226 
MR. J. ZELENY ON THE VELOCITY OF THE IONS 
§ 11. Hydrogen. 
The gas was prepared from pure zinc and hydrochloric acid, and bubbled through 
three bottles of strong caustic potash and potassium permanganate to free it from the 
acid and other impurities. Great difficulty was experienced in maintaining the gas 
sufficiently pure on standing, because of the large surface of rubber exposed in the 
gas bag and in the connecting tubes' of the apparatus. The density of hydrogen 
being so small compared to that of air, a small amount of the latter produces a large 
change in the density of the gas, and it was found that the ionic velocities were 
greatly affected thereby. 
The following plan was finally adopted as the most practicable under the circum¬ 
stances :— 
The forenoon of a day was spent in the preparation of fresh hydrogen, this length 
of time being required to generate the large quantity necessary for use and for 
washing the more impure hydrogen out of the apparatus. Beginning early in the 
afternoon, readings were taken as rapidly as possible until after midnight, thus giving 
about eleven hours of continuous observations. The density of the gas was then 
determined by weighing a 600 cubic centims. flask filled first with dry air and then 
with dry gas from the gasometer. Since 1 per cent, of air in the gas made a difference 
of over 6 milligrams in the weight, this permitted a sufficiently accurate determination 
of the amount of the air impurity. A test was made by the eudiometer method, 
which showed that the impurity was practically all air. 
The width of the beam of rays used was '3 centim., as the conductivity was much 
less with the hydrogen than in the other cases. 
The following is a set of readings taken for the negative ions in dry hydrogen :— 
Temperature = 20° C. X = 2'95 centims. Barometer = 76T 5 centims. 
Excess pressure in gasometer = ‘90 centim. 
,, ,. apparatus = '36 centim. 
5 cells = 10*5 volts. 
Table XVII.—Dry Hydrogen. Negative Ions. 
Voltage of outer 
cylinder. 
Electrometer deflection 
in 30 seconds. 
Descent of gasometer 
in 40 seconds. 
Cells. 
Divisions. 
Centims. 
-2-6 
12-5 
9-59 
— 3 
9-7 
9-52 
-3-4 
6-5 
9-31 
-3-8 
3-8 
9-44 
- 3-6 
G 
9-46 
-3-2 
8-8 
9-50 
-2-8 
11-2 
9-38 
-2-4 
14-2 
9-40 
