HISTORY OF P.RUSSIATES. 93 



which spare no other known metallic salt, have no action 

 on the triple prussiate, we are to a certain degree justified 

 in presuming, that the oxide of iron is not exclusively at- 

 tached to the acid of the triple prussiate ; unless indeed we 

 suppose, that the affinity of this acid for the oxide be so 

 great, as to defend it from the common fate of all other ox- 

 ides. We shall see however farther on, that an affinity so 

 extraordinary, unexampled as it has hitherto been in che- 

 mistry, is not impossible. I proceed to the trial of the hi.. 

 drosulphurct of potash on the triple prussiate. 



Ilidro sulphur et and Triple Prussiate. 

 The hidrosulphuret of potash or of ammonia, even as- The triple 



sisted by heat, has no action on this salt. If it contained prussiate not 



. , ' . • '■■ r ' " J decomposed by 



any remains of ferruginous carbonate, it would be freed hidrcsulphu- 



from them, for the hidrosulphuret decomposes this carbon- rets - 

 ate. It may be filtered, if necessary, and the prussiate 

 will nevertheless crystallize in its usual form. Such a result 

 leads us to acknowledge, as has been hinted above, a very 

 peculiar intimate combination between the three elements of 

 the triple prussiate. But we shall presently see these very 

 hidrosulphurets contribute to our obtaining the white prus- 

 siate in all its purity, or that combination in which the iron 

 is at a minimum state of oxidation, which I made known in 

 my former memoir on Prussian blue. 



White Prussiate, 

 Over a lamp place a matrass containing fifteen or eighteen White prussl- 

 grains of prussiate of potash, and two or three ounces of ateof iron - 

 hidrosulphuretted water. A few seconds after the ebulli- 

 tion and vapour have expelled the air, that occupied the up- 

 per part of the matrass, drop in slowly a very dilute solu- 

 tion of green sulphate of iron from a phial, into which a 

 few grains of sulphuret of the same metal have previously 

 been put, in order to keep its base at a minimum of oxida- 

 tion. Immediately a precipitate will be formed, rendering 

 the liquor as white as milk, and so it will remain as long as 

 the heat is kept up. This is the precipitate which I call 

 white prussiate, and is the same as has been obtained by 

 fourcroy, Vauquelin, Davy, an4 no doubt all, who, pay- 

 ing; 



