on the square inch, this is shown on the
thermometer of Fahrenheit as 212 deg., and on the simpler centigrade one, as
100 deg., water freezing at 0 deg. C. But if what I have said is true, when we
remove some of the atmospheric pressure, the water should boil with a
less heat than will cause the mercury in the thermometer to rise to 100 deg.
C., and if we take off all the pressure, the water ought to boil and
freeze at the same time. This actually happens in the Carre ice-making
machine. The question now arises, "Why does the water freeze in the
Carre machine?" All substances require certain amounts of heat to enable
them to take and to maintain the liquid state if they are ordinarily
solid, and the gaseous state if ordinarily liquid or solid, and the
greater the change of state the greater the heat needed. Moreover, this
heat does not make them warm, it is simply absorbed or swallowed up, and
becomes latent, and is merely necessary to maintain the new condition
assumed. In the case of the Carre machine, liquid water is, by removal
of the atmospheric pressure, coerced, as it were, to take the gaseous
form.
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