9 " 18.9 " 19.0 " 18.8 " 17.5 "
As in the titration with arsenates, an excess is dangerous to the assay;
a definite quantity (5 c.c.) should, therefore, be used.
~Effect of Foreign Salts.~--Besides the sodium acetate, &c., added, the
only salts likely to be present are those of ammonia and magnesia. In
three experiments, in one of which no foreign salts were introduced,
while in the other two 5 grams of ammonic chloride and of magnesium
sulphate respectively were added, there were required:--
With ammonic chloride 18.8 c.c. "Uranium" solution
With magnesium sulphate 19.0 " "
Without foreign salts 18.9 " "
~Effect of Varying Phosphate.~--
"Phosphate" solution added 10.0 c.c. 20.0 c.c. 50.0 c.c. 100.0 c.c.
"Uranium" required 9.8 " 18.9 " 47.6 " 94.5 "
The quantity of phosphoric oxide in the assay solution for the
conditions of titration should not be much less than 0.05 gram. For
smaller quantities the uranium solution should be diluted to half its
strength, and the assay solution concentrated by reducing its bulk to 50
c.c. and using 2.5 c.c. of the sodium acetate and acetic acid solution.
~Determination of Phosphoric Oxide in Apatite.~--Weigh up 0.5 gram of
the dried and powdered sample, and dissolve it in 5 c.
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