Plans Nos. 1, 2, and 3 are much the same, and in use where the dip of the seams is at a low angle. The modifications of these plans in the style of ventilation are as represented. The air is passed from face to face through the pillars and up one breast and down the other, or up the inside breast and down the outside one,—but always carried in an unbroken current through the entire mine, or that portion of it lying on one side or other of the shaft or slope.
Plans Nos. 3 and 6 are similar to each other, and differ only in the mode of leaving the main avenue. These plans are used generally when the dip of the seams is over 5° or under 25°. They are the most defective modes in operation, and are more liable to interruption and confusion than the other plans given ; while the difficulties of ventilation and the waste of coal are equally defective ; but in regard to the cost of mining and sending coal to the surface, this mode is perhaps as economical as any other, and much more so than the breast and shute method, unless the pitch is great enough to admit of the coal running into the cars without rehandling. Nos. 1, 2, and 7 are similar in this respect to Nos. 3 and 6 ; the former are the most simple, and less liable to derangement, but can be adopted only in horizontal beds, or where the dip is less than 5°. Plans Nos. 4 and 5 are likewise similar to each other, and are simple modifications of the same general plan.
It thus results that there are two general systems in use in the anthracite region 9,— one practised in all seams where the dip is less than 25° or 30°, and the other where the dips are above 30°.
In the first, the cars are taken into the breasts or chambers, and follow the miners to receive the coal direct from their hands ; in the second, " shutes" are used, down which the coal slides on the inclining bottom slate of the seams, or on sheet iron or plank laid for the purpose, when the dip is not steep enough for the coal to slide readily on the bottom slate. These shutes either lead direct into the cars, which stand on the main railroad in the gangway, or the coal is rehandled and thrown by hand into the cars. When the seam is large and the pitch steep enough to carry the coal down by gravity, the first method is used ; but when the seam is small and the angle of dip low, the second and more expensive method is used.
The system of ventilation is much the same in general principle, whatever plan of mining be used,—subject, however, to the modifications specified. The general and governing principle of the system, and its most objectionable feature, is the circulation of the air in a continuous column or channel throughout the mine, sweeping the impuri ties of the works before it, and carrying the foul air and accumulating gases from miner to miner and from breast to breast, until they become-obnoxious and dangerous.
In an extensive mine conducted on this principle, there can be no perfect ventilation. It is true that a strong current of air can be moved through the mine when the air courses are systematically arranged and kept in order by mechanical means; and the inflammable gases may be diluted beyond the explosive point; but the powder-smoke from frequent blasting, the smoke and carbonic oxide from hundreds of lamps, the exhalations of the workmen, and the accumulating foulness resulting from these and other causes, must pass from man to man, and render more and more deleterious the impure air they breathe.
But, while this serious difficulty exists in the best-ventilated collieries under our present system, those which are not well ventilated—and they are by far the most numerous—suffer from still more serious and additional difficulties from the lack of such air, bad as it is, and from the constant presence of explosive• gases. Thousands of our miners are obliged to work in an atmosphere as explosive as powder, and which the least forgetfulness or accident might ignite with sudden destruction to life and ruin to property. These difficulties and dangers will always exist as long as we persist in fol lowing an obsolete and wasteful system.
We will introduce the most improved method that has been, or which can be, adopted on this principle, before we discuss the improvements required by the present wants of the anthracite miners.