236 Relative Affinity of some Gas Molecules j or Electrons. 



change takes place in the dark, and is similar to an effect 

 found by Wellisch * when he studied the mobilities of 

 electrons in C0 2 . He found that the mobility rapidly 

 decreased in the gas with an increase of time after pre- 

 paration. An even more marked effect of this nature was 

 found by Wellisch f in the vapour of petroleum ether. 

 The small change in the value of n for N 2 with time was 

 accompanied with an increase in pressure of 13 mm. Such 

 •an increase in pressure was possibly due to a decomposition 

 of the N 2 0. If this were the case the change in n would be 

 quantitatively accounted for by the oxygen produced in the 

 process. 



It has been shown by Mr. Wahlin that the relative energy 

 of impact between electron and molecule does not influence 

 attachment. One may then conclude from the nature of the 

 values of n obtained, that n is dependent on either the elec- 

 trons striking a particular point in the atom in order to 

 attach, or in its striking a molecule in some particular state 

 of chemical or physical activity. 



Summary. 



1. The results obtained in a recent study of the mobilities 

 of electrons in pure nitrogen are discussed relative to the 

 theory of the formation of negative ions from electrons and 

 molecules developed by the writer. 



2. An equation is arrived at which gives the values of ?i, 

 the constant of attachment, with a greater degree of certainty 

 than the one previously given. The equation is, however, 

 not yefc satisfactory, owing to the lack of knowledge of the 

 electronic mobilities in the various gases. 



3. On the basis of the equation derived, the values of n for 

 a number of different gases are given as computed from 

 recent experiments. 



4. The results show that in spite of the uncertainties in 

 the determination of n it varies through such an enormous 

 range of values for the different gases, that the order of 

 magnitude of the quantity alone furnishes a characteristic 

 constant of the gas. 



In concluding, the writer desires to acknowledge with 

 thanks the assistance of Mr. Wahlin in the preparation and 

 measurements made on the gases C0 2 and N 2 0. The writer's 

 thanks are also due to Prof. R. A. Millikan for his kind 

 criticism of this paper. 



Byerson Physical Laboratory, 



July "15th, 1921. 



~ * E. M. Wellisch, Am. Journ. Sci. xliv. p. 11 (July 1917). 

 t E. M. Wellisch, ibid. p. 15. 



