LECTURE V.] HISTORY OF CHEMISTRY. 83 



Even if the cause of the acid nature was to be found in the 

 chlorine, iodine, etc., rather than in the hydrogen, still the latter 

 was the common constituent of them all, and hence better 

 adapted to the formation of a name. Davy's investigations upon 

 chloric and iodic acids lead him to much more general views. 

 " Acidity does not depend upon any peculiar elementary sub- 

 stance, but upon peculiar combinations of various substances." 61 



At this time he seeks to prove that it is not oxygen which 

 determines the peculiar character of an acid. Thus, for 

 example, when oxygen is united to common salt, the neutrality 

 of the substance is not disturbed ; whereas, on the other hand, 

 the saturating capacity of chloric acid is not altered when all 

 the oxygen is removed from it. This obliges Davy no longer 

 to regard chloric acid (in accordance with Lavoisier's view) as 

 an oxide of the radical chlorine, which, combined with water, 

 forms the hydrated acid. He finds that, without water, chloric 

 acid cannot exist ; and for this reason he regards it as a ternary 

 compound of hydrogen, chlorine, and oxygen. Again, the 

 existence of euchlorine, which he obtains from chloric acid 

 and hydrochloric acid, 62 provides him with a reason against 

 Lavoisier's hypothesis regarding acids. 



The principles of a new theory of acids are included in 

 Davy's discussions ; but he did not follow them up sufficiently, 

 otherwise, they might have prevented the distinction which 

 now began to be drawn between acids which did and those 

 which did not contain oxygen. The same remark holds 

 likewise with respect to Dulong, who had read a paper before 

 the French Academy in 1815, in which he had stated his view 

 regarding acids. This paper, unfortunately, does not appear 

 to have been printed in extenso, and therefore I am able to 

 give but little account of it. 63 Dulong, on this occasion, 

 examined oxalic acid. The behaviour of some of its salts, 

 which give off water when heated, led him to the opinion that 

 the acid might be regarded as a hydrogen compound of 



61 Phil. Trans. 1815, 219. 62 Ibid. 1811, 155 ; A.C.R. 9, 63. 63 Mem. 

 de 1'Acad. 1813-1815, Histoire, p. cxcviii. ; see also Schweigger's Journal. 

 17, 229; Ann. Phil. 7, 231. 



