The holes are
blasted simultaneously by the electric battery.
After noting another system used to a limited extent, and not to be
commended, viz., the use of inverted plugs and feathers (the plugs and
feathers being inserted as a sort of tamping which the blast drives
upward to split the rock), Mr. Saunders continues in substance as
follows:
It is thus seen that the "state of the art" has been
progressive, though it was imperfect. Mr. Sperr, in his
reference to this subject, made in the report of the tenth
census, says: "The influence of the shape of the drill hole
upon the effects of the blast does not seem to be generally
known, and a great waste of material necessarily follows."
This was written but a few years before the introduction of
the new system, and it is doubtless true that attention was
thus widely directed to the conspicuous waste, due to a lack
of knowledge of the influence of the shape of a drill hole on
the effect of a blast.
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