# Man's physical universe

220 PHYSICAL LIMITATIONS HAVE BEEN OVERCOME

No System of Classification Is Adequate.

The majorit>- of subst^uiccs can be classified definitely as gases,

liquids, or solids, but there are a few substances that show intermediate

properties; thus vitreous liquids show by X-ray analysis that there

are at least temporary crystalline structures present. Several hundred

liquids which show crystalline properties are known.

Solids Have Definite Specific Heats.

The specific heat of a substance is the ratio oj the amount of heat required

to raise the temperature of one gram of the substance one degree centigrade

to the amount similarly required for water.

A CALORIE is the amount of heat required to raise the temperature of

one gram of water from 15° to 16° C.

Table of Specific

Heats

Water .... 1.00 Sand .

Pine wood . . . 0.65 Iron

Alcohol . . . . 0.60 Copper

Ice 0.50 Zinc .

Aluminum . . . 0.22 Mercury

0.19

0.113

0.094

0.093

0.033

The unusually high specific heat of water has a number of important

applications. In a following section we shall see how the temperature

of land areas near large bodies of water is kept equable by the breezes

blowing from the water to the land areas. The temperature of large

bodies of water changes very little during a hot day because of the

high specific heat of water. On the other hand, large bodies of water

do not cool very much at night for the same reason. Inasmuch as the

specific heat of land areas is much less than that of water, they are

more quickly heated and cooled than large bodies of water.

Hot-water heating systems are possible because of the large amount

of heat that is carried by the water and given off as the water slightly

cools. The hot-water bottle is an application of the high specific heat

of water. The same weight of iron would yield less than one-ninth as

much heat for an equivalent temperature drop.

The Heat of Fusion of Water Is Unusually High.

When liquids solidify, heat is set free, and when solids melt, exactly

equivalent amounts of heat are used up for equivalent amounts of the

same substances. The amount of heat in calories required to melt one

gram of a true solid is called its heat offusion. The freezing of water into

ice liberates so much heat that winters are moderated and the advent

of spring is delayed in the neighborhood of large bodies of water because

of the heat absorbed by the ice as it melts.

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