Sir Humphry Davy. 231 



the philosophy of chemistry to be remodelled, and its nomenclature 

 to be changed. Lavoisier's definition of combustion, "the combin- 

 ation of oxygen with a combustible base," could no longer be admit- 

 ted, but a new classification was to be instituted, comprehending not 

 only those cases of combustion which depend on the agency of oxy- 

 gen, but those also which depend on the agency of chlorine, and 

 other analogous bodies which might afterwards be discovered.* 



Now combustion and acidification are processes of such extent^ 

 aiid are concerned in so many of the chemical changes which bodies 

 undergo, that any new theory which alters the explanation of these 

 phenomena, affects in a great degree the whole philosophy of chem- 

 istry. It is by the relations which a body sustains to chemical agents, 

 and especially to caloric and oxygen, that its chemical nature is de- 

 termined. Hence, a complete history of the properties of almost 

 any substance, in all its relations, involves an application of nearly all 

 the leading principles of the science. Scheele wrote an essay on 

 manganese, in which, after the labor of three years, he unfolded 

 most of the properties of that substance, many of which had been 

 before unknown. During his experiments on manganese, he discov- 

 ered both oxygen and chlorine, and learned the most important prop- 

 erties of these extensive agents. The selection of manganese, as a 

 subject for experimental research, was in some respects fortunate ; 

 but had Scheele investigated the properties of several other substan- 

 ces, with the same persevering attention and singular acuteness, he 

 would have made the same discoveries. In like manner, to settle all 

 the relations of chlorine to various chemical agents, must involve an 

 application of nearly all the leading principles of chemical science ; 



* Although it be admitted that the views of Sir Humphry Davy respecting chlo- 

 rine, required a new classification of the phenomena of combustion and acidifica- 

 tion, yet it must be admitted also that Lavoisier reasoned logically from his premises. 

 In a great multitude of cases of combustion and acidification which fell under the 

 examination of Lavoisier, oxygen was proved to be present, nor was any case of ei- 

 ther of those processes found where oxygen was not present; hence, upon the true 

 principles of induction, Lavoisier was entitled to lay it down as a general law* — " la 

 every case of combustion, oxygen combines with the burning body." But subse- 

 quent discoveries have shewn, that several other agents as well as oxygen act in pro- 

 ducing combustion, and in forming acids. Hence oxygen, which before stood at the 

 head of a genus, now takes its place at the head of a species only, comprehending a 

 a certain number of cases of combustion, while chlorine stands at the head of another 

 species, and iodine at the head of another, and all of tliem are to be classed under 

 some more general agent which is a still remoter cause of combustion. 

 * See Newton's Rules of philosophizing. 



