. 



94.] of the Yellow Colouring Matter of the Urine. 399 



any nrobilin that, may be present, as has been shown by G. Hoppe 

 Seyler,* who makes saturation with ammonium sulphate the start- 

 ing point of his process for the quantitative estimation of that sub- 

 stance. 



Acidulated alcoholic extracts from the precipitate usually show a 

 faint urobilin band, and sometimes still fainter bands of acid hsemato- 

 porpliyrin. Unusually pink precipitates will be turned green by 

 alkalies, which shows that they contain uroerythrin. 



If the precipitate be washed with water a yellow solution is ob- 

 tained, which is found to contain some of the yellow pigment precipi- 

 tated by the saturation. 



Lastly, in addition to mucus, there may remain upon the filter 

 paper a black residue, insoluble in water, alcohol, and dilute acids, 

 but slightly soluble in soda, potash, or strong ammonia, which is an 

 impurity derived from the ammonium sulphate. 



A morbid urine, highly coloured with urobilin, yields a yellow 

 filtrate, like that obtained with normal urine, which shows no urobilin 

 baud. I have reason to think that there is no such complete removal 

 of hferaatoporphyrin, but any traces of this pigment which may exist 

 in the filtrate are removed at a later stage. 



Stage II. To the saturated clear yellow filtrate absolute alcohol is 

 next added, which throws down some of the ammonium sulphate, and 

 after a small quantity has been added, quickly separates and collects 

 upon the surface as a clear layer, carrying with it the bulk of the 

 yellow pigment. 



The alcohol is then separated off from the partially decolorised 

 urine, from which a further supply of pigment can be obtained by a 

 fresh addition of alcohol. By repeated extraction the pigment may 

 be almost completely removed, but the result does not repay the 

 expenditure of alcohol entailed. If rectified spirit be used instea'd of 

 absolute alcohol, a considerably larger quantity is required to produce 

 satisfactory separation. 



The alcoholic extract thus obtained is next poured into a consider- 

 able bulk of distilled water, and the alcohol is again caused to sepa- 

 rate out by once more saturating with ammonium sulphate, with the 

 aid of gentle warmth. This washing process, which entails some loss 

 of pigment, is of much importance, as by this means urea and other 

 crystalline impurities are to a large extent got rid of ; and its omission 

 is apt to give rise to trouble at a later stage. 



The golden orange-coloured extract thus obtained is inflammable, 

 but will not mix with chloroform, as it still contains water and am- 

 monium sulphate. It is therefore poured upon some fresh ammonium 

 sulphate and gently warmed, when two layers will form, the lower of 

 which is almost colourless, and represents much of the water pre- 

 * ' Virchow's Arcliiv,' vol. 124, 1891, p. 30. 



