even a little earlier, Berzelius
suggested an incomparably more convenient notation, which is,
in essentials, the one that we now employ. In his Thdorie des
Proportions Chimiques (first edition, 1819; second edition, 1835),
he points out that the use of symbols greatly facilitates the ex-
pression of chemical facts. In order to render the usage general,
it would be quite sufficient to give each body its own particular
sign, which would represent the relative weight of its atom.
Berzelius 345
'We have chosen as the symbols for bodies the initial letters of
their Latin names/ he says. 'When the names of the several
bodies have the same initial, one adds the first letter which is not
common to them. For example, C signifies Carbon, Cl =
Chlorine, Cr == Chromium, Cu = Copper, Co = Cobalt. No
letter is added to the initials of non-metals, even when their
names begin with the same letters as those of certain metals ;
from this rule, however, chlorine, bromine and silicon must be
excepted, since their names have the same initials as those of the
other non-metals carbon, boron and sulphur.
'The number of atoms is indicated by figures. A figure on the
left multiplies all the atoms placed on its right, as far as the
first + or the end of the formula. A little figure placed to the
right of the letter, above, like an algebraic exponent, multiplies
solely those atomic weights on the immediate left. Thus S 2 O 5
indicates an atom [ultimate particle] of hyposulphuric acid, and
2 S 2 O 5 indicates two atoms of the same acid. . . . Here are the
symbols for each element :
Oxygen
H Hydrogen
N Nitrogen
S Sulphur
P Phosphorus
Cl Chlorine
Br Bromine
1 Iodine
Pt Platinum
Pd Palladium
Hg Mercury
Ag Silver
Cu Copper
U Uranium
Bi Bismuth
Sn Tin
Pb Lead
F Fluorine
C Carbon
Ta Tantalum
Ti Titanium
Os Osmium
Au Gold
Ir Iridium
R Rhodium
Te Tellurium
Co Cobalt
Ni Nickel
Fe Iron
M Manganese
Ce Cerium
Al Aluminium
Zr Zirconium
Th Thorium
246 Berzelius
Cd Cadmium Y Yttrium
Zn Zinc G Glucinum [beryllium]
B Boron Mg Magnesium
Si Silicon Ca Calcium
Se Selenium Sr Strontium
As Arsenic Ba Barium
Cr Chromium L Lithium
Mo Molybdenum Na Sodium (natrium)
W Tungsten (wolfram) K Potassium (kalium).'
Sb Antimony (stibium)
It will be observed that Berzelius 's list is practically identical
with ours, very few changes (except additions) having been made
since the publication of the original. Both his symbols and his
formulae, indeed, were so simple to use, so easy to remember,
and so concisely informative, that they very quickly gained
universal currency. There were a few malcontents, among
them Dalton. ' Berzelius 's symbols are horrifying/ he wrote to
Graham in 1837, 'a young student in chemistry might as soon
learn Hebrew as make himself acquainted with them. They
appear like a chaos of atoms. Why not put them together in
some sort of order? Is not the allocation a subject of investiga-
tion as well as the weight? If one order is found more consistent
than another, why not adopt it till a better is found? Nothing
has surprised me more than that such a system of symbols should
ever have obtained a footing anywhere/ Elsewhere he says,
'I do not, however, approve of his adopting and defending the
chemical symbols of Berzelius, which appear to me equally to
perplex the adepts of science, to discourage the learner, as well
as to cloud the beauty and simplicity of the atomic theory.'
Berzelius 's reply to his critics was dignified and convincing:
May I be allowed to reply to some objections which have been
made to the use of these formulae for the designation of the atomic
composition of bodies ? It has been said that they lack clearness,
induce error, and offer no advantage. Surely, they are obscure
only as long as one is unfamiliar with their meaning; once one
knows how to interpret them, nothing can be easier than to under-
Berzelius 247
stand them. In no case can they lead to error, for they are simply
the expression of the composition of a substance, according to the
opinion of him who constructed the formula. If this opinion is
incorrect, it will lead to error, in whatever manner it is expressed ;
the formula in itself contributes nothing to the error. It has also
been said that these formulae produce a disagreeable impression
upon the mathematicians, because the number, known in algebra
as the exponent and placed above to the right, has a greater value
than in these formulae, and that above all one should recognize the
rights of the mathematicians; such an objection is not worth
refuting. The letter P has the value of an R in the Greek and
Russian languages; and, in reading a book, it is not more probable
that in reading, say, Russian, one would be deceived over the
significance of this letter, than that one would be deceived, in
a chemical work, by taking a chemical sign for an algebraic formula.
In the one case, the use of letters and numbers is based upon
principles different from those in the other ; for there is no reason
why they should be the same. As far as concerns the objection of
uselessness, it will suffice to give one example, to prove how much
may be expressed by these formulae, and how clear the expression
is: KOSO 3 +A1 2 O 3 3SO 3 + 24H 2 O is ... the formula which ex-
presses the composition of alum. It shows that in this salt one
atom of potassium is combined with 2 atoms of aluminium, 4
atoms of sulphur, 48 atoms of hydrogen, and 40 atoms of oxygen;
that one atom of potash is combined with one atom of alumina,
4 atoms of sulphuric acid, and 24 atoms of water, or that an atom of
potassium sulphate is combined with an atom of aluminium
sulphate. . . . One may say it is true, that most of these data are the
immediate consequences the ones of the others : doubtless that is
so for those who know these consequences, but for them the word
alum says as much as the whole formula ; the latter 's object is, then,
to give with ease a summary of that which one should observe.
Berzelius 's last sentence gives the raison d'etre of the modern
formula, which expresses, in an extremely condensed form, that
information about a chemical compound which the chemist
regards as the most important. The system of notation has been
modified and extended since the time of Berzelius, but his con-
ception of a formula as a summary of experience still holds good.
248 Avogadro
By a mere inspection of its formula, a chemist may gather as
much about the constitution, preparation, properties and re-
actions of a substance as from several pages of prose description.
Chemical symbols are still a language 'not understanded of the
people', but to the chemist they are the chief medium of the
expression and transmission of knowledge.
52. Avogadro
ALTHOUGH Dalton's arguments and Berzelius's data were
successful in establishing the atomic theory, they failed to re-
move the fundamental difficulty to which reference has already
been made : that of discovering with certainty the number of
atoms in the ultimate particle of a substance. Both Dalton and
Berzelius attempted to take the position by flank attacks, for
they perceived its vital importance ; but their efforts were fruit-
less, and many chemists did not hide their belief that the problem
was insoluble. They had good reason to assume this attitude,
for it must have appeared quite hopeless to expect ever to
obtain a definite knowledge of the architecture of such minute
objects as the ultimate particles of matter.
The most that quantitative analysis could yield at that time
was the combining proportion of an element, or that number
which we now call its equivalent. By a consideration of various
fragments of incidental evidence, it was possible in certain cases
to reach a shrewd idea of the structure of the particles of the
substance under investigation, but in no single instance could
the result be taken as final. Early lists of 'atomic weights' are
therefore essentially lists of equivalents, though in many in-
stances collateral data demanded that the equivalent of an
element should be multiplied by some small whole number
a procedure that was duly carried out in compiling the list. It is
obvious that as long as atomic weights were uncertain, very
little progress could be made in discovering the domestic
arrangements of the atoms within the ultimate particle of a
compound, as even the number of these atoms could not be
definitely settled.
Avogadro 249
The glory of having shown how this grievous difficulty could
be overcome belongs to the Italian scientist Avogadro, a worthy
product of the country of Galileo and Leonardo. What greater
tribute to his genius could we pay than to emphasize the fact
Ffc. 81. A MliDKO AVOGADRO
that where those giants of chemistry, Dalton and Berzelius,
failed, Avogadro triumphed?
Lorenzo Romano Amedeo Carlo Avogadro, Count of Quaregna
and Cerreto, was born in Turin on 9 August 1776. The name
Avogadro is a corruption of Avvocato, a barrister, and recalls the
fact that Avogadro's ancestors had been advocates in ecclesias-
tical courts. Avogadro was himself trained for the courts as a
young man, and in 1796 was given the degree of doctor of
ecclesiastical law. From 1800-5, however, he assiduously studied
mathematics and physics, for which he had a deep predilection,
and on 7 October 1809, he was nominated Professor of these
subjects at the Royal College at Vercelli. In November 1820
250 Avogadro
King Victor Emanuel I established a chair of mathematical
physics in the University of Turin, and Avogadro became the
first professor. He held this post until July 1822 and again from
1834 until 1850, when he retired.
Avogadro married Donna Felicita Mazze di Biella, 'with
whom he shared for more than forty years the cares and joys of
life'. He had two sons: Luigi, who became a general in the
Italian army, and Felice, who, at the time of his death, was
President of the Court of Appeal.
As to his personal character, we are told that Avogadro was
'religious without intolerance, learned without pedantry, wise
without ostentation, a despiser of pomp, without care for riches,
not ambitious for honours ; ignorant of his own worth and fame,
modest, temperate, and lovable'. He died in 1856, after the 'life
of a philosopher of the ancient type, occupied wholly with his
studies, while not forgetting his duties as a citizen and father of
a family*. His features, as rendered by his portraits, well express
the charm of his character ; one feels that the eulogies just quoted
must have been fully justified.
Avogadro was a staunch adherent of the atomic theory, almost
from the moment of its publication, and was quick to perceive
its fundamental defect. How he was led to his brilliant hypo-
thesis which, as Nernst truly remarked, has proved to be 'a horn
of plenty* to chemistry, we shall discover by a consideration of
Gay-Lussac's work on gases.
Joseph-Louis Gay-Lussac (1778-1850) was a celebrated
French chemist, who became Professor of Chemistry at the
Jardin des Plantes, and was later made a peer of France. As
a man he is said to have been cold and reserved, but his private
life was not without its romance, as the following anecdote
(related by Sir William Tilden) will show :
At the beginning of the Revolution in 1789 there lived at Auxerre
a musician attached to the college in the town. On the suppression
of these establishments in 1791, it became necessary to educate his
three daughters with a view to gaining their living as teachers. But
the eldest, Josephine, in view of the family difficulties, preferred to
Avogadro 251
take a situation in a linen-draper's in Paris, and there Gay-Lussac
made her acquaintance. The young lady behind the counter he
noticed to be reading attentively a small book which on enquiry
turned out to be a treatise on chemistry. Naturally the interest in
such a subject displayed by a girl of seventeen excited his curiosity,
Fig. 82. JOSEPH-LOUIS GAY-LUSSAC
and something more, for his visits to the shop became more and
more frequent and in the end the young lady accepted his offer of
marriage. Gay-Lussac then placed her in a school in order to
finish her interrupted education, and in no long time, namely in
1808, she became his wife. The tender sympathy subsisting
between Gay-Lussac and his wife during forty years controlled so
completely their actions and even their habits as to extend even to
their handwriting, and in the end it was impossible to distinguish
the manuscript of a memoir copied by Madame from the original
as it proceeded from the hand of her famous husband.
The year 1808 was a memorable one for Gay-Lussac, for in it
occurred not only his marriage but also his enunciation of the
Law of the Combination of Gases by Volume, now generally known
252 Avogadro
as Gay-Lussacs Law. In a paper read to the Societe Philomatique
on 31 December, Gay-Lussac announced that when gases react,
their volumes bear a simple ratio to one another, and to the
volume of the product if that is gaseous. He had observed that
100 volumes of oxygen will combine with exactly 200 volumes of
hydrogen and, suspecting that other gases might also combine
in simple proportions by volume, he made several experiments
on the combination of gaseous acids with ammonia. His surmise
proved correct : 100 c.c. of ammonia require, for instance, looc.c.
of hydrochloric acid gas ; and further work showed that the law
was perfectly general. Thus, to form nitrous oxide, nitrogen
and oxygen combine in the proportion by volume of 2 : i ; in
nitric oxide the proportion is i : i ; and in nitrogen peroxide
1:2. Two volumes of carbon monoxide will combine with one
volume of oxygen to yield two volumes of carbon dioxide ; one
volume of hydrogen combines with one volume of chlorine to
form two volumes of hydrochloric acid gas ; and one volume of
oxygen combines with two volumes of sulphur dioxide to form
solid sulphur trioxide.
The remarkable simplicity of these figures indicated that they
possessed some deep significance, and the suggestion was made
that, possibly, equal volumes of all gases contain equal numbers
of atoms. Dalton had already considered and rejected this
hypothesis in the New System of Chemical Philosophy, where he
showed that it was not in accordance with experimental fact.
'For*, he says, 'if equal measures of azotic and oxygenous gases
[i.e. nitrogen and oxygen] were mixed, and could be instantly
united chemically, they would form nearly two measures of
nitrous gas [nitric oxide], having the same weight as the original
measures ; but the number of ultimate particles could at most be
one-half of that before the union. No two elastic fluids, probably,
therefore, have the same number of particles, either in the same
volume or the same weight/
Dalton was, indeed, inclined to believe that Gay-Lussac's
experimental figures were inaccurate, and that the simplicity of
his ratios was a deceptive one, due to this cause. He remarks
Avogadro 253
that he himself believes that 'gases do not unite in equal or exact
measures in any one instance; when they appear to do so, it is
owing to the inaccuracy of our experiments'. It is rather piquant
to listen to Dalton chiding Gay-Lussac for experimental in-
accuracy, when we remember that the great Englishman used to
get a different result for the 'atomic weight' of carbon almost
every time he determined it, while Gay-Lussac's manipulative
precision has scarcely ever been surpassed. Yet we can under-
stand the position : Dalton was firmly convinced of the truth of
the atomic theory, but failed to see how it could be reconciled
with Gay-Lussac's figures ; he was consequently led to question
the accuracy of those figures.
The way out of the impasse, which was also the way into the
vast territory of nineteenth-century chemistry, was discovered
by Avogadro. Accepting both Dalton 's theory and Gay-
Lussac's facts, Avogadro perceived that the two could easily be
brought into harmony if a distinction were made between the
ultimate chemical particle of an element, the atom, and the
ultimate physical particle of a substance, for which the name
molecule is now employed. In the July number, of the year 181 1 ,
of Delametherie's Journal de Physique, de Chimie, d'Histoire
naturelle et des Arts, he published his famous 'Essay on a Method
of determining the Relative Masses of the Elementary Molecules
of Substances'. Here is to be found the celebrated hypothesis
that, like a pillar of fire, led chemists out of the wilderness
into the promised land : 'Equal volumes of all gases at the same
temperature and pressure contain equal numbers of molecules?
