solution of alcohol
and water, plunge it into water of 20 deg.C., and put its interior in
hermetic communication with the receiver of a mercurial air-pump.
We vaporize at 20 deg. a certain quantity of the liquid, and the vapors
fill the known capacity of the pump. The pressure of the gases in the
interior is ascertained by a pressure gauge, and this pressure should be
constant if care is taken to act upon a sufficient mass of liquid and
with moderate speed. When the receiver of the air-pump is full of
vapors, communication between it and the test-tube is shut off, and
communication is effected with a second test-tube, like the first,
plunged into the same water at 20 deg.. Care must be taken beforehand to
create a perfect vacuum in this test-tube.
On causing the mercury to rise into the space that it previously
occupied, the vapors are made to condense in the second test-tube at the
same temperature as that at which they were formed.
We immediately ascertain that the pressure-gauge shows an elevation
of pressure; moreover, the proof of the condensed alcohol has very
perceptibly risen.
If, instead of causing these vapors to condense in the second test-tube,
we leave the first communication open, the vapors recondense in the
first test-tube without any elevation of pressure; and we do not see the
least trace of liquid forming in the second test tube.
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