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BOOK XII.

pegs or wedges driven into them. The vitriol adheres to these laths, andwithin the space of a few days congeals into cubes, which are taken awayand put into a chamber having a sloping board floor, so that the moisturewhich drips from the vitriol may flow into a tub beneath. This solution isre-boiled, as is also that solution which was left in the twelve tubs, for, byreason of its having become too thin and liquid, it did not congeal, and wasthus not converted into vitriol.

A—Wooden tub. B—Cross-bars. C—Laths. D—Sloping floor of the chamber.

E—Tub placed under it.

The fourth method of making vitriol is from vitriolous earth or stones.Such ore is at first carried and heaped up, and is then left for five or six monthsexposed to the rain of spring and autumn, to the heat of summer, and to therime and frost of winter. It must be turned over several times with shovels,so that the part at the bottom may be brought to the top, and it is thusventilated and cooled ; by this means the earth crumbles up and loosens,and the stone changes from hard to soft. Then the ore is covered with a roof,or else it is taken away and placed under a roof, and remains in that placesix, seven, or eight months. Afterward as large a portion as is required isthrown into a vat, which is half-filled with water; this vat is one hundred