218 
MR, J. ZELENY ON THE VELOCITY OF THE IONS 
aluminium surface was used, the effect of the surface ionization could not have been 
sufficient to produce any marked error in the results. 
The surface ionization also varies with the nature of the gas, but the values 
obtained by J. Perrin for aluminium with the gases used in these experiments were 
in all cases much less than for tin in air. 
§ 9. Oxygen. 
The gas used in these experiments was the commercial oxygen obtained from a 
cylinder, which contained about 5 per cent, of impurities, mostly nitrogen. Since 
the size and nature of the apparatus prevented the employment of the most pure 
gases, it seemed advisable to use the cylinder gas. The density vms changed but 
little by the presence of the impurities, and, so far as known, the velocity should 
therefore be but slightly affected. The drying of the gas and its saturation with 
aqueous vapour were carried out in the same manner as with air. The following set 
of readings was taken for the negative ions in oxygen saturated with aqueous 
vapour :—- 
Temperature = 17'3° C. X = 5‘01 centims. Barometer = 76'4 centims. 
Excess pressure in gasometer = 1*54 centims. 
,, ,, apparatus = ’55 centim. 
8 cells = 16'3 volts. 
Table IX.—Moist Oxygen. Negative Ions. 
Voltage of outer 
cylinder. 
Electrometer deflection 
in 30 seconds. 
Descent of gasometer 
in 40 seconds. 
Cells. 
Divisions. 
Centims. 
- 3 
194*5 
5*06 
-4 
157 
5*11 
-5 
106*5 
5*02 
-6 
41 
5*11 
-6*6 
17 
5*07 
-5*6 
67 
5*08 
-5*2 
93*5 
5*09 
-4*6 
125*5 
5*03 
The results are shown in Curve I. of fig. 10. 
The corrected value of U =: 18*83 centims. per second. 
A = 13 0 5 volts. 
18*83 
v — 5T18 —--= 1*413 centims. per second, and when reduced to 
5-01 x 13*55 1 
76 centims. pressure this becomes 1'43 centims. per second. 
T = *— "27 second, 
