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able to exhibit a drawing of one of the latter of an approved form and construction.

A kibble, such as is used with horse-whims, holds about 300 weight of ore, and 120 kibbles will just clear a cubic fathom of rock.

Miners' work under ground is chiefly divided into sinking, driving, and stoaping.

Sinking is applied to shafts, and to other smaller perpendicular openings from one level to another, usually called winzes.

Shafts are of different, dimensions according to the purposes they are designed for; the largest kind is the engine-shaft, in which are generally placed the pumps for draining the mine of water, the ladders for the men, and a part divided off and called the whim-shaft, for the kibbles to pass up and down. Plate II., MINING, will be found to represent a perspective view of a part

of the interior of these shafts.

A good engine shaft measures about eight feet by twelve, though some are sunk of larger dimensions. Shafts intended only for hauling ores through, and those for air and foot-ways, may be about six feet by four.

In large shafts, a set of twelve men are usually employed; in smaller ones eight, or even six, are a sufficient complement to keep the work going. They work two or three at a time, and relieve each other every six or eight hours, keeping good the whole twenty-four without intermission. The miners are attended by laborers, or winze men, who haul up the stuff out of their way as it is broken.

Sinking is contracted for by the fathom in depth, and the price therefore varies according to the dimensions of the shaft, as well as according to the hardness of the ground, and the circumstances relating to water, air, &c. A medium price is about £20 a fathom for shafts at some depth from the surface, but some have cost £80, and others are executed as low as £5.

Driving is the term applied to the execution of horizontal passages, which are called adits when used for the conveyance of water near the surface, and levels when made for opening the lode or vein, and forming communications from one shaft to another under ground. Levels ought to be seven feet in height, and two feet and a half wide; by constructing them as high as this, room is given to admit contrivances for ventilation, so that they may be continued to considerable lengths without inconvenience. More than two miners cannot work at one time on the end of a level, and the set of men therefore employed may consist of six, relieving every eight hours, or of four relieving twice in the twenty-four hours, or two men only, who may work as long as circumstances will permit. Driving is paid for by the fathom in length, the height and width being limited; a great variation of prices takes place according as the rock is hard or soft, as work of this sort is done from 10s. a fathom to £30, but about £5 a fathom is the most usual sum paid for this kind of work. These prices here, as well as in sinking shafts, include every expense, as the men pay for their tools, candles, and gunpowder, and likewise are charged with the wheeling the stuff, and hauling it to the surface.

Stoaping is that kind of work which is not included in sinking or driving, but more generally means the breaking away the ground between the levels on the course of the lode or vein, to get the ore. When the men work over head, it is called stoaping the backs, and when the work is carried downwards it is denominated stoaping the bottoms. As both these operations usually take place where ore is obtained, the mode of payment is quite different from that in sinking or driving, and is here called tribute-work, while the other is called tutwork. Tribute means payment by a proportion of the produce, so that the men agree to undertake a particular piece of ground for a certain part of the value of the ore they may procure, when completely merchantable and fit for sale, every operation and process to make it so being conducted at their expense. This mode of contracting is of great advantage to the owners of the mine, as the men have a constant interest concurring with that of their employers, in discovering and procuring the greatest possible quantities of ore, and of returning it in the best and cheapest manner. The proportion paid to the miner, varies of course exceedingly, as many things must be taken into account in estimating a fair tribute for any particular part of a mine, but the contracts are made at so much out of every pound's worth sold, and this fluctuates often in different parts of the same mine from three-pence to fourteen shillings. Nothing shows the necessity of a mine being in the hands of skilful and honorable managers more than the great variation in the prices of all kinds of work carried on in these extensive undertakings.

An engine-shaft is delineated in MINING, plate II.

A, A, A, A, timber-framing put in to support the ground, where, from the rock not being sufficiently hard to stand securely, this precaution becomes necessary. Where boarding is required the planks are driven perpendicularly between the transverse timber and the ground.

B, B, B, B, are dividing-pieces, or beams thrown across the shaft. They serve to support the sides of the shaft, to attach the casingboards to, which part off the whim-shaft from the foot-way and pump, or engine-shaft (it being usual to consider a large shaft of this kind as divided into the three kinds, each bearing its particular name). And, lastly, the dividing-pieces support the ends of the bearers which carry the pumps, ladders, &c.

C, C, C, C, casing-boards which part off the whim-shaft from the other parts; they are stout planks securely spiked to the dividing-pieces, and, when the shaft is not perpendicular, the kibbles slide upon them.

D, the whim-kibble which conveys up the ore and waste, two of which are employed in a shaft, one going up while the other goes down.

E, F, ladders for the workmen, forming what is usually called the foot-way.

G, saller, a small platform at the foot of each ladder.

