Materials for a History of the Prusskdes. 345 



the inquiries of Scheele and Berthollet, we have ascertained 

 that these recipes but imperfectly fulfilled the object in 

 view : for it is easy to see that it was not enough to strip a 

 lixivium of the oxide which the carbonate introduced into it: 

 it still remained to provide against the black oxide which 

 belongs to the triple prussiate, and which we might so much 

 the less suppose to exist, since the addition of the acids, with- 

 out the intervention of light or of heat could not render sen- 

 sible the products of its decomposition. 



I shall not stop to analyse the phaenomena presented du- 

 ring the preparation of the hot or cold lixiviums ; because, now 

 that we are well convinced of the inutility of the prussiates 

 with respect to the evaluation of the quantity of iron in ana- 

 lyses, the details are of little interest : for the same reason I 

 pass over the liquid tests proposed with ammonia, chalk, mag- 

 nesia, &c, because they are themselves triple prussiates, in 

 which we cannot place confidence, unless we employ t hern- 

 ia the same way as the counter-proof proposed by Berthollet. 

 I shall add, only because it is a fact worthy of beincr re- 

 corded in the history of science, that, when the chemist 

 would still take advantage of a lixivium or liquid test, which 

 he had purified by means of an acid, we may be assured he 

 has not attained (as he perhaps nattered himself,) the com- 

 plete separation of the iron ; for it is certain that every lixi- 

 vium which gives a blue colour with a solution of red oxide, 

 contains also black oxide, since without the assistance of 

 the same oxide it could not be dyeing prussiate : or, in other 

 words, every prussiate of potash, which has not been tripled 

 (trisule) by the black oxide ; consequently prussiate of 

 potass, when pure and simple, is not capable of form i no- 

 blue with a solution where the oxide is at the maximum i — 

 this has occurred to those most experienced in analytical pro- 

 cesses. It is a truth which Scheele has perfectly established. 

 1 repeat, therefore, that the saturated lixiviums or the al- 

 kaline prussiates cannot really serve as a dyeing {teignant) re- 

 asrent unless a portion of black oxide has rendered them triple 

 salts, the red oxide being by no means capable of supply- 

 ing the place of the black oxide for this purpose. Finally, 

 v»e may conclude from all these circumstances that the al- 

 kaline 



