The Mobility of Aged Ions in Air in Relation to the Nature of Gaseous Ions

The mobility of gaseous ions in air formed by intense x-radiation has been studied by the method of Tyndall and Grindley. The mobility of ions less than 0.08 seconds of age was found to be 2.21 cm/sec per volt/cm for the negative ion and 1.59 cm/sec per volt/cm for the positive ion in agreement with values observed by Loeb and by Tyndall and Grindley. A modification of the apparatus permitted the mobility of ions which had been aged for times up to 1.5 seconds to be studied. In this case a decrease in mobility was observed to values of 2.04 and 1.46 for the negative and positive ions after 1.5 seconds aging. The ionization chamber and source of ionization were the same as those employed by Luhr in recombination measurements. From the theoretical mobility equation of Langevin, the observed decrease in mobility cannot be correlated with the probable increase in ionic mass occurring in recombination measurements under the same conditions. A much larger decrease in mobility is predicted on this basis than is observed in these experiments.