alphabetically, as being simpler for reference.

It is a matter of some difficulty to judge the purity of essential oils,
not only because of their complex nature, but owing to the very great
effect upon their properties produced by growing the plants in different
soils and under varying climatic conditions, and still more to the
highly scientific methods of adulteration adopted by unscrupulous
vendors. The following figures will be found, however, to include all
normal oils.

_Anise Stell_, or _Star Anise_, from the fruit of Illicium verum,
obtained from China. Specific gravity at 15 deg. C., 0.980-0.990; optical
rotation, faintly dextro- or laevo-rotatory, +0 deg. 30' to -2 deg.; refractive
index at 20 deg. C., 1.553-1.555; solidifying point, 14 deg.-17 deg. C.; solubility
in 90 per cent. alcohol, 1 in 3 or 4.

The chief constituents of the oil are anethol, methyl chavicol,
d-pinene, l-phellandrene, and in older oils, the oxidation products of
anethol, _viz._ anisic aldehyde and anisic acid. Since anethol is the
most valuable constituent, and the solidifying point of the oil is
roughly proportional to its anethol content, oils with a higher
solidifying point are the best.

_Aspic oil_, from the flowers of Lavandula spica, obtained from France
and Spain, and extensively employed in perfuming household and cheap
toilet soaps; also frequently found as an adulterant in lavender oil.
Specific gravity at 15 deg. C., 0.904-0.913; optical rotation, French,
dextro-rotatory up to +4 deg., rarely up to +7 deg., Spanish, frequently
slightly laevo-rotatory to -2 deg., or dextro-rotatory up to +7 deg.; esters,
calculated as linalyl acetate, 2 to 6 per cent.; most oils are soluble
in 65 per cent. alcohol 1 in 4, in no case should more than 2.5 volumes
of 70 per cent. alcohol be required for solution.

The chief constituents of the oil are: linalol, cineol, borneol,
terpineol, geraniol, pinene, camphene and camphor.

_Bay oil_, distilled from the leaves of Pimenta acris, and obtained from
St. Thomas and other West Indian Islands. It is used to some extent as a
perfume for shaving soaps, but chiefly in the Bay Rhum toilet
preparation. Specific gravity at 15 deg. C., 0.965-0.980; optical rotation,
slightly laevo-rotatory up to -3 deg.; phenols, estimated by absorption with
5 per cent. caustic potash solution, from 45 to 60 per cent.; the oil is
generally insoluble in 90 per cent. alcohol, though when freshly
distilled it dissolve