1876.] of Coal-dust in Colliery Explosions . 369 



that if the same shot were fired in various mixtures of firedamp and air 

 its flame would be prolonged more and more as these mixtures drew 

 nearer to the explosive point, somewhat in the same measure as the cap 

 on the flame of a lamp enlarges under the same circumstances. This pro- 

 longed flame might even partake of the nature of a local explosion of 

 firedamp, especially if augmented by the presence of a small quantity of 

 coal-dust, although those who fired the shot had not been able to discover 

 the existence of any explosive gas beforehand. I undertook to investigate 

 the nature of mixtures of gas and air which are not explosive at ordinary 

 pressure and temperature, when I applied to the Government-Grant Com- 

 mittee for assistance in 1872 ; but I regret to have to say that, from various 

 causes, I have not yet been able to carry out the necessary experiments. 



M. Vital has given experimental results which tend to show that the 

 flame of a shot is prolonged in a mixture of coal-dust and air. I have 

 repeated his experiments with gunpowder, but without much success, 

 having only once succeeded in getting the flame to appear at the end of 

 the apparatus (fig. 3), when the shot was fired from a pistol in the posi- 

 tion p ; and as the mixture of coal-dust and air was travelling in the 

 same direction at the rate of about 500 feet per minute, some deduction 

 must be made on that account. The charge consisted of 1*365 gramme 

 of gunpowder well rammed. I also placed a shield at O, and fired many 

 shots through a hole in the centre into the current charged with coal-dust ; 

 the amount of gunpowder varied from 2| grammes downwards, but on 

 no occasion did the mixture seem to ignite. 



It is always possible, however, that if coal-dust could be made fine 

 enough, and were thoroughly mixed with dry air in the proportion of 

 about 1 pound to 160 cubic feet of air, the mixture might be inflammable 

 at ordinary temperature, or, if not, it might at least be so nearly inflam- 

 mable that an explosion begun in it in a confined space might be propa- 

 gated through it. Without some further proofs, therefore, it would be 

 premature to draw any positive inference from my experiments with 

 gunpowder-shots, as they are by no means so satisfactory as I could wish ; 

 and I am glad to be able to state that Professor Marreco, of Newcastle-on- 

 Tyne, intends to investigate this question with more substantial apparatus. 



The occurrence of three great explosions within as many days in the 

 beginning of December last, seemed to indicate the influence of some 

 external agency tending to produce the same result in each individual 

 case. The barometer was high and the temperature at the surface ex- 

 ceptionally low at the time ; and it is well known that these atmospheric 

 conditions are not favourable to the occurrence of explosions in which 

 firedamp alone is concerned. It had been often observed before that 

 disastrous explosions happen most frequently during the winter months, 

 and in some instances during very cold weather. Mr. Scott has recently 

 informed me that he pointed out the latter circumstance in the year 1867 

 in an official letter to the Home Office ; and in preparing the diagrams 



