Sapo Durus, B.P. Hard Soap.
Hard or Castile soap is prepared by heating olive oil, which consists chiefly of olein with sodium hydroxide and water, and subsequently "salting out." In India the olive oil may be replaced by arachis oil or sesame oil. The soap occurs as a white or greyish-white, dry, odourless solid, which softens on heating, and becomes horny when dried in warm air, being then readily powdered. When dried at 110° it should not lose more than 30 per cent. of moisture. Sapo, U.S.P. is hard, olive oil soap. "Mottled" Castile soap is obtained by adding a salt of iron to the soap mass.
Soluble in water (1 in 20), boiling water (1 in 1.5), only slightly soluble in alcohol, but entirely soluble in boiling alcohol (1 in 2).
Constituents.—The chief constituent of hard soap is sodium oleate. As in the case of Sapo Animalis, glycerin is formed as a by-product in making it, and remains in the liquid left on "salting out" the soap.
Action and Uses.—Hard soap is given internally as a cholagogue and laxative, also to increase the activity of other laxatives, such as aloin, scammony, jalap, and rhubarb. Large doses are reputed to assist in removing gall-stones, through its action as a solvent of cholesterol, and a pure form of sodium oleate is prepared for internal administration in pills or capsules. Hard Soap is a useful pill excipient for resinous substances and volatile oils. It is an ingredient of many plasters. Acid sodium oleate, so-called, is prepared by adding an excess of oleic acid (about 50 per cent.) to the normal oleate; the extra acid is said to be of value therapeutically. Eunatrol is a soft, white, soapy mass, said to consist of 70 per cent. of sodium oleate and 30 per cent. of oleic acid.
Dose.—3 to in decigrams (5 to 15 grains).
- Emplastrum Saponis, B.P.—SOAP PLASTER.
- Hard Soap, 15; lead plaster, 90; resin, 2.5. Mix the soap, plaster, and resin, having previously melted them separately at a low temperature, and evaporate with constant stirring to a suitable consistence. Soap plaster is used as a protection for corns and bunions and in place of resin plaster where the latter is too adhesive.
- Emplastrum Saponis, U.S.P.—SOAP PLASTER, U.S.P.
- Hard soap, 10; water, a sufficient quantity; lead plaster, 90. Prepared by mixing the hard soap with sufficient water to produce a semi-liquid, then adding the melted lead plaster, mixing, and evaporating to a proper consistence
- Linimentum Saponis, U.S.P.—SOAP LINIMENT.
- Hard soap, 6; camphor, 4.5; oil of rosemary, 1; alcohol (95 per cent.), 72.5; water, sufficient to produce 100.