298 



Scientific Proceedings, Royal Dublin Society. 



The latter was much more pronounced at the higher temperatures used, 

 and a further test on two samples at 350° C. showed a still higher increase in 

 dielectric absorption. 



While samples D, E, and F showed the latter to an appreciable extent, 

 the others were practically free from it. 



The directional effect for sample D is represented as follows, and is typical 

 also of the cases of E and F. 



in which the (+) indicates that the megger and leakage currents flowed from 

 the inside to the outside mercury, and (-) in the reverse direction. This 

 effect is still under investigation. 



The data for the leakage curves were often obtained several times for a 

 given temperature and found to be practically the same both for (+) and (-) 

 directions even in the case of the samples showing dielectric absorption at 

 the higher temperatures. 



As the results of the present work could only be regarded as approximately 

 representative of the insulation resistance of porcelain at different tempera- 

 tures, all the calculations were made with the slide-rule. 



The method of entry of the results is that used by Rasch and Hinrischen, 

 who, in an important paper, 1 showed that the change of resistance with 

 temperature of porcelain among other materials followed approximately a 

 simple law. 



Thus, if o- is the specific insulation resistance of the sample and T its 

 absolute temperature, 



in which a and b are constants for a given material. 



Zeit. Elektrochem. 14, 1908, p. 41, Table 3, fig. 19. 



