122 THE CHEMISTRY OF COLLIERY EXPLOSIONS 



heating and cracking rock that was not displaced ; the 

 products, however, retained an unexpended quantity, which 

 was projected through the planes of rupture into the coal- 

 dust at a high velocity, initiating distillatory action, which 

 left residues of coked coal upon the floor, timber, and other 

 surfaces over an area of 30 square yards in the immediate 

 vicinity. The first disruptions were at 136 and 140 yards 

 respectively from the shot, and the only heat available to 

 sustain the distillatory action in the coal-dust through these 

 distances, and supply other demands, was the surplus that 

 remained from the fired blasting powder. 



The charge of powder contained 12^ ounces, or 354*37 

 grammes, and, taking the calorific value as determined by 

 Abel and Nobel at 516*8 small calorics per gramme, the total 

 heat disengaged would be 354*375 x 516*8 = 183141 gramme 

 units. The quantity of heat transformed into work, causing 

 mechanical effects upon the rock, can only be estimated ; but 

 experience in the use of explosives enables this quantity to 

 be fixed with approximate accuracy, and in the case under 

 notice, less than one quarter of the charge would cause the 

 effects observed, leaving practically 140,000 gramme units 

 for other purposes. 



The products of explosion of mining powder of average 

 composition are, by weight : — 



Gaseous ..... 51*35 



Solid 47*04 



Water 1*64 



100-00 



The temperature of explosion of mining powder was deter- 

 mined by Abel and Nobel at 2896° C upon the specific heat 

 of the products of combustion ; but their experimental deter- 

 mination was 1800° to 2000° C in the conditions of the 

 experiment. 



