52 Materials for a History of the Prussiates, 



reason, that it is iron which is wanting in the prussiate; 

 and even if we reflect on it, it is astonishing to see that 

 the triple prussiate, which certainly exists in the lixiviums, 

 could defend its oxide against the effects of the charcoal, 

 which tends to reduce it continually. In short, all this part 

 of the subject is very obscure. We do not know the period 

 at which the prussic acid is formed, if it be destroyed in 

 order to be reproduced, nor finally the degree of heat to be 

 applied to the boilers, in order to obtain the greatest possible 

 quantity of the one or the other of the prussiates which it is 

 the object of the manufacturer to obtain. 



The existence of the triple prussiate is clearly demon- 

 strated in the lixiviums, by the following experiment : 



Saturate a lixivium with dilute sulphuric acid : carbonic 

 acid is first set free, afterwards comes prussic acid from the 

 free prussiate : but it must be afterwards heated : we then 

 obtain the triple prussiate, and the white prussiate of iron i» 

 set free. Besides this, the old concentrated lixiviums de- 

 posit octahedral crystals of triple prussiate. 



The prussic lixivium has two distinct tastes ; the one of 

 potash, and the other of kernels : and from this latter taste 

 we judge of its quality. If it perfumes the mouth but feebly 

 it is not good; and either the mixture has not been sufficient- 

 ly heated, or the charcoal has been used too sparingly. I 

 think also, that the calcination of the mixtures in the open 

 air ought not to contribute to the augmentation of the prus- 

 siates, and that it would perhaps be more advantageous, and 

 less troublesome, to heat them in close crucibles placed in a 

 reverberating furnace, since it is in other respects certain 

 that agitation is by no means necessary to the success of 

 this operation. 



When we have occasion to concentrate the lixiviums, in 

 order to diminish their volume, or in order to preserve them, 

 we should begin before every thing, as observed by Cura- 

 dcau, in placing the simple prussiate beyond the reach of 

 destruction : this may be at once effected by pouring green 

 aulphate into it by small portions at a time. The green sul- 

 phate is completely dissolved ; the lixivium at first becomes 

 red, and then yellow : an excess of sulphate does not alter 



it 



