Materials for a History of the Prussiates. 339 



unalterable iu dry op humid air : the longest continued ebul- 

 lition does not alter its nature in the least : the taste is 

 sweetish, slightly saline, and leaving a sensation of bitter- 

 ness behind : alcohol does not dissolve it. If we mix some 

 of it with a solution, the prussiate is separated like while 

 flakes of snow, which preserve their lustre when dried, and 

 resembling the silvery kind of gauze presented by the ace- 

 tate of mercury. When redissolved in water, it reproduces > 

 an ordinary solution of triple prussiate. 



This salt, which I shall denominate triple to distinguish 

 it from the simple prussiate of potash, is equally constant 

 in its attributes with the most perfect neutral salts. It is of 

 a fine citrine yellow colour, which never leaves it until it 

 changes its state : for this colour, as well as for its two other 

 characteristic properties,- of crystallizing and dyeing the red 

 oxide blue, it is indebted to a portion of black oxide, which 

 forms an essential part of its constitution. Without this. ox- 

 ide, subjected, like the two other elements of the triple prus- 

 siate, to an invariable proportion, this prussiate could in fact 

 neither crystallize, nor form blue with the solutions of iron, 

 the base of which was at the maximum. It is, in short, from 

 this very union that the principle which saturates the potash 

 of the triple salt extracts, as remarked by Berthollet, proper- 

 ties which singularly increase its analogies with the acids. 



In this view we may add, that the triple prussiate occupies 

 the middle between the alkaline and the metallic salts. When 

 we reflect, however, upon one property of this salt, which 

 we shall mention presently, it would be difficult to ascertain 

 whether it is to the prussic acid, or to the simple prussiate 

 collectively, that the oxide of iron attaches itself when it.is 

 raised tq the state of triple prussiate. What is certain, how- 

 ever, is, thajt we arc still ignorant of what aspect or what 

 properties a prussic acid should have, which should be united 

 m precisely a proper, proportion with that dose of black 

 oxide, by the assistance of which it can furnish a triple 

 prussiate. On treating the prussic acid with, this oxide, we 

 may make. Prussian blue, but not the ferruginous kind of 

 iicid, which is proper for converting potash into triple salt: 

 this must not be lost sight of; for we know verv weir that 



Y 2 Prussian 



