168 Fossils. 



and on this depends their very useful 

 property of becoming capable of being 

 -welded. 



Almost all metals may be combined 

 by fusion into one seemingly homogene- 

 ous mass, and from thence various metal- 

 lic mixtures, metallic alloys, or composi- 

 tions arise ; which, for their particular 

 properties, are often of very great utility. 



If metals be continued in fusion, the} 

 lose their brilliancy, and become an opaque 

 powder, or what is termed a metallic oxyd 

 or calx. 



All metals, gold, silver, and platina, 

 excepted, are oxyded or calcined in fire 

 with access of air. In this respect, those 

 which cannot be oxyed by fire have recei- 

 . ved the name of noble metals, to distin- 

 guish them from the rest which may be 

 calcined that way, and are called base 

 metals. 



Gold is a noble metal, of a yellow colour; 

 and, after platina, the heaviest of metals. 

 Its specific gravity is from 19,258 to 19,- 

 640. Its hardness and elasticity are in- 

 considerable ; but its tenacity is great ; 

 and with regard to ductility, or malleabili- 

 ty it exceeds all other metallic substances. 



