246 HYDROBILIRUBIN. 



ing it by passing the fumes of nitrous acid into the mixture. As 

 soon as the play of colours is complete and the solution is of a 

 pure yellow colour, it is poured into a large excess of water, from 

 which on more or less prolonged standing choletelin separates out 

 as a flocculent mass, which if washed and dried yields a brown 

 powder. 1 It is readily soluble in alkalis, as also in either alcohol, 

 chloroform, 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. The above statements scarcely 

 provide any certain means of identifying choletelin as a chemical 

 substance, and no specific test for it has as yet been described. 

 Neither is it quite certainly characterised by its absorption spec- 

 trum, so far at least as any specific bauds are concerned. Indeed 

 there has been very great difference of opinion as to whether it 

 ever gives any band at all, and if it does, where this baud is situ- 

 ated. With our existing knowledge it seems safe to say that in 

 alkaline solutions choletelin shows no absorption band, and that 

 in acid solutions a band may be, and frequently is seen, lying be- 

 tween b and F. The uncertainty as to its spectroscopic properties 

 led some of the older observers 2 to regard choletelin as identical 

 with hydrobilirubin (urobilin). This view is however quite un- 

 tenable both as the result of purely chemical investigations 3 and 

 of spectrophotometric determinations of the optical properties of 

 the two substances. 4 



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



When bilirubiu is dissolved in dilute caustic potash or soda or 

 suspended in water and treated with sodium-amalgam in succes- 

 sive 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 brown- 

 ish-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 acidu- 

 lated 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. It is purified 

 by being redissolved in ammonia, reprecipitated from this solution 

 by the addition of acid, and finally washed with water. At first 



1 Maly, Siiz. d. L Akad. d. Wiss. Wien, Bd. LVII. (1868), 2 Abth. Feb.-Hft. LIX. 

 (1869), 2 Abth. Ap.-Hft. 



2 Heynsius u. Campbell, foe. cit. Stokvis, Centralb.f. d. med. Wiss. 1873, S. 211, 

 449. 



3 Maly, Ibid. S. 321, and more particularly Liebermann, Pfliiger's Arch. Bd. 

 XI. (1875), S. 181. 



* Vierordt, Zt.f. Biol. Bd. x. (1874), S. 399. 



