Page:Popular Science Monthly Volume 89.djvu/112

 98

��Popular Science Monthly

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���An air-compressor supplies air to a chamber surrounding the water-pipe in the well. The air passes through small perforations into the water, producing bubbles which rise slowly

Making Water Pump Itself

��DOES water seek its own level? Yes, with an if — if the water is the same density throughout. If the density of water in two connecting \cssels differs, the le\c'l of the lighter water will he higher.

There are different ways in whidi density can be affected. One is by heat; another is by adding to the water some- thing that is lighter than itself — air, for instance. This can be shown in a very simple way with a tea-kettle and a short tube. l'"il! liie keltic with water and insert the tube in its spout until it nearly touches the bottom of the spout, riieii blow bul)i>ies into the spout through the tube, '{"he bubbles will mix with the water in the spout and lighten

��it. The solid water in the kettle will then overbalance the lighter aerated water in the spout ; the hea\ier water in the kettle will force its wa\- into the spout in an endeavor to establish equilibrium, antl the spout will over- flow. The water will continue to flow from the spout until the water le\-el in the kettle becomes so low that ecpiilib- riuin is established. Then the llow will cease. It is ai)|iarent that the force of the air has little to do witii the action, for the air is blowing ai^aiiist the direc- tion of llow of the wati'r. Thi' water really pumps itself.

Ki'cping the c.ise of the ki'tlk' in mind, we will now see how it suflicos to illustrate the princi|)le of the air-lift.

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