SESQU1CARB0NATE OF SODA.
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which it throws down with bichloride of mercury. Sulphate of magnesiacauses a white precipitate with it. As a soda salt it is recognised by thetests for this basic substance already stated (p. 310.)
Composition. —The perfect crystals of the ordinary carbonate of sodaof commerce have the following composition:—
Soda. 1 . . . 32 . . . 22*25 . 22
Carbonic Acid. 1 . . . 22 . . . 15*25 . 16
Water.. 10 . . . 90 . . . 62*5 . 62
Crystallized Carbonate of Soda. 1 . . . 144 . . . 100*00 . 100
Impurity. —The ordinary impurities of this salt are sulphates andchlorides. These are detected as follows:—Supersaturate with nitric acid,and then add, to separate portions of the solution, chloride of barium andnitrate of silver: if the first occasion a white precipitate, it indicates thepresence of a sulphate—if the second also produce a white precipitate,soluble in ammonia, it shews the presence of a chloride.
Physiological Effects. —Carbonate of soda is less acrid, and has amilder and less unpleasant taste, than carbonate of potash ; but in otherrespects the effects of these two salts on both vegetables and animals arethe same.
Uses. —Carbonate of soda is used in the same cases as carbonate ofpotash, over which it has the advantage of a less disagreeable taste.Fourcroy imagined that as soda is contained in animals in larger pro-portion than potash it was a better agent for medicinal use. Experience,however, has not confirmed this opinion, but has proved the reverse ; forboth Sir G. Blane {Trans, of a Society for the improvement of Med. andChirurg. Knowledge, iii. 347) and Mr. Brande [Quart. Journ. of Science,vol. vi. p. 205) state that they obtained beneficial effects, in calculouscomplaints, from the use of potash, where soda failed to give any relief.Sir G. Blane accounted for this by assuming that soda becomes appliedto the purposes of the economy before it reaches the kidneys, whereaspotash is earned to these organs in order to be thrown out of thesystem.
Administration. —Crystallized carbonate of soda is exhibited in dosesof from ten grains to half a drachm or a drachm, or five grains to ascruple of the dried carbonate, which may be given either in the form ofpowder or pills.
It is sometimes employed in the manufacture of the effervescingdraught. A scruple of the crystallized salt saturates about 9f grainsof the ordinary crystals of citric acid, lOf grains of crystallized tartaricacid, or 21 fluidrachms of lemon juice.
So'dee Sesquicar'bonas. — Sesquicar'bonate of So’da.
In the province of Sukena, near Tripoli , is found a substance which theAfricans call Trona— a word from which are probably derived the termsvlrpov, nitrum, and natron (vide Potass.® Nitras and Sod.e Carbonas).But the analyses of Klaproth ( Beitrage, iii. 83), Phillips {Quart. Journ.of Science, vol.vii. 297), and Beudant (quoted by Necker , liegne Mineral,