Add 10 c.c. of
nitric acid, nearly neutralise with ammonia, render acid with 3 or 4
c.c. of nitric acid, and add 10 or 20 c.c. of ammonic molybdate
solution. Heat for some time, allow to settle, filter, and wash the
precipitate with a solution of ammonic nitrate. Dissolve the precipitate
in dilute ammonia, nearly neutralise with dilute hydrochloric acid, and
add first "magnesia mixture," and then ammonia; allow to stand
overnight; filter, wash with dilute ammonia, dry, ignite, and weigh as
magnesic pyrophosphate. Calculate to phosphorus.
PRACTICAL EXERCISES.
1. Ten grams of an iron yielded 12 milligrams of pyrophosphate of
magnesia. What percentage of phosphorus did the metal contain?
2. Ten grams of an iron ore gave 12 milligrams of pyrophosphate. What
percentage of phosphoric oxide did it contain?
3. What weight of apatite 3Ca_{3}(PO_{4})_{2}.CaClF would require 50
c.c. of standard uranium solution (100 c.c. equal to 0.5 gram of
P_{2}O_{5})?
4. You have reason to believe that a precipitate which has been weighed
as magnetic pyrophosphate contains some arsenate. How would you
determine the amount of phosphate really present?
5. Twenty c.c. of a solution of sodic phosphate containing 0.100 gram of
P_{2}O_{5} was found to require a solution containing 0.700 gram of
hydrated uranium acetate in a titration.
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