_The Syphon_ is a bent pipe or tube with legs of unequal length, used
for drawing liquid out of a vessel by causing it to rise in the tube
over the rim or top. For this purpose the shorter leg is inserted in
the liquid, and the air is exhausted by being drawn through the longer
leg. The liquid then rises by the pressure of the atmosphere and fills
the tube and the flow begins from the lower end.
The general method of use is to fill the tube in the first place with
the liquid, and then, stopping the mouth of the longer leg, to insert
the shorter leg in the vessel; upon removal of the stop, the liquid
will immediately begin to run. The flow depends upon the difference
in vertical height of the two columns of the liquids, measured
respectively from the bend of the tube, to the level of the water in
the vessel and to the open end of the tube. The flow ceases as soon as,
by the lowering of the level in the vessel, these columns become of
equal height or when this level descends to the end of the shorter leg.
The atmospheric pressure is essential to the support of the column of
liquid from the vessel up to the top of the bend of the tube, and this
height is consequently limited; at sea height the maximum height is a
little less than 34 feet for water, but this varies according to _the
density of the fluid_.
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