Creta Preparata. Lond. Prepared Chalk

"Take of chalk, a pound; water, as much as may he sufficient. Add a little water to the chalk, and triturate it to a fine powder. Throw this into a large vessel with the remainder of the water, then stir it, and after a short interval pour off the supernatant turbid water into another vessel, and set it apart that the powder may subside; lastly, let the water be poured off, and dry the powder, and preserve it for use."

In the same manner, shells freed from sordes and washed with boiling water are prepared.

Carbonas Calcis praeparatus, Edin. Prepared Car-bonate of Lime.

"Let carbonate of lime, triturated to powder in an iron mortar, and levigated with a little water, on a porphyry stone, be put into a large vessel; then pour water upon it, which, after frequently snaking the vessel, is to be poured off, loaded with the fine powder. The subtle powder, which subsides when the water remains at rest, is to be dried. Let the coarse powder which the water could not suspend be again levigated, and treated in the same manner."

Creta Preparata, Dub. Prepared Chalk.

"Let it be triturated to powder in an earthen mortar, with the addition of a little water; then mix this with a sufficiently large quantity of water by agitation, and after a short interval, when the coarser particles have subsided, pour off the fluid. This may be frequently repeated, always previously triturating; and, finally, collect the very fine powder, which after some time will subside, and dry it upon an absorbent stone, or paper."

Syn. Craie prepare (F.), Rein Kreide ( G.), Carbonato di Calce preparato (I.).

By the suspension of the finer particles of the levigated chalk in water, they are reduced to a more impalpable form, and are more effectually separated from the coarser particles than could be accomplished by any other mechanical means; but the chalk is not freed from the foreign earths it generally contains (see Calx, Part ii.), although it be sufficiently pure for medicinal use.

Qualities.-Pure carbonate of lime, in the form of chalk, is a white, opaque, soft, light substance. It is a compound of 43 parts of carbonic acid + 56.5 of lime + .5 of water in 100 parts.

Medical properties and uses. - Chalk is antacid and absorbent. It is exhibited advantageously in acidities of the primae viae; and in diarrhoeas, after all irritating matters have been removed from the bowels by previous evacuation (see Mis-tura Cretae). As an external application, it is sprinkled over ulcers discharging a thin ichorous matter, which is thus absorbed by the chalk, and prevented from excoriating the neighbouring sound skin. In cases of burns it is applied in a similar manner, and a poultice laid over it, by which the skinning of the sore is much hastened. l

The dose of chalk is from grs. x. to Э ij., or more.

Officinal preparations. - Mistura Cretae, L. E. Hydrargyrum cum Creta, L. Pulvis opiatus, E. Trochisci Carbonalis Calcis, E. Confectio aromatica, L. E. Calcii Chloridum, L. Ammoniae Sesqui-