In order to avoid the frequent breaking out of the teeth, this trepan was lifted only 0.20. The progress made with it daily was from 1m.10 to 0.18 at the last, when a stratum of hard sandstone was encountered and the weight of the trepan was found to be insufficient. Two blades, one above the other, were then united to the fork by rings and bolts. Each of these blades carried the teeth so as to cut the strata in two steps. This new tool weighed about 5,000 kilogrammes. It worked four months, and required frequent repairs. The rate of progress per day was only 0.11. It was then decided to replace this trepan by a more massive one, weighing 8,000 kilogrammes, and 2.50 in diameter. With this the progress was increased to 0.34 a day, thus showing a second time that in hard rock heavy trepans are required.

The diameter of the pit at the beginning was 2.56; at 134m depth it was reduced to 2.45; at 155 depth it was reduced to 2m.40; from 155.00 to 155.50 depth it was reduced to 2.33; from 155.50 to 158.00 depth it was reduced to 2.25. At this depth the little pit was continued for a depth of seven metres, and a circular curb of 0.40 was fixed to receive the base of the tubbing.

The work of sinking this air-shaft lasted about twenty-eight months and a half. The central pit required 392 days, including 46 days during which work was stopped, so that only 346 of actual work were necessary. The enlarging operations to a diameter of 2.56 occupied 469 days, including 148 days of no work. The depth of the central pit being 143.70, (equal to 471.46 feet,) the mean progress for each working day was 4.15, (13 feet,) and the enlarging to 2.40 gave a daily mean of 25 for a depth of 136.60.

The expenses of boring were as follows:

TUBBING.-Before entering upon a description of the operation of tubbing the air-shaft, it will be best to explain the system adopted by Messrs. Kind and Chaudron.

The tubbing of the pits is accomplished by lowering into them a metallic cylinder, which finally rests upon a proper seat or foundation, carefully cut for it at the bottom. This cylinder is made smaller than the bore of the pits, and the space between the cylinder and the walls is afterward puddled or filled in with concrete, so as to make a solid continuous lining. The metallic cylinder or tubbing is formed in sections of a cylinder, made of cast iron, and provided with flanges projecting inward, by which they are securely bolted together. One section or length is added after another to the top as the whole descends in the pit, so that at the completion of the work the whole pit is lined with. iron from the top to the bottom. The outer surface of all these sections of the cylinder is quite smooth; but in the inside, besides the flanges for the bolts, there are horizontal ribs or webs cast with each segment, and intended to strengthen them.

The thickness of the tubbing will evidently vary with the diameter of

the pits and that of the different segments, according to their position in the pit. Messrs. Kind and Chaudron determine the thickness by the following formula:

E represents the thickness of the tub, R the radius, and P the pressure expressed in kilogrammes upon the square.

M. Gernaert, of the International Jury of the Paris Exposition, says that the principal merit of the success at L'Hôpital should be given to the inventors of the method of lining the shafts while full of water. The jury awarded the highest order of prizes under the title of co-operators to the engineer, M. Kind, of the kingdom of Saxony, and to M. Chaudron, of the mining corps of Belgium, particularly for the improvements in lining or tubbing, which form an indispensable complement to the process of boring shafts in watery strata, and without which the perforations, however large, would not have any great practical value.

The operation of boring was not new. Many engineers had succeeded in excavating shafts of large diameter in this manner, but the great difficulty was to secure a firm and water-tight lining for them. M. Kind had proposed to lower tubbings made of wooden staves held by metal hoops. Many shafts were lined in this way, but all or nearly all were failures. A shaft was finished in this manner at Dalbuch, in West

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phalia; but when the wa ter was pumped out, down to a certain level the pressure displaced the staves and it became necessary to insert very heavy iron rings throughout the whole extent of the tubbing. But notwithstanding these expensive efforts the quantity of water which forced its way through the vertical joints was sufficient to supply a powerful pump.

Cast-iron tubbing made in segments of a cylinder and bolted together was next employed; but even these,notwithstanding the great care used in fitting and placing them, allowed water to penetrate, espe cially along the vertical joints. But at L'Hôpital, M. Chaudron avoided these difficulties by casting sections of the cylin drical tubbing in one piece. These sections were made about 1.50 high and 3.40 in diameter and varied in thickness from 0m. 060 to 0.028, but were strengthened by ribs and flanges on the inside, which served also for bolting one section to another.

