1306 CHOLETELIN — HYDROBILIRUBIN. 



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 bilipur- 

 purin, of which however nothing definite is as yet known. The 

 yellow marks the final formation of choletelin. 



4. Choletelin. 1 C 16 H 18 N 2 6 . (?) 



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

 It is readily soluble in alkalis, as also in either alcohol, chloro- 

 form or ether, but least so in the two last solvents. None of 

 the solutions exhibit any fluorescence even after the addition 

 of zinc chloride. In this it differs markedly from urobilin, a 

 well-known yellow urinary pigment. In alkaline solutions 

 choletelin shews no absorption band; in acid solutions there 

 is a distinct absorption of light, resulting in an ill-defined band, 

 between b and F. 



5. Hydrobilirubin. C 32 H 40 N 4 O 7 . 



When bilirubin is dissolved in dilute caustic potash or soda 

 or suspended in water and treated with sodium-amalgam in 

 successive portions, air being at the same time carefully 

 excluded, it is observed that at first no hydrogen is evolved ; 

 the dark-coloured solution becomes gradually lighter in colour 

 and more transparent, until at the end of two or three days it 

 is bright yellow or brownish-yellow, and now hydrogen begins 

 to come off from the mixture. At this stage the supernatant 

 fluid should be poured off from the metallic mercury which has 

 accumulated, and if it is now acidulated strongly with either 

 hydrochloric or acetic acid, it yields a more or less copious 

 flocculent precipitate of a dark reddish-brown colour. This 

 precipitate is impure hydrobilirubin. When dried it takes 

 the form of a dark reddish-brown amorphous powder, which is 

 readily soluble in alcohol and chloroform, and but sparingly 

 soluble in pure ether. It is also very soluble in alkaline solu- 

 tions, to which it imparts a yellow colour as of normal urine: 

 when acidulated the solutions turn red. 



The acid solutions of hydrobilirubin shew a marked 

 absorption band between b and F which becomes fainter if 

 ammonia is added until the reaction is alkaline. But on the 

 subsequent addition of a few drops of a solution of zinc chlo- 

 ride, the band reappears with usually increased intensity, 

 though shifted slightly towards the violet end of the spectrum. 



1 The formula here given should probably be doubled. 



