288 ON PRUSSIAN BLUE 



the other constituent parts, and that it is absolutely 

 necessary that this water should be separated from them, 

 before a perfect union of the volatile alkali can take place. 

 We know that charcoal powder, brought into fusion with 

 fixed alkali, yields likewise a kind of lixivium sanguinis, 

 though weak. I digested the colouring matter with con- 

 centrated vitriolic acid, and the mixture remained colourless. 

 If this matter had contained any oily principle, the mixture 

 would have become black or brown. Having reduced some 

 pulverised blood, by calcination, to a coal, viz. the residuum 

 in the retort (Sec. xv. (#)), I mixed with it an equal quantity 

 of alkali of tartar, and exposed this mass in the ordinary 

 manner to a red heat, and thus I obtained a very good 

 lixivium sanguinis. It is hence evident that no oily 

 matter is required for the production of the colouring 

 matter. 



SECTION XVI. 



Lastly, I made the following experiments, which con- 

 vinced me of the truth of my conclusion. I mixed three 

 tablespoonfuls of charcoal powder with an equal quantity 

 of pulverised alkali of tartar, and put the mixture into a 

 crucible. I filled another crucible with a like mixture, and 

 placed both of them at the same time upon burning char- 

 coal. I kept them red hot for a quarter of an hour, and then 

 threw one of the portions, which was perfectly red hot, into 

 8 oz. of water. At the same time I put into the other half 

 1 oz. of sal ammoniac, in small pieces, agitated the whole 

 briskly together, taking care at the same time to push the 

 sal ammoniac down towards the bottom of the crucible, which 

 I then again placed in the fire. Observing, a couple of 

 minutes afterwards, that there arose even then no more 

 ammoniacal vapours, I threw the whole mass, red hot as it 



