268 



PHYSIOLOGICAL CHEMISTRY. 



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

 tained by treating the aqueous solution with cupric sulphate and 

 potassium hydroxide (see Biuret Test, p. 92). Certain hypo- 

 chlorites or hypobromites 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 



2H 2 0. 



This property forms the basis for a clinical quantitative determina- 

 tion of urea (see page 374). 



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 -HNO 3 , crystal- 

 lizes in colorless, rhombic or six-sided tiles (Fig. 86, below), which 

 are easily soluble in water. Urea oxalate,, 2 'CO(NH 2 ) 2 -HoCoO^ 

 crystallizes in the form of rhombic or six-sided prisms or plates 

 (Fig. 88, p. 270) : the oxalate differs from the nitrate in being 

 somewhat less soluble in water. 



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 alterations in metabolism, e. g., myxcedema, and in others as a 

 result of changes in excretion, as in severe and advanced kidney dis- 







FIG. 86. 



UREA NITRATE. 



ease. A pathological increase is found in a large proportion of 

 diseases which are associated with a toxic state. 



