Astronuc said:Apparently different gases were tried in cathode ray tubes at the time.
However based on the fact that Thompson used an evacuated tube (0.1 mmHg vs 1 atmosphere or 760 mmHg), the I would expect the gas was air.
http://www.aip.org/history/electron/jj1897.htm
A cathode-ray experiment is a scientific experiment that involves the use of a cathode ray tube, a sealed glass tube containing a vacuum and electrodes, to study the properties of electricity and the behavior of electrons.
The presence of gas in a cathode-ray experiment can impact the movement of electrons within the tube. The gas can either ionize and conduct electricity, or absorb the electrons and prevent them from reaching the other electrode.
The most commonly used gases in cathode-ray experiments are hydrogen, helium, and neon. These gases have low ionization energies and are easily ionized by the electric field in the cathode ray tube.
Changing the gas in a cathode-ray experiment can alter the properties of the electric field within the tube and affect the movement of electrons. This can lead to changes in the observed behavior of the electrons and the overall results of the experiment.
Gas pressure in a cathode-ray experiment is controlled by adjusting the voltage and current of the electrodes. This allows for the manipulation of the gas molecules and their behavior within the tube.