Materials for a History of the Prussiates, "55 



Jizable salt, which has always a constant proportion of black 

 oxide. 



If we employ the yellow prussiate in reproducing Prussian 

 blue, this oxide re-enters with the prussic acid into the new 

 combination. The black oxide is therefore an element ne- 

 cessary to the formation both of the crystallizable prussiate 

 and of the Prussian blue, and likewise of all the metallic 

 prussiates prepared with the triple prussiate of potash. 



There are metals which are susceptible of forming simple 

 and triple prussiates, such as copper, silver, manganese, cobalt, 

 nickel, uranium, &c. There are some which give simple 

 prussiate, such as gold, mercury, &c. There are some also 

 which give triple prussiate only, such as iron, &c. Lastly, 

 some of them do not appear susceptible either of the one or 

 the other. But, with the exception of Prussian blue and 

 prussiate of mercury, all the rest arc little known, and merit 

 examination. The black oxide united to the prussic acid 

 may pass from the one combination to the other without- 

 changing its state : the base of this combination may even 

 be raised from the minimum to the maximum, without the 

 black oxide on that account taking any part in this change. 

 The combination of the acid with this oxide is maintained 

 by so powerful an affinity that the aikalinehydro-sulphurets 

 cannot separate them, or rather they cannot touch the oxide 

 in the triple prussiate of potash, or in Prussian blue. 



The prussic acid united to this portion of black oxide, 

 which enables it to form triple, alkaline, or metallic prus- 

 siates, is a peculiar combination, the existence of which is 

 not doubtful ; but with which we are not as yet acquainted, 

 except in these prussiates alone. 



The triple prussiate of potash cannot undergo a red heat 

 without losing the black oxide, and consequently without 

 being reduced to the state of simple prussiate. 



The simple prussiate is also decomposed, but by a far 

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

 monia and carbonic acid : it is the destruction of this salt 

 by the heat of ebullition, which degrades the lixiviums for 

 preparing Prussian blue. > 



The simple prussiate assumes the character of triple prus- 



D 4 siate, 



