Soft paraffin is a mixture of various paraffin hydrocarbons, usually obtained by purifying the residue left when crude petroleum is distilled, by successive treatment with sulphuric acid, sodium hydroxide, and charcoal. It occurs as a semi-solid, white or yellow, translucent, bland, odourless, tasteless, soft mass, unctuous to the touch, and free from acidity or alkalinity. Petrolatum, U.S.P., corresponds to the yellow variety of soft paraffin; Petrolatum Album, U.S.P., to the white variety. Soft paraffins are also known under the following trade-names: Adepsine, Adeps Petrolei, Chrisma, Cosmoline, Fossiline, Geoline, Paraffin jelly, Petroleum jelly, Salvo Petrolia, Saxoline, and Vaseline. Specific gravity at the melting point, 0.840 to 0.870 (0.820 to 0.850 at 25°). Melting-point, 35.5° to 39°, or even somewhat higher. Melting-point of Petrolatum, U.S.P., 45° to 48°. No unpleasant odour or flavour should be developed on heating to 50°.
Insoluble in water, slightly soluble in alcohol, freely soluble in ether, chloroform, benzene, oil of turpentine, fixed or volatile oils.
Dissolves thymol, menthol, salicylic acid, phenol (about 1 in 30), atropine (1 in 120), cocaine (1 in 100), morphine (1 in 200), quinine (1 in 80), veratrine (1 in 80), the oleic acid solutions of the alkaloids in all proportions; when melted it mixes with oils, fats, hard paraffin, oleates, oleic acid, etc.
Action and Uses.—Soft paraffin is not irritating to the skin, is unoxidisable, and does not become rancid; the caustic alkalies have no action on it, but it is easily removed from the skin by soap and water. It is not readily absorbed, and is not so suitable a vehicle for drugs that are intended to pass through the skin as is hydrous wool fat; it is an excellent emollient, and the best ointment basis for reducible substances, especially mercuric salts. The white and yellow varieties are employed in the preparation of paraffin ointment, according as a white or coloured ointment is required. Paraffin ointment is a protective to the skin; it adheres to the dressing, leaving wounds clean. Ointments prepared with soft paraffin melt at the temperature of the body, and soak into the dressing. Soft paraffin is the best basis for ointments to be applied to the eyes, on account of the absence of acidity; ointments of atropine, eserine, cocaine, etc., may be prepared by dissolving the pure alkaloids in the soft paraffin melted at a low temperature. A mixture of hard and soft paraffins is used as a pill excipient (see Massa Paraffini). Soft paraffin has been given internally for coughs in doses of 1 to 4 grammes (15 to 60 grains); its action is probably confined to lubricating the intestinal tract, for which purpose it is also given in doses of 4 to 8 grammes (60 to 120 grains).
Also: Carbolised Paraffin.
- Ceratum Paraffini, B.P.C.—PARAFFIN CERATE.
- Beeswax, 6.25; soft paraffin, 93.75. This cerate may be prepared with the yellow or white varieties of beeswax and soft paraffin; if required as the basis of a white ointment, the white beeswax and paraffin should be employed. Paraffin cerate can be incorporated with half its weight of water.
- Parenol, B.P.C.—PARENOL. Syn.—Solid Parenol.
- Soft paraffin, white, 65; wool fat, 15: distilled water, warm, sufficient to produce 100. Parenol is a stable emulsion of soft paraffin, which is absorbed readily by the skin, and causes no irritation, It does not become rancid on keeping, and forms a useful vehicle for the application of various medicaments, for which rapid absorption is desired. Parenol can be made to take up more than its own weight of water, and mixes readily with all fats.