238 ESSAY XXII. 



duced the same effects as pure water mixed with a little 

 vitriolic acid. 



SECTION V. 



When I had thus discovered the possibility of obtaining 

 the colouring matter in its greatest purity, I proceeded to 

 make some experiments, in .order to obtain it separate from 

 the blue itself ; and this with a view partly to procure a 

 larger quantity of it than the lixivium yields ; partly also 

 to avoid the troublesome calcination of the blood and pre- 

 paration of the lixivium. This matter, though it may be 

 separated from the Prussian blue by distillation, yet it is 

 thus mixed with so many heterogeneous particles, that it 

 would not serve my purpose. On examining several sorts 

 of Berlin blue, I found in them marks of sulphur, volatile 

 alkali, vitriolic acid, and volatile sulphureous acid, which 

 substances are found as well in the lixivium sanguinis as in 

 the lixivium of soot, and adhere to the precipitate in the 

 preparation of Prussian blue. On distilling one sort of this 

 preparation, I obtained in the receiver a liquid which had 

 a smell of spiritus cornu cervi, precipitated vitriolated iron, 

 and, on the addition of an acid, was changed into Prussian 

 blue. In the neck of the retort there was a sublimate, 

 which proved to be a kind of neutral salt, consisting of 

 volatile alkali and volatile sulphureous acid ; the air in the 

 receiver was full of aerial acid, volatile alkali, and the colour- 

 ing matter. The remainder in the retort was black, obedient 

 to the loadstone, and yielded hepatic air with acids. Being 

 unable by these means to attain my purpose, I resolved to 

 examine a little more closely a neutral salt known in 

 chemistry, which is formed when lixivium tartari is boiled 

 with a sufficient quantity of Prussian blue. This salt 

 consists of the colouring matter of the lixivium, of calx of 



