_First procedure._—Add to the solution of the chlorides of sodium and
potassium a few drops of dilute hydrochloric acid (1 to 3) and 1 cc. of
10 per cent platinic chloride (PtCl_{4}) for each 30 mg. of the combined
chlorides. Evaporate to a thick syrup on the water bath, then remove
dish and allow it to come to dryness at laboratory temperature. Treat
the residue cold with 80 per cent alcohol and filter. Wash the
precipitate with 80 per cent alcohol until the filtrate is no longer
colored. Dry the precipitate and dissolve it in hot water. Evaporate the
solution to dryness in a platinum dish and weigh it as potassium
platinic chloride (K_{2}PtCl_{6}). The weight of potassium (K) is 16.1
per cent of this weight and the equivalent of potassium chloride (KCl)
is 30.7 per cent of this weight. Subtract the equivalent weight of
potassium chloride from the weight of the combined chlorides. The weight
of the sodium is 39.4 per cent of the difference.
_Second procedure._[86][103a]—Add to the hot solution of the combined
chlorides 20 per cent perchloric acid (HClO_{4}) slightly in excess of
the amount required to combine with the bases. One cubic centimeter of
20 per cent perchloric acid is equivalent to 90 mg. of potassium.
Evaporate the solution to dryness, dissolve the residue in 10 cc. of hot
water and a small amount of perchloric acid, and again evaporate to
dryness. Repeat the addition of water, perchloric acid, and evaporation
until white fumes appear on evaporating to dryness. Add to the residue
25 cc. of 96 per cent alcohol containing 0.2 per cent of perchloric acid
(1 cc. of 20 per cent perchloric acid in 100 cc. of 98 per cent
alcohol). Break up the residue with a stirring rod. Decant the
supernatant liquid through a weighed Gooch crucible that has been washed
with 0.2 per cent perchloric acid in alcohol. If the precipitate is
unusually large dissolve it in hot water and repeat the evaporation with
perchloric acid. Wash the precipitate once by decantation with the 0.2
per cent perchloric acid in alcohol, transfer the precipitate to the
crucible, and wash it several times with a 0.2 per cent perchloric acid
in alcohol. Dry the crucible at 120–130° C. for one hour, cool, and
weigh it. The increase in weight is potassium perchlorate (KClO_{4}).
The equivalent weight of potassium is 28.2 per cent and the equivalent
weight of potassium chloride is 53.8 per cent of the potassium
perchlorate. Calculate the content of sodium by difference.