402 IRON MANUFACTURE nected by a series of stave plates to form a cyl- inder. These have hollow ribs running longi- tudinally, which serve the double purpose of holding the fettling and keeping it cool. The cylinder is open at both ends ; one buts against the ring that is fastened to the bridge plate, and the other, which serves as a doorway, against the movable head piece. The chamber is made to revolve by a special engine attached to it by means of a toothed wheel. The fire- place is large, and is provided with blast under the grate and over the fire, by means of which the heat and character of the flame are easily regulated. Fig. 8 shows a vertical section through the fireplace chamber and head piece. The chamber is lined in the following manner: The initial lining is composed of a mixture of pulverized ore and pure lime, worked with water to the consistency of a thick paste. The inner surface of the chamber is completely covered with this mortar in a layer projecting about one inch over the hollow ribs. After 1'IQ. 8. this has become hard, the furnace is ready for the fettling. About one fifth of the whole quantity of iron ore required is thrown into the furnace in the form of powder. The fur- nace is then heated up and made to revolve slowly until the ore is completely melted. The apparatus is then stopped, and that part of the ore which has not been consumed in glazing the initial lining forms a pool in the bottom of the chamber, into which are put a number of lumps of ore of such a size that they project 2 to 6 in. above the surface. This is allowed to set, and then another lot of pulverized ore is put in, which is melted in the same way, and a pool collected on another part of the surface, into which lumps are put as before. About 2 to 2J tons of ore are required to fettle a TOO-lb. rotary furnace. The iron may be either charged in the solid form or run in molten from a cupola. When in the solid form, it has been found advantageous to have it granulated or otherwise finely divided, in order to hasten the melting. A quantity of hammer or roll cinder is added with each charge, as is usual in pud- dling. "When the iron is thoroughly melted, the furnace is made to revolve once or twice a minute for the first five or ten minutes. A stream of water is then injected through the stopper hole along and just above the line of contact between the floating cinder and the in- ner surface of the vessel, on the descending side. The cinder is thus partially solidified, and carried down with the molten iron and in- timately mixed with it. When the iron be- gins to thicken under this treatment, the rota- tion is stopped and the heat raised until the cinder melts thoroughly and floats on top of the iron, when it is tapped off. The furnace is again put into motion at the rate of six to eight revolutions a minute, which causes the charge to be dashed about violently in the fur- nace. When the iron begins to come to na- ture, the velocity of the apparatus is reduced to two or three revolutions per minute, when the ball speedily forms. The movable head piece is pushed to one side and the ball is removed in one mass. Special machinery is needed to work these large blooms, which in the furnaces hitherto con- structed weigh VOO Ibs. The yield of puddled bar is usually about 10 per cent, more than the weight of the pig charged, which is due to the reduction of the iron of the fettling. Owing to the thorough work- ing of the iron, and the inti- mate contact of every particle of the pig iron with the fet- tling, the product is much more uniform and pure than that made by hand puddling. Since the successful introduction of Danks's furnace, a number of rotary puddlers have been in- vented, which, though they may differ in mech- anism from Danks's pnddler, are yet lined and fettled in the same manner. In Sellers's rotary puddler the chamber is egg-shaped, and the flame from the fire, instead of pass- ing through, returns and goes out at the end through which it came. Pig iron may be com- pletely decarburized by heating in an oxidizing atmosphere, at a temperature below that of fusion. The removal of the carbon is effected gradually and slowly from the surface to the centre. This process is used extensively for making the so-called "malleable castings" (see IRON), also often malleable iron. Only articles of less than an inch in thickness are generally so treated, on account of the length of time re- quired for conversion. White iron, which is best adapted for the purpose, is cast in moulds, and the articles thus formed are packed in ox- ide of iron and exposed to a red heat for five or six days. When cold they are taken out, and are found to be tough and malleable if the iron from which they were made was of
