448 On the Fire-damp of Coal-mines ^ and on Methods 



The mixture vvliich seemed to possess the greatest explosive 

 power, was that of 7 or 8 parts of air to 1 of gas ; but the re- 

 port prockiced by 50 cubical inches of this mixture was less than 

 that produced by — of the quantity of a mixture of 2 parts of 

 atmospherical air and 1 of hydrogen. 



It was very important to ascertain the degree of heat required 

 to explode the tire-damp mixed with its proper proportion of 

 air. 



I found that a common electrical spark would not explode 5 

 parts of air and 1 of fire-damp, though it exploded 6 parts of 

 air and 1 of damp: but very strong sparks from the discharge of 

 a Leyden jar seemed to have the same power of exploding dif- 

 ferent mixtures of the gas as the flame of the taper. Well- 

 burned charcoal, ignited to the strongest red heat, did not ex- 

 plode any mixture of air and of the fire-damp ; and a fire made 

 cf well-burned charcoal, i.e. charcoal that burned without flame, 

 was blown up to whiteness by an explosive mixture containing 

 the fire-damp, without producing its inflammation. An iron 

 rod at the highest degree of red heat, and at the common de- 

 gree of white heat, did not inflame explosive mixtures of the 

 fire-damp ; but, when in brilliant combustion, it produced the 

 eiFect. 



The flame of gaseous oxide of carbon as well as of defiant 

 gas exploded the mixtures of the fire-damp. 



In respect of combustibility, then, the fire-damp differs most 

 materially from the other common inflammable gases. Olefiant 

 gas, which I have found ex])lodes mixed in the same proportion 

 with air, is fired by both charcoal and iron heated to dull red- 

 ness. Gaseous oxide of carbon, which explodes when mixed 

 with 2 parts of air, is likewise inflammable by red-hot iron and 

 charcoal. And hydrogen, which explodes when mixed with 

 3-7ths of its volume of air, takes fire at the lowest visible heat 

 of iron and charcoal ; and the case is the same with sulphuretted 

 hydrogen. 



I endeavoured to ascertain the degree of expansion of mix- 

 tures of fire-damp and air during their explosion, and likewise 

 their power of communicating flanie through apertures to other 

 explosive mixtures. 



I found that when 6 of air and 1 of fire-damp were exploded 

 aver water by a strong electrical spark, the explosion was not 

 very strong, and, at the moment of the greatest expansion, the 

 volume of the gas did not appear to be increased more than \. 



In exploding a mixture of 1 part of gas from the distillation 

 of coal, and 8 parts of air in a tube of a quarter of an inch in 

 diameter and a foot long, more than a second was required be- 

 fore the flame reached from one end of the tube to the other; 



and 



