4. And lastly, it can be rapidly drawn back to change the tools. The tool i a drill, with the cutting-edge in the form of a Z. It makes a hole of 0.09 and 0.04 in diameter; but in the first case it is furnished for 0.20 behind its head, with a bulge which trims or reams the holes to full size. The stroke of the machine is but 0.80, but it can make a hole to a depth of 0.90, by reason of the length of the drills, which vary from 0m.50 to 2m,

The apparatus placed before the breast of the gallery to be attacked carries 8 drills, which cover a section 4 metres wide by 3 metres high, equal to an area of 12 square metres. Eighty holes are bored, 6 of 0.09 and 74 of 0.04 diameter, and 0.90 deep. The daily work has varied evidently according to the hardness of the rock. In March, 1863, it was 1.10 in twenty-four hours; in April, 1m.40, and in some parts of the strata even 2.50; but when the bank of quartz was met, which was 308 metres thick, the advance was hardly 0.50 per day.

During the month of March, 1863, it was shown that each explosion of 0m.70 to 0m.80 required six hours for boring the holes, and four hours for the miners carrying away the rubbish.

The staff employed for the boring of the holes during twenty-four hours was as follows:

Men.

16

2

8

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In 1863 for 8 machines working there were 60 in the shop. In 1867 when the work was carried on both from the French and Italian sides the number of machines working was 16, and of those in the shop for repairs 200.

In 1863, for repairing 8 perforators working in a coarse sandstone, (grès à gros grains,) the staff attached to the workshops consisted of 24 men. In 1867 the number was much greater, but exact information could not be obtained. The work had, however, been offered to a company at 6,000 francs per running metre, the company taking all the apparatus and agreeing to repair the tools and clear away the débris. This was refused, although the price was equal to 500 francs per cubic metre. The enormous shocks which the machine was subjected to obliged them to change the iron beds for Krupp steel ones; the springs often broke, and the drills did not advance 0.20 or 0.30 without requiring repairs.

DÖRING'S DRILLING MACHINE.

Mr. Döring, of Ruhrort, in Westphalia, has constructed a drilling machine that has been used to great advantage in the zinc mines of the Vieille Montagne Company at Moresnet, near Aix-la-Chapelle. The di rector of these mines stated in 1867 that 11 of these machines, two of them of a recent construction, had been in actual use there, and that in one of the levels, where the rock was a very hard quartzose dolomite they had made an advance of 3 metres in 14 days, where by hand driving 12 metres only could be achieved. Sometimes the machine could advance

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4 metres in that time, and with only 2 men instead of 6. A six horsepower engine is required to work 2 machines; the air is compressed to 1 atmospheres. For one working machiné it requires 2 in reserve. The speed per minute is 0.03, including replacing the drills. Each drill will not bore more than 0.20 to 0.30 without being replaced. Its speed of advance at Vieille Montagne over ordinary borers may be considered to have been treble in hard rock, but only double in soft rock. This apparatus of Döring weighs 45 kilogrammes, and constitutes the borer, properly so called. It is erected upon a special carriage, which allows any direction to be given to the drill that is desired. The pressure of the air varies from of an atmosphere to 13. This machine is composed of a cylinder 0.400 in diameter, and 0.300 long. In this cylinder a piston moves, to which is fixed the stem of the drill. The compressed air is distributed by means of a slide valve, and, after acting freely, escapes into the air. Two ratchet wheels, furnished with dogs, are placed at the back of the cylinder, and are put in action by the prolonged rod of the piston by means of a fork which commands the dogs. One of the ratchet wheels serves to give to the drill a rotary movement on its axis; the other ratchet, which is nearest to the cylinder, by means of a toothed wheel advances the tool upon the support. The arrangement is such that the drill advances only when the piston has run its stroke. A jet of water is constantly thrown into the hole for the removal of the débris. The drill most used is pointed in the form of the letter Z; and it is found that when worked in the machine it does not blunt as rapidly as when worked by hand.

