.] of the Yellow Colouring Matter of the Urine. 401 



istilled water has been carried out, the filter paper will merely be 

 coated with an amorphous brown film, and there will be no appreciable 

 deposit of crystalline impurities. The filtrate of ether and alcohol 

 will have a yellow colour, as it is able to hold a considerable quantity 

 of pigment in solution. 



The filter paper, to which the pigment clings tenaciously, is allowed 

 to dry and is then soaked for a time in chloroform which remains un- 

 tinted, and afterwards in absolute alcohol. The alcohol becomes 

 coloured by the pigment, but does not dissolve it nearly so readily as 

 before. 



The paper is then allowed to soak for an hour or so in distilled 



water, by which means a clear orange- coloured or yellow aqueous 



! solution is obtained, which should yield no indigo reaction, and which 



I contains the pigment in a condition approaching to purity, although 



it is certainly not entirely pure. I believe, however, that no pigment 



| other than the yellow one is present, and the absence of those 



which show absorption bands can be definitely established. 



When it is treated with sodium hypobromite, a little nitrogen is 

 evolved, the freedom from urea being in proportion to the amount of 

 I washing or soaking in alcohol that the brown precipitate has received. 

 If only slightly washed, 1 c.c. of a concentrated solution tested by 

 means of Southall's apparatus, may give off nitrogen equivalent to as 

 much as OG03 gram of urea,- but if the washing has been more 

 thorough, the amount evolved is too small to be measured. 



Seeing how soluble urea is in alcohol and in water, whilst it is 

 almost insoluble in ether, it is only to be expected that this substance 

 should constitute the chief impurity in the specimens. 



When the residue obtained by evaporation of the aqueous solution 

 is burnt on a platinum dish, it yields a very bulky mass of carbon, and 

 ultimately a trace of colourless ash, varying in quantity, which is 

 readily soluble in water, contains no appreciable amount of carbonate, 

 and apparently consists of sodium phosphate.* 



* May 9th, 1894. It has been suggested that the yellow pigment may contain 

 some, at least, of the iron which is present in urine, but although I cannot state 

 that the product obtained by the above process is absolutely free from iron, the 

 amount of that element contained in it is, at most, exceedingly minute. After the 

 combustion of such small quantities as 1 or 2 cgrm. of the dry pigment, the 

 sulphocyanide test gave negative results, provided that iron-free reagents, and 

 filter-papers which had been extracted with hydrochloric acid, were employed in 

 the process ; but with as much as 6 cgrm. a just perceptible tint was obtained, in 

 no way comparable with that yielded by a fiftieth part of that weight of haemo- 

 globin. I am, therefore, inclined to look upon this minute trace of iron as an 

 accidental impurity, probably derived from the urine, rather than as a constituent 

 of the yellow pigment. 



When heated with potassium hydrate the yellow pigment was found to give off 

 ammonia freely. 



