ON THE ELECTRICAL PROPERTIES OF PURE SULPHUR. 
121 
sulphur was again heated and the resistance diminished steadily, till at 129-5 the 
spot began to move at a rate of 10 divisions per second, and went on faster and 
faster, till after three minutes it had gone off the scale. On cooling, the resistance 
was undoubtedly permanently reduced—say tenfold ; it increased, as before, down to a 
temperature of 90° C., when the sulphur evidently crystallized and the resistance sud¬ 
denly increased. A curve has been drawn (fig. 3) showing the variation of resistance 
with temperature, the observations being for the most part made with the voltage 
each way ; at the points of rapid change this was not possible. The hysteresis of 
the diagram is partly due to the time required during crystallization. The rate of 
variation of temperature at important points was never more than one degree in five 
minutes. The permanent reduction of specific resistance by heating was observed 
again with another film at a later date, and appears to be a natural phenomenon. 
Table IX.—Showing Resistance of the Film of October 28th, 1892, at Different 
Temperatures. 
Temperatures. 
Specific resistance in C.G.S. units. 
135-6° C. falling .... 
1-5 x 10 21 
124-4 „ „ .... 
1-8 x 10*1 
108-5 ,, .... 
2-9 x 10 21 
100 „ „ .... 
3-733 x 10 21 
96 .... 
3-3 x 10 22 
95 „ „ .... 
3-5 x 10 22 
101 "5 „ rising .... 
3-9 x 10 22 
Above this the resistance 
fell as shown on the curve till about 127°, 
when the sulphur melted, 
from the curve :— 
The two following relations are taken 
At 128° C. rising .... 
9 9 x 10 20 (uncertain) change very rapid 
On cooling again at 83° C. . 
3 X 10 22 
'* We provisionally attribute the fall of resistance to a change in the amount 
of insoluble sulphur present, probably, almost certainly, an increase. It may be 
objected that we ought to have melted our film at a lower temperature, and thus 
prevented the formation of insoluble sulphur at all. The reply to this is, that 
unhappily one cannot adjust the plates properly unless one has some time for the 
operation, and the cooling surface of the plates is so great that sufficient time is not 
afforded if the sulphur is nearer to its crystallizing point to begin with. 
Film of November 9th, 1892. 
It was now necessary to examine the behaviour of a film rapidly cooled so as to 
form a mixture of soluble and insoluble sulphur. Our first attempt failed, owing to 
* Further research shows that this provisional conclusion must be modified. 
MDCCCXCVI.—A. R 