Setting out from this hypothesis, [he continues] it will be seen that
we have a means of determining very easily the relative masses of
the molecules of compounds which can be obtained in the gaseous
state, and the relative number of these molecules in compounds;
for the ratios of the masses of the molecules are then the same as
those of the densities of the different gases, at equal pressure and
temperature, and the relative number of molecules in a compound
is given directly by the ratio of the volumes of the gases that form
it. For example, since the numbers 1-10359 and 0-07321 express
254 Avogadro
the densities of the two gases oxygen and hydrogen, taking that of
atmospheric air as unity, and the ratio of these two numbers con-
sequently represents the ratio between the masses of equal volumes
of these two gases, it will also express, on the hypothesis suggested,
the ratio of the masses of their molecules. Thus the mass of the
molecule of oxygen will be about fifteen times that of the molecule
of hydrogen, or, more exactly, 15*074 times. Similarly, the mass
of the molecule of nitrogen will be to that of hydrogen as 0-96913
is to 0-07321, that is, 13 to i, or more exactly 13-238 to i. On the
other hand, since we know that the ratio of the volumes of hydrogen
to oxygen in the formation of water is 2 to i , it follows that water
results from the union of each molecule of oxygen with two mole-
cules of hydrogen. Similarly, according to the proportions by
volume established by M. Gay-Lussac in the elements of ammonia,
oxide of nitrogen [nitrous oxide, N 2 O], nitrous gas [nitric oxide,
NO] and nitric acid [nitrogen peroxide, NO 2 ], ammonia will
result from the union of one molecule of nitrogen with three of
hydrogen, oxide of nitrogen from one molecule of oxygen with two
of nitrogen, nitrous gas from one molecule of nitrogen with one of
oxygen, and nitric acid from one of nitrogen with two of oxygen.
In the light of this hypothesis, let us re-examine the case of
nitric oxide, which Dalton found such a stumbling-block. It is
an experimental fact that if one volume of nitrogen and one
volume of oxygen are caused to enter into chemical combination,
the product is two volumes of nitric oxide. According to
Avogadro, therefore, one molecule of nitrogen will combine with
one molecule of oxygen to form two molecules of nitric oxide.
Each molecule of nitrogen, and of oxygen, must thus have been
halved, and consequently must consist of an even number of
atoms, at least two. It was Dalton 's failure to realize the
possibility that the smallest elementary particles normally exist-
ing in the free state might consist of a congeries of chemical atoms
of that element, and not of single atoms, that effectively blocked
his progress. "Thou knowest that no man can split an atom* was
such an idie fixe with him that it excluded the visualization of
elementary particles of atomic dimensions that yet consisted
of more than one atom. Avogadro, on the other hand, did not
Avogadro 255
shrink from the only conclusion to be drawn from the experi-
mental facts, and thus made the vital distinction between an
atom which retained the Daltonian indivisibility and a mole-
cule, which might or might not be divisible, according as to
whether it consisted of more than one atom or of a single atom.
SA~t*sr/'s
, ^^^
Fig. 83. SPECIMEN OF AVOGADRO'S HANDWRITING
With this efficient tool to help them, chemists might have
made rapid progress in the determination of atomic weights and
in the investigation of the structure of molecules. Thus, when
one volume of hydrogen enters into combination in such a way
as to yield a gaseous product, or one which can be volatilized, it
often yields two volumes of the product but never more. The
conclusion is that the molecule of hydrogen contains two, and
not more than two, atoms. Similarly, one volume of oxygen will
often yield two, but not more than two, volumes of a gaseous
compound, and the conclusion to be drawn is consequently that
the molecule of oxygen, like that of hydrogen, is diatomic. Now,
256 Avogadro
two volumes of hydrogen will combine with one volume of
oxygen to form two volumes of steam. Hence, by Avogadro 's
hypothesis, each molecule of steam must consist of one molecule
of hydrogen and half a molecule of oxygen: in other words, its
constitution must be H 2 O, and not IIO as Dalton had supposed.
This in turn requires the doubling of Dalton 's number 8 for the
atomic weight of oxygen : and so on.
After the publication of Avogadro's hypothesis, indeed,
chemists had it within their power to settle innumerable
problems that, in point of fact, were not settled until nearly half
a century later. This unexpected delay was due to several
reasons. In the first place, chemists had not thoroughly assimi-
lated the atomic theory, and although they accepted it in prin-
ciple they seem often to have regarded it more as a picturesque
flight of the philosophic imagination than as a solid, practical
scientific theory. Secondly, Dalton never lent his weighty
support to Avogadro 's hypothesis, and on matters connected
with atoms his verdict was unchallenged. Thirdly, experimental
methods had improved so much that men had their time fully
occupied with practical work : new elements and new compounds
were being discovered with amazing rapidity, and a minimum
of theory sufficed. Lastly, chemists appear to have shared with
Dalton the difficulty of conceiving a distinction between the
atom and the molecule, and thus overlooked the fundamental
importance of Avogadro 's suggestion. Perhaps, too, the political
state of Italy at that time, when Metternich could say * Italy is
a geographical expression', may have contributed to the neglect
that Avogadro suffered.
Avogadro himself returned to the attack again and again, but
with so little success that his hypothesis was not mentioned in
his obituary notice in the Nuovo Cimento of 1856, in Kekule's
great text-book of organic chemistry (1859-61), or even in
Kopp's History of Chemistry (1843-7). It was not until 1858,
two years after his death, that Avogadro at length triumphed.
In the half century that had elapsed, confusion over atomic
weights and molecular formulae had steadily grown, and
Modern Chemistry Established 257
there seemed little possibility of bringing the chaos to order.
Fortunately, however, Avogadro's fellow-countryman, Stanislao
Cannizzaro (1826-1910) had become thoroughly persuaded of
the basic importance of the then almost forgotten hypothesis,
and in a masterly pamphlet, entitled A Summary of a Course of
Chemical Philosophy, he so lucidly and convincingly explained
the manner in which it smoothed away the difficulties of con-
temporary chemical theory that chemists were at last converted.
Only a few years later, Avogadro was universally acclaimed as
one of the founders of theoretical chemistry ; atomic weights had
been definitely fixed; the structure of molecules could be in-
vestigated with confidence ; and chemistry strode forward shod
with seven-league boots.
Avogadro's hypothesis [wrote Lothar Meyer] has had a great in-
fluence particularly upon the development of chemical theories.
It was not until after it had been generally adopted and its con-
sequences studied, that the most important laws governing the
combinations of atoms with one another were discovered. From
Avogadro's laws dates the beginning of a general theory of
chemistry, a theory which explains the atomic constitution and the
major part of the properties of compound bodies. . . . The gradual
development of this theory has become the base of a science of the
equilibrium of atoms; it marks a new period in the history of
chemical statics.
53. Modern Chemistry Established
OUR story proper now ends, for after Lavoisier had replaced
phlogiston by o'xygen; Dalton had established the atomic theory ;
Berzelius had shown how it could be universally applied; and
Avogadro had crowned all with his brilliant hypothesis, chemistry
was already advancing on her present lines. The 'makers of
chemistry' those who fashioned it into the science as we know
it had accomplished their work, and a chemist of 1831 would
feel more at home with the chemistry of 1931 than with that of
1781 . True, he would be at first bewildered by the multitudes of
new compounds, new elements, new reactions, new applications,
but he would find the oxygen theory still reigning, the name of
2613-4 c
258 The Electrochemical or Dualistic Theory
Dalton in present reverence, and Avogadro's hypothesis in
universal currency. After the first amazement had evaporated,
he would realize that the basic theories of modern chemistry
were the basic theories of his own day ; he would find expansion,
extension, modification, but no such revolution as that which was
witnessed by the closing years of the eighteenth century. The
world has produced chemists of scintillating genius in the nine-
teenth and twentieth centuries, but their work, marvellous
though it be, is but a working out of the principles laid down by
Lavoisier, Dalton and Avogadro.
Yet the reader who has travelled thus far may wish to com-
plete his journey, and to take at least a passing glance at the
development of chemistry in the last hundred years. The short
survey that follows may serve to whet his appetite for more
detailed study, and to throw into bolder relief the great work
accomplished by those makers of a science 'which reveals,
creates, and indefinitely renews the dominion of human in-
telligence and labour'.
54. The Electrochemical or Dualistic Theory
THE rapid extension of chemical knowledge in the early years
of the nineteenth century gradually led to a ramification of
the subject into several distinct branches a process that has
become intensified with the passage of time. The first great
division was effected when the chemistry of mineral products, or
inorganic chemistry, was distinguished from that of animal and
vegetable products, or organic chemistry. The latter, as we shall
see, eventually resolved itself into the chemistry of the com-
pounds of carbon, while the former is concerned with all other
elements and their compounds. The distinction between in-
organic and organic chemistry is, at bottom, a matter of con-
venience of study only ; the same principles reign in both pro-
vinces, and the general theory of chemistry holds sway over
each, as the Pharaoh was King of both Upper and Lower Egypt.
For the first half of the century, inorganic chemistry was
chiefly concerned with the determination of the combining
The Electrochemical or Dualistic Theory 261
were passed through them. Two such bodies were caustic soda
and caustic potash. It is true that Lavoisier had expressed the
opinion that they were metallic compounds containing oxygen,
but the suggestion had never been substantiated and remained
a mere supposition, though an attractive one. In 1807, however,
Fig. 85. DAVY'S BATTERY
Davy subjected fused caustic soda and potash to the action of
a strong electric current, and had the intense satisfaction of
observing each of them to be split up : the soda into oxygen,
hydrogen and the soft metal now known as sodium , and the
potash into the same two gases and the similar metal potassium.
These astonishing phenomena, together with his own observa-
tions, led Berzelius in 1819 to publish his celebrated 'electro-
chemical' theory. Like Davy, he assumed that chemical and
electrical attraction are essentially identical, but he went con-
siderably, farther than Davy in the elaboration of detail and in
the correlation of theory with experimental fact. According to
Berzelius, all atoms are charged with electricity and show a
polarity, i.e. they have positive and negative poles. The two
poles are, however, not equal in strength; in some cases the
positive pole predominates and in others the negative. By reason
of this 'unipolarity' of their atoms, elements are either electro-
negative or electropositive, appearing at the anode or cathode
262 The Electrochemical or Dualistic Theory
respectively in electrolysis. The degree of chemical affinity of
a substance depends upon its intensity of polarization, which
itself varies with the temperature. Chemical combination con-
sists in the neutralization of electricity between oppositely
charged poles, and since each atom has both a positive and
a negative pole it is quite possible for two electronegative
elements to combine with one another, or two electropositive
ones, though in general, of course, combination occurs most
easily between elements of opposite electric character.
When an electropositive element combines with an electro-
negative one, the particles of the compound so formed may still
show a predominating residual polarity. Thus when copper (+)
combines with oxygen ( ), the copper oxide particles are still
slightly electropositive, while sulphur trioxide in which the
positive pole of the sulphur neutralizes part of the negative
electricity in the dominant pole of the oxygen is electronegative.
Copper oxide can therefore combine with sulphur trioxide to
form copper sulphate; but even this compound shows slight
polarity and is therefore able to combine with other sub-
stances to form more complex bodies, and so on. 'If the con-
jectures I have just explained give a just idea of the relation
between substances and electricity/ said Berzelius, 'it follows
that what we call chemical affinity, in all its varieties, is nothing
else but the effect of the electric polarity of the particles, and
that electricity is the prime cause of all chemical action. . . .
Every chemical combination follows solely from two opposing
forces, positive and negative electricity, and similarly every
compound is formed of two constituent parts united by the
effect of their electrochemical reaction, since no third force
exists. Thence it follows that every compound body, whatever
the number of its prime constituents, may be divided into two
parts, of which one is electropositive and the other electro-
negative. Thus, for example, sodium sulphate is not made up
[immediately] of sulphur, oxygen, and sodium, but of sulphuric
acid [SO 3 ] and soda [NaO], each of which may itself be split
up again into two elements, one positive and the other negative.'
The Classification of the Elements 263
Berzelius would, in fact, have written the formula for sodium
sulphate (using our notation) as Na 2 O . SO 3 rather than as
Na 2 SO 4 , to emphasize the view just expressed.
The electrochemical or 'dualistic' theory of the formation and
structure of compounds received widespread support, and led
directly to great progress in the investigation of molecular archi-
tecture. It finally encountered certain obstacles that rendered
it untenable in the form which Berzelius and his followers gave
it, but it was a remarkably penetrating conception, and its main
doctrine the intimate connexion between chemical and elec-
trical affinity has been revived in recent years and is now
universally held.
55. The Classification of the Elements
THE framework of inorganic chemistry was materially strength-
ened and enlarged during the nineteenth century by the slow
elaboration of a consistent scheme of classifying the elements.
The possibility of this scheme is due to Lavoisier, who first
drove home the definition of an element suggested by Boyle,
and himself drew up a ' Table of Simple Substances' in which
the elements known at that time were systematically arranged
in four groups, viz.
i. Simple Substances belonging to all the [three} kingdoms of
nature, which may be considered as the elements of bodies.
Light
Caloric (heat)
Oxygen
Azote (nitrogen)
Hydrogen
ii. Oxydable and Acidifiable simple Substances not Metallic.
'Miiriiim' 1 still unknown, but the existence of
Munum inferred Actua n y the
Phosphorus 'Fluorum' > muriates contained chlorine, the
Carbon 'BoraCUm' fl uorates fluorine, and the borate*
boron.
264 The Classification of the Elements
iii. Oxydable and Acidifiable simple Metallic Bodies.
Antimony Mercury
Arsenic Molybdenum
Bismuth Nickel
Cobalt Platinum
Copper Silver
Gold Tin
Iron Tungsten
Lead Zinc
Manganese
iv. Salifiable simple Earthy Substances.
at that time still regarded as elements,
Magnesia though Lavoisier foresaw that they
Baryta ^ 'must soon cease to be considered as
Argill (earth of alum)
simple bodies', and that they were per-
O . r haps metallic oxides.
Silica j F
More detailed classifications of the elements on the basis of
similarities in chemical properties were worked out by Dumas,
Odling and other chemists, and the existence of 'families' of
elements was recognized. Thus, fluorine, chlorine, bromine and
iodine form a natural family, as do oxygen, sulphur, selenium
and tellurium, and nitrogen, phosphorus, arsenic, antimony and
bismuth. Such schemes, however, had no fundamental unifying
principle, and were consequently in a perpetual state of flux.
Elements have numberless properties, and different selections of
the latter inevitably led to different classifications.
The problem was placed upon a new footing by the work of
Dobereiner (1829) and Pettenkofer (1850). Dobereiner observed
that many chemically related elements formed well-marked
groups of three (Dobereiner^ s Triads) , the atomic weight of the
middle member of each group being approximately the mean of
the atomic weights of the other two. Thus the atomic weight of
bromine (80) is roughly the mean of 35-5 and 127, the atomic
weights of chlorine and iodine respectively. Calcium (40),
The Classification of the Elements 265
strontium (87), and barium (137) form another such group.
