2^ 



HISTORY OF PRUSSIATES. 



with solutions of this oxide? Something else therefore is 

 wanting to the prussian bine, and the following facts will 

 complete the proof. 

 Proofs of this. On applying potash to prussian blue we obtain a yellow 

 chrystallizable salt, which has always a constant proportion 

 of black oxide of iron. If we employ this yellow prussiate 

 to reproduce prussian blue, the oxide repasses into the 

 new combination with the prussic acid. The black oxide 

 then is a necessary element in the formation both of the 

 crystallizable prussiate and of prussian blue ; as well as of 

 all the metallic prussiates, that are prepared with the triple 

 prussiate of potash. 

 Prussiates form There are some metals, that are capable of forming both 

 ed by different simple and triple prussiates, as copper, silver, manganese, 

 cobalt, nickel, uranium, &c. There are others, that form 

 only a simple prussiate, as gold, mercury, &c. There are some, 

 that admit only of a triple prussiate, as iron, &c. And lastly 

 others appear to be incapable of combining with the prussic 

 acid. Except prussian blue, however, and the prussiate of 

 mercury, we know but little of them, and they deserve far- 

 Union of black ther examination. The black oxide of iron combined with 

 ox »de of iron pv USS ic acid can pass from one combination to another with- 

 sic acid. ou t changing its state. The base of this combination may 



even be raised from a minimum to a maximum, without the 

 black oxide participating in the change. The combination 

 of the acid with this oxide is bound by an affinity so power* 

 ful, that the alkaline hidrosulphurets cannot separate them ; 

 or attack the oxide, if you please, either in the triple prus-* 

 siate, or in the prussian blue. 



. The prussic acid, combined with that portion of black 

 oxide which enables it to form triple prussiates, either alka- 

 line or metallic, is a peculiar combination, the existence of 

 which is not doubtful, but of which we know nothing sepa- 

 rately from these prussiates. 

 Heat reduces The triple prussiate of potash cannot support a red heat, 



the triple pms without losing the black oxide, and consequently being re- 



siate of potash ■. ' . - . , 



to simple, duced to a simple prussiate. 



and decompo- Tne sim P le prussiate is decomposed likewise, but by a far 



ses the simple lower temperature: its acid is destroyed, and reduced to am- 



prussiate. TOOma an d carbonic acid : and it is the destruction of this 



salt 



