due to Heating Aluminium Phosphate. 



583 



Thomson found for the positive ions from hot platinum 

 values ranging from 60 to 720. 



The value of e/m for the hydrogen atom in electrolysis is 

 taken as 10 4 . From this it is seen that these positive ions 

 are comparable in size with the hydrogen atom, if we assume 

 the same value for " e " in both cases. 



A quite appreciable though smaller diminution of the 

 current was also obtained under such conditions that e/m 

 when calculated was found to be some 3 or 4 times as 

 large as given above. Either the ions affected in this case 

 have a mass smaller than that of the hydrogen atom, or else 

 their velocity is much less than that due to the electrostatic 

 field applied ; in the latter case we might assume that they 

 started as free ions at some point between the two electrodes 

 and not as such from the surface of the heated salt. 



VIII. Velocity with which ions are shot off from 



the Salt. 



Earlier in the paper it has been suggested that some of 

 the ions escape from the salt on account of their kinetic 

 energy without the application of an electrostatic field. 



To put this in evidence a Dolezalek electrometer was 

 substituted for the galvanometer, since the ions so escaping 

 could not be detected with the latter. The sensitivity of the 

 electrometer was such that 1 volt produces a deflexion of: 

 180 scale-divisions. The pressure was reduced to O'Ol mm. 

 and the temperature varied as required. 



A weak magnetic field was imposed so as to remove any 

 eftVct which negative ions might produce, and both E and 

 the lower heated electrode are earthed initially. 



E was then found to receive a positive charge on discon- 

 necting it with earth. 



If the lower electrode was now given a negative potential, 

 this had to be raised to 1*2 volts to stop altogether the 

 charging up of E. 



If V = the negative potential to which the electrode e is 

 raised to prevent positive ions leaving it, e = the charge on 

 an ion, m = its mass, and v = its velocity ; then, from 

 Ye — \mv 2 we can calculate the velocity "v" with which 

 these ions are ejected from the heated salt. 



Taking the value of e/m obtained earlier, we find that 

 v = l'4:Xl0 6 cm. per sec, a velocity comparable with that 

 (10") of the positively charged particles which constitute the 

 anode rays. 



With weak magnetic field of too low a value to affect the 



