BOOK VII.

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palm long and a palm wide ; small pieces of charcoal, after being laid thereon,can be placed quickly in the furnace through its mouth with a pair of tongs,or again, if necessary, can be taken out of the furnace and laid there.

The iron assay furnace is made of four iron bars a foot and a half high,which at the bottom are bent outward and broadened a short distance to enablethem to stand more firmly ; the front part of the furnace is made from twoof these bars, and the back part from two of them ; to these bars on bothsides are joined and welded three iron cross-bars, the first at a height of a palmfrom the bottom, the second at a height of a foot, and the third at the top.The upright bars are perforated at that point where the side cross-bars arejoined to them, in order that three similar iron bars on the remaining sidescan be engaged in them ; thus there are twelve cross-bars, which makethree stages at unequal intervals. At the lower stage, the upright bars aredistant from each other one foot and five digits; and at the middle stage thefront is distant from the back three palms and one digit, and the sides aredistant from each other three palms and as many digits; at the highest stagefrom the front to the back there is a distance of two palms, and between thesides three palms, so that in this way the furnace becomes narrower at thetop. Furthermore, an iron rod, bent to the shape of the mouth, is set intothe lowest bar of the front; this mouth, just like that of the brick furnace,is a palm high and five digits wide. Then the front cross-bar of the lowerstage is perforated on each side of the mouth, and likewise the back one ;through these perforations there pass two iron rods, thus making altogetherfour bars in the lower stage, and these support an iron plate smeared withlute ; part of this plate also projects outside the furnace. The outside ofthe furnace from the lower stage to the upper, is covered with iron plates,which are bound to the bars by iron wires, and smeared with lute to enablethem to bear the heat of the fire as long as possible.

As for the clay furnace, it must be made of fat, thick clay, medium sofar as relates to its softness or hardness. This furnace has exactly the sameheight as the iron one, and its base is made of two earthenware tiles, onefoot and three palms long and one foot and one palm wide. Each side of thefore part of both tiles is gradually cut away for the length of a palm, sothat they are half a foot and a digit wide, which part projects from thefurnace ; the tiles are about a digit and a half thick. The walls are similarlyof clay, and are set on the lower tiles at a distance of a digit from the edge,and support the upper tiles ; the walls are three digits high and have fouropenings, each of which is about three digits high ; those of the back part andof each side are five digits wide, and of the front, a palm and a half wide, toenable the freshly made cupels to be conveniently placed on the hearth, whenit has been thoroughly warmed, that they may be dried there. Both tilesare bound on the outer edge with iron wire, pressed into them, so that theywill be less easily broken; and the tiles, not unlike the iron bed-plate, havethree openings three digits long and a digit wide, in order that when the upperone on account of the heat of the fire or for some other reason has becomedamaged, the lower one may be exchanged and take its place. Through these