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MEMORIAL LECTURES 



DELIVERED BEFORE 



THE CHEMICAL SOCIETY 



1901-1913 



BV 



Sir HENRY A. MIERS. 
ProfeHsor J. H. VAN'T HOFF. 
Professor W. H. PERK IN. 
Sir EDWARD THORPE. 
Professor F. WIOGLESWORTH 
CLARKE. 



Sir WJLLIAM A. TILDEN. 
Professor H. B. DIXON. 
Sir WILLIAM RAMSAY. 
Sir OLIVER LODGE. 
Professor J. WALKER. 
Professor F. S. KIPPINO. 



VOLUME II 




LONDON : 

GURNEY & JACKSON, PATEBNOSTER Row 
1914 



CONTENTS 



13. THE RAMMELSBERG MEMORIAL LECTURE. By Sir 

HENRY ALEXANDER MIERS, F.R.S. (Delivered on December 
13th, 1900). 

14. THE RAOULT MEMORIAL LECTURE. By JACOBUS HENRICUS 

VAN'T HOFF, F.R.S. (Delivered on March 26th, 1902). 

15. THE W1SLICENUS MEMORIAL LECTURE. By WILLIAM 

HENRY PERKIN, jun., F.R.S. (Delivered on January 25th, 
1905). 

16. THE CLEVE MEMORIAL LECTURE. By Sir THOMAS EDWARD 

THORPE, C.B., F.R.S. (Delivered on June 21st, 1906). 

17. THE WOLCOTT GIBBS MEMORIAL LECTURE. By FRANK 

WIGGLESWORTH CLARKE. (Delivered on June &rd, 1909). 

18. THE MKNDELEEFF MEMORIAL LECTURE. By Sir WILLIAM 

AUGUSTUS TILDEN, F.R.S. (Delivered on October 21**, 1909). 

19. THE TIIOMSEN MEMORIAL LECTURE. By Sir THOMAS 

EDWARD THORPE, C.B., F.R.S. (Delivered on February tfth, 
1910). 

20. THE BERTHELOT MEMORIAL LECTURE. By HAROLD BAILY 

DIXON, F.R.S. (Delivered on November 23rd, 1911). 

21. THK MOI8SAN MEMORIAL LECTURE. By Sir WILLIAM 

RAMSAY, K.C.B., F.R.S. (Delivered on February 29th, 1912). 

22. THE CANNIZZARO MEMORIAL LECTURE. By Sir WILLIAM 

AUGUSTUS TILDEN, F.R.S. (Delivered on June 26th, 1912). 



iv CONTENTS. 

23. THE BECQUEREL MEMORIAL LECTURE. By Sir OLIVER 

LODGE, F.R.S. (Delivered on October 17th, 1912). 

24. THE VAN'T HOFF MEMORIAL LECTURE. By JAMES 

WALKER, F.R.S. (Delivered on May 22nd, 1913). 

25. THE LADENBURG MEMORIAL LECTURE. By FREDERIC 

STANLEY KIPPING, F.R.S. (Delivered on October 23rd, 1913). 







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[To face p. 1. 



MEMORIAL LECTURES 



DELIVERED BEFORE 



THE CHEMICAL SOCIETY, 



RAMMELSBERG MEMORIAL LECTURE. 

(DELIVERED ON DECEMBER 13TH, 1900). 

By H. A. MIERS, M.A., D.Sc., F.R.S., Waynflete Professor of 
Mineralogy in the University of Oxford. 

THE Chemical Society has recently become only too familiar with the 
death of foreign members of patriarchal age, otherwise it would be diffi- 
cult to realise that a chemist whose death took place last year was the 
friend and associate of Berzelius. The man whose life and work we com- 
memorate to-day was an almost exact contemporary of another famous 
chemist whose great genius an4 high character have been recently 
depicted for us by his friend and fellow-worker. Rammelsberg was 
born two years later than Bunsen and outlived him by less than one 
year. 

Among the workers who during this period contributed to* raise 
the edifice of modern chemistry upon the foundations laid during the 
childhood of these two men, sjme, like Bunsen, were thinkers of the 
highest genius whose inspiring ideas directed the development of the 
structure, others, like Rammelsberg, were the skilful and indefatigable 
craftsmen who amassed and set in order the material. Owing to the 
fact that Rammelsberg's name is not associated with any of the great 
discoveries of a period which belongs mainly to organic chemistry, and 
that he purposely confined his life-work to inorganic research, uhere 
is some danger lest the value of his contributions to science should be 
underrated, except, indeed, among mineralogists \ I am, therefore, 
particularly glad to have this opportunity of sketching a brief record, 
however imperfect, of his colcssal labours. It will be made clear, I 



2 MIEBS : RAMMELSBERG MEMORIAL LECTURE. 

hope, that, although brought up in the school of Berzelius, IJammelsberg 
was by no means one who ignored the progress of the modern chemistry, 
but did, in fact, contribute in no small degree to its dissemination. 
To those among the younger generation of organic chemists who know 
anything of his work, the name of Rammelsberg will, I imagine, evoke 
the recollection of a vast number of papers whose titles relate to 
mineral and other inorganic analyses and to crystallographic measure- 
ments ; they may only, know hiin*as a patient worker and think of 
him as one who pursued his labours undisturbed by the growth of 
modern chemistry. This would be a very false estimate, and in order 
to dismiss such a misconception at the outset, I cannot do better than 
quote the words addressed to Rammelsberg on the occasion of his 
Doctor's Jubilaum, I believe by Hofmann, on behalf of the Berlin 
Academy of Sciences. After describing his labours in practical 
chemistry, he says, "It was not only the empirical but also the 
theoretical side of science which attracted your lively attention. 
Originally brought up in the school of Berzelius, and the contemporary 
of Heinrich and Gustav Hose, of Mitscherlich and Wohler, you subse- 
quently witnessed all the changes which chemical theory has ex- 
perienced up to the present day. With a quick eye you recognised 
early the advantages of the present views and you were among inorganic 
chemists the first to adopt the new system of formulas" 

While I am glad that it has fallen to my lot to recall these features 
of his life-work, I regret that I never had the opportunity of even seeing 
the man whom I have to describe. Whatever impression of his life and 
work I may succeed in conveying is derived solely from a study of his 
publications or from the reminiscences cf others to whom he was 
personally known ; and he was a man who more than any other led 
the uneventful laborious life of a student. 

Among the day dreams to which most persons have yielded, is the 
fascinating speculation as to what would have been their lot had their 
life been set in earlier times. Could any chemist choose for himself a 
more attractive period than the early part of the nineteenth century, 
when the influence of Berzelius had entered into the heart of the science ? 
In the youth of Rammelsberg, the electro-chemical theory had over- 
come all opposition and supplied a great principle of apparently 
universal application; the modern methods of analysis were being 
perfected ; and the chemist was for the first time really equipped for 
conquest in the fields of research. It is a commonplace of historical 
criticism that in the early history of any art there is a period when 
the materials, the instruments, and the methods have just been 
matured, although the art has not become self-conscious ; when the 
artist revels in his newly-acquired powers, and finds a pleasure in the 
exercise of the chisel or the brush without any thought of whither 



MIERS: BAMMELSBERG MEMORIAL LECTURE. 3 

his work tends or what purpose it is to serve. Something analogous 
happens, I think, in the early history of a science, and at the time 
when Rammelsberg began to work, a chemist must have felt that 
every analysis which he could make, every substance which he could 
prepare, was something new, of unknown import, and involved the 
exercise of new powers. To a young, ardent, and ambitious student, 
this in itself must have been an overpowering impulse to energetic 
labour; in no life is. this delight in work better exemplified than in 
that of Rammelsberg. 

Karl Friedrich Rammelsberg was born on April 1st, 1813, at 
Berlin. He was of humble origin, and was entirely a self-made man ; 
his family came from Altenbrak au der Bode in the Harz ; his father 
was in quite a small way of business in Berlin. As a boy he was 
educated in a private school, and in the Friedrich Werder Gymnasium ; 
he then entered the Realschule, in the Kochstrasse, where he seems to 
have received some little scientific training from the director, Spillecke. 
Here he remained for four years, and leaving at the age of 15 entered 
the Koch Apotheke, where he studied for the next four years, with 
the view of becoming an apothecary. In this Apotheke he seems 
to have learnt botany from Hayne and pharmaceutical chemistry from 
Heinrich Rose ; under the latter., Rammelsberg must have first become 
acquainted with the spirit of scientific research, and he himself says 
that he never forgot the teaching of this man, from whom he received 
such varied and valuable assistance. In 1832, at the age of 19, he 
obtained a place in the Apotheke at Dardesheim, near Halberstadt. 
After remaining there only one year, the young chemist took the step 
which determined his whole future career ; he suddenly abandoned 
the line of life upon which he had entered, and returned to Berlin with 
the object of obtaining a university education and devoting himself to 
pure science ; this step was probably taken by Rose's advice : it must 
have required great determination for a lad of his education and 
antecedents to enter this new world, and compete for the distinctions 
gained by men of the calibre of Mitscherlich and Heinrich Rose. In 
order to pass in the necessary examinations in Latin and Greek, he was 
obliged to teach himself unaided the latter language. This was 
accomplished at odd moments and in the intervals between other 
studies. In 1834, he was able to pass his Maturitatsexamen at 
the Gymnasium zum grauen Kloster, and was matriculated. Erman 
and Magnus were at this time the professors of physics, Mrtscnerlich 
and Heinrich Rose of chemistry, Weiss and Gustav Rose of mineralogy ; 
with all these he worked, as well as with Hoffmann in geology. His 
Arbeit was carried out in Mitscherlich' s laboratory and was a 
dissertation entitled " De cyanogenii connubiis nonnullis " (1837). 
The titles of his four doctoral theses are interesting in the light 

2A 



MIERS : RAMMELSBERG MEMORIAL LECTURE. 

ot the researches to which he devoted the remainder of his life ; they 
were entitled : 

(1) Experientia chemica in constituendis theonis geologicis praecipue 
est observanda. 

(2) Connubia chemica organica et inorganica .baud absolute 
discerni possunt. 

(3) In systematibus, qua* hucusque exstiterunt, chemicis theoria 
deflagrationis summum tenet locum. 

(4) Systema mineralogicum naturale neque indolem externam neque 
internam fossil ium negligere debet. 

A man's early work is generally a clue to his subsequent tendencies, 
and Rammelsberg's theses are no exception ; his interest in inorganic 
chemistry and in substances like the cyanides, which lie on the border- 
land between the organic and inorganic ; his leaning towards the 
geological aspects of chemistry ; his life-long study of both the chemical 
composition and the crystalline form of minerals, are all foreshadowed 
in these titles. 

Three years later he began to teach at the Hochschule ; in 1841, he 
was " habilitated " as Privatdocent at the university,. and was also a 
teacher at the Handels-Schule. 

At the age of 24 (in 1837), he had already begun to publish analyses 
of inorganic compounds and minerals the opening of a long series of 
researches in inorganic chemistry and mineralogy, many of them 
lengthy and laborious memoirs, which issued in an unbroken stream 
from 1838 to 1888. 

When he became Privatdocent there were only two laboratories in 
Berlin where a student could work, namely, those of Heinrich Rose and 
Mitscherlich, and in these only a few specially recommended pupils 
could find a place ; Rammelsberg, therefore, with characteristic energy, 
started a private laboratory of his own in which all his earlier pupils 
must have obtained their experience ; it was so small that only two 
students could be accommodated at a time, and when one pair went off 
a second pair came on ; the fee was the ridiculously small one of 50 
pfennigs. With this scanty help, he was also able to assist his mother 
to support herself. 

This small beginning was really the initiation of practical 
laboratory instruction in Berlin, and was the seed from which sprang 
thesecond chemical instituteof which Rammelsberg was ultimately made 
the first director. His time must have been very fully occupied, and 
yet not only did the publication of scientific papers continue unabated, 
but he began to add to them the first of a series of text-books and of 
monumental works of reference : in 1841 his dictionary of chemical 



MIERS : RA.MMELSBERG MEMORIAL LECTURE. 5 

mineralogy, in 1842 his text-book of stochiometry and theoretical 
chemistry. In a very short time he became a recognised authority on 
chemistry, mineralogy, crystallography, and metallurgy. 

In 1846, he was appointed Professor extraordinarius of inorganic 
chemistry, and in 1850 he was also made instructor in chemistry at 
the Gewerbe-akademie, where he was at last provided with an adequate 
chemical laboratory ; this academy ultimately developed into that 
splendid institution, the Technische Hochschule of Charlottenburg. 
He was. also instructor at the Mining Acadeay from the time of its 
foundation in 1860. In 1855, he was made a member of the Berlin 
Academy. 

It was not until 1874 that Rammelsberg attained the full recognition 
of his labours and was made ordinary Professor of inorganic chem- 
istry (in succession to Heinrich Rose), a position to which he had 
raised himself from a lowly origin and by the exercise of the most 
extraordinary industry. 

In 1846 he married the daughter of a man well known in the 
history of mineralogy, Oberbergrath Zincken, of Magdesprung. 

He took an active part in the foundation of the Berlin Chemical 
Society in 1868, and was its President in 1870 and 1874. 

From the impression which I have derived from those who knew him, 
he must have been a man of unusually short stature, energetic 
carriage, and somewhat austere manner ; an early photograph 
represents, by the sharply-cut features, the keen eye, and the com- 
pressed lips, a man of precision and determination ; he was clear and 
concise as a lecturer ; a very quick but accurate worker ; sharp in 
exposing the mistakes of others, but equally ready to learn from them 
and correct his own errors. 

Professor Liveing, who worked in his laboratory at the Gewerbe- 
akademie in 1852, kindly allows me to quote his recollection of that 
period. He regards Rammelsberg' s asperity of ma iner as due to his 
" habit of expressing himself in few words ; words however, which 
were always to the point, and expressed his meaning clearly." "He 
gave me the impression," he says, "of having a mathematical mind, 
and of being very accurate. His laboratory was, by comparison with 
those of the present date, a makeshift one ; nevertheless, good work 
could be done there, but the appliances required for a research had, 
for the most part, to be extemporised. He was, however, more ready 
than many to adopt improved methods and apparatus. When I first went 
to his laboratory we had no gas, and had to use spirit lamps, and 
charcoal braziers for heating, but while I was there he introduced gas 
and other improvements ; and I well remember that Mitscherlich 
remarked to me that so doing was a mistake, because the greater part 
of Rammelsberg's pupils would be dispersed in after life in places 



6 MIERS : RAMMELSBERG MEMORIAL LECTURE. 

where they could not get gas, and, would find themselves in difficulty 
because they could not command the resources they had learnt to 
depend on. Another point about him was that he did his work him- 
self. He had no assistant in research when I was with him. He 
had, of course, some of the more advanced students who acted as de- 
monstrators to the younger ones, and he used the results which his 
pupils obtained as checks to his own work, but that work, so far as I 
saw, was essentially his own. How it may have been afterwards I 
cannot say, but I think it was in his character to be very indepen- 
dent, and more desirous of doing good than of making a great show. 
He may have been a disappointed man ; his manner, rather suggested 
that, and his way of speaking of some of his contemporaries was perhaps 
a little cynical." 

It must be remembered that the time of which Professor Liveing 
writes was twenty years before Rammelsberg's labours were crowned 
with full recognition on the part of the university, and it is pretty 
certain that his rising claims for a long time met with constant opposition 
in Government circles. On the other hand, he was by no means a man 
whose efforts were directed to personal advancement, and whether he 
met with promotion or neglect, assistance or opposition, he was 
inspired by a single-hearted devotion to science, which impelled him 
to unremitting labour and research. 

Private appreciations and reminiscences are always more impressive 
and trustworthy than such as are written for publication, and I am glad 
to have the permission of Professor Wolcott Gibbs (himself now one of 
our oldest foreign members), who was his pupil in 1845, to quote from a 
letter which he wrote to his old teacher forty years afterwards. 
" Many, many years have passed since I entered your laboratory as a 
pupil, but I well remember the pleasant afternoons that I spent with 
you, and the kind and friendly interest which you showed in my 
instruction. The very room is fresh in my mind's eye, and I 
remember the names of the three Greek students who were my fellow 
pupils. Since then, your own noble example of earnest, constant work 
nas always been before me. Of the'many noble men whom I learned 
to know in Berlin, you, I believe, alone remain ; Poggendorf, Heinrich 
and Gustav Rose, Magnus, Dove, Riess, Johannes Muller, have 
gone. You presented me to Berzelius on the day of the dinner to him, 
and I sat next to you at table, when you spoke so well * im Namen der 
jiingeren Chemiker.' In all these years the memory of my first teacher 
in analytical chemistry "has always been cherished." 

"With reference to this occasion and the memorable visit of Berzelius, 
Professor Wolcott Gibbs writes to me : " Many German professors and 
chemists and physicists were present. Among them Jacob Grimm. 
Several speeches had been made, when Rammelsberg asked me how 



MIERS : RAMMELSBERG MEMORIAE LECTURE. 7 

they compared with speeches made on similar occasions in America. I 
told him they were admirable, but wanted what the French call verve, 
life and spirit. Then Rammelsberg rose, and made a more spirited 
speech, which was very well received." 

His skill as a raconteur is vividly in the minds of those who remem- 
ber those happy days of the Berlin University, when professors and 
students met together on terms of equality, and the latter had the 
opportunity of hearing the conversation of perhaps the most brilliant 
intellectual society in Europe. Among those who entertained each 
other with reminiscences in the informal evening gatherings after the 
meetings of the Geological Society, none could be more interesting 
than Rammelsberg. 

His scientific character, I think, may be understood from his pub- 
lished works; he possessed an extraordinary industry, which was 
devoted to the acquisition of all possible knowledge, the addition of 
countless new facts to the fabric of chemistry and mineralogy, and the 
patient repetition and correction of any observations of others which 
appeared doubtful. He was singularly unbiassed by any precon- 
ceived theory, because he was singularly distrustful of all speculation, 
and with his industry was combined a remarkable power of accepting 
new views as soon as they were established, and of relinquishing his 
old ideas as soon as they were disproved. 

His first text -book (1842) is an exposition of the electrochemical 
theory, and only mentions the n'ew substitution theory of Dumas in 
order to reject it ; but, as a matter of fact, at that date he had himself 
published a translation of Dumas' lectures on the Philosophy of 
Chemistry, and a subsequent text-book which he published (1881) is 
called a " Sketch of Inorganic Chemistry according to the New Views." 
In the preface he uses the following words : " In the subject of 
organic chemistry has latterly been introduced a gradual reform of the 
older views, based upon general principles which underlie the whole 
science. Those who feel with the author that the modern way of 
regarding the facts is a real advance, must regret that there is no intro- 
ductory book available for beginners containing the elements of 
inorganic chemistry set forth according to the new views. The 
present outline, without laying claim to any merit, endeavours to 
supply this need. A supplementary section contains the modern 
laws, theories, and views so far as they relate to inorganic 
chemistry." 

lUmmelsberg was, indeed, one of the first of the chemists brought 
up in the old school to assimilate the new views and to disseminate 
them. He published a number of text-books which must have been 
largely used. His "Grundriss der anorganischen Chemie" ran through 
five editions ; of his "Leitfaden fur die quantitative chemische Analyse" 



8 MIERS : RAMMELSBEBG MEMORIAL LECTURE. 

four editions were published ; and of his " Leitfaden fur die qualitative 
chemische Analyse " eight editions. In addition to these were published 
a text-book of chemical metallurgy which ran through two editions ; 
a treatise on theoretical chemistry, one on quantitative metallurgical 
and mineralogical analysis, and the book already mentioned upon the 
new views of modern chemistry ; it must be remembered that the 
purpose of all these books was not only to supply the student with a 
practical handbook, but also to give him an insight into the newer 
developments of the science. 

Combined with his readiness to accept new ideas was an obstinate 
adherence to the line of work which he marked out for himself, and he 
never showed the least interest in the development of organic chem- 
istry or took any part in it. His real interest was, I think, in mineral 
chemistry, of which he was for very many years the most prominent 
exponent. It is perhaps well that there was one man of untiring in- 
dustry qualified to receive the torch of mineral chemistry from 
Berzelius and to keep it alive by his own patient researches during 
the fifty years when most chemists were attracted by the more dazzling 
discoveries of organic chemistry. 

We will turn now to Rammelsberg's own work. His contributions 
to science are so numerous that to give an intelligible account of 
them within a small compass is impossible. They range over the 
whole domain of inorganic chemistry and mineralogy, and consist 
mainly of the preparation and analysis of innumerable substances, the 
measurement and description of innumerable crystals ; references to 
them can be extracted from three of his books " Chemische Abhandlun- 
gen," published in 1888 ; " Handbuch der krystallographisch-physik- 
alischen Chemie," published in 1881 1882 ; "Handbuch der Mineral- 
Chemie," published 1875 1895. In the endeavour to convey some 
impression of the magnitude and thoroughness of his work and of the 
extent to which the increase of chemical knowledge in the second half 
of the nineteenth century is indebted to his untiring industry, I 
shall select a few of his memoirs in chemistry, crystallography, and 
mineralogy respectively, and let them stand as examples of his labours 
a more complete summary being obtainable in the three books which 
I have just mentioned. 



Rammelsberg as Chemist. 

In the region of general inorganic chemistry, we can take his in- 
vestigations upon the halogen compounds, the phosphates, and the 
cyanides. 

Halogen Compounds. Many of the metallic bromides and iodides 
had of course been already prepared, and bromic, iodic, and periodic 



MIERS : RAMMELSBERG MEMORIAL LECTURE. 

acids had been discovered, but the knowledge of the iodates and 
periodates was very limited at the time when Rammelsberg ook up 
their study. He prepared and analysed the bromides of bariutn, 
strontium, calcium, magnesium, zinc, cadmium, nickel, cobalt, lead, 
copper, mercury, and silver ; the bromates of potassium, sodium, am- 
monium, lithium, barium, strontium, calcium, magnesium, zinc, 
copper, silver, lead, aluminium, cerium, lanthanum, manganese, iron, 
nickel, cobalt, cadmium, bismuth, uranium, and mercury. 

The bromide of barium was found to contain 2 mols. of water and 
not 5, as stated by von Hauer ; measurement of the crystals showed 
them to be isomorphous with the chloride. 

But the most important part of the work was the study of the am- 
monia compounds of the bromides and iodides; these were prepared 
either by treating a concentrated solution of the salt with ammonia 
solution, or by heating the dry salt in a stream of ammonia ; by the 
former process were prepared ZnI 2 ,4NH 3 ; CdI 2 ,2NH s ; CoI 2 ,4NH 3 ; 
NiI 2 ,6NH 3 ; 2(CuI 2 ,4NH 3 ) + 3H 2 ; ZnBr 2 ,2NH 3 ; CdBr 2 ,2NH 3 ; 
NiBr 2 ,6NH 3 ; CuBr 2 ,3NH 3 ; by the latter process: ZnI 2 ,5NH 3 ; 
CdI 2 ,6NH 3 ; CoI 2 ,5NH 3 ; NiI 2 ,3NH 3 ; 2Cu[ 2 ,9NH 3 ; PbI 2 ,2NH 3 ; 
2AgI,NH 3 ; 2SrBr 2 ,NH 8 ; CaBr^NHgj CdBr 2 ,4NH 3 ; CoBr 2 ,6NH 3 ; 
NiBr 2 ,6NH 3 ; CuBr 2 ,5NH 3 . The composition of all these compounds, 
their crystalline form where possible, and their behaviour on heating 
and on treatment with water were studied ; it was shown that am- 
monia is liberated on heating, and that treatment with water breaks 
them up into hydroxides and basic salts together with ammonia, 
and into ammonium bromide or iodide. 

The mercury compounds were found to behave differently ; treat- 
ment of the solution of mercuric iodide with ammonia solution at the 
ordinary temperature yields a white, unstable compound, HgI 2 -f NH 3 , 
identical with that obtained by the dry process, but at a temperature 
above 60 a brown substance is formed which is stable and is not de- 
composed by potash ; this has the composition Hg 2 INH 2 0, and is 
analogous to the chlorine compound. The now well-known properties 
of this compound and its behaviour on heating were studied by Ram- 
melsberg, who regarded it as a mercuric ammonium iodide in which 
4 atoms of hydrogen are replaced by 2 of mercury. 

In 1888, he returned to the study of the ammoniacal mercury com- 
pounds, when he determined anew the composition of Millon's base, 
studied the fusible and infusible varieties of " white precipitate," and 
by the direct action of acids on Millon's base prepared the mercury- 
ammonium sulphate, nitrate, carbonate, phosphate, bromate, iodate, 
and periodate. 

The goneral investigation of bromates, iodates, aud periodates be- 
longs to his earlier research ; the bromates were prepared either by 



10 MIERS : RAMMELSBERG MEMORIAL LECTURE. 

precipitation of metallic salts with potassium bromate or by solution 
of the oxides or carbonates in bromic acid, and yielded salts ^of barium, 
calcium, strontium, Iad, mercury, and cadmium crystallising with 
1 mol. of water, the copper salt crystallising with 5, and the salts of 
magnesium, zinc, cerium, lanthanum, nickel, and cobalt crystallising 
with 6 molecules of water ; in addition to these, the bromates of 
potassium, sodium, ammonium, lithium, silver, aluminium, and mer- 
cury were prepared, also basic salts of mercury, bismuth, and uranium, 
while efforts to obtain the bromates of manganese and chromium 
were not successful. The isomorphism of the bromates of barium and 
strontium with the corresponding chlorates was proved by crystalline 
measurements. In the course of this investigation, Rammelsberg also 
prepared the auimoniacal bromates of zinc, copper, silver, nickel, and 
cadmium. 

The iodates had only been previously studied by Gay Lussac and 
Senillas ; Rammelsberg was led to their investigation by a desire to 
test the opinion of Gay Lussac that basic iodates of the alkalis exist. 
He found that this was not the case, but he proceeded to an exhaus- 
tive study of the iodates, in the course of which he prepared and 
studied the salts of ammonium, potassium, sodium, lithium, thallium, 
barium, strontium, calcium, magnesium, aluminium, cerium, man- 
ganese, iron, cobalt, nickel, zinc, cadmium, lead, tin, bismuth, copper, 
mercury, and silver, and several of the double salts. This included 
the crystallographic description of the trimorphoup potassium iodate, 
HKT 2 6 , the double iodate and chloride of potassium, and the double 
iodate and iodide of sodium ; it was shown that sodium iodate crys- 
tallises with 1 mol. of water above 5, and with 5 mols. of water below 
that temperature ; the crystalline form of the latter salt was deter- 
mined, and it was found that the one substance may be converted into 
the other by change of temperature. 

The ammoniacal iodates of nickel, zinc, and copper were also suc- 
cessfully prepared. 

Continuing the research further, Rammelsberg made unsuccessful 
attempts to prepare perbromic acid and perbromates, and then turned 
his attention to the periodates. Periodic acid had been discovered in 
1833, and a few of the salts had been examined when he took up 
the subject ; he had already shown that among the iodates the potass- 
ium salt is the only one which is not converted into a periodate by 
heating, and in 1838, and again in 1869, he made a special study of 
the behaviour of the iodates and the periodates at high temperatures ; 
this inquiry included the iodates of potassium, sodium, barium, 
strontium, calcium, and the periodates of potassium, sodium, lithium, 
barium, silver, and magnesium. He found that the white, infusible 
residue which remains after evolution of iodine and oxygen is not a 



MIERS: RAMMELSBERG MEMORIAL LECTURE. 11 

mixture of oxides, but contains iodine. With considerable difficult} 
(by determining the volume of the oxygen liberated), it was proved thai 
in the case of the barium salt this is essentially the substance R" 5 I 2 12 , 
or, as it was then called, funftel-iiber-iodsaures JBaryum ; the existence of 
these compounds Rammelsberg afterwards confirmed by preparing them 
in other ways; The result of his laborious study of these compounds, 
which he made entirely his own, was to supplement, correct, and com- 
plete the work of Magnus, AmmermUller, and Langlois, and to estab- 
lish the whole series of periodates R'IQ 4 ; R' 4 I 2 9 ;. R' 3 I0 5 ; R' 8 I 2 O n ; 
B',IO, 

The very exhaustive research upon the halogen compounds, of which 
the above is a very brief sketch, may be taken as an example of 
Rammelsberg' s chemical work. He was not one of those lofty spirits 
who make a great discovery or are possessed ..by a great idea which 
leads them on from one intellectual triumph to another ; but he was 
dominated by a restless zeal for research which made him quick to see 
the weak points in the investigations of his predecessors, and to mark 
the missing links in the chain of their researches. This led him at 
once to take up some piece of work which should either correct or 
confirm what had gone before, and then his untiring industry tempted 
him on to make the research as complete as possible. 

This seems to me to have been the history of many of his investi- 
gations, and is a clue to the scientific character of the man. No 
difficulty was too great for him, no research was too laborious ; having 
set his hand to the plough there was to be no turning back until the 
work was finished to his own satisfaction, although from a more 
modern point of view his limitation of the problem might often 
appear narrow and his vision of its possibilities circumscribed. 

When we take into account that a man imbued with this spirit 
has worked with unceasing industry for 60 years, we should perhaps 
scarcely wonder that his discoveries were so numerous and his know- 
ledge so wide. If a complete catalogue were made of the actual facts 
added to the store of chemical knowledge by Rammelsberg, the result 
would be amazing by its magnitude. 

We must also remember that his independent spirit caused him 
always to work alone and to master every branch of his research him- 
self. There were few men in Europe between 1840 and 1870 whose 
practical knowledge of chemistry and crystallography was sufficient 
to achieve what was accomplished by Rammelsberg. 

Phosphates. It will be sufficient to glance still more briefly at his 
researches upon the phosphates and the cyanides, and only in such a 
manner as to illustrate two other features of his character. 

Having taken up a problem which was limited in itself, Rammels- 
berg was often led on by it from one research to another in his desire 



12 MIERS : RAMMELSBERG MEMORIAL LECTURE. 

to complete the work. This was the case with the particularly diffi- 
cult work upon the phosphates. 

In the course of his mineral analyses he had examined the blue 
phosphate of iron known as vivianite, which had always been re- 
garded as a ferric phosphate. Rammelsberg discovered that this 
mineral contained both ferrous and ferric phosphate ; his analysis led 
to the formula 

2[3Fe 3 (P0 4 ) 2 + 2Fe 2 (P0 4 ) 2 ] + Fe 2 (HO) 6 + 49H 2 0, 

but, since the crystals appear to be isomorphous with the cobalt 
arsenate, Co 3 (As0 4 ) 2 + 8tI 2 0, he concluded that vivianite was 
originally a ferrous phosphate, Fe 3 (P0 4 ) 2 + 8H 2 0, which by exposure 
to the air has become partly oxidised to a basic ferric salt. Rammels- 
berg was never content to express a view without searching patiently 
for all the evidence which might justify, or if adverse might lead him 
to modify, his opinion, and accordingly in this instance he proceeded 
to investigate the oxidation product of artificial ferrous phosphate, 
and so confirmed his theory. Its truth was still more firmly 
established, some years later by the actual discovery in a sand at 
Delaware of a colourless vivianite which Fisher showed to be a pure 
ferrous phosphate corresponding exactly to the cobalt arsenate in com- 
position. He also determined the composition of the ferric phosphate 
prepared from iron-alum and disodium phosphate, and showed how 
two basic salts can be derived from it. 

In the same way, his study of the minerals wagnerite, lazulite, 
and amblygonite, the last-named a phosphate of aluminium, lithium, 
sodium, and potassium- containing fluorine, which he himself regarded 
as one of the minerals most difficult to analyse, and whose composition 
he was the first to determine (1845), led him to work upon the phos- 
phates of magnesium and aluminium. He proved the gelatinous pre- 
cipitate yielded by concentrated solutions of magnesium sulphate and 
disodium phosphate, after washing in the cold, to have the composition 
HMgP0 4 + 3H 2 0, while the filtrate yielded Graham's crystallised 
hydrate, HMgP0 4 + 7H 2 O ; by treatment with boiling water, the 
normal salt, Mg 3 (P0 4 ) 2 + 5H 2 0, is obtained. A study of the gelatinous 
precipitate obtained by mixing solutions of alum and disodium phos- 
phate led him to the conclusion that the substance A1 2 (PO 4 ) 2 may 
contain either 9 or 6 mols. of water. 

The lithium phosphates, both mineral and artificial, were the sub- 
ject of repeated research on his part ; none had been quantitatively 
analysed with the exception of the sodium lithium salt ; Rammelsberg 
proved the existence of the three salts Li 3 P0 4 + aq, H 2 LiP0 4 , 
H 5 Li(P0 4 ) 2 + aq. He further investigated the double salt of di- 
and tri-lithium phosphate, the sodium lithium phosphate, and the 



MIERS : RAMMELSBERG MEMORIAL LECTURE. 13 

lithium pyrophosphate ; showed the precipitate obtained from one 
molecule of Na 4 P 2 7 and six molecules of lithium acetate to be an 
isomorphous mixture containing varying proportions of sodium and 
lithium, and found that the acid pyrophosphate, H 2 Li 2 P 2 7 , could not 
be obtained in a pure condition. 

His investigations on the phosphites were undertaken with the 
object of ascertaining the basicity of the acid. H. Rose had studied 
the behaviour of the phosphites on heating, and (like Berzelius) had 
found them to have the composition 2RO,P 2 3 , but to contain various 
proportions of water, the barium, strontium, and calcium salts having 
2 mols., and the lead and manganese salts only 1 mol. of water 
of constitution, so that they were to be referred to the two acids 
R 2 H 4 P 2 7 and RHP0 3 . Wurtz, on the other hand, regarded them all 
as neutral salts containing 1 mol. of water. The controversy turned 
mainly on the composition of the phosphite of barium which Rose 
had found to be H 4 Ba 2 P 2 O r , while Wurtz regarded it as HBaP0 3 . 
Rammelsberg repeated the analyses, and found the lead salt to be 
HPbP0 8 and the barium salt to be H 4 Ba 2 P 2 Q 7 , thus confirming the 
results of Rose and Berzelius. 

Having found that oxidation of barium phosphite with nitric acid 
yielded a mixture of oxide, metaphosphate,and pyrophosphate, he was led 
to investigate anew the phosphites of strontium, calcium, magnesium, 
zinc, manganese, nickel, cobalt, cadmium, lead, copper, and iron, 
especially as regards their behaviour on heating. As the result 
of these investigations, he concluded that there are three phos- 
phorous acids, H 3 P0 3 , H 8 P 2 7 , and H 5 P0 4 , derived from the union 
of H 4 P 2 5 with 1, 2, and 3 molecules of water respectively; 
to the first class belong the salts of potassium, sodium, ammonium, 
magnesium, zinc, cobalt, manganese, cadmium, lead, and copper; 
to the second, the salts of barium, strontium, calcium, magnesium, 
nickel, and zinc; and to the third the salt H 3 MgPO 4 . When 
Prinzhorn and Precht, in 1875, showed that the barium phosphite 
contained a certain proportion of phosphate, to which the incon- 
sistencies were due, Rammelsberg at once gave up all these views 
and convinced himself that the salt really has the composition 
HBaP0 3 , and that Wurtz was, after all, in the right. 

He subsequently undertook the study of the hypophosphites with 
the view qf supplementing the work of H. Rose and Wurtz, and of 
preparing as many of these interesting compounds as possible, especially 
for the purpose of a crystallographic investigation. He prepared and 
studied the hypophosphites of ammonium, sodium, thallium, lithium, 
barium, strontium, calcium, magnesium, zinc, manganese, cerium, 
cadmium, lead, cobalt, nickel, and uranium, and compared their iso- 
morphous relationships where they exist. 



14 3IIERS : RAMMELSBERG MEMORIAL LECTURE. 

When it is remembered that in this and many similar pieces of 
work Rammelsberg spared no pains in preparing, not only material 
for analysis, but also crystals which could be crystallographically 
studied with all the means at his command, and that the whole work 
of measurement and calculation was done by himself, one may well 
be surprised that even in his long life of activity so many of these 
researches were carried out. 

Cyanides. If our knowledge of the halogen compounds and of the 
phosphates, phosphites, and hypophospbites is largely derived from 
the labours of Rammelsberg, still more is this the case with the double 
cyanides. His work upon these began with his inaugural dissertation 
in 1837, of which the purpose was to complete the work of Gmelin, 
Wohler, and Ittner by the preparation of the potassium and cadmium 
double cyanides. 

It is scarcely necessary to recapitulate the long series of compounds 
which he prepared ; they have become a part of the edifice of inorganic 
chemistry, throughout the whole framework of which the handiwork 
of Rammelsberg is to be traced by those who care to look up the 
authorities for the accepted facts of the science. 

A large portion of the work was devoted to the behaviour of 
cyanides and double cyanides at' higher temperatures, to which he was 
led by Thaulow's discovery of paracyanogen and his work upon the 
decomposition of cyanide of silver by heat. He repeated these ex- 
periments and found that the so-called carbazote, obtained by heating 
cyanide of silver, differed in no respect from cyanogen ; his further 
experiments upon the double cyanides were chiefly devoted to the 
determination of the nature of the distillation residues obtained on 
heating. 

Upon the subject of the double cyanides, Rammelsberg held very 
decided views, and expressed himself as strongly opposed to the ferro- 
cyanogen theory of Porret and Liebig. His position is perhaps best 
stated in his own words, which will serve to illustrate the clear and 
direct character of his statements, and also, perhaps, the prejudices by 
which his views were limited : 

"According to the ferrocyanide theory, Prussian blue is not 3FeCy 2 + 
2Fe 2 Cy 6 , but Fe 4 ,3FeCy 6 . Gmelin's blue is not 3FeCy 2 +Fe 2 Cy 6 , but 



(Rammelsberg always in his teaching preferred to use the name 
'* Gmelin's blue " in place of "Turnbull's blue.") 

* Now, as is well known, there are two other compounds, namely : 
"(1) KCy + FeCy 2 , which is separated when yellow prussiate of potash is 
heated with dilute sulphuric acid. According to the ferrocyanide theory, it 
would be treated as K 4 ,FeCy 6 +Fe 2 ,FeCy e . ; ^ ( tf C fi f 



MIERS : RAMMELSBERG MEMORIAL LECTURE. 15 

"(2) KCy + 2FeCy 2 , the red precipitate obtained from potassium cyanide 
and ferrous salts, which was investigated by Stadeler. If it is treated as 
K,Fe 2 Cy 6 , a third radicle must be assumed. The adherents of the ferrocyanide 
theory maintain that all double cyanides fall into two classes : 

" A. Simple haloid salts of a substance consisting of cyanogen and a metal. 
To this class belong the series 4KCy+RCy 2 , and the series 6 KCy+B 2 Cy 6 , 
and also from the series 2KCy-f-RCy 2 , the platinum and palladium compounds. 
In these tne following radicles must be assumed : 

KtJy 4 ; RCy 6 ; K 2 Cy 12 . 

' " B. Double salts. This includes the remainder of the series, 2KCy+RCy 2 , 
and also the salts of gold, silver, and copper. 

" But why should this difference of constitution be assumed ? 

" The salts of the first class (we refer in particular to the potassium com- 
pound) yield in solution with dilute acids at ordinary temperatures no prussic 
acid, as do those of the second class. 

" The reason why the former apparently suffer no decomposition is to be 
found in the formation of a corresponding hydrogen compound. 

" This action of acids, however, is limited to a portion of the salts. Whilst 
yellow and red prussiate obey the rule, and potassium cobalt cyanide behaves 
in the same way, my experiments show that the solution of potassium man- 
ganese cyanide, which decomposes of itself with liberation of manganese 
oxide, yields prussic acid freely with acids, and the same is true of potassium 
chromium cyanide. The hydrogen compounds prepared from the correspond- 
ing salts liberate hydrogen cyanide freely when their solutions are heated. 
The ferrocyanide theory assumes that here H 4 ,FeCy 6 is converted into 4HCy 
and FeCy a . 

" The potassium salts of ruthenium and osmium are also decomposed by 
acids with formation of the hydrogen compounds, whose solutions quickly 
liberate prussic acid and deposit RuCy 2 and OsCy 2 . 

" How different may be the behaviour of analogous and isomorphous salts 
towards acids is illustrated by K 6 Ir 2 Cy 12) which behaves like the red prussiate, 
while K 6 Rh 2 Cy 12 yields prussic acid and Rh 2 Cy^ 

" Hence the action of the cyanogen compounds with acids is not a sufficient 
reason for assuming two classes of different constitution. Their liability to 
decomposition varies greatly, and is weakest in the iron compounds. 

" Closely related to the behaviour of the double cyanides towards acids is 
their physiological action. But to adduce this action, which is limited to the 
experiment with potassium iron cyanide, in support of the ferrocyanide theory 
is wholly unjustifiable, for the physiological action of a chemical compound 
does not depend upon the nature and association of its elements. 

" If now the behaviour of the double cyanides towards acids is not such 
that it implies a difference in their constitution, but only indicates a more or 
less intimate union of the two components, which, in the compounds of zinc, 
cadmium, copper, &c., is admittedly so weak that the precipitates yielded by 
the potassium salt with other metallic salts are either of a different composition 
or merely mixtures, then the only support for the hypothesis of a ferrocyanide 
and other metallic radicles falls to the ground. 

"The behaviour of the double cyanides towards hydrogen sulphide or 
alkaline sulphides, the impossibility of precipitating the iron as sulphide from 



16 MIERS : RAMMELSBERG MEMORIAL LECTURE. 

prussiate of potash, which is adduced by some as a further support of the ferro- 
cyanide theory, is based upon an almost incredible ignorance of the facts. 

"It has long been known that potassium cyanide dissolves many of the 
metallic sulphides with production of potassium sulphide, 6KCy + FeS = 
4KCy + FeCy 2 + K 2 S. It is therefore self evident that alkaline sulphides 
cannot precipitate sulphide of iron from prussiate of potash." 

It is easy now to see how Rammelsberg failed to appreciate modern 
distinctions between double salts and salts of complex acids. I think 
that even his later papers take no account of contemporary work upon 
electrolytic dissociation. Neither did he pay any attention to the 
important aid afforded by the complex cyanides in the periodic classi- 
fication of the metals, especially the Fe, Co, Ni, and Pt group. Anc 
similarly in the halogen compounds there is no evidence that he 
would have attached much importance to the use made of the salts oi 
silver bromide with ammonia in developing the theory of dissociatioc 
by Joannis and Crozier and others. But, perhaps, this is unfaii 
anticipation, for his own researches belong to a much earlier period. 

Among the other large contributions to general inorganic chemistry 
must be mentioned Rammelsberg's researches upon the sulph- 
antimonates; he was the first to determine the Composition oi 
Schlippe's salt, and to prepare and study a great number of these 
compounds, and the potassium antimonyl sulphantimonate was oi 
special interest 60 years ago as the first instance of a double salt whose 
constituents have the same electropositive element ; he also undertook 
a laborious repetition of Rose's work upon tantalum and niobium, 
which had been called in question and partly disproved by Mafignac 
and Blomstrand, so that a complete revision was necessary in order to 
confirm what was right and to eliminate what was wrong. In Ram- 
melsberg's own words : " It seems an irony of fate that H. Rose, the 
discoverer of the volatile oxychloride of chromium, who proved that 
the supposed superchlorides of molybdenum and tungsten are oxy- 
chlorides, should himself have taken niobic oxychloride for niobic 
chloride (Unterniobchlorid). Similarly, as is well known, Berzelius 
took the vanadium oxychloride for vanadium chloride, as was first 
proved by Roscoe. Of Rose's results, all that relates to his Unter- 
niobsaure is correct, but his niobium compounds were mixtures, and 
his tantalum compounds were not free from niobium. Rose's memoirs 
are to be found in Poggendorff's Annalen, volumes 63 113. I have 
extracted from them all that is firmly established both now and for the 
future of the science (ibid., 136, 177)." /Mention only. can be made of 
Rammelsberg's researches upon ozone, upon the hyposulphites, the 
sulphites, nitrosulphonic acid, the nitrites, titanic acid, the vanadates, 
the phosphomolybdates, the salts of uranium, of thallium, of cerium, 
and of lithium, and his determination of the atomic weights of 



MlERS : RAMMELSBERG MEMORIAL LECTURE. 17 

molybdenum, cerium, lanthanum, uranium, and of the metals of the 
yttrium group. In the last-mentioned he strongly opposed the view 
of Nordenskiold that the atomic weight of these metals is nearly 
constant in the minerals which contain them. 

One of his important papers was communicated to this Society, 
*' Experimental Researches on the Amalgamation of Silver Ores " 
(Trans., 1881, 39, 374). Being engaged upon a translation of Percy's 
metallurgy into German, he was struck by the very imperfect ex- 
periments which had been made with the object of discovering the 
chemical changes which take place in the Mexican amalgamation 
or Patio process. With characteristic energy he made it his first 
business to repeat and extend these experiments, and to obtain 
for the first time quantitative results. He studied the action of 
cuprous and cupric chlorides on silver chloride, sulphide, arsenide, 
sulpharsenide, and sulphantimonide, and although it cannot be said that 
his experiments dispelled the mystery that surrounds the Mexican 
process, they supplied for the first time numerical data on which the 
explanation of that process must be based. 

One of the most unintelligible features of Rammelsberg's scientific 
work has been alluded to above, and must be again noticed. During 
the period when the whole science of chemistry was being transformed 
by its development on the organic side, Rammeisberg, almost alone, 
remained steadfastly immersed in inorganic research, and was never 
tempted into the attractive region of the carbon compounds. With 
the exception of a few isolated researches, mostly of a crystallographic 
nature, his work upon the oxalic acids and their salts and upon the 
uranium acetates are the only important investigations which carried 
him across the borderland, and these are almost entirely of crystallo- 
chemical interest. 

It was not that he closed his eyes to the extraordinary development 
of organic chemistry, or failed to make use of its teaching ; indeed the 
subject is adequately treated in his own text-books, and, as I have 
pointed out, he was one of the earliest adherents of the new chemistry ; 
but he purposely confined himself to a path which he had marked out 
at the beginning of his career, except where his own researches led 
him to make temporary excursions into the region of allied subjects. 

Rammeisberg as Crystallographer. 

In 1801 Haiiyhad written that " at the Ecole des Mines, chemistry 
and crystallography, so long separated, had entered into a close part 
nership which they have promised never to dissolve." No one contri- 
buted more to the maintenance of this partnership than Rammeisberg. 

Of his own work on the acetates, he says : " The previous data con- 



18 MIERS: RAMMELSBERG MEMORIAL LECTURE. 

tained so many contradictions that, evidently, the material which was 
analysed and the material which was measured cannot always have 
been the same. A work carried out along both lines has removed all 
the doubt and error which resulted from the fact that the chemist did 
not measure the salts which he analysed, and the cry stall ographer did 
not analyse the salts which he measured." 

For example, he showed in this paper that two manganese uranyl 
acetates crystallise out in succession from a mixed solution of the 
acetates, and that the measurements of Grailich had been made upon 
one of these, and the analysis of Weselsky upon the other ; they had, 
of course, been supposed to relate to the same substance. 

It is painful to reflect how often this sort of thing may have 
happened during the nineteenth century, and the reproach against 
chemists that they lack a practical knowledge of crystallography, and 
against crystallographers that they lack a practical knowledge of 
chemistry, is by no means removed. It is, however, a hopeful sign of 
the times that a younger school of chemists is now rising against 
whom this reproach can no longer be brought. 

Even in 1881 Rammelsberg could use the following words on the 
subject ("Handbuch der krystallographisch-physikalischen Ohemie," 
preface) : 

" Physicists and chemists meet in a region which stimulates the research 
apirit of both. Has not specific heat acquired a great importance for chemistry ? 
Has not the electrolysis of compounds exercised an effect upon the views of 
pure chemistry ? Have not spectroscopic phenomena been transferred from 
the domain of optics to that of practical chemistry ? The chemist sees himself 
continually driven to the study of physical phenomena. . . . The chemist 
must investigate the geometrical and other physical properties of substances as 
well as their composition and reactions. ... If, however, we compare our 
chemical handbooks with the mineralogical, we cannot fail to notice the very 
unequal treatment which the individual properties receive. For each mineral 
is given a special description of the crystalline form ; i.e., the constants ob- 
tained by observation and calculation. . . . The handbooks of chemistry, 
even the more complete, treat the most important physical properties either in 
a fragmentary manner or not at all. This is true of the crystalline form, the 
optical characters, the expansion, specific heat, electrical and magnetic pro- 
perties ; the reader is left to seek the physical constants of a substance in 
physical treatises or journals. Leopold Gmelin's great work alone ta&es due 
account of the crystallographic elements. 

" A result of this neglect of the physical properties in our chemical text- 
books is the incompetence of young chemists to investigate their own prepara- 
tions crystallographically and optically. And yet it is not so difficult to 
acquire the requisite crystallographic and physical knowledge, instead of 
leaving this investigation to others. In a precisely opposite manner the miner- 
alogists formerly erred by confining themselves to the geometrical and physical 
properties, and neglecting the chemical, so that we learnt from them what a 



TUIERS : RAMMELSBERG MEMORIAL LECTURE. 19 

mineral looks like but not what it is. A substance bearing the same name, 
but analysed by another man in another place and at another time, was often 
an entirely different mineral. Such a division of labour frequently leads to 
blunders ; an instructive example is afforded by the memoir o^>Schabus, which 
was crowned by the Vienna Academy of Sciences (in 1855). In this, potassium 
lithium sulphate is described as lithium sulphate, the sulphates of didymium 
and lanthanum are described as the chlorides, under the name grape-sugar is 
described the compound with sodium chloride, &c." 

One of Rammelsberg's great books of reference, from the preface of 
which the above is quoted, was designed to supply the need of which he 
complains, and to give chemists a book in which they could find precisely 
what was wanting in their own treatises. With immense labour he 
collected for this book all the crystallographic, optical, and other 
physical constants of all the crystallised compounds which had been 
described, adding full references so that the reader could always turn 
to the original sources. It was, and is still, an invaluable book of 
reference, although, of course, the volume dealing with organic com- 
pounds is now quite inadequate, owing to the rapid accumulation of 
facts during the last 20 years ; it would no longer be possible to 
include all the physical as well as the crystallographic characters of 
chemical compounds in a single volume of reasonable dimensions ; and 
the modern method of treating the former in separate works is, no 
doubt, more convenient. 

To the crystallographic knowledge of chemical compounds no man 
contributed more largely than Rammelsberg himself. "Without his 
labours, the illuminating discovery of isomorphism would never have 
exerted such widespread influence, and no man was better fitted to 
carry on the work of his great master, Mitscherlich. 

In crystallography as a distinct science, Rammelsberg had, I think, 
no particular interest ; he regarded it only as a means to an end. 
Born only four years after the discovery of the reflecting goniometer 
by Wollaston, he became one of the most practised experts with 
that instrument, and regarded it as part of the armoury of the 
chemist. 

His student days were set at an interesting time in the history of 
the young University of Berlin. The Abbe Haiiy, the real founder 
of crystallography, was still alive, and the science had made rapid 
advances in the hands of German and English investigators. Weiss 
had recently introduced the use of axes to which the faces of a crystal 
can be referred and which suffice for its description ; he and Mohs 
had independently established the existence of the six systems ; the 
laws of the double refraction of crystals belonging to these different 
systems and the methods by which they can be studied had been 
elaborated by Brewster and Herschel. In no place could the newly 



20 MIERS: RAMMELSBERG MEMORIAL LECTURE. 

developed science be better studied than in Berlin ; Mitscherlich was 
Professor of chemistry, Weiss of mineralogy, and Gustav Rose had 
recently (1822) been appointed ausserordentlicher Professor of 
mineralogy. 

JRammelsberg worked with all these men, and his whole scientific 
career was determined by their inspiration, but he always remained 
content with the crystallographic methods of his student days, and 
was satisfied if he could determine the form of every crystallised com- 
pound which he prepared and express it in the manner which had 
become familiar to him in 1834. Weiss called the three axes of a crystal 
a b c, and denoted any face by its intercepts on these axes by means 
of a symbol such as [ma, nb y pc\. Kammelsberg always employed 
this notation; Neumann in 1823 had already introduced the con- 
venient method of denoting the faces of a crystal by their normals 
and by the points in which they intersect a sphere, and Whewell in 
the same year had suggested the use of indices, afterwards developed 
by Miller, according to which a face whose intercepts on the axes are 

J -, j is denoted by the symbol (324) ; yet he would not even adopt 
324 

the notation of Naumann, which became almost universal in Germany. 
He says in 1881 "I have used the notation introduced by Weiss, 
the founder of the new crystallography, because I regard it as in 
itself better than any other, and I employ the actual angles between 
the faces because they alone, and not the angles between the normals, 
are expressed by the crystal itself. It is certain that the study of 
crystals would have been much more widely diffused among chemists 
if crystallographers had followed neither Naumann nor Whewell 
and Miller." 

This was a curious piece of conservatism which would hardly have 
been expected on the part of one who, as we have seen, was so quick 
to absorb new views in chemistry and to change his position in con- 
formity with the advance of that science. Having regard to the rapid 
displacement of Weiss's system by Naumann's, and the present 
almost universal acceptance of Miller's notation, it is easy to see that 
this adherence to an antiquated notation was one of the chief causes 
which prevented his book from becoming more widely known. For 
this reason, also, it is probable that two elementary text-books of 
crystallography for chemists, which he published in 1857 and 1883 
respectively, never had a wide circulation, although they are written 
with admirable lucidity. 

None the less is the Handbook an invaluable storehouse of useful 
information, arid none the less were Rammelsberg's own contributions 
to chemical crystallography of immense importance. Let us, without 
entering into details, glance at a few of his investigations. Among 



MIERS : RAMMELSBERG MEMORIAL LECTURE. 21 

those of most general interest are his work upon the isomorphism of sul- 
phur and selenium, and of the compounds of vanadium and phosphorus. 
From experiments on the density and the solubility of selenium, 
Rarnmelsberg concluded that there are three, and not two, crystalline 
modifications of this element, in addition to the amorphous variety. 
Mitscherlich had measured crystallised selenium with great care, but 
found its form to be different from that of sulphur ; Rammelsberg 
showed that the crystals obtained from solution in carbon disulphide 
are probably isomorphous with the monoclinic variety of sulphur, and 
this conclusion was afterwards confirmed by vom Rath, who found that 
isomorphous mixtures of the two elements possess sometimes the form 
of orthorhombic, but sometimes the form of monoclinic sulphur, 
proving that a monoclinic modification does enter into such mixtures. 
He subsequently endeavoured to prepare the potassium tellurate which 
had been described as isomorphous with the selenate and sulphate, but 
found no justification for the suggested isomorphism of tellurates with 
selenates. The isomorphism of sulphur and selenium has since been 
the subject of research by Muthmann, who has established the crystal- 
lographic relationships between these elements so far as they are at 
present known, and he is not disposed to accept the isomorphism of 
the selenium crystals here alluded to with the ordinary monoclinic 
sulphur, although it may occur with another monoclinic modification. 

In 1856 R/ammelsberg pointed out that the mineral vanadinite, the 
chlorovanadate of lead, in which vanadium was first discovered, is 
undoubtedly isomorphous with pyromorphite, the chlorophosphate, and 
insisted that the isomorphism must imply an analogous formula, 
especially since vanadinite contains some phosphoric acid, as he found 
by the analysis of specimens from Carinthia. At that date, the views 
that were held concerning the constitution of vanadic acid did not 
render this interpretation possible, and Rammelsberg declared that 
this must either be a case of the isomorphism of substances which are 
not similar in constitution, or else vanadic acid is not V0 3 , but V 2 ^s 
hereby predicting the result of Roscoe's classic work. 

From what has been already said, it will be understood that, among 
the bromides, bromates, iodides, iodates, and periodates, the phosphates, 
phosphites, &c., and the cyanides, the isomorphous relationships of many 
series of salts were established by Rammelsberg ; the same is true of 
the double chlorides, such as 2R'C1 + R"C1 2 + aq ; the dithionates ; 
the arsenates, &c. 

Among the phosphates, he showed that H, K, Am, Tl replace one 
another in isomorphous salts. Among the uranyl double acetates he 
traced three series in one of which manganese is replaced by cadmium, 
and in another by magnesium, whilst in the third magnesium is replaced 
by zinc, nickel, cobalt, or iron ; the barium, strontium, and calcium 



22 MIERS : RAMMELSBERG MEMORIAL LECTURE. 

series, containing 2 a.toms of uranium and 6 mols. of water, con- 
stitute another isomorphous series, whilst in the alkali series potass- 
ium may be replaced by silver. Among the sulphates, he contributed 
cases of the isomorphism of yttrium, erbium, didymium, and cadmium, 
and of uranium with thorium. 

Many of these researches bore upon the isomorphism of compounds- 
containing the alkali metals. He was the first to establish (in 1853) 
the tetartohedral character of sodium chlorate by observing that a 
cube of this substance might have only four faces evenly replacing its 
corners and twelve faces unevenly replacing its edges ; he was also thfr 
first to make crystalline mixtures of cubic sodium chlorate with 
tetragonal silver chlorate ; his preparations were afterwards used by 
Lehmann and served to demonstrate the fact that silver chlorate is- 
dimorphous. He established also the dimorphism of manganese chloride* 
and proved the isomorphism of tin, platinum and palladium in the double 
chlorides. The polymorphism of tin itself was the subject of a special inves- 
tigation in which he studied in particular the transformation of ordinary 
into gray tin and came to the conclusion that there are three modifications 
of this element, and that gray tin may become transformed below its 
temperature of fusion into tetragonal and perhaps also into ordinary 
tin ; in this connection, the alterations which take place in the alloy 
used in organ pipes after continued use, possibly due to vibration, are 
of interest. He measured crystals of an alloy of tin and copper which 
proved to be hexagonal, and adduced strong reasons for regarding 
many other alloys such as those of copper and zinc, gold and tin, iron 
and tin, tin and antimony, gold and antimony, gold and mercury, as 
mixtures of isodimorphous substances. 

His early experiments on the solubility of mixed sulphates (in 1854) 
were the first observations of this sort, and were the beginning of a 
class of research which has subsequently, in the hands of Bakhuis 
Roozeboom and others, led to such fruitful results. In these and 
kindred researches, Eammelsberg may be regarded as one of the 
pioneers of modern physical chemistry. He was the first to suggest 
a principle which has since been elaborated by Wyrouboff and others, 
that the axial ratios of the substances which are capable of forming 
mixed crystals are not necessarily almost identical, but may bear a 
simple rational relation to each other ; the possibility of isomorphous 
substances presenting almost identical angles in some zones of crystal 
faces whilst differing considerably in others is brought out in his study 
of the phosphates of ammonium, thallium, and sodium. 

The most interesting of his memoirs on these subjects, and, con- 
sidering the date at which it was published (1854), the most remarkable, 
was that already referred to upon mixed crystals of the sulphates of 
the series R"S0 4> 7H 2 O. He found that the crystals obtained b^ 



MIERS : RAMMELSBERG MEMORIAL LECTURE. 23 

fractional crystallisation do not possess the same composition as the 
solution from which they crystallise, if the solubility of the con- 
stituent salts is not the same, but that successive crops are produced 
of which the last contain a greater proportion of the more soluble 
salt ; he also showed that in some of these cases the mixed crystals 
are only capable of forming within certain- limits, and that an excess 
of one constituent may crystallise out in a pure condition beside the 
crystals of mixed constitution ; further, that in such mixtures, for 
example, as those containing iron and magnesium, the crystals possess 
the rhombic form of magnesium sulphate when Mg : Fe is greater than 
3, and the monoclinic form of the ferrous sulphate when Mg : Fe is 
equal to or less than 1. 

At that date, such mixed crystals were usually supposed to be mere 
parallel growths consisting of alternate layers of the two constituents ; 
Bammelsberg made it very clear that their complete homogeneity 
and their optical properties proved them to be really molecular mix- 
tures. In this very important work, he was opening up a line of 
research which leads directly to all that has since been done upon the 
properties of solid solutions, and induces me to repeat that Rammels- 
berg, although he has not received the credit for it, was certainly one 
of the pioneers in modern physical chemistry. 

It is not necessary to pursue this subject further ; it is now familiar 
to all chemists, and an admi table summary of the subsequent work is 
to be found in the English translation of Fock's " Introduction to 
Chemical Crystallography." 

One striking result of Rammelsberg's work on the mixed sulphates 
deserves notice ; his analyses of the mixed sulphates led him to the 
conclusion that, in some of these at any rate, the mixture does not 
take place in arbitrary proportions, but only in certain fixed molecular 
proportions; in other words, that they are of the nature of double 
salts, although their properties may be indistinguishable from those of 
a mixture. Since the publication of Dufet's research, which indicated a 
continuous change of the geometrical and physical properties as the 
composition of the mixed zinc-magnesium sulphate changes, this result 
has been ignored; but Rammelsberg was a careful observer, and his 
experiments ought to be repeated. 

I have perhaps now quoted enough of his crystallographic work to 
show what valuable results he was able to obtain by his familiarity 
with the use of the goniometer, and his recognition of the fact that 
this instrument should form part of the equipment of a chemist. 

Of the all important work relating to isomorphism that formed so 
large a part of Rammelsberg's labours, the greater portion lies in the 
field of mineralogy, where his contributions to science were even more 



24 MIERS : RAMMELSBERG MEMORIAL LECTURE. 

extensive than the chemical and crystallographic researches which we 
have just surveyed. 

Rammelsberg as Mineralogist. 

In attempting now to form an estimate of Rammelsberg's labours, 
which have long become a part of the scientific heritage of the present 
generation, we must continually bear in mind that, although he died 
in 1899, he was beginning to publish in 1837, and it is necessary to 
picture to ourselves the condition of science at that date. This is true 
of his chemical and crystallographic work, and it is equally true of his 
mineralogical memoirs in which both chemistry and crystallography 
are combined. Fortunately, it is easy to get a picture of the 
condition of mineralogy at different periods in his career, for the 
standard text-book was the work of his exact contemporary, Professor 
James D wight Dana, and the successive editions of that book reflect ac- 
curately the successive stages of the science. The first edition was 
issued in 1837, the very year in which Rammelsberg's first work was 
published ; the sixth edition, edited by Professor Edward Dana, was 
issued in 1892, when Rammelsberg had just resigned his professorship ; 
the immense difference between the two in their chemical aspect is 
really an eloquent testimony to the influence of his work. 

In 1837, mineral chemistry did not exist except in the mind of 
Berzelius, and perhaps of one or two of his followers. In the first 
edition of Dana's mineralogy, not a single formula is given, and in 
the preface the following remarkable statement occurs : " When the 
crystallisation of a species is sufficiently distinct to serve as a guide in 
distinguishing species, the results obtained by chemical means should 
never modify the decisions of the mineralogist," and, subsequently, 
after it has been confessed that chemical and blowpipe tests are often 
a valuable assistance, " in making this admission it does not appear 
that we degrade the science of mineralogy from its rank among the 
natural sciences as some of its most distinguished authors would 
affirm." 

That a mineralogist should have to apologise for analysing a mineral, 
and regard an analysis as a degradation to his science, seems now 
scarcely credible, but so it was in 1837. It is true that some glim- 
mering of the influence of Berzelius may be discerned in the shape of 
a little appendix on chemical classification. Minerals, it is there said, 
may be classified either by their electropositive or by their electro- 
negative elements ; the latter is perhaps preferable, for Mitscherlich's 
principle of isomorphism has shown that the electropositive elements 
may replace each other without introducing any change into the 
physical characters. On the other hand, later discoveries indicate 



MIERS : EAMMELSBERG MEMORIAL LECTURE. 25 

that the electronegative constituents may also replace each other ; so 
that on the whole there is an objection to any chemical classification 
whatever. 

The second edition appeared in 1844. Here the classification 
adopted is that of Mohs the latest refinement of the so-called 
natural-historical system of Werner in which the species are defined 
by their external characters alone, especially the hardness and the 
specific gravity, and not by their composition. The species are grouped 
into genera, and the genera into orders, and they all receive Latin 
names like those used for plants. 

In this second edition, however, the appendix on chemical classifica- 
tion contains a survey of the mineral kingdom in which the species are 
arranged solely by their chemical constitution, and are defined by 
chemical formulae. The secret of this change is explained by the 
author himself; he says, "The very elaborate treatise on chemical 
mineralogy by E/ammelsberg, which has lately appeared in Germany, 
has afforded nearly all the materials for this part of the table." 

It will be found that at this date, over seven years after he had 
began to publish, Rammelsberg is already responsible for no less 
than 56 of the formulae, and in succeeding editions his influence is 
no less strongly felt. In the third edition of Dana, the natural history 
system is thrown over, and the classification becomes mainly a 
chemical one, and nearly identical with that adopted at the present 
clay. 

This transformation of mineralogy was, of course, originally due to 
Berzelius ; its beginnings are sketched in Whewell's " History of the 
Inductive 3ciences," where it is treated as an almost contemporary 
episode. 

Berzelius had first, in 1816, proposed a classification of minerals 
according to the electropositive elements, and subsequently, when 
this had been subjected to much criticism and was found to be in- 
compatible with various isomorphous relationships, he replaced it 
by an arrangement mainly according to the electronegative elements. 

No one interested himself more in the dissemination of the views of 
Berzelius than his friend Rammelsberg, who published in 1847 a small 
volume containing translations by Gmelin, Pfaff, and himself of seven 
memoirs by Berzelius relating to the classification of minerals. /Two 
of these are the schemes just referred to, the others are replies to his 
various critics, and the volume closes with a paper by Rammelsberg 
himself, a survey of the mineral kingdom upon the lines !aid down 
by Berzelius. 

In a preface, he remarks " According to this principle the different 
augites, hornblendes, garnets, <fec., which contain different bases 
cannot be placed together. But whatever may be the objections to 



26 MIERS : RAMMELSBERG MEMORIAL LECTURE. 

the chemical system from the purely mineralogical standpoint, it 
cannot be denied that it is based upon a single principle, and that 
this can be conveniently carried out through the whole scheme." 

It was, I think, characteristic of the man that he did not devote any 
more time to the academic discussion of the principles of classification 
in his own first treatise the minerals were arranged by the most 
convenient of all methods, an alphabetical order but, having con- 
vinced himself that a chemical system would be possible, he set ta 
work upon the analyses without which any such classification would 
be premature. 

The treatise was entitled " Handworterbuch des chemischen Theils 
der Mineralogie," and was published in 1841 ; it was dedicated to 
Heinrich and Gustav Rose. The book contains all the mineral analyses 
at that time published, including a number of new analyses by 
Rammelsberg himself, and gives the reactions and blowpipe tests for 
each species. All the formulae are calculated from the atomic weights 
of Berzelius, and the theoretical composition of each mineral is given. 
A few pages of introduction give the principles of mineral chemistry as* 
laid down by Berzelius, and the method of calculating formulae. 

The book was welcomed with acclamation by Berzelius, Leonhard, 
Kobell, and the other leaders of chemical and mineralogical science. In 
his Jahresbericht for 1843, Berzelius gives the following appreciation* 
of the work : 

" Mineralogy has been enriched by a work of the highest value to those who- 
believe that the study of the chemical composition of minerals belongs to this 
science. The minerals are arranged in alphabetical order and all their known 
analyses are given, accompanied by a profound criticism of the analytical 
methods employed therein, together, often, with a recalculation and the requi- 
site correction of the results deduced. It fulfils two requirements which are 
seldom simultaneously satisfied, it is exhaustive without being wearisome by 
excessive elaboration. The introduction contains a brief but clear and systematic 
representation of the chemical constitution of minerals, and the way in which 
they are to be criticised according to the results of the analyses. 

" Seldom has a book been so much needed or so well supplied the need. 
The industrious author deserves the greatest thanks for his usefuland laborious 
undertaking." 

Between the years 1843 and 1853, five successive supplements were 
issued at intervals ; not only did these contain all the new analyses 
which had been published, but the composition and formulae were all 
recalculated with the corrected atomic weights. 

It will by this time be suspected from what has gone before that most 
of Rammelsberg's life was devoted to the laborious accumulation of new 
facts, and that he did not publish much of a speculative nature or 
enter into the wordy strife of scientific controversy ; he was content 



M1ERS : BAMMELSBERG MEMOBIAL LECTURE. 27 

to criticise and correct by the quiet process of experiment and 
observation. 

Each of these supplements to the Handworterbuch contains a 
general introduction which gives a clue to what he considered most 
important and interesting in contemporary mineralogy and to his own 
opinions on controversial subjects. 

For instance, in the second supplement (1845), he explains that 
Gmelin had accepted SiO 2 , in place of Si0 3 , as the constitution of 
silica. The formulae of most of the important silicates on this 
hypothesis are given', and Rainmelsberg confesses that many are con- 
siderably simplified, but the principle is not yet accepted. 

The third supplement (1847) contains a notice of Wallmark's 
suggestions concerning silicates of the monoxide bases, namely, that in 
these, whatever may be their differences of system, two of the 
crystallographic axes bear nearly a constant ratio 0*92 : 1. The recent 
investigations which led to the detection of phosphoric acid and 
fluorine in Very many minerals, 'and Ebelmen's work on the decom- 
position of silicates, are also noticed. 

In the fourth supplement (1849), the recently suggested possibility 
of the isomorphism of sulphur and arsenic compounds is discussed, 
and Rammelsberg thinks it cann9t be maintained. 

The relationship between the rhombic bournonite (PbCuSbS 8 ) and 
the hexagonal red silver (Ag 8 SbS 8 ), which had been compared by 
Gustav Rose to that between aragonite and calcite, is in. his opinion 
due to proportionality of atomic volumes. 

Calcite _ 232 _ 1 ; Aragonite 214 _ 1 
Red Silver 1180 5 Bournonite 1073 5* 

The greater part of these introductions, however, is devoted to a criti- 
cism of Scheerer's polymeric isomorphism and of Hermann's heteromer- 
ism ; it is difficult now to appreciate the importance which these theories 
assumed in the eyes of their contemporaries, and it is almost forgotten 
how large a part was played by Rammelsberg in their demolition. In 
Ernst von Meyer's " History of Chemistry," Rammelsberg is dismissed 
in a paragraph (he is also killed before his time), and the Hermann 
Scheerer controversy is scarcely discussed ; and yet these views must 
have, for a time, held the field masterfully. Tn his fourth supple- 
ment, Rammelsberg' prefaces his criticism with the remark " The 
criticism of Scheerer's and Hermann's theories may, it is hoped, induce 
others to express their opinions openly." Scheerer, it will be 
remembered, believed that in many silicates and other minerals RO 
may be replaced by 3H 2 ; his argument relied chiefly upon the mineral 
aspasiolite, which has the form of cordierite, and also a similar com* 
position if 1 mol. of magnesium oxide may be regarded as replaced by 



28 MIERS I RAMMELSBERG MEMORIAL LECTURE. 

3 mols. of water. The serpentine crystals from Snarum in Norway 
were supposed to be another example. Rammelsberg insisted that 
aspasiolite and the allied minerals are only altered cordierite which 
has gained water during decomposition (the mineral has subsequently, 
owing to the work of Haidinger, Naumann, and others, been deposed 
from its high position, and is now known to be certainly a pseudomorph 
after cordierite) ; Rammelsberg also showed that the minerals of the 
scapolite group upon which also Scheerer largely relied are particularly 
liable to alteration. The arsenate of cobalt, according to Scheerer, 
contains 6 mols. of water, and its isomorphism with the ferric phos 
phate, vivianite, is only brought out by assuming that FeO is replaced 
by 3H 2 O ; Rammelsberg insists that both minerals contain 8 mols. of 
water. Scheerer's further hypothesis that CuO can be replaced 
by 2H 2 0, and 2Si0 2 by 3A1 2 3 , he stigmatise/S as entirely arbitrary. 

Hermann's heteromerism, which has also passed into the limbo of 
forsaken theories, and is dismissed by Arzruni in his volume on the 
physical chemistry of crystals in Graham-Otto's Lehrbuch as of no 
importance, was criticised by Rammelsberg with great care, and I 
think will be found on examination to be far less alien to modern 
views than is commonly supposed. The real hypothesis of Hermann 
was that substances of nearly the same form, but quite different com- 
position, can mix to form homogeneous crystals ; epidote, for example, 
is a mixture of the two following compounds : 



Zoisite ............... 

Bucklandite ...... 2R 3 Si + 3s. 

That substances of different composition may have nearly the same 
form Rammelsberg confesses ; that they can nter into isomorphous 
mixtures he regards as not proven, but contents himself with the 
principle. " Substances which have nearly the same crystalline form 
possess the same or proportional atomic volumes." 

The fifth supplement (1853) gives evidence of the rapidly extending 
acceptance (due largely to Dana and Kobell) of Kopp's idea that the 
isomorphism of minerals depends upon the equality or proportionality 
of their atomic volumes. Rammelsberg himself at that date regards 



Tourmaline as R 8 Si 2 + nRSi with 
Felspar as R w si + n&iSin. 
Mica as nRSi + nRSi". 

Hornblende as raRSi + nR 3 Si 2 . 

These are all instances of the multiplying cases of isomorphism among 
compounds which differ in the number of their atoms. 



MIERS : RAMMELSBERG MEMORIAL LECTURE. 20 

From that day to the present time, mineral chemistry has been 
mainly occupied with the endeavour to discover the isomorphous con- 
stituents which mix to form a mineral of complex composition such as 
tourmaline or epidote ; that they are isomorphous mixtures is, of 
course, firmly held, but the proportionality of atomic volumes is no longer 
invoked as a criterion, and similarity of composition is now so 
liberally interpreted that the views of Hermann should no longer 
be dismissed as wild speculations. 

In many of the questions concerning which controversy raged, such 
as whether only the constituents which enter into the mixtures are 
to be called mineral species, or whether the intermediate mixtures also 
deserve that name, Eammelsberg took little or no interest. His busi- 
ness was to supply the solid foundation of fact only to be attained by 
laborious analyses, upon which alone theory can be based. 

In my opinion, the most important contributions which Rammels- 
berg made to science were those which he made as a mineral chemist. 
If, as we have seen, he brought to the study of chemistry a much 
needed knowledge of crystallography, he certainly brought to the 
study of minerals an even more needed knowledge of chemistry. 

He himself deplores the fact that in the early days of the science 
Hatty was solely a crystallographer and Klaproth a chemist. "What 
rapid strides would have been made by mineralogy if Hatty's crystallo- 
graphic knowledge and Klaproth' s chemical ability bad been united 
in a single person." It is not often that a science suffers from over 
specialisation in its early periods, but the study of minerals is not so 
much a distinct science as a region in which three sciences meet, and 
few were gifted with the power of mastering all three. No man was 
better equipped than Rammelsberg to achieve conquests in this un- 
explored region. His published papers on mineralogical subjects are 
very numerous (including those on rocks and meteorites, about 300) - r 
their results are incorporated in his great treatise, " Handbuch der 
Mineralchemie," which succeeded the " Handwb'rterbuch," already 
mentioned. The first edition of the " Handbuch " was issued in 1860 y 
the second edition in 1875, an " Erganzungsheft " in 1886, and a second 
supplement in 1895. Rammelsberg's mineralogical work is so vast 
that here again in order to form an estimate of its character I 
propose to select only two or three examples, and to leave his " Hand- 
buch " to describe the remainder. 

Augite qnd Hornblende. Conspicuous among his early papers are 
those on the augite and hornblende group of minerals. These two 
minerals were only distinguished by their cleavage angle and form r 
Augite was known to be a "bisilicate of lime and magnesia in which 
part of the bases is replaced by protoxide of iron and part of the silica 
by alumina " \ hornblende was almost the same, " the analyses only 



30 MIERS: RAMMELSBERG MEMORIAL LECTURE. 

dfiii 

prove that augite usually contains' more lime, less alumina, and no 
hydrofluoric acid, which is peculiar, though in minute proportions, to 
hornblende " (Allan's " Mineralogy," 1 834, p. 149). Augite was made 
to include the minerals known as augite, diopside, baikalite, fassaite, 
coccolite, sahlite, and omphacite; hornblende included the species 
known as hornblende, actinolite, tremolite, asbestos, hedenbergite, and 
pargasite. 

Gustav Rose had proved that augite and hornblende may be re- 
ferred to the same crystal axes, and urged that they may therefore be 
regarded as the same mineral ; it is true that they have a different 
cleavage angle, and that the faces that occur upon the one are not 
found upon the other, so that they presont quite a different aspect, 
but they are sometimes found attached 7 to one another in parallel 
positions ; further, Rose showed that when hornblende is fused, it re- 
crystallises as augite ; it was therefore supposed that the temperature 
at which the mineral was formed may have been sufficient to deter- 
mine whether it should crystallise with the faces and cleavage of 
augite, or with the faces and cleavage of hornblende. 

Subsequently, Rose himself discovered that a mineral, to which the 
name uralite was given, possesses the faces of augite and the cleavage 
of hornblende, and is clearly augite which has been converted into 
hornblende. The balance of evidence, consequently, inclined again to 
a separation of these minerals into two distinct species. 

The chemical characters were very, imperfectly known. Heinrich 
Rose had found the non-aluminous augites to be simple bisilicates, 
RSiO g , and therefore analogous- in composition to the magnesia silicate 
hypersthene, whose cleavage is different, and to the lime silicate 
wollastonite whose angles are not those of augite. The non-aluminous 
hornblendes seemed from Bonsdorff's analyses to have a different 
composition, the oxygen ratio of acid to base being more than 2:1; 
they might be regarded as mixtures of the bisilicate RSiO 3 with 
trisilicate R 2 Si 8 8 , but if so the relative proportions were not constant. 
Rammelsberg himself was inclined to believe the mineral to be an 
isomorphous mixture of these two silicates rather an advanced view 
of isomorphism for that date. As for the aluminous augites and 
hornblendes, they were in hopeless confusion. 

It was in 1851 that Rammelsberg seriously grappled with this 
problem of the augite-hornblende group which had confronted him 
when he drew up his mineral system in 1847. In the first edition of 
the " Mineralchemie " in 1875, he was able to incorporate no less than 
15 analyses of augites and 15 analyses of hornblendes, made by 
himself. He had already pointed out that some hornblende undoubtedly 
has the composition of augite, and some augite undoubtedly has the 
composition of hornblende. He set himself to discover in particular 



MIERS : RAMMELSBERG MEMORIAL LECTURE. 31 

whether these minerals do not contain alkalis, whether the iron is 
ferrous or ferric, arid to determine the exact proportions of magnesia 
and alumina which were at that time only separable with considerable 
difficulty. Not content with isolated analyses, he undertook a com- 
plete revision of the whole group. With the help of Gustav Rose and 
Krantz, the mineral dealer, he provided himself with the very best 
material of all the available species ; he measured the crystals, revised 
and recalculated the results of previous observers, and made careful 
analyses and determinations of the (specific gravities, no less than 21 
analyses of augites and 24 of hornblendes being recorded. 

From the crystallographic point of view, he showed that the lime 
silicate wollastonite, the soda silicate segirine, the lime iron silicate 
babingtonite, and the manganese silicate rhodonite all' belong to the 
same group. 

From the chemical point of view, the minerals fall into four 
groups : 

A, containing neither Al nor Fe'". 

B, containing Fe'", but not Al. 

C, containing both Fe'" and Al. 

D, containing Al, but not Fe'". 

Group A contains many augites, and also the light-coloured horn- 
blendes known as tremolite and actinolite. 
Pure tremolite is CaSi0 3 + 3MgSiO s . 
Pure diopside is GaSi0 3 + MgSiO 3 . 
Group B contains the following : 

Augites. Hornblendes. 

Acmite. Arfvedsonite. 

^Egirine 
Babingtonite. 

These are mixtures of R"Si0 3 with Fe 2 (Si0 8 ) 3 in varying proportions. 
Hence Fe 2 (Si0 3 ) 3 is isomorphous with R"Si0 3 , and therefore also group 
B is isomorphous with group A. This was a new conception, and, 
being reluctant at that time to accept Gerhard t's view concerning the two 
modifications of iron, Rammelsberg was inclined to regard the relation 
as due to the dimorphism of the oxide, for Fe 2 3 is found both in a 
<jubic and a hexagonal form among minerals. 

Group C. Here the investigation involved great labour ; special 
care was required for the separation of aluminium, and the minerals 
were examined for alkalis and for fluorine. After the analysis of 
specimens from 15 localities, it was concluded that the alumin- 
iferous augites and hornblendes all contain both FeO and Fe 2 3 , and 
that all the aluminiferous hornblendes contain K and Na. In pre- 
vious analyses, the iron had all been reckoned as FeO. It might be 



32 MIERS : RAMMELSBERG MEMORIAL LECTURE. 

objected that there is no guarantee of the purity of these black, 
opaque minerals, but Rammelsberg insists that his specimens, although 
black, are transparent, and are shown by the microscope to be homo- 
geneous. In order to ascertain whether the alumina belongs to the 
electropositive or the electronegative constituents, he calculated in all 
the analyses the oxygen ratio for 

(1) RO + R 2 O 3 : SiO 2 . 

(2) RO:R 2 3 + Si0 2 . 

(3) R0 + Fe 2 3 : Si0 2 + A1 2 O 3 , 

and finding the last alone to be constant and to have the same value for 
the augites and hornblendes in group C, concluded (1) that augite and 
hornblende are shown by groups A and B to have the same compo- 
sition j they must therefore have the same composition in C ; and hence 
(2) Al is an acid and Fe a basic constituent, and the augites and horn- 
blendes are all to be regarded as bisilicates and bialuminat:. . 

Group D contains only spodumene, a lithium sodium aluminium 
bisilicate in which the aluminium is basic. 

In a subsequent paper (1867), Rammelsberg gives up this inter- 
pretation and regards the alumina in both the augite and hornblende 
group as an accessory constituent, A1 2 3 , entering into isomorphous 
mixture with RSi0 3 . This idea jaay be traced to Bonsdorff ; it was 
supposed to be justified by the isomorphism of haematite, Fe 2 O 3 , with 
ilmenite, FeTiO,. 

The subsequent history of these minerals may be added, since it 
serves to illustrate two features of Rammelsberg's character, his 
readiness during most of his long career to accept any view which 
appeared really better than his own, and the conservatism which only 
overtook him in old age. 

In 1871, l"schermak offered an explanation of the aluminiferous 
augites which was almost universally accepted ; their analyses were 
fully expressed by the formula mR 2 Si 2 6 + wRA! 2 Si0 6 . Subsequently 
Scharizer offered an explanation of the aluminiferous hornblendes 
according to which they are mixtures of the mineral actinolite, 
CaMg 3 (Si0 3 ) 4 , with a known variety of hornblende having the con- 
stitution of a garnet, R 3 Al 2 (Si0 4 ) 3 , to which he gives the name 
syntagmite. Since the latter can be expressed as 3RSi0 3 ,Al 2 3 , it is 
evident that all such mixtures will agree with Rammelsberg's second 
hypothesis. 

In the second edition of his handbook (1875), Rammelsberg adheres 
to his old view, but in the Erganzungsheft (1886) he confesses that 
A1 2 O 3 can hardly be regarded as isomorphous with RSiO 3 , since A1 2 O 3 
never has the form of augite, and accepts a more general form of 
Scharizer's interpretation according to which both augites and horn- 
blendes are isomorphous mixtures of the molecules RSi0 3 and 



MIERS : RAMMELSBERG MEMORIAL LECTURE. 38 

R 3 Al(Si0 4 ) 3 , and laboriously calculates the various atomic ratios of 
56 analyses on this hypothesis. 

It is curious that in the second supplement, published in his 83rd 
year, he should return to his original view and regard A1 2 3 as iso- 
morphous with RSi0 3 . 

At the present time, Tschermak's explanation is generally made the 
basis of any speculations upon the constitution of these minerals, but 
it must never be forgotten that the necessary facts were supplied by 
Rammelsberg' s analvses and by his discovery that they contain both 
Fe" and Fe'". 

In any case, whatever explanation be coffered, the augite-hornblende 
group is one of those in which we are driven to accept the intermixture 
of two molecules having very different constitutions quite as different 
as those suggested in other cases by Hermann, whose views are 
supposed to be long buried and forgotten. 

Felspars. Another example in which such intermixture is perfectly 
well proved, and even universally accepted, is afforded by the felspar 
group. The minerals known as albite, oligoclase, labradorite, and anorth- 
ite had long been classed together as felspar in spite of differences in 
composition, but their chemical relations were never understood until 
Tschermak in 1864 showed that they are not well denned minerals, but 
pass into each other and that the whole series consists of isomorphous 
mixtures in varying proportions of the soda-felspar, albite, with the 
lime-felspar, anorthite. But Rammelsberg had already (in 1850) ex- 
pressed his conviction that the felspars are an isomorphous group, in 
spite of the prevalent view that they were distinct minerals. " One and 
the same type of geometrical form," he says, " scarcely differing more 
than is usual in isomorphous substances, and a great similarity in all 
their physical properties unite these minerals which we call in general 
felspar, and it was only the chemist who found it necessary to separate 
them because he found that the different members, orthoclase and albite, 
oligoclase, labradorite and anorthite, cannot be treated as isomorphous 
by replacement of their individual constituents, but possess composi- 
tions which are stochiometrically different, the equivalents of the silica 
varying in the proportion 12:9:6:4. . . . The observation made upon 
tourmaline that silicates of different basicity united in different pro- 
portions are isomorphous, that is to say, have the same, or nearly the 
same, form, seems to be repeated in the most important and wide-spread 
minerals, felspar and mica." 

When Tschermak proposed his theory, Rammelsberg, in spite of 
the opposition of Streng, vom Rath, and others, was the first to give 
it his warm and undivided support, and here he found a powerful ally in 
Bunsen. Every subsequent attack upon the theory has only resulted 



34 MIERS : RAMMELSBERG MEMORIAL LECTURE. 

in its cr"firm&tion by renewed analyses, so that at the present time 
there are no isomorphous mixtures which have been so fully studied, 
both chemically and physically, and so well established, as those of 
albite, NaAlSi 3 8 , and anorthite, CaAl 2 Si 2 8 . 

