XOILti 245
temperature of the latter is gradually raised to 800-900°, as shown bv a
pyrometer.
After the crucible has been cooled transfer the contents to a 300-oc
porcelain dish, add sufficient hot water to cover the semi-fused mass, heat to
boiling and let stand until the whole mass is completely slaked. Some
samples are difficult to slake, due usually to heating to too high a temperature
or to the presence of too little calcium carbonate in the mixture. These
require digesting for some time on a steam bath; or the solution and residue
rnay be placed in a porcelain dish and ground gently with an agate pestle.
Filter the solution containing the disintegrated mass, collecting the filtrate
in a 400-cc Pyrex beaker. Macerate the residue in a mortar, rinse several
times with boiling water and finally filter and wash with boiling water until
about 350 cc of filtrate has been collected.
To the filtrate add enough ammonium hydroxide to make basic, then
ammonium carbonate to precipitate calcium. Heat to boiling then filter
into a platinum dish, evaporate to dryness on the steam bath and heat to dull
redness to expel most of the ammonium salts. Dissolve the residue in 5 cc
of hot water. If any insoluble residue remains, repeat the addition of
ammonium hydroxide and carbonate, filter through a small paper, wash the
paper with hot water, add 1 cc of dilute hydrochloric acid to the filtrate and
evaporate filtrate and washings in a platinum dish. Heat to dull redness for
a short time to expel ammonium salts. This residue of potassium and
sodium chlorides is ready for the determination of potassium.
Determination of Potassium: CUorplatinate Method.—(To be performed
in an atmosphere which is free from ammonia.) Dissolve the residue of
potassium and sodium chlorides, obtained as above directed, in 50 ec of hot
water and then add chlorplatinic acid (containing 10 per cent of platinum
or 26.5 per cent of chlorplatinic acid crystals), using about 1 cc more than
the theoretical amount, calculated upon the assumption that the chloride
residue was all potassium chloride. Evaporate on the steam bath to a thick
paste but not to dryness, cool and add 50 cc of 80-per cent alcohol, stir up
the solid matter and allow to stand, covered, for 30 minutes.
If the liquid is not visibly colored too little reagent has been used. In this
case new samples should be taken and the quantity of chlorplatinic acid
increased. Filter and wash the precipitate thoroughly with 80-per cent
alcohol, washing several times after the washings pass through colorless.
The wash bottle should be provided with ground-glass joints so that no rub-
ber will come into contact with the alcohol. Remove the filtrate and
washings, pouring these into the bottle provided for platinum waste residues^
and wash the precipitate again, thoroughly, with 80-per cent alcohol, using
particular care in washing the upper part of the paper. Wash until only a
faint turbidity is produced by the addition of a drop of silver nitrate solution
to the last washings.
Drain most of the alcohol from the paper (or see next paragraph), slip the
latter out of the funnel and dry in the oven at 100°. Place a weighed
porcelain crucible upon a piece of glazed paper, remove most of the precipi-
tate to the crucible, brushing up any particles that may have fallen upon the |||