If you were guessing you would naturally say that gold is, of course, the most valuable of the metals. But you would be wrong. The proper answer to this is iron. We do not mean the pound for pound value, for you could get much more for a pound of gold than for a pound of iron. We mean in useful value--iron is in that sense the most valuable metal known to man. This is true because iron is of such great service to man in so many ways, and it is very fortunate that there is such a great amount of it available for man’s purposes. Iron is not generally found in a pure state in the mines. It is generally found compounded with carbon and other substances, and we obtain pure iron by burning these other substances out of the compound. Iron is put upon the market in three forms, which differ very much in their properties. First, there is cast-iron. Iron in this form is hard, easily fusible and quite brittle, as you will know if you ever broke a lid on the kitchen range. In the form of cast-iron it cannot be forged or welded. Next comes wrought-iron, which is quite soft, can be hammered out flat or drawn out in the form of a wire and can be welded, but fusible only at a high temperature. Third comes steel, the most wonderful thing we produce with iron. It is also malleable, which means that it is capable of being hammered out flat and can easily be welded, and this is the great property of steel--it acquires when tempered a very high degree of hardness, so that a sharp edge can be put on it, and when in that shape it will easily cut wrought-iron. Ordinarily we make wrought-iron and steel from iron that has been changed from its original state to cast-iron. The term cast-iron is generally given to iron which has been melted and cast in any form desired for use. Stoves are made in this way. The iron is melted and then poured into a mold; while the product out of which wrought-iron and steel are made is technically cast-iron, the term pig-iron is used in speaking of iron which is cast for this purpose. The process by which pig-iron is changed into wrought-iron is called _puddling_. The object of puddling, which is done in what is called a reverberatory furnace (which is a furnace that reflects or drives back the flame or heat) is to remove the carbon which is in the pig-iron. This is done partly by the action of the oxygen of the air at high temperature and partly by the action of the cinder formed by the burning furnace. When this has been done the iron is made into balls of a size convenient for handling. These are “shingled” by squeezing or hammering and passed between rolls by which the iron is made to assume any desired form.