The effect of a gas film on metal surfaces used for electron recording

A platinum strip was exposed to electron beams of moderate velocity, and then exposed in situ to development by mercury vapour from a mall amount of mercury always present in the tube but cooled by a refrigerant during electron exposures. The system contained no grease or wax seals and the tube containing the platinum strip and electron gun was submerged during exposure in a refrigerant (CO2 in acetone). The platinum strip was so arranged that it could be heated by passing an electric current through it;A definite electron record secured under the following conditions: (a) If there was present on the strip a gas film resulting from exposure to dry air, commercial hydrogen, or commercial nitrogen (of the gases tried). (b) If the platinum strip itself had been outgassed by heating to 1200°C for some time but the system had not been thoroughly baked out;No electron record resulted under the following conditions: (a) If the strip had been soaked in an atmosphere of commercial Argon (in the tube) and then the system thoroughly evacuated. (b) If the strip and tuba, whatever their past exposure to contamination may have been, had been thoroughly outgassed, this last requirement was found to mean repeated periods of baking out at 450°C in vacuum and several heatings of the platinum strip to about 1200°C;It was found that the residuum of gas left after exposure to nitrogen responded to cathode rays in such a way as to leave a mercury vapour deposit exactly the opposite or negative of the records left after similar exposures of the strip with a residual gas film from hydrogen or the atmosphere