1813.] Chemical Properties of Animal Fluids. 199 



clear rust-coloured liquor is formed, from which a small addi- 

 tion of caustic alkali precipitates a little albumen, which is again 

 dissolved by a slight excess of the alkali; and then the solution 

 loses its red colour, and the subphosphate falls down, and may 

 be collected on the filter. -if 



In all these experiments the albumen dissolves the oxide 01 

 iron, even in greater quantity than exists in the colouring matter 

 of the blood; but this solution is yellowish, and has but little 

 body of colour; and the oxide of iron is shown by the usual 

 reagents. The albumen of serum will also dissolve many other 

 metallic oxides; for instance, that of copper, as Vauquelin has 

 lono- since proved; and it is doubtless the albumen which is the 

 menstruum of the oxide of mercury, found dissolved in the 

 blood during a course of this metal for the cure of syphilis. 1 he 

 oxidulum (or black oxide) dissolves easily, and still more co- 

 piously, in serum, forming a perfectly limpid sea-green liquor. 

 The solution is readily obtained by adding to serum some salt 

 of iron, which has the black oxide for its base, and neutralizing 

 its acid by an alkali. When this green solution is exposed to 

 the air, it absorbs oxygen, deposits red oxide of iron, and be- 

 comes yellow. The compounds of oxide of iron and albumen 

 are decomposed by the mineral acids, which precipitate the al- 

 bumen colourless, and retain the iron in solution. The prus- 

 siates alone do not disturb the solution bf iron in albumen, be- 

 cause the metallic oxide is not here dissolved by any acid; but 

 if, after mixing them, a little muriatic acid is added, an exqui- 

 sitely beautiful azure blue precipitate appeai-s, consisting ol al- 

 bumen and Prussian blue. If the acid phosphate of iron is 

 dissolved in acetic acid, and afterwards serum be added, fol- 

 lowed by a little caustic alkali, the albumen and subphosphate 

 are precipitated together, of a rust-colour, which is not changed 

 by drying, but has no resemblance to the colouring matter of 

 blood. In a word, I have not been able to find any method of 

 combining albumen with subphosphate of iron, or with any 

 other salt of this metal, so as to produce a compound identical 

 with the colouring matter of the blood. 



But from the result of all these experiments, what appears 

 to be the dilference between venous and arterial blood ? This 

 question I am unable to answer ; nor can I explain the differ- 

 ence between these substances before and after coagulation. 



I have already mentioned that the liquid, out ot which the 

 colouring matter has been coagulated by heat, has at first a tint 

 of red, which it loses by cooling ; at which time it further de- 

 posits a small quantity of colouring matter. This liquid, whilst 

 evaporating, becomes green, owing to the action of the un- 

 combined alkali on tlic small portion of colouring matter that 

 it still retains. This liquid holds also in solution all the salts, 



