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Page 8
In all six shots were fired, five of which were for the purpose of
winning coal, while the sixth was expressly arranged as a "blowout
shot." The roburite--which resembles nothing so much as a common
yellow sugar--is packed in cartridges of about 4� in. in length and 1�
in. in diameter, each containing about 65 grammes (one-seventh of a
pound) inclosed in a waterproof envelope. By dividing a cartridge, any
desired strength of charge can be obtained. The first shot had a
charge of 90 grammes (one-fifth of a pound) placed in a hole drilled
to a depth of about 4 ft. 6 in., and 1� in. in diameter. All the
safety lamps were carefully covered, so that complete darkness was
produced, but there was no visible sign of an explosion in the shape
of flame--not even a spark--only the dull, heavy report and the noise
made by the displaced coal. A large quantity of coal was brought
down, but it was considered by most of the practical men present to be
rather too much broken. The second shot was fired with a single
cartridge of 65 grammes, and this gave the same remarkable results as
regards absence of flame, and, in each case, there were no noxious
fumes perceivable, even the moment after the shot was fired. This
reduced charge gave excellent results as regards coal winning, and one
of the subsequent shots, with the same weight of roburite, produced
from 10 to 11 tons of coal in almost a solid mass.
It has been found that a fertile cause of accidents in coal mines is
insufficient tamping, or "stemming," as it is called in Yorkshire.
Therefore a hole was bored into a strong wall of coal, and a charge of
45 grammes inserted, and very slightly tamped, with the view of
producing a flame if such were possible. This "blowout" shot is so
termed from the fact of its being easier for the explosion to blow out
the tamping, like the shot from a gun, than to split or displace the
coal. The result was most successful, as there was no flash to relieve
the utter darkness.
The second set of experiments took place on October 24 last, in the
Monk Bretton colliery, near Barnsley, of which Mr. W. Pepper, of
Leeds, is owner. This gentleman determined to give the new explosive a
fair and exhaustive trial, and the following programme was carried out
in the presence of a very large gathering of gentlemen interested in
coal mining. The chief inspector of mines for Yorkshire and
Lincolnshire, Mr. F.N. Wardell, was also present, and the Roburite
Explosives Company was represented by Lieut.-General Sir John Stokes,
K.C.B., R.E., chairman, and several of the directors.
1. _Surface Experiments._--A shot fired on the ground, exposed. This
gave no perceptible flame (70 grammes of roburite was the charge in
these experiments).
2. A shot fired on the ground, bedded in fine coal dust. No flame nor
ignition of the coal dust was perceptible.
3. A shot fired suspended in a case into which gas was conducted, and
the atmospheric air allowed to enter so as to form an explosive
mixture. The gas was not fired.
4. A shot fired in a boiler flue 16 ft. by 2 ft. 8 in., placed
horizontally, in which was a quantity of fine coal dust kept suspended
in the air by the action of a fan. No flame nor ignition of the coal
dust took place.
5. A shot fired as above, except that an explosive mixture of gas and
air was flowing into the boiler tube in addition to the coal dust.
That this mixture was firedamp was proved by the introduction of a
safety lamp, the flame of which was elongated, showing what miners
call the "blue cap." There was no explosion of the gas or sign of
flames.
6. A shot of roburite fired in the boiler tube without any gas or
suspended coal dust. The report was quite as loud as in the preceding
case; indeed, to several present it seemed more distinct.
7. A shot of � lb. gunpowder was fired under the same condition as No.
5, i.e., in an explosive mixture of gas and air with coal dust. The
result was most striking, and appeared to carry conviction of the
great comparative safety of roburite to all present. Not only was
there an unmistakable explosion of the firedamp, with very loud
report, and a vivid sheet of flame, but the gas flowing into the far
end of the boiler tube was ignited and remained burning until turned
off.
_In the Pit._--1. A 2 in. hole was drilled 4 ft. 6 in. deep into coal,
having a face 7 yards wide, fast at both ends, and holed under for a
depth of 8 ft., end on, thickness of front of coal to be blown down 2
ft. 10 in., plus 9 in. of dirt. This represented a most difficult
shot, having regard to the natural lines of cleavage of the coal--a
"heavy job" as it was locally termed. The charge was 65 grammes of
roburite, which brought down a large quantity of coal, not at all too
small in size. No flame was perceptible, although all the lamps were
carefully covered.
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