Pettenkofer showed that certain arithmetical relationships
existed between the atomic weights of chemically similar
Fig. 86. STANISLAO CANNIZZARO
elements. Thus, the atomic weights of lithium (7), sodium (23),
and potassium (39), can all be represented by the formula
7+2/z8, where n = o, i, and 2 in the first, second and third cases
respectively. The atomic weights of other groups of elements
lent themselves to the same kind of mathematical expression,
and it was generally felt that such numerical relationships could
scarcely be due to chance.
Greater progress was not to be expected at the time, owing to
the uncertainty as to the atomic weights of many elements . How-
ever, after Cannizzaro, in 1858, had drawn the attention of
chemists to the great value of Avogadro's Hypothesis in deciding
266 The Classification of the Elements
between rival values for atomic weights, and the latter were at
last definitely fixed, further interesting relationships became
obvious almost at once. An important advance was made by the
English chemist Newlands in several short papers published
between 1863 and 1866. Newlands pointed out that when the
elements were arranged in order of their atomic weights, as
Fig. 87. CANNIZZARO'S AUTOGRAPH
determined in the light of Avogadro's Hypothesis, the eighth
element resembled the first, fifteenth, &c., the ninth resembled
the second, sixteenth, &c., and so on. Each element, in fact,
more or less closely resembled the elements that were seven, or
some multiple of seven, places before it or after it. One of
Newlands 's tables, published in the Chemical News of 1865 is as
follows :
No.
No.
No.
No. \
No.
No. \
No.
No.
H i , F 8
Cl 15
Co Ni
22 |
Br
29
Pd
36
I
42 Pt Ir 50
Li 2
Na 9 ; K 16
Cu
23
Rb
30
Ag
37
Cs
44 Tl 53
G 3
Mg 10 Ca 17
Zn
25
Sr
31
Cd
38
BaV
45
Pb 54
Bo 4
Al ii
Cr 19
Y
24
CeLa
33
U
40
Ta
46 Th 56
C 5
Si 12
Ti 18
In
26
Zr
32
Sn
39
W
47 Hg 52
N 6
P 13
Mn 20
As
27,
DiMo
34
Sb
4i
Nb
48
Bi 55
7
S 14 Fe 21
Se
28 ,
RoRu
35
Te
43
Au
49
Os 51
He says that, making a 'few slight transpositions', it will be
seen that elements belonging to the same group usually appear
on the same horizontal line. ' It will also be seen that the numbers
of analogous elements generally differ either by 7 or by some
multiple of 7; in other words, members of the same group
stand to each other in the same relation as the extremities of one
or more octaves in music. Thus, in the nitrogen group, between
nitrogen and phosphorus there are 7 elements; between
THE DISCOVER
THE PERIODIC LAW,
RELATIONS AMONG THE ATOMIC WEIGHTS.
BY
JOHN A. R. NEWLANDS, F.I.C, F.C.S.,
MEMBER OP THE SOCIETY OP PUBLIC ANALYSTS; LATE PROFBbSOR OF CHEMISTRY
IN THE CITY OF LONDON COLLEGE;
ANP AUTHOR OF VARIOUS SCIENTIFIC PAPERS IN *THE JOURNAL OF THE
CHEMICAL SOCIETY/ 'THE CHEMICAL NEWS/ ETC, ETC
LONDON:
E. & F. N. SPON, 16, CHARING CROSS.
NEW YORK: 35, MURRAY STREET.
1884.
Fig. 88
268 The Classification of the Elements
phosphorus and arsenic, 14; between arsenic and antimony, 14;
and lastly, between antimony and bismuth, 14 also. This pecu-
liar relationship I propose provisionally to term the "Law of
Octaves/ 1 '
When Newlands expounded his Law of Octaves before the
Chemical Society on i March 1866, it did not meet with an
enthusiastic reception. One member of the audience inquired,
pertinently, what provision the table made for elements still un-
discovered ; and a second, impertinently, whether Mr. Newlands
had ever tried arranging the elements in the order of their
initial letters ! Newlands was seriously discouraged by the good-
humoured, if tactless, derision his suggestion suffered, and after
brief replies to his critics pursued the matter no farther.
The 'simple but important' idea, as Wurtz described it, of
arranging the elements in order of increasing value of their
atomic weights had, however, already occurred independently
to two other chemists the German Lothar Meyer and the
Russian Mendeleeff. Like Newlands, Meyer and Mendeleeff
were struck by the periodicity of properties that become
apparent when such an arrangement was drawn up, but both
went much farther than Newlands in their treatment of the
subject. In its final form, the scheme elaborated by Mendeleeff
incorporated nearly the whole of Lothar Meyer's results, so that,
having given Germany her meed of honour, we may consider
the 'Periodic Law' in its Russian garb only.
In 1866 Mendeleeff a forceful personality of the genuine
Slav type was made Professor of Chemistry in the University
of St. Petersburg (bolshevike Leningrad). Three years later, at
the age of 35, he published his epoch-making paper on the
classification of the elements, in which he described the arrange-
ment that has since become celebrated as the Periodic System.
Like Newlands (of whose work it appears he was in ignorance)
he arranged the elements in order of their atomic weights,
starting from the lowest, and called attention to the fact that
chemically similar elements recurred at approximately equal
intervals. This, of course, had been already observed by New-
The Classification of the Elements 269
lands, but Mendeleeff had an incomparably greater knowledge
of general chemistry, and was able to overcome many of the
difficulties that had prejudiced chemists against the original 'law
of octaves'.
The conclusions at which Mendeleeff arrived are as follows :
Fig. 89. MENDELEEFF
1. The elements, if arranged according to their atomic
weights, exhibit an evident periodicity of properties.
2. Elements that are similar as regards their chemical pro-
perties have atomic weights which are either of nearly the same
value (e.g. platinum, iridium, osmium), or which increase
regularly (e.g. potassium, rubidium, caesium).
3. The arrangement of the elements, or of groups of
elements, in the order of their atomic weights corresponds to
their valencies as well as, to some extent, to their distinctive
chemical properties as is apparent among other series in that
270 The Classification of the Elements
of lithium, beryllium (glucinum), barium, carbon, nitrogen,
oxygen, and iron.
4. The elements which are the most widely diffused have
small atomic weights.
5. The magnitude of the atomic weight determines the character
of the element, just as the magnitude of the molecule determines
the character of a compound body.
6. We must expect the discovery of many yet unknown
elements, for example, elements analogous to aluminium and
silicon, whose atomic weight would be between 65 and 75.
7. The atomic weight of an element may sometimes be
amended by a knowledge of those of the contiguous elements.
8. Certain characteristic properties of the elements can be
foretold from their atomic weights.
Mendeleeff's brilliant scheme, springing fully armed from the
head of its creator, speedily conquered the chemical world. One
of its most compelling features was the confident boldness with
which it made predictions, and the breath-taking audacity it
showed in rejecting as erroneous atomic weights that did not fit
into its pigeon-holes. Tellurium has an atomic weight of 127-5,
while that of iodine is 127 ; the positions of these two elements in
the Table (p. 271) should therefore be reversed. On the contrary,
said Mendeleeff; iodine must clearly be classified with fluorine,
chlorine and bromine therefore the atomic weight of tellurium
must have been determined incorrectly and should be less than
that of iodine, probably 125. Again, arsenic has undoubted
affinities with nitrogen, phosphorus, antimony and bismuth, but
to put it in this group leaves two blank spaces in Groups III and
IV. Very well, remarks the undaunted Russian there must be
two elements not yet discovered that will, at some future time,
satisfactorily fill these vacant spaces.
It was this spirit of fearless prediction that fascinated con-
temporary chemists, even more than the patent success of the
system in grouping together elements which are chemically
similar. Mendeleeff nailed his colours to the mast, and showed
the firm faith that burned within him by predicting in detail the
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272 The Classification of the Elements
properties that the elements of atomic weight 44, 68 and 72,
and their compounds, would be found to possess when they
were discovered. The element of atomic weight 72, he foretold,
would have a specific gravity of 5-5. Its oxide would be of the
type MO 2 and possess a specific gravity of 4-7. Its chloride,
MC1 4 , would be a liquid of specific gravity i -9 and would boil at
a temperature just below iooC. It would form a derivative
M(C 2 H 5 ) 4 , and this would be a liquid boiling at i6oC. and
possessing a specific gravity of 0-96.
In 1887, Winckler discovered a metal of atomic weight 72-5.
He called it germanium (Ge). Its specific gravity was 5-5. It
formed an oxide GeO 2 , of specific gravity 4-7 ; a chloride GeCl 4 ,
which was a liquid boiling at 86 C. and possessing a specific
gravity of 1-9; and a derivative Ge(C 2 II 5 ) 4 , which boiled at 160
C. and had a specific gravity rather less than i. Small wonder
that Mendeleeff confessed to feelings of pride and gratification,
still further swollen by the discovery of gallium and scandium,
which admirably fitted the blank spaces between zinc and
germanium, and calcium and titanium, respectively.
The Periodic System proved useful in another direction,
namely, the correction of the atomic weights of certain elements.
It had, for instance, been shown that the equivalent of indium
(In) is 38, and the atomic weight was believed to be twice this,
i.e. 76. There was, however, no place in the system for an
element of atomic weight 76 having the properties of indium,
and Mendeleeff therefore suggested that the valency of indium
was 3 and the atomic weight 38 x 3, or 114. This would make
indium fall into the (at that time) vacant space in Group III
between cadmium and tin. Further research on indium com-
pounds proved that Mendeleeff was right. The atomic weights of
beryllium, uranium and Jjold were similarly corrected, but
MendeleefPs prediction that tellurium must have an atomic
weight less than that of iodine was definitely falsified. The dis-
covery of the rare gases (helium, neon, argon, krypton and
xenon) in the last decade of the nineteenth century provided the
periodic system with another anomaly of the same kind. While
The Rise of Organic Chemistry 273
there was no space for these gases in the table as Mendeleeff
constructed it, the difficulty was immediately overcome by con-
structing a new group Group O before Group I. But to get
argon (atomic weight 40) into this group meant that it had to
come before potassium (atomic weight 39) ; and in neither case
was there any doubt that the atomic weight had been determined
accurately.
These anomalies were not sufficient in number to detract from
the grandeur of the Periodic Classification, but they afforded
matter for speculation. No solution of the enigma could be
offered, however, until early in the present century, when it was
shown that the atomic weight of an element is a less fundamental
property than had been supposed. t If a more fundamental
characteristic, namely the atomic number of the element (p. 297)
is adopted as the basis of the classification, it is found that argon
and potassium, tellurium and iodine fall naturally into their
appropriate groups. Thus, although the atomic weight of argon
is greater than that of potassium, its atomic number is less ; and
the same is true of tellurium (atomic number 52) and iodine (53).
The essential significance of the Periodic System was to show
that the chemical elements are not 'mere fragmentary, incidental
facts in nature', but that they form successive units in the
sublime harmony of the universe.
56. The Rise of Organic Chemistry
IN the city of Cologne, some hundreds of years ago, two officers
of the Holy Inquisition wrote their terrible book Malleus
Maleficarum, or 'Hammer of Witches', in order to try to free
mankind from the supposed scourge of witchcraft. To-day, in a
delightful suburb of the city, one may see the house in which lived
Adolf von Baeyer, who did more than any other man to free the
world from the scourge of pain : for von Baeyer was the discoverer
of aspirin. Aspirin is a compound of carbon with hydrogen and
oxygen, and in this respect it is similar to ether, alcohol, sugar,
starch, acetic acid, mutton-fat and thousands of other sub-
stances. Petrol, fire-damp, lubricating-oil, paraffin, vaseline v
2613-4 T
274 The Rise of Organic Chemistry
benzene, acetylene and naphthalene are likewise compounds of
carbon, but in these examples the only other element present is
hydrogen. With hydrogen and nitrogen, carbon forms prussic
acid and hundreds of dyes ; with hydrogen, oxygen and nitrogen
it forms most of the modern high explosives; with hydrogen,
oxygen, nitrogen and phosphorus it forms the basis of living
matter or protoplasm. Carbon is, indeed, unique among the
elements in its power of entering into innumerable combinations,
and for this reason the study of carbon compounds has grown
into a distinct branch of chemistry a branch which is at once
the most systematic and, as many feel, the most fascinating.
The earliest known carbon compounds were all derived,
either directly or indirectly, from living or dead organisms
plants and animals and in this circumstance lies the origin of
the term 'organic' chemistry. As a distinct branch of the science,
organic chemistry is little more than a century old. Various
carbon compounds had, it is true, been known for hundreds
perhaps thousands of years, but they had not been so fully or
so satisfactorily studied from a chemical point of view as the
metals, metallic compounds, sulphur and other acids, and
mineral or 'inorganic' substances in general. Thus the nations
of the ancient world prepared wine, beer and mead, of which the
intoxicating principle is the organic compound alcohol '; vinegar,
containing acetic acid, was obtained by the souring of wine;
indigo and certain other dyes were employed; and starch, sugar
and fats formed part of man's daily food. Organic chemistry
proper, however, may be said to have begun in the hands of the
great Swedish chemist Scheele (1742-86), who was the first to
prepare pure specimens of such typical organic compounds as
glycerine, prussic acid, citric acid and oxalic acid.
Lavoisier was among the founders of organic analysis. He
showed that 'organic' compounds usually contain carbon,
hydrogen and oxygen, and less often nitrogen, sulphur and
phosphorus. Further improvements in the methods of analysis
were made by Berzelius, and it was at length realized that the
essential element in all organic compounds is carbon. One of
The Rise of Organic Chemistry 275
the first chemists to state this important fact was Gmelin, who in
his Handbook of Chemistry (1848) claimed that organic chemistry
should be'definitely regarded as the chemistry of the compounds
of carbon.
For many years, it was believed that the formation of organic
compounds in plants and animals was occasioned by a mysterious
vis vitalis or Vital force*, and that it was impossible to synthesize
them, or build them up from their elements, in the laboratory.
Even though many naturally occurring substances, such as
formic acid and oxalic acid, had been prepared artificially by
chemists, the starting-point in each of these preparations had
been other organic substances ; no one had succeeded in making
any organic compound from 'inorganic' material. The solution
of this problem was, in fact, very slow in coming, and disbelief
in the vis vitalis was not shattered at a blow, but died a lingering
death throughout a period of many years, during which a more
adequate study of organic substances had brought about a fuller
appreciation of the fact that they were amenable to the ordinary
chemical laws.
The term 'organic' chemistry, though it has now lost its
original significance, is less cumbersome than 'the chemistry of
the compounds of carbon', and is thus still used, in spite of the
fact that the majority of organic compounds at present known
have been built up in laboratories rather than by plants or
animals.
