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.