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ESTIMATION OF UKIC ACID. 711
i; e same beaker by the aid of a glass rod and a wash-bottle, withoul
destroying the filter. Now heat i<> boiling 10-20 ce. of the alkali-sulphide
solution, which has previously been diluted with an equal volume of
water, and allow this solution to flow through the above filter into the
beaker containing the silver precipitate; wash with boiling water, and
warm the contents of the beaker on a water-bath for a time, stirring
constantly. After cooling, filter into a porcelain dish, wash the filter
with boiling; water, auidify the filtrate with hydrochloric acid, evaporate
it to about 15 cc, add a few drops more of hydrochloric acid, and allow
it to stand for twenty-four hours. The uric acid which has crystallized
is collected on a small weighed filter, washed with water, alcohol, ether,
and carbon disulphide, dried at 100-110° C, and weighed. For each
10 cc. of aqueous filtrate we must add 0.00048 gram uric acid to the
quantity found directly. Instead of the weighed filter-paper a glass
tube filled with glass wool as described in other handbooks may be sub-
stituted (Ludwig). Too intense or too long continued heating with
the alkali sulphide must be prevented, otherwise a part of the uric acid
may be decomposed.
Salkowski deviates from this procedure by first precipitating the
urine with a magnesium mixture (50 cc. to 200 cc. urine), filling up to
300 cc, and filtering. Of the filtrate, 200 cc. are precipitated by 10-15
cc. of a 3-per cent silver-nitrate solution. The silver precipitate is shaken
with 200-300 cc. of water acidified with a few drops of hydrochloric
acid, decomposed by sulphuretted hydrogen, heated to boiling, the
silver-sulphide precipitate boiled with fresh water, filtered, the filtrate
concentrated to a few cubic centimeters, treated with 5-8 drops of hydro-
chloric acid, and allowed to stand until the next day. According to
Salkowski and Kashiwabara 1
the precipitation with zinc salts can also
be used in the estimation of uric acid.
Hopkins7
methcd is based on the fact that the uric acid is com-
pletely precipitated from the urine as ammonium urate on saturating
with ammonium chloride. The uric acid can either be weighed after
being set free by hydrochloric acid or it can be determined in several
ways—by titration with potassium permanganate or by the Kjeldahl
method. Several modifications of this method have been worked out
by Folin, Folin and Schaffer, Worner, and Jolles.2
Of these methods
we shall describe only that suggested by Folin-Schaffer.
Folin-Schaffer Method. Treat 300 cc. urine with 75 cc. of a solu-
tion containing 500 grams of ammonium sulphate, 5 grams of uranium
acetate, and 60 cc. of 10 per cent acetic acid in a liter, and filter after
five minutes. This removes an unknown constituent of the urine (a
protein substance) which would otherwise contaminate the uric acid.
Take 125 cc. of the filtrate (corresponding to 100 cc. of the urine) and
add 5 cc. of concentrated ammonia. After twenty-four hours the pre-
cipitate is filtered off and washed free from chlorine on the filter by means
of an ammonium-sulphate solution. The precipitate is washed off the
1
Zeitschr. f. physiol. Cheni., 4.
2
Hopkins, Journ. of Path, and Bact., 1893, and Proceed. Roy. Soc, 52; Folin,
Zeitschr. f. physiol. Chem., 24; Folin and Schaffer, ibid., 32; Worner, ibid., 29; Jolles,
ibid., 29; and Wien. med. Wochenschr., 1903.
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