The possibility of vast and rapid progress was secured to
organic chemists by the elaboration, at the hands of Justus von
Liebig (1803-73), of a simple but reliable method of quantitative
analysis. The method adopted by Berzelius was capable of yield-
ing excellent results, but it was very slow; he spent eighteen
months, for instance, in analysing seven compounds. Liebig's
method was such an improvement that seventy-two analyses
were completed in three months, without a single failure. In
a modified form, Liebig's procedure is still employed, and its
ease and simplicity rendered possible the accurate analysis of
innumerable substances in a comparatively short time. With
T2
276 The Rise of Organic Chemistry
the data thus available, theoretical speculations could be made,
and Liebig himself in collaboration with his life-long friend
Wohler established the extraordinarily fruitful Radical Theory.
The germ of this theory can be traced back to Lavoisier, who
regarded organic compounds as 'oxides of compound radicals',
the words compound radical here signifying a group of atoms one
at least of which is carbon. Adopting and amplifying Lavoisier's
conception, Liebig and Wohler defined a compound radical as
a group of atoms which (a) is present as such in a series of com-
pounds, (b) can be replaced as a whole in these compounds, and
(c) can enter into combination as a whole. This theory can
readily be understood by reference to the particular example
first chosen by Liebig and Wohler, namely, the benzoyl radical.
In modern notation, this radical is represented by the formula
C 6 H 5 . CO , and they proved that this group of atoms is present
in the following compounds :
Benzoicacid . . C 6 H 5 . CO . OH
Oil of bitter almonds . C 6 II 5 . CO . H
Benzoyl chloride . C 6 H 5 . CO . Cl
Benzoyl bromide . C 6 H 5 . CO . Br
Benzoyl iodide . . C 6 H 5 . CO . I
Benzoyl cyanide . . C 6 H 5 . CO . CN
Benzoyl sulphide . (C 6 H 5 . CO) 2 S
Benzamide . . C 6 II 5 . CO . NH 2 .
The publication of this classical memoir created great excite-
ment. Berzelius himself wrote: 'The results you have drawn
from the investigations of the oil of bitter almonds are certainly
the most important that have hitherto been obtained in the
domain of vegetable chemistry . . . one may indeed regard them
as the beginning of a new day' ; while Pelouze wrote to Liebig :
'Your experiments are the sole topic of the chemical world in
Paris. So come along, and bring M. Wohler, come and receive
the tribute of admiration that is due to you.'
Following up this initial success with many others, Liebig at
last felt justified in describing organic chemistry as the chemistry
The Rise of Organic Chemistry 277
of compound radicals, and the discovery of other radicals, such as
those of cinnamic and salicylic acids, and especially the cacodyl
radical, As(CH 3 ) 2 , lent emphasis to the importance of these
various groups of atoms as the structural units of organic mole-
cules. At the present time, by a mere inspection of its structural
Fig. go. JUSTUS VON LIEBIG
formula, a chemist can describe with confidence the chief pro-
perties of an organic compound he may never have seen or even
heard of simply because he knows the properties of the radicals
of which the molecule of the substance is composed.
Meanwhile, another fertile theory had been developed: the
theory of substitution or theory of types. The French chemist
Dumas had found that part or all of the hydrogen in certain
organic compounds could be replaced by chlorine without any
fundamental change in the structure of the molecule ; such com-
pounds he called types. At first, there was a sharp conflict
278 The J^ise of Organic Chemistry
between Liebig and his followers and the protagonists of the
theory of substitution, for it was hard to believe that the replace-
ment of an atom of the electropositive element hydrogen by an
atom of the electronegative element chlorine could have so
little effect upon chemical properties as the theory of Dumas
implied. The facts, however, were afterwards recognized to be
incontrovertible, and a reconciliation between the two schools
was effected by the work of the Frenchmen Laurent and
Gerhardt (1853). Into the details of their scheme it is not
possible for us to inquire, but it led to the elaboration of a com-
prehensive theory of molecular architecture by Frankland ( 1 825-
-99) and Kekule (1829-96).
In spite of the clarity of Laurent and Gerhardt 's views, a full
understanding of the structure of organic molecules was im-
possible until Cannizzaro, in 1858, had demonstrated the im-
portance of Avogadro's Hypothesis in deciding the true values of
atomic and molecular weights. Up to that time, some chemists
had taken the atomic weight of carbon to be six and others twelve,
so that no little confusion reigned. Those who adopted the
former number wrote twice as many carbon atoms in the formula
of an organic compound as the latter, with the result that any
decision on the way in which the atoms were arranged in the
molecule was merely provisional.
As soon as Cannizzaro 's views were generally accepted, how-
ever, these exasperating difficulties vanished, and it was univer-
sally agreed that the atomic weight of carbon is twelve. This
agreement in its turn led to unanimity on the number of carbon
atoms in the molecule of any particular organic compound, and
the way to a full elucidation of molecular architecture was open.
A phenomenon that early attracted the attention of chemists
was the existence of substances whose molecules consisted of the
same numbers of the same atoms, though the substances them-
selves were different from one another in chemical and physical
properties. In 1828 Liebig's collaborator Wohler obtained urea
from ammonium cyanate by merely dissolving the latter in
water and evaporating the solution. Analysis showed that each
The Rise of Organic Chemistry 279
compound had the formula CON 2 H 4 , so that to account for the
differences between them chemists had to assume that the atoms
were arranged in the molecule of urea in a different manner from
that in the molecule of ammonium cyanate. Other examples of
the same phenomenon were quickly forthcoming, and Berzelius
Fig. 91. KEKULE
coined the word isomerism to denote it (from the Greek, meaning
'of equal parts').
The existence of isomerism rendered ordinary formulae in-
sufficient to characterize organic compounds. It is not enough
to know how many atoms of each particular element are present
in the molecule of a compound of carbon ; to understand the
reactions of the substance and to give it an unequivocal formula,
the mode in which those atoms are grouped within the molecule
must be ascertained and expressed. That such a formidable
problem was triumphantly solved is due very largely to the work
280 The Rise of Organic Chemistry
of two chemists, Sir Edward Frankland (1825-99) an ^ Friedrich
August Kekulc (1829-96).
In a memorable paper published in the Philosophical Transac-
tions in 1852, Frankland set out his views on the 'combining
power' or saturation capacity of atoms, and thus laid the
foundation of the theory of valency. By the valency of an atom
is meant the number of units into which the combining capacity
of that atom may be divided ; thus the atom of oxygen will in
general combine with either one or two atoms of other elements,
but not more, while the atom of hydrogen will combine with one
atom of other elements, but not more : the valency of oxygen is
therefore considered to be two and that of hydrogen one. Frank-
land was led to this conception by a systematic survey of the
formulae of inorganic compounds. 'When the formulae of in-
organic chemical compounds are considered,' he says, 'even
a superficial observer is struck with the general symmetry of
their construction; the compounds of nitrogen, phosphorus,
antimony and arsenic especially exhibit the tendency of these
elements to form compounds containing three or five atoms of
other elements, and it is in these proportions that their affinities
are best satisfied. . . . Without offering any hypothesis regarding
the cause of this symmetrical grouping of atoms, it is sufficiently
evident, from the examples just given, that such a tendency or
law prevails, and that no matter what the character of the uniting
atoms may be, the combining power of the attracting element,
if I may be allowed the term, is always satisfied by the same
number of these atoms/
Kekule greatly improved and extended Frankland's theory,
and in his celebrated Textbook of Organic Chemistry (1859) he
insisted upon the facts (a) that carbon is uniformly quadrivalent
in organic compounds, and (b) that carbon atoms have the re-
markable power, unshared except in a very limited degree by
those of other elements, of linking up together to form chains. 1
1 Similar views were published almost simultaneously by a young Scottish
chemist, A. S. Couper, who was unfortunately unable to elaborate his thesis
on account of ill health.
The Rise of Organic Chemistry 281
To illustrate the valency of atoms, Kekule used curious dia-
grams (' Kekule 's sausages') of which the following are examples :
This unwieldly notation was very short-lived, for in 1865
Crum Brown introduced the modern system, in which each
Valency' or unit of combining power is indicated by a line.
Thus Kekule 's sausages shown above were represented by Crum
Brown as
-O- and -C-
|
respectively: a much more elegant, and equally intelligible,
device.
After the establishment of the theory of valency, and its
practical expression in such a simple form, insight into many
puzzling problems of organic chemistry was quickly obtained.
The existence of isomeric substances was afforded a mechanical or
spatial explanation, and this explanation could be conveyed in a
clear and concise manner in the 'structural' formulae of the com-
pounds. There are, for instance, two compounds known of the
formula C 2 H 6 O, i.e. the molecules of each of them consist of two
atoms of carbon, six of hydrogen, and one of oxygen. Assuming,
with Kekule, that carbon is quadrivalent, oxygen bivalent, and
hydrogen univalent, we can arrange these atoms in two ways, viz.
H H H H
(i) H-C-C-O-H and (ii) H-C-O-C-H.
H H H H
These are the only ways in which two carbon atoms, six
hydrogen atoms, and one oxygen atom can be combined, if the
rules of valency are to be observed ; and it is a matter of chemical
experience that two, and only two, compounds of the formula
C 2 H 6 O exist. In order to decide which formula is to be assigned
to which of the two compounds, the properties of the latter are
282 The Rise of Organic Chemistry
investigated. Thus, one compound of the pair, namely alcohol,
will react with sodium in such a way that one of its six hydrogen
atoms is replaced by the metal ; the other five cannot be replaced
by sodium by any known treatment. The deduction chemists
draw from this fact is that, in the molecule of alcohol, one of the
six hydrogen atoms must be in a unique position, different from
thekind of position occupied by the other five. Formula (i) shows
such an arrangement, for one of the hydrogen atoms is attached
to oxygen, while the other five are attached to carbon. In
formula (ii), on the contrary, all six hydrogen atoms are in exactly
equivalent positions. For this reason, and others of a similar
kind, formula (i) is assigned to alcohol. The general procedure in
determining the architecture of an organic molecule is to in-
vestigate as fully as possible the reactions of the compound and
then to construct a tentative formula that expresses them.
Such an analysis is followed, if possible, by the synthesis of a
compound known to have the formula so deduced . If the synthetic
product proves to be identical with the original substance, the
formula is fully established. Thus, in the case of alcohol, we
can easily prepare a compound known to have the structure
H H
H-C-C-O-H,
H H
by taking ethane,
H H
H-C-C-H
I
H II
the formula for which is unambiguous, treating it with chlorine
to form ethyl chloride,
H H
H-C-C-C1
I I
H H
The Rise of Organic Chemistry 283
and acting upon this with caustic soda, when
H H H II
I
-O-H = H-C-C-O-H + NaCl.
H H H H
The compound thus synthesized turns out to be alcohol, the
constitution of whose molecule, originally deduced by analysis,
has thus been confirmed by synthesis.
In the formula of alcohol a short 'carbon chain' will be
noticed, consisting of two carbon atoms linked together. This
is a very simple example of such a structure, but there appears
indeed to be no limit to the number of links a carbon chain may
contain. In paraffin wax, for instance, there may be as many as
sixty carbon atoms in the chain, while in mutton-fat there are
fifty-seven, and these are by no means among the most complex
of organic substances. The potentialities of carbon as the parent
substance of derivative compounds are thus practically illimi-
table, and already nearly half a million organic compounds have
been prepared. Some of the most interesting, as well as the most
valuable, contain a skeleton of carbon atoms of peculiar forma-
tion, in which the ends of the 'chain' have joined up together to
form a 'ring'. The prototype of this class of compounds is the
hydrocarbon benzene, C 6 H 6 , which was discovered in 1825 by
Faraday. Benzene has very different properties from those of
other organic substances of apparently similar structure (e.g.
C 6 H 14 ), and Kekule found it impossible to devise an ordinary
chain formula for its molecule. One evening, however, he was
dozing in front of the fire, and dreamt of the dance of the atoms.
'My mental vision,' he said 'rendered more acute by repeated
visions of the kind, could now distinguish larger structures, of
manifold conformation: long rows, sometimes more closely
fitted together; all twining and twisting in snake-like motion.
But look! What was that? One of the snakes had seized hold of
its own tail, and the form whirled mockingly before my eyes.
As if by a flash of lightning: I awoke ; and this time also I spent
284 The Rise of Physical Chemistry
the rest of the night in working out the consequences of the
hypothesis.' Kekule thus conceived the idea that in the mole-
cule of benzene the six carbon atoms, instead of forming an
open chain, have joined together to form a six-membered ring.
This hypothesis he expressed in the formula
a b c d e f
I I I
c- c-c- c-c = c
where a, b, c, d, e, and / represent the positions of the six
hydrogen atoms. Later, he wrote the formula
H
/C
UC^ \CH
i I!
HC CH
\ c /
H
which may be contrasted with the formula of an 'open-chain'
compound containing the same number of carbon and hydrogen
atoms :
CH 2 - CH-C EE C-CH = CH 2
All subsequent investigation has confirmed the 'ring' structure
of the benzene molecule, and if we remember that perhaps half
the total number of organic compounds at present known are
derivatives of benzene we shall form a just estimate of the value
of Kekule's work.
Vast as has been the expansion of organic chemistry since the
publication of his classical Lehrbuch, the theoretical framework
of the subject has remained materially as he left it. We may
therefore take leave to pass on to the story of the rise of physical
chemistry which, though scarcely half a century old, has
justified its claim to autonomous rank.
57. The Rise of Physical Chemistry
CHEMISTRY and physics form two adjacent territories between
which there is no well-defined line of demarcation. The study
The Rise of Physical Chemistry 285
of those topics that lie in the 'no man's land', the application of
physical methods to chemical problems, and the use of chemical
data in physics, have led to the establishment of an intermediate
branch of science known as 'physical chemistry'. The elemen-
tary distinction between chemical changes and physical changes,
Fig. 92. VAN'T HOFF
so earnestly impressed upon us in our school-days, is an entirely
arbitrary one and breaks down as soon as we bear upon it a little
heavily. Chemistry and physics both deal with the properties
of inanimate matter, and are but different methods of approach
to the same objective. Particularly is this true in such matters
as the effect of electricity upon bodies, the structure of the atom,
the thermal concomitants of chemical reactions, the optical and
magnetic properties of substances, the chemical action of light,
and radioactivity. To attempt to deal with problems such as
these from a purely chemical or purely physical point of view is
286 The Rise of Physical Chemistry
clearly an impossibility, and recognition of this fact was made in
1887, when Ostwald and van't Hoff founded the Zeitschrift fiir
physikalische Chemie or 'Journal of Physical Chemistry*.
