URINE 



391 



The biuret may be dissolved in water and a reddish-violet color obtained 

 by treating the aqueous solution with copper sulphate and potassium 

 hydroxide (see Biuret Test, page 99). Certain hypochlorites or hypo- 

 bromites in alkaline solution have the power of decomposing urea into 

 nitrogen, carbon dioxide, and water. Sodium hypobromite brings 

 about this decomposition, as follows: 



CO(NH 2 ) 2 +3NaOBr->3NaBr+N 2 +C0 2 +2H 2 O. 

 This property forms the basis for a clinical quantitative determination 

 of urea which was formerly in use, but which has been discarded because 

 of inaccuracies. 



The soy bean and jack bean have been shown to contain an enzyme 

 called urease which has the power to decompose urea with the liberation 

 of ammonia. 1 This fact is made use of in the quantitative determina- 

 tion of urea (see Chapter XXVII). 



FIG. 124. UREA NITRATE. 



Urea has the power of forming crystalline compounds with certain 

 acids; urea nitrate and urea oxalate are the most important of these 

 compounds. Urea nitrate, CO(NH 2 ) 2 .HN0 8 , crystallizes in colorless, 

 rhombic or six-sided tiles (Fig. 124, above), which are easily soluble in 

 water. Urea oxalate, [CO(NH 2 ) 2 ] 2 .H 2 C 2 4 , crystallizes in the form 

 of rhombic or six-sided prisms or plates (Fig. 126, page 393): the 

 oxalate differs from the nitrate in being somewhat less soluble in 

 water. The formation of the nitrate and oxalate and the decomposition 

 of urea by the enzyme urease are the most satisfactory methods for the 

 detection of urea. 



A decrease in the excretion of urea is observed in many diseases in 

 which the diet is much reduced and in some disorders as a result of 

 1 Takeuchi: Jour. College of Agr., Tokyo, 1909, Part I. 



