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BOOK XII. 



pegs or wedges driven into them. The vitriol adheres to these laths, and 

 within the space of a few days congeals into cubes, which are taken away 

 and put into a chamber having a sloping board floor, so that the moisture 

 which drips from the vitriol may flow into a tub beneath. This solution is 

 re-boiled, as is also that solution which was left in the twelve tubs, for, by 

 reason of its having become too thin and liquid, it did not congeal, and was 

 thus 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 months 

 exposed to the rain of spring and autumn, to the heat of summer, and to the 

 rime 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 thus 

 ventilated 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 place 

 six, seven, or eight months. Afterward as large a portion as is required is 

 thrown into a vat, which is half-filled with water ; this vat is one hundred 