The principal focus of physical chemistry in its early days was
the nature of solutions. We saw in an earlier section that solu-
tions of acids, bases and salts conduct electricity, by the passage
of which they are decomposed. Most organic substances, on the
contrary, form solutions that do not conduct the current. The
reasons for such disparity of behaviour have formed an in-
exhaustible subject of investigation, from the time of Faraday
(1791-1867) to the present day. Faraday 's own contributions
were of fundamental importance. In his Experimental Researches
in Electricity (1831-8) he enunciated his celebrated Laws of
Electrolysis, according to which
i. The weight of a substance liberated in electrolysis is pro-
portional to the quantity of electricity that has passed through
the electrolyte (i.e. conducting solution); and
ii. When the same quantity of electricity is passed through
different electrolytes, the weights of the substances liberated are
in the ratio of their chemical equivalents.
These laws afforded a striking confirmation of the views of
Berzelius and Davy upon the intimate connexion between
electrical and chemical forces, and incidentally foreshadowed
the 'atomic' theory of electricity. From the chemical standpoint,
however, they remained comparatively unproductive until
Raoult, in 1884, drew attention to the marked contrast in other
physical properties shown by conducting and non-conducting
solutions. Raoult observed, among other things, that electro-
lytes 1 exhibited anomalous behaviour in their effect upon the
depression of the freezing-point of a solvent in which they were
dissolved, and upon the elevation of its boiling-point, the
abnormality in each case being of such a nature that the effect
produced was greater than would have been expected. Now the
1 The word electrolyte now signifies a substance that, in solution or in the
liquid or fused state, will conduct electricity at the expense of its own
.decomposition.
The Rise of Physical Chemistry 287
phenomena mentioned are conditioned by the molecular con-
centration of the solute in the solvent, so that Raoult's results
seemed to indicate that, in a solution of an electrolyte, there
were more molecules of solute than had actually been in-
troduced.
It was left to Arrhenius (1859-1927) to gather up both the
Fig. 93. ARRHENIUS
normal phenomena of electrolysis and this abnormal behaviour
of electrolytes in a comprehensive theory known as the Theory of
Electrolytic Dissociation. One of the earliest papers in the
Zeitschrift fur physikalische Chemie contained an account of this
theory, which, after a period of neglect and opposition, finally
won an almost universal acceptance seasoned, it is true, by
a few examples of complete scepticism.
Arrhenius suggested that when an electrolyte is dissolved in
water it splits up, almost completely in dilute solution and to
288 The Rise of Physical Chemistry
a less extent in concentrated solution, into charged atoms or
groups of atoms, which (by a transference of a name first used
by Faraday) were called ions. During electrolysis, the current is
carried by the ions, which are themselves attracted to the
positive or negative electrode, according to whether the charge
they carry is negative or positive. On reaching the electrodes,
the ions give up their charges and become converted into
ordinary atoms or groups of atoms, which may or may not
appear as such : if they do not attack water chemically they may
remain unaffected, but if they do, then secondary products will
make their appearance. Each ion, according to Arrhenius, was
supposed to exert the same effect upon the depression of the
freezing-point of the solvent, and the elevation of its boiling-
point, as an ordinary undissociated molecule.
The theory thus provided a coherent and intelligible explana-
tion of entirely distinct categories of facts, an infallible criterion
of its worth. Yet it was of such a revolutionary character that its
merits remained unperceived, and had it not been for the efforts
of the German chemist Ostwald, Arrhenius might have
succumbed to the same kind of treatment as that which proved
fatal to Newlands. To appreciate some of the objections that
were levelled against the theory, let us consider a definite
example. If Arrhenius is to be followed, a small quantity of salt
when dissolved in a large quantity of water suffers a scission of
practically the whole of its molecules into positively charged
sodium atoms, or sodium ions, and negatively charged chlorine
atoms, or chlorine ions. Should an electric current now be passed
through the solution, the sodium ions are attracted to the negative
electrode or cathode, and the chlorine ions to the positive
electrode or anode. Here they give up their charges and become
converted into ordinary sodium and chlorine atoms. But
sodium acts upon water, forming caustic soda and hydrogen,
the former remaining in solution while the latter is evolved as
a gas. Chlorine, on the contrary, does not readily attack water,
and is therefore evolved as a gas from the anode.
It is essential to distinguish here between the observed facts
The Rise of Physical Chemistry 289
and the hypothetical explanation of them. The formation of
caustic soda, and the liberation of hydrogen and chlorine, upon
electrolysis of a solution of common salt, are experimental facts
about which no disagreement is possible ; but that such a solu-
tion, whether subjected to electrolysis or not, contains myriads
of highly charged sodium atoms and chlorine atoms is merely
an hypothesis. We cannot feel surprised that so extraordinary a
suggestion met with scant attention at first and then with violent
opposition. Critics objected that it was ridiculous to imagine
the presence of free atoms of sodium (a metal that vigorously
attacks water) and of chlorine (a poisonous, yellowish-green gas
with a pungent smell and great chemical and physiological
activity) in a solution of so innocuous a substance as common
salt. This criticism, however, really rests upon a misunderstand-
ing of the theory. Arrhenius's hypothesis was that these free
atoms are indeed present, but that they are each carrying an
intense electric charge. There is no difficulty in assuming that
highly charged atoms, or ions, have very different properties
from those possessed by the same atoms uncharged, for it is
a matter of common experience that objects carrying a charge
of electricity show peculiarities of behaviour. When this point
was made clear, much of the original opposition was silenced,
and Arrhenius and his followers were able to show that many
perplexing properties of aqueous solutions found a satisfactory
explanation in terms of the theory of electrolytic dissociation.
In its primitive form, the theory is now obsolete, but it has
formed the basis of all subsequent work in this province, and its
main dogmas are incorporated in the current doctrines of
chemistry.
The greater part of physical chemistry is of a mathematical
and technical complexity that does not lend itself to summary
description, and as it is of such recent growth as to be almost
contemporary it falls without our present limits. Yet since we
witnessed the birth of the classical Atomic Theory, we may
perhaps permit ourselves to assist at the unfolding of the greatest
of all physico-chemical themes, namely the structure of the atom.
2613-4 n
[290]
58. The Structure of the Atom
FOR nearly a hundred years, Dalton's atomic theory held un-
disputed sovereignty. Master and slave alike, the indivisible
atom ruled the destiny of chemistry and was also the means of
its fulfilment. In this twentieth century, however, the Daltonian
atom is an out- worn conception, whose place has been taken by
a congeries of units of positive and negative electricity. A con-
sideration of the latest views on the structure of the atom does
not lie within the scope of the present book, but the revolution
in chemical thought during the last thirty years has been so pro-
found that we may conclude our story with an account of the
work that led to it.
In 1896 Becquerel showed that uranium salts have the power
of acting upon a photographic plate even when the latter is
wrapped in black paper. Compounds of thorium behave in the
same way, and as the effect was believed to be caused by an
emission of 'rays', uranium and thorium compounds were de-
scribed as radioactive. Whilst examining the uranium mineral
pitchblende, Madame Curie found indications of the presence
of a much more powerfully radioactive body in it. She success-
fully devised methods of extracting this substance and showed
that it was a new element, which she isolated in the form of a
mixture of its bromide with barium bromide. This new element
was called radium. By fractional crystallization from alcohol it
was found possible to separate the radium bromide from the
barium bromide, and in 1910 metallic radium was prepared by
the electrolysis of a solution of radium chloride, using a mercury
cathode. The radium liberated at the cathode dissolved in the
mercury to form an amalgam, whence the mercury was distilled
off, leaving the radium as a white metal which quickly rusts in
the air, and which, like calcium and barium, acts upon water in
the cold with evolution of hydrogen.
Radium salts will discharge an electroscope, and investiga-
tion of this property led to the discovery that radium gives off
three different kinds of rays, called respectively the a-, /3-
The Structure of the Atom 291
and y-rays. The nature of these radiations will be discussed
later.
Metals, and solutions of acids, bases and salts in water and
certain other solvents, conduct electricity, but gases under
ordinary pressures are non-conductors unless high potentials
A
B-
Fig. 94. CROOKES' TUBE
are employed. If, however, the pressure is lowered, it is found
that gases begin to conduct more easily, but at still lower pres-
sures exceedingly high potentials must be employed to drive the
discharge through. The phenomena of conduction are very
characteristic. At a pressure of o-oi mm. a phosphorescence is
produced on the walls of the glass tube opposite the cathode.
The nature of this phenomenon was investigated by Sir William
Crookes, who showed that the phosphorescence was caused by
a stream of exceedingly minute negatively electrified particles
which he called the Cathode Rays.
The cathode rays are deflected by electric or magnetic fields
in exactly the way that would be expected of a stream of
negatively charged particles, and are capable of passing through
thin plates of various metals. In 1895 Rontgen showed that
from the phosphorescent spot produced by allowing cathode
rays to strike upon the end of the vacuum tube in which they
were formed, another beam of rays was projected, of great
penetrating power. These rays he called X-rays.
The particles of which the cathode rays consist are known as
[negative] electrons. Each electron has a mass of about T^
u 2
292 The Structure of the Atom
of that of a hydrogen atom, and carries a charge equal (but
opposite in sign) to that carried by a hydrogen ion.
It has been shown that X-rays are similar to light vibrations
except that their wave-lengths are very much smaller ; they can
be diffracted and polarized by suitable means. The beam of
X-rays produced from an ordinary X-ray tube consists of a
mixture of rays of different wave-lengths, in the same way that
white light consists of a mixture of light rays of different wave-
lengths. A very important fact is that every element is capable of
emitting X-rays of wave-lengths peculiar to itself, if stimulated in
an appropriate way. Such a way is to allow X-rays of a shorter
wave-length to strike the substance, when the latter at once
gives off its characteristic radiation. Now, just as the ordinary
spectrum of an element is mapped and measured by means of a
spectrometer, so it is possible to map and measure the X-ray
spectrum of a substance by means of an instrument called the
X-ray spectrometer.
To understand how this works it is necessary to know the
principle of a device called the diffraction grating. If ordinary
white light is passed through a prism it is split up into light of
various wave-lengths, and a spectrum may be produced. This
analysis of light can also be brought about by another arrange-
ment called the diffraction grating, which consists of a large
number of very fine parallel lines accurately drawn upon a plane
sheet of glass in such a way that the spaces separating the lines
are all equal. Light which falls on this grating is 'diffracted' or
bent out of its normal path through an angle which is constant
for a given wave-length of light but which differs for different
wave-lengths, so that the grating 'sorts out' the light into
a spectrum. If the width of the space between two lines of the
grating is known, it is possible to calculate the wave-length of
any line in the spectrum, and it is in this way that the wave-
lengths of rays of light are measured.
X-rays are of the same nature as light-rays, but the wave-
lengths of light-rays are several thousand times greater than
those of the X-rays. Hence the ordinary diffraction gratings are
The Structure of the Atom 293
much too coarse to be of any use for the purpose of forming an
X-ray spectrum and measuring the wave-lengths of the various
lines . However, in 1 9 1 2 Laue ( 1 879- ) suggested that the atoms
in a crystal might serve as the lines of a diffraction grating, and
Fig. 95. X-RAY SPECTROMETER
the spaces between two consecutive parallel planes of them as the
spaces of the grating. If this is so, then a crystal forms a natural
diffraction grating which should apparently be of suitable
dimensions for giving an X-ray spectrum. Upon investigation
this was found to be the case. When X-rays fall on a crystal they
are diffracted in exactly the same way as light is by an ordinary
diffraction grating. Hence, to measure the wave-length of X-
294 The Structure of the Atom
rays, all we need to know is the distance between the planes of
atoms of a particular crystal. Fortunately it has been found
possible to calculate this distance, and therefore to find the actual
wave-length of any X-ray.
The X-ray spectrometer (Fig. 95) makes use of the fact that a
crystal will act as a diffraction grating for X-rays. The X-rays
to be examined are passed through a slit in a sheet of lead and
then through a second slit that serves to cut off any scattered
radiations. The pencil of rays then impinges on and is diffracted
from a crystal fixed by means of a piece of wax on a horizontal
arm that can revolve on a vertical axis over a graduated circle.
After diffraction from the crystal the X-rays are made to pass
through a third slit into a tube containing a gas which is easily
'ionized' (or made to conduct) by the rays; sulphur dioxide is
commonly used for the purpose. In this 'ionization chamber' is
an electrode (placed in such a position that the X-rays entering
the chamber do not strike it) connected to an electroscope. The
ionization chamber is mounted on a horizontal arm which can
revolve around the same axis as that on which the crystal is
mounted.
To conduct the experiment, the X-rays are diffracted from
the crystal and the ionization chamber turned until an X-ray
passes into it, causing the gas inside the chamber to become
ionized ; this is indicated by the electroscope. The angle through
which the ionization chamber has been turned is noted, and the
latter is then moved still farther until the next X-ray passes into
it, as shown by the electroscope.
In this way the X-ray spectrum of the substance under
observation can be measured, and the intensity of any given line
in the spectrum is indicated by the degree to which the electro-
scope is affected.
If a pencil of X-rays is passed through a crystal and then on
to a photographic plate, spots are produced on the plate,
arranged in a symmetrical way. These spots are caused by the
scattering of the X-rays by the atoms in the crystal, and by con-
structing space-models from the photographs it has been found
The Structure of the Atom 295
possible to determine the spatial arrangement of the atoms
within the crystal. Thus Sir W. H. and Professor W. L. Bragg
have shown that the atoms in a crystal of potassium chloride are
arranged in the way shown in Fig. 96, the potassium atoms being
represented by black circles and the chlorine by white O .
The atoms of carbon in the diamond are arranged in groups of
Fig. 96. LATTICE OF POTASSIUM CHLORIDE
six in such a way that each carbon atom is at the centre of the
regular tetrahedron formed by the four atoms nearest it.
The method has recently been extended to liquids, and the
shape and even the size of the benzene molecule have been de-
termined. The shape is that of a regular hexagon, of side
0-0000000602 cm. and thickness 0-0000000119 cm.
Let us return now to the a-, /?- and y-rays emitted by radium.
It has been shown that the a-rays consist of positively charged
particles of atomic dimensions, and of atomic weight 4. Each
carries two unit positive charges. The -rays consist of negative
electrons moving with a very high velocity, while the y-rays are
X-rays of very short wave-lengths. These rays are produced by
the disintegration of the radium atoms. The atomic weight of
radium is 226 ; when one atom of radium gives off an a-particle
of atomic weight 4, an atom of atomic weight 222 should be left.
This is actually the case. It has been shown that the a-particle
296 The Structure of the Atom
is an atom of helium carrying two unit positive charges, while th<
Element' of atomic weight 222 has been isolated and is callec
'radium emanation' or radon. Radon itself is radioactive anc
splits up into helium and a solid substance called the *activ(
deposit', which is still radioactive.
