(b. Selby, Yorkshire, England, 30 November 1761; d. Boulogne, France, 22 February 1815)
Tennant’s father was the Reverend Calvert Tennant, a fellow of St. John’s College, Cambridge, and later vicar of Selby; his mother, Mary Daunt Tennant, was the daughter of an apothecary. Both parents had died by the time he was twenty, leaving him an inheritance of land. During 1781 he was a medical student at Edinburgh, where he attended Joseph Black’s lectures. In October 1782, he moved to Christ’s College, Cambridge, from which he received the M.B. in 1788 and the M.D. in 1796. He was elected fellow of the Royal Society in January 1785 and received the Copley Medal in 1804. In 1799 he was a founding member of the Askesian Society, which soon became the Geological Society. In 1813 he was appointed professor of chemistry at Cambridge. Tennant’s travels included a visit to Sweden in 1784, where he met Scheele and Gahn, and a journey to France in 1814–1815 that ended in a fatal riding accident.
Tennant wrote little and consequently was accused of indolence. In 1796 he communicated to the Royal Society his study of the combustion of the diamond. Lavoisier had carried out a series of similar experiments and observed that the gaseous product turned limewater cloudy, as in the burning of charcoal. However, he maintained that this common result merely showed that both charcoal and diamond were in the class of combustibles. Reluctant to stress the analogy further, Lavoisier even wrote that the nature of diamond might never be known. But Tennant insisted that since equal quantities of charcoal and diamond were entirely converted in combustion to equal quantities of fixed air, then both substances must be chemically identical. Certain scientists, notably Humphry Davy, continued to suspect that there were minute chemical differences between these forms of carbon; but Davy soon returned to the interpretation first given by Tennant.
Tennant’s most important work, the discovery of two new elements in platinum ore, was described in a paper to the Royal Society in 1804. The extraction of pure, malleable platinum from its crude ore was a problem that taxed eighteenth-century chemists. A notebook preserved at Cambridge on Tennant’s travels shows that he had discussed the problem with Gahn and Crell in 1784. At that time the standard procedure was to digest the crude ore in aqua regia; this technique left an insoluble black residue that Proust mistook for graphite. At about the same time Collet-Descotils, Fourcroy, Vauquelin, and Tennant realized that this residue contained something new. Collet-Descotils inferred the existence of a new metal from the red color it gave to platinum precipitates; Fourcroy and Vauquelin called the new metal ptáne but soon admitted that they had confused two different metals. Tennant alone recognized that the black powder contained two new metals, which he proceeded to isolate and characterize. He called one iridium on account of the variety of colors it produced; the other he named osmium because of the distinctive odor of its volatile compounds.
Tennant had interested William Wollaston in platinum while they were students at Cambridge. By 1800 they had became business partners, selling platinum boilers for the concentration of sulfuric acid and other products made of platinum.
See Donald McDonald, “Smithson Tennant, F.R.S. (1761–1815),” in Notes and Records. Royal Society of London, 17 (1962), 77–94. On Tennant’s MSS, see L. F. Gilbert, “W. H. Wollaston MSS. at Cambridge,” ibid., 9 (1952), 311–332. His memoirs are listed in the Royal Society Catalogue of Scientific Papers.
D. C. Goodman