Vol.. 6, 1920 
PHYSICS: L. B. LOEB 
437 
from stopcock greases and sealing waxes. The filling of the chamber was 
accomplished by exhausting to 1.5 cm. pressure and filling slowly with 
the purified gas six or seven times. 
The curves numbered I in figures 1, 3 and 4, give the characteristic 
photoelectric saturation curves obtained in air at 95 mm. pressure, and 
in hydrogen and nitrogen at about 750 mm. pressure, when the current 
to the electrometer plate, under a constant accelerating potential is plotted 
against the potential. When the measurement of the current to the upper 
4 
I 
f 
\ 
) — 
A 
t 
r> 
y in Volts 
FIG. 2 
H2 1^743 mm. O2 12 mm. I— Saturation; II— Press =293 mm., N= 360; Ill- 
Press =151 mm., N=364 
plate was made using the alternating potentials the results obtained in 
air, and in hydrogen contaminated with O2 are entirely different. The 
current remains nearly 0 until a certain critical voltage Yo is reached, 
and then rises rapidly eventually approximating a curve of the same shape 
as the saturation curve, but of half the ordinate. A curve of this type 
obtained in air at a pressure of 95 mm. using a frequency of alternation 
of 148 cycles is shown in figure 1, curve II. Figure 2, curves II and III 
show the results obtained in a mixture of 98.4% hydrogen and 1.6% 
oxygen at pressures of 293, and 151 mm., respectively. The frequency 
of the alternating potential was 362 cycles per second. Taking the value 
of the intercept of these curves with the voltage axis (Vo), one can de- 
