Electricity for Blasting Operations.
Although half a century has passed since blasting by electricity was
effected by Col. Pasley, in his submarine explosions for removing the
wreck of the Royal George, at Spithead, the apparatus for exciting
the electricity necessary to explode many charges simultaneously, is
still (May, 1872), very unsatisfactory. Mr. H. Julius Smith, of Boston,
taking the Austrian friction battery, recommended by Baron Abner, in
his report at Vienna, for his basis, has ameliorated the arrangements
by enclosing the working parts in a better vulcanite casing, and
securing the discharge by reversing the motion of the handle, but the
objections remain that an ebonite plate is scratched by the rubbers,
that specks of the sulphuret of tin, used as an amalgam, cause a
partial discharge all over the surface of the plate, rendering it a
short-lived machine whose power is limited, unless the priming of the
exploders is made very sensitive, and liable to explode by atmospheric
electricity. Several fatal accidents have occurred to miners, from
premature explosions of the charge whilst loading the holes, and these
fatalities having been traced to the “over-sensitive priming” used, it
behooves the mining engineer to look well to the exploders offered him,
and in every case he will find where cotton immersed in a varnish is
sufficient insulation to protect the wire from losing its electricity,
the priming used for charging such exploders is too dangerous for
miners’ use, and involves a grave responsibility.
Mr. Abel’s Electro-magnetic Exploder limits the discharge to a series
of five mines, or blasts in each series, being the Verdu or Savare
system, and involves several leading wires for numerous explosions, and
although yielding electricity in quantity it lacks intensity.
The Holtz machine is altogether too vicarious in its operation for
blasting purposes. A machine or apparatus that will discharge 100
blasts, if needed, durable, and not liable to derangement or wear, is
a necessity, and it should evolve enough electricity and of sufficient
tension to jump between the wires 1-20th of an inch apart, necessary
to fire priming, so as to secure simultaneous firing. The heated wire,
or a quantity of electricity heating wire by the resistance a small
wire offers to the current, since it occupies time, brief though it
be, involves, as I think, the objection that the discharges cannot be
simultaneous in, say twenty blasts. Of this class are the machines
now in course of construction by Mr. Moses Farmer, of Boston, where
the exciting power is manual labor, being a dynamo-electric machine.
Breguet’s electro-magnetic exploder, giving a spark by breaking
contact, is altogether too weak, at least for the American contractor.
The ordinary Ruhmkorff coil is accompanied with the objection, that in
a numerous series of blasts, the spark, when it has passed some five or
six holes, seems to vanish in a glow, and to lose the heat necessary to
effect decomposition of the priming, besides the incumbrance of acids
and battery; in brief, it is not sufficiently portable for the use of
contractors.
During the past four years I have given this subject much attention,
and, having experimented pretty extensively, I have secured the first
point, viz.: a safe priming which is not affected by the induced
electricity caused by machinery running, friction of handling, or
atmospheric electricity. My present aim—the evolution of electricity
of sufficient intensity to leap fifty to one hundred solutions of
continuity, i. e., effect fifty blasts simultaneously, I hope I have
secured, but this subtile force, electricity, is so readily affected by
so many interfering elements in blasting operations, that it would be
premature in this patent-demanding age, to communicate the progress I
have obtained, until the several apparatus I am now constructing (three
forms of machine), are complete, and have been subjected to actual work
in severely critical hands. An inventor is no judge of the success of
his own bantlings.
