234 ESSAY XXII. 



Having at last, after many repeated trials, found means to 

 obtain it in this pure state, and unmixed, so that I was 

 able to make several experiments with it, I now take the 

 liberty of presenting an account of them to the Eoyal 

 Society. 



SECTION I. 



(a) If the lixivium sanguinis, the preparation of which is 

 universally known, be exposed for some time to the open air, 

 it loses its property of precipitating the iron of a blue 

 colour ; and the precipitate thus obtained is entirely dissolved 

 in the acid. Now, in order to ascertain whether the air 

 had hereby undergone any change, I put some recently 

 prepared lixivium into a glass vessel, which was well sealed 

 with rosin ; but some time afterwards I found the enclosed 

 air as before, and the lixivium sanguinis unchanged ; whence 

 I conclude that the colouring matter is not absolutely simple 

 phlogiston. 1 It occurred to me that the aerial acid, which 

 was not present in sufficient quantity in air confined as in the 

 preceding experiments, but exists in a much larger quantity 

 in the open air, might be the principal cause of the separa- 

 tion of this colouring matter from the lixivium, (b) I there- 

 fore filled a glass vessel with aerial acid, and poured a little 

 lixivium sanguinis into it, carefully preventing the access 

 of the external air. On examining this lixivium the day 

 after, I found that my conjecture was well founded ; for calx 

 of iron, precipitated with this lixivium, was entirely soluble 

 in acids, (c) I further tried whether other acids had the 

 same effect upon the lixivium sanguinis. For this purpose 

 I supersaturated that preparation with all the known acids, 



1 Le bleu de Prus.se est unpivcipite de fer, avec suraboiidance de 

 phlogigfique. Maequer, Did. de Chemique, 2de edition. 



