VAN'T HOFF, JACOBUS HENRICUS Dutch physical chemist, was born in Rotterdam on Aug. 30, 1852. He studied at the Polytechnic at Delft, at the University of Leyden, then under Kekule at Bonn, Wurtz at Paris and, finally, with Mulder at Utrecht, where he obtained his doctorate. In 1876 he became lecturer in physics at the veterinary school, Utrecht, and in 1878 he was appointed professor of chemistry, mineralogy and geology in Amsterdam university. In 1896 he went to Berlin as professor to the Prussian academy of sciences but as this position involved no teaching duties he accepted an honorary professorship in the university so that he might lecture if he wished. He was elected a foreign member of the Royal Society in 1897 and awarded its Davy medal in 1893 ; he received the Nobel prize in 1901 and died on March 1, 1911, at Steglitz.
Van't Hoff's first research was on cyanacetic and malonic acids but his earliest important contribution to science was made in 1874. Starting with the results of the work of Wislicenus (q.v.) on the lactic acids, van't Hoff showed that the four valencies of the carbon atom were probably directed in space towards the four corners of a regular tetrahedron ; in this way optical activity, shown to be always associated with an "asymmetric carbon atom," could readily be explained. An identical idea was put forward two months later (Nov. 1874), quite independently, by J. A. Le Bel, whose name is generally linked with that of van't Hoff in connection with the theory of asymmetric carbon. The concept was attacked by Kolbe (q.v.), but its value was soon universally realized and it laid the foundation stone of the science of stereo chemistry (q.v.). In 1884 was published van't Hoff's second im portant work; it dealt with the application of thermo-dynamics to chemical reactions, and was probably his gteatest contribution to physical chemistry. He developed the principles of chemical kinetics, described a new method of determining the order of a reaction, and applied thermodynamics to chemical equilibria; in the course of this work lie deduced the connection between the equilibrium constant of a reaction and the temperature, in the form of an equation known as the "van't Hoff isochore." He
generalized this in the form of the "principle of mobile equi librium," a special case of the principle developed by Le Chatelier at the same time (1884). In the course of the same study van't Hoff introduced the modern concept of chemical affinity as the maximum work obtainable as the result of a reaction and showed how it may be calculated from measurements of osmotic pres sure, gas pressure and the e.m.f. of reversible galvanic cells. In 1886 he published the results of his study of dilute solutions and showed the analogy existing between them and gases, since both obey equations of the type pv =RT. During the next nine years he developed this work in connection with the theory of electrolytic dissociation enunciated by Arrhenius (q.v.) in 1887. As part of this work he carried out a series of researches on the conditions of formation and decomposition of double salts, and on his translation to Berlin in 1896, he developed this into the important study of the formation of oceanic salt deposits with special reference to those at Stassfurt, Saxony. With W. Ostwald (q.v.) he started the important Zeitschrift fur physi kalische Chemie in 1887 and the first volume contained the famous paper by Arrhenius on electrolytic dissociation. Van't Hoff's publications include La Chimie dans l'Espace (1875); German edition 1876, and English 1898; Etudes de dynamique chimique (1884), revised and extended by E. Cohen as Studien zur Chemischen Dynamik (1896); Vorlesungen fiber Bildung und SPaltung Doppelsalzen (1897) ; and Zur Bildung der Ozeaniachen Salz ablagerangen (i., 19o5; ii., 1909).
See E. Cohen, Jacobus Henricus van't Hoff, Sein Leben und Werken (Leipzig, 1912) ; also obituary notice in Proc. Roy. Soc., vol. 86.