The reason why Raramelsberg was so quick to accept the felspar 
theory of Tschermak and so reluctant to accept his augite theory is 
easy to see. In the one case, the two constituents were- known to 
exist, in the other case one of them was hypothetical, and no man 
was more averse to speculation than Eammelsberg. 

In 1872, he published a paper entitled "The Present State of our 
Knowledge of the Felspars," in which he made an elaborate calculation 
of all the felspar analyses in order to ascertain how closely they 
agree with Tschermak's formula. This was followed in 1884 by a 
paper on "Isomorphous Minerals which are not Chemically Analogous," 
in which, after mentioning olivine, garnet, tourmaline, epidote, and 
idocrase as minerals whose constituents are analogous, the author 
admits that silicon, like molybdenum, tungsten, vanadium, &c., forms 
acids of different basicity ; among these, he prefers to accept only the 
simpler as independent, and regards the more complex as mixtures of 
these, for example, H G Mo 7 24 as 2H 2 Mo 2 7 + H 2 Mo 3 10 . Thus the 
only silicic acids of which it is necessary to assume the existence are 
H 2 Si 2 5 ; H 2 Si0 3 ; H 4 Si0 4 ; H 6 SiQ 5 ; and H 8 Si0 6 . 

If a salt contains metals of different valencies, it is to be regarded 
as admixture of molecules of the same basicity; thus 

Anorthite, CaAJ 2 Si 2 8 is Ca 2 Si0 4 + Al 4 (Si0 4 ) 3 . 
Albite NaAlSi 8 8 is Na 4 Si 3 O 8 + Al 4 (Si 3 8 ) 3 . 

But we are driven to regard the salts of H 4 Si0 4 as capable of entering 
into isomorphous mixture with the salts of H 4 Si 3 8 . 

Whatever speculations have subsequently been entertained regarding 
the felspars and other silicates, I fear we must confess that mineral 
chemistry has not progressed much beyond this point : it is certain 
that the anorthic soda-lime-felspars are mixtures of albite and anorth- 
ite ; it is equally certain that no explanation why they should form 
isomorphous mixtures is sufficiently complete to supply the clue to all 
the other complex silicates found in Nature. 

Towards the end of his life, Rammelsberg returned to the subject 
again ; one of his last papers, published in 1896, contains a number of 
fresh calculations made with the object of ascertaining which analyses 
conform to the theory and which deviate from it. 

Other Silicates. Rammelsberg's memoir of 1884 is really inspired 
by his work on the minerals known as scapolite, chabazite, and 
phillipsite, which was published in the same year. Here again he 









MIERS : RAMMELSBERG MEMORIAL LECTURE. 35 

holds by the principle that we are not justified in assuming a mineral 
to be a mixture of two or more definite silicates unless we have inde- 
pendent evidence of their existence. 

Thus in the scapolite group, according to him, sarcolite is 
(R' 4 E" 2 ) 3 Al(Si0 4 ) 3 . 

Humboldtilite \ 

Meionite > are mB/ 2 Si0 3 + nR/ 4 Si0 4 . 

Wernerite 

Marialite is wR/ 2 Si0 3 + nR' 2 Si 2 5 . 

Tschermak's explanation of these minerals as a mixture of two 
hypothetical silicates he refuses to accept. 

Again, in the chabazite group, after an elaborate criticism of all 
the analyses which indicates that R" : A1 2 = 1 : 1, he selects the three 
simplest formulae : 

R/'Al 2 Si 3 10 
R"Al 2 $i 4 12 
R"Al 2 Si 5 14 

and shows that all the analyses may be interpreted as mixtures of these 
three molecules. 

Similarly, in the phillipsite group, R" : A1 2 = 1 : 1, and the minerals 
may be regarded as mixtures of : 

2R"Al 2 Si 3 10 + 7H 2 
2R"Al 2 Si 4 12 
R"Al 2 Si 6 16 

The theory of Fresenius that the minerals of these two last groups 
can be represented by w(R,"Al 2 Si 2 8 + 4H 2 0) 4- w(R,"Al 2 Si 6 16 + 6H 2 0) 
appears to Rammelsberg a mere speculation, since although one of 
these silicates has the constitution of desmine the other is hypothetical. 
His views are best expressed in his own words : " When shall we 
appreciate the fact that we do not yet know the cause of isomor- 
phism, and that equality of form and analogy of composition do not 
stand to one another in the relation of cause and effect. Nearly 
forty years ago, Hermann stated the following law : in isomorphous 
compounds which are not analogous in composition, there are always 
two members at the ends of the series, and from their mixture in 
varying proportions all the remainder result. This he called Hetero- 
merism and endeavoured to establish his views in numerous papers. 
By the progress of mineral chemistry, the facts upon which this theory 
was based have been abundantly discredited, and it has never enjoyed 
the confidence of chemists because it rests upon hypotheses which 
cannot be tested by experiment. It was therefore a matter of the 
greatest scienti6c importance that Tschermak discovered the law of 

2B 



38 MIERS : RAMMELSBERG MEMORIAL LECTURE. 

mixture in the soda-lime-felspars, and it would be equally important 
to establish similar laws in other groups in which similarity of form 
is accompanied by difference in composition. But for this, it is neces- 
sary that the terminal members of the series should be really known, 
and that, as with the felspars, the composition of every mixture 
should , by the atomic ratios of its elements^ supply a proof of the 
law." 

Towards the end of his long life, it was perhaps natural that 
Rammelsberg should feel himself somewhat out of sympathy with the 
views of younger chemists. One of the fruitful conceptions in modern 
mineral chemistry has been that of the mutual replacement of hydr- 
oxyl and fluorine which has been brought forward by Penfield and 
established in the case of several minerals. The first of these was the 
lithium-aluminium phosphate, amblygonite, in which the proportion of 
water was found to vary between 1*75 and 6*61, and that of fluorine 
between 11 '26 and 1'75. Penfield showed that in all the analyses 
P : Al : R : (F,OH) = 1 : 1 : 1 : 1, so that if the water be calculated as 
hydroxyl replaceable by fluorine, the formula becomes quite simple. 
Wagnerite and triploidite were already recognised as isomorphous. 

In 1884, Rammelsberg expressed himself as follows on this view : 
"The hypothetical atomic group hydroxyl, which plays a great part 
in modern chemistry, is now beginning to figure in the formulae of 
minerals. Penfield having found in some amblygonites less fluorine 
and more water, regards all these as unaltered compounds in which 
HO replaces fluorine ; according to this, potassium fluoride and potash 
would be analogous compounds. I have already protested against this 
highly unchemical view.*' 

Penfield has subsequently confirmed his theory by analyses of herderite, 
hamlinite, topaz, and other minerals ; it enabled him to give to topaz 
the beautifully simple formula Al 2 (F,OH) 2 Si0 4 . But even with these 
before his eyes, Eammelsberg in the second supplement to his " Mineral- 
chemie" (1895) repeats that the theory is "in hohem Grade unchemisch " ; 
he persisted in regarding the water in topaz as merely due to incipient 
decomposition. 

It must be remarked that a very recent research by Fels, published 
in the present year, has failed to find any replacement of hydroxyl by 
halogen elements in the benzene derivatives. 

Professor Penfield, in writing to me about Rammelsberg as a mineral 
chemist, uses the following words : 

" He was without question a man of great energy and enthusiasm, and he 
accomplished an enormous amount of work. When I studied Rammelsberg's 
early tourmaline papers, I was impressed by the magnitude of the under- 
taking, and with the excellent character of the work. He made at the outset 
mistake in deciding that tourmaline had no water, and in assuming that loss 



MTERS : RAMMELSBEEG MEMORIAL LECTURE. 37 

on ignition was SiF 4 , and, having once made the mistake, he seemed never to 
be able to get his analyses into good shape. He revised the analyses from 
time to time, always changing some of the figures, and no man probably will 
ever be able to tell just what results Rammelsberg placed most confidence in. 
He practised a sort of chemical sleight-of-hand work with his results, moulding 
H 2 and F somewhat to suit his own ideas. I believe that his results, as 
modified by Foote and me in our paper on tourmaline, and founded on the 
assumption that the bases were probably determined with a good degree of 
accuracy, are fairer than any of Rammelsberg's own modifications of his 
analyses. Although Rammelsberg could be very severe as a critic, he seemed 
to me to be a man of tender feeling. He took occasion to criticise me at one 
time, stating that my ideas concerning the composition of amblygonite were 
rein unchemisch. I am willing to admit that following the method adopted by 
Rammelsberg, and writing the composition of amblygonite A] 2 P 2 8 ,2LiF with 
isomorphous Al 2 P 2 8 ,2LiOH was somewhat unchemisch, although I did not 
intend to convey the idea that amblygonite contained a soluble neutral salt, 
LiF, and a soluble alkali, LiOH, any more than Rammelsberg intended to 
convey the idea that apatite contained soluble CaCl 2 when he wrote the com- 
position as 3Ca 3 P 2 8 ,CaCl 2 . It certainly is a decided improvement to write 
amblygonite Li(AlF)P0 4 with isomorphous Li(Al,OH)P0 4 . On the subject of 
the isomorphism of fluorine and hydroxyl, he said that he could not bring 
himself to believe in it. To him, water in topaz, for example, would indicate 
partial decomposition." 

Upon some groups of minerals he held quite peculiar views. The 
arsenic and antimony compounds of iron, nickel, and cobalt, he regarded 
as isomorphous mixtures of these elements, in fact as alloys ; in one 
of his last papers (1897), he extends this view to the sulphur which 
these minerals contain, and explains the whole group either as mixtures 
R, n A TO S, or as mixtures of this molecule with RS 2 . Other instances 
might be quoted in which his own interpretations of the analyses which 
he had made have not been generally accepted. 

If it was difficult to give a summary of Rammelsberg's work in 
chemistry on account of the extent of his labours, in mineralogy it is 
quite impossible ; to give a catalogue of the minerals which he 
analysed would be to mention about two-thirds of the mineral king- 
dom ; they can be extracted from his handbook of mineral chemistry, 
which contains references to all of them. I have contented myself 
with mentioning a very few of the more important, and especially 
such as led to the discussion of general principles. Among those 
which I have been compelled to pass over are the memoirs on mica, 
on the borates, the tantalates and niobates, on epidote, idocrase, and 
a host of other large groups, not to mention tourmaline, which is now 
the subject of lively discussion between Penfield, Clarke, Tschermak, 
and others. Rammelsberg published important memoirs on this sub- 
ject in 1850 and 1870, and returned to it in 1890. I believe that he was 
engaged upon another memoir on tourmaline at the time of his death. 



38 MIERS : RAMMELSBERG MEMORIAL LECTURE. 

It is noteworthy that in a science which has suffered terribly from 
the over-multiplication of names, Rammelsberg was entirely free from 
this infirmity of intellectual conceit, and probably added fewer mineral 
names to the literature in proportion to the work which he did than 
any other mineralogist. In order to emphasise this fact, a list of the 
new names which he introduced is subjoined : 

Antimonial arsenic. Gotthardite. 

Castillite. Heteromorphite. 

Chiviatite. Hydromagnocalcite. 

Chlorapatite. Magnoferrite. 

Crednerite. Pseudolibethenite. 

Cuprodescloizite. Sigterite. 

Epichlorite. Tachydrite. 

Eluorapatite. Waldheimite. 

Ginilsite. Xonotlite. 



Writing to Wolcott Gibbs in 1882, Rammelsberg complains that 
since the duties of the second professorship at the University had 
been added to his other occupations he had very little leisure for work ; 
but his ideas of work and leisure were not those of other men. How, 
among the numerous investigations to which I have already alluded, he 
found time for research in other subjects besides mineralogy, is 
hard to understand. There are yet two other important branches of 
his work which must not be overlooked. In Humboldt's " Cosmos," he 
is alluded to as " a sagacious chemist who has recently devoted him- 
self uninterruptedly, and with equal activity and success, to the 
analysis of aerolites," and numbers of his memoirs relate to the analysis 
of meteorites. Another considerable group of his published papers 
contain laborious rock analyses ; and in 1854 he had made for Hum- 
bold t an analysis of the trachyte of Chimborazo. A paper published 
in 1847 dealt with the inorganic materials contained in plants. Be- 
fore middle life, he had attained the reputation of being the most ex- 
perienced inorganic chemist in Europe. Among the letters which ho 
received are to be found requests from Brooke, Miller, and Lettsom, 
in England, that he should analyse minerals which they had dis- 
covered ; from Schliemann, in Germany, that he should determine the 
composition of metals from Ilios ; from Lawrence Smith, in America, 
that he should introduce certain methods of silicate analysis into Ger- 
many ; from Grailich, in Vienna, that he should supply him with 
crystals of the substances which he had analysed. Many of his papers 
were translated into other languages as soon as they appeared. 

"Writing in 1852, James Dana says, " Your researches are to me 
always the highest authority." And again, in 1876, " Your 'Handbuch' 
gives me anew an exalted idea of the value of your labours for the 



MIEES: RAMMELSBERG MEMORIAL LECTURE. 39 

progress of inineralogical science. I have carried forward my studies 
so much of the time \vith your book in hand that I feel as if I had 
always enjoyed your companionship and your personal aid, and I may 
add that it was this aid which made my work possible." 

Senarmont, in 1855, cannot refrain from writing to the author of 
the " Handbook of Crystallographic Chemistry," although he does not 
know him personally, to express his appreciation of its great value, 
and his desire to assist Rammelsberg in these labours, in which, he is 
sure, Marignac joins him. 

Marignac himself, in 1881, referring to the second edition, writes, 
" You have already rendered chemists a great service in your preced- 
ing work by giving them everything relating to the crystalline 
form of chemical compounds, but the service is still greater now that 
you have added a description of all the physical properties. This 
must have involved immense labour, and science will always owe you 
a debt of thanks." 

In addition to his own treatises and memoirs, Rammelsberg pub- 
lished translations of Dumas' " Philosophic der Chimie," of Percy's 
" Metallurgy," and of several papers, such as that of Berzelius on 
mineral classification, and of Scacchi on polysymmetry. 

It would be inconceivable that one man could accomplish all the 
work which I have now surveyed without assistance, even in a long 
lifetime, and many of the mineral analyses which issued from Ram- 
melsberg's laboratory were made wholly or in part by his assistants. 
I find in his treatise on mineral chemistry the names of more than 
60 assistants or pupils mentioned as responsible for the analysis of 
as many minerals ; his own analyses are, of course, far more 
numerous. This will serve to indicate the activity of his laboratory 
and at the same time, perhaps, the fact that his heart was always 
really more in the development of research than in the routine work 
of education ; in fact, I do not think that he ever undertook much of 
the personal supervision of the laboratory during the later part of 
his career. 

I have quoted Professor Liveing's recollection of Rammelsberg as 
he was in the early prime of life. Dr. Liebert, who worked with 
him towards the end of his career as a teacher, tells me that the name 
of Rammelsberg always recalls to his mind the vision of a little, man, 
with his head thrust half into the balance case, rapidly changing the 
weights with a quick, nervous action. All such operations he con- 
ducted with extraordinary rapidity. He was never without a cigar 
held in the corner of his mouth, and always encouraged his students 
to smoke in the laboratory. At that time he was still engaged in 
analytical work, although his hand shook so much that he used a 
silver wash-bottle for fear of breakage. Dr. Liebert says that he was 

CO -*r 



40 MIERS : RAMMELSBERG MEMORIAL LECTURE. 

extraordinarily accurate in his lectures, and very rarely showed that 
absent-mindedness (Zerstreutheit) which is a proverbial failing of 
German professors ; he recalls only one occasion on which Rammelsberg 
lost his equilibrium. " He was lecturing on the oxygen compounds 
of nitrogen. As usual, the demonstrator had prepared the different 
experiments beforehand. All went well until nitric oxide was 
reached ; the Professor had stated that vividly burning bodies 
undergo further combustion when brought into contact with this gas, 
and proceeded to illustrate this by experiment. Having first intro- 
duced several heated metal wires which burnt with a vivid light, and 
having repeated the experiment with potassium and burning phos- 
phorus, he finally asked for sulphur, which he ignited and introduced 
into the gas. The flame was quickly extinguished. Rather irritated, 
he repeated the experiment with the same result ! Rammelsberg 
prided himself on his accuracy, and began to grow vexed at the 
repeated failure. With an angry glance at the demonstrator he 
demanded flowers of sulphur. The result was the same. This was 
too much for Rammelsberg's patience ; turning abruptly to the 
demonstrator, he said in an * undertone ' distinctly audible to all, 
1 You have made a mistake ; this carelessness will not do,' and turn- 
ing to his audience, apologised for the mistake which his demonstrator 
had made in preparing the wrong gas. 

" When the demonstrator repeated the process after the lecture, 
and compared what he had done with the notes of Rammelsberg's 
handbook, he found the explanation of ' his ' mistake. The state 
ment in the notes was : vividly burning bodies undergo further 
combustion in NO (examples enumerated) ; burning sulphur is ex- 
tinguished." 

Among the many chemists or mineralogists who at different times 
worked with him are to be mentioned Liveing, Wolcott Gibbs, Groth, 
Max Bauer, Riidorff, Friedheim, Stahlschmidt, Philipp, and Schone. 

As a lecturer and teacher he was, according to the testimony of all 
his pupils, admirably lucid and thorough ; but what seems to have 
impressed them most was his indomitable energy in research ; he 
would spare no trouble in repeating the experiments of others; he 
would spend weeks, or even months, in ascertaining by practical ex- 
perience the best methods before entering on a difficult analysis ; he 
was supremely careful in obtaining the best possible mineral specimens 
for analysis ; many of them he must have been obliged to purchase 
for himself at a considerable cost. Mineral chemistry has suffered 
much in the past from the fact that early analyses were made upon in- 
different material, and that there is usually no evidence to show 
exactly what was used for analysis. Rammelsberg's analyses have 
never been doubted, his material was beyond reproach, and it is 



MIERS : RAMMELSBERQ MEMORIAL LECTURE. 41 

satisfactory to know that the original specimens which he employed 
are now in the Berlin Museum fur Naturkunde ; I have little doubt 
that any further research which may ever be done upon these speci- 
mens will only tend to confirm the accuracy of his work, which was 
maintained until he became too old to carry out analysis at all. Even 
the very last of his published analyses, those of tourmaline, are quoted 
with high approval by Penfield, and were regarded by Rammelsberg 
himself as among his very best. 

His labours met with full recognition abroad, and he was an 
honorary member of more than thirty scientific societies. 

It only remains to mention the simple events of his life subsequent 
to the point at which it was left above, namely, the year 1874, when 
he was made ordinary Professor of inorganic chemistry in the Uni- 
versity of Berlin. In 1859, he had married his second wife, the 
daughter of the well-known naturalist, Chr. G. Ehrenberg ; by her he 
had two sons and one daughter, all of whom survive him. In 1883, he 
ceased to be Professor at the Gewerbe-akademie (which was trans- 
ferred as the Technische Hochschule to Charlottenburg), and was made 
Director of the newly-founded second chemical institute of the Uni- 
versity. There was much discussion concerning this appointment, to 
which Kopp might possibly have been elected, but it was felt that the 
director of a teaching laboratory ought to be pre-eminently a practical 
analyst, and no one had higher qualifications in this respect than Ram- 
melsberg. 

All his subsequent work was carried on in this laboratory, where 
his mineral analyses were continued uninterruptedly for nine years. 

In 1891, owing to failing eyesight, he retired from all the appoint- 
ments which he held, and resided quietly for the remainder of his life 
at Gross Lichterfelde, in the neighbourhood of Berlin, in a house 
which he had built adjoining that of his married daughter. 

In 1892, he underwent an operation which restored his vision, and 
he was able to devote himself for the next seven years to the recal- 
culation of mineral formulae and the writing of the second supplement 
to his "Mineralchemie ; " in this he was aided by the care of his loving 
wife, to whom he dictated much of his latest work. The evening of 
the old man's life was a happy and peaceful close to an honourable and 
active career ; his ambitions were realised ; his family was settled in life ; 
his faculties were unimpaired. Even now, although he was troubled 
by frequent headache, the veteran chemist was never idle, but when 
lying on the couch in his library would call his wife from the next 
room and dictate to her the thoughts which entered his mind. 

Professor Penfield, one of the leading representatives of the fciodern 
school, has told me of a visit which he paid to Rammelsberg in his 



42 MIERS : RAMMELSBERG MEMORIAL LECTURE. 

old age, when he had begun to feel himself out of touch with the 
younger school of mineral chemists. It was an interesting occasion 
for both, and to my mind it marks a chapter in the history of 
mineralogy : the termination of the old rigid reading of isomorphism 
and the introduction of wider views concerning replacement which, 
are destined to simplify the interpretation of mineral analyses. 
Professor Penfield writes: "It was in the summer of 1894 that I 
saw him, when he was 81 years old. He was living a very quiet 
life at Gross Lichterfelde, near Berlin, and his home seemed to be 
an ideal one for an elderly man. He was at that time still engaged 
in scientific work, although he was not strong enough to do very 
much. He presented me, for example, with a copy of one of his 
recent articles, in which he criticised my views concerning the 
chemical composition of staurolite, and he showed me the manuscript 
for the completion of his " Mineralchemie," which was printed one or 
two years later. I especially enjoyed hearing him tell of Berzelius, 
the Roses, and men of that generation, for he knew them well and 
appreciated their qualities. . . . He said that it was a keen pleasure 
for him to differ from others ; it added a certain spice and zest to 
life to have and hold scientific opinions at variance to those of 
others. He certainly was a most friendly and genial old gentleman." 

It is pleasant to think of the old man softened in character but 
still retaining the fierce love of battle and adhering doggedly to his 
views. 

Those who knew him towards the close of his life were most im- 
pressed by his extraordinary juvenility ; he possessed a power of 
work, a keenness of debate, and a freshness of memory which few 
retain at such advanced years. His power of concentration enabled 
him to work undisturbed and rapidly among any distractions. Even 
when he was an old man, the presence of his little grandchildren was 
no hindrance to him while writing. 

His interest was throughout his life so centred in his scientific work 
that he had few relaxations, and did not take much interest in general 
literature ; books of travel were his chief delight. He possessed an 
extraordinarily retentive memory, and astonished his friends by his 
knowledge of the facts of history and geography ; his acquaintance 
with modern languages was extensive. 

In early life he travelled a good deal during his vacations, but always 
made the best use of his time ipr scientific purposes, studying the 
geology of the countiies in which he stayed, and collecting minerals 
for analysis. One of his early journeys was to Sweden (1844), and 
for the purpose of visiting Berzelius ; another (1867) was a geological 
tour in Auvergne, in company with the well-known mineralogist, 



MIERS: RAMMMELSBURG MEMORIAL LECTURE. 43 

Professor Sadebeck; he was twice sent to Paris (1855 and 1867) by 
the Government to act as a representative at international exhibitions. 
Only in later life were his journeys made as pleasure trips. 

His keenness of memory and juvenility of mind remained to the 
end of his life, and he found great pleasure in recounting reminiscences 
of his travels and of the men whom he had known. Writing to 
Wolcott Gibbs in 1893, he says, " I have left my 80th year behind, 
and have for the last two years given up all educational work. 
Except, however, for the weakness of old age, I feel myself to be 
active both in mind and body." 

It was not till he had attained the ago of 86 that the peaceful 
and industrious evening of his life was brought to a close. He had 
never completely recovered from an attack of influenza which had 
prostrated him a few years previously ; in the winter of 1899 he was 
thrown back by an attack of bronchial catarrh, and on the 28th of 
December sank to final rest from his labours after a life of unexampled 
industry. 

His character recalls irresistibly the spirit of Browning's gram- 
marian : 

" He knew the signal and stepped on with pride 
Over men's pity, 

Left play for work and grappled with the world 
Bent on escaping. 
* What's in the scroll,' quoth he, * thou keepest furled ? ' " 

The great men of genius when they die leave the example of a life 
which all can admire but to which few can attain ; the men of great 
talent, like Kammelsberg, who make unceasing use of their powers, 
and by a life of industry contribute, perhaps, equally to the increase 
of knowledge, leave an equally valuable legacy, an example that all 
can emulate. 





[To face p. 45. 



EAOULT MEMORIAL LECTURE. 

(DELIVERED ON MARCH 26rn, 1902.) 

By J. H. VAN'T HOFF, Member of the Prussian Academy of Science, 
and Professor in the University of Berlin. 

THE foreign honorary member whom the Chemical Society lost a year 
ago, although of an amiable, social character, seems to have been a 
man of retiring disposition. He rarely left France, and for the larger 
part of his life lived in that somewhat out of the way town, Grenoble. 

Raoult's life thus offers little of attractiveness ; it is not romantic ; 
yet, after many years of work, the romance of his life was that 
almost sudden rise to fame, spreading from this nearly unknown 
corner, first over the frontier of his country, and then back to France, 
which made him one of the most prominent men of science of his age. 

Frangois-Marie Raoult, born on the 10th of May, 1830, in Fournes, 
in the departement du Nord, in France, was of modest origin, his 
father having been an employ^ des Contributions. It was intended 
that he should enter the Bureaux de 1'Enregistrement, but this career 
did not satisfy his aspirations, so he left the Enregistrement and ob- 
tained permission to go to Paris, there to pursue his studies. Without 
fortune or patronage, young Raoult was a student struggling for a 
livelihood, unable to finish his studies without himself providing the 
means. 

So he gave up studying at Paris, some years later, in 1853, after 
presenting to the Academic des Sciences a short communication, probably 
his first, containing observations on the transport of electrolytes by 
the action of the galvanic current as well as on electrical endosmosis 
(Compt. rend., 1853, 36, 826). Characteristic of the circumstances in 
which he pursued these investigations are his concluding words : " Je 
laisse k d'autres plus fortunes que moi le soin de mener la, science plus 
avant dans la voie nouvelle que je viens de lui ouvrir." 

It was in the same year, 1853, that Raoult accepted the appointment 
of Aspirant repetiteur in the Rheims Lyce'e, becoming in 1855 Regent 
de physique.iu the College of St. Die* ; in 1856, Professeur adjoint, and 
subsequently Charge de cours de physique in Rheims again ; in 1860 in 
Bar-le-Duc ; his leisure having been employed in obtaining his degree 
as Licencie es-sciences physiques and Agrege de I' Enseignement secondaire 
special. In 1862, he left Bar-le-Duc for a corresponding position in 
Sens, and in this small country town, with no intellectual resources, 
left to his own initiative amid adverse material surroundings, fore d 



46 VAN'T HOFF: RAOULT MEMORIAL LECTURE. 

by want of means to construct his own apparatus, he prepared the Thtee 
on electromotive force for which, in 1863, he obtained his degree in 
Paris of Docteur h-sdences physiques. 

With this publication, Raoult began his scientific career, which 
may be divided into three distinct periods, physical, chemical, and 
physico-chemical . 

Raoult as a Physicist. 

. The above-mentioned thesis at once characterises Raoult as an 
accurate and independent investigator, already in advance of his age 
in conclusions founded on careful examination of fact. 

Firstly, employing different galvanic cells of the Daniell type, 
Raoult measured the heat due to the chemical action (ckaleur chimique) 
and that due to the electric work produced (chaleur voltaique). 
Contrary to the opinion then adopted, he found that these two values 
were by no means identical ; in some cases, as in the ordinary Daniell 
cell, Cu | CuS0 4 , ZnS0 4 | Zn, both practically correspond, for each is 
about 23 '6 cal. for a gram-equivalent (the most exact recent measure- 
ment gave 24-8) ; in an analogous cell, Cu | Cu(N0 3 ) 2 , AgN0 8 | Ag, 
however, the "chaleur chimique" amounted to 16*4, whereas the 
" chaleur voltaique" was only 7*8. Keeping as closely as possible 
to the direct results of experiment a characteristic of Raoult' s way 
of working he closes this communication with a mere question : 
" Pourquoi cette difference 1 VoiU une difficulte serieuse digne de 
1'attention des physiciens." 

A second part of this research was devoted to decompositions pro- 
duced by a galvanic current in the so-called voltameter. Raoult studied 
especially the heat development accompanying decompositions, explain- 
ing it by the excess of heat corresponding to the electric work done 
in the voltameter over the heat absorbed by the chemical change 
produced, in this way applying to the voltameter the principle under- 
lying his discovery of the difference between the two values found for 
the cell. Thirdly, this conception enabled him to determine indirectly 
the heat absorbed by the chemical change which occurs in the volta- 
meter. It was thus, for example, that he found the heat absorbed in 
decomposing 9 grams of water to be 33'8 cal., whereas JFavre and 
Silbermann found the heat developed in the formation of the same 
amount of water to be 34*5 cal. 

The conclusion to his two papers on this subject (Ann. Chim. 
Phys.y 1864, [iv], 2, 317 ; 1865, [iv], 4, 392) may be given in his own 
words : 

"J'ai, le premier, mesure et compart la chaleur chimique et la 
chaleur voltaique des piles.' 1 



VAN'T HOFF; RAOULT MEMORIAL LECTURE. 47 

" J'ai decouvert les ve*ri tables lois qui president au degagement de 
la chaleur dans les voltametres." 

"J'aidonn6 le premier moyen de mesurer la chaleur degag^e ou 
absorbee dans les actions chimiques accom plies sous 1' influence des 
courants electriques." 

In his further investigations on electro- and thermo-chemistry, 
Raoult liked to come back to that same question of difference between 
voltaic and chemical heat which he considered to be fundamental. A 
very striking proof of the non-identity of the two was given in the fact 
established by him (Compt. rend., 1869, 68, 643) that solid and liquid 
metals, at the temperature of fusion, produce in the cell the same 
electromotive force ; he insisted on this especially in the case of bis- 
muth, which metal, having a latent heat of fusion corresponding to 
1'327 cal. for an equivalent of 105 grams, ought to produce in melting 
a difference in electromotive force of 0-055 Daniell. 

A second indication in the same direction is not less valuable. 
Finding that the electromotive force in a Daniell cell increases on dilut- 
ing the solution of zinc sulphate surrounding the zinc, but decreases 
on diluting that of the copper sulphate (ibid., 1869, 69, 823, 826), he 
insisted on the conclusion that in taking a saturated solution of zinc 
sulphate and so increasing the heat development of the reaction by 
that arising from the crystallising out of the solid sulphate, the 
electromotive force changes in the opposite sense and becomes smaller. 

Raoult's attention being claimed by other pursuits, it was in 1870 
that he summed up his views in a very interesting paper on the 
difference between voltaic and chemical heat (Bulletin de la Societe 
de Statistique de I'Isdre). He concluded that in the galvanic cell two 
different kinds of change take place, the one incapable, the other 
capable, of producing electromotive force. Those incapable are changes 
of state of aggregation, such as melting and dissolving ; those capable 
are chiefly chemical change and change in concentration.* We now 
see how far Raoult had already gone in the right direction and how 
some further experiments on this influence of concentration, and 
especially how an application of theoretical considerations, might have 
led him to a definite solution of the problem. 

* Dans les e'le'ments voltaiques analogues a celui de Darnell, la de"sagregation 
chimique des corps et leur diffusion dans 1'eau, de meme que les actions inverses ne 
participent en rien a la production du courant e*lectrique, et ce sont les seules 
actions qui sont dans ce cas. 



48 VAN'T HOFF: RAOULT MEMORIAL LECTURE. 



Raoult as a Chemist. 

It was while he was carrying out this electro- and thermo-chemical 
research, in which many new facts and relations came to light, and 
on which, perhaps, it is not necessary to dwell on this occasion, that 
Raoult entered the Faculte des Sciences de Grenoble, in 1867, as Charge 
du cours de chimie, being promoted, in 1870, to the Chair of Chemistry 
as successor to Leroy. This chair he occupied until his death on 
April 1st, 1901. From this time, a change is visible in the direction 
of Raoult's work, as he devoted himself more to purely chemical in- 
vestigation, although he always had a tendency to look at the physical 
side of every problem. 

This change in the field of Raoult's investigations explains how the 
hitherto continuous character of his work gave place to one of greater 
variety. 

We now find Raoult occupied in examining the gas evolved 
by a "Fontaine ardente," at St. Barthelemy, near Grenoble, and 
proving it to be merely methane ; next as a judicial expert we see 
him prove the presence of zinc and copper as normal constituents of 
the human liver, especially in advanced age (Compt. rend., 1877, 85, 
40). The absorption of ammonia by ammonium nitrate he studied 
simultaneously with, but independently of, Divers (ibid., 1873, 76, 
1261), and further, he recommended the use of retort-carbon as a 
means of preventing irregular boiling in the distillation of sulphuric 
acid. He also demonstrated the inverting action of light on sugar 
(ibid., 1871, 73, 1049). Then we find him studying the influence of 
carbon dioxide in air on respiration with the interesting result that it 
diminishes the production of the gas, this effect, however, being 
counteracted by the increased pulmonary action (ibid. t 1876, 82, 
1101). Lastly, aiming probably at a lecture experiment, Raoult 
investigated the formation of a basic carbonate of lime, CaO,CaC0 8 , 
produced by heating calcium oxide in carbon dioxide (ibid., 1881, 
92, 189, 1110, 1457) which compound has probably played a part 
in Debray's work on dissociation and has the property of setting 
like gypsum after addition of water. Medals made with this material, 
which has the properties of gypsum but is somewhat harder, were 
presented by Raoult to the French Academy. 

This was Raoult's last purely chemical publication, for he had now 
found the right direction in which he was to go until death put an end 
to his labours. 



HOFF: RAOULT MEMORIAL LECTURE. 49 



Raoult as a Physico-ckemist. 

It was in 1878 that Raoult 's first publication on freezing points 
appeared (Compt. rend., 87, 167). This was merely of an empirical 
character, and pointed to the proportionality (already indicated by 
Guldberg) between lowering of freezing point, lowering of vapour 
pressure, and rise of boiling point. Raoult thus entered at once into 
an investigation of the two subjects which were to form the corner- 
stones of his fame. As he himself afterwards relates, the lowering of 
vapour-pressure formed the primary subject of study,, and I suppose 
that, finding the difficulty of determining the strength of alcoholic 
solutions by measuring their boiling points or vapour-pressures because 
of the volatility of alcohol, he applied himself to the indirect method 
of determining the freezing points. At all events, 'his next paper 
(ibid., 1880, 00, 865) is devoted to the freezing points of mixtures of 
alcohol with water. He determines the proportionality between the 
lowering of the freezing point and the percentage of alcohol present in 
the solvent, thus stating for this mixture the law which Blagden had 
found for solutions of inorganic substances. That this stood in close 
connection with practical application is obvious from the list of alco- 
holic liquids added to the paper, beginning with cider and ending with 
Marsala, indicating that their freezing points (-2 and - 10 -1) were 
fairly proportional to their alcoholic strength. Moreover, he pointed 
out that a wine may be strengthened by freezing out part of the 
water. 

Having by a happy stroke of luck passed from the investigation of 
ethyl alcohol to other alcohols and from these to other organic sub- 
stances, which had not been examined by Blagden, by Rudorff, or by 
de Coppet, and having introduced de Coppet's conception of molecular 
depression, Raoult as early as 1882 attained a wider view of the 
subject, and published his now historical table of 29 organic com- 
pounds (Compt. rend., 1882, 94, 1517) (see next page). 

Following Raoult's conclusion, it is obvious from this table that the 
product obtained by multiplying the depression for a solution contain- 
ing 1 gram of substance in 100 grams of water by the molecular 
weight of the dissolved substance, is a constant : 



where C stands for the depression caused by P grams in 100 grams of 
water, and K the molecular constant. 

It is astonishing how easily Raoult abandons the narrower view of 



50 



VAN'T HOFF: RAOULT MEMORIAL LECTURE. 



Substance. 


Formule. 


Poids 
mol^culaire. 


Abaissement 
du point de 
congelation 
par gramme 
de substance 
dans 100 gr. 
d'eau. 


Produit du 
poids molec. 
par 1'abaisse- 
ment du a un 
gramme de 
substance. 


Alcool me'thylique. . . 


C.H.O 


32 


- 0-541 


17-3 


,, ethylique 
butvlioue 


CHO 
C 8 H 10 0, 


46 
74 


0-376 
0'232 


17-3 
17-2 


Glycerine 


C 6 H 8 8 


92 


0-186 


17-1 






182 


0*099 


18'0 


Sucre interverti 


C'HA* 


180 


0-107 


19-3 


,, de lait 


C ,Ho40oJ 


360 


0-050 


18*1 




v '24"24~24 

CoAH,0~, 


342 


0-054 


18-5 


Salicine 


C*HX 


286 


0-060 


17-2 


Phenol 


c! 2 H 6 O a 


94 


0-165 


15-5 


Pyrogallol 


CiXoJ 


126 


0-129 


16'3 


Chloral (hydrate) 


C 4 HC1,0 2 + H 2 2 


165'5 


0-114 


18-9 


Acetone 


C 8 H 8 0, 


58 


0-294 


17-1 


Acide formique ... 


CoHo! 


46 


0-419 


19-3 


,, acetique 


C 4 H 4 4 


60 


0-317 


19-0 


butvriaue 


C 8 H 8 4 


88 


0-212 


187 


,, oxalique 


C.HoOa^^HoOa 


126 


0-182 


22-9 


lactiaue 


C 6 H 6 8 


90 


0-213 


19 '2 


,, malique . 


C a H 8 10 


134 


0-139 


187 


, , tar trique 


C!HO, 


150 


0-130 


19-5 


,, citrique 


CloHoOll+HnOo 


210 


0'092 


19-3 


Ether 


cXoO, 


74 


0-224 


16-6 


, , acetique 


CaHa(X 


88 


0-202 


17-8 


Acide cyanhydrique ... 
Acetamide 


tfAzC, 4 


27 
59 


0718 
0-301 


19'4 
17-8 


Uree 


C^H^AzoCX, 


60 


0*286 


17'2 


Ammoniaque 


AzHT 4 


17 


1-117 


19-9 


fithylamine 


C^H^Az 


45 


0-411 


18 '5 


Propylamine 


CH Az 


59 


0-312 


18*4 













practical application for the wider scientific horizon, and instead of a 
list of ciders and Marsalas, an expression like this occurs : 

" Cela tend & montrer que, dans la plupart des cas, les molecules 
des composes organiques sont simplement separees par 1'acte de la 
dissolution et amenees a un meme etat, sous lequel elles exercent la 
meme influence sur les propriety physiques de 1'eau." 

Of course Raoult does not omit to indicate that a new mode of deter- 
mining molecular weights may be founded on freezing point experi- 
ments. 

Two more papers appearing in the same year (Compt. rend., 95, 
187, 1030) show that Raoult's general formulation of the freezing 
point law for solutions holds not only for water bat also for other 
solvents. 

Each solvent has its moleculat constant which, in some cases, prob- 



VAN'T HOFF : RAOULT MEMORIAL LECTURE. 51 

ably owing to the formation of double molecules by the dissolved sub- 
tance, may be reduced to half the normal value. These constants are 
proportional to the molecular weight of the solvent (i/i), being on an 
average : 

I-0-63.' 

Raoult's data are as follows : 

Substance. K. M r . K/M lt 

Acetic acid 39 60 0'65 

Formic acid 28 46 0-61 

Benzene 49 78 0*63 

Nitrobenzene 68 123 0'55 

Ethylene dibromide 117 188 0-62 

Water. 37 3x18 0-69 

vVe observe the assertion by Raoult that the constant 18 '5 for organic 
compounds in water is abnormal and is due to the formation of double 
molecules, whereas the molecular weight of water as a solvent is taken 
as 54, and is due to a polymerisation in the liquid state corresponding 
to (H 2 0) 8 . 

Cryoscopy. Inorganic Compounds. 

Having thus obtained an insight into the laws governing organic 
compounds, Raoult enters the more difficult field of salt solutions, in 
which a good deal had already been done by Riidorff and de Coppet, 
who nevertheless had not reached any general conclusions. 

Raoult took acids and bases as intermediate links and found that 
strong monobasic acids, like hydrochloric acid, and strong mono-acid 
bases, like potassium hydroxide, have a molecular depression (37) 
double that of the weaker ones and of organic compounds (18*5). On 
this observation he founded a neat method of determining the amount 
of substitution which takes place when a strong acid or base acts on 
the solution of the salt of a weak one (Compt. rend., 1883, 96, 560, 
1650; 97,941). 

The next year (1884) witnessed the publication of his systematic 
researches on the behaviour of salts, and it is curious to observe, by 
the way, that at this stage of his inquiry Raoult first adopted the new 
atomic weights and thereby the system of Avogadro, which, it might 
almost be said, he had unconsciously adhered to for more than two 
years. His first paper on salts (Compt. rend., 1884, 98, 509) still 
contains the formula KN0 6 for saltpetre, but in the next (ibid., 1047 ; 
99, 324), he adopts the values H= 1, O = 16. The amount of system- 
atic work done in this short space of time is astonishing, the different 
groups of salts being taken one by one in the order of the valency of 



52 VAN'T IIOFF : RAOULT MEMORIAL LECTURE, 

their metals and the basicity of their acids, and, grouping them in this 
happy way, Raoult reaches at once the general and unexpected result 
that the molecular depression of salts, strong acids, and bases can be 
calculated by a summation of numbers, relating to their radicles : 

Univalent negative radicles (Cl,Br,OH,N0 3 )... 20 

Bivalent (S0 4 ,Cr0 4 ,CO 3 ) ... 11 

Univalenc positive (H,K,Na,NH 4 ) ... 15 

Bi- and poly-valent positive radicles (Ba,Mg,Al 2 ) 8* 

Applying the method of calculation, for example : 

for KOH we get 15 + 20 = 35, instead of 35 -3 found. 
forAl 2 01 6 8 + 6x20 = 128, 129 

Let me state this in Raoult's own words in order to show in what 
an impartial and objective way his own conviction is subordinated to 
fact: 

" Ces faits pfrouvent que, contrairement & ceque j'avais cru jusqu'ici, 
la loi gtnerale de congelation ne s'applique pas aux sels dissous dans 
1'eaii . . . ; par centre, ils tendent & montrer qu'elle s'applique aux 
radicaux constitutifs des sels, & peu pres comme si ces radicaux etaient 
simplement melanges dans les dissolutions." 

As mentioned by Eaoult, this additive character had been found by 
Favre and Valson to apply to the density, and by Hugo de Vries to the 
osmotic pressure of salt solutions. 

An application of these results is made in deciding whether a double 
salt exists in solution as such, or is split up into its components, the 
former being the case, for example, in such a compound as sodium 
platinichloride, and the latter for the alums (Compt. rend., 1884, 99, 
914). Most important, however, is the fact that from this time dates 
the great international co-operation in the field which Eaoult had 
opened. 

Whereas Raoult's early work on electromotive force and heat- 
development lay fallow, because the theoretical conceptions to which 
they could be attached were only developed about fifteen years later, 
it was an extraordinarily happy coincidence that his freezing point 
investigations met with corroborative theoretical views, which could 
only enhance the high value already attached to Raoult's achieve- 
ments. 

His first work on electromotive force, although important in 
character, left Raoult's name almost unknown, because it appeared at 
least ten years too soon, and was therefore overlooked when the stream 
of general development reached that field. Raoult at this period was 

* In Raoult's Cryoscopie (1901), these numbers are 19, 9, 16, 8, respectively, the 
'ast number for bivalent radicles only. 



VAN'T HOFF : RAOULT MEMORIAL LECTURE. 53 

Officier d'academie (1865), and Officier de V Instruction publique (1872), 
and had received the Medaille des societes savantes in 1872. 

The work on cryoscopy came just at a time when an ardent activity 
was developing in different countries and from different points of view. 
Victor Meyer in Germany and Patern6 in Italy applied Raoult's 
method of determining molecular weights as early as 1886; de Vries 
has already been quoted ; then came the theory of solutions, developed 
by Arrhenius in Sweden and by myself in Holland, and then the great 
support lent by Ostwald in his Zeitschrift fur physikalische Chemie, in 
which Raoult at once took part with enthusiasm, as the facsimile of 
his letter published with this lecture proves. Rarely has science seen 
such international interest centred on one problem, and Raoult stood 
at once foremost, in the position of great advantage belonging to the 
man who relies on fact in the first instance, and is eager for generalisa- 
tion, absolutely independent in his opinions, and open to every achieve- 
ment on his way. 

An unbroken series of distinctions now showered down on Raoult, 
beginning in 1888 with the Prix international de chimie La Caze, 
followed by the Davy Medal in 1892, Correspondent de VInstitut in 
1890, and honorary or foreign Fellow of the Society of Rotterdam 
in the same year, of the Literary and Philosophical Society of Man- 
chester in 1892, of the Chemical Society of London in 1898, and of the 
Academy of St. Petersburg in 1899. In 1900, he was crowned with 
the Commandership of the Legion d'honneur, a distinction which gave 
him the highest gratification. > 

Cryoscopy. Theory of Solutions. 

In the meantime, in 1892, Raoult recommenced his freezing 
point investigations, which had been interrupted in 1884, but now 
received a new direction with special relation to the theory of solutions. 
As is well known, this theory treats of the laws governing extreme 
dilution, and assumes that it is possible to calculate Raoult's freezing 
point constants under these conditions. We therefore see him occupied 
in accumulating experimental data for these conditions with the ac- 
curacy and impartiality so characteristic of his work. 

Let us notice that at first Raoult deemed the molecular con- 
stant 18' 5 found for organic compounds in aqueous solution to be 
abnormal, and assumed 37 as the normal value, thus considering 
organic compounds to be present in the form of double molecules (ibid., 
1882, 95, 1030). It was natural to try, from this point of view, 
whether extreme dilution would not break down those double mole- 
cules and consequently double the molecular constant. A first series 
of experiments made with cane sugar (Compt. rend., 1892, 114, 268, 



54 VAN'T HOFF: RAOULT MEMORIAL LECTURE. 

440) seemed favourable to this view, and extreme dilution appeared 
to show an increase in the molecular constant up to 20' 9. As, how- 
ever, ethyl alcohol did not show an analogous increase (ibid., 1897, 
124, 851, 885), 'the experiments with cane sugar ^ere again taken u{ 
with increased precautions (ibid., 1897, 125, 751) and, by a small 
extrapolation, gave 18*7 as the limit for extreme dilution, alcohol 
giving 18*3. At the same time, Raoult examined sodium and potassium 
chlorides with the utmost care, and finding, as the limiting values, 37*4 
and 3 6 '4 respectively, he openly declared himself in favour of the new 
theory of solutions : 

" En definitive, il est maintenant demontre, pour moi, que les 
abaissements moleculaires du chlorure de potassium et du sucre, 
comme ceux du chlorure de sodium et de Palcool, opt des valours limites 
conformes aux provisions de M. Arrhenius." 

In the summary of his work in this direction (Cryoscopie, Scientia, 
No. 13, 1901), written in the last year of his life, Raoult grants all 
the conclusions of the theory of solutions, but as a thoroughly 
experimental investigator he objects to build it up on that large but 
hypothetical principle called the extended law of Avogadro. He con- 
sequently prefers generalisation, and in such a sense expresses his 
views on solutions as follows in concluding a lecture at the Paris 
International Congress of Chemistry in 1900. "A une m6me tempe"- 
rature 1'acte de la dissolution et celui de la vaporisation reduisent chaque 
corps en particules, qui ont la me me masse et la meme force vive de 
translation & l'e"tat dissous et a 1'etat gazeux." 



Vapour-pressure. 

We now come to the parallel series of experiments on vapour-pres- 
sure which Raoult executed. As has been observed, it was the 
proportionality between the rise of boiling point, the lowering of 
vapour-pressure, and the depression of freezing point, which first led 
Raoult to his freezing point investigations. It was the fertility of this 
field which brought him back to a study of vapour-pressure once more. 

As had already been proved in some cases by Wiillner, Raoult found 
proportionality to exist between the lowering of the vapour-pressure 
(/-/') and the pressure (/), at least for dilute solutions, and hence 
the relative lowering of pressure 

f-f_ 

f 
is independent of temperature. 

The second step was to prove the consequence of proportionality 
between the lowering of vapour-pressure and of freezing point and to 



VAN'T HOFF: RAOULT MEMORIAL LECTURE. 



55 



test the constancy of the so-called molecular lowering which was found 
(Compt, rend., 1886, 103, 1127; 1887, 104, 967) and could be ex- 
pressed by 

jp-M = K, 

where, as before, P is the number of grams of substance dissolved in 
100 grams of the solvent, and M its molecular weight. 

The third step was fundamental and may be considered as the 
happiest generalisation which Raoult reached (Compt. rend., 1887, 104, 
1430). It was indicated by the results of freezing point determina- 
tions in which Raoult had hoped to detect proportionality between 
molecular lowering and the molecular weight of the solvent (a relation, 
however, which did not prove to be general). The molecular lowering 
of vapour-pressure was therefore compared with the molecular weight 
of the solvent, with results which are shown in the following table : 



Dissolvant. 


Poids 
mole'culaire du 
dissolvant 
M'. 


Diminution 
moleculaire 
uormale de 
tension 
K. 


Diminution de 
tension produite 
par 1 mol. dans 
100 mols. 
K 
M'' 


Eau 


18 


0*185 


0-0102 


Chlorure phosphoreux 
Sulfure de car Done 


137-5 
76 


1-49 
0-80 


0-0108 
0*0105 


Bichlorure (CC1 4 ). 
Chloroforms 


154 
119'5 


1-62 
1*30 


0-0105 
0-0109 


Amylene 


70 


074 


0-0106 


Benzine 


78 


0*83 


0*0106 


lodure de me'thyle . . 


142 


i'49 


0-0105 


Bromure d'e'thyle 


109 


18 


0-0109 


Ether 


74 


071 


0-0096 




58 


0'59 


0-0101 


Alcool me'thylique 


32 


0'33 


0"0103 











Raoult formulates the relation thus found as follows : " 1 Mol. 
de substance fixe, non saline, en se dissolvant dans 100 mol. d'un 
liquide volatil quelconque, diminue la tension de vapeur de ce 
liquide d'une fraction a peu pres constante de sa valeur et voisine 
de 0-0105," that is, 

~ = 0-0105. 
M i 

It was this conclusipn that at once brought Raoult into relation 
with my theory of solutions (Bihang K. Svenska Vet.-Akad. Handl, 
1886, 21, No. 17), with which it is in agreement, as Raoult himself 
states (Compt. rend., 1887, 106, 859) : 



56 VAN'T HOFF: RAOULT MEMORIAL LECTURE. 

" L'accord entre 1'exp^rience et la theorie est done, sur tous lea 
points, aussi complet qu'on pent le desirer en pareille mature." 

It was the investigation of this law which Kaoult pursued in detail 
in the latter part of his life ; he found it to apply also to salts such 
as sodium chlorate, potassium acetate, sodium acetate, lithium chloride, 
lithium bromide, potassium thiocyanate, calcium nitrate, calcium 
chloride, and mercuric chloride, at least in alcoholic solution, in which 
they behave as non-electrolytes (Compt. rend., 1888, 1O7, 442), whereaa 
in aqueous solution they behave, to use his own words, ," comme s'ils 
etaient decomposes en leurs ions" 

But the best part of his work was still to be done, in cooperation 
with Becoura (Compt. rend., 1890, 110, 402; 1896, 122, 1175). In 
using acetic acid, and afterwards formic acid, as a solvent, Raoult 
found that KjM l had a value of about 0-0161, instead of 0:0105, and 
at once attributed the discrepancy to the abnormal vapour density of 
acetic acid (which again is involved in the theory of solutions, as M l 
means, on this basis, the molecular weight of the solvent as derived 
from the density of its saturated vapour), a number which also exceeds 
the normal value by about 60 per cent. It was on this account that, 
in a later publication (ibid., 1893, 117, 833), he gave this most general 
and exact expression for his vapour-pressure observations : 



_ 

f ' P 'M 1 d M l 

where d l is the observed density in the saturated vapour and d that 
calculated from M r 

Although by this plan Raoult obtained absolute identity with the 
expression derived from the theory of solutions, he preferred to 
regard his formula, founded on fact, as an equation essential to the 
osmotic law, osmotic pressure still being a value unsuited for direct 
estimation. This Raoult had learned, by a preliminary investigation 
(Compt. rend., 1895, 121, 187), abandoned when the manometer broke 
after the highest osmotic pressure ever observed, namely, 50 atmo- 
spheres, had been attained, a value far higher than is wanted in these 
experiments. 

We are now coming to the end. Raoult's constitution seems to 
have been a vigorous one ; the only indication to the contrary which 
I can discover is that in 1887 he resigned an additional professorship 
of Chemistry and Toxicology at the Grenoble Medical School, which 
he had held since 1873; this he resigned on account of his health, at 
first provisionally, and then, in 1892, for good. The 7th of April, 
1900, was the date for his official superannuation, but by a special 
decision of the Board of Trustees, he remained in office, hors cadre, a 





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[To face p. 56. 



VAN'T HOFF : RAOULT MEMORIAL LECTURE. 57 

very high distinction and a proof of his unbroken vigour at that time. 
Yet, wise man as he was, he used well those days, no doubt fearing 
that they might not last, and in two exhaustive treatises, dated 1900 
and 1901, he published his final views on Tonometry and Cryoscopy 
(Scientia, No. 8 and No. 13) ; it was just in time, for, without any 
warning symptoms, he died, almost suddenly, on April 1st, 1901. 

As I had not the honour of being personally acquainted with Raoult 
and only occasionally corresponded with him, I must rely on the 
verdict of others if I venture to consider him as a man. Yet his 
character may be read in his papers : activity, patience, tenacity to an 
extreme degree in pursuing an aim, having an eye as much for detail 
as for vaster and vaster horizons, absolute independence of mind, 
power of criticising or of admitting without passion the views of others 
as well as his own, and of testing both with the same calm conviction 
that the last word must rest with experiment ; this is what we read in 
every page and what the whole chemical world may know. 

Looking at him still more closely, let us read what was said in the 
name of the University and of the Faculty at the grave in that 
Grenoble which Raoult had chosen for his residence during more than 
thirty years. Possessor of the highest local distinctions, if such may 
be counted ; doyen ; holder of the only medal of the French Government 
for services given by him as vice-president of the Conseil d'hygttne de 
I'Isbre, the representative man of the University : words fail me to 
express how greatly he was regretted both on account of his character, 
and of the distinction which he had conferred on the city which 
mourned him. 

To her who best must have known Raoult I am indebted for my 
last and best words* : 

" ' Ce que f ut 1'homme prive, tous ceux qui 1'ont connu ont apprecie" 
cet esprit bienveillant, fin, spirituel, cette extreme bonte, cette modestie 
a toute epreuve. 

' II ne m'appartient pas de vous dire ce qu'il f ut pour les siens, se 
devouant & eux entierement, les entourant de son amour, de sa 
sollicitude. 

* Tendre pere, il eut 1'immense douleur de se voir enlever une enfant 
de 8 ans, et plus tard une fille de 26 ans, laissant un enfant & qui il 
prodigua toutes nes tendresses. 

'Puisse ce recit bien douloureux pour moi vous faire comprendre 
que comme homme et comme savant celui que je pleure merite tous 
les regrets.' " 

* Letter from Mme. Raoult, Grenoble, January 24th, 1902. 





[To face p. 59. 



WISLICENUS MEMORIAL LECTURE. 1 
By W. H. PERKIN, jun. 

WHEN Johannes Wislicenus passed away, two years ago, an acute 
sense of loss was felt, not only in the world of Science, where his 
name had long been placed among those of the great organic 
chemists, but also in other fields where men of science have but 
seldom left deep impressions of their personal influence. 

Innate qualities, obscured as they so often may be by others 
adventitious or assumed, are not always easy to trace unless history 
gives the clues. But the character of Wislicenus was even higher 
than his scientific work, and I am tempted to dwell upon it, rather 
than on the achievements which are familiar to chemists, because 
the simplicity and personal force of the man were known to com- 
paratively few, while his chemical fame was, of course, world-wide. 

During the seventeenth century, a family of Poles, victims of the 
intolerant spirit and religious persecution of the time, wandered 
homeless into Germany, and finding at last congenial surroundings 
in Schonburg, where for many generations afterwards the family made 
their home, they took up priestly duties and devoted their lives to the 
welfare of their fellow-men. Among their descendants was Gustav 
Adolf Wislicenus, a man who sustained the family traditions and 
shone with all the fine qualities of his race. The story of his life 
reveals the fearlessness of his character, and aids us in forming a true 
conception of the forces in the composition- of his son Johannes, for 
between the two men there was more in common than is usual between 
father and son. 

Gustav \dolf Wislicenus felt the weight of religious oppression at 
an early age, for whilst yet a student he was condemned to imprison- 
ment on account of his connection with certain sectarian societies, 
This was in 1824, and it was not until 1829, five years later, that hin 
friends were able to obtain for him a formal pardon and the remission 
of the remainder of his sentence. After his release he chose the 
vocation of a Lutheran priest, and from 1834 pursued this calling at 
the little village of Klein-Eichstadt, near Querfurt, until he was 
preferred to the Neumarkt-Kirche at Halle in the year 1841. 

This period in Prussia was marked by the rapid growth of popular 
antagonism to the efforts made by the more powerful of the clergy to 
regulate the form of religious worship throughout the country, and 

1 The author wishes to acknowledge the very valuable assistance which he 
received from Dr. A. Lapworth while compiling this Memorial Lecture. 



60 PERK1N: WISLICENUS MEMORIAL LECTURE. 

this feeling^ first reached its climax in Saxony, and in particular among 
the rationalistic clergy. With these pastor Wislicenus threw in his 
lot. At the great meeting of " Lichtfreunde " at Cothen in 1844, he 
gave full expression to his revolutionary views on the foundations of 
faith, the result being that the supporters of the new ideas found 
themselves denounced as traitors and their meetings proscribed, 
Wislicenus himself being expelled from his office two years later. 

The growth of the spirit of independence had led to the formation in 
different parts of the country of a number of ' free congregations,' 
and the foundation of one of these at Halle was the first object which 
"Wislicenus set himself to attain after his loss of position. Political 
movement culminated in the revolution of 1848 and the Frankfort 
Parliament. In the latter, which was a Parliament without states- 
men, we find Gustav Wislicenus and many other leaders in the free 
religious movement occupying positions of prominence and playing 
active parts. 

At this time Johannes Wislicenus was about fifteen years of 
age. He was born at Klein-Eichstadt on June 24, 1835, the year 
following his father's appointment at that place, and, when Halle 
becama the home of the family, was sent to the Realschule der 
Frankeschen Stif tungen, where his marked zeal was followed by well 
deserved success. He was one of a numerous family whom the 
expulsion of the father from office threw into dire distress, and the 
boy's experience of some of the bitter hardships of life helped to steel 
his youthful frame. Even in these early days he took first place among 
his comrades and excelled in swimming and gymnastics, but above all 
in his favourite study, the German language. 

Science early attracted his special regard, and on passing from school 
to the university he soon found himself able to pay her the single- 
hearted devotion she claims. With his appointment as assistant 
to Professor Heintz in 1853, he finally dedicated himself to 
chemistry. 

His absorbing chemical studies, so auspiciously begun, were not 
long to be continued without interruption. The family prospects 
were clouding over, and in this same year the father was condemned 
to two years' imprisonment as a consequence of the publication of 
his work " Die Bibel im Lichte der Bildung unserer Zeit." This 
new disaster left flight the only chance, and, with the help of 
trusty friends, Gustav succeeded in making his escape, while the 
family, under the charge of the young Johannes, followed him. 

Proceeding first to England, they embarked for the United States. 
Ill fortune again overtook them, for the vessel in which they set sail 
was soon discovered to be cholera -stricken. The ship's doctor found 
his time and energies fully occupied in attending to the first-class 



PERKIN: WISLICENUS MEMORIAL LECTURE. 61 

passengers, and, in characteristic manner, it was young Wislicenus who, 
in this emergency, acted as physician and nurse to the forsaken 
occupants of the steerage. When all hope of stamping out the scourge 
at last disappeared, the ship put back to England, where the family 
lived in straitened circumstances until they were again able to set out 
for the New World. 

The sojourn in America was not of long duration, for at the end of 
two years they found it possible to return to Europe. During this 
time the scientific knowledge of Johannes was the means of support 
on which the family relied, and he was fortunate enough to 
obtain an appointment as an assistant to Professor Horsford, of 
Harvard, and afterwards he conducted an analytical laboratory of his 
own in New York. 

Zurich became the headquarters of the family on their return to 
Europe. The son was able to resume his interrupted scientific career 
at Halle, under Heintz, whom he rejoined in 1857, and with whom he 
remained until the autumn of 1859. 

The friendship which sprung up between the two chemists lasted 
until the death of Heintz, twenty years later. Their association was 
marked by the publication of several joint researches. One of these 
dealt with a base they isolated from the products obtained by heating 
aldehyde-ammonia on the water-bath, to which, in the symbols then in 
use, they assigned the formula C^H^NC^. 1 The compound is that 
now known as " oxytetraldin," C 8 H 18 NO. 

A second communication dealt with experiments on goose-gall 
and the nature of some of its complicated acidic constituents. 2 A 
third one, of more general interest, resulted in the disappearance from 
literature of the " aldehydic acid " which Liebig considered was an 
intermediate step in the oxidation of acetaldehyde to acetic acid. The 
paper by Heintz and Wislicenus 3 exposed the slender character of 
Liebig's evidence, and indicated that acetic acid is the only definite 
product obtained when acetaldehyde is treated with silver oxide in 
accordance with Liebig's directions. 

It was at this time also that the first papers by Wislicenus himself 
appeared. 4 These dealt with his own views as to the relationship of 
glycol and glycerine in the light of the type theory which was then 
the guiding principle of classification. 

In 1859 Wislicenus left Halle for Ziirich. This step was his reply 
to the action of the governing body of the Halle Hochschule, who, 
before allowing him the title of ' Privatdocent,' required him to offer 

J Poggendor/'s Annalen, 1858, 105, 577. z 2bid. t 1859, 108, 547. 

3 Ibid., 101. 

4 Halle, Zeit. Gcsammt. Naturw., 1859, 13, 270, 442; 14, 97; /. pr. Ckem., 
1859, 77, 149. 



62 PERKIN: WISLICENUS MEMORIAL LECTURE. 

guarantees that he would in future refrain from all public e_xpression 
of his political opinions. Such an attempt to bring pressure on him 
was foredoomed to failure. His principles, absorbed first from his 
father and afterwards from his friends in freedom-loving America, 
were already firmly fixed ; he had come to regard the enunciation of 
his political and religious principles as part of his life's work, and 
throughout his career he was ever active in their furtherance. 

At Zurich his progress was rapid. He was appointed Professor of 
Chemistry and Mineralogy, under the Council of the Canton, at the 
School of Industries, in 1861. Three years later he was made Extra- 
ordinary Professor and Director of the Laboratories in the University, 
and in 1867 Ordinary Professor. In 1870 the Education Council 
conferred on him the Chair of Chemistry in the Polytechnic, and a year 
later he was made Director. 

In Zurich the problems connected with his investigation of the lactic 
acids absorbed his special interest. The question of the most suitable 
formula for the acid, which Scheele had discovered in the eighteenth 
century, was engaging much attention among chemists and provoking 
interesting controversy. On some points a preliminary agreement 
seems to have been attained, but it was generally recognised that 
searching experimental study was necessary if a final verdict was to 
be pronounced. The natural development of his earlier research work 
led Wislicenus to examine the points at issue, and he soon perceived 
that, to a certain extent, the facts as then known were in harmony 
with prevailing theories of structure, but that much was left without 
explanation, and appeared to call for some modification or extension of 
the existing views. 

According to the conceptions of structure in use at that time, two, 
and only two, isomeric lactic acids should be capable of existence, and 
these should be characterised by complete disparity in properties. 
Wislicenus had isolated from meat-extract a lactic acid which was not 
identical with Scheele's well-known substance, but the difference was 
not so marked as was to be anticipated in the case of an isomeride 
such as the theory predicted. The effort to ascertain, by synthetic 
methods, the constitution of the two acids proved exceedingly difficult, 
the products being mixtures of several substances of which ordinary 
lactic acid certainly appeared to be the main constituent. Finally, 
a third distinct compound having the composition of a lactic acid 
was discovered by Beilstein ; in regard to this latter substance, 
however, its recognition as a third isomeride was greatly delayed by 
an unfortunate mistake on the part of its discoverer. The discovery, 
in fact, increased instead of simplifying the complexity of the question. 

At the present time, having the key in our possession, we are able 
to trace without difficulty the structural relationship of these acids 



PERKIN : WISLICENUS MEMORIAL LECTURE. 63 

which, to those workers, was obscured by masses of detail. These 
details are now of secondary importance. They serve, however, to 
make clear to us the way in which the first suspicions in the mind of 
Wislicenus were aroused. 

Even when surmise became conviction, it would not have been 
characteristic of his judicial intellect had he altogether discarded the 
theories which he perceived to be in the main so fruitful and so nearly 
accurate. To him it was more natural to assume that the explanation 
might be found in some extension of these theories, and with brilliant 
discernment he showed the precise direction in which that extension 
was to be made, namely, by taking into account the arrangement of 
the various parts of the molecule in tridimensional space, and he even 
attempted to represent such a conception in a graphic manner. 

His views were expressed in his address to the Nat urf or sober ver- 
sammlung at Innsbruck in 1869, and shortly afterwards he gave 
them a wider publicity in the new Berichte der deutschen chemischen 
Gesellchaft l in connection with a paper on the modifications of lactic 
acid. The precise words he employed are worthy of quotation. 
"Tatsachen wie diese werden dazu zwingen die Verschiedenheit 
isomerer Molecule von gleicher Structurformel durch verschiedene 
Lagerung ihrer Atome in Raum zu erklaren und sich nach bestimmten 
Yorstellungen daruber umzusehen." 

The new shoot which was thus grafted on the stock of structural 
chemistry did not at once show signs of growth, although it was 
imperceptibly acquiring vitality as the external conditions were 
becoming more suited to its free development. 

It was at Ziirich, also, that Wislicenus interested himself for a time 
in the question of the origin of muscular energy, his association with his 
friend and colleague Adolf Fick being doubtless responsible for his 
temporary divergence in this direction. 

At that time Liebig's theory held the field, it being generally 
supposed that the energy necessary for muscular power was furnished 
by the combustion of the muscle-substances, that is to say, of nitro- 
genous albuminous materials, whilst that supplied by the oxidation of 
the carbohydrates and fats was mainly of use in maintaining the 
temperature of the body. This theory did not commend itself to Fick 
and Wisliceaus, and on August 30, 1865, they undertook the ascent 
of the Faulhorn, near Interlaken, for the purpose of obtaining direct 
experimental evidence on the point. The minimum work done in 
the ascent was easily calculated, whilst the amount of nitrogen in 
the urine voided during the journey supplied the basis for computing 
that part of expended energy which was supplied by tl)e destruction 
of the muscle-material, a computation which subsequent experiments 

1 1869, 2, 620. 



64 PERKIN: WISLICENUS MEMORIAL LECTURE. 

of Frankland rendered even more simple. The results indicated that 
the nitrogenous constituents were responsible only for a certain part 
of the energy expended, and the later investigations of Voit, Petten- 
kofer, and others have entirely confirmed this conclusion. 

In 1872 Wislicenus was invited to succeed Adolf Strecker at 
Wiirzburg, and the move must have been congenial to him, for it 
brought him closely into contact with a number of men of intellect, 
including Kohlrausch, von Wagner, Sachs, and Sandberger. Here 
his attention turned more particularly to problems of a nature suited 
to the powers of the numerous young workers whose studies he was 
called on to direct. From his fertile imagination fell the ideas which 
were the starting points of many fruitful and varied experimental 
investigations. In particular, the syntheses with the aid of molecular 
silver, and those involving the use of acetoacetic or malonic ester, led 
to the development of fields in which his students found abundant 
space for useful work. The extraordinary volume and the importance 
of the new observations which flowed from his laboratories during this 
period evoked the admiration of the scientific world. 

The time and attention which his synthetic researches claimed left 
Wislicenus few opportunities for other investigations, and the develop- 
ment of the conception of space configuration and its influence on 
isomerism was making but little progress, at least on the practical side. 
In the interval, however, the theoretical foundation on which is based 
our present view of stereochemical relationships among carbon com- 
pounds had been laid by van't Hoff and Le Bel. " La Chemie dans 
1'Espace," van't Hoff's famous thesis, appeared in 1875, and.it is not 
to be doubted that Wislicenus, perhaps more clearly than any other 
chemist, foresaw at once the vast fields of research which the new 
theory was to open up. At his desire, a German edition of van't 
Hoff's work was undertaken by Felix Hermann. This appeared in 
1877 under the title "Die Lagerung del Atome im Raume," and 
contained the matter of the French edition together with a preface by 
Wislicenus himself, who did not rest with this effort to make the new 
hypothesis familiar to a wide circle, but took every available oppor- 
tunity to press its merits n n the chemical world, which was disposed to 
accord it a cold reception, and, in some quarters, even to greet it with 
derision. 

The death of Kolbe, the most uncompromising opponent of 
"chemistry in space," left vacant the Chair of Chemistry at Leipzig, 
and the University was set the difficult task of finding the man most 
fitted to take his place. The great, and perhaps not unexpected, 
honour fell to Wislicenus, and in 1885 he entered on his new duties, 
which he continued to discharge until his death two years ago. 

U Leipzig, Wislicenus was at last able to give his whole mind to 



PERKIN: WISLICENUS MEMORIAL LECTURE. 65 

the question of the space distribution of the molecule, the first definite 
step forward being found in a paper to the Konigl. Sachs. Gesellschaft 
der Wissenschaften in 1887. 1 This paper was entitled " Ueber die 
raumliche Anordnung der Atome in organischen Moleculen und ihre 
Bestimmung in geometrischisomeren Verbindungen," and was based on 
van't HofFs conception of the analogy between a carbon atom and 
a regular tetrahedron, but involved considerations of a chemical nature 
on which van't Hoff had barely touched. The mutual attractive or 
repulsive forces of the groups attached to adjacent carbon atoms 
were considered in connection with the relative positions which these 
atoms, when only singly bound to one another, would be likely to 
adopt. 

The history of his subsequent investigations in this field is so recent 
and generally so well known that I may leave the details for letter 
discussion, since it is impossible in a few words to convey an adequate 
impression of the services which they rendered to the science of stereo- 
chemistry. 

Turning for a while to Wislicenus in the rdle of teacher, it may be 
at once asserted that his claim to our grateful recollection is of the 
highest. He was endowed with all the qualifications which should 
form the real basis of a great teacher, and on that foundation he 
built with scrupulous care, and the words he used in speaking of 
his old master Heintz applied not less truly to himself : " Wie der 
Forschertatigkeit, so war ihm auch sein Lehramt und der Umgang 
mit der Jugend Hertzensache." 

Doubtless to the beginner and to young medical students the 
matter of his lectures must have seemed somewhat tough, but his 
hearers, one and all, were impressed by his lucidity and by the lively 
and interesting way in which he presented the material he handled. 
The feeling that the lecturer was thoroughly at home in all depart- 
ments of his subject quickly won the confidence of every audience 
which he addressed. 

In the laboratory he was equally conscientious and successful. 
Everyone there, down to the youngest worker, was personally known 
to him. By the careful questions he put, he aroused their pride in 
making accurate observations, and urged them to think arid investigate 
for themselves, thus awakening their interest and developing their 
skill. He found the way to imbue those who worked under him with 
something of his own persistence, so that, in spite of experimental 
difficulties or long series of reverses, they came to regard the abandon- 
ment of a piece of work as an idea not to be entertained. 

Discussions with his pupils were a source of veal pleasure to 

1 Wislicemis gave the substance of this paper in a lecture to Section B. at tlo 
meeting of the British Association in Manchester in 1887. 



PEKKIX: WISLICENUS MEMORIAL LECTURE. 

Wislicenus, and by founding the Chemical Societies of Zurich, Wiirz- 
burg, and Leipzig, of which he was always the life and soul, he aimed 
to bring students and staff more closely into contact, and thus simul- 
taneously to strengthen their desire to acquire a wide knowledge and 
to increase their interest in research work. It is perhaps not toa 
much to say that the intellectual development of young chemists was- 
to Wislicenus a study as absorbing as any of his chemical problems. 

Many of us must recall with pleasure the weekly meetings at which 
Wislicenus gathered his students round him at his simple mid-day 
meal. His house was open to students and friends of all ages and 
positions, and here, as well as at the annual " Bierfriihsciioppen," where 
he entertained his colleagues and pupils, the genial and kindly nature 
of their host was patent to all. 

Those of us who shared these privileges are not likely to forget the 
impression produced by his personality. His long beard, his fine head 
with its intellectual features, and his majestic carriage aided in pro- 
duciog a sensation which in younger men was not far from .veneration. 

The warm feelings entertained towards him by his students doubt- 
less gave him keen pleasure, but formal tokens were always distasteful 
to him. At +he approach of his sixtieth birthday it came to his ears 
that covert preparations were on foot to give special recognition to the 
occasion, and the distress which he showed was so. evidently sincere 
that nothing remained but to abandon any idea of celebration. 

To his love for teaching may be traced the reappearance of Strecker's 
text-book, originally based on Regnault's "Premiers Elements de 
Chemie." After the death of Strecker in 1871, Wislicenus took upon 
himself the task of rewriting this book, which involved him in many 
years' work. In 1874 the organic portion was published (sixth edition), 
but the inorganic portion (ninth edition) did not make its appearance 
until 1887 ; both were in reality new works, for during the years which 
intervened the condition of chemistry had undergone a complete 
transformation . 

If to the task of carrying on his scientific work and to the guidance 
of Ins pupils he devoted most scrupulous care, he was not less punc- 
tilious in the fulfilment of other duties which fell in no short measure 
on his shoulders. Of his professorial functions one of the least agree- 
able was that of examining, but the irritation which an examination 
entailed on him did not affect the sincerity of his efforts to form a just 
estimate of the men who came before him. 

His colleagues have borne eloquent testimony that his thorough 
grasp of detail as well as principle was noticed in all his dealings with 
the faculty of his University. Seldom was he absent from a business 
meeting, and it was not often that an important question was mooted 
on which he had not some illuminating suggestion to make. His 



PERKIN: WISLICENUS MEMORIAL LECTURE. 67 

advisory reports were always constructed with great care, and were 
clear and finished. In addition to the duties of his chair, he found 
time in Leipzig to fill the offices of Dean and Rector raagnificus r 
positions to which, as was generally conceded, he brought exceptional 
dignity. Twice in Wurzburg he was honoured by a call to the Rector's 
seat, and on the second occasion the summons implied more than 
ordinary confidence in the man selected, for the tenure of office was 
intended to cover the celebrations in commemoration of the 300th year 
of the University's existence. 

In spite of the extraordinary calls which his acadamic and scientific 
work made on his energy, he still was able to take a prominent part in 
political affairs. So far as was possible, he held himself aloof from 
party strife, and for this reason he staunchly resisted all proposals 
that he should submit himself for election to the Reichstag, and only 
consented with reluctance to take office as a town-councillor at Leipzig. 
But when the call came to fight for large ideals and for the future of 
the German people, the instincts of the leader always brought him to- 
the front. 

Wislicenus was a German to the core. At school the German 
language was one of his hobbies, and the folk-lore and mythology of hi& 
country were an absorbing study. His long exile in other lands only 
served to strengthen his patriotism, and he followed heart and soul the 
efforts of his countrymen to form a united nation. He was an ardent 
follower of Bismarck, and never hesitated to give the freest expression 
to his opinions. He strove constantly to promote a German colonial 
policy, and was a keen advocate of proposals to form a great German 
navy. Nevertheless throughout his life he kept a warm pkce in his- 
heart for Switzerland, his foster-mother. 

An incident which illustrates some of the prominent features in the 
character of Wislicenus may be related. Shortly, after the conclusion 
of peace between France and Germany, a gathering of the German 
inhabitants of Zurich was held to celebrate the occasion, and 
Wislicenus was nominated chairman. The Francophile portion of the 
population attacked the meeting hall wi,th stones, and set fire to the 
staircase. A panic arose among the merry-makers, but Wislicenus,. 
with a well-timed appeal to their patriotism, restored their confidence r 
and then proceeded, with the utmost coolness, to show them how 
defences might be formed, and to extinguish the burning stairs with 
beer. 

He left the hall immediately afterwards, and walked quietly through 
the mass of excited people whose intention it had been to stone him. 
But his commanding presence at once put a stop to any such idea, and 
no one ventured to assault him. 

Shortly after he settled in Zurich, Wislicenus married Katherine 

2C 



68 PERKIN: WISLICENUS MEMORIAL LECTURE. 

Sat tier, the grand-daughter of Wilhelm Sattler, of Schweinfurt, wh 
shared with Russ the discovery of " Schweinfurt green." His 
happiness was not long unmarred by misfortune, for in 1866, Hugo, his 
brother, who at the time was Privat-docent in the Faculty of Germanic 
Archaeology at Zurich, lost his life as the result of an accident in the 
Alps. This blow was followed by others even more severe. His wife, 
after ten cloudless years, was seized with an incurable mental disorder, 
and two gifted sons were taken from him before attaining manhood. 
The marks made by these calamities were never effaced, but the 
interest which he took in his fellow men was not thereby lessened. 
He sought to save his friends distress by striving to conceal his pain, 
and it is more than likely that the restraint which he thus imposed 
on himself started the first tremor which finally led to the breakdown 
of his overburdened frame. 

His two remaining sons followed in their father's footsteps, and he 
was able to rejoice in their successes. Of his two daughters, the elder, 
Emilie, remained with him until his death, sharing his joys and 
troubles ; his second daughter, Marie, lived in Zurich after her marriage, 
and in later years father and daughters met there at frequent 
intervals. The relations between Wislicenus and his children were 
ideal, and the sympathy which bound the household can fully be 
realised only by those who have had the privilege of entering the 
family circle. Holidays, to them, meant the fields and woods. The 
father had built a charming country house in the Schonungen district, 
not far from Schweinfurt, and there, in the peaceful valley below the 
picturesque fortress of Mainberg, he spent a part of his vacations in 
quiet study, or sought to gain new energy by tramping the woods 
with gun on shoulder and his mind full of the interests of country 
life. 

I may now be permitted to review in greater detail some of the 
scientific work associated with the name of Johannes Wislicenus. At 
the commencement of his career, the study of organic chemistry had 
greatly weakened the hold of the Berzelius dualistic electrochemical 
theory, at least as a universal principle, for the direct application of 
that conception to carbon compounds had proved fruitless, and it was 
beginning to be felt that even the " radical " theory of Liebig and 
Dumas would prove inadequate. A brilliant procession of new and un- 
expected observations was passing before the eyes of the chemical world, 
and the revolutionary ideas of Gerhardt were attracting the fancies of 
the younger schools of chemists, although, as is usually the case when 
doctrines of tried utility are threatened by overthrow, the new views 
were opposed by several of the elder men. 



PERKIN: WISLICENUS MEMORIAL LECTURE. 69 

It was entirely in accordance with the independence of thought 
which his judgment so often displayed that, in his first contribution 
to chemical literature, of which mention has already been made, 
Wislicenus dissociated himself from the conservatism of his teacher, 
Heintz, and proclaimed himself an adherent of the new principles. 
Simultaneously with this theoretical paper on glycerine and the poly- 
atomic alcohols appeared others in which was detailed the experimental 
basis for the conclusions drawn, the principle that theory and ex- 
periment must yield each other mutual support being his guide 
throughout his scientific career. 

When Wislicenus resumed work at Zurich, the problem of the con- 
stitution of lactic acid was in the air. The discovery of glycol by 
Wurtz in 1856, and the publication of Heintz's synthesis of glycollic 
acid from chloracetic acid, had paved the way for a preliminary agree- 
ment between the schools of Wurtz and Kolbe. The former saw in 
lactic acid a " diatomic radical, C 3 H 4 S " ; the latter based his views 
on the broader conception that the substance was really a monobasic 
acid, and endeavoured to show that it was very simply derived from 
propionic acid, which he conceived as " ethyl formic " acid ; to lactic 
acid he, therefore, attributed the functions of a " (hydr)oxyethyl formic " 
.acid, and, in the older symbols to which he permanently adhered, he 

expressed its structure by the type formula HO(C | TTQ J[C 2 O 2 ],O. 

Wislicenus entered the field without preformed notions, and, recog- 
nising that the difference of opinion arose largely as the result of too 
narrow conceptions of the type theory, endeavoured to show that it 
was easy, merely by extending the idea of radicles within radicles, to 
express all that was then known as to the behaviour of lactic acid. 
He emphasised the fact that, in accordance with Kolbe's view, lactic 
acid is monobasic, and th^t the second replaceable hydrogen atom has 
the same character as the replaceable hydrogen in alcohols. 1 The 
^'sodium derivative of lactic acid behaves in much the same manner as 
does an alcoholate, being decomposed by carbon dioxide, and even by 
water, into the wionosodium derivative and sodium carbonate or 
hydroxide, whilst the formation of a sodium derivative of ethyl lactate 
is in accordance with the belief that this ester still retains an alcoholic 
function. He considered, in the terms then in vogue, that the divalent 
carbonyl radicle is " neutralised " on one side by union with a positive, 
univalent alcohol radicle, leaving it negatively univalent, whilst in the 
alcohol radicle itself there is also the hydrogen atom, which is replace- 
able by acid groups and capable of being removed with the oxygen 
atom in exchange for an atom of chlorine. 

1 Annalen, 1863, 125, 4170. 



70 PERKIN: WISLICENUS MEMORIAL LECTURE. 

The formula he employed to crystallise his view of lactic acid was 




and he indicated how clearly this accounted for the isomerism of the- 
two methyl derivatives' : 

O0' 

and G2 H 4 }- 

H CH 3 

and by hydrolysing Perkin's ethyl acetyl-lactate he succeeded in isolating 
acetyl-lactic acid and its salts : 

C0' 

o 




C 2 H 5 H 

Ethyl acetyl-lactate. Acetyl-lactic acid. 

He went on, shortly after this, to the study of malic, tartaric, citric, and! 
mucic acids, 1 to which similar views appeared to be capable of applica- 
tion. These acids were generally recognised to be dibasic in character,, 
and Kekule" regarded malic acid, for example, as a " triatomic dibasic "' 
acid, whilst Kolbe preferred to picture it as a " dibasic monp(hydr)oxy " 
acid. In order to determine how far the additional oxygen atoms in 
these acids correspond in function with the third oxygen atom in 
lactic acid, Wislicenus investigated the action x>f acetyl chloride on 
their neutral esters, the conclusions which he was able to draw being,. 
(1) that the so-called atomicity of an acid is the sum of the positive 
hydrogen atoms which are easily replaceable by metals or alcohol 
radicles and of the negative hydrogen atoms which are replaceable by 
acid radicles ; (2) that the number of the negative hydrogen atoms of 
the second type is best determined by the action of acetyl chloride on. 
the neutral esters. 

While dealing with his conception of the univalent radicle 2 TT f ^ 
in his lactic acid formula, he pointed out that such a radicle is 



existent in glycolmonochlorhydrin, H / > , and other glycol com- 
pounds. 2 He endeavoured to replace the halogen atom in glycolmono- 
chlorhydrin by the cyano-group through the agency of potassium, 
cyanide, and by hydrolysis of the product to convert the compound 
1 Aniialen, 1864, 129, 175200. 2 Ibid., 1867, 128, 167. 



PERKIN: W1SLICENUS MEMORIAL LECTURE. 71 

into one of the carboxylic type. The method afforded him an acid 
having the formula C 3 H 6 3 , which at the time he considered in all 
probability to be paralactic acid (now known as a-hydroxypropionic 
.acid), trusting to observations on the properties of its zinc salt for the 
evidence as to its identity. It must be said, however, that subsequent 
experiments of Erlenmeyer 1 proved that the conclusion drawn by 
Wislicenus was erroneous, for the acid obtained from glycolchlorhydrin 
by the above mode of treatment yields the characteristic zinc-calcium 
salt of hydracrylic acid (or j8-hydroxypropionic acid) ; Erlenmeyer also 
showed that this method gives but a poor yield of the synthetic 
product, which is more easily obtained if the intermediate ethylene 
cyanohydrin be prepared by leaving together a mixture of ethylene 
oxide and hydrocyanic acid. 

The existence of a genetic relationship between acetaldehyde and 
lactic acid proper had been rendered probable by Staedler and by 
Engelhardt among others, for aldehyde could be obtained from the acid 
in several different ways ; Strecker, moreover, had effected a synthesis 
of lactic acid from acetaldehyde by way of alanine (a-aminopropionic 
acid). These facts suggested to Wislicenus that the divalent radicle, 
C 2 H 4 ", of ordinary lactic acid was identical with the " ethylidene " 
radicle of acetaldehyde, and he confirmed this suggestion experiment- 
ally by a synthesis of lactic acid from the aldehyde a synthesis which 
was analogous, at least in appearance, to that by means of which 
glycolchlorhydrin had yielded him the isomeric acid. The process con- 
sisted in preparing the requisite ethylidenechlorhydrin by the direct 
addition of hydrogen chloride to aldehyde, and subjecting the halogen 
compound to the usual processes ; he also effected the synthesis by the 
now well-known method involving the formation of ethylidenecyano- 
hydrin by direct addition of hydrogen cyanide to the aldehyde. 

At this juncture he considered the results of experiments to justify 
the conclusion that the existence of two isomeric C 2 H 4 " radicles in 
paralactic acid from meat juice and ordinary lactic acid respectively 
as established; in the paper appear for the first time the names 
' ethylenelactic acid " and " ethylidenelactic acid," and these terms 
have remained in common use up to the present time, although the 
error made by Wislicenus in the application of the former term 
to paralactic acid was soon corrected when Erlenmeyer showed that 
hydracrylic acid was the compound to which it should properly be 
assigned. 