H, a column of pumps drawing out of a cistern K, which is supplied by a lower tier of pumps I, furnished at the top with a collar

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launder J, which delivers into the cistern, which likewise receives the stream flowing from the level at L.

M, a set off, which connects the pump rods, so that one set goes into the column I, and another is continued lower to a deeper lift of pumps.

N, N, N, N, bearers, or timber beams, which support the pumps and keep them steady in their places.

The ventilation of mines is so important a subject that we insert at length the following account of a machine invented and applied to that purpose by Mr. Taylor, late the manager of the principal copper mines in Devon; and for which he received the silver medal from the society for the Encouragement of Arts, Manufactures, and Commerce.

"Next in importance to the means employed for draining underground works from water, may be reckoned those which are intended to afford a supply of pure air, sufficient to enable the workmen to continue their operations with ease and safety to themselves, and to keep up, undiminished, the artificial light upon which they depend. It is well known, indeed, to all who are practically engaged in concerns of this kind, that men are frequently obliged to persevere in their labor, where a candle will scarcely burn, and where not only their own health materially suffers in the end, but their employers are put to considerable additional expense by the unavoidable hindrance and the waste of candles and other materials.

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The following remarks are confined to such mines as are worked upon metalliferous veins, according to the practice of this district, and that of the great seat of mining in the neighbouring county of Cornwall, from which indeed ours is borrowed. We find then that a single shaft, not communicating by levels to another, can hardly be sunk to any considerable depth, nor can a level (or, as the foreign miners call it, a gallery) be driven horizontally to any great distance, without some contrivance for procuring currents of air to make up the deficiency of oxygen, which is so rapidly consumed by respiration and combustion in situations like these, where otherwise the whole remains in nearly a stagnant condition.

We are here unacquainted with the rapid production of those gases which occasionally in the collieries are the cause of such dreadful effects; such as hydrogen gas, or the fire-damp, carbonic acid, or the choke-damp; the inconvenience we experience takes place gradually as we recede from the openings to the atmosphere, and seems to arise solely from the causes which have been before assigned, though it is found to come on more rapidly in certain situations than in others.

'The most obvious remedy, and that which is most frequently resorted to, is the opening a communication either to some other part of the mine, or to the surface itself; and as soon as this is done, the ventilation is found to be complete, by the currents which immediately take place, often with considerable force, from the different degrees of temperature in the subterVOL. XIV.

ranean and upper atmospheres; and these currents may be observed to change their directions as the temperatures alternate.

"The great objection to this mode of curing the evil is the enormous expense with which it is most commonly attended. In driving a long level, or tunnel, for instance, it may happen to be at a great depth under the surface, and the intervening rock of great hardness; in such a case every shaft which must be sunk upon it for air alone, where not required (as often they might not) to draw up the waste, would cost several hundred pounds; or in sinking a shaft it may be necessary, at an expense not much less, to drive a level to it from some other for this purpose alone.

To avoid this, recourse has been had to dividing the shaft or level into two distinct parts, communicating near the part intended to be ventilated, so that a current may be produced in opposite directions on each side the partition; and this, where room is to be spared for it, is often effectual to a certain extent. It is found, however, to have its limits at no very great distance, and the current at best is but a feeble one, from the nearly equal states of heat in the air on each side. The only scheme besides these has hitherto been to force down a volume of purer air, through. a system of pipes placed for the purpose, and a variety of contrivances have been devised for effecting this; most of them are so old that they may be found described in Agricola's work, De Re Metallicâ. The most common are by bellows worked by hand; by boxes or cylinders of various forms placed on the surface with a large opening against the wind, and a smaller one communicating with the air-pipes by a cylinder and piston working in it, which when driven by a sufficient force has great power. But the cheapest and most effectual scheme for this purpose, where circumstances will admit of its being applied, is one which was adopted some time since in the tunnel of the Tavistock canal. It is by applying the fall of a stream of water for this purpose, and it has been long known that a blast of considerable strength may may be obtained in this manner, which has the advantage of being constant and self-acting. The stream, being turned down a perpendicular column of pipes, dashes in at a vessel so contrived as to let off the water one way, with an opening at another part for the air, which, being pressed into it by the falling water, may be conveyed in any direction, and will pass through air-pipes with a strong current, which will be found efficacious in ventilating mines in many instances, as it has likewise, in some cases, been sufficient for urging the intensity of fires for the purposes of the forge. It is easily procured where a sufficient fall is to be had; and the perpendicular column can be so fixed as that the water from the bottom may pass off, while the air is forced into a pipe branching from the airvessel, and which is to be continued to the part of the mine where the supply of fresh air is required.

