water, until the washings cease to become opalescent with a soluble
chloride. Now dissolve the pure urate by washing it through the filter
with a few cubic centimeters of the special nitric acid. The process
is carried out thus: Add to the liquid in the beaker a few drops of
the ferric-alum solution to act as an indicator, and from a burette
carefully drop in centinormal ammonic thiocyanate until a permanent
red coloration of ferric thiocyanate barely appears. The number of
cubic centimeters used of the thiocyanate solution multiplied by
0.00168 gives the amount of uric acid in the 25 c.c. One milligramme
may be added to compensate for loss, and the whole multiplied by four
gives the percentage of uric acid in the urine. The whole process
depends on the fact that argentic urate fails to dissolve in ammonia,
but is soluble in nitric acid, and is thus easily obtained in the pure
state. By determining the amount of combined silver, the percentage of
uric acid can readily be calculated. The addition of sodic bicarbonate
prevents the otherwise inevitable reduction of the silver salt.


BILE.

In diseases affecting the liver, the urine frequently becomes
contaminated with biliary constituents. If the coloring matter of bile
is present (_bilirubin_, etc.), the liquid is darkened considerably in
tint, and may assume various shades of brown or green. Should the
color be decided, the fluid will be found to foam strongly on shaking,
and white blotting-paper will be stained by it yellow or greenish.
These characters point to the presence of bile in fair quantity, and
it is only necessary to apply a single confirmatory test. Allow some
of the urine to flow carefully, according to Heller's method, over a
couple of drachms of yellow nitric acid (i.e., acid containing traces