ELECTRICAL PROPERTIES OF PURIFIED SULPHUR. 251 
reversal should take place, as the direction would originally be in 
the direction of the insoluble quadrants, and the induction charge 
would tend the same way. To obtain a sufficiently great negative 
charge, a small Wimshurst machine was used, with results that 
had been anticipated. The deflection was towards the insoluble 
quadrants, increasing with increasing charge, but no reversal of 
the direction could be obtained. 
The charging was repeated with rotation of the needle and of 
the quadrants in all possible positions, but with the same effect 
each time—deflection towards the insoluble with a negative charge, 
and to the soluble with a positive charge, the latter of which 
reversed in direction upon sufficiently increasing the charge. 
Care had to be taken that the needle was well discharged 
before every charging, as it was found that the residual charge of 
the jar was sometimes sufficient when the needle bad been imper- 
fectly discharged to re-charge it beyond the position of reversal. 
The general conclusion arrived at, therefore, was that there is 
a difference of potential set up upon contact between soluble and 
insoluble sulphur, the positive charge being on the insoluble, and 
the negative on the soluble. This conclusion was always con- 
sistent with the results obtained with the sulphur quadrants 
when care was taken to diselectrify them. All possible induction 
effects were either eliminated by reversal or accounted for in the 
phenomena observed. Although no consistent results were given 
with the sulphur needles, it has been shown that this may easily 
be due to the inherent defects of the method, and not to any 
uncertainty as to the contact voltage under consideration. 
It was not possible by this method to measure the difference 
of potential obtained. As the proportion of insoluble sulphur 
in the so-called insoluble quadrants is a very variable quantity, 
decreasing slightly with a lapse of time, the voltage probably 
varies largely also, so that a particular result would not have any 
general applicability. To get an idea, however, of the voltage 
noted, a Leclanché cell was used with the brass quadrants ; and it 
was found that on charging the needle as before, deflections were 
obtained not differing very widely from those given with the 
sulphur quadrants. It is, therefore, probable that the voltage 
developed between soluble and ordinarily insoluble sulphur 
amount to something of the order of one volt. 
The so-called insoluble sulphur is really a mixture of about 5 
per cent. of insoluble with 95 per cent. of soluble sulphur, the 
latter being at first mostly prismatic and afterwards mostly 
octahedral. As no difference of effect was observed after several 
days ageing of the quadrants, we may consider that the above 
results are not dependent on the particular crystalline condition 
of the soluble sulphur. 
