Chap. 1 8.] [ 109 ] 



CHAP. XVIII. 



METALS. 



Ijes of Metals. Their Properties. Weight, Opacity, Mattealil:'-?, 

 Ductility, FuJibility.Mix 4uith each other. '-'Their Inflammabilitf. 

 Calcination. Entire and Semi-metals. PerfeS and imperfta, 

 Natural Hijiory of Metals. Working of Mines. AJ/~aying.- 

 Smelting.-* "Union <voith Acids. -Ariion of other Subftances on .Ml?- 

 t!s. 



METALLIC fubftances are valuable for their 

 durability, their capacity of affuming and re- 

 taining all forts of forms and impreflions; the clofeneis 

 of their texture, which renders them capable of polifh j 

 the firm cohefion of their particles, which renders them 

 highly proper for utenfils, where great ilrength is 

 required to be combined with moderate bulk. Several 

 of the metals are alfo highly ufeful as medicines. 



The firft and moft obvious property of metals is 

 their remarkable weight, in which they exceed ail other 

 "bodies. By this circumftance they are diftinguifhed 

 from earths ; the Hghteft of metals, which is tin, being 

 feven times the weight of water, whereas the heavieft 

 earth is only between four and five times the weight 

 of that fluid. 



Metallic fubftances are by far the mod opake of 

 all bodies. The moil opake ftone divided into thin 

 plates, ha,s more or lefs of tranfparency, whereas gold 

 is the only metal which admits of being reduced to 

 fuch a degree of thinnefs as to afford the fmalleft 

 perceptible tranfmiffion of light. Gold in leaf, which 

 is about -i-roV^-B- P art ^ an i nc ^ ^ n thicknefs, tranfmits 

 light of a lively green colour , but filver and brafs leaf 



are 



