BOOK VIII. 



349 



teeth, and now again levelled down with a hoe, both of which are made of iron. 

 The very fine tin-stone requires to be burned less than that of moderate size, 

 and this again less than that of the largest size. While the tin-stone is being 

 thus burned, it frequently happens that some of the material runs together. 



A — Furnace. B — Its mouth. C — Poker. D — Rake with two teeth. E — Hoe. 



The burned tin-stone should then be washed again on the strake, for in this 

 way the material which has been run together is carried away by the water 

 into the cross-trough, where it is gathered up and worked over, and again 

 washed on the strake. By this method the metal is separated from that 

 which is devoid of metal. 



Cakes from pyrites, or cadmia, or cupriferous stones, are roasted in quad- 

 rangular pits, of which the front and top are open, and these pits are generally 

 twelve feet long, eight feet wide, and three feet deep. The cakes of melted 

 pyrites are usually roasted twice over, and those of cadmia once. These latter 

 are first rolled in mud moistened with vinegar, to prevent the fire from con- 

 suming too much of the copper with the bitumen, or sulphur, or orpiment, or 

 realgar. The cakes of pyrites are first roasted in a slow fire and afterward in 

 a fierce one, and in both cases, during the whole following night, water is let in. 