This spontaneous disintegration of atoms led scientists t(
formulate hypotheses on the structure of the atom, since atoms
were clearly no longer to be considered as indivisible. Man)
suggestions were made, but that which agreed best with observec
facts considered the atom to consist of an exceedingly minute
positively charged nucleus surrounded by a number of elec-
trons that revolve in more or less spherical orbits around the
nucleus. Bragg showed that the a-particles emitted frorr
radium could pass through thin sheets of solid substances, anc
proved that in doing so they pass not only through the spaces
between the atoms of these substances, but also actually through
the atoms themselves if these happen to be on their path. Wher
the a-particles pass through atoms most of the particles are nol
deflected from their rectilinear path, but a small number of their
suffer large deflections. This phenomenon is explained by
assuming that when an a-particle passes through an atom and is
not deflected thereby, it has not gone near the nucleus but only
through the outer regions of the atom those in which the
electrons revolve in their orbits. If we compare the atom
to our solar system we could regard the sun as the positive
nucleus and the planets as the electrons ; now it is conceivable
that a foreign sun might rush through our solar system and
still not come anywhere near the Sun. It seems that the
chances of an a-particle coming within close range of the nucleus
of an atom are about equally unlikely. When, however, an
a-particle does happen to pass close to the nucleus of an atom
it is violently deflected. In Lord Rutherford's words, 'to
account for these results, it was found necessary to assume
that the atom consists of a charged massive nucleus of dimen-
sions very small compared with the ordinarily accepted magni-
tude of the diameter of the atom. This positively charged
The Structure of the Atom 297
nucleus contains most of the mass of the atom, and is surrounded
at a distance by a distribution of negative electrons equal in
number to the resultant positive charge on the nucleus. Under
these conditions, a very intense electric field exists close to the
nucleus, and the large deflection of the a-particle in an encounter
with a single atom happens when the particle passes close to the
nucleus. Assuming that the electric forces between the a-
particle and the nucleus varied according to an inverse square
law in the region close to the nucleus, [Lord Rutherford]
worked out the relations connecting the number of a-particles
scattered through any angle with the charge in the nucleus and
the energy of the a-particle. Under the central field of force,
the a-particle describes a hyperbolic orbit round the nucleus,
and the magnitude of the deflection depends on the closeness of
approach to the nucleus. From the data of scattering of a-
particles then available, it was deduced that the resultant charge
on the nucleus was about J A e y where A is the atomic weight and
e the fundamental unit of charge [i. e. e is equal in magnitude to
the charge carried by a single negative electron]. . . .
* Since the atom is electrically neutral, the number of external
negative electrons surrounding the nucleus must be equal to the
number of units of resultant charge on the nucleus. It should be
noted that, from consideration of the scattering of X-rays by
light elements, Barkla had shown, in 1911, that the number of
electrons was equal to about half the atomic weight. . . .
'Two entirely different methods had thus given similar results
with regard to the number of external electrons in the atom, but
the scattering of a-rays had shown in addition that the positive
charge must be concentrated on a massive nucleus of small
dimensions. It was suggested by van den Broek that the scatter-
ing of a-particles was not inconsistent with the possibility that
the charge on the nucleus was equal to the atomic number of the
atom, i. e. to the number of the atom when arranged in order of
increasing atomic weight/ taking hydrogen as i, helium as 2,
lithium as 3, and so on.
It will be convenient here to consider the results of an in-
298 The Structure of the Atom
dependent line of research carried out by Moseley, who in-
vestigated the X-ray spectra of various elements by means of the
X-ray spectrometer. He found that the X-ray spectra obtained
in this way show two strong lines for each element, accompanied
by a number of weaker lines (see Fig. 97). Of the two strong lines,
one is stronger than the other and is called the a-line, while the
weaker is called the /Mine. It has been shown that if v is the
frequency (i.e. number of vibrations per second) of the a-line,
and TV the atomic number of the element, then
i) = %(N i) 2 a constant.
This constant is called Rydberg's constant and its value is
known. If, therefore, we measure the frequency of the a-line of
the X-ray spectrum of an element, we can calculate the position
which it ought to occupy in the Periodic Table, that is, its
Atomic Number.
This important discovery made it possible for the first time to
call the roll of the chemical elements and to determine how many
there were and how many remained to be discovered. There
are between and including hydrogen and uranium ninety-two
possible elements, of which only two (1931) remain to be found.
Moseley's work, in fact, showed that the 'properties of an
atom were defined by a number which varied by unity in
successive atoms. This gives a new method of regarding the
periodic classification of the elements, for the atomic number,
or its equivalent the nuclear charge, is of more fundamental
importance than its atomic weight.' Most of the physical and
chemical properties of an atom depend upon the number
and arrangement of the electrons in the atom, and these will
clearly depend upon the charge on the nucleus. In other words,
the actual mass of the atom is of secondary importance.
Hence we are led to the conclusion that 'it is quite possible to
imagine the existence of elements of almost identical physical
and chemical properties, but which differ from one another in
mass, for, provided the resultant nuclear charge is the same,
a number of possible stable modes of combination of the
The Structure of the Atom 299
different units which make up a complex nucleus may be
possible/ In other words, we may get atoms which are chemi-
cally indistinguishable and yet of different atomic weights. Are
we to regard such atoms as atoms of different elements, or as
atoms of the same element? According to Dalton, all the atoms
Fig. 97. X-RAY SPECTRA
of the same element have the same atomic weight; hence
from this point of view atoms that are chemically identical but
have different atomic weights belong to different elements. On
the other hand, chemical considerations would lead us to regard
atoms that are chemically identical as atoms of the same
element. Soddy gave the name isotopes or isotopic elements to
those elements which fall into the same place in the periodic
system, and are chemically identical, but have differing atomic
weights.
We have already seen that when an a-particle (or helium atom
carrying two positive charges) is expelled from a radium atom,
the product (radon) is an element which falls into Group O of
the periodic system, or two columns to the left of that in which the
parent radium atom is placed. Study of other radioactive pro-
300 The Structure of the Atom
ducts has shown that this is a general phenomenon expulsion
of an a-particle from the atom of an element in Group *N* re-
sults in the formation of an atom of an element which falls into
Group 'N-2* and has an atomic weight differing by four units
from that of the parent atom. Further investigation has pro-
duced evidence to show that when one ^-particle is expelled
from the atom (probably from the nucleus), an atom is formed
which is that of an element that falls into a column one to the
right of that in which the parent element is placed, but of the
same atomic weight. 'Each of the successive places in the periodic
table thus corresponds with unit difference of charge in the con-
stitution of the atom/ a conclusion previously arrived at by van
den Broek. We see, too, that there is, in addition to the existence
of isotopes, a possibility of the existence of different elements
with the same atomic weight: these have been called isobaric
heterotopes. Elements which differ in chemical properties and
also in atomic weight have been called heterobaric heterotopes.
All heterotopes are separable by chemical means.
The existence of isotopes suggested above is rendered still
more probable by the following considerations. Suppose an
atom loses an a-particle by radioactive change. We have seen
that an atom will be formed of atomic weight four units less, and
belonging to an element two columns to the left in the periodic
table. Suppose now this daughter-atom loses two ^-particles.
It will have moved two places to the right in the table and will
therefore have reached the position from which it set out, with
no further change in atomic weight. We should now have two
atoms differing by four units in atomic weight, but absolutely
identical in chemical properties, that is, they are isotopic elements,
or isotopic forms of the same element with different atomic
weights. Fig. 98 will make this clear.
It will be seen that atoms A and B occupy the same position
in the table, and are chemically identical; but they differ in
atomic weight by four units: they are isotopes. C and D are
isobaric heterotopes.
The first case in which these views were tested experimentally
The Structure of the Atom 301
was that of lead. It had been proved that the end-products of
the radioactive disintegrations of thorium and of uranium both
fell into the place in the periodic table occupied by lead, but a
consideration of the intermediate stages led to the conclusion
that the lead derived from uranium should have an atomic
Group N+1
Fig. 98. ISOTOPES AND HETEROTOPES
weight of 206, while that from thorium should have an atomic
weight of 208. Now uranium minerals often contain small
quantities of lead, and it is reasonable to suppose that this lead
has been derived from uranium by radioactive changes;
similarly, the lead found in thorium minerals has probably been
derived from thorium. Lead was extracted from both these
sources, and the atomic weights of the specimens were carefully
determined by chemists skilled in atomic weight determinations.
It was found that the lead from uranium minerals had an atomic
weight of 206-05 and that from thorium minerals 207-9. Thus
the theory was triumphantly justified. Ordinary lead, of atomic
weight 207-2, is a mixture of these isotopes in the appropriate
proportion. The 206-05 lead and the 207-9 ^ eac ^ wer ^ proved
to be chemically identical, as predicted by the theory.
Further investigations have shown that many other elements
are heterogeneous, that is, the 'element' as ordinarily encountered
302 The Structure of the Atom
is a mixture of isotopes. A very significant fact is that in every
case the atomic mass of a pure isotopic element is a whole
number, taking O = 16-00 as the standard of comparison. To
afford an explanation of this arresting phenomenon, it was
suggested that the nuclei of other atoms are composed of
hydrogen nuclei and helium nuclei. This theory has received
support from work of Lord Rutherford, who was able to
show that by bombarding nitrogen atoms with swiftly moving
a-particles it is possible to disintegrate a few of the former, one
of the products of disintegration being positively charged
hydrogen atoms.
Here we stand upon the threshold of present-day research,
and must at length part company. If our long association has
done nothing else, it will at least have taught us a juster apprecia-
tion of chemical achievement, which, as old Geber put it,
demands 'a Natural Ingenuity, and Soul, searching and subtily
scrutinizing Natwal Principles, the Fundamentals of Nature, and
Artifices which can follow Nature, in the properties of her
Action 9 .
INDEX OF NAMES
Abu'l-Qasim al- c lraqi, 81-2.
Abu Mansur Muwaffak, 67-8.
Adelardof Bath, 84, 88.
Adet, 216, 244.
Agatharchides, 7.
Agathodemon, 46.
Aidamir al-Jildaki, 52, 56, 75, 81-2.
'Ala al-Daula, 70.
Alexander of Aphrodisias, 68.
Alexander the Great, 16, 32, 46, 48.
Alfred the Englishman, 72, 86, 91.
Ali al-Rida, 56.
Ali, Caliph, i, 43.
Ali ibn Sahl, 64.
Al-Jildaki, 52, 56, 75, 81-2.
Al-Juzjani, 70.
Al-Khwarizmi, 87.
Al-Ma'mun, 52, 56.
Alston, Dr., 166.
Al-Tughra'i, 75.
Apollonius, 32, 54, 78.
Aquinas, Thomas, 90.
d'Arcet, see Darcet.
Archimedes, 32.
Aristotle, i, 16-21, 22, 23, 32, 33,
39, 54, 56, 58, 67, 68, 69, 70, 78,
88, 90, 96.
Armstrong, H. E., 208.
Arnold of Villanova, 89, 98.
Arnold, Sir Thomas, 41.
Arrhenius, 287-9.
Assurbanipal, 13.
Averroes, 91.
Avicenna, 68-77, 8 3, 9, 9 l > 9 2 , 97,
100, 101, 109.
d'Avisonne, see Davidson.
Avogadro, 121, 249-57, 258, 278.
Bacon, Francis, 134.
Bacon, Roger, 81, 89, 90-8, 104.
Baeyer, Adolf von, 273.
Bailey, Cyril, 217.
Banks, Sir Joseph, 177, 259.
Barkla, 297.
Bartholomew the Englishman, 98-
101.
Basilides, 33.
Bauch, 187.
Baume'. 217.
Beauvais, Vincent de, 89-90.
Becher, 20, 141, 143-150, 154.
Becquerel, 290.
Be"guin, Jean, 128.
Bergman, 208.
Bernouilli, Jean, 160.
Berthelot, 30, 35, 48, 104.
Berthollet, 200, 211, 214, 236.
Berzelius, 238, 239, 240-8, 249, 257,
259-60, 261-3, 274, 275, 276, 279,
286.
Biwan the Brahman, 27.
Black, Joseph, 164-9, T 76, 179, 192,
236.
Blagden, 200.
Boerhaave, i, 161, 179,
Boyle, 67, 122, 124, 131, 132-43,
153-4, 156, 160, 201, 203, 218,
219, 220, 263.
Bragg, Sir W. H., 295, 296.
Bragg, W. L., 295.
Breughel, Peter, 119.
Brosse, Guy de la, 128.
Brown, Crum, 281.
Brun, Sieur, 151-2.
Buffon, 191.
Burke, 170.
Cannizzaro, 256, 266, 278.
Cardanus, 151.
Carlisle, 259.
Carra de Vaux, 68, 75.
Cavendish, 130, 164, 177-86, 189,
197, 200, 209.
Champollion, 6.
Chandler, John, 120.
Charlemagne, 103,
Charles the Hammer, 41.
Cleopatra, i.
Coffinhal, 213.
Cohen, J.B., 156.
Crivelli, 6.
Crookes, Sir William, 291.
Cullen, William, 164-6.
Curie, Madame, 290.
Dalton, 22, 23, 121, 221-40, 244,
246, 248, 249, 252-4, 256, 257,
2<?8. 2QO. 2QQ.
304
Index of Names
Dalton, Jonathan, 221.
Darcet, 192, 200.
Davidson, William, 128.
Davy, Sir Humphry, 1 89, 227 -8, 242,
260-1, 286.
Democritus, i, 21, 36, 44, 46, 54.
Descartes, 217, 218.
Desch, 5.
Diderot, 198.
Diocletian, 29-30.
Diodorus Siculus, 7.
Dobereiner, 264-5.
Dudu, 12.
Dumas, 215, 264, 277-8.
d'Eldment, Moitrel, 160.
Empedocles, 23, 54.
Enlil, 12.
Entemena, n, 12.
Epicurus, 21, 217.
Erasmus, 1089.
Eratosthenes, 32.
Euclid, 32, 54.
Faraday, 283, 286, 288.
de Faye, 33.
Fischer, Emil, 188.
Fourcroy, 211, 214.
Frankland, Sir Edward, 278, 280.
Franklin, Benjamin, 200.
Frobenius, Johannes, 108-9.
Fugger, Sigismund, 108.
Galen, 27, 109.
Galileo, 67, 249.
Gamble, 259.
Garland, 5.
Gassendi, 21718.
Gay-Lussac, 121, 186, 2504, 259.
Geber, see Jabir ibn Hayyan.
Gerard of Cremona, 84, 88.
Gerhardt, 278.
Gibbon, 29.
Gilbert, Davis, 227-8.
Glaser, Christopher, 128.
Glauber, 184, 195.
Gmelin, 275.
Gossage, 259.
Graecus, Marcus, 104.
Graham, 246.
