make experiments in the hope of finding improved processes
for the production of his wares, and thus his son early acquired
familiarity with practical chemistry. For the theoretical side
he read all the text-books which he could find, somewhat to the
detriment of his ordinary school studies. Having determined
to make chemistry his profession, at the age of fifteen he entered
the shop of an apothecary at Appenheim, near Darmstadt;
but he soon found how great is the difference between practical
pharmacy and scientific chemistry, and the explosions and other
incidents that accompanied his private efforts to increase his
chemical knowledge disposed his master to view without regret
his departure at the end of ten months. He next entered the
university of Bonn, but migrated to Erlangen when the professor
of chemistry, K. W. G. Kastner (1783–1857), was appointed in
1821 to the chair of physics and chemistry at the latter university.
He followed this professor to learn how to analyse certain
minerals, but in the end he found that the teacher himself was
ignorant of the process. Indeed, as he himself said afterwards,
it was a wretched time for chemistry in Germany. No laboratories
were accessible to ordinary students, who had to content
themselves with what the universities could give in the lecture-room
and the library, and though both at Bonn and Erlangen
Liebig endeavoured to make up for the deficiencies of the
official instruction by founding a students’ physical and chemical
society for the discussion of new discoveries and speculations,
he felt that he could never become a chemist in his own country.
Therefore, having graduated as Ph.D. in 1822, he left Erlangen—where
he subsequently complained that the contagion of the
“greatest philosopher and metaphysician of the century”
(Schelling), in a period “rich in words and ideas, but poor in
true knowledge and genuine studies,” had cost him two precious
years of his life—and by the liberality of Louis I., grand-duke
of Hesse-Darmstadt, was enabled to go to Paris. By the help
of L. J. Thénard he gained admission to the private laboratory
of H. F. Gaultier de Claubry (1792–1873), professor of chemistry
at the École de Pharmacie, and soon afterwards, by the influence
of A. von Humboldt, to that of Gay-Lussac, where in 1824 he
concluded his investigations on the composition of the fulminates.
It was on Humboldt’s advice that he determined to become a
teacher of chemistry, but difficulties stood in his way. As a
native of Hesse-Darmstadt he ought, according to the academical
rules of the time, to have studied and graduated at the university
of Giessen, and it was only through the influence of Humboldt
that the authorities forgave him for straying to the foreign
university of Erlangen. After examination his Erlangen degree
was recognized, and in 1824 he was appointed extraordinary
professor of chemistry at Giessen, becoming ordinary professor
two years later. In this small town his most important work
was accomplished. His first care was to persuade the Darmstadt
government to provide a chemical laboratory in which the
students might obtain a proper practical training. This laboratory,
unique of its kind at the time, in conjunction with Liebig’s
unrivalled gifts as a teacher, soon rendered Giessen the most
famous chemical school in the world; men flocked from every
country to enjoy its advantages, and many of the most accomplished
chemists of the 19th century had to thank it for their
early training. Further, it gave a great impetus to the progress
of chemical education throughout Germany, for the continued
admonitions of Liebig combined with the influence of his pupils
induced many other universities to build laboratories modelled
on the same plan. He remained at Giessen for twenty-eight years,
until in 1852 he accepted the invitation of the Bavarian government
to the ordinary chair of chemistry at Munich university,
and this office he held, although he was offered the chair at
Berlin in 1865, until his death, which occurred at Munich on
the 10th of April 1873.
