URINE. 93 



inter-reaction between the acid phosphates and the biurates 

 in which quadriurates are formed; the latter immediately 

 break up into uric acid and biurate, and the former is 

 thrown out of solution. 



Pure uric acid forms a white powder. As it separates 

 out from urine in the presence of impurities, it assumes a great 

 diversity of crystalline forms, all of which are characteristic, 

 however; the crystals are always tinged with pigment de- 

 rived from the urine. 



Uric acid is practically insoluble in hot and cold water, 

 alcohol or ether. The sodium, potassium, and lithium salts 

 are soluble, especially the latter. The ammonium, calcium, 

 and magnesium salts are insoluble. The quantity excreted 

 in 24 hours varies according to the individual and the diet, 

 but usually amounts to 0.5 1.0 grms. (average 0.7 grm.). 

 If urine is made sufficiently acid with HC1 to react strongly 

 to litmus (about 30 c.c. cone. HC1 to the liter) and allowed 

 to stand, uric acid will separate out in crystals of a dark 

 red color. 



For the following tests make use of the uric acid prepared 

 in this way: 



(a) Examine the crystals under the microscope. Sketch 

 as large a variety as can be found. 



(6) Test the solubility in water, NaOH and NH 4 OH. 



(c) Dissolve some of the crystals in a few c.c. of dilute 

 NaOH and then add NH 4 C1 to saturation. What is the pre- 

 cipitate? 



(d) Heat a crystal on platinum-foil. 



(e) Dissolve some uric acid in a small quantity of dilute 

 NaOH. Add concentrated H 2 S0 4 carefully, drop by drop, 

 until the solution is too warm to touch; then add a few c.c. 

 of potassium permanganate solution. What is the reaction 

 which takes place? 



