It is a white powder, or in small lumps which break into powder readily on pressure. It has no taste or smell.

Preparation. - Prepared chalk is simply chalk freed from sand and other impurities by elutriation (p. 647).

Solubility. - It is insoluble in water, but it dissolves in acids such as acetic acid.

Reactions. - While doing so it effervesces strongly, showing that it is a carbonate, and the solution gives the reactions of calcium (p. 646).

Impurities. - Silica, barium, strontium, magnesium, iron.

Test. - It should dissolve without leaving any residue in hydrochloric acid (absence of silica), B.P. The solution in acetic acid should give no precipitate with test solution of sulphate of calcium (absence of strontium and barium), and the tests for magnesium and iron should not indicate more than traces of these substances, U.S.P.

Dose. - 10 to 60 gr.

Officinal Prepaeations

B.P.

Dose.

Mistura Cretae. Chalk mixture. Chalk (1) suspended in cinnamon water (30) by means of gum (1)and sweetened with syrup (2)..................................................

1-2 fl. oz.

Pulvis Cretae Aromaticus. Aromatic powder of chalk.

Cinnamon (8), cardamoms (2), cloves (3), nutmeg (6), saffron (6), sugar (50), chalk (22) .................................

10-60 gr.

Pulvis Cretae Aromaticus cum Opio. Aromatic powder of chalk thoroughly mixed with powdered opium.

10-40 gr.

U.S.P.

Mistura Cretaa. Chalk mixture. Compound chalk powder (20),cinnamon water (40), water (40)

1/2-2 fl. oz.

Pulvis Cretae Compositus. Compound chalk powder. Prepared chalk (30), powdered acacia (20), sugar (50).........

8-60gr.(1/2-4gm.).

Trochisci Cretae. Chalk lozenges.

4 grains in each..........................................................................................

Ad lib.

Chalk is also contained in Hydrargyrum cum Creta, B. and U.S.P.

Action. - Carbonate of calcium or chalk possesses the astringent and antacid powers of lime itself, and is without its irritating qualities. It can therefore be given in much larger doses, and so chalk is used, instead of liquor calcis, in the diarrhoea of adults accompanied by acidity.

Uses. - Chalk may be used as a dusting powder to the skin in excoriations, burns, and ulcers. It forms a useful tooth-powder. Internally it serves to arrest diarrhoea, and is often given, whatever be the cause of the diarrhoea; but when the disease depends upon some irritating substance in the intestine, the irritant should be removed by a dose of castor oil previous to the administration of the chalk. In the form of whiting, chalk forms a useful antidote in cases of poisoning by acids, and especially by oxalic acid.