A series of experiments of great interest and vital importance to
colliery owners and all those engaged in mining coal has been carried
out during the last ten days in the South Yorkshire coal field. The
new mines regulation act provides that any explosible used in coal
mines shall either be fired in a water cartridge or be of such a
nature that it cannot inflame firedamp. This indeed is the problem
which has puzzled many able chemists during the last few years, and
which Dr. Roth, of Berlin, claims to have solved with his explosive
"roburite." We recently gave a detailed account of trials carried out
at the School of Military Engineering, Chatham, to test the safety and
strength of roburite, as compared with gun cotton, dynamite, and
blasting gelatine. The results were conclusive of the great power of
the new explosive, and so far fully confirmed the reports of the able
mining engineer and the chemical experts who had been sent to Germany
to make full inquiries. These gentlemen had ample opportunity of
seeing roburite used in the coal mines of Westphalia, and it was
mainly upon their testimony that the patents for the British empire
were acquired by the Roburite Explosive Company.
It has, however, been deemed advisable to give practical proof to
those who would have to use it, that roburite possesses all the high
qualities claimed for it, and hence separate and independent trials
have been arranged in such representative collieries as the
Wharncliffe Silkstone, near Sheffield, Monk Bretton, near Barnsley,
and, further north, in the Durham coal field, at Lord Londonderry's
Seaham and Silksworth collieries. Mr. G.B. Walker, resident manager of
the Wharncliffe Colliery Company, had gone to Germany as an
independent observer--provided with a letter of introduction from the
Under Secretary of State for Foreign Affairs--and had seen the
director of the government mines at Saarbruck, who gave it as his
opinion that, so far as his experience had gone, the new explosive was
a most valuable invention. Mr. Walker was so impressed with the great
advantages of roburite that he desired to introduce it into his own
colliery, where he gladly arranged with the company to make the first
coal mining experiments in this country. These were recently carried
out in the Parkgate seam of the Wharncliffe Silkstone colliery, under
the personal superintendence of the inventor, Dr. Roth, and in the
presence of a number of colliery managers and other practical men.
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 4½ in. in length and 1½
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 1¾ 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 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 gasometer had been arranged at a
suitable distance by means of a paraffin cask having a capacity of 6
cubic feet suspended inside a larger cask, and by this means the
boiler was charged with a highly explosive mixture of gas and air in
the proportion of 1 to 12.
1. A charge of gunpowder was placed in the closed end of a piece of
gas pipe, and strongly tamped, so as to give the conditions most
unfavorable to the ignition of the firedamp. It was, however, ignited,
and a loud explosion produced, which blew off the wooden cover and
filled the boiler tube with flame.
2. Under the same conditions as to firedamp, a charge of roburite was
placed on a block of wood inside the boiler, totally unconfined except
by a thin covering of coal dust. When exploded by electricity, as in
the previous case, no flame was produced, nor was the firedamp
ignited.