This section is from the book "A Treatise On Beverages or The Complete Practical Bottler", by Charles Herman Sulz. Also available from Amazon: A Treatise On Beverages.
Bicarbonate of soda appears in commerce under the name of "bi- carbonate " - bi-carbonate of natron - either as white transparent crystals or more generally as a white powder, without smell but of an alkaline taste. It is found in alkalic mineral waters and is of importance in the manufacture of artificial mineral waters and other sparkling beverages. It consists of 47.6 per cent. of natron (soda) and 52.4 per cent. of carbonic acid its chemical sign is NaHc03.
Bi-carbonate of soda yields an excellently pure carbonic acid gas, and imparts to the water a sparkle and effervescence unapproachable by any other gas-producing material; but it is too expensive for ordinary, everyday bottlers, hence the few carbonators using it. For the manufacture of champagne or mineral waters in small quantities, without much trouble of washing the gas, it is quite pure, and may be conveniently employed.
Marble dust and whiting have superseded its use in the manufacture of carbonated beverages, owing to the great cost of the "bi-carbonate" as it is familiarly known. The name "soda water" was derived from the employment of this salt in the early days of the trade, though it is now a misnomer.
Bi-carbonate of soda is tested in regard to its purity by dissolving a spoonful of it in water, adding starch liquor and one drop of iodine solution. If the bi-carbonate of soda be pure the solution will immediately turn blue.
Soda bi-carbonate, the commercial salt, usually contains a little sulphuric acid and chloride. The former is found by super-saturating the liquid with nitric acid, and adding baric chloride, when, if sulphuric acid is present, a white precipitate will be thrown down. The chloride is tested by adding nitric acid, as in the previous case, and then argentic nitrate, with which it forms a white precipitate. The impurer varieties contain, in addition to the above, sulphide of sodium and sulphide and 10 hyposulphite of soda; extract these by adding dilute sulpnuric, and passing evolved gas through a solution of plumbic acetate. The precipitate formed ought to be white (carbonate of lead), not brown; also, no sulphur should be thrown down on addition of the sulphuric acid.
Bi-carbonate of soda is decomposed by the action of sulphuric acid, of which but a small quantity is required. The residue is sulphate of soda (glauber salt).