Makch 10, 1899.] 



SCIENCE. 



359 



given in Mining Accidents and their Pi-e- 

 vention by Sir Frederick Abel, N. Y., 1889. 

 It was early i-ecognized that the presence of 

 naked light was a. constant soiirce of danger, 

 and hence the invention of the safety 

 lamp by Sir Humphrey Davy, in 1816, * 

 was hailed as a most beneficent gift of 

 science, and this was soon followed by the 

 lamps of George Stephenson and Dr. Clauny. 

 When exposed but a short time in at atmos- 

 phere rich in gas and which is moving at a 

 low velocity these lamps protected the miner, 

 but if allowed to remain for some time in the 

 gas-rich atmosphere the gauze becomes 

 heated to the ignition point of the gas, from 

 the gas mixture burning within it. By the 

 inti'oduction of ventilating appliances to re- 

 move the gas the currents of air in the 

 main ways frequently reach a. velocity of be- 

 tween twenty and twenty-five feet, and be- 

 tween two airwaj'S it may rise to thirty-five 

 feet per second. In breaking down the 

 coal the confined gas may rush out at a 

 very high velocity', it being found by experi- 

 ment at the Boldon Colliery that the gas 

 may be under as great a pressure as 461 

 poundsto the square inch. And, finallj', the 

 air and gas may be set in motion at a high 

 velocity by the firing of explosives to bring- 

 down the rock or coal, and more especially 

 by a ' blown out ' shot. Under such con- 

 ditions the primitive safety lamps above de- 

 scribed failed, but protected lamps have been 

 invented which have resisted currents of 

 even fifty feet per second for a brief period, 

 though it is said that these are insecure in 

 certain positions to which they may be 

 tilted in practice, and that the glass cylin- 

 ders are liable to fracture. 



Instead of relying upon the safety lamps 

 for protection a better method of procedure 

 is to test the atmosphere of workings for the 

 presence of fire damp before allowing the 

 workmen to operate. Various methods 

 have been pursued, and these are resumed 



* Trans. Roy. Sec. 106, 1. 



in ' The Detection and Measurement of In- 

 flammable Gas and A^apor in Air, by Dr. 

 Frank Clowes, 1896, London,' and he there 

 describes a very ingenious and efficient fire 

 damp detector which he has devised. This 

 consists of a simple and convenient hydro- 

 gen lamp by which one can detect 1/10 of 

 one per cent, of methane or 25/100 of one 

 per cent, of coal gas in air. He attaches a 

 small steel cylinder (weighing about four- 

 teen ounces) charged with hydrogen under 

 100 atmospheres of pressure to the side of a 

 safety lamp, and leads the gas through a 

 minute copper tube up beside the wick 

 holder of the lamp, there being a reducing 

 valve attached to the cylinder by which to 

 feed the hydrogen to the lamp as desired in 

 order to control the height of the flame. 



The lamp is lighted as usual at the oil 

 wick and covered ; then, when the atmos- 

 phere which it is desired to test is reached, 

 the hydrogen is turned on and ignited, the 

 oil flame is pricked out, the hydrogen flame 

 adjusted to a regulation height of 10 mm. 

 and the flame observed through the chimney 

 against a black background. If an inflam- 

 mable gas be present it will produce a pale 

 blue cap about the hydrogen flame, and the 

 height of this cap will increase with the 

 per cent, of the gas in the atmophere. By 

 means of a scale on the chimney the height 

 is measured and the per cent, determined. 



In his experiments Clowes obtained the 

 following : 



LIMITING EXPLOSIVE MIXTURES OF VARIOUS GASES 

 WITH AIE. 



Combustible gas Percentage o£ Method of Kindling 

 used. Gas in Air. 



Lower Explo- Higher Explo- 

 sive Limit. sive Limit. 

 Methane 5 13 Upward. 



6 11 Downward. 



Coal gas Nottingham 6 29 Upward. 



9 22 Downward . 



Water gas 9 55 Upward. 



Hydrogen 5 72 " 



Carbon monoxide 13 75 " 



Ethylene 4 22 " 



Acetylene 3 82 Downward. 



