Solidification
المؤلف:
GEORGE A. HOADLEY
المصدر:
ESSENTIALS OF PHYSICS
الجزء والصفحة:
p-268
2025-11-24
49
is the reverse of fusion, and takes place when a liquid is cooled below its melting point. 'The temperature at which any substance solidifies is the same as the melting point, and for some substances, as water and mercury, this temperature is called the freezing point. Every liquid in freezing gives off an amount of heat equal to that which would be required to melt it if frozen. The freezing point of vegetables is a little lower than the freezing point of water. For this reason, pans of water are sometimes placed in vegetable cellars, in order that the water, while freezing, may give out heat enough to keep the air above the freezing point of the, vegetables.
Most liquids shrink on solidifying; but water, on the contrary, expands. Water expands so that 917 c.c. of water becomes 1000 c.c. of ice. Were it to decrease in volume instead, the crystals of ice forming at the surface of a lake would sink, and during a cold winter the water would become solid ice from the bottom to the top.
Demonstration. - Fill with water an air thermometer bulb with a long stem, and pack the bulb in a freezing mixture. The water in the stem will be seen gradually to sink, then to turn and rise, indicating that the minimum volume has been passed, and then suddenly to rise again. On taking the bulb out after some minutes, it will be found broken, and the water will be a ball of ice.
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