TILDEN, SIR WILLIAM AUGUSTUS 'British chemist, was born on Aug. 15, 1842, at St. Pancras, Lon don; he was first apprenticed to a pharmacist, and in 1863 became demonstrator at the Pharmaceutical Society's school. In 1872 he was appointed senior science master at Clifton college; then, in 188o, he became first professor of chemistry at Manor college, Birmingham, and in the same year was elected to the Royal Society; in 1894 he transferred to the chair at the Royal College of Science, London, and there he remained until his retirement in 1919. He died on Dec. II, 1926.
Tilden's first contribution to chemical research was in con nection with the per-iodides of organic bases (1865), and for some years he studied the alkaloids (q.v.) and other substances obtained from plants. In 1874 he examined, together with W. A. Shenstone, the properties of aqua regia and nitrosyl chloride, and whilst investigating the action of the latter on various organic compounds he discovered the nitroso-chloride of pinene. This discovery eventually led to a valuable method for the identification of terpenes (q.v.), and the reaction with nitrosyl chloride was
subsequently used by many workers in this field. Tilden also studied terpineol and related bodies, and the action of heat on terpenes. In 1892 he observed the presence of a rubber-like substance in a bottle of isoprene which had been standing for some years, but owing to the fact that rubber was not then so valuable as it is to-day, the matter was not further investigated. In addition to his researches in organic chemistry Tilden con tributed to physical chemistry. He determined the specific heats of elements at various temperatures, and thus showed the limits of applicability of Dulong and Petit's law. (See CHEMISTRY : Physical.) He also verified Neumann's law of the additivity of the specific heats of elements in certain compounds.
His published works include An Introduction to Chemical Philo sophy (1876) ; A Manual of Chemistry (1896) ; Chemical Discovery and Invention in the Twentieth Century (1917) ; Life of Sir William Ramsay (1918) ; and Famous Chemists (1921).