Ions produced by Rontgen Rays. 69 



of a are then determined for different conditions of gas- 

 pressure by means of a variation of equation (2) which is 

 indicated below. 



This method is believed to have the following advantages : 



(1) By using radiation of smaller intensity and by 



shortening the time-intervals, the effect of diffusion 

 is greatly reduced. 



(2) By restricting the beam of rays between the 



electrodes diffusion is further reduced and corpus- 

 cular radiation practically removed. 



(3) By the use of single flashes of X-rays the difficulty 



of maintaining uniformity in the rays is greatly 

 lessened. 



(4) Since the duration of the flash is very brief, it is 



possible to study the initial stages of recom- 

 bination. 



In connexion with (4) it is worthy of mention that in 

 previous investigations no information has been afforded 

 with regard to the initial stages of recombination. In a 

 steady state of ionization, ions of practically all ages are 

 present, diffusion has become very appreciable except in the 

 case of the ions of recent formation, and the ionization is 

 necessarily very intense, so that, on the whole, a prac- 

 tically uniform distribution of the ions prevails at the instant 

 when the rays are cut off. 



With single flashes of Rontgen rays the case is different. 

 At the instant when the flash has ceased the ions are 

 approximately all of the same age, and diffusion has been 

 practically inoperative ; so that any peculiarity in the initial 

 distribution of the ions is capable of being detected by expe- 

 rimental observation. Such an initial effect has made itself 

 manifest in the present series of experiments, and will be 

 described later. 



Preparation of Gases and Vapours. 



The carbon dioxide gas used in these experiments was 

 obtained in the usual way by the action of hydrochloric acid 

 on marble in a Kipp generator. The sulphur dioxide was 

 taken from a cylinder of the compressed gas. The vapours 

 were evaporated in each case from the liquid as supplied by 

 the chemist. In all cases, before admitting the gas or 

 vapour, the apparatus was pumped out to a few millimetres 

 of mercury. The substance to be tested was then let in 

 until the greatest allowable pressure was reached, and then 



