430 
DE. HAROLD A. WILSON OX THE 
t(j a small power of the ahsolute temperature such as the square root over small 
ranges of temperature. 
Hence at temperatures near 1000° 0., and may he taken as constant over 
small ranges (^f temperature witliout serious error, so that the current with a small 
E.M.F. is proportional to n, and n is proportional to x when x is small. Hence in 
the foi'inula 
provided we take and Tg very near together, we may replace [xjx^^ by the square 
of the latio of the two currents obtained at and To. 
The following table gives values of q obtained from diagram No. 8 ;— 
(Ti-273.) 
(To- 273.) 
Cl. 
Co. 
</• 
1000° 
950° 
0-9 
0'5 
71,000 
1200° 
1150° 
7-0 
4-7 
64,000 
1300° 
1250° 
12-G 
9-6 
49,000 
Thus q for 1 gramme molecular weight of air is about 60,000 small calories between 
1000° and 1300° C. 
If we take the charges on the ions to be the same as in the electrolysis of solutions 
then we can obtain an estimate of the potential difference, through which the 
charo’e on an ion must fall to do enouo’h work to ionize a molecule of air. To 
O O 
electrolyse 1 gramme molecular weight of any substance requires 9‘6 X 10^ 
coulombs, consequently the required P.D. is 
60,000 X 42 X 10*^’ 
9'6 X 10^ X 10' 
= 2'6 volts. 
The energy set free in a solution when 1 gramme molecular weight of water is 
formed from its ions H and OH, is well known to be about 17,000 calories, and when 
ozone O3 decomposes into oxygen 30,000 calories are set free. It is interesting to 
note that the energy in these two cases is of the same order of magnitude as the 
value just calculated for the energy necessary to ionize air. 
PtLTTHERFORD has detei'inined the energy of the Pontgen rays absorbed by a given 
volume of air, and the number of ions produced in the same volume l)y the rays. 
From this he deduces the energy reqiiired to ionize (me molecule of air at the 
ordinary temperature. His result expressed in volts multiplied by the charge 
on one ion is 170, which is 70 times greater than the value I have obtained at 
temperatures above 1000°. 
It is probable that in Professor Rutherford’s experiment the greater })art of the 
Rontgeii rays absorbed by the air is not used up in producing ions. 
If Ave suppose that the energy required to ionize a molecule is due to the electric 