Mr. Döring has put his machines into operation in a very deep minethe Tincroft, in Cornwall-where the rock is the hardest in that country, and one is to be introduced at the Dolcoath mine. It is represented as making good headway in the hard rock of the Tincroft.

BERGSTRÖM'S DRILLING MACHINE.

Bergström's drilling machine originated in Sweden, and has been in use there at the Persberg mine. A machine exhibited at Paris in 1867 was said to have worked for 700 days under ground, and to have bored in the aggregate 1,000 metres. Upon hard granite, in trials with the drill, it bored 2 metres in 1 hour. The drill is impelled by compressed air, in a cylinder similar to that of Döring's machine, but without an automatic advance movement. It gives from 300 to 400 blows per minute, and the diameter of the drills varies from 0.018 to 0.025. The weight of the whole apparatus is only 120 pounds, and it is supported upon a steel bar, which must be fixed in a direction parallel to that of the intended bore-hole. The cylinder is made to travel along this bar. It may here be mentioned that in 1856 Karl Schumann, of Freiberg, Saxony, constructed a boring machine, to which those above described and the drill of General Haupt are similar in some respects.

HAUPT'S DRILL.

This percussion borer differs essentially in its construction from those described. It works by means of steam. The drill passes down a hollow piston rod, to which it is fixed by the extremity which is before the Workman. The reciprocating movement is communicated directly to the drill, and by a special arrangement of the slide valve the introduction of the steam into the cylinder is avoided until the piston has arrived at the end of its forward stroke.

The force of the blow of the drill upon the rock depends on the pressure of the steam upon the piston. It will be observed, besides, that the useful effect of the drill depends much more upon the section of the piston and the pressure of the steam, than on the length of the stroke of the piston, and that the consumption is proportioned to this last dimension. The length of the stroke of the piston is 0.102, and the number of blows per minute is 375.

The movement of rotation is given to the drill in the following way: The box in which the shaft of the drill is held, and which turns with it, carries a ratchet wheel on one part of its circumference, and around this wheel is a ring furnished with a pawl, which catches in the teeth of the ratchet wheel. This ring also carries a projecting tappet, which passes in an inclined groove left in the outer envelope of sheet iron which surrounds the steam cylinder. The tappet participates in the movement of the piston and drill, and by sliding in the inclined groove turns a screw with which it is combined, and by means of the pawl gives the ratchet wheel and the drill a rotary motion.

This arrangement would be insufficient alone, since the tappet mor ing in both directions in the groove destroys, to a certain extent, during the forward stroke, the useful effect produced during the back stroke. To obviate this imperfection, and to maintain the rotation transmitted to the drill, there is a second ratchet wheel placed at the front end of the box that carries the drill. A steel spindle placed in a recess formed by the cylinder jacket locks into the teeth of this second ratchet wheel. so that the movement of rotation only takes place one way. The first ratchet wheel allows the transmission of the rotating movement to the tool; the second forces this movement to be always effected one way. Mr. Haupt has contrived a special arrangement which causes the drill to always strike upon the rock with the same force, and to vary its advance according to the hardness of the rock. If the drill is put into the drill-carrier in such manner that at any given time the motion of this latter can be suddenly arrested while the tool itself continues to move, it is clear that each stoppage of the tool-carrier will be followed by an advance of the tool; but as this stoppage would diminish the force of the blow upon the bottom of the hole, it is only allowed to take place at intervals.

Mr. Haupt estimates that three horse-power is required for each borer, and that the rate of progress in rocks of ordinary hardness is 0.05 per minute.

BEAUMONT AND LOCOCK'S DRILLING ENGINE.

This machine is worked by compressed air; its object is to pierce a gallery of two metres diameter entirely by the machine, aided by powder for disengaging the core of rock which is left in the middle of the an nular trench cut by the drills.

This machine is composed of a cast-iron plate which carries on its circumference thirty-six drills made of cast steel, and in its center a similar drill. The diameter of the plate is about two metres, and is the same as that of the gallery to be driven. It is fixed on iron shaft, about two-thirds of its length being a piston, which moves in a cylinder.

