This difference of pressure in the two foregoing experiments must be
attributed, then, to the specific action of the water on the vapors of
alcohol. Now we can calculate the difference of the work of the pump,
and put at 1 kilogramme of condensed liquid the difference of mechanical
work represented in kilogrammeters. What is remarkable is that this
difference is absolutely the equivalent of the heat disengaged when the
condensed liquid and the old liquid are remixed; there is a complete
identity. Thus the affinity of the water for the alcohol modifies the
tension of the vapors which form or condense upon the free surface of
the mixture. The two phenomena are closely connected by the law of
equivalence.
It results from all the laws that we have cited that by properly
regulating the tensions of the vapors of a mixture of alcohol and water,
and the temperature of the liquid, we shall be able to obtain a liquid
of a desired richness by the condensation of these vapors.
III. It was likewise indispensable to make sure of one important fact:
When the temperature of a liquid like alcohol is considerably lowered,
can the distillation of a given weight of this substance be effected
with sufficient rapidity for industrial requirements? Repeated
experiments with a host of volatile liquids have demonstrated the
following laws:
If we introduce a volatile liquid into two spherical receivers connected
by a wide tube, and if these be kept at different temperatures after
driving out all the air from the apparatus, the liquid distills from the
warmer into the cooler receiver, and we ascertain that:
h.
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