ON PRUSSIAN BLUE 235 



adding afterwards a solution of vitriolated iron to them ; 

 but neither did I now obtain any precipitate. 



SECTION II. 



(a) I now inverted my experiments ; I mixed a little 

 vitriolated iron with lixivium sanguinis, which immediately 

 grew yellow ; I then poured some of this mixture into 

 a glass vessel filled with aerial acid. The day after, I poured 

 this lixivium into a solution of vitriolated iron, then super- 

 saturated the lixivium with acid, and obtained a considerable 

 quantity of Prussian blue. (b) To the same lixivium 

 sanguinis, in which I had dissolved a little vitriolated iron, 

 I added of the other acids somewhat more than was necessary 

 for saturation ; and, on mixing afterwards a solution of 

 vitriol with them, I instantly obtained Berlin blue, (c) I 

 precipitated a solution of vitriolated iron with alkali, and 

 boiled the greenish precipitate for some minutes in lixivium 

 sanguinis, which dissolved part of it ; I then filtered the 

 lixivium. This lixivium underwent no change when 

 exposed to the open air or to the aerial acid ; it precipit- 

 ated the solution of iron of a blue colour, as well before as 

 afterwards ; and although the lixivium was supersaturated 

 with acid, and some vitriolated iron was added, a very 

 beautiful Prussian blue was obtained. Hence it appears 

 that the calx of iron in some manner fixes the colouring 

 matter in the lixivium ; so that neither aerial acid nor 

 any other acid is capable of separating this matter from the 

 alkali. This is likewise the reason why the colouring neutral 

 salt, which is formed on boiling alkali with Prussian blue, 

 does not so easily lose its power of precipitating iron of a 

 blue colour, either by the action of the aerial or any other 

 acid. (d) But if lixivium sanguinis be boiled with a 



