DUE TO GAS DERIVED FROM COAL-DUST. 127 



per square inch, or 432 lbs. per square foot, and the 

 resistance of the side walls of the tunnel to external 

 pressure would be diminished to that extent. The pressure 

 of 432 lbs. per square foot represents a wind velocity of 

 300 miles per hour. The highest velocity ob.^erved by 

 Rouse was 117 miles per hour, which overturned buildings; 

 and this fact will remove any difficulty in understanding 

 how the walls in the branch roads of the tunnel were over- 

 whelmed when suddenly deprived upon one side of a pres- 

 sure represented by a wind velocity more than twice as high 

 as Rouse's greatest hurricane, while the pressure upon the 

 other side was undiminished. 



No. 18 explosion was the final outburst in that direction, 

 and the door beyond was forced open by the air upon the 

 opposite side, also showing reduced pressure in the field of 

 the explosion. This phenomenon of doors lying open 

 towards the seat of explosion is not uncommon in colliery 

 explosions. 



The partial vacuum that is seen to have a place in the 

 field of explosion, and arising in the chemical changes in the 

 educts of the coal, iadicates that the products of these 

 changes were not permanent gases, but a gas that was 

 instantaneously condensible, and gaseous water was the 

 only body of this nature that could be produced from the 

 educts. 



The remaining phenomena of the explosions also demand, 

 for their explanation, the chemical changes that have been 

 advanced . 



The theory of the explosive wave enunciated by Berthelot 

 is of great interest in connection with the foregoing phe- 

 nomena. It will be remembered that he experimentally 

 determined the velocity of the wave in the explosion of 

 a mixture of two volumes of hydrogen and one volume of 



