URIC ACID, URATES, ETC. 103 



When the urine is passed it is quite clear, but on standing for 

 a time it becomes turbid, and a copious reddish -yellow some- 

 times like pea soup or purplish precipitate occurs, because 

 urates are more soluble in warm water than in cold ; and when 

 there is only a small quantity of water to hold the urates in 

 solution, on the urine cooling they are precipitated. Their 

 occurrence is favoured by an acid reaction, a concentrated condi- 

 tion of the urine, and a low temperature. 



The urates deposited in urine consist chiefly of sodic urate, 

 mixed with a small amount of ammonium urate. 



5. Tests. Secure a specimen of " urates " in urine. 



(a.) Observe the naked-eye characters. The deposit is 

 usually copious = yellowish-pink, reddish, or even shading 

 into purple. The deposit moves freely on moving the 

 vessel, and its upper border is fairly well denned. 



(6.) Place some in a test-tube. Heat gently the upper 

 stratum. It becomes clear, and on heating the whole mass 

 of fluid, it also becomes clear, as the urates are dissolved by 

 the warm liquid. 



(c.) Place some of the deposit on a glass slide, add a drop 

 of hydrochloric acid, and uric acid is deposited in one or 

 more of its many crystalline forms. Examine the crystals 

 microscopically. 



(d.) Examine the deposit microscopically. The urates are 

 usually " amorphous," but the urate of soda may occur in 

 the form of small spheres covered with spines, and the 

 ammonium urate, of spherules often united together (Fig. 

 17, 6). 



(e.) Make a saturated solution of uric acid in caustic 

 soda. Place a drop of the mixture 

 on a slide, allow it to evaporate. 

 Examine it microscopically, when 

 the urate of soda in the form of 

 spheres covered with spines will be 

 obtained. (Fig. 27.) 



(f.) The same result as in (e.) Fig. 27. Urate of soda, 

 is obtained by dissolving the ordi- 

 nary deposit of urates with caustic soda, and allowing 

 some of it to evaporate on a slide. 



