materially the practical result. M. Regnault has shown that the total
amount of heat, existing in a given weight of steam, increases slightly
with the pressure, so that the sum of the latent and sensible heats do not
form a constant quantity. Thus, in steam of the atmospheric pressure, or
with 14.7 Lbs. upon the square inch, the sensible heat of the steam is 212
degrees, the latent heat 966.6 degrees, and the sum of the latent and
sensible heats 1178.6 degrees; whereas in steam of 90 pounds upon the
square inch the sensible heat is 320.2 degrees, the latent heat 891.4
degrees, and the sum of the latent and sensible heats 1211.0 degrees. There
is, therefore, 33 degrees less of heat in any given weight of water, raised
into steam of the atmospheric pressure, than if raised into steam of 90
Lbs.[1] pressure.

167. _Q._--What expansion does water undergo in its conversion into steam?

_A._--A cubic inch of water makes about a cubic foot of steam of the
atmospheric pressure.

168. _Q._--And how much at a higher pressure?

_A._--That depends upon what the pressure is. But the proportion is easily
ascertained, for the pressure and the bulk of a given quantity of steam, as
of air or any other elastic fluid, are always inversely proportional to one
another. Thus if a cubic inch of water makes a cubic foot of steam, with
the pressure of one atmosphere, it will make half a cubic foot with the
pressure of two atmospheres, a third of a cubic foot with the pressure of
three atmospheres, and so on in all other proportions. High pressure steam
indeed is just low pressure steam forced into a less space, and the
pressure will always be great in the proportion in which the space is
contracted.