370 



Article XL 



On the Theory of the Formation of Mther. By Heinrich 

 Rose, Professor of Chemistry in the University of Berlin.* 



[From Poggendovff's ^««a/er«, vol. xlviii., part 11, November 1839.] 



It is well known that many salts of the oxide of bismuth, of 

 the oxide of mercury, of antimony, and several other metallic 

 oxides are decomposed by water. They are generally convert- 

 ed by it into basic salts ; but sometimes, by employing a suffi- 

 cient quantity of water, the decomposition even goes to the 

 separation of the pure oxide, as in the case of the nitrate of the 

 oxide of mercury. 



The explanation usually given of these decompositions is, 

 that the water resolves the neutral salt of a metallic oxide 

 into an acid and a basic salt, in a similar manner as nitric 

 acid converts the red superoxide of lead into protoxide of 

 lead and the brown superoxide. But the existence of acid salts, 

 which are said to be formed by the action of water on several 

 neutral salts of metallic oxides, is far from being proved ; in 

 most cases the water only deprives the salt of a part of the acid, 

 and this dissolves a portion of the neutral salt, which, after the 

 acid solution has been concentrated by evaporation, most fre- 

 quently crystaUizes as a neutral salt, and rarely as a double 

 combination of neutral salt and acid hydrate. In many cases 

 the quantity of the salt which dissolves in the liberated acid is 

 exceedingly small, frequently none at all, and the entire quan- 

 tity of the oxide forms an insoluble basic salt. 



The simplest explanation that can be given of such de- 

 compositions produced by water, appears to me to be this, 

 that water, acting the part of a base, separates the metallic 

 oxide as a basic salt, or at times even in the pure state, and 

 combines with the acid to form a hydrate. This explanation 

 is the more admissible, as we have been long accustomed to 

 regard the hydrates of acids as saline combinations in which 

 water replaces a fixed base. It is well known what happy 

 conclusions tor the whole theory of chemistry, more espe- 



* Translated and communicated by Mr. William Francis. 



