Ions of Alkali Salt Vapours in Flames. 717 



under f. The value of fky was taken to be 70 cms. 

 per sec. 



The value of k L can be calculated roughly on the kinetic 

 theory of gases, for in a flame at about 2000° 0. the free 

 path (A,) of an atom is probably about 10 -4 cm* The well 

 known formula Jc 1 = e\/mY gives 1^ = 300 cms. per sec. for 

 an atom of hydrogen, or 120 for an atom of lithium. This 

 is about one-third the value of & x as estimated above, which 

 is as near as could be expected. 



I think, therefore, that the evidence provided by the 

 measurements made with the object of finding the velocities 

 of the positive ions in flames is not inconsistent with the 

 view that these ions are single atoms of the alkali metal. 



Measurements on the negative ions in flames have 

 also been made by the writer and others f . The negative 

 ions appear to be free electrons, so that their deposition on 

 the positive electrode cannot be supposed to cause an increase 

 in the current, as in the case of the positive ions at the 

 negative electrode. It seems, therefore, that the supposed 

 determinations of the velocity of the negative ions in flames, 

 by finding the least P.D. required to make them move against 

 or across the stream of gas, are based on a fallacy. When 

 the salt is put in near the negative electrode the large re- 

 sistance there is diminished, so that the current ought to be 

 increased, whether the P.D. is big enough to make the 

 negative ions move against the stream or not. The 

 following table contains the currents observed taken from 

 my paper J. 





Cur 



•ent. 



P.D. 



(Volts). 







(Without salt.) 



(With salt.) 







-3 



-13 



0-25 



o 



-10 



0-5 







- 7 



075 



+ 2 







10 



+ 3 



+ 5 



15 



+ 3 



+ 20 



20 



+ 3 



+ 30 



3 



+3 



+33 



* Sir J. J. Thomson, { Conduction of Electricity through Gases.- 

 2nd ed. 



t Marx, Moreau, and E. Gold. 



\ Phil. Trans. A. ccxxxvii. p. 517 (1899). 



