STEAM-CRANE. The application of steam to the working of cranes was an obvious one, and is now universal where much hoisting work has to be done; it not only effects a great saving in labor, but causes the work to be much more quickly done, a consider. anon quite as nt. Steam-cranes and winches arc now almost invariably used on Loard all large steamboats, both for loading and unloading, heaving the anchor, warping the ship along by means of a cable, anSother purposes. When working on a wharf, and in many other situations, it is often very convenient that the crane should be mov aUta, so that it may go to its work in the multitude of cases where that n•rangement is more convenient than the converse. For this purpose it is mounted on a plain railway truck, either of wood or iron. the truck being generally provided with elanips at the ends, by which it can be firmly secured to the rails when lifting weights. The balance construction, now universally adopted for portable era ties, was invented or suggested by the late R. W. Thomson, c.N., in 1856—its essential feature being the use of the boger as a counterpoise to the weight to be lifted. The principal parts of a steam-crane arc: 1. The boiler, which must be of some very simple construction, as it has so fre quently to be worked with excessively dirty water; 2. The framing, which is generally made of bast-iron, and supports the boiler, the engine and gear, and the jib; 3. The engine (which has almost always two small cylinders, and is fitted with reversing gear), and the pinions, wheels, drums, etc., for the hoisting and other motions; 4. The " jib"
(either of wood or iron), over a pulley iu the top of which the chain passes, and the pur pose of which is to enable.the different objects to be lifted quite clear of the ground, and deposited, when necessary, on trucks, 'etc.; 5. The pillar, which is firmly attached ito the truck, and which, passing upward through the center of the framc, forms the ;pivot on which it turns round; 6. The truck itself, which supports the whole machine. If the crane is stationary, the truck, of course, is not required, the bottom of the pillar being imbedded in masonry; and for large cranes the boiler is generally made separate from the machine itself, and sometimes the engines also. A portable balance steani-crane is, when complete, fitted following motions: 1. Gear for hoisting, generally with two or more speeds, to be used according to the weight to be lifted; 2. Gear for raising or lowering the outer end of the jib; 3. Gear for slewing the jib (with boiler and frame attached to it); 4. Gear for propelling the truck along the rails. A complete and well designed crane of this kind, made by Messrs. Alexander Chaplin & Co., of the Cranston hill works, Glasgow, will lift from 5 to 7 tons, according to the position of the jib.