220 
BRITISH PHARMACEUTICAL CONFERENCE. 
tendency to overcome the pressure of the air from that direction, and thus admit of the ■ 
pressure of air on the upper surface manifesting itself. 
Mr. Evans said that Mr. Schacht’s filter closely resembled one that had been patented 
some years ago by Mr. Britten, of Liverpool, for the filtration of oil. 
ON THE ADULTERATION OF ESSENTIAL OILS WITH TUR¬ 
PENTINE, AND THE MEANS OF ITS DETECTION. 
BY H. SUGKDEN EVANS, F.C.S. 
It is well known, and admitted on all hands, that the adulteration of essen¬ 
tial oils is very extensively practised, both abroad and in this country. Many 
means have been suggested for the discovery of this fraud, but all have 
proved more or less defective and unsatisfactory in their results, giving evi¬ 
dence only of the fact of an adulteration having been practised, without any 
approximation to a determination of the extent or proportion of the adulte¬ 
ration. 
A readily applied method of testing, whereby the value of an essential oil 
can be easily determined, has been much desiderated. 
I propose to describe an apparatus I have arranged, and the results I have 
obtained from its use, showing that by availing ourselves of the power most 
essential oils possess of rotating the plane of polarization of a beam of polarized 
light transmitted through them, either to the right-hand or to the left, we may 
obtain an index of values closely approximating to the actual extent of adul¬ 
teration or deterioration existing. To those possessing a microscope with 
polarizing prisms attached, the arrangement of this apparatus or polariscope 
is simple and inexpensive, as the annexed sketch will 
explain. A B E F is an upright box, 2 feet high and 
3 inches square in internal measure. The upper part, 
to D C, is capable of being entirely closed in by a door, 
]3 C, and at D C there is a shelf having a hole truly bored 
in its centre -g- inch in diameter. The lower portion of 
the box is open in front at C F. Beneath the shelf or 
stage D C is centrally fixed the Nichols prism, or polar¬ 
izer of the microscope. M is a plane mirror to reflect a 
ray of light through the polarizer and body of the appa¬ 
ratus. In the centre of the top of the box at H a plane 
convex lens of low power is fixed, and above it, at i, a 
perforated stop. The eye-piece, J K, consists of the 
second or analysing prism of the microscope, J, or better, 
a double-image prism, set in a circular disk of brass or 
stiff cardboard, K, the circumference of which is di¬ 
vided into a vernier of 360°. This eye-piece and vernier 
disk fits into a socket in the tube I, and is capable of easy 
and true revolution. L is an upright pillar carrying an 
index hand. Thus arranged, and the prisms adjusted 
so that the ordinary image of a ray of light transmitted 
through the apparatus is at its maximum intensity when the index hand points 
to zero on the vernier disk, the polariscope is ready for use. 
The essential oil to be examined is contained in a glass tube, N, which is 
simply an ordinary piece of glass tubing, ^ inch in diameter, 12 inches long, 
the cut extremities of which are roughly ground flat; to one end is cemented, 
