ussure have shown that volatile
oils absorb oxygen immediately they have been drawn from the plant, and
are partially converted into a resin, which remains dissolved in the
remainder of the essence.

He remarked that this property of absorbing oxygen gradually increases,
until a maximum is attained, and again diminishes after a certain lapse
of time. In the oil of lavender this maximum remained only seven days,
during each of which it absorbed seven times its volume of oxygen. In
the oil of lemons the maximum was not attained until at the end of a
month; it then lasted twenty-six days; during each of which it absorbed
twice its volume of oxygen. The oil of turpentine did not attain the
maximum for five months, it then remained for one month, during which
time it absorbed daily its own volume of oxygen.

It is the resin formed by the absorption of oxygen, and remaining
dissolved in the essence, which destroys its original flavor. The oil of
lemons presents a very great analogy with that of oil of turpentine, so
far as regards its transformations, and its power of rotating a ray of
polarized light. Authorities differ as regards this latter property.
Pereira states that the oil of turpentine obtained by distillation with
water, from American turpentine, has a molecular power of right-handed
rotation, while the French oil of turpentine had a left-handed rotation.
Oil of lemons rotates a ray of light to the right, but in France a
distilled oil of lemons, sold as scouring drops for removing spots of
grease, possesses quite the opposite power of rotation, and has lost all
the original peculiar flavor of the oil. Oil of lemons combines with
hydrochloric acid to form an artificial camphor, just in the same manner
as does oil of turpentine, but its atom is only one half that of the oil
of turpentine. The artificial camphor of oil of lemons is represented by
the formula, C_{10}H_{8}HCl; the artificial camphor of oil of turpentine
by C_{20}H_{16}HCl.

According to M. Biot, the camphor formed by the oil of lemons does not
exercise any action on polarized light, whilst the oil of lemons itself
rotates a ray to the right. The camphor from oil of turpentine, on the
contrary, does exercise on the polarized ray the same power as the oil
possessed while in its isolated state, of rotating to the left. These
molecular properties establish an essential difference between the oils
of turpentine and lemons, and may serve to detect adulterati