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686 URINE.
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
CON2H4+3NaOBr = 3NaBr-r-C02+2H20+N2 .
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(NH2)2-HN03. On crystallizing quickly this
compound forms thin rhombic or six-sided overlapping tiles, or colorless
1
Zeitschr. f. physiol. Chem., 29.
1
Huppert-Neubauer, Analyse des Harns, 10. Aufl., 296.
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