“East End, 120 feet; Central Shaft, eastward, 100 feet; West End, 140 feet, total, 360 feet. Total lengths opened to April 1, 1862: East End, 10,166 feet; Central Shaft, east, 617 feet, west, 325 feet, total, 942 feet; West End, 7,494 feet. Lengths remaining to be opened: between East End and Central Shaft, 2,054 feet—586 feet less than half a mile. Between West End and Central Shaft, 4,375 feet—855 feet more than two-thirds of a mile.”

A reference to the [wood cut opposite page 80], shows the profile of the mountain and progress of the Tunnel to January 1, 1872.

The distance made during the month of March, in the East heading, was 120 feet of heading, 24 feet wide and 9 feet in height, exclusive of first enlargement or roof, and second enlargement of roof to full size or stopeing, which is usually carried on simultaneously to about 250 feet per month. This heading is being attacked by twelve of the Burleigh drilling machines, mounted on two carriages manned by eight miners and a foreman, who work for eight hours, with brief intermission whilst the charges are being fired. The drills are impelled by compressed air, making 300 strokes per minute, and calculated to strike with a force of 200 lbs. at each blow, perforating from one inch to five inches per minute, of a hole two inches in diameter when powder is used, and 1½ inch diameter for Nitro-Glycerin blasting. At the East heading, partly owing to the rock being softer than either at the West End or in the Central Shaft, partly to the miners being accustomed to powder, partly to the heavy battery of drills enabling twelve drilling machines to work at once, and thus make progress satisfactory to the contractors, who, wisely, let well enough alone, the holes when drilled to a depth of from two feet six inches to three feet, are each charged with from one to two and one-half pounds of blasting powder, then tamped; the carriages are drawn back, and the sixteen to twenty-six holes are fired simultaneously by means of a frictional electric machine. This takes place every four hours, exploding from 100 to 150 cartridges every twenty-four hours. The reader must not infer from this that every blast makes from two feet six inches to three feet of advance; because, first, the holes are never drilled for powder in a horizontal plane, but at an angle, sometimes upwards, sometimes downwards, to the right or left, the aim being, that a straight line drawn from the bottom of the hole to the face of the rock shall be shorter than the extreme length of the drilled hole, so that the charge or blast which exerts its force in the line of least resistance, may displace the rock between the bottom of the hole and the surface of the rock, and not collar the hole, that is, merely remove the rock surrounding the outlet of the drilled hole. It is usually found also, that the power exerted by powder is not sufficient, in working a heading, to blast out the rock from the bottom of the hole, but, most frequently, from the point where the cartridge begins, and the tamping terminates. Thus, if a hole be drilled at an acute angle from the face to a depth of thirty inches, with a line of least resistance of twenty-four inches from the bottom of the hole, and a fifteen inch cartridge of blasting powder be inserted, and tamping to the extent of fifteen inches be rammed in above the cartridge, the rock removed, will, under ordinary circumstances, be removed from about where the cartridge commences, that is about 12 inches, or it may be 14 inches, in a direct line from the face. And herein lies the very important distinction between powder and Nitro-Glycerin; the latter, bottoms, i. e., removes the rock from the bottom of (in roofing and quarry work beyond) the hole; with powder this is rarely the case. Moreover, as the depth of the holes is increased, so must the diameter be increased in proportion to the depth when powder is the blasting agent, but when the drilled hole is to be blasted out with Nitro-Glycerin, a diameter of 1¾ inches is sufficient for a hole having a depth of ten feet, and a line of least resistance of eight feet, a depth wholly inadmissible for powder, because the rock at that depth would act like the breech of a cannon, and the explosion would issue direct from the hole, only fracturing the edge, i. e., collaring the hole. With Nitro-Glycerin the holes need not be drilled at so acute an angle to the face of the rock, and need no tamping, that is, the drilled hole is left entirely open, and no time is occupied therefore in ramming materials over the explosive, and no risk is incurred in cutting the fuse or electric wire, as with powder, dualin or dynamite, all of which must be tamped. The explosion of Nitro-Glycerin differs from that of every other explosive in this, that the explosion is instantaneous, consequently the rock yields before any flash can reach the mouth of the drilled hole, and the work is done before the gases can travel six feet. Hence the necessity of deep holes; to charge holes only 30 inches deep (except they are from ⅝ to ⅞ inch diameter) is a waste of the material. The same charge will clear the rock to the bottom, with a hole drilled six feet deep, and in fact bottom the six foot hole, whilst a similar charge inserted in a 30 inch hole may leave three or six inches of the hole visible with its surrounding rock, after the blast. And here I cannot refrain from narrating what a narrow escape Nitro-Glycerin had at one time from being rejected at the Tunnel. In the dark days of this enterprise, when every cent expended was narrowly watched, and when it was favor enough for a miner to condescend to allow Nitro-Glycerin to be used in his shift, requests and entreaties for deep holes, and remonstrances that the holes were not drilled deep enough to give this explosive a fair chance, were found fruitless; until, finally, a consultation was held in the time-keeper’s office at the West End, the purport of which was, to notify the writer that no more Nitro-Glycerin was needed, as it did not answer expectations. The superintendent, at the West Shaft, was asked what reason I gave that greater progress was not made with the new explosive. His reply was: “Mowbray says the holes are not drilled deep enough, and, I think (he added) it is but fair his demand for deep holes should be complied with, before you throw up the use of Nitro-Glycerin. He has outlaid some $5,000 for the experiment, and you ought at least to see the effect of deep holes, before you decide.” Agreed; the superintendent then went to the foreman of the shift, and requested deeper holes, ordering six feet holes. “It’s no use,” was the reply; “it’s all nonsense; why, I tell ye, it won’t bottom a hole 30 inches deep; then how is it going to fare with a six foot hole; besides, we can’t drill six feet holes by hand in one shift.” “Then take two shifts to do it, and take three if it is necessary; this Nitro-Glycerin man says he must have deep holes, and he shall for this once, if I drill them myself, and it takes a week to do it.”

