Voltaic Ignition to Lighting Mines. 443 



-{\|fc Bpussingault is inclined to believe that some of the acci- 

 hul^htsin mines have ocduretl from draughts or currents of in- 

 T&immable gas, and not from the carelessness of the workmen 

 <liu the use of the safety-lamp, to which they are generally at- 

 ■ itributed ; he considers that the voltaic arc, being independent 

 lof atmospheric air or other supporter of combustion, in the 

 '^'frsual sense of the word, might be rendered practically avail- 

 able. M. De la Rive states that he has been occupied with 

 the subject, and pix)poses a cylinder of close-textured charcoal, 

 similar to that of Bunsen, with a metallic ring or plate above 

 it} the carbon being renderecl the positive terminal of a vol- 

 taic pile, the particles transferred from it to the disc fall down 

 again by their own gravity, and a tolerably constant light is 

 obtained ; the vessel containing the electrodes is hermetically 

 sealed, and the oxygen being soon exhausted by the ignited 

 charcoal, the ignition proceeds in the residual nitrogen. M. 

 De la Rive appears, however, to have met with but partial 

 successy ^ud ^ays thenei are still many difficulties to contend 



With"*^.'-. 'M i., . .■: . V.I, 



M iFour or five years ago, soon after publishing the nitric acid 

 batter}', ] was naturally struck by the facility and constancy 

 with which the voltaic arc could be obtained by that combi- 

 nation, as compared with any previous one, and made several 

 attempts to reduce it to a practical form for the purposes of 

 illumination, but my success was very limited. By attending 

 to certain precautions, which I will not stop to describe, I 

 could occasionally keep up a steady voltaic light in attenuated 

 nitrogen for four or five hours, but it was never sure ; from 

 some unseen imperfection in the charcoal, or other cause, it 

 would become suddenly extinct; the glass also in which it 

 was ignited became gradual!}' dimmed by a deposition of con- 

 densed carbon vapour; it was costly, from the number of series, 

 and consequently of equivalents of zinc and acid consumed ; 

 too bulk^' for portable purposes, and from the intensity of the 

 heat, unless the recipient was very large, the collar of lea- 

 thers and joints, into which the wires were sealed or cemented, 

 were destroyed ; and when ground plates were employed, 

 the grease was liquefied. M. De la Rive does not state his 

 method of hermetically sealing the vessel he employs; this I 

 found one of the most difficult parts of the process. Not 

 being able satisfactorily to overcome these difficulties, I aban- 

 doned it for the time, and made some experiments on another 

 method of voltaic illumination, which appeared to nie more 



• A translation of jVI. Deki Rive's paper will be found at p. 406 of the 

 present volurap.-^Ee, , 



