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764 URINE.
smallest amount of soluble uranium salt. The solutions necessary for
the titration are: 1. A solution of a uranium salt of which each cubic
centimeter corresponds to 0.005 gram P2O5 and which contains 20.3
grams of uranium oxide per liter. 20 cc. of this solution corresponds
to 0.100 gram P2O5. 2. A solution of sodium acetate. 3. A freshly
prepared solution of potassium ferrocyanide.
The uranium solution is prepared from uranium nitrate or acetate. Dissolve
about 35 grams uranium acetate in water, add some acetic acid to facilitate solu-
tion, and dilute to 1 liter. The strength of this solution is determined by titrat-
ing withasolution of sodium phosphate of known strength (10.085 grams crystallized
salt in 1 liter, which corresponds to 0.010 gram P2 6 in 50 cc). Proceed in the
same way as in the titration of the urine (see below), and correct the solution by
diluting with water, and titrate again until 20 cc. of the uranium solution cor-
responds exactly to 50 cc. of the above phosphate solution.
The sodium-acetate solution should contain 10 grams sodium acetate and
10 grams cone, acetic acid in 100 cc. For each titration 5 cc. of this solution
is used with 50 cc. of the urine.
In performing the titration, mix 50 cc. of filtered urine in a beaker
with 5 cc. of the sodium acetate, cover the beaker with a watch-glass,
and warm over the water-bath. Then allow the uranium solution to
flow in from a burette, and when the precipitate does not seem to increase,
place a drop of the mixture on a porcelain plate with a drop of the potas-
sium-ferrocyanide solution. If the amount of uranium solution added
has not been sufficient, the color will remain pale yellow and more
uranium solution must be added; but as soon as the slightest excess of
uranium solution has been used the color becomes a faint reddish brown.
When this point has been obtained, warm the solution again and add
another drop. If the color remains of the same intensity, the titration
is ended; but if the color varies, add more uranium solution, drop by
drop, until a permanent coloration is obtained after warming, and now
repeat the test with another 50 cc. of the urine. The calculation is so
simple that it is unnecessary to give an example.
In the above manner one determines the total quantity of phosphoric
acid in the urine. If we wish to know the phosphoric acid combined
with alkaline earths and with alkalies, we first determine the total phos-
phoric acid in a portion of the urine and then remove the earthy phos-
phates in another portion by ammonia. The precipitate is collected on
a filter, washed, transferred into a beaker with water, treated with acetic
acid, and dissolved by warming. This solution is now diluted to
50 cc. with water, and 5 cc. sodium-acetate solution added, then
titrated with uranium solution. The difference between the two deter-
minations gives the quantity of phosphoric acid combined with the
alkalies. The results obtained are not quite accurate, as a partial trans-
formation of the monophosphates of the alkaline earths and also calcium
diphosphate into triphosphates of the alkaline earths and ammonium
phosphate takes place on precipitating with ammonia, and the method
gives too high results for the phosphoric acid combined with alkalies and
remaining in solution.
Sulphates. The sulphuric acid of the urine originates only to a very
small extent from the sulphates of the food. A disproportionately
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