1882.] on Some of the Dangerous Properties of Dusts. 103 



fire-damp, which were passed through the apparatus at different 

 velocities up to 1000 feet per minute. Small cannon, specially 

 constructed to ensure uniformity in the volume of flame produced at 

 different times, were fired in them, either singly or in pairs in rapid 

 succession ; and exposed heaps of guncotton and of slow- and quick- 

 burning gunpowder were exploded in the dust-laden air. The results 

 occasionally confirmed to some extent those of Marreco and !\Eori5on and 

 the Chesterfield experiments. At velocities of iOO feet per minute the 

 dust, which was either passing at the time or was raised by the con- 

 cussion of a first shot, did not appear to produce any increase in the 

 volume of flame furnished by the cannon, but a decided though incon- 

 siderable lengthening of the flame was several times observed at higher 

 velocities and with the employment of the most inflammable dusts. 

 Some of these, when thickly suspended in air travelling at velocities 

 of 500 to 1000 feet per minute, and exposed to the action of a large 

 flash of flame (as produced by the loose heaps of guncotton and 

 hlasting powder), exhibited a tendency not only to bum explosively in 

 and close around the flame, but also to propagate flame, or cause it to 

 travel along some distance ; but the most decisive results of these 

 experiments were not of a nature to warrant the conclusion that 

 flame could be carried alonsf indefinitelv, or even to a verv consider- 

 able distance, by coal dust in the complete absence of fire-damp, as 

 now maintained by IMr. Gralloway. There can be no question that 

 the scale of magnitude upon which the first ismition in the dust-laden 

 atmosphere is produced must greatly influence the extent to which 

 the propagation of flame in this way will extend, and Air. Gralloway's 

 experiments at Llwynpia. therefore, were likely to develop conditions 

 more nearly approaching those of the real state of things in a mine 

 than experiments in galleries of smaller dimensions, and with small 

 initiating volumes of flame. But the necessity for caution in de- 

 ducting very decided conclusions from even large-scale experiments, 

 appears to be illustrated by some of I\Ir. Galloway's results, inasmuch 

 as some of the great distances to which the flame extended were 

 observed under conditions decidedly favoui*able to the projection of the 

 flame by causes which would not come into play in the same way in 

 a mine-working. The experiments made some years ago by !3J!r. 

 Hall in an adit (which have already been referred to) appear to have 

 a more direct bearing upon results likely to be actually produced 

 underground in a dust-laden atmosphere. In those experiments, the 

 extreme distance to which flame was carried by dust, first ignited by 

 the flame from a very excessive charge of powder (4: lb.), was 180 feet. 

 It is of course possible that the coal used was not of the most 

 inflammable description, and that its fineness and density were not 

 most favourable to its becoming very thickly suspended in air. On 

 the other hand, Mr. Hall stated, in his evidence before the Eoyal 

 Commission, that the atmosphere in the adit was only ** practically " 

 free from gas. 



The volume of flame from a blo^vn-out shot in a mine- working: is 



