BOOK XII. 



577 



feet long, twenty-four feet wide, eight feet deep. It has an opening at the 

 bottom, so that when it is opened the dregs of the ore from which the vitriol 

 comes may be drawn off, and it has, at the height of one foot from the bottom, 

 three or four little holes, so that, when closed, the water may be retained, 

 and when opened the solution flows out. Thus the ore is mixed with water, 

 stirred with poles and left in the tank until the earthy portions sink to the 

 bottom and the water absorbs the juices. Then the little holes are opened, 

 the solution flows out of the vat, and is caught in a vat below it ; this vat is 

 of the same length as the other, but twelve feet wide and four feet deep. If 

 the solution is not sufficiently vitriolous it is mixed with fresh ore ; but if it 

 contains enough vitriol, and yet has not exhausted all of the ore rich in vitriol, 

 it is well to dissolve the ore again with fresh water. As soon as the solution 

 becomes clear, it is poured into the rectangular leaden caldron through 

 launders, and is boiled until the water is evaporated. Afterward as many thin 

 strips of iron as the nature of the solution requires, are thrown in, and then 

 it is boiled again until it is thick enough, when cold, to congeal into vitriol. 

 Then it is poured into tanks or vats, or any other receptacle, in which all of it 

 that is apt to congeal does so within two or three days. The solution which 

 does not congeal is either poured back into the caldron to be boiled again, or 



A CALDRON. B MOULDS. C CAKES. 



