285 
APPENDIX TO A PAPER ON THE ELECTRICAL RESISTANCES 
OF FIXED AND VOLATILE OILS. 
BY MR. T. T. P. B. WARREN. 
The following is a description of the apparatus employed in the experi¬ 
ments described in the October number of the Pharmaceutical Journal:— 
A brass cylinder of symmetrical bore is cemented into a vulcanite base, 
and is supplied with a binding screw. A plunger, surmounted with a vulca¬ 
nite collar, is inserted into the tube, and drops into a cavity in the base, the 
object being to enable the plunger to be inserted always in the same position. 
The collar insulates the plunger from the cylinder, and also serves to keep it 
in its place. The pluuger is made of stout brass rod, and lias &lso a binding 
screw attached to it. The cylinder being filled with oil, and the plunger 
inserted, if one of the terminals of the battery is connected to the one side of 
the galvanometer, and the pluuger connected to the other side, a current will 
pass through the oil to the galvanometer, when the circuit is completed either 
by connecting the exterior of the cylinder with the other battery terminal, 
direct, or through earth. The deflections produced will be proportional to the 
conducting powers. 
The following are the dimensions of the cylinder and plunger employed in 
my experiment:— 
Diameter of plunger .... *304 inch. 
Length of ditto.3'450 ,, 
Internal diameter of cylinder . ‘409 ,, 
Precautions required fur the Practical Application of this Test. 
It is evident that, so long as the space between the cylinder and the plunger 
contains any non-conducting medium, no current will flow on depressing the 
contact-key ; this should always be done previous to performing a test. 
An ordinary sine galvanometer might be used in testing the volatile oils, 
when it will be necessary, for comparison, to take the sines of the angles of 
deflection instead of the deflections themselves ; but for some of the fixed oils 
it is necessary to use a great number of elements, or to employ a very deli¬ 
cate galvanometer. 
The dimensions of the cylinder and plunger should be noted, since the de¬ 
flection will vary with the length and diameter; corrections must therefore 
be made to reduce the dimensions to one standard size; and I purpose, on a 
future occasion, to reduce the resistances here given to what would have been 
obtained with columns of oil having the length of one metre, and a sectional 
area of one millimetre. In the absence of this, the corrections required are—■ 
1. Since the leakage will be proportional to the length of the tube, other 
circumstances being equal, the resistances will vary directly as the length. 
2. The leakage will vary according to the thickness of the column of oil, 
and this is proportional to the logarithm of the ratio of the diameters of the 
cylinder and plunger. 
The battery contacts should be as short as possible, but in all cases should 
be of the same duration. In my tests, I observed the deflections after half¬ 
minute and one-minute contacts, and the results are given after one minute’s 
contact with the battery. The reason of this arises from the variable effects 
produced by electrolysis, which is extraordinarily marked in turpentine and 
oil of poppies. A few minutes’ application of 150 cells converts them into 
very good conductors, which arises, no doubt, from a portion of metal dis- 