In the same paper which contains the account of these results 2 is 
to be found an interesting discussion on different modes in which the 
tions of lactic acid could be expressed by type-theory formulae, and 

free translation of the concluding remarks on this subject may be 

1 Annatcn, 1867, 141, 261. 2 Ibid., 1863, 128, 1 et scq. 



72 PERKIN: WISLICENUS MEMORIAL LECTURE. 

given. " The formulae for lactic acid, which I have given above, 
represent, not different, but one and the same kind of combination 
between the parts of the lactic acid molecule; the radicles in them 
are identical, the kind of mutual saturation is the same throughout, 
and the only change made is the order in which they come. Such 
a change in order would always be justified even if we understood the 
mode in which the atoms are distributed in space, because our present 
f ormulse can do no more than present us with a picture of the com- 
pound in one plane. If we wish to represent the properties of a 
compound from all points of view, many different formulae, emphasising 
different characteristics, are necessary, and so long as these different 
chemical formulae exhibit the differences in order only and not in the- 
type of union of the adjacent parts, so long, in my opinion, will they 
be wanting in scientific precision." He here seized the opportunity to- 
point out that the theory of molecular structure must be set on a 
broader basis, remarking that it was no longer possible to contend that 
the equivalent substitution of hydrogen produces only secondary effects- 
on the general character of a compound. 

The properties of the so-called "anhydrous lactic acid" next 
absorbed his energies. 1 Pelouze had investigated the action of 
ammonia on this substance, and found that ammonium lactate was 
formed, whilst Laurent found that only one-half of the ammonia 
absorbed could again be directly obtained in the form of platini- 
chloride, the other half being combined in a non-separable form. 
Laurent drew the conclusion that the product he obtained arose as 
the result of a decomposition of an ammonium aminolactate or 
lactamate, Wislicenus 2 had already suggested that "anhydrous 
lactic acid " was ester-like in character, one residue of lactic acid 
functionating as the acid radicle and another as the alcoholic radicle, 
so that by the action of ammonia it might be expected to afford one 
molecule of lactamide and another of lactic acid, or rather of its 
ammonium salt; by carrying out the reaction with ammonia in an 
alcoholic solution of ' anhydrous lactic acid," he was able to prove 
that both these compounds are formed immediately, and therefore are 
not merely secondary products as Laurent had supposed. 

During the next two or three years a great advance was made, 
because Frankland's graphic methods of representing the constitu- 
tion of carbon compounds began generally to be adopted, and we 
find them employed in all the subsequent communications from 
Wislicenus on the subject of lactic acid, hence it will not be in- 
consistent if at this point I follow the sequence of historical 
events, and at once employ the modern graphic symbols to depict 
the process by which Brugger, in 1864, confirmed the views of 
Annakn, 1865, 133, 257. 2 Ibid., 1863, 128, 60. 



PERKIN: WISL1CENUS MEMORIAL LECTURE. 7$ 

Wislicenus regarding the nature of "anhydrous lactic acid," or 
" dihydrolactic acid," as it has more recently been termed. Brugger's 
method l consisted in heating potassium lactate with a-bromopropiunic 
acid, the product proving to be the anhydro-compound in question. 

CH 3 9H 3 CH 3 CH 3 

CH(OH) + BrCH = CH(OH)_CH + KBr. 

COOK COOH COO-" COOH 

A striking observation of Strecker's arrested the attention of 
Wislicenus ; by the action of heat on sarcolactic acid, an anhydride of 
ordinary lactic acid was obtained, and Wislicenus, who at this time 
considered that sarcolactic or paralactic acid was ethylenelactic 
acid, supposed that this involved a conversion of /J-hydroxypropionic 
acid into a-hydroxypropionic acid, and in order to determine if such 
a change might be brought about in the homologues of lactic acid, 
he examined the properties of the hydroxybutyric acid which he 
prepared for the purpose by the reduction of Geuther's acetylacetic 
ether. This acid he considered to be the analogue of paralactic acid, 
for the isomeric acid prepared by Friedel and Machucca from 
brominated butyric acid he correctly supposed to be the corresponding 
a-hydroxy-acid. He was unable to satisfy himself that, on heating 
/3-hydroxybutyric acid, any change took place corresponding with that 
noticed by Strecker in the case of paralactic acid, but observing that 
the salts of /?-hydroxybutyric acid swelled when heated, he suggested 
that the non-occurrence of the expected isomeric change was the result 
of the conversion of the compound into the unsaturated acid by loss 
of a molecule of water. 2 It is now clear, of course, that the change 
which paralactic acid undergoes when heated is a simple case of race- 
misation, such as occurs also in the case of mandelic acid, involving 
no further structural alteration. 

It was at about this time that his first important paper on the acid 
from /?-iodopropionic acid made its appearance. 8 Beilstein had pre- 
viously carried out the hydrolysis of the lodo-acid by moist silver 
oxide, but, unfortunately, had failed to recognise the true character of 
the product, to which he assigned the name " hydracrylic acid " and 
the formula C 12 H 22 O n . Two years afterwards, Moldenhauer found 
that Beilstein's acid could be converted into a compound having the same 
empirical formula as lactic acid by heating it with a solution of alkaline 
hydroxides, and this paper was succeeded by others emanating from 
Wichelhaus and from von liichter. Wislicenus re-examined Beilstein's 
acid, and, by preparing its crystalline salts, succeeded in proving that 

Zeit.far Chem., 1869, 5, 338. 

2 Annalen, 1869, 149, 205215. 

3 Zeit. fur Ckcm., 1868, 4, C83 684. 



74 PERKIN: WISLICENUS MEMORIAL LECTURE. 

ifc was isomeric with lactic acid. He returned to the subject some 
years later 1 in consequence of an expression of opinion from 
Wichelhaus, who considered that hydracrylic acid was identical with 
ethylenelactic acid ; an opinion which Wislicenus did not share, 
although, as he believed, ethylenelactic acid is undoubtedly present in 
small quantities in the crude acid from meat-extract. It is only fair 
to note that both Erlenmeyer and Klimenko failed to confirm the 
latter statement. Wislicenus showed that the action of silver oxide 
on /3-iodopropionic acid affords, not only a lactic acid, but also acrylic 
acid, C 3 H 4 2 , and two isomeric acids having the formula C 6 H 10 O 5 . 
which he termed dehydracrylic and paradipimalic acids respectively, 
Heintz, by warming /3-iodopropionic acid with milk of lime, also 
observed the formation of lactic and acrylic acids, but did not detect 
the other acids discovered by Wislicenus; he also discovered the 
characteristic double zinc-calcium salt of the lactic acid formed. 
Heintz, like Wichelhaus, believed that Beilstein's acid must be 
regarded as ethylenelactic acid. 

The reason urged by Wislicenus in support of his contention that 
hydracrylic acid is not ethylenelatic acid was that he was unable to 
convert it into malonic acid, which the latter afforded him without 
difficulty; moreover, the acid which he had obtained from ethylene- 
chloroh}drin had refused to yield )3-iodopropionic acid on treatment 
with hydrogen iodide, and gave only amorphous salts, whilst hydra- 
crylic acid could be reconverted into /2-iodopropionic acid without 
difficulty. 

He considered that the two "compounds were very closely related, 
however, and suggested that /3-iodopropionic, glyceric, hydracrylic and 
acrylic acids were not true carboxylic acids, and his conception of their 
relationship was expressed by the following formulae : 



CH 2 -OH 
!H 




OH } CH-OH CH-OH 

-Iodopropionic Glyceric acid. Hydracrylic Acrylic acid. 

acid. acid. 

It was the experiments of Erlenmeyer, 2 to which reference has 
already been made, which revealed the trap into which Wislicenus had 
fallen, and served to establish the identity of hydracrylic and ethylene- 
lactic acids. 

Wislicenus, in 1873, once more took up the investigation of the acids 
from meat-extract, 3 and confirmed Strecker's observation that para- 
lactic acid may be converted into the anhydride of ordinary lactic acid, 

1 Annalen, 1873, 166, 3, et seq. 2 Ibid., 1878, 191, 261. 

3 Ibid, 1873, 166, 364 ; 167, 302346. 



PERKIN: WISLICENUS MEMORIAL LECTURE. 75 

and proved that, by heating the former at 135140, a complete 
conversion of the active into the inactive acid may be brought about. 
Comparative experiments on the two acids showed him that both 
compounds yield aldehyde and under precisely similar conditions, 
forcing him to the conclusion that there is no profound difference in 
structure between the two, so that the facts accumulated up to that 
time indicated clearly enough that paralactic acid and fermentation 
lactic acid must be represented by the same chemical formula, 




It is worth while to quote the words in which he announced his 
conclusion to the German Chemical Society, 1 for they must be memor- 
able as marking the first step towards the development of chemistry in 
space. " Es ist damit der erste sicher constatierte Fall gegeben, dass 
die Zahl der Isomeren die der Struckturmbglichkeiten iibersteigen 
kann. Tatsachen wie diese werden dazu zwingen, die Verschieden- 
heit isomerer Molecule von gleicher Struckturformel durch verschied- 
ene Lagerung ihrer Atome im Raum zu erklaren und sich nach 
bestimmten Vorstellungen dariiber umzusehen." 

For the type of isomerism which depends on the varying space 
distribution of the atoms in the molecule, he used the term "geo- 
metrical isomerism," 2 a name which was afterwards replaced in 
1888 by the word " stereoisomerism," coined by Victor Meyer. 

The years over which the investigations on lactic acid extended were 
not without results in other fields. At one time Wislicenus seems to 
have taken some interest in inorganic chemistry and in water and 
gas analysis, but this was in his earlier years, and his later work lay 
almost exclusively in the domain of carbon chemistry. 

In 1869 appeared his first paper on the subject of the dibasic acids 
of the oxalic series C n H 2n (C0 2 H) 2 . 3 The nomenclature which he here 
proposed for the first few members of the series is practically the 
same as that in use at the present time, except that " lipic acid " has 
become " glutaric acid." In this communication the use of " molecular 
silver" as a synthetic agent is described for the first time; this agent, 
prepared by the reduction of silver chloride in the cold, was heated 
with /3-iodopropionic acid, first at 100 120, and then at 150160, 
the product being adipic acid, 



1 Eer.> 1869, 2, 620. 2 Annalen, 1873, 167, 345. 

8 Ibid., 1869, 149, 215224. 



76 PERKIN: WISLICENUS MEMORIAL LECTURE. 

A synthesis of another member of this series, namely, succinic acid, 
was also accomplished, and this experiment appears to have given 
rise to the long and valuable series of researches on acetoacetic ester 
which emanated from the laboratories of Zurich and Wurzburg under 
the auspices of Wislicenus. The synthesis referred to consisted in 
bringing ethyl chloroacetate into reaction with the product obtained 
by the action of sodium on ethyl acetate a product which wa& 
generally held to be a simple substitution derivative, although Geuther 
himself maintained the view which is now known to be the correct 
one. The conception which, at the time, Wislicenus formed of the 
process was as follows : 

CTT OO *P TT 
ai-OHjOOfOfr + Na-CH 2 -C0 2 -C 2 H 6 = jC^^jXf + NaOL 

UJ 2 'U<J 2 'G 2 i 5 

The method was found to lead to the formation of a by-product, 
the investigation of which Wislicenus left in the hands of his pupil 
Noeldecke, who succeeded in proving it to be acetopropionic acid, 
CH 8 *CO*CH 2 'CH 2 'C0 2 H ; this substance, as was afterwards shown, 
is produced by the elimination of carbon dioxide from acetosuccinic 
acid, from the ethyl ester of which in reality the succinic acid formed 
in the reaction is also produced. 

In the same year appeared communications on duplothioacetone, 1 
which he prepared from acetone by means of phosphorus trisulphide, 
and on the dibromobenzenes. His investigations on the latter subject 
were carried out in conjunction with Eiese, and included experiments 
on the action of sodium on the crystalline dibromo-compound, a process 
which gave rise to diphenyl, diphenylbenzene, and other products ; the 
oily " /J-dibromobenzene " which accompanies the former was purified 
and converted into its nitro-derivative, and the latter shown to be 
different from the nitro-compound of crystalline dibromobenzene. 

Among the first papers published by Wislicenus after his promotion 
to Wurzburg was a communication on a synthesis of hydantoic acid, 
which was shown to be the product obtained when cyanic acid acts on 
glycocoll. 2 

CH 2 -NH 2 + HCNO = CH 2 -NH-CONH 2 
C0 2 H C0 2 H 

The synthesis of ethylmalonic acid from normal butyric acid was 
accomplished by him in conjunction with Urech, 3 the process 
involving the conversion of the butyric acid into its a-brominated 
derivative, which, by the action of potassium cyanide, followed by 

1 Zeit.fiir Chcm., 1869, 5, 324326. a Annalen, JL873, 165, 103. 
3 Ibid. 9398 



PERKIN: WISLJCENUS MEMORIAL LECTURE. 77 

the hydrolysis of the resulting a-cyanobutyric acid, gave the sub- 
stituted malonic acid without difficulty, 

CH 8 -_CH 2 -CHBr-C0 2 H ~> CH 8 -CH 2 -CH(CN)*C0 2 H > 

CH 3 -CH 2 -CH(C0 2 H) 2 . 

The years 1874 and 1875 were signalised by the appearance of a 
long series of communications from the Wurzburg laboratories. 1 
These were mainly the results of work undertaken by his 
students, and covered a very wide range. With Goldenberg, benzoin 
was shown to be capable of reduction to Zinin's desoxybenzoin, and 
the latter to dibenzyl, while benzoinpinacone was obtained for the first 
time. Bonne, Goldenberg, and Zimmermann investigated silver deriva- 
tives of biuret and its allies, and used them to prepare alkyl derivatives. 
To Zimmermann was entrusted an interesting piece of work on the 
constitution of phosphorous acid, the possibility that triethyl phosphite 



might be represented by the formula OIP^-0'C 2 H 6 being tested and 

N>C 2 H 5 

disposed of by showing that the ester yields no ethylphosphinic acid 
on hydrolysis, but only phosphorous acid, and that by absorption of oxygen 

/0-C 2 H 6 
it is converted into ethyl phosphate, OIP^-OC 2 H 5 ; it was also observed 

X OC 2 H 5 

that, on addition of sodium hydroxide to concentrated phosphorous acid, 
a syrup may be obtained in which the ratio P : Na is approximately 
1 : 3, the conclusion being drawn that P(OH) 3 correctly represents the 
properties of the acid. 

The investigation of the behaviour of zinc ethyl towards dichloro- 
ether fell into the hands of Kessel, and Frankland's " dinitroethylic 
acid " gave Zuckschwerdt results which appeared to Wislicenus to 

justify the formula O<Q r * 6 for that compound. Zuckschwerdt, 

" 



r 

IN 

also re-examined the complex product obtained when sulphur dioxide is 
brought into contact with zinc ethyl. 

A useful synthetic process was worked out by Forster, who found 
that mercuriphenylammonium chloride reacts smoothly with thio- 
carbamides, the process leading to the production of guanidines, 

NHg(C 6 H 5 )HCl + S:C(NHC 6 H 5 ) 2 = HgS + N(C 6 H 5 ):C(NH-C 6 H 6 ) 2 ,HC1. 

The study of the isomeric solid and liquid crotonic acids was 
undertaken by V. Hemilian ; the pure solid acid gave both "a" and 
"/2" sulpho- and iodobutyric acids, a fact which led Wislicenus to 
conclude that the formula CHg'CHICH-COjjH represented the struc- 

1 Ber. t 1874, 7, 286298, 683692, 892893 ; 1875, 8, 10341040, 1206-1209. 



78 PERKIN: WISLICENUS MEMORIAL LECTURE. 

ture of solid crotonic acid, whilst the liquid acid was presumably 
CH 2 :CH'CH 2 'C0 2 H, although, as he admitted, malonic acid is not 
among the products formed when the liquid acid is fused with potas- 
sium hydroxide. This communication is of especial interest when it is 
remembered that the difference between the two acids was afterwards 
assigned by Wislicenus to stereochemical causes, the existence of 
which he was at this time being led to infer from his lactic acid 
researches. 

In the same set of papers is one containing an account of the work 
which initiated the long series of syntheses by the aid of pure aceto- 
acetic ester which were carried out in the Wiirzburg laboratories. 1 
Wislicenus cited here the new evidence confirming Geuther's views and 
refuting the suggestions of others that the metal compound obtained 
by the action of sodium on ethyl acetate is a simple substitution deri- 
vative of the latter ; the substance was definitely shown to be ethyl 
sodtoacetoacetate, and attention was drawn to the improvement in the 
synthetic process which may be effected if, instead of employing the 
crude material prepared by heating ethyl acetate with sodium, the pure 
acetoacetic ester is first isolated ; the use of benzene as a diluent 
and of excess of sodium, afterwards to be removed, was also suggested. 
Goldenberg, Ehrlich, Zeidler, Saur, and others carried out the experi- 
mental details of the work, proving that the product so prepared may 
afford nearly quantitative yields of substituted acetoacetic esters on 
treatment with alkyl iodides, benzyl chloride or benzoyl chloride. 
Finally, it was shown that the mowo-substituted products are capable 
once more of reacting with sodium and alkyl iodides, affording the di- 
substituted derivatives, so that the complicated theories put forward 
by Frankland and Duppa and by Geuther in explanation of the pro- 
duction of dialkylacetic acids, as by-products in the old process, were 
rendered unnecessary. 

With Conrad, whose name afterwards became so closely identified 
with the progress of the acetoacetic ester and malonic ester syntheses, 
Wislicenus was able satisfactorily to explain the origin of the dehydr- 
acetic acid which is formed by the distillation of acetoacetin ester, four 
molecules of which interact so that four molecules of ethyl acetate 
are eliminated, 

4CH 8 -CO-CH a -C<VC 2 H 6 C 8 H 8 4 + 4CH 8 -C0 2 -C 2 H 6 , 
whilst to Ruegheimer and Harrow is due the joint honour of the 
discovery of the synthetic reactions by which the sodium derivatives 
of /J-ketonic acids may be converted into diacetylsuccinic esters, 



1 Ber., 1874, 7, 683. 



PERKIN: WISLICENUS MEMORIAL LECTURE. 79 

Other papers published at this period, with Ehrlich, Rohrbeck, 
Waldschmidt, Saur, Conrad, and others as joint authors, dealt with the 
continuation of this work. The /J-hydroxy-a-substituted butyric acids 
obtained as reduction products from the alkylacetoacetic esters came 
under observation, as well as the a-substituted crotonic acids which 
are produced by their dehydration ; thus from methylacetoacetic ester, 
by this series of changes, 

CH 3 -CG-CH(CH 3 )-C0 2 -C H 5 > CH 3 -CH(OH)-CH(CH 3 )-C0 2 H -- > 
CH S -CH:C(CH 3 ):C0 2 H. 

a methylcrotonic acid was isolated and identified with the pro- 
duct prepared by Frankland and Duppa from ethomethoxalic acid, 
CH 8 -CH 2 'C(CH S )(OH)-C0 2 H, by removal of the elements of water. 
The hydrolysis of methylethylacetoacetic ester yielded a valeric acid 
which resembled ordinary valeric acid in nearly all particulars, except 
that its barium salt could not be obtained in a crystalline condition. 
With reference to this acid the remark is made, " aus dieser Synthese 
geht mit Sicherheit hervor, dass, Erlenmeyer's Vermuthung der 
sogenannte optisch-active Amyl Alcohol entspreche der Formel 
CH 3 -CH 2 -CH(CH 3 )-CH 2 -OH und die daraus dargestellte Valerian- 
saure CH 3 -CH 2 'CH(CH 3 )COOH in der That richtig sei," a conclusion 
which, although since proved to be correct, was perhaps scarcely justified 
by the results of the experiments just mentioned. 

Arising out of the study of the action of sodium on ethyl acetate, an 
examination was made of the compound first isolated by von Fehling 
as the product of the action of sodium with ethyl isuccinate. Herrmann 
was instrumental in proving that the substance is similar in character 
to ethyl acetoacetate, but yields a mono- and also a di-potassmm 
derivative decomposed by carbon dioxide, the results seeming at that 
time to indicate that the substance was a ring compound of the 

, 
formula 



The investigation of the isomeric ethylacetosuccinic esters 
Wislicenus assigned to Clowes and Huggenburg ; the first of the 
isomerides was prepared by the interaction of ethyl sodioacetoacetate 
and ethyl a-bromobutyrate, 

CHNa(CO-CH 8 )-C0 2 -C 2 H 6 + CHBr(C 2 H 5 )-CO 2 ^C 2 H 5 = 
CH(CO-CH 3 ).C0 2 .C 2 H 5 
CH(C 2 H 6 )'C0 2 -C 2 H 6 

and the second by ethylating acetosuccinic ester, 

CHNa-CO-CH 3 9(C 2 H 6 )(CO-CH 8 )-C0 2 -C 2 H 5 

<bH 2 -C(VC 2 H 5 h !iH ' 1 6H 2 -C0 2 -C 2 H 6 



80 PERKIN: WISLICENUS MEMORIAL LECTURE. 

in accordance with the formulae assigned, the former was attacked at 
once by sodium, hydrogen being evolved, whilst the latter was 
practically unaffected. 

The most important communication from the pen of Wislicenus 
during the year 1877 was, without doubt, a masterly summary of the 
knowledge which had accumulated up to that time on the subject of 
ethyl acetoacetate and its applications as a synthetic agent. 1 In the 
following year this was supplemented by a valuable treatise on the 
manner in which the proportion of "acid" and "ketone" decomposi- 
tions is regulated by varied conditions which may be imposed during 
the hydrolysis of the ester and its substitution derivatives, 2 the 
remarkable point elicited being the irregular modes in which the 
esters decompose and the consequent difficulty in foretelling even 
to a rough degree of approximation the way in which a new ester 
may behave under given circumstances. 

It should be recorded that at about the period of which we are 
speaking, Conrad and Limpacb, pupils of Wislicenus, worked out the 
details of the method, since then almost universally adopted in carry- 
ing out syntheses such as those involving the use of acetoacetic or 
malonic ester, namely, that of preparing the necessary sodium 
derivative by a process of double decomposition, the ester being added 
to alcohol in which the calculated quantity of sodium has previously 
been dissolved. 

The work which Wislicenus entrusted to the author during his stay 
of two years (1880 1882) in Wurzburg was the investigation of the 
condensation products which are formed when cenanthol is treated with 
caustic potash or other reagents, a subject which at that time was little 
understood, but which has since, in the case of other aldehydes, been 
thoroughly worked out by Lieben and his pupils. But in a laboratory 
like that of Wurzburg, in which so much work of so varied a nature is 
being carried on, more, perhaps, is learnt by watching others than from 
the research the student is actually engaged in. The constant contact 
with men engaged in syntheses with the aid of ethvl sodioacetoacetate 
and sodiomalonate familiarised the author with these reagents and 
undoubtedly helped to suggest the methods which were subsequently 
employed in his researches on the formation of closed carbon chains. 
Indeed the first small experiment on the action of ethylene dibromide 
on the sodium compound of ethyl malonate was carried out in the 
Wurzburg laboratories, but at that time without result. 

The scientific papers associated with the name of Wislicenus 

between the years 1877 and 1887 are few in number ; one or two 

dealing with compounds obtained by the acetoacetic ester synthesis, 

as well as others containing the results of experiments on dichloro- 

1 Annalen, 1877, 186, 161228. * Ibid., 1878, 190, 257281. 



PERKIN: WISLICENUS MEMORIAL LECTURE. 81 

ether and on reduction products of phthalic anhydride, are to be found, 
but these studies appear to have aroused in him only a passing interest. 
The work involved in the revision of Strecker's text-book, his academic 
and political duties, his translation to the Leipzig chair in 1885, were 
doubtless all in part responsible for the apparent falling off in im- 
portance of his contributions to chemical literature. The appearance 
in 1888 and 1889 of his epoch-making papers on space relations of 
the atoms in carbon compounds, on which he had pondered for many 
years, synchronised with a renewed activity in research work more 
commensurate with the expectations of the scientific world which 
knew his powers. From this time onwards his laboratory was the 
spring from which issued the stream of work which has helped to 
justify the use of those conceptions first foreshadowed by himself, 
and afterwards endowed with definite shape by the genius of 
van't Hoff. 

Since the appearance of the original papers by Le Bel and van't Hoff, 
no serious attempt had been made to apply the theory to non-enantio- 
morphous isomerism, although van't Hoff had discussed the isomerism 
of compounds s\ich as fumaric and maleic acid in considerable detail. 
In order to explain the intraconversion of these two compounds, 
through the medium of the halogen derivatives of succinic acid, 
"Wislicenus assumed that the groups on neighbouring carbon atoms 
act on one another in a manner determined by their "chemical 
affinities," and that in cases where these adjacent atoms are singly 
interbound, and hence doubtless free to rotate about the point of 
mutual attachment, such a rotation will take place as to lead to the 
adoption of the most favourable (" begunstigte ") configuration. An 
arrangement so brought about would, he considered, be stable at low 
temperatures, but as the oscillations increased! in violence with rise of 
temperature a new configuration might result. 

In dealing with compounds of the type of fumaric and maleic acids, 
and represented by the generalised formula 

a-C-b a-C-b 

and M , 

b'C-a a'C'b 

1 ' Centrally "or ' * Plane " 

' ' axially " symmetrical. symmetrical. 

he pointed out that, in the conversion of substances of the centro- 
symmetrical type into saturated compounds, it is a matter of in- 
difference to which of the doubly-bound carbon atoms either part of 
the additive agent attaches itself, as the products are identical. In 
the planosymmetrical series, the products of addition are enantio- 
morphous, but in both cases there are equal chances that eitlier of the 
two common " bonds " may be ruptured, as the molecule is symmetrical 



82 PERKIN: WISLICENUS MEMORIAL LECTURE. 

about the plane containing the groups affixed to the doubly-bound pair 
of carbon atoms. The last condition is also present in the more 
general case where any doubly-bound carbon atom is attached to two 
different groups, 



except in the single instance where the molecule is already an 
asymmetric one, that is to say, where it already contains one or 
more asymmetric atoms, or is built on one of the types which 
comply with the conditions necessary for the existence of enantio- 
morphism, and to which attention was drawn by van 't Hoff in his 
original treatise. It follows, therefore, that whilst, in general, by the 
conversion of a group 

x 

1 1 into a saturated one a \ 

y 

an asymmetric carbon atom is produced, the right- and left-handed 
individuals are formed in approximately equal numbers, 1 and thus the 

In accordance with the usual convention, the enantiomorphous forms here are 

x x 

a*C'& 

and 



4- 



Throughout the following pages, however, only one of the two mirror images is 
represented in any instance, as the results here arrived at by the manipulation of the 
formulae apply with equal truth to both, and such inactive mixtures will be indicated 
by the letter (r) affixed to the one formula given. It may be pointed out that a 
rotation of either carbon atom about the " bond "joining the two may be represented 
by an exchange in the position of the other three groups attached to that atom 
providing that their order, clockwise or counter-clockwise, around that carbon atom 
remains the same ; thus, the three figures 

x b a 

a'C'b x'fra b'frx 

A.- 4- and 4. 

represent three phases in the rotation of the upper carbon atom about the vertical 
" bond," as the order abx about that atom is counter-clockwise in each case. 

For numerous reasons, the parts of the agent added at a double binding will, in 
all oases, be represented as becoming attached in the mode above indicated, namely, 
in the line of the original ethylenic linkage, and, inversely, the withdrawal of two 
groups in the formation of an ethylenic union is imagined to occur only in the 



PERKIN: WISLICENUS MEMORIAL LECTURE. 83 

non-production of optically active substances from inactive compounds* 
of this class is at once accounted for. 

Malic acid, according to Wislicenus, 1 is probably to be regarded as- 
constituted with opposed carboxyl groups 



C0 2 H 




C0 2 H' 



the affinity of the carboxyl group for hydrogen doubtless being greater 
than that of carboxyl for another carboxyl group or for hydroxyl, and 
the production of fumaric acid, 

C0 2 H-C-H 
H-C-C0 2 H ' 

as the main product when the elements of water are withdrawn from 
malic acid is precisely in agreement with this assumption. The con- 
version of ethyl maleate into ethyl fumarate by means of iodine was 
explained by aid of the supposition that di-iodosuccinic acid is the 
initial product, and the mutual repulsion of the two iodine atoms then 
results in the rotation of the two parts of the molecule, a more 
favoured configuration being adopted ; from the molecule in this new 
disposition hydrogen iodide is then withdrawn, a process leading to 
the production of iodomaleic acid, which is afterwards converted into 
maleic acid itself by the reducing action of the hydrogen iodide 
present. 

I H 

C0 2 H-OH C0 2 H-C-H I-C-C0 2 H 

H-OC0 2 H " H>OCO a H W * H-C-C0 2 H (r) " 



Fumaric acid. Externally compensated di-iodosuccinic acid. 

I-C-C0 2 H 
H-OC0 2 H ' 

Iodomaleic acid. 

instance when they are represented on the paper as in a straight line with the 
"double bond " about to be formed : 



a'C'b I a'C'b 

I ; -> I 1 

d'C'e d'C'e 

......... 

Annalen, 1888 246, 5396. 



84 PERKIN : WISLICENUS MEMORIAL LECTURE. 

The process by which hydrobromic acid effects the reverse change of 
maleic ino fumaric acid was shown to be capable of explanation on 
similar lines. 

In the original memoir presented to the Konigl. Sachs. Gesellschaft 
der Wissenschaften, attention was drawn to certain observations of 
Petrie and of Bandrowski which appeared to be inconsistent with the 
theory of the relations of maleic and fumaric acids therein put for- 
ward. Petrie found that fumaric acid is the sole product of the action 
of bromine on maleic acid in presence of water at ordinary tempera- 
tures, and Bandrowski obtained dibromosuccinic acid as the result of 
the interaction of bromine and acetylenedicarboxylic acid. Wislicenus 
was able to show later l that these reactions are in reality very com- 
plicated, the products being mixtures of a number of compounds such as 
his theory was capable of explaining. 

In replying to certain criticisms of Lessen, Wislicenus took occasion 
to remark that the conception of atoms as mere material points was 
antagonistic to his views, for he regarded the atoms as aggregations 
of the primitive element and analogous to compound radicles, being, 
therefore, endowed with a space configuration of their own. To his 
mind it appeared not improbable that the carbon atom has a tetra- 
hedral shape, and that the forces which are displayed in the " affinities " 
or "bonds" are concentrated in the four corners of this configuration, 
perhaps for reasons such as lead to the accumulation of the presumably 
analogous electric charge at the points and corners of a conductor ; 
if so, the carriers of energy must be the primitive atoms, exactly as 
the chemical energy of compound radicles is the resultant of the 
energy of the elementary atoms. 

Among the first compounds which Wislicenus proceeded to investigate, 
with the aid of his stereochemical ideas, were the isomeric tolane di- 
chlorides. 2 By the immediate application of van 't Hoff's conception, it 
was concluded that the product obtained by the direct addition of chlorine 

C H C'f 1 ! 

to tolane must be the planosymmetric compound ~ 6 TT 5 Ji ~,, so that 

'' 



the isomeride of lower melting point is therefore to be represented by 

f 1 IT C*C 1 1 

the axially symmetrical formula 6 5 . U 

d*L/*L/ 6 H 5 

TT'P'P TT O1T 
Wislicenus assigned to /?-coumaric acid the structure i| * A. , 

.O.*L'*UU2-tL 

for the reason that it is more readily converted into the lactone, 
coumarin, than is the isomeric acid; in order to account for the 
conversion of the latter into coumarin by hydrogen bromide, the 
assumption was made that the elements of hydrogen bromide are 

> Annalcn, 1888, 246, 5396. 2 Ibid., 248, 134 



PERKIN : WISLICENUS MEMORIAL LECTURE. 85 

added at the ethylenic linkage, and that a subsequent internal rotation 
of the molecule takes place consequent on a supposed inclination 
towards the formation of the lactone. 

The practical investigation of the isomeric crotonic acids fell to his 
pupils Teisler and Langbein. 1 

The results led him to infer that solid crotonic acid has the structure 

H-j>CH 3 
H-OC0 2 H' 

leaving for the liquid isocrotomc acid the formula 

CH 3 -C-H 

3 1 1 
H-OC0 2 H 

The former, with chlorine, yielded a/3-dichlorobutyric acid, 

01 

H.C.CH S 

H-C-C0 2 H ( } 
01 

01 

CH C > TT 

whilst a/?-isodichlorobutyric acid, * I TT M> w ^s the product from 

** 



01 

wocrotonic acid. By removal of the elements of hydrogen chloride from 
<i/3-wodichlorobutyric acid, the product a-chlorocrotonic acid was 
obtained, 

01 01 

r' H (r) CH.-C-H (r) cH 3 .c-H - 

H-C'C0 2 H C0 2 H-C-C1 C0 2 H-C-C1 ' 

01 H 



ajS-woDichlorobutyric acid. o-Chlorocrotonic acid. 

and the same substance, when warmed with an aqueous solution of 
sodium carbonate, by simultaneous loss of carbon dioxide and hydrogen 

OTT O*TT 

bromide afforded a-isochloropropylene, * N ; the latter was rapidly 

li'L'C'l 

CH *C 

attacked by alkalis at 100, yielding allylene, 3 m, whilst the iso- 

U*C 

CH *C*H 

meric a-chloropropylene, * U , prepared by a similar series of 

reactions, applied to crotonic acid, reacted with alkalis very much more 
1 Annalen, 1888, 248, 281355. 



86 PERK1N: WISLICENUS MEMORIAL LECTURE. 

slowly, a result which is in harmony with the structures assigned to 
the isomeric crotonic acids. 

The additional observation was made that by heating a/J-dichloro- 
butyric acid a partial conversion of the compound in a/J-wodichloro- 
butyric acid may be effected. 

The study of the relations subsisting between angelic and tiglic acids 
gave results of an equally interesting character. 1 

H*C*OH 

Tiglic acid, represented by the formula .Rro H' giv68 a dibromide 

which, when warmed with sodium carbonate in aqueous solution, is 
converted into crotonylene hydrobromide, 

Br Br 



H'C'CH 3 
CH 3 -OC0 2 H 


H-C-CHg ] 
" CH 3 -C-C0 2 H (1 * 1 
Br 


C0 2 H 



Tiglic acid. Tiglic acid dibromide. 

H-C-CH 
Br-OCH 3 

Crotonylene hydrobromide. 

the isomeric angelic acid yielded in his hands as main product angelic 
acid dibromide, a compound which had previously been overlooked, and 
which with sodium carbonate was found to yield isodibromopsevdo- 
butylene, 

Br Br 

3.H CHo-C-H 



(r) _v UX1 3 Y ^ (r) 
CH 3 -(>C0 2 H ' CH 3 -C.C0 2 H Br-C-CH; 

Br CQ 2 H 

Angelic acid. Angelic acid dibromide. 



Br-C-CHg* 



The last-named substance was also obtained by removal of the elements 
of hydrogen bromide from jt?ewdobutylene dibromide, 
Br Br 



H (r) CH 3 -H (r) CH 3 -C-F 

CH 3 -C-H CH 3 -6-H V Br-C-CH 3 V Br-C-CH 

Br H 



pseudoButylene. ^se^oButylenedibromide. 

butylene. 

1 Annalen, 1893, 272, 199 ; 1893, 274, 99119 ; 1900, 313, 207209, 
210-228. 



PERKIN : WISLICENUS MEMORIAL LECTURE. 87 



Crotonylene, with bromine, gave /Jy-dibromopsewcfobutylene, 

CH 3 -OBr 
CH 3 -C-Br' 



CH 8 -C CH-OBr 



CH 3 -C 



Crotonylene. 

the isomeride of which, namely, /ty-isodibromopsewcfobutylene, was 
prepared by removing the elements of hydrogen bromide from /3yy- 
tribromobutane, 

Br Br 



OHXj-Br C 

CHg-C-Br CH 3 -(>H Br-C-CH 3 

Br H 



)877-Tribromobutane. 



CH -OBr 



Br-OCH 3 

iso-Py-DibromopseudobvLtylene. 

From both of these dibromqpsewrfobutylenes, the same crotonylene 
tetrabromide was obtained by addition of bromine. 

The hope expressed by Wislicenus in this paper that it might som* 
day be "found possible to prepare the hydrobromides of angelic and 
tiglic acids, and afterwards to convert these into the isomeric pseudo- 
butylenes, was, strictly speaking, not realised, although some time later 
the same end was attained by the employment of the hydriodides 
of these two acids. 1 Tiglic acid hydriodide, warmed with an aqueous 
solution of sodium carbonate, lost hydrogen iodide and carbon dioxide, 
affording a hydrocarbon which, when passed 'into bromine, gave rise to 
a dibromide ; the latter, on treatment with potassium hydroxide, was 



converted into isobTomopseuddbuiylene, 3 N Angelic acid, 

Br'C'OJdg. 

by the same series of reactions, was finally transformed into bromo- 

pseudobutylenQ proper, 3 u* . These results are exactly in 

** 



accordance with the general conclusions which Wislicenus had pre- 
viously drawn, and the changes may be followed in a graphic manner 
in the case of tiglic acid : 

I I 

CH 3 C-H CH 3 -C-H CH 3 -C-H 

C0 2 H-C-CH 3 C0 2 H-C-CH 3 W CH 3 -C-H W 

H C0 2 H 



Tiglic acid. Tiglic acid hydriodide. 

1 Wislicenus, Talbot, and Henze, Annalen, 1900, 313, 228242. 



88 PERKIN: WISLICENUS MEMORIAL LECTURE. 

Br CH 8 

CH 3 -C*H CHg-C-H H-C-Br CH 3 -C*H 

CH 3 -OH CHg-C-H CH 3 *C*H Br*C-CH a - 

Br Br 



pseudoHntylene. ysgucfoButylene dibromide (meso). 

butylene. 

Fittig and Pagenstecher had actually observed that angelic acid 
when brominated yielded tiglic acid dr'bromide as main product ; the 
difference between these results and those of Wislicenus and Piickert 
proved to be due to the fact that unless a low temperature be main- 
tained during the addition of bromine, and strong light carefully 
excluded, isomeric change of the angelic to tiglic dibromide may occur. 
Wislicenus was not disposed to assume an undue amount of credit 
for his discovery of the true dibromide of angelic acid which Fittig 
and Pagenstecher had overlooked, but drew attention to the circum- 
stance that the draught cupboards in Fittig's laboratory at Strassburg 
were placed in the windows, and thus received a strong light, whilst in 
his own laboratory at Leipzig they lay between the windows, other- 
wise, as he remarked, angelic acid dibromide might have remained 
unknown. 1 

Later, with Schmidt, Wislicenus prepared jtwemfobutylene by the 
method employed by Le Bel and Greene, namely, by the dehydration 
of isobutyl alcohol. It was found 2 that a mixture of the centro- 
symmetrical and planosymmetrical hydrocarbons was formed, and the 
mixture of dibromides made by passing the mixture of hydrocarbons 
into bromine was separated into two portions by fractional dis- 
tillation. The higher boiling portion, on treatment with potassium 
hydroxide, yielded the bromo-derivative of the planosymmetrical 

OH "C^H 

pseudobuiyleue, 3 H , in larger quantity than did the lower 
-* 



boiling fraction, but the main product from both was the bromo-derivative 

OH C-H 

of the centrosymmetrical hydrocarbon, 8 H , which in presence 

jBr-O-CJcig 

of hydrogen bromide or on exposure to sunlight was found to undergo- 
a slow conversion into its stereoisomeride. Of the two bromopseudo- 

OTT OTT 

butylenes, the one assigned the formula 3 H gave crotonyl- 

** .t>r 



ene the more readily when heated with potassium hydroxide, an 
observation quite in accordance with the relative position of the 
hydrogen and bromine atoms in the formulae assigoed. 

Henze assisted in adducing new evidence in support of Wislicenus' s 

1 Annalen, 1893, 272, 98. Ibid., 1900, 313, 210-228. 



PERKIN: WISLICENUS MEMORIAL LECTURE. 89 

view. 1 The dibromide of angelic acid, as was anticipated, yielded 
/3-bromotiglic acid under the influence of strong potassium hydroxide, 
whilst the dibromide of tiglic acid was converted into /?-bromoangelic 

acid, 

Br H 



CH 3 .C-H CH 8 H Br-C-OH, 

CH 3 -C-C0 2 H CH 3 -C-C0 2 H (T) CH 3 -C-C0 2 H (T) 

Br Br 



Br 
H-C-CH 3 
CH 3 -OC0 2 H ( ' 
Br 


CH, 
CHJ 


H 

|-C-C0 2 H^ 
Br 


Tiglic acid 

CH 3 -(>Br 
CH 3 -OC0 2 H 


dibromide. 





Angelic acid. Angelic acid dibromide. 

Br-OCHg 
CH 3 -C-C0 2 H 

jS-Bromotiglic acid. 

H.C-CH 3 
CH 3 -OC0 2 H 

Tiglic acid. 



j8-Bromoangelic acid. 

Of these /8-bromo-unsaturated acids, the latter was the more easily 
converted into crotonylene by means of sodium carbonate solution, an 
observation which again is in harmony with the conclusions previously 
formed, as this isomeride is the one to which was assigned the formula 
having the bromine atom and the carboxyl , group in the position 
most favourable to the occurrence of this change. 

Stilbene gave Wislicenus and Seeler two dibromides, the main 
product being the ^derivative, which was considered to be the normal 
product, although, unlike the great majority of such normal addition 
products, it was found to be produced in larger proportion at a high 
temperature and in presence of intense light. 2 Either dibromide, when 
boated, underwent a partial conversion into the other; both yielded 
monobromostilbenes on treatment with alkalis, the a-compound afford- 
ing an oily bromostilbene, the latter a crystalline one, and of these the 
crystalline compound was the more easily converted into tolane when 
boiled with alcoholic potassium hydroxide, showing that it has the 

C 1 FT 'P'TT 

structure 6 5 1 1 . These observations led to the following view 
-' 



of the changes studied : 

1 jLnnalen, 1900, 313, 243250. 2 er., 1895, 28, 26932703. 



90 



PERKIN: WISLICENUS MEMORIAL LECTURE. 



C 6 H 5 -OH 



Stilbene. 



C 6 H 5 -OH 



II 
H-OC,EL 



woStilbene (?) 



C, 



Br 



Br 



Br 



* 



Br 



C 6 H 5 



o-Stilbene dibromide 
(internally compensated). 



Br- 



Oily dibromo- 
stilbene. 



C 6 H,C 

C H 5 -C 

Tolane. 



Br 



Br 



Br 






C 8 H 5 -OBr 



j8-Stilbene dibromide 
(externally compensated). 



Crystalline 
bromostilbene. 



Although at the time no direct evidence as to the existence of iso- 
meric stilbenes could be adduced, Wislicenus with Jahrmarkt after- 
wards succeeded in obtaining centrosymmetrical isostilbene l by 
reducing the oily bromostilbene from a-stilbenedibromide. 



' 
r-C- 

Oily bromostilbene. 



Br-C-C 6 H 5 



woStilbene. 



Thit, hydrocarbon, unlike stilbene itself, is a liquid which yields 
ordinary stilbene when distilled under atmospheric pressure, or when 
left with traces of bromine or iodine ; when dissolved in carbon disul- 
phide and mixed with bromine in absence of light it gives /?-stilbene 
dibromide to the extent of 83 per cent, of that theoretically possible. 

The investigation of stereoisomerism in cyclic compounds led 
Wislicenus, with Peters, Schramm and Mohr, to a study of the iso- 
meric forms of ^-dibromohexane. 2 On heating this dibromo-com- 
pound with ethyl disodiomalonate, an oil having the composition of 
a diethyl dimethylcycfopentanedicarboxylate was formed, and this, on 
hydrolysis, afforded a mixture of ester-acids, dicarboxylic acids, and 
monocarboxylic acids, each of which was shown to be related to one 
or other of the two dimethylcycfopentanedicarboxylic acids, 



H-C-CH 



and 



H-C-CH, 
CH fl 



H-C-CH 3 
C0. 2 H-C-COoH 
CH-C-H " 



2 

cis-cis. 



(r). 



cis-trans. 



1 Her. K. Sachs. Wiss. Math. Phys. CVj.,1900, 52, 117123. 
- Ber, y 1901, 34, 25652583. 



PERKIN: WISL1CENUS MEMORIAL LECTURE. 



91 



The constitution of the two acids was ascertained by heating them 
so as to cause the loss of one molecular proportion of carbon dioxide, 
and in these circumstances one of them gave rise to two stereo- 
isomeric monocarboxylic acids, and the other to one monocarboxylic 
acid only. The former must have been produced from the cit-cis 
derivative and the latter from the cis-trans-one. 

The formulae of the isomerides from the cw-cis-dicarboxylic acid are 



H-C-C0 2 H 
H-C.CH. 



m) 



and 



C0 2 H-C-H 
H-C-CH 
CH 2 



(m), 



and represent internally compensated inactive compounds. Those of 
the possible products arising from the cis-tfraws-dicarboxylic acid, in 
the same manner, are 



CH 2 

H-9'CH 3 
H-C-C0 2 H 
CH-C-H 



(r) 



and 




C0 2 H-C-H 
CH 3 -C-H 



but these are in reality identical, and represent one of the two 
enantiomorphous forms of an inactive mixture. 

The /3/3'-dibromohexane employed was separated by freezing into 
two parts, one solid and the other a liquid ; the former of these, 
when condensed with ethyl disodiomalonate, afforded ethyl citcvs- 
dimethylcj/cfopentanedicarboxylate, and was, therefore, the meso- 
compound 



H-OBr 



CH 2 
CH 2 



H-C-Br 
CH S 

the liquid isomeride, on the other hand, gave rise to the cis-trans- 
dicarboxylic derivative, and was, therefore, an inactive mixture of the 
d- and ^-compounds. 

It is perhaps hardly necessary to say that the foregoing sketch 
deals only with a part of the scientific work which was carried out by 
Wislicenus himself or by his pupils under his direction. No 

mention has been made of his recent contributions to the study of 

r> 



92 PERKIN: WISLICENUS MEMORIAL LECTURE. 

the reactions of dichloroether, 1 his investigations on the interaction 
of chloral with ketones, 2 on adipinketone, 3 of his discovery of the 
true vinylacetic acid, 4 or of his numerous researches on the stereo- 
isomerism of the cyclic pinacones obtained by the reduction of 
diketones. 5 To each of these much interest attaches, but considera- 
tions of space have led me to select from his more recent work that 
part which appears to have the most importance in connection with 
the growth of the science of stereochemistry, with which his nam^ 
is indissolubly connected. 

During the last few years of his life, Wislicenus became more and 
more the victim of severe attacks of ill-health, against which he 
fought with all his fine energy and determination, working steadily 
almost to the last. In the summer of 1902, he found his most strenuous 
efforts at resistance unavailing, and at last took refuge in complete 
rest at health resorts. His condition in the autumn gave his friends 
cause for the gravest anxiety, and early in the morning of December 
5th, 1902, he passed away. 

Two days later, a mournful but impressive ceremony was seen in the 
lecture-room attached to the Leipzig Chemical Laboratory ; Beckmann, 
Ostwald, His, Liity, Hantzsch, Medicus, and Bucher, colleagues of 
Wislicenus, representing their respective departments and faculties, 
expressed in moving terms their appreciation of the exalted and many- 
sided character of their departed friend. 

The concluding word? which fell from Ostwald were these : " Und 
wenn wir betrachtend vor ihnen stehen, so fiihlen wir es lebendig ; 
du warst nicht nur ein grosser Forscher, du warst auch ein guter 
Mensch ! " and this is the note which persistently rings in the 
memory of all who have tried to understand the man. 

There can be no doubt that in Wislicenus the world lost a man, 
not only of great and many-sided ability, but also of extraordinary 
directness of purpose and splendid character. 

1 Annalen, 1884, 226, 261281 ; 1888, 243, 151192. 

2 Ber.> 1893, 26, 908915. 

3 Annalen, 1893, 275, 312-382. 

4 Ber., 1899, 32, 20472048. 

8 Annalen, 1898, 302, 191244. 





lTofacep.93. 



CLBVB MEMORIAL LECTURE. 

DELIVERED ON JUNE 21sT, 1906. 
By THOMAS EDWARD THORPE, C.B., F.R.S. 

No circumstance in the national and personal history of experimental 
science is more remarkable than the position which Sweden and 
the Swedes occupy in relation to chemistry. When regard is had 
to her position among Continental nations to her chequered 
political history, to her geographical isolation, the comparative 
sparseness of her population, her relative poverty, the fewness of 
her seats of learning the influence which Sweden has been able 
to exert on the development of that branch of science which it is 
the proper function of this Society to foster must always excite 
our wonder, admiration, and gratitude. The mere mention of the 
names of Bergmann, Scheele, Berzelius, Mosander, Gadolin, Nilson, 
is sufficient to remind us how great have been her services to the 
science of chemistry. 

In Per Theodor Cleve, who was elected a Foreign Member of 
this Society in 1883, we had a man who throughout a strenuous 
life, wholly devoted to academic pursuits, and to the cultivation of 
pure science, worthily upheld and handed forward the traditions 
which his countrymen had succeeded in associating with his calling 
and particular office. In compliance with our custom, and at the 
request of the Council, I am privileged this evening to offer you 
some account of the life work of our deceased Foreign Member. 

I owe the invitation doubtless to the circumstance that I enjoyed 
the personal acquaintance and friendship of Cleve, who for some 
years past did me the honour to accept of my hospitality during his 
visits to London. Although I had thereby opportunity of learning 
at first hand something of his personal history and of his achieve- 
ments, and of noting his mental and intellectual characteristics 
and of forming impressions such as can only v be acquired by 
social intercourse and personal contact, I am conscious that niy 
account of the man and of his work owes whatever of completeness 
it may possess to the assistance which has been afforded to me in 
its compilation by Cleve's daughter and her husband. On learn- 
ing of the duty which had been imposed upon me by your Council, 
Dr. and Mrs. Euler were good enough to forward to me an advance 
copy of the obituary notice which they were preparing for tho 
Berichte of the German Chemical Society, and which has now been 
published. Of this account I have, with their permission, made 
full use in putting together what I have to tell you this evening. 



94 THORPE: CLEVE MEMORIAL LECTURE. 

Per Theodor Cleve was born in Stockholm on February 10th, 
1840. He was the thirteenth child of the merchant F. T. Cleve, 
whose ancestors had emigrated from Western Germany and settled 
in Sweden during the middle of the eighteenth century. It is told 
of the young Cleve that even during his school-time his leaning 
towards natural science, and especially towards natural history, was 
strongly marked, and that he spent hours which should have been 
devoted to classical studies in rambling round the country in search 
of animals, plants and stones to the despair of the philologs, who 
set him down, as they had previously done his great countryman 
Berzelius, as a youth of very little promise. This love for natural 
history was an abiding passion with Cleve, and constantly struggled 
with, and in the end conquered, his allegiance to chemistry. Destiny, 
indeed, intended that he should be a naturalist : the stress of cir- 
cumstance only made him a chemist. The boyish love of rambling 
strengthened into a constant yearning for foreign travel. His 
sympathy with the natural objects around his home with the 
birds and flowers of his native woods and fields, and the many won- 
derful minerals in his native rocks grew into an intense desire to 
see and to know Nature in her every mood, and under many skies. 
Had fortune favoured him Cleve would probably have followed in 
the footsteps of Humboldt and Darwin, and spent his life in 
scientific travel; compelling circumstances kept him for the most 
part at home, and in the end made him what he was. 

Although it is clear that Cleve's predilections were towards an 
academic life, it is not very obvious why he became a chemist. It 
may have been that the outlook as regards natural history was 
not very hopeful : Scandinavia forty years ago was not as convinced 
as now of the supreme importance to her national prosperity of those 
studies to which Cleve was inclined. As regards chemistry the 
times were more propitious. The early sixties was a period of 
great unrest in that science, and, as we all know, it culminated 
in nothing less than a revolution. Although speculation and theory 
had never much attraction for Cleve, the young candidat could 
not have been wholly uninfluenced by the movement of the time, 
or insensible to the effect it was exerting on the development of 
chemistry. Be this as it may, Cleve, who after five years' residence 
at Upsala had taken his degree, became when twenty-three years 
of age a lecturer on Organic Chemistry in the University. At that 
time the Chair on General Chemistry at Upsala was held by Lars 
Svanberg, who almost exclusively occupied himself with miner- 
alogicai inquiries. He was a fairly prolific contributor to the litera- 
ture on mineral chemistry of the period, and occasionally associated 
himself with his students in mineral analyses, but Cleve apparently 



THORPE: CLEVE MEMORIAL LECTURE. 95 

owed little to his teaching and still less to his example or encour- 
agement. 

Cleve's earliest contribution to chemical literature, made when 
he was twenty-one years of age, was " On Some Ammoniacal 
Chromium Compounds," and consisted in an extension of the work 
of Fremy, by whom this interesting class of substances was first 
made known. The chromammonium derivatives are among the most 
complicated and perplexing of inorganic compounds, and their 
discovery undoubtedly gave a great, extension to the conception 
of isomerism in mineral chemistry. Cleve thus early entered on a 
field of inquiry which occupied him for several years, and which 
has taxed the energies of many successive investigators, notably 
Jorgensen and Christensen. Cleve's first communication definitely 
established the existence and fixed the composition of the initial 
member of the chromtetrammonium series, namely chlorochrom- 
tetrammonium chloride, Cl 2 'Cr 2 '8NH 3 Gl 4 *2H 2 0, or, as he termed 
it, tetramminchromchlorid, a salt forming beautiful deep red 
trimetric crystals. 

The study of isomerism, using that term in its widest sense, and 
the influence of structure and constitution on the properties of 
bodies, may be said to have been the guiding principle which 
actuated the major part of Cleve's experimental labours, whether 
in inorganic or organic chemistry. The most cursory inspection of 
his published work shows that this was the dominant, underlying 
motive of his inquiries the silver thread which ran, as it were, 
through the fabric he elaborated. This fact requires to be borne 
in mind, in justice to Cleve, as indicating his philosophic habit of 
mind, and the real objective of his intellectual activity. Accident 
and opportunity no doubt at times appeared to change the main 
current of his thoughts; his mind was too active not to perceive 
and even occasionally to follow the many side-issues to which his 
inquiries gave rise, but with a true economy he invariably returned 
to what he recognised to be the proper direction of his energies. 
Singleness of aim and tenacity of purpose are the hall-marks of 
every successful prosecutor of scientific inquiry, and Cleve possessed 
these characteristics in an eminent degree. 

His work on the chromammonium compounds naturally led him 
to undertake the investigation of similar groups of inorganic sub- 
stances, in the hope of further elucidation of the problems 
in which he was interested, and he next occupied himself 
with the study of the platinum bases, the chemistry of which was 
even in a more chaotic condition than that of the more recently 
discovered chromium compounds. The history of the platinum 
bases, or platinammines, takes its rise from the discovery by Magnus 



9G THORPE: CLEVE MEMORIAL LECTURE. 

in 1828 of the famous " green salt " with which his name is 
associated, and which he prepared by the action of aqueous ammonia 
on platinous chloride. Ten years later, Gros, under Liebig's direc- 
tion, obtained a series of chlorinated derivatives of this salt, con- 
taining the group N0 3 , and shortly afterwards Reiset prepared the 
base Pt(NH 3 ) 4 (OH) 2 , of which the compounds prepared by Gros 
and the green salt of Magnus were regarded as salts. 

The relation between these substances was expressed as follows : 

Reiset' s first base Pt(NH 3 ) 4 (OH) 2 . 

Gros's salt Cl 2 Pt(NH s ) 4 (N0 3 ) 2 . 

Green salt of Magnus Pt(NH 3 ) 4 * PtCl 4 . 

In 1844 Reiset obtained a second series of salts con- 
taining only half as much ammonia as the first series, 
and from which a new base could be prepared the so- 
called Reiset's second base. Peyrone some time afterwards 
prepared a chloride which had the same composition as 
the chloride of Reiset's second base, namely, PtCl 2 *2NH 3 , 
but which was altogether different from it in properties. Isomerism 
among inorganic substances was at that time unknown, and to 
Berzelius, who first gave us the term, was inconceivable. Personal 
friendship and trust in Wbhler may have predisposed him in the 
first instance to tolerate the existence of isomerism among carbon 
compounds, to which his own work on tartaric acid may have further 
inclined him, as something exceptional and peculiar to organic 
substances, but, in the main, to Berzelius identity of composition 
meant identity of character : there was no room in his system for 
inorganic isomerides, and Peyrone's discovery was met by flat 
incredulity. But evidence as to its truth steadily accumulated. 
Raewsky discovered the analogues to Gros's compounds, and Ger- 
hardt and Laurent made known the existence of the platiriammine 
salts. The theoretical aspect of these facts was everywhere recog- 
nised as of the highest importance. They constituted so many test 
cases by which the sufficiency of a doctrine which had long domi- 
nated chemistry could be tried, and served to augment the slowly 
accumulating body of testimony which eventually overthrew it. 
Driven to recognise the existence of these compounds, Berzelius 
made futile efforts to reconcile them with his electro-chemical 
system. But the inadequacy of these attempts was apparent to 
all but the blindest adherents of the Swedish school. On the 
other hand, Gerhardt, by an extension of the theory of types, 
gave a more or less plausible explanation of the mode of structure 
and constitution of these groups of substances, which was not 
out of harmony with prevalent conceptions, and which, indeed, 



THORPE: CLEVE MEMORIAL LECTURE. 97 

in some respects, foreshadowed present-day developments in its 
recognition of variable valency. But the swing of the pendulum 
is not confined to that particular department of intellectual 
activity we call politics; we have constant examples of it in 
every sphere of human thought, for the movement is eventually 
controlled and regulated by the gravitational tendency which is 
inherent in the truth itself. The explanations of Berzelius might 
be partial and imperfect, but the underlying truth in his doctrine 
could never be wholly obscured, and when the system of types, as a 
theory of chemistry, in its turn gave way to a more rational 
generalisation, what there was of permanent value in both became 
incorporated in the new philosophy. 

As I have said, the theoretical significance of these compounds 
was very generally recognised, and in this connection I may recall 
the early work of Buckton, extending from 1851 to 1854, and of 
Hadow, published in our Journal for 1866. 

It was at about this period that Cleve undertook the study of 
the ammonia platinum compounds. He had, of course, been reared 
under the doctrine of Berzelius, whose influence, indeed, was 
paramount in Sweden long after it had waned in the rest of Europe, 
and he had no disposition or inducement at the time to trouble 
himself about its limitations. Speculative chemistry had never, at 
any period, much attraction for Cleve. In this respect he resembled 
Bunsen, with whose mental characteristics he had other points of 
resemblance and sympathy. His first papers on the platinum bases, 
published by the Royal Society of Sciences of Upsala, are, there- 
fore, as might have been anticipated, written wholly in the spirit 
and from the standpoint of an adherent of the orthodox school of 
chemical philosophy in Sweden. He was induced, he says, to under- 
take the investigation of these substances as a sequel to his work 
on the chromammonium compounds in the hope of eventually 
obtaining an independent view of the general constitution of the 
metal-ammonia compounds. The first object of his inquiry was 
sufficiently modest ; it was to determine the position of the chlorine 
in the salts obtained from Gros's base. Gros's base he found to be 
free from halogen; it could be regarded as an oxidised derivative 
of Reiset's first base. The salts obtained by Gros, as well as those 
of Raewsky, were, in fact, derivable from the hydroxyl compound 

(OH) 2 Pt(NH s ) 4 (OH) 2 . 

a formula which further serves to indicate one of the most re- 
markable properties of its salts, namely, that the halogens and 
acid radicles which they may contain are not removable with equal 
facility. Thus, for example, the four chlorine atoms in Gros's 



98 THORPE: CLEVE MEMORIAL LECTURE. 

chloricl* 1 are not equally precipitable by silver nitrate, a fact which 
may be explained by saying that it contains two chlorine ions and 
two undissociated chlorine atoms. One of the sulphates prepared 
by Cleve had the same empirical composition as a basic sulphate 
derived from Gros's base, but only one of the three equivalents of 
sulphuric acid was precipitable by barium salts. From this salt he 
prepared a platinum base, which he termed Sulphatodiplatinammin, 
and to which he subsequently gave the formula 



NH Q NH Q OSO fl 



Some of the early work on the platinum bases, more particularly 
that on Gros's compounds, was done in Wurtz's laboratory in 
Paris, but in 1868 Cleve returned to Sweden and worked for some 
months in the mineralogical laboratory of the Stockholm Academy 
of Sciences. Here he discovered an entirely new series of these 
complicated compounds, which he obtained by the action of ammonia 
on the iodine derivatives of Gros's base. They were the first repre- 
sentatives of these bases containing the double platinum atoms, and 
were termed by him the diplatinammin compounds. He eventu- 
ally gave to them the following rational formula : 

j p < NH-NHN0 
* ^ 



I <r NH 3 -NH 3 N0 8 
I. Pfc \NH 8 -NH 3 N0 3 - 

In his attempt to gain a true conception of the constitution of 
the metal-ammonia bases Cleve undoubtedly obtained great assists 
ance from Blomstrand, and there is no question that the " Chemie 
der Jetztzeit," which was published in Heidelberg in 1869, and in 
which Blomstrand developed and extended his views of the mutual 
relations of these various groups of substances into an orderly and 
systematic arrangement, gave Cleve his first clear insight into their 
constitution and intradependence. The effect on him was imme- 
diate, and is to be seen in his next memoir in 1870 on the isomeric 
platinum bases, in which he finally renounces the Berzelian system 
of representation and notation in favour of the more comprehensive 
and rational scheme, founded on valency, which still satisfies us. 

In this paper he describes a number of derivatives of Reiset's 
second base, as well as a series of salts isomeric with these. The 
first members of these latter salts were discovered by Peyrone, but 
their true relations remained hitherto obscure. These compounds 
were termed by Cleve the platinoxydulammonium salts. His 



THORPE: CLEVE MEMORIAL LECTURE. 99 

study of the properties of the two isomeric series led him. to suggest 
the following formulae as expressing their constitution: 

NH 8 Cl p< NH 8 -NH a Cl 

NH 3 Cl b ^Cl 

Chloride of Reiset's second base. Platinoxydulammonium chloride. 

Cleve further found that tetravalent platinum gave rise to a 
series of salts, obtained from platinoxydammonium, isomeric 
with Gerhardt's platinammine compounds. The two series of com- 
pounds discovered by Cleve, Pt(NH s NH 3 R)R and 

R 2 Pt(NH 3 -NH 3 R)R, 

were subsequently termed by Blomstrand, whose classification and 
nomenclature of the platinammonium compounds is still commonly 
adopted, the platososemidiammines and platinsemidiammines, whereas 
the isomeric bases of Reiset, Pt(NH 3 R) 2 , and Gerhardt, R 2 Pt(NH 3 R) 2 , 
were styled respectively platosammines and platinammines. 

In order to obtain further experimental support for his views 
of the constitution of these isomerides, Cleve studied their behaviour 
towards aniline. He found that in the case of the compound 
obtained from the platosammine chloride the two aniline molecules 
were readily split off, whereas in that derived from the platosemi- 
diammine chloride a molecule of aniline remained. In the first 
3ase we had 



whilst in the second we had, according to Cleve, 



NH 3 C1 



<NHjGT 



Cleve's view that both classes of salts contain divalent platinum 
is, however, hardly probable in view of Jorgensen's later work. The 
constitution of the corresponding chlorides would seem, dn the 
whole, to be better represented by the formulae 



p3 1 

b 



although Cleve's expression has the merit of clearly indicating 
the important fact of the different behaviour of the chlorine in 
the two isomeric, chlorides. 

This paper was followed (1871) by a short communication in 
which Cleve explained the relation between the green salt of 
Magnus, piatodiammine chloride platinous chloride, 

Pt(.NH 3 -NH 3 Cl) -PtCl 2 , 

2D 



100 THORPE: CLEVE. MEMORIAL LECTURE. 

and the brown salt discovered by Peyrone the first member of the 
platosamminesemidiammine series 

NH-NH 8 01 



"NH 01 
The chloride PtxCvttV, 8 ma y ke caused to combine with two 



atoms of chlorine, when it forms Pt 



The corresponding platinamminesemidiamminc derivatives were also 
prepared by Cleve. 

In the same year he published two papers on the sulphites and 
nitrites of the isomeric bases of platosammine and platosemidiam- 
mine 

The work on the ammoniacal platinum bases occupied Cleve 
nearly BIX years, and he put togethei his results in a remarkable 
memoir, written in English and published by the Swedish Academy 
of Sciences in 1872, a copy of which is to be found in our Library. 
In this memoir, which extends to upwards of 100 4to. pages, Cleve 
arranges all the known derivatives of the ammoniacal platinum 
bases in accordance with Blomstrand's scheme of classification, 
using his system of terminology, 'rhe whole of these bodies many 
hundreds in number may be grouped under three main divisions, 
each division being subdivided into several series, as follows : 

Group I. Plato- or Platoso-compounds. 

Series I. Platosemiammines, RPtNH 3 R. 
II. Platosammines, Pt(NH 3 R) 2 . 
III. Platodiarnmines, Pt(NH 3 NH 8 R) 2 . 
IV. Platosemidiammines, Pt(NH 3 -NH 3 -R)R. 
V. Platomonodiammines, Pt(NH 3 .NH 3 R)(NH 2 R). 

Group II. Platini- or Platin-compounds. 

Series I. Platinammines, R 2 Pt(NH 3 R) 2 . 

II. Platinidiammines, R 2 Pt(NH 3 -NH 3 R) 2 . 

III. Platinisemidiammines, R2Pt(NH 3 -^H 3 R)R. 

IV. Platinimor.odiammines, R 2 Pt(NH 3 -NH 3 )R(NH 3 R). 

V. Platinitriammines, R 2 Pt(NH 3 -NH 3 'NH 3 R) 2 . 



THOKPE: CLEVE MEMORIAL LECTURE. 101 



Group III. Diplatinum Compounds. 

Pt(NH 3 -NH 3 R) 
Series I. Diplatodiammines, | 

Pt(NH 3 -NH 3 R) 

RPt(NH 3 -NH 3 R) 

Series II. Diplatosodiammines, , 

RPt(NH 3 -NH 3 R) 
Pt(Nfi 8 -NH 8 R) 
or 

R 2 Pt(NH 3 -NH 3 R) 
RPt(NH 3 R) 2 
Series III. Diplatinammines 

RPt(NH 3 R) 2 

RPt(NH 3 -NH 3 R) 2 
Series IV. Diplatinidiammines 

RPt(NH 3 -NH 3 R) 2 

Although Cleve entitles his memoir " On Ammoniacal Platinum 
Bases/' its subject-matter really comprehends the discussion and 
systematic arrangement of all the metalline ammoniacal bases and 
their salts at that time known, and must have involved great labour 
and research in its compilation. 

From this review -of all the known ammoniacal compounds of the 
different metals Cleve concluded : 

I. The highest number of molecules of ammonia which occur 
united together in ammoniacal compounds is 4. Tetrammints of 
calcium, strontium, and perhaps of cuprobuin are as yet the only ones 
known. 

II. Triammines are formed by calcium, magnesium, cobalt, nickel, 
zinc, cadmium, silver, rhodium and iridium. 

III. Diammmes are produced by most metals. 

IV. Consequently, as a rule, the most positive metals sem to 
have the power of uniting the greatest number of molecules of 
ammonia, but more negative metals, such as platinum, form the 
most stable ammoniacal compounds.* 

During some portion of the time over which this work extended, 
Cleve found opportunity to gratify his inclination towards the 
study of natural history. Shortly after his return from Paris he 

* The prefixes mono-, di-, &c. , denote the ntimber of NH 3 groups directly united 
with one another, and not the number of such groups in direct union with the Ft 
atom. Tims, as the compounds in Series III, Group II, contain (NH 3 vN"H 3 ) or one 
diammiue chain, they are called semi-diammiiies ; and as those in Series TV, Group 
II, contain one diammine and one monoammine chain, they are termed mono- 
diammincs. 



102 THORPE : CLEVE MEMORIAL LECTURE. 

was enabled, by means of a grant from the Stockholm Academy 
of Sciences, to undertake a journey to the West Indies with a view 
to an inquiry into the geological structure of the Antilles, the results 
of which were published in 1871 in English, by the Swedish 
Academy. 

On his return he was made Adjunct in Chemistry in what was 
then known as the Stockholm Technological Institute, but which 
has now developed into a polytechnic of the type of Charlottenburg 
or Zurich. Whilst occupying this position he did a considerable 
amount of literary work, compiling text-books and putting together 
many contributions to the periodical literature of the time on 
botanical and geological subjects. On Svanberg's retirement he 
was called to the Chair of Chemistry in Upsala, where he remained 
until the age-limit of sixty-five which operates in Sweden required 
him to resign the Professorship. 

Shortly before his removal from the Swedish capital to Upsala, 
Cleve turned his attention to the study of the rare earths a branch 
of chemical inquiry with which the names of Scandinavian investi- 
gators are pre-eminently associated. As is well known, Sweden has 
the good fortune to possess an uncommon share of those minerals 
which are characterised by containing the so-called rare earths one 
small locality alone, namely, Ytterby, not far from Stockholm, was 
famous as the happy hunting-ground of the collector and the 
investigation of this material was long the monopoly of Swedish 
chemists, as the names of Gadolin, Ekeberg, Mosander, Berzelius, 
Hisinger, and Bahr testify. The greater part of their work in this 
special department of mineral chemistry was done during the first 
third of the nineteenth century, and resulted in the addition of 
no fewer than seven substances to the list of the chemical elements 
then known, namely, yttrium, cerium, thorium, lanthanum, 
didymium, terbium, and erbium. The death of Berzelius and the 
consequent disappearance of his school, together with the extra- 
ordinary development of organic chemistry, due mainly to Liebig and 
his associates in Germany, and to Dumas, Laurent and Gerhardt, 
and others in France, undoubtedly checked the progress of inquiry 
in the special field which the Swedish chemists had cultivated with 
such brilliant success. But the discovery of the remarkable absorp- 
tion spectrum of didymium by Gladstone, and of that of erbium by 
Bahr, led to renewed activity in rare-earth chemistry, and the 
services of the spectroscope as an analytical instrument were at once 
brought into requisition in connection with this department of 
inorganic chemistry. 

It was at this juncture that Cleve and his collaborator Hoglund 
entered the field, and in a paper published in 1872 they gave the 



THORPE: CLEVE MEMORIAL LECTURE. 108 

results of an inquiry which covered much the same ground as a 
prior investigation by Bahr and Bunsen on the gadolinite earths. 

Incidentally, however, Cleve and Hoglund prepared a large 
number of hitherto undescribed salts of yttrium and erbium, both 
of which they regarded at that time as divalent elements. 

The publication by Mendele"eff of the epoch-making memoir in 
which he first made known the great generalisation which is as- 
sociated with his name resulted in further attention being paid to 
the chemistry of the rare earths. As will be remembered. 
Mendeleeff in this paper discussed the position of certain of the rare- 
earth metals in the periodic system, and showed that all the known 
facts rendered it in the highest degree probable that the greater 
number of these elements must be regarded as belonging to the 
third group of his scheme of classification. Cleve at once recognised 
that the systematic study of this group of elements in the light of 
MendeleefFs generalisation would constitute one of the strongest 
tests of its validity. He repeated and extended his work with 
Hoglund on the compounds of yttrium and erbium, and then 
attacked the chemistry of the elements thorium, lanthanum, and 
didymium. No stronger evidence of Cleve's power of work 
could be adduced than is shown in the monograph pub- 
lished in 1874, embodying the results of the two years' labour, on 
the compounds of these five metals. Concurrently with this inquiry, 
Jolin, under Cleve's direction, took up the study of the salts of 
cerium. As the result of this comprehensive investigation, Clevt 
established that thorium is certainly a quadrivalent element, whilst 
the other metals constitute a natural group of chemically related 
bodies, of which cerium and lanthanum, on the one hand, and 
yttrium and erbium on the other, form subgroups, the respective 
members of which stand in close relationship to each other, their 
compounds, as Marignac and Topsoe had shown, being respectively 
isomorphous; whereas didymium would appear to occupy an inter- 
mediate position, as it forms salts which are isomorphous sometimes 
with the one subgroup and sometimes with the other. If we assume 
with Cleve that lanthanum is to be regarded as trivalent, it follows 
that the remaining four elements are also trivalent, a conclu- 
sion which Cleve sought to establish by the preparation of a large 
number of typical salts. Cleve's main conclusions were not uni- 
versally accepted at the time of their publication, and indeed were 
freely criticised by Delafontaine and by Wyrouboff, but all subse- 
quent inquiry has served to establish their validity, and the position 
of these elements in the schemes of classification at present in vogue 
is practically that which Cleve indicated. 

Some years later, and mainly in consequence of the work of 



104 THORPE: CLEVE MEMORIAL LECTURE. 

Frerichs and Smith, Cleve was induced to repeat certain of his 
observations on the compounds of lanthanum and didymium. He 
confirmed his results, with, however, this significant difference, that 
for the first time he was led to give expression to his doubt as to 
the individuality of didymium, He founded this surmise mainly 
on the behaviour of didymium oxide on heating, the change in 
colour suggesting the presence of another element. 

How well founded was this surmise was established by Auer von 
Welsbach in 1885 by the discovery of praseodymium. 

In the years immediately following the publication of Cleve's 
papers, the chemistry of the rare-earth metals received important 
extensions by the discovery of ytterbium by Marignac and of 
scandium by Nilson. Shortly after the existence of the latter 
element was made known, Cleve was enabled to prepare a number 
of its salts, and to make the first determinations of its atomic 
weight, with the result of proving that scandium was identical 
with Mendel tSeff's ekaboron. It is hardly necessary to remind 
you of the effect on the chemical world of this discovery. It was the 
second instance of the realisation of Mendele"eff's prediction as to the 
existence of hitherto unknown elements the properties of which he 
had been able to forecast by the aid of the principles he first clearly 
indicated. The realisation of these predictions, coming so soon 
after the promulgation of the Periodic Law, did more to secure its 
general acceptance among men of science than any other set of facts. 

Marignac's discovery of ytterbium in what was generally regarded 
as a homogeneous earth rendered it almost certain that the pro- 
perties up to that time associated with erbia were not those of 
an individual substance, and accordingly Cleve set himself to prepare 
pure erbia with a view to an accurate study of its characters and a 
redetermination of its atomic weight. No erbia that Cleve could 
at the outset obtain furnished constant atomic weight values, and 
he concluded, therefore, that Mosanders erbia was even a more 
complicated mixture than had hitherto been surmised. Thalen's 
investigation of the spectroscopic behaviour of the several fractions 
obtained by Cleve showed that they contained, in addition, possibly, 
to other substances, at least two new elements, one having an 
atomic weight between that of erbium and of yttrium that is 
between 166 and 89, and the other having an atomic weight between 
those of erbium and ytterbium that is between 166 and 173. The 
former Cleve named holmium, the latter he called thulium. 
Holmium appears from its spectroscopic indications to be identical 
with Soret's X. It is still doubtful, however, whether holmia and 
thulia are actually simple substances ; there is good reason to believe, 
indeed, that Cleve's holmia is in reality a mixture containing 
possibly unknown elements. 



THORPE: CLEVE MEMORIAL LECTURE. 105 

Unfortunately, these substances are present in the gadolinite 
earths in extremely small quantity, and their separation is both 
tedious and imperfect. 

Although Cleve was unable to do more than indicate the probable 
existence of these new elements in gadolinite, he eventually suc- 
ceeded in obtaining pure erbia, and the atomic weight which we now 
associate with that element is based upon his determinations. 

The discoveries made subsequent to 1874 led Cleve to undertake 
a revision of his determinations of the atomic weights of yttrium, 
lanthanum and didymium. As regards yttrium and lanthanum, 
the repetition resulted in comparatively unimportant changes; in 
the case of didymium the number was much too high, owing to the 
presence of samarium, prior to that time unknown. The number 
obtained by Cleve on repetition was 142, almost the arithmetic 
mean of the' atomic weights of its two subsequently discovered com- 
ponents, praseodymium, 140-5, and neodymium, 143-6. 

Cleve next studied the action of hydrogen dioxide upon the rare 
earths, and described a number of their peroxides, and in 1883 
and 1885 he published important papers on samarium and its salts, 
and gave the first accurate estimation of its atomic weight. 

These constituted his last contributions to this department of 
mineral chemistry, although he continued to the end to take an 
interest in its further development, placing the stores of material 
which he had accumulated in the Upsala laboratory at the disposal 
of such of his students as were willing to devote themselves to its 
investigation, and who were, at the same time, capable of taking 
advantage of the advice and counsel which his own ripe experience 
enabled him to give. It is only necessary to name the monographs 
on praseodymium by Scheele, on ytterbium by Astrid Cleve, on 
gadolinium by Benedicks, and on neodymium by Holmberg, to show 
that these treasures have been turned to good account. 

As is well known to all here, the rare earths have acquired an 
increased importance within recent times owing to their technical 
value in connection with artificial illumination, and the whole world 
is now being searched for new sources of supply. Even now un- 
dreamt-of amounts of certain of them resulting from the operations 
needed to extract the commercially valuable oxides are at the dis- 
posal of investigators, and we may confidently anticipate, therefore, 
fresh additions to knowledge in a field of inquiry where much still 
remains to be done. 

Cleve's services to inorganic chemistry, and especially to rare- 
earth chemistry, were recognised by the Royal Society in 1894 by 
the award to him of the Davy Medal. In presenting the medal, the 
President, Lord Kelvin, said : " This field of inquiry is pre- 
eminently Scandinavian. By the manner in which he has cultivated 



106 THORPE: CLEVE MEMORIAL LECTURE. 

it, Professor Cleve has shown himself a worthy successor of such 
forerunners as Gadolin, Berzelius and Mosander, and by sound and 
patient investigation he has faithfully upheld the traditions insepar- 
ably associated with these names. All chemists are agreed that 
no department of their science demands greater insight or more 
analytical skill than this particular section. Many of the minerals 
which furnish the starting point for investigation are extremely 
rare, and the amounts of the several earths which they contain are 
frequently very small. Moreover, the substances themselves are 
most difficult of isolation, and their characters are so nearly allied 
that the greatest care and judgment are required in order to de- 
termine their individuality. A remarkable example of Professor 
Cleve's power in overcoming these difficulties is seen in his masterly 
inquiry into the affinities and relations of the element scandium, 
discovered by Nilson. This, one of the rarest of the metals, is found 
only in gadolinite to the extent of 0-003 per cent.; and in yttro- 
titanite to the extent of about 0-005 per cent. The whole amount 
of the material, as oxide, at Cleve's disposal was only about 1 gram, 
but with this small quantity he determined the atomic weight of 
the element, and ascertained the characters of its salts with such 
precision as to leave no doubt of the identity of scandium with 
the element Ekabor, the existence of which was predicted by 
Mendeleeff, in the memorable paper in which he first enunciated 
the Law of Periodicity. Cleve's research, indeed, constitutes one 
of the most brilliant proofs of the soundness of the great generalisa- 
tion which science owes to the Russian chemist. 

" A not less remarkable instance of Cleve's skill as a worker is 
seen in his research on samarium and its compounds, which he com- 
municated, as one of its Honorary Foreign Fellows, to the Chemical 
Society of London. The existence of samarium was inferred inde- 
pendently by Delafontaine and Lecoq de Boisbaudran, but we owe 
to Cleve the first comprehensive investigation of its characters and 
chemical relations. From the nature of its compounds, a large 
number of which were first prepared and quantitatively analysed 
by Cleve, and from the value of its atomic weight, which was first 
definitely established by him, it would appear that samarium most 
probably fills a gap in the eighth group of Mendele'eff s system." 

And perhaps I may be pardoned for saying that there is no 
circumstance in my official connection with the Royal Society which 
I have greater pleasure in recalling than the share I was permitted 
to take, as a member of its Council, in thus testifying to the 
appreciation which all British chemists feel of the value of Clevp.'s 
services to their science. 

Cleve's name is associated with descriptive mineralogy in con- 



THORPE: CLEVE MEMORIAL LECTURE. 107 

nection with a mineral first made known by Nordenskjold in 1878, 
and which is of importance from its relation to the history of 
argon and helium. It will be remembered that Hillebrand, in 1890, 
announced that gaseous nitrogen was a constituent of cleveite. 
Shortly after the discovery of argon, Cleve directed his pupil Langlet 
to make a further investigation of the gases in this mineral. The 
results of this inquiry were, however, anticipated by Ramsay, who 
discovered that the characteristic gases of cleveite were helium and 
argon. Langlet made use of the helium thus extracted to make 
the first accurate determinations of its atomic weight, and obtained 
the value He = 4-0 which finds its place in our tables. 

As director of the Upsala laboratory, then, as now, the most 
important school of chemistry in Sweden, Cleve was anxious to 
secure for organic chemistry its proper position in the scheme of 
instruction in the University. Since the death of Berzelius, Sweden 
had mainly won her laurels in the fields of mineral chemistry, but 
no teacher in Cleve's position could be unmindful of the extra- 
ordinary development of the chemistry of the carbon compounds 
which had resulted from the activity of French and German 
workers, or oblivious of the material benefits which followed from 
the technical applications of their discoveries. 

It was incumbent on him, therefore, to arrange that Upsala should 
take her due share in the cultivation of this great and rapidly 
extending branch of inquiry. Although it might be expected that 
Cleve's predilections as a worker would be to continue in the line 
of investigation with which he had been associated for so many 
years past, and in connection with which he had accumulated such 
rich stores of material, he determined to embark himself upon the 
great ocean of organic research with such of his pupils as were 
disposed to accompany him. As might have been surmised, he was 
mainly attracted by problems of isomerism and constitution, and he 
found in the chemistry of naphthalene ample scope for the exercise 
of his powers. Cleve began by attacking the constitution of the 
nitrosulphonic acids. This he and Atterberg sought to unravel 
by converting them into the corresponding dichloronaphthalenes 
by the methods of Carius, Koninck and Marquardt. This field of 
inquiry occupied the Upsala laboratory for about eighteen years. 
When Cleve entered it only two of the ten possible dichloronaph- 
thalenes were known. He himself prepared six of the isomerides, 
and Atterberg obtained two more in addition. Only those who 
have occupied themselves with work of this character can fully 
realise how tedious and time-consuming it is owing to the very 
slight differences in physical characters which certain of the sub- 
stances possess. 



108 THORPE: CLEVE MEMORIAL LECTURE. 

The nitrosulphonic acids prepared by Cleve of which he was 
able to determine the constitution were the 1-5, the 1-6, 1-3, 1-7, 1-8 
and 1*4. He also prepared the corresponding amino-acids, of which 
the 1*6 and 1'7 are of special importance in the colour industry, 
and are known in technology as Cleve's naphthylaminesulpho-acids. 

Cleve and his pupil Arnell also prepared and studied eight of 
the fourteen possible chloronaphthalenesulphonic acids, namely, the 
1-4, 2-6, 2-8, 1-5, 1-6, 1-3, 1-2 and 1-7 isomerides, and he further pre- 
pared many of the nitro-compounds, the constitution of which he 
determined by conversion into the trichloronaphthalenes. Other 
coadjutors in this work in the Upsala laboratory were Jolin, 
Widman, Ekstrand, Forsling and Ekbom. 

In awarding the Davy Medal Lord Kelvin also made allusion to 
the naphthalene work, and to the manner in which Cleve had thus 
gradually brought order out of confusion, adding that: "Within 
recent years a score of workers have occupied themselves with the 
same field of research, and no greater proof of Cleve's accuracy and 
care as an investigator could be furnished than the manner in 
which his naphthalene work confessedly one of the most intricate 
and complicated sections of the chemistry of aromatic compounds 
has stood the ordeal of revision." 

No account of the outcome of the Upeala laboratory whilst under 
Cleve's direction would be complete without some allusion to the 
fact that it was during that period and in that place that Svante 
Arrhenius acquired his knowledge of chemical science. The cele- 
brated memoir of 1884 in which Arrhenius first promulgated the 
theory which has made him famous was his Doctor-Dissertation at 
Upsala. 

Cleve, who, I have good grounds for stating, greatly appreciated 
his honorary membership of our Society, published several of his 
contributions to the literature of chemistry in our Journals. Among 
these was his first memoir on samarium, which appeared in our 
Transactions in 1883. He also published a short note in our 
Proceedings, in 1891, on the formation of an explosive substance 
from ether. Lastly I may remind you of the obligation which the 
Society is under to him for the admirable critical estimate of the 
life-work of his friend Marignac which forms the memorial lecture 
on our distinguished Foreign Member. 

Although Cleve continued to the end of his academic career to 
interest himself in the proper work of his chair, reading the 
periodical literature of our science with regularity, and studying to 
keep himself informed of its development, towards the close of 
his life he became more and more absorbed in those biological 
studies to which he had never ceased to be attracted, and latterly 



THORPE : CLEVE MEMORIAL LECTURE. 109 

he gave himself entirely to them. Of his work on the diatoms 
and on plankton most of which was published in English this 
is not the place to speak, even if I were competent to offer any 
opinion concerning it. That it should have secured for him the 
honorary membership of the Royal Microscopical Society a dis- 
tinction which he prized not less than his fellowship in our Society 
is some evidence of the value which contemporary workers set upon 
his labours. 

