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ELEMENTS OF MATERIA MELMCA.
In consequence of the enormous consumption of sulphate of soda inthe manufacture of carbonate of soda, makers of the latter article areobliged to procure sulphate purposely, by the addition of sulphuric acidto chloride of sodium.— [For the theory of this process, see p. 149.]Properties. —The primitive form of the ordinary crystallized sulphateof soda is the oblique rhombic prism. To the taste this salt is cooling,and bitterish saline. By exposure to the air it effloresces. When heatedit undergoes the watery fusion, gives out its water of crystallization, andthereby becomes a white solid, and at a red heat it again becomes liquid.One part of it dissolves in three parts of water at 60°, or one part ofwater at 212°. It is insoluble in alcohol.
Characteristics. —Its constituents, sulphuric acid and soda, may bedetected by the tests for these substances before mentioned (pp. 265 and310). From the bi sulphate of soda it is distinguished by its not redden-ing litmus, and by its less solubility. Crystals of anhydrous sulphate ofsoda are distinguished by their form being the rhombic octahedron.
Composition.— The ordinary crystals of sulphate of soda have thefollowing composition:—
Soda. 1 . . 32 ... . 19*75 .... 19'24 .... 19*5
Sulphuric Acid. 1 . . 40 ... . 24*69 .... 24’76 .... 24*3
Water. 10 . . 90 ... . 55*56 .... 56*00 .... 55*2
Ordinary Crystals of Sulph te . of Soda . 1 . . 162 .... 100*00 .... 100*00 .... 99*0
Purity. —The crystallized sulphate of soda of the shops is usuallysufficiently pure for medical purposes. The presence of chlorides in itmay be detected by nitrate of silver
Physiological Effects.— It is a mild but efficient cooling laxativeor purgative salt, promoting secretion and exhalation from the mucousmembrane of the stomach and bowels, without causing inflammation orfever.
Uses.— It may be employed as a common purgative, either alone oradded to other purgatives. It is applicable in fevers and inflammatoryaffections, where we want to evacuate the bowels without increasing orcausing febrile disorder.
Administration. —The usual dose of it is from six to eight drachms.When dried, so as to expel the water of crystallization, three and a halfdrachms act as an efficient purgative.
So'dce Bibo'ras. — Bibo'rate of So'da.
History. —Pliny {Hist. Nat. lib. xxxiii) describes a substance underthe name of chrysocolla, which has been supposed by some to be biborateof soda. The term bauracon or baurach (from w hich our word borax isderived) first occurs in the writings of the Arabians. By some of theseauthors (as Mesue and Avicenna ) it was applied to nitre (Beckmann,Hist, of Invent, and Discov. vol. iv. p. 559): it is not improbable, how-ever, that Geber ( Search of Perfection , ch. iii.) used it to indicate ourborax. By modern chemists the salt has been termed biborate, borate, orsub-borate of soda.