In the exceptional cases
it is got into solution by treating with a boiling solution of sodium
carbonate; the nitrate will contain it as an alkaline nitrate.
Since, however, in their determination, nitrates are never separated and
weighed as such, the difficulty of separating them has little
importance. Usually, the determination can be made on the original
aqueous solution, and it is never necessary to do more than remove any
special substance which has a bad effect; and this is easily done by the
usual reagents.
GRAVIMETRIC DETERMINATION.
It follows from what has been said that there is no direct gravimetric
determination. The percentage of nitrogen pentoxide (N_{2}O_{5}) in a
comparatively pure nitrate is sometimes determined indirectly in the
following way:--Place in a platinum-crucible 4 or 5 grams of powdered
and cleaned quartz. Ignite, cool in a desiccator, and weigh with the
cover. Mix 1 gram of the dried and powdered salt with the quartz in the
crucible by stirring with a stout platinum-wire. Cover the crucible, and
heat in a Bunsen-burner flame at scarcely visible redness for
half-an-hour. Cool and weigh. The loss in weight gives the amount of
nitrogen pentoxide. Sulphates and chlorides in moderate quantity do not
interfere. The following is an example of the process:--
Crucible and sand 26.
Pages:
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737