Grimm, 191.
Grossette, 92.
Gudea, 12.
Gunther, Dr., 143.
Hales, Stephen, 122, 161.
Harbi al-Himyari, 50.
Harun al-Rashid, 50, 52, 54.
Haskins, C. H., 84.
Hassenfratz, 216, 244.
Hatchett, 178.
Hathor, 7.
Hayyan, 49-5-
Heliodorus, 39.
Heraclius, 46.
Hermann the Dalmatian, 86, 88.
Hermes, i, 2, 35, 46, 104, 114.
Hipparchus, 32.
Hippocrates, 54.
Hisinger, 259.
Hoefer, 121, 189.
Hooke, Robert, 155, 156, 219.
Hunain ibn Ishaq, 75.
lamblichus, 33.
Ibn Abi Usaybi'a, 70.
Ibn al-Nadim, 52.
Ibn Arfa' Ra's, 76.
Ibrahim, 69.
Ingenhousz, Dr., 178.
Isidore, 100.
Jabir ibn Hayyan, 49-63, 66, 70, 73,
78, 79, 81, 82, 83, 84, 90, 92, 101,
106, 132, 143, 144, 151, 184, 302.
Ja'far al-Sadiq, 50, 52.
Jason, i.
Joachim, 20-1.
Johnson, O. S., 24.
Kanada, 27.
Kekule, 256, 278, 280-1, 283-4.
Khalid ibn Yazid, 43-4, 52, 79, 82.
Khammurabi, 13.
Khayyam, Omar, 217.
Kirwan, Richard, 183, 211, 212.
Ko Hung, 24-5.
Kopp, 256.
Lagercrantz, 30.
Lagrange, 200, 213.
Langdon, S. H., ir.
Laplace, 200.
Laue, 293.
Laurent, 278.
Lavoisier, 58, 78, 140, 155, 156, 158,
176, 177, 183, 192, 196, 197-213.
214, 215, 216, 221, 236, 257, 258,
261, 263, 274, 276.
Lefe"bure, Nicolas, 128.
Index of Names
35
Leibnitz, 124.
Lemery, 124-31, 132, 133, 152, 187.
Lepsius, 6.
Leucippus, 21, 27, 220.
Libavius, 11719, 120, 132.
Liebig, Justus von, 275-7, 278.
Lippmann, E. O. von, 25.
Locke, John, 143, 219.
Lucas, 4.
Lucretius, 21, 22, 23, 24, 217, 220.
Lully, 89, 98.
Macquer, 150, 166, 177, 200, 208.
Magnus, Albertus, 89, 90-8.
Mansur al-Kamily, 77.
Marcion, 33.
Marduk, 13.
Marianus, 434.
Mary the Jewess, 46.
Maslama of Madrid, 77.
Mayow, 154-8, 160.
Mellor, J. W., 142.
Mendeleeff, 268-73.
de la Metherie, 211.
Metternich, 256.
Meyer, Lothar, 257, 268.
Miriam, i .
Monge, 211.
Morveau, Guyton de, 153, 200, 211,
213, 214, 21516, 208.
Moseley, 298.
Moses, i.
Muhammad, i, 41, 43.
Muspratt, 259.
Natih, 69.
Nebuchadrezzar, 13.
Nernst, 250.
Newlands, 266-8, 288.
Newton, Sir Isaac, 22, 133, 217-21,
223-4.
Nicholson, 259.
Nin-girsu, 12.
Norton, Thomas, 76.
Odling, 264.
Oecolampadius, 108.
Olympiodorus, 39.
Ostanes, 44, 46.
Ostwald, 286, 288.
Palissy, Bernard, 190.
Paracelsus, 106-15, 119, 120, 128,
132, 144, 190.
2613*4
Partmgton, 184.
Paulze, Marie- Anne-Pierrette, 177,
200.
Pelagius, 39.
Pelletier, 222.
Pelouze, 276.
Peregrinus, Petrus, 93.
Perignon, Dom, 15960.
Peter the Venerable, 86.
Petrie, Sir Flinders, 10.
Pettenkofer, 264, 265.
Philalethes, 76.
Pinas, J., 119.
Plato, i, 23, 39, 46, 54.
Plato of Tivoli, 86.
Pliny, 27.
Plotmus, 33, 34, 35.
Porphyry, 33, 35.
Priestley, 78, 122, 163, 164, 169-77,
180, 182, 183, 185, 186, 187, 188,
J97, 2OO, 204, 2O7, 2O8, 2O9, 2IO,
211-12, 222.
Proust, 236-7.
Ptolemy, "54, 78.
Ptolemy Euergetes, 32.
Ptolemy Philadelphus, 32.
Ptolemy Soter, 32.
Punctis, Madame, 197.
Pyrophilus, 135.
Pythagoras, i, 23, 54.
Ramsay, Sir William, 186.
Raoult, 286.
Rayleigh, Lord, 186.
Razi, 63-7, 78, 82, 83, 90, 112, 132.
Rey, Jean, 151, 154-5-
Richter, 239.
Richthofen, 25.
Ritter, 259.
Robert of Chester, 86-9, 92.
Rontgen, 291.
Roscoe, Sir Henry, 222.
Rossellini, 6.
Rouelle, 164, 189-96, 198.
Rutherford, Lord, 296-7,^302.
Rydberg, 298.
St. John, 2.
St. Victor, Adam de, 2.
Sardanapallos, 13.
Sargon, 12.
Sayce, 15.
Scheele, 164, 186-9, J 97> 2O 7> 208,
242, 274-
306
Index of Names
Shamash, 13
Shams al-Daula, 70.
Shelburne, Lord, 169, 176.
Shem, 2.
Singer, (Mrs.) Dorothea Waley, 88,
98.
Smith, Elliot, 7.
Socrates, 54.
Soddy, 299.
Stahl, 20, 141, 143-5) IS 1 * *53> !54>
158, 194, 211.
Stapleton, 66-7.
Steele, Robert, 98.
Steen, John, 1 19.
Steno, Nicholas, 72.
Sthael, Peter, 143.
Stradanus, John, 119.
Sultzback, Eck de, 151.
Synesius, 39.
Teniers, David, 119.
Thales, 120.
Theophrastus, 119.
Theosebeia, 35.
Thompson, R. Campbell, 13, 14.
Thomson, in.
Thomson, Thomas, 224-7, 238.
Thorpe, Sir Edward, 187.
Thoth, see Hermes.
Tiberius, 100.
Tiglath-Inurta, 13
Tilden, Sir William, 250.
Trithemius, see Trittenheim.
Trittenheim, Hans von, 108.
Tubal-Cam, i.
Ur-Nina, n, 12.
Valentine, 33.
Vallot, 128.
van den Broek, 297, 300.
van Helmont, 76, 119-24, 128, 132,
i^o.
van Ranst, Marguerite, 119.
van't Hoff, 238, 286.
Venel, 153.
Vinci, Leonardo da, 72, 249.
Volta, 259.
Warltire, 180.
Watson, R., 148, 150.
Watt, James, 200.
Winckler, 272.
Wohler, 241-2, 276, 278.
Wollaston, Dr., 227-8, 238.
Wurtz, 221, 268.
Wu Ti, 24.
Yahya ibn Khalid, 51-2.
Zosimos, 33, 35-9, 44, 46, 130
SUBJECT INDEX
abaru, 47.
'Abbasids, 50.
Absorbent earths, 195.
Acetic acid, 59.
Acid potassium sulphate, 196.
Acids, 194.
Aerial acid, 209.
Aethiops, 215.
Affaire Brinvilliers, 128.
Aim of chemistry, Boyle on, 136.
Paracelsus on, 112-13.
Air, 1 6-20.
consists of two gases, 203-9.
explosion with hydrogen, 180-1.
necessary for combustion, 154.
part played in calcination by,
151-2.
Scheele on, 188.
sparked with clephlogisticated air,
186.
Al-Azd, 49.
Alchemical works, false attribution
of, 46.
Alchemy, 40, 132.
Muhammad and, 43.
Newton's interest in, 219.
origins of in Islam, 43 -9.
'practical', 96.
speculative', 96.
Alchyniia, 86, 118.
Alcohol, 14, in, 112, 274.
constitution of, 2823.
earliest preparation of, 103.
Alembic, 66.
Alexandria, Library not destroyed
by Muslims, 42.
Alexandrian School, 32.
Algebra, of Al-Khwanzmi, 87.
Alkali, 13.
Alkalis, 194.
Black on, 167-9.
Al-koholy in.
Al-kufil, in.
Alluvial gold, 9.
Almagest, 54, 78.
Alpha-particle, 295-6.
Alum, 72, 80.
used as mordant, 10.
Alums, in.
Ammonia, 131.
formula of, 233.
anaku, 14.
Analysis, 282.
Antimony, 14, 264.
Apparatus, 38, 118.
aquafortis, 131.
aqua regia, 131.
Arab Arabic-writing Muslim, 42.
Arabic words, used in Latin alchemy,
Argill, 264.
Argon, 1 86.
Arsenic, 37, 264.
Arsenious oxide, 68.
Askalon vessels, 38.
Asphalt, 12.
Aspirin, 273.
Astrolabe, 88.
athaha, 46.
atisyus, 46.
Atom and molecule, distinction be-
tween, 253-7.
structure of, 290302.
Atomic number, 297-8.
Atomic Theory, 21748.
chief points of, according to Dalton,
230-2.
classical, 214.
Indian, 27.
reception of, 227.
Atomic weights, 233, 248.
correction of, by Periodic System,
272.
Atoms, charged with electricity,
2612.
indestructible and uncreatable,
230-1.
number of, in, molecules, 234-5.
aurum potabile, 109.
Authentic Memoirs (Zosimos), 35.
Azote, 263.
Ba-en-pet, 4, 15.
Balance-room, not in Libavius's
chemical house, 118.
Barmecides, fall of, 54.
Baryta, 264.
barzel, 15.
X 2
308
Subject Index
karzi-ili, 15.
barzillu, 15.
Benzene, 283-4.
origin of word, 102.
Benzoyl radical, 276.
Bible, contains whole realm of know-
ledge, 94.
Bicarbonates, 169.
Bismuth, in, 264.
Bleaching action of chlorine, 188.
Blossom, Book of the, 52.
Bodies (metals), 67.
Book of Quintessence, The, 104.
Book of the Remedy, 70, 91 .
boracum, 263.
Brethren of Purity, 77, 81.
Bronze, 103.
Cacodyl radical, 277.
Calces, 147.
reduction of, 148, 150.
Calcination, 58-9.
Boyle on, 153-4.
increase in weight on, 151.
of tin and lead, 151.
Calomel, 196.
Caloric, 263.
Calx, 146.
of mercury, 171-7, 188, 204.
Canon, of Apollonius, 78.
Canon of Medicine, 70.
caput mortuum, 214.
Carbon, 263.
chain, 283.
dioxide, 179, 238.
action on lime, 167-9.
formula of, 244.
essential element in organic com-
pounds, 274-5.
oxides, formulae of, 233.
ring, 283.
Carbonic acid, 207, 226, 228.
Carbonic oxide, 226, 228, 238.
Carburetted hydrogen, 226, 228, 230,
238.
Cathode Rays, 291.
Caustic potash, electrolysis of,
261.
Caustic soda, electrolysis of, 261.
Ceration, 67.
chalkanthos, 38.
Charge against Lavoisier, 199.
Charlatanry of alchemist, 75-6.
Chemeia. i*.
Chemical affinity, 262.
analysis, 118.
apparatus, Razi's classification of,
66.
attraction, related to electrical
attraction, 260.
combination, 20, 21.
industry, 259.
substances, disco\ered by Scheele,
187-8.
Chemicals, classification of in The
Sage's Step, 79.
Razi's classification of, 65.
Chemist, a servant of Nature, 78.
Chemistry, 'a French science', 221.
Chest of Wisdom, The, 60.
China, chemistry in, 24-6.
Chinese alchemy, 46, 47.
Chlorine, 188, 189, 242.
Cinnabar, preparation of, 105-6.
production of, 58.
Classification of the Elements, 263 -73 .
cloud of arsenic, 37.
Coagulation (solidification), 67.
Cobalt, 5, in, 264.
cohothar, 215.
Collyrium, 47.
Combining proportion, 248.
volumes of gases, 252-3, 254.
Combustion, 200-13.
Hooke on, 155.
in saltpetre, 155-6.
Mayow on, 155-6, 158.
theories of, 143 ff.
Compendiun of Twelve Treatises, 64.
Compositions ad tmgenda, 103.
Composition of Alchemy, 86, 87.
Compound radical, 276-7.
Compounds, Proust on, 237.
Conservation of Matter, 122.
Copper, 4, 11-13, 73, 264.
removal from gold, 80.
removal from silver, 79, 80.
oxide, used as hair darkener, 68.
salts, blue colour with ammonia,
118.
sulphate, on electrochemical
theory, 262.
vitriol, 68.
Coral, artificial, 14.
Corks, use of, for stoppering, 15960.
Cours de Chymie, 128, 130.
Criminals, employed in Egyptian
mines. 8
Subject Index
309
Crusades, 84.
Cry of tin, 74.
Crystals, structure of, 294-5.
Cultivation of Gold, 82.
Cupellation, 77, 79, 80.
De Caelo, 16.
De Caelo et Mundo, 78.
Defence of Phlogiston , 211.
De general ione et corruptione, 16.
De Mineralibus, 91.
Dephlogisticated air, 175-7, 182-6,
204, 207, 208.
Dephlogisticated marine acid, 188.
De Re Metallica (De Metallis}, 77,
219.
De Rerum Natura, 21.
Descensory, 58, 66.
Dictionary of Chemistry, 221.
Dictionnaire de Chirme, 150.
Diffraction grating, 292-4.
Distillation of sea- water, 68.
Dualistic Theory, 258-63.
Dyeing, 59.
metals, 74, 9 r .
Dyes, 274.
Earth, 16-20.
Egypt, chemistry in, 2-10.
Elastic fluids, 220, 223.
Electric battery, 259.
Electrochemical Theory, 25863.
Electrolysis, 259-62, 2869.
Electrolytic dissociation, early criti-
cism of, 289.
theory of, 287-9.
Siemens de Chymie, 128.
Elements, Aristotelian, 16-20, 133-5,
137-40.
Boyle on, 137-8, 140.
Lavoisier on, 140-2.
Mellor on, 142.
Paracelsan, 114.
unknown, existence predicted, 270.
Elixir, 25, 39, 44, 52, 67, 83.
Empyreal air, 207.
End of the Search, 82.
Equivalent, 248.
Essai de Statique Chimique, 236.
Evaporation of the Divine Water that
fixes Mercury (Zosimos), 35.
Execution of Lavoisier, 212-13.
Exhalations, 19, 57.
