108 



Boiling con- 

 verts the prus- 

 siate into a car- 

 bonate. 



Exp«rim«nt. 



Decomposed 

 by heat. 



The simple 

 prvHsiate a 

 ■weak combina- 

 tion. 



But not the 

 triple prussiate 



Boiling the 

 lixivia in ma- 

 nufactories of 

 Prussian blue 

 injurious, 



HISTORY OF PRUSSIATES. 



Prussiate of potash does not render turbid a solution of 

 muriate of lime; but after it has undergone ebullition for 

 some time, it precipitates it copiously in the state of car- 

 bonate. The prussiate of potash therefore must have been 

 converted into carbonate of potash. 



Two measures of solution of prussiate, one in its na- 

 tural state, the other altered by long boiling, were employ- 

 ed to precipitate common sulphate of iron. Each afforded 

 blue; but after the brightening, that produced by the 

 former was three times as much as the other. 



If dry simple prussiate be heated to redness, carbonate 

 of ammonia will pass over, contaminated by an oily vapour 

 similar to that of hartshorn. The saline mass being dis- 

 solved leaves behind charcoal, and is carbonate of potash 

 mixed with a portion of prussiate not decomposed. 



Consequences. 



All these results unquestionably authorise us to conclude, 

 that the simple prussiate of potash is a feeble combination, 

 as Scheele had already found, the principles of which are 

 easily dislodged, like all that are complex. We see in fact, 

 that part of the acid separates from the potash by the 

 effect of dilatation simply ; while another part, subjected 

 longer to the agency of caloric, is destroyed by being 

 changed into ammonia and carbonic acid. Let us proceed 

 to the application. 



That the triple prussiate of potash is not deranged by 

 repeated ebullition is a fact. The lixiviums employed in 

 manufacturing prussian blue contain, as we shall see below, 

 both the triple prussiate and the simple prussiate. There 

 js not found in them, however, any ammoniacal salt. It 

 might be presumed, indeed, that the great excess of car- 

 bonate of potash they contain would be incompatible with 

 such a salt ; yet they evolve ammonia, as long as they con- 

 tinue in ebullition. Whence then can this ammonia pro- 

 ceed, if not from the decomposition of the simple prus- 

 siate? We may infer, therefore, that boiling the lixivia, 

 or concentrating them by evaporation, is liable to injure 

 them by the destruction of that very prussiate, which can- 

 . not be too sedulously preserved; and as the carbonate of 



potash 



