HISTORY OF PRtfSSJATES. {(ft 



potash, their affinity being so weak-. When it-is not corn- 

 it will not crystallize by concen- 

 in which'- however some saline 

 laminae are distinguishable. 



This prussiate is the test liquor proposed by Scheele. Its Of little use as 

 utility in analysis is very confined; since all solutions, in * te<t - 

 which the iron is at a maximum of oxidation, and this is the ^ 

 most common case, are not in the least affected by this re- 

 agent, as he himself observed. To employ it with utility, 

 part of the oxide of the solution must be brought back to 

 a minimum, which is not easy, or to be done without 

 risk of increasing the difficulties of the process. 



Its Decomposition, o 



The aqueous solution of this prussiate gives out part of Decomposed 

 its acid at a boiling heat, which sufficiently demonstrates, eaSi ' r ' 

 that this combination is neither solid, nor comparable to 

 any of those formed by oxigenized acids. It froths con- 

 tinually, and has something saponaceous. A lighted 

 candle, applied to the orifice of the retort, sets that por- 

 tion of acid on fire : but its loss is not confined to this, for 

 that portion, which the salt retains more strongly by means 

 of the potash that begins to predominate, likewise expe- 

 riences a slow but regular destruction from the effect of the 

 heat, which converts it into ammonia and carbonic acid. 

 Examine the product at whatever period of the boiling you 

 please, there will always be found in it carbonate of am- 

 monia mixed with a little prussic acid; and at length, when 

 the water begins to fail, this carbonate condenses in needles 

 in the neck of the retort. 



If water be supplied, that the boiling may continue, the 

 *ame products will be found in the water of the receiver; 

 but after four or five successive distillations in the same , 

 manner, they cease to be perceptible, though the saline 



residuum still evidently contains prussic acid. >■ 



On treating this residuum with alcohol, part is dissolved, The residuum, 

 which is found to be prussiate of potash ; but the saline 

 matter left undissolved is carbonate of potash. The two 

 following experiments leave no doubt of the destruction of 

 the simple prussiate by a boiling heat. 



I 2 Prussiate 



