i 5 4 THE MICROSCOPE. 



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

 ment dissolves, but reappears again on cooling, then it consists of 

 the amorphous urates. The urate of soda dissolves at about ioo c 

 Fahr., while the urate of ammonia does not dissolve much below 

 2oo°. 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 ammonia enter largely into the composition of the de- 

 posit. Filter some of the boiling urine, the filtrate 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 sur- 

 face of which project sharp points of uric acid crystals. 



Urate of Ammonia. — Under the microscope urate of ammonia 

 appears as an amorphous deposit. When prepared artificially and 

 allowed to crystallize, it forms delicate needle-shaped crystals col- 

 lected in spherical groups, or in opaque masses with fine projecting 

 points. 



To distinguish between the urates of sodium and potassium 

 and the urate of ammonium is very easy under the microscope. The 

 washed sediment is treated with hydrochloric acid and allowed to 

 evaporate on a glass slide. If the deposit be either urate of sodium 

 or potassium then the microscope will show, besides the crystals of 

 uric acid, the cube crystals of the chloride of sodium and potassium. 

 If the deposit be urate of ammonia then the leafy crystals of 

 chloride of ammonium will be found. If the urate of ammonia de- 

 posit be treated with nitric acid and then filtered, and the deposit 

 allowed to dry on the filter, and if to this dry deposit ammonia be 

 added, a beautiful purple or violet-red color will be produced. This 

 is known as the "murexide test." 



Oxalate of Lime. — Urine containing oxalate of lime has usually 

 an acid reaction and a high color. The deposit is scanty and gen- 

 erally conjoined with uric acid and the urates. After the urine has 

 been allowed to stand for a short time a drop of the colorless, 

 mucous-like deposit is placed on a slide and examined with a high 

 power of the microscope. The drop of urine to be examined should 

 be taken from a little above the bottom of the vessel, for the mucous 

 deposit at the bottom appears to hold these crystals in its upper 



