Piston. Packing.—Prof. John E. Sweet (Trans. Soc. J[ec/. Emprs., Vol. IX.) proposes a new principle in steam-piston packing, which is shown in Figs. 10 and 11. It is a common eccen tric ring hooked together by a clamp which forms a part of the ring itself, and this hook clamp limits the expansion of the ring and changes the whole prineiPle of its action. The rings are east heavy, rough-turned very much larger than the cylinder, a piece cut out, sprung together, and fitted with the hook clamp or shoes, left slightly larger than the cylinder, and then returned to a tight fit. It will be noticed that the rings can compress to a limited extent, but cannot expand.
In use they act, or arc supposed to act, as follows : When the engine is first started and the hot piston moves to the cold end of the cylinder. the rings compress and allow it to go free ; but when both cylinder and piston get up to working tempera ture, the rings just fit and work with out any pressure and very little tendency to wear. Filing out the books compen sates for wear when it has taken place.
It will be seen that the hook clamp is longer at one end than the other. The object of this is to break joints when two rings are placed side and side in the same groove, and thus cut off the leak which would other wise take pl ac e through the gaps.
The hook clamps or shoes are placed at the bottom of the piston, in the horizontal engines, and secured by leaving them a tight fit and allowing the follower to bind them fast. Figs. 10 and 11 show the arrangement as used in a large piston with spicier, bull ring, and follower, and the method of lining up the rod with liners between bull ring and spider. The objection to the plan is that it is only applicable, with any prospect of success, to parallel cylinders, a thing not always obtainable.
Ducat's Metallic Packing consists of fine filaments or wires of hard brass laid up into strands and then braided to form gaskets of various cross sections.
Panel liaising : see Moulding Machines, Wood.
Paper Cutters : see Book-binding Machines.
Pea Harvester : see Harvesting Machine, Grain.
Pebbling Machines : see Leather-working Machines.
Petroleum Engines see Engines, Gas. Fuel : see Locomotives.
PlIONOGRAPIL This instrument has undergone many improvements, but it cannot be said yet to have come into commercial use. As now constructed (Fig. 1) it is mounted on a hollow wooden base, which contains an electric motor. The spindle of the motor extends from the top of the base and drives a governor which can be adjusted to produce any number of vibrations a minute, within limits. It also drives the phonograph itself. The spindle
on which the main driving-pulley is fixed is carried in two bearings, and the part between the bearings is very finely screw-threaded, and an extension of the spindle carries a taper brass mandrel, on which the cylinder which receives the record is slipped. The fine-threaded screw serves to give the feed to the diaphragms. carrying them lengthwise of the wax cylin der. so that the style traces a helix which is of the same. pitch as the screw.
There are two diaphragms— the first of glass, for receiving and recording the message, and the second of silk for interpreting the record, and articulating it afresh. Both dia phragms are enclosed in metal cases having openings to which flexible tubes are connected. The listening tube is bifurcated, and at each extremity carries a small, bent nozzle which rests easily in the ear. The other tithe, which is shown lying beside the instrument, is an ordinary speaking tube. In the centre of each diaphragm is a style, the one for engraving being stiff and sharp, while the other is hook-shaped, so that it drags over the record without any tendency to cut down the elevated portions. The frame which carries the dia phragm can tilt on the back guide, its weight being carried by a set screw sliding along the rail in front of the cylinder. By means of this screw, the style can be adjusted exactly in relation to the wax cylinder. The rail is carried by a cam by which it can be raised at will, the cam being turned by hand, or in sonic cases by the foot of the operator. A par tial movement of the cam lifts the style clear of the wax cyl inder, and at the same time tilts the hack frame, lifting the part nut off the screw. Thus the instrument is thrown out of ac tion. By turning the cam still further, a finger on the nut lever is brought into en gagement with the comparatively coarse threaded screw shown in front, and then the frame with the dia phragm is moved rapidly back. The wax is of considerable thickness, so that after it has once served its purpose, its surface is skimmed off. To enable this to be done, there is attached to the under side of the plate which carries the diaphragm, a cutting tool which always precedes the engraving style, and trims up the wax surface in front of it. One cylinder will serve for more than forty successive records.