Mr. H. F. Morley on Grove's Gas-Battery. 279 



repeated ; and the mean of the two swings is the number given 

 above. The result agrees with M. Gaugain's experiment. 



X. On another occasion I measured the electromotive force 

 of wholly submerged wires in a gas-couple by connecting them 

 to a condenser, and afterwards discharging the condenser 

 through a galvanometer. The electromotive force of thick 

 and thin platinum wires was the same ; but this was 15 times 

 that of a wire of gold. Probably in the gas-couple, as else- 

 where, platinum exerts some specific attraction on hydrogen. 



XI. M. Gaugain considers the falling-off in the strength of 

 a gas-couple after short-circuiting to be due to the deposition 

 of hydrogen on the positive wire, which hydrogen is produced 

 by the decomposition of water by hydrogen ; and he says that 

 when the electromotive force of a couple fell from 152 to 30, 

 that of the hydrogen- wire fell 2Q, while an antagonistic force 

 of 96 was developed by the wire in oxygen*. From other 

 experiments of M. Gaugain, I infer that the potential of each 

 wire was compared with that of a third wire plunged in the 

 liquid between the two tubes of the couple. He does not di- 

 stinctly say that the positive wire of the couple actually became 

 negative to the third wire, though this may perhaps be inferred 

 from the expression " antagonistic." I consider the loss of 

 potential to be due to the liquid near the wires becoming im- 

 poverished of gas ; and even should the oxygen-wire become 

 negative to the third wire, it may only show that the liquid in 

 its neighbourhood contains less oxygen than that surrounding 

 the third wire. But since a little hydrogen must have found 

 its way into the oxygen-tube, this has a much better chance 

 of becoming attached to the platinum when there is little 

 oxygen near to use it up (that is, when a current is passing) 

 than when the circuit has been broken and the wire is sur- 

 rounded by a strong solution of oxygen. Using a gas-couple 

 with wholly submerged platinum wires, and comparing these 

 with a third wire in the liquid between the tubes by means of 

 a condenser periodically discharged through a galvanometer, 

 I found in two different cases, a and 5, just before short- 

 circuiting: — a. b. 



Hydrogen-wire 108 74 



Oxygen-wire 12 17 



120 91 

 and in the same soon after breaking the circuit: — 



a, b. 



Hydrogen-wire 41 12 



Oxygen-wire 12 



41 24 

 * Comptes Hendus, 1867. 



