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the depth; the workmen soon corrupt the air by breathing it, and by the combustion of candles; and in addition to these things, noxious gases exude from the coal itself in greater or lesser quantities. Ventilation, therefore, has always been a mining problem of difficulty; and when the excavations become large, and long, and tortuous, this difficulty is greatly increased. An open door and chimney cause a current through a room, and two separate shafts would cause a current in a mine. If a church had two towers, one at each end, open, hollow, and communicating with each other, the whole pews and aisles would be naturally ventilated. So, again, would a mine be aired by two open shafts. But in practice the thing is far more complicated, although the principle is the same. The complex problem is, how to carry a continual current of fresh air through all the passages of the pit, to every working or walking man and boy, and to convey this current, after it has swept the pit, to the upper skies freely and safely. By the unaided natural principle of circulation the current would be too languid, and in time so loaded with impurities as to fail of use. For many years, however, a single feeble current was all that could be delivered. A happy idea occurred to a Mr. Spedding,* and was improved upon by a Mr. Buddle, an eminent local authority. This was to split the current of air, and subdivide it into two, or more, currents, one of which might take one direction and another a different course, as two fellow-travellers may pursue their journey together up to a certain direction-post on cross-roads, and then part company and take different ways. If our readers have ever watched a large meadow in process of irrigation, they will have seen the water curiously and obediently divide itself and flow into all the provided channels, and thus irrigate the whole meadow. So, in a large mine the current of air drawn in by the downcast' shaft is conducted through every passage, however narrow or remote, and made to perform a complete and continuous journey of the whole pit, as if it were inspecting it, and bringing blessings to every deeply and darkly immured labourer on its errand of benevolence.

The contrivances by which the current is split and managed are ingenious and effective. Wooden or brick divisions (brattices) are erected, which act as long walls in dividing the air lengthways, as the passage and parlour walls do in an ordinary house. By these a mining mainway or sideway may be divided, in some

The scientific principles of ventilation were given in 1764 by the French Academician Jars. Mr. Spedding, of Newcastle, in 1760, had carried the air in one current through every part of the mine. Mr. Buddle, of Wallsend, in 1813, introduced the greatest improvement in ventilation, by splitting the air, or providing several courses in lieu of one.

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places into two, and the air-current go up on one side of the division, and down, reversely, on the other side. At the end of any passage a whole 'stopping' will make the air to halt, and a partial stopping, to divide and go right and left. By certain stoppings the air can even be made to ascend or descend and perform a summerset upon itself. In particular parts of the mainways of a pit the air-current must be kept back, and yet there can be no immovable stopping there, as it would hinder the large and continuous traffic of the mine. If the air ran through, the ventilation would be deranged; if the air were blocked out, the traffic would be stopped. How is this difficulty surmounted? Thus:Thus-a strong wooden door (a trap-door') is erected, moving freely on stout hinges, and a little boy (trapper') sits behind this door while the pit is at work. When the loaded wagons approach it he opens the door, and closes it after they pass. The momentary rush of air is readily compensated. On one side of this door visitors can hear the air rushing upon and hissing against it. In a peculiar condition of the ventilation the noise is very audible, and then the men say, 'the doors are a-singing. On the other side no sound is heard. It is evident that natural differences of temperature would not excite a sufficiently large and impulsive air-current for great mines; therefore the draught is vastly augmented by the employment of a huge furnace kindled at the bottom of one of the main-shafts-termed the 'upcast-shaft. This furnace has the same effect, on a large scale, in creating and maintaining a powerful draught, as a fire in our parlours. The column of air in the upcast-shaft being rarefied by the furnace at its base, of course the air is drawn in down the downcast-shaft,' which is not heated. The effective power of this system depends upon the height and sectional area of the ascending and descending columns. Several points, of a strictly scientific character, are connected with the consideration of the extreme power and the limits of the furnace plan. Suffice it here to say, that there is a limit, but it is not capricious. The circulation of air originating, and being partly maintained, by its expansion, it is certain that when it is overheated, that which was an active moving force becomes inert. Instead of being a propelling power, it becomes an additional load to the motive powers, thus lessening the velocity of the current and reducing the quantity of air passing through the mine. As the practical result of the whole, we say, -You may raise the heat of the furnace to such a height as rather to diminish its power of ventilation, and further to a height where the power ceases altogether, providing the current be taken through the furnace; but if you divide the current, and take part of it through the

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upcast-shaft without going through the furnace, although the air in the shaft be cooled, yet it will be found that the effect is materially increased.

What quantity of air will suffice to ventilate a large mine, and to supply enough for combustion and respiration to each man? We find that, for one man during one hour in the mine, 432-2 cubic feet of air are necessary, at the lowest estimate; for combustion of one light, 593 cubic feet; and for one-fifth of air needed by a horse, 517 cubic feet; making in all 1008 5 cubic feet of air per hour for the use of one man, with his accessories. A horse requires 571 times as much oxygen as a man for breathing; and the number of horses, on an average, in coalmines, is one-fifth the number of the men. Fifty miners, with their lights, will give off sufficient heat to raise 50,000 cubic feet of air, at a certain temperature, by one degree every minute. From these and similar data, we may calculate the quantity of air necessary as a minimums but a larger quantity than the minimum is supplied in the best mines, and especially where fire-damp exudes. In such mines the quantity of air actually circulating through the workings varies from 200 to 600 cubic feet per man per minute. The subjoined table exhibits some interesting information on this head, showing also the power of the furnace system :

Amount of Ventilation in Newcastle Collieries.

