Scientific American Supplement, No. 620 | Page 9

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 ½ 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.
2. A 2 in. hole drilled 4 ft. 6 in. into the side of the coal about 10 in.
from the top, fast ends not holed under, width of space 10 ft. This was
purposely a "blowout" shot. The result was again most satisfactory, the
charge exploding in perfect darkness.
3. A "breaking up" shot placed in the stone roof for "ripping," the hole
being drilled at an angle of 35 deg. or 40 deg. This is intended to open a
cavity in the perfectly smooth roof, the ripping being continued by
means of the "lip" thus formed. The charge was 105 grammes (nearly 4
oz), and it brought down large quantities of stone.
4. A "ripping" shot in the stone roof, hole 4 ft. 6 in. deep, width of
place 15 ft. with a "lip" of 2 ft. 6 in. This is a strong stone "bind," and
very difficult to get down. The trial was most successful, a large heap
of stone being brought down and more loosened.
5. A second "blowout" shot, under the conditions most likely to
produce an accident in a fiery mine. A 2 in. hole, 4 ft. 6 in. deep, was
drilled in the face of the coal near the roof, and charged with 105
grammes of roburite. A space of 6 in. or 8 in. was purposely left
between the charge and the tamping. The hole was then strongly
tamped for a distance of nearly 2 ft. The report was very loud, and a
trumpet-shaped orifice was formed at the mouth of the hole, but no
flame or spark could be perceived, nor was any inconvenience caused
by the fumes, even the instant after the explosion.
_Further Experiments at Wharncliffe Colliery._--On Tuesday, October
25, some very interesting surface trials were arranged with great care
by Mr. Walker. An old boiler flue was placed vertically, and closed at
top by means of a removable wooden cover, the interior space being
about 72 cubic feet. A temporary