The soaps prepared with olive oil are of two distinct kinds: Sapo durus, or hard soap, in which the other chief ingredient is soda; and Sapo mollis, or soft soap, in the manufacture of which potash is employed. Hard soap is of a grayish-white color, corneous when cold and dry, and then reducible to powder, though, if warmed, readily yielding to pressure. Water dissolves it, and, if the solution be treated with lime or lead, it precipitates. Rectified spirit dissolves it entirely. Incineration leaves a residue of non-deliquescent ash.

Soft soap, instead of being solid, in consistence resembles honey or jelly. It is yellowish, translucent, and scentless, often speckled with white, owing to the presence of minute crystals, and is soluble in rectified spirit. The residue, after incineration, is an ash, which rapidly deliquesces.

These two descriptions of soap, though differing much in physical qualities, are both composed of oleates and palmates. Hard soap consists of oleate and palmate of soda; soft soap of oleate and palmate of potash. Neither of them, when pure, should impart an oily stain to paper.

Soap, whether hard or soft, is in pharmacy useful for little besides external purposes. The Sapo durus used to be given as an antacid, in doses of five to twenty grains; it is employed in the preparation of the Pilula saponis composita, and of various other pills, not so much, however, for any service it may render as a medicine, as for its suitableness as a vehicle or adjunct; it is valuable, also, in the preparation of certain plasters, such as the Emplastrum saponis, and of the Linimentum saponis. The Sapo mollis has likewise been administered as an antacid, in doses of five to twenty grains.

Preparations and Dose. - Pilula Saponis Co., gr. v. (.30); Ceratum Saponis; Emplast. Saponis; Linimentum Saponis.