(From Crete, the place whence it was first brought). Chalk. The only kind now used in medicine is the white chalk, which is found in most parts of the world. It is a pure white mineral calcareous earth of different degrees of hardness; it crumbles between the fingers, and stains them white; readily diffuses in water when finely powdered, and as soon subsides; sticks to the tongue without any astringency. Its form is amorphous, stalactitical, or crystallized; specific gravity from 2.3 to 2.7. Its crystals are rhomboidal parallelopiped, and when transparent their refraction is double.

The best is that which is perfectly white, soft, close, and solid, equal and uniform when broken, free from sand and flints, and insipid to the taste; though chalk, when first dug, has often a slight pungency, as it has not a full proportion of carbonic acid. Many other earths are of a similar nature, but this being the purest is preferred.

It dissolves in all the acids, particularly in the nitrous and muriatic; even totally in vinegar. The vitriolic precipitates it from all other acids, and forms with it a selenite. It is convertible into quick lime: with borax it melts into a transparent glass. The solutions of it in acids are bitterish.

Chalk is employed as a remedy against the heartburn, and other disorders that have acidity in the primae viae for their cause. Some use it, when finely powdered, to sprinkle on erysipelatous inflammations. Two drachms for a dose, and repeated at proper intervals, have often effected, it is said, a speedy cure both in a diarrhoea and a dysentery; but this effect, if true, must be owing to its absorbing those acids whose stimuli caused the morbid excretion. When milk turns sour on the stomach, a scruple of chalk may be given with each half pint. This, however, is a very uncommon effect; but chalk is also added when milk forms a hard coagulum, and lies heavy on the stomach. When on any account a free use of chalk is required, if the belly is inclined to costiveness, laxative medicines should occasionally be taken, as the earth may otherwise accumulate.

Chalk should be finely powdered, and separated from its grosser parts by elutriation. Boerhaave prefers it to the cornu cervi calcinatum for making the white decoction with. Bates formerly used to boil half a pound of chalk in three pints of water to a quart, after which he just permitted the grosser parts to fall, and poured off the yet turbid fluid for use; and the London college directs the following chalk mixture, formerly called julepum e creta: take of the whitest chalk prepared, one ounce; of double refined sugar, six drachms; of gum arabic, finely powdered, two ounces; of distilled water, a quart: mix. Pharm. Lond. 1788.

See Dale. Lewis's Mat. Med. Diet. ofchem. Neumann's Chem. Works. Culleu's Mat. Med.

Besides these, the following are often used:

Compound ointment of chalk: neutral cerate of Kirk -land.-R. Cretae pp. aceti distillati, olei olivae aa iv. emplastri lithargyri 8. aq. lithargyriacetati ss. The chalk and vinegar are to be mixed together, and over a slow fire, incorporated with the litharge plaster, and oil; when sufficiently united, the water of acetated litharge is to be added. This is allowed to be an efficacious remedy, when applied to inflamed parts and ulcers, and is much employed in practice. Chalk is often applied to ulcers in its dry state, when the discharge is thin and acrimonious, with success; and it is sprinkled on the poultices in burns, according to Mr. Cleghorn's plan, with singular advantage.

We find in some foreign authors an acetat and a citrat of lime recommended in scrofula, pruritus, hernia, hu-moralis, tumours of the mesenteric glands, in a dose of one or two ounces daily. In this kingdom, the muriat of lime formed by saturating common muriatic acid with chalk, is recommended in scrofula and obstructed glands; of which from half a drachm to half an ounce, in a pint of water, is to be taken daily.

Decoctum e creta. (See Cornu Cervi.) Pulvia e creta compositus; pulvis e creta comp. cum opio. See Bolus.

The two last supply the place of the pulvis e bolo compositus, a pulvis e bolo compositus cum opio, of the old London Pharmacopoeia.

Creta nigra. Black chalk, called also humus nigra pictoria; has never been employed in medicine. Creta rubra. See Ochra.

Creta selenusia, called also terra selenusia. The best is of a shining white friable appearance, and readily diluted with a fluid. It is drying and astringent.

Creta cimolia. Tobacco pipe clay. And creta fullonica. Fuller's earth. See Cimolia alba.