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Earths and Earthy Salts.

part III.

Medical properties and uses. — It is a miJd cathartic, ex-cellently adapted for children, and others who have a fasti-dious taste. It may be given dissolved in gruel, or broth,made without salt, by which its taste is very effectually covered.The dose is from gyj. to ^ij. Although phosphate of sodawas known before 1740, at which time it was described byHaupt under the name of sal mirabilc perlatum, yet, it wasnot introduced into medical use as a purgative until about thirtyyears since, when it was recommended by Dr. George Pearsonof London.

MURIAS SODiE SICCATUM, Dub. Dried Muriateof Soda.

" Take of muriate of soda, any quantity. Roast it over thefire in an iron vessel slightly covered, until it cease to decre-pitate, occasionally agitating."

Syn. Muriate de Soude sec (-F-)> Getrocknetes salzsaures Natrum (G.),Muriate- di Soda seeco (/■)•

One hundred parts of crystallized muriate of soda contain,according to Kirwan, 8"12 of water, which is nearly dissipatedby the heat; and the salt was thus supposed to be rendered ofa more uniform strength : but in this state it contains no muri-atic acid, being in fact a chloride of sodium. It is employedchiefly for the distillation of muriatic acid, which is obtainedcolouriess from the dried salt.

EARTHS and EARTHY SALTS.

Earths possess peculiar properties, which distinguish themfrom other bodies, and constitute them a distinct class ofnatural productions. They are opaque, solid, uninflammable,of very difficult fusibility, very sparingly soluble in water, andof a specific gravity not exceeding 4\9. Some of them resem-ble the alkalies in several particulars; are caustic, change togreen the vegetable blues and reds, and neutralize acids ; andhave, therefore, been denominated Alkaline Earths; butnevertheless are in truth metallic oxides. Of this division threeare medicinally employed; namely, Lime, Magnesia, andBarytes; but the two former only are used as remedies intheir pure state, Those earths which do not possess alkalineproperties, although they, also, are metallic oxides, are de-nominated Proper Earths ; of which one only, Alumina,is a medicinal agent; and it is not used in its uncombinedstate.

Although some of the old chemists conjectured that thepure earths were metallic oxides, yet no direct proofs in sup-port of the supposition were obtained, and they were generally