Compressed air can do much else than impel pistons of familiar type. In one remarkable device it has put pistons out of business altogether.
Air-Lifts.
Fill a tumbler to the brim with water, take a straw and dip it to the bottom of the glass, blowing as heartily as you can. At once the water overflows because displaced by rising bubbles of air. Instead of a tumbler take a long upright pipe filled with water, send to its base compressed air of adequate pressure, and you have the Pohle air-lift, which carries water into the reservoirs of Fort Madison, Iowa, of Dixon, Illinois, of Asbury Park, New Jersey, and many other towns and villages. On a smaller scale the air-lift brings up water from thousands of wells, rivers, and lakes. Aboard ship it moves water ballast from one compartment to another, so as to give the vessel just the trim or inclination desired. In chemical works it raises liquids so corrosive that no other lifter is feasible. It has no valves or other moving parts to be deranged or hurt in case its stream bears sand or dirt, so that it is a capital drainage pump; after serving thus it may bring sewage to farms and distribute it thoroughly. To be fairly efficient the air-lift requires that two thirds of the length of its upright pipe be immersed below the surface of the liquid to be raised.
Liquids Lifted by Expanding Air.
For oil wells, which may be 2000 or more feet in depth, a lifter not so simple is employed. A pipe, comparatively large, is lowered to the oil. Its base forms a receiver which, at will, may be closed on its earthward side, then through a small inner tube compressed air reaches the oil to force it bodily to the surface of the ground. The Harris pump lifts oil, water, or other liquids with high efficiency: it allows the compressed air after use to act expansively; this helps to drive the compressor; then this expanded air is once more highly compressed, and so recurrently.
Harris system of pumping by compressed air, showing switch. Pneumatic Engineering Co., New York.
A Jack-of-All-Trades.
Compressed air readily moves liquids as masses; it as easily impels them as particles. A lady’s toilet table usually displays an atomizer. Its rubber bulb, sharply squeezed, emits a tiny stream of perfume as a quick air blast breaks a drop of liquid into spray. Magnify this apparatus and you have a painting machine for freight and passenger cars, fences, and out-buildings. Driven as it is with projectile force the pigment penetrates further than if laid on by hand, reaching crannies and crevices which evade a brush. On the same principle Hook’s spraying machine sends Bordeaux mixture into the foliage of an orchard, or delivers a solution of carbolic acid upon the floors, walls, and ceilings of a hospital or a sick-room. Strengthen such a blast and you can elevate, dry, and aerate grain, or lift the culm from a coal heap to a furnace, and then discharge the ashes as they tumble from a grate. Where stretches of water are sandy and muddy, compressed air dredges a channel by stirring up deposits at the bottom.