82 HISTORY OF CHEMISTRY. [LECTURE V. 



also, would then necessarily fall into two classes ; or in other 

 words, it would be necessary to assume differences in con- 

 stitution in a series of substances whose behaviour is similar in 

 ever-y respect. He thinks, further, that he is justified in con- 

 cluding from the laws of combination, that chlorine is not an 

 element. I do not enter more minutely into the matter since 

 his arguments had little effect. They came too late. Gay- 

 Lussac's investigation of hydrocyanic acid in the same year, 58 

 indisputably proves the acid nature of this compound, and the 

 fact that it does not contain oxygen ; and hence even Ber- 

 zelius cannot maintain Lavoisier's definition of the acids and 

 of the acidifying principle. 



Some other cause which might furnish the acid character 

 observed in certain substances was now sought for. The 

 conception of an acid seemed so definite at that time, and the 

 substances included in this class were so distinctly separated 

 from all other substances, that it was necessary to enquire into 

 the cause which occasioned this difference. Besides, it cannot 

 be denied that Lavoisier, and even the chemists of the beginning 

 of this century were still influenced, in a certain respect, by the 

 ideas of the Greek philosophers. Just as the latter ascribed 

 general properties to the" presence of a common constituent and 

 identified the particular property to a certain extent with a 

 particular constituent just as they explained combustibility, 

 for example, by the presence of a fire-material so Lavoisier 

 and his adherents believed that in oxygen they had discovered 

 the acidifying principle. 



In a similar manner we find Davy, after he was satisfied 

 that hydrochloric acid contains hydrogen and chlorine only, 

 stating the view that the chlorine is the acidifying principle in 

 it, and the hydrogen its basis or radical. 59 At a later date 

 Gay-Lussac 60 introduces the name " hydracids " for the acids 

 free from oxygen, and places hydrochloric acid, hydrocyanic 

 acid, sulphuretted hydrogen, and hydriodic acid in this class. 



53 Ann. Chim. 95, 136. 59 Phil. Trans. 1810, 231 ; A.C.R. 9, 21. 



* Ann. Chim. 91, 148 ; 95, 162. 



