Man's physical universe

xanabras

THE PHYSICAL PROPERTIES OF SOLIDS 225

Platinum has been used when it was necessary to fuse a metal into

lime glass because it has the same coefficient of expansion as this glass.

Metals of a different coefficient of expansion would cause cracks to

form around the seal when it was cooled. Satisfactory cheap alloys

such as kovar, which consists of a mixture of iron, nickel, cobalt, and

manganese, and "Dumet" wire, consisting of a copper-clad steel wire,

are now used to replace platinum in the manufacture of electric-light

bulbs and other products in which metal wires must be sealed in glass.

STUDY QUESTIONS

1. How does a true solid differ from a vitreous solid?

2. Give five examples of true solids and of vitreous solids.

3. Mention two respects in which water shows unusual properties.

4. State Le Chatelier's principle and illustrate it with several examples.

5. Explain the effect of adding heat to, or subtracting heat from, a mixture of

ice and water.

6. Mention three advantages of dry ice as a refrigerant.

7. Mention some of the consequences of the fact that water has its maximum

density at 4° C.

8. Explain how the principle of the expansion of metals is used in a thermostat.

9. Why is borosilicate glass better than lime glass for cooking-utensils?

10. Explain how the formation of ice moderates winters.

IL Give the principle back of each of the applications listed in the summary.

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