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* LIEBIG. 215 riEBKNECHT. was made professor of chemistry at the Uni- versity of Giessen (1824), where lie remained for more than a quarter of a century, attracting students from all parts of Germany and from foreign countries. In 1845 tlie Grand Duke of Hesse raised him to the rank of baron. In 1852 he became professor of chemistry at ilunich, and in 1800 president of the Academy of .Sciences and curator-general of tlie scientihc collections of Bavaria. He remained in ilunich until his death. When Licbig began his career chemistry was in its infancy. Above all, organic analysis w-as in an extremely undeveloped state; so that a great deal of ingenuity was required in carrying out wliat are now very simple analytical determina- tions. At the time of Liebig's death chemistry, both pure and applied, had developed beyond all expectations ; and Liebig had contributed more than any one of his contemporaries to its pro- digious growth. Liebig established the first laboratory where students might receive a thor- ough practical training in chemistry, to supple- ment the instruction given in the lecture-room (see Laboratory), and in Liebig's own laboratory some of the most distinguished nineteenth-cen- tury chemists w-ere trained. Anotlier great ser- ice was his introduction of the well-known method if organic analysis. (See Chemistry, .section Organic Chemistry.) The number of carbon com- pounds discovered and studied by Liebig liim.self was very great. He analyzed many important natui'al alkaloids ; investigated the action of chlorine on alcohol and discovered chloral and chloroform ; studied the products of oxiilation of alcohol and discovered aldehyde; determined the basicity of many organic acids: investigated tl>e chemical composition of urine and the derivatives of nr'u; acid; analyzed the juice of flesh, etc. His theory of the constitution of alcohol, ether, and chloroethane, and the celebrated researcli carried out jointly with Wiihler (q.v. ) on the benzoyl compolind-i. gave a powerful impulse to the de- velopment of chemical theory. Among his con- tributions to chemical technology may be men- tioned his method of making the cyanide of potassium, a compound extensively used in elec- troplating and in the manufacture of ferrocy- anides. The discovery of aldehyde, mentioned above, has led to important improvements in the manufacture of mirrors and of vinegar. The phenomena of animal and vegetable life formed one of Liebig's favorite branches of re- search, and he was the first to advance the theory that the activity of physical and chemical forces is the same in the organized as in the mineral world. He proved experimentally that animal heat is nothing but the energy liberated by the combustion in the organism mainly of fats and carbohydrates. Foods which serve as fuel and supply the heat of the body he termed respiratory foods. Xitrogerious substances, which — as he showed — serve to build up the tissues of the body, he termed plastic foods. He was also the fir.st to prove that the transformation of inorganic into organic substances takes place exclusively in the organisms of plants, from which animals receive ready-formed the principal substances of their flesh and blood. Plants, on the other hand, receive their nourishment from the soil and the air. the former supplying them with the sulphates, sulphites, and phosphates of sodium, potassium, calcium. magnesium, and iron: while the atmospheric air supplies them with carbonic acid, water, ammonia, and nitric acid. It thus became clear that, in order to maintain the fertility of the soil, the saline ingredients necessary for the growth of plants must from time to time be restored to it, either in isolated form or in the form of the sewage of towns, in which they are contained in considerable quan- tity. The importance to agriculture of the manufacture of saline fertilizers, which has thus originated in Liebig's researches, is inestimable, and Liebig may justly be considered as one of the founders of agricultural chemistry. See Chemistry, Agricultural. Liebig's Chemistry in Its' Application to Agri- culture and Physiology appeared in Brunswick and in London in 1840. The second part of this epoch-making work was publisbe<l under the title. The Natural Law of Husbandry (Brunswick, 1862; London, 1863). His Animal Chemistry, or Chemistry in Its Appliralion to Physiology and Pathology, appeareii in 1842 (Brunswick and London ; 3d German ed., Brunswick, 1846). An English translation of his paper on foods ap- peared in London in 1847, under the title. Re- searches on the Chemistry of Food. The cele- brated Handbook of Organic Analysis was pub- lished in Brunswick and in London in 1853. Liebig's publications further include: Hand- loortcrbuch der Chemie. the compilation of which he began in conjunction with Poggendorft' (9 vols., Brunswick, 1836-64, and a later edition) ; Handbuch drr organisrhen Chemie (Heidelberg. 1839-43) ; Theorie iind Pruxi» in der Landwirt- schaft (Brunswick, 1856); Naturipissenschaft- liche Brief e iiber die moderne Landuirtschaft (Leipzig, 1859), etc. The celebrated Chemische Bricfe (Familiar Letters on Chemistry) first appeared in the .iiigsburger Allgemeine Zeitung (6th German ed. Leipzig. 1878) ; it has been translated into most European langiiages. The list of Liebig's scientific papers comprises more than 300 titles, each paper forming a valuable contribution to organic science. In his private life Liebig was kind and hospitable, noble in thought and generous in feeling. Numberless honors were bestowed upon him. Consult Hof- mann. The Life-Work of Liebig in Experimental and Philosophic Chemistry (London, 1876). LIEBKNECHT, lep'knoKt. Wilhelm (1826- 1900). A German social democrat, horn at Gies- sen. He studied in the university there and at Berlin and ^larburg. In 1848 he took part in the revolt in Baden; was imprisoned, but escaped in 'May of 1849. going first to Switzerland and then to London. There he earned his living as correspondent for German newspapers and as a member of the Communistenhund. associated with Marx and Engels. In 1862 he took advantage of the amnesty, returned to Germany, and began to write for the Xorddeulsche .1 llnemeine Zeitung. But in 1865 he was banished from Berlin and Prussia for socialistic agitaticm. Two years later he was elected to the North German Parliament, and in 1868 he began to edit the Demokratisches JTorhenhlatt. in which he attacked Bismarck 80 bitterly that in 1872 he was imprisoned for two years, with liis fellow-editor Bebel. But before he was released he had been elected to the Ger- man Reichstag. Save for brief periods he sat there until his death. In 1879 he was elected to the Second Chamber of the Saxon Legislature. He was editor of the Berlin Vnnmrt.s from 1890 to 1900, and in 1895 was imprisoned for four