113 
ON THE ELECTRICAL PROPERTIES OF PURE SULPHUR, 
It will be noticed from the above that the residual charge in the case of mica— 
properly treated and very dry, is less by far than is generally supposed—but by 
exposure to air, even when heated, the effect is much increased. Booty's best results 
went to show that the residual charge was only about 1 per cent, of the initial 
charge ; these experiments show that mica can be prepared so as to give still less. 
It is difficult to account for the experiment on September 21st, when the mica had 
been heated. Botjty attributes the residual charge almost entirely to the action of 
the edges, which are varnished, and we are inclined to agree with this, but we do not 
see how the polarisation can be galvanic in the ordinary sense, for in our case it must 
have amounted to more than 10 volts. We think it is due to a creeping of the 
charge (see Rowland and Nicoll, £ Phil. Mag,’ [5], vol. 2, p. 414, 1881). The sulphur 
is really phenomenal. We are inclined to attribute most of the small effects observed 
to the residual sources of uncertainty, contact action, imperfect shielding, imperfect 
insulation, imperfect prevention of the creeping of the charge, in spite of these 
effects having been eliminated apparently before the sulphur condenser was inserted. 
Because these uncertainties are suggested, it must not be thought that they were 
overlooked at the time. We believe that everything was done that could be done, 
and that we are, in fact, at about the limit of the applicability of these methods. 
However, taking the numbers as they stand, they are sufficiently remarkable, and 
show that the residual charge, if it exists, is less than, say, four parts in ten thousand 
of the original charge, even when the duration of charge amounts to ten minutes. 
In our previous experiments using the film between the old gilded plates, we made 
use of enormously greater voltages derived from an electrophorus, but some uncertainty 
arose from the possible parting of the plates, and from the burning of the film where 
the spark had jumped across. However, we never detected any residual effect at all 
with the film in question, under circumstances where the residual charge from 
the mica amounted to more than 50 divisions ; this was with a voltage estimated from 
the spark length at about 5000 volts. 
The electric strength of sulphur from the broken film is in the neighbourhood of and 
probably greater than 730 volts per '22 millim., or at the rate of about 3300 volts per 
millim., or 33,000 volts per centimetre, but too much weight must not be attached to 
this, for the influence of a small air bubble in disturbing the field might be very 
considerable, and would reduce the strength very materially. 
We defer the discussion of these results till the similar data for other films have 
been dealt with. 
The residual charge having been found to be so small, rather greater interest 
attached to the specific inductive capacity of the film, which had to be taken again in 
any case in order to give us security as to the permanence of the contact between the 
plates and the sulphur. As the results of a complete series of very careful experiments 
by the ballistic method, using one division of the microfarad only, the one chosen as 
a provisional standard, the capacity of the sulphur was found to be-— 
MDCCCXCVI.—A. Q 
