These,
however, are not so easy to recognise or obtain as the sodium one.
Concentrated solutions of potassium salts give a yellow crystalline
precipitate with platinum chloride, and a white crystalline one with the
acid tartrate of soda. For these tests the solution is best neutral.
These tests are only applicable in the absence of compounds other than
those of potassium and sodium.
GRAVIMETRIC DETERMINATION.
This process serves for its separation from sodium. Take 1 gram of the
sample and dissolve it in an evaporating dish with 50 c.c. of water.
Acidify with hydrochloric acid in quantity sufficient (if the metals are
present as chlorides) to make it acid, or, if other acids are present,
in at least such quantity as will provide the equivalent of chlorine.
Add 3 grams of platinum, in solution as platinum chloride, and evaporate
on a water-bath to a stiff paste, but not to dryness. Moisten with a few
drops of platinic chloride solution without breaking up the paste by
stirring. Cover with 20 c.c. of strong alcohol, and wash the crystals as
much as possible by rotating the dish. Allow to settle for a few
moments, and decant through a filter. Wash in the same way two or three
times until the colour of the filtrate shows that the excess of the
platinum chloride used is removed. Wash the precipitate on to the filter
with a jet of alcohol from the wash-bottle; clean the filter-paper,
using as little alcohol as possible.
Pages:
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626