THE MINERAL DEPTHS 



drainage, there is comparatively little danger of ex- 

 tensive accumulation of this gas. 



The danger from this choke damp, therefore, is 

 one that concerns the individual workman rather than 

 large bodies of men or the structure of the mine itself. 

 With fire damp, however, the case is different, as an ex- 

 plosion of this gas may destroy the mine itself and all 

 the workmen in it. It is, therefore, the most dreaded 

 factor in mining, and is the one to which more atten- 

 tion has been directed than to almost any other problem. 



This fire damp is a mixture of carbonic oxide and 

 marsh gas which, being lighter than air, tends to rise 

 to the upper part of the mines. For this reason ex- 

 plosions are more likely to occur near the openings 

 of the mine, frequently entombing the workmen in a 

 remote part of the mine even when not actually killing 

 them by the explosion. As this gas is poisonous as 

 well as explosive the miners who survive the explosion 

 may succumb eventually to suffocation. 



Previous to the year 1816 no means had been devised 

 for averting the explosions of fire damp except the 

 uncertain one of watching the flame of the candle 

 with which the miner was working. On coming in 

 contact with air mildly contaminated with fire damp 

 the candle flame takes on a blue tint and assumes a 

 peculiarly elongated shape which may be instantly de- 

 tected by a watchful workman. But miners were, and 

 still are, a proverbially careless class of men even where 

 a matter of life and death is concerned, and too fre- 

 quently gave no heed to the warning flame. But in 1816 

 Sir Humphrey Davy invented his safety lamp, a device 



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