92 itlSTORY OF PlttSSlATES'. 



potash, is as constant in its qualities as the most perfect 

 neutral salts. It is of a fine lemon colour, which it never 

 Containing loses without changing its state. For this, as well as for 

 black oxide of j| S fher two characteristic properties, that of crystallizing, 

 and of changing the red oxide of iron blue, it is indebted 

 to a portion of black oxide, which is essential to its consti- 

 tution. Without this oxide, confined like the other two 

 elements of the triple prussiate to an invariable proportion, 

 this prussiate in fact could neither crystallize, nor form blue 

 with solutions of iron, the base of which is at a maximum 

 This gives ttie of oxidation. In short, it is from this very union, that the 

 prussic arid principle which saturates the potash of the triple salt de- 



more decidedly \ . 



acid properties, fives those properties, as Berthollet remarks, that singularly 

 increase the analogies it bears to acids. 



In this point of view we may add, that the triple prussi- 

 ate occupies a mean betwixt alkaline and metallic salts. — 

 However, when we reflect on one property of this salt, 

 "Which will be mentioned below, it is difficult to say, whe- 

 ther it be to the prussic acid simply, or to the combination 

 of this acid and potasli, that the oxide of iron attaches it- 



This combina- self, when it converts the prussiate into a triple salt. Thus 



tion of black mucn } s CC rtain, that we do not yet by any means know 

 oxide and prus- , .... 



sic acid not ob- what appearance or properties a prussic acid might have, 

 tamable by that'should be combined with the precise dose of black ox- 

 ide, by means of which it can furnish a triple prussiate. 

 By treating this oxide with prussic acid we can form Prus- 

 sian blue, but not that kind of ferruginous acid, which is 

 capable of converting potash into a triple salt. Of this we 

 must not lose sight; for it is well known, that Prussian blue 

 is not of a nature to combine with potash without leaving a 

 residuum. In short, the triple prussiate divestsd of its al- 

 kaline base, if I may so say, is a compound, Avhich no fact, 

 no appearance authorizes us to consider rather as a salt, the 

 acid of which has been particularly exalted by its union with 

 Ihe oxide, than as a combination perfected altogether by this 

 •oxide. 

 Apparently a One property, which appears in fact to militate against 



joint affinity our admitting the prussiate as a salt, the acid of which is 

 between the ° ' 7 



acid, oxide, exclusively united to the black oxide, is that c; its resisting 

 andalkuii. ^e action of alkaline hidrosulphurets. If these reagents, 



which 



