42 S. J. Plimpton — Recombiriation of Ions 



recombine in the absence of any external field for small inter- 

 vals of time which can be regulated and determined mechanic- 

 ally, and by the sudden application of a strong electric field 

 driving over to the electrodes those ions which remain in the 

 gas. In this way we obtain a series of values of n correspond- 

 ing to different values of t, and values 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 shorten- 

 ing 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 corpuscular radiation practi- 

 cally 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 recombination. 



In connection with (4) it is worthy of mention that in previ- 

 ous 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 practically 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 approx- 

 imately 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 experimental observa- 

 tion. Such an initial effect has made itself manifest in the 

 present series of experiments and will be described later. 



Preparation of Gases and Vapors. 



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 vapors 

 were evaporated in each case from the liquids as supplied by 

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

 the apparatus was pumped out to a few millimeters of mercury. 

 The substance to be tested was then let in until the greatest 

 allowable pressure was reached and again pumped out as 

 before. This process was repeated at least three times. 



Great care was taken in every case to make the gas or vapor 

 dust free by passing it through several inches of glass wool 

 and then allowing it to settle for several hours.* 



