so as to produce the gradual expulsion of the water of the stones; the heat should not be higher than the boiling-heat of water. The slabs are cemented together by fire-clay; in fact, the joints of the whole interior are so united. Small boxes are often set without heads; but it is preferable to have flues on both ends, as well as along the sides.

CHARGING OF THE BOXES.

The boxes are charged with iron in the following manner: On the bottom of each trough is placed a layer of coarsely-powdered charcoal, about two inches thick. Upon this layer of charcoal, or cement, a layer of iron bars is laid edgwise, leaving a space of an inch at each side, and also between each bar a space equal to the thickness of the bar. The bars

are to be within a couple of inches of the length of the box; but in case they are too short, small pieces may be used to make them of the requisite length. Above the first layer of iron, a layer of cement is spread, of half or three-quarters of an inch thick, and upon this another layer of bars with spaces, as in the first layer. The spaces between the bars are closely filled-in with charcoal powder, or cement; care must be exercised to have every crevice well

filled with cement.

The bars are never allowed to

touch each other or the trough. The boxes are filled to within six inches of the top, and this space is filled with the refuse cement of former operations. Finally, a layer of fine sand or mud is spread over this last cement. The material used for this purpose in Sheffield consists of the sand worn off of grindstones, which is a mixture of particles of iron, fine quartz, and a little clay or lime. This is called in Sheffield "wheelswarf," and makes a very close and compact cement, almost impervious to water and air.

THE CEMENT

Consists of ground charcoal, made from hard wood, sometimes mixed with soot, or of soot only. This charcoal powder is intimately mixed with one-eighth or one-tenth of its weight of wood-ashes, and a little common salt. Good steel is made without ashes or salt, by using simply charcoal powder; but the general practice is to use a cement of the kind above described.

WORKING OF A CONVERTING FURNACE.

When the boxes are well packed and covered, fire is kindled, and very gradually raised. For the first twenty-four hours the heat is merely sufficient to expel the moisture in the boxes, cement, and cover. A rapid heat will injure the stone slabs or bricks of which the chests are made. The fire is gradually increased so as to raise the heat a little every day; and at the end of six days, if it is designed to make spring-steel, the bars are ready to be drawn. Shearsteel requires eight days, and cast-steel from ten to twelve days, to be sufficiently cemented, or carbonized. Two days, and often a much longer time, are required to cool the furnace; after which the workmen enter it and discharge the steel bars. Twelve tons of steel are generally made in a double furnace. In a single furnace, or where there is but one chest, only six or eight tons are made at a time. For the purpose of enabling the workmen to charge and discharge the chests, iron plates are laid over the fire-brick arches, on which they stand.

THE DEGREE OF CEMENTATION

Is a nice point to determine, and cannot be decided by the length of time for which the iron has been exposed to the cementing process; practice must be had, and is always depended upon in wellregulated establishments. Experience teaches us that steel for coach-springs requires a low degree of conversion; after this comes blistered steel for common use; then, shear-steel, steel for cutlery, and steel for files. Cast-steel requires a higher degree of conversion than any other. Some steel, such as cast-steel for bits, is frequently returned to the box two or three times, and is then called twice or thrice-converted steel. The point where to stop cementation is decided by the steel-maker in drawing and trying the trial-rod, or rods. The trialrods are somewhat longer than the others; they reach at one end through the thickness of the slabs of which the chest is formed, and may be drawn out from between the other bars by a pair of tongs. The bar itself may be but three or four feet long. The trial-holes, marked in the cuts D D, are called "tap-holes;" they are but a few inches wide, and are closed around the trial-rods by clay or wheelswharf;

its

they are almost in the centre of the chest. An experienced steel-maker uses but one trial-rod, though some persons think it necessary to have two or three bars. If a trial-rod has been once drawn, it cannot be returned to the box; it is then broken, and from appearance on fracture the quality of the steel is adjudged. The fire is cautiously kept so low, that the highly converted steel at the bottom of the box does not melt. If it happens that it does melt in the box, it is generally converted into cast-iron, and is useless for steel. The success of this converting operation depends, therefore, in a great measure, indeed almost entirely, on the knowledge and sagacity of the steel-maker. On his care and judgment the avoidance of losses mainly depends. Too much stress cannot be laid upon this point.

GAIN IN WEIGHT.

The bars in the process of conversion gain about a half to three-fourths of one per cent. in weight. They are entirely covered with blisters, whence the name "blistered steel" is derived. The steel is very irregular in the different layers of the box, as also in each bar. The fracture of a bar is very crystalline,