There is nothing charged for repairs, which for the month were trifling, and could be covered for a cent per ton. This answers the question whether the Burleigh drill will pay or not; and I have no hesitation in saying that better figures than these can be attained. These two machines broke, with twelve men and three boys, as much rock as could be obtained from thirty good miners. Better work can be done in a shaft where the ground is moderately hard, because a great deal more working time can be got out of the machine. Very much depends on the facilities for handling the machine; and it will require thought, experience, and time to decide what appliances are best. The mechanic puts into the miner's hands a machine that will drill 2-inch or 3-inch holes in diameter, from 40 to 60 feet in the shift, and he ought surely to have brains enough to handle that power to the best advantage. There surely can be no reason why a charge of powder in machine-drilled hole cannot break the same amount of rock as if exploded in a hole drilled by hand-labor. Going back to the time when the United mines, Gwennap, were at work, I remember that over £100 per fathom was paid to sixteen men for cross-cutting toward the "hot lode," when, but for the excessive heat, £10 would have been a good price. What would have been the value of cold-compressed air and the Burleigh drill there? How many deep and hot engineshafts are now being sunk, where the rate of sinking is nearer 6 feet than 12 feet per month, and where the sinking could be doubled, or even quadrupled, by using a drilling-machine?

I am not writing in the interest of the manufacturer, who, by the way, could improve the machines by putting in better material, but simply as one who firmly believes that machinery will, in less than ten years, very generally supersede hand-labor in mines. MINER.

KEWEENAW COUNTY, Michigan, October 9.

To these statements I add the following, from a paper read before the American Society of Civil Engineers, on the Nesquehoning tunnel, in Pennsylvania, in the construction of which the Burleigh drill was employed. The paper contains valuable statistics of its economy:

Nesquehoning tunnel, in Carbon County, Pennsylvania, is a work of the Lehigh Coal and Navigation Company. It pierces Locust Mountain, and will connect their railroad in Nesquehoning Valley with their extensive coal operations in the valley of Panther Creek. At present this coal finds its way to market by that interesting system of inclined planes and gravity-roads known as the "Switch-backs of Mauch Chunk," which has commanded the admiration of travelers for more than forty years, not only on account of the beautiful scenery which the route displays, but also from its early and admirable adaptation to the purpose for which it was designed. It has, however, become worked up to its capacity, and in arranging to extend their coal-mining operations, the company have wisely determined to avail themselves of the locomotive, which has had its practical development since they were the pioneers in railway enterprise. It passes through the base of the mountain at an elevation of some 15 feet above the water on either side, and 554 feet below the crest, and cuts the strata at right angles, where they have a south dip of about 459. Its length is 3,800 feet, of which 1,300 feet are through the coal-measures, with all their various strata of coal, coal-shale, sandstone, and conglomerate; 1,200 feet through the conglomerate formation, with its occasional strata of coal-slates and sandstone; 1,000 feet through the red shale, with occasional strata of sandstone, and 300 feet at the north end through the débris, and soft and decomposed red shale which is found overlying the red shale formation. It has encountered in its progress as hard and as soft material as is often met with in tunneling.

After mature investigation it was determined to use the Burleigh drills, driven by compressed air. With the advantage of the experience at Mont Cenis and Hoosac before us, we should, and it is believed we have, obtained better results, as to cost and progress, than attended either of those works in their early stages, and I may here state that I believe no other known process is capable of penetrating this conglomerate formation with that economy and rapidity which are necessary to meet the present demands of capital. This whole work has been done with 6 of the "two-drill" compressors, made at Fitchburgh, Massachusetts, and with sixteen-drill engines, and we have averaged as much as one-half of the drill-engines constantly in operation, and sometimes two-thirds.

