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PROPERTIES OF URIC ACID. 709
lateritium. Whether these quadriurates, which have recently been studied
by Ringer, Kohler and Schmutzer, 1
are chemical combinations of 2 molecules
uric acid and 1 atom of K or Xa or are mixtures, so-called solid solutions of uric
acid in monourates, is still a disputed question.
If a little uric acid in substance is treated on a porcelain dish with
a few drops of nitric acid, the uric acid dissolves on wanning, with a
strong development of gas, and after thoroughly drying on the water-
bath a beautiful red residue is obtained, which turns a purple-red (ammo-
nium purpurate or murexide) on the addition of a little ammonia. If
instead of the ammonia we add a little caustic soda (after cooling), the
color becomes deeper blue or bluish violet. This color disappears quickly
on warming, differing from certain purine bodies. This reaction is called
the murexide test.
A solution of phosphotungstic acid, prepared according to certain
directions, gives with a solution of uric acid, when treated with an excess
of sodium carbonate, a beautiful blue solution. This extremely delicate
reaction (1:500,000) was suggested by Folin and Denis.2
Uric acid does not reduce an alkaline solution of bismuth, while, on
the contrary, it reduces an alkaline cupric-hydroxide solution. In the
presence of only a little copper salt we obtain a white precipitate consist-
ing of cuprous urate. In the presence of more copper salt red cuprous
oxide separates. The compound of uric acid with cuprous oxide is formed
wr
hen copper salts are reduced by glucose or a bisulphite in alkaline
solution in the presence of a sufficient amount of urate.
If a solution of uric acid in water containing alkali carbonate is treated
with magnesium mixture and then a silver-nitrate solution added, a
gelatinous precipitate of silver-magnesium urate is formed. If a drop
of uric acid dissolved in sodium carbonate is placed on a piece of filter-
paper which has been previously treated with silver-nitrate solution,
a reduction of silver oxide occurs, producing a brownish-black or, in the
presence of only 0.002 milligram of uric acid, a yellow spot (Schiff’s
test)
.
If a weak alkaline solution of uric acid in water is treated with a soluble zinc
salt, a white precipitate is produced, which on the filter in the presence of alkali
is oxidized by the air, and becomes sky-blue in color, especially in sunlight.
Potassium persulphate causes a blue coloration immediately’ (Ganassini’s
reaction 3
).
The precipitation of free uric acid from its alkali salts by means of acids can
be prevented to some extent by the presence of thymic acid or nucleic acid (Goto).
According to Seo we are here dealing with combinations of 1 molecule nucleic
1
Ringer, ibid., 67 (literature) and 75; Kohler, ibid., 70 and 72; Ringer and Schmut-
zer, ibid., 82.
s
Journ. of biol. Chem., 12.
* Cited f. Bioch. Centralbl., 8, 250.
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