When the time for his retirement from the Chair at Upsala 
arrived, he moved to Gothenburg that he might be near the sea and 
in touch with the hydrographic station at Borno, and thus pursue 
uninterruptedly and in quietude the study of his beloved plankton. 
Of a sound constitution and of good bodily strength, regular and 
methodical in his habits, active in mind, serene in temper, and 
unimpaired in intellectual vigour, he might still at sixty-five 
look forward to many years of scientific activity. But these years 
were not to be his. In December of 1904 he was suddenly seized 
with pleurisy. His heart became affected, and cardiac asthma 
supervened. In the spring of 1905 he was somewhat better and 
journeyed to Uppala, but died there, within three weeks of his 
arrival, on the 18th of June, 1905. 

His memory will be cherished by those who had the privilege of 
his friendship as that of a true man, vigorous in intellect, rich in 
mental acquirement, wide in sympathy with every branch of natural 
science, courteous in manner, calm and unimpassioned in judg- 
ment, of a humour ironical at times and even mordant, but withal 
tolerant and large-hearted, and of a flexibility of opinion, especially 
on theoretical questions, which was often disconcerting to his friends. 
And in the annals of science his name will continue to live as- that 
of one who followed her unselfishly and gave unstintedly to her 
service all that was best in him. 




[To face p. 111. 



WOLOOTT GIBBS MEMORIAL LECTURE. 

DELIVERED ON JUNE 3RD, 1909. 
By FRANK WIGGLESWORTH CLARKE. 

IT is easy to write biography when one is satisfied with a mere 
chronicle of events. But to clothe the skeleton of fact with flesh 
and blood, so that the man shall, as it were, live again, is difficult, 
and yet, figuratively speaking, that seems to be the sort of task 
which you have set before me. What manner of man was Wolcott 
Gibbs? What influences helped to mould his character? What 
did he do, and under what conditions was his work accomplished ? 
These are the questions which I must try to answer. 

Oliver Wolcott Gibbs (he dropped the Oliver early in his career) 
was born in the city of New York, on February 21, 1822. His 
father, Colonel George Gibbs, was a man of some wealth, who 
owned a large country place at Sunswick, on Long Island, not 
far from the then small city. He was an enthusiastic mineralogist, 
and gathered a collection which, ultimately sold to Yale College, 
became the micleus of the great cabinet since made famous by the 
labours of the two Danas, Brush, and Penfield. It was perhaps 
the control of the Gibbs collection which first led J. D. Dana to 
write his classical System of Mineralogy. Colonel Gibbs, after 
whom the mineral gib b site was named, was himself the author of 
several memoirs upon mineralogical subjects, and his eldest son, 
also named George, achieved some reputation as a geologist and 
as a student of ethnology. Wolcott Gibbs was born into an 
atmosphere of scientific interests, and his early associations must 
have influenced his choice of a career. A taste for science ran 
in the family. 

Laura Gibbs, the mother of Wolcott, came of distinguished 
ancestry. Her father, Oliver Wolcott, rose through various 
positions to that of Secretary of the United States Treasury, a 
post which he held during the latter part of Washington's 
administration and well into the administration following. He 
then became a Justice of the United States Circuit Court, and 
during the last ten years of his life he was Governor of .the State 
of Connecticut. His father, another Oliver, was a magistrate, a 
major-general of militia, a member of Congress, and a signer of 
the American Declaration of Independence. He, too, was a 
Governor of Connecticut, and so also was his father, Roger 
Wolcott, the first noteworthy member of the line. In short, the 
ancestors of Wolcott Gibbs were people of far more than average 



112 CLARKE: WOLCOTT GlBBS MEMORIAL LECTURE. 

ability, who had the confidence and esteem of their fellow citizens, 
and were therefore entrusted with positions of high rank and 
responsibility. Even though there was no commanding genius 
among them, no man of world-wide fame, they at least left to their 
descendants a legacy of lofty examples, well worthy of emulation. 
We may differ in our opinions as to the significance of heredity; 
but we can recognise the fact that Gibbs received from his forbears 
a sound mind in a sound body, together with traditions of well-doing 
that could not be disregarded. A good ancestry is a good beginning 
for any man. 

In his early environment Gibbs was also fortunate. Although 
he was only eleven years old when he lost his father, his mother 
survived for many years, and gave him the best of opportunities 
for healthy development. She was a woman of strong character 
and unusual ability, and her home became a centre in which the 
best intellectual society of New York was to be found. Her 
character, forceful, positive, patriotic, and public-spirited, was 
reflected in that of her son. 

The early childhood of Wolcott Gibbs was largely spe^it at his 
father's estate of Suns wick, where, as he tells us in a brief auto- 
biographical note, " he was often occupied with making volcanoes 
with such materials as he could obtain, and in searching the stone 
walls . . . for minerals, and the gardens and fields for flowers." 
At the age of seven he was sent to a private school in Boston, 
where he was under the care of a maiden aunt, whose sister had 
married the famous Unitarian divine, William Ellery Channing. 
The winters were passed in Boston, and the summers with the 
Channings at their country place near Newport, Rhode Island. 
Here again he was surrounded by choice influences, and saw many 
distinguished people. The reputation of Dr. Channing attracted 
many visitors, including more than a few from abroad, and the 
boy must have come to some extent in contact with them. Being 
but a child, he may not have understood or appreciated his 
opportunities, but his imagination could not have been entirely 
unaffected. His early associations foreshadowed his later career. 

When he was twelve years old, Gibbs returned to New York, 
and began his preparation for college, in 1837 he entered 
Columbia College as a freshman, and graduated in 1841. It was 
in his junior year that he published his first scientific paper, a 
description of a new form of galvanic battery, in which carbon 
was used, probably for the first time, as the inactive plate. This 
achievement, unimportant as it may seem now, was really remark- 
able in two ways; first, on account of the youth of the author, 
and, secondly, because of the conditions under which the work was 



CLARKE: WOLCOTT GIBBS MEMORIAL LECTURE. 113 

done. In those days the American colleges, like the public 
schools of England, were intensely classical in their aims, and 
science received the minimum of attention. Latin, Greek, and 
mathematics ruled the curriculum, with only a smattering of other 
subjects. Even in the classics literature was subordinate to 
grammar, and as for the modern languages they were almost, if 
not quite, ignored. What science was cultivated was taught by 
lectures and text-book recitations, for the era of laboratory instruc- 
tion had not begun. That a pupil of eighteen shpuld make an 
original investigation under such conditions was surprising, but 
it showed the irresistible tendencies at work in his mind. The 
early impulses, received from his father, could not be overcome. 

After receiving his bachelor's degree, young Gibbs went to 
Philadelphia, where he served as assistant in the laboratory of 
Robert Hare, the well-known inventor of the compound blow-pipe, 
who was then Professor of Chemistrv in the Medical School of the 
University of Pennsylvania. Gibbs's purpose was to fit himself 
for holding a similar professorship, and so, after several months 
of experience with Hare, he entered the College of Physicians and 
Surgeons in New York, and in 1845 became a full-fledged Doctor 
of Medicine. He never practised, and probably never intended 
to do so, for the study of chemistry was the main purpose of his 
life, and his medical studies were only a means to an end. 
Indeed, they stood him in good stead when, many years later, he 
undertook " to study the physiological effects of isomeric organic 
substances on animals. 

Up to this point the training of the future chemist had been 
only preliminary, a laying of foundations, so to speak. In his 
time advanced scientific education was ^not easily obtained in 
America, and ambitious students who were able to do so sought 
their higher opportunities in Germany. Accordingly, Doctor 
Gibbs, as we- must now call him, went abroad, and began by 
spending several months with Rammelsberg in Berlin. After this 
he studied for a year under Heinrich Rose, which was followed 
by a semester with Liebig at Giessen. He next went to Paris, 
where he attended lectures by Laurent, Dumas, and Regnault, 
and in 1848 he returned home, ready to begin the real labours of 
his life. Among his teachers the one who most impressed him 
was Rose, whom Gibbs greatly admired, and who doubtless gave 
his pupil his strong bias towards analytical and inorganic chemistry. 
From his other teachers, however, Gibbs acquired a breadth of 
view and an insight into difterent fields of research, which *nade 
him all the stronger as an investigator. He was a chemist in the 
largest sense of the term, and not a mere sub-specialist. 



114 CLARKE: WOLCOTT GIBBS MEMORIAL LECTURE. 

After returning to America, Gibbs first delivered a short course 
of lectures at a small college in Delaware. Then, in 1849, his 
native city claimed his services, and he was appointed professor 
of chemistry in the newly established Free Academy, now the 
College of the City of New York. He remained in this position 
for fourteen years, chiefly occupied in teaching elementary students, 
and at first doing, apparently, little else. He was not idle by 
any means, but he was finding himself, and his time was not 
wasted. In was in 1857 that his first really notable research was 
given to the world, namely, the joint memoir of Gibbs and Genth 
on th^e ammonio-cobalt bases. Of this I shall speak more at length 
later. In 1851 he became an associate editor of the American 
Journal of Science, and began the preparation of a series of 
abstracts which brought the results of foreign investigations to 
the attention of American readers. These abstracts amounted in 
all to about 500 pages, and, despite their brevity, were con- 
spicuously clear and comprehensive. In 1861 the first of his papers 
on the platinum metals appeared, and his reputation was at last 
firmly established. 

Notwithstanding his recognised ability, Dr. Gibbs, during this 
period, suffered one serious disappointment. The chair of 
chemistry in his alma mater, Columbia College, became vacant, 
and Gibbs, backed by the recommendations of nearly all the 
leading men of science in America, was a candidate for the position. 
He was, however, a Unitarian, and Columbia was then an institu- 
tion under sectarian control. Purely on religious grounds, his 
candidacy was rejected, and a man of far smaller attainments 
received the appointment. This was unfortunate for Columbia, 
but not altogether so for Gibbs. In 1863 he was called to a 
more desirable post, the Rumford Professorship in Harvard 
University. Nominally, this was a professorship of the " Applica- 
tion of Science to the Useful Arts," but its incumbent, in addition 
to lecturing on heat and light, was expected to take charge of 
the chemical laboratory in the Lawrence Scientific School, and 
this gave Gibbs a great opportunity for usefulness. Furthermore, 
the position was a delightful one on its social side, and he was 
thrown into close association with many congenial spirits. There 
were Louis Agassiz the zoologist, Asa Gray the botanist, Jeffries 
Wyman in comparative anatomy, Benjamin Pierce in mathematics, 
and J. P. Cooke in chemistry. Literature was represented by 
Longfellow, Lowell, Holmes, and other less famous writers; 
altogether an aggregation of distinguished men which could not 
be matched elsewhere in America, or equalled at few places in the 
world. Gibbs was among his peers, and in a place where his worth 
could be fully appreciated. 



CLARKE: WOLCOTT GIBBS MEMORIAL LECTURE. 115 

Dr. Gibbs remained in charge of the Scientific School laboratory 
for eight years, and during that time his researches were, for the 
great part, although not exclusively, devoted to analytical methods. 
The school was technically a department of Harvard University, 
and yet its work was carried on quite independently. The students 
were usually men of definite purposes, who knew what they wanted 
and went where it could be best obtained. They went to Agassiz 
for zoology, to Gray for botany, and to Gibbs for chemistry, because 
those men were the leaders in their respective subjects, and they 
worked, not in classes, but as individuals. The students in chemistry 
had little or nothing to do with the students in other branches, 
for the school was distinctly professional in its aims. Teachers 
from other institutions, seeking to enlarge their knowledge, were 
often among them. Gibbs was now training men who intended 
to become chemists, and some among them were qualified to assist 
in his investigations. Moreover, he was not overloaded by numbers, 
for he rarely had more than twenty students in attendance afr any 
one time. There was one assistant, to relieve him of routine work ; 
his lectures on light and heat cost him little effort, and he was 
therefore able to devote his energies to research more advantageously 
than ever before. 

It was my good fortune to have been a student under Gibbs 
during the greater part of four years, from 1865 until X869. I may 
therefore be permitted to speak of his teaching from my own 
experience, believing that in such matters the personal note is not 
without value. There was nothing unusual about the course of 
instruction so far as ordinary details went, for that necessarily 
followed certain well-established lines. Most of the students had 
already gained some elementary knowledge of chemistry ; their -work 
began with the usual practice in analytical methods and chemical 
manipulations, and as the men showed capacity they were admitted 
to the confidence of their master and aided him in his investiga- 
tions. This procedure may seem commonplace enough to-day, but 
in the years of which I speak it was new to American institutions, 
and was looked upon doubtfully .by some of the old-fashioned 
pedagogues. The students who chose to do so attended the excellent 
chemical lectures of Cooke in Harvard College, bnt that work was 
wholly optional. The only formal examination was the final 
examination for the bachelor's degree, and therefore there was no 
cramming for examinations. Gibbs apparently believed, although 
his belief was not stated in set terms, that a good teacher who 
kept in touch with his pupils should know perfectly well where 
they stood, and no examination could tell him anything more. 
In fact, examinations are often misleading, for the reason that 
even a fine scholar of nervous temperament may become confused 



116 CLARKE: WOLCOTT GIBBS MEMORIAL LECTURE. 

and helpless during the ordeal, and fail to answer the simplest 
questions. On the other hand, a poor student with a fair memory 
may cram for an examination, pass triumphantly, and amount to 
nothing afterwards. The real examinations under Gibbs were daily 
interviews, when he visited each student at his laboratory table 
and questioned him about his work. This, together with the 
reported analyses, gave the teacher a clear conception of the true 
standing of each man. The fewness of the pupils was a distinct 
advantage, for all worked together in one room, beginners and 
research students often side by side. The result was that they 
learned much from one another, and there were many discussions 
among them over the burning problems of the day. The men 
were taught to stand on their own feet, and to think for them- 
selves, laying thereby a foundation for professional success which 
was pretty substantial. The course of instruction had no definite 
term of years prescribed for it, and graduation came whenever the 
individual had done the required amount of work and submitted 
an acceptable original thesis. The final examination was usually 
oral, each man alone with his master, and was conducted in an 
easy conversational way which tended to establish the confidence 
of the candidate from the very beginning. In my own case I 
remember that the questions covered a fairly broad range of 
chemical topics, and at the end of it Dr. Gibbs drew me into a sort 
of discussion or argument with him over the then modern doctrine 
of valency. I now see that his purpose was not merely to ascertain 
what I had read on the subject, but what I really thought about 
it, if indeed I was entitled to think at all. Gibbs invariably 
treated his students, not as so many vessels into which knowledge 
was -to be poured, but as reasonable beings, with definite purposes, 
to whom his help must be given. That help was never denied to 
any man who showed himself at all worthy of it. The research 
work in which the advanced students shared, and for which they 
received public credit, served to teach them that chemistry was 
a living and growing subject, and to train them in the art 
of solving unsolved problems. They were taught to do, and 
encouraged to think, and if, on going forth into the world, they 
sometimes felt themselves qualified to revolutionise all science, their 
vanity did no harm and was soon remedied. An enlightened 
ignorance is only gained with advancing years, and the enthusiastic 
beginner cannot be expected to appreciate it. It is the last polish 
that the ripened scholar acquires. 

What now is the meaning of this long disquisition upon the 
methods of Gibbs's laboratory ? What was there at all unusual in 
his teaching ? Nothing, perhaps, from a modern point of view, 



CLARKE: WOLCOTT GIBBS MEMORIAL LECTURE. 117 

but much that was new to America in the middle 'sixties. It was 
Gibbs's peculiar merit that he, more than any other one man, 
introduced into the United States the German conception of 
research as a means of chemical instruction, a conception which 
is now taken as a matter of course without thought of its origin. 
Gibbs worked with small resources and no help from outside; he 
was a reformer who never preached reform; his students rarely 
suspected that they were doing anything out of the ordinary; but 
they had the utmost confidence in their master, and took it for 
granted that his methods were sound. There was nothing of the 
drill master about Gibbs, no trace of pedantry, no ostentation of 
profound learning; but the students never doubted his sincerity 
of purpose and interest in their work, nor questioned his ability 
as a teacher. As for Gibbs himself, it is doubtful whether he ever 
imagined that his teaching was at all remarkable. He did what 
was to him the natural and obvious thing to do, simply and without 
pretence, and the results justified his policy. The success of his 
students is perhaps the best monument to his memory. 

In 1871 the chemical instruction at Harvard University was 
reorganised, in spite of vigorous protests from Gibbs and many 
other leaders in science. The laboratory of the Scientific School 
was consolidated with that of the College, and Gibbs had no more 
students in chemistry. His work was limited to that of the 
Rumford professorship, a change which left him more time for 
personal research, but took from the students the inspiration of 
his teaching. The change may have been justifiable on grounds 
of economy, but it was otherwise a mistake, and it was so recognised 
among chemists generally. The economy was only financial; but 
an important asset of the University, the ability of a great teacher, 
was not turned to the best account. Fortunately for Gibbs, he 
had independent means, although he was not a rich man, and he 
was able to equip a small laboratory of his own and to employ a 
private assistant. In that laboratory he carried out those brilliant 
researches on the complex inorganic acids which marked the 
culmination of his career. The equipment was most modest, and 
in some respects it reminded one of the famous kitchen of Berzelius. 
Indeed, Gibbs's favourite piece of apparatus was that homely 
utensil, a cast-iron cooking stove; which served for several useful 
purposes. Precipitates could be dried in the oven, crucibles were 
buried in the coals, water was kept hot on top of it. As an 
instrument cf research it was neither elegant nor orthodox, but 
it did the work, and what more could be desired ? Gibbs adapted 
himself to circumstances, and cared little for the instrumental 
refinements which so many chemists seem to regard as necessary. 



118 CLARKE: WOLCOTT GIBBS MEMORIAL LECTURE. 

The real essentials were provided; mere conveniences, the luxuries 
of research, he could do without. 

For sixteen years after the closing of the Scientific School 
laboratory, Dr. Gibbs lectured to small classes of students on the 
spectroscope and on thermodynamics. In 1887 he retired, as 
Professor-Emeritus, and went to live in his house at Newport, 
where he had been accustomed to spend his summer vacations. 
His private laboratory was moved to Newport also, and there he 
continued his investigations until, enfeebled by old age, he was 
obliged to rest on his laurels. As a recreation, he cultivated a 
flower garden, and was proudest of his roses. In that way his 
love of the beautiful found its chief expression. On December 9, 
1908, he passed away, at the age of nearly eighty-seven. His wife, 
whose maiden name was Josephine Mauran, and whom he had 
married in 1853, died several years earlier, leaving no children. 

So much for biography. It now remains for us to consider the 
contributions of Gibbs to science, and to trace their relations, so 
far as may be practicable, to later work. An investigation never 
stands alone; each one touches other investigations at several 
points; and its worth may be greatest as the progenitor of later 
researches. The suggestiveness of a discovery, its influence in 
stimulating thought, is fully as important as its immediate outcome. 
It is a seed, whose value is finally determined by its fertility. 

Gibbs's first paper, a " Description of a New Form of Magneto- 
Electric Machine, and an Account of a Carbon Battery of Con- 
siderable Energy," published when he was a junior student at 
Columbia, has already been mentioned. In 1844 he attempted to 
discuss the theory of compound salt radicles, and in 1847, while a 
student abroad, he published a number of mineral analyses. In 
1850, Gibbs pointed out the interesting fact that compounds which 
change colour when heated do so in the direction of the red end 
of the spectrum. In 1852 he published the first of his memoirs 
upon analytical methods, in which he proposed the separation of 
manganese from zinc by means of lead peroxide; and in 1853 he 
prepared, and partly described, an arsenical derivative of valeric 
acid. In all of this work there was nothing of great importance, 
but its varied character is suggestive. It represents the efforts of an 
active mind, feeling its way under unfavourable conditions, and 
not quite sure of its true capacities. Mineral chemistry, organic 
chemistry, analytical chemistry, chemical theory, and physics, in 
turn attracted his attention during this formative period of his 
career. It was in the great research on the ammonio-cobalt bases 
that Gibbs finally found himself, and forced the world to recognise 
his ability. His apprenticeship was ended, and his work as a 
master had begun. 



CLARKE: WOLCOTT GIBBS MEMORIAL LECTURE. 119 

The first of the ammonio-cobalt compounds, the oxalate of 
luteocobalt, was prepared by Gmelin in '1822, the very year in 
which Gibbs was born. It was supposed, however, to be a salt of 
cobaltic acid, and several other chemists, who studied it later, 
shared in the same misapprehension. In 1847, Genth,- then at 
Marburg, discovered other salts of these bases, but it was not 
until 1851, after his emigration to America, that he published his 
description of them in a rather obscure journal. Genth was the 
first to recognise the true character of the new compounds, and 
he was followed by Claudet and Fremy, the three chemists working 
independently of one another and almost simultaneously. Up to 
this point Fremy's work was the most exhaustive, but it left much 
to be desired. 

Genth had identified the two bases since known as luteocobalt 
and roseocobalt. In 1852 Gibbs discovered the salts of xantho- 
cobalt, which contained, in addition to the ammonia, a nitro-group. 
It was therefore quite natural that the two chemists should join 
forces, and in 1856 their celebrated memoir appeared. In this 
memoir thirty-five salts of the four bases roseocobalt, purpureo- 
cobalt, luteocobalt, and xanthocobalt were described, with adequate 
analyses, and, in eleven cases, crystallographic measurements by 
J. D. Dana. The roseo- and purpureo-compounds were for the first 
time clearly discriminated, although they were supposed to be 
isomeric, a misconception which could hardly have been avoided at 
that time. There was also an elaborate theoretical discussion on 
the constitution of the bases, but that also was premature. The 
fundamental theories of structure were yet to be developed. 
Blomstrand, Jorgensen, and Werner, in later years, utilised the data 
of Gibbs and Genth, and Werner especially made the ammonio- 
cobalt compounds the base of his famous theory of the constitution 
of the metal-amines. Gibbs and Genth laid the foundations, on 
which later investigators have built an imposing structure. 

Gibbs was an experimentalist rather than a theorist, and yet he 
neither underrated nor avoided theory. In 1867 he published a 
paper on atomicities, or valences as they are now called, in which 
he developed the idea, then vaguely held by others, of residual 
affinities. He argued in favour of the quadrivalency of oxygen, 
and showed that on that supposition a molecule of water must be 
bivalent, and any chain of water molecules would be bivalent also. 
He then considered ammonia in the same way, with the two bonds 
of quinquevalent nitrogen unsatisfied. Ammonia, therefore, was 
weakly bivalent, and so, too, would be a chain of ammonia molecules. 
This conception he applied to the interpretation of the ammonio- 
cobalt bases, and so, too, did Blomstrand two years later. If we 
consider theories of this kind, not as finalities, but as attempts 



120 CLARKE: WOLCOTT GIBBS MEMORIAL LECTURE. 

to express known relations in symbolic forms, we must admit that 
Gibbs's conception was useful, and served well for the time being. 
That it has given way to other views more in harmony with modern 
discoveries, is not at all to the discredit of its author. In the later 
papers by Gibbs, published in 1875 and 1876, he made good use 
of his hypotheses, and described many more ammonio-cobalt com- 
pounds. Among them were the salts of an entirely new base, 
croceocobalt, in which two nitro-groups were present. In all, five 
distinct series were studied, their chlorides being represented, in 
modern notation, by the subjoined formulae : 

Luteocobalt chloride, Co(NH 3 ) 6 Cl 3 . 

Roseocobalt chloride, Co(NH 3 ) 5 'H 2 OCl 3 . 

Purpureocobalt chloride, Co(NH 3 ) 5 Cl'Cl 2 . 

Xanthocobalt chloride, Co(NH 3 ) 5 -NO 2 -Cl 2 . 

Croceocobalt chloride, Co(NH 3 ) 4 (NO 2 ) 2 -Cl. 

Gibbs's formulae were somewhat different from these, being 
doubled, and with the water of roseocobalt regarded not as con- 
stitutional, but as crystalline. The simpler, halved expressions were 
established by cryoscopic methods which did not exist when Gibbs 
conducted his investigations. 

The researches on the platinum metals, published by Gibbs in 
the years 1861 to 1864, relate mainly to analytical methods. 
Processes for the solution of iridosmine were carefully studied, and 
various new separations of the several metals from one another 
were devised. Incidentally, a number of new compounds were 
prepared, which, with a few exceptions, Gibbs never fully described. 
In 1871, however, he published a brief note on the remarkable 
complex nitrites formed by indium, and in 1881 he described a 
new base, osmyl-ditetramine, OsO 2 ,4NH 3 , together with several of 
its salts. These researches were never pushed very far, and were 
discontinued for lack of proper facilities. They were, nevertheless, 
distinct additions to our knowledge of the platinum group. 

I have already mentioned the work done by Gibbs and his 
students in the laboratory of the Lawrence Scientific School. This 
covered a wide range, partly in developing and perfecting old 
analytical methods, partly in devising new ones. There were 
improvements in gas analysis, especially in the determination of 
nitrogen, and a great variety of analytical separations. I will not 
attempt to give a catalogue of these investigations, but will limit 
myself to a few of the more noteworthy. A new volumetric method 
for analysing the salts of heavy metals was worked out, in which a 
metal such as copper or lead was precipitated as sulphide, the acid 
being afterwards determined by titration, The estimation of 



CLARKE: WOLCOTT GIBBS MEMORIAL LECTURE. 121 

manganese as pyrophosphate was another of these contributions 
to analysis. But the most important of all was the electrolytic 
determination of copper, now universally used, which was first 
published from Gibbs's laboratory. It is true that a German 
chemist, Luckow, claimed to have used the method much earlier, 
but so far as I can discover he failed to publish it. Gibbs, there- 
fore, is entitled to full credit for a process which was the progenitor 
of many others. The entire field of electrochemical analysis was 
thrown open by him, and it has been most profitably cultivated. 
Gibbs also, during this period of his activity, invented several 
instrumental devices of great convenience. The ring burner, and 
the use of porous septa when precipitates are to be heated in gases, 
are due to him. Furthermore, in co-operation with E. E. Taylor, 
he devised a glass and sand filter which was the forerunner of 
the porous cones invented by Munroe when the latter was a student 
in Gibbs's laboratory. That, in turn, preceded the well-known 
perforated crucibles of Gooch, who was one of Gibbs's assistants. 
The genealogy of these inventions is perfectly clear. 

We come now to the remarkable series of researches on the 
complex inorganic acids, which Gibbs began to publish in 1877, 
and continued well into the 'nineties. The ground had already 
been broken by others; silicotungstates, phosphotungstates, 
phosphomolybdates, etc., were fairly well known, but they were 
commonly regarded as exceptional compounds rather than as 
representatives of a very general class. In his first, preliminary, 
communication upon the subject, Gibbs indicated the vastness of the 
field to be explored, and showed that the formation of complex 
acids was characteristic of tungsten and molybdenum to an extra- 
ordinary degree. The phenomena were general, not special; and 
no limit could be assigned to the possible number of acids which 
these elements might form. 

In his systematic work, following his preliminary announcement, 
Gibbs first revised the sodium tungstates in order to determine 
their true composition. Then, after preparing a number of 
phosphotungstates and phosphomolybdates, he studied the corre- 
sponding compounds containing arsenic in place of phosphorus. 
He next obtained similar vanadium compounds, and also showed 
that the phosphoric oxide of the first known acids was replaceable 
by phosphorous and hypophosphorous groups. Later still, he 
replaced the normal phosphates by pyro- and meta phosphates, and 
also prepared complex salts containing arsenious, antimonious, and 
antimonic radicles. Stanno-phosphotungstates and molybdates, 
platinotungstates, and complex acids containing mixed groups were 
discovered, together with analogous compounds of selenium, 



122 CLARKE: WOLCOTT GIBBS MEMORIAL LECTURE. 

tellurium, cerium, and uranium. One salt described, a phospho- 
vanadio-vanadico-tungstate of barium, had the formula 

60WO 3 ,3P 2 O 5 ,V 2 O 3 ,VO 2 ,18BaO,150H 2 O, 

with a molecular weight of 20066. Compared with this substance, 
the supposed complexity of most organic compounds becomes 
simplicity itself, and their interpretation .seems relatively like child's 
play. In all, Gibbs described complex salts belonging to more than 
fifty distinct series, and did his work in a small private laboratory 
with only a single assistant. With greater resources at his 
command, what might he not have accomplished? 

In 1898, in his address as retiring president of the American 
Association for the Advancement of Science, Gibbs summed up 
his views as to the constitution of the complex acids. His pre- 
sentation of the subject, however, can hardly be regarded as final. 
The problems involved are too complicated to be easily solved, and 
much future investigation is needed in order to determine the true 
character of these extraordinary substances. Gibbs was a pioneer, 
breaking pathways into a tangled wilderness; but the ways are 
now open, and he who wills may follow. Possibly some of the 
compounds so far obtained were double salts; others may have 
been isomorphous mixtures; and in some instances phenomena of 
solid solution perhaps obscured the truth. By physical methods, 
cryoscopic or ebullioscopic, the molecular weights of the salts must 
be determined; their ionisation needs to be studied, and in such 
ways cheir true nature can be ascertained. These methods of 
research have been mainly developed since the work of Gibbs was 
done; he, therefore, cannot be criticised for not employing them. 
Since his time chemists have come to recognise many compounds 
as salts containing complex ions, such as, for example, the oxalates, 
tartrates, etc., of iron, aluminium, chromium, and antimony with 
other bases of lower valency. Even many of the silicates are 
easiest to interpret as salts of alumino-silicic acids, although the 
physical proof of their nature is difficult to obtain. The con- 
stitution of the complex acids is one of the great outstanding 
problems of inorganic chemistry. 

Although he was distinctively an inorganic chemist, Gibbs djd 
not entirely neglect organic chemistry. In 1868 he discussed the 
constitution of uric acid and its derivatives, and in 1869 he 
described some products formed by the action of alkali nitrites 
on them. He also produced several memoirs on optical subjects, 
such as one on a normal map of the solar spectrum, and another 
on the wave-lengths of the elementary spectral lines. Again, he 
devoted some time to the study of interference phenomena, and 
discovered a constant, which he called the interferential constant. 



CLARKE: WOLCOTT GIBBS MEMORIAL LECTURE. 123 

that was independent of temperature. One of Gibbs's latest papers, 
published when he was seventy-one years old, related to that 
extremely difficult subject, the separation of the rare earths, a 
subject in which he had always taken a deep interest. In this 
paper he developed a new method for determining the atomic 
weights of the rare-earth metals, which was based upon analyses of 
their oxalates. The oxalic acid was determined by titration with 
permanganate solutions, and the oxides by ignition of the salts. 
From the ratios between the oxalic acid and the oxides, the 
molecular weights of the latter could be computed without reference 
to the amount of moisture in the initial substances. This method 
has since been employed by others, and especially by Brauner, in 
his work on the atomic weights of cerium and lanthanum. It is 
worth noting here that Gibbs had previously taken some part in 
atomic weight determinations. Those of Wing on cerium, and of 
Lee on cobalt and nickel, were made in Gibbs's laboratory and 
under his guidance. Furthermore, Gibbs was one of the earliest 
American chemists, if not the fiifst, to accept the modern or 
Cannizzaro system of atomic weights, and to use it in his teaching. 
His mind was never closed to new ideas. It welcomed light from 
all sources. 

Gibbs wrote no books and delivered no popular lectures. He 
was therefore little known to the public at lare, but within scientific 
circles he received high honours. He was one of the founders of 
the National Academy of Sciences, and at one time its President, 
and he also presided over the American Association for the 
Advancement of Science. Honorary membership in the German, 
English, and American chemical societies, and in the Prussian 
Academy, was conferred upon him, and he received honorary 
degrees from several universities. His life was that of a devoted 
scholar, caring most for research, and indifferent to popularity. 
Sensationalism and self-advertising were most obnoxious to, him ; 
indeed, in these respects, no man could be more fastidious. The 
approval of his fellows he fully appreciated, but only when it was 
spontaneous and deserved. It must not be inferred from these 
remarks that Gibbs was deficient in public spirit, for that would be 
most untrue. During the Civil War, from 1861 to 1865, he was 
strongly patriotic, and did much to help the Union side. The 
Union League Club of New York, organised to bring together the 
more patriotic citizens of that city, was founded at a meeting 
in his house, and is to-day a strong social institution. Gibbs was 
also active in the Sanitary Commission, an organisation modelled 
upon the work of Florence Nightingale in the Crimea, and the 
forerunner of the Red Cross Society of to-day. 

Wolcott Gibbs was a man of striking personality, tall, erect, and 

8 E 



124 CLARKE: WOLCOTT GIBBS MEMORIAL LECTURE. 

dignified. As with most men of positive character, he had strong 
likes and dislikes, but the latter never assumed unworthy form. 
To his friends he was warmly devoted, and always ready to help 
them in their work with manifold suggestions. His breadth of 
mind is indicated by the range of his researches, and his liberality 
by the way in which he encouraged his students to develop his 
ideas. More than one important investigation was based upon 
hints received from him, and was carried out under his supervision, 
to appear later under another name. Gibbs never absorbed the 
credit due even in part to others, nor failed to recognise the merits 
of his assistants in the fullest way. Had he ISBen more selfish, 
his list of publications would have lengthened; but his sense of 
justice was most keen, and therefore he held the esteem and 
confidence of his co-workers. No man, not even among his 
opponents, for such there were, could ever accuse him of unfairness. 
He deserved all honour, and his name ^ill live long in the history 
of that science to which his life was given. 





[To face p. 125 



T1LDEN: MENDELEEFF MEMORIAL LECTURE. 125 

MENDELEEFF MEMORIAL LECTURE. 
DELIVERED ON OCTOBER 21sT, 1909. 

By W. A. TILDEN, D.Sc., LL.D., F.R.S., Past-President of the 
Chemical Society. 

To many of the present generation of English chemists, the com- 
manding, patriarchal figure of Mendeleeff was quite familiar. 
Though his several visits to London were often connected with 
official business of the Russian Government Department of Weights 
and Measures, of which he was the chief official during the later 
years of his life, he came several times with more purely scientific 
objects. In 1889 the occasion of his presence in London was the 
Faraday Lecture which he had been invited to give to the Chemical 
Society, but which, owing to a sudden and urgent recall to his 
home, he was unable to deliver in person. His last appearance in 
this cpuntry was in November, 1905, when the Copley Medal was 
awarded to him by the Royal Society. 

The Chemical Society can see his face no more, and all that 
it can now do is to inscribe high on its roll of honour the name 
which, more than any other, will be for ever associated with the 
development of the great generalisation known as the periodic 
system of the elements. 

Dmitri Ivanovitsch Mendeleeff * was the fourteenth and youngest 
child of his parents, Ivan Pavlovitsch and Maria Dmitrievna, nee 
Kornileff. His father, a former student of the Chief Pedagogic 
Institute of St. Petersburg, obtained the appointment of Director 
of the Gymnasium at Tobolsk, in Siberia, where he met Maria 
Dmitrievna, who became his wife. After a few years at Tobolsk, 
he was transferred to school directorships in Russia, first at 
Tambov, and afterwards at Saratov. But in order to satisfy the 
ardent wish of his wife, he took advantage of an opportunity of 
exchange, by which he became once more Director of the College 
at Tobolsk, and the family returned' to Siberia. Here on January 
27th, 1834 (O.S.) was born Dmitri Ivanovitsch, the youngest son. 

* For many of the details of Mendeleeff s career and of his home life the writer 
is indebted to the family chronicle compiled, soon after his death, by his niece, 
N. J. Gubkina (n6e Kapustina), and published in St. Petersburg, also co pamphlets 
by A. Archangelsky and P. J. Robinowitsch. He also desires to express his thanks 
to Mr. D. V. Jequier, of St. Petersburg, as well as to several Russian friends, for 
valuable assistance in translation. 



126 TILDEN: MENDELEFF MEMORIAL LECTURE. 

Soon after his birth the father became gradually blind from 
cataract in both eyes, and was obliged to resign, the whole family, 
including eight children, having to subsist on a small pension of 
1000 roubles (about 100 per annum). The mother, Maria 
Dmitrievna, belonged to the old Russian family, Kornileff, settled 
at Tobolsk. They were the first to establish in Siberia the manu- 
facture of paper and glass. In 1787 the grandfather of Dmitri 
opened at Tobolsk the first printing press, and from 1789 produced 
the first newspaper in Siberia, the Irtysch. The glass works were 
situated in the village of Aremziansk, a short distance from 
Tobolsk. 

According to the family tradition, one of the Kornileffs in a 
previous generation had married a Khirgis Tartar beauty, whom 
he loved so passionately that when she died he also died of grief. 
The pure Russian blood thus received a strain of the Mongolian 
race, and some of their descendants preserved traces of the 
Oriental type. This, however, was not very noticeable in the 
features of the chemist. 

From her childhood, Maria Dmitrievna was distinguished by 
her intelligent wish for instruction,. and having no other resource 
when her brother Basile went to school she repeated by herself 
all his lessons, and thus, unaided, obtained some part of the 
knowledge so eagerly desired. There can be no doubt she was a 
woman possessed of remarkable vigour of mind, who exercised great 
influence over her children. Her activity and capacity are further 
illustrated by the fact that when her husband became blind she 
revived the business of the glass works, and carried it on till after 
his death from consumption in 1847. 

Tobolsk was at that time a place of banishment for many 
political exiles, the so-called Decembrists, one of whom, Bassargin, 
married Olga, an elder sister of Dmitri. To these Decembrists the 
boy owed his first interest in natural science. His mother had 
always cherished the hope that at least one of her children would 
devote himself to science, and accordingly, after her husband's 
death and the destruction of the glr.ss works by fire, and spite of 
failing health and scanty means, she undertook the long and 
tedious journey from Tobolsk to Moscow, accompanied by her 
remaining children, Elizabeth and Dmitri Ivanovitsch, with the 
object of entering the latter, then nearly fifteen years of age, at 
the University. Disappointed in this object, owing to official 
difficulties, she removed in the spring of 1850 to St. Petersburg, 
where ultimately, with the assistance of the Director, Pletnoff, of 
the Central Pedagogic Institute, a friend of her late husband, 
she succeeded in securing for her son admission to the Physico- 



TILDEN: MENDELEEFF MEMORIAL LECTURE. 127 

^Mathematical Faculty of the Institute, together with much-needed 
pecuniary assistance from the Government. 

The debt which Dmitri Ivanovitsch owed to hia mother he 
.acknowledged later in the introduction to his work on " Solutions," 
which he dedicated to her memory in the following interesting 
lines : 

" This investigation is dedicated to the memory of a mother 
by her youngest offspring. Conducting a factory, she could 
educate him only by her own work. She instructed by example, 
corrected with love, and in order to devote him to science she 
left Siberia with him, spending thus her last resources and 
.strength. When dying, she said, ' Refrain from illusions, insist 
on work, and not on words. Patiently search divine and scientific 
truth.' She understood how often dialectical methods deceive, 
how much there is still to be learned, and how, with the aid of 
science without violence, with love but firmness, all superstition, 
untruth, and error are removed, bringing in their stead the safety 
of discovered truth, freedom for further development, general 
welfare, and inward happiness. Dmitri Mendeleeff regards as sacred 
a mother's dying words. October, 1887." 

In the Pedagogic Institute Dmitri Ivanovitsch was thus able to 
devote himself to the mathematical and physical sciences under 
the guidance of Professors Leng and Kupfer in physics, Woskresen- 
sky in chemistry, and Ostragradsky in mathematics. Unfortunately, 
-at the end of his course, his health failed", and about this time 
his mother died. Having been ordered to the South, he fortunately 
obtained an appointment as chief science master at Simferopol, in 
the Crimea. The southern climate soon alleviated the serious 
symptoms of lung disorder, and removal being necessary in con- 
sequence of the Crimean War, he was able soon afterwards to 
undertake a post as teacher of mathematics and physics at the 
Gymnasium at Odessa. In 1856 he returned to St. Petersburg, 
and at the early age of twenty-two he was .appointed privat docent 
in the University, having secured his certificate as master in 
chemistry. 

At this time he. appears to have passed rapidly from one subject 
to another, but he soon found matter for serious and protracted 
study in the physical properties of liquids, especially in their 
expansion by heat. And when, in 1859, by permission of the 
Minister of Public Instruction Mendeleeff proceeded to study under 
Regnault in Paris and afterwards in Heidelberg, he devoted him- 
self to this work, communicating his results to Liebig's Annalen 
and the French Academy of Sciences. Returning two years later 
to St. Petersburg, he secured his Doctorate, and was soon after- 



128 TILDEN : MENDELEEFF MEMORIAL LECTURE. 

wards appointed Professor of Chemistry in the Technological 
Institute. In 1866 he became Professor of General Chemistry in 
the University, Butlerow at the same time occupying the Chair 
of Organic Chemistry. 

As a teacher, Mendeleeff seems to have possessed a special talent 
for rousing a desire for knowledge, and his lecture room was often 
filled with students from all faculties of the University. Many 
of his former students remember gratefully the influence he 
exercised over them.* One of these writes : " I was a student in 
the Technological Institute from 1867 to 1869. Mendeleeff was 
our professor, and in 1868 taught organic chemistry. The previous 
course by the professor of inorganic chemistry consisted of a 
collection of recipes, very hard to remember, but, thanks to 
Mendeleeff, I began to perceive that chemistry was really a science. 
The most remarkable thing at his lectures was that the mind of 
his audience worked with his, foreseeing the conclusions he might- 
arrive at, and feeling happy when he did reach these conclusions. 
More than once he said, ' I do not wish to cram you with facts, 
but I want you to be able to read chemical treatises and other 
literature, to be able to. analyse them, and, in fact, to understand 
chemistry. And you should remember that hypotheses are not 
theories. By a theory I mean a conclusion drawn from the 
accumulated facts we now possess which enables us to foresee new 
facts which we do not yet know.' He was considered among the 
students a most liberal man, and they thought of him as a comrade. 
More than once during a disturbance between the students and 
the administration Mendeleeff supported the students, and under 
his influence many matters were put right." (L. G.) Another 
former student in the University writes as follows: " I am sorry 
to say I did not know Mendeleeff personally. I only had the good 
fortune to follow, in the years 1867-69, his lectures on both. 
Organic and Inorganic Chemistry. The former was an abridged: 
course, which he had the admirable idea to deliver for us students 
of the mathematical branch of the physico-mathematical faculty. 
He reduced this course of one lecture a week during one year to 
a general review of organic compounds and the general laws of 
their structure. You can imagine what it must have been in 
the hands of Mendeleeff, thirty-three or thirty-four years old at 
that time, in the full enjoyment of his mental powers, and just 
then plunged into the study of his great generalisations. For me- 
it was a revelation, being occupied with the great questions con- 
nected with the development of the new system of atomic weights, 

* For the following reminiscences, the writer is indebted to Mr. L. Goldenberg. 
and Prince P. Kropotkin respectively. 



T1LDEN: MENDELEEFF MEMORIAL LECTURE. 129 

the mechanical theory of heat, etc. Grove's, Thomson's, Joule's, 
Seguin's works were then just out, and in these years a sudden 
blossoming of the natura) sciences in all directions seemed to bring 
us near to the solution of the great problems of the nature of 
matter and of gravitation. Then I followed Mendeleeff's lectures 
on Inorganic Chemistry. The ' Principles of Chemistry ' was not 
yet out, but he was evidently writing it at that time. You know 
how much is said in the footnotes to his ' Principles ' ; well, imagine 
-each of these notes developed into a beautiful improvisation, with 
all the freshness of thought of a man who, while he speaks, 
evolves all the arguments for and against, there on the spot. The 
hall was always crowded with something like two hundred students, 
many of whom, I am afraid, could not follow Mendeleeff, but for 
the few of us who could it was a stimulant to the intellect and a 
lesson in scientific thinking which must have left deep traces in 
their development, as it did in mine." (P. K.) 

Onp of Mendeleeff's most remarkable personal .features was his 
flowing abundance of hair. The story goes that, before he was 
presented to the late Emperor, Alexander III., his Majesty was 
curious to know whether the professor would have his hair cut. 
This, however, was not done, and he appeared at Court without 
passing under the hands of the barber. His habit was to cut 
his hair once a year in spring, before the warm weather set in. 
His eyes, though rather deep set, were bright blue, and to the 
nd of his life retained their penetrating glance. Tall in stature, 
though with slightly stooping shoulders, his hands noticeable for 
their fine form and expressive gestures, the whole figure proclaimed 
the grand Russian of the province of Tver. 

At home, Mendeleeff always wore an easy garment of his own 
design, something like a Norfolk jacket without a belt, of dark 
grey cloth. He rarely wore uniform or evening coat, and attached 
no importance to ribbons and decorations, of whibh he had many. 

As to his views on social and political questions, many people 
thought him a rigid monarchist, but he said of himself that he 
was an evolutionist of peaceable type, desiring a new religion, of 
which the characteristic should be subordination of the individual 
to the general good. He always viewed with much sympathy what 
is called the feminine question. At the Office of Weights and 
Measures, he employed several ladies, and about 1870 he gave 
lectures on chemistry to classes of ladies. Nevertheless he con- 
sidered women inferior to men both in business and in intellectual 
pursuits, and he thought the chief promoters cf the feminine 
movement aimed, not so much at equality of political position, as 
at opportunities for work and to escape inactivity. But he thought 



130 TILDEX: MENDELEEFF MEMORIAL LECTURE. 

the feminine temperament specially suited to all branches of art 
in the broadest sense of the word, including education. 

Mendeleeff held decided views on the subject of education, which 
he set forth in several publications, especially " Remarks on Public 
Instruction in Russia" (1901). Here he says, "The fundamental 
direction of Russian education should be living and real, not based 
on dead languages, grammatical rules, and dialectical discussions, 
which, without experimental control, bring self-deceit, illusion, 
presumption, and selfishness." Believing in the soothing effect of 
a vital realism in schools, he considered that universal peace and 
the brotherhood of nations could only be brought about by the 
operation of this principle. Speaking of the reforms desirable,, 
he says that " for such reforms are required many strong realists; 
classicists are only fit to be landowners, capitalists, civil servants, 
men of letters critics, describing and discussing, but helping only 
indirectly the cause of popular needs. We could live at the present 
day without a Plato, but a double number of Newtons is required 
to discover the secrets of nature, and to bring life into harmony 
with 'the laws of nature." Mendeleeff was evidently a philosopher 
of the same type as our own Francis Bacon. 

" I am not afraid," he says later, " of the admission of foreign, 
even of socialistic, ideas into Russia, because I have faith in the 
Russian people, who have already got rid of the Tartar domination 
and the feudal system." 

Mendeleeff always dined at six o'clock, and liked to entertain 
his friends and relations, but in his own diet he was extremely 
moderate. After dinner he enjoyed reading light literature, 
especially books of adventure, such as those of Fenimore Cooper or 
Jules Verne. But his literary tastes were peculiar. Though 
interested in serious literature and appreciating Shakespeare, 
Schiller, Goethe, Viator Hugo, and Byron as well as the Russian 
classics, beginning with Zhoucovsky and Pouschkin, his favourites 
among Russian poets were Maicoff and Tuttcheff, and among the 
rest Byron. Of the last-named he preferred to all his other works 
the gloomy poem called " Darkness," and among the rest the 
" Silentium " of Tuttcheff. 

He rarely went to the theatre, and did not approve of frequent 
visits to the theatre by his children, as he considered such distrac- 
tions tend to destroy concentration and fill the mind with " trifles 
and foolishness." On the other hand, he was very fond of pictures, 
and he visited all the exhibitions. That he was interested in 
questions relating to art, and had given much thought to aesthetic 
problems, is indicated by a letter * which he addressed in Novem- 
be*-, 1880, to the well-known Russian daily paper of that time, 
* Considerably condensed in the following abstract. 



TILDEN: MENDELEEFF MEMORIAL LECTURE. 131 

Goloss (The Voice), on the subject of a picture by Kouindji, 
"Night in the Ukraine." Writing of the influence of landscape 
on different minds, he says, " At first it seemed to me a matter of 
personal taste, of individual sensitiveness of different persons to 
the beauty of nature." But, rejecting this simple view, he was 
led to a conception which he regarded as really satisfactory, and 
which he wished to share with others. He says, " Landscape was 
depicted in antiquity^ but was not in favour in those times. Even 
the great masters of the sixteenth century made use of it merely 
as a frame to their pictures. It was the human form which prin- 
cipally inspired artists of that epoch; even the gods and the 
Almighty Himself appeared to their minds in human shape. In 
this alone they found the infinite, the inspiring, the divine. And 
this was because they worshipped human mind and human spirit. 
This found expression in science in an exceptional development of 
mathematics, logic, metaphysics, and politics. Later, however, 
men lost faith in tfre absolute and original power of human reason, 
and they discovered that the study of external nature assists even 
in the correct appreciation of the nature of the human inner self. 
Thus nature became an object of study; a natural science arose 
unknown either to antiquity or to the period of the Renaissance. 
Observation and experience, inductive reasoning, submission to 
the inevitable, soon gave rise to a new and more powerful, more 
productive method of seeking truth. It thus became evident that 
human nature, including its consciousness and reason, is merely a 
part of the whole, which is easier to comprehend as such from 
the study of external nature than of the inner man. External 
nature thus ceased to be merely subservient to man, and became 
his equal, his friend. Dead and senseless as it had been, it now 
became alive. Everywhere it presented motion, stores of energy, 
natural reason, simplicity, and plan. Inductive and experimental 
science became a crown of knowledge, royal metaphysics and 
mathematics had now to be content with modest questioning of 
nature. Landscape painting was born simultaneously with this 
change, or perhaps a little earlier. Thus it will probably come to 
pass that our age will hereafter be known as the epoch of natural 
science in philosophy, and of landscape in art. Both derive their 
materials from sources external to man. . . . Man has, however, not 
been lost sight of as an object of study and of artistic creation, but 
he now appears, not as a potentate or as a microcosm, but merely as 
part of a complex whole." 

In 1863, when twenty-nine years of age, Mendeleeff married his 
first wife, nee Lestshoff, by whom he had one son, Vladimir,* and 
a daughter, Olga; but the marriage proved unhappy, and after 
* Died in 1899, aged 34. 2 1 



132 T1LDEN : MENDELEEFF MEMORIAL LECTURE. 

living apart for some time there was a divorce. In 1877 he fell 
in love with a young lady artist, Anna Ivanovna Popova, of 
Cossack origin, and in 1881 they were married. This lady exercised 
considerable influence over his views about art, and the wall* of 
his study were furnished with many products of her ptncil, notably 
portraits of Lavoisier, Descartes, Newton, Galileo, Copernicus, 
Graham, Mitscherlich, Rose, Chevreul, Faraday, Berthelot, and 
Dumas, and others of relatives. After his second marriage, 
Mendeleeff lived first at the University, and afterwards in the 
apartments built for the Director at the Bureau of Weights and 
Measures, and here his younger children were born, Lioubov 
(Aimee), Ivan (Jean), and the twins, Maria and Vassili (Basile). 

In 1890, in consequence of a difference with the administration, 
Mendeleeff retired from the Professorship t in the University. 
During the disturbances among the students in that year, he 
succeeded in. pacifying them by promising to present their petition 
to the Minister of Education. Instead of thanks for this service, 
however, the Professor received a sharp reprimand from the 
authorities for not minding his own business. The consequence 
was that Mendeleeff resigned. Independently of the petition, 
however, there were probably deeper reasons for his being out of 
favour with the Ministry, connected with his irreconcilable enmity 
to the classical system of education already referred to (p. 130). 
Of this he had made no secret, and it had already brought him 
into Conflict with the authorities-. In 1893, however, he was 
appointed by M. Witte to the office of Director of the Bureau of 
Weights and Measures, which he retained till his death. 

In the earlier part of his life, Mendeleeff was interested in 
'carrying on a series of agricultural experiments on his Tver estate, 
Boblovo. The peasants, much struck by his success and the 
abundance of his crops, inquired of him whether this was due to 
his luck or to his " talent." With a smile and the patois which 
he always affected in speaking to the country people, he informed 
them that he certainly had " talent," and, as he said afterwards 
at home, there is no merit in having luck. 

Once during the solar eclipse in 1887 he ascended alone in a 
balloon wih the object of making scientific observations. His 
assistant, Kovanko, who sat with him in the basket, alighted at 
the last moment, probably ordered to do so by his chief because 
the balloon would not rise. When the balloon shot up quickly 
and disappeared in the clouds, his family was naturally very much 
alarmed. Fortunately the hero of the adventure was able to 
descend safely, and a few hours later returned to his family from 
Moscow. The peasant women thereafter used to tell that Dmitri 



TILDEN : xMENDELEEFF MEMORIAL LECTURE. 133 

Ivanovitsch flew on a bubble and pierced the sky, and for this the 
authorities made him a chemist ! 

Mendeleeff was very democratic in his habits, and when travelling 
from the Capital to his estate, six or seven hours by rail, he always 
made use of the third class, and on the way talked freely to his 
fellow-passengers on all sorts of subjects, so that at the end of 
the journey he was surrounded by all sorts of people. At the 
railway station, about twelve miles from Boblovo, he was always 
met by the same driver, Zassorin, who with his troika of greys* 
transported the whole family at full gallop, according to Russian 
custom. 

Such, then, are the chief features of a great personality. If it 
be admitted that stories are told of his occasional irritability of 
temper, we can well place on the other side of the account the 
cordial relations always subsisting between the Professor and his 
assistants, the confidence and respect between the Master and his 
servants, the deep affection between the Father and his children, 
which are known to have persisted throughout his life, and whiqh 
could be illustrated by many anecdotes. These stories merely serve 
" to give the world assurance of a man." 

For us who live on the other side of Europe, separated as we 
are by race, by language, by national and social customs, and by 
form of government, it is not easy to understand completely the 
texture of such a mind, tjhe quality of such genius, and the 
conditions, social or political, which may have served to encourage 
or to repress its activity. The Russian language may be eloquent, 
expressive, versatile, and harmonious, or it may possess any other 
good quality that may be claimed for it by those to whom it is 
a mother tongue, but the fact remains that it is a barrier to free 
intercourse between the Russian people and the world outside the 
Russian Empire. This alone creates a condition which must 
influence the development of thought, and must give to Russian 
science and philosophy a colour of its own. Mendeleeff was, like 
many educated Russians, a man of very liberal views on such 
subjects as education, the position of .women, on art and science, 
and probably on national government. We can hardly guess what 
would be the influence on such a nature of a rigid administrative 
regime which forbids even the discussion of such questions. We 
in England are almost unable to imagine such a state of things 
as would be represented by the closing of, say, University College 
for a year or more, because the question whether the House of 
Lords ought to be abolished had been debated in the Students' 
Union. Imagine the Professor of Chemistry, along with his 
colleagues, for such a reason deprived of the use of his laboratory 



134 TiLDEN: MENDELEFF MEMORIAL LECTURE. 

by the police, and only allowed to, resume his studies when someone- 
down at Scotland Yard thought proper. Such being the experience- 
of most of the Russian Universities and Technical High Schools, 
it is, not surprising that the output of Russian science, notwith- 
standing the acknowledged genius of the Russian people, appears 
sometimes comparatively small. The amount of work done by 
Mendeleeff, both experimental and theoretical, was prodigious, and 
all the more remarkable considering the cloudy atmosphere under 
'which so much of it was accomplished.* 

In 1882 the Royal So.ciety conferred on Mendeleeff, jointly with 
Lothar Meyer, the Davy Medal. In 1883 the Chemical Society 
elected him an Honorary Member, and in 1889 it conferred upon 
him the highest distinction in its power to award, namely, the 
Faraday Lectureship, with which is associated the Faraday Medal. 
In 1890 he was elected a Foreign Member of the Royal Society, 
and in 1905 he received the Copley Medal. So far as England is 
concerned, his services to science received full acknowledgment. It 
is all the more remarkable, therefore, that he never became a 
member of the Imperial Academy of Sciences of St. Petersburg. 

Towards the end of 1906 Mendeleeff 's health began to fail. 
Nevertheless he was able to attend the Minister on the occasion 
of an official visit in January to the office of 'Weights and 
Measures, but he caught cold and, enfeebled as he had been by 
influenza in the preceding autumn ^inflammation of the lungs set 
in. Retaining consciousness almost to the last, he requested even 
on the day of his death to be read to from the " Journey to the 
North Pole," by his favourite author, Jules Verne. He died in 
the early morning of the 20th January (O.S.), 1907, within a few 
days of his seventy-third birthday. He was buried in the Wolkowo 
Cemetery beside the graves of his mother and son. 

Turning now to a survey of Mendeleeff's "work as a man of 
science, it will be sufficient if we pass lightly over his first essays. 
Like so many other chemists, he began by handling simple questions 
of fact, his first paper, dated 1854, when he was twenty years of 
age, being on the composition of certain specimens of orthite. It 
was not till 1859 that he settled down to serious examination of 
the physical properties of liquids, which led him to a long series 
of experiments on the thermal dilatation of liquids, of which the 

"* Professor Walcien, at the end of a biographical notice recently published in the 
Serichtc d. Deut. Chem. Gcs., April, 1909, gives a list of 262 printed publications by 
Mendeleeff. These include, not only memoirs on physical and chemical subjects, 
but books, pamphlets, reports; and newspaper articles relating to exhibitions, to 
the industries of Russia, to weights and measures, to education, to art, and even to 
spiritualism. 



TILDEN : MEXDELE.EFF MEMORIAL LECTURE. 135 

chief ultimate outcome was the establishment of a simple expres- 
sion for the expansion of. liquids between and the boiling point 
(Trans., 1883, 45, 126). This formula is liable to the same kind 
of modification which has been found necessary in the case of gases. 
It is, of course, applicable only to an ideal liquid from which all 
known liquids differ by reason of differences of chemical constitu- 
tion and consequent differences of density, viscosity, and other 
properties. Thorpe and Riicker, by applying van der Waals r 
theory of the general relation between the pressure, volume, and 
temperature of bodies to Mendeleeff' s expression for the thermal 
expansion, developed a simple method of calculating the critical 
temperature of liquids from observations of their expansion (Trans., 
1884, 45, 135). 

Mendeleeff devoted a large amount of time and of experimental 
skill to the estimation of the densities of various solutions, 
especially mixtures of alcohol and water and of sulphuric acid and 
water, and of aqueous solutions of a large- number of salts. In 
1889 he embodied the whole in the monograph already referred to. 
In a paper communicated to the Transactions in 1887 (51, 779), 
he stated his. views in the following words: "Solutions may be 
regarded as strictly definite atomic chemical combinations at tem- 
peratures higher than their dissociation temperatures. Definite 
chemical substances may be either formed or decomposed at tem- 
peratures which are higher than those at which dissociation 
commences^ the same phenomenon occurs in solutions; at ordinary 
temperatures they can be either formed or decomposed." This 
view was retained by Mendeleeff, and appears in a footnote (p. 64) 
in the 7th Russian Edition (3rd English Edition) of the Principles, 
1902, where the following passage occurs: "The conception of 
solutions as dissociated definite liquid chemical compounds is based 
OQ the following considerations : (1) That there exist certain 
undoubtedly definite crystallised chemical compounds (such as 
H. 2 SO 4 ,H 2 O, or NaCl,2H 2 O, or CaCl 2 ,6H 2 O, etc.), which melt on a 
certain rise of temperature and then form true solutions; (2) that 
metallic alloys in a molten condition, are real solutions, but on 
cooling they often give entirely distinct and definite crystallised 
compounds; (3) that between the solvent and the substance dis- 
solved there are formed in a number of cases many undoubtedly 
definite compounds, such as compounds with water of crystallisa- 
tion; (4) that the physical properties of solutions, and especially 
their specific gravities (a property which can be very accurately 
determined), vary with a change in composition, and in such a 
manner as would be required by the formation of one or more 
definite but dissociating compounds. . . . The increase in specific 



136 T1LDEN: MENDELEEFF MEMORIAL LECTURE. 

gravity (ds) varies in all well-known solutions with the proportion 
of substance dissolved (dp), and this dependence can be expressed 
by a formula ds/dp = A + 'Bp between the limits of definite com- 
pounds, whose existence in Solutions must be admitted." Applying 
this method, he concludes that mixtures of alcohol and water may 
contain several definite compounds, such as C 2 H 6 O + 3H 2 O. These 
views, however, did not prevent his recognising van't Hoff's gas 
theory as applicable to dilute solutions. 

In conjunction with some of his students, Mendeleeff also studied 
minutely the' question of the elasticity of gases, and published 
several papers on the subject (see Royal Soc. Catalogue), extending 
over a period of some ten years from 1872. From the earlier 
researches of Regnault and others, it was known that the law of 
Boyle and Marriotte is not strictly applicable either to all gases 
or at all pressures. Mendeleeff and his assistants devoted special 
attention to the departures from the theoretical requirements of 
the law exhibited by* gases under very greatly reduced pressures. 
He found that for hydrogen the value of pv diminishes with the 
pressure down to 20 mm., while for air, carbon dioxide, and some 
others, pv increases sliglitly to a maximum.. 

Another subject to which Mendeleeff gave a good deal of attention 
was the nature and origin of petroleum. Having already reported 
in 1866 on the naphtha springs in the Caucasus, in the summer of 
1876 he crossed the Atlantic and surveyed the oil fields of Penn- 
sylvania. In the course of these investigations, he was led to 
form a new theory of the mode of production of these natural 
deposits. The assumption that the oil is a product of the decom- 
position of organic remains he rejects on a variety of grounds, 
which are set forth in a communication to the Russian Chemical 
Society (Abstract; see Ber., 1877, 10, 229). Mendeleeff assumes, 
as others have done, that the interior of the earth consists largely 
of carbides of metals, especially iron, and that hydrocarbons resiilt 
from the penetration of water into contact with these compoimds, 
metallic oxide being formed simultaneously. The hydrocarbons 
are supposed to be driven in vapour from the lower strata, where 
temperature is high, to more superficial strata, where they condense 
and are retained under pressure. In 1886, in consequence of 
rumours as to the possible exhaustion of the Russian oil fields, he 
was sent by the Government to Baku to collect information, and 
in 1889 he made a communication on this subject to Dr. Ludwig 
Mond, which is printed in the Journal of the Society of Chemical 
Industry (1889, 8, 753.) 

The influence of the great generalisation known as the periodic 
law can best be estimated by reviewing the state of knowledge 



TILDEN: MEXDELEEFF MEMORIAL LECTURE. 137 

and opinion before the announcement and acceptance of the prin- 
ciple by the chemical world, and subsequently glancing at the 
influence which, directly or indirectly, it has produced on scientific 
thought, not only in regard to the great problems to which it 
immediately relates, but to the whole range of chemical theory. 

The use of the expression, " atomic weight," implies the adoption 
of some form of atomic theory. But forty or more years ago 
Dalton's atomic theory was by many of the most philosophical 
chemists and physicists regarded as only a convenient hypothesis, 
which might be temporarily useful, but could not be accepted as 
representing physical reality. Since that time, however, a variety 
of circumstances have contributed to consolidate the Daltonian 
doctrine. The estimation of the ratios called atomic weights has 
been the subject of research, attended by more and more elaborate 
precautions to secure accuracy, from the time of Dalton himself 
onward through successive generations down to the present day. 
Though the atomic weights of the majority of the common elements 
are now known to a high degree of accuracy, the acknowledged 
errors have been sufficiently great to render abortive various 
attempts to reduce them to any common scheme of mathematical 
relationship. As is well known, the most important step toward 
the systematisation- of atomic weights was taken about 1860, 
mainly on the grounds eloquently and convincingly set forth by 
Cannizzaro,* in consequence of which the arbitrary selection of 
numbers for atomic weights was superseded by the practical 
recognition of the law of Avogadro and the application of the law 
of Dulong and Petit, so that a common standard was established. 
No general scheme of atomic weights was previously possible, 
partial and imperfect efforts in this direction being represented by 
Dcebereiner's triads and the principle of homology made use of by 
Dumas. Only so soon as numbers representing the atomic weights 
of calcium, barium, lead, a,nd other metals were corrected and 
brought into the same category as those of oxygen, sulphur, and 
carbon was there some chance of determining whether these 
numbers possessed a common factor or were capable of exhibiting 
mathematical interrelations which might be regarded as symbolic 
of physical relations or even directly dependent upon them. The 
first step in this direction was taken by J. A. R. Newlands, who, 
after some preliminary attempts in 1864-1865, discovered that when 
the elements are placed in the order of the numerical value of 
their atomic weights, corrected as advised by Cannizzaro, the 
eighth element^ starting from any point on the list exhibits a 
revival of the characteristics of the first. This undoubtedly repre- 
* 1858, and later, Faraday Lecture, 1872. 



138 TILDEN: MENDELEEFF MEMORIAL LECTURE. 

sents the first recognition of the principle of periodicity in the 
series of atomic weights, but whether discouraged l^y the cool 
reception of his " law of octaves " by the chemical world or from 
imperfect apprehension of the importance of this discovery, 
Newlands failed to follow up the inquiry. It was not long, 
however, before the matter was taken up by others, and doubtless 
the improvements in the estimation of atomic weights, following 
on the work of Stas, then only recently published, inspired greater 
confidence in the approximate accuracy of the numbers adopted 
as atomic weights, and thus encouraged inquiry into their relations. 
The subject is, indeed, an attractive one, for it involves con- 
siderations which lie at the foundations of all our notions respecting 
the physical constitution of matter, and accordingly we find papers 
by many chemists dealing with the question of these numerical 
relations. Odling especially seems to have given much thought 
to the subject, and, ignoring Newlands' previous attempts, he drew 
up towards the end of 1864 * a table containing a list of all the 
then well-known elements, arranged horizontally in the order of 
their generally accepted groups, and perpendicularly in the order 
of their several atomic weights. He concludes an article in Watts's 
Dictionary a few months later with these words : " Doubtless some 
of the arithmetical relations exemplified in the foregoing table 
are merely accidental, but, taken altogether, they are too numerous 
and. decided not to depend on some hitherto unrecognised law." 
It is important to note the words -I have italicised. 

Such, then, was the state of knowledge about this time. Evidently 
the wav was being prepared, but the prophet had not made his 
appearance, the seer who could look with the eves of confidence 
beyond the clouds of uncertainty which obscured ail ordinary 
vision. 

In March, 1869, Mendeleeff communicated to the Russian 
Chemical Society an enunciation of the principle of periodicity 
and a statement of some of the consequences of this recognition 
of the relation of properties to atomic weight throughout the whole 
range of the known elements, and this statement was accompanied 
by a table which, while it bears a close resemblance to Odling's 
table of 1864, was apparently connected in his mind with an idea 
which became clearer and more decisive in the modifications which 
he immediately afterwards introduced into the arrangement, f 

* Quart. J. Sci., 1864, 1, 43 ; and Watts' Diet., Vol. Ill, 975. 
t Subjoined is a translation, as literal as possible, of the German Abstract (Zcitsch. 
f. Chem., 5, 405). Several obvious misprints have been corrected. 



T1LDEN: MENDELEEFF MEMORIAL LECTURE. 139 



On the Relation of the Properties to the Atomic Weights of the 

Elements. 

By D. MENDELEEFF. 

When the elements are arranged in vertical columns, according 
to increasing atomic weight, so that the horizontal lines contain 
analogous elements, again according to increasing atomic weight, 
the following arrangement results, from which several general 
conclusions may be derived : 

Ti =50 Zr = tfO ? =180 

V = 51 Nb= 94" Ta =182 

Cr= 52 Mo= 96 W =186 

Mn= 55 - Rh = 104-4 Pt =197 '4 

Fe = 56 Ru =104-4 Ir =198 

Ni=Co= 59 Pd =108-6 Os =199 

H =1 Cu= 63-4 Ag=108 Hg=200 



Li =7 



1. The elements arranged according to the magnitude of atomic 
weight show a periodic * change of properties. 

2. Chemically analogous elements have atomic weights either in 
agreement (Pt, Ir, Os), or increasing by equal amounts (K, Rb, Cs). 

3. The arrangement, according to atomic weights, corresponds 
with the valency of the elements, and to a certain extent the 
difference in chemical behaviour, for example, Li, Be, B, C, N, O, F. 

4. The elements most widely distributed in nature have small 
atomic weights, and all such elements are distinguished by their 
characteristic behaviour. They are thus typical elements, and the 
lightest element, hydrogen, is therefore rightly chosen as the typical 
unit of mass. 

5. The magnitude of ^-the atomic weight determines the pro- 
perties of the element, whence in the study of compounds regard 
is to be paid not only to the number and properties of the 
elements and their mutual action, but to the atomic weights of the 
elements. Herce the compounds of S and Te, 1 Cl and I, show, 
beside many analogies, yet striking differences. 

* Here an error in the German translation doe* an injustice to the original, 
inasmuch as the Russian word for periodical is rendered " stutenweise " (gradual). 



Be 
B 


= 9-4 
= 11 


Mg = 24 Zn = 
Al =27-4 ? = 


65 

68 


2 


Cd 
U 


= 112 
= 116 


Au 


= 197? 





= 12 


Si 


= 28 


? 





70 




Sn 


= 118 






N 


= 14 


P 


= 31 


As 





75 




Sb 


= 122 


Bi 


= 210 ? 





= 16 


S 


= 32 


Se 





79 


4 


^Te 


= 128 ? 






F 


= 19 


Cl 


= 35-5 


Br 





80 




I 


= 127 






JN c 


i = 23 


K 


= 39 


Rb 


SB 


85 


4 


Cs 


= 133 


Tl 


= 204 






Ca 


= 40 


Sr 


= 87-6 


Ba 


= 137 


Pb 


= 207 






i 


= 45 


Ce 


SB 


92 
















?Er 


= 56 


La 





94 
















m 


= 60 


Di 





95 
















?Iu 


= 75-6 


Th = 118 



140 TILDEX: MEN'DELEEFF MEMORIAL LECTURE. 

6. It allows the discovery of many new elements to be foreseen, 
for example, analogues of fcji and Al with atomic weights between 
65 and 75. 

7. Some atomic weights will presumably experience a correction; 
for example, Te cannot have the atomic weight 128, but 123 to 126. 

8. From the foregoing table, new analogies between elements 
become apparent. Thus U appears as an analogue of B and Al,. 
which, as is well known, has long ago been established experi- 
mentally. 

Previous students of the subject had been, for the most part,, 
struck with the relations obviously subsisting between the members 
of the several natural families of elements, but had, with few 
exceptions, failed to perceive that there must be a general law 
binding the whole together. However, Mendeleeff, with that noble 
sentiment of justice which always animates the truly scientific 
mind, admits that the idea of a general law. had already been 
foreshadowed by others, and he says (Faraday Lecture, , 1889), 
" I now see clearly that Strecker, de Chancourtois, and Newlaiids 
stood foremost in the way towards the discovery of the periodic 
law, and that they merely wanted the boldness necessary to place 
the whole question at such a height that its reflection on the facts 
could be clearly seen." 

It may be remarked that Strecker did little more than call 
attention to the sequence in the values of the atomic weights of 
certain elements, and states that "we must leave to the future 
the discovery of the law of the relations which appear in these 
figures " (Tbflorien u. Experimente zur Bestimmung der Atom 
Gewichte der Elemente, 1859). De Chancourtois, in his work 
entitled " Le Vis Tellurique " (1863), devised a geometric method 
of representing the atomic weights by coiling round a cylinder a 
helix with an angle of 45, the cylinder being divided vertically 
into sixteen equal parts by lines drawn from the circular base. 
The points of intersection of the helix with these lines were 
supposed to represent the atomic weights of elements which differed 
from one another by 16 or by multiples of 16. 

Mendeleeff 's table of 1869 was subsequently in 1871 modified 
so as to assume the form with which we have all been so long 
familiar, and which is to be found in every modern text-book. 
Thus it may be claimed for Mendeleeff that he was actually the 
first, not only to formulate a general law connecting atomic weights 
with properties, but was the first to indicate its character, and, 
as himself (Principles, 1905, II, p. 28) has pointed out, he was 
the first "to foretell the properties of undiscovered elements, or 



TILDES : MENDELEEFF MEMORIAL LECTURE. 141 

to alter the accepted atomic weights " in confidence of its validity. 
The time was, in fact, ripe for the enunciation of this general 
principle, and, the suggestion once given, the relations embodied 
in the law could not fail to attract other chemists. Accordingly, 
in December, 1869, Lothar Meyer, with such knowledge of 
Mendeleeff's scheme as could be derived from the imperfect German 
version of his paper of the previous March, proved himself a 
convinced exponent of the idea by contributing to Liebig's 
Annalen a paper containing a table, substantially identical with 
that of Mendeleeff, and his famous diagram of atomic volumes, 
which, more clearly even than the tabular scheme, illustrates the 
principle of periodicity. 

The history of science shows many instances of the same kind. 
Great generalisations have often resulted from the gradual 
accumulation of facts which, after remaining for a time isolated 
or confused, have been found to admit of co-ordination into a 
comprehensive scheme, an'd, this once clearly formulated, many 
workers are found ready to assist in its development. The case 
is nearly parallel to the recognition of the operation of natural 
selection by Darwin and Wallace, or it might be compared to the 
discovery of oxygen by Priestley and Scheele and the utilisation 
of this knowledge by Lavoisier. In each case much preparatory 
work had been done, and a body of knowledge had been gradually 
accumulated which, when duly marshalled and surveyed by the 
eye of a master, could scarcely fail to reveal to him the underlying 
principle. The full consequences, however, would appear only to 
a few. 

The law of periodicity was expressed by Mendeleeff in the 
following words: * 

" The properties of the elements, as well as the forms and pro- 
perties of their compounds, are in periodic dependence on, or 
(expressing ourselves algebraically) form a periodic function of 
the atomic weights of the elements." After a brief historical 
account of the discovery of the law by himself, Mendeleeff 
concludes by saying (Principles, p. 18) : "I consider it well 
to observe that no law of nature, however general, has 
been established all at once; its recognition has a 1 ways been 
preceded by many presentiments; the establishment of a law, 
however, does not take place when the first thought of it takes 
form, or even when its significance is recognised, but only when 
it has been confirmed by the results of experiment which the man 
of science must consider as the only proof of the correctness o 
his conjectures and opinions." 

* Principles, 1905, Vol. II, p. 17. 



142 TILDEN: MENDELEEFF MEMORIAL LECTURE. 

I regard it as unnecessary, in the presence of the Fellows of the 
Chemical Society, to review with any detail the multitudinous 
applications of the scheme of the elements constructed on the basis 
of the periodic law. These are the commonplaces of modern 
theoretical chemistry. They are embodied in every text-book of 
any importance, and are related by every lecturer and teacher as 
familiar and indisputably recognised consequences of the system. 
We may therefore pass lightly over the story of the prediction by 
Mendeleeff of the properties of undiscovered elements, confirmed 
so remarkably by the discovery of scandium, gallium, and ger- 
manium, and related in dramatic language by Mendeleeff himself 
(Faraday Lecture). ( We may also pass over the applications of 
the system to the correction of atomic weights, illustrated by the 
case of beryllium, the recognition of previously unnoticed relations, 
and the discovery of new elements, notably the companions of 
argon (Ramsay, Presidential Address to Section B, British Associa- 
tion, 1897, and Proc. Roy. Soc., 1898, 63, 437). 

It will be more profitable to consider a few of the difficulties 
which still encumber the application of the law, and which, while 
limiting our acceptance of it in an unqualified form as applicable 
to the whole of the elements, tempt the speculative mind to wander 
in wide fields of conjecture. 

Can it be truly said that the elements arranged in the order of 
their atomic weights show without exception periodic changes of 
properties? This question has been propounded already, but has 
nevqr been fully discussed, even by Mendeleeff. An examination 
of the facts seems, however, to indicate the possibility of some 
Bother principle, which, while it does not supersede the periodic 
.scheme, would, if it could be recognised^ supplement it. This 
involves other considerations which we may turn to first. 

If the whole of the known elements are drawn up in the order 
of their atomic weights (using the values given by the International 
Committee for 1908), we find a progression in value from H = 1'008 
to U = 238'5, with differences between the successive elements 
which vary from 0'3 (Co-Ni)* to 4'3 (Co-Cu) among the 

* Mendeleeff held the view that "in general,. cobalt is more nearly allied to iron 
than nickel, and the latter more nearly to copper" (Principles, Eng. Ed., 1905, 
p. 879). Accordingly, in the first edition of his book, he assigned to cobalt the 
atomic weight 58*5, and to nickel, the atomic weight 59. In the later edition of 
1905, he makes them both 59, and expresses the belief that eventually the atomic 
weight of cobalt will be found less than that now accepted and less than nickel 
(Eng. Ed., 1905, II, footnote 25, p. 45). Whatever may be the exact values of the 
atomic weights of these two elements, there can be no doubt that the atomic weight 
of cobalt is greater than that of nickel. This is proved by the estimations of the 
specific heats of both these metals purified by methods which preclude the possibility 



TILDEN: MENDELEEFF MEMORIAL LECTURE. 143 

common elements of which the atomic weights have been most 
accurately estimated. The large difference, 7*4, between Sb and Te 
is manifestly due to some error in the atomic weight of tellurium 
of which no sufficient explanation is yet forthcoming, and it is 
only when we get to the element Bi that there seems reason for 
thinking that it must be followed by some hitherto unrecognised 
elements, since the gap between Bi and the next known element, 
Ra, is 18' 7 units. The atomic weights of the long series of elements 
beginning with La are confessedly uncertain, but that they all lie 
between La and Ta seems probable, because although the individual 
numbers are doubtless inexact, the average difference between any 
two consecutive terms is roughly the same as the average difference 
between successive atomic weights among the better known 
elements preceding them. Ta-La = 181 -138'9 = 42-1 for sixteen 
intervals. 

It must also be noted that the differences, approximately three 
units each, among the three elements with smallest known atomic 
weights, namely, 

H 1-008, He 4, Li 7'03, 

are greater than the differences observed among the elements which 
immediately succeed them, namely, 

Li 7-03, Be 9'1, B 11, C 12, N 14'01, O 16, F 19. 

It will be seen later that, as regards this part of the scheme, 
Mendeleeff had put forth a special hypothesis. 

If these considerations are to be regarded as having weight, it 
seems probable that few additional elements are to be expected, 
except possibly one following Mo and another following W, save 
in the region already indicated from Bi to, Ra. This suggests the 
remark that, after all, it is not necessary to assume that the 
materials of which the earth consists should necessarily include a 
sample of every possible element indicated by such a scheme. 
Some which are missing from terrestrial matters may perhaps be 
responsible for phenomena recognisable by the spectroscope in stars 
or nebulae far distant in cosmical space. The unexpected, however, 
often happens, and, remembering the discovery of terrestrial 

of appreciable error or of mutual contamination. The following results were 
obtained by different observers using different methods : 

Temperature. Cobalt. Nickel. 

From 100 to 15 G'10303 0*10842 

15 to -78-4 0-0939 0*0975 

,, 78-4 to -182-5 0-0712 0*0719 

Tilden, Phil. Tram., 1900, 194 A, 249. 

From 100 to 20 0*104 0*108 

Copaux, Compt. rend., 1905, 140, 657. 



144 T1LDEX: MENDEL^EFF MEMORIAL LECTURE. 

helium, it is permissible to hope that some of the vacant spacer 
may hereafter be filled by earthly occupants. 

There is one important point to be noted here, namely, that if 
the so-called rare earth metals, praseodymium, neodymium r 
samarium, gadolinium, terbium, dysprosium, erbium, ytterbium, 
and others of which the existence is doubtful, do lie in the position 
indicated, the original statement of the periodic law breaks down 
at this point. Enough is already known o^ their properties to show 
that they are very closely allied together, and cannot fall into 
separate periods. Mendeleeff says (Principles, 1905, Vol. II, p. 45), 
" This appears to me to be one of the most difficult problems 
offered to the periodic law." He prefers, however, to leave open 
the question as to the position of these elements. The discordance 
of. argon and of tellurium with the places assigned to them are 
also matters which must be left for the consideration of future 
workers. 

One result of the recognition of the periodic law is that theories 
concerning the genesis of the elements have received a stimulus 
previously unknown. It is, however, interesting to note the 
attitude of Mendeleeff toward this question, and the small extent 
to which this attitude appears to have become modified with the 
lapse of time. When, in 1889, twenty years after the discovery of 
the law, he composed the Faraday lecture, he seems to have 
regarded speculation in this direction as a kind of abuse of the- 
periodic system. He was, of course, fully justified in stating 
(Faraday Lecture) that " the periodic law, based as it is on the 
solid and wholesome ground of experimental research, has been 
evolved independently of any conception as to the nature of the 
elements; it does not in the least originate in the idea of a unique 
matter; and it has no historical connexion with that relic of the 
torments of classical thought." But it is at least questionable 
how far he was justified in continuing that " therefore it affords 
no more indication of the unity of "matter, or of the compound 
character of our elements, than the law of Avogadro or the law 
of specific heats, or even the conclusions of spectrum analysis. 
None of the advocates of a unique matter have ever tried to- 
explain the law from the standpoint of ideas taken from a remote 
antiquity, when it was found convenient to admit the existence of 
many gods and a unique matter." And again, later, " From the 
foregoing, as well as from the failures of so many attempts at 
finding in experiment and speculation a proof of the compound 
character of the elements and of the existence of primordial matter, 
it is evident, in my opinion, that this theory must be classed 
among mere Utopias." 



TILDEN: MENDELEEFF MEMORIAL LECTURE. 145 

Fifteen years later, after the discovery of the argon group of 
^elements, of the phenomena of radioactivity, and of radium, it 
became necessary to consider the relations of these substances to 
the periodic scheme. In a remarkable article contributed to the 
new Russian Encyclopaedia, and subsequently printed as Appendix 
III to the Principles (English Edition, 1905), Mendeleeff gives 
a new table of the elements, in which places are found, not only 
for the argon group and radium, but for two hypothetical elements 
which are placed before helium and designated and y. 

As this table may be assumed to represent his latest views 
concerning the relations of the elements, it is here reproduced.* 

The y in the table is supposed to be an analogue of helium, and 
may be identified hereafter with " coronium," which has been 
recognised in the sun's coronal atmosphere. This gas would 
have, according to Mendeleeff, a density about 0'2, and therefore 
a molecular weight about 0*4, or about one-tenth that of 
helium. 

x is the "ether " of the physicist, for which Mendeleeff, dis- 
regarding conventional views, supposes a molecular structure. He 
also assumes that, like the argon group, this element is chemically 
inert and possesses a very low density and atomic weight, estimated 
at 0-000,00^,000,053. 

His views in connexion with this matter are put forward merely 
as speculations and without dogmatism, but it is clear that he 
retained his repugnance to the conception of a unique matter to 
the last. In his essay entitled " A Chemical Conception of the 
Ether " (translated by Kamensky, 1904), the following passage 
occurs, p. 32: " Being unable to conceive the formation of the 
known elements from hydrogen, I can neither regard them as 
being formed from the element x, although it is the lightest of all 
the elements. I cannot admit this, not only because no fact points 
to the possibility of the transformation of one element into another, 
but chiefly because I do not see that such an admission would in 
any way facilitate or simplify our understanding of the substances 
and phenomena of nature." 

Chemists and physicists have, however, -found it impossible to 
resist the fascination of this problem, and accordingly there have 
been many hypotheses as to the origin of the elements and the 
nature of their connexion with one another. These seem to be 
inseparable from the periodic scheme itself, which at once provokes 
the inquiry, Why do these numerical relations occur, and what 

* The spaces left vacant in Series I, after hydrogen, are the positions of hypo- 
thetical elements having approximately the atomic weights, 1'4, 1*8, 2 '2, 2'6, 2 '8, 
3-0, and 3 '4, and standing at the head of groups II to VIII respectively. 



146 



TILDEN: MENDEL^EFF MEMORIAL LECTURE. 







^ 




M 


^* 








O 






<J 






1 1 1 1 


TfS 

|.H 


I 


if ' 'i 


II 1 


1 


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^^ 




22 


I " 




> 




rfS 




1 1 


B| 




& 


1 I 1 1 


J ii 

o o 


1 


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^ li 1 


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ag 


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oo 




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boll 


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EZJ ^^ r^i ^^ 


Cj WH 




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Group VI. 


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OO 030Q 


Chromium, 
Cr=52-l 


Selenium, 
Se = 79 


Si IS 


M 

p 

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1 1 c& 5 


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ll 

w II 


is fi 

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Sc = 44'l 


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4 



TILDEN: MEXDELEEFF MEMORIAL LECTURE. 147 

is the meaning of them if they do not point to a common genesis 
or the operation of some process of evolution? 

Hypotheses concerning the evolution of the elements have hitherto 
been usually based on the assumption that the successive stages of 
condensation of elemental matter proceeded from a single primary 
stuff, which by a process analogous to polymerisation among carbon 
compounds gave rise to atoms of greater and greater mass, which 
were stable at the prevailing and any lower temperature. The 
physical cause of the successive condensations is supposed to be ,a 
falling temperature. It is, of course, possible to imagine that if 
to the stuff of which hydrogen atoms consist are added successive 
portions of matter of the same kind, stable structures may at 
intervals result which we know as the atoms of the elements helium, 
lithium, beryllium, boron, carbon, nitrogen, oxygen, and fluorine, 
provided the idea of internal structure in these atoms is allowed. 
Otherwise, from the mere accretion of matter upon a central 
nucleus, there seems no sufficient reason why there should not 
have been formed an indefinite^ number of intermediate masses 
corresponding to an indefinite number of what would be called 
elements. Further, it is difficult to understand why simple increase 
of mass should change, say, oxygen into fluorine, while a further 
addition of the same kind should change negative fluorine into 
inert neon or positive sodium. The possibility of the condensation 
of a single " protyl " so as to produce, at successive though unequal 
stages of cooling, the elements known to the chemist has been most 
ably discussed long ago by Sir William Cropkes. 

