Prep. Formerly derived from kelp or barilla, the ashes obtained from burning sea-weeds, and species of salsola; it is now almost always made from common salt, by converting the chloride of sodium into a sulphate by means of sulphuric acid, and afterwards, by combustion with small coal and chalk, resolving this salt into a sulphuret, and then into a carbonate; it is manufactured on a very large scale.
Prop. & Comp. Carbonate of soda forms large rhombic octahedrons, colourless, transparent except on the surface, with an alkaline and caustic taste; it effloresces and crumbles when exposed to air; it imparts a yellow colour to flame; very soluble in water; dissolves with effervescence in hydrochloric acid, forming a solution which does not precipitate with chloride of platinum. By heat it undergoes aqueous fusion, and loses 63 per cent. of its weight. When supersaturated with nitric acid it precipitates slightly, or not at all, with chloride of barium or nitrate of silver. One hundred and forty-three grains require for neutralization at least 96 measures of the standard solution of oxalic acid. Composition (Na O, Co2+10 HO).
Off. Prep. Sodae Carbonas Exsiccata. Dried Carbonate of Soda. (Carbonate of soda, eight ounces. Apply heat to the carbonate, until the crystals fall to powder, and afterwards heat it to redness; lastly, rub it to powder.) It is simply the last salt deprived of its water of crystallization, which amounts to 62.93 per cent. by heat; it is soluble in water, and contains 41.51 per cent. of carbonic acid, and 58.49 of soda. Composition (Na O, Co2).
Therapeutics. The action of carbonate of soda resembles that of the corresponding salt of potash, but is perhaps less caustic. The general effects of soda salts will be described under Soda Bicarbonas.
Dose. 10 gr. to 30 gr. Of sodae carbonas exsiccata, 5 gr. to 15 gr.: this last is convenient when it is desired to administer the drug in powder or pill.
Adulteration. It usually contains a little sulphate of soda, detected by the baryta test above given.