Williamson, Alexander William (1824-1904), chemist, was born on 1 May 1824 in Wandsworth, Surrey, the second of three children of Alexander Williamson, a clerk in the East India House, and Antonia McAndrew Williamson, daughter of a London merchant.
After attending day schools in Kensington, Paris, and Dijon, in 1841 he enrolled at the University of Heidelberg, intending to study medicine. He was, however, soon attracted to chemistry through the lectures of Leopold Gmelin (1788-1853). In 1844 Williamson transferred to the University of Giessen in order to study under the world-famous chemist Justus Liebig (1803-1873). Here he made a minor sensation with his first published paper, on a subject (the reactions in solution of 'bleaching salts') which Liebig had assigned as a simple analytical exercise.
Williamson received his PhD from Giessen in 1845 and the following year took up temporary residency in Paris. Here he became acquainted with the principal French chemists, including Jean-Baptiste Dumas, Adolphe Wurtz, Auguste Laurent, and Charles Gerhardt. He also took private lessons in mathematics from Auguste Comte, the founder of French positivism, who had been recommended to him by John Stuart Mill.
Although Williamson published no research during this period, it appears that it was in Paris that he began his fundamental investigations in etherification and reaction mechanics. In 1849, supported by the eminent chemist Thomas Graham, Williamson successfully applied for the professorship of analytical and practical chemistry at University College, London, which was vacant following George Fownes's death. This was one of the earliest academic laboratories in Great Britain in which students were required to perform practical exercises. In 1865 he published a successful elementary textbook, 'Chemistry for Students'.
Williamson's novel reaction by which ethers could be synthesized was first announced on 3 August 1850 at the Edinburgh meeting of the British Association for the Advancement of Science. The Williamson ether synthesis was one of the earliest reactions designed with the intent to build up larger molecules from smaller pieces and remains one of the most elegant reactions in organic chemistry. An ether is a molecule with a central oxygen atom connected to two hydrocarbon radicals; Williamson's reaction allowed the chemist to select each radical in advance and then join them together, thus designing new ethers at will.
Williamson's 1850 paper, two additional, more detailed, articles on the same reaction published about a year later, and a further series of papers on related subjects in the following years were widely influential. They are all collected in 'Papers on Etherification and on the Constitution of Salts' (1902). The theoretical strategy he had designed to demonstrate the true structural relationships of alcohols and ethers was applied to various molecular systems by a number of other chemists during the 1850s. In the process, much of the existing confusion over relative atomic and molecular weights was eliminated, and a revised system, virtually identical to that in modern use, was established. Williamson's work had the advantage (to chemists) of deriving its force entirely from chemical evidence; chemists were inclined to distrust the growing physical evidence, for example from the theory of gases, that tended to support the new ideas which Williamson was championing.
By the end of the first six years of his professorship Williamson had published a series of papers describing some of the best chemical research of the century. On Graham's resignation in 1855 he was rewarded by his appointment to the chair of general (theoretical) chemistry in addition to his other duties. The increase in income enabled him to marry Emma Catharine Key (d. 1923), the daughter of a university colleague, Thomas Hewitt Key, on 1 August 1855. They had two children, Oliver Key (d. 1941) and Alice Maude, later Mrs A H Fison (d. 1946).
From 1850 onwards he was a leading personality in the Chemical Society of London, and twice served as its president (1863-1865 and 1869-1871). He was much involved with the British Association for the Advancement of Science and was its president for the 1873 session. He was elected a fellow of the Royal Society in 1855, served two terms on its council, and was its foreign secretary from 1873 to 1889.
Williamson retired in 1887, and moved to an estate which he had purchased in Hindhead, near Haslemere, Surrey, where he practised agriculture on scientific principles. He died at his home on the estate, High Pitfold, Shottermill, after a long illness, on 6 May 1904. He was buried at Brookwood cemetery, Surrey.