328
ELEMENTS OF MATERIA MEDICA.
and 10 parts of water. The proportions ordered by MM. Henry andGuibourt ( Pharm. Raisonnee, t. 2 nd . p. 409, ed. 2 n>< ‘.) are 6 parts of thecrystallized carbonate of soda, 2 parts of sesquicarbonate of ammonia,and 4 parts of water.
Properties. —Bicarbonate of soda usually occurs in the form of awhite crystalline mass. The perfect crystals are, according to Dr. Thom-son [Chem. of Inorg. Bodies, vol. ii. p. 54), oblique rectangular prisms.The taste of this salt, and its reaction on vegetable colours, are slightlyalkaline. By exposure to the air it effloresces superficially. Whenheated it evolves carbonic acid and water, and becomes the anhydrouscarbonate. It dissolves in 13 parts according to Rose, or 8 parts accord-ing to Berthollet , of cold water. By heat the solution loses first one-quarter, and subsequently one-half of its carbonic acid.
Characteristics.— To recognize the carbonic acid and soda of thissalt, the tests are the same as before described (vide p. 324) for the car-bonate of soda. From the latter salt the bicarbonate of soda is distin-guished by its causing neither a brick-red precipitate with the bichlorideof mercury, nor a white precipitate with the sulphate of magnesia. Thesodaic powder of the shops {soda sesquicarbonas, Ph. L.) being a mixtureof carbonate and bicarbonate produces a red precipitate with bichlorideof mercury, but no precipitate with sulphate of magnesia; and whenwashed with a small quantity of cold distilled water, leaves a whitepowder (bicarbonate of soda), which, when dissolved in water, gives awhite precipitate or slight opalescence to a solution of bichloride ofmercury.
Composition. —Crystallized bicarbonate of soda has the followingcomposition:—
Soda. I ... 32 ... 34-04 ... 37 . . . 3175 . . . 29-85
Carbonic Acid.... 2 ... 44 ... 40*80 ... 49 . . . 44"40 . . . 49*95
Water . 2 . . . 18 . . . 19*14 ... 14 . . . 23*85 . . . 20*20
CrystA Bicarb. Soda . 1 ... 94 ... 99*98 . . . 100 . . . 100*00 . . . 100*00
According to Dr. Thomson’s analysis ( First Principles of Chemistry ,vol. ii. p. 2(i8), this salt contains only one equivalent of water of crys-tallization.
Purity. —When quite pure, this salt occasions no precipitate withchloride of platinum, perchloric acid, or tartaric acid, by which its free-dom from potash is demonstrated. When supersaturated with pure nitricacid, it gives no precipitate with either chloride of barium or nitrate ofsilver, by which the absence of sulphates and chlorides is shewn. Lastly,it occasions a white precipitate with bichloride of mercury, by which thefreedom from a simple or mono-carbonate is shewn.
Physiological Effects. —The effects of this salt are analogous tothose of bicarbonate of potash, than which it is regarded as having asomewhat less disagreeable taste and a slighter local action. It is ofcourse less caustic and irritant than the sesquicarbonate, and still moreso than the carbonate of soda. Its remote or constitutional effects areanalogous to those of the caustic alkalies. (Vide Potassa, p. 275.)
Uses. —It is employed as an antacid in those forms of dyspepsia whichare attended with an inordinate quantity of acid in the stomach; as alithontriptic in those kinds of lithiasis which are accompanied with an