In Lavoisier we see a master mind, not only capable of devising and executing beautiful experiments, but of assimilating those of others, and deducing from them their true meaning. Although his additions to the known chemical compounds were few in number, and cannot be compared with those of Scheele or of Priestley, yet his reasoning in disproof of the phlogistic theory was so accurate and so exact that it rapidly secured conviction. With the exceptions already mentioned, almost all the eminent chemists of the day accepted his conclusions; and one, Kirwan, who had written a formal treatise in defence of the phlogistic theory, was so fair-minded, that after his work had been translated into French and published with comments, he acknowledged that the old theory was dead, and that truth had conquered. It will be interesting now to trace Cavendish’s part in developing the history of the discovery of the constituents of air, and to note his arguments in favour of the phlogistic theory. Although Cavendish never publicly acknowledged its insufficiency, yet he had ceased to occupy himself with chemical problems at the time when its adoption was universal, and his true opinions have never been recorded. [4] _Experiments and Observations on Different Kinds of Air_, vol. ii. By Joseph Priestley, LL.D., F.R.S. Second edition (1776), p. 29. [5] _Chemical Treatise on Air and Fire_ (1777), § 3. [6] _Loc. cit._ p. 46. [7] _Loc. cit._ p. 55. [8] _Loc. cit._ p. 94. [9] _Loc. cit._ p. 102. [10] The accurate translation of Scheele’s _Treatise_ published by the Alembic Club (William F. Clay, 1894) has been made use of here. [11] § 4. [12] § 5. [13] § 16. [14] § 16. [15] § 22. [16] § 23. [17] § 24. [18] § 29. [19] § 80. [20] § 87. [21] § 93. [22] This, as previously remarked, had already been noticed. In Maquer’s _Élémens de Chymie-pratique_, published in 1752, a work which ran through many editions, we read (p. 307): “There happens during all these calcinations, and especially in that of lead, a very strange phenomenon for which it is very difficult to assign a reason. It is that those bodies, which lose no small proportion of their substance, whether by the dissipation of phlogiston, or because part of the metal is exhaled as vapour, yield _calces_ increased in weight after calcination; and this increase is by no means inconsiderable.... Physicists and chemists have devised many ingenious systems to account for this phenomenon, but no one of them is absolutely satisfactory. As no well-established theory has been devised, we shall not undertake to attempt an explanation of this singular fact.” CHAPTER IV “PHLOGISTICATED AIR” INVESTIGATED BY CAVENDISH--HIS DISCOVERY OF THE COMPOSITION OF WATER