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

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86 CORK INSULATION<br />

The heat of fusi<strong>on</strong> of a substance is the number of thermal<br />

units required to change a unit mass of a solid at its melting<br />

point into liquid at the same temperature. The accompany-<br />

ing table gives the heat of fusi<strong>on</strong> of various substances.<br />

HEAT OF FUSION OF VARIOUS SUBSTANCES.*<br />

Substance B.t.u. per Pound<br />

Bismuth 22.7<br />

Lead 9.7<br />

Mercury 5.04<br />

Nickel 8.3<br />

Platinum 49.0<br />

Silver<br />

38.0<br />

Tin 25.7<br />

Zinc 50.6<br />

Ice<br />

Hydrogen<br />

144.0<br />

28.8<br />

51.—The Boiling Point.—The temperature at which the<br />

liquid and its pure vapor can exist together in equilibrium, is<br />

the boiling point of that liquid, and such temperature is invari-<br />

able if the pressure is c<strong>on</strong>stant.<br />

The vapor of a substance under given pressure will c<strong>on</strong>dense<br />

to a liquid if it is cooled below the temperature that is<br />

its boiling point at that pressure; and the vapor of a substance<br />

at given temperature will c<strong>on</strong>dense to a liquid if its pressure<br />

is increased bey<strong>on</strong>d a certain maximum value for that sub<br />

stance, although all vapors have a critical temperature above<br />

which they can not be liquified regardless of the amount of<br />

pressure to which they are subjected.<br />

The accompanying table gives the boiling points of various<br />

liquids at atmospheric pressure.<br />

BOILING POINTS OF VARIOUS LIQUIDS.*<br />

Substance<br />

Ether<br />

Chloroform<br />

Boiling Point, F.<br />

95°<br />

142°<br />

Alcohol 172.2°<br />

Benzine<br />

Water<br />

Glycerine<br />

Mercury<br />

176.7°<br />

212°<br />

554°<br />

675 °<br />

Sulphur dioxide<br />

Amm<strong>on</strong>ia<br />

Carb<strong>on</strong> dio.xide<br />

Oxygen<br />

Hydrogen<br />

14°<br />

— 29°<br />

— 108.5°<br />

—296°<br />

—422°<br />

52.—Vaporizati<strong>on</strong>.—The c<strong>on</strong>versi<strong>on</strong> of a substance into<br />

the gaseous form is called vaporizatioin. If the change to a gas<br />

takes place slowly and from the surface of a liquid, at a tem-<br />

•Chas. R. Darling, 1908.

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