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BOOK VII.
holes, the ashes from the burning charcoal, as I have stated, fall down, andair blows into the furnace after passing through the openings in the walls ofthe chamber. The furnace is rectangular, and inside at the lower part it isthree palms and one digit wide and three palms and as many digits long. Atthe upper part it is two palms and three digits wide, so that it also growsnarrower ; it is one foot high ; in the middle of the back it is cut out atthe bottom in the shape of a semicircle, of half a digit radius. Notunlike the furnace before described, it has in its forepart a mouth which isrounded at the top, one palm high and a palm and a digit wide. Its dooris also made of clay, and this has a window and a handle ; even the lidof the furnace which is made of clay has its own handle, fastened on with ironwire. The outer parts and sides of this furnace are bound with iron wires,which are usually pressed in, in the shape of triangles. The brick furnacesmust remain stationary ; the clay and iron ones can be carried from oneplace to another. Those of brick can be prepared more quickly, while thoseof iron are more lasting, and those of clay are more suitable. Assayersalso make temporary furnaces in another way; they stand three brickson a hearth, one on each side and a third one at the back, the fore-part liesopen to the draught, and on these bricks is placed an iron plate, upon whichthey again stand three bricks, which hold and retain the charcoal.
The setting of one furnace differs from another, in that some are placedhigher and others lower ; that one is placed higher, in which the man who isassaying the ore or metals introduces the scorifier through the mouth with thetongs ; that one is placed lower, into which he introduces the cruciblethrough its open top.
In some cases the assayer uses an iron hoop 4 in place of a furnace ;this is placed upon the hearth of a chimney, the lower edge being daubedwith lute to prevent the blast of the bellows from escaping under it.If the blast is given slowly, the ore will be smelted and the copper will melt inthe triangular crucible, which is placed in it and taken away again with thetongs. The hoop is two palms high and half a digit thick ; its diameter isgenerally one foot and one palm, and where the blast from the bellows entersinto it, it is notched out. The bellows is a double one, such as goldworkersuse, and sometimes smiths. In the middle of the bellows there is a board inwhich there is an air-hole, five digits wide and seven long, covered by alittle flap which is fastened over the air-hole on the lower side of the board ;this flap is of equal length and width. The bellows, without its head, isthree feet long, and at the back is one foot and one palm wide andsomewhat rounded, and it is three palms wide at the head ; the head itselfis three palms long and two palms and a digit wide at the part where it joinsthe boards, then it gradually becomes narrower. The nozzle, of which thereis only one, is one foot and two digits long ; this nozzle, and one-half of thehead in which the nozzle is fixed, are placed in an opening of the wall, thisbeing one foot and one palm thick ; it reaches only to the iron hoop on the
l Circulus. This term does not offer a very satisfactory equivalent, as such a furnacehas no distinctive name in English. It is obviously a sort of forge for fusing in crucibles.