Experience, Roger Bacon's interpre-
tation of, 96.
Experiment, Lavoisier's, 205-7.
Experimental Researches in Electri-
city, 286.
Experimental temper, of Arabs, 86.
Experiments on Magnesia Alba, 166.
Explosives containing saltpetre, 104.
Factitious Air, 178.
Families, of elements, 264.
Fermiers generaux, 199.
Feuerluft, 188.
Fire, 16-20.
Fire-air, 188.
Fixed air, 167, 179.
fliiorum, 263.
Formulae, 242-8, 280.
of organic compounds, 278.
structural, 281-3.
Four Elements, 16-20, 133, 138.
Fulminating gold, 131.
Furnaces, The Book of, 60.
Fusible subtances, 72.
Galenical liquors, 116.
Gas, invention of name, 121.
Gas ptngue, 122.
Gas silvestre, 122.
Gases, conduction of electricity in,
291.
method of drying, 179.
stored over mercury, 179.
Gay-Lussac's Law, 252.
Geometrical conception of atoms,
238.
Germanium, 272.
Glass, 10.
analysis of Pompeian, 14.
'discovery' of, 98, 100.
of antimony, 118.
pliant, 100.
Glass-blowing, 10.
Glass-making, 13, 14.
Glass-moulding, 10.
Glauber's secret arnnioniacal salt, 1 95 .
Gnosis, 33.
Gnosticism, 33, 34.
Gold, 5-10, 12, 73, 264.
alchemical, tested by Albertus
Magnus, 91.
assaying of, 77.
calcination of, 104-5.
fulminating, 131.
parting of from silver, 77, 105.
purification of, 79, 80.
310
Subject Index
Gold-mine, plan of, 6.
Golden Calf, i .
Golden Fleece, i.
Great Book of Properties, 106.
Greece, 1524.
Greek books, imported into Islam,
52-
fires, 104.
Grotto del Cane, 122.
guhlu, 14.
Gunpowder, 24.
Bacon's 'cipher', 97.
early recipe for, 104.
Gypsum, 12.
plaster, 68.
Haematite, 14, 80.
Hair-dyes, 59.
Handbook of Chemistry, 275.
Harran, 48.
hayuli, 46.
Heat, part played by, in combustion,
201-3.
Helium, 296.
Heterotopes, 300-1.
Highly respirable air, 207.
History of Chemistry (Thomson),
224.
(Kopp), 256.
House of Wisdom (Baghdad), 52.
Hydrochloric acid, 188.
Hydrogen, 130, 149, 263.
discovery of, 179-
Hypostatical Principles, 134-5, 138.
Hypothesis, Avogadro's, 253, 266,
278.
its importance, 257.
latrochemistry, ii3ff.
iksir, 46. See elixir.
Illuminating ink, 59.
immanakku, 14.
Incendiary substances, 104.
India, chemistry in, 26-7.
Indium, 272.
Inflammable air, 179.
Invention of Verity, 60.
Investigation of Perfection, 60.
Iodine, 270, 273.
'Ions, 288-9.
Iron, 4, 5, 73, 264.
Islam, chemistry in, 4184.
Isomerism, 279.
Jahiliyya, The, 43.
Jardin des Plantes, see Jardin dn Roi.
Jar din du Roi, 128, 189, 190-?. '198,
208, 250.
Journal dc Delametherie, 253.
Jundi-Shapur Academy, 48.
Kabbala, 108.
Khem, 35.
kibaltu, 15.
Kit ab al-Fihrist, 52.
krasis, 20.
Kufa, foundation of, 49.
kuhl, 14.
knraja, 79.
Laboratories, early chemical, 118.
Laboratory, Berzelius's, 2412.
Latin alchemical terms, adopted
from Arabic, 1012.
works of Geber, 60-3.
works on alchemy, many spurious,
88.
Law of ConstantComposition, 236-7.
of Multiple Proportions, 236-8.
of Octaves, 266-8.
of Partial Pressures, 224.
of Reciprocal Proportions, 236, 239.
of the Combination of Gases by
j Volume, 251.
' of the Conservation of Matter, 230,
2 3 6 /.
Laws ot Electrolysis, 286.
Lead, 5, 74, 264.
acetate, 37.
isotopes of, 301.
oxide, 13.
Leyden Papyrus, 29-32, 103.
Libellus de Alchimia, 91 .
Liber igmum, 103, 104.
Light, 263.
Lime, 13, 264.
Limestone, nature of, 167-9.
Litharge, 37, 58, 148.
Magic, 34.
Magnesia, 264.
magnesia alba, 167-8, 197.
Malleus Maleficarum y 273.
Manganese, 264.
dioxide, 14, 59, 188.
Manuscript, of Rouelle's lectures,
Subject Index
Mappae Clavicula, 103.
Marble, 12.
Marcasite, 14, 59.
marhaSi, 15.
Marine acid, 188.
Mechanical mixture, 20, 21.
Mercuric oxide, 78-9.
Mercury, 73, 264.
Bartholomew on, 100.
from cinnabar, 37.
preparation from minium (cinna-
bar), 101.
used in pneumatic trough, 163,
179, 180.
Mercury-sulphur theory. See sul-
phur-mercury theory.
Mercy, The Book of, 60.
Meshed, 50.
Metal industry, Babylonian, 15.
Metallic calces, composition of, 207.
Metallurgists, Egyptian, 310.
Metals, acted upon by sulphuric acid
179.
constitution of, 57, 72, 73, 146.
genesis of, 19.
Meteorologica, 16, 19, 78.
Methode de Nomenclature Chimique,
214, 216.
methridatic, 109.
Minerals, Book on, 90.
Minerals, classification of, 89, 90
formation of, 72.
genesis of, 19.
Mines, Egyptian, 3.
Minium, 177.
mix is, 20.
Moh's scale, 14.
Molecule, 2537.
Molybdenum, 264.
murium, 263.
Muslim Chemistry, review of, 82-4.
Names, 'kitchen', ridiculed by
Dumas, 215.
namrutu, 14.
Natron, 10, 38.
natrun, 68.
Natural History (Pliny), 27.
Neo-Platonism, 33, 34.
Neo-Platonists, 108, 114.
New System of Chemical Philosophy,
224, 230, 252.
Nickel, 264.
Nitre, 195.
Nitric acid, 77, 207, 209.
composition of, 1846.
discovery of, 60.
'Nitric acid' (nitric oxide), 238.
Nitro-aerial spirit, 156, 158.
Nitrous air, 209.
ammomacal salt, 195.
gas, 238.
oxide, 238.
Nomenclature, principles of, 215-17.
revision of, 21317.
nub (gold), 6.
nub-en-mu, 9.
nub-en-set, 9.
Nucleus, 2967.
Numbers, mystical powers of, 34.
Nymphs, 1 14.
Octaves, Newlands', 2668.
Olefiant gas, 226, 228, 230, 238.
Op ticks, 219.
Opus Tertium, 94, 104.
Organic analysis, 2745.
Chemistry, rise of, 273-84.
compounds, 2734.
Ortus rnedicinae, 120.
Oxalates of potassium, 228, 238.
Oxygen, 24, 156, 208, 263.
and phlogiston theories contrasted,
209.
Oxygen, explosion with hydrogen,
182-3.
theory, Lavoisier's claim to, 212.
Oxymel, 52.
Oxymuriatic acid, 242.
Particles of Gold, 76.
parzel, 15.
parzillu, 15.
Pearls, artificial, 10.
Pelican, 214.
Periodic System, 26873.
anomalies in, 2723.
Table, 271.
Peripatetic theory, of the elements,
133-
Perizzites[? Metal-workers], 15.
Persian influence, on alchemy in
Islam, 46.
Pharmacology, Persian, 67-8.
Philosopher's stone, 39, 40, 109, 122,
I2 4-.
Philosophical Transactions, 178, 280.
312
Subject Index
Phlogiston. 146 ff., 179, 183, 1 88.
Lavoisier's attack on, 210.
negative weight of, 153.
theory, 20, 58, 146-54, 169, 171-7.
fall of, 197-213.
Phosphorescent substances, 104.
Phosphoric acid, 207.
Phosphorus, 263.
combustion of, 200 i .
Physica Auscultatio, 78.
Physical Chemistry, rise of, 284-9.
Physica Subterranea, 144, 146.
Platinum, 264.
plombe rouge, 177.
Pneumatic Chemistry, 158-63.
trough, 121 .
evolution of, 160-3.
Polarity of atoms and groups, 261-3.
Potassium, 261.
carbonate, 68, 179, 216.
sulphate, 194.
powder of Algaroth, 215.
precipitate per se, 177.
prima materia, 16.
Prime matter, 97.
Principia, 220, 224.
Principle acidifying, 208.
oxygine, 208.
Principles, Lemery's, 130.
Paracelsan, 134.
Probierbuechlein, 77.
Properties of Things, On the, 98.
purple of Cassius, 14.
Pyrites, 15.
Pyrolusite, 188.
Qali, 68.
qambar, 46.
Qualities, Aristotelian, 16.
doctrine of, 135.
Quicklime, used as depilatory, 68.
Quintessence, 109.
Book of, 104.
Radical Theory, Book of, 104, 276-7.
Radioactivity, 290-1, 295-6, 301.
Radium, 290, 299.
emanation, 296.
Radon, 296, 299.
Rare gases, in Periodic System , 272-3 .
Rays, 290-302.
Realgar, 72.
Recipe-book, thirteenth - century,
105.
Reduction of calces, 58.
Refining-furnace, 80.
Reflexions sur Phlogistique, 207.
Refutation of alchemy, 74.
Relative masses of molecules, 253-7,
weights, 233.
of atoms (Dalton), 226.
Remedy, The Book of the, 70, 91.
Respiration, 175.
Rome, chemistry in, 27-9.
Rotisserie de la Heine Pedauque, 114.
Rouen-green, 105.
Sabians, 48.
sadanu, 14.
Sage's Step, The, 77-80.
sal Alembroth, 215.
Salamanders, 114.
Sal-ammoniac, 72, 195.
sal nit rum, 156.
Salt, middle, 194.
neutral, 194-6.
'salty', 194.
Saltpetre, 188.
Salts, 72.
acid, 195-6.
perfect, 195.
Rouelle's work on, 194-6.
sandarach, 14, 37.
Sapphire, 14.
Sausages, Kekule's, 281.
Sceptical Chymist, 137, 140.
Sciences, handmaids of Theology,
94.
Scientific method, 134.
Sea-salt, 195.
Secrets, Book of, 64.
Seventy, The Book of, 60 i .
shadana, 14.
Shi'ites, 50.
Sicily, a centre of learning, 84.
Silica, 13, 122, 264.
Silicic acid, 68, 122.
Silver, 12, 73, 264.
chloride, 196.
extraction by amalgamation, 77.
recovery by amalgamation, 80.
separation from lead, 79.
Silver-mountains [? Taurus], 12.
Simple substances, table of, 2634.
Sindu arqu, 14.
siprn, 14.
Soap, 10.
Soda, 58.
Subject Index
Sodium carbonate, 68.
discovery of, 261.
"sesqui-carbonate, 10.
sulphate, on electrochemical
theory, 262-3.
Solutions, nature of, 286-9.
physical properties of, 2869.
Song of Solomon, 2.
Souls, 59.
Spain, transmission of knowledge in,
84, 86, 87.
Specific gravity, 83.
Specimen Becherianum, 146.
Spirit of salt, 179, 1 88.
Spirits, 59.
Stannic chloride, 118.
Steel, 59.
Stockholm Papyrus, 29-32.
Stones, 72.
Structure of the Atom, 290-302.
Sulphur, 72, 263.
dioxide, bleaching action of, 1 1 1 .
Sulphuric acid, 118, 149, 207, 209.
action on metals, 179.
Sulphur-mercury theory, 57, 81, 83,
90, 97, 100, 11415, 118, 143.
Sulphurs, 72.
Sum of Perfection, 60 i .
Summary of a Course of Chemical
Philosophy, 257.
Sylphs, 114.
Symbols, 216, 242-8.
Dalton's, 226, 243.
of Ber/ehus, criticized by Dalton,
246.
Sympathetic properties, 34.
Synthesis, 20, 282-3.
Syrian translators, 48.
Syrup of violets, 196.
System of Chemistry, 224.
Tabarmaq of Khurasan, 75.
tabashir, 68.
Tao-ism, 24.
Technical Tradition, 98-106.
Tellurium, 270, 273.
terra lapida, 146.
terra mercurialis, 146.
terra pinguis, 146.
Testament of Geber, 60.
Textbook of Organic Chemistry, 280.
Theorie des Proportions Chimiques,
244.
Theory of Substitution, 277.
of Types, 277.
theriac, 109.
Thorium, radioactive degradation of
301.
Timaeus, 23.
Tin, 5, 73, 264.
calcination of, 201-4.
cry of, 74.
origin of, 38.
oxide, 14.
Tincture of the Philosophers, no.
Translators, of Arabic works, 84-6.
Transmission of alchemy to Islam,
46.
Transmutation, 19, 24, 36, 83, 103,
122.
disbelief in, 63.
scepticism concerning, 73-6, 90, 91.
Treatise on Chemistry, 200.
Treatise on Instruments and Furnaces
(Zosimos), 35.
Treatise on the Alembic with Three
Beaks (Zosirnos), 35.
Tria prima, 114, 118, 120, 133, 134,
138.
Triads, Dobereiner's, 264-5.
Tungsten, 264.
turbith mineral, 215.
Tus, 50.
Types, 277.
uhulu, 14.
Umayyads, 50.
Universal Matter, 130.
Uranium, radioactive degradation of,
301.
Valency, 280.
indication of, 281.
of carbon, 280.
Vegetable Staticks, 161.
Verdigris, preparation of, 105.
Vermilion, 105.
Virtue, Book o/(Zosimos), 35.
Vital air, 207.
force, 275.
Vitriol, 72, 73, 103.
oil of, 130-1
Vitriolated tartar, 194-5.
Vitriols, in.
Volatile alkali, 195.
Voltaic pile, 259.
Volumetric analysis, 259.
Subject Index
Water, 16-20.
as sole primitive element, 120.
composition of, 180-4.
electrolysis of, 259.
formula of, 232-3, 256.
Water-bath, i.
Water-glass, 122.
Waterproofing cloth, 59.
Weighing, Arab accuracy in, 83.
Weight, oldest known, 12.
White lead, 37,68.
] X-ray spectrometer, 292-4.
spectrum, 294.
X-rays, 291 ff.
Yang, 24.
yin, 24.
Zarnikh, 46.
Zeitschnjt fur physikahscJie Chemie t
286-7.
Zinc, in, 264.
PKINTLD IN GREAT BRITAIN' \T I HE LNIVPRSITY PRPSS, OXFORD
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