474 HANDBOOK OF PHYSIOLOGY. 



out undergoing decomposition; at a still higher temperature ebullition 

 takes place, and carbonate of ammonium sublimes. When heated with 

 water in a sealed tube to 100 C., urea splits up into carbonic acid and 

 ammonia; when heated to a high temperature urea loses ammonia and 

 first yields biuret, C 2 H 5 N 3 2 , which gives a rose color with caustic potash 

 and a trace of copper sulphate, and afterward cyanuric acid, C 3 H 3 3 N3, 

 which gives a violet color with caustic potash and a trace of copper sul- 

 phate. It is decomposed by sodium hypochlorite or hypobromite or by 

 nitrous acid, with evolution of X. It forms compounds with acids, of 

 which the chief are urea hydrochloride, CILt^O.HCL; urea nitrate, 

 CH 4 N 2 OHN0 3 ; and urea phosphate, CH 4 N 2 O.H 3 P0 4 . It forms com- 

 pounds with metals such as HgO.CH 4 K 2 0; with silver CH 2 N 2 OAg.;; 

 and with salts such as HgCl 2 and HgN0 3 . 



Chemical Nature. Urea is i so me He with ammonium cyanate 

 NH 4 ,CN(X It was first of all artificially prepared from that substance. 



It may also be produced artificially by treating carbonyl chloride (CO C1 2 ) 

 withammonia; or by heating ethyl carbonate with ammonia CO + 2 NH 3 = 



CON 2 H 4 2C 2 H 6 O ; by heating ammonium carbonate CO QNH 4 = 



H 2 O ; by adding water to cyanamide CN. NH 2 , or by evaporating ammonium 



cyanate in aqueous solution. 



It is usually considered to be a diamide of carbonic acid, in other 

 words, carbonic acid, CO (OH)' 2 , with two of hydroxyl, (OH)' 2 , replaced 

 by two of amidogen (NH 2 )' 2 . It may also be written as if it were a 

 monamide of carbamic acid (COOHNH 2 ), thus CONH 2 .NH 2 ; one of 

 amidogen, NH 2 , in the latter replacing one of hydroxyl in the former. 

 Decomposition of the urea with development of ammonium carbonate 

 takes place from the action of the bacteria (micrococcus ureae), when 

 urine is kept for some days after being voided, and explains the ammo- 

 niacal odor then evolved. The urea is sometimes decomposed before it 

 leaves the bladder, when the mucous membrane is diseased, and the 

 mucus secreted by it is abundant; but decomposition does not often occur 

 unless atmospheric germs have had access to the urine. 



Variations in the Quantity excreted. The quantity of urea excreted 

 is, like that of the urine itself, subject to considerable variation. For 

 a healthy adult about 512.4 grains (about 33.18 grms.) per diem may be 

 taken as rather a high average. Its percentage in healthy urine is from 

 1.5 to 2.5. Its amount is materially influenced by diet, being greater 

 when animal food is exclusively used, less when the diet is mixed, and 

 least of all with a vegetable diet. As a rule, men excrete a larger quan- 

 tity than women, and persons in the middle periods of life a larger 

 quantity than infants or old people. The quantity of urea excreted by 



