This section is from the book "Materia Medica Pharmacy, Pharmacology And Therapeutics", by W. Hale White. Also available from Amazon: Materia Medica Pharmacy, Pharmacology And Therapeutics..
A mixture of Hydrocarbons, chiefly of the Marsh-gas series, obtained by distilling off the lighter and more volatile portions from Petroleum, and purifying the residue when it has the desired melting point.
A fat-like mass, of about the consistence of a cerate, varying from white to yellowish, or yellow, more or less fluorescent when yellow, especially after being melted, transparent in thin layers, completely amorphous, and without odor or taste, or giving off, when heated, a faint odor of Petroleum. If a portion of Hard Petrolatum be liquefied, and brought to a temperature of 1420 F.; 61.1° C., it will have a specific gravity of about 0.820 to 0.850. The melting point of Hard Petrolatum ranges between about 113° and 1250 F.; 450 and 51.3° C.
Fixed oils, fats of animal or vegetable origin, resin, and organic impurities.
Petrolatum is used exclusively as a bland, neutral protective, and, because it does not become rancid nor act as an irritant, and as it is not affected by acids, alkalies or powerful reducing agents, it is employed as a substitute for fatty materials in ointments. But as it is absorbed with difficulty it is not a suitable vehicle for drugs which are intended for absorption through the skin. Liquid petrolatum has been used as a local soothing application in inflammation of the mucous membrane of the nose, throat, larynx, and even of the bronchial tubes. It is then applied with an atomizer and may be employed as a vehicle for medicinal substances. None of the petroleums are nutritive.