4.  A saturated solution of ferric alum. 5.  Strong solution of ammonia (sp. gr. 0.880).  The uric acid estimation is conducted as follows:  Place 25 per cent. of urine in a beaker with 1 gramme of sodic bicarbonate.  Add 2 or 3 c.c. of strong ammonia, and then 1 or 2 c.c. of the ammoniated silver solution.  If, on allowing the precipitate caused by the latter reagent to subside, a further precipitate is produced by the addition of more solution, the urine contains an iodide, and silver solution must be added till there is an excess.  The gelatinous urate must now be collected, the following special procedure being necessary:  Prepare an asbestos filter by filling a 4 oz. glass funnel to about one-third with broken glass, and covering this with a bed of asbestos to about a quarter of an inch deep.  This is best managed by shaking the latter in a flask with water until the fibers are thoroughly separated, and then pouring the emulsion so made in separate portions on to the broken glass.  On account of the nature of the precipitate and of the filter, it is necessary to use a Sprengel pump, in order to suck the liquid through.  The small apparatus sold to students by chemical instrument makers will answer the purpose admirably.  Having collected the precipitate of silver urate on the prepared filter, wash it repeatedly with distilled 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,