THE ORGANIC CONSTITUENTS OF THE URINE. 



475 



THE ORGANIC CONSTITUENTS OF THE URINE. 

 UREA: CO(NH 2 ) 2 . 



Urea, the diamid of CO 2 or carbamid must be considered as the 

 principal end-product of the oxidation of the nitrogen-containing consti- 

 tuents of the body. It has the following extremely simple composi- 

 tion: i atom of carbon dioxid 

 -f- 2 atoms of ammonia i 

 atom of water. It crystallizes 

 in silky-glistening, four-sided 

 prisms, with oblique ends, be- 

 longing to the rhombic system 

 (Fig. 146, i, 2), without water of 

 crystallization ; when rapidly 

 crystallized it forms delicate, 

 white needles. It has no in- 

 fluence upon litmus, is odorless, 

 and of a feeble bitter, cooling 

 taste like that of potassium ni- 

 trate. It is readily soluble in 

 water and in alcohol, but almost 

 insoluble in ether. It is isomeric 

 with ammonium cyanate, from 

 which it develops on evapora- 

 tion through atomic displace- 

 ment. Numerous other modes 

 of artificial preparation are 

 known. 



Heated to a temperature above 

 120 it is decomposed, with the de- 

 velopment of vapors of ammonia, 

 and leaving a vitreous mass of biuret 

 and hydrocyanic acid. In the pro- 

 cess of ammoniacal putrefaction and 

 as a result of treatment with strong 

 mineral acids, of boiling with alka- 

 line hydrates and of heating with 

 water at a temperature of 240 C., 

 it takes up two atoms of water 

 and yields ammonium carbonate: 

 CO(NH 2 ) 2 + 2 H 2 O = CO(ONH 42 ). 

 Brought in contact with nitrous acid 

 it is decomposed into water, carbon 

 dioxid and nitrogen. The last two 

 forms of decomposition have been employed for the quantitative estimation of urea. 



The amount of urea in normal urine is between 2.5 and 3. 2 per cent. 

 Adults excrete daily about from 30 to 40 grams; women less; children 

 relatively more. In accordance with the more active metabolism in the 

 latter, the amount of urea furnished by the weight-unit of the child's 

 body, as compared with that of the adult, is as 1.7 to i. If the body is 

 in a condition of metabolic equilibrium almost as much nitrogen is 

 eliminated in the form of urea as is introduced into the body with the 

 food. 



The amount of urea increases with the amount of proteids in the food, 



FIG. 145. Graduated Buret. 