This hypothesis, however, was put forward long before the work 
of Sir J. J. Thomson and his school was given to the world and 
the electron was accepted as a physical reality. The hypothesis 
that one elemental stuff may give rise to the whole array of 
known elements by a process of condensation accompanied by a 
loss or gain of electrons, the mass of which is approximately one- 
thousandth of the mass of an atom of hydrogen, forms the subject 
of a paper by Mr. A. C. G. Egerton in a recent number of our 
Transactions (1909, 95, 239). The atomic weights calculated by 
his formula agree closely with the experimental atomic weights 
of the first fifteen elements, but the hypothesis gives no explanation 
of the facts observed in the physical properties of the elements 
arranged according to the Mendeleeff scheme, their alternation 
. of odd and even valency, the transition from positive on one side of 
the table to negative on the other, the periodicity of properties 
shown by the sudden change of character in passing from fluorine 
to the next element, whether it be neon or sodium. 

Another paper by Messrs. A. C. and A. E. Jessup (Phil. May., 



148 TILDEN : MEXDELEEFF MEMORIAL LECTURE. 

1908, [vi], 15, 21) has recently provided a hypothesis of an entirely 
different character. From a study of the spectra of the nebulae, 
these authors have been led to assume the existence of two hitherto 
unrecognised elements, to which the names protoglucinum and 
protoboron are assigned. These with hydrogen and helium are 
supposed to represent four initial substances, or protons, which, by 
condensation directly or indirectly, give rise to all the rest of the 
elements. The arguments of these authors are ingenious, but 
rather artificial in view of the fact that the number of groups 
in the periodic scheme to be provided for is greater than four. 

In the Mendeleeff chart of the elements, there is nothing more 
striking than the gathering of the negative elements toward what 
may be called the N.E., and the segregation of the positive elements 
toward the S.W., the centre of the intermediate territory being 
occupied by elements which play a more or less undecided part. 
I have elsewhere (Presidential Address, 1905, Trans., 87, 564) 
drawn attention to the fact that carbon, at any rate, is not directly 
deposited by electrolysis from any of its compounds, with positive 
hydrogen on the one hand, or negative chlorine on the other. I 
believe the same is true of silicon, these two elements standing in 
a middle position between the extremes occupied by lithium and 
fluorine respectively. 

If we assume tEafc atoms are made up of two parts (protyls), 
positive and negative, in proportions which determine by the 
preponderance of one or the other whether the element shall exhibit 
the positive character of a metal like lithium or the negative 
character of a halogen, we arrive at a hypothesis which recalls 
the ideas put forward nearly a century ago by Berzelius. His 
views are familiar to every student of the history of chemistry, 
but have long been relegated to the lumber room of worn-out 
doctrine. The last, few years have, however, given us the remark- 
able experimental investigations of J. J. Thomson already referred 
to, and the new conceptions concerning the nature of atoms, which 
revive the fundamental idea that they are made up of two com- 
ponents.* 

Carnelley, in 1885 (Brit. Assoc. Reports), brought forward the idea "that the 
elements are not elements in the strict sense of the term, but aie, in fact, compound 
i-adicals made up of at least two simple elements, A and B." The element A was 
supposed to be identical with carbon, while to B was assigned a negative weight, - 2, 
and it was suggested that it might be the ether of space. C. S. Palmer (Proc. 
Colorado Scient. Soc.) assumed the existence of two sub-elements, to which he gave 
the names "kalidium" and "oxidium," and his views appear to have a general 
resemblance to the hypothesis suggested in the text. The original article is abstracted 
in Venables' Periodic Law and is referred to in footnotes in Palmer's translation of 
Nernst's Theoretical Chemistry. 



TILDEN : MENDELEEFF MEMORIAL LECTURE. 149 

Setting out the known elements in the order of the numerical 
-value of their atomic weights, we find that between the first three 
elements, H = l, He =4, and Li = 7, the difference, 3, is greater 
than would be expected by comparison with the differences noticed 
between the elements of greater atomic weight which immediately 
follow them. In order to satisfy the hypothesis just put forward, 
there appears to be wanting an element which should stand in the 
same relation to fluorine as hydrogen to lithium. This would 
have an atomic weight 2 '7 approximately. Whether this exists, 
and whether its existence is indicated by the unappropriated 
spectral lines of nebulae or corona, can only be a matter of con- 
jecture. Mendeleeff, in his (1905) latest speculations concerning 
the possibility of still undiscovered elements, has suggested the 
existence of a new element of the halogen group with an atomic 
weight about 3.* But, as already sufficiently shown, he accepted 
no hypothesis which involved any idea of the composite nature 
of the elements. It would therefore have been foreign to his 
system to employ this element in any such manner. But the idea 
seems to me to assist materially conceptions as to the process of 
condensation hypothetically occurring in the evolution of the 
known chemical elements. For to suppose that the typical 
elements, so different as they are in character, forming the first 
line of Mendeleeff' s scheme, have -all resulted from the condensation 
of a single protyl has always seemed to me a difficult proposition. 
There is comparatively little difficulty in the view that the succes- 
sive terms of a family of what, by analogy, may be called a 
homologous series, may have originated in this way. A con- 
sideration of all the properties of the alkali metals, for example, 
coupled with the character of their spectra, suggests quite naturally 
the passage from lithium to sodium, and so forth, step by step, 
by the addition of successive accretions of the same matter to the 
primal element, the character of which, including valency, is not 
-only sustained through the whole family, but becomes more 
strongly marked in proportion to the gradual increase of atomic 
-weight. At the opposite end of the table, on the other hand, a 
reduction of the negative character of the element, in passing from 
fluorine to iodine, seems to suggest that the negative protyl which 
preponderates in the smaller atom is modified in the larger atom 
by the addition of a certain proportion of the positive protyl. 

The conceptions presented to us in J. J. Thomson's work permit 
of several supplementary hypotheses, especially the idea that if 

* It may also, perhaps, be worthy jf note that Mr. Egerton's calculations (loc. 
cit.) lead him to postulate an element oi nearly this atomic weight, namely, 2 '9844, 
^although his paper gives no indication as to~its character. 



150 TILDEN : MENDELEEFF MEMORIAL LECTURE. 

atoms are really made up of smaller corpuscles these are not thrown 
together in confusion but, as he has shown, must be distributed 
within the mass in a definite order, which is determined by the 
attraction of the electro-positive shell and the self-repulsion of 
the negative corpuscles included in it. Once the idea of structure 
within the atom is admitted, the possibility presents itself of there 
being for the same mass more than one arrangement corresponding 
to what is called isomerism in compounds. In this way the case 
of elements with similar properties and identical or nearly identical 
atomic weights, for example, cobalt and nickel, and even such a 
case as tellurium, might perhaps be explained. Further, now that 
the materials which have so long received the unsatisfactory 
designation of the " rare earths " are found in unexpected 
abundance, it may be hoped that the study of their chemical 
characters may be completed. It may turn out that this group 
may include elements of identical atomic weight, though exhibiting 
different properties. It does not seem very long ago in the memory 
of many now living that the nature of the isomerism of the 
derivatives of benzene was a deep mystery, from which nearly all 
obscurity cleared away in the light of the then new theory of the 
constitution of benzene. 

I have dwelt at some length on these various hypotheses, because 
the discussion of the subject to which they relate indicates, in my 
opinion, one of the consequences of the promulgation and general 
acceptance of the periodic scheme of the elements. This is, how- 
ever, not the only result of the recognition of its validity and 
usefulness by chemists generally. That the elements stand in a 
definite relation to one another implies that their compounds also 
fall into their places in an orderly system, and consequently a basis 
is provided for the complete systematisation of the whole science 
of chemistry. There is scarcely a treatise on chemistry which does 
not bear evident witness to this influence. And this is perhaps 
not the least among the services rendered by this generalisation, 
for not only is the learner enabled to remember a much larger 
number of facts than previously, but he is led to perceive a 
connexion between phenomena and processes which was almost 
entirely wanting so long as practical chemistry consisted mainly 
of a bundle of recipes. And here it is fitting that we should glance 
at the famous treatise by Mendeleeff himself, " The Principles of 
Chemistry," of which we possess three editions in English, the last 
of which, issued in 1905, is a rendering of the seventh edition 
(1903) of the original. An eighth Russian edition began to be 
issued in 1905, but" is incomplete. To this remarkable book it is 
impossible to do justice in a brief notice or to communicate to 



TILDEN : MENDELEEFF MEMORIAL LECTURE. 151 

those who have not read it an adequate impression. Clearly it is 
a work of genius, but such work^ are not always the most suitable 
for beginners, though for the advanced student nothing can be 
more inspiring. The " Principles " embody in reality two distinct 
treatises, for the text, which is written in an easy style, open to 
quite straightforward reading, is accompanied by notes which are 
often more voluminous and usurp -entire pages. Even the preface 
is attended by these commentaries, which are all interesting as 
showing the spirit of the writer and the restless activity of his 
mind. A few extracts from the preface will serve to illustrate 
the truism too often neglected by writers of biographies, that it is 
impossible to separate a man's work from his life, and that the 
character and quality of the former are dependent upon the 
personal characteristics of the man, independently of the oppor- 
tunities or influences which may have served to assist or to repress 
his activities. 

" If statements of fact," he says, " themselves depend upon the 
persons who observe them, how much more distinct is the reflection 
of the personality of him who gives an account of methods and 
philosophical speculations forming the essence of a science! For 
this reason there will inevitably be much that is subjective 
bearing the stamp of time and locality in every objective 
exposition of science. And as an individual production is only 
significant in virtue of that which has preceded it and that which 
is contemporary with it, it resembles a mirror, which in reflecting 
exaggerates the size and clearness of neighbouring objects, and 
causes a person near it to see reflected most plainly those objects 
which are on the side to which it % is directed, and sometimes even 
the person holding the mirror. Although**! have endeavoured to 
make my book a true mirror directed toward the whole domain 
of chemical changes and of the elements taking part in them, yet 
involuntarily those influences near to me being most clearly 
reflected and the most brightly illuminated have tinted the entire 
work with their colouring. In this way the chief peculiarity of the 
book has been determined. Experimental and practical data and 
their application in life and industry occupy their place, but thiE 
philosophical principles of our science form the chief theme of the 
work.*' 

Later on he says, " The thought that this book might fall not 
only into the hands of the beginner for whom it is intended, but 
also of authorities who might wish to know the views held by an 
old disciple of science on the current problems of chemistry, greatly 
complicated the preparation of a new edition, for it necessitated 
making a selection of the most v essential of the vast number of 



152 TILDEN: MENDELEEFF MEMORIAL LECTURE. 

new researches published year by year and explaining my views on 
them without greatly enlarging the bulk of the work. After 
having closely followed all the chief conquests of chemical science 
since the days of Berzelius, Liebig, Dumas, and Gerhardt, and 
having seen the triumph of much that lay neglected, and the fall 
of much that was exalted, I involuntarily acquired a tendency to 
analyse new facts, and a desire to transmit to my readers the 
results of such analysis, if it could, in my opinion, help towards 
a proper explanation and generalisation of the chemical elements. 
In carefully preparing this edition, I have not lost sight of the 
fact that I am hardly likely to publish another, and I have 
therefore in many cases spoken more definitely than formerly. 
After having been an insignificant but zealous worker in chemistry 
for almost half a century, I wished my book should retain some 
braces of how a confirmed disciple of Gerhardt regards the funda- 
mental problems of the theory of the chemical elements at the 
beginning of the twentieth century. As an example, I may 
mention that the more I have thought on the nature of the 
chemical elements, the more decidedly have I turned away from 
the classical notion of a primary matter, and from the hope of 
attaining the desired end by a study of electrical and optical 
phenomena, and the more clearly have I recognised that first and 
foremost are needed truer conceptions of ' mass ' and ' ether ' than 
those in vogue at the present time. The return to electro- 
chemism which is so evident in the supporters of the hypothesis 
of ' electrolytic dissociation/ and the notion of a splitting up of 
atoms into ' electrons/ in my opinion only complicate, and in no 
way explain, so real a matter (since the days of Lavoisier) as the 
chemical changes of substances, which led to the recognition of 
the invariable and ponderable atoms of simple bodies. The 
definition of mass gave a means for analysing and grasping 
vchemical transformation of substances, and for arriving at the 
atom, while the mass of the atom was shown by the periodic law 
to influence all its chief chemical properties. Thus chemistry in 
its principles stood on the firm foundations laid by Galileo, Newton, 
and Lavoisier, and in order to gain further insight and knowledge 
of the atoms themselves, the fundamental conceptions of mass, 
gravity, and ether will have to be explained by a method of 
experiment alone, otherwise the realism of science will again open 
its doors to such metaphysical and ' metachemical ' conceptions as 
phlogiston and other mystical dreams. For my part I endeavour 
to remain true to the testament of realism left by Newton and 
Lavoisier, and it is my wish to instil this sentiment into my young 
readers." 



T1LDKN : MEXDELfiEFF MEMORIAL LECTURE. 15S 

This is very clear, and little more remains to be said. In the 
seventeenth century Robert Boyle taught us how to distinguish 
elements from compounds, and how to give to the word " element " 
a definite connotation clearly distinguishing it from the elusive 
and fantastic language of the alchemists. In the eighteenth 
century Lavoisier showed the true nature of the most familiar of 
chemical compounds, namely, acids, bases, and salts, and helped 
to lay the foundation of quantitative chemistry. At the beginning 
of the nineteenth century Dalton gave to chemistry the Atomic 
Theory, of which it is not too much to say that it provided the 
scaffold by the aid of which the entire fabric of modern theoretical 
chemistry has been built up. Sixty years later this conception, 
developed and adorned by the labours of an army of earnest 
workers, has been shown to us in a brilliant new light thrown 
over the whole theory by Mendel 6eff. 

The views of Boyle, of Lavoisier, and of Daltor have been 
corrected by experience and broadened by extended knowledge, but 
the fundamental and essential parts of their ideas remain, and 
their names are immortal. In like manner the expression of the 
periodic law of the elements as known to the present generation is 
destined, we may believe, to be absorbed into a more comprehensive 
scheme by which obscurities and anomalies will be cleared away, 
the true relations of all the elements to one another revealed, and 
doubts as to the doctrine of evolution resolved in one sense or the 
other. But as with the Atomic Theory itself, there is no reason 
to doubt that the essential features of the periodic scheme will 
be clearly distinguished through all time, and in association with 
it the name of Mendeleeff will be for ever preserved among the 
Fathers or Founders of Chemistry. 




lTofacep.155. 



THOMSEN MEMORIAL LECTURE. 
DKLIVEKED ON FEBUUAUY 17in, 1010. 

By SIR EDWARD THORPE, C.B., LL.D., F.R.S., Past-President of the 

Chemical Society. 

AMONG} the Danes whose names are inscribed as men of science on 
the eternal bead-roll of fame, that of Julius Thoniseu stands pre- 
eminent linked indeed with that of Oersted. It is significant of 
the position which Thomsen acquired in physical science, and oi; 
the respect which that position secured for him in the eyes of his 
countrymen, that his statue should have been erected during his 
lifetime and placed in the vicinity of that of Oersted in the court- 
yard of the Polytechnic High School of Copenhagen. Thomsen, in 
fact, played many parts in the intellectual, industrial, and social 
development of Denmark. To Europe in general he was mainly 
known as a distinguished man of science. By his fellow-citizens he 
was further recognised as an educationist of high ideals, actuated 
by a strong common sense and a stern devotion to duty; as an 
able and sagacious administrator; as a successful technologist and 
the creator of an important and lucrative industry based upon his 
own discoveries; and as a man of forceful character, who Drought 
his authority, skill, and knowledge of men and afiairs to the service 
of the communal life of Copenhagen. 

Thomsen was a municipal councillor of that city for more than 
a third of a century. He occupied a commanding position on the 
Council, and was invariably listened to with respect. The gas, 
water, and sewage works of Copenhagen are among the monuments 
to his civic activity. From 18815 up to the time of his death he 
was a member of the Harbour Board of the port, in these respects 
Thomsen sought to realise Priestley's ideal of the perfect man- that 
he should be a good citizen hrst and a man of science afterwards. 

Hans Peter Jurgen Julius Thomsen was born in Copenhagen on 
February 16th, 1826. He was educated at the church school of 
St. Peter in that city, and subsequently at von Westens Institute. 
In 1843 he commenced his studies at the Polytechnic, and in 1846 
graduated there in Applied Science, and became an assistant to 
Professor E. A. Scharling. Of his earliest years comparatively 
little is known. Thomsen, always a reserved and taciturn man, 

talked little about himself even to his intimate friends and least 

of all about the days of his youth. It was known to a few that 
these days had not been smooth. Those who were best informed 



156 THORPE: THOMSEN MEMORIAL LECTURE. 

were conscious that to these early struggles much of that dour and 
resolute nature which formed a distinguishing trait in his character 
was dub. Thorn sen, indeed, began life as a fighter, and a fighter 
he remained to the end of his four-score years. 

In 1847, he became assistant to Forchhammer, passing rich, like 
Goldsmith's pedagogue, on 40 a year. Georg Forchhammer, whose 
earliest work dates back to the period when Berzelius was in his 
prime, was an active and industrious investigator of the old school, 
mainly in inorganic chemistry, and more particularly on problems 
of chemical geology and physiography. He was a frequent visitor 
to this country, and was well known to early members of the 
British Association. Although doubtless influenced, in common 
with all teachers in Northern Europe, by the example and methods 
of Berzelius, such influence as he himself was able to exert died 
with him. Forchhammer attracted few pupils, and created no school, 
and Thomsen probably derived no. inspiration or acquired any 
stimulus from this association. For a time Thomsen supplemented 
his scanty income by teaching agricultural chemistry at the 
Polytechnic. In 1853 he obtained a travelling scholarship, and 
spent a year in visiting German and French laboratories. He 
probably owed this scholarship in great measure to his first con- 
tribution to the literature of chemistry, namely, his memoir, 
" Bidrag til en Thermochemi^k System " (contributions to a thermo- 
chemical system), communicated to the Royal Society of Sciences 
of Copenhagen in 1852, and for which he received the silver medal 
of the Society and a sum of ten guineas to enable him to procure 
a more accurate apparatus. In this memoir he sought to develop 
the chemical side of the mechanical theory of heat, doubtless under 
the influence of Ludwig Augustus Colding, an engineer in the 
service of the Municipality of Copenhagen, and a pioneer, like 
Mayer, in the development of that theory. Indeed, the Danes now 
claim for Colding, who had made experiments on the relation 
between work and heat as far back as 1842, but whose labours were 
practically ignored by his contemporaries, the position which the 
Germans assign to Mayer (see Mach's " Development of the Theory 
of Heat ' J ). In 1861 Thomsen further developed his ideas in a 
memoir on the " General Nature of Chemical Processes, and on a 
Theory of Affinity Based Thereon/' published in the Transactions of 
the Danish Academy of Sciences. In this paper he laid the 
foundations of the chief scientific work of his life. 

In 1853 Thomsen patented a method of obtaining soda from 
cryolite, so-called " Greenland/" or ice-spar, a naturally occurring 
fluoride of sodium and aluminium, AlgF^GNaF, found largely, 
indeed, almost exclusively, in Greenland, and particularly at 



THORPE: THOMSEN MEMORIAL LECTURE. 157 

Ivigtut. It derives its mineralogical name from its ice-like 
appearance and ready fusibility even in the flame of a candle. Hi 
seems to have been first brought to Europe in 1794, and to have 
been described by Schumacher in *he following year. Klaproth 
first showed that it contained soda, and its composition was further 
established by Vauquelin, Berzelius, and Deville. 

Thomson's process consists in heating a finely divided mixture of 
cryolite and chalk in a reverberatory furnace, whereby carbon 
dioxide is expelled and calcium fluoride and sodium aluminate 
are formed, the roasted mass is lixiviated with water, so as 
to dissolve out the sodium aluminate, which is then treated with 
carbon dioxide. Alumina is precipitated, and sodium carbonate 
remains in solution. The alumina is either sold as such, or con- 
verted into sulphate (so-called "concentrated alum" or "alum- 
cake "), and the sodium carbonate is separated by crystallisation. 
Both products are obtained in a remarkably pure condition, and the 
cryolite-soda yields excellent " caustic." 

Thomson's process, although simple enough in principle, requires 
considerable skill and pains in its practical execution, and most of 
the manufacturing details were worked out by him, or under his 
direction. Success largely depends upon the maintenance of a 
proper temperature ; the decomposition begins below a red-heat, but 
requires to be finished at that temperature, and care must be taken 
to avoid fusion or even sintering of the mass. In 1854 Thomsen 
obtained the exclusive right of mining for cryolite and of working 
up the mineral in Denmark for soda and alumina. Actual manu- 
facturing operations were begun on a small scale in 1857, and in the 
following year Thomsen planned the present large factory at 
Oeresund, near Copenhagen, which was opened on his thirty-fourth 
birthday. The importance of this industry to Denmark may be 
seen from the circumstance that during the fifty years of its 
existence the firm have paici the Danish Government nearly 
300,000 for the concession. Other factories were started in 
Germany, Bohemia, and Poland, but met with little success. The 
Pennsylvania Salt-manufacturing Company at Natruiia, near 
Pittsburg, eventually obtained the right to work up two-thirds of 
all the cryolite mined in Greenland. Prom the start Thomsen took 
a large share in the management of the Oeresund works, and by 
his energy, foresight, and skill placed the undertaking on a sound 
commercial basis. 

Although Thnmsen died a rich man, mainly as the result of the 
industry he created, in the outset of his career as a teacher and a 
technologist his means were very straitened. He came of poor 
parents, of no social position or influence, and they were unable to 



158 TITORPE : THOMSEN MEMORIAL LECTURE, 

further his inclinations towards an academical career. In 1854 he 
applied unsuccessfully for a position as teacher of chemistry at the 
Military High School in Copenhagen. During three years from 
1856 to 1859 while still engaged in developing his cryolite process, 
he acted as an adjuster of weights and measures to the Municipality 
of Copenhagen. It was a poorly paid position, but it kept the 
wolf from the door. At about this period he betook himself to 
literature, and published a popular book on general subjects con- 
nected with physics and chemistry somewhat in the style of 
Helmholtz's well-known work entitled " Travels in Scientific 
Regions," which had a considerable measure of success. He was, 
however, not altogether unknown even at this time as an author, 
since in 1853 he had collaborated with his friend Colding in 
producing a memoir on the causes of the spread of cholera and on 
the methods of prevention, which attracted much attention at the 
time of its appearance. 

In 1859, whilst engaged in the Oeresund factory, he again 
applied to the authorities for a position as teacher at the Military 
High School, and succeeded in obtaining an appointment to a 
lectureship in physics, which he held until 1866. During his tenure 
of this office he devised his polarisation battery, which received 
many awards at International Exhibitions and was used for a time 
in the Danish telegraph service. 

In 1859-60 he was " vicarius " for Scharling at the University, 
and in 1865 became a teacher, and in the following year Professor 
of Chemistry and Director of the Chemical Laboratory, a position 
which he retained active to the last until 1901, when he retired 
in his seventy-fifth year of age. 

Before his connexion with the University, he founded and edited, 
from 1862 to 1878, in association with his brother, August Thomsen, 
the Journal of Chemistry and Physics, one of the principal organs 
of scientific literature in Denmark. 

In 1863 he was elected a member of the Commission of Weights 
and Measures, and was instrumental in bringing about the adoption 
of th& metric system and the assimilation of the Danish system to 
that of the Scandinavian Kingdom. 

In 1883 Thomsen became Chancellor of the Polytechnic High 
School of Copenhagen a position which he held for about nine 
years. During this period he entirely changed the character and 
spirit of the school, and stamped it with the impress of his earnest- 
ness and industry. Under his direction, new buildings were erected 
and arranged in accordance with the best Continental and American 
models. Thomsen's administration was in marked contrast to that 
of his somewhat easy-going predecessor, but it is doubtful if it 



THORPE: THOMSEN MEMORIAL LECTURE, 159 

brought him popularity in the school. The students respected and 
even feared him, but his cold and unsympathetic nature evoked 
no warmer feeling. It was said of him by one who knew him 
intimately that he never learned to draw the young to him, to 
create in them an interest for his work, to form a school. Thomsen 
was a homely man, but not even in his home, says the same 
authority, was it possible for him to change his active, earnest, 
strenuous disposition what his friends called his fighting character. 
But if he was always the serious master of the house, he was also 
its obedient servant. In reality he was a man of deep feeling, and 
was not without power to give that feeling expression in words, 
sometimes in verse, and occasionally even in music. 

It was while occupying the position of Director of the Chemical 
Laboratory of the University that Thomsen executed the thermo- 
chemical investigations which constitute the experimental develop- 
ment of the ideas he had formulated in his memoir of 1861. The 
results of these inquiries were first made known- in a series of 
papers published from 1869 to 1873 in the Transactions of the Royal 
Danish Society of Sciences, and from 1873 onwards by the Journal 
fur Praktische Chemie. The papers were republished in collected 
form in four volumes (1882-1886) by a Leipzig house under the 
title of Thermochemische- Untersuchungen. A summary of this 
experimental labour, which extended over a third of a century, 
was subsequently prepared by Thomsen, and published in 1905 in 
Danish under the title of Thermokemiske Eesultater. 

In this work he reviewed the whole of the numerical and 
theoretical results, to the exclusion of the greater portion of the 
experimental details. A translation of this volume by Miss 
Katharine A. Burke, entitled "Thermochemistry," renders it 
readily accessible to English readers. Miss Burke has supple- 
mented the original work by a short account, taken from the 
Thermochemische Untersuchungen, of the experimental methods 
employed, thereby rendering the whole more intelligible to the 
student. Moreover, in the English edition a partial attempt has 
been made to translate Thomsen's deductions into the language of 
modern theory based on the conception of ionisation, which, of 
course, was not known to science at the time the Thermochemische 
Untersuchungen was published. 

It is impossible within the limits of such a notice as this to deal 
in detail with the immense mass of experimental material which 
this work embodies, and I shall not attempt, therefore, to do more 
than to offer a generalised statement, based mainly upon the 
admirable account of Thomsen's work given by Professor Bronsted 
to the Chemical Society of Copenhagen on the occasion of the 



160 THORPE: THOMSEN- MEMORIAL LECTURE; 

meeting held on March 2nd, 1909, to commemorate Thomson's 
services to science. 

The conception of affinity as a cause and determining condition 
of chemical change is traceable in some of the earliest efforts to 
co-ordinate and explain chemical phenomena. It certainly existed 
long prior to the time of Boyle, and was at the basis of every 
philosophical system after his period. We need only mention the 
names of Bergman, Wenzel, and Berthollet to indicate this fact. 
But to Thomsen belongs the credit of being the first to make the 
attempt to measure the relative value or strength of affinity 
quantitatively, and to express it numerically in definite terms 
which admitted of exact comparison. Thomson's theory of affinity, 
as enunciated by him in his 1851 paper, was based upon his con- 
viction that affinity could be measured quantitatively bv estimating 
the amount of heat evolved in the chemical process. We are not 
immediately concerned to show whether the theory is right or 
wrong, or in what respect it fails. The point is that the enunciation 
of this principle upwards of half a century ago constituted an 
important step forward, inasmuch as it sought to estimate affinity 
in relation to a quantity which can be fixed by experiment, and is 
capable of expression by numbers. 

In this and in the subsequent paper of which mention has been 
made already, he thus defines his conception of thermochemistry, 
and discusses, for the first time, its laws. 

" The force which unites the component parts of a chemical 
compound is called affinity. If a compound is split up, whether 
by the influence of electricity, heat, or light, or by the addition 
of another substance, this affinity must be overcome. A certain 
force is required the amount of which depends on the strength of 
the affinity. 

" If we imagine, on the one side, a compound split up into its 
component parts, and on the other side these parts again united 
to form the original compound, then we haVe two opposite processes 
the beginning and end of which are alike. It is therefore evident 
that the amount of the force required to splil up a certain compound 
must be the same as that which is evolved if the compound in 
question is again formed from its component parts. 

" The amount of force evolved by the formation of a compound 
can be measured in absolute terms; it is equal to the amount of 
heat evolved by the formation of the compound. 

" Every simple or complex action of a purely chemical nature is 
accompanied by evolution of heat. 

" By considering the amount of heat evolved by the formation 
of a chemical compound as a measure of the affinity, as a measure 



.THORPE: THOMSEN MEMORIAL LECTURE. 161 

of the work required again to resolve the compound into its 
component parts, it must be possible to deduce general laws for the 
chemical processes, and to exchange the old theory of affinity, 
resting on an uncertain foundation, for a new one, resting on the 
sure foundation of numerical values." 

As has been proved by later theoretical and experimental investi- 
gations, the theory of thermochemical affinity is not absolutely 
correct at ordinary temperatures. But, on the other hand, it has 
been shown that a comparatively large number of processes are 
approximately in unison with it. Not only do they agree quali- 
tatively, that is to say, that heat is evolved during the process, but 
also in the fact that the results which newer and more exact 
methods for estimating affinity have produced, agree numerically 
with what would bo required by the thermochemical theory. We 
meet here with a fundamental phenomenon which Thomsen deserves 
great credit for having first poirted out, but the explanation of 
which could not be given at the time he indicated it. It can be 
demonstrated theoretically that the lower we reduce the tempera- 
ture and the nearer we get to the absolute zero, the more nearly is 
the condition for the theory fulfilled, so that at the absolute zero 
the theory would be found to be an exact law of nature. If it were 
possible to work at such low temperatures it would be found that 
the evolution of heat, or the evolution of energy by the chemical 
process, would be an exact measure of the affinity of the process, 
and that under this condition the theory of Thomsen would be the 
accurate expression of a natural law. 

But under ordinary conditions this is not so, for in reality an 
ever-increasing number of endothermic processes are found to 
occur, that is, processes which proceed with the absorption of heat. 
Thomsen tried at first to explain these phenomena in such a way 
as to keep them within his system, and he drew a distinction 
between a purely chemical process running confbrmably to his 
theory and a physico-chemical process which did not fall within 
the law. But he was gradually convinced that his theory could 
not be maintained in its entirety. It 'is to his credit that he did 
not seek to uphold an untenable principle, or try to defend it as 
did Berthelot, who almost to his dying day maintained the validity 
of the principle in spite of all facts. 

These ideas have, in the words of Ostwald, been the scientific 
confession of faith of chemists throughout half a century. They 
have had the greatest influence on scientific thought in every 
branch of chemistry. It is on the basis of them that we have 
arrived at a 'theory of affinity which at the present moment is 
being developed into one of the most perfect chemical theories, 



162 THORPE: THOMSEN MEMORIAL LECTURE, 

Lastl), it is due to these ideas that the experimental material has 
been produced which during all time will place the name of Julius 
Thomsen in the first rank of men of science. 

To go through this material in detail is, as I have said, impossible 
here. It may be stated generally that practically every simple 
inorganic process has been investigated calorimetrically by 
Thomsen, or can be calculated by means of the calorimetric data 
furnished by him. In the case of organic substances, data have been 
given for estimating the heat of combustion of a large number of 
compounds. All these estimations were made by Thomsen per- 
sonally, according to a pre-arranged plan, and in systematic suc- 
cession during a period of more than thirty years. They comprise 
more than 3500 calorimetrical estimations. It has been truly said 
that this work is unique in the chemical history of any country. 

Among the results of Thomson's thermochemical inquiries which 
have special value for physical chemistry is his investigation of the 
phenomena of neutralisation, in which he shows that the basicity 
of acids can be estimated thermochemically, and that it can in this 
way be proved whether or not a point of neutrality exists. His 
observation that the heat of neutralisation is the same for a 
long series of inorganic acids, such as hydrochloric acid, hydro- 
bromic acid, hydriodic acid, chloric acid, nitric acid, etc., supports 
the theory of electrical dissociation, inasmuch as this requires that 
the heat of neutralisation of the strong acids must in all cases be 
independent of the nature of the acid, because the process of 
neutralisation for all of them is the combination of the ion of 
hydrogen in the acid with the ion of hydroxyl of the base to form 
water. These investigations also led to the important thermo- 
chemical result that the heat of neutralisation of acids (or the heat 
of their dissociation) cannot be considered as a measure of the 
strength of the acids. 

Another important result is the proof by experiment of the 
connexion which exists between tile changes of the heat-effect with 
the temperature and the specific heat of the reacting substances. 
The first law of thermodynamics requires the relation indicated 

by Kirchhoff: d ~ =C r 1 -(7 2> where U is the heat>effect, T the 

CL J. 

temperature, and C^ and (7 2 are the heat capacities of the two 
systems before and after the reaction, and Thomsen showed by 
investigation of the heat of neutralisation, the heat of solution, and 
the heat of dilution, that this relation was satisfied For the 
purpose of his inquiry, the specific heats of a large number of 
solutions of salts were estimated by an ingenious method, and 
with an exactness hitherto unattained. 



THORPE : THOMSEN MEMORIAL LECTURE. 163 

Of no less importance are Thomson's thermochemical investi- 
gations on the influence of mass. In the year 1867 Guldberg and 
Waage published their theory of the chemical effect of mass. But 
they had only verified the theory to a small extent and in par- 
ticularly simple cases. They had not investigated the complete 
homogeneous equilibrium, because at that time no method existed 
for experimental investigation of such homogeneous equilibrium. 
Thomson showed that the estimation could be made thermo- 
chemically. By allowing, for instance, an acid to act on a salt 
of another acid in an aqueous solution, the latter acid will be 
partly replaced by the first, which will form a salt. By mixing, 
for instance, a solution of sodium sulphate and nitric acid, there 
is formed sodium nitrate and sulphuric acid, but the process will 
not proceed to completion. If we have estimated the heat of 
neutralisation of the two acids with sodium hydroxide, the difference 
between these two heat-phenomena will give the amount of heat 
corresponding to the total decomposition of the sodium sulphate, 
and the heat found experimentally by mixing the two solutions will 
therefore show to what degree the transformation has taken place. 
It would be possible to estimate thermochemically the amount of 
the four substances in solution, and thereby, by varying the con- 
centration or the proportion between the initial quantities of 
substances, to calculate whether the Guldberg- Waage theory- on the 
effect of mass was confirmed in this case. 

Thomsen applied this method to a large number of different 
acids and bases, and was enabled thereby to prove the agreement 
with the law of the influence of mass in all the cases which he 
examined. He found particularly that the proportion of the 
one acid which remained combined with the base was constant 
with mixtures of constant proportion. On this basis he propounded 
the term avidity, which he defined as the tendency of the acid to 
unite with the base, and he showed that the avidity was independent 
of the concentration, and only to a small extent varied wfth the 
temperature. The term avidity has since acquired great importance, 
particularly since other and more exact methods for its estimation 
have been found. Concurrently with this, its meaning has been 
made clear by the theory of electrolytic dissociation. 

On the basis of these estimations, Thomsen drew up the first 
table, based on experiments, of the relative strength of the acids, 
and the numbers in this table have been found to agree with the 
results obtained by examining the electrical conductivity of the 
acids. 

It is worth noting that Thomsen not only produced the experi- 
mental proof of the correctness of the Guldberg- Waage theory of 

2F 



164 THORPE: THOMSEN MEMORIAL LECTURE. 

the effect of mass soon after the appearance of this theory, but 
also that he was the first to acknowledge and adopt it. It is- 
remarkable that this work of Thomsen received so little attention, 
although it appeared in a widely circulated German journal, and 
it was not until ten years later that the law of the effect of mass 
was generally recognised, as the result of the work of Ostwald and 
van't Hoff. 

Although Thomson's title to scientific fame rests mainly upon 
his thermochemicat work, his interests extended beyond this par- 
ticular department of physical chemistry. He worked on chloral 
hydrate, selenic acid, on ammoniacal platinum compounds, and on 
glucinum platinum chloride, on iodic acid and periodic acid, on 
hydrogen peroxide, hypophosphorous acid, and hydrogenium. He 
early recognised the importance of Mendeleeff's great generalisation, 
and contributed to the abundant literature it produced. His paper 
of 1895, "On the Probability of the Existence of a Group of 
Inactive Elements/' may be said to have foreshadowed the 
discovery of the congeners of argon. He pointed out that in 
periodic functions the change from negative to positive value, or 
the reverse, can only take place by a passage through zero or 
through infinity; in the first case, the change is gradual, and in 
the second case it is sudden. The first case corresponds with the 
gradual change in electrical character with rising atomic weight in 
the separate series of the periodic system, and the second case 
corresponds with a passage from one series to the next. It therefore 
appears that the passage from one series to the next in the periodic 
system should take place through an element which is electrically 
indifferent. The valency of such an element would be zero, and 
therefore in this respect also it would represent a transitional stage 
in the passage from the univalent electronegative elements of the 
seventh to the univalent electropositive elements of the first group. 
This indicates the possible existence of a group of .inactive elements 
with the atomic weights 4, 20, 36, 84, 132, the first five numbers 
corresponding fairly closely with the atomic weights respectively 
of helium, neon, argon, krypton, and xenon (Zeitach. anorg. Chcm., 
1895, 9, 283; Journ. Chem. Soc., 1896, 70, II, 16). He subse- 
quently made known the existence of helium in the red fluorite 
from Ivigtut. 

As evidence of Thomson's manipulative ability and his power 
of accurate work may be mentioned his determination of the atomic 
weights of oxygen and hydrogen, and incidentally of aluminium. 
For the atomic weight of hydrogen he obtained the value 1*00825 
when O = 16, which is practically identical with that of Morley and 
Noyes. He further made most accurate estimations of the relative 






THORPE: THOMSEN MEMORIAL LECTURE. 165 

densities of these gases, and of the volumetric ratios in which they 
enter into the composition of water. His value for the atomic 
weight of aluminium is nearly identical with that adopted in the 
last Report of the International Committee on Atomic Weights. 

Thomsen maintained his interest in thermochemical problems up 
to the end, and was a keen and clear-sighted critic of the work 
which appeared from time to time during the later years of his 
life. This interest occasionally gave rise to controversy, and some 
of his latest papers were wholly polemical. 

Thomsen was a pronounced atomist, and to him a chemical 
process was a change in the internal structure of a molecule, and 
the chief aim of chemistry was to investigate the laws which 
control the union of atoms and molecules during the chemical 
process. He considered that chemistry should be treated 
mathematically as a branch of rational mechanics. But no one 
insisted more strongly than he how little we really know of these 
questions. In summarising his theoretical ideas in the Thermo- 
kemische Resultater, he says, " An almost impenetrable darkness 
hides from us the inner structure of molecules and the true nature 
of atoms. We know only the relative number of atoms within 
the molecule, their mass, and the existence of certain groups of 
atoms or radicles in the molecule, but with regard to the forces 
acting within the molecules and causing their formation or destruc- 
tion our knowledge is still exceedingly limited." He fully realised 
that his own work was only the foundation on which the future 
elucidation of these questions must rest. " He worked," says 
Bronsted, " in tlie conviction that what we somewhat vaguely call 
the affinity of the atoms their interaction, their attraction, and 
varying effect, etc. follows the general laws of mechanics, and that,, 
as he worded it, the principle that ' might is right/ holds good in 
chemistry as in mechanics. On this foundation he hoped to be 
able to evolve the laws for the statics and dynamics of chemical 
phenomena, even although the true nature of the action is 
unknown." 

Thomson's merits as an investigator received formal recognition 
from nearly every country in the civilised world. As far back as 
1860 he was elected one of the thirty-five members of the Danish 
Royal Society of Sciences of Copenhagen, and from 1888 until his 
death he was its President. In 1876 he became an Honorary 
Foreign Member of the Chemical Society of London. On the 
occasion of the fourth centenary of the foundation of the University 
of Upsala (created in 1477), he received the degree of Doctor of 
Philosophy honoris causa. In 1879 he was made an honorary M.D. 
of the University of Copenhagen. Two years later he was made a 



166 THORPE: THOMSEN MEMORIAL LECTURE. 

Foreign Member of the Physiographical Society of Lund, and in 
1888 he was elected a member of the Society of Science and 
Literature of Gothenburg. In 1885 he became a member of the 
Royal Society of Sciences of Upsala, and in 1886 of the Stockholm 
Academy of Sciences. 

In 1883 he and Berthelot -were together awarded the Davy 
Medal of the Royal Society a fitting and impartial recognition on 
the part of the Society of the manner in which the two investigators, 
whose work not infrequently brought them into active opposition, 
had jointly and severally contributed to lay the foundations of 
thermochemistry. 

In the same year Thomsen was made a member of the Accademia 
dei Lincei of Rome, and in the following year he was elected into 
the American Academy of Arts and Sciences in Boston, and of the 
Royal Academy of Sciences of Turin. In 1887 he was made a 
member of the Royal Belgian Academy: 

In 1886-87 and again in 1891-92 he was Rector of the University 
of Copenhagen. In 1888 he became Commander of the Dannebrog, 
and in 1896, and on his seventieth birthday, he was made Grand 
Commander of the same order. On the same occasion the Danish 
chemists caused a gold medal to be struck in his honour. In 1902 
he became a Privy Councillor (Geheime Konferenz raad). In the 
same year he was elected a Foreign Member of the Royal Society 
of London. 

He died on February 13th, 1908, full of years as of honours, 
and was buried on the eighty-third anniversary of his birth and 
on the jubilee of the opening of the Oeresund factory. His wife, 
Elmine Hansen the daughter of a farmer on Langeland pre- 
deceased him in 1890. 

I desire to express my acknowledgments to Director G. A. 
Hagemann, of Copenhagen, and to Professor Arrhenius, of 
Stockholm, for their assistance in obtaining information concerning 
Thomson's personal history. I am also much indebted to our 
Fellow, Mr. Harald Faber, for his kindness in making for me 
a translation of Professor Brb'nsted's account of Thomson's scientific 
work, on which my own resume is mainly based. 





[To face p. 167. 



BERTHELOT MEMORIAL LECTURE. 
DELIVERED ON NOVEMBER 23RD, 1911. 

By HAROLD BAM DIXON, M.A., Ph.D., F.R.S., Past-President 
of the Chemical Society. 

(1) His Career. 

IN this age of extreme specialisation, the life and work of Berthelot 
teach the world the much-needed lesson that men of science are 
not necessarily men of one idea, but may be great, not only as 
experimenters, but great also as thinkers and as citizens. On &U 
that he turned his mind to and few things were foreign to his 
interest Berthelot brought to bear, not only an exact scientific 
method and an exquisite clearness of statement, but an imagination 
as foreseeing as it was comprehensive, a patriotism as pure as it 
was enlightened. In the work of his life whether as a philosopher 
or as a Cabinet Minister Berthelot looked to Science as his guide. 
He believed in science as an illuminating and humanising force; he 
believed that in science lay the secret of the progress of France 
and of mankind. To pursue science was to ensure progress ; science 
was to him a mission, a recreation, a religion. " To the end of my 
life," he wrote half-sadly to Renan (in 1892); " I shall be the dupe 
of this desire for progress which you so wisely relegate to the 
sphere of illusions." But of the reality of the progress achieved by 
Berthelot no chemist can doubt. In the realm of industry alone 
what tempting offers were made to him for a monopoly of his 
synthetic processes in organic chemistry. But Berthelot never 
bargained with or patented his discoveries. " The man of science," 
he declared, " should make the possession of Truth his only riches." 
Not that Berthelot considered the applications of science beneath 
him; on the contrary, he believed that science should be pursued 
largely by reason of its service to mankind. "Science has a double 
aim," he wrote, " an ideal aim which is the search for pure truth, 
and a positive and human aim which is the good of man and the 
development of civilisation." 

Pierre Eugene Marcelin Berthelot* was born in the heart of the 
old Paris, in the Place de Greve now Haussmannised out of recog- 
nition into the Place de 1'Hotel de Ville on October 25th, 1827. 

* I am indebted to the kindness of Berthelot's son Prof. Daniel Berthelot for 
exact names and dates, and also for much other valuable information. I desire also 
to express my obligation to my old student, Mr. A. S. Robinson, for making me a 
precis of Berthelot's papers. 



168 DlXOtt: BERTHELOT MEMORIAL LECTURE. 

He died in Paris, March 18th, 1907. As he was born and bred, 
so he lived and died a Parisian. 

Through his father, Dr. Jacques Martin Berthelot, the son 
inherited his scrupulous regard for duty, his serious love for 
science, his liberal instincts, and his philosophic outlook on life; 
through his mother, Ernestine Sophie Claudine Beard, he inherited 
his ardent and responsive nature, his amazing industry, his versa- 
tility, and his curiosity. From the Place de Greve his family moved 
to a house near by in the narrow Rue des Ecrivains, just opposite 
the Tour Sainte- Jacques. The somewhat delicate and highly- 
strung boy grew up in sight of those royal ceremonials the Corpus 
Christi processions from the Tuileries to Notre Dame when people 
in the street were obliged to kneel, under penalty of sacrilege, as 
the procession passed. As a child the roar of the revolution must 
have sounded in his ears, for his father's house overlooked the 
scene of many of those deeds of violence that marked the popular 
upheaval against the Ordinances of the 25th of July (1830). Then, 
as again in the later revolutions, the house became a hospital 
equally for Royalist and for Republican, for Dr. Berthelot made no 
distinction between his patients, however much his sympathy went 
out to the suffering people. 

Even from the age of ten, Berthelot tells us, he began to ponder 
on the problems of life, and was troubled by the insecurity of the 
future. Nevertheless, he was an industrious and brilliant scholar, 
and made rapid progress at the school he attended -the College 
Henri IV. Sixty years later at the Jubilee Celebration, M. Fouque, 
the President of the Academie des Sciences, bore striking testimony 
to Berthelot's gifts as a boy. " Everyone admires in you your 
power of work, your spirit of invention, your logic of ideas, your 
grasp of memory, your skill in experiment. . .-. I affirm that these 
precious gifts you already possessed in the germ when you were 
still a simple schoolboy. More than half a century ago we sat 
side by side on the benches of the mathematical class in the College 
Henri IV.; a close comradeship grew up between us. My recollec- 
tions bring back with pleasure the long talks we had on every 
kind of question. ... I still see myself in discussion with you on 
the muddy road that led to your house at the foot of the Tower 
of Saint-Jacques. There I met the kindest greeting from your 
father, and then we climbed to your attic and resumed our inter- 
rupted argument our only distraction being the swallows that 
built among the sculptures of the old tower." 

At the end of his school course in 1846 he took the highest prize 
in competition with all the best students from the lycees of Paris 



: BfeBTHELOT MEMORIAL LECTURE. 

the " prix d'honneur de philosophic." To his sound classical educa- 
tion he attached great value, and his love of ancient literature 
lasted through life. Two old editions of Lucretius and of Tacitus, 
preserved from his schooldays, were his constant companions when- 
ever he left Paris. He quoted Horace familiarly, and he has told 
us that he soon recovered his Greek when he began to decipher the 
Alexandrine MSS. on Alchemy/ 

His school studies ovex, he made up his mind to pursue natural 
science as a career, and he even mapped out a programme for the 
methodical study of the principles of all branches of science in 
what he afterwards called the "naive confidence of youth." But, 
however much he may have had to curtail his educational ambition, 
he completed during the next few years a full medical course, he 
studied chemistry in the laboratory of Pelouze, and passed the 
University examinations for Bachelor and Licencie-es-Sciences. To 
carry out this programme he took a small lodging in the Rue de 
1'Abbe-de-rEpee, and attended the school of M. Crouzet. In this 
school happened that fortunate meeting between Berthelot and 
Ernest Renan the beginning of a friendship which became from 
that day a principal element in the lives of both. Renan, then 
twenty-two, had renounced his clerical orders, and retired from 
Saint-Sulpice. Lonely and depressed by his mental struggles, he 
had become an assistant master in the school, but could not shake 
off his melancholy. Berthelot spoke to him, the talk became 
intimate, something in each ardent nature was touched and 
responded, and the two were drawn together until soul reacted 
with soul like acid and alkali. " Our friendship," wrote Renan, 
" was something analogous to that of the two eyes when they fix 
upon the same object, and from the two images there results a 
single impression in the brain." Renan and Berthelot would take 
long walks together, and on Sundays would visit Neuilly, then in 
the country, where Berthelot's parents had taken a house, and 
always they discussed the eternal problems that torture the human 
mind. One day Renan called his young friend a "Revolutionist." 
But Berthelot had one sure faith, built on the ruins of other 
beliefs. "la Revolutionist," he cried, " clear your mind of that 
notion; call me rather an 'Evolutionist.'" We must remember 
that this was said a decade before Darwin gave us the " Origin of 
Species." 

The ideas resulting from their stimulating intercourse took 
different shapes in the two minds, and though Renan admitted his 
indebtedness to Berthelot, it is impossible for us, as it was for them, 
to separate what was due to each. On the monument of Berthelot 



170 DIXON: BERTHELOT MEMORIAL LECTURE. 

which is to be placed in the Gardens of the Luxembourg, the 
sculptor, Saint Marceau, has introduced the face of Kenan as a 
memorial of one of the most notable friendships of our time. 

Under Pelouze the experimental skill of the young chemist 
rapidly developed, and in 1850 he presented his first paper to the 
Academy of Sciences " On a simple method of demonstrating the 
liquefaction of gases." He showed how the gases chlorine, ammonia, 
and carbon dioxide could be liquefied in the capillary end of a 
glass tube by the expansion of mercury filling the body of the 
tube. When oxygen and nitric oxide showed no sign of liquefaction 
under pressures of 700 to 800 atmospheres he rightly concluded 
that under certain conditions of temperature it was not possible 
to liquefy gases by pressure alone. A second paper appeared in 
the same year, and in January, 1851, Berthelot received his first 
appointment, that of lecture-assistant to Balard, the discoverer of 
bromine, then Professor of Chemistry in the College de France. 
Unluckily the stipend was not a living wage 800 francs (32) a 
year and to earn a living Berthelot had to give private lessons. 
Luckily the official duties of the post were not heavy, and the 
resources of the laboratory were placed freely at his disposal by 
Balard, who in proposing him for the post wrote : " Everything 
allows us to hope that M. Berthelot will know how to utilise for 
the advancement of science the position I ask for him." In three 
years, from his appointment Berthelot had obtained his doctorate 
by his remarkable thesis, "On the combinations of glycerine with 
acids, and on the synthesis of the immediate principles of animal 
fats." A year later he began to publish his work on the sugars, 
and the same year (1855) made the memorable syntheses of ethyl 
alcohol from ethylene, and of formic acid from carbon monoxide, 
which revolutionised the accepted ideas on the formation of organic 
compounds. Then followed in quick succession researches on the 
synthesis of hydrocarbons, of methyl alcohol, and of oxalic acid. 
After eight years' brilliant work, Berthelot was appointed Professor 
in the Ecole Superieur de Pharmacie, where he lectured, but he 
continued to act as assistant and to research in the College de 
France. This was the first public recognition of his discoveries. 
Early in the following year (1860) this Society honoured itself and 
him by electing him a Foreign Member. At the invitation of 
Alexander Williamson, then President, Berthelot lectured before 
the Chemical Society, " On the synthesis of organic substances," on 
June 4th, 1863. It is pleasant to think that oar Chemical Society 
set, rather than followed, the fashion. 

With the appearance of his first book, "Organic Chemistry 
founded on Synthesis " (1860), the fame of Berthelot quickly spread. 



DIXON: BERTHELOT MEMORIAL LECTURE. 171 

The Jecker Prize was awarded to him in 1861 by the Academy of 
Sciences. The professors of the College de France, headed by 
Balard, petitioned the Minister of Public Instruction to found a 
Chair for Berthelot, and this movement resulted in his being 
appointed to a Professorship in the College in 1861, and finally 
(in August, 1865) in the formation of a special Chair of Organic 
Chemistry, which Berthelot held until his death. But though his 
early academic promotion was slow, honours came thickly to him 
in his middle age. The French Academy of Medicine elected him 
a member in 1863; he was elected to the Academy of Sciences in 
1873, and of this body he succeeded Pasteur as Perpetual Secretary 
in 1889. In 1900 he became one of the forty French Academicians. 

I cannot attempt any enumeration of the various learned societies 
of which he became an honorary fellow; I will only mention that 
he was elected a foreign fellow of our Royal Society in 1877, and 
that a Davy Medal was awarded in duplicate to him and to his 
friendly rival in thermochemistry, Julius Thomsen, in 1883, and 
that he received the Copley Medal, the highest distinction the Royal 
Society has to bestow, in 1900. 

On his appointment to a Professorship in the College de France, 
Berthelot was enabled to fulfil his engagement to Mademoiselle 
Sophie Caroline Niaudet, niece of M. Louis Breguet, a French 
Swiss, whose family had been prosperous manufacturers of scientific 
instruments for many years, and who himself was the constructor of 
a well-known telegraph and induction coil. The story goes that 
the Berthelot and Breguet families had been intimate for some 
years, but Marcelin had not lifted his eyes to the beautiful 
Mademoiselle Sophie until one day accident brought them into 
collision on the Pont-Neuf. She was crossing the long bridge in 
front of Berthelot, and making her way with difficulty in the teeth 
of a strong wind, when a stronger gust catching her skirt and 
Tuscan hat blew Mademoiselle round into the arms of her future 
husband. 

They were married on May 10th, 1861. Never was a happier 
match, or a more devoted family than Berthelot's. Madame Berthe- 
lot was endowed above most women with grace, with tact, and with 
sympathy ; she brought into his life that great gift of serenity which 
Berthelot regretted he had not inherited from his mother. Well 
might he have appreciated our homely English saying, "It's an 
ill wind that blows nobody any good." 

Busy in his laboratory by day and in his study by night, Berthelot 
took little part in public life under the imperial regime until the 
overthrow of Louis Napoleon and the siege of Paris in 1870. Then 
he threw himself whole-heartedly into the work of resisting the 



D1XON : BERTHELOT MEMORIAL LECTURE. 

invaders, and as president of the Scientific Committee of National 
Defence superintended the manufacture of explosives to be used 
against the enemy. After the war Berthelot continued the study 
of explosives, to which he applied all his experimental skill and the 
knowledge he had acquired in his thermochemical researches. In 
collaboration with Vieille he began a systematic investigation of the 
phenomena of explosions, which finally resulted, not only in the 
invention of a powder that gave to French arms for some years a 
remarkable superiority, but in the addition to science of a new 
chemical constant Vondt explosive. 

His work on the combination of nitrogen with organic bodies 
under the influence of the silent electric discharge turned his 
attention to the fixation of nitrogen by plants in the soil; in 1884 
a laboratory was built for him on the heights of Meudon, and here 
he devoted himself every summer to problems of vegetable chemistry. 
Determined to take his share in the government of his country, 
he was elected a Permanent Senator in 1881, and in 1886 became 
Minister of Public Instruction in the Cabinet of M. Goblet. Here 
he found the opportunity of impressing on his generation his 
strong convictions on the educative and liberalising power of 
science. But he was no advocate of an illiterate mechanical train- 
ing; he held firmly that science should be taught on the sound 
basis of a literary culture It was in this spirit that he met the 
demand for " technical education " which swept over Europe. 
Industry demands two things, according to Berthelot : capable 
directors and competent workers. To be capable the director must 
be a judge of men and a judge of things; he must be trained in 
literature, history, and science; the high school and the university 
will prepare him for hie business. To be competent the worker 
must be intelligent nd skilful; the elementary school and the 
workshop will fit him for his job. Berthelot saw no need for 
ordinary technical schools except as evening schools to help the 
workman. Can we yet say that Berthelot was wrong^? At all 
events, he knew what he wanted, and he helped France to get it. 

In 1895 Berthelot accepted the Portfolio of Foreign Affairs in 
the Bourgeois Cabinet. In this difficult post he had to negotiate 
the Anglo-French treaty dealing with the status and boundaries of 
Siam, whicli found herself in the uncomfortable position of " buffer " 
state between the French in Annam and the English in Burmah. 
Berthelot did not feel the duties of the Foreign Office congenial, 
and he resigned shortly after signing the treaty with Great Britain. 
But this, I think, we can say- that as a politician he had a sincere 
regard for England, and had he continued to guide the foreign 
relations of France the Entente, that has happily smoothed away 



DIXON: BERTHELOT MEMORIAL LECTURE. 173 

so many difficulties between the two nations, might have blossomed 
a decacU earlier. 

That Berthelot was a man of peace is evident from his book, 
" Science et Libre Pensee." It contains a strong plea for inter- 
national arbitration. Of Jlis other books mention must be made 
of his studies of the Greek and Arabian alchemistic writings. In 
1869 Berthelot visited Egypt, where his imagination was struck 
with the early records of chemical and metallurgical experiments 
and ideas. He returned to this subject later, and followed it up 
with his characteristic eagerness. By his influence he obtained the 
publication of many rare manuscripts on alchemy, which he edited 
in collaboration with M. Ruelle, "Collection des Alchimistes 
Grecs," and with MM. Duval and Houdas, "La Chimie au Moyen- 
Age." 

Few more interesting chemical papers have ever been published 
than the hundred and one preparations and recipes comprised in the 
Papyrus of Leyden translated by Berthelot. They reveal some of 
the methods of the Egyptian priesthood, who were the holders of 
the secrets of chemistry. How pithily is described the conversion 
of a copper vessel into a beautiful vase of gold (by rubbing it with 
gold amalgam and heating) a vase which will stand the regular 
test of the touch-stone! With what cynical pleasure Berthelot 
remarks that such a fraud was no doubt quite natural, and even 
commendable in the eyes of a priest ! 

In 1880 it was my great privilege to be introduced to Berthelot 
in his laboratory at the College de France by Sainte-Claire Deville 
and Alexander Williamson. I had just been showing for the first 
time non-explosive mixtures of dried carbon monoxide and oxygen 
at the British Association Meeting at Swansea. Deville was enthu- 
siastic over the discovery since it upset one of our cherished ideas; 
but Berthelot was more philosophical, Carbon monoxide was a 
gas, he said, "a little capricious" in its ways. One must repeat 
and again repeat such experiments. Most sound advice ! I had, by 
the way, been repeating these experiments for four years before I 
published them; and it was in "again repeating" them that, all 
unconsciously, I struck across one line of Berthelot's own work 
the measurement of the rate of explosion in gases. 

But except for this natural attitude of philosophic doubt 
Berthelot was kindness itself. We were taken to his home in the 
Institute, and were entertained by Madame Berthelot, whose silver 
hair heightened the saint-like beauty of her face. Berthelot was 
full of fire and quick replies. When Williamson rallied him on the 
rapidity with which his memoirs appeared, Berthelot replied, " Ah ! 
you English are too cautious, too frightened of committing your- 



174 DIXON : BERTHELOT MEMORIAL LECTURE. 

selves ; what is worth doing is worth publishing ! " It was perhaps 
characteristic of him that an hour before he had given me the 
opposite and better advice. 

Those who m'et Berthelot in his prime could not but be struck 
with the intellectual sincerity and the intense enthusiasm of the 
man. The broad forehead, the brilliant, blue eyes, the clean-cut 
features, and the thoughtful expression impressed all who saw him ; 
while his musical voice and clear enunciation charmed the ear. It 
would be impossible to forget that first impression. 

Students who attended his lectures speak in the highest terms 
of the inspiration they drew from his teaching. He gave of his 
best, and delighted to show his audience the new experiments he 
was engaged upon. But it was when he forgot the immediate 
experiment in hand, and began to think aloud, that the inspiration 
was highest. Here truly was science "in the making." 



(2) His Scientific Work. 

In considering the amazing output of scientific work we owe to 
Berthelot, it would be useless to enumerate, and hopeless to discuss 
individual memoirs. Luckily they can be grouped into well-marked 
divisions, for Berthelot always followed up a train of thought until 
some logical explanation was reached that satisfied his mind. Then 
some idea suggested by the first research was followed up experi- 
mentally until another generalisation was reached, and other trains 
of thought could be pursued. 

Study of Glycerine. As soon as he was installed in Balard's 
laboratory in the College de France, Berthelot took up a line of 
research which led him on to discoveries of the highest interest. 
He began to study the modes of combination of glycerine with acids, 
and proved that it was an alcohol capable of combining with acids, 
to form " etherial salts "- thus bearing out the views of Chevreul 
that fats were " compound ethers," and justifying the modern name 
"glycerol "; but he also showed that glycerol differed from ordinary 
alcohol by its ability to combine with three equivalents of an acid 
instead of with one, just as phosphoric acid differs from nitric acid 
in combining with three equivalents of a base. By what seems a 
curious mental slip Berthelot likened the three classes of esters 
formed by glycerol to ortho-, para-, and meta-phosphates, instead 
of to their true analogues, the three salts of ortho-phosphoric acid. 
Wurtz not only made the correction, but by his synthesis of glycol 
the " diatomic " intermediate between the " monatomic " alcohol 
and the " triatomic " glycerol confirmed the importance of 
Berthelot's discovery. The work of Berthelot and Wurtz on the 



DIXON: BERTHELOT MEMORIAL LECTURE. 175 

polyatomic alcohols must rank in importance with that of Liebig 
on the organic polybasic acids. I think also, it is clear that the 
analogies shown by alcohols to inorganic bases and I may specially 
mention the analogy between glycerol and bismuth hydroxide 
pointed out by Odling led to the general adoption of the idea of 
valency which had been given to chemistry by Edward Frankland. 
The proof that glycerol is an alcohol led Berthelot to prepare and 
examine many other bodies of a like nature. We are indebted to 
Berthelot for a considerable number on the list of substances recog- 
nised as alcohols, and we constantly employ his method of 
acetylisation as the means of recognition. 

Synthesis of Organic Substances. I can only make a passing 
mention of very few of the many compounds of glycerol prepared 
by Berthelot by submitting it to the action of acids. Hydriodic 
acid, he found, yielded two substances, wopropyl iodide and allyl 
iodide; from the latter he made for the first time artificial oil of 
mustard. 

The curious reducing power of hydriodic acid, especially at a high 
temperature, he afterwards made good use of in reducing benzene- 
to hexane-derivatives (1867). But the most stimulating thing to 
Berthelot's mind was the discovery that glycerol would combine, if 
time were given it, with all sorts of different acids, producing new 
fatty bodies, and that one could predict the formation of an endless 
number of new structures through a "creative power greater than 
that realised in nature." This idea, once planted in his mind, 
grew apace. He sought and found methods for preparing the 
simpler types of organic compounds, and from these to pass on 
to the higher and more complicated. To appreciate the boldness 
of Berthelot's conceptions we must remember the firm conviction 
that chemists held throughout the first half of the last century, that 
there was a gulf fixed between inorganic and organic substances; 
the chemist might build up, or synthesise, inorganic salts, but he 
could only break down, or analyse, the substances created in plants 
and animals by the " vital force." This gulf had not been really 
passed in the eyes of most chemists by the synthesis of urea by 
Wohler or the formation of acetic and propionic acids from their 
nitriles by Kolbe and Frankland, for the cyanides from which these 
substances were formed were regarded as organic products 
themselves. 

Berthelot's first success on his new path came in 1855. He shook 
up pure sulphuric acid in a large globe holding 32 litres of ethylene 
gas until 30 litres of the gas had been absorbed. The liquid was 
then mixed with water and distilled. The liquid coming over was 
dried and redistilled until 45 grams of a liquid having all the 



176 DIXON: BERTHELOT MEMORIAL LECTURE. 

properties of pure alcohol were obtained. But the original ethylene 
had itself been obtained from alcohol so the synthesis might be 
said to be contaminated at its source. Berthelot next prepared 
ethylene iodide from coal gas, and from this prepared a sample of 
ethylene, which he treated as before. It yielded alcohol, which was 
thus made for the first time without fermentation. 

Now since ethyl alcohol on heating with sulphuric acid yields 
ethylene and water, and formic acid on heating with sulphuric 
acid yields carbon monoxide and water, if the first process can be 
reversed, it might be predicted that the second would also : 



CH 2 2 = CO + H 2 0. 

Berthelot placed 10 grams of potash in a half -litre flask, which he 
filled with carbon monoxide, sealed, and heated for three days on 
a water-bath. When the flask was opened under mercury the gas 
was found to be completely absorbed; on dissolving the potash 
salt in dilute sulphuric acid and distilling, Berthelot obtained a 
distillate of formic acid. 

In the following year (1856^ a more difficult synthesis was effected 
that of marsh gas, together with ethylene and acetylene. Formic 
acid on heating yields all its carbon as carbon monoxide and its 
hydrogen as water; but if there is present a strong b'ase, which 
might cling to some of the carbon, a substance containing carbon 
and hydrogen might be evolved. Berthelot prepared formic acid 
on a large scale from carbon monoxide, combined it with baryta, 
and distilled the barium formate at a red heat. He condensed a 
small amount of liquid, caught the unsaturated hydrocarbons in 
bromine, and collected the marsh gas over water. The unsaturated 
hydrocarbons were ethylene and propylene. On decomposing their 
bromides by means of water and copper fofl in thick glass tubes 
at 275, Berthelot regenerated the ethylene and propylene, and 
found about 10 per cent, of acetylene the result of a secondary 
action. From this ethylene he again prepared pure alcohol. 

Berthelof's next starting point was carbon disulphide. If carbon 
disulphide were heated with a metal capable of combining with the 
sulphur, while at the same time hydrogen were liberated in contact 
with the nascent carbon, the two might combine to form a hydro- 
earbon. Passing hydrogen sulphide and carbon disulphide vapour 
through a broad tube packed with copper turnings freshly reduced 
and heated to a dull red heat, Berthelot condensed a trace of 
naphthalene, and collected ethylene in bromine and marsh gas over 
water. Iron acted in the same way as copper, and hydrogen 
phosphide and steam could be used instead of hydrogen sulphide, 



DIXON: BERTHELOT MEMORIAL LECTURE. 177 

Berthelot regenerated the ethylene as before (finding acetylene 
produced), and prepared alcohol from it. One cannot help feeling 
in reading Berthelot's account of this experiment that in his mind 
the ethylene (with its resulting alcohol) was more important than 
the marsh gas. But a year later Berthelot chlorinated marsh gas 
in diffused daylight, separated the methyl chloride from the residual 
marsh gas and higher chlorides by solution in anhydrous acetic 
acid, and prepared methyl alcohol from the chloride. 

Just as Berthelot had got ethyl alcohol from ethyiene and 
sulphuric acid, so he obtained propyl alcohol from propylene and 
sulphuric acid. The propylene was prepared from the propyl 
iodide obtained from glycerc! and phosphorus iodide. Again he 
showed that the higher olefmes could be combined with hydrogen 
chloride and the chlorides turned into the corresponding alcohols 
a general method by which he prepared many alcohols; and vice 
versdy by abstracting the elements of water the olefines could be 
prepared from the alcohols. Again, as barium formate yielded 
on distillation several hydrocarbons, so might the acetate of sodium 
yield other hydrocarbons than marsh gas. Berthelot found that it 
yielded higher olefines as well, namely, propylene, butylene, and 
amylene. 

But among the most memorable of Berthelot's syntheses was the 
direct combination of hydrogen and carbon in the electric arc to 
form acetylene (1862), and the condensation of acetylene into 
benzene (1866); thus the barrier between inorganic and organic 
chemistry was broken down at all points, and Berthelot's disciples 
could exclaim with justice: "There is but one chemistry, and 
Berthelot is its propLet." 

In working on acetylene Berthelot investigated the properties of 
the acetylides of silver and copper. This work led him in 1866 to 
make the suggestion that the mineral oils found in the earth might 
have been formed from acetylene produced by the action of water 
and carbonic acid on the acetylides of the alkali metals. By 
reducing the carbonaceous matter found in meteorites he produced 
some liquid petroleum. 

A ction of Heat on Hydrocarbons. Berthelot's work on the hydro- 
carbons included a study of the mode in which these bodies behave 
at a red heat. A hydrocarbon, he says, is not directly resolved into 
its elements, but either polymerises (for example, acetylene into 
benzene) or by a condensation of two or more molecules forms a 
denser hydrocarbon with elimination of hydrogen; thus marsh gas 
gives mainly acetylene and hydrogen, ethane yields ethylene and 
hydrogen, while ethylene yields mainly acetylene and hydrogen. 
Acetylene itself is not resolved into its elements, but polymeri 



ses 



178 DIXON: BERTHELOT MEMORIAL LECTURE. 

or condenses with hydrogen or other hydrocarbons into compounds 
of great density naphthalene, anthracene, etc. When carbon is 
finally separated, it is therefore not a simple molecule, but in the 
form of a highly complex group of atoms corresponding with the 
dense hydrocarbons yielding it. This attractive theory of Berthelot 
has not, however, been fully borne out by later work. Sir Edward 
Thorpe showed that the decomposition of a paraffin (under heat 
and pressure) gave rise to the formation of an olefine and a lower 
paraffin; and Haber showed that ?i-hexane gave methane and 
amylene, but confirmed Berthelot's observation that benzene con- 
densed to diphenyl with loss of hydrogen. Bone and his colleagues 
have shown that methane is formed directly from its elements 
between 1000 and 1200, and breaks up again into carbon and 
hydrogen without forming acetylene. Ethylene, on the other hand, 
gives acetylene, which itself can either recombine with hydrogen 
or break down into carbon and hydrogen. 

Action of Mass. The observation made by Berthelot that time 
was required for the union of glycerol with acids led him, in con- 
junction with his pupil, Pean de St. Gilles, to investigate the course 
of the reaction between alcohols and acids, especially that between 
ethyl alcohol and acetic acid. Here, again, Berthelot was a pioneer 
in a subject that had hardly been touched experimentally. He 
found that when equivalent amounts of alcohol and acid are 
brought together, the reaction proceeds slowly (at a rate depending 
on the temperature) until a limit is reached, and that the same 
limit is reached when the corresponding amounts of ester and water 
are brought together. "An equilibrium is established between 
the affinity of the acid for the alcohol, which tends to unite them, 
and the inverse affinity of the water for the neutral ether, which 
tends to regenerate the acid and the alcohol." We can put the 
result into an equation : 

C 2 H 3 2 -C 2 H 5 xH 2 =4 
O 2 H 4 O 2 x C 2 H 6 O 

It is clear, I think, that Berthelot regarded the equilibrium as a 
statical, and not as a dynamical, one; he did not see that the two 
opposite reactions were taking place at the same time; Guldberg 
and Waage recognised this, and used Berthelot's figures in illus- 
tration of their principle. Nevertheless, Berthelot and St. Gilles' 
memoirs form the starting points of much of the subsequent work 
on equilibrium and mass action. They showed the effect on the 
equilibrium of varying the amounts of one of the reacting sub- 
stances; they showed that an increase of temperature or of con- 
centration greatly shortened the time for the equilibrium to be 



DIXON: BEBTHELOT MEMORIAL LECTURE. 179 

reached, although pressure alone had little effect. They suggested 
an equation for the determination of the velocity of a bimolecular 
reaction similar to that of Harcourt and Esson. Few researches 
indeed have been more fruitful in physical chemistry than those of 
Berthelot and St. Gilles. 

Of other equilibrium problems Berthelot was the first to investi- 
gate the partition of a dissolved substance between two solvents. 
He showed, for instance, that when succinic acid is dissolved in 
ether and water, the coefficient of distribution is constant whatever 
the amounts dissolved; but other substances showed a variation 
with concentration, an anomaly explained by Nernst in 1891 as 
due to a difference of the molecular aggregation of the substance in 
the two solvents. In 1875 Berthelot studied the partition of acids 
between several bases in solution. 

Thermochemistry. Berthelot 's great work on thermochemistry 
was begun in 1863, and was continued until 1879, when he published 
the two volumes entitled, " Mecanique C'himique fondee sur la 
Thermochimie." This and his later book, " Thermochimie, Donnees 
et Lois numeiiques," constitute a monument of elaborate experi- 
ment and calculation, which men of science rank alongside the 
" Thermochemische Untersuchungen," the life-work of Julius 
Thomsen. It is not at all to the disadvantage of Chemistry that, 
the Frenchman and Dane worked in rivalry. When we want to 
know the heat of formation of any compound we look up the two 
authors, and if they agree we are entirely satisfied. I think each 
respected the other's work. I can point to an instance the heat 
of formation of ammonia where Thomsen corrected his first result, 
and to another the heat of formation of ethane where Berthelot 
corrected his; in each case as the result of the other's work. They 
both put forward a theorem, though not quite in the same terms, 
that every action of a purely chemical nature gives out heat and 
produces the result that is accompanied with the maximum evolu- 
tion of heat. Berthelot defended with great skill his " principle of 
maximum work " ; it required the genius of Helmholtz and Boltz- 
mann to prove that the principle required that the heat of reaction 
should be independent of the temperature, and was only strictly 
true at absolute zero. JBut although these limitations must be 
accepted, and Berthelot finally accepted them, the " law " is never- 
theless a useful guidft which is often appealed to. Was not Deacon 
inspired by Berthelot's ideas when he sought and finally found a 
practical method of liberating chlorine from hydrochloric acid by 
the oxygen of the air? 

Much of the apparatus devised by Berthelot for his thermo- 



180 DIXON: BERTHELOT MEMORIAL LECTURE. 

chemical determinations has come into general use; in -particular, I 
may mention his " calorimetric bomb " for combustions in oxygen 
under pressure. 

Explosions. Berthelot's experiences in the war led to his system- 
atic work on explosives and on the theory of explosions. In conjunc- 
tion with Vieille he studied the rapidity of combustion and the 
heat of reaction of various explosives. In July, 1881, he published 
his first short paper on the explosion-wave in gasee. He states that 
he would not have published it had not MM. Mallard and Le 
Chatelier sent him their memoir on the same subject, which they 
had attacked by a different method. It is a curious coincidence 
that a few months before I had myself begun to measure the rate 
of explosion of carbon monoxide and oxygen with different quanti- 
ties of water-vapour, and found that the. accepted rate was altogether 
too slow. 

Berthelot's first paper contains the germ of his theory the 
identity of the rate of explosion with the mean velocity of the 
molecules formed in the reaction before any heat had been lost. 
Other papers quickly followed. Berthelot made the important 
discovery that the rate of explosion rapidly increased from the 
point of origin until it reached a maximum which remained con- 
stant, however long the column of gases might be. This maximum 
Berthelot stated to be independent of the pressure of the gases, 
of the material of the tube, and of its diameter above a small limit. 
The rate of explosion thus forms a new physico-chemical constant, 
having important theoretical and practical bearings. The name 
" 1'onde explosive " was given by Berthelot to the flame when 
propagated through an explosive mixture of gases at the maximum 
velocity, and this velocity could be predicted if the heat of combina- 
tion and the density and specific heat of the products were known. 
For instance, the total heat given out when hydrogen and oxygen 
combine is known. If this heat is contained in the steam produced, 
its temperature may be calculated if its heat capacity be known; 
and if the temperature of the steam be known, the mean velocity 
with which the molecules must be moving can be calculated. Now 
Berthelot supposed that the heat is all contained in the steam 
produced. He assumed that the heat capacity of steam was the 
same as the sum of those of its constituents; and he supposed, 
moreover, that the steam was heated at constant "pressure. Making 
these assumptions, he calculated out the theoretical mean velocity 
of the products of combustion of various mixtures, and found a close 
accordance between these numbers and the explosion rates of the 
same mixtures. He concluded that the explosion-wave was propa- 
gated by the impact of the products of combustion of one layer 



DIXON: BERTHELOT MEMORIAL LECTURE. 181 

upon the unburnt gases in the next layer, and so on to the end of 
the tube at the rate of movement of the products of combustion 
themselves. If this theory be true, it accounts, not only for the 
extreme rapidity of explosion of gaseous mixtures, and gives the 
means of calculating the maximum velocity obtainable with any 
mixture of gases, but it aUo affords information on the specific heats 
of gases at very high temperatures, and explains the phenomena 
of detonation whether of gases or of solid or liquid explosives. 

Table I shows the explosion rates found by 'Berthelot, compared 
with the theoretical velocity of the products of combustion : 

TABLE I. 

Velocity in 
metres per second. 



Gaseous mixture. Calculated. Founl. 

Hydrogen and oxygen H g +0 2830 2810 

Hydrogen and nitrous oxide H 2 +N 2 O 2250 2284 

Carbon monoxide and oxygen CO +0 1940 1090 

Carbon monoxide and nitrous oxide ... CO +N 2 1897 1106 

Marsh gas and oxygen CH 4 +0 4 2427 2287 

Ethylene and oxygen ... C,H 4 + 6 2517 2210 

Cyanogen and oxygen C 2 N 2 +0 4 2490 2195 

Acetylene and oxygen C S H 2 + 8 2660 2482 

Two facts established by these experiments impressed on me the 
conviction that Berthelot might have found the true theory of 
explosions : first, the close coincidence between the rates of explosion 
of hydrogen (both with oxygen and nitrous oxide.) and the calculated 
mean velocities of the products of combustion; and, secondly, the 
great discordance between the found and calculated rates for 
carbonic oxide with both oxygen and nitrous oxide, for I had 
previously discovered that pure carbon monoxide cannot be 
exploded either with pure oxygen or pure nitrous oxide. The dis- 
cordance found by Berthelot was what I should have expected from 
my own experiments. Again Berthelot examined the effect of inert 
gases in damping down the velocity of the explosion-wave; for 
instance, on adding nitrogen to different explosive mixtures he 
found : 

TABLE II. 

Velocity in 
meti* s per second. 

Gaseous mixture. Calculated. Found. 

H 2 + 0...... 2831 2810 

H 2 +0 + N, 1935 2121 

H 2 + + 2N 2 1820 1439 

CH 4 + 20 2 : 2427 2287 

CH 4 + 20 2 + 2N 2 2002 1858 

C 2 N + 20 a f;.\*^\'/Si;*;2i 2490 2195 

C 2 N 2 ' + 20 2 +N 2 . 2334 2044 

' C a N 2 +20 a +2N 2 2152 1203 



182 DIXON: BERTHELOf MEMORIAL LECTURE. 

These experiments seemed to Berthelot to show that a small 
amount of inert gas does not prevent the propagation of the true 
explosion-wave, but damps it down according to its calculated 
effect. A large amount of inert gas, on the other hand, destroys 
the character of the explosion-wave which must always be 
regarded as the " maximum possible " velocity. 

In comparing the rates of explosion determined in his tube with 
those calculated from his formula, Berthelot, I think, was not 
justified in his argument that the specific heats of the gaseous 
products must be reckoned as at constant pressure, since the whole 
change took place in a closed tube. In the damping experiments 
with nitrogen he did not allow for the fact that with inert gases 
a longer run is required before the explosion-wave is set up, and 
he began to time the flame before it had acquired its maximum 
pace. In the cyanogen experiments he did not appreciate the fact 
that in the wave-front the carbon only burns to carbon monoxide. 
But in spite of these criticisms, which required years of work to 
establish, I have always thought it one of Berthelot's strokes of 
genius to identify the maximum velocity of the flame with the 
mean translational velocity of the molecules themselves, a concep- 
tion which all later investigators have used in working out the 
propagation of an intense pressure-wave which preserves its type 
by being continually reproduced from point to point by the 
chemical action. 

Fixation of Atmospheric Nitrogen. In Berthelot's synthetic 
researches we find him using the silent electric discharge to cause 
nitrogen to enter into combination, for example, as in the direct 
formation of hydrocyanic acid from acetylene and nitrogen. This 
fixation of nitrogen led him to investigate its absorption by plants, 
and generally the action of electricity on vegetable growth in his 
laboratory at Meudon. Berthelot asserted that free nitrogen could 
be assimilated by plants, a statement that was vehemently opposed 
until Hellriegel proved that leguminous plants can take up nitrogen 
through the agency of bacteria. Berthelot was the first to point 
out that atmospheric nitrogen was fixed in the soil by micro- 
organisms, a new departure of supremo interest to agriculture. 
Among other developments of Berthelot's idea, Dr. E. J. Russell 
has recently shown how the fertility of a soil might be enormously 
increased by killing off the infusorial enemies of these bacteria. 
Four solid volumes, entitled, " La Chimie vegetale et agricole," 
published in 1899, contain the record of Berthelot's work at 
Meudon. 

Looking back at the enormous mass of experimental detail 
published by Berthelot I am astonished at the small percentage of 



DIXON : BEBTHELOT MEMORIAL LECTURE. 183 

error that has been detected. The accuracy of his experiments is 
really marvellous. It is not in his experiments, but in his inter- 
pretation of them that Berthelot has to meet criticism. Although 
Berthelot was a rapid worker, he was a still more rapid thinker. 
Not once or twice, but almost throughout the range of his researches 
we see the theoretical conception outstripping the experiment. 
Sometimes deliberately, sometimes unconsciously, he chooses his 
experiments to illustrate his theory. It is a question of idiosyn- 
crasy; genius must work its own way. The nineteenth century 
praised Dalton for basing his Atomic Theory on the sure foundation 
of the Law of Multiple Proportions; the twentieth century knows 
that Dalton sought for cases of multiple proportion to support his 
preconceived theory of atoms. 

Berthelot's imagination gives a distinction to all his work; his 
rapidity of generalisation fascinates us, and compels our interest. 
Can we say which, is the better for knowledge on the one hand, 
the dashing advance of an explorer into an unknown country, the 
rapid survey, the approximate location of a great lake and a great 
mountain range, and the publication of a fascinating sketch-map 
giving us the possible sources of a Nile or a Congo ; or, on the other 
hand, the deliberate advance of a surveyor with his levels and 
theodolites? May it not with justice be maintained that had it 
not been for the pioneer and his map the surveyor would never 
have started at all ? Berthelot might rightly claim that he had 
pointed out the trend of the country and the possibilities that lay 
that way, and had stimulated the curiosity of the exploring world. 
" For myself," he wrote, " I shall be happy if, in the development 
of science, some of my results are valued some day as the origin 
of the discoveries of the future." I believe this was no conventional 
phrase of self-depreciation, but an expression of his thought used 
in all sincerity. 

Again, like other great men, Berthelot found it hard, even when 
the creatures of his thought had been proved to be " unemployables," 
to dismiss them from his service. I ventured just now to compare 
Berthelot's mode of thought with Dalton's. May we extend the 
parallelism further, and say that the intensity of conception in the 
mind of each was sometimes too strong to yield to facts ? Dalton, 
firm in his conviction that different elements had atoms of different 
sizes (the very genesis of his theory), could see neither the relevancy 
of Gay-Lussac's Law of Volumes nor the beauty of Avogadro's 
explanation. For him the formula of water was always HO. 
Berthelot, equally firm in his conviction that in chemical reactions 
we are dealing with "equivalents," could see the force of Gay- 
Lussac's experiments, but not of Avogadro's argument. For him 



184 DIXON: BERTHELOT MEMORIAL LECTURE. 

the formula of water (the molecule occupying 2 volumes) was 
H 2 O 2 . 

If we, then, as the result of the steady progress of experiment 
and thought, can see the limitations of Berthelot's vision, we can 
also, I hope, appreciate the brilliancy of the conceptions that guided 
his work, and the intensity of the stimulus given by his ideas to 
contemporary science. 

(3) The Last Phase. 

Berthelot enjoyed a wonderfully active and honoured old age. 
To celebrate his seventy-fifth birthday and the jubilee of his first 
appointment in the College de France, his colleagues inaugurated 
a great meeting of congratulation, and commissioned M. Chaplain 
to design a medal in his honour. 

The Chamber of Deputies and the Senate declared that the 
occasion demanded a public ceremonial, in which the State should 
participate. Abroad, all the great societies passed resolutions con- 
gratulating Berthelot on his achievements^ and sent delegates to 
present their felicitations in person. The meeting was held in the 
great hall of the Sorbonne on November 24th, 1901. Berthelot 
declined the procession and the military escort offered by the State, 
and went oh foot to the hall. He was received by the President 
of the Republic. Then amid the acclamation of his colleagues, who 
thronged the hall, he heard perhaps for the first time from the 
mouths of his most distinguished contemporaries the deep veneration 
in which the world held his genius and his career. In acknowledg- 
ing this great demonstration, Berthelot once more insisted on the 
humanising ^spirit of science. "It is not," he cried, "for the satis- 
faction of our private vanity that the world to-day pays homage 
to men of science. No! it is because it knows that the man of 
science really worthy of the name corisedrates his life disinterestedly 
to the great work of our age the amelioration of the lot of all, the 
rich and the happy, the poor and the suffering. It is this that my 
friend Chaplain has sought to express on the beautiful medal which 
the President of the Republic is to offer me. I know not if I have 
completely fulfilled the noble ideal the artist has drawn, but at 
least it has brought me strength to have made this the aim that has 
directed my life." 

"Pour la Patrle et la Verite" the design was well chosen by 
Chaplain to sum up Berthelot's career. 

Berthelot continued to work to the end. Although he ceased to 
lecture, he seldom passed a day without visiting his laboratory. 
There and in his home he found his happiness, for husband and 
wife seemed to grow nearer as the years went by. In his last months 



D1XON: BERTHELOT MEMORIAL LECTURE. 185 

he had the sorrow of losing a daughter and then a beloved grandson. 
The shock preyed on his wife, who developed heart disease. Berthe- 
lot, himself a victim to the same disease, watched assiduously at 
her bedside, and wasted his strength in his nightly vigils over her. 
A Sunday came when she seemed better, and Berthelot visited his 
laboratory at Meudon, where he was studying the effects of radium 
emanations on vegetation. On his work table there was found 
afterwards an alchemic manuscript from Morocco, written in 
Hebrew, which he was deciphering, for he had not forgotten the 
early lessons he had received from Kenan. 

He returned to find his wife failing, and they both knew the end 
was near. " What will become of him when I am no longer there ? " 
were the last words she spoke to her daughter. Berthelot was alone 
with his wife when she died. He called his children, kissed the dead, 
walked into the next room, and threw himself upon a couch. One 
of his sons followed him, and hearing him sigh, ran to seize his 
hand. But the hand was lifeless : he had joined his beloved one. 

The pagan poet whom Berthelot loved has perhaps made us feel 
most keenly the cry of the heart that cannot survive separation : 

" Ah ! ie meae si par torn animae rapit 
Maturior vis, quid moror altera, 
Nee cams aeque nee superstes 
Integer ? I lie dies utramque. 

