[Footnote 1: H. Schmerber, Genie Civil, xxix, No. 11.--From the
Colliery Guardian.]
In a previous paper[2] a description was given of the experimental
gallery at the St. William pit of the Kaiser-Ferdinands-Nordbahn
Colliery at Mahrisch-Ostrau (Moravia). In the present article a
similar experimental station, designed for the same purpose, but
presenting certain considerable advantages on the score of economy by
reason of the moderate expense of its installation, will be described.
[Footnote 2: Reproduced in the Colliery Guardian, vol. lxxi,
p. 317.]
Some few years ago the Société des Explosifs Favier obtained
permission from the proprietors of the Marchienne-au-Pont, near
Charleroi, Belgium, to construct there an experimental station for
testing the explosives manufactured by the company. Though of but
modest proportions, this station is well designed, and many valuable
researches and tests have been made on the explosives used in the
fiery pits of Belgium, thanks to which investigations one is able to
readily determine in a practical manner the degree of security offered
by any explosive intended for use in pits containing coal-dust in
suspension or firedamp.
In order to avoid the expense of constructing a large gallery above
ground, recourse was had to the cylindrical shell of a disused boiler
of large dimensions--some 5 m. in length by 1½ m. internal
diameter--one end of which was taken out, and the shell made to do
duty for a testing gallery. With this object it was mounted on two
settings of brickwork (Fig. 2), and the further end backed by a brick
wall of very substantial construction, being 1½ m. thick and 2 m. in
height, and forming the base of a high bank of earth. The boiler, as
may be seen in Figs. 1 and 2, was let into the ground a little, in
order that in case of an explosion there might be less chance of the
debris being projected to a distance. On one side the boiler was
pierced by six rectangular openings 20 cm. in height fitted with thick
glass panes in caoutchouc frames, to prevent their becoming fractured
by the aerial vibrations resulting from explosions. These windows
enable the operators to observe the phenomena occurring within the
chamber at the moment the explosion is produced. At the top of the
boiler, two circular apertures, each 50 cm. diameter, were made for
the purpose of acting as safety valves. By means of two rabbets, one
fixed at the open end of the gallery and the other in the center, the
testing chamber could be made either large or small by means of paper
disks pasted on to the first or second rabbet. The capacity of the
large chamber was double that of the smaller one, and the cubical area
of each was known beforehand.
[Illustration: FIG. 1, FIG. 2, and FIG. 3. Firedamp Testing Station]
In the backing wall was fitted a large mortar of cast steel, which in
carrying out the tests served to replace the borehole used in actual
mining operations. A pipe for conveying the gas and another for steam
were laid on the floor of the chamber, the latter for heating
purposes, in order to ascertain whether, in certain cases, an increase
in temperature exerts any sensible influence on the inflammability of
the explosive mixture. The temperature of the chamber is read off from
a thermometer placed at the top of the boiler, its position being
indicated by T in Fig. 2.
In view of the possibility of the boiler, notwithstanding its
strength, bursting, in the event of a violent explosion of the gas, it
became necessary to make special arrangements for allowing the
operators to observe everything occurring in the testing chamber
without being themselves exposed to the consequences of any accident
that might ensue. A special shelter was, therefore, erected for
occupation by the operators at the moment of the explosion. This
shelter, at about a dozen yards away from the boiler, consisted of a
chamber protected on the side next the gallery by a stout bank of
earth, in which a longitudinal aperture was provided (by means of a
lining of boards) at about the height of the face, through which the
operators could observe the progress of the tests, without danger. It
may be stated, however, that hitherto no accident has occurred, the
boiler effectually resisting the force of the explosions. The chamber
of shelter likewise contained the gasometer for regulating the supply
of gas to the testing apparatus, and the electrical machine for firing
the cartridges under test.
There being no continuous current of firedamp at disposal, use was
made of illuminating gas in preparing the explosive mixtures for the
tests. The borehole is charged with the explosive to be fired, and the
temperature is regulated by means of the steam pipe. The entrance of
the chamber and the two safety apertures in the roof having been
closed by disks of paper fastened by paste, the gas is turned on until
the desired percentage, has been introduced; the mixture of the air
and gas takes merely a short time to effect by diffusion, the
difference in density causing the gas to rise on issuing from the jet,
which is on the floor of the chamber. The detonating cap is then
ignited by the passage of the electric current and the shot fired. The
operator, placed in his shelter, can observe, by means of the small
lateral windows, whether any flame is produced, and indeed, a little
experience will enable him to determine by the sound alone, whether an
explosion has ignited the mixture or not.
Fig. 1 is a front view of the testing chamber with transverse section
of the shelter. Fig. 2 is a longitudinal section of the chamber along
CD, and Fig. 3 a view, half in plan, half in section, along AB. The
following are the references: M, backing wall; C, boiler; G, gas pipe;
V, steam pipe; M, mortar; E, electric wires; A, shelter; RG,
gasometer; ME, electrical machine; R', protective bank; R", backing of
earth; R, glazed windows; S, apertures serving as valves; T,
thermometer.
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