to dryness in a tared platinum basin, and
heat the residue gradually to dull redness. Cool in a desicator, weigh,
and express the result as "mixed chlorides," _i.e._ chlorides of soda
and potash. To the mixed chlorides add 10 c.c. water, and platinic
chloride in excess (the quantity may be three times the amount of the
mixed chlorides) and evaporate nearly to dryness; add 15 c.c. alcohol
and allow to stand three hours covered with a watch-glass, giving the
dish a gentle rotatory movement occasionally. The clear liquid is
decanted through a tared filter, and the precipitate well washed with
alcohol by decantation, and finally transferred to the filter, dried and
weighed. From the weight of potassium platino-chloride, K_{2}PtCl_{6},
is calculated the amount of potassium oxide K_{2}O by the use of the
factor 94/488.2 or 0.19254.

_Chlorides_, determined with N/10 silver nitrate solution, and
calculated to KCl.

_Sulphates_, estimated as barium sulphate, and calculated to
K_{2}SO_{4}.

_Sodium Carbonate_, found by deducting the K_{2}CO_{3} corresponding to
the actual potassium as determined above, from the total alkali.

_Iron_, precipitated with excess of ammonia, filtered, ignited, and
weighed as Fe_{2}O_{3}.

SODIUM CHLORIDE (COMMON SALT).

This should be examined for the following:--

_Actual Chloride_, either titrated with N/10 silver nitrate solution,
using neutral potassium chromate solution as indicator, or, preferably,
estimated gravimetrically as silver chloride by precipitation with
silver nitrate solution, the precipitate transferred to a tared filter
paper, washed, dried and weighed.

_Insoluble matter_, remaining on dissolving 5 grammes in water, and
filtering. This is washed, dried, ignited and weighed.

_Moisture._--5 grammes are weighed into a platinum crucible, and heat
gently applied. The temperature is gradually increased to a dull red
heat, which is maintained for a few minutes, the dish cooled in a
desicator, and weighed.

_Sulphates_ are estimated by precipitation as barium sulphate and
calculated to Na_{2}SO_{4}.

_Sodium._--This may be determined by converting the salt into sodium
sulphate by the action of concentrated sulphuric acid, igniting to drive
off hydrochloric and sulphuric acids, and fusing the mass until constant
in weight, weighing finally as Na_{2}SO_{4}.

POTASSIUM CHLORIDE.

This should be examined, in the same way as sodium chloride, for
chloride, insoluble mat