No I. AN — 3Iobilities of Ions Produced by Spraying. 



15 



This can be investigated in two ways — (1) by varying the rate at which 

 they are drawn from the sprayer, and (2j by keeping the rate constant, and 

 varying the length of their path by interposing lengths of tubing. 



Tables are given for positive and negative ions, showing the mobilities 

 found with different rates of drawing air. 



The numbers derived from experiments in which there was some doubt 

 about the exact point of Isending of the curve have been indicated by a note 

 of interrogation. 



Many of the above mobilities, especially for rates h and c, are the means 

 of a great number of determinations. These tables show, in the first place, 

 what has been stated above — that there is no difference between positive and 

 negative as regards mobility. They also show that the five classes of ions are 

 present together in the air drawn from the sprayer, and that their mobilities 

 do not change appreciably with time. Of course the agreement between the 

 mobilities is not good in some cases ; but if the positive and negative are 

 taken together, and if allowance is made for the difficulty of obtaining good 

 numbers for mobility, this conclusion is justified. Special care was taken in 

 determining the mobility of the slowest ion. In this case we find a very 

 good agreement between the mobility values for all rates. Irregularities in 

 the mobilities of Class 2, which will be dealt with later, prevented so good an 

 agreement in that class. 



The unvarying mobility of the ions is also made clear by experiments on 

 the effect of introducing lengtlis of tubing between the spraying-chamber and 

 the place of observation. The following table shows the results of one set of 

 experiments. Each successive observation was made after introducing about 

 1 metre of tubing. Under the conditions of experiment each length of 

 tubing was equivalent to an increase of about 9 seconds in the time. 



Table II. 

 Eate — 5 litres in 75 sec. 



No. j Mobility of slowest Ion 



1 



Proportion of total lonisatioa due to 

 slowest Ion. 



1 

 2 

 3 

 4 



•0003S 

 •00037 

 •00040 

 •00039 



18 per cent. 



25 



33 „ 



40 



This table shows that the mobility of the slowest ion at least is unaffected 



