Look under "
oil" in Dorland's Medical Dictionary (Merck Source). There are about 100 definitions of different types of oil, including essential and fixed oil (and oil of male fern). It says an essential oil (also called distilled, ethereal or volatile oil)is "an oil that evaporates readily; such oils are usually found in aromatic plants, to which they give odor and other characteristics. Most consist of a mixture of two or more terpenes", while a fixed oil (also called expressed or fatty oil) is "an oil that does not evaporate on warming. Such oils, consisting of a mixture of fatty acids and their esters, are classified as solid (chiefly stearin), semisolid (chiefly palmitin), and liquid (chiefly olein). They are also classified as drying, semidrying, and nondrying, depending on their tendency to solidify when exposed, in a thin film, to air".
I wondered why it was called "essential". Then I found a site from the Biology Department of the College of St. Benedict/St. John's University, Collegeville, MN:
I. What is an essential oil?
A. Definition.
An aromatic liquid (oil). They usually smell pleasant. Since these oils have an odor or essence, they are called “essential oils”.
B. Fixed vs. volatile oil
Essential oils are volatile, or in other words, they evaporate readily. In contrast, the fixed oils like corn, safflower and peanut, do not evaporate. The Grease Spot Test is a test to determine whether an oil is volatile or fixed. Simply spot a small sample of the oil on a sheet of paper. If it leaves an oily mark, like after eating some potato chips, the oil is fixed. If it disappears, it is an essential oil.
There's a lot more on this site about perfumes and spices, in case you're interested. It says that light and oxygen can ruin perfumes, perfumes work as antiseptics, and increase perspiration rate and cool the body. If you want to know more, you'll have to click
here.
Tinman
