due to Heating Aluminium Phosphate. 



589 



0*01 mm. The outer Faraday cylinder was earthed and the 

 inner one connected to the leaf of an electroscope which 

 was charged to a definite potential, positive or negative, as 

 required. 



Fig. 7. 



"VExj-^h, 



i&aftirtj 



The insulation was such that the rate of leak of electricity 

 from the leaf when the salt was not heated was imperceptibly 

 small when the charge was of either sign. 



As soon as heating was commenced quite a distinct leak 

 was noticed, and the rate of leak was the same whether the 

 leaf was charged positively or negatively. 



On the other hand, after the inner cylinder had been 

 reduced to zero potential, no charging up could be detected, 

 thus showing that there was no excess of free ions of either 

 sign in the neighbourhood of the inner cylinder. 



No positive ions could pass through the field between P 

 and E, and it is highly improbable that any free negative 

 ions leave the salt when the latter is charged positively, as 

 in the experiment. Again, the field between P and the outer 

 cylinder is a further preventive against any stray negative 

 ions passing through the small hole into the space between 

 the cylinders. Hence it seems that any ionization produced 

 in the Faraday cylinder when the salt is heated, can only be 

 brought about by the split up of doublets which have passed 

 through the various electrostatic fields and diffused into the 

 space between the two cylinders. 



An effect of a similar nature has been noted by Sir J. J. 

 Thomson * when working with a hot lime cathode. 



Phil. Mag. Dec. 1909, pp. 829 et seq. 



