Materials for a History of the Prussiafes. 343 



more concentrated may alter the whiteness of the prussiate, 

 but will never bring it to a perfect blue. 



The marine acid, boiled over prussiate also does not make 

 it blue. 



This boiling acid is not without action upon the white 

 prussiate. The following is what I remarked on this subject: 

 Some white prussiate is destroyed, some prussic gas disen- 

 gaged, and we find black oxide in solution : in this case 

 the little Prussian blue formed by the introduction of the 

 air during the interval of the mixtures, predominates over the 

 white, and changes its whiteness to greenish. 



The blue prussiate, boiled with the same acid, also gives 

 prussic gas and abandons red oxide, but less is destroyed of 

 it than white prussiate. We may infer from these facts 

 that the muriatic acid, aided by heat, could, strictly speak- 

 ing, decompose the prussiates, and resume over the prussic 

 its rights as a more energetic acid : — this would not be an 

 astonishing, but it would be at least a tedious, experiment. 



Prussiate of Potash and Acids. — Heat marine or weak 

 sulphuric acid in a matrass with crystals of prussiate. When 

 ebullition commences, the gas escapes; let it be received in 

 a bell-glass full of mercury, or burn it by presenting the 

 flame of a candle to it. The flame it emits is variegated red, 

 violet, and yellow : during the dissipation of the gas, the 

 liquor is thickened by the production of a white precipitate, 

 which passes to the blueish. The gas b?ing totally separat- 

 ed, throw the mixture into boiling water, revive with oxy- 

 genated muriatic acid ; wash and dry the product in a cap- 

 sule. Four experiments, made at distinct periods, yielded 

 me from 0*34 to O'ob of complete blue, for a hundred parts 

 of triple prussiate. 



Inferences. — 100 parts of Prussian blue, without alum, 

 vield 0*55 of red oxide by combustion. This same blue 

 destroyed by the nitric acid also gives 54. Thus then it is, no 

 doubt, that pure blue of Prussia only contains from 0*54 to 

 0'55 of red oxide. According to these data, 0-35 parts of 

 blue should render about 0*-l 7 of black oxide, or 0*19 of red 

 oxide. Hence it follows, .when we formerly separated the 

 iron of a solution bv the prussiate of potash, this salt added 



Y4 to 



