PART III.

Earths and Earthy Salts.

625

its weight of hot distilled water, as may be sufficient to preci-pitate the chalk. Wash the precipitate three times in a suffi-cient quantity of water; then collect it, and dry it on a chalkstone or on bibulous paper."

A double exchange takes place in this process; the muriaticacid separates from the lime and unites with the soda, whilethe carbonic acid of the subcarbonate combines with the lime:the muriate of soda thus formed remains dissolved in the water,but the carbonate of lime is precipitated in the form of a whitepowder. It is an expensive preparation, and the benefit to bederived from a great degree of purity in this substance is notvery obvious.

Officinal preparations. Hydrargyrum cum Creta, D. Electuariumaromaticum, D. Mistura Creta, D.

MURIAS BARYT^E, Edin. Muriate of Barytes.

" Take of carbonate of barytes, muriatic acid, each, onepart; water, three parts. To the water and the acid mixedtogether add the carbonate broken into small pieces. Theeffervescence being finished, digest for an hour; then filter,and after due evaporation set the solution apart that crystalsmay form. Repeat the evaporation as long as any crystals areformed.

" If the carbonate of barytes cannot be procured, the muri-ate may be prepared from sulphate of barytes in the followingmanner :

" Take of sulphate of barytes, impounds; charcoal in pow-der, four ounces ; muriatic acid, a sufficient quantity. Roastthe sulphate, that it may be the more easily reduced to a veryfine powder, and mix it with the powder of charcoal. Putthe mixture into a crucible, and having fitted to it a cover, letit be exposed to a strong fire for six hours; then, having welltriturated the matter, put it into six pounds of boiling water, ina glass or earthern vessel, and mix by agitation, preventing, asmuch as possible, the action of the air.

" Let the vessel stand in a vapour-bath until the undissolvedpart shall have subsided, and then pour off the liquor. Pourupon the residue four pounds of boiling water, which, afteragitation and subsidence, add to the former liquor: and then,while it is still hot, or, if it shall have cooled, after it is againheated, let muriatic acid be dropped into it as long as any effer-vescence is excited. Then let the solution be filtered and eva-porated, that crystals may be formed."

Syn. Muriate de Baryte (F.), Salzsaure Schwererde (C.)> Murwtodi Barita (/.).

The simplicity of the first of these processes, in which thesuperior affinity of the muriatic acid for barytes effects the de-composition of the carbonate, recommends its gene'al adoption;and we believe this mineral can now be procured without dif-

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