PART It.

Materia Medtca.

81

carbonic acid is driven off, and lime, or quicklime, as it is com-monly called, is obtained; the properties of which shall benoticed under the title Calx, among the preparations. It isnot, however, perfectly pure, but contains generally portionsof silex, argil, or magnesia. To obtain pure lime, let whitemarble be dissolved in dilute muriatic acid, leaving an excessof marble undissolved. A solution of pure ammonia beingadded to the solution of marble will indicate by a precipitatethe presence of argil and magnesia, which are to be separatedby filtration; and the lime itself precipitated in the form ofcarbonate by a solution of pure sub-carbonate of potash. Thisprecipitate, after it is washed with water and dried, and exposedto a very violent heat in a platinum crucible, is pure lime. 1

Until the introduction of the galvanic battery as a chemicalagent, lime was regarded as a simple substance; but it has sincebeen found to be a compound of a peculiar metallic base, namedcalcium by Sir H. Davy, and oxygen, in unknown proportions. 1We have here to notice the calcareous fossils only which aremedicinally used.

1. Chalk. Friable carbonate of lime.Officinal. Creta. Land. Dub. Carbonas Calcis. a. Mollier,

Creta alba. Edin. Chalk.

Syn. Craie (F.) Kreide [G.) Gasso (/.) Greda (S.) Khurree muttee (H.) Kilo (A.)

This mineral is found in the north of France, Poland, someof the Danish islands, and in great abundance in the south ofEngland, within a range which commences at FlamboroughHead, in Yorkshire, and is continued, with irregular interrup-tions, through the midland counties to Surrey, Sussex, Hamp-shire, and into Dorsetshire. It generally occurs massive inbeds; and contains numerous relics of marine animals, andoccasionally those of the hard parts of land animals.

Qualities. — Chalk is inodorous and insipid; but adheresslightly to the tongue. Its colour is either white, or yellowish,or grayish white. It feels meagre and rough; is not very hard,but is pulverulent; breaks with an earthy fracture; stains thefingers, and marks. Its specific gravity is from 2.3 to 2.6. Iteffervesces with acids; and generally contains, besides lime andcarbonic acid, a small portion of argil. The average propor-tion of lime is 53 per cent.

Medical properties and uses. — Chalk is antacid; but it mustundergo levigation and washing, before it can be internallyadministered. In powder it is externally advantageously em-ployed as an absorbent in burns and excoriations.Officinal preparations. Creta preparata. L. E. D.

2. Limestone. Hard carbonate of lime.

1 Cbenivix, Memoirs of the Irish Academy, 1802.

G

* Phil. Tnns, not.