9 



all different forms of the same phlogiston, united with a minute portion 

 of different bases; we find it combining with oxygen, in one propor- 

 tion, to form carbonic acid, in another, nitrogen, in another, water. 

 Its affinities with these bases, and with all the metals, had been deter- 

 mined by Bergman, as well as the relative weights in which it entered 

 into composition : and to complete all, the year before the publication 

 of Cavendish's experiments, Kirwan had proceeded to give a table of 

 the absolute weights — had computed for instance that fourteen cubic 

 inches of nitrous air contain 0*938 of a grain of phlogiston, and had 

 actually deduced a law for these weights, corresponding with the spe- 

 cific gravities of the metals. 



You will easily conceive. Gentlemen, the effect on a purely experi- 

 mental science of such a hypothesis as this, and you must add the effect 

 of other hypotheses, equally prevalent, which bestowed similar che- 

 mical affinities on the principles of light and heat. Bergman calcu- 

 lated the weight of phlogiston " in pollice cuhico decimali " of hydrogen 

 to be y§YT of ^ pound, and the weight of specific heat in the same to 

 be yf Q of a pound. His method of arriving at results which have such 

 a face of precision furnishes a very curious specimen of analytical rea- 

 soning. He assumes — 1st, That charcoal consists of fixed air, alkaline 

 earth, and phlogiston : he ascertains as well as he can the weight of 

 the two former constituents, and calculates that of the latter from the 

 loss in his analysis. 2nd, He assumes that phlogiston exists in iron in 

 the ratio to that in charcoal of their respective effects in phlogisticaiing, 

 or alkalizing, an equal quantity of nitre ; he determines this proportion, 

 and from the 1st experiment deduces the absolute weight of phlogiston 

 in a given weight of iron. 3rd, He assumes hydrogen to consist of 

 phlogiston, and matter of heat ; he assumes further that the phlogiston 

 in a given volume of hydrogen is proportionate to the phlogiston in 

 the iron from which it is evolved by the action of acids ; he deter- 

 mines by experiment what the weight of iron is which produces a 

 given volume of hydrogen, and he concludes from the two data before 

 obtained the absolute weight of the phlogiston ; this he subtracts from 

 the total weight of the hydrogen, and thus determines the absolute 

 weight of the matter of heat*. In like manner you find the ideas of 

 Watt respecting the composition of water connected with, and spring- 

 ing out of the idea, that it was reconvertible, not simply into phlogiston 

 and dephlogisticated air, but, by an intimate union of the latter with the 

 principle of heat, into phlogiston and atmospheric air. By such loose 



* See Bergman ' de Attract, electivis', pp. 413, 440, ' de Analysi Ferri,' p. 

 24, Opuscula Phys. et C/tem. vol. iii. Upsal. 1783. 



