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708 URINE.
in the dissociation on the addition of strong acids, uric acid is soluble
with difficulty in the presence of mineral acids. It is soluble in a warm
solution of sodium diphosphate, and in the presence of an excess of uric
acid, monophosphate and acid urate are produced. It is ordinarily-
assumed that sodium diphosphate forms a solvent for the uric acid in
the urine, while according to Gudzent this is not dissolved by the mono-
phosphate. Rudel l
believes that urea is an important solvent, but
this view has not been confirmed by the observations of His and Paul.
Uric acid is not only dissolved by alkalies and alkali carbonates, but also
by several organic bases, such as ethylamine and propylamine, piperidine
and piperazine. Uric acid can form supersaturated solutions with alkalies
and these, according to Schade and Boden 2
contain colloidal uric acid
and they may gelatinize on cooling as well as under other conditions.
Uric acid dissolves, without decomposing, in concentrated sulphuric
acid. It is completely precipitated from the urine by picric acid (Jaffe3
).
Uric acid gives a chocolate-brown precipitate with phosphotungstic
acid in the presence of hydrochloric acid.4
Uric acid is dibasic and consequently forms two series of salts, neu-
tral and acid. Of the alkali urates the lithium salts are the most soluble
and the acid ammonium salt is the most insoluble. The acid alkali
urates are very insoluble and separate as a sediment {sedimentum later-
itium) from concentrated urine on cooling. According to Gudzent
1 liter of water at 18° C. dissolves (as primary salts) 1.5313 grams
potassium, 0.8328 gram sodium, and 0.4141 gram ammonium urate,
and at 37° C. 2.7002, 1.5043 and 0.7413 grams of the respective urates.5
The salts of the alkaline earths are soluble with great difficulty. The
above solubilities apply only, in Gudzent’s 6 experience, to the freshly
prepared solution, as the solubility to a certain limit gradually dimin-
ishes, due to intramolecular transposition (change of the uric acid from
the lactam-form into the lactim-form)
.
Besides the mono- and diurates also " quadriurates " have been described
and these occur in the excrement of snakes and birds and in the sedimentum
1
His, Jr., and Paul, Zeitschr. f. physiol. Chem., 31; Smale, Centralbl. f. physiol.,
D; Rudel, Arch. f. exp. Path. u. Pharra., 30; Gudzent, Zeitschr. f. physiol. Chem.,
60 and 63.
2
Zeitschr. f. physiol. Chem., 83.
3
IUd., 10.
4
In regard to the combinations of formaldehyde and uric acid, see Nicolaier,
Deutsch. Arch. f. klin. Med., 89 (1906).
6
Determinations of the solubility of the monourates in serum have been made by
Gudzent, Zeitschr. f. physiol. Chem., 63. See also Bechhold and Ziegler, Bioch. Zeitschr.,
20.
8
Zeitschr. f. physiol. Chem., 56 and 60.
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