Carbon sulphide is employed therapeutically in doses of 2 drops, gradually increased to 5, as a sudorific in rheumatism. It is also dropped (40 to 50 drops) on the part, to promote the reduction of strangulated hernia. Externally, it is employed in liniments for rheumatic pains.
CAR′BONATE, a salt in which the hydrogen of (hypothetical) carbonic acid (H2CO3) is replaced by a metal or other basic radical.
Prep., &c. The processes by which the commercial carbonates and many others are prepared are described under the respective bases. Most of the earthy carbonates are found abundantly in nature. In general the salts of this class may be formed by adding an alkaline carbonate to a salt of the metal in solution by double decomposition.
Prop. The carbonates of the alkalies are soluble in water; those of the other bases are for the most part insoluble, except the water is highly charged with carbonic acid. From most of them carbonic anhydride or anhydrous carbonic acid can be easily expelled by heat.
Tests. The carbonates are easily distinguished by the following reactions:—They dissolve with effervescence in hydrochloric acid and in most other acids; in some cases a gentle heat is required to promote the disengagement of the gas.—The gas evolved in the last, passed into lime water and baryta water, occasions white precipitates, which redissolve in acids with effervescence, and after the solution has been boiled are not reprecipitated by liquor of ammonia.—Chloride of calcium and chloride of barium give white precipitates in solutions of the neutral alkaline carbonates, but in solutions of the alkaline bicarbonates only after ebullition; and the precipitates are readily soluble with effervescence in acetic acid.
Estim. The quantity of the metal in an alkaline or earthy carbonate may be easily determined by the ordinary volumetric methods of alkalimetry (which see), and the quantity of carbonic acid, by the method of Fresenius and Will (see Alkalimetry). The apparatus figured on next page, or preferably that shown in the article on Alkalimetry, may be used instead of the more complicated contrivance of the German chemists.
A weighed sample of the carbonate to be examined is placed in the flask a along with a little water, and the small tube, b, filled with either sulphuric or hydrochloric acid, is carefully introduced. The cork, with its chloride of calcium tube, d, is then fitted to the flask, and the whole apparatus very accurately weighed.
On inclining the apparatus the acid escapes over the side of the small tube, and mixing with the liquor in the flask, expels the carbonic
acid of the carbonate, which is then dried by passing over the chloride of calcium. After effervescence has ceased heat should be applied to the bottom of the flask, until it be filled with steam, to expel the carbonic gas it contains. The loss of weight gives the weight of the carbonic acid gas that was contained in the sample. The quantity of carbonic acid in the carbonates of the metals that do not contain water may be determined by heating them to redness in a platina crucible.
