

HISTORY OF PRUSSIATES. 101 



blue, and keep the mixture closely stopped : at the expira- 

 tion of a few days, the hidrosulphuret will be converted 

 into a triple sulphate, and the red oxide of the prussian 

 blue only changed into black hidrosulphuret. Whence it 

 appears, that, if the red oxide have followed the example of 

 all other oxides, when the hidrosulphuret finds them com. 

 bined with acids, it is not the same with the black oxide. 



Hidrosulphuretted water brings back prussian blue to Experiment 2 

 the state of white prussiate, as it does the red sulphate to 

 that of green sulphate. This is a fact which I made known 

 in my first memoir, and the power of this reagent never 

 goes farther; but the hidrosulphuret of potash completely 

 changes the red and green sulphates into black hidrosul- 

 phuretted oxide. Why then cannot this hidrosulphuret 

 extend its action to the black oxide in question ? Certainly 

 some singular affinity, of which I believe there are few in- 

 stances in chemistry, enables the prussic acid, the weakest 

 of all acids in so many respects, to protect this oxide 

 against all the power of the alkaline hidrosulphurets. 



All the metallic solutions, that afford prussiates with tile The same in 

 triple prussiate of potash, no doubt follow the example of _ tes '" ri,ru;> 

 those of iron. The prussiates resulting from it will re- 

 tain in- all its integrity the black oxide, which the prussic 

 acid carries with it ; but it is time to lay before the reader 

 the capital experiment, which demonstrates, that prussian 

 blu^ is a triple salt; and that the black oxide, which had 

 passed from the triple prussiaie of potash into the prussian 

 blue, is capable of passing back again from the prussian 

 blue to potash, without having for a moment quitted its 

 state of a minimum oxide. This experiment I have no 

 doubt is anticipated by every one, who has formed a clear 

 idea of the triple prussiate of potash. 



Let us take, for instance, a prussian blue, which bas Proof that 



experienced all the action that the atmosphere, or the most P russ,a » Wu , e 

 r \ l ■ ■ • A is a tnple sair. 



oxiding acids, can exert upon it. Let us apply to it pure 



potash, and we shall obtain a lixivium, which will yield 



only a triple prussiate, or that combination in which we 



jfind the prussic acid constantly united with the usual dose 



of black oxide. If this prussiate be really such as I have 



.announced; and the^eader will have no difficulty to believe, 



there 



