The Bessemer process makes enormous masses of steel and makes it very cheaply; but it has one fault--it is too quick. The converter roars away for a few minutes, till the carbon and other impurities are burned out; and the men have no control over the operation. In what is called the "open-hearth" process, pig iron, scrap iron, and ore are melted together with whatever other substances may be needed to make the particular kind of steel desired. This process takes much longer than the Bessemer, but it can be controlled. Open-hearth steel is more homogeneous,--that is, more nearly alike all the way through,--and is better for some purposes, while for others the Bessemer is preferred. Steel is hard and strong, but it has two faults. A steel bar will stand a very heavy blow and not break, but if it is struck gently many thousand times, it sometimes crystallizes and may snap. A steel rail may carry a train for years and then may crystallize and break and cause a wreck. Inventors are at work discovering alloys to prevent this crystallization. The second fault of steel is that it rusts and loses its strength. That is why an iron bridge or fence must be kept painted to protect it from the moisture in the air. If all the iron that is in use should suddenly disappear, did you ever think what would happen? Houses, churches, skyscrapers, and bridges would fall to the ground. Railroad trains, automobiles, and carriages would become heaps of rubbish. Ships would fall apart and become only scattered planks floating on the surface of the water. Clocks and watches would become empty cases. There would be no machines for manufacturing or for agriculture, not even a spade to dig a garden. Everybody would be out of work. If you wish to see how it would seem, try for an hour to use nothing that is of iron or has been made by using iron. VIII OUR GOOD FRIEND COPPER Where did rocks come from? Some were deposited in water, like limestone and like the shale and sandstone that lie over the strata of coal. Others were made by fire, and were thrown up in a melted state from the interior of the earth. Such rocks are the Giant's Causeway in Ireland and the Palisades of the Hudson River. They are called "igneous" rocks, from the Latin word _ignis_ meaning "fire." When the igneous rocks were thrown up to the surface of the earth, they brought various metals with them. How the metals happened to be there ready to be brought up, no one knows. Some people think they were dissolved in water and then deposited; others think that electricity had something to do with their formation. However that may be, metals were brought up with the igneous rocks, and one of these metals is copper.