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

80 CORK INSULATION
sion. If a substance is heated from 0° C. to 1° C, the fraction
of its length that the body expands is its cofficient of linear expan-
sion, the fraction of its area that the body expands is its coeffi-
lient of superficial expansion and the fraction of its volume that
the body expands is its' coefficient of cubical expansion.
The expansion of most substances has been found to be nearly
constant for each degree of temperature, and it is therefore the
practice to determine the mean coefficient for a change of several
degrees. If 1^ is the length of an iron bar at temperature t^
and I2 the length at temperature tg, then the expansion in
length for 1° C. is expressed by
l^li 1,-1,
ts—t, t
if tj— ti is expressed by t. Now the fraction of its length that
a body expands when heated from 0° C. to 1° C. is taken as its
coefficient of linear expansion, which shall be designated as a.
Therefore, the original length, l^, times the coefficient of linear
expansion of the material, a, or 1^ a, must equal the expansion
in length for 1° C, or
lia= ,
I2— li U—U
or a= ,
t li t
or h^hCl+at);
and, similarly, if k is the coefficient of cubical expansion, Vj
and V2 the volumes at temperatures t^ and tg, respectively, then
V2—Vi Va—Vi
k= = ,
Vi (t:—ti) Vi t
or V2=Vi (1+kt).
Superficial and cubical expansion for solids are computed
from the linear expansion, the coefficient of superficial expansion
being twice and the coefficient of cubical expansion being three
times the coefficient of linear expansion.
41.—Determination of the Expansion of Substances.—The
linear or cubic expansion of a solid may be determined by the
actual measurement of its dimensions at different temperatures,
or its cubic expansion may be determined indirectly by
measuring the volume of the solid at various temperatures by
the gravimetric method, in common use by chemists.
The determination of the expansion of water and all other
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