8 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



known metal, although the use of iron had superseded 

 that of bronze partially amongst the Gauls and other Celtic 

 races. LEAD was known to the Romans at the time of their 

 conquest of Britain ; the mining of lead ores was carried 

 on by them in Derbyshire and in other parts of the island. 

 Fire was also used as an agent in the purification of the 

 so-called " noble metals," gold and silver, from baser im- 

 purities, such as tin and lead, the latter being converted into 

 dross. The dross obtained by burning lead in order to 

 separate it from the silver which it contained, received 



a special name, 



LITHARGE, that 



is, the stone 

 (Greek, Ai<9os) 

 obtained from 

 silver (Greek, 

 apyvpos) ; it was 

 valued because 

 it could be con- 

 verted by gentle 

 roasting into the 

 scarlet paint 

 known as 



MINIUM Or RED 



FIG. 6 ARROWHEAD CRYSTALS OF MARCASITE 

 British Museum (Natural History). 



LEAD. 



Substances produced by weathering or decay. New 



materials were also obtained by the natural processes of 

 weathering or decay. SALTPETRE, WINE, and VINEGAR have 

 been mentioned as examples of this kind, but special 

 reference may be made to the green, glassy substance which 

 is formed when the minerals MARCASITE and PYRITES (Figs. 

 6, 7, 8) are allowed to weather. The brilliant golden nodules 

 of marcasite, which in England are often found as " thunder- 

 bolts," embedded in the chalk, decay and become " rusty " 

 almost as easily as iron. When the rusty mass is extracted 



