12 M. W. Beetz on the Excitation of Electricity 



trodes makes the comparison unsafe. The almost perfect 

 agreement between Pt, CI and C, CI was also remarked by 

 Macaluso*. It looks as if the plate dipping in the chlorine 

 solution served solely as a conductor ; and in fact we cannot 

 here speak of the electromotive force excited by a gas, but 

 have simply to do with the electromotive action of a liquid, 

 which increases with the degree of concentration of the liquid. 



The solubility of sulphuretted hydrogen in water is similar 

 to that of chlorine ; but it behaves otherwise to platinum and 

 palladium than to retort-carbon. The latter, again, occurs 

 only as a body immersed in a solution, by which it is the more 

 intensely electrically excited the more concentrated the solu- 

 tion. Platinum and palladium are already strongly excited by 

 the first quantities of gas ; they evidently draw it from the 

 liquid to condense it in or upon themselves. 



The rest of the gases which have been taken into considera- 

 tion are but little soluble in water. Of course, in the usual 

 form of the gas battery, something even of these must at first 

 be dissolved in the conducting liquid in order to become 

 active ; but the quantity is too inconsiderable to cause the so- 

 lution to act on the conducting plate essentially otherwise 

 than the liquid which has absorbed no gas at all. In these 

 cases something else must come into play to generate a differ- 

 ence of tension — namely, either an affinity (or, generally, an 

 action of molecular forces by which the gases incorporate 

 themselves with the metal plate), or the action of an electro- 

 lyzing current which either drives the gases into the metal or 

 condenses them upon its surface. On palladium hydrogen 

 exhibits this penetration in the highest degree, on platinum 

 in a less degree, on retort-carbon not at all. The aid of gal- 

 vanic polarization is superfluous with palladium, useful with 

 platinum, absolutely necessary with retort-carbon to generate 

 a difference of tension. Carbonic oxide and ethylene act in 

 the same manner as hydrogen, but far more feebly. If we 

 could condense them by galvanic polarization, it would in all 

 three cases be useful ; with carbon, indeed, it would be indis- 

 pensable. Sulphuretted hydrogen stands, with reference to 

 its behaviour to platinum and palladium, near to hydrogen, 

 and near chlorine in consequence of its solubility. 



I made an experiment to ascertain if chlorine, which so 

 readily attacks the surface of metals, penetrates also into or 

 through them. Exactly as in Boot's experiment, two glass 

 vessels were cemented to the two sides of a much broader 

 sheet of palladium b. Both vessels were filled with diluted 

 hydrochloric acid ; and palladium electrodes a and c dipped 

 * Loc. cit. p. 362. 



