142 Messrs. Gee and Holden on 



f. Influence of Temperature. — Inspection of the curves 

 (figs. 6, 7, and 8), giving the variation of the film-forming 

 current-density with the temperature will show that A is 

 markedly affected by a change of temperature, and particu- 

 larly so at the higher temperatures ; an increase in the 

 temperature requiring a corresponding increase in A, the rate 

 of increase of A with temperature being greater at the 

 higher temperatures. The observations from which the 

 curves are drawn were obtained in the following manner: — 

 The anode and kathode were placed in separate beakers, each 

 containing strong pure H 2 S0 4 . Connexion was made be- 

 tween the two vessels by means of several inverted U-tubes 

 filled with acid. The beaker containing the kathode was 

 kept at a constant temperature throughout. Starting with 

 both beakers at about 15° C. the current was put on in the 

 /3 direction, and the current-resistance varied until the film 

 was formed and the corresponding value of A noted. The 

 current was then reversed for a moment in order to remove 

 the film, the beaker containing the anode heated, and for 

 every few degrees of rise of temperature A was found as 

 just described. In the case of falling temperatures the pro- 

 cess was somewhat different and yielded more regular results. 

 After A had been found for the highest temperature, the 

 resistance in circuit was slightly increased, the film being 

 removed by reversing for an instant, and the anode vessel 

 allowed to cool. The temperature was then noted at which 

 the film again formed with the slightly diminished current. 

 This procedure was repeated until the anode vessel had cooled 

 down to the desired extent. 



g. Influence of Viscosity. — It was thought probable that if 

 we made dilute H 2 S0 4 (say 10 per cent, acid) sufficiently 

 viscous that the film would be produced ; but negative results 

 have accompanied the addition of both glycerine and gelatine 

 to the dilute acid. With a 50 per cent, acid to which 2 per 

 cent, of gelatine had been added, the value of A was reduced 

 to one third by this addition. Addition of glue to strong 

 H 2 S0 4 has a similar effect in lessening the value of A *. 



h. Effect of Platinizing the Electrodes. — Some difficulty has 

 been experienced in trying to estimate the effect which 

 platinizing a platinum electrode has on the value of A, on 

 account of the impossibility of accurately measuring the 

 surface of the platinized wire. There is no doubt that after 

 platinizing a few moments much greater currents than that 



* It is perhaps worth mentioning that a jelly made of glue and water 

 gave the film at the kathode. In one case, when the electrodes were a 

 wire and a Wollaston's point, the resistance was 2000 ohms when the wire 

 was kathode, and 45,000 ohms with the point as kathode. 



