KEACTIONS OF UKINE TO CHEMICAL TESTS. 



385 



and the faintly acid reaction of the urine, which was enough to hold 

 them in solution at ordinary temperatures, is no longer sufficient after 

 the application' of heat, and the phosphates are accordingly thrown 

 down as a deposit. The precipitation from this cause is never very 

 abundant, and it is instantly cleared up again by the addition of a drop 

 of nitric acid, which restores the normal acidity of the urine. The tur- 

 bidity thus produced by boiling, from the precipitation of the earthy 

 phosphates, is not, therefore, usually due to an increased quantity of 

 these salts in the urine, but simply to a deficiency of its acid reaction. 



Diseased urine may also become turbid on boiling, from the coagula- 

 tion of albumen. This is readily distinguished from a precipitation of 

 the earthy phosphates by two facts namely, first, that it may take 

 place in urine which is distinctly acid ; and second, that the addition of 

 nitric acid, which redissolves the phosphatic precipitate, only increases 

 the turbidity which is due to albumen. 



Acids. The addition of the mineral acids to healthy urine produces 

 no immediate visible effect, beyond increasing its acidity and slightly 

 modifying its color. They, however, decompose its urates ; and the uric 

 acid thus set free is slowly deposited in the crystalline form. If nitric 

 or hydrochloric acid be added to fresh filtered urine, in the proportion 

 of about 2 per cent, by volume, and the mixture be allowed to remain 

 at rest for twenty-four or forty-eight hours, the sides and bottom of the 

 vessel become covered with a thinly scattered deposit of uric acid 

 crystals. These crystals have 

 usually the form of transparent 

 rhomboidal plates, or oval 

 laminaj with pointed extremi- 

 ties, and are generally tinged of 

 a yellowish hue by the coloring 

 matter of the urine. They are 

 frequently arranged in radiated 

 clusters, or small spheroidal 

 masses, presenting the appear- 

 ance of minute calculous con- 

 cretions, which vary much in 

 size and regularity, according 

 to the time occupied in their 

 formation. 



The deposit of uric acid crys- 

 tals, thus formed in healthy 

 urine from the addition of a 

 mineral acid, is always scanty in amount, and only becomes visible as 

 a crystalline precipitate after several hours. 



In rare cases, when the urine is loaded with an unusual proportion 

 of the urates, a few drops of nitric acid will produce at once a per- 

 ceptible turbidity, from the precipitation of abundant microscopic crys- 



CRYSTALS OF URIC ACID; deposited from 

 urine, after the addition of nitric acid. " 



