344 Materials for a History of the Prussiates. 



to the product the 0*19 of red oxide, which resulted from 

 its own decomposition : but the surplus was still ereater 

 when, instead of .crystallized prussiate, we used a simple al- 

 kaline lixivium of Prussian blue. We shall see the reason of 

 this presently. 



When we pass a ley of common potash over Prussian 

 blue, a part of the alkaline carbonate is charged with red oxide; 

 there results a solution which answers to Stahl's martial 

 tincture, and of which pure potash is not susceptible. This 

 solution, which may be also prepared by throwing some 

 drops of nitrate into liquid carbonate, may be mixed with 

 the prussiate of potash without occasioning the least change 

 even by remaining in it. It is this same ferruginous car- 

 bonate which, as I have said, is recovered in its mother 

 waters. Now if we add an acid to the mixture of these salts, 

 we precipitate perfect blue from it, because the new solution 

 of oxide which replaces the ferruginous carbonate decom- 

 poses in its turn the prussiate of potash, as any solution of 

 iron would do*. 



The instant, therefore, that we employ in anv analysis a 

 prussic lixivium in place of a crystallized prussiate, we do 

 nothing else than add to the product; in the first place, the 

 red oxide, which formed part of the ferruginous carbonate, 

 then the black oxide which is a constant element of the 

 triple prussiate contained in this lixivium. 



Chemists very soon discovered the vicious effects of 

 these lixiviums, although they did not at first perceive 

 that they contained two very different ferruginous com- 

 binations : the carbonate already mentioned, and the 

 triple prussiate. Several experimenters, even when they 

 jgaw the blue they furnished with the acids, thought this blue 

 was natural, or, in other words, oxide or blue of Prussia ; 

 they endeavoured lo precipitate it, however, without touch- 

 ing the alkaline prussiate, which they thought to be endow- 

 ed with the property of dyeing without owing it to the iron. 

 From their efforts arose the recipes for precipitated lixiviums 

 which we find in every book upon chemistry. But since 



* It is the mixture of these same salts which prepares the mother waters of 

 soda, for giving Prussian blue when we add an acid to them. 



the 



