172 Fossils. 





in open fire, without addition, whereby 

 it is rendered capable of being cast into 

 moulds. The colour of crude iron is 

 more or less of a pale grey. 



Steel differs from both the ductile and 

 the crude iron. Its distinguishing pro- 

 perty is, that when it is tempered^ that 

 is to say, when it is hastily plunged in 

 cold water while ignited to redness, it be- 

 comes harder, more brittle, and inflexi- 

 ble ; and that, before this tempering or 

 hardening, it is ductile, whether cold or 

 ignited ; and also, that after having been 

 hardened, it reassumes its ductility by a 

 fresh igniton and gradual cooling, with- 

 out quenching. Its colour is a light grey, 

 its fracture finely granular. 



Cobalt is a base metal, of a lead grey 

 colour, brittle and hard, and of specific 

 gravity from 7,000 to 7,700. This metal 

 is rather of difficult fusion. 



Tin is a base metal of a white colour, 

 a little more verging to blue than that of 

 silven -It is very soft, pretty malleable 

 and tractable ; its compactness and elas- 

 ticity are but slight. When broken or 

 bent, or when compressed betwen the 

 teeth, it makes a peculiar crackling noise 7 



