_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} 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 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.