Outside each furnace hearth there is a small pit full of powder which is compressed by ramming, and in this manner is made the forehearth which receives the metal flowing from the furnaces. Of this I will speak later.
In this manner the front part of the building is made, and is divided into three parts; the first part is twelve feet wide and is under the hood, which consists of two walls, one vertical and one inclined. The second part is the same number of feet wide and is for the reception of the ore to be smelted, the fluxes, the charcoal, and other things which are needed by the smelter. The third part is nine feet wide and contains two separate rooms of equal size, in one of which is the assay furnace, while the other contains the metal to be melted in the cupellation furnaces. It is thus necessary that in the building there should be, besides the four long walls, seven transverse walls, of which the first is constructed from the upper end of the first long wall to the upper end of the second long wall; the second proceeds from the end of this to the end of the third long wall; the third likewise from this end of the last extends to the end of the fourth long wall; the fourth leads from the lower end of the first long wall to the lower end of the second long wall; the fifth extends from the end of this to the end of the third long wall; the sixth extends from this last end to the end of the fourth long wall; the seventh divides into two parts the space between the third and fourth long walls.
To return to the back part of the building, in which, as I said, are the bellows[6], their frames, the machinery for compressing them, and the instrument for distending them. Each bellows consists of a body and a head. The body is composed of two "boards," two bows, and two hides. The upper board is a palm thick, five feet and three palms long, and two and a half feet wide at the back part, where each of the sides is a little curved, and it is a cubit wide at the front part near the head. The whole of the body of the bellows tapers toward the head. That which we now call the "board" consists of two pieces of pine, joined and glued together, and of two strips of linden wood which bind the edges of the board, these being seven digits wide at the back, and in front near the head of the bellows one and a half digits wide. These strips are glued to the boards, so that there shall be less damage from the iron nails driven through the hide. There are some people who do not surround the boards with strips, but use boards only, which are very thick. The upper board has an aperture and a handle; the aperture is in the middle of the board and is one foot three palms distant from where the board joins the head of the bellows, and is six digits long and four wide. The lid for this aperture is two palms and a digit long and wide, and three digits thick; toward the back of the lid is a little notch cut into the surface so that it may be caught by the hand; a groove is cut out of the top of the front and sides, so that it may engage in mouldings a palm wide and three digits thick, which are also cut out in a similar manner under the edges. Now, when the lid is drawn forward the hole is closed, and when drawn back it is opened; the smelter opens the aperture a little so that the air may escape from the bellows through it, if he fears the hides might be burst when the bellows are too vigorously and quickly inflated; he, however, closes the aperture if the hides are ruptured and the air escapes. Others perforate the upper board with two or three round holes in the same place as the rectangular one, and they insert plugs in them which they draw out when it is necessary. The wooden handle is seven palms long, or even longer, in order that it may extend outside; one-half of this handle, two palms wide and one thick, is glued to the end of the board and fastened with pegs covered with glue; the other half projects beyond the board, and is rounded and seven digits thick. Besides this, to the handle and to the board is fixed a cleat two feet long, as many palms wide and one palm thick, and to the under side of the same board, at a distance of three palms from the end, is fixed another cleat two feet long, in order that the board may sustain the force of distension and compression; these two cleats are glued to the board, and are fastened to it with pegs covered with glue.
The lower bellows-board, like the upper, is made of two pieces of pine and of two strips of linden wood, all glued together; it is of the same width and thickness as the upper board, but is a cubit longer, this extension being part of the head of which I have more to say a little later. This lower bellows-board has an air-hole and an iron ring. The air-hole is about a cubit distant from the posterior end, and it is midway between the sides of the bellows-board, and is a foot long and three palms wide; it is divided into equal parts by a small rib which forms part of the board, and is not cut from it; this rib is a palm long and one-third of a digit wide. The flap of the air-hole is a foot and three digits long, three palms and as many digits wide; it is a thin board covered with goat skin, the hairy part of which is turned toward the ground. There is fixed to one end of the flap, with small iron nails, one-half of a doubled piece of leather a palm wide and as long as the flap is wide; the other half of the leather, which is behind the flap, is twice perforated, as is also the bellows-board, and these perforations are seven digits apart. Passing through these a string is tied on the under side of the board; and thus the flap when tied to the board does not fall away. In this manner are made the flap and the air-hole, so when the bellows are distended the flap opens, when compressed it closes. At a distance of about a foot beyond the air-hole a slightly elliptical iron ring, two palms long and one wide, is fastened by means of an iron staple to the under part of the bellows-board; it is at a distance of three palms from the back of the bellows. In order that the lower bellows-board may remain stationary, a wooden bolt is driven into the ring, after it penetrates through the hole in the transverse supporting plank which forms part of the frame for the bellows. There are some who dispense with the ring and fasten the bellows-board to the frame with two iron screws something like nails.