Apart from Liebig’s labours for the improvement of chemical teaching, the influence of his experimental researches and of his contributions to chemical thought was felt in every branch of the science. In regard to methods and apparatus, mention should be made of his improvements in the technique of organic analysis, his plan for determining the natural alkaloids and for ascertaining the molecular weights of organic bases by means of their chloroplatinates, his process for determining the quantity of urea in a solution—the first step towards the introduction of precise chemical methods into practical medicine—and his invention of the simple form of condenser known in every laboratory. His contributions to inorganic chemistry were numerous, including investigations on the compounds of antimony, aluminium, silicon, &c., on the separation of nickel and cobalt, and on the analysis of mineral waters, but they are outweighed in importance by his work on organic substances. In this domain his first research was on the fulminates of mercury and silver, and his study of these bodies led him to the discovery of the isomerism of cyanic and fulminic acids, for the composition of fulminic acid as found by him was the same as that of cyanic acid, as found by F. Wöhler, and it became necessary to admit them to be two bodies which differed in properties, though of the same percentage composition. Further work on cyanogen and connected substances yielded a great number of interesting derivatives, and he described an improved method for the manufacture of potassium cyanide, an agent which has since proved of enormous value in metallurgy and the arts. In 1832 he published, jointly with Wöhler, one of the most famous papers in the history of chemistry, that on the oil of bitter almonds (benzaldehyde), wherein it was shown that the radicle benzoyl might be regarded as forming an unchanging constituent of a long series of compounds obtained from oil of bitter almonds, throughout which it behaved like an element. Berzelius hailed this discovery as marking the dawn of a new era in organic chemistry, and proposed for benzoyl the names “Proïn” or “Orthrin” (from πρωί and ὄρθρυς). A continuation of their work on bitter almond oil by Liebig and Wöhler, who remained firm friends for the rest of their lives, resulted in the elucidation of the mode of formation of that substance and in the discovery of the ferment emulsin as well as the recognition of the first glucoside, amygdalin, while another and not less important and far-reaching inquiry in which they collaborated was that on uric acid, published in 1837. About 1832 he began his investigations into the constitution of ether and alcohol and their derivatives. These on the one hand resulted in the enunciation of his ethyl theory, by the light of which he looked upon those substances as compounds of the radicle ethyl (C2H5), in opposition to the view of J. B. A. Dumas, who regarded them as hydrates of olefiant gas (ethylene); on the other they yielded chloroform, chloral and aldehyde, as well as other compounds of less general interest, and also the method of forming mirrors by depositing silver from a slightly ammoniacal solution by acet aldehyde. In 1837 with Dumas he published a note on the constitution of organic acids, and in the following year an elaborate paper on the same subject appeared under his own name alone; by this work T. Graham’s doctrine of polybasicity was extended to the organic acids. Liebig also did much to further the hydrogen theory of acids.
These and other studies in pure chemistry mainly occupied his attention until about 1838, but the last thirty-five years of his life were devoted more particularly to the chemistry of the processes of life, both animal and vegetable. In animal physiology he set himself to trace out the operation of determinate chemical and physical laws in the maintenance of life and health. To this end he examined such immediate vital products as blood, bile and urine; he analysed the juices of flesh, establishing the composition of creatin and investigating its decomposition products, creatinin and sarcosin; he classified the various articles of food in accordance with the special function performed by each in the animal economy, and expounded the philosophy of cooking; and in opposition to many of the medical opinions of his time taught that the heat of the body is the result of the processes of combustion and oxidation performed within the organism. A secondary result of this line of study was the preparation of his food for infants and of his extract of meat. Vegetable physiology he pursued with special reference to agriculture, which he held to be the foundation of all trade and industry, but which could not be rationally practised without the guidance of chemical principles. His first publication on this subject was Die Chemie in ihrer Anwendung auf Agricultur und Physiologie in 1840, which was at once translated into English by Lyon Playfair. Rejecting the old notion that plants derive their nourishment from humus, he taught that they get carbon and nitrogen from the carbon dioxide and ammonia present in the atmosphere, these compounds being returned by them to the atmosphere by the processes of putrefaction and fermentation—which latter he regarded as essentially chemical in nature—while their potash, soda, lime, sulphur, phosphorus, &c., come from the soil. Of the carbon dioxide and ammonia no exhaustion can take place, but of the mineral constituents the supply is limited because the soil cannot afford an indefinite amount of them; hence the chief care of the farmer, and the function of manures, is to restore to the soil those minerals which each crop is found, by the analysis of its ashes, to take up in its growth. On this theory he prepared artificial manures containing the essential mineral substances together with a small quantity of ammoniacal salts, because he held that the air does not supply ammonia fast enough in certain cases, and carried out systematic experiments on ten acres of poor sandy land which he obtained from the town of Giessen in 1845. But in practice the results were not wholly satisfactory, and it was a long time before he recognized one important reason for the failure in the fact that
