URINE. 173 



If this urine is allowed to stand for some hours, there are 

 deposited, partly at the bottom, and partly on the sides of the 

 vessel, (and they are not unfrequently observed on the surface,) 

 small crystals perceptible to the naked eye, whose form, under 

 the microscope, usually appears as delineated in fig. 23 , some- 

 times as in fig. 23 b. Vigla 1 states, that in addition to the crys- 

 tallized uric acid, a portion separates as an amorphous powder. 

 It is only rarely that I have observed uric acid deposited in this 

 amorphous form : the amorphous sediment of a yellow or red- 

 dish colour, which frequently occurs in large quantity in acid 

 urine, may be shown to consist of urate of ammonia, by its ready 

 solubility when the urine is warmed. Rayer, in his work on 

 Diseases of the Kidneys, describes the crystalline form of uric 

 acid, which is represented in fig. 23 c. 



As a further evidence that these crystals are composed of uric 

 acid, they may be tested with nitric acid in the manner explained 

 in page 116. 



A brown or reddish-brown sediment is sometimes observed 

 to be deposited in dark reddish-brown urine, which does not 

 disappear either upon the application of heat or the addition of 

 hydrochloric acid, and in fact in the latter case is rather in- 

 creased. Under the microscope it exhibits the described forms 

 of uric acid. "We also observe, although more rarely, that dark 

 urine will deposit a dense gray or yellow granular sediment, 

 which is shown, by the application of heat, by the addition of 

 hydrochloric acid, and by the microscope, to consist also of uric 

 acid coloured by a peculiarly small quantity of uroerythrin. 

 If the amount of uric acid is to be determined quantita- 

 tively in these instances, we must have regard not merely to 

 the uric acid which is deposited, but also to that which remains 

 in solution. The amount of the whole urine is determined as 

 accurately as possible, the sedimentary uric acid collected on a 

 weighed filter, washed with distilled water, dried, and weighed. 

 Any uric acid that adheres to the glass, and cannot be removed 

 by a feather or a glass rod, or by washing out the glass with 

 water, must be treated with some warm solution of potash, until 

 it is dissolved. 



1 Etude microscopique de 1'urine, eclaree par 1'analyse chymique. (L'Experience, 

 vol. 1, p. 193.) 



