[ ^3 ] 



VI. 



EXPEEIMENTS ON LARGE IONS IN AIR. 

 By professor J. J. NOLAN, M.A, D.Sc, 



AND 



J. ENTRIGHT, B.A., M.Sc, University College, Dublin. 



[Read May H. Publislied July 24, 1923.] 



We propose in this paper to set forth the results of some experiments on 

 the origin, constitution, and behaviour of the large ion in air. The work 

 described deals principally with the effect on the large ions of certain 

 substances such as SOo and NH3, with the effect of temperature, with the 

 decay of large ions by combination with small ions, and with the occurrence 

 of multiple charges. 



Genesis of the Large Ion. 



The ions dealt with in our experiments are almost exclusively those 

 produced by ordinary Bunsen flames. Large ions may be produced in many 

 ways, but there appears to be no doubt that whatever the manner of pro- 

 duction, or whatever differences may a,ppear at the beginning, the ions under 

 similar conditions ultimately become identical. It has been well established, 

 for example, that large ions, produced in different ways, will, under normal 

 circumstances, ultimately attain a mobility of about -yo-'oo cm. /sec. in a field 

 of 1 volt /cm. For the production of large ions two things would appear to 

 be essential. In the first place, something must be present which will serve 

 as an original nucleus. This, in many cases, appears to be a body of a 

 hygroscopic character, which in a moist atmosphere rapidly accumulates 

 water and grows to a stable size. The stable water spherule thus formed is 

 the ordinary uncharged " iiucleus." The second essential to the formation of 

 the large ion is, of course, the electric charge, which is generally supplied in 

 the form of a " small " ion. 



In the gas from a Bunsen flame both the large ions and the uncharged 

 nuclei are present, normally about half of the total nuclei being uncharged. 

 If, by means of an electric field, the ions are removed from the flame-gas, the 

 uncharged nuclei, while recombining slowly amongst themselves, will pick 



K.l.A. PROC, VOL. XXXVI, SECT. A. [10] 



