584 



THE URINE 



[CH. XXXIX. 



that this was the first organic substance which was prepared syntheti- 

 cally by chemists.* 



When crystallised out from the urine it is found to be readily 

 soluble both in water and alcohol : it has a saltish taste, and is neutral 



to litmus paper. The form of its 

 crystals is shown in fig. 378. 



When treated with nitric acid, 

 nitrate of urea (CON 2 H 4 . HN0 3 ) is 

 formed ; this crystallises in octahedra, 

 lozenge-shaped tablets or hexagons (fig. 

 379). When treated with oxalic acid, 

 flat or prismatic crystals of urea oxa- 

 late(CON 2 H 4 .H 2 2 4 + H 2 0) are formed 

 (fig. 880). 



These crystals may be readily ob- 

 lined by adding excess of 



FIG. 378. Crystals of urea. 



tained by adding excess of the respective 

 acids to urine which has been concen- 

 trated to a third or a quarter of its bulk. 

 Under the influence of a micro-organism, the niicrococcus 

 urese, which grows readily in stale urine, urea takes up water, 

 and is converted into ammonium carbonate [CON 2 H 4 + 2H 2 = 

 (NH 4 ) 2 C0 3 ]. Hence the ammoniacal odour of putrid urine. 



By means of nitrous acid, urea is broken up into carbonic acid, 

 water, and nitrogen, CONH + 2HN0 = C0 + 3H0 + 2N. The 



FIG. 379. Crystals of urea nitrate. 



FIG. 380. Crystals of urea oxalate. 



evolution of gas bubbles which takes place on the addition of fuming 

 nitric acid may be used as a test for urea. 



Hypobromite of soda decomposes urea in the following way : 



CON 2 H 4 + SNaBrO = CO 



N 



[Urea.] 



2H 9 O 



[Sodium [Carbonic [Nitrogen.] [Water.] 



hypobromite.] acid.] 



SNaBr. 



[Sodium 

 bromide.] 



This reaction is important, for on it one of the readiest methods 

 for estimating urea depends. There have been various pieces of 



* Meldola has pointed out that the English chemist Henry Hennell prepared 

 alcohol from olefiant gas simultaneously with Wohler's synthesis of urea. The 

 honour of founding the science of organic chemistry must, therefore, be shared 

 between the two men. 



