APPENDIX. 523 



observed the blue tint developed by nitrate of urea artificially 

 prepared and kept moist, and has likewise produced it by 

 adding nitric acid to an old solution of urea partially converted 

 into carbonate of ammonia. 



The existence of a large quantity of uroxanthin in urine 

 is indicated : 



1. By the clear light-yellow colour of the urine when that 

 secretion is acid, as in cholera, and sometimes in Bright's 

 disease. 



2. By the presence of the products of its oxidation, uro- 

 glaucin and urrhodin, which either of themselves form a violet- 

 coloured sediment, or communicate that tint to a sediment 

 already formed. 



On allowing urine abounding in uroxanthin to stand for 

 some time, it is observed that after the formation of the 

 sediment has ceased, the fluid from the surface downwards 

 assumes a violet tint, and this change of colour takes place with 

 a rapidity proportional to the amount of carbonate of ammonia 

 produced by the decomposition of urea. 



Hence, on keeping such urine in a high cylindrical glass, 

 three distinct strata are observed ; lowermost, a violet sediment; 

 in the middle, yellow and nearly clear urine ; and superiorly, 

 a violet or purple turbid layer. 



On shaking the glass, the whole urine assumes a bluish- 

 green tint, because the urrhodin, formed principally at the 

 surface, becomes converted, by agitation with a full supply of 

 atmospheric air, into uroglaucin which, mixing with the central 

 yellow layer of urine develops a green tint. The uroglaucin 

 thus formed ultimately settles as a blue powder on the sides 

 and at the bottom of the vessel. Hence there is obviously no 

 fixed proportion between the quantities of uroglaucin and 

 urrhodin. 



3. If much uroxanthin is present, the crystals of uric acid 

 (separated either spontaneously or by the addition of an acid) 

 have a beautiful blue or amethyst tint. 



4. Lastly, if much uroxanthin is present, it may be recog- 

 nized by the addition of concentrated nitric acid, (ten drops to 

 half an ounce of urine,) which at once communicates a brilliant 

 violet colour to the fluid : if a smaller amount is present, the 

 change of colour is developed more slowly. 



