ing above it the pulley G. It is evident that, if this pulley is raised I foot, the tool suspended in the hole must be raised 2 feet, because the rope on the other side is made fast by the clamp; by opening a valve the steam escapes from under the piston, which then drops, and the tool, which falls twice as fast as the piston, strikes a smart blow at the bottom of the hole, the hardness of the blow being regulated by the height to which the tool is lifted, the engine-driver being able to regulate this by special P B a FIG. 100.-Mather and Platt's FIG. 101.-Mather and valve-gearing (the valves work automatically). An ingenious device is employed for twisting the tool between each stroke; this will be understood on reference to Fig. 100. The sliding collar J has a toothed edge top and bottom. On raising the rope this sliding collar fits into a fixed collar at the top of the boringbar, the lower edge of which has a corresponding set of teeth; on lowering the rope when the tool strikes the bottom, the sliding collar descends, and the lower set of teeth on the lower fixed collar become engaged, but in order that they may fit together the sliding collar receives a slight twist; upon raising the collar the upper teeth now engage in the teeth above, but not in the same teeth as before, the collar having turned one tooth, thus putting a slight twist upon the rope. When the weight of the tool is lifted from the ground, the tension due to this weight tends to untwist the rope and slightly to turn the tool as it is held in suspension, so that when it strikes the bottom of the hole it cannot strike in precisely the same place as before. To cleanse the hole the sand-pump is used (Fig. 101) in a similar manner to that already described in round-rope boring. With this machine holes varying in diameter from 8 inches up to 2 feet have been bored, with varying success. It would appear, however, that in hard ground there is some liability to fracture. Hollow Rods.-In place of solid rods, hollow rods made of steam tubes screwed together are sometimes used, the chisel being attached rigidly to the rods, down which a stream of water is pumped (Fig. 102). The water, issuing from the rods just above the cutting chisel, returns outside them, and carries with it the sludge and gravel made by the chisel; the sludge is deposited in a can, from which the water flows at the top, and by continual observation of the deposit brought up by the water the nature of the strata can be gathered. By this method of boring it is only necessary to draw the chisel when it is blunt. It is not, however, largely practised, and it is only suitable for soft ground. Broken Rods.-In case the rods should break, a grapnel is used to extract the portion remaining in the hole. Fig. 75 (9) shows a simple kind of grapnel used for the ordinary iron rods. It is a tube about 5 feet long, open and bell-shaped at the bottom, with a screw at the top by which it is attached to the rods; inside the tube are four steel blades which spring from the sides near the bottom. To extract the broken rods this tube is lowered until it passes over the broken end of the rod, which rises up inside the tube until the broken end has reached the top; the tube or grapnel is then raised until the steel blades catch against the shoulder on the broken rod, beyond which they will not pass, and the tube cannot now be withdrawn d d F- Fg from the hole without either a fracture of these steel blades or else raising the broken rod. There are many forms of grapnel. Wolff's Grapnel.-This grapnel is designed to catch hold of a broken rod, but is so constructed that, if it is found impossible to withdraw the rods which it has seized, they may be unfastened, and thus the upper length of rods can be withdrawn, which otherwise would be impossible if they were held fast by the grapnel to the broken rods below, which, in their turn, were jammed fast in the hole. Fig. 103 shows this grapnel.1 BB is a bell-mouth suspended by the fork d d and the nut e from the screw f, the thread of which is turned in the lowest boring-rod; c are steel jaws with sharp teeth slanting up, kept apart by the piece of wood n, and suspended from the rod g by the collar P. When B is lowered over the end of a broken rod, h, the wood is pushed out by the rod, and the jaws spring together upon the rod, and if the upper rods are now turned round, the jaws and the bell are prevented from turning, consequently the nut e is 1 J. C. Jefferson, Midland Institute of Mining Engineers. B -h B FIG. 103.