194 On Sir H. Davy's Safe-lamp for Mines. 



before. The mixture took fire in the tray as soon as enveloped 

 by the inflamed gas, and burnt with a very large flame mixed 

 with iinumierable scintillations ; but no explosion (though the 

 experiment was continued till all the gas of a very large bladder 

 was expended) could be produced. 



Exp. 3. Tlie lamp and lanthorn being arranged as before, the 

 gas was thrown in at one of tlie lovve.st side apertures, and tiie 

 coal-dust and gunpowder at an upper one, and a current of air 

 forced on the inllamcd gas from another bladder through the 

 opposite middle opening. The whole burned with a very full and 

 strong flame, and the scintillations were so violent as almost to 

 resemble the tail of a sky-rocket, and the wire-gauze soon be- 

 came red hot, but no explosion ensued. Had I continued the 

 experiment till the wire-gauze became nearly white hot, an ex- 

 plosion of course would have followed ; but it would take place 

 as certainly without the coal-dust. It Ls therefore fairly esta- 

 blished that coal-dust cannot communicate flame to the external 

 air, when the lamp is immersed in the most explosive mixtures. 



I repeated the last experiment with the double lamps, and also 

 without the coal-dust, and used every endeavour to produce an 

 explosion, but without effect. I raised the wire-gauzes to a dull 

 red heat, but could not get them hot enough to suflPer flame to 

 pass through. In every case possible, therefore, the double lamp 

 is perfectly secure; and, unless in the hands of an idiot or a mad- 

 man, the single is hardly less so ; — nothing but a current of air, 

 directing the flame with considerable force to one point, can 

 heat the gauze sufficiently for flame to traverse it j — and should 

 such a current be met with in the mine, it must inevitably ex- 

 tinguish the lamp, and thus be itself the safeguard from its own 

 dangeF. 



Mr. Holmes, however, caused explosions by holding the lamp 

 over a small gas tube, and juojecting coal-dust and gunpowder 

 and even coal-dust alone, on it ; and I understand the same ef- 

 fect has been produced in the lal)oratory of the Royal Institution. 

 In those experiments, I am told the lamp was held nearly hori- 

 zontally over the pipe of the large gasometer (and consequently 

 the full heat of the flame from the wick of the lamp con- 

 stantly directed to one point), and coal-dust thrown on the top 

 of the gauze. Mr. Holmes does not state in what direction he 

 held his lamp. In this arrangement it is obvious that a current 

 of fresh air round the lamp is established, the coal-dust is 

 heated red by contact with the wire-gauze, and its ignition in- 

 creased by the current of air; and thus it reaches the tempera- 

 ture at which it can explode the circumambient gas ; but this 

 will not happen, without that partial current, which can never 

 prevail in the mine; nor I believe will it happen at allj if the lamps 



be 



