The directions that usually come with electric irons, toasters, and stoves say that the connection should be broken by pulling out the plug rather than by turning off the switch. This is because the switch in the electric-light socket sometimes loses its spring and instead of snapping all the way around and quickly leaving a big gap, it moves only a little way around and an arc is formed in the socket; if you hear a sizzling sound in a socket, you may be pretty sure that an arc has been formed. But when you pull the plug entirely out of the iron or stove, the gap is too big for an arc to form and you are perfectly safe. Fire commissions usually condemn extension lights, because if the insulation wears out on a lamp cord so that the two wires can come in contact, a dangerous arc may easily form. And the insulation might suddenly be scraped off by something heavy moving across the cord. This can happen whether the light at the end of the cord is turned on or off. So it is best if you have an extension light always to turn it off at the socket from which the cord leads, not at the lamp itself. Many people do not do this, and go for years without having a fire. But so might you live for years with a stick of dynamite in your bureau drawer and never have an explosion. Still, it is not wise to 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?