solution (10 per cent.) until it ceases to give a
precipitate, the precipitate allowed to settle, and the clear
supernatant liquid decanted off, the precipitate transferred to a filter
paper and well washed, and the filtrate titrated with N/1 acid, using
phenol-phthalein as indicator. The second titration gives the amount of
caustic alkali present, and the difference between the two the
proportion of carbonate.

When methyl orange solution is used as indicator, titrations must be
carried out cold.

Reference has already been made (p. 39) to the manner in which the
alkali percentage is expressed in English degrees in the case of caustic
soda.

_Chlorides_ are estimated by titrating the neutral solution with N/10
silver nitrate solution, potassium chromate being used as indicator. One
c.c. N/10 AgNO_{3} solution = 0.00585 gramme sodium chloride.

The amount of acid necessary for exact neutralisation having already
been ascertained, it is recommended to use the equivalent quantity of
N/10 nitric acid to produce the neutral solution.

_Sulphides_ may be tested for, qualitatively, with lead acetate
solution.

_Aluminates_ are determined gravimetrically in the usual manner; 2
grammes are dissolved in water, rendered acid with HCl, excess of
ammonia added, and the gelatinous precipitate of aluminium hydrate
collected on a filter paper, washed, burnt, and weighed.

* * * * *

_Carbonated Alkali (Soda Ash)._--The total or available alkali is, of
course, the chief factor to be ascertained, and for this purpose it is
convenient to weigh out 3.1 grammes of the sample, dissolve in 50 c.c.
water, and titrate with N/1 sulphuric or hydrochloric acid, using methyl
orange as indicator. Each c.c. of N/1 acid required represents 1 per
cent. Na_{2}O in the sample under examination.

A more complete analysis of soda ash would comprise:--

_Insoluble matter_, remaining after 10 grammes are dissolved in warm
water. This is washed on to a filter-paper, dried, ignited, and weighed.

The filtrate is made up to 200 c.c., and in it may be determined:--

_Caustic soda_, by titrating with N/1 acid the filtrate resulting from
the treatment of 20 c.c. (equal to 1 gramme) with barium chloride
solution.

_Carbonate._--Titrate 20 c.c. with N/1 acid, and deduct the amount of
acid required for the Caustic.

_Chlorides._--Twenty c.c. are exactly neutralised with nitric acid,
titrated with N/10 AgNO_{3} soluti