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encountered in the course of devising an improvement upon the cam. Numberless modifications and improvements in every detail have marked the slow and expensive process of evolution of the " High-Speed " gravitation stamp, and each change has been made the subject of searching tests in the various experimental batteries, but there is now ample reason to believe that the machine in its present form fulfils the exacting requirements of milling practice. Numerous tests have been made at Hartlepool with a five-head "High-Speed" gravitation stamp-battery of the latest design, and, although it is not necessary to explain the minute details of construction, it may be confidently stated that every possible care has been taken to insure ample strength, adequate wearing surfaces, good lubrication, facility of repair and adjustment, security of all fastenings, and general reliability and immunity from break-down. The hydro-pneumatic lifting-cylinder illustrated in Fig. I. is of cast-iron, and is cast with an annular chamber W surrounding the upper portion, which acts as a reservoir for the water used in effecting the cushioning action. The working portion of the cylinder-barrel Bis bored out and fitted with a plug piston forged solid with the piston-rod R, which passes through the metallicpacked gland G, and is connected to the stamp-head by means of a sleeve and stem hereafter described. The top of the cylinder is fitted with a cover F provided with two lugs to receive the gudgeon-pin and the bottom end of the connecting-rod. Water is supplied to the reservoir Wby means of a free telescopic pipe-connection I, communicating with a water-channel formed in one of the cast-iron members of the frame of the machine. In order to insure the maintenance of the requisite supply of water in the reservoir, and to carry off the small amount of heat generated by the cushioning action, the water is continuously slowly circulated by means of a small supplypump. The water is conveyed from the cylinder to a channel formed in one of the lower members of the framework by means of another free telescopic pipe-connection 0, and it should be observed that, as there are neither glands nor wearing surfaces in these telescopic pipe connections, it is quite impossible for them to become a source of trouble. In the lower portion of the workingbarrel there is a port P, communicating with the reservoir W, and in another portion of the barrel, at a slightly lower level than the port, is a passage communicating with the air-vessel A. Free communication is provided between the top of the cylinder and the water-jacket W to permit of the transfer of the enclosed air. The action of the cylinder is as follows : When the stamp is resting upon the die, and the cylinder is at the bottom of the stroke, the port P is open and the lower portion of the cylinder is filled with water. When the cylinder begins to ascend, the port is gradually closed by the piston, and the water, displaced by reason of the relative motion of the cylinder and the piston, is forced partly into the air-vessel and partly out through the port of gradually decreasing area, at a gradually increasing pressure, until the point is reached at which the pressure below the piston is sufficient to raise the stamp at the then moderate velocity of the cylinder. The cylinder, carrying the stamp with it, continues to ascend at a velocity which increases up to about mid-stroke, and gradually diminishes from that point on to the end of the stroke. The pressure established in the air-vessel being that due to the maximum accelerating force exerted by the cylinder upon the piston, which occurs at the point of pick-up, it follows that as the rate of acceleration falls the air re-expands and does work upon the piston by raising it relatively to the cylinder. When the cylinder reaches the top of the stroke it momentarily comes to rest, but the stamp, in virtue of its acquired momentum, continues to ascend through a height dependent upon the square of its velocity. Before the stamp reaches the top of its stroke the cylinder has commenced its descent, and when the stamp falls its motion is not influenced by the motion of the cylinder, because the port P has been opened by the before-mentioned relative motions of the piston and cylinder, and consequently the water under the piston is perfectly free to escape as the increasing velocity of the falling stamp causes it to gain upon the cylinder as the velocity of the latter is reduced during.the lower portion of its stroke. The design and adjustment of the stamp and its lifting mechanism are such that the stamp comes to rest upon the ore on the die when the cylinder is about 1-Jin. from the end of its stroke ; it therefore overruns the piston and opens the port by that amount, thus permitting the water to flow into the cylinder to make up any deficiency, and the cycle is repeated. By opening the cylinder drain-plug S any individual stamp can be quickly, though gradually, brought to rest, whilst the cylinder continues to reciprocate, and without affecting any other stamp. As soon as the plug is screwed up again the stamp commences to work with a gradually increasing lift until the normal conditions are established. The above description will have made it clear that, within moderate limits, the relative positions of the cut-off edge of the piston and the bottom of the port, when the cylinder and the stamp are each at the bottom of their respective strokes, should be maintained, and as the wear of the shoe and die is continually lowering the piston relatively to the cylinder, an easy means of adjustment has been provided, in the form of the sleeve S, shown in Figs. 11. and V.. The end of the piston-rod R is slightly tapered, and fits into a corresponding tapered hole in the top end of the sleeve, being held there by friction in the same manner that a stamp-stem is secured to the "head." As, however, the piston and rod form a comparatively light falling part, a cotterway is provided in the bottom of the piston-rod, so that it can be forcibly drawn into the sleeve, and thus obviates the possibility of any troublesome slackness. In the lower portion of the sleeve is bored a long parallel hole into which the top end of the stamp-stem fits, and is held in place by a gib and key frictional fastening exactly similar to that now used for cam-stamp tappets. The internal dimensions of the sleeve are such as to permit of .the required range of adjustment, whilst insuring that when the stamp has been withdrawn from the sleeve to the fullest extent necessary it will still have a bearing over the whole length of the gib. To provide for the easy, quick, and correct performance of this adjustment, for about every half an inch of wear of shoe and die, and to make certain that the adjustment shall not become accidentally altered through slippage occurring between the sleeve and the stem, the latter is forged