VOLTAIC IGNITION. 



343 



Fig. 2. 



gases and liquids, yet in the former it is apparently of very 

 trifling import in comparison with the real physical cause of 

 the differences, whatever that may be. 



Supposing, as is stated by Faraday,* that gases possess 

 feeble conducting powers for voltaic electricity, and suppos- 

 ing hydrogen, from its close analogy in chemical character 

 to the metals, to possess a greater conducting power than 

 the other gases, this would account for its peculiar effect on 

 the ignited wire, as a certain portion of the current, instead 

 of forcing its way through the wire, would be carried off by 

 the surrounding gas. In order to ascertain this I arranged 

 the following experiments. 



ist. Into the closed end of a bent tube, fig. 2, a loop 

 of platinum wire, A B, and 

 two separate platinum wires, 

 C D, were hermetically sealed, 

 the extremities of the latter 

 being approximated as 

 closely as possible, and the 

 interval between them being 

 close to and immediately 

 over the apex of the loop. 

 The tube was filled with 

 hydrogen, and the wire A B 

 connected with a voltaic battery of sufficient power to raise it 

 to as high a degree of ignition as it would bear without fusion ; 

 C and D were now connected with the poles of another bat- 

 tery, a delicate galvanometer being interposed in the circuit. 

 Not the slightest effect on the galvanometer needle could be 

 detected, and a similar negative effect took place when the tube 

 was filled with atmospheric air. 



2nd. Parallel portions of platinum wire were now arranged 

 in close proximity (see fig. 3), and so that each might be 

 ignited to a full incandescence by separate insulated batteries. 

 When surrounded by atmospheres, both of atmospheric air 

 and of hydrogen, and fully ignited, not the slightest conduc- 

 tion could be detected across the interval between the wires, 

 with ten cells of the nitric acid battery ; and being enabled by 

 * Experimental Researches , 272, 441, and 444. 



