222 
BRITISH PHARMACEUTICAL CONFERENCE. 
indicated in the table in some commercial specimens of turpentine. These 
variations lead to discrepancies in the results of examinations, but the occa¬ 
sion of them is most readily detected by dilution of the suspected oil vllh 
boiling water, when the odour of petroleum, if present, soon manifests itself, 
and further, the difficulty arising from the contrary powers of rotation of 
Trench and American turpentine is resolved, by framing tables of values 
based upon calculations of both the Bordeaux and American turpentine. 
It will generally be found that an oil adulterated on the Continent of Eu¬ 
rope, accords, in its reactions with polarized light, with the table framed upon 
the Bordeaux calculation, while oil adulterated here, in ordinary times when 
the American turpentine is easily obtainable, corresponds with the table cal¬ 
culated from the American data. Thus a further advantage is presented, that 
not only is the nature and amount of the adulteration determined, but it is also 
localized. 
The following tables will illustrate the mode of estimating the values of 
essential oils, and such tables may be multiplied, to refer to nearly every oil. 
Tor a considerable period I have employed this mode of valuing essence 
of lemons, and I have found the indications of the polariscope as indexed in 
the following table, to accord very accurately with the accredited commercial 
values of the samples examined, and I consider the process one by which the 
commercial value of almost any essential oil may be accurately determined 
within certain very moderate limits of variation. 
? TABLE OP VALUES. 
Essence of Lemons. 
American. 
Bordeaux. 
Value. 
+150° 
+ 150° 
100 
+ 120° 
+ 90° 
75 
+ 90° 
+ 35° 
50 
+ 60° 
- 20° 
25 
+ 50° 
- 50° 
Oil of Lavender. 
10 
American. 
Bordeaux. 
Value. 
- 24° 
- 24° 
100 
- 18° 
- 40° 
75 
+ 11° 
- 56° 
50 
+ 27° 
- 75° 
25 
+ 36° 
- 82° 
Oil of Rosemary. 
10 
American. 
Bordeaux. 
Value. 
- 35° 
- 35° 
100 
- 14° 
- 51° 
75 
0° 
- 62° 
50 
+ 16° 
- 75° 
25 
+ 28° 
- 83° 
10 
Liverpool, 1865. 
In the course of the discussion, it was stated that experimenters of repute had failed 
in applying the polariscope to the detection of adulterants in essential oils, chiefly be¬ 
cause different specimens of an oil or an adulterant often differed widely in their power 
of rotating plane polarized rays. Thus Pereira* had found that French turpentine dif¬ 
fered from American, not only in degree, but in the direction of rotation, the former 
being Icevo-gyrate, the latter dextro-gyrate. 
* Pharmaceutical Journal, vol. v. p. G7. 
