Materials for a History of the Prussiates* 53 



it at all, because the potash which predominates reduces it 

 to oxide. The latter is then deposited without passing to 

 the state of prussiate. To attain this, it must be accom- 

 panied by an acid, for the oxide in question (being only at 

 the minimum) has no effect upon the triple prussiate. The 

 following experiment clearly demonstrates the advantages of 

 this method : 



I divided a lixivium into two equal parts: the one was 

 prepared or tripled by green sulphate, the other not. I af- 

 terwards distilled them : the former gave no suspicion of 

 the presence of ammonia, and the latter furnished it as 

 usual. It is indispensable, therefore, to prepare lixiviums be- 

 fore concentrating them. Lastly, neither the red oxide, nor 

 its sulphate, as Scheele experienced, can be dissolved in the 

 simple prussiate, and give it the quality of triple prussiate : 

 this oxide, although fit to become the base of Prussian blue, 

 cannot decompose the triple prussiate : it must necessarily 

 be used when dissolved in an acid. 



Recapitulation, 



The pru6sic acid is composed of carbon, azote, and hy- 

 drogen, in proportions with which we are not yet acquaint- 

 ed. Considering the great Quantity of charcoal, however, 

 which it leaves after its destruction in several eases, we mav 

 conjecture that it contains carbon in a greater proportion 

 than the two other substances. No person has supposed 

 that oxygen entered into its composition ; and in truth the 

 well-known affinities of its three elements, added to the cir- 

 cumstances attending its formation, have not as yet per- 

 mitted us to hazard the opinion. 



The prussic acid, when by itself, has very few of the 

 general qualities of the acids. It has not a sour taste : it 

 does not redden turnsole : it is not so easily dissolved in 

 water (the true solvent of the acids) as it is in alcohol : in 

 this last solvent it is decomposed even spontaneously, and 

 without the assistance of the external air. It forms with the 

 alkali* combinations so imperfect, that we find in them, 

 almost in a state of perfect separation, the specific proper- 

 ties of the component parts, and the carbonic acid, the 



D 3 weakest 



