BICARBONATE OF SODA.

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So'da Bicar'bonas. — Bicar’bonate of So'da.

History. —This salt was discovered by Valentine Rose. In someworks it is termed natron carbonicum perfecte saturatum sen acidulum.Mixed or combined with carbonate of soda it constitutes the soda sesqui-carbonas of the Pharmacopoeia —the carbonate or bicarbonate of soda orthe shops.

Natural History. —It is a constituent of the mineral waters calledacidulo-alkaline, as those of, Carlsbad and Seltzer.

Preparation. —There are several methods of procuring it. Of these Ishall briefly notice three.

1. Process of the Pharmacopoeia. —The substance called in the London Pharmacopoeia soda sesquicarbonas is ordered to be prepared as follows:—Dissolve seven pounds of carbonate of soda in a gallon of distilledwater, and strain: then pass carbonic acid into the solution to satura-tion, that the salt may subside. Dry this with a gentle heat, wrappedand pressed in cloth. According to Mr. Brande ( Manual of Chem.)160 lbs. of carbonate should be dissolved in 13 gallons of water, and car-bonic acid thrown into the solution in a proper apparatus. About 50lbs. of bicarbonate fall: and when separated should be dried in anhydraulic press, and afterwards by exposure to heat not exceeding 100° F.A fresh portion of carbonate is dissolved in the mother liquor, and theoperation repeated as before.

The carbonic acid used in this process is usually procured artificiallyby the action of dilute sulphuric acid on carbonate of lime. In somecountries, however, it is obtained from natural sources, as at Vichy,where it is collected from the mineral waters. (For a description andsketch of the apparatus used in the collection of the gas by D’Arcet, seeDiet , del’Indust. 3 me . t. p. 61.)

2. Smith's process. —This consists in placing the ordinary carbonateof soda in a box, and surrounding it by an atmosphere of carbonic acidgas under pressure. As the bicarbonate combines with much less waterof crystallization than is contained in the carbonate, a considerable por-tion of water is liberated, which, saturated with part of the salt, is allowedto drain off: when the gas ceases to be absorbed, the salt is taken outand dried. On examination it is found to have retained the originalform of the pieces; but they have become of a porous and loose texture,presenting the appearance of numerous crystalline grains, aggregatedtogether, and having a snow-white colour. ( Journ . of the Philadelphia Col-lege of Pharm. vol. i. quoted by Dr. Bache in the United States Dispen-satory. For a sketch of the apparatus employed by Souberain in per-forming Smith’s process, see his Nouv. Traite de Pharm. t. 2 me . p. 341.)

3. Process by sesquicarbonate of ammonia. —This is the processdirected to be followed in the London Pharmacopoeia for 1809. Sesqui-carbonate of ammonia is to be added to a solution of carbonate of soda,and a heat of about 100° F. applied to drive off the ammonia : the solu-tion is then to be set aside to crystallize. The proportions employed inthe Pharmacopoeia of 1809 were a pound of carbonate of soda, threeounces of sesquicarbonate of ammonia, and a pint of distilled water.Winckler ( Lehrb . d. Pharm. Chemie. l er - Th. S. 292) directs 4 parts oicrystallized carbonate of soda, If parts of sesquicarbonate of ammonia,