The explosive used was gunpowder, ignited by the electic spark; but the requirements of ventilation and the hardness of the rock demanded powder of the highest Government standard. Some doubts which existed as to the economy in the use of the more powerful explosives, when the cost of drilling was reduced by machinery, and their greater danger, with the existing knowledge of workmen of their use, caused them to be rejected, and the result, in the freedom from serious accident, has been satisfactory, as we have not, thus far, lost a life from premature explosions.

American steel has been used. Several of our own makers produce a better and cheaper article for the purpose than can be obtained from abroad, and the best we have had is from the William Butcher Steel-Works at Philadelphia.

Month.

The headings are driven at the bottom, 8 feet high by 16 feet wide, and where arching is required, the full width for a double track is taken out, that the tunnel may hereafter be enlarged without disturbing the arches. At this date both headings are in the red shale and about 500 feet apart; they will be joined in August, and, until the tunnel is finished, full details of the work cannot be given; but the accompanying statement of Thomas C. Steele, chief assistant engineer, of the operations at the south end, up to June 1, may be of some interest.

The heading to which the tabular statement refers has been twelve months in the conglomerate, and two months in the red shale; the progress in the conglomerate has been about 100 feet per full month's work, and in the red shale 160 feet. The holes drilled per cubic yard of rock removed have been in the conglomerate about 11 feet, and in the red shale about 6 feet. The powder used per cubic yard has been in the conglomerate about 6 pounds, and in the red shale about 34 pounds, though a bad lot of powder ran the consumption in the conglomerate up to 75 pounds for two months. The operation in the enlargement to which the statement refers has been eight months in the coal-measures, and two months in the conglomerate; its average monthly progress has been 166 feet; its average holes drilled per cubic yard of rock removed, 3 feet; and its average powder used 2 pounds per cubic yard.

In this enlargement a portion of hand-drilling is included, which extended over the operations of one month, and it increased both the holes drilled and the powder consumed, showing that men do not use better judgment in directing hand than machine drilling. Statement of the workings of the south end of Nesquehoning tunnel.

Cubic yards of
progress.

Fect of holes

per cubic yard.

Pounds of pow

der per cubic

yard.

CHAPTER XXI.

STAPFF'S CONTINUOUS JIG.

I find no space in the present volume for a discussion at length of the principles of the concentration and separation of ores, which I hope to publish next year. Meanwhile, I desire to describe and recommend a continuous jig, designed by Dr. F. M. Stapff, M. E., a Swedish engineer of skill and experience, who, having tested its efficiency in practice, offers it for trial and the free use of the American mining community, at the same time preventing its being patented by publishing this description. He does not claim the entire invention of an apparatus which is a combination of parts frequently and successfully used in jigs of different construction, it being easy enough for experts to recognize those new and essential features in arrangement and construction by which his machine surpasses similar ones of older date.

The cut subjoined represents a machine built in full accordance with Dr. Stapff's designs, which was constructed at Bethlehem, Pennsylvania, for the Dolores lead mine, Mexico. The ores from this mine, galena and black carbonate of lead, are associated with small quantities of zinc-blende, copper and iron pyrites; they contain calespar as essential gangue, and are easily dressed. But in Sweden good.use has been made of quite similar jigging-apparatus for dressing copper-ores, containing copper pyrites, iron pyrites, and blende in a gangue of quartz, hornblende, and other silicates.

Sizing. It should be understood that the jigger is constructed for the treatment of sized stuff. We cannot here enter into a description of sizing-machines, and will only mention that the size of meshes in the sizing-screens, and the number of screens subsequently used, must be made dependent upon the specific gravity of the minerals to be separated by the jigging process. For the separation of calcspar and zincblende from galena, (Dolores,) the width of meshes in successive sizingscreens should be about 1.00, 0.64, 0.41, 0.26, 0.17, 0.11, 0.07, 0.04 inches, when perforated plates, with round holes, or, 0.70, 0.44, 0.29, 0.18, 0.12, 0.07, 0.05 inches, when wire-gauze with square holes is used. Stuff passing through 0.04-inch meshes is too fine, and stuff remaining upon to 1 inch meshes is too coarse for proper treatment by this jig, which, however, by some slight alterations in constructive details, can be made fit also for the working of coarser or finer stuff. All material fed on the jig should be free from dust.

