CORRECTION OF THE OXYGEN THEORY. 159 



at Edinburgh in 1812, this experiment was made in 

 the presence of several eminent philosophers ; 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 chemists, 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 chemists 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 

 not peculiarly engaged in chemical research, but 

 who was often distinguished by his rapid and happy 

 generalizations, M. Ampere. He supported this 

 analogy by many ingenious and original arguments, 

 in letters written to Davy, while that chemist was 

 engaged in his researches on fluor spar, as Davy 

 himself declares 2 . 



Still further changes have been proposed, in that 

 classification of elementary substances to which the 

 oxygen theory led. It has been held by Berzelius 

 and others, that other elements, as, for example, 



1 Paris, Life of Davy, i. 337- 2 Ib. i. 370. 



