Materials fur a History of the Prussiates, 34 f) 



state of white prussiate, as it does the red sulphate. This 

 fact I have published in my first memoir, and the power of 

 this reagent never passes beyond j but the hydro-sulphuret 

 of potash totally changes the red and green sulphates into 

 black hydro-sulphureted oxide. Why cannot, the' hydro-- 

 sulphuret extend its action to the black- oxide in question ? 

 There must be ^singular affinity, and of which there are 

 few examples in chemistry, which enables the prussic acid, 

 the weakest of the acids in so many respects, to protect 

 this oxide against the whole power of the alkaline hydro- 

 sulphurets. 



All the metallic solutions which give prussiates with the 

 triple prussiate of potash, certainly follow the example of 

 those of iron. The prussiates resulting from it will preserve 

 in all its purity the black oxide which the prussic acid car- 

 ries with it. But it is now time to lay before my readers 

 the grand experiment which demonstrates that Prussian 

 blue is a triple salt, and that the black oxide, which had 

 passed from the triple prussiate of potash into the Prussian 

 blue, may still repass from the Prussian blue into the potash, 

 without having at any moment abandoned its quality of 

 oxide at the minimum. 



I presume that this experiment is already anticipated by 

 those who have conceived a clear idea of the nature of the 

 triple prussiate of potash. 



Take a Prussian blue, for instance, which has undergone 

 all the reactions which the atmosphere or the most highly 

 oxidating acids may have produced upon it. Apply pure 

 potash to it, and we shall procure a lixivium which will only 

 give triple prussiate, i. e. a combination in which we shall 

 find the prussic acid constantly associated with the common 

 dose of black oxide. If this prussiate is really what I have 

 described it to be, which the reader can scarcely doubt, there 

 will be no objection, I think, against the new point of the- 

 ory which establishes " that the white or blue prussiates are 

 triple combinations, as well as the prussiate of potash which 

 has concurred to their formation." 



From the potash of prussiate of manganese there results 

 crystallizable triple prussiate of potash, yellow, and provided 



with 



