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.
When Petrolatum is prescribed or ordered without further specification, soft Petrolatum (Petrolatum Molle) is to be dispensed.
A fat-like mass, of about the consistence of an ointment, 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 Soft Petrolatum be liquefied, and brought to a temperature of 1400 F.; 6o° C, it will have a specific gravity of about 0.820 to 0.840. The melting point of Soft Petrolatum ranges between about 1040 and 113° F.; 400 and 450 C.