374 PHYSIOLOGICAL CHEMISTRY. 



The quantity of urine passed in a day also varies widely, an 

 adult discharging from 500 to 2300 c.c. in twenty-four hours. 

 The quantity of total solids contained in this urine varies from 

 60 to 120 grams, and of urea from 20 to 40 grams. 



Urea, Carbamide, COH 4 N 2 , or COnf or N=H 2 or 



GO"(NH,) l r Urea is the most important constituent of urine, 

 and is the substance which carries off by far the largest quan- 

 tity of all nitrogen taken in the food. Urea has never yet been 

 found as a product of vegetable life, but is found as a normal 

 constituent of the urine of the mammalia, and in smaller quan- 

 tity in the excrement of birds, fishes, and some reptiles. It 

 occurs also in the blood, muscular tissue, chyle, lymph, bile, 

 perspiration, and many other animal fluids. 



When pure, urea crystallizes from an aqueous solution in 

 colorless prisms; it is odorless, and has a cooling, bitter taste; 

 it easily dissolves in water, the solution having a neutral reac- 

 tion; it fuses when heated to 130, but decomposes at a higher 

 temperature, giving off ammonia gas and water, whilst a num- 

 ber of other substances are formed at the same time. A pure 

 solution of urea does not decompose at ordinary temperature, 

 but on boiling, and especially under pressure, it takes up water, 

 and is decomposed into ammonia or carbon dioxide, or into 

 ammonium carbonate : 



CO(NH 2 ) 2 -f H 2 = CO 2 + 2NH 3 . 



The same decomposition takes place in urine under the influ- 

 ence of a ferment (most likely present in urine, or perhaps de- 

 rived from the air), if the temperature be not too low. 



A solution of urea is decomposed by the action of chlorine 

 or bromine with generation of hydrochloric (or hydrobromic) 

 acid, carbon dioxide, and nitrogen : 



CO(NH 2 ) 2 + 601 + H 2 = 6HC1 + CO 2 + 2N. 



Alkaline hypochlorites or hypobromites cause the similar de- 

 composition, upon which is based the quantitative estimation of 

 urea. 



