Alkali Salt Vapours in Flames. 123 



I£ these ions consist o£ atoms o£ the alkali metal, and if we 

 suppose that the light emitted also comes from atoms of the 

 metal, then we can calculate the charge carried by the atoms 

 of the metal in the flame. We have the well-known 

 equation 



ve _ k 



where e is the charge carried by one ion, n the number of 

 molecules per c.c. in a gas at pressure p, k the ionic velocity, 

 and K the coefficient of diffusion of the ions. If the metal 

 atoms are only charged part of the time, then the observed 

 value of the velocity will be kf, where /'is the fraction of the 

 time during which the atom is charged. 



We have therefore If— 60. Hence for alkali salts in the 

 flame 



60p 



In a previous paper I have given values of/ deduced from 

 the observed conductivities of flames containing salt vapours. 

 The values found were 



Caesium 0*99 



Rubidium 0'96 



Potassium 0"91 



Sodium 0*41 



Lithium 0*21 



Taking the temperature of the flame to be 2000° C, we get 



in electrostatic units, where n denotes the number of molecules 

 per c.c. in a gas at pressure p and at 0° C. 



Taking p = 1*01 x 10 6 dynes per sq. cm., we get the following 

 values of 7i e: — 



n e. 



/?o^l-3xl0 10 - 



Csesium 3-47 xlO 10 2-67 



Rubidium 3*58 ., 2-75 



Potassium 3'53 ., 2'71 



Sodium 3*21 „ 2-47 



Lithium 4-96 „ 3*81 



