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

HEAT AND THERMAL EXPANSION 79
iron is 0.0000122. Since 0.0001 -^ 0.0000122 = 8+, then a
change of temperature of approximately 8° C. will produce
the same change in the length of the bar as a force of one ton.
39.—Application of Expansion and Contraction.—Many of
the phenomena that are commonly encountered are traceable
directly to the expansion and contraction that results from
the rise and fall of temperature. One of the commonest of
these is the explanation for a pendulum clock losing time in
hot weather and gaining time in cold weather, due to the
expansion and contraction, respectively, of its pendulum with
the seasons. The wagon-maker heats his iron tires, thus
expanding them, and after being put in place they contract
and bind the wooden wheel solidly and securely. Very hot
water if poured into a cold glass will often crack the glass
due to unequal expansion of the inner and outer surfaces.
The steel framework of modern buildings is put together with
red-hot rivets hammered down as tight as possible with pneumatic
hammers. When the rivets cool they contract and
draw the steel members together with an enormous force.
Virtually all pipe lines must be so arranged or equipped as
to allow for expansion and contraction, to avoid serious dam-
age and trouble from leaks. Paved streets, cement sidewalks,
viaducts, bridges and all such items of general utility must
be provided with a certain freedom of motion of their stand-
ardized parts to prevent buckling and cracking from expan-
sion and contraction. The terrific force exerted by the ex-
pansion of freezing water splits off the solid rock from the
side of the granite hills with the ease of a mythological giant.
J*avements come up, trees are lifted out of the ground, building
foundations are damaged, water pipes burst, mountain
ranges slowly crumble away, all because the terrific force
exerted by the expansion of freezing water is irresistible.
Other phenomena are traceable to expansion and con-
traction due to humidity rather than to temperature.
40.— Coefficient of Expansion.—It has been noted that,
with very few exceptions, substances expand in every direc-
tion when heated. Expansion in length is quite naturally
termed linear expansion, expansion in area is known as super-
ficial expansion and expansion in volume is called cubical expan-