50 MICROSCOPICAL' DIAGNOSIS. 



Urate of Soda. Urate of soda forms a very common urin- 

 ary deposit, and it is found in the urine of persons in good 

 health. It is held in solution in the healthy urine, but it is 

 frequently precipitated. It appears, generally, in the form of 

 amorphous, irregular, very small granules. It is slightly sol- 

 uble in cold water and is readily soluble in warm water ; sol- 

 uble in the alkalies and in solutions of the alkaline carbon- 

 ates and phosphates. If a solution of pure urate of soda be 

 prepared and the salt allowed to crystallize, it will form small, 

 acicular crystals. The deposit containing urate of soda varies 

 very much in color from a pale, white cloudy precipitate to a 

 pink, brown, or even dark red color. The urine containing 

 this deposit is never turbid when freshly voided ; it is only 

 after the urine has cooled that the cloudiness occurs. Some 

 of the urine is placed in a test-tube and heat applied. If the 

 sediment dissolves, but reappears again on cooling, then it con- 

 sists of the amorphous urates. The urate of soda dissolves at 

 about 100 Fahr., while the urate of ammonia does not dis- 

 solve much below 200 Fahr. After the urine has stood for 

 some time the supernatant fluid is poured off and half its bulk 

 of a solution of potash added. If this causes the mixture to 

 become clear, not viscid, then the urates of soda and ammo- 

 nia enter largely into the composition of the deposit. Filter 

 some of the boiling urine, the nitrate will give a deposit of 

 urates when it is cool. Add some strong acetic acid to the 

 deposit ; it will be dissolved, but will soon recrystallize, which 

 shows under the microscope the rhombic crystals of uric acid. 

 Urate of soda is found in spherical, globular masses from the 

 surface of which project sharp points of uric acid crystals. 



Urate of Ammonia. Under the microscope urate of am- 

 monia appears as an amorphous deposit. When prepared arti- 

 ficially and allowed to crystallize, it forms delicate needle-shaped 

 crystals collected in spherical groups, or in opaque masses with 

 fine projecting points. 



To distinguish between the urates of sodium and potas- 

 sium and the urate of ammonium is very easy under the mi- 

 croscope. The washed sediment is treated with hydrochloric 

 acid and allowed to evaporate on a glass slide. If the de- 

 posit be either urate of sodium or potassium then the micro- 



