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.