CORRECTION OF THE OXYGEN THEORY. 283 



peak of sonic erroneous opinions entertained by the author of the 

 theory ; as, for instance, that the heat produced in combustion, and 

 even in respiration, arose from the conversion of oxygen gas to a solid 

 consistence, according to the doctrine of latent heat. Such opinions 

 not being necessarily connected with the general idea of the theory, 

 need not here be considered. But the leading generalization of La- 

 voisier, that acidification was always combination with oxygen, was 

 found untenable. The point on which the contest on this subject 

 took place was the constitution of the oxymuriatic and muriatic, 

 acids ; as they had been termed by Berthollet, from the belief that 

 muriatic acid contained oxygen, and oxymuriatic a still larger dose of 

 oxygen. In opposition to this, a new doctrine was put forward in 

 1809 by Gay-Lussac and Thenard in France, and by Davy in Eng- 

 land ; namely, that oxymuriatic acid was a simple substance, which 

 they termed chlorine, and that muriatic acid was a combination of 

 chlorine with hydrogen, which therefore was called hydrochloric acid. 

 It may be observed, that the point in dispute in the controversy on 

 this subject was nearly the same which had been debated in the 

 course of the establishment of the oxygen theory ; namely, whether 

 in the formation of muriatic acid from chlorine, oxygen is subtracted, 

 or hydrogen added, and the water concealed. 



In the course of this dispute, it was allowed on both sides, that the 

 combination of dry muriatic acid and ammonia afforded an experimen- 

 tum crucis ; since, if water was produced from these elements, oxygen 

 must have existed in the acid. Davy being at Edinburgh in 1812, 

 this experiment was made in the presence of several eminent philoso- 

 phers ; and the result was found to be, that though a slight dew 

 appeared in the vessel, there was not more than might be ascribed to 

 unavoidable imperfection in the process, and certainly not so much as 

 the old theory of muriatic acid required. The new theory, after this 

 period, obtained a clear superiority in the minds of philosophical che- 

 mists, and was further supported by new analogies. 1 



For, the existence of one hydracid being thus established, it was 

 found that other substances gave similar combinations ; and thus che- 

 mists obtained the hydriodic, hydrofluoric, and hydrobromic acids. 

 These acids, it is to be observed, form salts with bases, in the same 

 manner as the oxygen acids do. The analogy of the muriatic and 

 fluoric compounds was first clearly urged by a philosopher who was 



1 Paris, Life of Davy, i. 837. 



