URINE 377 



one of the methods in common use for the quantitative determination of urea. 

 Write the equation showing the decomposition of urea by sodium hypobromite. 



9. Furfural Test. To a few crystals of urea in a small porcelain dish add 1-2 

 drops of a concentrated aqueous solution of furfural and 1-2 drops of concentrated 

 hydrochloric acid. Note the appearance of a yellow color which gradually changes 

 into a purple. Allantoin also responds to this test (see page 392). 



It is claimed that all ammonium compounds and all compounds 

 containing the amino ( NH^) group yield nitrogen when treated with 

 hypobromite as in this test. 



HN CO 



I I 



URIC ACID, OC C-NH 



>CO. 

 HN C HN 



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 excreted 

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

 larly under certain dietary and pathological conditions. It has been 

 shown, however, 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. On a purine-free diet the uric 

 acid output may be o. 1-0.5 gram per day, whereas a high purine diet may 

 I yield a daily output of 2 grams. Uric acid is a diureide and consequently 

 upon oxidation may yield two molecules of urea. It acts as a weak 

 dibasic acid and forms two classes of salts, neutral and acid. The neutral 

 'potassium and lithium urates are the most easily soluble of the alkali 

 alts; the ammonium urate is difficultly soluble. The acid-alkali urates 

 ire more insoluble and form the major portion of the sediment which 

 eparates upon cooling the concentrated urine; the alkaline earth urates 

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

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

 leposits in crystalline form. This property forms the basis of one of 

 he older methods for the quantitative determination of uric acid 

 Heintz Method, Chapter XXVI). 



Uric acid is very closely related to the purine bases as may be seen 

 rom a comparison of its structural formula with those of the purine 

 )ases given on page 127. According to the purine nomenclature it is 

 lesignated 2-6-8- trioxypurine. Uric acid forms the principal end- 

 product of the nitrogenous metabolism of birds and scaly amphibians; 

 n the human organism it occupies the fourth position inasmuch as here 



