Page:The American Cyclopædia (1879) Volume XI.djvu/637

 MINT 619 the strips are fed by hand. The gold planchets are subjected before coining to a careful adjust- ment by weight. This is done by women, whose delicacy of touch fits them admirably FIG. 5. Drawing Bench. for this service. Seated at a long table, each one has a balance before her and a flat file in her hand ; and the gold planchets are succes- sively tried against a counter weight. Those that are too light are thrown aside to be re- melted, and those that are too heavy are brought to the proper weight by moving the file lightly round the edge. The planchets are now ready FIG. 6. Cutting Press. for the milling machine (fig. V), an American invention, by which the planchets, as rapidly as they can be fed by hand into a vertical tube, are caught one by one edgewise, and caused to rotate in a horizontal plane in a channel formed on one side by a revolving wheel, and on the other by a fixed segment of corresponding curve, but slightly nearer the wheel at one end than at the other. The effect is that each piece in passing through this nar- rowing channel has its edge evenly crowded up into a border or rim. After being annealed and cleaned or "whitened," the planchets are ready for the coining press. The coining press (fig. 8) in use in all the mints of the United States is constructed after the plan of the French lever press invented by Thonnelier. The pressure upon the die is effected by a lever moved by a crank and operating a toggle FIG. 7. Milling Machine. joint. The planchets being fed by hand into a tube or hopper in front of the machine, the lower piece in the tube is seized by steel feed- ers and carried forward and lodged in the col- lar between the upper and lower dies. At the same moment the lever is descending, and by the time the planchet is in position the toggle joint, brought into a vertical position, imparts to the piece a pressure which within the nar- row limits of its motion is almost incalculable. The immediate relaxation of the joint causes the upper die to be lifted, when the feeders, coming up with a second planchet, push away the one already coined. The planchet before being struck is slightly less in diameter than