Ion Mobilities Using the Erikson Method on Gases of Controlled Purity

Measurements of mobilities of ions in air and air mixed with known quantities of other gases, were made with the Erikson air-blast method under conditions in which the nature of the purity of the gas could be reasonably controlled. The results show that there is no ageing effect as observed by Erikson in air dried over P₂{O}₅$ and liquid air, or even in air passed slowly over Ca${Cl}₂$. In these two cases the normal positive and negative ionic mobilities are observed. If air from the room of 60 percent or 90 percent relative humidity at 20^∘{}C, is used the well-known ageing effects of Erikson are observed. With mixtures of 5 percent and 25 percent HCl no ageing effects are observed and the mobilities show the same general behavior observed by Loeb with the A. C. method. With 5 percent NH₃ the positive ion has the same mobility as the negative ion, but at ages over about 0.01 seconds both negative and positive ions show an apparent ageing, the positive ion going over to the usual value observed while the negative ion forms an ion having a mobility between the old and new positive ions. In pure C₂{H}₂$ positive and negative mobilities were observed in agreement with those found by Loeb and Du Sault and Wahlin while in dry air with 5 percent ${C}₂H₂ normal air mobilities were observed with no ageing effect. It is concluded that the ageing of positive ions in dry air in general proceeds very much more rapidly than Erikson assumes and possibly consists in the attachment of the initial positive ion to a bulky molecule of some impurity present. Water vapor and NH₃ inhibit this action either by forming groups which delay attachment to molecules of impurities present, or by removing the latter. Thus Erikson's ageing effects do not appear to be the true ageing but rather retarded ageing effects due to the action of water vapor or other substances.