Mr. J. Taylor's Lechires on MetaUuvgij. 285? 



The specific gravity in metals is different in those which 

 are merely fused or cast, and in those which are hammered or 

 laminated, by which they become more consolidated, and con- 

 sequently heavier. 



Th.e fusibility of metals is a property that eminently con- 

 tributes to their usefulness ; for without this it would be im- 

 possible to separate them from the earths and other impurities 

 with which they are naturally mixed ; not to mention the vast 

 advantage of produchig useful forms by the simple operation 

 of casting into moulds of any required shape. The range of 

 temperature at which various metals become fluid, extends from 

 the highest degree that our fiirnaces can produce, to a degree 

 of cold hardly ever occurring naturally. 



Thus, platina is scarcely fusible in the greatest furnace heat ; 

 Iron and some others require an intense white heat ; 

 Gold, silver, and copper, a bright red or low white heat ; 

 Antimony, a low red heat ; and tin, bismuth, lead, and zinc, 

 melt from about 450° Fahrenheit, to a temperature just under 

 a red heat; — 



While mercury is fluid unless it be in a state of cold equal 

 to about 40° below zero. 



At certain heats several of the metals may be volatilized, or 

 driven off in the state of vapour; and it is not improbable that 

 all may be so, if we could raise the temperature high enough. 

 But a considerable difference exists in this respect ; and advan- 

 tage is taken of it, in many processes of smelting and refining, 

 of thereby separating the one metal from the other; — those 

 which are called fixed metals remaining in the state of strong 

 ignition without evaporation, and those which are called vo- 

 latile rising in dense fumes. 



Mercury, arsenic, antimony and zinc, ai-e highly volatile. 

 Lead, tin and bismuth, are less so, but are evapoi'ated in 

 a strong fire ; — while gold, silver, copper and iron, are not 

 sublimed by any heat which we can usually employ. 



The next striking and valuable property is their extensi- 

 bility. This by the ancients was reckoned one of the essential 

 characters of metallic bodies ; but has ceased to continue so, 

 in consequence of the discovery of a number of metals desti- 

 tute of this ciuality. Its high importance however may be 

 well judged of, by observing that for almost all mechanical 

 purj)oses, the intrinsic value of metals is intimately dependent 

 on llieir extensibility. This property may be classed under 

 two iieads, — malleability, and ductility : that is to say, metals 

 may either l)e extended by hammering, when they are said 

 to be malleable: or by laminating, when they are said to be 

 ductile. 



The 



