434 METALLIC ELKMENTS. 



All the metals are capable of uniting with oxygen, but they 

 differ greatly from each other in their affinity for that ele- 

 ment. The greater number of them absorb oxygen from dry 

 air at the usual temperature, and undergo oxidation, which 

 is only slight and superficial in many, when they are in mass, 

 but may be complete and perfect in the same metals, when they 

 are highly divided, and in a favourable state for combination, 

 as in the lead and iron pyrophorus exposed to air. The same 

 metals exhibit, at a high temperature, a more intense affinity 

 for oxygen, and combine with combustion. The only metals 

 which do not unite with oxygen directly in any circumstances 

 are silver, palladium, platinum, gold, and probably rhodium 

 and iridium. 



The metals have been arranged in six groups or sections, 

 differing in their degrees of oxidability. 1. Metals which de- 

 compose water even at 32, with lively effervescence, namely, 

 potassium, sodium, lithium, barium, strontium, calcium, and 

 probably magnesium. 2. Metals which do not decompose 

 water at 32, like the metals of the preceding class; they do not 

 decompose it with a lively effervescence, except at a tempera- 

 ture approaching 212 or even higher, but always much below 

 a red heat. In this class are found glucinum, aluminum, 

 zirconium, thorium, yttrium, cerium, and manganese. 3. Me- 

 tals which do not decompose water except at a red heat, or 

 at the ordinary temperature with the presence of strong acids. 

 This section comprehends iron, nickel, cobalt, zinc, cadmium, 

 tin, chromium, and probably vanadium. Iron is rapidly cor- 

 roded in water containing carbonic acid, with the evolution of 

 hydrogen. 4. Metals which decompose the vapour of water 

 at a red heat with considerable energy, but which do not de- 

 compose water in presence of the strong acids. They are 

 tungsten, molybdenum, osmium, columbium, titanium, anti- 

 mony, and uranium. These metals appear to be incapable of 

 decomposing water in contact with acids, because their oxides 

 have but a small basic power, being indeed bodies which are 

 ranked among the acids. 5. Metals of which the oxides are 

 not decomposed by heat alone, and which decompose water only 

 in a feeble manner, and at a very high temperature. They are 

 also distinguished from the preceding class by their tendency to 

 form basic and not acid oxides. These metals are copper, lead, 

 and bismuth. G. Metals of which the oxides are reducible by 



