Cork insulation; a complete illustrated textbook on cork insulation ...

HEAT AND THERMAL EXPANSION 11
lish that "the volume of a given mass of any gas under constant
pressure increases by a constant fraction of its volume
at zero for each rise of temperature of 1°C." The ratio of
standard steam temperature (the minimum temperature of
pure steam at 16 cm. pressure) to ice temperature (the temperature
of pure melting ice at 76 cm. pressure) has been
found by the air thermometer to be 1.367, or
Steam temp. S
=—= 1 .367
Ice temp. I
On the Centigrade scale S — I = 100, and from these
two simple equations we find that S = ZTh° and I = 273°,
approximately, Centigrade. Any other temperature may be
determined by measuring its ratio to I or to S by means of
the air thermometer. Temperatures measured in this way
are called absolute temperatures, and thus it will be noted that
the absolute zero on the Absolute scale is 273 degrees below
the freezing point on the Centigrade scale. It has been
established, since Jacques Alexandre Cesar Charles (1746-
1822), a French physicist and aeronaut, gave us his Law of
Charles, that the volumes of the same mass of gas under
constant pressure are proportional to the temperature on
this Absolute scale, or
V t+213 T
vi U+213 T,
if t + 273 is expressed by T, and t^ -f 273 by Tj.
37.—Expansion and Contraction.—If equal volumes of
various gases are heated, under constant pressure, they were
thought by Joseph Louis Gay-Lussac (1778-1850), a French
chemist and physicist, to expand equivalent amounts for the
same rise in temperature, but very careful measurements have
since demonstrated quite perceptible differences of expansion
of various gases, ammonia, for example, being distinctly dif-
ferent in its expansion from hydrogen. Gases that are near
their points of liquefaction depart widely from Gay-Lussac's
law ; ammonia, sulphur dioxide and methyl chloride gases are
easily liquefied and are commonly referred to as vapors.
Hydrogen, on the other hand, is not easily liquefied under