The deep (only six feet) holes were drilled, and charged; cartridges of same size as those inserted in 30 inch holes, were used, and fired, every hole bottomed, every miner was astonished, and from that day the use of Nitro-Glycerin was a necessity for the heading in the West End. But it was a narrow escape from what would have been deemed a failure. On another occasion, during a drought, the supply of water at the West End, where the Nitro-Glycerin was manufactured, gave out, and, being a necessity in the manufacture, we had to haul it by team. This was troublesome work, and cost money. There had been a change of engineers, and the gentleman now in charge, on the difficulty reaching him, determined first to ascertain whether Nitro-Glycerin was a necessity, before complying with the contract the Commissioners had made, and which involved a supply of compressed air and water, if they used Nitro-Glycerin. And to make no mistake, the holes of what is termed the “cut” in the heading, that is, two series of four holes each, in a parallel line from the roof, about nine feet high, were drilled about five feet apart at the face of the heading, and six feet deep, tending towards each other so that at the bottom of the holes they terminated about three feet apart. After charging and firing, the above gentleman and his assistant inspected the result. A mass of rock eight feet in height, five feet wide in front, and about five feet deep, with the rear end three feet wide, had been blown from its seat, some ten feet from the heading, and there stood, a monument (until block-holed) of the use of Nitro-Glycerin, when properly applied. “You shall have all the water you want, sir, if I bring it myself in pails,” was the energetic assurance of this gentleman, who felt satisfied that Nitro-Glycerin was a necessity for the Hoosac Tunnel.

“Stopeing out” Roof Enlargement
(East End.)

