386 



Mr. A. S. Eve on 



curve for these. But in the case of ether, and of water, the 

 curves for positive and negative ions are similar in type, but 

 unequal in magnitude, proving that the number of ions are 

 unequal. Again, the first four curves from the left are 

 somewhat similar in character, and show that the greater 

 part of the ions are drawn to the central cylinder during the 

 time the air enters the electroscope ; hence the curves bend 

 sharply, and the effects end in two or three minutes, after 

 which the curves become horizontal straight lines. These 

 curves are representative of liquids which give rise to mobile 

 ions. But in the case of ether, fig. 3, and still more of 

 benzyl alcohol, fig. 4, the initial quarter-minute fall is but a 

 small fraction of the whole; hence the curves bend gradually, 

 and the fall of potential can be observed for more than ten 

 minutes before the electroscope returns to its natural leak. 

 Therefore some of the ions are extremely inert, and move 

 very slowly across the electric field. These differences in 

 character are indicated in the following table, in which the 

 percentage falls of potential, during the periods stated, are 

 compared with the total falls. 



Table I. 

 Percentage falls of potential. 





Water. 



Amyl 



Alcohol. 



Ethyl 

 Alcohol. 



Acetic 

 Acid. 



Ether. 

 26 



Benzyl 

 Alcohol. 



During first \ min. 



91-4 



81 



73 



62 



14-7 



second £min. 



57 



15-7 



21 



26 



30 



17-6 



second § min. 



2-8 



2-5 



4 



8-5 



20 



17-6 



remaining time. 







•8 



1-6 



3-5 



24 



50 



It is easy to calculate approximately the velocity of the 

 slower moving ions, treating the electroscope as if it consisted 

 of two long concentric cylinders. The slowest ions of benzyl 

 alcohol have a velocity of about 10~ 4 cm./sec. in a field of 

 1 volt/cm. They are therefore large inert ions such as 

 Langevin has found in the atmosphere, and Giese in the gases 

 from a flame, and Aselmann by the splashing of salt water. 



An important result may be deduced from these curves. 

 Since their shapes and sizes are identical for positive and 

 negative ions, in the case of most liquids tested (water and 

 ether being notable exceptions), we must conclude that the 

 positive and negative ions are similar in mass and constitution. 

 It does not appear that one set of ions consists of liquid and 