'It has been found, however, that the forcing into vitiated air a mixture of that which is purer, even when the best means are used, though

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a measure which affords relief, is not, in bad cases, a complete remedy; and, where the operation depends on manual labor, or any means that are not unremitted in their action, it becomes quite ineffectual. The foul air, charged with the smoke of gunpowder used in blasting, and which it strongly retains, is certainly meliorated by the mixture of pure air, but is not removed. While the blast continues, some of it is driven into the other parts of the mine; but, when the influx of pure air ceases, it returns again or if, during the influx of pure air, a fresh volume of smoke be produced by explosions, which are constantly taking place, it is not until some time afterwards that it becomes sufficiently attenuated for the workmen to resume their stations with comfort.

'A consideration of these circumstances led me to the supposition that the usual operation of ventilating engines ought to be reversed, to afford all the advantages that could be desired; that, instead of using the machines which serve as condensers, exhausters should be adopted; and thus, instead of forcing pure air into that in a vitiated state, a complete remedy could only be had by pumping out all that was impure as fast as it became so.


Many modes of doing this suggested themselves, by the alteration of the machines commonly applied, and by producing an ascending stream of air through pipes by a furnace constructed for the purpose. The latter mode would, however, have been here expensive in fuel as well as in attendance; and the others required power to overcome the friction of pistons, and so on, or considerable accuracy in construction. * At length the machine was erected of which the annexed is a drawing; which, while it is so simple in construction, and requires so small an expense of power, is so complete in its operation, and its parts are so little liable to be injured by wear, that nothing more can be desired where such an one is applied. This engine bears considerable resemblance to Mr. Pepys's gazometer, though this did not occur to the inventer until after it was put to work. It will readily be understood by an inspection of the engraving, plate III., where the shaft of the mine is represented at A; and it may here be observed that the machine will be as well placed at the bottom of the shaft as at the top, and, in either case, it is proper to fix it upon a floor, which may prevent the return of the foul air into the mine, after being discharged from the exhauster: this floor may be furnished with a trap door, to be opened occasionally for the passage of buckets through it.

'B, the air-pipe from the mine passing through the bottom of the fixed vessel or cylinder C, which is formed of timber, and bound with iron hoops; this is filled with water nearly to the top of the pipe B, on which is fixed a valve opening upwards at D.

'E, the air or exhausting-cylinder made of cast-iron, open at the bottom and suspended over the air-pipe, immersed some way in the water. It is furnished with a wooden top, in which is an opening fitted with a valve likewise opening upwards at F.

The xhausting-cylinder has its motion up and down given to it by the bob G, connected to any engine by the horizontal rod H, and the weight of the cylinder is balanced, if necessary, by the counterpoise I.

The action is obvious.-When the exhausting-cylinder is raised, a vacuum would be produced, or rather the water would likewise be raised in it, were it not for the stream of air from the mine rushing through the pipe and valve D. As soon as the cylinder begins to descend, this valve closes, and prevents the return of the air which is discharged through the valve F.

The quantity of air exhausted is calculated of course from the area of the bore of the cylinder, and the length of the stroke.

The dimensions which have been found sufficent for large works are as follow:'The bore of the exhausting-cylinder two feet. The length six feet, so as to afford a stroke of four feet.

'The pipes which conduct the air to such an engine ought not to be less than six-inch bore.

The best rate of working is from two to three strokes a minute; but, if required to go much faster, it will be proper to adapt a capacious air-vessel to the pipes near the machine, which will equalise the current pressing through them.

'Such an engine discharges more than 200 gallons of air in a minute; and I have found that a stream of water supplied by an inch and a half bore falling twelve feet is sufficient to keep it regularly working.

'A small engine to pump out two gallons at a stroke, which would be sufficient in many cases, could be worked by a power equal to raising a very few pounds weight, as the whole machine may be put into complete equilibrium before it begins to work, and there is hardly any other friction to overcome but that of the air passing through the pipes.

The end of the tunnel of the Tavistock Canal, which it was my object to ventilate, was driven into the hill at a distance of nearly 300 yards from any opening to the surface; and being at a depth of 120 yards, and all in hard schistus. rock, air-shafts would have been attended with an enormous expense; so that, the tunnel being a long one, it was most desirable to sink as few as possible, and, of course, at considerable distances from each other. Thus a ventilating machine was required which should act with sufficient force through a length of nearly half a mile; and, on the side of the hill where it first became necessary to apply it, no larger stream of water to give it motion could be relied on than such a one as is mentioned after the description of the engine, and even that flowed at a distance from the shaft where the engine was to be fixed, which made a considerable length of connexiónrods necessary.

Within a very short time after the engine began to work, the superiority of its action over those formerly employed was abundantly evident. The whole.extent of the tunnel, which had been uninterruptedly clouded with smoke for some months before, and which the air that was forced

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