TILDEN, SIR WILLIAM AUGUSTUS

(b. London, England, 15 August 1842; d London, 11 December 1926)

chemistry.

The eldest son of Augustus Tilden, William had a mixed early education resulting from the numerous moves of his family. He attended East Dereham School briefly before being apprenticed in 1857 to the pharmaceutis Alfred Allchin, who so encouraged Tilden to chemistry that he allowed him to spend the last year of his apprenticeship studying at the Royal College of Chemistry. In 1863 Tilden became a demonstrator at the Pharmaceutical Society, a post he held for nine years while studying at London University for his B.Sc. (1868) and D.Sc. (1871).

Tiden married Charlotte Pither Bush in 1869 (d. 1905). He joined Clifton College as science master in 1872 and there began to investigate nitroso derivatives of terpenes, especially ±-pinene and limonene. In 1880 he was elected a fellow of the Royal Society and the first professor of chemistry at Mason College. In 1894 he succeeded T. E. Thorpe as professor of chemistry at the Royal College of Science of London. Tilden married his second wife, Julia Mary Ramie, in 1907. He was named emeritus professor of Imperial College, which was formed from the Royal College of Science, and created a knight in 1909. Although retirement ended his bench chemistry, he continued to write and publish books.

Familiarity with aqua regia and nitrosyl chloride led Tilden to study hydrocarbon derivstives of NOCI, first with phenol, then with α-pinene and limonene. During this time the structures of the terpenes including pinene and limonene were subjects of controversy. The ease with which terpenes formed nitrosyl chlorides not only permitted characterization of these compounds but also provided ready intermediates for further reaction. Nitroso terpene derivatives, prepared from the nitrosyl chlorides by base hydrolysis, allowed Tilden to classify terpenes into a limited number of classes bringing some order to the previous chaos. His scheme divided terpenes into three types based on their nitroso derivatives: the turpentines, of which αpinene is the principal constituent, gave derivatives m.p. 126°C; citrenes, of which limonene is the most commonly occurring, gave derivatives m.p. 76°C; and sylvestrene, which was recognized as different from the other two. Once this division was made, the structure determination of a terpene in a particular class was quite rapid. The first class would be recognized later as containing bicyclic terpenes, and the second and third as monocyclic terpenes, each of a different structure. From his first work in 1877 with the nitroso derivatives Tilden continued throughout his career to study terpenes. One further investigation led him to study the thermal decomposition of terpenes in a red-hot iron tube. He obtained, as one of the many products in the decomposition, isoprene, which is now recognized as the building block not only of the C₁₀ terpenes but also the C₁₅ sesquiterpenes, the C₂₀ diterpenes, and the C₃₀ triterpenes. The sticky material he obtained from isoprene exposed to sunlight was a precursor of synthetic rubber, but Tilden never pursued its uses.

The problem of relating specific heat to atomic weight caught Tilden’s interest late in his career; he measured specific heat as a function of temperature for a number of metals and found that it was a marked function of temperature. His work demonstrated that specific heat was determined by uncertain physical forces and not the work required to separate the atoms of the substance.

Tilden served the Institute of Chemistry as president from 1891 to 1894, the Chemical Society as treasurer from 1899 to 1903 and as president from 1903 to 1905, and was awarded the Davy Medal in 1905.

BIBLIOGRAPHY

I. Original Works. No collected volume of Tilden’s papers is extant. Most of his terpene papers were published in Journal of the Chemical Society (1865–1907) and papers on specific heat in Philosophical Transactions of the Royal Society.

Preparation of α-pinene nitrosyl chloride appeared in Journal of the Chemical Society,28 (1875), 514 ; and preparation of limonene nitrosyl chloride, ibid., 31 (1877), 554.

Tilden wrote several books; the most signal are A Short History of the Progress of Scientific Chemistry (London, 1899), The Elements (London, 1910), Chemical Discovery and Invention in the Twentieth Century (London, 1917), A Life of Sir William Ramsay (London, 1918), and Famous Chemists (London, 1912).

II. Secondary Literature. Two excellent biographical sketches are Journal of the Chemical Society (1927), 3190–3202; and Proceedings of the Royal Society, 117A , no. 778 (1928), i–v, with bibliography.

Gerald R. Van Hecke