1880.] Colouring-matters of Human Urine. 217 



purified by being passed into a solution of sulphate of copper, then 

 strong sulphuric acid and, lastly, U -tubes containing chloride of 

 calcium, is made to pass through a solution of bilirubin in chloroform 

 dried by chloride of calcium for some days previously, the colour of 

 the fluid changes much more rapidly, but the changes in colour are 

 accompanied by the same changes in the spectrum already noticed. 



On the 'Reduction of the Figment present in the last stage to the con- 

 dition of Febrile Urobilin by means of Sodium Amalgam. — It is evident 

 that the changes which take place are similar to those which 

 are seen in Gmelin's reaction, that at the penultimate stage choletelin 

 is formed, and that even at the last stage this is also further oxidised, 

 as proved by the complete disappearance of the band at F. If chole- 

 telin be a fully oxidised bile pigment and febrile urobilin a less oxidised 

 bile pigment we should be able to reduce choletelin back to febrile 

 urobilin by the action of reducing agents. Accordingly, I proceeded 

 to isolate the pigment of the yellow stage, having first filtered the 

 chloroformic solution. It was then evaporated on the water-bath. 

 The residue was a light yellowish-brown pigment, perfectly soluble in 

 alcohol with a yellow colour. I could not see a band at F, for the 

 pigment had been oxidised beyond the stage at which it gives this 

 band. When a piece of sodium amalgam was introduced into the 

 alcoholic solution the latter immediately became of a reddish colour. 

 After it had acted for a short time the fluid was found to have the 

 power of absorbing the violet end of the spectrum. When hydrochloric 

 acid was added to the solution before the action of sodium amalgam no 

 change took place, but when it was added to the red fluid after the 

 action of the amalgam, it gave a black band, a, wave-length 506 to 481, 

 sp. 11, Chart II. And when caustic soda was added until an alkaline 

 reaction was developed a band, 8, appeared from wave-length 513 to 

 wave-length 488. 



After the action of the amalgam had gone on for twenty-four 

 hours the colour of the fluid was light yellow, and hydrochloric acid 

 then produced a reddish fluid giving a band of intensity, a, from 

 wave-length 502 to wave-length 478. 



But this pigment had gone just beyond the stage of choletelin, so 

 that it became necessary to prepare that pigment. I thought that by 

 preparing it by another method I should have additional evidence of 

 the truth of the idea that it can be made to yield febrile urobilin by 

 reduction, if the result should turn out favourably. 



Preparation of Choletelin from pure Bilirubin and its Conversion into- 

 Febrile Urobilin. — Some pure bilirubin, prepared as before, which 

 gave only general absorption in the deepest and thinnest layers when 

 dissolved in chloroform, was treated with a little caustic soda in a 

 chloroformic solution and exposed to the air in an evaporating dish. 

 After the lapse of twenty-four hours the residue was found to be sap- 



