Pocketbook of Useful Formulæ and Memoranda
for Civil and Mechanical Engineers

444 moleswobth’ø pocket-book Steel Manufacture—continued. The converter (7' 6" diameter for 5 tons) has a lining of gannister from 9 to 12 inches thick, cased with boiler plates. The converter is supported on trunnions, through which the blast is introduced; the bottom is loose, pierced with from 7 to 12 fire-clay tuyeres about < inch diameter. Spare bottoms are always in reserve. __ Pressure of blast from 15 to 25 lbs. per square inch. . The converter is first heated to redness by a coke fire inside it, urged by a gentle blast. The fire is then turned out and the molten iron run into it whilst in a horizontal position; the blast is then put on and the converter turned into an upright position. The air allows the carbon, silicon, and manganese to burn out, the temperature rising rapidly and the colour changing from orange to dazzling white. The silipon and manganese with a little Iron burn first, and after a few minutes the carbon begins to burn freely. The length of the blow varies from 5 to 6 to 30 minutes, ar even more, depending on the metal and the amount of decarbonization necessary, which is sometimes determined by the- eye and sometimes by the spectrum. In some cases in the middle of the blow from 15 to 20 per cent, of rail crop ends are added. As soon as the spectrum bands have disappeared, the con- verter is turned down to a horizontal position, and a little slag taken out and cooled in water.. At Seraing the colour of the Blag denotes the percentage of carbon,—lemon yellow denotes 0 • 75 of carbon or more; orange" 0’6; light brown 0 • 45; dark brown 0-3; bluish black 0-15. The globules of metal adhering to the slag are also tested by hammer; if a globule, of about J- inch diameter, flattens down too easily under the hammer with unbroken edges, the metal is too soft. If it cracks readily at the edges it is too hard. If the metal is too hard the blast is again started, and the converter brought into an upright position; if too soft, some melted manganiferuus iron is added. When the metal is of the proper character it is poured out into ingots. At Seraing it. is found that metal con- veyed direct from the blast furnace to the converter is tougher than that obtained from a remeltiug cupola. Sometimes the ingots, when eufliciently cool to be removed, are hammered under a I5-ton steam hammer. Dr. Siemens states that in America 72 “ blows ” have been