356 



Scientific Proceedings, Royal Dublin Society. 



The results of Table 15 are shown plotted in Figs. 5 and 6. These show- 

 that the graphite is the worst electrode for making contact with the material. 



In the case of line C, Tig. 6, the lowest observed point was that corre- 

 sponding to temperature 61° C, Table 15. 



At the time the data for this point were obtained, the wetted surfaces of 

 the sample had been penetrated by a film of absorbed water. This film then 

 increased in thickness as the temperature fell, that is, as time proceeded, until 

 the last determination at 20 - 5 c C, was made. 



sUio 

 55 . 

 3V - 

 33 . 

 31 • 

 31 . 

 30 . 

 aq. 

 it • 



*I 



It 



I 



a. 



IjOGABITHMIC VALUES OF THE SPECIFIC RESISTANCE. 



Fig. 6. — The relation between Logio a and — fur blue erinoid when different electrodes are used. 



Curve A is for graphite ; B for mercury ; C for water ; D for mercury after lj hour's 

 drying in air at ordinary temperature. 



It follows, therefore, that the resistance of the sample woitld in this case 

 have a double decrease as the temperature fell, one due to fall of temperature 

 and which if there were no extra penetration of water, would probably give 

 a straight line approximately parallel to B; the other due to the thickening 

 of the film of water reducing the thickness of the unwetted part of the walls 

 of the tube. This explains in a general manner the divergence of line G 

 from parallelism with B. 



A more detailed explanation would involve a knowledge of the rate and 

 degree of uniformity of the water absorption. Dependence would also have 

 to be placed to a slight extent upon the fact, already demonstrated, that 

 decrease of thickness of erinoid is accompanied by increase of resistance. 



