Sodae Carbonas. Lond. Carbonate of Soda

"Take of impure carbonate of soda, two pounds; distilled water, four pints. Boil the impure carbonate of soda in the water for half an hour, and filter the solution whilst it is hot. Finally, set it apart that crystals may be formed."

Subcarbonas Sodae. Subcarbonate of Soda.

"Take of impure carbonate of soda, any quantity. Bruise it, and then boil it in water until all the saline matter be dissolved. Filter the solution through paper, and evaporate it in an iron vessel, so that after refrigeration crystals may form."

Sodae Carbonas, Dub. Carbonate of Soda.

"Take of barilla, in powder, one part; water, two parts. Boil the barilla in the water, in a covered vessel, for two hours, occasionally stirring; filter the liquor; then bruise the barilla that remains with an equal quantity of water, and again boil it: this may be repeated a third time. The leys being filtered and mixed, evaporate them to dryness in a wide iron vessel, taking care that the saline mass, which will remain, be not again liquefied by too great a heat: stir it with an iron spatula till it become white; finally, dissolve it in boiling water, and after due evaporation, set it apart, that, as it cools, crystals may form. These will be purer if the barilla before each boiling be exposed for some time to the air. The crystallization should be effected when the air is at the freezing temperature, and in a liquor the specific gravity of which is, to that of water, as 1220 to 1000. If the salt be not very pure, repeat the solution and crystallization."

Syn. Natron Praeparatum, P. L. 1787. Soucarbonate de Soude (F.)> Sotto-carbonato di Soda (I.).

Barilla, which was formerly used in the process of the London Pharmacopoeia, and still is in that of Dublin, besides the carbonate of soda, contains sulphate of soda, and chloride of sodium, charcoal, lime, magnesia, argil, and silex, from which these processes are intended to separate it. The earths, being insoluble, are separated by the solution and fitration; while the foreign salts remain dissolved in the residuary liquor after the carbonate of soda has crystallized. In the present process of the London College, a purer carbonate is employed, which is manufactured on a great scale, by the decomposition of sulphate of soda and of chloride of sodium: it should supersede altogether the use of barilla.

1 London Medical Review, April, 1808, 130.

Qualities, - Carbonate of soda has a mild alkalescent taste, and changes the vegetable blue and red colours to green. Its crystals are large transparent octahedrons with a rhombic base, truncated at the angles, which contain a large proportion of water: they effloresce when exposed to a dry air, and crumble down into a white, opaque powder. They undergo the watery fusion at 150° Fahr.; are soluble in two parts of water at 60°, and in considerably less than their weight of boiling water. Its constituents, according to the late analysis of D'Arcet1, are, in 100 parts, 16.04 of acid, 20.85 of alkali, and 63.61 of water. Mr. Phillips makes them 15.3 of carbonic acid, 22.2 of soda, and 62.5 of water; or 1 eq. of acid=22.12+ 1 of soda = 31.3 +10 equivalents of water=90 = 143.42. By treating this salt in the method described under carbonate of potassa, any chlorides or sulphates it may contain are detected, while tartaric acid, added to its solution, discovers potassa, by forming a precipitate of the bitartrate.

Carbonate of soda is incompatible with acids and acidulous salts, hydrochlorate of ammonia, and most metallic salts.

Medical properties and uses.-This salt is antacid and deob-struent. It is less acrid than the carbonate of potassa, and thence is in more general use in dyspepsia and acidities of the stomach, and in scrofulous affections. Its use has been of late strenuously recommended in hooping-cough, the protraction of which it is said to prevent. It is given, after the stomach and bowels have been duly evacuated, at first in combination with ipecacuanha and opium, and afterwards, when the violence of the cough has abated, with myrrh or cinchona.2 The dose of this salt is from grs. x. to 3ss. given twice or thrice a day. M. Peschier has lately successfully employed it for the cure of bronchocele, and he considers it much more efficacious than iodine in this disease.1 In bronchocele, Dr. Peschier gave it to the amount of 118 grains in a day, dissolved in water.

1 Annales de Chimie, xxi. 208.

2 Medico-Chirugical Transactions, vol. i.

Officinal preparations.-Sodae Carbonas exsiccata, L. D. Sodae Sesquicarbonas, L. Aqua Supercarbonatis Soda, E. Phosphas Soda, E. D. Sodae Potassio-tartras, L. E. D.