310 



Dr. Taylor and Mr. Inglis : 



Fig. 1. 



For in the case of A1 2 (S0 4 ) 3 , neither ion would pass through 

 the film, and the resistance measured should be high ; in the 

 case of AICI3, and of K 2 S0 4 , only one ion could pass through, 

 and the resistances should be of the same order, though 

 much smaller than in the first case. The presence of the 

 film should not make much difference to the resistance 

 of the KC1 solution, since both ions can pass through ; this 

 solution should, therefore, have the smallest resistance. 



The apparatus which we used consisted of two glass tubes 

 with flanges ground to fit one another. 

 Between the two tubes was placed a 

 piece of filter-paper which had been 

 soaked in a dilute gelatine solution. The 

 flanges were pressed together while the 

 gelatine was hot, so that a close and 

 water-tight junction was made. Dilute 

 solution of aluminium sulphate was 

 poured into one tube which was closed 

 with a rubber stopper provided with 

 an overflow tube ; the apparatus was 

 then reversed and a dilute solution of 

 ammonia was poured into the other 

 tube. In this way a film of Al(OH) 3 

 was formed in the gelatinized paper, 

 and after a few hours the whole was 

 carefully washed out with distilled 

 water. One tube was then filled with 

 the solution to be examined, the corre- 

 sponding electrode adjusted to a definite „ 

 mark — an overflow tube preventing ~ 

 rupture of the film ; the apparatus was 

 then reversed and the other tube filled 

 with the same solution, and the electrode 

 inserted. The whole was placed in a 

 thermostat at 25° C. and measurements 

 of the resistance made. They were as 

 follows : — 



AlsfSOJ. 



A1C1 3 



KC1 



289 ohms 

 259 ohms 

 '2±8 ohms. 



These differences are very small, espe- 

 cially as we found the error of adjust- 

 ment of the electrodes to be considerable. 



It is doubtful if it is practicable to determine these differences 



