keep dynamite in your bureau.

Arc lights themselves, of course, are no more dangerous than is a
fire in a kitchen stove. For an arc light is placed in such a way
that nothing can well come near it to catch fire. The danger from
the electric arc is like the danger from gasoline spilled and
matches dropped where you are not expecting them, so that you are not
protected against them.

Fortunately ordinary batteries have not enough voltage to cause
dangerous arcs. So you do not have to be as careful in wiring for
electric bells and telegraph instruments. It requires the high voltage
of a city power line to make a dangerous electric arc.

So many fires are caused by electric arcs forming in buildings, that
you had better go back to the beginning of this section and read it
all through again carefully. It may save your home and even your life.

After you have reread this section, test your understanding of it by
answering the following questions:

1. How can you make an electric arc?

2. Why should wires not be twisted together to make electric
connections?

3. Why should wires be brought into houses and through walls in iron
conduits?

4. Why should you pull out the plug of an electric iron, percolator,
toaster, heater, or stove?

5. Why do fire commissions condemn extension lights?

6. If you use an extension light, where should it be turned off?

7. If you hear a sizzling and sputtering in your electric-light
socket, what does it mean? What should you do?

8. Is there any danger in defective sockets with switches that do not
snap off completely? What is the danger?

9. In Application 55, page 228, if the rat had gnawed the wire in two
while the electric iron was being used, would anything have happened
to the rat? Would there have been any danger to the house?

10. Where a wire is screwed into an electric-light socket, what harm,
if any, might result from not screwing it in tightly?

11. How can a wire be safely spliced?

12. Why is an electric arc in a circuit dangerous?

INFERENCE EXERCISE

Explain the following:

351. White objects look blue when seen through a blue glass.

352. When you pull the plug out of an electric iron, the iron
cools.

353. People who do not hear well sometimes use speaking
trumpets.

354. The sounding board of a piano is roughly triangular; the
longest strings are the extreme left, and those to the right
get shorter and shorter