(1731–1810) [q. v.] is a question about which there has been much and bitter controversy. It seems clear, however, that Watt, as early as 13 Dec. 1782, wrote to Jean André Deluc [q. v.], ‘I believe air is generated from water. … If this process contains no deception, here is an effectual account of many phenomena, and one element dismissed from the list.’ Later on, 26 April 1783, Watt wrote to Dr. Priestley a letter setting forth his discovery of the composition of water, and requesting that it might be given to Sir Joseph Banks, then president of the Royal Society, with a view to its being read at a meeting. Owing to Priestley's doubts, Watt requested that the reading should be delayed to ascertain the result of some experiments Priestley said he was about to make; it further appears that in the meanwhile Watt's paper was pretty freely shown among the leading members of the society. On 26 Nov. 1783 Watt wrote a letter to Deluc on the same subject; this letter was not read to the society until 29 April 1784; while Cavendish's communication on the same subject was read on 15 Jan. 1784. Lord Brougham traced out various interpolations in the ‘Philosophical Transactions’ in Cavendish's favour by Sir Charles Blagden [q. v.], then secretary; and a curious double misdating of these transactions was also found; making it appear that Watt's communication of 26 Nov. 1783 was 26 Nov. 1784, and that Cavendish's paper was of the date of 15 Jan. 1783, and not, as was the fact, of 15 Jan. 1784. On 22 April 1783 Watt, in writing to Gilbert Hamilton, made this declaration of faith: ‘Pure inflammable air is phlogiston itself.’ ‘Dephlogisticated air is water deprived of its phlogiston, and united to latent heat.’ ‘Water is dephlogisticated air deprived of part of its latent heat, and united to a large dose of phlogiston.’ Watt directs that one part by measure of ‘pure air’ ( = dephlogisticated air = oxygen) and two parts by measure of inflammable air ( = phlogiston = hydrogen) are to be mixed and fired. It is quite certain that Arago in his éloge of James Watt delivered in 1839, though thoroughly aware of the claims that had been put forward by the friends of Cavendish, unhesitatingly ascribed the first discovery of the fact that water was not an element, but was a compound body, and also the ascertaining the nature and proportion of the two constituents, to Watt.
Watt had his interest in chemical science still further stimulated by the hope of benefiting the health of his invalid son, Gregory, by the inhaling of gases, called in those days ‘factitious airs.’ This mode of cure was advocated by the celebrated Dr. Thomas Beddoes [q. v.], and Watt devised an apparatus to be used in hospitals, and of a smaller size in private houses, for the generation of the ‘airs,’ and in 1796 published a pamphlet, with illustrations, prices, and directions for use. Two principal ‘airs’ were to be produced, the one oxygen and the other hydro-carbonate; this appears to have been a mixture of hydrogen, carbonic acid, and some carbonic oxide. This horrible compound was not supposed to be of the best kind, nor to do its work properly, unless it had the effect of producing in the unhappy inhaler an attack of vertigo. Watt had advocated the employment of lime in the case of the oxygen gas to purify it, but he cautions the user of the apparatus when making the hydro-carbonate to be careful not to let any lime come in contact with the gas, as, if so, it will not produce the desired giddiness. The pamphlet is one of extreme interest, and the writer is indebted to Mr. George Tangye for a copy.
Watt fitted up a garret in Heathfield Hall as a workshop, and late in life returned to the practice of that delicate manual work in which he had always been so great a proficient. He specially devoted himself to the invention and constructing of apparatus for the copying and reproduction of sculpture, and he produced some very admirable specimens of this work, of which he was not a little proud. In 1883 there remained in this workshop a most interesting collection of models of several of Watt's inventions, including models of his various modes of obtaining rotary motion. They are most clearly described in a paper by Mr. E. A. Cowper, read before the Institution of Mechanical Engineers in November of that year. Now, practically the whole of these models have been removed, leaving only the sculpture copying machines.
Among the very interesting letters in the possession of Mr. George Tangye are some from Argand, on behalf of himself and of Montgolfier, relating to that most ingenious water-raising implement, the hydraulic ram, and to the Argand lamps. There are also four original letters from Robert Fulton to Boulton and Watt, ranging from 1794 to 1805, in which orders are given for steam engines, to be used in the steamboats Fulton was building.
Watt's first and greatest invention—condensation in a vessel separate from the steam cylinder—was the very life of steam engines working at the low pressure prevailing in those days, as such engines owed their power