220 CALORIC THE CAUSE OF OXIDATION, 



ceptible attraction for atmospheric oxygen ; 

 hence it is that in the polar regions, and during 

 excessive winters in the middle latitudes, metals 

 are not corroded by oxidation, but speedily ac- 

 quire a coating of rust in tropical climates.* The 

 process of oxidation augments with every ad- 

 dition of caloric up to the fusing point. It is 

 therefore preposterous to maintain, that the at- 

 traction of metals for oxygen is owing to some 

 inherent property of their particles, or that ca- 

 loric operates merely by overcoming their cohe- 

 sion, and thus enabling their chemical forces 

 to come into play. So powerful is the attraction 

 of iron for oxygen when raised to a white heat, 

 that it takes it from potassium, which, at ordi- 

 nary temperatures, is the most oxidable of all 

 the metals. As the attraction of potassium for 

 oxygen is known to be augmented by .every 

 increase of temperature, there is every reason 

 to believe that its latent caloric is the primary 

 and efficient cause of the chemical force by 

 which it is enabled to decompose water, and 

 even ice and that if its temperature could be 

 r 



* If a piece of cold polished iron be inserted into fluid mer- 

 cury, there is little or no attraction exerted between them ; but 

 if the iron be made red hot before immersion, it acquires a coat- 

 ing of mercury, which adheres firmly. Even gold, which ad- 

 heres to mercury at common temperatures, attracts it still more 

 powerfully when heated, and so of other metals. 