-Grapnel jaws. -B lifted and the bell B is drawn up and compresses the jaws, so that they hold the rod firmly. In order to relax this grip the rods must be turned the other way; then the nut e will be lowered and the bell with it. Other tools for recovering broken rods are shown in Fig. 104, and in Fig. 105 is shown the application of the hook-grappler. Parachutes. In boring deep holes it sometimes happens that, in withdrawing the rods, by some accident they are allowed to fall; if they had to fall a great distance before a striking the bottom, the result would be a disastrous smash. Parachutes are therefore placed at intervals on the rod. These are pistons loose on the rods, sliding between two collars; they do not fit tight in the bore-hole, but leave space for the water to pass by them as they are raised up and down. When the bore-rods are raised, these pistons are supported by the bottom collar; when the boring-beam goes down and the rods are lowered for the blow, they slide through the piston faster than it can fall with them, owing to the resistance of the water; thus there is not much resistance to the working of the rods on account of these safetypistons. If, on the other hand, the rods should be accidentally dropped, the pistons, catching against the upper collar and bearing against the water in the hole, limit the velocity of descent, and thus reduce the chances of breakage. FIG. 104.-Tools for FIG. 105.-Application of hookgrappler. Lining-Tubes.-When a hole is bored through soft ground the sides of the hole are apt to break off in places and encumber the bottom of the hole with debris. This is due partly to the rods occasionally knocking against the sides, partly to the wash of the water, and partly to the pressure of the ground itself upon a soft stratum, whether this be sand, gravel, or clay. To prevent this falling-in of the sides, it is necessary to line the hole with tubes; these tubes have been made of wood, copper, zinc, cast iron, and wrought iron, and perhaps of steel. Wrought-iron tubes are those that have hitherto been chiefly adopted; these are sometimes made with a longitudinal seam riveted, but for small holes a welded seam is now generally used; the joints at the end of each tube are sometimes riveted and sometimes screwed (see Fig. 75). When riveted joints are used, the rivet is lowered from the top of the last tube by means of a wire (see Fig. 106), and by means of a hook is pulled through the rivet-hole. When the rivets have been all placed in position, a metal block somewhat tapered (see Fig. 107) is lowered down inside the tube until it presses tight against all the rivet-heads inside, which are then riveted over cold on the outside; these riveted joints are sometimes slightly tapered (see Fig. 75, 8a), so avoiding the use of a collar. Sometimes an outside collar is used (see Fig. 75, 6), and sometimes a flush-joint is preferred (see Fig. 75, 7). Where the joints are screwed, there is sometimes an outside collar (see Fig. 75, 8), and sometimes there is a flushjoint (see Fig. 75, 5); where there is a FIGS. 106, 107.—Method of riveting flush-joint the middle of the tube must be thick enough to have nearly half turned down before it is threaded, and therefore it requires to be nearly twice as thick as where there is an outside collar. This system of flush-jointed tubes is therefore more expensive than the other, but it is often more convenient, because, in lowering the tubes down the hole, there are no external projections to catch against the sides of the hole, and in case the tubes should have to be withdrawn-an operation which is sometimes done-there are no projections to hinder. tubes. Reduction in Diameter of Hole.-It is evident that, if a lining-tube has been placed in the hole, the next boring-tool introduced must be smaller than the original one, and this reduction in diameter can hardly be less than inch, while it may sometimes amount to 1 inch; therefore the introduction of two or three lining-tubes will reduce a hole of moderate size to a diameter which is too small for practical purposes. For this reason, if the hole has to go a great depth, it must be started of such a diameter that numerous linings may be introduced, and still leave a sufficient diameter for further boring; thus if a hole was started 12 inches in diameter, six lining-tubes might be introduced, and still leave a hole 6 inches in diameter at the bottom. And very deep holes, that is to say, holes of 2000 feet and upwards, should not be started less than about 18 inches in diameter. Of course, if it is known at the outset that sands and very soft clays will be met with near the surface, a still larger diameter might be adopted. It frequently happens that the necessary number of liningtubes has not been foreseen, and that the hole has been already |