Ducet ruinam. Non ego perfidum 
Dixi sacramehtum. Ibimus, ibimus 
Utcumque praeccdes, supremnm 
Carpere iter comites parati." * 

The state procession and military escort which Berthelot had 
declined alive, were fitting attendants round the hearse that bore 
the bodies of husband and wife to honourable sepulchre in the 
Pantheon. 

So passed away a great man, full of years and honour. To 
France and to Science he gave his life, and he was not without 
reward in the love and veneration of his countrymen. Happy the 
country that produces such genius; happier still the country that 
can appreciate and use it. 

* At the request of the Publication Committee, I subjoin the English renderin 
of these stanzas I gave at the Lecture : 

'" If Death, untimely, snatch away 

That half ah ! dearer half ray soul. 
Why should this other half delay ? 
Could life be sweet no longer whole ? 

The day that strikes thee strikes us both : 

Together, when thou goest, we go 
Sworn comrades ('tis no idle oath) 

To tread the last long path below." 

Horace II. xvii. 




[To face p. 187i 



MOISSAN MEMORIAL LECTURE. 

DELIVERED ON FEBRUARY 29iH, 1912. 

By SIR WILLIAM RAMSAY, K.C.B., F.R.S. 

FRANCE has always held one of the highest places among the 
nations in the brilliance and originality of her sons. In the domain 
of chemistry, especially, many names of illustrious Frenchmen 
suggest themselves ; Lavoisier, Guyton de Morveau, Berthollet, 
Gay-Lussac, Dumas, and Berthelot stand out among a crowd of 
others hardly less distinguished. We have recently heard from 
the eloquent lips of our late President, Professor Dixon, a charming 
account of the life and work of the last named of these eminent 
men ; it is my duty to-night to ask you to listen to a brief Discourse 
on a contemporary of Berthelot's, who, though cut off by fate at a 
comparatively early age, stood only second to him among the 
representatives of chemistry in France in his time. 

Henri Moissan was born in Paris on September 28th, 1852. His 
father was a native of Toulouse; his mother, whose maiden name 
was Mitelle, was of an Orleans family. Moissan's features and 
his bright, vivacious manner betrayed his southern origin; he was 
of the best French type.* 

His education, after school life, began in the College de Meaux, 
and in his twentieth year he entered the laboratory of Fremy at 
the Muse"e d'Histoire Naturelle attending at the same time the 
lectures of Henri Sainte-Claire Deville and Debray. He made 
good progress, and after spendyig a year at elementary ' work he 
removed to the neighbouring laboratory of Decaisne and Deherain, 
in the Ecole Pratique des Hautes Etudes, with whom he worked 
on practical problems bearing on vegetable life. Whilst there, he 
passed the examinations required for graduation, taking the pre- 
liminary degree of Bachelier in 1874; of Licentie in 1877; in 1879 
he became " Pharmacien de premiere Classe"; and in 1880 he 
qualified as "Docteur es Sciences physiques." 

After working with Deherain for little more than a year, he 
left the Museum to direct a small laboratory of his own ; and he then 
abandoned the study of vegetable chemistry for that of inorganic 
chemistry, a branch to which he remained faithful during the rest 
of his life, and in which he achieved the highest distinction. This 

* Madame Moissan has had the kindness to place at my disposal the photographs 
and specimens exhibited during the lecture. 

,G 



188 RAMSAY: MOISSAN MEMORIAL LECTURE. 

private laboratory was given up somewhat later; and he then 
found quarters with MM. Debray and Troost, in the laboratories 
of the Sorbonne, of which in after time he was to become Director. 

In 1879 he was appointed " Repetiteur de Physique" at the 
Agronomic Institute, and after spending a year in that position 
he was promoted to the post of "Maitre de Conferences" and 
"Chef des Travaux Pratiques," or lecture assistant and senior 
demonstrator at the Ecole Superieure de Pharmacie, a position 
which he held until 1883. A year before this change, he had been 
appointed, after a competitive examination, "Agrege des Sciences 
physiques-chimiques," and his standing among his fellows at that 
date was such that on the death of Professor Bouis in 1886 he was 
elected to the Professorship of Toxicology in the School of 
Pharmacy; he retained that Chair until 1899, when his turn came 
in rotation to occupy the Chair of " Mineral " or Inorganic Chem- 
istry; he then for the first time delivered a course of lectures on 
that branch of chemistry. 

In 1900 he was appointed Assessor to the Director of that 
School, and in the same year, on the retirement of Professor Troost, 
the Professor of Inorganic Chemistry in the Faculte des Sciences 
in the University of Paris, Moissan was unanimously chosen as his 
successor, for his name had become very widely known owing to his 
remarkable discoveries. At the same time, he retained the title 
of Honorary Professor at his old school, the Ecole de Pharmacie. 

Moissan's first research was conducted in conjunction with 
Deherain ; it had reference to the interchange of oxygen and carbon 
dioxide in the leaves of plants which had been exposed to the 
subdued light of a darkened room. 

His first work in the domain of inorganic chemistry dealt with 
the oxides of the iron group of metals, and especially with the 
compounds of chromium. His thesis for the doctorate contained 
an account of a portion of this research. In it he described the 
existence of two allotropic modifications of chromium sesquioxide; 
one obtained by igniting ammonium chromate, as well as by other 
methods, insoluble in acids, unattacked by hydrogen sulphide and 
by oxygen; the other, produced by careful drying of the hydrated 
oxide at 440, which, when heated to 140 in a current of hydrogen 
sulphide, gave a black sulphide, Cr 2 S 3 , reducible to chromous 
sulphide, CrS, by further heating in a current of hydrogen. Oxygen 
converted this variety of sesquioxide into the analogue of manganese 
dioxide, CrO 2 , a dark grey powder. 

This train of thought led Moissan to investigate the products of 
reduction of the oxides of the iron group. The so-called " pyrophoric 
iron," obtained by heating ferrous oxalate, was shown to consist 



RAMSAY : MOISSAN MEMORIAL LECTURE. 189 

of ferrous oxide, FeO ; the same substance is produced by reducing 
the oxide, Fe^s, in a current of a mixture of carbor dioxide and 
hydrogen. The action of hydrogen at 330 440 reduces Fe 2 O 3 
to Fe a O 4 , and the magnetic oxide is also formed by heating the 
sesquioxide in a current of carbon monoxide at the temperature of 
melting zinc. It is only at 500 600 that ferrous oxide is produced ; 
it is pyrophoric at the ordinary temperature. But pyrophoric iron 
itself can be obtained by heating the sesquioxide for a long time 
in a current of perfectly dry hydrogen to 440, or by distilling 
away the mercury from an amalgam of iron. The amalgam, indeed, 
prepared by electrolysing a solution of ferrous chloride with 
mercury as the cathode, turns very hot on exposure to air. 

An allotropic variety of the magnetic oxide, Fe 3 O 4 , was produced 
by heating the monoxide, or metallic iron reduced by hydrogen, to 
redness in a current of moist hydrogen. It formed a black 
magnetic powder, incandescing and changing to Fe 2 O 3 when heated 
in air. At 1500 Fe 2 O 3 gave off oxygen, and was converted into a 
very resisting modification of the magnetic oxide. 

Somewhat similar researches were carried out on the oxides of 
manganese, nickel, and cobalt, and pyrophoric varieties of the 
metals were prepared. 

Having obtained metallic chromium from its amalgam, Moissan 
next investigated the little-known chromous salts, preparing pure 
chromous chloride, CrCl 2 ; also the blue sulphate, CrSO 4 ,7H 2 O, which 
is isomorphous with copperas; also chromous bromide, chromous 
acetate, and chromous oxalate. The acetate or chloride, on treat- 
ment with a solution of potassium cyanide, gave the interesting 
compound, K 4 CrC' 6 N 6 , analogous to yellow prussiate of potash, 
oxidisable to the red K 3 CrC 6 N 6 . A final paper on the blue 
compound of Cr0 3 with peroxide of hydrogen, in which it was shown 
that the ratio between the two is CrO 3 : H 2 O 2 , ends the series. 

In 1884 Moissan turned his attention to the investigation of 
compounds of fluorine. He prepared phosphorus fluoride first, by 
heating copper phosphide with lead fluoride. It is a gas, exploding 
when sparked with oxygen, and yielding the oxyfluoride, POF 3 . He 
next prepared fluoride of arsenic, by distilling a mixture of arseni- 
ous oxide, sulphuric acid, and calcium fluoride. He electrolysed 
this liquid, and produced from it elementary arsenic, and a gas 
which attacked the platinum electrode. On submitting phosphorus 
fluoride to a rain of sparks, phosphorus was deposited ; the product, 
however, was not fluorine, but phosphoric fluoride, PF 5 , the 
liberated fluorine combining with the phosphorus fluoride. These 
researches occupied him until 1888. In that year he investigated 
some organic fluorides, obtaining ethyl fluoride, C 2 H 5 F, by the 



190 RAMSAY: MOISSAN MEMORIAL LECTURE. 

interaction of ethyl iodide and silver fluoride, and the correspond- 
ing methyl and wobutyl fluorides. In the following year he made 
the capital discovery that whilst the compound KF,2HF melts at 
65, KF,3HF remains liquid at -23, and conducts electricity 
electrolytically ; and this long series of researches culminated in the 
discovery of elementary fluorine. 

During this work he accumulated useful information, which 
enabled him to adapt his apparatus to the end he had in view. 
One method which he attempted for the isolation of fluorine was 
to pass* phosphorus and phosphoric fluorides over red-hot platinum 
sponge. A gas was evolved which liberated iodine from a solution 
of potassium iodide; but this gas came off very slowly, and was 
largely absorbed by the platinum tube in which the experiment 
was made. He next tried the electrolysis of arsenious fluoride; 
but he found that that liquid is a very poor conductor, and he 
attempted to increase its conductivity by the addition of anhydrous 
hydrogen fluoride; better results, however, were obtained on 
addition of anhydrous potassium fluoride to the mixture of arsenious 
fluoride and hydrogen fluoride > and from this it was but a step 
to omit the arsenious fluoride ano! to electrolyse the mixture of acid 
and potassium salt. 

His first apparatus was made of platinum ; the electrodes were 
rods of platinum-iridium alloy, thickened at the ends so as to last 
longer, for the negative electrode was always rapidly corroded. 
Paraffined corks closed the ends of his first platinum U-tube. The 
cork closing\the limb into which the negative electrode passed was 
corroded and charred ; hence in his next experiment, corks were 
replaced by fluor-spar stoppers, cemented into hollow platinum 
cases, on which a screw was turned, so that the stoppers could be 
screwed tight into the open ends of the U-tube. This experiment 
was successful in yielding fluorine; whilst hydrogen came off at the 
negative electrode, and passed out through a side-brajich of 
platinum tube, fluorine was evolved at the positive pole ; it passed 
out through a similar platinum tube, and was made to play on 
various materials exposed to its action in a platinum capsule. It 
was subsequently discovered that as copper exposed to fluorine 
immediately becomes covered with a deposit of the fluoride, which 
protects it from further action, copper could be substituted for 
platinum in the structure of the U-tube, and an important economy 
could thus be effected. 

It was found that sulphur, selenium, and tellurium inflamed, 
giving white deposits; the first combines,, as Moissan subsequently 
found, to form a gas, SF 6 , sulphur hexafluoride. From phosphorus, 
PF 3 and PF 5 were obtained ; iodine caught fire and burned ; Moissan 



RAMSAY: MOISSAN MEMORIAL LECTURE. 191 

subsequently found that IF 5 was the product; bromine lost its 
colour, and later, Moissan and his pupils proved this to be due 
to the formation of BrF 3 ; on pure carbon at the ordinary tempera- 
ture fluorine had no action ; but both boron and silicon caught fire 
and burned, giving SiF 4 and BF 3 . 

By blocking the exit of either of the tubes conveying away the 
hydrogen or the fluorine, one or other gas could be caused to pass 
round the bend and mix ; when a bubble passed round, a detonation 
occurred, showing that hydrogen and fluorine combine even in the 
dark at the low temperature of -35, for the apparatus had to 
be maintained at this low temperature to prevent the admixture of 
gaseous hydrogen fluoride with the fluorine. The low temperature 
was conveniently attained by surrounding the U-tube with liquid 
methyl chloride. 

Most metals were instantly attacked, some with inflammation ; 
even platinum and gold could not resist its action; but they had. to 
be raised to 40$ before attack took place. Salts such as potass- um 
iodide, mercuric iodide, and lead iodide were completely decom- 
posed, giving fluorides both of the metal and of the iodine. Chlorine 
was liberated from potassium chlorate, along with oxygen, on which 
fluorine had no action; chlorine was also evolved from carbon 
tetrachloride, the tetrafluoride being formed; and water was 
instantly decomposed, its oxygen being liberated partly as ozone. 

Although all these properties of this gas could be most easily 
explained on the assumption that it consisted of fluorine, still they 
might conceivably appertain to a mixture of ozone and hydro- 
fluoric Ucid, or to a perflucride of hydrogen, HF n . The former 
supposition was disproved by trying the action of such a mixture ; 
but none of the properties of the gas was manifested. The second 
hypothesis was also disproved by leading the fluorine over iron, 
and proving that no hydrogen passed on. 

Subsequent research showed that the formation of fluorine was 
not so simple as had' at first been supposed. Investigation of a 
muddy deposit, which was always found at the bend of the U-tube 
on dismantling it, showed that that substance consisted mainly of 
potassium platinifluoride, K 2 PtF c , and that in all probability it 
was the substance undergoing electrolysis, the equivalent of the 
potassium being liberated at the cathode as hydrogen, and fluorine 
at the anode, the group PtF 4 again combining with potassium 
fluoride. The operation did not proceed with regularity until a 
considerable quantity of platinum had dissolved from the anode. 

The density of the gas was found to be 18' 3, on the hydrogen 
standard. This figure, which is too low, was almost certainly due 
to the presence of oxygen, produced by the electrolysis of water 



102 RAMSAY: MOISSAN MEMORIAL LECTURE. 

still dis )lved in the electrolytic mixture. Moissan for long supposed 
that, on passing the current, the water accidentally present first 
underwent electrolysis before the fluorine appeared; but it was 
subsequently found that water still remained to be electrolysed, 
even after much fluorine had been separated. Later experiments, 
in which the gases other than fluorine were estimated in the gaseous 
mixture, weighed, and allowance was made for their presence, proved 
that the true density of fluorine is 19, a figure identical with the 
atomic weight. The supposition that fluorine consisted partly of 
monatomic molecules mixed with an excess of diatomic molecules 
had therefore to be abandoned. The activity of fluorine was not to 
bo explained by its monatomicity. 

The reason why fluorine cannot be produced by heating tetra- 
fluoride of platinum, PtF 4 , was found as soon as that substance 
had been prepared by the action of fluorine on platinum; it is 
because that compound decomposes water, and therefore cannot be 
prepared in the wet way. 

Moissan also attempted to induce combination between argon 
and fluorine, and helium and fluorine, but without success, even 
when the mixture was submitted to the discharge of powerful 
sparks. 

The preparation of two gaseous fluorides of carbon led Moissan 
to attempt to remove the fluorine, in the hope that the carbon 
would be liberated in the form of diamond. But this hope was 
disappointed; the product was always lamp-black. These experi- 
ments, however, led to the discovery of the method of preparing 
the diamond artificially; it had been found that a meteorite from 
Canon Diablo, consisting, as meteorites usually do, mainly of 
metallic iron, had imbedded in it small crystals of diamond; and 
Moissan's genius led him to devise the cause of their formation; 
his theory was that the carbon had originally been dissolved in the 
iron when it was in a molten state'; that the surface of the iron 
had suddenly cooled, and that the iron in the interior, on solidify- 
ing, was subjected to great pressure, for solid iron containing 
carbon in solution occupies a larger volume than molten iron. 
These considerations directed his experiments, which were crowned 
with success. 

His first experiments, however, in which the iron was saturated 
with carbon at about 1000, were not successful; he accordingly 
argued that at higher temperatures the solubility of carbon in iron 
should increase, as is the general rule; and he devised the electric 
furnace to attain much higher 'temperatures. His three great 
investigations are thus seen to hang together; one suggested the 
other, and Moissan's skill and patience brought all to a successful 



RAMSAY: MOISSAN MEMORIAL LECTURE. 193 

conclusion. The spirit in which he carried out his work is well 
expressed in his own words, which occur in the preface to his book 
on the " Electric Furnace " : " But what I cannot convey in the 
following pages is the keen pleasure which I have experienced in 
the pursuit of these discoveries. To plough a new furrow; to have 
full scope to follow my own inclination; to see on all sides new 
subjects of study bursting upon me, that awakens a true joy which 
only those can experience who have themselves tasted the delights 
of research." 

Moissan's electric furnace, designed not for technical, but purely 
for experimental work, was of the simplest construction. It con- 
sisted of a rectangular block of lime, made of the excellent Paris 
limestone, in the centre of which a hole had been scooped. This 
block was covered with a rectangular lid; two grooves of circular 
section admitted the carbor, poles which served as electrodes, and 
an arc was made between the poles. Later, an electromagnet was 
used to deflect the arc downwards, so that it might play more 
directly on the object to be heated. A current of 100 to 125 
amperes at 50 or 60 volts was employed in his earlier researches. 

The volatilisation of the material of the furnace, lime, was the 
first fact to be chronicled. Indeed, two torrents of what appeared 
to be flame poured out through the holes admitting the electrodes. 
These apparent flames were, however, only white-hot lime dust, 
condensed from the lime-vapour which filled the furnace. Subse- 
quently, to save cost, the body of the furnace was constructed of 
limestone. The crucible to be heated stood on magnesia, to avoid 
the rapid formation of calcium carbide; and for some purposes, 
crucibles were constructed of a grid of alternate slices of carbon 
and magnesia. By heating an inclined carbon tube in the arc, and 
feeding in at one end a mixture of an oxide such as chromium 
oxide and carbon, the metal flowed out at the other end, and a 
continuous supply was thus obtainable. 

The temperature of the electric furnace appeared to depend on 
the quantity and intensity of the current; but it is limited, no 
doubt, by the temperature of volatilisation of carbon. 

By help of this powerful engine of research, Moissan succeeded 
in causing many -changes to occur, and in producing many com- 
pounds previously unknown. Some of these compounds have had 
important commercial applications; others are of great interest, 
owing to the reactions which they undergo, and the light that they 
shed on the problems of chemical combination. 

In his systematic search for a method of producing artificial 
diamonds, Moissan investigated numerous varieties of graphite; he 
subjected different kinds of carbon to the intense heat of the 



194 RAMSAY: MOISSAN MEMORIAL LECTURE. 

electric furnace, in order to study their behaviour, and, as before 
remarked, he studied the Canon Diablo meteorite, in which small 
diamonds are embedded. These researches made him familiar with 
the behaviour of carbon in all. possible circumstances, and enabled 
him to separate diamonds from other materials with which they 
might be mixed. 

The first actual experiment of crystallising carbon under pressure 
from iron was made with 200 grams of Swedish iron, fused in the 
electric furnace for six minutes with sugar-charcoal in a carbon 
crucible. The crucible was then seized with tongs, and plunged 
into a vessel full of cold water. Moissan relates the anxiety with 
which this was first attempted; an explosion was feared; but, 
although the water boiled, no accident occurred then, or, indeed, 
during some hundreds of similar experiments. The iron was dis- 
solved in dilute hydrochloric acid; the residue, chiefly -jonsisting 
of carbon in various forms, was extracted with nitrohydrochloric 
acid, and alternately with boiling sulphuric and hydrofluoric acids. 
It was then, in order to remove graphite, boiled with nitric acid 
and potassium chlorate. The final residue was floated in bromo- 
form, in which some transparent dust, of density 3 to 3'5, sank, 
whilst a black substance floated. The transparent particles scratched 
ruby, burned to carbon dioxide, and showed octahedral facets. 

Among the other products of the electric furnace were: crystal- 
lised lime, strontia, baryta, and magnesia; metallic and reguline 
chromium, manganese, molybdenum, tungsten, uranium, vanadium, 
zirconium, and titanium; also distilled copper, silver, platinum, 
gold, tin, iron, and uranium; volatilised carbon and silicon, and 
many other similar products. The metals were obtained by heating 
the oxides mixed with powdered sugar-charcoal; and in most cases 
a carbide of the metal, or a solution of carbide in the metal, was 
obtained. The presence of carbon monoxide, due to the presence 
of the carbon electrodes, no doubt contributed to the formation 
of carbide. In order to obtain the pure metal, therefore, a second 
operation was necessary, as a rule; the metal was again heated in 
the furnace in a crucible lined with its own oxide; the combined 
carbon thus obtained oxygen, and was -evolved as oxide, whilst the 
metal was left in the reguline state. 

Moissan made an exhaustive study of the properties of the 
compact metals, and of their carbides. It would be impossible in 
a discourse like the present one to do justice to the enormous 
number of interesting observations which he made; indeed, he 
added a very large chapter to the book of chemistry. All that 
can be done is to pick out a few examples to illustrate the 
character of his work. 



RAMSAY : MOtSSAN MEMORIAL LECTURE, 

Let us first take chromium. This metal was prepared by allowing 
a mixture of the sesquioxide with carbon to run down a sloping 
tube of carbon, heated to whiteness in the electric furnace ; metallic 
chromium ran out at the lower end, and Moissan says that it is 
easy to prepare as much as 20 kilograms of chromium at one 
operation. The amount of carbon in the product varied between 
8'6 and 11 '92 per cent. The carbides of this metal were then 
studied. On melting metallic chromium with a large excess of 
carbon in the furnace for ten or fifteen minutes, a brittle button 
was obtained, consisting of crystals of C 2 Cr 3 . It is unattacked by 
concentrated hydrochloric acid, by weak or strong nitric acid, or 
by aqua regia, but is acted on slowly by dilute hydrochloric acid. 
Nor is it attacked by fused potassium hydroxide, although potassium 
nitrate destroys it easily. Another carbide was produced during 
the preparation of metallic chromium, covering the surface of the 
metal with brilliant needles; its formula was CCr 4 . 

The carbide, produced as the raw material, was converted into 
the metal by the method already indicated, that is, by fusing it in 
a crucible lined with chromium oxide, and covering it with the 
same material. The button of metal thus obtained, however, was 
" burnt," that is, contained oxide in solution. To remove the oxide, 
it can be re-melted with lime; or, what is simpler, the original 
carbide can be deprived of carbon by fusion with lime, the lime 
forming calcium carbide, together with carbon monoxide. This 
action is, however, a reversible one; there is a double oxide of 
chromium and calcium formed, which forms fine crystals. This 
substance, fused with more carbide, yielded pure chromium. 
Chromium was found to ^e unalterable in air, but when heated to 
2000 in oxygen it burned, emitting sparks even more brilliantly 
than iron does. Chromium filings heated with sulphur become 
incandescent, producing the sulphide. When heated with carbon, 
CCr 4 is produced. A silicide is produced when chromium and 
silicon are heated together in the electric furnace, which is very 
hard, scratching the ruby, 'and not attacked by acids, or by fused 
potash or nitre. 

This method of refining chromium was applied to commercial 
" ferro-chrome," and was found to be successful in depriving 
it of carbon ; and it was shown that, starting from chrome-iron ore, 
ferro-chrome of 60 per cent, chromium could be made by passing 
it, mixed with 'carbon, through the electrically heated tube; it 
contained 6 per cent, of carbon and 1 per cent, of silicon. Potassium 
or sodium chromate could be made from it by fusion with potassium 
or sodium nitrate, the iron remaining behind as insoluble oxide. 
In conclusion, Moissan found that copper, allied with half a per 

2G 



196 RAMSAY: MOISSAN MEMORIAL LECTURE. 

cent, of chromium, acquired twice the tensile strength of : pure 
copper; it took a fine polish, and was less tarnished on exposure 
to air than copper. 

In a similar manner he treats of manganese, molybdenum, 
tungsten, uranium, vanadium, zirconium, titanium, silicon (inci- 
dentally having discovered " carborundum "); he finds that 
aluminium is not easily reduced in the furnace, but yields a 
carbide. In this connexion he in some measure anticipates the 
"thermite" process, for he projects a mixture of aluminium filings 
with the oxide of the metal to be produced on to the surface of 
molten aluminium; in this way he prepared alloys of nickel, 
molybdenum, tungsten, uranium, and titanium with aluminium. 

Moissan also prepared numerous carbides, and submitted them 
to an exhaustive study. Lithium carbide, prepared from litliium 
carbonate and carbon in the furnace, has the formula Li 2 C 2 , and 
on treatment with water yields pure acetylene. 

In our Proceedings of the year 1893, Travers described the pre- 
paration for the first time of calcium ca-rbide by heating together 
metallic sodium, calcium chloride, and carbon. A month before, 
Moissan had stated that the lime of his furnace reacted with the 
carbon of his electrodes, " forming a carbide of calcium, easy to 
collect." But it was not until March, 1894, that he described this 
compound, since become so important industrially. Travers used 
his carbide for the production of acetylene; but Wilson, who 
patented the same compound in 1893, in America, was ignorant 
that the gas evolved .on treating it with water was acetylene ; indeed, 
he does not appear to have treated it with water at all. Moissan 
made a most careful study of this important compound, and 
described its chemical properties in great detail. He also made the 
carbides of barium and strontium; and he described the action 
on them of chlorine, bromine, iodine, sulphur, selenium, and phos- 
phorus; in each case both metal and carbon combine with the 
element used for the attack. 

The action of water on the carbides of cerium, lanthanum, 
yttrium, and thorium produced in a similar manner is not so 
simple; acetylene, ethylene, methane, and liquid and solid hydro- 
carbons were formed from G 2 Oe, C 2 La, C 2 Y, and C 2 Th. Aluminium 
carbide, however, has the formula C 3 A1 4 , and yields pure methane. 
Manganese carbide, in its turn, belongs to a different type; its 
formula is CMn 3 ; and with water, hydrogen and methane in equal 
volumes are the products; and uranium carbide, C^^ gives 
methane and a complex mixture of liquid hydrocarbons. 

From these experiments Moissan was induced to propound a 
theory of the formation of petroleum ; he does not consider it exclu- 



RAMSAY: MOISSAN MEMORIAL LECTURE. 197 

sive of the production of hydrocarbons by the natural distillation 
of coal and shale; but he thinks that in certain formations, where 
the existence of such deposits is improbable, the occurrence of 
petroleum may be explained by the attack of carbides of the 
metals by water. 

Moissan also prepared many silicides and borides. Among these 
were silicides of iron, of chromium, and of carbon; although he 
had obtained crystals of " carborundum " in 1891, he did not at 
that time publish any account of it; and he concedes the merit 
of its discovery to Acheson. The borides of iron, nickel, cobalt, 
calcium, strontium, barium, carbon, and some others were also 
prepared and carefully studied. These researches took many years, 
and are a model for accurate experimentation and luminous exposi- 
tion. They were described in two works, " Le Fluor," published 
in 1887, and " Le Four Electrique," published ten years later. 
Since that date Moissan 's chief researches dealt with : The prepara- 
tion of metallic calcium by heating calcium iodide with sodium ; its 
success depends on the easy attack of sodium by alcohol, whilst 
calcium is hardly affected. The investigation of sodium ammon- 
iums and methyl-ammoniums, obtained by the action of sodium on 
liquid ammonia and on methylamine; and similar substances 
obtained from lithium and calcium. The preparation in the pure 
state of the hydrides of calcium, sodium, and potassium ; he showed 
that these bodies are non-conductors of electricity, and that the 
hydrogen which they contain must be supposed to exist in combina- 
tion as a non-metal, in contrast to its condition in palladium 
hydrogen alloy. In later papers on these compounds, he described 
a most ingenious formation of sodium formate by the action of 
carbon dioxide on sodium hydride, and of sodium hyposulphite, 
Na 2 S 2 O 4 , by treating the hydride with sulphur dioxide. 

Moissan did not, however, desert his old favourites, fluorine 
and the products of the electric furnace; for in later years he 
prepared thionyl fluoride, SOF 2 , and sulphuryl fluoride, SO 2 F 2 , both 
gases; and he re-determined the density of fluorine in a dry glass 
vessel. The electric furnace yielded him metallic niobium and 
tantalum, many metals of the rare earths, and borides of silicon. 
A silicide of lithium, Li 6 Si 2 , was prepared ; and a new hydride of 
silicon, SigHg, the analogue of e&hane. He also studied the 
aoetylides of metals of the alkalis. His last research, of which 
an account appeared in the Compt. rendus for 1906, p. 675, dealt 
with the distillation of titanium in the electric furnace. In all, he 
published more than three hundred memoirs and notices. 

This incomplete account of Moissan's work shows how productive 
his laboratory was; he was full of new ideas, most of them offshoots 



1 98 RAMSAY : MOISS AN MEMORIAL LECTURE. 

of his original great discoveries; much of his work was carried out 
in conjunction with students, of whom an increasing number came 
from abroad, for his reputation both as a skilled chemist and as an 
attractive personality had become world-wide. His work lay almost 
entirely in the field of inorganic chemistry, and it contributed to 
turn the tide which had set so long in favour of organic research. 

He pubKshed, along with many other collaborators, a treatise on 
inorganic chemistry " Traite de Chimie Minerals " in five large 
volumes, which has a large circulation in France, and in point of 
detail is a very complete account of inorganic compounds. 

Moissan was tUe recipient of numerous honours, not only in his 
own country, but also abroad. In 1888, after his isolation of 
fluorine, he was elected a member of the Academic de Medecine ; 
in 1891, of the Academie des Sciences; in 1895, Membre of the 
Conseil d'Hygiene de la Seine ; and in 1898, of the Comite Consul- 
tatif des Arts et Manufactures. He was Foreign Fellow of the Royal 
Society of London; of our own Society; an honorary member of 
the Royal Institution, and of the Academies of Denmark, Vienna, 
Belgium, Upsala, Haarlem, Amsterdam, New York, and Turin, 
besides numerous others. He was albo Commandeur de la Legion 
d'Honneur. 

In 1887 the Institut awarded him the Prix Lacaze, one of its 
most valuable gifts; he was the Davy medallist in 1896, and the 
Hofmann medallist in 1903; and he obtained honours from the 
Franklin Institute of Philadelphia, from the Societe d'Encourage- 
ment pour 1'Industrie Nationale, and the Societe Industrielle du 
Nord de la France; and in 1906, shortly before his death, he was 
awarded the Nobel Prize for Chemistry. 

Moissan was a practised speaker and a perfect expositor. His 
lectures at the Sorbonne were crowded with enthusiastic students, 
all eager to catch every word, and he kept their attention for an 
hour and three-quarters at a time by a clear, lucid exposition, 
copiously illustrated by well-devised experiments. His command 
of language was admirable; it was French at its best; the charm 
of his personality and his evident joy in exposition gave keen 
pleasure to his auditors. He will live long in the memories of til 
who were privileged to know him ; as a man full of human kindness, 
of tact, and of true love of -the subject which he adorned by his life 
and work. Perhaps the key to his character lies in his own words : 
" Nous devons tous placer notre ideal aesez haut pour ne pouvoir 
jarnais 1'atteindre; " or as our own poet has put it : " O but a man's 
reach should exceed his grasp ; or what's a heaven for ? " 




S. CANNIZZARO IN 1858. 
From a Portrait by D. Salorson. 



[To face p. 199. 



CANNIZZARO MEMORIAL LECTURE. 

DELIVERED ON JUNE 26TH, 1912, 

By SIR WILLIAM A. TILDEN, D.Sc., LL.D., P.R.S., Past-President 
of the Chemical Society. 

THE minutes of the Ordinary Scientific Meeting of the Chemical 
Society for June 19th, 1862, contain the following entry : " Messrs. 
Cannizzaro, Kekule, Lowig, Malaguti, Marignac, Pasteur, Stas, and 
Zinin were elected Foreign Members." 

Of this illustrious band not one now remains,* and the Society 
having paid its tribute to each in turn is gathered on this occasion 
to commemorate the name which, of those enumerated, was the 
last to disappear from its roll of Honorary Members. 

The career of Stanislao Cannizzaro was completed in an age and 
country full of romance. Born as he was under* the reign of a 
Bourbon in the kingdom of the two Sicilies, he lived to see the 
miserable conditions which beggared and enslaved hi* own com- 
patriots swept away; he took a part as soldier and Senator in the 
regeneration of Italian nationality, and during the latter half of his 
long life he enjoyed the freedom which belongs to a united people 
under a constitutional Monarchy. 

His experiences as a man of science were no less remarkable, for 
it may be said he began work almost before modern chemistry, of 
which he helped to lay the foundations, had been called into 
existence. When Cannizzaro was twenty years of age, Liebig in 
Germany, and Dumas in France were at the height of their fame ; 
while in England Williamson's ideas were beginning to attract 
serious attention. Many years 'had yet to elapse before a real 
system could be applied to the masses of facts then so rapidly 
accumulating. 

Stanislao Cannizzaro was born in Palermo on July 13th, 1826. f 
The family came from Messina, and its members at different times 
held important offices in that city and' elsewhere in Sicily. Stanis 
lao'd father, Mariano Cannizzaro, was born in Messina, but he 
became a magistrate in Palermo and Minister of Police, and later 
President of the Gran Corte dei Conti. The mother was Anna di 
Benedetto, a member of a noble Sicilian house. There was a' large 
family, of which Stanislao was the youngest. He was educated 

* Kekule died in 1896, Lowig in 1890, Malaguti in 1878, Marignac in 1894, 
Pasteur in 1895, Stas in 1891, and Zinin in 1880. 

t For the facts relating to his father's life, I am indebted chiefly to Mr. Mariano 
Cannizzaro 



200 TILDEN: CANNIZZARO MEMORIAL LECTURE. 

partly at the Reale Collegio Calasanzio, where he won prizes, with 
distinction especially in mathematics. As may be imagined, the 
school curriculum in Sicily, as in the whole of Southern Italy, in 
Cannizzaro's youth was entirely under the control of the priests. 
Education, " frowned on as a design of the Liberals to revolutionise 
the State, was so successfully discouraged that in 1837 it was 
calculated that 2 per cent, of the rural population could read, and 
not very much more of the dwellers in the towns." * The subjects 
were confined to the classical languages, grammar, and rhetoric, 
with a little mathematics. 

In 1841, at the age of fifteen, Cannizzaro began the study of 
medicine at the University of Palermo, and especially the study of 
physiology under Professor Fodera. The University was at that 
time in a very imperfect cbndition, degrees being conferred only 
in the faculties of medicine, law, and theology. Cannizzaro took 
no degree, but in 1845 proceeded to Naples, where his sister 
Angelina had married the Marquis Ruffo, son of King Ferdinand's 
Prime Minister. Here, after taking part in the proceedings of the 
physiological section of the scientific congress held in that year, he 
made the acquaintance of the famous physicist Melloni, and after 
working for a short time in his laboratory he proceeded, with a 
warm recommendation from Melloni, to Professor Piria at Pisa. 
The influence of Piria over his young assistant was fortunately 
sufficient to determine the latter to devote himself permanently to 
chemistry. Piria was just then a't the height of his fame, justly 
following his discovery of the constitution of salicin, a very note- 
worthy feat in those early days of organic chemistry. 

Cannizzaro, although an enthusiastic student, could not escape 
the effects of the political agitation which exercised an influence 
so powerful on his compatriots at that time. Those were dark days 
in the history of the country, and the atrocities committed in the 
name of order by Ferdinand's government had aroused not only 
the spirit of the Sicilians, but the indignation of, at least, the 
English people. Beside, Italian soil was occupied in the north by 
the armies of Austria, there was clerical misrule in the Papal 
States, and throughout Europe revolution was the order of the day. 
Cannizzaro responding to the prevalent f eelings of patriotic fervour, 
joined in the premature rebellion in Sicily. Returning from Pisa 
to his native country in 1847, he joined the Sicilian artillery, and 
commanded a battery at Messina. After the fall of Messina he was 
sent to Taormina with a Government. commission to oppose the 
advance of the Neapolitan troops under the General Principe 
Filangeri, but after March, 1849, the defeat at Novara, and the 

* Trevelyau's "Garibaldi and the Defence of the Roman Republic," p. 55. 



TILDEN : CANNIZZARO MEMORIAL LECTURE. 201 

abdication of Charles Albert, the Sicilians were obliged to retreat 
towards Palermo, Cannizzaro being among the last to oppose 
the .Neapolitans. On the fall of the Sicilian Government he 
embarked with some others on board the frigate Independente, 
which, escaping the Neapolitan fleet, succeeded in reaching 
Marseilles. After some months Cannizzaro made his way to Paris, 
and having found admission, presumably through the introduction 
of Piria, into the laboratory of Chevreul, he resumed his chemical 
studies. Here he joined Cloez in work on cyanogen chloride and the 
production of cyanamide, and their results, published in 1851, 
constituted Cannizzaro's first contribution to the records of chemical 
research (Compt. rend., 1851, 32, 62). 

At the close of 1851 he was able to return to Italy, having been 
appointed professor at the National School at Alessandria, where 
he had the advantage of a small laboratory and the services of an 
assistant, " un farmacista giovane intelligente " (letter to Bertag- 
nini). Here he was so occupied, body and mind, with his teaching 
that, as he complained to his friend Bertagnini, he had little hope 
of being able to pursue his own studies. Notwithstanding these 
unfavourable conditions, however, he discovered in 1853 the alcohol 
corresponding to benzoic acid, which he obtained by the action 
of potassium hydroxide on benzaldehyde (Annalen, 1853, 88, 129), 
and; which he continued to study during several succeeding years 
(Ann. Ghim. Phys., 1855, [iii], 43, 349; Nuovo dm., 1855, 2, 212). 

The summer holiday of 1852 was spent with Bertagnini, who 
had a small private laboratory at Montignoso, and here the friends 
carried out work on anisic alcohol, which, however, was nofc 
published until 1856 (Ann. Chim. Phys., 1856, [iii], 47, 285). In 
1854 Piria, in association with Matteucci, produced the first number 
of the new journal 11 Nuovo Cimento, which was to be the 
organ of the Pisan school, and to the second volume Cannizzaro 
made the contribution referred to above. II Nuovo Cimento was 
not established without some suspicion on the part of the Censor, 
the Chancellor Cardinal Archbishop, that chemistry and physics, 
" scienze pericolose," might cause some damage to the faith (Nuova 
Antologm, June, 1911, 490). 

In 1855 Cannizzaro accepted an invitation to the Chair of 
Chemistry in the University of. Genoa, at the same time Piria * 
being transferred to Turin, while Bertagnini was appointed to 
replace him at Pisa. 

* That Piria was the founder of the Italian School of Chemistry was attested by 
Liebi. Piria held Cannizzaro in high esteem, which was repaid by the admiration 
of the pupil, and expressed many years later in Cannizzaro's " Vita e opere di 
R. Piria," 1883, 



202 TILDEN : CANNIZZARO MEMORIAL LECTURE. 

At Genoa there was at first no laboratory, and it was only in the 
year following his appointment that Cannizzaro could obtain rooms 
in which to carry on his work. 

At this time, or probably earlier, he must have begun to meditate 
on those fundamental questions in chemical theory which led to 
the famous " Sunto di un Corso di Filosofia Chimica," communi- 
cated, in March, 1858, through Professor di Luca to the Nuovo 
Gimento (7, 321). But his philosophical and scientific studies, as 
well as his teaching, were destined to be once more interrupted by 
the political events which at this time followed one another so 
rapidly in Italy. In the spring of 1860, the discontent of Southern 
Italy, responding to the unhappy events in the North, found vent 
in the insurrection which broke out in April of that year, although 
it was crushed almost immediately by the Neapolitan Royalist 
troops. However, Garibaldi with his famous thousand succeeded 
in effecting a landing at Marsala, in Sicily, on May llth, and ulti- 
mately forced his way into Palermo. The story has been often 
told, and is full of the most astounding and romantic incidents.* 
As soon as Garibaldi had entered Palermo, Gannizzaro started for 
Sicily with the second expedition under General Medici, although 
he took no part in any battle. In Palermo he became a member 
of the Extraordinary Council of State of Sicily. 

In October of the following year, 1861, he was called from 
Genoa to his native town, and was appointed Professor of Chemistry 
in the University of Palermo. Here, again, he had no laboratory, 
and it was only in 1863 that provision was made for practical 
work. His activity extended beyond the duties of the office he held 
in the University, for beside occupying a position on the Municipal 
Council he made great efforts to secure the establishment of schools, 
which were almost entirely wanting, as well as to provide for the 
higher education of women, f He also established an evening 
drawing school for workmen, and in this school his only son, then 
a child, received his first lessons in art. Later he became Rector 
of the University, and in 1867 he acted as Commissioner of Public 
Health during one of the severe outbreaks of cholera, in the course 
of which he lost a sister, struck down by the disease whilst nursing 
the sick. 

Cannizzaro remained in Palermo about ten years, and during this 
period the work he was able to accomplish in chemical research 
related chiefly to the derivatives of benzylic alcohol and other 
aromatic substances. It is interesting to recall in this connection 

* See Trevelyan's " Garibaldi and the Thousand." 

t Nuova Antologia (June, 1911, 492) gives a full account of his benevolent 
exertions in this and other directions. 



TILDEN : CANNIZZARO MEMORIAL LECTURE. 203 

the fact that among the young men who came under his influence 
at that time was one whose name a very few years later became 
renowned throughout the chemical world on account of the great 
memoir (1874), in which was established once for all the principle 
by which the orientation of all the derivatives of the so-called 
aromatic substances can be determined. Korner's rule is familiar 
to even junior students of organic chemistry. The names of Korner 
and Cannizzaro are associated together in the authorship of a paper 
on anisic alcohol (Gazzttta, 1872, 2, 65). 

In 1871 Cannizzaro was called to Rome to occupy in the new 
University the Chair of Chemistry, which he retained until death 
summoned him away so many years later. Even in the capital city 
he again found no laboratory, and he was obliged to suspend his 
researches whilst occupied in organising the chemical institute 
which found shelter in the old monastic buildings in the Via 
Panisperna. Here he ultimately established a school, and in spite 
of the heavy official duties which devolved on the professor he 
continued during many years the study of the complex and interest- 
ing compound, santonin, and worked out its constitution with the 
co-operation of his pupils and assistants, Amato, Carnelutti, Gucci, 
Sestini, Valente, and others. 

At the same time that he received the call to the University he 
was made a Senator of the kingdom, and as a Moderate Liberal 
played his part in shaping the Constitution, and establishing reform 
in the affairs of the now united Italy. Among other duties which 
fell to his lot was the organisation of the Customs laboratory and 
the State Regia dei Tabacchi. He was also a member of the 
higher Council of Public Instruction, of which for some time he 
was President. He further occupied himself with the provision 
of public instruction in agriculture, and generally in helping 
forward the advancement of science and of the liberal professions 
in Italy. When the Congress of Applied Chemistry met in Rome 
in the year 1906, Cannizzaro was Honorary President, and it was 
gratifying to the visitors from so many lands to see the vivacity 
and energy with which the old man, then in his eightieth year, 
entered into all the proceedings. He was still lecturing, and some 
of the members had the privilege of hearing him address his class 
in the lecture room of the Chemical Institute. It was from this 
room four years later that his remains were borne by a company 
of his students to their last resting place. We are informed that 
he continued to lecture until the year before his death : " for him 
to teach was to live/' As soon as he perceived that his strength was 
failing so much that he could not lecture, all his ailments appeared 
to increase, and the end soon came. He died on May 10th, 1910. 



204 TILDEtf : CANNtZZARO MEMORIAL LECTURE. 

Cannizzaro married in Florence, in 1856 (or 1857 ?), an English 
lady, Henrietta Withers, daughter of the Rev. Edward Withers, 
who held a living in Berkshire. He left one son, who practices in 
Rome as an architect, and a daughter. 

Active as he was as an investigator in the domain of organic 
chemistry, Cannizzaro's chief claim to the admiration of his con- 
temporaries and to a distinguished place in the history of modern 
chemistry is based on the systematic course of theoretical teaching 
which he sketched in 1858. 

To form a just estimate of the influence exercised on the 
progress of scientific chemistry by Cannizzaro's famous essay, a 
brief review of the state of knowledge and opinion in the chemical 
world up to and about the year 1858 is necessary. 

The atomic theory of Dalton was just fifty years old, and although 
well rooted in the literature of chemistry there were not a few 
who still refused to recognise it, and there were many super-cautious 
chemists who preferred to speak of it as " at the best but a graceful, 
ingenious, and in its place useful hypothesis." * Evidence of the 
persistence of this attitude so late as 1869 is afforded by William- 
Bon's lecture,! and especially by the discussion which ensued upon 
it. Some thought to perceive a distinction between physical atoms 
and chemical atoms, but generally they seem to have retained the 
fundamental notion of Dalton, which conceives each atom to be a 
sphere existing either alone or in close contiguity with other 
similar atoms, and separable more or less from one another by 
the influence of heat. Students at this time were generally unfami- 
liar with the word " molecule," + for chemists spoke as compla- 
cently, and in a sense as justly, about an atom of water as about 
an atom of oxygen. For the most part, also, they had never heard 
the name of Avogadro. Considerable advances had been made 
toward the estimation with exactitude of what were then usually, 
although incorrectly, called " atomic weights," notably by Berzelius, 
Dumas, Pelouze, de Marignac, and Stas. The figures thus afforded 
by experiment were only equivalents or combining proportions, 
uucorrected by reference to any standard, for the excellent reason 
that there was no standard generally recognised; and even in the 
use of the term " equivalent " there was the utmost confusion, of 
which evidence is provided by the statement in one of the most 
widely circulated text-books of the period (Fownes, 1856) that the 

* "Fownes' Chemistry,'' 6th ed. (1856), p. 210. Edited by Beucc Joiies and 
Hoi'mann. 

t Journ. Chcm. Soc., 1869, 22, 328. 

The word molecule was occasionally used by Dalton, e.g., "Chemical Philosophy," 
Vol. I., p. 70, and in the sense of atom by Ampere (Ann. Chim. Phys., 1814, 90, 
43). 



TlLDEtf : CANNI2ZARO MEMORIAL LECTURE. 205 

numbers called equivalents " represent quantities capable of exactly 
replacing each other in combination," the list of numbers referred 
to including nitrogen 14, carbon 6, whilst hydrogen was 1, and all 
were said to be equivalent to oxygen taken as 8. In the same book 
the law of Gay-Lussac relating to combination of gases by volume 
is " explained " by the statement (p. 203) that " quantities by 
weight of the several gases expressed by their equivalents, or, in 
other words, quantities by weight which combine, occupy, under 
similar circumstances of pressure and temperature, either equal 
volumes or volumes bearing a simple proportion to each other." 
Examples quoted in connexion with this passage show that the 
volumes of equivalents of elements and compounds as then recog- 
nised varied from \ vol. for O to 2 volumes for HC1 and NH 3 . 

The consequences of bringing them all to the same volume were 
at this time, and even much later, not considered by the great 
majority of teachers, and although vapour densities were frequently 
the subject of experiment, the results were used merely to check 
the empirical formula deduced from analysis of the substance, and 
few thought of adopting a standard volume and revising the 
empirical formula so as to harmonise with it. If, for example, the 
vapour density of acetone was found, it would be used merely to 
substantiate the formula deduced from analysis, namely, 
C H 8 O (C = 6, O = 8), and "whether the rational formula of 
acetone is C 3 H 3 O or C 6 H 6 O 2 or C 9 H 9 O 3 , the vapour density does 
not enable us to decide" (Galloway's " Second Step/' 1864, p. 68). 

This is surprising in view of the fact that so far back as 1826 
Dumas, in the memoir in which he describes his well-known method 
of taking vapour densities,* refers to the fact that all physicists 
agree in supposing that in elastic fluids under the same conditions 
the molecules are placed at equal distances, or in equal numbers 
in the same volume. The difficulties encountered in the general 
application of this principle to the determination of formulae arose 
chiefly from the lack of trustworthy experimental data. But these 
were gradually accumulating in the years which followed, and by 
the time Gerhardt and Laurent began to handle the fundamental 
propositions relating to theoretical chemistry there was a large 
body of facts, sufficient as it now appears to have provided safe 
ground for generalisation. 

Up to this time also the conception that the ultimate particles 
of the elements themselves might contain more than one atom had 
not been commonly accepted. It was believed that combination 
could only occur between substances of opposite chemical or electro- 

* "Surquelques points de la Theorie atomistic[ue " (Ann. Chim. Phys. y 1826, 33, 
337). 



206 TlLDfcN : CANNI2ZARO MEMORIAL LECTUfeE. 

chemical character, hydrogen with oxygen, for instance, but that 
hydrogen could unite with hydrogen, or oxygen with oxygen, was 
not generally admitted. 

It is evidence of the complete neglect with which Avogadro's 
great memoir* of 1811 had been treated that chemists generally 
at this time did not know or had completely forgotten that the 
constitution of elementary molecules in the gaseous state had been 
very clearly explained by him. The passage is rather long for 
quotation in full, but in the second division of the memoir he 
discusses the case of the " elementary molecules/' and his position 
is indicated clearly enough by the case of water. He says: " Ainsi 
la molecule integrante de Teau, par exemple, sera composee d'une 
demi-molecule d'oxigene avec une molecule, ou, ce qui est la meme 
chose, deux demi-molecules d'hydrogene." This view of the consti- 
tution of elementary molecules did not, therefore, originate with 
Gerhardt, to whom the idea is usually attributed. 

Gerhardt in 1843 had pointed out that the equivalents accepted 
for organic compounds did not agree with those assigned to mineral 
substances, and in order that they might correspond with H 2 O, CO 2 , 
and NH 8 , the formulae he assigned to water, carbon dioxide, and 
ammonia respectively, they required to be reduced to one half. 
At the end of a series of papers on the subject (Ann. Chim. Phys., 
1843, 7, 129, and 8, 238) he sums up his conclusions in the follow- 
ing sentences: 

" Atomes, equivalents et volumes sont synonymes. 

" Les densitcs des gaz sont proportionelles a leurs equivalents." 

The fourth volume of his famous " Traite de Chimie Organique " 
(1856) contains an exposition of his system, in which the molecule 
of water is taken as the unit, and is represented by the formula 
H 2 O (O = 16). From this he was led to represent elementary 
hydrogen as hydrogen hydride, HH, and gaseous chlorine as 
chlorine chloride, C1C1. This conception of the constitution of 
elementary molecules was not derived from any direct consideration 
of the views of Avogadro or Ampere, whose names are not men- 
tioned. They arose doubtless from acceptance of the principle 
already acknowledged by Dumas as the prevailing doctrine among 
physicists, namely, that equal volumes of gases contain the same 
number of molecules, but Gerhardt never explicitly accepted this 
principle as a means of settling molecular magnitudes, nor did he 
seem to give it a position of prime importance among recognised 

* Essai d'une maniere de determiner lea masses relatives des molecules 
e'le'mentaires des corps, et lea proportions selon lesquelles elles entrent dans ces 
combinaisons (J. de Physique, etc., 73, 6876. Paris, July, 1811. Translated 
in No. 4 Alembic Club Reprints. Also reprin.ted in full by the R. Academy of 
Sciences, Turin, 1911. 




[To /oce p. 207. 



TILDEN : CANN1Z2ARO MEMORIAL LECTURE. 207 

principles. In his little book * published in 1848 before the issue 
of his great work on organic chemistry, the following passage occurs 
(p. 43) : " Comme il iraporte toutefois <T adopter une notation 
exprimant les plus de faits a la fois, j'ai propose il y a quelques 
annees, de tenir compte des volumes, et de ramener a un meme 
volume les for mules des composes volatils, not am men t des composes 
organiques. . . . Comme OH 2 correspond a 2 volumes j'ecris aussi 
les corps suivants ainsi: CO, CO^, NH 3 , C1H, NO 2 , C 2 H 6 O, SO 3 , 
etc." 

His system of formulae appears to have been based chiefly on his 
own view that every chemical change is a form of double decom- 
position, and he is at great pains to show that in chemical reactions, 
whether of combination or decomposition, the proportion of water 
or of carbonic acid involved was never less than the amount repre- 
sented by the formulae H 2 O and CO 2 , in which H = l, O = 16, and 
C=12; and, similarly, the amount of free oxygen or hydrogen was 
never less than the amount represented by O 2 and H 2 with the 
values as just stated. In his " Traite " (Vol. IV., p. 568) he distin- 
guished the radical hydrogen from the gas hydrogen, the radical 
chlorine from free chlorine, and he explains that it is the study 
of reactions which has led him to write hydrogen gas as made up 
of the two radicals HH, and chlorine gas as composed of the two 
radicals C1C1; and he goes on to say: "Dans la nomenclature 
usuelle le gaz hydrogene serait done Thydrure d'hydrogene, et le 
gaz chlore serait le chlorure de chlore; cela veut dire que le gaz 
chlore et le gaz hydrogene resultent de doubles decompositions." 

This mode of viewing the subject led him into some mistakes, of 
which an example occurs a few pages further on (p. 571), where he 
represents the action of hydrochloric acid *on zinc by an equation 
in which the zinc molecule is represented as a double structure like 
that of hydrogen; thus: 



and ZnH + C1H = HH + ClZn. 

The molecule of mercury is also represented by a corresponding 
formula, HgHg (p. 575). 

As regards the constitution of the molecules of the elements, it 
should not be forgotten that it was in 1850 that Brodie published 
his views " on the Condition of Certain Elements at the Moment 
of Chemical Change " (Phil. Trans., 1850, II, 759, and Quart. Journ. 
C/tem. Soc., 1852, 4, 194). In this memoir he expresses the opinion 
" that at the moment of chemical change the same chemical relation 
exists between the particles of which certain elements consist, as 
between the particles of compound substances under similar cir- 

* Introduction a 1'etude de la Chimie par le systeme unitaire, 848. 



208 TILDEN : CANNIZZARO MEMORIAL LECTURED 

cumstances, on which relation the phenomena of combination 
depend ; that, in short (to use the common language), the particles 
of the elements have a chemical affinity for each other " ; and then 
he goes on to suggest that the term affinity, which is unsatisfactory, 
should be replaced by the term " polar relation," which serves to 
indicate an analogous condition " between a series of particles 
undergoing chemical change and a series of particles conducting 
electricity or magnetism." These views are illustrated by reference, 
inter alia, to the decomposition of oxide of silver by hydrogen 
peroxide, previously observed by Thenard, and the mutual inter- 
action of cuprous hydride discovered by Wurtz with hydrochloric 
acid. The former of these two changes results in the evolution 
of oxygen gas, and the latter in the production of hydrogen gas, 
and they were explained by Brodie on the assumption of 
opposite polar relations in the atoms which combined together 
in pairs 

Gerhardt's system of four types water, hydrochloric acid, 
ammonia, and hydrogen was adopted by him only for the purpose 
of classifying reactions, as he insisted repeatedly that any know- 
ledge of the arrangement of atoms in a compound is inaccessible 
to experiment. Dumas' earlier theory of types had implied the 
idea of arrangement in the constituent parts of bodies, and, indeed, 
the existence of transferable radicals, or residues as they were 
called by Gerhardt, such as cyanogen, benzoyl, and ammonium, 
involved some notion of order within the ultimate particle. 

At the time under review the conflict between the notation in 
equivalents and the notation corresponding to Gerhardt's types 
had not been decided. The notation which presented water as HO 
and hydrogen sulphide as HS, involved the anomaly that such 
formulae represented two volumes of vapour, whilst HC1 and NH 3 
represented four volumes. The unitary system of formulae was 
still unacceptable to the great majority of chemists, although many 
occupied themselves in testing the capacities of the several systems 
of types with a view to the discovery of relationships among the 
very numerous carbon compounds daily issuing from every labora- 
tory. The water type of Williamson, the ammonia type of Wurtz 
and Hofmann, the hydrochloric acM and hydrogen types of 
Gerhardt afforded for some years a basis for discussion which, 
although ultimately fertile, inasmuch as it led indirectly to the 
idea of the linking of atoms, was too often barren enough for all 
immediate practical purposes. The time had not arrived when the 
property of atoms, which is now called valency, could be recognised, 
and although ifraiikland as early as 1852 (Phil. Trans., 1852, 142, 
417) had drawn attention to the fact that the combining powers 



TiLDEN : CANNIZZARO MEMORIAL LECTURE. 209 

of elements arfc limited and constant, it remained until many years 
later among the numerous unutilised curiosities of observation. It 
might be said that those who made use of the water type and the 
ammonia type for various compounds implicitly admitted the idea 
that the oxygen and the nitrogen in these compounds respectively 
did hold together, in the one case two and in the other case three 
atoms. This, however, was not definitely recognised until much 
later, when, in 1858, Kekule (Annalen, 1858, 106, 129) and 
Couper (Ann. C/iim. Phys.. 1858, 53, 469; Phil. Mag., 1858, [iv], 
16, 104) independently showed that in carbon compounds the 
element carbon must be the nucleus to which the other atoms are 
attached, and that atoms of carbon, in such compounds, must be 
united to one another. 

At this point it would be, to say the least, unjust not to call to 
remembrance the great services to science rendered throughout 
this period by one who was then the junior secretary and is now 
the senior Fellow of the Chemical Society. If the expositions* 
addressed by Odling to the Society, and thence to the chemical 
world outside, failed to clear away much of the confusion and 
many of the anomalies then permeating theoretical chemistry, it 
was due to no lack of clearness of thought, knowledge of facts, or 
cogency of reasoning on the part of the lecturer, but rather to the 
conservative indisposition to change which often enchains the 
scientific world, in spite of the precepts of the science which it 
professes. 

During all this long period the name of Avogadro had been 
treated with a neglect which is scarcely compensated by the 
recognition now accorded to it nearly a century after his time. 
Among the French, Ampere gets more cyedit in this connexion 
than seems to belong to him, for his paper (Ann. Chim. Pkys., 
1814, 90, 43) three years later than the memoir of Avogadro shows 
little evidence that he attached the same importance to the theorem 
that equal volumes of different gases under the same conditions 
contain the same number of particles as did Avogadro. The memoir 
of Ampere is chiefly devoted to a consideration of the probable 
forms of the " particules " (molecules) of crystallised substances. 

Even those chemists who are generally supposed to have made 
use of Avogadro s idea have neglected all reference to its origin. 
Gerhardt, for example, ignored the Italian physicist, and Dumas 
in the paper on vapour densities already quoted only mentions his 
name in the following passage, which forms the conclusion of the 
memoir : " Nous sommes bien eloignes encore de 1'epoque ou la 

* Especially "On the Atomic Weights of s Oxygen and Water" (Quart. Journ. 
Che,*. Soc. t 1858, 11, 107). 



210 TILDEN : CANNIZZARO MEMORIAL LECTURE. 

chimie moleculaire pourra se diriger par des regies certaines, 
malgre les avantages immenses que cette partie de la philosophic 
naturelle a retires des travaux de MM. Gay-Lussac, Berzelius, 
Dulong et Petit, Mitscherlich, ainsi des vues theoriques de MM. 
Ampere et Avogadro. L'activite singuliere de M. Berzelius et le 
bon esprit des chknistes dont il a enrichi 1'Allemagne pourraient 
cependant faire esperer sur ce sujet important une revolution 
prochaine et durable/' 

It was not, however, until thirty years later that this revolution 
was brought about, and its author was a chemist from no northern 
school. The year 1858 must for ever be distinguished in the history 
of chemistry, for it was then that Cannizzaro led the way out of the 
darkness in which all had been so long struggling. 

After this preamble we may more easily realise the nature and 
extent of the revelation, as it may well be called, which students 
of chemistry owe to Cannizzaro. That it remained for some years 
almost unknown may be attribute4 in part to the barrier consti- 
tuted by the language in which his essay was originally published. 
But it is not creditable to the chemists of. 1860 that the Congress 
held at Carlsruhe in September of that year, at which Cannizzaro 
was present and expounded his views, should have dispersed without 
a general acceptance of the fundamental principles which to us 
seem unassailable. The only excuse which presents itself now is 
the fact that at this period the difficulties arising out of dissociation 
of compounds like sal-ammoniac and sulphuric acid when volatilised 
by heat, and which gave rise to the so-called anomalous vapour 
densities, had not been cleared away. To contend, as some speakers 
seem to have done, that these subjects are matters of opinion, and 
that every scientific man is entitled to perfect freedom in respect 
to the views he adopts, is to misunderstand the cade. In art, in 
which field sentiment, emotion, and taste are the only considera- 
tions involved, complete freedom is clearly necessary, but in science 
whenever facts have been established and an agreement has been 
arrived at in regard to fundamental assumptions, reason ought 
to be the only, as it is the sufficient, guide. Unfortunately, 
this has not always been the case. 

It is only fair to mention that of those chemists who were 
present at the Carlsruhe Congress in 1860, one at least came away 
convinced. In a prefatory note to the German edition (published 
in 1891) of Cannizzaro's " Sketch," Professor Lothar Meyer relates 
how he received at the meeting a copy of this paper, which he 
read with surprise at the clearness with which all the most impor- 
tant difficulties were removed. He says : " It was as though scales 
fell from my eyes, doubt vanished, and was replaced by a feeling 



TILDEN: CANNIZZARO MEMORIAL LECTURE. 211 

of peaceful certainty." In 1864 Meyer published his well-known 
treatise on the " Modern Theories of Chemistry," in which the views 
of Cannizzaro are fully developed. 

To those who have read Cannizzaro 's " Sketch of a Course of 
Chemical Philosophy," of which a belated English translation has 
been produced by the Alembic Club, it must be a matter of wonder 
that the facts and arguments set forth should not have been 
sufficient to have cleared away the previous confusion immediately. 
With small and unimportant corrections, it represents a course of 
instruction which mignt have been given as embodying the accepted 
views of the chemical world down to quite recent times, and a 
perusal of this essay, even now, would be of the utmost value to 
many teachers. 

Cannizzaro's " Sketch " begins with the following words * : "I 
believe that the progress of science made in these last years has 
confirmed the hypothesis of Avogadro, of , Ampere, and of Dumas 
on the similar constitution of substances in the gaseous state; that 
is, that equal volumes of these substances, whether simple or com- 
pound, contain an equal number of molecules; not, however, an 
equal number of atoms, since the molecules of the different- 
substances, or those of the same substance in its different states, 
may contain a different number of atoms, whether of the same 
or of diverse nature." 

The* author then proceeds to trace the history of this conception, 
of the consequences to chemical theory, and of the ideas which 
prevented the immediate acceptance of this hypothesis, and the 
confusion which resulted from the failure to distinguish molecules 
from atoms. In order to bring harmony into the various branches 
of chemistry, he then shows that by applying the hypothesis of 
Avogadro the weights of molecules may be determined before their 
composition is known, and that a knowledge of their composition 
is not necessary to this end. Having settled the molecular weights 
of a series of substances containing one element in common, the 
discovery is made that the different quantities of the same element 
contained in different molecules are always whole multiples of 
one and the same quantity, which represents the atomic weight. 
After studying the constitution of various volatile chlorides, 
bromides, and iodides, the question of the constitution of mercuric 
and mercurous compounds arises, and the author proceeds to show 
that the smallest proportion of mercury present in any molecule 
containing that element is 200, and that this is therefore the 
atomic weight of the metal. This number is then confirmed by 
appeal to the law of specific heats. The analogy of the chlorides 

* I have made use of the Alembic Club version in these quotations, 



212 TILDEN : CANNTZZARO MEMORIAL LECTURE. 

of copper with those of mercury next leads to the examination of 
these compounds, but as the vapour densities of these salts are not 
known, the specific heat of copper and of its compounds leads to 
the number 63 as the atomic weight of copper. Whether this is 
the molecular weight of the uncombined metal there is no means of 
knowing until the vapour density of this substance can be deter- 
mined. Many other metals are then examined, and the author 
points out that in such cases as tin, which produces compounds 
volatile without decomposition, and of which the molecular weight 
can be determined, the atomic weight deduced from specific heat 
is in agreement with that deduced from vapour density. But then 
the question arises : " Are the atoms of all these metals equal to 
their molecules, or to a simple submultiple of them ? " And he 
proceeds . " I gave you above the reasons which make me think it 
probable that the molecules of these metals are similar to that of 
mercury; but I warn you now that I do not believe my reasons to 
be of such value as to lead to that certainty which their vapour 
densities would give if we only knew them." Herein he differs 
from Gerhardt, who had represented the atoms of all the 
metals as fractions of the respective molecules, as in the case of 
hydrogen. 

A little later Cannizzaro comes very near to the modern idea of 
valency when discussing the capacity of saturation of different 
atoms. When referring to diatomic radicals as " those which, 
not being divisible, are equivalent to two of hydrogen or to two of 
chlorine," he proceeds to show " that cacodyle, C 2 H 6 As, methyl, 
CH 3 , ethyl, C 2 H 5 , and the other homologous and isologous radicals 
are like the atom of hydrogen, monatomic, and, like it, cannot form 
a molecule alone, but must associate themselves with another mon- 
atomic radical, simple or compound, whether of the same or of a 
different kind, and that ethylene, C 2 H 4 , propylene, C 8 H 6 , are 
diatomic radicals analogous to the radicals of mercuric and cupric 
salts, and to those of the salts of zinc, lead, calcium, magnesium, 
etc. ; and that these radicals, like the atom of mercury, can form a 
molecule by themselves. The analogy between the mercuric salts 
and those of ethylene and propylene has not been noted, so far 
as I know, by any other chemist." 

There is much more in the " Sketch " which was important for 
the elucidation of the views put forward by the author, but the 
extracts given are sufficient k to show how clear, how systematic, and 
how logical was the mind which could thus choose out from the 
tangled mass of fact and fiction constituting chemical theory in his 
day, the materials for a consistent, orderly, and productive system 
of scientific chemistry. 



T1LDEN : CANNIZZARO MEMORIAL LECTURE. 213 

What Cannizzaro did for chemistry may be broadly stated under 
the two following heads: 

First, he laid down for all time the two principal methods by 
which atomic weights are determined, the one by reference to the 
molecular weights derived from an application of Avogadro's rule, 
and the other by the adoption of the principle originally discovered 
by Dulong and Petit as to the general relation of atomic weight 
to specific heat among the solid elements, and he showed that these 
two methods when applicable to the same case lead to the same 
results. 

Secondly, he placed inorganic chemistry in a new light by 
applying to inorganic compounds the same principles which had 
been applied to organic compounds, and- thus finally disposed of 
the superstition which had hovered so long in the minds of chemists 
that organic chemistry was subject to laws different from those 
prevailing among mineral substances. 

There is, in fact, but one science of chemistry and one set of 
atomic weights. 

It will not be without interest to recall some of the consequences 
of the ultimate adoption, tardy as it was, of the principles laid 
down by Cannizzaro. The unanimity which has prevailed among 
chemists during the last forty years or mord as to the fundamental 
principles inculcated by Cannizzaro is a proof that his system is 
not only reasonable but is practically convenient. We are not now 
divided into parties on the subject of atomic weights, and although 
some may still incline to use hydrogen as the unit, whilst others 
prefer an exact integer for oxygen, these differences do not affect 
the notation nor the common language of chemistry. As a result 
of a uniform standard for atomic weights w.e now possess a natural 
system of classification of the known elements in the form of the 
periodic scheme with all its consequences, which I need not describe 
to a Society of chemists. Out of the revised and uniform system 
of atomic weights we also have a universally acknowledged system 
of constitutional formulae, based on valency, which we may define 
as the habit in regard to combination exhibited by the several 
elementary atoms, without necessarily forming any hypothesis as 
to the cause or nature of chemical "affinity." The wonderful 
discoveries which have been brought to light in the department of 
stereochemistry provide a body of evidence in favour of atomic 
structure which can never be set aside; and the day is now gone 
by when serious support can be found for any form of anti-atomic 
doctrine, since we have been shown how single atoms can be seen 
and counted. 

That all this knowledge would have come into the possession of 



214 TILDEN : CANNIZZARO MEMORIAL LECTURE. 

mankind sooner or later cannot be doubted, but that this genera- 
tion enjoys all the fruits of experiment in chemistry we owe to 
Cannizzaro. Without the clear light which his doctrine cast into 
the dark places of chemical theory sixty years ago chemistry might 
have remained a mass of unclassified, incoherent, and perplexing 
facts. 

This is why it is incumbent on this generation of chemists to do 
honour to his memory. The Chemical Society cannot be charged 
with indifference to the great services rendered to science by 
Cannizzaro, for, as mentioned at the outset, his name was placed 
on the limited roll of Honorary Members of the Society so far 
back as 1862. Ten years later he was invited to give the second. 
Faraday Lecture, and again in 1896, on the occasion of his seven- 
tieth birthday, an address was presented to him on behalf of the 
Society, in which full expression was given to the feelings of 
respect and admiration entertained by all the Fellows toward the 
veteran chemist. 

The Royal Society, also, awarded to him in 1891 the Copley 
Medal, which is regarded as the highest honour in the power of 
the Society to v bestow. 

Although English chemists have thus given what may be called 
official recognition to the author of the great reform, it would be 
unbecoming in any of us to hint at indifference or injustice on the 
part of French or German chemical writers while there are large 
and prominent English treatises in which the name of Cannizzaro 
is not even mentidned. Surely this is an occasion when in remem- 
brance of the unity of scientific thought throughout the world, fed 
by the contributions of all nations, a plea may be entered, not 
only for justice to individuals, but for complete international 
impartiality in matters of science. 

Italian science is no mushroom growth. Before our own Royal 
Society was founded, or perhaps even thought of, before the French 
Academy of Sciences came into existence, Galileo and Torricelli 
were making discoveries of world-shaking significance. In those 
times, however, to have observed natural phenomena, and even 
to be suspected of holding unfamiliar, novel, and therefore heretical 
opinions about the world in which man is placed, was to draw 
down on the unhappy philosopher the condemnation of political 
and ecclesiastical ignorance And fanaticism. No wonder that those 
whose interest was excited by the new knowledge then coming to 
light endeavoured to conceal their discussions and places of meeting 
under all kinds of fantastic and often ridiculous masquerade.* 

* See, for example, Disraeli's Cariosities of Literature : "On Ihe Ridiculous Titles 
assumed by the Italian Academies." 






TJLDEN : CANN1ZZAKO MEMORIAL LECTURE. 215 

Happily such prejudice, although occasionally showing itself, as 
in the instance already mentioned of the publication of II Nuovo 
Cimcnto, is now powerless, and the neglect of Avogadro's hypothesis 
cannat be put down to the influence of ecclesiastical authority. The 
obscurity which prevented its recognition arose out of the very 
nature of chemistry itself, and even the prosecution of research 
seemed for a time only to add to the prevailing confusion by 
producing crowds of new and unclassified facts. Science had, in 
fact, to wander in the wilderness until the great leader came to 
show the way. That Avogadro's life should have come to a close 
only two years before th formal proclamation and application of 
his doctrine before a congress of chemists seems a harsh dispensa- 
tion, but if he had lived only a little longer it would surely have 
been to him an added satisfaction that that doctrine should have 
been established by his fellow-countryman. 

As to Cannizzaro himself, we may rejoice that he not only led 
chemistry out of the shadow of the pillar of cloud, but in living 
to see the complete triumph of the system he had laid down so long 
ago he truly entered into, the enjoyment of the promised land. 

On the scutcheon which bears the names of Galileo and Torri- 
celli, of Galvani and Volta, of Avogadro and Piria, Italy may 
proudly write another glorious name, STANISLAO CANNIZZARO. 







[To face p. 217. 



BBCQUBEBL MEMORIAL LBOTUEB. 

DELIVEBED ON OCTOBER 17TH, 1912. 
By SIB OLIVER LODGE, D.Sc., LL.D., F.R.S. 

CONTENTS. 

A. GENERAL Page 

I. The General Tendency o/ Modern Science. 

General Effect of New Discoveries ... ... 219 

Discovery of Radioactivity 220 

Rapid Survey of Immediate Developments 222 

Intrusion of Scepticism ... 225 

Materialising Tendency in Physics ... ... ... 228 

Tendency to return to Ancient Views ... ... ;.. ... 229 

II. The Attitude to Established Laics. 

General Physical Laws... 230 

Relativity 232 

Life and Radioactivity 233 

Tendency to Discard Established Laws 234 

Unification . Multiplicity of Causes ... 235 

III. Tendency to Concrete Realisation, or Materialisation, 

throughout Science. 

Discoveries in Biology ... ... ... 237 

Demonstrations in Molecular Theory ... 239 

Crystal Structure ... 240 

Brownian Movement ... ... ... ... ... 241 

Maxwell's Demons 242 

IV. Scientific Consequences of the Discovery of Radioactivity ... ^*. 248 
B. HISTORICAL. 

I. Work of Henri Becquerel. 

Scientific Life of Henri Becquerel ... ... ... ... ... 244 

Personal Account of his Chief Discovery ... ... ... ... 246 

II. Work of the Becquerel Family. 

Summary of work of Antoine Becquerel 251 

Edmond Becquerel 252 

,, ,, Henri Becquerel ... 253 



218 LODGE: BECQUEREL MEMORIAL LECTURE. 



The Discovery of Radioactivity, and its Influence on 
the Course of Physical Science. 

PART I. GENERAL. 

THE atmosphere of physical science at the present time is rather 
a strange one. It is characterised by a large amount of speculative 
activity, on the one hand, and by an exceptional amount of funda- 
mental scepticism on the other. The two attitudes in fact coexist,, 
may coexist in the same individual, and one majf be a consequence 
of the other. For much of the speculation is sceptical in origin,, 
and much of the scepticism is speculative. 

There was a time, within easy memory, when the progress of 
discovery was placid and peaceful. It seemed to proceed along 
well-worn channels, and to be based upon the most thoroughly 
substantial knowledge of the past. The great Victorian era in 
physics was a development of Newtonian mechanics; and the 
foundation-stones of science seemed well and truly laid. 

Philosophers and biologists attended to their owji fields of work,, 
and so for the most part did mathematicians and chemists; each 
group proceeding on its own lines without much regard for the 
others. Now, all is changed: 

Chemistry has borrowed the idea of evolution fjrom biology, and 
is trying to extend it from the origin of species to the origin of 
atoms; though some chemists reject all this as baseless speculation,. 
and pour modulated scorn upon the few recent discoveries which 
physicists are willing to accept. 

Biologists have been ultra-speculative in their quest for the 
origin of life, and are turning their attention to metaphysics and 
philosophy, some of them in an energetic and pugnacious manner. 

Mathematicians disport themselves destructively among what 
have seemed the realities, the very data, of physics; distributing 
an atmosphere of doubt and hesitation almost equally over space, 
time, matter, and motion, and treating the ether with a veiled 
contempt. Philosophers question the correctness of our most funda- 
mental laws doubting, for instance, even the conservation of 
energy, and readily assimilating the sceptical utterances of those 
whom I have for the nonce described as mathematicians, though 
it is but an active group or school of mathematicians who take 
this line. 

And physicists, or some of them, are seeking to dispense with 
Newton's laws of motion, to supersede that dynamical basis on 
which they have built for so long, to regard ail laws as merely 



LODGE: BECQUEREL MEMORIAL LECTURE. 219 

conveniences of expressidn, and are trying if they can manage to 
sustain their science on a basis of action at a distance, fluid elec- 
tricity, corpuscular light, and caloric heat. 

General Effect of New Discoveries. 

Bethinking oneself of a cause for all this, it appears that, when- 
ever a discovery of striking novelty has been made, there is a 
tendency to consider that it not only supplements, but also super- 
sedes and even negatives, a great many of the opinions which were 
held before ; and hence an epoch of discovery is often followed by 
an era of scepticism. 

Discoveries are of two chief kinds the discovery of law and the 
discovery of fact. The two tend to become inextricably inter- 
woven : the discovery of law often leads to the discovery of new 
facts, and the discovery of new facts to either the formulation of 
new laws or new modes of statement, or to the resuscitation of 
discarded ones. 

As examples of the discovery of law, I instance Newton's gravi- 
tational theory of astronomy, and Maxwell's electromagnetic theory 
of light. Discoveries of this kind take their place among the most 
prodigious efforts of the human intellect. 

Smaller in achievement, but great as generalisations, I naturally 
mention also the atomic theory of chemistry and the conservation 
of energy. 

As examples of the discovery of fact, I might instance the pre- 
historic discovery of flame, the discovery of static electrification, of 
the electric current, and of magneto-electricity; and with these I 
would place the discovery of the electron, and the discovery of 
spontaneous radioactivity. 

Of all the facts discovered during the last half century, I suppose 
that Rontgen's JT-rays excited the most popular astonishment; and 
certainly they were sufficiently new. Nevertheless, existing theory 
had a place for them, as so6n as the electronic notion of cathode 
rays was admitted at least, on the assumption that they are pulses 
in the ether, a view held by most people, and still to be regarded 
as orthodox. For their immunity from refraction was provided for 
in Helmholtz's singularly comprehensive " Theory of Dispersion," 
their penetrative quality was a natural consequence of the thinness 
of the pulse shell ; whilst then origin, as due to the sudden stoppage 
of a minute electric charge, was not only accounted for, but actually 
necessitated, by the radiation theory of Larmor. 

Hence, if called upon to compare the discovery of Rontgen with 
the discovery of Becquerel, I should give the palm of novelty to the 
latter; for the spontaneous splitting up of atoms, and f he conse 



220 LODGE: BECQUEREL MEMORIAL LECTURE. 

quent expulsion of constituent fragments, was not provided for 
on any theory. It was a revolutionary new fact; although it is 
true that this view of it was not immediately recognised as an 
explanation, and although certainly Larmor's electronic theory of 
radiation, combined with Zeeman's experimental discovery, made 
some of us very willing to recognise the truth of the disintegration 
hypothesis as soon as it was promulgated on a basis of fact. Mean- 
while, and quite independently of any explanation, the bare fact 
of radioactivity, with a convenient means of detecting and measur- 
ing it, was quickly followed by the brilliant and exciting discovery 
by Madame Curie of a substance which exhibited the power to an 
extraordinary degree. 

A discovery of real and essential novelty can never be made by 
following up a train of prediction. It is often made during the 
process of following a clue, but the clue does not logically lead to 
it. A really new fact comes always as a side-issue something 
unexpected and something that might easily have been overlooked. 
In so far as it fails to have these characteristics, it cannot be 
essentially, and in the completest sense, new. The discovery which 
has been pointed to by theory is always one of profound interest 
and importance, but it is usually the elope and crown of a long and 
fruitful period; whereas the discovery which comes as a puzzle 
and a surprise usually marks a fresh epoch and opens a new 
chapter in science. 

Discovery of Radioactivity. 

So it is with the discovery of spontaneous radioactivity. The 
thing that was being looked for by Monsieur Henri Becquerel was 
the possible emission of Rontgen rays by a substance in a state 
of fluorescence. It was a reasonable thing to look for, although no 
theory exactly pointed in this direction; and had it been found 
it would have been an interesting extension of our knowledge ; but 
the kind of radiation actually detected turned out, when critically 
examined, to be for the most part not Rontgen rays at all, but 
corpuscular, and to have nothing to do with fluorescence. 

Stimulated by his father's researches in the fluorescence of 
minerals, and by the possession of many fine specimens, among 
others a beautifully fluorescent salt the double sulphate of 
uranium and potassium which had been made by him for his father 
many years ago, Henri Becquerel set himself carefully and critically 
to examine the kind of penetrating radiation which fluorescent 
substances exposed to light might possibly be found to emit, such 
as was also in a preliminary way detected by Niewenglowski, and 
later confirmed by Troost. What he sought he did not find, but by 



LODGE: BECQUEREL MEMORIAL LECTURE. 221 

deserved good fortune he had the happiness to find something 
much more important, thus writing his name large in the history 
of Chemistry and Physics for all time. 

The process of discovery is well known, but may be briefly 
recapitulated. This will, however, be most conveniently done later 
on, when giving a general outline of his life work. 

Such a discovery is quite easy to miss. The late F. Jervis Smith, 
of Oxford, told me that ho missed the discovery of Rontgen rays 
by a trifle; and other experimenters with Crookes's tubes must 
have missed it too; for whenever the vacuum in such a tube rises 
considerably, J-rays are likely to be emitted, and to take effect, 
whether perceived or not, on anything susceptible in their neigh- 
bourhood. Jervis Smith, in fact, noticed that boxes of photo- 
graphic plates which he needed for his work were liable to be 
fogged if allowed to remain in the neighbourhood of active Crookes's 
tubes. Presumably he thought the cause to be some merely 
chemical effluvium, such as ozone or oxides of nitrogen getting into 
the box, or perhaps he did not speculate on the cause at all, but 
merely regarded it as a nuisance, interfering with the steady course 
of his work. Anyhow, he seems to have instructed the laboratory 
attendant to keep the boxes in a cupboard well away from the 
fogging influence a >most natural thing to do, and one with which 
every experimenter must sympathise. 

Rontgen, however, as is well known, instead of a box of photo- 
graphic plates, happened to have a surface coated with fluorescent 
salt near his vacuum tubes, and although screened from the light 
its shine caught his eye in a more attractive and attention-compel- 
ling manner. 

In BecquereFs case the phenomenon looked for appeared to exist, 
in the way expected, although it was feeble and needed long 
exposure; but repetition in different circumstances showed that the 
agent which was expected to produce the effect, namely, fluorescence 
under the action of light, was inoperative: the action turned out 
to be spontaneous, and to be dependent only on the kind of mineral 
used.. So much so that no method of hastening or stimulating 
nor, indeed, of retarding this kind of radioactivity, beyond 
judicious selection of substance, is known to this day. 

The following statement concerning the discovery is made by 
Professor the Hon. R. J. Strutt: 

"It occurred to Professor Henri Becquerel, of Paris, to try whether 
these salts, when luminescent under the influence of light, would give 
out Rontgen rays. He exposed a photographic plate, wrapped in black 
paper, to the action of the luminescent salts, and found, after an exposure 
of some days, that a distinct impression had been produced on the plate, 



222 LODGE: BECQUEBEL MEMORIAL LECTURE. 

which appeared on development. It was natural to conclude that Rontgen 
rays were given off, as had been thought likely. 

"Extraordinary as it may seem in face of the result, this conclusion, 
as well as the reasoning which led to it, was quite mistaken. We now 
know that the fluorescence of the glass has nothing to do with the pro- 
duction of Rontgen rays. We know, further, that the fluorescence of 
uranium salts is quite unconnected with the invisible rays which they 
emit. And lastly, we know that these latter are of u quite different 
nature from the Rontgen raysl It seems an extraordinary coincidence 
that so wonderful a discovery should result from the following up of a 
series of false clues. For we can obtain the Rontgen rays even better 
by letting the cathode rays fall on a metal surface which is not fluorescent 
instead of a glass one which is. We can obtain invisible radiation, able 
to penetrate opaque substances, from uranium in ohe metallic form, 
which is not fluorescent. And lastly, as we shall see in the sequel, these 
uranium rays differ altogether in their nature from the Rontgen rays." 

All this does not detract from the merit of the discovery ; it rather 
enhances its practical importance, for, as we have already said, it 
is a feature inevitable when the facts to be discovered are really 
and essentially new. 

Rapid Survey o/ Immediate Developments. 

Discovery of the nearly non-deflectable and readily absorbable, 
or a, rays was made by Professor Curie by the electrical method. 
The most important examination of their properties was made by 
Professor Rutherford. His results were confirmed by M. Becquerel, 
who likewise examined the o-rays emitted by polonium, where they 
are unaccompanied by rays of the j8- and -/-varieties, and showed 
that their magnetic deviation increased at a distance from the 
source. 

An early photographic study of -rays, and of their magnetic 
deflexion, was made with fair completeness by Becquerel himself. 
One of his experiments, exhibiting the deflexion in a striking way, 
consists in placing a little radium salt in a lead vessel on the back 
of a photographic plate which is thus screened from any direct 
action and then deflecting the rays, by means of a magnet, right 
round on to the under surface of the plate, whereon shadows of 
interposed objects can be thrown in curious fashion by these 
circularly-travelling rays. 

The non-deflectable but very penetrating variety, the so-called 
y-rays, were discovered by Villard, whose results were soon 
confirmed by Becquerel. 

The discovery of the new element radium followed on a purely 
quantitative investigation as to the radioactivity of different 
materials carried out with exemplary pertinacity and genius by 
Madame Curie; just as the other rather sensational and admirable 



LODGE: BECQUEREL MEMOIIAL LECTURE. 223 

discovery of argon resulted from a quantitative investigation by 
Lord Rayleigh into the varieties of nitrogen apparently obtainable 
from different sources. 

In both these cases the discoverer himself, with a colleague, 
worked out many of the properties of the new material ; in the case 
of Becquerel this work was from the first conspicuously shared in 
by others; thus, Sir William Crookes chemically separated off the 
greater part of the activity of uranium, as what he called 
uranium-Z, and by systematic treatment, renewed after the lapse 
of a year, detected the prime facts of (a) the gradual decay in its 
activity, and (6) the renewal of the activity of the original stock 
to a compensating extent: thus beginning to open the eyes of 
physicists to what was really happening, and paving the way for 
the brilliant and extensive series of experiments by Professor 
Rutherford and his associates. 

The history of all this is so recent, the facts are so numerous 
and so fairly well known, they are related in so many accessible 
books, and they are of so great bulk and variety, that it would be 
impossible usefully now even to touch upon them or to attempt to 
follow the historical course of development any further. Suffice 
it to say that Rutherford measured the atomic weight of the 
^-particles by applying a magnetic field to their trajectory, and 
thereby showed that they were corpuscular, not in the electronic 
sense but in a sense definitely material, being probably either a 
molecule of hydrogen carrying the electrolytic unit of positive 
charge, or else an atom of helium with a double unit of charge; 
and he also displayed a gas-like emanation of high atomic weight, 
great activity, and short life; on the strength of all of which he, 
together with Soddy, started the idea of atomic disintegration, not 
as a speculation, but as an actually observed fact. Later Ramsay 
and Soddy by spectrum analysis definitely established helium as 
-one of the products of disintegration of this radium emanation, 
which itself appears to have a characteristic spectrum and is 
regarded as a short-lived element. 

