Fig. 152.—Melting ice by pressure.
Since water expands on freezing, pressure would on compressing ice at 0°C., tend to turn it into water. Pressure does lower the melting point of ice, so that a little ice may melt when it is subjected to pressure. On removing the pressure the water freezes. This may be shown by placing a loop of fine piano wire (see Fig. 152) over a piece of ice supported so that a weight may be hung upon the wire. The wire will be found to gradually cut through the ice, the melted ice refreezing above the wire.
Important Topics
1. Specific heat.
2. Heat of fusion of ice.
3. Crystalline substances have fixed melting points.
4. Expansion on freezing, importance.
Exercises
1. What are two advantages in the high heat of fusion of ice?
2. What are two advantages in the expansion of water while freezing?