Metals^ 245 



Of the forty-two metals at present known, 

 only eleven had been discovered before the year 

 1 730. Those of the first class are the most use- 

 ful, and most generally known. Antimony and 

 arsenic are chiefly remarkable for the use of their 

 oxides and compounds in medicine ; cobalt and 

 manganese are useful in the manufactures of 

 china and glass. Bismuth, dissolved in an acid, 

 and precipitated in the form of an oxide, pro- 

 duces that pernicious cosmetic called pearl white. 

 The new metals have not been found, as yet, of 

 any use whatever, and are only objects of cu- 

 riosity to the mineralogist. 



I shall conclude this lecture with a summary 

 view of the most remarkable properties observ- 

 able in the metallic bodies of the first class, 

 which are by far the most important. 



1st. Gold, as the most precious of the metals, 

 holds the first rank. It is more ductile and 

 malleable (that is, more easily beaten out with a. 

 hammer) than most metals; but it has less of 

 tenacity than some others. It is unalterable in 

 lire, or by exposure to air or water. In philo- 

 sophical language, it is not oxidizable by these 

 means. From its unchangeable nature and beau- 

 tiful appearance, as well as its scarcity, it has been 

 adopted as a standard of value for the transfer of 

 all other commodities. 



Gold is, however, not altogether unchangeable; 

 for it may be dissolved by the nitro-muriatic acid 

 (commonly called, on this account, aqua regia), 

 and also by the oxygenated muriatic acid. If a 



