Physical Properties
Petroleum jelly is a mixture of hydrocarbons, having a melting-point usually within a few degrees of human body temperature, which is approximately 37 °C (99 °F). It is flammable only when heated to liquid, then the fumes will light, not the liquid itself, so a wick material like leaves, bark, or small twigs is needed to light petroleum jelly. It is colorless, or of a pale yellow color (when not highly distilled), translucent, and devoid of taste and smell when pure. It does not oxidize on exposure to the air and is not readily acted on by chemical reagents. It is insoluble in water. It is soluble in dichloromethane, chloroform, benzene, diethyl ether, carbon disulfide and oil of turpentine.
There is a common misconception that petroleum jelly and glycerol (glycerine) are physically similar, because they feel similar when applied to human skin. While petroleum jelly is a non-polar hydrocarbon hydrophobic (water-repelling) and insoluble in water, glycerol (not a hydrocarbon but an alcohol) is the opposite: it is so strongly hydrophilic (water-attracting) that by continuous absorption of moisture from the air, it produces the feeling of wetness on the skin, similar to the greasiness produced by petroleum jelly.
Depending on the specific application of petroleum jelly, it may be USP, B.P., or Ph. Eur. grade. This pertains to the processing and handling of the petroleum jelly so it is suitable for medicinal and personal care applications.
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