The reason that water runs of a duck’s back, is that the feathers of ducks are oily and, as water and oil will not mix, the water runs off instead of soaking in. The feathers on a duck are so thick on the body of the duck, top and bottom, that even if it were not for the oil which is on the feathers the water would have some difficulty in soaking through the feathers. But the main reason why the feathers on a duck’s back cause water striking them to run off is that the duck has an oil gland which is constantly producing grease or oil and which the duck uses in giving his feathers a thin coating of oil to make them slick with oil and when any water strikes the duck it runs off. Other birds which live in the water a great deal have this oil gland for the same reason. THE STORY IN A STEEL RAIL [Illustration: A Blast Furnace. Molten iron is brought from the blast furnaces to the open-hearth furnaces, and dumped into a receptacle called a mixer, the capacity of which ranges from 400 tons to 1000 tons, depending upon the number of furnaces to be served.] [Illustration: One-thousand-ton Mixer.] Pictures in this story by courtesy of Bethlehem Steel Co. [Illustration: INSIDE OF OPEN HEARTH FURNACE Charging Side of an Open-hearth Furnace. An open-hearth furnace consists of a long, shallow hearth, suitably enclosed in fire-brick, and bound together with steel binding. The furnace is heated by burning gas and air, which have previously been preheated, so that a temperature is obtained in the furnace ranging from 2900 to 3050 degrees Fahrenheit.] [Illustration: Pouring Side of an Open-Hearth Furnace. The open-hearth process consists of the purification of iron by oxidizing out the impurities and burning out the carbon of the iron until a tough and ductile steel is produced, which can be made of any desired composition by the addition of the necessary quantities of alloys just previous to tapping and pouring. The impurities in the iron are oxidized by the slag lying on top of the metal, and the burning out of the carbon, which is a very slow operation, is hastened by the addition of iron ore, the oxygen of which combines with the carbon of the iron and passes off is a gas going up the stack. When an open-hearth furnace is ready for a charge, a variable amount of scrap, say 30 per cent of the total weight of material used for the heat, is charged into the furnace. With this scrap is charged sufficient lime or limestone to make the slag, as well as some iron ore to assist in reducing the carbon of the iron. In about two or three hours the required amount of molten iron is brought from the mixer in ladles, and poured into the furnace on top of the scrap, lime and ore.] [Illustration: MOLTEN STEEL BEING POURED LIKE WATER Molten Steel Being Poured Into Ladle.