438 
PHYSICS: L: B. LOEB 
Proc. N. a. S. 
termine the velocity {u) of the ion in unit field from the equation u = 
Nd^/Vo (where d is the distance between the plates and N is the frequency 
of commutation). By multiplying u by the ratio p/7Q0 (where p is the 
pressure at which the measurement was made) one obtains the mobility 
constant k of the ion. Now the mobility constant of an ion under normal 
conditions is of the order of magnitude of 2 cm. per second while that of 
the electron, though not definitely known, is of the order of magnitude of 
200 cm. per second or greater. It is obvious then that by determining the 
—> 
I 
r 
\ 
I 
I 
y in Voli-5 
FIG. 3 
Pure H2. Press = 730 mm. I— Saturation ; II— N =712; III— N = 14.5 
mobilities of the carriers in the gases the nature of the carriers may be de- 
termined. 
The value of k obtained from the curves for air is 3.25 cm. /sec. The 
values of k obtained in the mixture of hydrogen and oxygen above are 
12.9 and 20. 3t cm/sec. respectively, for the two pressures 293 and 151 
mm. vSince the normal values of k in air and in hydrogen are of the order 
of 2 cm. /sec. and 7.5 cm. /sec. respectively, while those for the electrons 
in these gases are above 200 and 750 cm. /sec, it is to be concluded that 
the carriers observed above are chiefly ionic in character. 
When, however, these measurements were carried out in the carefully 
purified gases N2 and H2 the results were very different. These are illus- 
trated in curves II and III, figure 4 for N2, using frequencies of 714 and 
