A ll 
G@na7eus) 
XXIV.—On the Discharge of Electricity through Ou of Turpentine. By AvEx- 
_ ANDER MaAcFARLANE, M.A., B.Sc., and R. J. S. Simpson. (Plate XXIV.) 
(Received 7th February 1878. Read 4th March 1878.) 
At the beginning of this session we proceeded to apply the method of 
measuring large differences of potential described in former papers, to the 
investigation of the disruptive discharge through liquid dielectrics. We have 
now obtained some results for oil of turpentine. 
A vessel capable of holding the liquid, and at the same time of forming an 
electrode, was constructed by fixing on a metal plate to one end of a hollow 
glass cylinder of diameter slightly less than that of the receiver of the air- 
pump. ‘The vessel was placed on a metallic support, so as to be in conducting 
‘connection with the metal parts of the air-pump, and with the earth. The 
other electrode, which was either a circular disc, a spherical ball, or a conical 
| ‘point, was screwed on to the brass rod passing through the stuffing-box on the 
top of the receiver, and was thus capable of being adjusted to various heights 
} in the turpentine. The bottom of the vessel is 16-7 centimetres, and the brass 
disc, which commonly formed the upper electrode, is 10 centimetres in diameter, 
and 4 millimetres thick. 
The metal bottom of the vessel was first made of copper; but it was found 
‘that the turpentine, when charged, acted upon the copper very rapidly, forming 
a compound which it afterwards dissolved. Tinfoil pasted on the surface of 
‘the copper plate prevented the action taking place. To raise the surface of 
‘the lower electrode that it might be better seen, we put in a lead plate of 16°4 
‘centimetres diameter and °85 centimetres thick. When the liquid was charged, 
a lead compound was formed with great rapidity, and remained undissolved. 
| The substance formed arranged itself in columns between the electrodes, in 
| the direction of the lines of force. The charge made its way through the 
dielectric by these columns. We found that a tin plate was not acted on, but 
| that it was always necessary to filter the liquid to get rid of any solid particles, 
| as these, when present, never failed to arrange themselves in the lines of force ; 
| and when not of sufficient number to form a continuous chain, dissipated the 
' charge by dancing between the plates. When a chain, so formed, was stretched 
between the electrodes, the index of the electrometer behaved as if a current 
| Were passing by means of the chain,—when the Holtz machine was turned at a 
VOL. XXXVIII. PART II. 8M 