Aware of the short life of the frictional electric machine, as at
present constructed; knowing how the ordinary induction coil diminishes
its intensity of spark, in proportion to the number of blasts to be
fired; seeing that the Electro-magnetic machine is limited to a series
of five blasts, which can only be exploded consecutively; that the
Electro-dynamic machines are open to this last objection, besides
destruction of their conducting parts by overheating, whilst in the
matter of adopting “over-sensitive priming” to compensate for the
deficiency of electricity or cheap conducting wire, there looms up the
danger to the miner of handling exploders, which “go off by looking
at” them, it seemed that, unless some amelioration was effected in
these details, the great economy of simultaneous blasting by means
of electricity would have to be abandoned. Add to these difficulties
the fact that any casualty occurring from any of the above causes
would reach the public as caused by Nitro-Glycerin, and my reader will
comprehend the interest I have felt, during the past four years, in
solving the following problem:
To construct an apparatus that will, under every condition of
atmosphere, whether damp, dense or rarefied, evolve, at the will of
the operator, abundance of electricity; such electricity to possess
the property of developing intense heat, so as not to need a very
sensitive priming, and to possess sufficient tension to overleap
numerous solutions of continuity, say fifty, at a flash. Next, to
discover a priming composition, to insert between the solutions of
continuity, that would not be affected by moisture, that would bear
handling without danger of exploding, be unchangeable for years,
unaffected by the induced electricity of the atmosphere, whether caused
by thunder storms, lightning on the rail, machinery belting in motion,
or steam blowing off from a safety valve, ozone, etc., and yet not too
exhaustive of the electric force of the spark required to fire it.
The above seemed to me the conditions necessary for the apparatus and
the exploder in firing with electricity.
In addition to these, for conducting such electricity to the points
required, the best conductor, and the best insulation attainable.
Further, that as Nitro-Glycerin was an expensive explosive to waste, to
supplement the above details with some material that would absolutely
develope its extreme force instantaneously, and not as is easily the
case, burn a part, explode a part, and throw the remainder into the
atmosphere, to poison the miners, or by missing fire, endanger life,
and waste time. How these objects, so desirable, have been obtained, I
now proceed to relate.
By modifying the ordinary induction coil, so as to make it yield a
highly heating spark, and remedying its property of losing tension
rapidly after leaping four or five solutions of continuity, the Messrs.
Ritchie & Sons, of Boston, have constructed for me a coil that fires
18 intervals when charged with rifle powder simply; and they are now
constructing another coil capable of firing fifty mines, when charged
with priming that is perfectly safe to handle, and fulfilling the
conditions enumerated above. One spark alone is required to effect
these results, which may be summed up as “eliminating the heating
properties of induced electricity.”
I have previously referred to the necessity of using a heavy charge
of fulminate of mercury, in order to secure perfect and instantaneous
explosion of a charge of Nitro-Glycerin, without confining the latter;
the manipulating this explosive salt (fulminate of mercury) without
hazard to the operators (generally girls), was accomplished by
precipitating gum mastich from its alcoholic solution, by the addition
of water, and mixing in the moist fulminate, and then filling the pasty
compound into a stout copper capsule, which is subsequently enclosed in
a wooden case, saturated with paraffine. The resistance of the stout
copper capsule, immensely adds to the effective force of the exploder,
and ensures the most effective explosion of the Nitro-Glycerin, which
cannot be obtained by a wooden capsule alone. These details as to
the requirements for effectively exploding the nitro-compounds, have
been very fully examined and proved, by Abel, Article, Pyroxylin,
Watts’ Chem. Dictionary, Vol. 4, p. 776, et seq., and daily use
confirms them. My observation of the fatalities that have occurred
with over-sensitive priming composition, introduced with a view to
compensate for deficient electric force, and thus to permit the use of
a weak battery and cheap cotton covered wire varnished over (instead
of gutta-percha insulation), in order to substitute a weak current
that would be sufficient to fire these over-sensitive exploders for
the stronger current required to fire a safe priming, satisfy me that
electric blasting had better be discontinued, and tape fuse resumed,
unless the work will bear the expense of absolutely safe materials.
Better to face the difficulty, construct efficient electric apparatus,
convey the electricity along wires of perfect insulation to a safe
priming, and by complete and violent explosion of the Nitro-Glycerin,
or powder, make such effective blasting as not to throw away the labor
of drilling, candles, power, and blasting materials. I believe this the
true economy. These details may seem wearisome, but the casualties of
blasting can best be diminished by avoiding missed holes, a result only
attainable by using materials absolutely reliable; and the reader, if
he has ever attempted to harness up as a team those subtile, evasive,
terrific forces—electricity and explosives, for the service of his
fellowman, will excuse the writer’s earnestness and agree with him that
in such a task the rule should be “Aut nunquam tenta aut perfice.”
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