686 UKINE. 



of acid occurs after the cutting out of the liver has been especially shown 

 by SALASKIN and ZALESKi. 1 



For the present we are not justified in the statement that the liver 

 is the only organ in which urea is formed, and only continued investiga- 

 tion can yield further information as to the extent and importance of the 

 formation of urea, from ammonium compounds, in the liver. 



Properties and Reactions of Urea. Urea crystallizes in needles or in 

 long, colorless, four-sided, often hollow, anhydrous rhombic prisms. 

 It has a neutral reaction, and produces a cooling sensation on the tongue 

 like saltpeter. It melts at 132 C. At ordinary temperatures it dis- 

 solves in an equal weight of water and in five parts alcohol; it requires 

 one part boiling alcohol for solution; it is insoluble in alcohol-free anhy- 

 drous ether, and also in chloroform. If urea in substance is heated in a 

 test-tube, it melts, decomposes, gives off ammonia, and finally leaves a 

 non-transparent white residue which, among other substances, contains 

 cyanuric acid and biuret, which latter dissolves in water, giving a beautiful 

 reddish-violet liquid with copper sulphate and alkali (biuret reaction). 

 On heating with baryta-water or caustic alkali, also in the so-called 

 alkaline fermentation of urine caused by micro-organisms, urea splits 

 into carbon dioxide and ammonia with the addition of water. The 

 same decomposition products are produced when urea is heated with 

 concentrated sulphuric acid. An alkaline solution of sodium hypo- 

 bromite decomposes urea into nitrogen, carbon dioxide, and water accord- 

 ing to the equation 



With a concentrated solution of furfuroi and hydrochloric acid, urea 

 in substance gives a coloration passing from yellow, green, blue, to violet, 

 and then after a few minutes beautiful purple-violet (SCHIFF'S reaction). 

 According to HuppERT 2 the test is best performed by taking 2 cc. of a 

 concentrated furfuroi solution, 4-6 drops of concentrated hydrochloric 

 acid, and adding to this mixture, which must not be red, a small crystal 

 of urea. A deep violet coloration appears in a few minutes. 



Urea forms crystalline compounds with many acids. Among these 

 the one with nitric acid and the one with oxalic acid are the most 

 important. 



UREA NITRATE, CO(NH 2 )2.HN03. On crystallizing quickly, this 

 compound forms thin rhombic or six-sided overlapping tiles, or colorless 



1 Zeitschr. f. physiol. Chem., 29. 



2 Huppert-Neubauer, Analyse des Hams, 10. Aufl., 296. 



