ADULTERATION OF ESSENTIAL OILS WITH TURPENTINE. 
221 
with gelatine and lioney, a piece of microscope glass. A column of 10 inches 
is accurately measured and the tube with the oil introduced into the upper 
part of the box, as at IN’. A ray of light being now transmitted through the 
apparatus a great change will be found to have taken place, and instead of 
the point of maximum intensity of the ordinary ray being at zero, it will be 
found only by turning the eye-piece a greater or smaller number of degrees 
to the right-hand or the left, the direction being determined by the order in 
which the colours of the spectrum follow each other, and whether it is neces¬ 
sary to revolve the analyser to the right or the left-hand to obtain the fol¬ 
lowing sequence, viz. violet, red, orange, yellow, green, blue. 
Thus the power possessed by the essential oil under examination of rotating 
the plane of polarized light is measured, and a pretty constant index for com¬ 
parison is obtained. 
Having determined the number of degrees required by a well-authenticated 
sample of pure oil, as well as of its supposed, or possible adulterants, it be¬ 
comes a simple matter of calculation to determine the proximate amount of 
adulteration present; for it is proved by repeated experiments that the amount 
of rotation recorded is the mean of the combined rotating force of each of the 
components. 
The following tables show the results of a careful examination of essential 
oils of known purity, and of ordinary commercial qualities. 
Table showing the amount of rotatory power of— 
Pure Essential Oil of 
Commercial Essential 
Oil of 
Caraway, English .... 
+ 212 ° 
Caraway, Foreign . . 
+ 1G° 
„ Foreign .... 
+ 156° 
Dill „ 
+ 200 ° 
Cloves, English . 
+ 9° 
Lemon, super . . . 
+145° 
Dill . 
+ 200 ° 
,, fine .... 
+ 78° 
Berganiotte . 
+ GO 0 
,, medium . . . 
+ 36° 
Lemon . 
+ 150° 
„ low .... 
+ 12 ° 
Orange . 
+ 99° 
33 35 .... 
+ 5 
Juniper, English .... 
-155° 
Juniper, Foreign 
- 9° 
Lavender, English .... 
- 26° 
Lavender, „ 
- 34° 
„ Foreign .... 
- 22 ° 
33 33 * 
- 72° 
Rosemary . 
- 35° 
Rosemary . 
- G3° 
Turpentine, American . 
+ 35° 
Turpentine .... 
- G 8 ° 
,, French . . . 
- 89° 
33 • * * 
- 4G° 
Peppermint, English a . . 
- 64° 
Peppermint, English . 
- 68 ° 
55 55 0 * • 
- 72° 
„ American 
- 35° 
,, American . . 
- 53° 
The above table has been formed from the results of a large number of ex¬ 
periments, and the numbers assigned to the pure oils arc an average of the 
various results which have been found to vary to a certain limited extent, 
owing to the age of the oil and other circumstances. A degree or two more 
or less in a commercial point of view is not a matter of much consequence, 
the points requiring chief attention in the observation are perfect transparency 
and uniform temperature ; my results have all been noted at the temperature 
of the laboratory, viz. 68° F. 
The principal adulterant of essential oils is spirit or oil of turpentine. On 
reference to the table, it will be observed that American turpentine rotates 
the plane of polarization to the right-hand, while Bordeaux turpentine ro¬ 
tates it to the left; hence at first sight a difficulty arises as to the integrity 
of the test proposed ; and again, still further perplexity arises from the fact 
that turpentine itself has been recently very subject to adulteration .with 
petroleum, which, having no action upon the polarized ray, lowers by dilution 
the power of rotation enjoyed by the original turpentine ; lienee the low power 
