URINE. 271 



8. Decomposition by Sodium-Hypobromite. Into a mixture 

 of 3 c.c. of concentrated sodium hydroxide solution and 2 c.c. of 

 bromine water in a test-tube introduce a crystal of urea or a small 

 amount of a concentrated solution of urea. Through the influence 

 of the sodium-hypobromite, NaOBr, the urea is decomposed and 

 carbon dioxide and nitrogen are liberated. The carbon dioxide is 

 absorbed by the excess of sodium hydroxide while the nitrogen is 

 evolved and causes the marked effervescence observed. This 

 property forms the basis for one of the methods in common use for 

 the quantitative determination of urea. Write the equation show- 

 ing the decomposition of urea by sodium-hypobromite. 



9. Furfurol Test. To a few crystals of urea in a small por- 

 celain dish add 1-2 drops of a concentrated aqueous solution of 

 furfurol and 1-2 drops of a concentrated hydrochloric acid. Note 

 the appearance of a yellow color which gradually changes into 

 a purple. Allantoin also responds to this test (see page 287). 



HN-C 

 URIC ACID, OC C-NH 



II 



1 1 > 



N-C-NH 



Uric acid is one of the most important of the constituents of the 

 urine. It is generally stated that normally about 0.7 gram is ex- 

 creted in 24 hours but that this amount is subject to wide variations, 

 particularly under certain dietary and pathological conditions. 

 Very recently it has been shown that the average daily excretion of 

 uric acid for ten men ranging in age from 19 to 29 years and fed a 

 normal mixed diet was 0.597 gram, a value somewhat lower than 

 the generally accepted average of 0.7 gram for such a period. 

 Uric acid is a diureide and consequently upon oxidation yields two 

 molecules of urea. It acts as a weak dibasic acid and forms two 

 classes of salts, neutral and acid. The neutral potassium and lith- 

 ium urates are the most easily soluble of the alkali salts; the am- 

 monium urate is difficultly soluble. The acid-alkali urates are more 

 insoluble and form the major portion of the sediment which sepa- 

 rates upon cooling concentrated urine ; the alkaline earth urates are 

 very insoluble. Ordinarily uric acid occurs in the urine in the form 

 of urates and upon acidifying the liquid the uric acid is liberated 

 and deposits in crystalline form. This property forms the basis 



