Reagent to detect the quantity of Urea in the Urine.—Mr. Liebig
lias recently made known the following prompt and easy way of detect-
ing the quantity of urea in the urine. First prepare a neutral solution
of nitrate of mercury in distilled water, to be kept by itself, and add a
little of this gradually to the urine to be examined, until no further
precipitate takes place. The quantity of the solution necessary to this
result is, to a certain point, the measure of the proportion of urea. But
the precipitate, which is formed, is composed of one equivalent of nitric
acid and three equivalents of bi-oxide of mercury; hence for every
equivalent of urea precipitated, there will be three equivalents of free
nitric acid in the liquid. But the presence of this free acid interferes
with the further formation of the nitrate, so that when precipitation has
ceased, there is still more or less urea which has not entered into the new
combination, and which can only be precipitated after the free acid has
beeD saturated. This is accomplished by a solution of barytes, which
must be gradually added so as not to exceed the limit of saturation. A
fresh quantity of the solution of nitrate of mercury must then be added
to produce a new precipitate; and thus, by the successive additions of
this solution and of the solution of barytes, the whole of the urea con-
tained in the urine will be precipitated. The quantity of the solution
of nitrate of mercury used thus forms a sufficiently accurate measure of
the quantity of urea in the urine.—Bull, de Ther.—From Gaz. des
Hop., 37 Juillet, 1852.