5 " 14.5 " 14.5 " 14.0 "
Solution added 20.0 " 30.0 " 40.0 " 50.0 "
"Uranium" required 13.2 " 10.0 " 6.0 " 2.0 "
These show that the quantity ordered (5 c.c.) must be adhered to.
~Effect of Foreign Salts.~--In these experiments, 10 grams of the salt
(the effect of which it was desired to determine) were added to a
solution in other respects resembling those previously used:--
Salt added {Ammonic Ammonic Ammonic Magnesium
{sulphate nitrate chloride sulphate
"Uranium" required 15.5 c.c. 15.5 c.c. 15.3 c.c. 15.3 c.c.
Without any addition, 15.0 c.c. were required; and in another
experiment, in which 30 grams of ammonic salts were present, 15.6 c.c.
of uranium solution were required. Such variations in the amount of
ammonic salts as occur in ordinary working are unimportant.
Phosphates, of course, interfere. In fact, the uranium acetate solution
can be standardised by titrating with a known weight of phosphate, and
calculating its equivalent of arsenic. Thus, in an experiment with 0.6
gram of hydric sodic phosphate (Na_{2}HPO_{4}.12H_{2}O), equivalent to
0.05195 gram of phosphorus, or 0.1256 gram of arsenic, 23.25 c.c. of a
solution of uranium acetate were required.
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