96 METALS. 



of them may be hardened by art: thus the moderns 

 make cutting instruments of iron and steel, and 

 the ancients made them of a combination of cop- 

 per and tin. 



All the metals are capable of combining with 

 oxygen, and thus forming oxides ; but they differ 

 very much in the readiness with which they com- 

 bine with it, which occasions their division into 

 several classes. 



The oxides of metals have none of the metallic 

 brilliancy, and no malleability : their appearance 

 and nature are totally different from that of the 

 metals themselves. 



The oxides of some metals, as potassium and so- 

 dium, are akaline ; others are acid, constituting the 

 metallic acids : the rest have neither acid nor alca- 

 line properties, but are, as well as others, capable 

 of being dissolved by the acids, thus forming salts. 



Some of the metals attract oxygen so strongly, 

 that they become oxidized almost immediately in 

 the open air, and even take oxygen from all its 

 combinations, so that they are, with great difficulty, 

 preserved in the metallic state ; of this nature are 

 metals that produce the alkalies and earths, which 

 can only be kept in pure bitumen called naphtha, 

 which has no oxygen in its composition. 



Some of the metals do not experience any 

 change on being kept in fusion by a strong heat 

 with an access of air ; but others are by this means 

 converted into oxides. The first have been called 

 perfect metals, and comprehend gold, platina, sil- 

 ver, and palladium. The rest differ very much in 

 the degree of heat necessary to oxidize them. 

 Arsenic, manganese, and the bases of the earths 

 and alkalies become oxides at the usual temperature 

 of the atmosphere, even when perfectly dry. Lead 



