DYNAMITE IN MINES.

Inangahua Times, Volume X, Issue 1505, 4 February 1885, Page 2

DYNAMITE IN MINES.

(To the Editor, Inanoahua Times.) Sir. — A few years ago dynamite as an agent for blasting rock was unknown in our mines, but quite the opposite obtains now. Contractors for driving tunnels and sinking shafts first brought it into use. Commencing a contract with powder, and after a time coming against a hard bar of rock in which powder made little impression, the new explosive was tried, and with surprising effect, for contracts that would otherwise have been a failure have turned out, with the use of dynamite, a success. It is particularly useful in ground that is wet, or shaft sinking in water, as with ordinary care the charge is rendered as certain to explode as in dry ground. A smaller borehole will answer than when using powder, consequently greater speed is attained in drilling, and to do the same amount of work the holes do not require to be bored so deep, for dynamite being bo sudden in its explosion it acts on overy side with equal effect, often tearing for inches below the bottom of the hole. Powder being slow in combustion has more of a lifting nature in it and its force is mostly upward. With powder larger bits are required ; the hole to bt deeper, and tam pod, and tho process is slower and dearer, more especially where water is in the ground. Strong objections were urged against the use of dynamite by most of the miners, and many held aloof from nynes in which it was becoming usod, the fumes having a most injurious effect upon some constitutions, so much so, that workers in dynamite could be easily distinguished by their pallid appearance from those who wore using powder. Much improvement has however been effected in the explosive of late by destroying, or rendering less obnoxious the fumes or gases that aro liberated when it explodes, and fewer complaints arc hoard of it, so that it. has now come into very general nso. Where tho ventilation is good nothing can be said against it, but in a close, badly ventilated portion of a mine its .fleets are felt inconveniently. Powerful as it is as nn explosive, it requires to bo used with judgment, as it still remains that, the I eat nrorKer with powder can givo a corresponding satisfactory return when using lynamite. The ordinary charge for p»wler is one-third tho depth of hole, thus if ;he bore be two feet, eight inches of »owdor would be used, sometimes moro lomotiines less, according to the work i

has to do. Dynamite is from four to six i times stronger than powder, the rule for f the strength of an ordinary charge y has not been reached yet, one reason . being that the strength of dynamite . cartridges seems to vary, one case con- ' taining large cartridges than another, 1 and again the burden, or amount of rock ( to be shattered by the shot, is usually 1 more than would be attempted if using < powder, so that it is still a good deal a matter of guess, the rule most acted Wjon being, "Give it plenty." Directions coming with the dynamite state that when ground is dry, sand or something to correspond may be used as tamping, and lightly rammed. The impression, however, prevails amongst many that, like powder, it requires to be rammed hard, and tamped to the mouth of the hole to render it more effective. This is a fallacy, as can be very easily proved ; also wiih a few inches uf tamping lightly rimmed there is less danger, for if the charge does not explode, or what is termed, a unVfite occurs, after a reasonable interval of waiting, another charge and detonator can be placed on the tamping, and the shot exploded with the same effect as if at first discharged. Dynamite is invariably used in ground where the walls are weak, and the timber requires to be kept close up to the face. From the strength and suddenness of its exph sion it shatters the i rock into small fragments, which rarely Ido damage ; powder throws it out in lirge masses, and one of those s riking a set would likely bring it down, even if well stayed, and causes much loss of time in repairs. Powder, however, retains its supremacy in some places. After the levels have been driven, and the lode is being stoped out, in mines where the reef is large, such as the Keep-ii-Dark, it is mostly used, for in such cases where there is one side rr floor free, it gives better results than dynami-e. A n<>t unusual plan with miners when stoping a big reef, and the face is favorable for the experiment, is as follows : — Having put in a deep bore, say, three to four feet, then to insert a single dynamite cartridge, tamp lightly, and fire. The charge is not sufficient to break the ground, but it blows the tamping out, and at the bottom of the hole where the cartridge was placed a circular cavity has been hollowed out by the explosion of the dynamite. The hole is now re-charged, but this time with powder, treble the quantity going into the cavity that would ordinarily be used in a bore of that depth, tamped hard and fired. The result in some cases is Burprising. Possibly the reef, even if large, is split from wall to wall, at any rate large masses are dislodged, and sledges and hammers have a fine time breaking it up. Dynamite has now come into such general use that there are mines on this field where a keg of powder is not used in twelve-months. Its effect has been te lessen the cost of driving and sinking from 12 to 15 per cent also to considerably lessen the time of doing certain work, and, where the rock-borer is used the time is still further reduced . I am, etc. , Thady. Reefton, January 31st, 1885. " Buchu-paiba." — Quick, complet* cure, all annoying Kidney, Bladder and Urinary Diseases. At Druggists Kempthorne, Prosser t Co.. Agents hristohurch.