When a pit is divided, so as to form three pits, it is a more difficult process to form the brattice, as none of the buntons stretch across the pit, the three which form the divisions meet, forming angles with each other near the centre of the pit; and in order to give them stability and strength in their position, they do not lie across in a horizontal line, but have a rise from the sides to the centre of about nine inches where they meet, and a iron strap hinds them together by means of a bolt at each tongue. Fillets of wood are carried down the whole depth, not only at the juinings of the brattice with the sides of the pit, but also at the meetings of the brattice at the centre of the pit ; and, for farther security, a prop of wood reaches from the centre of one set of buntons to the centre of those immediately above; by this means a very strong piece of carpentry is formed, having its strength depending tiaon the principles of the couple of a roof. These buntons are clad on all sides with deals from top to bottom ; and the ends of all the deals meet each other in the middle of a bunion.
In quadrant pits the buntons cross each other in the centre of the pit at right angles, and are generally only let in about an inch into each other, in place of being half checked. Plate CCCXC. Fig. 9 is a double pit, A the engine pit, B pit for orawing coals ; Fig. 10 is a triple pit, A the engine pit, B and C pits for drawing coals ; Fig. I 1. is a quadrant pit, A the engine pit, B the pit for the ventilating furnace, C and D pits for draw ing coals.
These methods now described, being such as are used in the practice of mining when sinking through the cover, securing the sides of the pit, and dividing the pits by brattices, it must be remarked, that several of these processes are attended with such immense ex pence, that it is only in districts where great returns of profit are made, that they can be attempted. It is at Newcastle and Whitehaven where by far the greatest capitals are employed, and where the very expensive methods of sinking through quicksand are adopted and prosecuted with vigour and success. As engine-pits are now sunk in winnings of collieries made from the depth of 20 to 150 fathoms, that is, with pits having one set of pumps, to those having five sets, the operation, though in most of the circumstances the same, is very different as to labour, difficulties, expellees, arid skill re quired. In winnings of a moderate depth, if the water found in the cover is kept from descending the pit, the feeders found in the rock are allowed to flow down.
In deep winnings, the most minute attention is paid to prevent any water from descending, by methods to be described afterwards.
As 75 fathoms is reckoned rather beyond the aver age depth of winnings or of engine-pits in Great Bri tain, and as in practice it embraces three sets of pumps, by describing this operation, we describe also the more simple winnings of one and two sets.
As soon as the pit is sunk to such a depth that the engine must be applied to pump the water, the first set of pumps is let down the pit ; these are termed the sinking set, they are jointed with strong flanges and bolts, having a jointing of lead of about half an inch thick, covered with tarred flannel. There are se veral methods for suspending them during the process of sinking, as they must rest on the bottom of the pit, and he lowered gradually as the rock is blown up and wrought away. The common practice in pits with one or two sets of pumps, and where the sets are of no great size or weight, is to have two shroud-laid ropes or cables, named ground ropes, of abundant extra strength to meet casualties and heavy strains. These ropes are made fast below the clack-seat door, and are passed up each side of the pumps, having a piece of service or lapping put round them, opposite to each flange, to prevent their being chafed or cut ; and a strong lashing of pliable hand line acts as a collar at each pump, which connects the whole pile firmly to gether. The ropes are sometimes passed over two large pulleys at each side of the pit mouth, and several turns are taken round a strong circular post of wood, fixed deep and firmly in the ground. As the pumps sink down, the wound ropes are slacked off or eased away, care, however, being taken to keep a considerable bearing upon then), so as to have at least a fourth or a third of the weight suspended ; this is a very rude and a very old plan, though still in practice. Tnia method is greatly improved by having strung five-fold tackles attached to the top of the ground-ropes, and the fold of the tackles passed round the post as above described ; by this plan the lowering is not only per formed more correctly and easily, but the pumps can be lifted up immediately by applying the tackiefolds to crabs or capstans. In this pioctss a caution is neces sary while the pumps ate lowering, that their flanges do not catch any of the timber-work in the pmt, as the weight would not only break them, but endanger the lives of the men at the bottom.