Intelligence and Miscellaneous Articles. 395 



ON THE GALVANIC CONDUCTIVITY OF HEATED GASES. 

 RY M. R. BLONDLOT. 

 Gases are generally considered incapable of transmittiug the 

 current furnished by a pile consisting of only a few elements. A 

 single exception has been pointed out by M. E. Becquerel* — that 

 of gases brought to red heat. M. Becquerel ascertained that at 

 this high temperature different gases, among others air, permit the 

 current of a pile to pass, and even that of a single Bunsen element. 

 He found, however, that the resistance of gases followed very dif- 

 ferent laws from those wmich have been established for solids and 

 liquids : it depends on the intensity of the current, the number of 

 the pile-elements, and, between two electrodes with unequal sur- 

 faces, on the direction of the current. The singularity of these 

 laws has not only caused them to be called in question, but even 

 the existence of the conducting-power of gases to be contested. 

 G. Wiedemannf supposes that in M. Becquerel's experiments the 

 current may have been transmitted, not through the gas, but 

 through the cements used for sealing the electrodes, they having 

 become conductive in consequence of the rise of temperature : in 

 support of his opinion he cites a negative experiment of Grove'sj. 

 In view of these divergences I have thought it would be useful 

 to place beyond dispute the existence of the conductivity of gases, by 

 means of an experiment in which every part of the apparatus would 

 be constantly accessible to observation. For that purpose I had 

 recourse to the following arrangement : — 



Into a circuit the sulphate-of-copper cell and a capillary electro- 

 meter are introduced. The circuit is interrupted at one point ; 

 and each of the extremities of the wire is attached to a platinum 

 disk of about 3 centims. diameter ; the two disks are kept vertical, 

 facing and parallel to one another, by means of long pipe-stems in- 

 sulated at the lower part. The distance of the disks being regu- 

 lated at 2 or 3 millims., it is clear that the circuit is interrupted by 

 the interposed air, and that the electrometer remains motionless. 



The experiment is commenced by closing the electrometer upon 

 itself by means of a bridge annexed to it. Then, with the aid of 

 an enameller's blow-pipe, the two platinum disks are made red- 

 hot : during this operation the electrometer remains constantly at 

 zero, since it is closed by the bridge. The flame is then removed, 

 and, a moment after, the bridge ; the mercury of the electrometer 

 immediately goes out of the field of the microscope. Consequently 

 the continuity of the circuit, which was interrupted by the cold air, 

 is restored by the heated air, and no doubt can remain of the ex- 

 istence of the galvanic conductivity of hot gases. 



M. Becquerel had verified the appearance of the conducting- 

 power of gases only at red heat ; I have been able to observe that 

 power at much lower temperatures. The apparatus which I have 

 employed is the same as the preceding, except that the pile con- 

 sists of five Bunsens. An illuminating-gas flame placed below the 



* Annates de Chimie et de Physique, ser. 3, t. xxxix. p. 355 (1853). 

 t Wiedemann, Galv. u. Elektr. Bd. i. p. 339. 

 % Athenaeum, 1853, p. 1131; Inst. 1854, p. 35*. 



