Evaporate to dryness the filtrate from the precipitation of barium
sulfate. Add a few cubic centimeters of hot water and then a saturated
solution of barium hydroxide until a slight film collects on the top of
the solution. Filter and wash the precipitate with hot water. Add to the
filtrate an excess of ammonium hydroxide and ammonium carbonate
solution. Filter, evaporate the filtrate to dryness, dry, and ignite at
low red heat to expel ammonium salts. Repeat the operations including
the addition of barium hydroxide until no precipitate is obtained by
barium hydroxide or by ammonium hydroxide and ammonium carbonate.
Evaporate the final filtrate to dryness in a weighed platinum dish, dry,
cool, and weigh the residue. Dissolve the residue in a few cubic
centimeters of water, filter, wash the filter paper twice with hot
water, then ignite the filter paper in the platinum dish. Cool and weigh
the residue. Subtract this weight from the first weight including the
residue. The difference is the weight of the chlorides of sodium and
potassium and lithium. If it is not desired to separate sodium and
potassium the weight of sodium and potassium as sodium may be calculated
from this difference by multiplying it by 0.394.