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ESTIMATION OF PURINE BASES. 715
Quantitative Estimation of Purine Bases according to Salkowski.1
400-600 cc. of the urine free from protein are first precipitated by mag-
nesia mixture, and then by a 3-per cent silver-nitrate solution as described
on page 710. The thoroughly washed silver precipitate is decomposed
by sulphuretted hydrogen after being suspended in 600-800 cc. of water
with the addition of a few drops of hydrochloric acid. It is heated to
boiling and filtered hot, and finally evaporated to dryness on the water-
bath. The residue is extracted with 20-30 cc. of hot 3-per cent sul-
phuric acid and allowed to stand twenty-four hours; the uric acid is
filtered off, washed, the filtrate made ammoniacal, and the purine bodies
again precipitated by silver nitrate, the precipitate collected on a small
chlorine-free filter, washed thoroughly, dried, carefully incinerated,
the ash dissolved in nitric acid, and titrated with ammonium sulpho-
cyanide according to Volhard’s method. The ammonium-sulphocyanide
solution should contain 1.2-1.4 grams per liter, and its strength should
be determined by a silver-nitrate solution: 1 part silver corresponds
to 0.277 gram nitrogen x>f purine bases, or to 0.7381 gram purine bases.
By this method the uric-acid and purine bases can be simultaneously
determined in the same portion of urine.2
Malfatti 3
determines the nitrogen of the purine bases in the hydrochloric-
acid filtrate from the separated uric acid. This filtrate is evaporated with mag-
nesia until all the ammonia has been expelled and the residue used for the Kjel-
dahl determination.
The nitrogen of the purine bases is also determined as the difference between
the uric-acid nitrogen and the total nitrogen of the purine bodies of the silver
precipitate (Camerer, Arxstein4
). Certain objections have been raised
against this method but they can be overcome by using the modified method
as suggested by Kexxaway.5
According to the method of Kruger and Schmid 6
the uric acid and the
purine bases are precipitated as a cuprous compound by copper-sulphate solu-
tion and sodium bisulphite. The precipitate is decomposed in sufficient water
by sodium sulphide, and the uric acid precipitated from the concentrated filtrate
with hydrochloric acid, and the purine bases again precipitated from this nitrate
as cuprous or silver compounds. Finally, the nitrogen in the uric-acid part and
the part containing the mixture of purine bases is estimated.
Oxaluric Acid, C3 HA204 = (COX2 H3 ).CO.COOH. This acid, whose relation
to uric acid and urea has been spoken of above, does not always occur in the
urine, and then only in traces as the ammonium salt. This salt is not directly
precipitated by CaCla and XH3 , but on boiling it is decomposed into urea and
oxalate. In preparing oxaluric acid from urine the latter is filtered through
animal charcoal. The oxalurate retained by the charcoal may be obtained by
boiling; with alcohol.
1
Pfluger’s Arch., 69.
1
In regard to the details we refer the reader to the original paper.
3
Centralbl. f. innere Med., 1897.
4
Camerer, Zeitschr. f. Biologie, 26 and 28; Arnstein, Zeitschr. f. physiol. Chem., 23.
8
Journ. of Physiol., 39.
6
Zeitschr. f. physiol. Chem., 45, and Hoppe-Sevler-Thierfelder’s Handbuch, 8.
Aufl., 590.
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