The Romance of Modern Chemistry

FLAME: WHAT IS IT? As already stated, the ignition temperature of hydrogen is lower than that of marsh gas, and if we attempted to obtain with hydrogen the results just described, we should not succeed. In all cases the hydrogen flame would strike through the gauze. The remarkable power of metal gauze to limit the extension of a marsh gas flame was utilised long ago in the well-known miner’s safety lamp devised by Sir Humphry Davy. Coal measures are frequently highly charged with marsh gas, and large quantities of this gas find their way into coal mines. Since this “fire- damp,-” as it is called, is inflammable, and forms a very explosive mixture with air, its presence in these mines is a source of great danger, and has repeatedly led to serious disasters. The risk of using naked flames in such “ gassy ” mines had to be got over somehow, and Davy was able to show that if the oil flame in the miner’s lamp was surrounded by wire gauze the danger of explosions was very much reduced. An explosive mixture of fire-damp and air will not as a rule be fired by such a lamp, but will indicate its presence by burning inside, and so warn the miner of danger. The action of the gauze in conducting away the heat prevents the explosive mixture outside reaching its ignition temperature. The old form of Davy lamp has been found defec- tive in some respects, and has been continuously im- proved ; thus the wire gauze cut off a great deal of the light, so the lower part was replaced by a glass cylinder. Then it was found that a strong draught might blow the flame against and even through the gauze, with the result that an explosive mixture outside would be ignited. The newest form of the safety lamp 163