THE BULLI COLLIERY. 183 



themselves and how familiarity with danger breeds contempt, 

 more especially in cases where serious consequences have not 

 been experienced by the individual. The shot holes appear 

 to have been generally tamped with small coal or dust, not 

 even properly danipe.d- This, as is well known, elongates the 

 name produced by blasting, especially in the case of blown 

 out shots, and as the miners frequently neglected to thoroughly 

 undercut the coal before firing a shot, they practically blasted 

 coal out of the solid, so that either a heavier charge had to 

 be used to break down the coal, or the tamping, offering less 

 resistance, was blown out. The stump left of the hole that is 

 supposed to have caused this great loss of life showed that 

 the charge did not do the work expected of it. The Com- 

 missioners consider that the disaster was largely due to the 

 absence of proper precautions in thoroughly undercutting the 

 coal and preparing shots, also probably to an error of judg- 

 ment in gauging the necessary amount of explosive required. 

 The danger of coal dust is now so well recognised that in 

 properly appointed mines when necessary to fire several shots 

 in a dusty place, they are either fired simultaneously, or suffi- 

 cient time is allowed between shots for the dust to settle or 

 be carried away by the ventilating current. 



The heat generated by exploding gun. powder in a confined 

 space, such as a drill hole, is greater than that generated in 

 the retorts of gas works : the temperature in each particular 

 case varying with the quantity of powder in the charge, and 

 the duration of the explosion. The amount of energy devel- 

 oped by an explosive substance is often OA^erlooked. A single 

 pound weight of ordinary black powder when exploded de- 

 velops 360 foot tons. A pound of ordinary fine bituminous 

 coal suspended in the air, when converted into gas, as in the 

 case of a mine explosion, develops 4600 foot tons. Of the 

 gases, a pound of methane (23.4 cub. ft. at 60 degrees F. and 

 29.925 bar. press.), develops in explosion 9146 foot tons: a 

 pound of carbon-monoxide (13.5 cub. ft.), 1682 foot tons, and 

 oru.' pound of olefiant gas, 8302 foot tons. 



The distribution of dust in a mine is more general than 

 gas, so a dust explosion tends to travel further, but having 

 to first convert the dust into carbon-monoxide, and then into 

 carbon-dioxide, the explosion is not so sudden. Carbon-mon- 

 oxide is also one of the gases given oif by the explosion of 

 gunpowder. A trace of this gas in a dust-laden atmos- 

 phere is as explosive as a much larger quantity of firedamp, 

 and, what is more, it is ignited at a much lower temperature 

 than a mixture of marsh gas and air. It has been demon- 

 strated that a blown out shot is capable of igniting mixtures of 

 coal dust, marsh gas and carbon-monoxide with air. A small 

 local explosion, which in itself would be of little moment, may 



