246 BILICYANIN. CHOLETELIN. 



bile-pigments as obtained from gall-stones. Biliprasin is apparently only impure 

 biliverdin (Maly). 



3. Bilicyanin 1 . (Cholecyanin, Choleverdin). 



This is the substance which results from the oxidation of biliverdin 

 and is the cause of the blue colour observed when bile is treated with 

 fuming (yellow) nitric acid as in Gmelin's reaction. It has riot as yet 

 been isolated either in sufficient quantity, and still less in a condition 

 of sufficient purity, to admit of such a chemical investigation as would 

 lead to the determination of its composition. But by analogy with the 

 known relationship of biliverdin to bilirubin, and from the evidence 

 afforded by the composition of choletelin (see below) into which 

 bilicyanin may be readily converted by further oxidation, bilicyaniii 

 will probably be found to differ from biliverdin simply by the addition 

 of oxygen to the molecule of the latter. 



Preparation. Bilirubin is dissolved in chloroform or suspended in 

 alcohol and slowly oxidised either by gradual addition of bromine or 

 fuming nitric acid ; as soon as the mixture is of a bright blue colour, 

 the bilicyanin is precipitated by an excess of water. As thus obtained 

 it is insoluble in water, almost insoluble in either ether or chloroform, 

 but soluble in alcohol and alkalis. In presence of alkalis it is still 

 almost insoluble in either ether or chloroform ; in presence of acids it 

 is now scarcely soluble in water, but soluble in ether and chloroform. 



Bilicyanin is for practical purposes characterised solely by its 

 marked absorption spectrum. This consists of three bands, one on 

 each side of Z>, that to the red side of D being the darkest, and 

 one between b and F. The latter is probably identical with the band 

 seen in acid solutions of choletelin and due to the production of this 

 substance in small quantity during the oxidation of bilirubin. The 

 position of the bands varies somewhat according to the solvent employed 

 and as to whether the solution is acid or alkaline. 



During the application of Gmelin's test for bile-pigments the blue due to 

 bilicyanin is bordered by a violet colour and this by a red, the final and 

 permanent colour being yellow. Of these three the first is not as yet known 

 to be definitely due to one specific substance; it is most probably the result 

 of a mixture of the blue of bilicyanin with the red of the next product. The 

 red colour is on the other hand supposedly due to a definite pigment sometimes 

 called bilipurpurin, of which however nothing definite is as yet known. The yellow 

 marks the final formation of choletelin. 



4. Choletelin. C 16 H 18 N 2 6 - (?) 



This is the final product of the oxidation of bile-pigments. It is 



1 Heynsius u. Campbell, Pfliiger's Arch. Bd. iv. (1871), S. 526, x. 1875, S. 246, 

 gives literature of this and other bile-pigments. 



