We shall not attempt to pass in review the several apparatus that have
hitherto been devised for igniting blasts in mining operations, but
shall simply describe in this place a machine recently invented for
this purpose by Mr. Bornhardt, an engineer to the Grand Duke of
Brunswick.
This apparatus (shown in the accompanying engravings) consists
essentially of two hard-rubber disks, A (Figs. 2 and 3), keyed to an
iron axle, and of two rubbers, B, that are formed of skin and are held
against the disks by small springs, R; motion is communicated to the
axle, _a_, by means of a pair of gearings, _a_ and _b_, and a crank,
_f_.
[Illustration: BORNHARDT'S ELECTRIC MACHINE FOR BLASTING IN MINES.]
Each disk revolves between two metallic rings, _c_, provided with
points that attract and collect in Leyden jars, D, the electricity
produced by the friction. For discharging the condensers there is
employed a manipulator formed of a rod, mm, which can be acted upon,
from the exterior, by means of a button, _k_. Upon bringing the ball,
_m_, of the rod in contact with the ball, _p_, of the condenser, the
lever (which then takes the position shown by the dotted line)
continues to remain in connection with a small ring, _q_, through a
special spring. Another ring, _t_, is connected in the same way with
the external armature of the condenser. Upon connecting the rings, _p_
and _t_, by a wire to which cartridges are attached, any number of the
latter may be ignited.
The parts that we have just enumerated are inclosed in a tin box
covered with a wooden casing, P. Between the two there is inserted a
sheet of hard rubber in order to prevent a loss of electricity; the
whole is held in place by strong springs.
In order to show the normal state of the condenser, a scale consisting
of 15 metallic buttons to give the dimensions of the sparks, is
arranged at X. This scale is capable of being connected with the
rings, _q_ and _t_, by means of chains; when the spark obtained after 15
or 20 revolutions considerably exceeds the intervals of the scale, it
is a sure thing that the machine is in a proper state.
In order to prepare the apparatus for carriage, the winch is taken off
and placed in the compartment, _m_, which is closed by means of a
door, Q.
Figs. 5 and 6 show the arrangement of the dynamite cartridges and
wires in the blast hole. Figs. 7 to 10 show different arrangements of
the igniting wires. Figs. 11 and 12 give the general arrangement for
igniting a number of cartridges simultaneously by means of the
electric machine. Fig. 13 shows the arrangement where powder is
employed. Fig. 14 shows the arrangement of a horizontal
hole.--_Annales Industrielles._
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