106 



Animal char- 

 coal affords 

 sulphur. 



Characters of 

 the si nple 

 prusMate. 



Blackness from 

 hidrosulphuret 

 removed by an 

 acid. 



Must be closely 

 itoppod. 



HISTORY OF PRUSSIATES. 



it from time to time; and the progress of the solution will 

 be discovered by the alkaline and bitter taste of the alcohol. 

 The lixiviums of charcoal of blood or of leather are 

 seldom exempt from a little hidrosulphuret, because the 

 sulphate that contaminates potash introduces sulphur into 

 them. In this case it enters into the alcoholic solution ; 

 but the charcoal contributes to it likewise, for I have pre- 

 pared lixivia with charcoal of blood and very pure carbonate 

 of potash, and yet found hidrosulphuret in them, though 

 in smaller quantity. It must not be forgotten indeed, 

 that sulphur is found among the products of blood. It 

 even appears, that, like phosphorus, it is capable of 

 fixing in the charcoal, but not combined with the iron it 

 contains ; for the aromatic hidrogen, mentioned above, 

 does not afford the least indication of sulphur by its 

 smell. 



The simple prussiate is easily recognized by its bitter 

 alkaline taste, and the aromatic flavour with which it 

 strongly perfumes the mouth. It precipitates solution of 

 copper yellow, and does not afford blue M'ith a solution of 

 the red oxide of iron, but precipitates it of an ochry 

 yellow, as a pure alkaji would*. Finally, it affords blue 

 with a solution of common sulphate of iron, because it 

 first constitutes itself a triple prussiate, and afterward pro- 

 duces white or blue prussiate of iron. If the prussiate be 

 black, it is because the alkaline hidrosulphuret introduces 

 into it hidrosulphuretted oxide ; but it may be freed from 

 this by a few drops of acid, and the prussiate of iron wirt 

 appear alone. The simple prussiate does not keep well 

 unless closely stopped. Scheele has shown, that the car- 

 bonic acid is sufficient to separate the prussic from the 



* In a memoir on the stone of Sigena, I had mentioned this 

 combination as possible, but it was from mistake. A sulphate of 

 iron, which 1 had superoxided by nitric acid, retained notwith- 

 standing a portion of black oxide, and this deceived me; and 

 Scheele, whom I contradicted on this point, saw more clearly 

 than I. 



In our abridgment of this memoir, Journ. Vol. XII. p. 2. we 

 did" not insert the remark here alluded to, as we were persuaded 

 that Scheele was right, and that our author must have been de~ 

 ceived by some circumstance or other. T. 



* potash, 



