532 
MU. 0. W. RICHARDSON ON THE ELECTRICAL CONDUCTIVITY 
The numbers on 530 and 531 yield the curves in fig. 16, The straight line on the 
right is drawn from the observations on p. 530, and corresponds to lower temperatures 
than the other. The experimental points for this curve are denoted by O. The 
other curve from the observations on p. 531 refers to somewhat higher temperatures. 
The experimental points for this curve are indicated thus ; X. 
All these three curves are fairly close approximations to a straight line ; it is 
therefore quite evident that the observations are represented very closely by 
assigning to the saturation current a formula of the type C/eS = \ 
When we come to the actual values of the constants in the above formula, the 
agreement with the simple theory is not so good as in the case of platinum, though 
possibly this is partly due to the greater difficulty of the experiments. The curves 
in fio’s. 15 and 16 give for the value of h 
11‘9 X 10^, 97 X 10^, and 7‘8 X 10^ respectively. 
In order that the differences of the values of h should be proportional to the contact 
E.M.F. between carbon, platinum, and other metals, h for carbon should be 5'2 X 10'^, 
since its value for j^latinum is 4’9 3 X I Ob The difference between this and the above 
numbers does not appear to be very great, but the effect of a small error in h is 
enormous when we come to calculate from it the value of n, the number of corpuscles 
in a cub. centim. of carbon. 
If we take 7‘8 X 10^ as the best value of h, and C = 2180 at 1515° absolute as 
being the mean of the two series of temjDerature measurements, we find A is of the 
order 10®* and n is of the order 10'®. Now, Mr. Patterson^ finds that at ordinary 
temperatures n = 10^®, The effect of temperature on the resistance of carbon 
indicates that the concentration of the corpuscles would be at least ten times as 
great at 1000° as at 0° C., so that we should expect to find n of the order lO'A As 
a matter of fact, if we take h = 5'’2 X 10* instead of 7‘8 X 10*, we find n = 5 X 10“^ 
instead, of 10-®. 
Pteasons which might make this method of determining n give values which are too 
large, will be considered at some length after the experiments on sodium have been 
described. 
III. Experiments with Sodium. 
§ 1. Nature of Pruhlem. 
Sodium was selected as the next metal to be investigated on account of its strong 
electropositive character. Since this implies a great attraction for positive electricity, 
we should expect its power of retaining the negative corpuscles to l3e much smaller 
than that of the conductors hitherto examined. If the foregoing theory is correct the 
cor])uscles ought to escape from the alkali metals at a much lower temperature than 
* ‘ Phil. Mag.,’ 6, HI., 655. 
