WATT, James. Thoughts on the constituent Parts of Water and of Dephlogisticated Air; with an Account of some Experiments on that Subject. In a Letter from Mr. James Watt, Engineer, to Mr. De Luc, F. R. S.
London: Lockyer Davis & Peter Elmsly, 1784. First edition.

The first of two letters by Watt setting forth his views on the composition of water. “Watt’s career as a scientist centered on his interest in chemistry. He performed numerous experiments, was in contact with several of the foremost chemists of the day (including Black, Priestley, and Berthollet), and occasionally ventured into the realm of theory. In 1783 he formed the opinion that water is a compound; but his designation of its components was ambiguous, inasmuch as he described them as ‘dephlogisticated and inflammable air, or phlogiston,’ where ‘phlogiston,’ as he often used the term, signified various gases. During the nineteenth century a spirited debate arose among the partisans of Watt, Cavendish, and Lavoisier over credit for priority in the discovery of the ‘composition of water’ J.R. Partington, the historian of chemistry after closely evaluating the conflicting claims has lent his authority to the view that while Watt is entitled to credit for first stating that water is not elementary, it was Lavoisier who clearly specified what its components are.” (D.S.B. XIV:197). “Two letters by Watt setting forth his views on the composition of water were published by the Royal Society: ‘Thoughts on the Constituent Parts of Water and of Dephlogisticated Air; With an Account of Some Experiments on that Subject. In a Letter From Mr. James Watt, Engineer, to Mr. De Luc, F.R.S.,’ in Philosophical Transactions of the Royal Society, 74 (1784), 329 – 353; and ‘Sequel to the Thoughts on the constituent Parts of Water and Dephlogisticated Air: In a Subsequent Letter From Mr. James Watt, Engineer, to Mr. De Luc, F.R.S.,’ ibid., 354 – 357. Watt’s biographer, James Patrick Muirhead, later reprinted these letters with additional material relevant to the composition-of-water controversy: Correspondence of the Late James Watt on His Discovery of the Theory of the Composition of Water, James Patrick Muirhead, ed. (London, 1846).’ (D.S.B. XIV:198). See also David Philip Miller: Discovering Water: James Watt, Henry Cavendish and the Nineteenth-Century ‘Water Controversy’; and Jungnickel & McCormmach: Cavendish.

8vo: 241 x 178 mm. Extract from: Philosophical Transactions of the Royal Society of London, Vol. 74 (1784). 4to, pp. 329-53. Stapled into early 20th century stiff blue wrappers, label of Henry Sotheran Ltd. on upper cover.