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. Na2O 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 AgNO3 solution, 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 Na2SO4.
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 Na2SO3.