In addition to the atomic bombardment or ct-particle projection, 
electrons are thrown off as if from a cathode, although with excep- 
tional velocity, as -rays; and -y-rays are likewise ejected, appa- 
rently akin to those of Rontgen, although with exceptional pene- 
trating power. All these exert an ionising action on the substances 
through which they travel, into the consequences of which a great 
many observations have been made by Professors Barkla, Townsend, 
and others ; and there appear to be other rays, probably electrons 
travelling at too slow a rate to ionise effectively and perhaps asso- 
ciated with emission of a-particles, which have been called 5-rays. 



224 LODGE: BECQUEREL MEMORIAL LECTURE. 

But their slowness is relative, for it is about 3 x 10 8 c.g.s. or 
2000 miles a second. 

All these forms of activity are of profound interest, but their 
importance is overshadowed by the less purely physical, and mor& 
directly chemical, phenomena namely, the emanation, the o-rays r . 
and the other products of disintegration ; for thus is demonstrated, 
for the first time in the history of science, the conversion of one- 
substance into another, the gradual breaking up of an atom by 
some kind of successive explosions or disruptions, and the conse- 
quent generation of one substance after another; among which* 
radium and its emanation, and possibly lead, occur successively at 
the heavy or gun end, whilst helium and probably hydrogen are- 
found at the light or shot end of the explosion. 

(Taking this as the origin of all the lead there is that is, assum- 
ing that it has all descended either from uranium or from some- 
heavy atomed substance of which uranium is the best known surviv- 
ing representative and a stage through which the process must have- 
passed radium being another stage, but too short-lived to be- 
usefully considered in the present connexion a little arithmetical 
calculation concerning the age of the earth, in this sense, can be- 
made, thus: 

Let U represent the original amount of uranium at the begin- 
ning ; and let it decay at rate k, so that after a time, t , the residue- 
in existence is 



Let lead represent the final result of the decay, itself being con- 
sidered comparatively permanent, so that the amount of lead now 
existing is 



= U -U. 



Finally, let the amount of lead existing at the present time be- 
n times the amount of uranium now existing, so that 

Pb = nU; 

it will follow, by combining these three equations, that the 
elapsed since the beginning of the planet in this sense is 



Now Professor Rutherford's estimate of the numerical value of 
the logarithmic decrement of uranium is 10 ~ 9 per annum; hence 
l/k equals a thousand million years. 

What estimate to make for n, the ratio of the extant lead to the 
extant uranium at the present time, I have no idea ; but the datum 
only enters into the result under a logarithm, and therefore does 
not affect its magnitude very conspicuously. If we guess, from the 
relative prices, that n = 20, the calculated age is 3000 million years; 



LODGE: BECQUEREL MEMORIAL LECTURE; 225 

whilst if we make a much larger estimate and suppose n to be 200 r 
the 3000 only increases to 5000 ; and, inversely, if n is only 2, the 
age is still 700 million years.) 

It is needless to emphasise the extraordinary suggestiveness which 
the instability and intense energy of atomic structure, thus demon- 
strated, confers upon our ideas of material atoms in general, since- 
it is surely probable that the stability of the atom of the better 
known elements, especially of the heavy ones like lead, mercury,, 
and gold, is, after all, only a question of degree. Some sub- 
stances last a few minutes, others a few weeks or years, some 
centuries, and others millions of aeons these last being naturally 
more plentiful, like a population with a low death-rate yet it must 
surely be considered unlikely that any such atomic groupings are 
so devoid of internal energy as to be endowed with an absolutely 
permanent structure incapable of further subdivision. 

(Incidentally, I would heartily deprecate any squeamishness about 
applying the historic term " atom " to elementary units, able to give 
a definite spectrum and to form chemical compounds of customary 
character, merely because the progress of discovery has rendered 
the derivation of the word inappropriate.) 

Intrusion of Scepticism. 

So far, it has all seemed plain sailing; but now has come the 
era of scepticism, and an attempt to limit science to purely material 
entities and to reduce Physics to a sort of glorified Chemistry, to. 
return, in fact, to the kind of ideas which prevailed in the golden 
age of Chemistry, near the early part of last century, and to discard 
everything relating to an ether of space. 

For instance, as to the nature of the y-rays, Professor Bragg, late 
of Adelaide, now of Leeds, has raised an interesting controversy; 
and has adduced experiments of his own in support of his view 
that they, as also their congeners the ..Y-rays, are not ether pulses 
at all, but are corpuscular; being neutral molecules, consisting, 
it may be, of positive and negative electricity in combination, 
ejected in a singularly penetrating manner; ejected possibly, not 
with exceptionally high velocity, but with their electric field so 
shut up in the molecular interior as to have no links with the 
outside world, and therefore to be able to travel far through crowds 
of other molecules without ionising them, and so without being 
stopped by the exhaustion of energy required for the ionising 
process. Sc long as the oppositely charged hypothetical constitu- 
ents are combined, they have little chemical influence; but Professor 
Bragg supposes y-rays to be broken up after a certain length of 
adventurous journey, and thus, by dissociation, to give rise to 



226 LODGE: BECQUEREL MEMORIAL LECTURE. 

j3-rays, and I suppose to some kind of positive rays also. Certainly 
7-rays, as they are absorbed, do give rise to j8-rays ; but this is also 
a natural consequence of their nature on the orthodox or ether- 
pulse theory ; for just as pulses are generated by means of suddenly 
stopped electrons, so, in the act of starting other electrons, the 
pulses may be destroyed. 

Professor Bragg's arguments as to their corpuscular nature are 
based on the secondary effects of -/-radiation, and on the unsym- 
metrical character of the resulting -ray distribution before and 
behind a pair of absorbing plates of different obstructive powers. 
The arguments are set forth in a properly substantiated manner 
by their author, and are not to be treated cavalierly. They 
appear to have secured the adhesion of Professor Callendar, 
who, in his Presidential Address to Section A at Dundee this 
year, expressed approbation of Professor Bragg's view; but 
for myself I feel unable to entertain the idea seriously, not only 
because, so far as I can follow the argument, it appears far from 
crucial, but because the ether pulses ot the orthodox view are so 
clearly indicated and indeed necessitated by theory. This is 
markedly true in the case of A'-rays, which are known to arise at 
the sudden stopping place of rapidly flying electrons; and Z-rays 
Are not supposed by anyone to differ greatly from y-rays. 

Larmor's radiation-theory makes the rate of loss of energy of any 



accelerated electric charge e quite definite, and equal to - (ace) 2 , 

'6v 

where v is the velocity of light. 

This furnishes in my judgment a quite fundamental point of 
view. Ethereal radiation is certainly due to the acceleration of 
electrons proportional, in fact, to the square of the acceleration. 
So when an electron is suddenly stopped or started, an ether pulse 
is inevitable. In the case of stoppage we call the pulse an Jf -ray ; 
in the case of starting we call it a y-ray. And the properties of the 
thin shell of radiation, which must then be started, agree with the 
known properties of X- and y-rays, which all admit to be alike. 

This statement Professor Bragg and those who adopt his opinion 
^will somewhere disagree with, for reasons given ; although in what 
way precisely they meet the theoretical objection, manifestly or at 
least superficially opposed to the conclusion which they draw 
from the experiments, I do not yet know, although I can make a 
surmise from some considerations which follow. 

Certainly quickly-flying electrons are stopped at the target of a 
cathode-ray tube; and certainly electrons are started, with still 
higher velocity, and more suddenly, at a source of radioactivity of 
the kind which emits electrons such as radium-C. When only 



LODGE: BECQUEREL MEMORIAL LECTURE. 227 

a-rays are emitted, y-rays are not found, or are not plentiful ; but 
they invariably accompany 0-radiation ; and the reason for this is 
manifest in the light of an ether theory of radiation. 

The question therefore arises as to what ethereal radiation is 
really like. In so far as Professor Callendar intends to advocate 
a dual constitution for the whole ether of space, making it consist 
essentially of interlocked positive and negative electricity which 
whatever it really means must at least denote two constituents of 
exactly opposite properties which are constantly being sheared, 
that is, strained in opposite directions (compare " Modern Views of 
Electricity ") I am in sympathy with the attempt, for I have long 
felt that the progress of discbvery would lead us somewhere in that 
direction, although a great deal more definiteness must be intro- 
duced before it is anything but a guess and an anticipation. On 
this view, however, it becomes just possible to conceive of an 
isolated unit of ether travelling among the rest, like a minute 
ejected double corpuscle, a combined plus and minus unit of charge, 
of the order of electronic size without associated matter; not so 
much an ether pulse as a minute ether projectile. The idea is not 
unreasonable, but at present I am unable to agree, without further 
evidence, that it represents the probable nature of y- and X-rays. 

There are those, however, who hold that even light, which for a 
century has certainly seemed to consist of ethereal waves or pulses, 
is likewise corpuscular; and that if it is not wholly explicable in 
terms of particles shot off from bodies, such ejected particles must 
form the beginning and substratum of an explanation, with some- 
thing periodic superposed upon the projectiles, after the manner of 
Newton. 

It is not surprising that an attempt should be made to revive in 
some form the corpuscular theory of light, even if light be now 
regarded as an electric manifestation ; for electricity, too, has become 
corpuscular, and ihe flow of electricity through metals is now 
regarded as a streaming of actual bodies detached, or so nearly 
detached as to be readily interchangeable, from the fixed atoms of 
a solid, and therefore migratory flowing from one metal to another 
across a junction as a fundamental kind of material thing which is 
able to exist in association with every kind of matter, its associa- 
tion is loose enough in metals, which are therefore good conductors ; 
whereas in another class of substances the corpuscles are so tightly 
held in combination with individual atoms that they cease to be 
migratory, and the substance is an insulator, that is, one which can 
only transmit a current by violence and disruption. 

The migratory and ionic theory of liquid conduction, and of the 
constitution of electrolytes generally, entered the field first, and, 

2H 



228 LODGE: BECQUEREL MEMORIAL LECTURE. 

although stoutly resisted by some chemists, appears to be holding 
its own, and to be invading one province of physical chemistry 
after another with marked success. 



Materialising Tendency in Physics. 

The ionisation doctrine and its many developments may be 
regarded as an encroachment of physics on the preserves of chem- 
istry, since it has certainly modified ideas about the nature of 
solution ; but there is a converse process now going on, and in the 
course of a sort of triumphant materialisation of obscure entities, 
achieved at any rate hypothetically and speculatively if not yet in 
any substantial manner, Chemistry seems to be dominating emanci- 
pated parts of Physics. 

The latest and most astonishing attempt towards the reconversion 
of Physics into Chemistry appears in a brilliantly clever and 
apparently serious Address to Section A by Professor Callendar, 
this year, on the resuscitation of caloric or the material theory of 
heat a theory which carries with it the ancient view that physical 
changes of state, such as vaporisation and liquefaction, are really 
the solution of matter in the substance of that apparently imponder- 
able material caloric, and vice versa. 

After this it is barely surprising to hear the biologists call upon 
the chemist to explain the phenomenon of life, and to produce in 
their glass vessels if only they can stumble on the right environ- 
ment, and on a judiciously combined assortment of material some 
low form of living matter. 

In view of the remarkable experiments recently made on the 
influence of various strengths of mere salt solutions in fertilisation 
and cross-breeding, it is not surprising that an anticipation of the 
kind should be promulgated. At present it is no more than a 
speculation, but if followed up, although it may not lead to the 
result anticipated, it may lead to others of perhaps equal interest. 

The careful and accurate and painstaking and recording experi- 
menter is always justified, and sometimes he is rewarded by results; 
but experiments of this kind, conducted in the dark as it were that 
is, without a clue of theory conspicuously need the utmost care; 
and concerning such experiments considerable scepticism is for a 
time legitimate and necessary. Of such kind, in that respect at 
least I may incidentally mention are some experiments and 
observations with which I have been more or less associated in 
connexion with what is known as psychical research. Positive 
results in this subject, when established, must be of extraordinary 
importance and novelty, but to establish them excessive care is 



LODGE : BECQUERBL MEMORIAL LECTURE. 229 

necessary, and until they are substantially verified respectful 
scepticism is entirely legitimate.* 



Tendency to Return to Ancient Views. 

All this tendency to return to discarded hypotheses and revivify 
old beliefs for spontaneous generation is, I suppose, a very old 
belief or superstition is a matter of great interest; and it is 
astonishing to find how much can still be said for ancient views. 
Forty years ago the Caloric theory of heat seemed dead beyond 
redemption, and I do not say that it yet lives, but the ingenuity of 
Professor Callendar finds a great deal to say for it, some of it of a 
cogent kind; it appears to be quite a possible mode of expressing 
facts, and one that is perhaps convenient for several non-elementary 
purposes. 

At any rate, Professor Callendar's Address to Section A at 
Dundee confers on the abstract mathematical idea of entropy a 
local habitation and a name which I for one had never previously 
recognised, and which I fancy neither Kankine nor Clausius recog- 
nised either ; whilst it emphasises, what was really never doubtful, 
the extreme brilliancy of Carnot's treatise on the motive power of 
heat. Moreover, it unifies the treatment of heat engines and electric 
motors, so far as can reasonably be expected without the opposition 
of sign familiar in electricity but presumably without meaning in 
heat. It is true that the production of fresh caloric during any 
irreversible process raises a difficulty about regarding heat as a 
substance ; but, from Professor Callendar's point of view, the diffi- 
culty is by no means insuperable. The source of the substance can 
perhaps be traced AS readily as we at present trace the source of 
heat-energy when that too is freshly generated by the like irrevers- 
ible processes. 

Then again in early days it was customary to jeer at the prevalent 
popular habit of speaking of electricity as a fluid, and until we 
knew more about it the practice was certainly to be deprecated; 
but now, in the light of further knowledge, something very like an 
improved and more definite fluid theory seems likely to hold the 
field. 

Hitherto, Rontgen radiation has seemed to belong almost wholly 

* When I speak of psychical phenomena as novel, I do not mean that testimony 
for their reality is limited to recent times folk-lore legends about them are as old 
as humanity ; the novelty consists in their now trying to make good their position 
in a scientific age, and in their appearing in a scientific dress. If we succeed in 
exposing them to rigid scrutiny, it will be another case of materialising the vague, 
the discredited, and the unseen. But that seems rather the tendency of science at 
the present day, and is noticeable in many branches, as I will emphasise later. 



230 LODGE: BECQUEREL MEMORIAL LECTURE. 

to Physics, whilst Becquerel radiation belonged largely also to 
Chemistry, to which science our friend the late Dr. Russell's 
radiation or emanation has always belonged wholly ; but now judg- 
ment as to the nature of Rontgen rays may have to be regarded as 
open to revision. 

We have already called attention to the fact that the undoubtedly 
corpuscular nature of some kinds of radiation, such as cathode rays, 
o-rays, and -rays, has inevitably led to an attempt to resuscitate a 
corpuscular theory of light; and, if the anti-ether speculators who 
support the Principle, of Relativity are to pave their way into 
anything approaching smoothness, some form of corpuscular light 
would clearly be necessary. 

THE ATTITUDE TO ESTABLISHED LAWS. 

General Physical Laws. 

Amid this sea of conflicting hypotheses and guesses what should 
be our attitude ? and how far should we condemn those philosophers 
who in their anxiety to stem the tide of materialistic philosophy 
(in which enterprise I for one am a sympathiser) have tried to 
throw doubt upon certain well-established and fundamental laws 
of physics an enterprise wherein, as in duty bound, I part company 
with them. 

I urge that our attitude should be this : 

Let us admit that any law applicable to concrete objects (not 
merely to abstractions), and established by induction on a basis of 
experience, must necessarily be of the nature of a postulate; but 
let us hold some of the postulates as so well established and secure 
that any argument that would necessitate their overhauling is 
ipso facto to that extent discredited, and not to be countenanced 
unless supported by new and revolutionary facts; and even these 
new facts we must try to explain in harmony with all well-estab- 
lished laws, rather than as disturbing or negativing them. 

In other words, let us seek to reconcile all new facts with the 
fundamental laws of physics, applied in a proper manner, until 
compelled to cast about for some higher generalisation. For in all 
probability that higher generalisation, when it comes, will be supple- 
mentary rather than superseding; and the conditions which necessi- 
tate its admission will be specifiable and definite when the subject 
is properly understood. 

Among such well-established laws I should place first Newton's 
laws of motion; remarking that they apply to matter only, not 
necessarily to ether ; and remarking also that effective mass may be 
variable under ce'rtain conditions, as it often is, for instance, 



LODGE: BECQUEREL MEMORIAL LECTURE. 231 

simply enough, in the case of a falling raindrop, or of a sphere 
entering a perfect fluid. 

Measurements of ejm t made on particles flying at two-thirds 
of the velocity of light, are by some said to invalidate Newton's- 
second law. It is to my mind unquestionably preferable to express 
the fact in terms of variable inertia the value of the inertia 
becoming in that case a known function of speed through ether. 

Those who disbelieve in ether cannot, of course, agree with this 
dictum. 

Again, the recently discovered pressure of light is sometimes said 
to invalidate Newton's third law. I should prefer to express the 
fact by saying that, when applying the law quite generally, an 
ethereal wave-front must be taken into account, as well as matter; 
and that we thereby get our first mechanical touch with the ether 
of space. 

Supporters of the Principle of Relativity will consider this 
nonsense. 

Another law I should place high and dry out of the reach of 
immediate controversy, is the Conservation of Energy. 

In so far as the actions of living beings seem to conflict with this 
law, in so far as the facts of guidance and control appear to militate 
* against it (as I for one hold that they do not), I would rather look 
for some new form of energy, or some ethereal seat of force or 
reaction, rather than doubt the generality of a comprehensive 
law of that kind. That law I should assume true; provided 
always that every form of energy, known and unknown, is taken 
into account. 

Again, the conservation of matter, although it is a law that 
requires caution in its statement, and although the disintegration 
of material atoms is sometimes said to upset it, is probably true in* 
essence. We must admit that our category of the thing conserved 
may have to be enlarged, so as to include electrons and other 
ethereal groupings or peculiarities, but it seems to me distinctly 
best to adhere to the idea of the conservation of fundamental 
substance until irrefragable evidence to the contrary is adduced. 

All these laws may some day have to be revised, and at any 
time they may have to be more carefully formulated; but it is a 
mistake to be willing too easily to pluck them up and discard 
them. So it was once with the law of gravitation. Every new 
perturbation detected in astronomy was liable to raise doubts about 
the exactness of the index 2 in the statement of the law of inverse 
square. I do not say that such doubts were illegitimate, although 
they have proved unnecessary, but I do say that this mode of 
explanation should be only seriously contemplated when other 



232 LODGE: BECQUEREL MEMORIAL LECTURE. 

resources had failed ; and as far as I know, other resources have not 
yet finally failed in any single case. 

Among other postulates of high authority I should be inclined 
to place a wave theory of light interpreted, of course, in terms 
of electricity and magnetism, not an elastic solid theory but 
definitely in terms of ether. For it seems to me that to try to 
discard the ether on the basis of a Michelson-Morley experiment, 
which after all is thoroughly and well explained by the FitzGerald- 
Lorentz hypothesis, is both retrograde and injudicious. 

Relativity. 

Some mathematicians, among them the late Professor Poincare, 
are willing to give away their kindred subject of physics by admitting 
or maintaining that our laws are not important statements of fact, 
but are only conveniences of expression. And many philosophers 
seem eager to accept this vicarious generosity at their hands. 

But such repudiation of our claims, and reduction of our life 
work to insignificance, I altogether deprecate. If we are not 
seeking real truth, if we are only seeking convenience of expression, 
the science of physics is not the noble structure which I for one 
think it. 

To take the simplest and most rudimentary example : 

Are we to suppose that it is only a matter of convenience whether 
we say that the earth turns on its axis, or that the host of heaven 
revolves round it once a day ? I hold that the one is a genuine 
and absolute truth, whilst the other is a genuine and absolute false- 
hood; and that convenience of expression has nothing whatever 
to do with the matter, except that the truth must always be ulti- 
mately more convenient than error ; just as I say that it is true that 
a train is travelling over the surface of the country, and not true 
that the ploughed fields and hedgerows are contorting themselves 
in the eyes of stationary travellers. The relativity of motion, thus 
pressed, and taking matter alone into account, is really absurd. Yet 
those who discard the ether are constrained to assert that there is 
no pragmatic difference between the two forms of statement, and 
no mode of ascertaining which is true : no meaning, in fact, in 
absolute motion at all. 

On the other hand, those who accept the ether attach a definite 
meaning to motion through it, and are ready to admit as probable 
that in ordinary circumstances motion as great as the velocity of 
light can only be asymptotically reached; or at least that if it is 
reached or exceeded the first law of motion will, so to apeak, break 
down, that is, become inapplicable, because to maintain the motion 
a propelling force will be required. Indeed, some day these 



LODGE: BECQUEREL MEMORIAL LECTURE. 233 

physicists with whom I agree expect to be able to measure the actual 
velocity of masses of matter through the ether of space by some 
definite phenomenon due to this kind of relative motion which is 
not the kind contemplated by the Principle of Relativity. That 
principle would lead us to maintain that inasmuch as this kind of 
motion is meaningless it certainly can never be experimentally 
proved. 

The great thing to avoid in science is negations. Let us make 
and substantiate positive assertions. But negative assertions 
statements as to what does not happen, or what is not possible 
although occasionally necessary, are always dangerous, and should 
be kept in rigorous check. 

Life and Radioactivity. 

Take, for instance, the attempts to construct living matter out of 
artificially combined materials. It may be impossible, but the 
attempt is quite legitimate, and no one can positively say that it 
will never be successful. 

In so far as life demands energy for its peculiar manifestations 
and trigger-pullings, an available source of such energy can easily 
be suggested. It may or may not be a useful, that is, a true, 
suggestion, but the phenomenon of radioactivity indicates a possi- 
bility. We know now that atoms possess a store of energy which 
they give off in random directions as they periodically and spon- 
taneously disintegrate. We have also long known, or supposed, that 
organic compounds left to themselves, apart from the cohering or 
integrating influences of life, likewise disintegrate and evolve energy 
gradually passing down a series of stages, giving off emanations 
and heat, and ultimately becoming inorganic. A decaying heap of 
refuse, a pile of manure, represents to me a sort of chemical analogy 
to the physical activity of uranium. 

The one is an affair of atoms, the other of molecules ; but in order 
to be conspicuously radioactive the atom must be large and massive, 
whilst in order to exhibit organic instability to a high degree, the 
molecule must be large and complex. 

In both cases there appears to be a complex grouping which, 
either with or without stimulus, disintegrates into something 
simpler, and generates heat or evolves energy in the process. 

Here, then, is a stock of energy running to waste : it would seem 
eligible for guidance. What life has to do is to control this spontane- 
ous disintegration of protoplasmic cells, to regulate the activity 
of the ganglia in the brain, for instance, or to suspend the disin- 
tegration of organic material until some appointed time, and then 
to direct it along a determined channel. That is all that a sports- 



234 LODGE: BECQUEREL MEMORIAL LECTURE. 

man or artilleryman does with the energy of gunpowder. He with- 
holds its explosion until an appointed time, and then he liberates 
it in a definite direction. To say that he propels the projectile, and 
thereby conflicts with the conservation of energy, is absurd. This 
process of timing and aiming is typical of the control of life 
throughout. The manner and method by which life achieves this 
control, it is true, we do not yet know. It is one of the many things 
which we have to find out. But those who say that life cannot 
guide material processes unless it is itself a form of energy (which 
is false, a man is not a form of energy) those who hold that life 
cannot, in fact, act at all unless energy is at its disposal (which is 
certainly true) forget the apparently spontaneous activity of 
complex otganised molecules, forget the ato'mic disintegration mani- 
fested by radioactivity. Energy is not a guiding or controlling 
entity at all. It is a thing to be gtf ided. Energy by itself is as idjnd 
and blundering as a house on fire or a motor-car without a driver. 

There is a great difference, moreover, between matter potentially 
living and actually alive. It must never be forgotten that in the 
physical universe our power is limited to the movement of matter : 
all that happens, after that, is due to the properties of matter and 
of its ethereal environment. If potentially living matter is ever 
artificially produced, by placing things in juxtaposition and bring- 
ing natural physical resources to bear upon the assemblage which 
is all that we can do then it may become alive. But if this last 
step is taken, it will be because something beyond matter, and 
outside the region of physics and chemistry, has stepped in and 
utilised the material aggregate provided in the same way, pre- 
sumably, as that in which it now steps in and utilises the material 
provided, say, in an egg or a seed. That is my belief, and only in 
that sense do I anticipate that the artificial incarnation of life 
will ever be possible. Certainly life has appeared on the earth 
somehow, and some day it may perhaps appear under observation. 
In that, case it will be said to have been manufactured. It will be 
manufactured just as much as radium or radioactivity has been 
manufactured, and no mor3. 

The spontaneous properties of matter, however, are far from 
exhausted : there may be many yet to be discovered. Twenty years 
ago no one knew or suspected the property of spontaneous radio- 
activity accompanied by atomic disintegration. Now it is a 
recognised commonplace of science. 

Tendency to Discard Established Laws. 

When radium was discovered many people jumped to the con- 
clusion that the law of conservation of energy had " gone by the 



LODGE: BECQUEREL MEMORIAL LECTURE. 235 

board," and that there was not only mystery but " miracle " about 
the constant evolution of heat by a speck of radium salt. Miracle 
about it there is none, in any ordinary sense; and the mystery 
has reduced itself into a consideration of what is the best theory 
of the way in which electrons and the other atomic ingredients are 
grouped together, and as to whether their internal energy is due 
to their static configuration (as Lord Kelvin argued) or to their 
kinetic orbital movements, as others of us have urged as more 
explanatory and far more probable. 

To suppose the law of conservation upset because a new source 
of heat is discovered an unexpected intra-atomic store of energy 
opened up is just one of those mistaken attitudes which I 
deprecate. 

In the ether, so I believe, the amount of energy stored ia 
immensely greater than anything which can be housed in a corre- 
sponding bulk of matter ; and whenever humanity becomes able to- 
tap this ethereal store, our descendants will be' liable to go through 
the same revolutionary perturbation as some of us have gone 
through; unless they are wise enough to take warning by the past. 
Whether the ethereal source is being, by any means whatever,, 
unconsciously tapped already, I do not know. There are a few 
observed facts which to me seem to hint at the possibility of such 
utilisation : but possibly the store of energy now known to exist 
inside atoms of matter is more than ample to account for anything 
of the kind. 

Unification v. Multiplicity of Causes. 

It is reasonable to enter a protest against entertaining the hypo- 
thesis of a multiplicity of causes for the same thing, without strong 
evidence that such multiplicity is necessitated by the facts; In 
some of the more complex, though it may be ordinary and familiar 
phenomena, a multiplicity of causes is obvious; for instance, to 
explain the death of an animal, or the fall of a house, or, again, 
such things as the settling of dust or of dew, the occurrence of 
wind, or the variation of terrestrial magnetism, several reasons can 
be given. But for fundamental things, one cause or one explanation 
must be expected to overpower and replace all the others, as soon 
as it is known ; for instance, to explain magnetism, or light, or gravi- 
tation, or inertia, one explanation of each must surely be funda- 
mental. 

To illustrate the matter further : to explain the occurrence of a 
sound, hundreds of possible causes may be suggested ; but to explain 
sound itself, a definite type of motion of the molecules is all that 
need be appealed to; and, whatever the kind or the origin of the 



236 LODGE: BECQUEREL MEMORIAL LECTURE. 

sound, the same kind of motion, in essentials, is all that we demand. 
Plenty of variety exists under the main head. 

And this commonsense attitude I would adopt in cases where 
the explanation is not known. Thus, for instance, Larmor has shown 
that ethereal radiation must be generated by the acceleration of 
electric charges. If this be granted, as I think it must, the straight- 
forward attitude is to seek to explain all radiation of an ethereal 
kind in that way, and to deny, except on definite evidence, that 
there is any kind of ethereal wave motion that cannot be traced to 
electronic acceleration. 

Corpuscular radiation, however, undoubtedly exists likewise ; and 
the question of to which category a given radiation belongs is 
perfectly open. 

So also the more general and far more important and difficult 
question remains an open one whether in some not yet worked-out 
way a corpuscular radiation can be imagined which has all the 
essential properties of an ethereal wave or pulse; for in that case 
we may be able to recognise essential Tightness in both points of 
view, and so be able to unify them as has so often happened before 
in the history of science. 

Alternative views are not always hostile and mutually destruc- 
tive, although it sometimes conduces to the progress of science if 
their supporters think they are; but ultimately it may be found 
that they represent opposite aspects of a truth as yet imper- 
fectly perceived. Certainly the fact that an advancing wave-front 
has momentum, exerts pressure, and sustains reaction has, in fact, 
many of the properties of matter, except that it cannot rest is 
calculated to attract attention and to give pause to anyone inclined 
to be dogmatic and dictatorial. 

Again, J. J. Thomson showed in 1881 that an electric charge 
possessed the property of inertia, so that when moving it possessed 
momentum and kinetic energy. It was premature then to pay 
great attention to this curious and interesting result, which seemed 
to indicate that mass could be reduced to an electromagnetic or 
ethereal phenomenon ; but now that electrons have been discovered, 
that is, electric charges so concentrated as to exhibit the properties 
of momentum and kinetic energy to a marked degree and now 
that metrical experiments have shown that the electromagnetic 
part of their inertia is the whole of it, it becomes natural and 
proper to assume, in default of definite evidence to the contrary, 
that electromagnetic inertia is the only inertia that exists. That is 
very far from saying that electromagnetic inertia is thoroughly 
understood; all that the hypothesis or postulate does is to cause 
us to look for an underlying meaning for mass in ethereal proper- 



LODGE: BECQUEBEL MEMORIAL LECTURE. 237 

ties, to regard the explanation of inertia as a possible quest for 
science, and not merely to sit down with folded hands and regard 
it as one of the fundamental and inexplicable properties of 
Newtonian matter. 

If all mass is reducible to electric charge; if all radiation not 
of a projectile character is to be attributed to electric acceleration 
of which ionic collision or chemical clash is one variety; if all 
electric currents are electrons or electric charges in motion; if all 
magnetism is due to the spinning of electrons; if all chemical 
affinity is really electric attraction over molecular distances or, 
what is the same thing, if electrostatic attraction is chemical affinity 
a long way off then clear statements of these various facts, when 
established, would be great generalisations and unifications, such 
as physicists used to strive for in old days and strenuously look 
forward to; although in these degenerate days mere convenience 
of expression is all that appears to be hoped for, and multiplicity 
of causes, like unexplained action at a distance, seems to be 
regarded with equanimity. 

Meanwhile, I recommend these unified generalisations as postu- 
lates, as guides to inquiry, to be held, not dogmatically, but as 
working hypotheses; the burden of proof being thrown, not so 
much upon facts which support them for those are manifestly 
numerous as upon facts which render any of them uncertain. 
Such facts when adduced must be rigorously scrutinised, and not 
lightly accepted at their face value; still less, of course, must they 
be rejected as contrary to the laws of nature. 

It may seem absurd that any facts could ever be rejected or 
excluded from contemplation on this latter ground, at this stage 
of the world's history, and with all the dogmatic errors of the 
past to guide us ; but, nevertheless, I have reason for asserting that 
it is not so impossible as it ought to be. 

MATERIALISING TENDENCY THROUGHOUT SCIENCE. 

Discoveries in Biology. 

The tendency of present-day science to materialise the invisible 
or to make concrete and tangible the vague influences previously 
thought of, has been well emphasised in a paper by Dr. Fraser 
Harris, of Halifax, Nova Scotia (see a paper called " The Metaphor 
in Science " in the American magazine called Science for August 
30th, 1912). 

The instances which he adduces are such as the following: 
The " acidifying principle," or dephlogisticated air, called by 
Lavoisier " the oxygine principle for those who prefer the same 



238 LODGE: BECQUEREL MEMORIAL LECTURE. 

meaning in a Greek dress," is now the familiar oxygen, purchasable 
at so much per cubic foot, like timber. 

So likewise Harvey in 1628 emphasised the probability of some 
movement in the blood " movement as it were in a circuit "- 
an motionem quandam quasi in circulo haberet. He had begun to 
think whether there might not be such a movement, and later on 
had said " this motion we may be allowed to call circular " ; thus 
the phrase " circulation of the blood " entered into physiology, 
although the actual fact was not visibly demonstrated until 1660 
- three years after Harvey's death. Then it became a concrete 
reality, and is now a common microscopic demonstration in the 
tissues of a frog's foot. 

Again, the " animal spirits," supposed by Willis in 1650 to be 
driven inwards by the impression of an outside object, so as to give 
rise to sensation, and then to rebound from within outwards so as 
to excite movement, are now the constantly experimented-on nerve- 
impulses, the physical speed of which was measured by Helmholtz in 
1850. Furthermore, the energy of even this nerve-impulse is being 
traced to minute granules or prisms alternately accumulated and con- 
sumed in the nerves, called after their German discoverer, the 
granules of Nissl. " These appear to be the dynamogenic material 
widely distributed throughout the nervous system ; and " nervous 
exhaustion," so far from being fanciful, is becoming associated with 
visible depletion of these microscopic granules. 

Then, again, muscular fatigue, understood by most people as 
merely a particular kind of feeling or sensation, is now made 
concrete and shown to be the result of mild muscular poisoning, or 
the deposit of fatigue-toxins in the system. 

As for malaria, a term which merely means " bad air," and ague, 
also- vaguely called paludism or the influence of marshes, they are 
now traced, as everyone knows, to a parasite of the mosquito 
traced, that is, to the bite of a thing which can be crushed with 
the fingers. 

Plague or pestilence, also, was in ancient times attributed to 
various mysterious causes such as a conjunction of the planets, 
the taking of a census, or the iniquities of the Jews but it has 
now been proved due to a minute vegetable parasite inhabiting the 
fleas of rats. 

The microbe of " influenza," even, the very name for " influ- 
ence " has now been seen by the trained eye of the microscopist ; 
and it is not to be doubted but that further progress in the same 
direction will be made. 

Everywhere, as Fraser Harris well says, indefinite and elusive 
things have been identified and shown to have a local habitation 



LODGE: BECQUEREL MEMORIAL LECTURE. 239 

or a distribution in the recesses of the living body. The whole 
tendency has been towards the objectifying of the subjective and 
the visibility of the unseen. 

It would lead too far away from the subject to speak of the way 
in which other vague and unseen entities or imaginaries, such as 
spiritual existences and phantasms, are being brought to book and 
materialised; nor are the facts yet ripe for public discussion; but 
in passing I may express my opinion that a materialising tendency 
is becoming conspicuous here also, and that ordinary mechanical 
acts and appearances will have to be directly attributed to ordinary 
or perhaps rather extraordinary mechanical and material causes, 
whatever their ultimate or indirect meaning may be. In even 
higher matters, I am convinced that progress lies in the direction 
of postulating definiteness and of thrusting vagueness out of the 
field. Skill and instinct are needed, however, to determine when 
it is time to move, and to discriminate genuine advance towards 
daylight from benighted blundering into a bog. 

Demonstrations in Molecular Theory. 

Another thing that has often been considered rather a vague 
matter of inference, and one on which a good deal of scepticism 
has persisted for a century, that is, since the time of Dalton 
although the hypothesis in one form or another is as old as the 
Greeks is the existence of those material discontinuities which are 
styled atoms. Although the atomic theory of chemistry has 
held its own, and although chemists have tried to picture to them- 
selves the kind of atomic arrangement or grouping which would 
account for the observed properties of molecules among other 
things for their crystalline interlockings and angular facets yet 
chemists have always been careful to say that these pictorial repre- 
sentations were not to be taken literally or supposed to correspond 
with actual fact, but that they were to be treated in a more or less 
metaphorical or allegorical manner rather than as statements of 
reality. Indeed, the tendency was to doubt whether the actual fact 
of such arrangements could ever be perceived; and a good deal 
of scepticism persisted in the minds of at least a few chemists as to 
whether " atoms of matter " were more than a convenient verbal 
expression. It was clearly realised by physicists that atoms and 
molecules were of so minute a size as to be always beyond direct 
tnicroscopic vision, since the waves of light, although exceedingly 
small, are much larger than molecules; and accordingly the eye, 
however much assisted, could never hope to see such things by 
aid of the comparatively coarse vibrations of visible light. 

But that has not prevented the invention of the ultra-microscope, 



240 LODGE: BECQUEREL MEMORIAL LECTURE. 

whereby diffraction phenomena can be ingeniously arranged so as 
to show, in a sense, the appearance of things far below ordinary 
possibilities of vision. 

Crystal Structure. 

And now, quite recently, the announcement is made from Russia 
that by the use, not of visible or even ultra-violet light, but of 
ethereal pulses of immensely shorter wave-length of pulses excited 
by the sudden stoppage of electrons, and therefore comparable in 
size rather to electrons than to atoms of matter by the use, that 
is to say, of JT-rays and a photographic plate^ it has been possible 
to examine into and depict the actual molecular arrangement and 
interior architecture of crystals, whereby the anticipations and 
geometrical arrangements laboriously arrived at as probable, by the 
life-work of Mr. William Barlow, F.R.S., and by him in association 
with Professor Pope, appears likely to be verified, improved, and 
made definite. 

Whatever may be the results achieved so far (and at present 
detailed information is lacking), the report is too probable to be 
disbelieved ; and however incipient may be the method as at present 
realised, it can hardly be doubted that on some such lines definite 
progress will eventually be secured, and the invisible and hypo- 
thetical and mysterious once more be brought under actual and 
definite observation. 

I base these anticipations on the diffraction photographs obtained 
recently by Drs. Knipping and Friedrich, and treated theoretically 
by Professor Laue; and also upon the testimony of Dr. A. E. H. 
Tutton, F.R.S., himself an eminent and experienced worker in 
crystallography. For he has described in a preliminary way 
discoveries made by Professor von Fedoroff, of St. Petersburg, con- 
firmed apparently in the laboratories of Professors Rbntgen and 
von Groth in Munich, whereby diffraction photographs of what he 
calls the space-lattice or molecular arrangement in the crystals of 
zinc blende can be obtained by the use of X-rays ; the molecules and 
their actual arrangement in the crystal becoming visible, or infer- 
able, and being such as apparently to confirm the independently 
discovered and identified types of homogeneous and symmetrical 
arrangements of the many classes of crystals studied with so 
much skill and pertinacity by our countrymen above mentioned. 
This, if it be a fact, will have to be recognised as a striking 
and admirable case of scientific prediction, the various crystalline 
structures and accuracy of characteristic facets having been indi- 
cated by theory long before there was any hope of actually seeing 
them; so that once more always assuming that the heralded 



LODGE: BECQUEREL MEMORIAL LECTURE. 241 

discovery is substantiated the theoretical abstraction will have 
become concrete and visible. 

Brownian Movement. 

But, after all, these are static things in comparison with certain 
discoveries of extraordinary interest developed during very recent 
years in connexion with the Brownian movement; whereby the 
kinetic theory of gases has been extended both theoretically and 
experimentally, and shown, to apply, not to molecules only, but also 
to the spherical particles of a precipitate or liquid emulsion 
particles which are perfectly visible in the microscope, and the move- 
ments of which can with care be projected on a screen for popular 
observation. I understand that, quite lately, they have been even 
kinematographed, by instantaneous photography, at intervals of 
I/ 20th of a second. 

These particles have been skilfully shown, by M. Jean Perrin, 
Professor of Chemical Physics in the University of Paris, to obey 
gaseous laws in complete detail; and, by measurements made on 
them, he has not only obtained determinations of the various 
gaseous constants and atomic magnitudes, but, in the light of the 
beautiful theory of Einstein, he has furthermore gained ocular 
evidence of the truth of a great many previously abstract and 
mathematically formulated laws. 

For instance, Maxwell's law of the equipartition of energy 
originally applicable to gaseous molecules considered as a system 
of elastic bodies colliding at perfect random has been proved to- 
hold in the case of these comparatively great masses, some of them 
as much as the hundredth of a millimetre in diameter, as well as 
to the atoms themselves; and certain molecular processes, such as 
coagulation or the formation of colloids, seem to be becoming 
visible by their means. 

Some of these particles of which the Brownian movement has 
been observed ere truly immense compared with atoms, since- 
particles of ten microns (the hundredth of a millimetre) in diameter 
are as much bigger than atoms as atoms are bigger than electrons. 
Their osmotic pressure is less than the thousand-millionth of an 
atmosphere, but their atomic weight is such that if conceived of as 
a gas at normal pressure and temperature, and still subject to 
Avogadro's law, their so-called gram-molecule would amount to- 
200 thousand tons. 

If M. Perrin's contentions are justified, it is, as he virtually says, 
rather singular to find the number of particles emitted by radium 
to be connected with Avogadro's constant ; and this with the equili- 
brium distribution of particles in a liquid, and the distribution of 



242 LODGE: BECQUEREL MEMORIAL LECTURE. 

energy in the infra-red spectrum^ as well as witTi many other things 
of extremely diverse character. 

Furthermore, these particles can be shown to be disobeying the 
second law of thermodynamics, at least in a form in which it is 
often stated; since they rise sometimes in a lighter liquid, and 
thereby extract work from it, although the temperature is perfectly 
uniform and the liquid stagnant ; thus showing what indeed is well 
known that the liquid is only statistically stagnant, whilst its 
individual molecules are in a state of strong agitation, and that 
the uniformity of pressure experienced by every side of a submerged 
body is only an average effect, true when the surface is sufficiently 
large for the law of averages to be valid. These particles are too . 
small to satisfy this condition, and accordingly they are bombarded 
in an unbalanced manner, and move irregularly. But the behaviour 
of these particles also emphasises the fact, whicn appears to be less 
well known than it ought to be, that the second law of thermo- 
dynamics is essentially a statistical law, not a fundamental law of 
nature; it concerns practical methods of using the irregular and 
unorganised motion called heat. That is to say, the second law 
is only applicable when the terms heat and temperature are appro- 
priate ; and these terms are necessarily concerned with large groups 
of molecules, and have no ultimate meaning when individual 
particles are attended to, for then their heat energy may be con- 
ceived of as being as available as any other kind of motion energy, 
for instance, that of a piston, rod or a flywheel. 

Maxwell's Demons. 

In the case of the Brownian movement the particles watched are 
small enough to demonstrate the bombarding influence of small 
groups of particles; and accordingly they behave somewhat as 
Maxwell's demons behave, except that they are purely inert and 
unintelligent taking blows as they find them by chance, not 
looking for them and therefore do not exert any demoniacal or 
discriminating influence the effects of which can be detected on a 
large scale; they require to be watched individually for any 
incipiently demoniacal occurrences to be observed. 

And, further, it appears that the motion of these particles is so 
intricate and irregular, so polygonal and revolutionary and discon- 
tinuous, that no reasonable tangent can be drawn at any point of 
their path, so that they have suggested to M. Perrin no doubt half- 
j ocularly the physical realisation of those curious curves, invented 
by mathematicians and hitherto supposed limited to abstract mathe- 
matics, which, although essentially continuous, have an infinitude 
of tangents at every point and no differential coefficient. 



LODGE: BECQUEREL MEMORIAL LECTURE. 243 

I doubt if physicists ever expected to be able to measure, still 
less actually to see, the effect of a single atom. But the extra- 
ordinary energy with which o-particles are ejected from a radio- 
active substance has now enabled this remarkable step to be taken. 
The ionising effect of a single particle, admitted through a minute 
orifice, is measurable by an electroscope; and the flash which it 
produces, when it strikes a target of sulphide of zinc, is popularly 
familiar in Crookes's spinthariscope. 

The speed of these charged atomic projectiles, thus spontaneously 
ejected from radium by intra-atomic energy, is such that a milli- 
gram of matter travelling with the same speed could do as much 
damage as a one-and-a-half ton shot fired from a cannon.* So, 
knowing this, it is not surprising that, although only single atoms, 
they can make a crystal flash where they strike, or can ionise 
86,000 molecules of air ; but it remains still surprising to learn from 
Rutherford's measurements that a milligram of radium is continu- 
ously ejecting 34 million of such projectiles every second. Yet these 
are things about which scepticism is quite inappropriate. 

Scientific Consequences of the Discovery of Radioactivity. 

The discovery of radioactivity, developed as it has been by the 
labour of physicists still working in full blast, has resulted in such 
important consequences as the following : 

1. Definite speculation as to structure of the atom. 

2. Discovery of an immense quantity of intra-atomic energy. 

3. A new kind of chemical change independent of any physical 
surroundings. 

4. Transmutation of one element into others, and an estimate of 
the life-time of each. 

5. A probable source for helium and the other inert gases. 

6. The probable parentage of lead, and ultimately of other well- 
known substances. 

7. Detection of the ionising power of rapidly-moving charged 
particles. 

8. Calculation of the energy required to ionise an atom of a gas. 

9. " The close connexion of the photographic and phosphorescent 
actions of the a-rays with their property of producing ions, raises 
the question whether photographic and phosphorescent actions in 
general may not, in the first place, be due to a production of ions in 
the substance." (Rutherford.) 

10. Data required for calculating the age of the earth supple- 
mented so greatly that previous calculations are superseded. 

11. Incipient computation of geological eras and dates. 

* At a speed of 1700 feet a second. 



244 LODGE: BECQUEBEL MEMORIAL LECTURE. 

12. A possible additional source of solar and stellar energy. 

13. Ability to make observations on matter and electric charges 
moving with nearly the speed of light. 

14. An experimental reduction of material inertia to electro- 
magnetic and ethereal influence. 

15. A method of gaseous analysis which exhibits not only the 
kind of substance, but its state of molecular aggregation, and like- 
wise the electric charge which each molecule or group carries. 

16. A method of determining atomic weights, even of very 
evanescent substances. 

And the list can be extended. 



PART II. HISTORICAL. 
Work of Henri Becquerel. 

Henri Becquerel, born in 1852, lived from his infancy in the 
atmosphere of the laboratory of the National Museum of Natural 
History in Paris. At the age of nineteen he entered the Ecole 
Polytechnique. Prom it he went into the Corps des Ponts et 
Chaussees, and studied as an engineer for three years. In 1875 he 
published a work which gained him a position as Demonstrator at 
the Ecole Polytechnique, where he became Professor in 1895. In 
1878, at the death of his grandfather, he became assistant in the 
Museum, under his father, then Professor; and him also he suc- 
ceeded in 1892. He was admitted into the Academy of Sciences 
in 1889, at the age of thirty-six. 

He was greatly attracted by Faraday's discovery of the action 
of magnetism on light, and considered that the department of 
magneto-optics was likely to be fruitful in discoveries. He seems 
to have detected a relation between the rotary magnetic power and 
the index of refraction of substances, the function being /iV(/i 2 1), 
which he claims approximately for bodies belonging to the same 
chemical family. This was published in 1875. He found, however, 
afterward^ that the law for magnetic substances is quite different 
from that for diamagnetic, the negative rotations varying approxi- 
mately, not as the inverse square, but as the inverse fourth power 
of the wave-length, and, in the case of dissolved magnetic substances, 
as the square of the concentration. 

Up to that time the Faraday effect had not been observed in 
gases, but with this law as a clue he was able to realise the magni- 
tude of the effect to be expected in their case; and in 1878-1880 
he demonstrated that gases enjoyed the same rotatory power as 
liquids and solids oxygen, however, on account of its magnetic 
properties, being anomalous. 






LODGE: BECQUEREL MEMORIAL LECTURE. 245 

He was accordingly interested in the influence of terrestrial 
magnetism on the atmosphere, especially on the effect of a great 
thickness of magnetised oxygen on light; and as a preliminary he 
determined the intensity of the earth's magnetic field by its action 
on carbon disulphide. Moreover, at the International Congress 
on Electric Units he proposed this as an absolute standard of 
current strength. 

He developed some theoretical views as to the cause of magneto- 
optic phenoir 3na, and became specially interested in the discovery 
of Zeeiuan. 'The interest of this, indeed, deflected him for a time 
from his researches in radioactivity which he had just himself 
discovered since he thought that the Zeeman effect corresponded 
exactly with that magnetic molecular action which he had been 
looking out for; and he illustrated magnetic rotation, the Zeeman 
effect, and anomalous dispersion, by an ingenious experiment OD 
sodium vapour. Electrons seemed to him just to fill the lacuna 
between ether and matter, and so to be of value in sustaining the 
vortex or spinning theory of magnetism which he favoured. 

He seems to have told his son that he had looked for the Zeeman 
effect in 1888, as indeed Faraday had before him; but, in both 
cases, without theoretical guide, and without being aware of the 
kind of magnitude which they must be able to detect. 

(Sir J. Larmor had anticipated the effect theoretically, but, suppos- 
ing radiation at that time to be due to atoms rather than electrons, 
had found the calculated effect too small for observation. He had, 
in fact, corresponded with me on the subject, and, stimulated by 
him, I repeated Zeeman's experiment, and showed it at a soiree 
of the Royal Society immediately after the Amsterdam discovery.) 

In 1879 H. Becquerel published a memoir on magnetic details 
in nickel and cobalt, and showed that ozone was more magnetic 
than oxygen; whilst nickel-plated iron became curiously magnetic 
after having teen heated to redness. 

With his father he made many experiments on the temperature 
of the underground -soil, and verified Fourier's theory for the case 
of underground temperature. 

He applied a discovery of his father in 1873 namely, that 
infra-red rays were able to extinguish certain kinds of phosphor- 
escence to a study of the bands of the infra-red solar spectrum, 
and likewise to the spectra of other substances, in particular of 
water, of the atmosphere, and of rare earths ; likewise of numerous 
metallic vapours. The new field thus opened to spectrum analysis 
must have covered a range of wave-length more extensive than the 
whole of the luminous region and of the ultra-violet portion at that 
time known (1883-1884). 



246 LODGE: BECQUEREL MEMORIAL LECTURE. 

He specially examined the phosphorescence of uranium salts, 
and studied the spectrum of their phosphorescence which his father 
had discovered, attempting to give the law of distribution of these 
bands. The non-phosphorescent salts of uranium appear to have 
absorption bands governed by the same law, revealing an excep- 
tional molecular constitution. 

He studied the absorption bands of a great number of minerals, 
attending specially to the spectrum of didymium which Bunsen had 
observed in 1866, together with their variation with the plane of 
polarisation of the incident light. 

From all this he argued thai the absorption of a molecule is 
independent of the action of neighbouring molecules, and goes on 
as if the absorbing molecule were alone ; so that if a crystal exhibits 
absorption bands corresponding with its various directions other 
than the axial directions, it must mean that other substances are 
present. The occurrence of neodymium and praseodymium verified 
these deductions. 

Becquerel considered that this method of absorption spectra, 
applied to crystals, conferred upon the observer a power of 
mapping out their intimate constitution; and he likens it to 
observing the arrangements of furniture and movements of people 
who dwell in a glass house. 

Some years later (1891) he described for the first time the spectra 
of the phosphorescence emitted by minerals when they are heated ; 
and, by differences of duration and brightness, considered that he 
could detect different components; thus, in the natural course of 
things, he was led to his fundamental and most brilliant discovery, 
with which physicists have been concerned ever since. 

Personal Account of his Chief Discovery. 

The following is a paraphrase of Henri Becquerel's own account 
of the matter: 

The idea of examining whether bodies could emit an invisible 
and penetrating radiation was suggested to me by the announce- 
ment of the first experiments of Bontgen. Poincare showed the 
first radiographs of Rontgen at the Academy of Sciences in Paris 
on January 20th, 1896, and in answer to a question from me 
[Becquerel] stated that the source of the rays was the luminous 
spot on the wall of the glass tube which received the cathode 
stream. I immediately thought of examining whether this new 
emission was caused by the vibratory movement which gave rise to 
the phosphorescence, and whether all phosphorescent bodies could 
emit similar rays. At this epoch no one imagined it a spontaneous 
production of energy; it was natural to suppose that a transforma- 



LODGE: BECQUEREL MEMORIAL LECTURE. 247 

tion of energy must be going on. In other words, that energy must 
be supplied in order to get the radiation. 

Becquerel seems to have mentioned his project to Poincare, and 
to have begun a series of experiments the very next day. On 
January 30th Poincare wrote in the Revue Generate des Sciences 
an article on Rontgen rays, in which he said: 

" Thus it is the glass which emits the rays, and it emits them by 
becoming fluorescent. May we not ask, therefore, whether all bodies 
whose fluorescence is sufficiently intense may not emit beside- 
luminous rays the X-rays of Rontgen, whatever may be the cause 
of their fluorescence? These phenomena would then be no more- 
[necessarily] connected by [being the consequence of] an electric 
stimulus. It may not be very probable, but it is possible, and 
doubtless easy enough to verify." 

This pronouncement seems to have started a considerable number 
of experiments. 

Thus, for instance, M. Charles Henry placed' on a photographic 
plate, enveloped in black paper, an iron wire with a few coins, and 
on one of the coins some phosphorescent zinc sulphide, and exposed 
the whole to Rontgen rays. On developing the radiograph he found 
that the shadow of the iron wire appeared lighter under the coin 
covered with zinc sulphide, and concluded that that substance had 
emitted rays through the metal on to the photographic plate. The 
experiment, however, was not convincing, and has not been con- 
firmed. M. Henry made other experiments, such as one on the 
action of the rays emitted by hexagonal blende across leaves of 
aluminium and cardboard an experiment subsequently developed 
by M. Troost. 

Some experiments seem also to have been made by Monsieur 
Le Bon, which, however, M. Becquerel mentions only to discard, 
since he considers that they have been wrongly associated with his- 
new phenomenon. They have to do with rays from luminous 
sources said to be capable of traversing metallic screens, but stopped 
by black paper. Henri Becquerel considered them all due to known 
causes, but to be arranged and described in so confused a manner 
as to mask the real reason of the observed facts; he says that it 
suffices to re-read, in the Comptes rendus, M. Le Bon's first publica- 
tions to convince anyone that the author had no idea of the pheno- 
menon of radioactivity. M. le Bon's experiments were also 
reviewed by MM. Niewenglowski, Lumiere, and Perrigot, and were 
shown to have been due to infra-red rays which are known to be- 
able to traverse ebonite. Becquerel himself verified the complete- 
ness of these explanations, but says that one note of Monsieur 
Niewenglowski deserves attention, namely, this: A screen covered 



248 LODGE: BECQUEREL MEMORIAL LECTURE. 

with powdered calcium sulphide, after having been exposed to 
light, emits radiations which are able to impress a photographic 
plate through cardboard and black paper; and Becquerel goes on 
to say that he has repeated similar experiments, which are remark- 
able possibly indicating the presence of either infra-red or ultra- 
violet rays of penetrating character but that the phenomenon does 
not appear to be the same as that which constitutes radioactivity. 

His own first observations on the radiating properties of the 
salts of uranium were published at the sitting of the Academy of 
Sciences on February 24th, 1896. 

In the first series, photographic plates enveloped in black paper 
were exposed to the radiation of phosphorescent substances stimu- 
lated in vacuum tubes too slightly rarified to give Z-rays ; but the 
exposure given was insufficient to show any result. 

In another series, bodies such as fluorspar, hexagonal blende, etc., 
excited in ordinary air by sparks, were applied to a covered photo- 
graphic plate in the same way ; but still chey gave no result, either 
during or after excitation, although the exposure lasted several 
hours. He says he hesitated to try some beautiful preparations of 
phosphorescent sulphides or other salts which he possessed, in these 
circumstances, because of their deliquescence. 

Nevertheless, in spite of the negative results obtained so far, he 
still built great hopes on experimentation with uranium salts, of 
which he says : I had formerly many opportunities of studying their 
phosphorescence as a sequel to the work of my father. These bodies, 
he goes on, appear to have a peculiarly remarkable molecular con- 
stitution, regarded from the point of view of phosphorescence and 
absorption. 

Among the preparations of uranium salts in his possession there 
were some beautiful plates of the double sulphate of uranium and 
potassium, which he had prepared about fifteen years before. These 
crystals, unalterable in air, seemed entirely suitable for the projected 
experiment, but he happened, to have lent them to his friend, 
Monsieur Lippmann, in connexion with his researches on interfer- 
ential photography, of which the beautiful results ate well known. 

The same day, however, on which M. Lippmann returned those 
crystalline plates, Becquerel made the first successful observation; 
whence originated the whole series of his radiographic positive 
results. 

He placed two crystals of the double sulphate on a photographic 
plate enveloped in a double sheet of thick black paper, putting 
under one of them a piece of silver ; then he exposed the whole to 
the sun a procedure which subsequent knowledge showed to be 
entirely useless and after some hours developed the plate, and saw 



LODGE: BECQUEREL MEMORIAL LECTURE. 249 

a light impression corresponding with the silhouettes of the crystals, 
and a shadow of the piece of silver. The luminosity of uranium 
salts ceases in the one-hundredth of a second after exposure to light, 
so that it appeared quite necessary to maintain the luminous 
stimulus during the attempt. 

He then repeated the experiment, interposing a thin sheet of 
glass or of mica in order to stop anything due to vapour or other 
chemical emanation. The same result was obtained, only feebler. 
These were the results communicated by him to the Academy of 
Sciences on February 24th, 1896. 

On March 2nd, 1896, he described further experiments, where 
he showed that plates protected by aluminium 2 millimetres thick 
were not affected at all by a whole day's exposure to the sun unless 
a crystal of the uranium salt was added. 

Other simple variations were described, and then came the oppor- 
tunity for discovery. He usually affixed the uranium salt to the 
aluminium or other opaque coating by strips of gummed paper. He 
prepared some in this way on Wednesday the 26th and Thursday 
the 27th of February, and as on these days the sunlight was very 
intermittent, and the exposure quite unsatisfactory, he preserved 
the plates, fully prepared for subsequent treatment, in a dark 
cupboard, without developing them or removing from them the 
crystals of uranium. Fortunately, however, the sun did not shine 
on either of the two following days, and so he developed the plates 
on March 1st, expecting to find only very feeble impressions. On 
the contrary, they came out stronger than he had seen them before, 
and he perceived that the action had continued in the dark. He 
announced this fact to the Academy of Sciences at its sitting on 
March 2nd, and naturally proceeded to repeat the whole of the 
experiments without any exposure at all, subsequently concluding 
thus: 

It thus appears that the phenomenon cannot be attributed to 
luminous radiations emitted by reason of phosphorescence, since, 
at the end of one-hundredth of a second, phosphorescence becomes 
so feeble as to become imperceptible. 

So he announced the fundamental new fact of the emission of 
penetrating rays without apparent exciting cause. Either the 
diffuse light had long stored its energy in these substances, or else 
there was some phenomenon of a completely new order. In the 
first case the effect must gradually decay with time ; and it was to 
the examination of that possibility that his next series of experi- 
ments were directed. He proceeded to keep crystals in complete 
darkness for years, and naturally the complete disproof of the 
alternative or slow decay hypothesis was a matter of time. Suffice 



250 LODGE : BECQUEREL MEMORIAL LECTURE. 

it to say that although the cause of the phenomenon was not then 
ascertained, the fact of apparently spontaneous radioactivity was 
definitely established. 

It is doubtful whether with uranium salts alone anything more 
than a small fraction of our present knowledge of radioactivity 
could have been attained; but very soon after the first discovery, 
namely, on March 7th, 1896, Becquerel made the important 
and practically useful observation that the new radiation had the 
power of discharging electrified bodies, that is, of rendering the 
surrounding gas a conductor. He employed a gold-leaf electroscope, 
of which the leaves were examined by a microscope, and measured 
their rate of subsidence under the influence of various salts. The 
comparative ease and rapidity and metrical character of this 
method of examination induced Madame Curie to take as the 
subject of her Doctor ial Thesis the measurement of the radio- 
active powers of an immense number of minerals, and so led her 
gradually to one of the most brilliant and striking discoveries of 
modern times, the whole representing a new epoch in our knowledge 
of atoms, and therefore in physico-chemical science. 



WORK OF THE BECQUEREL FAMILY. 

The name " Becquerel " is so familiar to students of physics, 
and it seems so natural that the name should occur in connexion 
with physical investigations throughout the past century, that we 
are rather apt to take the work for granted and neglect considera- 
tion of the personality behind the work. Moreover, when there are 
three or four workers of the same name, some care is needed to 
discriminate the individual. 

As this is a Becquerel Lecture it may be convenient here, there- 
fore, to make a kind of summary of the work of this eminent family, 
especially as they constitute a group notable from the point of 
view of Galtonian heredity. 

The present Professor of Physics in the Natural History Museum 
in Paris, Monsieur Jean Becquerel, has made a convenient summary 
of the work of his ancestors, that is to say, of his father, grand- 
father, and great-grandfather, in an inaugural Address which he 
gave on the assumption of his inherited Chair; and this I shall 
make use of in the summary that follows. 

The earliest and most prolific of the group of four was Antoine- 
Cesar Becquerel, who, in the course of an exceptionally long life 
devoted wholly to Science, made a series of familiar discoveries, of 
which we are too apt to forget the origin. They lay chieHy in the 
direction of the voltaic, pile, electrometallurgy, and the applications 



LODGE: BECQUEREL MEMORIAL LECTURE. 251 

of electrical knowledge to natural history, meteorology, and 
agriculture. 

His son, Edmond Becquerel, succeeded him, and his researches 
are mainly connected with photography, spectroscopy, and phos- 
phorescence. 

Work of Antoine Becquerel. 

The work of Antoine Cesar Becquerel may be thus briefly sum- 
marised : 

In 1819 Antoine Becquerel seems to have investigated piezo- 
electricity, or the electric manifestation displayed by minerals 
under pressure, generalising the observations of the Abbe Haiiy 
very considerably; thus it was that he was led from the subject 
of mineralogy to that of electricity. 

In 1823 he worked at thermo-electricity and the seat of the 
E.M.F. in a voltaic pile, being a strenuous supporter of what was 
called the chemical theory, and arguing against Volta and Davy. 

In 1825 he was comparing the electric conductivity of different 
metals, and devised the first differential galvanometer for the 
purpose. 

In 1829 (nine years apparently before Daniell) he invented a 
constant battery, explaining why the power of the ordinary voltaic 
cell fell off so rapidly, owing to deposits on the plate, and indicating 
the necessity of dissolving or avoiding such deposits. So he says 
the best results are obtained when the copper is plunged into a 
solution of copper nitrate, and the zinc into a solution of zinc 
sulphate; the two being separated by a membrane of gold-beaters' 
skin. A pile so constructed, he says, with each metal plunged into 
a separate vessel ^enclosing a suitable liquid, avoids the ordinary 
polarisation of the plates, whereby currents tend to be produced in 
the inverse sense to the main current. Professor Becquerel now says 
that sulphate of copper was as often used by his ancestor as the 
nitrate, and that this constant battery was then called a pile 
cloisonnee-, although in an improved and more practical form it 
became universally known subsequently as the Daniell cell. 

In 1846 he constructed the first silver chloride cell; and in the 
year following invented an electromagnetic balance for measuring 
electric currents a glorified edition of which, designed by Viriamu 
Jones and W. E. Ayrton, is now set up at the National Physical 
Laboratory under Dr. Glazebrook at Bushey. 

For forty years his work lay in the direction of applying ins 
electrical knowledge to natural history, to agriculture, and to 
physiology. He also considered electrical effects in meteorology and 
other terrestrial manifestations; attending also to such subjects as 
the climatic effect of forestry on rainfall. 



252 LODGE: BECQUEREL MEMORIAL LECTURE. 

In 1850 he worked in electro-metallurgy, studying the deposits 
of many kinds of metals, and the conditions under which they could 
be obtained ; among other things finding how to deposit nickel and 
cobalt. 

In 1867 he discovered the phenomenon of electro-capillarity, and 
demonstrated its influence in connexion with endosmose and 
exosmose. He doubted the existence of the muscular currents 
discovered by Du Bois Reymond, and ultimately attributed them to 
capillary causes. He found an E.M.F. between different liquids 
separated by porous diaphragms ; and at the age of eighty-seven he 
considered all this in relation to the phenomena of life. 

He died in January, 1878, and only a few months earlier, at the 
age of ninety, published his last work, on the E.M.F. and the heat 
production of electro-capillary actions. 



Work of Edmond Becquerel. 

Some idea of the work of Edmond Becquerel can be thus given : 

Edmond Becquerel, born 1820, became, at the age of eighteen, 
assistant to his father; and, stimulated by the discoveries of 
Daguerre, studied the production of electricity by light, and 
endeavoured to make an electro-chemical actinometer. Among 
other photographic discoveries he photographed the ultra-violet 
spectrum in 1842, and began the photography of colours. His 
coloured photographs had to be kept in the dark, where they have 
lasted seventy years, but they cannot be exposed to even diffuse 
daylight. 

In 1843 he studied Joule's law cf heat production by electric 
currents in liquids, and made a liquid rheostat for use with a 
differential galvanometer to measure liquid conductivities. 

In 1846 he examined Faraday's? magnetic rotation of light, 
showing that it varied inversely as the square of the wave-length, 
and he verified the magnetic properties of oxygen. 

In 1853 he investigated the conductivity of hot gases, and 
measured furnace temperatures by photometric means, showing 
that they were not so high as had been supposed. (A development 
of this method has since been applied to the temperature of sun 
and stars.) He also constructed a thermo-electric pile with about 
one-third of a volt E.M.F. 

But the work for which he is chiefly known is that on phosphor- 
escence. This had been begun by his father in 1839; the phosphor- 
escence having been excited by electric discharges. 

In 1843, in his work on the ultra-violet spectrum, he examined its 
phosphorescent influence, and thus saw the dark lines in that 



LODGE: BECQUEREL MEMORIAL LECTURE. 253 

region of the spectrum which he had already discovered by photo- 
graphy. 

In 1857 he described the preparation of many phosphorescent 
substances, with the region of the spectrum appropriate for exciting 
each. He also excited them by the induction coil, and in 1858 
invented that beautiful instrument the phosphoroscope, with which 
naturally ne made many observations. 

In 1859 he showed that rarefied oxygen remained luminous some 
instants after the passage of a discharge a phenomenon which, in 
the case of nitrogen, has been so admirably pursued recently by 
our Professor Strutt. 

In 1869 he published a work on phosphorescence called " Light, 
its Causes and Effects," in two volumes; which book is said by 
Professor Becquerel to have been full of suggestions to young 
physicists on almost every page. 

In 1872 he began to examine the phosphorescent properties of 
uranium, and in 1873 devised a method of studying the infra-red 
rays of the spectrum, by their power of extinguishing the phos- 
phorescence of a screen coated with hexagonal blende on which 
they fell. This became the basis for his work in making iso- 
chromatic plates by the use of different absorbing substances and 
of chlorophyll; and, throughout, he applied his researches to 
meteorology and to the action of light on vegetation. 

Conclusion. 

The experimental labours of Henri Becquerel, based on the 
work of his predecessors, has been already dealt with. It lies 
chiefly in the domain of phosphorescence and spectroscopy, especi- 
ally the absorption spectra of crystals. He concerned himself also 
with magneto-optics, and was the discoverer of the spontaneous 
radioactivity of matter. 

Professor Jean Becquerel concludes his Address with some 
useful remarks on matters of general interest, especially concern- 
ing the association of a Chair of Physics with a Museum of 
Natural History. It appears that the creation of such a Chair was 
judged useful in 1838, after some of the work of his great-grand- 
father. A small and modest laboratory was then established, 
devoted to pure physics for the- sake of its possible application to 
natural history of the most general kind. The discovery of radio- 
activity alone would have justified such a foundation, for the influ- 
ence of that material property is now known in the ground, in 
mineral waters, in the atmosphere, and in geological formations; 
likewise in biology and medicine the rays have proved of high 
interest. But, as can be deduced from the preceding summary, a 



254 LODGE: BECQUEREL MEMORIAL LECTURE. 

great many other applications and practical consequences have 
followed from the researches conducted in that small laboratory. 

Professor Becquerel claims that one of the causes conducive to 
the productiveness of this laboratory was the continuity of the 
work accomplished there. Antoine Becquerel began the study of 
phosphorescent substances under electric discharge. Edmond 
Becquerel continued the work, and recognised the exceptional 
properties of the salts of uranium. Henri Becquerel pursued the 
subject, and effected the climax. He himself definitely recognised 
the long tradition of pertinacious and successful inquiry on which 
lie had built, and he spoke thus : 

It was perfectly appropriate that the discovery of radioactivity 
should have been made in our laboratory, and if my father had 
lived in 1896 he it is who would have made it. 




[To face p. 255. 



VAN'T HOPF MEMORIAL LECTURE). 

DELIVERED ON MAY 22ND, 1913, 
BY JAMES WALKER, D.Sc., Ph.D., LL.D., F.R.S. 

THE work of van't Hoff is indissolubly woven in the texture of the 
chemistry of to-day. Whether we are organic chemists, inorganic 
chemists, or physical chemists, we constantly utilise and apply his 
ideas, reap the benefit of the intense thought he devoted to the 
fundamental problems of our science. This is his splendid and 
enduring memorial. Nothing can add to it, nothing detract from 
it. Feeling this profoundly, I conceive that I may best discharge 
the honourable responsibility laid upon me by the Society if I give a 
sketch of his life, his main achievements, and his way of thinking 
with as little discussion and elaboration as possible, and as simply 
as I may.* 

Jacobus Henricus van't Hoff was born in Rotterdam on the 
30th of August, 1852. He came of pure Dutch stock, and his 
ancestry can be traced back to one Adriaen van't Hoff, who lived 
in the latter half of the seventeenth century at Groote Lind, near 
Rotterdam. His father was a practising physician in that city, 
his mother the daughter of a wine dealer of Middelharnis. The 
well-known landscape of Middelharnis, by Hobbema, in the National 
Gallery, shows the garden where van't Hoff often played in his 
boyhood. 

Van't Hoff was sent to a private school, in which the education 
seems to have been of a liberal character, the usual scholastic 
subjects being relieved by sports, games, and physical exercises. 
Henry, as he was then called, to distinguish him from a brother 
likewise named Jacob, excelled in mathematics, and received com- 
mendation for his work in natural science. His mind, however, was 
not wholly occupied with his regular school studies, for at fehis 
time he was awarded prizes by a local musical society for singing 
and for pianoforte playing. Long country walks were a favourite 
recreation, and his letters show both his acute observation of nature 
and his keen appreciation of scenery. At the age of fifteen he 
entered the newly founded " Hoogere Burgerschool," a non-classical 
institution of the type of a German Real-schule.. Whilst constantly 

* My information has been mostly derived from "J. H. van't HoflTs 
Amsterdumer Periode 18771895," by W. P. Jorissen and L. Th. Reicher 
(Helder, 1912), and in particular from the interesting biography by Professor 
Ernest Cohen, "Jacobus Henricus van't Hoff, sein Leben uiid Wirken " (Leipzig 
1912). Both of these works contain full bibliographies. 



256 WALKER: VAN'T HOFF MEMORIAL LECTURE. 

near the head of his class, he never succeeded in reaching the first 
place, if, indeed, he ever tried. 

Here he received his first instruction in chemistry. A school 
companion relates that they were taught according to the old system 
of formulae, the formula of water, for example, being HO, although 
they were told in the highest class that a new formulation with 
H 2 O was beginning to make headway. Practical instruction in 
chemistry was given in the school, and this evidently interested 
young van't Hoff, for he with some companions secretly repaired 
to the school on Sundays to finish their class exercises, and to 
perform additional unauthorised experiments. 'As they, boylike, 
enthusiastically chose to Work with highly poisonous or explosive 
substances, their private investigations, when discovered, were 
brought to an abrupt end. Van't Hoff, however, continued his 
experiments at home, and conducted them on business-like lines, 
as he is reported to have- charged spectators a small fee, which was 
expended in the purchase of fresh apparatus and material. A few 
months before van't Hoff completed his curriculum, the chemist 
Hoogewerff was appointed head of the school, and gave a sketch 
of the development of theories of organic chemistry, which, although 
too far advanced for the majority of the scholars, was welcomed 
and appreciated by van't Hoff. His leaving certificate reads as 
follows : 

Mathematics and mechanics Excellent 

Physical science Very good 

History, etc Good 

Languages and literature Satisfactory 

Drawing Satisfactory. 1 

The following two years were spent by van't Hoff at the 
Polytechnic School of Delft. He had not yet decided what line 
of life he would take up, beyond that it should be practical. A 
holiday experience in a sugar factory, however, convinced him that 
technical chemistry was a somewhat monotonous occupation, and 
his inclination turned more and more towards pure science. He 
therefore on returning to the Polytechnic studied with increased 
zeal, and to such purpose that he received his diploma at the end 
of the second year, whereupon he left Delft for the University of 
Leiden. 

What chiefly weighed with van't Hoff in moving to Leiden was 
the better opportunity afforded there for the study of the higher 
mathematics, the want of which he had greatly felt at Delft. At 
the University he frequented student society but little. On his 
rare appearances at the Debating Club, however, his comments on 
questions of the day and on topics of art or science provoked and 
enlivened discussion. Freedom and originality of thought were 



WALKER: VAN'T HOFF MEMORIAL LECTURE. 257 

even then characteristic of him. Indeed, he complained in later 
years of his University studies that they were too matter-of-fact, 
took too little account of his being a man and not a mere organ 
for the acquisition of knowledge; and declared that under their 
influence he would have become a dried and shrivelled scientific 
conglomerate had it not been for the counter influence of the 
intensely subjective and personal Byron. The writers who 
influenced him at this impressionable period of his life were, on 
the philosophic-scientific side, Comte and Whewell, on the literary 
side, Burns and Heine. But Byron was his favourite and hero. 
References to Byron, quotations from Byron, abound in his letters, 
and together with much verse in his native tongue van't Hoff wrote 
many Byronic stanzas in English. 

Van't Hoff now definitely decided on the study and prosecution 
of chemistry as his work in life, and since Leiden offered no special 
facilities in the subject, he passed his candidate's examination, a 
necessary step towards the doctorate, and left the University at 
the end of a year. 

Kekule's fame attracted him to Bonn. The romantic surround- 
ings of the Rhine University town made a strong appeal to him. 
He wrote later : " In Leiden all was prose the town, the country, 
the people. In Bonn all is poetry." 

Only a year was spent by van't Hoff in Bonn. That he became 
unsettled, melancholy, even bitter, is clearly shown by the tone 
of his letters. He found Kekule unsympathetic, but made a lasting 
friend in Walthere Spring, of Liege. 

There can be little doubt that Kekule's teachings on the constitu- 
tion of organic substances deeply interested van't Hoff, and it was 
on Kekule's advice that he continued his scientific studies elsewhere 
instead of accepting a technological or teaching post, van't Hoff's 
choice fell on the " Ecole de medecine," in Paris, where the genial 
Adolphe Wurtz directed the studies of his enthusiastic pupils, but 
before proceeding to France he entered the University of Utrecht 
for three months in order to pass the doctoral examination pre- 
liminary to the doctorate. The most noteworthy circumstance of 
van't Hoff's sojourn in Paris is that there he made the acquaintance 
of the Alsatian, Joseph Achille Le Bel, who a year later was to 
share with him the credit of the invention of the asymmetric carbon 
atom, van't Hoff apparently did little in the way of practical 
research while in Paris, and it is recorded of him, "II etait si 
tranquille qu'on ne faisait pas grande attention a lui." 

In order to obtain his doctor's degree, van't Hoff re-matriculated 
in the University of Utrecht in October, 1874, and was promoted 
to his doctorate in December of the same year. His dissertation 



258 WALKER: VAN'T HOFF MEMORIAL LECTURE 

was entitled " A Contribution to our Knowledge of Cyanacetic 
Acid and Malonic Acid." It was of a routine character, and 
contained nothing beyond the powers of an ordinary advanced 
laboratory student. This is at first sight surprising, for van't Hoff 
had in the preceding September issued as a pamphlet his famous 
paper on space-formulae. The original pamphlet was in Dutch, 
and bore the title, " An attempt to extend to space the present 
structural chemical formulae, with an observation on the relation 
between optical activity and the chemical constitution of organic 
compounds." It argues well for the sound common sense of the 
young van't Hoff that he presented a humdrum piece of practical 
work for his dissertation rather than the startling innovation con- 
tained in his pamphlet, for the latter might have had an even 
worse fate than the equally famous thesis of Arrhenius, containing 
the first statement of the theory of electrolytic dissociation. 

In giving this sketch of van't Hoff's educational career, I have 
made no attempt to treat it otherwise than in a superficial, mainly 
topographical, manner; and this because I fancy that the accidents 
of his education had little influence on his mental development. 
Now at the beginning of his productive career we find him a quiet, 
unassuming young man of twenty-two, with a physique by no means 
robust; reserved, but of agreeable manners; cultivated on many 
sides ; with a taste for the writing of verse and for natural science, 
in particular entomology. He differed from the bulk of his 
academic contemporaries in being essentially a man of ideas, a 
thinker. He had pondered over the properties of the atoms, on 
their actions on one another at small distances, and over the 
problem of how the chemical and physical properties of compound 
molecules were to be conceived as a function of the nature of the 
Constituent atoms and of their arrangement. The first tangible 
result of this cogitation was the laying of the foundation of stereo- 
chemistry. 

It is a constant phenomenon, ana always a fresh surprise in the 
history of science, to find a pioneer, capable, one might think, of 
any mental step, stopping short by a hand's breadth of some 
important discovery or generalisation. The driving force of the 
original idea exhausts itself, or the general state of knowledge 
fails in some particular, and years may have to elapse before a 
fresh mind with a new stimulus, and possibly a different goal, can 
take the required step. The early history of stereochemistry 
illustrates this peculiarity of scientific advance in striking fashion. 

In a lecture published in 1860 Pasteur said: "We know, on the 
one hand, that the molecular structures of the two tartaric acids 
are asymmetric, and, on the other, that they are rigorously the 



WALKER: VAN'T HOFF MEMORIAL LECTURE, 259 

same, with the sole difference of showing asymmetry in opposite 
senses. Are the atoms of the right acid grouped on the spirals 
of a dextrogyrate helix, or placed at the summits of an irregular 
tetrahedron? We cannot answer these questions." The ideas of 
the quadrivalent carbon atom and of molecular structure based 
upon it were still too novel and also too remote from Pasteur's 
practical line of thought, to enable him to take the short but, as 
it turned out, difficult step to the asymmetric carbon atom. 

That the necessity for space-formulae became increasingly felt is 
evident from the following quotations. 

In 1867 Kekule wrote: "The incompleteness of the old models 
may be avoided if, instead of arranging the four affinities of the 
carbon atom in a plane, we place them in the directions of hexagonal 
axes, so that they run out from the spherical atom and end in the 
planes of a tetrahedron." 

A definite example of the use of space-formulae is given by 
Patera 6 in 1869, who writes as follows: 

" Three isomerides, C 2 H 4 Br 2 , supposing that they really exist, 
can be easily explained, without the necessity of assuming with 
Butlerow a difference amongst the four affinities of the carbon 
atom, if we postulate that the four valencies of the atom of carbon 
are arranged in the sense of the four angles of a regular tetra- 
hedron : then the first modification would have the two atoms of 
bromine (or any other univalent group) attached to the same atom 
of carbon; whilst in the other two modifications, the two atoms 
of bromine would be each attached to a different carbon atom, 
with the difference that in one case the two atoms of bromine would 
be symmetrically arranged, and in the other not." 

Wislicenus in the same year clearly indicates the general nature 
and mode of solution of the problem in connexion with the lactic 
acids: "Facts like these will force us to explain the difference 
between isomeric molecules with the same structural formula by 
means of a different arrangement of their atoms in space, and to 
seek for definite ideas concerning this," a statement which he 
reiterates and emphasises in 1873. 

These definite ideas were given practically at the same time by 
?an't Hoff and by Le Be,l, the former publishing his pamphlet in 
September, 1874, and the latter a paper in the Bulletin de la Socittt 
Chimique in November of the same year. One would naturally 
imagine that the idea which gave the key to the problem must have 
originated in one of the frequent discussions in Wurtz's laboratory, 
for here we have two young men parting at the end of June, and 
a few months later publishing separately a notion which was at 
the time generally regarded as something entirely novel and 



260 WALKER: VAN'T HOFF MEMORIAL LECTURE. 

revolutionary. Yet van't Hoff tells us that no communication on 
the subject had passed between them. He says: "That shortly 
before this we had been working together in Wurtz's laboratory 
was purely fortuitous; we never exchanged a word about the 
tetrahedron there, though perhaps both of us cherished the idea in 
secret. To me it had occurred the year before, in Utrecht, after 
reading Wislicenus's paper on lactic acid." 

In view of the passages I have quoted above from earlier workers, 
it might almost be asked : What, then, did van't Hoff and Le Bel 
discover ? Wherein lies the merit of their work that they should 
be acclaimed as the originators of stereochemistry when the problem 
and the fundamental ideas seem to have been so clearly enunciated 
before them ? On the one hand, the idea of the asymmetric 
structure of optically active molecules was given by Pasteur; on 
the other, Paterno uses tetrahedral carbon atoms to explain a case 
of isomerism in much the same way as they would be used to-day, 
except that he regards the carbon tetrahedra as not being capable 
of rotation round the axis joining their centres. Separate, these 
ideas remained unproductive ; correlated, they became endowed with 
marvellous fertility. Van't Hoff and Le Bel's great contribution 
to stereochemistry was to define the conditions under which the 
asymmetric structure appeared, namely, when the carbon atom was 
attached to four different groups. Van't Hoff, in addition, boldly 
adopted the tetrahedron as the formal representation of the carbon 
atom in this new aspect; Le Bel, whose considerations are more 
general, only mentions it once in his paper. Not only did they 
state the bare principle, however; they showed it was a living one, 
drew deductions from it, applied it on all sides, and delivered it, in 
short, as an effective instrument into the hands of their fellow- 
workers in chemistry. Otherwise, like Avogadro's principle, it 
might have been forgotten, and for years perhaps have awaited 
some Cannizzaro to rediscover or revivify it. 

It is of interest to quote van't Hoff's own words as to the origins 
of his conception and that of Le Bel, and as to the points in which 
they differed : 

"On the whole, Le Bel's paper and mine are in accord; still, the 
conceptions are not quite the same. Historically, the difference lies 
in this, that Le Bel's starting point was the researches of Pasteur, 
mine those of Kekule. 

" The researches of Pasteur had made plain the connexion between 
optical activity and crystal-form, and had led to the idea that the 
isomerides of opposite rotatory power correspond with an asymmetric 
grouping and to its mirrored image. Indeed, the possibility of a 
tetrahedral grouping was suggested. Le Bel closely follows Pasteur, 



WALKER: VAN'T HOFF MEMORIAL LECTURE. 261 

then, when he sees this grouping in the four atoms or radicles 
inactive bodies all different united to carbon. 

" My conception is, as Baeyer pointed out at the Kekule festival, 
a continuation of Kekule's law of the quadrivalence of carbon, with 
the added hypothesis that the four valencies are directed towards the 
corners of a tetrahedron, at the centre of which is the carbon atom. 

"Practically our ideas, so far as they concern the asymmetric 
carbon, amount to the same thing explanation of the two isomerides 
by means of the tetrahedron and its image, disappearance of this 
isomerism when two groups become identical, through the resulting 
symmetry and identity of the two tetrahedra." 

Le Bel's general treatment was more purely geometrical and in 
certain ways more thorough than that of van't Hoff, which was 
better calculated to appeal to chemists, and, indeed, gave the stamp 
to stereochemistry in its subsequent development. In detail the 
following points of difference between the authors may be noted. 
Le Bel accounts for the existence of internally compensated inactive 
forms, such as mesotartaric acid; van't Hoff, by means of the 
tetrahedra, clearly explains the nature of unsaturated inactive 
isomerides, such as maleic and fumaric acids. 

The following lines contain a brief resume of the original 
pamphlet of September, 1874. Van't Hoff shows that if we imagine 
the four affinities of the carbon atom to lie in a plane, the groups 
attached to them being fixed, and their positions not interchangeable, 
a great many more isomerides are predicted than actually exist. If, 
on the other hand, the affinities are not in a plane, but directed 
to the -summits of a tetrahedron from its centre, the number of 
compounds predicted in general coincides wifh the number of 
compounds existing. His chief statements are given in the follow- 
ing terms: 

(a) If the four affinities of a carbon atom are satisfied by foui 
different univalent groups, two and not more than two tetrahedra 
are obtained, of which one is the mirror image of the other and 
cannot be superposed on it; that is, we encounter two isomeric 
structural formulae in space. 

(6) Each carbon compound which in the dissolved state effects a 
rotation of the plane of vibration of a polarised ray, contains an 
asymmetric carbon atom, that is, one whose affinities are satisfied 
by four different univalent groups. As examples, he gives lactic 
acid, aspartic acid, asparagine, and malic acid, with one asymmetric 
carbon atom; tartaric acid with two; the sugars, mannitol, etc., 
with at least one. Further, camphor and borneol, according to 
Kekule's formulation, contain an symmetric carbon atom, and are 
correspondingly active. 



262 WALKER: VAN'T HOFF MEMORIAL LECTURE. 

The derivatives of optically active compounds lose their activity 
if the asymmetry of all the carbon atoms disappears ; for example, 
inactive maleic acid from active malic acid, inactive succinic acid 
from active tartaric acid, inactive cymene from active camphor. 

In a list of compounds the formulae for which contain an asym- 
metric carbon atom, there are many cases in which the compound 
is not active. This may be accounted for in one of the following 
ways : 

1. The compound may be an inactive mixture of two equally and 
oppositely active isomerides. 

2. If the activity is small, it may be lost in the experimental 
error. 

3. The condition "asymmetric carbon atom" may not in itself 
be sufficient, the nature of the different groups being of moment as 
well as their mere difference. 