Cylinder and Moss Box.

The opposing faces of these cylindrical sections were truly turned or planed down at right angles with the axis, so that they fitted accurately one upon another. The joint was made more perfect and tight by a packing of heavy sheet lead.

The shaft having been bored to the proper depth through the watery ground, and a firm seat or socket secured at the bottom in solid and comparatively impermeable rock, the next operation was to lower the cast-iron tubbing to its place. This was accomplished in the most ingenious manner by M. Chaudron, by tightly closing the bottom segment of the cylinder with a hemispherical cap, so secured that it could be afterward removed, and then floating the cylinder in the water of the pit. But in order to secure the descent as section after section was added at the top a central open column or tube e e was bolted to the bottom, and through this, by means of holes drilled at proper distances, water was allowed to enter the inside of the cylinder for the purpose of sinking it, and to aid in keeping it in a vertical position. The annexed woodcut shows, in section, the cylinder, the convex bottom, the central or equilibrium column, the moss-box, and the suspending rods b b and b' V. The moss-box is a contrivance similar in its objects and application to the seed-bag used by the borers of petroleum wells to cut off the ingress of water from strata around the pipe. By means of the moss, expanded laterally when the cylindrical column of cast-iron tubbing is allowed to rest upon it, a tight joint is formed between the firm rock at the bottom and the cast-iron tubbing, thus effectually shutting out the

water.

The entire cost of sinking the first shaft (or shaft No. 1) at L'Hôpital through the watery strata to a depth of 140 metres, the internal diamter being 1m.80, amounted to 255,041.27 francs, divided thus:

Which gives an expense of 1,600 francs per running metre.

The cost of shaft No. 2 is estimated as follows:

or at the rate of 3,100 francs per running metre. The preliminary work commenced in September, 1863, and on the 6th of April the concreting was finished; the work lasted three years and a half.

H. Ex. Doc. 207-35

CHAPTER LXX.

MACHINES FOR CUTTING OUT COAL.

Before proceeding to throw down coal from its place in the bed it is necessary to undercut it, that is, to excavate a space at the floor of the seam, partly in the floor and partly in the coal, thus undermining the coal so that its gravity assists in bringing it down. This undercutting operation is known as holing, baring, kirving or undercutting, and is one of the most laborious and difficult duties which the miner is called upon to perform. It is often effected under the greatest disadvantages, especially when the seam of coal is very thin, and is cut on the end, to improve its salable qualities. The work is usually accomplished by means of a pick in the hands of a miner, while he rests extended upon his side. An experienced miner makes about forty blows a minute with a pick and cuts from three to four feet under the coal, at the rate of one to one and a half linear yards per hour. In order that the miner may have the necessary space for his body in working so far under the coal, much of the coal has to be cut away and destroyed. It is estimated that the miner under such circumstances exerts about one-sixth of a horse-power, which is applied percussively. He works into the coal as a mechanic with a hammer and cold-chisel used to cut away iron before planing and slotting machines were invented. The proposition to substitute machines for manual labor in cutting out coal was made some twenty years ago, by Mr. Peace, of Wigan. He invented a machine called the iron-man, but it met with ridicule and contempt. Much attention has of late been given to the construction of machines for the purpose, and a very considerable degree of success has been attained; but it cannot be said that any of the machines yet put into operation give entire satisfaction under all conditions. Most of the efforts in this direction have been made in England, where several machines have been brought prominently before the public by means of descriptions and advertising, and by the exhibition of the machines or models at the Paris Exposition of 1867.

The following observations upon the value and importance of machines for excavating coal are taken from the Colliery Guardian, November, 1869:

