Preparation

Bicarbonate of soda is prepared by exposing the crystals of the carbonate to an atmosphere of carbonic acid, in a close box, under pressure. The carbonic acid is absorbed, and the water of crystallization of the crystals, not being wanted for the new salt, separates and flows off". To admit of its escape, the crystals are placed on a diaphragm in the instrument, pierced with holes. They lose their crystalline appearance in the process, and become opaque, white, and porous. When the absorption is completed they are removed from the apparatus, dried, and pulverized.

Properties

As in the shops, this salt is always in the state of a fine white powder. It is inodorous, and has a saline slightly alkaline taste, which is less disagreeable than that of the corresponding salt of potassa, or indeed of any of the soluble antacids. it is unchanged in the air. At the boiling temperature it gradually gives out carbonic acid, and is converted into the sesquicarbonate. Thirteen parts of cold water are required for its solution. When quite pure, it consists of two equivalents of carbonic acid, one of soda, and one of water, and contains nearly twice as much soda in 100 parts as the crystallized carbonate, in consequence of the abundance of water of crystallization in the latter. Thus, the percentage of soda in the crystals of the carbonate is 20, in the bicarbonate about 37. The ordinary bicarbonate of commerce is seldom quite free from carbonate, a small portion of the latter having escaped decomposition in the process for preparing it.

Medical Effects and Uses

This is the mildest, least disagreeable, and most largely employed of all the alkaline antacids. To the carbonate of soda it is preferable on account of its more uniform dose and greater mildness, and to the preparations of potassa for its greater neutralizing power, less unpleasant taste, and greater acceptability to the stomach. in all cases calling for the use of an antacid, without any special indication for an astringent or laxative effect on the bowels, this salt may be selected. The carbonates of potassa may have more influence on the secretions, and may be more effectual in altering the blood; but for the neutralization of acid in any part of the system, this preparation of soda is to be preferred. in the cases of red sediment in the urine, it often acts like a charm in correcting it, and is above all other remedies useful in the urinary affections, connected either with excess or deposition of uric acid. it has here the advantage over the carbonate that it does not endanger, if in excess, a precipitation of the phosphates; as the excess of carbonic acid is said to hold them in solution. in the acidity of indigestion, in sick-headache from the same cause, in the sour breath and sour cutaneous exhalations of febrile disease, especially in children, this is the best remedy to which we can have recourse. it may be given dissolved in pure water, or in some aromatic water, sweetened if desired; but the most agreeable vehicle is, on the whole, carbonic acid water. it should always be thus administered when there is a conjoint indication for an antiemetic and antacid; as in an irritable stomach with acidity. it is also preferable in the urinary affections; as it secures that predominance of carbonic acid which favours the solution of the phosphates. A solution of a drachm of bicarbonate of soda, with half a fluidounce or a fluidounce of ginger syrup, in eight fluidounces of carbonic acid water, is an excellent formula for administering the salt in disorders of the urine. One-third of the quantity may be taken morning, noon, and night; the bottle being immediately and carefully closed after each dose, turned up on its cork, and kept in a cold place, surrounded with ice if to be had. The dose of the bicarbonate of soda is from twenty grains to a drachm, twice or three times a day, when repetition is required.

Troches of Bicarbonate of Soda (Trochisci Sodae Bicarbonates, U. S.) are an officinal of the U. S. Pharmacopoeia, made by forming into a mass with mucilage of tragacanth a mixture of the bicarbonate and sugar. Each troche weighs ten grains, and contains about two grains of the salt. They are useful in chronic acidity of the stomach, two or three being taken occasionally, as required.