the oxigen of the oxide combining with bidrogen from the 



acid, while the oxiouriatic acid rombiues with the metallic 



mercury to form the i'aioip.elr Mr* jDuvy seems to dpu^t 



indeed if calomel can be formed by presenting mviriatic 



acid to oxide of mercury. If the metal is highly oxidated, 



corrosive sublimate, it has long been known, is fo^med; but 



it is equally true, that cuiomel is the product of the mutual » 



action of muriatic acid and mercury in a low state of oxi« * A, 



dation. 



I bad given as an example of hypothetical assumption in Production of 

 Mr. Davy's system, the explanation of the production of <*^.'"'wiatic 

 oxiniuriatic acid by distilling muriatic acid from oxide ^^ tliiUc dc'id ^nk 

 manganese; the explanation £Mppo«i»g-, that the oxigen of "X'^^e ©f man- 

 the oxide combines with the hydrogen of the acid and/orw* ^*"*'*®' 

 water, while the oxi muriatic acid is set free. To this Mr. / 

 J. Davy replies : ** Mr. M. asserts, that Mr. Davy is ob^ 

 liged to suppose, that water is produced in the common 

 mode of making oximuriatic gas from muriatic acid by 

 means of the black oxide of manganese. Mr. Davy has as- 

 certained the/ac^ that oximuriatic gas and water are pro* 

 duced, when black oxide of manganese is heated in muriatic 

 acid gas." It is almost superfluous to remark, that here the 



i leading term in the proposition, and on which the whole dis- 

 cussion rests, is changed. 1 had asserted, that Mr. Davy 



'is obliged tosuppose, thatin this experiment \s2Xer\s formed'. 



.and the assertion is strictly correct. To say, that Mr. 



' Davy has ascertained the fact, that water is produced, is 

 saying nothing to the point. TheprorfMc^ioji of water in an 

 experiment is not its ybr/no/ion, nor is it a proof of it ; it is 

 as probable a priori, that it is deposited, as that it is 

 formed : unless there be particular evidence indeed for the 

 latter conclusion, the former is to be preferred as more sim- 

 ple and direct; and though water is produced, in other 

 words becomes sensible, when muriatic acid gas acts on 

 black oxide of manganese, I repeat, that Mr. Davy 

 is obliged to suppose it is formed ; and that he has no other 

 proof of its formation than the supposed truth of his hypo- 

 thesis, which is of course assuming the point in dispute. 



In a different part of his reply Mr. J. Davy, from not at- t^- .• .• 

 tendmg to this dwtmction between the production of water beiwe«o pro* 



and 



