on, using potassium chromate as
indicator.

_Sulphates._--Twenty c.c. are acidulated with HCl, and the sulphates
precipitated with barium chloride; the precipitate is collected on a
filter paper, washed, dried, ignited, and weighed, the result being
calculated to Na_{2}SO_{4}.

_Sulphides and Sulphites._--The presence of these compounds is denoted
by the evolution of sulphuretted hydrogen and sulphurous acid
respectively when the sample is acidulated. Sulphides may also be tested
for, qualitatively, with lead acetate solution, or test-paper of sodium
nitro-prusside.

The total quantity of these compounds may be ascertained by acidulating
with acetic acid, and titrating with N/10 iodine solution, using starch
paste as indicator. One c.c. N/10 iodine solution = 0.0063 gramme
Na_{2}SO_{3}.

The amount of sulphides may be estimated by titrating the hot soda
solution, to which ammonia has been added, with an ammoniacal silver
nitrate solution, 1 c.c. of which corresponds to 0.005 gramme Na_{2}S.
As the titration proceeds, the precipitate is filtered off, and the
addition of ammoniacal silver solution to the filtrate continued until a
drop produces only a slight opacity. The presence of chloride, sulphate,
hydrate, or carbonate does not interfere with the accuracy of this
method. The ammoniacal silver nitrate solution is prepared by dissolving
13.345 grammes of pure silver in pure nitric acid, adding 250 c.c.
liquor ammoniae fortis, and diluting to 1 litre.

_Carbonate of Potash (Pearl Ash)._--The total or available alkali may be
estimated by taking 6.9 grammes of the sample, and titrating with N/1
acid directly, or adding 100 c.c. N/1 sulphuric acid, boiling for a few
minutes, and titrating the excess of acid with N/1 caustic soda
solution, using litmus as indicator. In this case each c.c. N/1 acid
required, is equivalent, in the absence of Na_{2}CO_{3}, to 1 per cent.
K_{2}CO_{3}.

Carbonate of potash may be further examined for the following:--

_Moisture._--From 2-3 grammes are heated for thirty minutes in a
crucible over a gas flame, and weighed when cold, the loss in weight
representing the moisture.

_Insoluble residue_, remaining after solution in water, filtering and
well washing.

_Potassium_ may be determined by precipitation as potassium
platino-chloride thus:--Dissolve 0.5 gramme in a small quantity (say 10
c.c.) of water, and carefully acidulate with hydrochloric acid,
evaporate the resultant liquor