BOOK X.

441

The first of these consists of one libra of verdigris and three-quarters ofa libra of vitriol. For each libra there is poured over it one-sixth of a libraof spring or river water, as to which, since this pertains to all these com-pounds, it is sufficient to have mentioned once for all. The second com-position is made from one libra of each of the following, artificial orpiment,vitriol, lime, alum, ash which the dyers of wool use, one quarter of a libraof verdigris, and one and a half unciae of stibium. The third consists of threelibrae of vitriol, one of saltpetre, half a libra of asbestos, and half a libra ofbaked bricks. The fourth consists of one libra of saltpetre, one libra of alum,and half a libra of sal-ammoniac . 6

The furnace in which aqua valens is made 7 is built of bricks, rectangular,two feet long and wide, and as many feet high and a half besides. It iscovered with iron plates supported with iron rods ; these plates are smearedon the top with lute, and they have in the centre a round hole, large enough tohold the earthen vessel in which the glass ampulla is placed, and on each side ofthe centre hole are two small round air-holes. The lower part of the furnace,in order to hold the burning charcoal, has iron plates at the height of a palm,likewise supported by iron rods. In the middle of the front there is themouth, made for the purpose of putting the fire into the furnace ; this mouthis half a foot high and wide, and rounded at the top, and under it is thedraught opening. Into the earthen vessel set over the hole is placed cleansand a digit deep, and in it the glass ampulla is set as deeply as it is smearedwith lute. The lower quarter is smeared eight or ten times with nearly liquidlute, each time to the thickness of a blade, and each time it is dried again,until it has become as thick as the thumb ; this kind of lute is well beatenwith an iron rod, and is thoroughly mixed with hair or cotton thread, or withwool and salt, that it should not crackle. The many things of which thecompounds are made must not fill the ampulla completely, lest when boilingthey rise into the operculum. The operculum is likewise made of glass,and is closely joined to the ampulla with linen, cemented with wheat flourand white of egg moistened with water, and then lute free from salt is spreadover that par^ of it. In a similar way the spout of the operculum is joinedby linen covered with lute to another glass ampulla which receives the distilledaqua. A kind of thin iron nail or small wooden peg, a little thicker than aneedle, is fixed in this joint, in order that when air seems necessary to theartificer distilling by this process he can pull it out; this is necessary whentoo much of the vapour has been driven into the upper part. The four air-holes which, as I have said, are on the top of the furnace beside the largehole on which the ampulla is placed, are likewise covered with lute.

6 This list of four recipes is even more obscure than the previous list. If they weredistilled, the first and second mixtures would not produce nitric acid, although possibly somesulphuric would result. The third might yield nitric, and the fourth aqua regia. In viewof the water, they were certainly not used as cements, and the first and second are deficientm the vital ingredients.

7 Distillation, at least in crude form, is very old. Aristotle {Meteorologica, iv.) statesthat sweet water can be made by evaporating salt-water and condensing the steam.Dioscondes and Pliny both describe the production of mercury by distillation (note 58, p.432). Ihe Alchemists of the Alexandrian School, from the 1st to the 6th Centuries, men-d? „ orms imperfect apparatus—an ample discussion of which may be found in Kopp,Beitrage zur Geschichte der Chemie, Braunschweig, 1869, p. 217).