CAPACITY AND RESIDUAL CHARGE OF DIELECTRICS. 
II7 
The figures given are the deflections of the galvanometer in scale divisions corrected 
for the shunt used. Recalling that one scale division means a known value in 
amperes, that a known potential in volts is used, these figures can readily be reduced 
to ohms The capacity of the flask is 0‘0026 microfarad at ordinary temperatures 
and times, and the specific inductive capacity of its material under similar conditions 
is about 8. Hence one could reduce to absolute conductivities of the material. It is 
more interesting to consider how fast the capacity is changing. Take the first result 
given in Table HI. for another flask 75 at 10 seconds ; this means a conductivity 
75 X 0‘358 X 10“®/ 1,500 — about 0'179 X 10“^°, and this is, of course, the rate 
in farads per second at which the capacity is changing in that experiment compared 
with a capacity of the flask 1-10“^ microfarad measured with the shortest times, or, 
to put it shortly, the flask owing to residual charge is changing capacity at the rate 
of about 3 per cent, per second. These figures also show that the residual charge up 
to 20 seconds increases greatly with the temperature; the residual at 60 seconds 
rises with the temperature up to about 70° C. or 80° C., and then diminishes ; residual 
charge at 300 seconds begins to diminish at about 60° C. One may further note the 
way in which the form of the function t/; (oj) changes as temperature rises. Compare 
in Table I. the values for 20 and 30 seconds, the ratios are :— 
Temperature. . . 15 34^ 54^ 70 85 117 132, 
Ratio. 1-39 1-27 1*16 1-25 1*38 1-67 1-74. 
In other words, if we expressed ^ (co) in the form C/f", we should find m first 
diminishes as temperature rises to 54°, then increases as the temperature further 
rises. This has an important bearing upon the effect of residual chai’ge on apparent 
capacity and resistance. 
It will be noticed that the residual charge, for the same time, at high temperatures, 
is somewhat greater in Table II. than I. The results in Table I. were obtained on 
November 7th, 1894 ; those in Table II. on November 13th, 1894. There is no doubt 
but that heating this glass and submitting it to charge when heated, alters the 
character of the results in such manner as to increase residual charge for high 
temperatures. To test this more thoroughly, a new flask was blown out of window 
glass composed of silica lime and soda without colouring matter, and on January 3rd, 
1895, was charged and discharged in the ordinary manner. After the results given 
in Table III. for January 3rd were obtained, the flask was charged for 21 minutes at 
1,500 volts, the direction of charge being reversed after 10 minutes, the temperature 
of the flask being 133°. We see that on January 4th, Table III., the same effect is 
observed, namely an apparent increase in residual charge for the same time at high 
temperatures. This may probably be attributed to a change in the composition of 
the material by electrolysis. 