The principle that an optically active compound probably 
contains an asymmetric carbon atom gives the means of choosing 
between possible formulae; for example, optically active primary 
amyl alcohol must have the formula (CP 3 )(C 2 H 5 )CH-CH 2 OH. 
There is a certain degree of probability that an inactive compound 
contains no asymmetric carbon atom. Thus, the formula of citric 
acid is probably CO^H-CH2-C(OH)(CO 2 H)-CH 2 -COoH, and not 
C0 2 H-CH(OH)-CH(C0 2 H)-CH 2 -C0 2 H. 

Formulas are given for the simplest optically active monohydric 
alcohol, monobasic acid, dihydric alcohol, saturated hydrocarbon, 
and aromatic hydrocarbon ; and attention is drawn to the fact that 
there are no optically active normal hydrocarbons, alcohols, or 
acids. 

(c) If two doubly bound carbon atoms are each united to two 
radicles which differ from each other, two isomerides, hitherto 
unforeseen, are predicted ; for example, maleic and f umaric acids. 

In van't Hoff's pamphlet the carbon tetrahedra are figured 
exactly as they are met with now in text-books of organic chemistry. 

A French translation of the paper appeared soon afterwards in 
the Archives N eerlandaises, and a condensed French account in the 
Bulletin de la Societe chimique. Finally, a much expanded French 
pamphlet, " La chimie dans I'espace," was published at Rotterdam 
in May, 1875. 

Disappointment followed the publication. Instead of his 
hypothesis provoking discussion, as he had hoped, it was received 
by the majority of chemists with indifference, if not with coldness. 
Wurtz, Spring, and Louis Henry wrote warm acknowledgments of 
its receipt, but made no attempt to discuss or criticise. Berthelot, 
whilst admitting the general interest of van't Hoff's formulae, took 



WALKER: VAN'T FOFF MEMORIAL LECTURE. 263 

up the ground that a complete representation of constitution 
involved a representation of the rotatory and vibratory movements 
of the atoms and groups, and was disposed to attribute optical 
activity to these movements. The physicist, Buys Ballot was the 
first to give serious attention to van't Hoff's theory, and in the 
MaandUad voor Natuurwetenschappen he published an open letter 
to van't Hoff, who replied in a paper (November, 1875), discussing 
many interesting points which had been raised in the letter. He 
gives, for example, the configurations of the ten isomeric saccharic 
acids. A cordial letter from Wislicenus then followed, suggesting 
that the pamphlet should be translated into German, which was 
done by Herrmann, and issued in 1877 under the title Die Lagerung 
der A tome im Raume, with a preface by Wislicenus. The German 
version, which differs in many ways from the original, was widely 
read, and van't Hoff's ideas now began to gain ground. Strenuous 
opposition by Kolbe, who at that time was tilting at graphic 
formulae of every sort in a eries of lively articles in the Journal 
fur praktische Chemie, perhaps, if anything, increased their vogue 
by drawing more attention to the subject. 

Meanwhile van't Hoff had graduated, and was on the look-out 
for a situation. He failed to obtain any teaching post as science 
master in a school, but in March, 1876, he succeeded in becoming 
assistant in the Veterinary College of Utrecht, there to teach 
chemistry and physics. He had command of good apparatus, and 
during the two years of his tenure of the office he worked at a 
variety of subjects, the substances obtained from storax claiming 
much of his attention. He wrote several stereochemical papers, 
one on carbon rings, one 6,n Ladenburg's benzene formula, one on 
the direction of the valencies of the nitrogen atom, and one on the 
connexion between optical activity and constitution. 

To this period belongs his book, " Ansichten uber die organische 
Chemie" the preface of which is dated Utrecht, October, 1877. In 
itself the book is almost unreadable, but it affords the clearest 
evidence of the author's independence of thought, his keen eye 
for essentials, and the painstaking way in which he sought to 
isolate materials and problems of pure chemistry from the traditional 
associations which obscured them. The first part is purely 
systematic, and treats of the physical and chemical properties of 
organic substances regarded and classified as derivatives of methane. 
In the introduction to the second part (published in 1881), he 
expresses himself as follows : 

"The purpose of the second part is to obtain a knowledge of 
the chemical nature of carbon in itself and of the changes which 
it undergoes when the element combines with other atoms or 



264 WALKER: VAN'T HOFF MEMORIAL LECTURE. 

groups of atoms. To succeed in this purpose we must obtain a 
general view of the chemical reactions in which the carbon atom 
plays a part, and the changes in physical character which accompany 
them. If such a reaction is expressed by the general equation : 

(=0)X + Y-Z = (=0)Y +X-Z, 

the knowledge of the reaction must include a knowledge of the 
heat change which accompanies the reaction, and of the velocity 
with which it takes place under given conditions, whilst a knowledge 
of the changes of property is attained by comparison of the physical 
nature of (EEC)X and (EEC)Y. The reaction expressed above in 
general form may be followed out for particular carbon compounds 

(0 o) X in the same two directions. What ultimately appears as 
independent of o, , y is the expression of the chemical nature of 
carbon in itself; the difference due to the changes of o, /3, y are, 
on the other hand, regarded as the changes which carbon undergoes 
when -it combines with other atoms or groups of atoms." 

In the text of the second part we find the beginnings of those 
studies in chemical thermodynamics and affinity which were after- 
wards pursued to such good purpose. 

In September, 1877, van't Hoff was appointed lecturer in 
chemistry in the Town College of Amsterdam, which a month later 
was raised to the dignity of a State University. In June, 1878, at 
the age of twenty-six, he became ordinary Professor of Chemistry, 
Mineralogy, an4 Geology ; and six months later he married Johanna 
Francina Mees, the daughter of a Rotterdam merchant, whom he 
had known from early youth. 

Van't Hoff spent eighteen years in the University of Amsterdam. 
Although the old laboratory in which he worked was small and 
inconvenient, he refused a call in 1887 to the newly created Chair 
of Physical Chemistry in Leipzig, eventually filled by Ostwald. His 
teaching duties were onerous. With two assistants he had to give 
instruction in organic and inorganic chemistry, crystallography 
(which he had studied with Groth), mineralogy, geology, and 
palaeontology, and to conduct practical classes for 100 medical and 
20 science students. Notwithstanding this, the amount of prac- 
tical work he executed and supervised was very great. The 
atmosphere of his laboratory may be described in the words of his 
assistant, van Deventer. " Whoever knows the Amsterdam labora- 
tory knows that things do not take place there in any ordinary 
way. There is something mystical, something uncanny in the air. 
And this demonic something is the belief one might call it the 
superstition if success had not so often followed it the belief of 
van't Hoff that his fundamental idea, the analogy between chemical 



WALKER: VAN'T HOFF MEMORIAL LECTURE. 265 

and physical phenomena, is profoundly true." Elsewhere van 
Deventer says : " It must be said that van't Hoff's work is in many 
ways more French than German. Soundness and solidity he 
certainly values, but he is in love with the idea in its general 
form, and his proofs are directed more towards establishing his idea 
in the world as a great rough block that cannot be overthrown, than 
to modelling and rounding it off that he willingly leaves to others. 

" This love of the idea is often found, too, in the experimental 
method which he adopted. Transition points were studied with 
an instrument which a well-trained physicist would only have used 
for preliminary experiments. Van't Hoff used it for the decisive 
investigation, and the proof is unimpeachable." 

It is characteristic of van't Hoff's devotion to the idea that he 
chose as the subject of his inaugural address in Amsterdam, "The 
role of Imagination in Science," and strove to show how great a 
part imagination played in scientific investigation. He drew 
attention to the imposing number of scientific men with a leaning 
towards poetic and romantic invention, and closed his address with 
a quotation from Buckle : " There is a spiritual, a poetic, and, for 
aught we know, a spontaneous and uncaused element in the human 
mind, which ever and anon, suddenly and without warning, gives 
us a glimpse and a forecast of the future, and urges us to seize 
truth as it were by anticipation." 

Following out the 'line of thought already indicated in his intro- 
duction to the " Ansichten" van't Hoff investigated various types 
of reaction velocity and chemical equilibrium, which he collected 
in his Etudes de dynamique chimique, published in 1884. It is 
true that much had been done by others in these fields of investi- 
gation; for example, in velocity by Harcourt and Esson and by 
Goldberg and Waage, and on the thermodynamical side by 
Horstmann and by Willard Gibbs, although the work of the latter 
was then unknown to van't Hoff, as indeed it was to chemists 
generally. Van't Hoff, however, systematised, exemplified, and 
applied the principles involved, and, in fact, left the subject of 
chemical dynamics much in the state in which we find it to-day. 
For example, he classified reactions into unimolecular, bimolecular, 
termolecular, according to the number of molecules taking part in 
the transformation. He showed how to determine the number of 
molecules taking part in a chemical action, and investigated 
secondary actions and disturbing influences. He discussed "tem- 
perature of inflammation." He introduced the symbol ^ for 
reversible actions. He introduced and illustrated the term 
"transition point," and showed the close analogy between the 
chemical "transition point" and the physical melting point, in 



WALKER: VAN'T HOFF MEMORIAL LECTURE. 

V 

particular as regards the effect of pressure. He stated clearly the 
principe de I'equilibre mobile as follows: "Every equilibrium 
between two systems is displaced by fall of temperature in the 
direction of that system in the production of which heat is 
developed." He showed that Berthelot's principe du travail 
maximum is only strictly true at the absolute zero. Finally, he 
devoted the last section of the book to a study of chemical affinity. 
He shows how affinity may be measured by electromotive force, 
how at a point of transition the work of affinity is zero, and con- 
stantly uses the important equation : 

= --, 
22* 

although he does not prove it, merely stating that it had been 
deduced in a rigorous manner from the principles of thermo- 
dynamics. I remember having read these Etudes in 1885 or 1886, 
and I can well recall the mingled feeling of revelation and bewilder- 
ment which the book produced on me. I had perused such books 
on theoretical and physical chemistry as were then available, but 
had derived comparatively little satisfaction from them. Here, I 
thought, was the real thing at last, hard to comprehend, certainly, 
but something definite. What I understood was excellent. What 
I did not quite succeed in understanding seemed, somehow, even 
better. 

Arrhenius, at that time personally unknown to van't Hoff, in 
reviewing the Etudes , wrote as follows : " This work, which is of 
the greatest interest, consists of two essentially different parts : the 
first experimental, the second theoretical. The former is, however, 
of quite subordinate significance, notwithstanding the many peculiar 
and interesting phenomena discussed in it. In the latter portion 
the author displays an extraordinary talent for bringing a great 
series of different facts under one point of view, and he succeeds 
with relatively scanty experimental material in developing an 
imposing and harmonious scheme for the whole subject of chemical 
influence and action. Although the author has already gained a 
great name by his power of wresting secrets fro -n Nature, his former 
efforts are placed entirely in the shade by this work. An enormous 
perspective has been opened up for future investigation. There 
are, however, but few workers in the promising field, though possibly 
this will shortly be remedied; for since Helmholtz, who sets the 
fashion in physical circles, has turned his attention of late years to 
such subjects, it will probably not be long before eager investigators 
are working at them." 

A few years later this prediction was fulfilled, chiefly through the 



WALKER: VAN'T HOFF MEMORIAL LECTURE. 267 

instrumentality of Ostwald, the first occupant of the chair of 
physical chemistry in Leipzig. 

In ths Etudes we have the first appearance of osmotic pressure 
from the physico-chemical point of view. Through his distinguished 
countryman, the botanist, Hugo de Vries, van't Hoff had become 
acquainted with Pfeffer's osmotic measurements. He at once saw 
the thermodynamic importance of the conception, and used it in 
conjunction with the lowering of vapour pressure to calculate the 
affinity of certain salts for their water of crystallisation. In the 
following year (1885) he published in the Archives neerlandaises a 
paper bearing the title " L'equilibre chimique dans les systemes 
gazeux ou dissous a Vetat dilue, gazeux ou dissous " ; and in 1886 
he published in the Transactions of the Swedish Academy three 
memoirs, entitled "Lois de Vequilibre chimique dans Vetat dilue, 
gazeux ou dissous," " Une propriete generate de Vequilibre 
chimique," and " Conditions electriques de I'equilibre chimique." 

In these papers van't Hoff had arrived at the complete analogy 
between gases and substances in dilute solution. He tells us that 
in giving the proof of his equation: 

dlog e K _ q 

dT ' '2T 2 ' 

by means of reversible cycles for dilute gaseous systems, it occurred 
to him that with the help of semi-permeable membranes all the 
reversible processes which make the application of thermodynamics 
to gases so simple might as readily be applied to substances in dilute 
solution. It at once followed that the osmotic pressure must vary 
with the temperature according to G-ay-Lussac's law. Pfeffer's 
measurements for 1 per cent, sugar solutions seemed to confirm 
this conclusion, although they were scarcely sufficiently accurate to 
afford absolute proof of the relation. Then Pfeffer had shown that 
the osmotic pressure was proportional to the concentration, that is, 
Boyle's law was followed as well as Gay-Lussac's, and it was possible 
to write for dilute solutions an equation similar to that for gases, 
namely : 

PV=ET. 

The only thing left was to calculate R, the solution-constant, and 
compare it with the gas-constant, van't Hoff did this for sugar 
solutions from Pfeffer's measurements, and found to his surprise 
that the value was identical with that of the gas-constant. At first 
he looked upon this identity as a mere coincidence, but further 
consideration showed it to be fundamental, and that osmotic and 
gaseous pressure were always equal, when molecular concentration 
and temperature were equal, that, in short, Avogadro's law held 
without alteration for substances in dilute solution as well as for 



268 WALKER: VAN'T HOFF MEMORIAL LECTURE. 

gases, and that the molecular weights of dissolved substances could 
be determined on the same theoretical grounds as those of gases. 

Raoult had in the meantime shown empirically how molecular 
weights might be determined from the lowering of the freezing 
point, and van't Hoff was now in a position to give the theoretical 
justification of this method, by deducing thermodynamically fronr 
Avogadro's law and the properties of the solvents, the quantitative 
rules for the lowering of vapour tension, the depression of the 
freezing point, and 'the elevation of the boiling point of solutions. 

It should be noted that van't Hoff was from the first very careful 
to point out that all these relations were strictly applicable only 
to very dilute solutions, to " ideal solutions," as he calls them, and 
that Ve never claimed the theory of osmotic pressure as a complete 
theory of solutions. He definitely stated, indeed, in his address 
to the German Chemical Society (Ber. t 1894, 27, 15): "It is not 
even necessary to choose osmotic pressure as the starting point [of 
these relations]; the whole might be deduced as readily from 
Henry's law or from Raoult's law. Only osmotic pressure is a very 
simple and handy expression for the whole behaviour, and its 
physical meaning is very readily stated and grasped, thus: If a 
substance in a state of dilution exists in surroundings into which 
it can expand by diffusion, then, at a given temperature, the 
pressure which will prevent this diffusion is dependent only on the 
number of dissolved molecules, and not on the nature of the 
medium." To van't Hoff's mind the real theory of the intimate 
nature of solutions begins where the simple laws cease to be obeyed^ 
In a sense this is true, and a good example of what it means is ; 
afforded by the early history of the osmotic pressure theory. 
Van't Hoff had found that the value of the osmotic constant was 
not for all substances equal to the gas constant R. With his 
customary skill in handling such matters, he wrote the equation 
for these substances as follows: 



using a factor i, which was thus the measure of the abnormality 
of the substance. The work of Arrhenius supplied two years later 
the explanation of the abnormality in the case of the great class 
of electrolytic solutions. The abnormally great value of i for such 
solutions was held by Arrhenius to be due to the molecular con- 
centration in such solutions being greater than had theretofore been 
accepted. According to his theory of electrolytic dissociation, some 
of the original dissolved molecules had split up under the influence 
of the solvent into simpler positive and negative ions, so that the 
total number of molecules was increased, the excess of i over 1 
being the measure of the increase. This, then, is a contribution 



WALKER: VAN'T HOFF MEMORIAL LECTURE. 269 

to the theory of solution for a certain class of solutions, and it 
appears to me that every future contribution will be of the same 
nature, dependent on the nature of the solvent and dissolved sub- 
stance, and therefore of a different scope entirely from van't Hoff's 
generalisation. 

Two distinct points may be noted in connexion with the papers 
just referred to. First, there is the introduction of the conception 
of osmotic pressure into thermodynamics generally, and the use of 
semipermeable membranes for reversibly changing the concentration 
of solutions. Second, there is the special application of the con- 
ception in deducing the simple general laws for ideal solutions. As 
van't Hoff himself has said, it would be possible to substitute for 
osmotic pressure in the purely thermodynamical treatment some 
other magnitude which is proportional to it, but it may be con- 
fidently predicted that the conception once introduced, and through 
which such advances have been made, will never be discarded. 

One often encounters among chemists the impression that van't 
Hoff was essentially a mathematician, or at least a man of mathe- 
matical formulae^ who cared nothing for atoms or molecules. 
Nothing could be further from the truth. Van't Hoff's actual 
knowledge of mathematics is surpassed, I fancy, by the average 
honours B.Sc. student of to-day. His ability in this direction lay 
rather in the power of handling the mathematical tool for his own 
purposes. But, as is apparent from the passages I have already 
quoted, the essential thing for him is the reciprocal action and 
influence of atoms and molecules. The nature of osmotic pressure, 
as well as its law, was of profound interest to him. He first of all 
conceived it as having its origin in the mutual attractions of 
solvent and solute molecules, but soon discarded this view for one 
of molecular bombardment in analogy with the kinetic theory of 
gases. This kinetic theory of the origin of osmotic pressure, despite 
criticisms, still seems superior to any other that has been proposed, 
and awaits further development. 

Although, as has been said, the papers comparing dilute sub- 
stances with gases were published in 1885, it was only in 1887 that 
the ideas became generally known. Ostwald, the organiser of the 
campaign in favour of the new ideas of van't Hoff and Arrhenius, 
associated himself with the former in founding the Zeitschrift fur 
pJiysikalische Chemie, in the first volume of which the fundamental 
papers of the two pioneers of modern physical chemistry appear. 

With the foundation of this journal van't Hoff's scientific life 
may be said to have reached its climax. His fame became world- 
wide, and many honours awaited him. A new chemical laboratory, 
built according to his designs, was opened in 1891, and many 



270 WALKER: VAN'T HOFF MEMORIAL LECTURE. 

foreign students visited him who could not have been accommodated 
in the old building. With the increase of his department, van't Hoff 
found that he had to devote more and more time to administrative 
duties, as is the universal experience 'of the heads of large labora- 
tories. He naturally disliked to see his leisure for personal research 
slip away from him, and asks, "Besides men whose duty it is to 
teach, and who, if they have time and inclination for it, may 
prosecute research, is there not room for another class of men whose 
duty should be to investigate, and who, if they pleased, might also 
teach ? " In the spring of 1895 a position of the latter kind was 
offered to him in Berlin. Great efforts were made by his colleagues 
in the University of Amsterdam to induce the Government of the 
Netherlands to retain him in Holland on similar terms, but these 
efforts were unsuccessful. Van't Hoff, in the spring of 1896, moved 
to Berlin, as a member of the Prussian Academy of Sciences and 
as a Professor in the University. His academic duties were of the 
lightest, one lecture a week being all that was required of him. 
His research work was carried out in a small laboratory situated in 
a pleasant suburb of Berlin. Here his cnief collaborator was his 
friend and former pupil, Meyerhoffer. Often in conjunction with 
younger men, thoy studied the physical chemistry of the Stassfurt 
salt deposits, and similar phase-rule problems. 

Such work, though of much general and special interest, is not 
to be placed on a par with van't Hoff's former achievements. It 
is true that in plan and in performance it may be taken as a model 
for an investigation on the grand scale, yet one cannot but entertain 
the feeling that a lesser maa than van't Hoff, for example, his 
own countryman, Bakhuis Roozeboom, might have carried it to 
an equally successful conclusion. The conception of solid solutions 
(1890) is van't Hoff's last contribution to novel chemical ideas. 

Van't Hoff had now more leisure, , not only for practical research, 
but for travel. He has left an interesting journal of his impressions 
of America in 1901. In December of the same year he journeyed 
to Stockholm to receive the first Nobel Prize for Chemistry; and 
it may be recalled that he delivered the Raoult Memorial Lecture 
here in 1902. 

The death of Meyerhoffer in 1906 affected him deeply, and later 
in the same year his own health began to give way. He himself 
writes : " My health, almost invariably good, seemed in the summer 
of 1906 to be even better than usual. In early spring I had visited 
the neighbourhood of Vesuvius at the time of the eruption, and 
returned home rejuvenated. Hay-fever, for many years my bugbear, 
had vanished, and it appeared as if my Bonn student days, with 
all their poetry, had, comet-like, returned. And yet I found in 



WALKER: VAN'T HOFF MEMORIAL LECTURE. 271 

all this something abnormal, and recalled to mind a saying of a 
former medical colleague, that a feeling of specially good health 
in one's later years is a bad omen. In October came the first 
indications of what six months later developed into an illness which 
for a time laid me aside from all work." From that date van't Hoff 
had to spare himself, a thing peculiarly distasteful to a man of his 
active mind and temperament. He brought his work on the salt- 
deposits to a close, and devoted himself to the lighter labour of 
revising some of hrs older books, and projecting new ones. 

His last scheme of investigation was a study of the intimate 
nature of the chemical processes occurring in plants. To this end 
he began in 1909 a research on reversible enzymatic action, and 
published a preliminary account in the Sitzungsberichte of the 
Prussian Academy (October, 1909, and November, 1910). These 
admirable fragments show a last flash of van't Hoff's illuminating 
genius. The clearness of the theoretical conceptions, the simplicity 
of the experimental execution recall the best period of his activity. 
He proved that the action of the enzyme emulsin in the formation 
and decomposition of glucosides was that of an ordinary catalyst in 
accordance with the mass-action law, the rates of the reverse 
reactions alone being affected and the point of equilibrium remain- 
ing unchanged. 

The last experiments were carried out in a small private labora- 
tory which had been built for him on the Imperial Crown-lands at 
Dahlem. Here from time to time he was able to do a little work, 
but the progress of his malady slowly enfeebled him. The entry 
in his diary for December llth, 1910, reads, "Article on 'Teaching 
and Research ' finished : a last effort." On the evening of March 1st, 
1911, he died peacefully. 

With no great mathematical or experimental attainment, with 
no striking gift as a teacher, van't Hoff yet influenced and moulded 
the current thought, and even much of the practice, of chemistry 
for decades. He set out with a clear scientific ideal. Native 
inspiration and unflagging ardour in pursuit of this ideal led him 
to the discovery of principles of the widest and most far-reaching 
import. He was, in my judgment, the greatest chemical thinker 
of his generation. If any should dispute this judgment, I can only 
reply that our science is indeed favoured when such dispute is 
possible. 




[To face p. 273. 



LADENBURG MEMORIAL LECTURE. 

DELIVERED ON OCTOBER 23RD, 1913. 
BY FREDERIC STANLEY KIPPING, D.Sc., Ph.D., F.R.S. 

A MEETING of this Society which is held to commemorate the life 
and work of a distinguished chemist is an occasion which we 
approach with mingled feelings. For although we have to deplore 
the loss of a great man, there remain with us the recollection of 
his high achievements, and the example of his life worthily devoted 
to the advancement of knowledge. 

In the minds of all chemists now living, and of all those who, 
in the future, trace the development of the science of our time, 
the name of Ladenburg is, and always will be, closely associated 
with the chemistry of those interesting and wonderful products of 
nature's laboratory, the vegetable alkaloids. 

The study of some of the difficult problems presented by these 
complex compounds formed the main part of the experimental 
work of the man whose memory we honour to-day. It was a task 
which might well have deterred the boldest and the most sanguine 
spirit; but. by him it was faced with persistent industry and 
indomitable perseverance, and brought to an issue the brilliancy of 
which few could have foreseen. The synthesis of cW-coniine, 
followed by the resolution of the synthetic alkaloid into its optically 
active components, the culminating point of these researches, was 
perhaps the greatest of Ladenburg's successes, 

It is sometimes possible to trace the steps by which an explorer 
of the secrets of nature has passed from one dark region to yet 
another even more obscure; sometimes, however, not a single foot- 
print remains to mark the track. In Ladenburg's case, the study 
of the nitrogenous products of the vegetable kingdom was preceded 
by an investigation of the compounds of that element which 
dominates the mineral world; the derivatives of benzene seem to 
have formed the bridge by which he crossed the gulf between those 
two so widely different tracts, but there is no clear record of the 
inspiration by which he was guided. It may have been that, while 
searching among the musty archives of the days long past, during 
the preparation of his historical work on the development of 
chemistry, he became fascinated by the mystery surrounding the 
nature and the action of those potent poisons which are elaborated 
by plants ; the product of a common weed, even such as the deadly 
nightshade, which could either enhance the charms of a fair lady 
or lead to delirium and death, might well appeal to the imagination 



274 KIPPING : LADENBURQ MEMORIAL LECTURE. 

of the youthful chemist, and become to him an object of absorbing 
scientific interest. 

However this may have been, the more difficult part of the task, 
with which I have been entrusted, '*s not that of tracing Ladenburg's 
progress as an investigator; it is that of passing in brief review 
the leading personal incidents of his distinguished career.. 

Happily, some of the difficulties ordinarily associated with such 
a task have in this case been dispelled by the existence of an 
authentic account of many of these events from his own pen. 
Towards the close of his life, he suffered from severe bodily ailments, 
which prevented him from carrying out his official duties. It was 
then that, at the suggestion of his friends, and as a means of 
intellectual recreation, he undertook the preparation of a short 
autobiography. A copy of this work was very kindly lent to me 
by Ladenburg's second son, Dr. Rudolph, and from this authorita- 
tive source most of the following particulars have been taken. 

Born of Jewish parents on July 2nd, 1842, at Mannheim, in the 
Grand Duchy of Baden, Albert Ladenburg was one of a family of 
eight, of whom, however, five died quite young. Although his 
parents were in a good position (his father was a Rechtsanwalt), 
and lived in a large, many-roomed house, he and his brother and 
sister were brought up in the old-fashioned way, and were seldom 
allowed in the apartments of their father and mother. 

The school to which he was sent was one in which little Latin 
was taught, and no Greek ; one reason for this choice was that his 
father's experience of the classical education given at the 
Gymnasium had been that it took away all desire for work. From 
school he went on to the Polytechnicum at Karlsruhe, where he 
applied himself industriously to the study of mathematics, modern 
languages, machine construction, and other subjects, and, as he 
himself says, tried to make good a part of what he felt had been 
wanting in his earlier education. 

In I860, at eighteen years of age, he went to Heidelberg, where 
he attended lectures at the University, and worked very diligently 
at home. At first he had the idea of specialising in mathematics ; 
but he also studied chemistry under Bunsen, and later, physics, 
under Kirchhoff. The lectures of Bunsen, however, proved so 
inspiring that Ladenburg very soon went over to chemistry, and 
spent the livelong day in Bunsen's laboratory. Here he met, 
among others, C. Graebe, H. Wichelhaus (who remained his close 
friend for many years), C. Liebermann, Soret, and W. Preyer. He 
also became acquainted with Roscoe, who often visited Bunsen 
in those days. 

During the winter session 1862-1863, Ladenburg studied in 



KIPPING: LADENBUR'O MEMORIAL LECTURE. 275 

Berlin, attending lectures by Magnus, Ranke, and others, and in 
the spring of 1863 he took the Ph.D. degree at Heidelberg Univer- 
sity, summa cum laude, in chemistry, physics, and mathematics. 

Up to this time he had devoted himself principally to inorganic 
chemistry, but he now began to work with Carius, who, although 
Ausserordentlichtr Professor in the University of Heidelberg, 
had to work in a small private laboratory outside. Here it was 
that Ladenburg carried out his first research work, which was on 
a new method of elementary organic analysis, and it was during 
this period that he made the acquaintance of Erlenmeyer, an 
acquaintance which resulted in a lasting friendship. 

In the spring of 1865, Ladenburg decided to go to Ghent to 
work under Kekule, who at that time was at the height of his 
scientific activity, and had just published his first paper on the 
structure of aromatic compounds. At Ghent he met Korner and 
Glaser, who were assistants to Kekule; he also carried out two 
researches on benzene derivatives, one on the " Synthese de 1'acide 
anisique," the other, in conjunction with Fitz, on "Quelques 
derives de 1'acide paraoxybenzoique." Except for the opportunities 
of intercourse with Kekule, and with the staff and students of the 
laboratory opportunities which Ladenburg prized very highly 
he found life in Ghent very dull, and after a short visit to London, 
where he met Frankland, he proceeded to Paris. Acting on 
Kekule's advice, he there interviewed Berthelot, and asked for 
permission to become one of Berthelot's pupils; his request was 
granted forthwith, but when he proceeded to inquire where he 
should work, he was shown a large, empty room, devoid of all 
fittings, of which he would be the sole occupant. 

Dissatisfied with the prospect of sacrificing a considerable pro- 
portion of his time in Paris to the fitting up of this room, and of 
having no fellow-students with whom he could converse, in order 
to improve his French, he obtained an introduction to Wurtz, who 
was professor in the Institut de chimie, and started work in his 
laboratory. It was there that Ladenburg met Friedel, Caventou, 
Naquet, A. Gautier, and others; from Wurtz's laboratory he 
published with Lever kus a paper " Ueber die Konstitution des 
Anethols." 

At the beginning of the winter of 1866, after spending a few 
months in Germany, he went, at Friedel's invitation, to work in 
the ]cole des mines, where, with Friedel, he began that important 
series of researches on derivatives of silicon to which reference will 
be made again. Shortly after the commencement of this work, 
he was very seriously hurt by an explosion, so seriously, in fact, 
that his parents, who happened to be in Paris at the time, were 



276 KIPPING: LADENBURG MEMORIAL LECTURE. 

hardly allowed to see him. The cause of this explosion is not 
mentioned in his Lebenserinnerungen, but judging from the 
work described in the first paper published by himself and Friedel, 
it was very probably the ignition of a mixture of the vapour of 
silicochloroform and air. Whatever the cause of the accident may 
have been, as soon ae he was better, he set to work again and 
remained in Paris during the whole of a very hot summer, in order 
to make up for the days lost during his temporary disablement. 

Up to this time, apparently, he had not definitely chosen a 
profession, but now he decided to become a teacher. To this course 
his father consented, although he lacked faith in his son's ability. 
Having consulted Bunsen and Kopp in Heidelberg on the matter 
of his Habilitation, and having been informed that the original 
work which he had done would be accepted, Ladenburg went for 
a short period to Berlin, there to undertake a projected research 
with Wichelhaus. This collaboration led to no definite result, but 
his stay in Berlin was very pleasant; it gave him an opportunity 
of meeting Wallach, who was assistant to Wichelhaus, and also of 
renewing his acquaintance with Baeyer and Martius, both of whom 
he had previously met in Paris. At the instance of Wichelhaus, 
steps were then being taken to found the Deutsche Chemische 
Gesellschaft, and both Baeyer and Martiue shared with Wichelhaus 
this important undertaking. 

In January, 1868, Ladenburg successfully underwent the ordeal 
of his Habilitation, and having spent a short time in Paris, where 
he continued his work with Friedel, he returned to Heidelberg, in 
order to rent and equip a laboratory in which he could also lecture. 
In those days rooms were not available in the large institute 
occupied by Bunsen; and Erlenmeyer, Horstmann, W. Lossen, and 
all the chemistry Privatdocenten had their own laboratories outside. 

At the beginning of the term, Ladenburg commenced his first 
course of lectures, the subject being the history of the development 
of chemistry during the last hundred years. He had composed 
the earlier lectures while he was in Paris, and later, when con- 
tinuing the task at Heidelberg, he had the advantage of the 
advice and criticism of Erlenmeyer. It was the matter of these 
lectures, carefully revised, wlr'ch was published in 1869 under the 
title, "Vortrage iiber die Entwicklungsgeschichte der Chemie in 
den letzten hundert Jahren," a comprehensive, lucid, and critical 
work, which passed through several editions. At the end of his 
four years as Privatdocent in Heidelberg, he was given the title of 
Professor extraordinarius. The award of this honour, it seems, 
had been delayed a year, a delay which Ladenburg regarded as a 
punishment for his having petitioned the Ministry, on behalf of 



KIPPING : LADENBURG MEMORIAL LECTURE. 277 

his colleagues and himself, to provide Privatdocenten with 
laboratories suitable to their work, and to allow them to attend 
the University lectures at nominal fees. 

In 1872, he accepted, after some hesitation, the offer of the chair 
of chemistry in the University of Kiel. The prospects there were 
not attractive. On his first visit, the town itself, the University, 
and some of the public buildings, gave him the impression of 
wretchedness, an impression, however, which was afterwards modi- 
fied. There was, moreover, no chemistry department; and although 
it was understood that one should be built and equipped in about 
three years, there was no place in which he could work in the 
meantime. Nevertheless, he finally decided to accept the pro- 
fessorship, and in 1873 he began to teach at Kiel in a temporary 
laboratory, which had been rapidly fitted up in a vacant dwelling 
house. 

At first he had only a few students, and could give much time 
to his own work, although he was worried by frequently occurring 
committee meetings, at which there were long and acrimonious 
disputes among the professors, each of whom was eager to secure the 
best site for his own projected buildings. During this period of 
comparative freedom from his teaching duties, he was able to 
commence, in conjunction with various other chemists, the pre- 
paration of his "Handworterbuch der Chemie," a work which was 
finally pubished in thirteen royal octavo volumes. 

The new Chemistry Institute in Kiel, of which Ladenburg was 
appointed Rector in 1884, was not ready for occupation until the 
winter session of 1878-1879. Attracted by the fame of the pro- 
fessor, and by the lucidity and fire of his lectures, students came 
in rapidly increasing numbers, and soon^ his laboratory became 
crowded. While at Kiel he was responsible for passing more than 
twenty-five doctors of philosophy in chemistry, and it was there 
that he carried out many of his more important researches on 
the alkaloids, including the synthesis of coniine. Towards the end 
of his stay in Kiel, he suffered a very severe blow in the loss of 
his mother, to whom he was deeply attached. 

In 1889, he was offered the professorship of chemistry in the 
University of Breslau. At first he decided to decline the call, as he 
found, on visiting the town, that it was devoid of all attractions, 
while the so-called laboratory was hardly worthy to be dignified by 
such a name. However, having obtained a promise that the build- 
ings then in use should be immediately reconstructed, and that a 
large new Institute should very soon be erected, he accepted the 
chair, and took up his residence in Breslau. 

At first he was very disappointed that only twenty-five students 



278 KIPPING: LADENBURO MEMORIAL LECTURE. 

came to work with him, and that his lectures were only very 
sparsely attended, but as time went on, and especially after the 
new Institute had been opened in 1897, the number of his students 
increased to such an extent that on his resignation of the chair 
in 1909, he had the satisfaction of having passed 160 doctors of 
philosophy in chemistry. Few could show such a splendid record, 
even in those days, when the stream of prospective German 
chemists was at its flood. 

During his first twelve years at Breslau nothing occurred to 
diminish Ladenburg's mental or bodily activity, but from 1901 
onwards, one great trouble quickly succeeded another. He lost his 
youngest son, who had been ill for many years; his relations with 
friends and colleagues were sorely embittered by a controversy 
arising out of an address entitled " Einfluss der Naturwissen- 
schaften auf die Weltanschauung/' delivered at the Natur- 
forscherversammlung in Kassel in 1903; and in 1904 he himself 
became ill, and shortly afterwards had to undergo a serious 
operation. Although, after many months of suffering, he recovered 
sufficiently to be able to resume fitfully his academic duties, his 
health soon gave way again. The tragic loss of his eldest son, 
who was drowned in 1908; the death of his wife, after a most 
distressing illness; and his own serious ailments, led him in 1909 
to tender his resignation. He died two years later, on August 
15th, 1911, in his seventieth year, 

A man, like Ladenburg, who, in spite of poor health, leaves a 
record so deeply graven on tne roll of fame, must have been 
possessed of inexhaustible and indomitable will-power and untiring 
industry. Even as a youth, his devotion to his work led him to 
refuse the delights of a long tour in Switzerland in order to spend 
the time in Bunsen's laboratory; and it was by this spirit that 
the whole of his life was ruled. 

The honours which were bestowed on him and which were earned 
by this stern self-sacrifice on the altar of science, were not confined 
to those which he received in Germany; for in addition to the 
title of geheimer Regierungsrath, the Rectorship of the University 
of Kiel, and the membership of the Akademie der Wissenschaften 
of Berlin, he was an Honorary and Foreign Member of this 
Society, a member of the A cademie des Sciences, and correspondent 
for the chemistry sections of numerous other scientific societies; he 
was awarded the Hanbury Medal of the Pharmaceutical Society in 
1902, and the Davy Medal of the Royal Society in 1907. 

Well might these honours and the place which he had gained for 
himself in the scientific world afford him some consolation in the 
dark days of his closing years; but possibly they seemed to him of 



KIPPING : LADENBUKQ MEMORIAL LECTURE. 279 

little import in comparison with the glad memories of more- than 
thirty years of happy wedded life. 

His wife was Margarete, the eldest daughter of Pringsheim, 
professor of botany in the University of Berlin. He met her late 
in 1875, during a visit to the capital, and with him it was a case 
of love at firs f . sight; he proposed the following Easter, and they 
were married on September 19th of the same year. They had 
three sons, of whom only one survives. 

Except when writing of nis relations and friends, for whom he 
expresses freely his deep love end affection, Ladenburg preserves 
in his recollections a dignified silence as to his own feelings, and a 
reserved modesty as to his own achievements. He does not even 
refer to his great " Handworterbuch der Chemie," the completion 
of which must have given him profound satisfaction; nor is there 
a word to intimate the acute intellectual gratification which he 
must have felt when he had brought some important research to, 
a successful issue. To a man of his devotion to science, however, 
the joy of adding a stone to the eternal edifice of truth must have 
been intense; and, though unrecorded, his feelings when he first 
glanced through the polarimeter tube containing his synthetic 
optically active coniine, might perhaps have been expressed in the 
words which Biot once addressed to Pasteur : " J'ai tant ainie les 
sciences dans ma vie, que cela me fait battre le coeur." 

However great may have been Ladenburg's own satisfaction on 
that occasion, he hastened to share it with his wife, who happened 
to be away from Kiel at the time ; the brief telegram, " Gretchen, 
es dreht," which he sent to her,* conveyed no doubt infinitely more 
than was expressed in those three words. 

In spite of the reticence as to his own characteristics which 
pervades his Lebenserinnerungen, there are a few passages which 
throw dim sidelights on his personality. He was the kind of man 
we call resolute or stubborn, strong-willed or obstinate, according as 
his point of view agrees or disagrees with our own. When he felt 
himself in the right, he defended his position tenaciously, a course 
which involved him in litigation on more than one occasion, and 
which led him to publish a considerable number of polemical 
papers. 

The unremitting attention which he gave to his academic duties 
left him but little time for relaxation; nevertheless, like so many 
of his race, he possessed musical talent of a high order, and culti- 
vated this gift in his rare moments of leisure. In his early youth 
at Karlsruhe, he spent many hours at the piano; later at Heidel- 
berg he played in quartets and other concerted music, and obtained 

* Dr. Rudolf Ladenburg kindly gave inc this information. F. S. K. 



280 KIPPING: LADENBURG MEMORIAL LECTURE. 

a great mastery over his instrument. He was a great lover of 
Brahms, with whoso compositions he had been made familiar by 
Frau Schumann, a frequent visitor at his father's house and his 
own. He would travel a long distance in order to hear a new 
work of this composer, and when at Kiel he considered it his duty 
to cultivate among his friends a taste for Brahms, whose music at 
that time was little known in the town. On several occasions he 
met Brahms, and had the intense pleasure of hearing that great 
genius interpret his own compositions. 

This brief outline of Ladenburg's life, drawn by one who had 
not the honour of his acquaintance, must necessarily fail completely 
to give a picture of the living man. As this defect could not be 
remedied, the delineation of Ladenburg's character may be left to 
the more competent pen of one of his own countrymen and col- 
leagues, the writer of the memorial published in the Berichtt. 

When in 1866 Ladenburg was invited by Friedel to go and work 
in Paris on compounds of silicon, only a few organic derivatives 
of that element were known; those containing a silicon atom 
directly united to a carbon atom could, in fact, be counted on the 
fingers of one hand. If this state of knowledge is contrasted with 
that which obtained in 1883, when Beilstein's " Handbuch der 
organischen Chemie " was first published, some idea may be gained 
of the progress which had been made during the intervening years,. 
TL's great advance was principally due to those researches which, 
commenced with Friedel, were continued by Ladenburg alone, and 
which formed, not the very first, but one of the earlier chapters of 
the latter's scientific record. 

The first joint communication, published in 1867 (Annaltn, 
143, 118), contained an account of silicochloroform. Some ten 
years previously Buff and Wohler had heated crystalline silicon in a 
stream of dry hydrogen chloride, and had obtained a liquid to which 
they had given the formula Si 2 Cl 3 +2HCl (Si = 21); this formula 
was subsequently altered by Wohler to Si 6 Cl 10 H 4 (Si = 14), but he 
recognised the fact that he had been unable to obtain the liquid 
in a pure state, and that consequently its formula was not definitely 
established. Friedel and Ladenburg prepared this compound in a 
state of purity, and proved it to have the molecular formula SiHCl 3 ; 
its further study led them to the discovery of several interesting 
and novel reactions. One of its derivatives, namely, triethyl ortho- 
silicoformate, which was obtained by treating the trichloro-com- 
pound with ethyl alcohol, underwent a remarkable decomposition 
when it was warmed with sodium; the metal remained unchanged, 
but the ester was decomposed, giving pure silicomethane, SiH 4 , and 



KIPPING: LA.DENBURQ MEMORIAL LECTURE. 281 

an ester of orthosilicic acid, a change which is expressed by the 
following equation : 4SiH(OEt) 3 = SiH 4 + 3Si(OEt) 4 . 

This reaction, which is comparable to the decomposition by heat 
of the lower acids of phosphorus into phosphine and orthophos- 
phoric acid, passed into the text-books of inorganic chemistry as a 
method for the preparation of pure silicomethane, and the equation 
just given has certainly been committed to memory, for examina- 
tion purposes, by many puzzled students, who had not the remotest 
idea of the nature of triethyl orthosilicoformate. 

As silicomethane had not until then been prepared in a pure 
state, Friedel and Ladenburg established its composition, and 
found that the pure gas was not* spontaneously inflammable in air 
at the ordinary temperature and pressure, but was so under lower 
pressures. In addition to silicochloroform, they investigated other 
purely inorganic silicon compounds, more particularly silicon oxy- 
chloride, SiCl 3 'OSiCl 3 , which they prepared by passing the vapour 
of silicon tetrachloride through a white hot porcelain tube (Ber., 
1868, 1, 86); although unable to discover how this compound was 
produced, they proved that it reacted with alcohol, giving the 
ethoxy-derivative, Si(OEt) 3 *OSi(OEt) 3 , and with zinc ethyl at 
180, giving silicoethyl oxide, SiEt 3 OSiEt 3 . 

The only method available in those days for bringing about the 
direct union of silicon and carbon was to heat silicon tetrachloride 
with zinc alkyls in sealed tubes. By using sodium in conjunction 
with the zinc compound, Friedel and Ladenburg succeeded in 
bringing about the displacement of the chlorine by an alkyl group 
at much lower temperatures and without the use of sealed tubes 
(Ber., 1870, 3, 15). In this way they prepared triethyl orthosilico- 
propionate, SiEt(OEt) 3 , from triethoxysilicic chloride, which was 
itself obtained by the interaction of silicon tetrachloride and ethyl 
alcohol. 

This ester was not completely hydrolysed by alcoholic potash 
in the cold, and when boiled with a concentrated aqueous solution 
of the alkali, it gave a product which had only approximately the 
composition EtSiOOH. For the preparation of the pure acid the 
ester was heated in sealed tubes with acetic chloride, and the 
product, ethylsilicon trichloride, SiEtCl 3 , was hydrolysed with water. 
Silicopropionic acid, EtSiOOH, was thus obtained as an amorphous 
powder; it was the first representative of the silicon analogues 
of the carboxylic acids. Although, later on, Ladenburg prepared 
silicoacetic acid, MeSiOOH (Ber., 1873, 6, 1029), and silicobenzoic 
acid, PhSiOOH, and several compounds supposed to be of this type 
have been obtained in recent times, little is known of their nature : 
except for the fact that such acids give soluble potassium salts, 



282 KIPPING: LADENBtTRQ MEMORIAL LECTURE. 

they are extremely inert, and behave in every respect differently 
from the carboxylic acids. 

The discovery of silicopropionic acid raised in Ladenburg's mind 
a question which, some years afterwards, he attempted to solve 
(Her., 1872, 5, 568), namely, whether the silicon which is contained 
in plants is in combination with carbon or is a constituent of a 
purely mineral silicate. This problem, apparently, is still awaiting 
solution. 

The main object of the joint researches just referred to was to 
gain some information as to the extent of the analogy between 
compounds of silicon and carbon; to ascertain whether the new 
theories which were just, then being developed in connexion with 
organic compounds could also be applied to the so-called inorganic 
elements, or whether, as some believed, these new theories were 
both "unniitz und verwirrend." 

As a further step in this direction, Friedel and Ladenburg (Bull. 
Soc. chim.j 1867, [ii], 7, 65) attempted the synthesis of a quatern- 
ary hydrocarbon, and succeeded in obtaining dimethyldiethyl- 
methane, CMe 2 Eto, the first known compound of this type; the 
existence of this hydrocarbon proved that the carbon atom, like the 
silicon atom in Friedel and Craft's tetraethylsilicane, SiEt 4 , could 
unite directly with four hydrocarbon radicles. 

They next tried to obtain a compound in the molecule of which 
two silicon atoms were directly united, as are the carbon atoms 
in ethane; after many fruitless attempts they finally succeeded 
(Bull. Soc. chim., 1869, [ii], 12, 92; Annalen, 1380, 203, 241) in 
preparing silicoethane, SiEt 3 'SiEt 3 , in the following manner: 
Silicon tetraiodide was heated with molecular silver at about 300, 
and was thus converted into the hexaiodide, Si 2 I 6 (from which the 
corresponding bromide, Si 2 Br 6 , and chloride, Si 2 Cl fi , were prepared). 
The hexaiodide was hydrolysed with ice-cold water, yielding an 

amorphous product, silico-oxalic acid, I _,, which showed an 

' 



interesting behaviour; when heated in the air, the acid was decom- 
posed into silica and hydrogen; when warmed with potassium 
hydroxide it gave potassium metasilicate with evolution of 
hydrogen : 

H 2 SiO 4 + 4KOH - 2K2SiO 3 + 2H 2 + H 2 . 

The interaction of silicon hexaiodide and zinc ethyl took place 
very readily, giving a colourless liquid, boiling at 250 253, which 
was proved to be the desired compound, hexaethylsilicoethane, 



During the preparation of triethyl silicolormate from triethyl- 
fiilicic chloride, Friedel and Ladenburg had observed the formation 



KIPPING! LADENBURQ MEMORIAL LECTURE. 283 

of diethoxydiethylsilicane, SiEt^OEt^, as a by-product. This 
observation led Ladenburg to study the action ^f zinc ethyl and 
sodium on ethyl orthosilicate, Si(OEt) 4 . In a series of papers (Ber., 
1871, 4, 727, 901; 1872, 5, 565, 1081) he showed that the ethoxy- 
groups in this ester might be successively displaced by ethyl 
radicles, giving the compounds SiEt(OEt) 3 , SiEt 2 (OEt) 2 , SiEt 3 OEt, 
and SiEt 4 , as well as triethylsilicane, SiEtgH. 

The diethoxydiethyl derivative, SiEt^OEt)^ could not be hydro- 
lysed to the corresponding dihydroxy-compound with alcoholic 
potash, but when heated with acetyl chloride in sealed tubes it 
gave the halogen derivatives SiEt2(OEt)Cl and SiEtgC^; the latter, 
with water, yielded a thick syrup, which Ladenburg regarded as 
silicon diethyl ketone, or oxide, SiEt^O, but the analytical results 
did not agree well with those required for this formula. 

The monoethoxy-derivative was hydrolysed by hydriodic acid, 
but gave the oxide SiEtg'O'SiEts; when heated at 180 with acetyl 
chloride, it was converted into silicoheptyl chloride, SiEt 3 Cl, which, 
with ammonia, gave silicoheptyl alcohol, SiEtyOH. This was the 
first known silicon derivative of the alcohol type, and for this and 
analogous compounds, Ladenburg proposed the class name "sili- 
cole," corresponding with Kolbe's " carbinole." 

A few silicon derivatives containing aromatic radicles were also 
prepared, as, for example, phenylsilicon trichloride, SiPhCl 3 , which 
was obtained by heating silicon tetrachloride with mercuric phenyl 
(Ber., 1873, 6, 379). This trichloride and the ester, SiPh(OEt) 3 , 
prepared from it, gave on hydrolysis products whi n !i seemed to be 
identical, and which were believed to be silicobenzoic acid, 
PhSiO-OH. 

Some thirty years later Ladenburg's thoughts again turned to 
these aromatic silicon compounds, and he prepared various deriv- 
atives of silicon tetraphenyl (Ber., 1907, 40, 2274), but apparently 
his attempts to sulphonate triphenylsilicol were not successful (Ber., 
1908, 41, 966). 

This short summary of Ladenburg's researches on silicon com- 
pounds can give little idea of the very great experimental diffi- 
culties with which he had to contend, and of the time which he 
must have devoted to these investigations. But in spite of the 
exacting character of this work, during its progress he was also 
able to study some organic compounds of tin. 

The object here was not, as might have been expected, to estab- 
lish some analogy between tin and silicon; it was to try and find 
out whether the molecule of a stannous compound contained one 
or two atoms of tin. In his opinion, the ous compounds of iron, 
manganese, chromium, and other metals contained two atoms of the 

K 



284 KIPPING: LADENBURG MEMORIAL LECTURE. 

metal in their molecules (Ber., 1869, 2, 706), but experiments with 
certain inorganic iron, manganese, and tin compounds failed to 
give any evidence in support of this view. He therefore prepared 
" stanntriathyl," a compound which had been obtained by Cahours, 
but the formula of which had not been established. This ethyl 
derivative was proved to have the composition, Sn 2 Et 6 , and the fact 
that two atoms of tin could unite directly was thus established, 
although the molecular structure of stannous compounds slill 
remained unknown (Ber., 1870, 3, 353). 

From the hexaethyl derivative Ladenburg prepared various other 
organic tin compounds; he showed that it was decomposed by 
iodine, giving tin triethyl iodide, SnEtgl, from which, with the aid 
of sodium and bromobenzene, ho obtained tin phenyltriethyl, 
SnEt s Ph (Ber., 1871, 4, 17). He also found (Ber., 1871, 4, 19) 
that the hexaethyl compound underwent the following interesting 
decompositions : 

Sn 2 Et 6 + 2EtI = 2SnEt 3 I + C 4 H 10 . 
Sn 2 Et 6 + 2CH 2 C1-C0 2 H = 2SnEt 2 Cl 2 + 2CO 2 + 2C 2 H 6 + C 4 H 10 . 

A much more important chapter of Ladenburg 's work is that 
containing his numerous contributions, both theoretical and prac- 
tical, on benzene and its derivatives. That a young and enthusi- 
astic chemist, who had worked in Kekule's laboratory, would take 
an active part in the solution of the many interesting problems 
suggested by the theory of the structure of benzene was, of course, 
only to be expected; it was merely a question of how far his own 
efforts would meet with success. 

As a matter of fact, of the many who assisted in the examination 
of the fundamental propositions of the aromatic theory, few played 
a more prominent part than Ladenburg, or brought perspicacity 
and critical acumen of a higher order to the discussion of the 
experimental data. His first researches on aromatic compounds, 
carried out in Kekule's laboratory and published in 18661867, 
have already been mentioned. During the next two years, although 
fully occupied with silicon compounds in the laboratory, his mind 
was evidently running on the aromatic theory, and as early as 1869 
he contributed a paper in which he had the temerity to criticise 
Kekule's formula, and to suggest alternatives, among which 
occurred the now well-known prism formula, originally put forward 
by Claus. 

In this paper (Ber., 1869, 2, 272) Ladenburg showed that 
whereas, according to Kekule's formula, the positions 1 : 2 and 
1 : 6 must be, and the positions 1 : 3 and 1 : 5 may be, different, 
certain experimental data of Hubner and Petermann pointed 
strongly to the contrary conclusion, namely, that in the benzene 



KIPPING: LADENBURG MEMORIAL LECTURE. 285 

nucleus there are two hydrogen atoms which are symmetrically 
situated with respect to a third such atom. The argument was as 
follows: 7w-Bromobenzoic acid gives two bromonitrobenzoic acids, 
which, on reduction, are converted into the same aminobenzoic 
acid. The nitro-groups in the bromonitro-acids must have displaced 
two hydrogen atoms, which are differently situated with regard to 
the bromine atom, but identically situated with respect to the 
carboxyl group. Therefore either the position 1 : 2 = 1 : 6, or 
1: 3 = 1: 5. 

A few years later (Ber., 1872, 5, 322) he discussed the isomerism 
of benzene derivatives. The view that only three di-substitution 
products could be obtained was at that time supported by negative 
evidence only; no more than three such isomeric compounds had 
ever been prepared. From data established by Carstanjen 
(/. pr. Ghent., 1871, [ii], 3, 50) in an experimental -investigation 
of hydroxythymoquinone, Ladenburg not only deduced important 
conclusions regarding the symmetry of the benzene molecule, but 
also argued from Carstanjen's facts that only three di-substitution 
products of benzene were theoretically possible. 

Two papers on pentachlorobenzene (Ber., 1872, 5, 789; 1873, 6, 
32) may next be mentioned, as they illustrate the experimental 
skill with which Ladenburg overcame a very difficult practical 
problem. 

Two pentachlorobenzenes had been described, the one by Otto, 
the other by Jungfleisch. As the result of a most laborious 
investigation, involving hundreds of fractional crystallisations 
(Annalen, 1874, 172, 331), Ladenburg was able to show that the 
supposed isomerides did not exist, and that a statement which 
could not be reconciled with the " Gleichwertigkeit " of the six 
hydrogen atoms of benzene had no foundation in fact. 

In his work on mesitylene, which was published shortly after- 
wards (Ber., 1874, 7, 1133; Annalen, 1875, 179, 163), he proved 
that the three displaceable hydrogen atoms in this hydrocarbon 
were all " gleichwertig," and consequently that mesitylene was 
symmetrical trimethylbenzene. 

The proof was as follows: Dinitromesitylene, which may be 

a b e 

represented by the formula C 6 Me 3 HNO 2 NO 2 , was converted into 

a ft e 

nitromesidine, C 6 Me 3 HNO 2 NH2, by reduction, and the acetyl 
derivative of this base was transformed into dinitracetmesidine, 

a b c 

C 6 Me 3 NO 2 NO 2 NHAc. This compound was hydrolysed, and the 
dinitroamino-derivative converted into a dinitromesitylene, 

o. be 

C Me 3 NO 2 NO 2 H, by Griess' method. The substance thus obtained 



286 KIPPING: LADENBURG MEMORIAL LECTURE. 

was identical with the original dinitromesitylene ; therefore two of 
the displaceable hydrogen atoms, a and c, are " gleichwertig." 

a b e 

The nitromesidine, C G Me 3 HNO 2 NH 2 , obtained from the dinitro- 

a b e 

mesitylene, C 6 Me 3 HNO 2 NO 2 , gave the mononitro-derivative, 

a b e 

C 6 Me 3 HNO 2 H, when the ammo-group was displaced by hydrogen. 
The nitro-compound was then reduced to mesidine, acetylmesi- 
dine was nitrated, and the product was hydrolysed to a nitro- 

a b f (i b e 

mesidine, CgMegNQgNB^H, or C 6 Me 3 HNH 2 NO 2 ; but since a = c t 
these formulae are identical. Since, moreover, this nitromesidine 

a b e 

was identical with that, C 6 Me 3 HNO 2 NH 2 , obtained from dinitro- 
mesitylene, 6=c, and therefore a = b = c. He frankly recognised 
that the fact that mesitylene was symmetrical trimethylbenzene 
afforded strong evidence against the prism formula, and he con- 
cluded therefore that "there is at the present time no symbolic 
representation of benzene which satisfies all requirements." 

Another paper wjhich has become a classic is that in which 
Ladenburg showed that in the benzene nucleus there were at least 
four hydrogen atoms which were identically situated {Btr. y 1874, 
7, 1684). His proof, which is of such fundamental importance 
that it is given in most of the test-books of organic chemistry, was 
the following. Phenol, treated with phosphorus pentabromide, gave 
bromobenzene, from which, with the aid of sodium and carbon 
dioxide, benzoic acid was obtained. Now benzoic acid was known to 
give rise to three isomeric hydroxybenzoic acids, C 6 H 4 (OH)*CO 2 H; 
in each of these compounds the hydroxyl group must have dis- 
placed a different hydrogen atom from the benzene nucleus, and 
none of these hydrogen atoms was identical with that displaced by 
the hydroxyl group in the original phenol. All three hydroxy- 
benzoic acids were converted into a phenol and carbon dioxide; 
the phenol thus obtained was in every case identical with the 
original compound. 

The substance of Ladenburg's more important contributions to 
the chemistry of benzene is to be found in his " Theorie der 
aromatischen Verbindungen," published in 1876, a few years after 
he went to Kiel. In this monograph he gave a critical review of 
the position of the aromatic theory at that time, and also did a 
fc.eat service to chemistry by drawing attention to the importance 
of Korner's method for the orientation of benzene derivatives. 

Various other researches on aromatic compounds, including those 
on the aldehydine bases (Ber., 1878, 11, 590, 1648; see also Ber , 
1878, 11, 1653, 1656), were carried out between 1876 and 1878, 



KIPPING: LADENBURG MEMORIAL LECTURE. 287 

but in the following year he began his study of the alkaloids and 
related compounds, a task which, with its side issues, occupied him 
almost exclusively during the rest of his working life. 

In those days there were known various vegetable products, 
which were used in medicine for different purposes, but had in 
common the remarkable property of dilating the pupil of the eye. 
Among these alkaloids were belladonine and atropine, obtained 
from the deadly nightshade (Atropa belladonna), henbane, or 
hyoscyamine, from Hyoscyamus niger, duboisine, from Duboisia 
myoporoideSy and daturine, from Datura strammonium. The 
only one of these substances that had been investigated other than 
very superficially was atropine; Lessen had shown that this base 
was hydrolysed by concentrated hydrochloric acid, giving tropine 
and tropic acid: 

C 17 H 23 3 N + H 2 = C 8 H 15 ON + C 9 H 10 O S ; 

from tropic acid, atropic acid, C 9 H 8 O 2 (and isatropic acid) had been 
obtained, and atropic acid had been reduced to hydratropic acid, 
C 8 H 10 2 . 

Ladenburg first succeeded in preparing atropine from its decom- 
position products by evaporating a dilute hydrochloric acid solution 
of tropine with tropic acid (Ber., 1879, 12, 941) ; he found that 
this artificial atropine was identical with the natural product in 
every respect, including its physiological action. 

He then showed that tropine reacted with other organic acids 
in a similar manner, in presence of hydrochloric acid, giving com- 
pounds which he named tropeines (Ber., 1880, 13, 1081; 1882, 
15, 1025); of these, the product from tropine and mandelic acid, 
phenylglycolyltropeine, or homatropine, C 16 H 21 O 3 N, had a mydriatic 
action not quite so strong as, but much more rapid than, that of 
atropine; homatropine, moreover, was less poisonous than atropine. 
This partially synthetic alkaloid found application in ophthalmic 
surgery. 

The results of the further investigation of atropine were 
published in numerous papers during 1880-1882, and were briefly 
as follows: Hydratropic ac'd, C 6 H 5 'CHMe-CO 2 H, oxidised with 
permanganate (Ladenburg and Rugheimer, Ber., 1880, 13, 373), 
gave an acid, C 9 H 10 O 3 , which was identical with the atrolactinic 
acid obtained by Fittig and Wurster (Annalen, 1879, 195, 145) 
by treating atropic acid with hydrobromic acid and hydrolysing the 
product; this fact showed that atrolactinic acid had not the con- 
stitution C 6 H 5 -CH(CH 2 -OH)-CO 2 H assigned to it by Fittig and 
Wurster, but C 6 H 5 -C(OH)(CH 3 )-CO 2 H. Atrolactinic acid, heated 
with hydrochloric acid, was converted into atropic acid ; the latter 



288 KIPPING: LADENBURQ MEMORIAL LECTURE. 

combined with hypochlorous acid to form a chlorohydroxy-acid, 
from which tropic acid was obtained when the chlorine was displaced 
by hydrogen. 

These results showed that tropic acid was not 

C 6 H 6 -C(OH)(CH 3 )-C0 2 H, 

as suggested by Fittig and Wurster, and that the relationship 
between the four acids just mentioned was as follows : 



(I.) Hydratropic acid. (II.) Atrolactinic acid. 



(III.) Atroi-ic acid. (IV.) Tropic acid. 

The synthesis of tropic acid was then accomplished in conjunction 
with Riigheimer (Ber., 1880, 13, 2041). Acetophenone dichloride, 
boiled with potassium cyanide in alcoholic solution, gave the com- 
pound C 6 H 6 *CMe(OEt)*CN, which, on hydrolysis, was converted 
into the acid C 6 H 5 CMe(OEt)CO 2 H; the latter, with concentrated 
hydrochloric acid, gave atropic acid (III), from which tropic acid 
was prepared in the manner described above. 

The determination of the constitution of tropine, the other 
decomposition product of atropine, was a much more difficult task, 
which Ladenburg attacked with great vigour. He found that when 
tropine, C 8 H 15 ON, was heated with concentrated hydrochloric acid, 
it was converted into tropidine, C 8 H 18 N (Ber., 1879, 12, 944 ; 1880, 
13, 252); when heated with hydriodic acid, it gave an iodide, 
C 8 H 16 NI 2 (Ber., 1881, 14, 227), which, on reduction with zinc and 
hydrochloric acid, yielded hydrotropidine, C 8 H 15 N (Ber., 1883, 16, 
1408). When distilled with soda-lime, tropine gave methylamine, 
trimethylamine, hydrogen, and a hydrocarbon which was suspected 
to be valerylene, but its nature was not established (Ber., 1881, 14, 
227). 

As these results seemed to indicate that tropine was a derivative 
of a reduced pyridine or an oxidised piperidine nucleus, he prepared 
various alkylpiperidine derivatives, among others, JV-propyl- and 
#-*opropyl-piperidine, and tried to convert these compounds by 
oxidation and other means into a base, which might prove to be 
identical with tropine or tropidine (Ber., 1881, 14, 1342). These 
experiments having failed, and the degradation of tropine by 
distillation with soda-lime having given such poor results, he next 
applied to this base a method which had been recently discovered 
by Hofmann, the now well-known process of exhaustive methylation. 

From tropine and methyl iodide he obtained an iodide of methyl- 
tropine, C Q H, 7 ON, and found that this base was decomposed by 



KIPPING: LADENBURQ MEMORIAL LECTURE. 289 

potassium hydroxide, giving dimethylamine (Ber., 1881, 14, 2126). 
Methyltropine, on further methylation, gave dimethyltropine iodide, 
from which by distillation, he obtained trimethylamine, an oil, 
C 7 H 10 O, which he named tropilene, and a hydrocarbon of the 
composition C 7 H 8 , which he called tropilidene (Ber., 1881, 14, 
2403); this hydrocarbon seemed to be identical with that which 
he had previously obtained from tropine. 

The composition and properties of tropilene led Ladenburg to 
conclude that this compound was related to suberone; he oxidised 
it with nitric acid, and found that it gave an acid which was prob- 
ably normal adipic acid (Ber., 1882, 15, 1028). At the same time 
he discovered another very important fact, namely, that t opidine 
hydrobromide, heated with bromine at 170 180, gave ethylene 
dibromide and dibromomethylpyridine ; with excess of bromine it 
gave ethylene dibromide and dibromopyridine (Ber., 1882, 15, 
1140). From all these observations he concluded that tropine was 
probably a methylpiperidine or methylpyridine derivative of the 
following constitution (Ber., 1882, 15, 1028): 

N-CH 3 

CH 2 CH/\CH 

CH 2 -OH CH 2 \/CH 

OH 2 

While these experiments were in progress he also examined 
several of the other mydriatic drugs; in the course of this work 
he showed that duboisine and daturine were probably identical 
with hyoscyamine, that belladonine probably contained atropine, 
and that hyoscyamine and atropine were very closely related, so 
closely, in fact, that atropine could be synthesised from the decom- 
position products of hyoscyamine. 

About 1882, Ladenburg's direct study of these mydriatic alkaloids 
gave place to his synthetic work on piperidine and pyridine deriv- 
atives. The main object of these researches was, no doubt, the 
synthesis of tropine, since he thought that this base was related to 
pyridine in the manner shown above. 

The first important step in these synthetical experiments was the 
discovery that pentamethylenediamine could be obtained by the 
reduction of trimethylene dicyanide with zinc and hydrochloric 
acid (Ber., 1883, 16, 1149). This base, heated with sodium 
hydroxide, gave a compound, C 5 H n N, which seemed to be piperi- 
dine, and the identity of the synthetic base with that obtained 
from pepper was fully established by Ladenburg and Roth (Ber., 
1884, 17, 513). As the yield of pentamethylenediamine in the 
above process was very unsatisfactory, Ladenburg devised a better 



290 KIPPING: LADENBURG MEMORIAL LECTURE. 

method for the preparation of the base, which consisted in reducing 
the dicyanide with sodium and alcohol (Ber., 1885, 18, 2956); he 
also showed that the hydrochloride of the diamine was converted 
into piperidine and ammonium chloride when it was distilled ; as 
this change was evidently no far-reaching decomposition, the 
synthesis of piperidine in this way established the constitutional 
formula at that time assigned to that base. 

While this synthesis of piperidine was in progress, he studied 
the behaviour of pyridine ethiodide at high temperatures (Ber., 
1883, 16, 1410), and found that it gave ethylpyridine hydriodide 
when it was heated, by intramolecular change, just as the 2V-sub- 
stituted anilines were known to give homologues of that base 
(Hofmann). He proved that the product contained y-ethylpyridme 
by oxidising a fraction of it to i'sonicotinic acid (Ber., 1883, 16, 
2059), and also showed later (Ber., 1885, 18, 2961) that a-ethyl- 
pyridine and ay-diethylpyridine were also produced, together with 
the y-ethyl derivative, when pyridine ethiodide was heated. 

It was now possible to obtain derivatives of pyridine from that base 
itself; in order to convert these compounds into the corresponding 
piperidine derivatives, Ladenburg investigated a method described 
by Konig for the reduction of pyridine to piperidine with zinc 
and hydrochloric acid, but he was unable to obtain any piperidine. 
He next tried reduction with sodium and alcohol, a process used 
by Wischnegradsky, and by a suitable improvement of this method, 
he was able to reduce coal tar picoline almost completely. In this 
way he obtained ce-methylpiperidine, mixed with the j8-compound, 
the first homologues of piperidine, excluding the ^-derivatives, 
which had been prepared (Ber., 1884, 17, 388). He also reduced 
his y-ethylpyridine to the piperidine derivative, and found that the 
latter had an odour of coniine. 

This observation and the results of Hofmann's work, which had 
shown that coniine was in all probability o-propylpiperidine, led 
Ladenburg to attempt the synthesis of the last-named compound. 
With this end in view, he heated pyridine propiodide, and obtained 
a mixture of bases; one of these compounds gave, on oxidation, 
pyridine-y-carboxylic acid, and seemed to be y-propylpyridine ; the 
other could not be obtained in a state of purity. The pure and the 
impure isomerides were separately reduced to piperidine derivatives ; 
these compounds resembled coniine, but neither was identical with 
the latter. Immediately afterwards, with Schrade, he prepared 
a- and y-isopropylpyridine in a similar manner from pyridine 
asopropiodide (Ber., 1884, 17, 1121). As these two compounds, 
like the supposed propyl derivatives, could not be completely 
separated by distillation, he converted the crude bases into the 



DIPPING: LADENBURG MEMORIAL LECTURE 291 

corresponding piperidine derivatives by reduction with sodium and 
alcohol (Be? ., 1884, 17, 1676), and then purified the latter with the 
aid of their platinichlorides. 

The a-sopropylpiperidine thus obtained in a pure condition was 
carefully compared with coniine, and found to be remarkably 
similar to that base in all its properties, including its physiological 
action; the observed differences might be due merely to the optical 
inactivity of the synthetical base. 

It was then found (Ber., 1885, 18, 1587) that the a- and y-iso- 
propylpyridines and also the supposed corresponding propyl deriv- 
atives could be completely purified with the aid of their platini- 
chlorides; in each case the base of lower boiling "point gave on 
oxidation picolinic acid, and was therefore the a-derivative, whilst 
the isomeride gave sonicotinic acid, and was therefore the y-deriv- 
ative. 

The pure a-pyridine bases (propyl and sopropyl) were carefully 
compared with conyrine, which Hofmann had obtained by heating 
coniine hydrochloride with zinc dust, and had shown to be either 
o-propyl or a-asopropylpyridine. They both differed from conyrine. 
Therefore, either the difference was merely due to stereoisomeriem, 
or else the two synthetical bases must both be isopropylpyridine. 
The latter alternative was proved to be the true one; when pyridine 
propiodide was heated in order to convert it into propylpyridine, 
the n-propyl was transformed into the wopropyl group. 

Since it had thus been proved that conyrine must be a-propyl- 
pyridine, Ladenburg attempted to prepare this base from pyridine 
allyl iodide, but obtained tsopropylpyridine in place of the desired 
propyl compound (Ber., 1885, 18, 1587). Next he tried to condense 
picoline with paracetaldehyde in the presence of zinc chloride (Ber., 
1886, 19, 439), a reaction which Jacobsen and Reimer had applied 
to obtain benzylidenequinaldine from quinaldine and benzalde- 
hyde. In this way he obtained only very small quantities of an 
oily base, but the product had an odour of conyrine, and on analysis 
seemed to be allylpyridme. On reduction with sodium and alcohol, 
it gave a base having properties similar to those of coniine. These 
experiments were repeated with larger quantities of material (Ber., 
1886, 19, 2578) ; 380 grams of picoline were treated in sealed tubes, 
and 45 grams of allylpyridine were obtained; the product was 
proved to be the a-derivative by oxidising it to picolinic acid, and 
was reduced to propylpiperidine ; the latter was oxidised by 
Hof mann's method (Ber., 1884, 17, 825) to a base, which was found 
to be identical with conyrine.. The synthetical propylpiperidine 
was finally converted into the acid tartrate, and the solution of the 
latter was seeded with a crystal of coniine acid tartrate ; the crystal- 



292 K1PPIKG: LAbENBURG MEMORIAL LECTURE. 

line deposit was decomposed with potassium hydroxide, and the 
liberated base was found to be dextrorotatory. The complete 
identity of the synthetical base with coniine, obtained from the 
hemlock, was then fully established ; the alkaloid which had caused 
the death of the wisest of men was the first to succumb to the 
synthetic skill of the chemist ! 

This synthesis of coniine was accomplished in 1886, and for 
nearly twenty years afterwards Ladenburg continued his researches 
with undiminished activity. During this period he was occupied 
to a great extent with various issues arising out of hie earlier work ; 
it will therefore be more convenient to deal with the discoveries 
of this period under certain definite headings rather than to 
consider them in strict chronological sequence. 

His studies of the diamines may be first considered (Ber., 1886, 
19, 2585). He showed that his synthetical pentamethylenediamine 
was identical with cadaverine, a base isolated by Brieger from 
putrefying flesh. Tetramethylenediamine (Ber., 1886, 19, 780; 

CM *C 1 ]T 
1887, 20, 442) was converted into pyrrolidine, 1 u 2 ^ TI 2 >NH, by 

L/llg'C/ Ii2 

the same method as that by which piperidine had been obtained 
from pentamethylenediamine, and pyrrolidine was also synthesised 
by reducing succinimide with sodium and alcohol (Ber., 1887, 20, 
2215). The action of heat on ethylenediamine hydrochloride 
resulted in the formation of a base (Ber., 1888, 21, 758; 1890, 23, 
3740; 1891, 24, 2400)/ which is now well known as piperazine. 



By the distillation of ethylenediamine hydrochloride with sodium 

CFT NFI'^ 

acetate he obtained a base, lysidine, I 2 _ i>C-CH 3 (Ber., 1894, 

L -tlo 

27, 2952), identical with a compound prepared by Hofmann (Ber., 
1888, 21, 2332) in an analogous manner. Lysidine, like piperazine, 
formed with uric acid a salt which was very readily soluble in 
water (Ber., 1894, 27, 2952), and clinical experiments, carried out 
at Ladenburg's suggestion, showed that a case of acute, and also 
one of chronic arthritis were both quickly cured by large doses of 
this base. 

The action of heat on trimethylenediamine hydrochloride resulted, 

not only in the formation of trimethyleneimine, CH s < Orn f ^^ M> 

but also in the production of two picolines (Ber., 1890, 23, 2T27); 
the production of these two pyridine derivatives was explained by 
assuming that the diamine first gave rise to a homologue of 



KIPPING: LADENBURG MEMORIAL LECTURE. 293 



piperazine, NH< 2 g 22 >NH, which then decomposed with 

formation of ammonia and two molecules of hydrogen, the eight- 
membered ring suffering disruption, and .passing into a mixture of 
two j8-picolines (compare also Ber., 1890, 23, 2688) : 

CH CH 

s \ / \ 

< /CH 2 .CH 2 -CH 2>NH OH C-CH 3 CH C-UH 8 





CH or ij H CH 

\ / \ S 

JSI - N 1 

His investigations on pyridine derivatives led him to consider 
the orientation of the pyridinecarboxylic acids, and he pointed out 
the important fact that when a pyridinedicarboxylic acid was 
heated, the a-carboxyl group was always the first to be eliminated 
(Ber., 1885, 18, 2967). He isolated lutidine (Ber., 1885, 18, 913) 
and y-picoiine (Her., 1888, 21, 285) from coal tar, and reduced 
these compounds to the corresponding piperidine derivatives. He 
showed that a-methyl- and a-ethylpiperidine could be resolved into 
their optically active components (Ber., 1886, 19, 2584, 2975), and 
that picolinic acid (Ber., 1891, 24, 640), as well ae nicotinic and 
isonicotinic acids (Ber., 1892, 25, 2768) could be reduced with 
sodium and alcohol to the corresponding piperidinecarboxylic acids. 
A summary of his work on pyridine and piperidine derivatives 
down to 1888 is given in the Annalen, 1888, 247, 1. 

The partial synthesis of piperine from piperidine and the chloride 
of piperic acid having been carried out by Riigheimer in the Kiel 
laboratory, the last link required to complete the chain was forged 
by Ladenburg and Scholtz (Ber., 1894, 27, 2958). Piperonal was 
condensed with acetaldehyde to piperonylacrolein, 

o / \CH:CH-CHP 
i \ / 

CH 2 -0 

and the latter, with the aid of sodium acetate and acetic anhy- 
dride, WPS converted into an acid, 

CH 2 <Q>C 6 H 8 -CH:CH-CH:CH-C0. 2 ll, 

identical with the piperic acid obtained from piperine. 

His analytical and synthetical experiments on tropine, which 
had been interrupted by his work on coniine, were continued inter- 
mittently down to 1902. Hydro tropidine hydrochloride, when 
heated, gave methyl chloride and a base, C 7 H 13 N, which he named 
norhydrotropidine ; the hydrochloride of the latter, under similar 
conditions, gave a-ethylpyridine, together with a small quantity of 



294 KIPPING : LADENBURG MEMORIAL LECTURE. 

a hydrocarbon (Ber., 1887, 20, 1647). He also showed that tropi- 
dine was converted into tropine by treatment with hydrobromic 
acid (Ber., 1890, 23, 1780, 2225; 1902, 35, 1159, 2295). 

The resolution of tropic, acid into its, optically active components 
(Ladenburg and Hundt, Ber., 1889, 22, 2590) led to the prepara- 
tion of optically active atropines, which were obtained by evapor- 
ating the active acids with a solution of tropine hydrochloride. 

A large proportion of his work on tropine at about this time 
consisted of repeated but fruitless attempts to synthesise this 
elusive base. For this purpose, starting from piperidine deriv- 
atives, and using Hofmann's method (Ber., 1885, 18, 111), he 
prepared various tetrahydropyridine derivatives (Ber., 1887, 20, 
1645) which he thought were related to tropine. He also prepared 
cc-picolylalkine, C 5 NH 4 'CH 2 'CH 2 *OH, by the condensation of pico- 
line and formaldehyde; this compound on distillation gave vinyl- 
pyridine, C 5 NH 4 'C 2 H 3 , which had a strong odour of conyrine, and 
on reduction was converted into a-pipecolylalkine, 

C 5 NH 10 -CH 2 -CH 2 -OII, 

a base nearly related to tropine in composition and properties 
(Ber., 1889, 22, 2583). These synthetical experiments were, of 
course, predestined to fail, because they were founded on an errone- 
ous view of the constitution of tropine ; this fact, however, does not 
detract from the value of Ladenburg's positive results, which threw 
so much light on the nature of tropine and formed so excellent a 
foundation for the brilliant synthesis ultimately accomplished by 
Willstatter. 

In another long series of papers, published between 1893 and 
1906, Ladenburg follows up the discovery of a base which he 
regarded as a stereoisomeride of coniine. He found (Ber., 1893, 
26, 854) that when coniine hydrochloride was distilled with a 
relatively small quantity of zinc dust, in addition to conyrine and 
unchanged coniine, it gave an optically active propylpiperidine, 
which differed from coniine in specific rotation and in certain other 
respects. He accounted for the existence of this base, which he 
named isoc&miue, by assuming that the arrangement of the atoms 
or groups around the nitrogen atom was an asymmetric one, or, at 
any rate, that such an arrangement could modify the optical 
activity conditioned by the asymmetric carbon group (Ber. t 1896, 
29, 2718). By a method similar to that used in the conversion of 
coniine into ^ocdniine, he prepared from d-pipecoline an isomeric 
base, wopipecoline (Ber., 1894, 27, 853), and by heating Z-stil- 
bazoline (Ber., 1903, 36, 3694), a compound obtained by resolving 
the reduction product of stilbazole, C 5 NH 4 -CH:CH'C 6 H 5 , he pre- 
pared isostilbazoline (Ber., 1904, 37, 3688). He made many 



KIPPING: LADENBURG MEMORIAL LECTURE. 295 

experiments to try and prove that these optically active so-bases 
were definite compounds, and not mere mixtures in unequal pro- 
portions of the d- and Z-isomerides (Ber., 1895, 28, 163; 1896, 29, 
2706; 1897, 30, 485), and he also attempted unsuccessfully to 
obtain other nitrogenous compounds showing isomerism of the same 
nature (Ber., 1896, 29, 2710; 1897, 30, 1582). In his last paper 
on this subject (Ber., 1906, 39, 2486), although he maintained the 
existence of isoconiiiie, the facts which he himself had established 
were so difficult to reconcile with his views that he was obliged to 
conclude that his own synthetical coniine was in reality the iso~ 
base, and that the latter was only converted into natural coniine 
when it was strongly heated. An impartial verdict on this branch 
of Ladenburg's work may perhaps be implied by the statement 
that he is not the only chemist who has unsuccessfully devoted 
time and effort to prove the existence of asymmetry in tervalent 
nitrogen compounds. 

In the course of his experiments on the resolution of piperidine 
derivatives and during his study of the active bases, Ladenburg 
made some important contributions to our knowledge of asym- 
metric compounds. He was the first to show that dZ-hases could 
be resolved by the method discovered by Pasteur, and used by the 
latter for the resolution of dl-acids. He also showed that a lowering 
of temperature occurred when d- and Z-coniine were mixed (Ber., 
1895, 28, 163), whereas no change in temperature was observed in 
the case of certain other liquids of similar character, having the 
same specific gravity (Ber., 1895, 28, 1991). From these facts he 
argued that d- and Z-coniine united to form a racemic liquid. 

A general method for distinguishing solid racemic compounds 
from ^-mixtures was also put forward (Ber., 1894, 2|7, 3065), but 
as the result of adverse criticism, this method was modified as 
follows (Ber., 1899, 32, 864) : " To decide whether an inactive, 
resolvable substance is a racemic compound or a mixture of active 
components, the solubility of the substance is determined with and 
without the addition of a smfll quantity of one of the active 
components (at the same temperature and in the same solvent). 
If the solubilities are different, the substance is racemic; if the 
same, it is an enantiomorphous mixture. 

During some experiments on the resolution of j8-pipecoline with 
the aid of tartaric acid, he found that when crystallisation occurred 
at about 100 the experiments failed, whereas at the ordinary 
temperature the dl-lo&se was resclved (Ber., 1894, 27, 75) ; also, that 
the resolution of pyrotartaric acid (methylsuccinic acid) could be 
accomplished with the aid of strychnine (Ber., 1895, 28, 1170), 
but not with quinine. These results led him to conclude that the 



296 KIPPING: LADENBTTRO MEMORIAL LECTURE. 

d/-base formed with the d-acid and the dl-acid formed with the 
Z-base a salt, one part of the molecule of which was racemic, the 
other part optically active. To such salts he applied the term 
half or partly racemic, which had been previously used by 
E. Fischer (Ber., 1894, 27, 3225) to denote mixtures, or compounds, 
of two optically active components which were similar but not 
enantiomorphously related. 

The study of these partly racemic salts was described in numerous 
papers (Ber., 1898, 31, 524, 937, 1969; 1899, 32, 50; 1903, 36, 
1649; 1907, 40, 2279; 1908, 41, 966), and a summary of the 
results was given in the Annalen (364, 227) in 1909. His experi- 
ments were chiefly directed towards obtaining evidence that the 
two types of partly racemic salts, namely, dAlB, IAIB, and dAlB, 
dAdB, were not merely mixtures, but were definite compounds. 
For this purpose he compared the properties of partly racemic 
strychnine e?/-tartrate, dAlB, IAIB, with those of the dAlB anu 
IAIB salts of strychnine and tartaric acid. He showed that the 
three compounds differed as regards the hydration of their crystals : 
also in solubility, specific gravity, specific rotation, and so on; 
and that the qualitative data could not be reconciled with the 
view that the partly racemic salt was a mere mixture of the dAlB 
and IAIB components. He also proved that partly racemic 
strychnine tartrate and brucine hydrogen tartrate had a transition 
temperature above which they underwent resolution. On the other 
hand, c?-pipecoline d-tartrate, which was deposited as a partly 
racemic salt at high temperatures, had a transition temperature 
below which it was resolved; <$-tetrahydroquinaldine hydrogen 
d-tartrate behaved in a similar minner. From all these results, 
Ladenburg concluded that the formation of partly racemic salts 
was a very general phenomenon; further, that the formation of 
such salts was strong evidence in support of the view that racemic 
compounds could exist in a dissolved state. 

In 1898 he was able to break new ground with the aid of an 
apparatus for the liquefaction of air. He described various lecture 
experiments suitable for the illustration of low temperature effects 
(Ber., 1898, 31, 1968), and also determined the specific gravities 
of liquid air and other liquefied gases (Ber., 1899, 32, 46), as well 
as their boiling points (Ber., 1899, 32, 1818). He liquefied 
ozonised oxygen (Ber., 1898, 31, 2508), purified the ozone by 
fractional evaporation, and determined the density of this purified 
material with the aid of Schilling's apparatus; the purity of the 
samples, that is to say, the proportion of ozone which they contained, 
was checked by a titration of the iodine liberated from potassium 



KIPPING : LADENBURG MEMORIAL LECTURE. 297 

iodide by a known>quantity of the gas. The density was thus found 
to be 1-456 (O = l). 

In other papers (Ber., 1898, 31, 2830; 1900, 33, 2283) dealing 
with this matter, he replied to objections which had been raised 
to his method on the grounds that he had used the formula O 8 for 
ozone in calculating the proportion of this gas in his samples. He 
then worked out the details of a process- for estimating the ozone 
in a weighed quantity of ozonised oxygen with the aid of turpentine 
(Ber. y 1901, 34, 631); he was thus able to determine the density 
of ozone without the use of potassium iodide. Later still (Ber., 
1901, 34, 1184) he showed that the usual method for the estimation 
of -ozone, with the aid of an acidified solution of potassium iodide, 
gave results which were 50 per cent, higher than the true values, 
but that correct estimations could be made if the gas were first 
absorbed in neutral solutions of potassium iodide, which were then 
acidified before titration. 

The interesting question as to the relative positions of iodine and 
tellurium in the periodic system led Ladenburg to take up the 
study of the first^named element. He showed (Ber., 1902, 35, 
1256) that silver iodide could be readily freed from silver chloride 
by repeated extraction with a concentrated solution of ammonium 
hydroxide until the solubility of the iodide became constant; he 
reduced the pure iodide with zinc and sulphuric acid, decomposed 
the zinc iodide which was thus formed with nitrous acid, and 
distilled the well-washed precipitated iodine in steam. He then 
determined the melting point, boiling point, and specific gravity of 
the pure halogen. 

Shortly afterwards (Ber., 1902, 35, 227b) he made a series of 
determinations of the atomic weight of iodine, based on the con- 
version of silver iodide into silver chloride and a knowledge of the 
atomic weights of silver and chlorine. From the results of this work, 
he found the atomic weight, I = 126'96, a value considerably higher 
than that (126' 85) obtained by Stas, but which approximates very 
closely to that (126'92) which is given in the last report of the 
International Committee on Atomic Weights. 

A list of Ladenburg's papers is given in the Berichte (1912, 45, 
3636). 



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