44 Chemistry. [Lecture 25. 



this term we now reject, because it implies that 

 it is always the product of combustion, whereas 

 oxides are produced equally by the solution of 

 the metals in the acids, and afterwards preci- 

 pitating them by an alkali. 



Oxygen combines with the metals in different 

 proportions, and these products are marked by 

 modern chemists by the Greek numerals. The 

 protoxide means the metal combined with the 

 smallest portion of oxygen, dadojride.vnfa a still 

 larger portion, and peroxide the largest it is ca- 

 pable of receiving. 



Some of the metals become oxidized hy mere 

 exposure to the damp and moisture. In most 

 cases, however, heat is necessary ; and the perfect 

 metals, as they were formerly called, gold, silver, 

 and platinum, will not oxidize by h^at alone, but 

 require the agency of an acid, from which they 

 may be precipitated by an alkali in the state of 

 an oxide. 



All oxides are heavier than the quantity of 

 the metal which produced them in proportion 

 to the quantity of oxygen with which they are 

 combined. 



III. NITROGEN derives its name from being 

 the basis or constituent of the nitric acid. This 

 is proved by an easy experiment. If a tube is 

 inverted in mercury in the pneumatic apparatus 

 (Plate VI. fig. 19.), and filled with thirteen parts 

 of nitrogen gas and eighty-seven parts of oxygen 

 gas, and an electric spark is made to pass through 