In drilling holes for blasting with Nitro-Glycerin, a depth of not less than five feet should be reached; six feet are better, but ten and twelve feet are the right depth for a heading, whilst fifteen feet for bench work, and eight feet apart, or, for quarry work ten feet apart, and ten feet from the face, provided the rock is hard enough (in clay, owing to the sudden shock Nitro-Glycerin is ineffective); exploded in holes of such a depth it will throw out everything before it—and make progress. How difficult to get miners to drill such holes, how many frivolous objections, how the wires and their connections will be tampered with to interfere with the intended blast, and how criminal, contrary, and pig-headed, they deem the contractor and Nitro-Glycerin man who insists on such depth of holes, I have often experienced, and it needs the firmness and vim of desperation to enter a quarry, descend a shaft, or go into a rock cutting, and oppose the life-long habits of men who believe honestly they know everything that concerns mining, and what they do not know is not worth knowing. But if once a blast is shewn, and they have to hoist out the rock, their obstinacy succumbs, and in three months, men, who knew it was poison, and so dangerous it was wicked to ask them to drill holes to receive it, have positively refused to descend a shaft if powder was attempted to be used merely in a comparative experiment, alleging, that the powder was unhealthy and not fit to be used at the bottom of a shaft, where the air was confined. And here let me truly add, I have never sent Nitro-Glycerin to be experimented with in any rock work, rock cutting, or rock tunnel, that was not followed by a large order, repeated until the end of the work, during my past experience of four years’ manufacture. Indeed, there have been only two cases where it was found inapplicable, and these were in hard clay, where it seems actually to mould for itself a chamber, compressing the walls of the drill hole, as if an enormous hydraulic ram had been inserted; but the tenacious mass is not displaced, it only suffers compression. When, therefore, holes can be made with a crow-bar, and not drilled, do not use Nitro-Glycerin, but if you have rock, be it as hard as emery, or as the magnetic iron ore of the Lake Superior or Ottawa Iron mines, the harder the better for the economy of drilling, which is very great, so few holes being required, the introduction of Nitro-Glycerin, with a good steam or air drill, causes the progress of the work to advance to that degree that it is only limited by the ability to remove the debris of blasted material. To return from this digression to my subject.

To effect this progress of 120 feet, probably about 3,000 holes have been drilled in an area not exceeding 24 feet by ten feet, requiring twelve drilling machines, and 60 horse steam power to compress the air requisite to drive the drills; add to this the powder, over a ton and a half, the electric exploders, the candles and oil for miners, and the fact that a mass of rock 120 feet long, ten feet high and twenty-four feet wide, has to be carried out and dumped two miles from where it was excavated, and some slight idea of the labor at this one point may be formed. Now take double this length of rock, viz.: 250 feet, increase its height to 15 feet, keeping its breadth of 24 feet—I say, take this mass which is torn from the roof, whilst the heading is being pushed, and bring it and dump it 1¾ miles from where it lay solid, and you have again another point on which you can begin to estimate the East End work. About 350 men, a locomotive, forty cars, 200 horse water power, machinists, blacksmiths a legion, for sharpening drills is hand work, so is picking up rock, loading cars, making track, and all this is done in the smoky, wet, grimy, confined tunnel, or round about its entrance, and you have a mixed, confused suspicion that this tunnel driving is a work needing high powers of organization; and, with the license of the miner, his pay day, his weddings and his wakes and funerals, which are all powerful reasons for quitting work, you have a still clearer idea of the anxiety such work involves.

CENTRAL SHAFT.

[The Plate, opposite page 74], conveys an idea of the sinking of the Central Shaft at 891 feet depth; at the time of writing, May, 1872, however, this shaft had not only reached grade, but to a sump beneath grade at a depth of 1,040 feet; headings and enlargements have been also driven at grade, east and west, to meet the works from the East End, and from the Western Shaft. Owing to the stratification of the rock, which dips towards the west, great progress was anticipated in this direction; but man proposes and God disposes; on reaching about 300 feet westward, seams of water were struck, of so threatening a nature that a powerful Cornish pump was erected, at a cost reaching, in all its details, $80,000, and now, May, after enlarging the diameter of the former plunger pump, prudence suggests the temporary delay of any further disturbance of this water inlet (immediately under the divide of the mountain), until the present pumping force has sufficiently drained the sources of water supply to permit a further advance of this (the western) heading of the Central Shaft to be driven without involving a flooding out of the men working at the eastern heading. Meanwhile, from the sump, the excavations are enlarged to full tunnel size, the capacity of the Cornish and plunger pumps are being tested, and all energy summoned to meet any difficulties to be overcome when this western heading of the Central Shaft shall resume work. All the rock here has to be moved from the heading by hand power, and lifted (by steam power) 1,000 feet to the surface, yet, notwithstanding these adverse circumstances, during March, 100 feet was driven to the eastward alone. I append a memorandum furnished by Mr. E. A. Bond, of actual drilling and blasting, taken at this point during the dates given, being about the average performance.