
DISCHARGE OF ELECTRICTY THROUGH TURPENTINE. 675 
distances between the surfaces. The spark always passed from or to where 
the gas bubbles were ; and bubbles seemed to be formed in the path of the 
spark. When the upper electrode was negative, it was easier to get a succes- 
sion of sparks ; and the number of gas bubbles formed was greater. This was 
probably due to the fact that in this case the bubbles adhered firmly to the 
surface. When the air pressure inside the receiver was diminished, the gas 
bubbles formed were larger and more numerous. Ata pressure of half an 
atmosphere, with the upper plate positive, and at a distance of half a centi- 
metre from the lower, the bubbles were observed to effect the discharge, by 
carrying the electricity with them to the negative electrode. It is possible to 
cause a shower of bubbles to descend from the upper to the lower surface. 
When they impinge on the lower plate, they emit a slight flash and correspond- 
ing sound. At very low pressures we found it impossible to get a spark. 
When we substituted a brass ball of 8 mm. diameter for the upper disc, 
and charged it positively, the gas bubbles rolled outwards along the lower plate 
in straight lines from the centre, until they reached a point where their buoy- 
ancy lifted them up. There was a more rapid formation of gas bubbles when 
the ball was negative than when positive. 
_ We also tried, for the upper electrode, a conical point 3 centimetres in 
height, by a diameter of 5 mm. at the base. When the extremity of the cone 
was 1 or 2 mm. from the lower electrode, the jars being off, the discharge 
passed in the form of an arc, which rotated in the direction of the hands of a 
watch, as we looked down uponit. Ata distance of 2 centimetres the spark 
was sinuous and in the form of an arc. 
It is probable that the gas liberated is due to the decomposition of the oil of 
turpentine, and not merely to the liberation of a gas loosely held; for the supply 
' seemed inexhaustible, and after we had passed a great number of sparks, the 
liquid assumed a brownish tint, and a black deposit was found on the plates. 
We have not as yet got a sample of the oil of turpentine analysed. 
We made several series of observations of the difference of potential re- 
quired to produce a disruptive discharge at different distances between the 
| disc and the plate. They all point to the same conclusion, and the following 
| is representative :— 
