[Illustration]

Among the number of instruments which have been introduced for the
purpose of conveniently measuring the evolved gas, that of Gerrard, an
illustration of which we give, is one of the simplest, cheapest, and
best. The ureometer tube, _b_, is connected at the base with a movable
reservoir, _c_, and by means of a rubber tube passing through a cork
at the top to the generating bottle, _a_. To use the apparatus, fill
_b_ to zero with water and have the reservoir placed so high that it
contains only an inch or so of the liquid. Replace the cork with
attached tube tightly in _b_. Now pour into the generating bottle 25
c.c. of a solution prepared by dissolving 1 part of caustic soda in 2½
parts of distilled water, and dexterously break in the liquid a tube
containing 2.2 c.c. of bromine. The tubes will be found very
convenient, obviating entirely the suffocating fumes diffused in the
act of measuring bromine. Allow to stand in the solution of sodic
hypobromite thus prepared a test tube containing exactly 5 c.c. of the
urine under examination. Cork the bottle as shown in the illustration,
see that the water is at zero, and that the liquid in the reservoir is
at the same level, and then allow the urine to gradually mix with the
hypobromite solution. Cool the evolved gas by placing the bottle in
cold water, adjust the levels of the water in the tube and reservoir
(to obviate a correction for pressure), and read off the percentage of
urea in terms of which the tube is graduated. Stale urine, the urea of
which has largely been converted into ammonic carbonate, still yields
a very fair result, that salt being also completely split up by the
powerful oxidant employed. Should the urine contain albumen, it is
advisable to remove it by boiling and filtering, as, although only
slowly decomposed by the hypobromite solution, it communicates to the
liquid such a tendency to froth that the disengagement of the nitrogen