Irreciprocal Conduction. 147 



and reduction of platinum, and explains the catalytic action 

 of platinum according to this view. Schonbein, on the other 

 hand, quite as firmly upheld the theory that the oxygen did 

 not combine with the platinum, but formed a condensed 

 gaseous film on its surface. Faraday also seems to have 

 shared this view*. 



Again, it should be mentioned that, using large current- 

 densities, McLeod t found that very fine platinum wires were 

 destroyed during the electrolysis of H 2 S0 4 of density 1*3; but 

 whether this was due to actual solution of the platinum or 

 to its disaggregation or to traces of CI is doubtful. If solu- 

 tion of the platinum really occurs, it would support the 

 theory that the film is due to a solid oxide or sulphate layer, 

 as in the case of the oxidizable electrodes. In this relation 

 an experiment of ours may be quoted. A platinum wire was 

 carefully cleaned and weighed, and then used as anode in 

 strong H 2 S0 4 , the film being then formed on it. It was 

 taken out quickly, and wiped (with asbestos), which, as said 

 previously, removes the film. The anode was then replaced, 

 the film again formed and again wiped off. This was repeated 

 a great number of times, but no variation of the weight of 

 the anode could be detected after the experiment, nor was 

 there any difference in the appearance of the wire. We have 

 further electrolyzed sulphuric acid with platinum electrodes 

 continuously for many hours without finding any variation 

 in the weight of the electrodes. Negative experiments of 

 this nature, however, cannot be regarded as having much 

 value. 



In endeavouring to ascertain the nature of the film we are 

 met by the difficulty that removal from the acid speedily 

 brings about the destruction of the film, and other evidences 

 of its instability have been previously given. Thus, there is 

 no possibility of applying the direct tests that have led to 

 the generally accepted view in the case of the oxidizable elec- 

 trodes, and although the film sticks with some firmness w T hen 

 in the electrolyte and the battery-current is not broken, yet 

 there are no chemical tests which can be directly applied 

 under these conditions that can be thought very satisfactory. 

 We may, however, mention that the film remains undisturbed 

 when a stream of hydrogen is passed in small bubbles over the 

 anode, but is speedily removed if the acid round the anode be 

 diluted by a stream of water. The formation of the film with 



* Exp. Res. vol. i. p. 165. It may be noted that Dulong and Thenard 

 have shown in a research (Ann. de Chim. vol. xxiii. p. 440, 1823, and vol. 

 xxiv.p. 380, 1823) that all bodies have the catalytic power, more or less. 



t Journ. Chem. Soc. vol. xlix. p. -091. 



L 2 



