constantly exposed is by this means kept lower than the point of its fusion, and, consequently, the plate remains uninjured, when otherwise it would become rapidly destroyed. The puddling of fine metal in this furnace is conducted as follows:-The iron is conducted to the furnace by a shovel, and is piled up round the sides of the hearth till it almost touches the dome, but taking care to keep the centre of the sole clear for working the charge, as well as to allow the heated air to freely circulate round the broken fragments. A portion of rich slag and iron scales is added afterwards to the broken metal. The doors are then closed, fresh fuel put on the grate, and the damper at the top of the chimney closed. In about half-an-hour's time the sharp edges of the fine metal begin to melt, and flow on the bottom of the hearth. At this stage the workman removes a small iron plate, by which, during the first operation, a small opening in the working door is closed, and with an iron rod stirs the melted portions of metal, so that new surfaces may be exposed to the oxidising gases passing through the furnace; and to prevent it running together in one mass, he removes it to a certain distance from the bridge. When the whole charge has been thus brought to a pasty state, the fire is lowered, the

damper closed gradually, and a little water may, if necessary, be thrown into the furnace. From the evolution of carbonic oxide gas, the metallic bath now appears to boil; this gas, on reaching the furnace, immediately takes fire, and burns with a blue flame. The metal has now to be kept constantly stirred by the puddler with an iron tool called a paddle, and thus fresh surfaces are continually exposed to the action of the gases in the furnace. It is desirable, however, that the metal should not be exposed to the direct action of the atmospheric air, as it would become rapidly oxidised, and for this reason the working door is not opened, unless it is quite necessary to the carrying on of the work. After a while the metal begins to lose its coherence and gets sandy, or what the workman would call dry. The evolution of oxide of carbon now rapidly declines, and soon ceases altogether; but the mass is kept continually stirred till it has obtained a uniform granular appearance. When this state is arrived at, the fire is again forced, and the damper gradually raised; the sandy particles now agglutinate, and offer considerable resistance to the paddle. The iron now is said to work heavily, and for this purpose the floss-hole at the end of the furnace farthest from the bridge is opened, and a portion of the scoria run

off. All that remains is for the workman to form the iron into balls, which he does by attaching a small portion to the end of the paddle, and so rolling it in the hearth as to collect other fragments, which become firmly welded to it. The charge is in this way collected into lumps, weighing from 60 lb. to 70 lb. each, which are placed in the hottest part of the furnace by a kind of rake called a dolly, which is heated to redness before being used, and in this place they are pressed, in order to squeeze out the slag contained in the spongy mass. The time occupied in this making of the balls is about twenty minutes, when the doors are closed for a little, and the dampers opened so that the particles of the metal may be welded closely together. The loupes are then removed successively from the furnace, and placed either under the hammer or squeezer, in which case they are often welded to a long iron rod, which serves the purpose of a handle to the workman. On the contrary, when they are passed directly to the roughing rollers, as in most parts of Wales, they are lifted directly from the earth by the help of heavy tongs only.

The charge of a puddling furnace is usually from 3 cwt. to 6 cwt. of fine metal. When very pure castiron is to be treated, such as that prepared from

charcoal, the preliminary operation of refining is sometimes dispensed with, but its previous purification is almost indispensable for ordinary rough metal. In the course of twenty-four hours each furnace receives from ten to eleven charges, and the average loss experienced by the fine metal is about 9 per cent. on the quantity treated. For each finery, about five puddling furnaces are required, and every charge of puddled metal requires the combustion of just its own weight of coals. The operation may be divided into four distinct periods. The melting of the refined metal begins at the expiration of twenty or twenty-five minutes. When an hour-and-a-half has expired the charge is completely reduced to a sandy state. While in this state, it is kept heated for another half-hour, and thus the boiling is begun; and this occupies the same length of time."

CHAPTER III.

STEEL.

(26.) STEEL occupies a position between wrought and cast iron, containing what may be called an intermediate quality of carbon. It is capable of having great hardness given to it by the process of what is called "tempering," that is, heating it and then plung ing it into cold water. The usual mode of making steel is by introducing bars of wrought-iron along with carbon into retorts, and maintaining them in a furnace at a red heat for a considerable time. This process is known as that of " cementation." It is also made by the direct process, invented by Mr Bessemer, of which we shall hereafter give details, noticing meanwhile more fully the process of cementation above alluded to. The iron bars, which are of the best quality, the charcoal-iron of Sweden and of Russia being held in the highest estimation, are placed in retorts, which are set in a furnace somewhat like that used in