General arrangement and modus operandi.-The main box contains six compartments, viz: A, open for the circulating water; B' and B", concontaining the pump-pistons E and E"; C', and C", receptacles for the jigged products; D, a space for filtration of the water from the refuse. The raising pistons press water through the sieve-beds, F' and F", while they draw water from A through the valves, e' and e", to the chambers B' and B". A consequence of the water's rising in B' and B", and of its sinking at the same time in A, is a current from left to right along the sievebeds to D, and thence through the holes, k' and k', back to A, by which the medium water-level in the whole vessel is restored. The valves, d", d", allow the water to pass through the sinking pistons, so that there is no suction against the sieve-beds, and no current from right to left is

effected by the back-stroke of pistons. Sized stuff fed upon the sievebed F', from hopper G, is jigged by the thrusts of water from below; but at the same time being exposed to the horizontal water-current, its lighter particles are carried across the ridge c', and after being exposed to a new jigging operation on sieve-bed F", the refuse is carried across the ridge c' to the chamber D. The heaviest parts of the jigged ore move close along the sieve-beds F' and F", and enter the receptacles C/ and C", through the gates g' and g", respectively. Screens of 'woven wire, attached before the holes and k", prevent the refuse from being carried to chamber A. Along the inclined screen ", the refuse is led to a discharge-opening, m". Continual feeding from hopper G is regulated by moving the plate f, which allows more or less stuff to be

drawn from the hopper by the fluctuations of the water. The regular horizontal movement of the ore from left to right is promoted by a slope of sieve-beds of 1 to 36. By slides h' and h", in front of the openings g' and g", the quantity of products entering the receptacles C' and C", is so regulated that the upper surface of the ore in process of treatment is about level with the ridges C' and C". If plenty of water (one cubic foot per second) can be disposed of, the discharge through the holes m', m", m, from the chambers C', C", and D, should be continual; but if water is scarce, the receptacles C' and C" are emptied periodically. The

refuse-hole m" should never be totally closed, in order to allow the refuse to escape continually with a certain quantity of water, which has to be replaced from above.

The pistons, by through-rods and cross-heads connected with levers O, receive their movement from cams L, working against the lever. It being favorable for the

jigging process that the pistons sink slowly, but rise rapidly, the downstroke is caued directly by cam, and the upstroke effected by a counterpoise Q, on the end of lever O. By alteration of the weight of this counterpoise, the velocity of the rising pistons may be changed at pleasure. Fine ore must be jigged by short strokes, coarse ore by long ones. For changing the length of stroke at pleasure, a set-screw, t, is placed over the guide-bar v of the lever O. By this means the back-arm of lever O can be raised so much that the cam L does not catch the head of the other lever-arm at all. Then the piston will rest, though the cam-axle is rotating; or it can be lowered so much as to allow the cam to catch the lever-head 3 to 4 inches above the releas

e

ing points, and then the stroke will be about 3 inches. The set-screw can be moved along the guide-bar while the machine is in full motion. An elastic cushion of rubber, r, is applied above the set-screw, to moderate the shocks of the falling lever.

All other circumstances unchanged, the quantity of ore jigged in a certain time depends essentially upon the number of piston-strokes. But this number must not be increased so much that the ore on the bed has not time enough to settle between two strokes, consequently the jig should be run slowly, (about 60 strokes a minute,) if coarse ore is jigged by long strokes, and fast, (about 180 strokes a minute,) if the finest ore is jigged by very short strokes. The most favorable number of strokes in any case can easily be produced by running the drivingbelt on one of the three pulleys of different diameter on the same camshaft.

From the preceding it is easy enough to see the wide applicability of this jig. If the hopper is regularly filled, and everything else regulated in accordance with the nature of the ore jigged, viz, supply of water,