In every ton of molten cast iron there are approximately 70 pounds of carbon, 25 pounds of silicon, and 15 pounds of manganese or a total of about 2000 pounds of these metalloids in the fifteen-ton charge of molten metal which goes into the ordinary steel plant converter. We know that if burned in a furnace this ton of high grade fuel would generate much heat. Burned _inside_ of the mass of molten metal it generates exactly that same amount of heat and the heat is applied with such rapidity, directness and efficiency that the molten iron which had a temperature of 2300° F., say, when charged, in nine or ten minutes has become steel with a temperature of about 3000° F. simply through this rapid oxidation of its 4 to 6 per cent of metalloids. How the blast under 15 to 30 pounds per square inch is applied through little nozzles in the bottom of the modern “converter” and the several types of vessels with which Bessemer experimented in the course of his investigations are shown in the illustrations. Nor is it necessary that the air be blown through the metal. Air blown upon its surface accomplishes practically the same purpose, and in many of the steel foundries of to-day smaller converters of this “surface-blown” type are used for producing steel for castings. The large steel plants, however, use the larger “bottom-blown” converter. Two or three of these vessels, working with proper metal from the “mixer,” produce an immense tonnage of steel each 24 hours. The “mixer” is quite necessary. It is a large vessel or furnace holding and keeping hot from 75 to 300 or more tons of metal from the blast furnace. It mixes and equalizes irons of various compositions, so that the converters have the advantage of uniform and hot metal with which to work. In addition it is made to perform a “refining” service. By mixing into the metal a quantity of manganese, considerable of the sulphur present (a deleterious substance) is removed. The fifteen or twenty minute blowing of 15 tons of metal in the big egg-shaped converters of a steel plant presents a spectacle which, when once observed, will never be forgotten. One sees a little “dinky” engine come shooting into the converter building with its ladle of molten iron from the “mixer.” With America’s time saving routine not a single minute is lost while emptying the metal into the converter, now in a horizontal position. Almost before the ladle is out of the way, the converter swings to the upright position with the blast already on, for otherwise the metal would flow into the tuyère holes at the bottom. [Illustration: COMPARISON OF INGOTS