STEAM SHOVEL. A modified form of dredge adapted for excavating material on dry land. The steam shovel was invented in 1840 by an American named Otis, but it did not come into general use until about 1865. The large in crease in railway construction in the United States created an active demand for a rapid ex cavating machine. As will be seen from the ac companying outline drawing, the steam shovel consists essentially of a strong frame mounted on wheels to form a base to which the working parts are attached. The digging mechanism con sists of a crane hinged to a mast or support at the front end of the car, and a dip per handle and dipper carried by the crane. The operating machinery consists of a main engine, which hoists the dipper and swings the crane, and of a thrusting mechanism for forcing the dipper into the earth. The operation begins with the dipper at the position shown by the dotted lines in the illustration. The engine man begins to hoist and thus swing the dipper upward along a curved path; at the same time the crane man by means of the thrusting mechan ism forces the dipper into the earth so that a layer is scooped off the face of the bank and falls into the dipper. The depth of the cut is so regu piston; in the ease of the steam turbine the wort: is developed by the kinetic energy of particles of steam which are given a high velocity by reason of the steam expanding from one pres:,.ure to a lower pressure. In the zeolipile (q.v.) or
'Ilero's steam engine,' invented by Hero of lated by the crane man that the dipper is just filled when at its topmost position. The dipper is then hauled back and the crane is swung so as to carry the dipper over the car set along side the shovel, and the latch is pulled, setting free the swinging bottom of the dipper. which falls open and permits the contents of the dipper to fall into the ear. In actual operation these several movements are com bined to a greater or less ex tent, and are accomplished by various devices which will be found described in Hermann, Steam, Shovels and Steam Shovel Work (New York, 1894). The various parts of the shovel, body, mast, crane, and dipper handles, are con structed either of wood or steel, the latter material being most generally used for the heavier types of shovels. The dipper is always made of steel or iron plates, and its size or capacity varies from one to five cubic yards, but capaci ties of 1, 2, and 23., yards are the ones most com mon. For digging blasted rock the front edge or lip of the dipper has steel teeth. The excavating capacity of steam shovels varies from 2-100 cubic yards of sand to 600 cubic yards of loose rock per ten hours, with a cubic yard dipper. For extensive records of actual op eration in various kinds of material, consult Hill, The Chicago Main Drainage Channel (New York, 1896).