198 Chemical Properties of Animal Fluids. [Sept. 



change. — (D.) A solution of sulphuret of potash produces no 

 change in the solution of colouring matter, except that the red 

 colour is slowly converted into green by the action of the alkali. 

 A drop of acetic acid precipitates the sulphur of a white colour. 

 — (E.) It iswell known that none of the mineral acids deprive the 

 colouring matter of its colour, which ought to be the case if that 

 colour had been owing to the presence of the subphosphate ol 

 iron. The phosphoric acid mixed with the colouring matter 

 blackens without precipitating it : whereas, if the opinion of the 

 French chemists were correct, it ought to produce a neutral and 

 colourless phosphate. — (F.) A drop of a solution of acetate of 

 lead exalts the colour of the colouring matter, and a larger 

 quantity throws down a fine red precipitate. — (G.) The nitrates 

 of silver, of lead, and of mercury, blacken the colouring matter, 

 and when added in larger quantity precipitate it. 



These experiments prove that the iron in the colouring mat- 

 ter is not contained in it in such a way as to admit of being de- 

 tected by the best re-agents we possess, until the composition 

 of the colouring matter is totally destroyed. 



But how can these facts be reconciled with the following, 

 mentioned by Fourcroy in his Systeme des Connoissances Chy- 

 miques P " Vauquelin and I," says he, " have found that the 

 subphosphate of oxide of iron is easily dissolved in albumen by 

 a slight agitation, and without the aid of heat, and that this 

 solution possesses a bright red colour, similar to that of the 

 blood. This colour becomes still more vivid by adding a little 

 caustic alkali, which facilitates still more the solution of the 

 subphosphate in albumen." 



It was not till after having made and carefully repeated many 

 experiments, that I could venture to pronounce this opinion to 

 be void of foundation. I shall not seek to form any conjecture 

 with regard to the circumstances which may have deceived these 

 distinguished chemists, but shall merely relate my own experi- 

 ments on the subject. 



The subphosphate in question, newly prepared and still moist, 

 easily mixes with serum, giving it the colour of rust; but it 

 subsides in process of time, and may be entirely separated from 

 it by means of a filler. The neutral phosphate of oxide of iron, 

 mixed with serum also, does not dissolve, and the addition of 

 caustic alkali instantly produces the subphosphate; but this last 

 remains undissolved, and communicates to the liquor a colour 

 of rust, which is quite dissimilar to that of the colouring matter 

 of blood. The serum deprived of subphosphate by filtration 

 retains a pale yellowish colour, which is owing to a small quan- 

 tity of oxide of iron held in solution. 



If serum is mixed with the subphosphate in question, and 

 phosphoric acid is added, so as to dissolve the subphosphate, a 