How to win and work coal most economically, is a problem the satisfactory solution of which is of the highest moment to the colliery owner, the mining engineer, and the public at large. In this matter producers and consumers are alike interested, and the question is one the growing importance of which is becoming daily more evident. In these times of keen competition, the most successful man in any branch of industry will generally be the one who has at his command the most efficient appliances in the way of improved machinery and skillful modes of operation. To this rule-applicable to trade and manufacture generally-coal-mining is no exception. A saving of a very insignificant amount-say but a few farthings-per ton, upon the whole of the out-put of a large colliery, will make a marvelous difference in the financial prosperity of the concern, and will present a very satisfactory result in the profit and loss account. To this fact colliery owners and managers are fully alive. Hence, in the meetings of the North of England Institute of Mining Engineers, and other kindred associations established in the several mining districts of Great Britain, attention is perpetually directed to this one point, and a patient and painstaking examination is given to every proposal, the professed object of which is to facilitate any of the numerous operations connected with mining industry. Any improvement in boring or sinking-in coalgetting or underground conveyance-in winding or shipping the produce of the mine, need only be fairly brought under the notice of the mining community to insure for it careful consideration and impartial judgment. Special attention has of late years been directed to the subject of coal-getting by machinery. More than a century has elapsed since the first apparatus designed for the effecting this object was patented, and since that time "iron men" and coal-getters in great numbers, and almost equally

great variety, have been presented to the mining public. Additional impetus was given to inventive genius by the appointment of a committee of the North of England Institute, commissioned to investigate the subject, and to report upon the value of existing patents; by the prizes offered by the South Lancashire and Cheshire Coal Association for the best coal-cutting machine; and by the encouragement afforded by mining engineers, both in their individual capacity and when incorporated into associations. It was felt that, looking at the success which in other departments of industry has attended the substitution of machinery for hand labor, there was good ground for the belief that machinery might also be advantageously applied to the cutting of so uniform a substance as coal, and the driving of airways through it. The purely mechanical operation of cutting, by means of a light pick, a groove of from 24 feet to 4 feet deep along the face of coal which is to be removed, is not only slow and laborious, but also wasteful, inasmuch as a considerable amount of the seam is necessarily cut into slack; and forming, as this process does, the chief item of expense in the excavation of coal, it has of late been more seriously forced upon the attention of coal owners by the irregularities and strikes of the workmen, which have so often brought the operations of coal mines to a ruinous stand-still. The introduction of efficient machinery is also calculated to have an important bearing on the safety of mines, enabling them to be more rapidly opened out, and the seam to be intersected or the winning to be surrounded by air-ways so as to drain off the dangerous gases. It is not to be wondered at, therefore, either that an efficient machine for getting coal should have become an acknowledged want, or that so many ingenious inventors should have applied themselves to the production of apparatus to meet that want. It is true that many of the inventions have been crude, and some of them designed without much regard to some of the first requisites to extended application, but others have been tested in actual working, and found to give satisfactory results.

Machines for coal-cutting may be classed under two distinct types, being, like the machines for rock-drilling, made upon two very different principles. One type is percussive, and imitates the cutting operation of the pick as swung by the miner; the other concentrates and applies the power continuously through cutters which are pressed against the coal and shave it off little by little. Prominent among the machines of the second type is that of Carret, Marshall & Co., of Leeds, England.

CARRET, MARSHALL & COMPANY'S COAL CUTTING MACHINE.

This machine works like a hand-plane; and it is claimed that it has the power of eighteen men, that it can work effectively in a space only two feet high, and cut into coal as a scoop cuts into cheese, accomplishing more in one minute than 700 blows from a pick can in the same time. It is about two feet high, weighs one ton, has four legs of adjustable length, and is provided with a holding piece adjusted so as to touch the roof of the drift and hold the machine firmly to its work. The motor is water, under a pressure of about 20 atmospheres or 300 pounds, and supplied through a 2-inch pipe at the rate of 30 gallons per minute. This water pressure acts vertically on a 5-inch piston pressing against the roof, and horizontally on one about the same size, reciprocating 18 inches and 15 to 20 times in a minute. There is a pressure of 5,000 pounds against roof, and the same pressure acting horizontally, forcing three steel cutters shaped like cheese scoops into the coal. These cutting tools are 3 inches wide, and penetrate 4 feet, with a power equal to 3 horses or 18 men; and this is effected by a consumption of 50 pounds of coal per hour to feed the boiler of the engine, which makes the water pressure, and pumps the same over and over again.

The construction in detail is shown by the figures, which embrace a front elevation, a ground plan, and an end view, all drawn to a scale of three quarters of one inch to one foot, or one-sixteenth the real size.

The machine in operation fixes itself dead fast upon the rails during the cutting stroke, and releases itself at the back or return stroke, and traverses forward the requisite amount for the next cut without any

* Supplied for this report by Messrs. Carrett, Marshall & Co., the manufacturers.