Presses less powerful produce scores of parts for sewing machines, typewriters, cash registers, bicycles, and so on; or, at a blow, strike out a gong from a disc of bronze. Presses of another kind stamp out cans in great variety, and even a mandolin frame in all its irregular curves. Tubs are quickly pressed from sheets of metal; a pair of such tubs, tightly joined at their rims by a double seam, form a barrel impervious to oil or other liquid, and hence preferable to a wooden barrel. A press operated by a double crank may be arranged to supersede the forging of hammers, axes, and mattocks. Another press at a blow cuts out the front for a steel range. Still another press invades the foundry, producing excellent gear wheels for trolley cars, not weakened by being cut from a casting across the grain of the metal. Sometimes the article manufactured requires a series of operations, as in the case of a kettle cover with its knob. At the Lalance & Grosjean factory, Woodhaven, New York, a Bliss press makes such covers in a single continuous round. Another press treats soft alloys, so that a disc one inch in diameter when hit by a plunger is forced into the shape of a tube suitable to hold paint or oil. In large manufactures as in small the hydraulic forge has wrought a quiet revolution. If a steel freight car were produced by planing, turning, slotting and similar machines, it would be much heavier and dearer than as turned out to-day from ingeniously fashioned dies under severe pressure. Its girders are molded of the same strength throughout with no waste of material, and without rivets; corner pieces are avoided; stiffeners are built up from the plates themselves through the introduction of ridges and depressions: and in a structure having the fewest possible parts, uniform strength is attained because dimensions everywhere may freely depart from uniformity. [Illustration: Range front pressed from sheet steel.] [Illustration: Pressed paint tube and cover.] Non-Conductors of Heat.