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BOOK VII.

anyone coming at an inopportune moment might disturb his thoughts whenthey are intent on the work. It is also necessary for him to place his balancesin a case, so that when he weighs the little buttons of metal the scales maynot be agitated by a draught of air, for that is a hindrance to his work.

Now I will describe the different things which are necessary in assaying,beginning with the assay furnace, of which one differs from another inshape, material, and the place in which it is set. In shape, they may beround or rectangular, the latter shape being more suited to assaying ores.The materials of the assay furnaces differ, in that one is made of bricks,another of iron, and certain ones of clay. The one of bricks is built on achimney-hearth which is three and a half feet high ; the iron one is placedin the same position, and also the one of clay. The brick one is a cubit high,a foot wide on the inside, and one foot two digits long ; at a point five digitsabove the hearth—which is usually the thickness of an unbaked 2 brick—an iron plate is laid, and smeared over with lute on the upper side to preventit from being injured by the fire ; in front of the furnace above the plate is amouth a palm high, five digits wide, and rounded at the top. The iron plate

A —Openings in the plate. B— Part of plate which projects beyond the furnace.

has three openings which are one digit wide and three digits long, one is ateach side and the third at the back ; through them sometimes the ash fallsfrom the burning charcoal, and sometimes the draught blows through thechamber which is below the iron plate, and stimulates the fire. For thisreason this furnace when used by metallurgists is named from assaying, butwhen used by the alchemists it is named from the wind 3 . The part of theiron plate which projects from the furnace is generally three-quarters of a

*Crudorum ,—unbaked ?

3 This reference is not very clear. Apparently the names refer to the German termsprobier ofen and windt ofen.