What are essential oils?

Volatile oils are the odorous principles found in various plant parts. When they are exposed to air at ordinary temperatures they evaporate, therefore they are called volatile oils, ethereal oils, or essential oils. The last term is applied because the oils represent the "essences" or odor constituents of the plants. As a result, they are usually colorless, particularly when fresh, but with age they may oxidize and resinify, thus becoming darker. Therefore, storage should be in a cool, dry place, tightly stoppered, preferably full in amber glass containers.

Essential oils are highly concentrated plant extract (steam distilled, molecular or chemically extracted) - highly volatile (evaporate readily) with characteristic odors - many are non-oily (more like water than oil); though most are oily-feeling - usually lighter than water (most float on top of water) - insoluble in water (however, will impart odor to water) - soluble in alcohol, ether, fixed oils (vegetal), organic solvents - they dissolve grease, iodine, sulfur and phosphorous; reduce certain salts - generated or secreted by specialized plant cells

Physical Characteristics: although differing in their chemical constitution, they have many physical properties in common: boiling points vary from 160° to 240° C, densities are from 0.759 to 1.096, high refractive indices, most are optically active, specific rotation is often a valuable diagnostic property mixtures of many constituents.

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