Air Pump

“The air pump is an engine by which the air can be pumped out of a vessel, or withdrawn from it. The vessel so exhausted, is called a receive, and the space thus left in the vessel, after withdrawing the air, is called a vacuum. The principles on which the air pump is constructed are readily understood, and are the same in all instruments of this kind, though the form of the instrument itself is often considerably modified. Let R be a glass vessel, or receiver, closed at the top, and open at the bottom, standing on a perfectly smooth surface, which is called the plate of the air pump. Through thie plate is an aperture, which communicates with the inside of the receiver, and the barrel of the pump. The piston rod works air tight through the barrel. At the extremity of the barrel, there is a valve which opens upwards, and is closed as the piston rises.” —Comstock, 1850

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