98 COLORING MATTERS. 



tains iron, which has been found in the proportion of 2.5 parts per 

 thousand in the incombustible residue. 



Melanine is insoluble in water, alcohol, ether, and solutions of the 

 organic and mineral acids. Boiling solutions of potassium hydrate 

 dissolve it without change of color, but its color is destroyed by chlo- 

 rine. It is regarded as derived from the coloring matter of the blood, 

 but there is no positive evidence of this, further than the fact that it 

 contains iron, and that it forms the coloring matter of the hair, in 

 which most of the iron of the blood-globules is probably deposited. 



Bilirubine, C 16 H I8 N 2 3 , 



The red or orange-red coloring matter of the bile. This substance 

 has been designated, by different writers, under the various names of 

 Biliphaein, Bilifulvine, Hematoidine, and Cholepyrrhine. It is formed 

 in the substance of the liver, and may be extracted from the liver- 

 cells in a pure form. From these it is taken up by the biliary 

 ducts and mingled with the other ingredients of the bile. It is crystal- 

 lizable, soluble in chloroform, less so in alcohol, and slightly soluble 

 in ether. It is readily soluble also in alkaline liquids, but quite insolu- 

 ble in pure water. In the crystallized form its color is red; in the 

 amorphous condition, orange ; and in solution, reddish-brown or yellow, 

 according to the degree of concentration. According to Hoppe-Seyler, 

 it gives a perceptible yellow color when viewed in a layer of 1.5 centi- 

 metre's thickness, even if dissolved in 500,000 times its weight of fluid. 



Solutions of bilirubine exhibit a well-marked reaction with nitroso- 

 nitric acid, which is known as " Gmelin's bile test." If to such a solu- 

 tion we add a small quantity of nitric acid, in which nitrous acid is also 

 present, a series of colors is produced in the following order : green, 

 blue, violet, red, and finally a dingy yellow. These colors are produced 

 by transformation of the bilirubine, and represent successive degrees 

 of its oxidation by nitric acid. The reaction is a very sensitive one, 

 and, according to Hoppe-Seyler, will produce a visible result in solu- 

 tions containing only one part in 70,000. 



Bilirubine is generally regarded as derived from hemoglobine. The 

 reasons for this opinion are: First, its reddish color, similar, in some 

 degree, to that of diluted blood. Secondly, it has been found in various 

 parts of the body, in old bloody extravasations, evidently produced 

 from an alteration of the blood upon the spot. When found under 

 these circumstances, it was formerly known as hematoidine. Thirdly, 

 if hemoglobine, in the living animal, be withdrawn from the blood- 

 globules, and made to assume a liquid form by alternately freezing 

 and thawing a portion of freshly drawn blood, and then re-injected 

 into the bloodvessels, this operation is followed by a discharge of bili- 

 rubine with the urine. If hemoglobine, however, be normally trans- 

 formed into bilirubine, its iron and sulphur must enter into some other 

 combination, as neither of these substances exists in the coloring matter 



