Agency of Carbonic Acid, 267 



The galvanic agency has been supposed by M. Thenard to 

 be evolved by the contact of the metal and its oxide, in those 

 cases in which the latter was present. But, in this case, the gal- 

 vanic circle would not be interrupted by the addition of sub- 

 stances which merely abstract the carbonic acid. The oxide is, in 

 fact, a carbonate, and the acid still exerts its agency in deter- 

 mining the decomposition of the water. But when this pro- 

 cess is thus rapidly proceeding, it is at once arrested by the 

 addition of a small portion of lime water, by means of which 

 the carbonic acid is withdrawn, although the metal still remain 

 in contact with its oxide. 



In M. Guibourt*s experiments, it is quite obvious that the 

 agency of carbonic acid was not excluded ; he speaks of re- 

 moving the rust from the iron filings which he used, by merely 

 washing them with water*. It is evident that the oxide, 

 or rather carbonate, could be removed in this manner but very 

 imperfectly. 



It is quite plain to me that in all M. Guibourt's experiments 

 there would have been a decomposition of the water, had suf- 

 ficient time been given to allow this effect to take place. In 

 some of my experiments, especially in those in which I had 

 taken the greatest pains to expel the air from the water by long 

 boiling, and to exclude it afterwards, I waited several months 

 before I observed the slightest evolution of hydrogen gas, which, 

 however, eventually took place in all in which the agency of 

 the carbonic acid was not entirely excluded. The last expe- 

 riments detailed by M. Guibourt led to a more prompt decom- 

 position of the water, because the quantity of carbonic acid 

 was obviously greater in them. 



I propose, now, to conclude this short Memoir by a few re- 

 marks, rather of a desultory kind, which, however, naturally 

 flow from the facts which have been stated. 



M. Guibourt was led, by his experiments, to doubt the cor- 

 rectness of M. Thenard's definition of the third section of his 

 classification of the metals, one part of which was, that they 

 did not induce any decomposition of water at ordinary tempe- 

 ratures. It is plain, however, from the facts which have been 



♦ Page 248. 



