360 Prof. Stokes on the Reduction and Oxidation [June 16, 



point of merging into one by the absorption of the intervening bright band, 

 when the two appear about equal. 



Like cruorine, reduced hsematin is oxidized by shaking up its solution 

 with air. I have not yet obtained hsematin in an acid solution in more 

 than one form, that which gives the spectrum fig. 3, and which I have 

 little doubt contains hsematin in its oxidized form ; for when it is with- 

 drawn from acid ether by an alkali, I have not seen any traces of reduced 

 hsematin, even on taking some precautions against the absorption of oxygen. 

 As the alkaline solution of ordinary hsematin passes, with increase of thick- 

 ness, through yellow, green, and brown to red, while that of reduced 

 hsematin is red throughout, the two kinds may be conveniently distin- 

 guished as brown hcematin and red hcp.matin respectively, the former or 

 oxidized substance being the hsematin of chemists. 



13. Although the spectrum of scarlet cruorine is not affected by the addi- 

 tion to the solution of either ammonia or carbonate of soda, yet if after such 

 addition the solution be either heated or alcohol be added, although there 

 is no precipitation decomposition takes place. The coloured product of de- 

 composition is brown hsematin, as may be inferred from its spectrum. Since, 

 however, the spectrum of an alkaline solution of brown hsematin is only 

 moderately distinctive, and is somewhat variable according to the nature of 

 the solvent, it is well to add hydrosulphate of ammonia, which immediately 

 developes the remarkable bands of red hsematin. This is the easiest way 

 to obtain them ; but the less refrangible edge of the first band as obtained 

 in this way is liable to be not quite clean, in consequence of the presence 

 of a small quantity of cruorine which escaped decomposition. 



Some very curious reactions are produced in a solution of cruorine by 

 gallic acid combined with other reagents, but these require further study. 



14. Hoppe proposed to employ the highly characteristic absorption- 

 bands of scarlet cruorine in forensic inquiries. Since, however, cruorine 

 is very easily decomposed, as by hot water, alcohol, weak acids, &c., the 

 method would often be inapplicable. But as in such cases th^ coloured 

 product of decomposition is hsematin, which is a very stable substance, 

 the absorption-bands of red hsematin in alkaline solution, which in sharp- 

 ness, distinctive character and sensibility rival those of scarlet cruorine 

 itself, may be employed instead of the latter. The absorption-bands of 

 brown hsematin dissolved in a mixture of ether and acetic acid, or in acetic 

 acid alone, are hardly less characteristic, but are not quite so sensitive, re- 

 quiring a somewhat larger quantity of the substance. 



15. I have purposely abstained from physiological speculations until I 

 should have finished the chemico-optical part of the subject ; but as the 

 facts which have been adduced seem calculated to throw considerable light 

 on the function of cruorine in the animal economy, I may perhaps be 

 permitted to make a few remarks on this subject. 



It has been a disputed point whether the oxygen introduced into the 

 blood in its passage through the lungs is simply dissolved or is chemically 



