3 55 Materials Jbr a History of the Prussiates. 



INFERENCES. 



All these results certainly bear us out in the conclusion, 

 that the simple prussiate of potash is, as Schtele has already 

 discovered, a fragile combination, the elements of which 

 are as easily separated as those of complex combinations. We 

 find, in short, that a part of the acid is removed from the 

 potash by the sole force of dilatation ; while the other part, 

 which is longer subjected to the action of caloric, is de- 

 stroyed in order to be changed into ammonia and carbonic 

 acid. Let us now make the application of this conclusion. 



The triple prussiate of potash undergoes no derangement 

 by repeated ebullitions. The lixiviums employed in the 

 manufacture of Prussian blue contain, as we shall presently 

 see, triple prussiate and simple prussiate. Besides, there is 

 no ammoniacal salt in them. We are of opinion, that the 

 great excess of carbonate of potash which they contain 

 would not admit of their presence ; but they exhale am- 

 monia while in a state of ebullition. From whence could, 

 this ammonia proceed, if it was not from the decomposition 

 of the simple prussiate ? We may therefore conclude, that 

 the boiling or concentration of "the lixiviums exposes them 

 to be deteriorated by the destruction of this same prussiate, 

 which we cannot too much preserve : and as the carbonate 

 of potash is also one of the principal .results of this destruc- 

 tion, it does not cease to add to what is already there. 



Curadeau was well aware of the deterioration which the 

 boiling of the lixiviums produces, and he very happily pre- 

 vented the bad effects by adding a little sulphate of iron to 

 them. This is conformable to Scheele's principle, who has 

 *hown that the simple prussiate changes into triple prussiate 

 a» soon as it can be associated with a portion of black oxide, 

 and thereby be guarded against decomposition. As to the 

 products from the destruction of the prussiate by fusion or 

 by ebullition, there is certainly nothing extraordinary in 

 them, since it is sufficient to know the nature of the prusr 

 sic acid in order to prevent them ; but it is not so with re- 

 spect to the carbonic acid which is presented during one of 

 these destructions. Whence comes the oxygen, for example, 

 - which; during the ebullition of the aqueous prussiate, suc- 

 ceed^ 



