374 Mr. Briggs on Distribution of Active Deposits of 



about twenty times that at which Wellish * showed that 

 aggregation set in, together with the additional strong source 

 of alpha-ray ionization, resulted in the production of aggre- 

 gates of deposit atoms which are known to be able to take 

 positive or negative charges. They are likely then to assume 

 a positive or negative charge according as to whether they 

 are in a region in which there is an excess of positive or of 

 negative ions. The additional source of alpha-ray ionization, 

 together with the separation of the ions by the electric field, 

 would produce a distribution of positive and negative ions in 

 the gas which would account for the results on this theory. 



On searching for a general law connecting the results 

 obtained and the properties of the various gases, it was seen 

 that the percentage of either RaA or RaB positively charged 

 was generally high for those gases whose heat of formation 

 was large. However, a closer relationship appeared to exist 

 between the results and the stability of the gases for increase 

 of temperature : this latter quality, of course, depends partly 

 on the heat of formation. In the table, data estimated from 

 the results of various observers are given concerning the 

 temperatures at which the various gases begin to dissociate. 

 For the gases investigated, the percentage of recoil atoms 

 positively charged decreases with the temperature of dis- 

 sociation of the gas. It is well known that alpha-rays 

 decompose many gases, and as the initial energy of a recoil 

 atom is of the order 10 10 times the average energy of a 

 gaseous molecule at 0° C, it is to be expected that a recoil 

 atom will dissociate many of the molecules in its path, even 

 in the case of elementary gases such as hydrogen and oxygen, 

 and that a part at least of the observed dissociation is pro- 

 duced in this way. The dissociation of gases by heat is 

 usually a bimolecular process ; whereas if dissociation by 

 recoil atoms occurs, it will probably consist in the disruption 

 of single particles. Hunter f, for example, has shown that 

 the dissociation of nitrous oxide by heat is represented by the 

 equation 



2N 2 = 2Nj.+,Qj ; 

 and Wourtzel * gives reasons for believing that in the case 

 of alpha-rays some of the gas is dissociated according to the 

 equation 



N 2 = NO + N. 



If a bi-atomic molecule, for instance one of carbon monoxide, 



* Wellish, Phil. Mag. xxviii. p. 417 (1914). , 

 f Hunter, Zeit. Phys. Chem. liii. p. 441 (1905). 

 J Wourtzel, Le Radium, xi. p. 333 (1919). 



