224 



BOOK VII. 



anyone coming at an inopportune moment might disturb his thoughts when 

 they are intent on the work. It is also necessary for him to place his balances 

 in a case, so that when he weighs the little buttons of metal the scales may 

 not 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 in 

 shape, material, and the place in which it is set. In shape, they may be 

 round 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 a 

 chimney-hearth which is three and a half feet high ; the iron one is placed 

 in 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 digits 

 above the hearth — which is usually the thickness of an unbaked^ brick — 

 an iron plate is laid, and smeared over with lute on the upper side to prevent 

 it from being injured by the lire ; in front of the furnace above the plate is a 

 mouth a palm high, five digits wide, and rounded at the top. The iron plate 



A — Openings in the plate. B — P.^rt of plate which projects beyond the furnace. 



has three openings which are one digit wide and three digits long, one is at 

 each side and the third at the back ; through them sometimes the ash falls 

 from the burning charcoal, and sometimes the draught blows through the 

 chamber which is below the iron plate, and stimulates the fire. For this 

 reason this furnace when used by metallurgists is named from assaying, but 

 when used by the alchemists it is named from the wind^. The part of the 

 iron plate which projects from the furnace is generally three-quarters of a 



^Crudorum, — unbaked ? 



'This reference is not very clear. Apparently the names refer to the German terms 

 probier ofen and windt ofen. 



