rotary press

Printing press that prints on paper passing between a supporting cylinder and a cylinder containing the printing plates. In contrast, the flatbed press has a flat printing surface. The rotary press is used mainly in high-speed, web-fed operations in which the press takes paper from a roll, as in newspaper printing. Many of these large presses not only print as many as four colours but also cut and fold and bind in a cover, all in one continuous automatic process. Paper passes through some presses at nearly 20 mph (30 kph); large presses can print up to 60,000 copies of 128 standard-size pages in an hour. Seealso R. Hoe.

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Ability of a substance to rotate the plane of polarization of a beam of light passed through it, either as crystals or in solution. Clockwise rotation as one faces the light source is “positive,” or dextrorotary; counterclockwise rotation “negative,” or levorotary. Louis Pasteur was the first to recognize that molecules with optical activity are stereoisomers (see isomerism). Optical isomers occur in pairs that are nonsuperimposable mirror images of one another. They have the same physical properties except for their effect on polarized light; in chemical properties they differ only in their interactions with other stereoisomers (see asymmetric synthesis).

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Internal-combustion engine in which the combustion chambers and cylinders rotate with the driven shaft around a fixed control shaft to which pistons are attached. The gas pressures of combustion are used to rotate the shaft. In the Wankel engine, the most fully developed and widely used rotary engine, a triangular rotor rotates with an orbital motion in a specially shaped casing, and forms rotating crescent-shaped combustion chambers between its sides and the curved wall of the casing.

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