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The furnace power, measured by the consumption of coal and by the heat imparted to the upcast-shaft, is equal to the production of aerial currents three or four times as swift as those

Great differences of opinion are found on all such matters amongst miners; and no authoritative statements are anywhere given. We state amounts which a manager of long experience considers proper. One of the Government inspectors thinks that 100 cubic feet of air per minute are necessary for each man and boy in

the mine.

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really obtained. But much of this power is consumed in overcoming the resistance on the path of the air, &c. The largest quantity of air made to circulate through any one colliery upon this plan is at Hetton pit (Durham), where, in the year 1849, the circulation was ascertained to be no less than 190,000 cubic feet of air per minute! The swiftest current in a heated upcast-shaft is at Haswell pit (Durham), where the velocity is 1740 feet in one minute in a shaft of nine feet diameter, reduced by linings to a clear area for air of 58 square feet.

An attempt to increase the motive power by the use of steam jets in the shaft has excited much interest in colliery circles of late years. Evidence was taken upon it before a Parliamentary Committee, and a favourable decision was arrived at. This was exclaimed against by many mining magnates; experiments were made upon an adequate scale by Mr. N. Wood, and, after much and sharp discussion, the opinion prevails that the furnace system must still be adopted, as, on the whole, the most expedient. A subsequent Parliamentary Committee took this latter view.

The two greatest enemies to coal-miners are, water while sinking, and gas when the pit is sunk. These are hidden, secret, mighty foes. We have hitherto spoken of the ordinary condition of the pit, except as to the feeders of water in winning the mineral. We now come to speak of the extraordinary condition of the pit arising from exudations of fire-damp. This gas is light carburetted hydrogen. Its specific gravity is 0.5802 (air being 1), and therefore about half the weight of common air. Hence it tends to ascend and hang about the roofs of the passages, when it extricates itself from the coal, and especially accumulates in the waste parts of the mine. It is also liberated from the fiery seams as they are worked. Careful observations lead us to think that it naturally exists in these seams in a high state of tension, equivalent, in some instances, to very nearly threeand-a-half atmospheres, and, adding the natural atmosphere, to fourand-a-half atmospheres at the moment of issue. This immense force seems to be ever pressing to evolve the gas from the most fiery coal seams, for this highly elastic state seems to be the natural one of the gas in those situations where no means of escape, and of consequent decrease of tension, are afforded to it. We do not find it developed constantly in this high-pressure form, only because the very tension named enables it, so long as the lines of drainage are uninterrupted, to force a passage through the semi-crystalline structure of the coal, and thus to drain off the interior magazines. The tension was made visibly clear, on one occasion, in Walker Colliery, where a block of coal, weighing about

eleven tons, was displaced in a violent manner by the pent-up gas while the hewers were at work. A very great discharge of fire-damp ensued, and made foul the whole of the workings in that district, to an extent certainly of 41,681 cubic feet. The current of air circulating in that part of the mine was 10,483 cubic feet per minute, moving at the rate of 6-24 feet per second in an area of 26 feet.

In the Wallsend Colliery, which was particularly fiery in the Bensham seam, the superintending engineer said: 'I simply 'drilled a hole into the solid coal, and stuck a pipe in the aperture, surrounded it with clay, and lighted it, and immediately I 'had a gas-light. The quantity of gas evolved was such that, in every one of the places I have mentioned, I had nothing to do 'but to apply a candle, and could then have set a thousand pipes on fire. The whole face of the working was a gas-pipe 'from every pore of coal.' The same engineer conducted a pipe to a district in the Wallsend pit, consisting of about 50 acres of Bensham seam coal, which had been lying waste and barred up for above 19 years. Through this pipe (4 inch diameter) there rose to the surface of the ground 95 cubic feet of gas per minute, it afterwards fell to 70 cubic feet, and at the present time it is about 34 feet (cubic) per minute. Taking the mean of these quantities-viz., an average discharge of 66 cubic feet per minute, then the mean annual quantity of gas naturally escaping from this coal-tract has been no less than 34 millions of cubic feet, equal to the solid contents of a coal-bed 5 feet thick and 160 acres in extent. Further, in 19 years the capacity of 19 such coal-beds has been drained off; or, which is the same thing, the contents of one bed 5 feet thick and 3010 acres in extent have been drained off. Where could such an immense volume of gas find stowage? Only in the highly condensed or compacted state of tension which we have supposed. The piped gas at Wallsend was carried some height above the ground, and kindled. For 19 years has that natural gas-light been burning thus, night and day. It is a remarkable object to the visitor at night, as the streamer of flame is fluttered by the wind. Often have we watched it with much interest.

Where inflammable gas thus prevails, it is self-evident that the * The following notice may interest those connected with collieries :

Gases found in Coal Pits.

(In General)-Fire Damp is light carburetted hydrogen, and is often spoken of as 'the gas.'

(In Lancashire and some other Districts)-Black Damp, Choke Damp, Stythe, &c., are names for carbonic acid gas, commonly called After-Damp.

(In General)-After-Damp follows explosions, and is a combination, in varying proportions, of nitrogen, carbonic acid, carburetted hydrogen and air, loaded

with fine coal dust.

(In some Mines)-White Damp is sulphuretted hydrogen gas.

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