1882.] on Some of the Dangerous Properties of Dusts. Ill 



to cost, facility of use and general efficiency. Attemjits have been 

 made to render the employment of powder in the presence of fire- 

 damp safe, by using it in conjunction with water. In the first 

 instance it was proposed by Dr. Macnab to bring the latter into 

 direct operation as the cleaving or blasting agent by inserting a 

 cylinder containing water into the blast hole, and connecting it with 

 a very strong external vessel, in which the powder charge was fired, 

 much as the powder charge is fired in the powder chamber of a gun, 

 the generating gas being brought to bear upon the confined column of 

 water, and causing the latter to exert a rending force uj)on the coal by 

 which it was surrounded. As the results furnished by this method of 

 operation were not promising, the comparatively very simple expedient 

 was resorted to by Dr. Macnab of emjdoying water simply as tampiug 

 in a charge hole, a cylinder containing the liquid and of suitable 

 length to fill the hole, being inserted over the charge of powder. In the 

 event of a charge blowing out, the disjDcrsion of the water in a very 

 finely divided condition was relied upon to eftect the extinction of the 

 volume of flame which, under these conditions, would be projected 

 into the air of the mine. Some carefully conducted experiments, with 

 blast holes charged by this method and surrounded by an exj)losive 

 gas-mixture, showed that occasionally no ignition of the gas resulted 

 from the blowing out of the shot, but that in most instances, the 

 conditions of the exjDeriments being the same, the gas-mixture in 

 front of the blast hole was exploded, when the shot blew out. It is 

 possible that a careful regulation of the charge and length of tamjDing 

 may render this mode of operation a comjjaratively safe one, though 

 it may be doubtful whether absolute reliance could be j^laced upon the 

 invariable extinction of flame in the case of blown-out charojes. When 

 the attention of the Eoyal Commission was directed to the subject of 

 the dangers attending the employment of explosives in coal mines, it 

 occurred to Mr. Abel to attempt the application to the getting of coal 

 of the principle which he developed some years ago, in the course of 

 his researches on explosive agents, namely, the sudden transmission 

 in all directions of the force exerted instantaneously by a detonation, 

 by surrounding the detonating charge with water. It was found in a 

 large number of experiments that when comparatively small charges 

 of guncotton or dynamite (the latter being preferable) were enclosed 

 in cylinders of light metal or paj)er filled with water, and occuj)ying 

 the entire available space (or nearly so) in a blast hole, the detonation 

 of the charge in holes of excessive strength, when employed in proper 

 proportion to the amount of water by which it was surrounded, 

 was always accomplished without ignition of the explosive gas-mix- 

 ture with which the opening of the blast hole was surrounded. The 

 interesting fact was moreover established, by operations carried out 

 in hard coal in Lancashire, that the action of the detonating; charge is 

 modified to great advantage, by enclosing the envelope in a long 

 column of water. Instead of exerting a j)owerfully crushing or 

 disintegrating action, confined within comparatively narrow limits, 



