EXPERIMENTAL STUDY OF LARGE IONS IN THE AIR. 



57 



gradient of one volt per centimetre. The mobilities are 

 given as calculated by Zeleny's formula without any cor- 

 rections. In the investigation no leak was observed with 



zero air stream. 



Table I. 



Date. 



Temper- 

 ature. 



Hta3*& 



1/fc- 



1905 

 Oct. 6 



„ 13 

 Dec. 7 



„ 8 



„ 21 

 1906 

 Jan. 22 

 Feb. 12 



„ 15 



Ap. 28 



9 8 



23° C. 



25 



26 



25 



24 



23 

 20 

 23 

 23 

 23 



756 



76% 





2856 



765 



59 



2833 





771 



68 





2796 



768 



78 





2916 



766 



55 





2901 



761 



72 



2836 





755 



68 



2524 





760 



76 



2678 





767 



64 



2565 





767 



64 





2476 



3. Absorption of ions by hygroscopic substances.— When 

 air flows over hygroscopic material both small and large 

 ions are absorbed. To get some idea of the magnitude of 

 the effect, observations have been made of the percentage 

 reduction in the number of ions, and of the percentage of 

 moisture absorbed when the air stream is passed over 

 calcium chloride and over phosphorus pentoxide before 

 entering the testing pipe. The calcium chloride was used 

 in a glass tube and the phosphorus pentoxide in an iron tray. 

 The tray had a base 30 X 22*5 cms., divided by partitions 

 which forced the air to flow over the whole surface of the 

 drying agent, and was provided with a cover the edge of 

 which dipped into a mercury seal so that the phosphorus 

 pentoxide, when spread over the bottom of the box, could 

 be quickly protected from the moisture of the outside air. 

 The air stream flowed over the surface of the pentoxide 



