286 ON PRUSSIAN BLUE 



tillation, in order to verify this observation, I prepared on 

 purpose some perfectly pure Prussian blue from vitriol of 

 iron, and from the precipitating liquor. 



SECTION XV. 



(a) I distilled this Prussian blue in a glass retort, to which 

 I adapted a receiver, in which I had put a little distilled 

 water. I pushed the fire till the bottom of the retort was 

 red hot. After the distillation was over, I found that the 

 water in the receiver contained colouring matter and volatile 

 alkali, but no oil. The air in the receiver was impregnated 

 with the same matter, and with aerial acid. What remained 

 in the retort was black, and obeyed the loadstone. It 

 therefore appears that the volatile alkali enters into the com- 

 position of the colouring matter. I thought it, however, of 

 importance to examine what phenomena the other metallic 

 precipitations, prepared with the same precipitating liquor, 

 would show when distilled in the same manner, (b) The 

 yellow-brown precipitate of cobalt (Sec. xm. (%)) yielded just 

 the same products as the precipitate of iron. The residuum 

 in the retort was black, (c) The yellow precipitate of copper 

 took fire, and emitted from time to time slight sparks 

 during the distillation. It yielded but a very small quantity 

 of colouring matter ; but much more aerial acid and volatile 

 alkali than the precipitates before mentioned. There was 

 likewise a sublimate in the neck of the retort ; but in too 

 small a quantity for making experiments. The residuum 

 in the retort was reduced copper, (d) The precipitate of 

 zinc showed the same phenomena as Prussian blue, (e) The 

 precipitate of silver yielded likewise volatile alkali and 

 aerial acid, but chiefly colouring matter. There was like- 

 wise a little sublimate in the neck of the retort, which 



