PART III.

Earths and Earthy Salts.

623

and expose it in a crucible to a very strong fire for an hour, oruntil the carbonic acid be so completely expelled, that on theaddition of acetic acid no air-bubbles are extricated.

" Lime may be made in the same manner from shells, afterthey have been washed in boiling water, and freed from allimpurities."Syn. Chaux (F.), Kalkerde (G.\ Cake (/,}, Calviva (&).

Lime prepared on the great scale for the ordinary purposesof art, is sufficiently pure for medicinal use; but for some phar-maceutical purposes it is required to be more completely burntthan is usually the case of that which is obtained from thekilns; and perhaps it is with this view that the above pre-paration has been ordered by the London College. It may,however, be observed, that neither ot' the substances orderedaffords lime in a state of absolute purity; limestone frequentlycontaining silex, alumina, magnesia, and marine shells; and aportion of phosphate of lime which is not decomposed by thefire. To obtain perfectly pure lime, dissolve white marble orclean oyster-shells in diluted muriatic acid, and to the filteredsolution add solution of ammonia as long as any precipitatefalls; then filter again, and decompose the muriate by a so-lution of pure carbonate of potass; wash the precipitate, andexpose it to violent heat in a platina crucible, till it cease tolose weight. The result is pure lime.

Qualities. — Well prepared lime is of a white colour, mo-derately hard, and brittle. Its specific gravity is 2'3. Itstaste is hot, pungent, and bitter; on animal matter it operatesas a most powerful caustic; changes the vegetable blues togreen, and is infusible. Water poured on it is absorbed witha hissing noise, much heat is evolved, and the lime swells,falls to pieces, and is then* said to be slaked; in which state itreadily combines with sulphur, forming a sulphuret, and is toa certain degree soluble in water. It appears to be a com-pound of a peculiar metal which has been named calcium ', andoxygen.

Use. —Lime in this state is chiefly employed for pharmaceu-tical purposes and for forming the solution.

Officinal preparations. Liquor Calcis, L. E. D. Polassa cumCalce, L.

CRETA PREPARATA, Lond. Prepared Chalk.

" Take of chalk, a jwund. Add a little water to the chalk,and triturate it to a fine powder. Throw this into a large ves-sel of water, stir it, and after a short interval pour off the su-pernatant turbid water into another vessel, and set it apart that

1 This nietal has the colour and appearance of silver, is solid, four times heavierthan water, absorbs oxygen, and burns brilliantly in the open air, and by beingoxidized is converted into quicklime, Phil. Trans, 1808.