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BOOK XI.

are so placed on the sole-stones that they project a palm at the sides, and at thefront the sole-stones project to the same extent; if rectangular stones arenot available, bricks are laid in their place. The copper plates are four feettwo palms and as many digits long, a cubit wide, and a palm thick ; eachedge has a protuberance, one at the front end, the other at the back; theseare a palm and three digits long, and a palm wide and thick. The plates areso laid upon the rectangular stones that their rear ends are three digits fromthe third long wall; the stones project beyond the plate the same numberof digits in front, and a palm and three digits at the sides. When the plateshave been joined, the groove which is between the protuberances is a palmand three digits wide, and four feet long, and through it flows the silver-leadwhich liquates from the cakes. When the plates are corroded either by thefire or by the silver-lead, which often adheres to them in the form of stalac-tites, and is chipped off, they are exchanged, the right one being placed to theleft, and the left one, on the contrary, to the right; but the left side of theplates, which, when the fusion of the copper took place, came into contactwith the copper, must lie flat; so that when the exchange of the plates hasbeen carried out, the protuberances, which are thus on the underside, raisethe plate from the stones, and they have to be partially chipped off, lest theyshould prove an impediment to the work ; and in each of their places islaid a piece of iron, three palms long, a digit thick at both ends, and a palmthick in the centre for the length of a palm and three digits.

The passage under the plates between the rectangular stones is a footwide at the back, and a foot and a palm wide at the front, for it graduallywidens out. The hearth, which is between the sole-stones, is covered with abed of hearth-lead, taken from the crucible in which lead is separated fromsilver. The rear end is the highest, and should be so high that it reaches towithin six digits of the plates, from which point it slopes down evenly to thefront end, so that the argentiferous lead alloy which liquates from the cakescan flow into the receiving-pit. The wall built against the third long wallin order to protect it from injury by fire, is constructed of bricks joinedtogether with lute, and stands on the copper plates ; this wall is two feet, apalm and two digits high, two palms thick, and three feet, a palm and threedigits wide at the bottom, for it reaches across both of them ; at the top it isthree feet wide, for it rises up obliquely on each side. At each side of this wall,at a height of a palm and two digits above the top of it, there is inserted in ahole in the third long wall a hooked iron rod, fastened in with molten lead;the rod projects two palms from the wall, and is two digits wide and onedigit thick ; it has two hooks, the one at the side, the other at the end.Both of these hooks open toward the wall, and both are a digit thick, andboth are inserted in the last, or the adjacent, links of a short iron chain. Thischain consists of four links, each of which is a palm and a digit long and halfa digit thick ; the first link is engaged in the first hole in a long iron rod, andone or other of the remaining three links engages the hook of the hooked rod.The two long rods are three feet and as many palms and digits long, twodigits wide, and one digit thick; both ends of both of these rods have holes,