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The stroke of the piston is about 0m.30. A slide valve introduces the air (compressed to two atmospheres) to each face of the piston, and gives it an alternate movement of 250 blows per minute. A worth worked by a special mechanism, turns the axle with the drills by means

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ck depeof a screw wheel combined with the axle. The carriage on which the piston shaft is mounted receives a forward motion by a special arrangement. The water which is thrown into the groove formed by the drills enters the interior of the shaft, and by pipes branched upon this axle is conducted to the circumference of the plate.

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This is evidently one of those machines that cannot long withstand the extreme violence of the impact essential to rapid drilling. If it is almost impossible to construct a machine with one drill that will work long enough without repairs to make it an economical success compared with hand labor, how much can we expect from an engine armed with thirty-seven drills, all rigidly attached to one piston?

FORD'S DRILLING MACHINE.

A power-drilling machine has been constructed and put into operation in one of the mines at Sandhurst, Australia, and is said to effect a very considerable saving over the ordinary process of drilling by hand. Mr. Joseph Millin, the manager of the Hustler's Reef Company, states that drilling in ground that would cost forty shillings per foot with hand labor can be wrought with the machine for thirty shillings; or, if with hand labor at sixty or eighty shillings, with the machine for forty shillings. The harder the ground the greater the saving. The machine appears, from the description given, to be similar in construction to the Burleigh drill. The constructor, Mr. R. G. Ford, of Sandhurst, describes the drill as follows:

In Ford's rock-boring machine the motion of the rock-boring tool is reciprocating, and the motive power is compressed air or steam, at a pressure of sixty pounds per square inch, acting on a piston in a cylinder. It presses constantly on a small annular space in front of the piston, and intermittingly on the whole area of the back of the piston; a percussive action is thus given by the borer carried by the piston rod. The ports for the alternate admission of the compressed air behind the piston, and for the exhaust, are opened and closed by a valve worked by a small piston, thus securing the full pressure on the back of the piston, and giving a free blow and a clear exhaust for the return stroke.

The air-ports and the movement of the valve are so arranged that the piston cannot strike the front and back of the cylinder. The rotation of the boring tool is self-acting, and is caused by the piston rod working a ratchet and click round a cylinder attached to the front of the working cylinder, and as the piston reciprocates it carries itself round the cylinder and makes a complete revolution every twenty-one blows, by which means the machine bores a perfectly round hole, and the drill cannot move more or less than a twenty-first part of a revolution at each stroke. The feed is self-advancing and self-adjustable and variable, feeding with precision as fast as the tool has power to penetrate the rock, but no faster, varying its feed in the same hole with the varying hardness of the rock or sharpness of the tool. This is effected by the working cylinder being provided with an exterior cylinder in which it can slide, and the compressed air is constantly tending to propel the working cylinder forward, but is retained by a screw, which is prevented from turning by a pawl, which the piston strikes when it makes a full stroke, thus releasing the screw and permitting the working cylinder to advance forward as the hole increases in depth.

An ordinary drill is used; the only alteration required is the head, which is made to fit the machine. The drills can be made to bore holes from three-quarters of an inch to two inches in diameter. The weight of the blow struck by the machine can be varied from 1 pound to 510 pounds, and the number of blows from 20 to 600 per minute, by the attendant simply moving the handle of a small air-cock.

The air-compressor used at this mine with Ford's machine is very simple, consisting of a cylinder nine inches in diameter, bent like the letter U, with a piston working in one leg only, the other being filled with water. The piston has a stroke of two feet, and as it moves up and down in one leg the water rises and falls in the other, thus making it double-acting. The piston works through a stuffing-box at the bottom, and the inlet and outlet valves are placed at the top. A small supply

of water is admitted at the inlet valve with each stroke, and is thrown into the receiver at each return stroke, thus circulating through the apparatus, and carrying off the heat given out by the air when com pressed. An old boiler is used as the receiver, and the compressed air is conveyed to the drilling machine in iron gas-piping.

LESCHOT'S ANNULAR DIAMOND DRILL.

The drills about to be described work upon an entirely different principle from those noticed in the preceding pages. The latter are all of the