UREA. 153 



from this. The absolute weight varies between 20 and 40 

 grammes daily, being somewhat less for a woman than for 

 a man. In round numbers, we can say that it is about one 

 ounce in twenty-four hours for the adult male. 



Urea crystallizes in long, colorless, rhombic prisms. 

 It is easily soluble in alcohol and in water; hence it never 

 forms a sediment. It forms double compounds with acids, 

 some .of which, like the. nitric and oxalic acid compounds 

 are not easily soluble, and are used in separating the urea 

 from urine. It forms similar insoluble compounds with 

 many salts of the heavy metals, mercury, copper, etc. 



When urea is brought into contact with a hypobro- 

 mite or a hypochlorite, it is decomposed into carbon dioxid, 

 nitrogen, and water: 



CO(NH) 2 + 3NaOBr = 3NaBr + C0 2 + N 2 + 2H 2 0. 



This decomposition is made use of to determine the 

 amount of urea in urine by measuring the volume of the 

 nitrogen set free. There are a great number of modifica- 

 tions in form of the apparatus employed, Hiifner's, 

 Doremus's, Squibb's, and many others, all based upon the 

 same principle. They do not give absolutely accurate re- 

 sults, but are sufficiently exact for clinical tests, and have 

 the advantage of requiring but a short time for their exe- 

 cution. Where it is desirable to learn accurately the 

 amount of nitrogenous compounds excreted, it is best to 

 find the total nitrogen by KjeldahPs method. The solu- 

 tion of sodium hypobromite should be freshly prepared 

 from bromin and sodium hydrate, as it decomposes on 

 standing. 



Doremus's ureometer for determining the percentage 

 of urea in urine consists of a short graduated tube closed 

 at the upper end. Below it is bent upward and expands 



