THE FORMATION OF UREA 381 



Urea is colorless when pure; when impure it may be yellow or brown. 

 It is without smell and of a cooling niter-like taste. It has neither an acid 

 nor an alkaline reaction, and deliquesces in a moist and warm atmosphere. 

 At 15 C. it requires for its solution less than its own weight of water. It is 

 soluble in all proportions of boiling water, and requires five times its weight 

 of cold alcohol for its solution. It is insoluble in ether. At 120 C. it melts 

 without undergoing decomposition; and at a still higher temperature ebulli- 

 tion takes place, and carbonate of ammonium sublimes. 



Urea is decomposed by sodium hypochlorite of hypobromite or by nitrous 

 acid, with evolution of nitrogen. It forms compounds with acids, of which 

 the chief are urea hydrochloride, CON 2 H 4 .HCL; urea nitrate, CON 2 H 4 .- 

 HNO 3 ; and urea phosphate, CON 2 H 4 .H 3 PO 4 . It forms compounds with 



FIG. 293. Crystals of Urea Nitrate. FIG. 294. Crystals of Urea Oxalate. 



metals such as HgO.CON 2 H 4 , with silver, CON 2 H 2 Ag 2 . Urea is isomeric 

 with ammonium cyanate, NH 4 CNO, and was first prepared artificially from 

 that substance. 



The Formation of Urea. Proteids in the body have their nitrog- 

 enous moiety broken down to ammonia, by what Folin considers essentially 

 a series of hydrolytic cleavages, which is then built up into urea, as described 

 more fully in the chapter on Metabolism. This last step is essentially a 

 synthetic process which, from the fact that ammonium carbonate introduced 

 into the blood is eliminated as urea, may be supposed to occur as follows: 



NH 2 NH 2 



/ / 



CO H 2 O =CO 



\ \ 



ONH 4 NH 2 



Ammonium 



Carbamate Urea 



Urea is present in varying amounts in all organs and fluids of the body, as 

 shown by the following determinations of Schoendorff on the dog: 



Per cent of 

 Organ. Urea. 



Blood 0.116 



Muscle 0.080 



Kidney o. 670 



Liver 0.112 



Heart o. 173 



Brain o. 128 



Spleen 0.122 



