240 ESSAY XXII. 



fire. As soon as the mass began to boil, it grew thick, from 

 the production of a great quantity of Prussian blue, which 

 was separated. I perceived, at the same time, a smell which 

 penetrated through the lute, and perfectly resembled the 

 smell of water impregnated with the colouring matter (Sec. 

 iv. (c)). I continued the distillation till 1 oz. had passed 

 over into the receiver, and then poured the water containing 

 the colouring matter into a phial. The air in the receiver 

 had likewise absorbed this colouring matter, which I detected 

 as in Sec. m. (a). The blue mass remaining in the retort I 

 put upon a strainer, and into the liquid which passed 

 through I put a piece of vitriolated iron, in order to see 

 whether there was still remaining any of the neutral salt 

 undecomposed. But no Prussian blue was produced, and 

 thus the salt was decomposed during the boiling. The blue 

 which now remained on the filter, and was free from the 

 neutral salt, I again boiled with lixivium tartari ; the 

 solution was freed by filtration from its ochre of iron, and 

 the mass was then distilled a second time, with the addi- 

 tion of vitriolic acid in excess. It now showed the same 

 phenomena as at first ; for as soon as it began to boil, 

 Prussian blue was again separated, though in less quantity, 

 and the colouring matter came over into the receiver. 

 After one-third of the mass had passed over, I added it to 

 that obtained by the first distillation, and then separated 

 the regenerated Prussian blue from its acid, which I again 

 extracted by lixivium tartari, and then distilled it the 

 third time. Here I again obtained some blue ; and it thus 

 evidently appears that, by repeated extractions and distilla- 

 tions, all Prussian blue might at last be entirely decomposed. 

 It is not difficult to account for the series of phenomena 

 that occurred in this whole process. The neutral salt 

 consists of alkali, a little iron, and the colouring matter ; 



