268 EREMACAUSIS OR DECAY. 



from mucilage and other substances,, only twenty- 

 one volumes of carbonic acid were formed for every 

 146 volumes of oxygen gas absorbed. 



It must be remembered, that combustion or oxi- 

 dation at low temperatures produces results quite 

 similar to combustion at high temperatures with 

 limited access of air. The most combustible element 

 of a compound, which is exposed to the action of 

 oxygen, must become oxidized first, for its superior 

 combustibility is caused by its being enabled to unite 

 with oxygen at a temperature at which the other 

 elements cannot enter into that combination ; this 

 property having the same effect as a greater affinity. 



The combustibility of potassium is no measure 

 of its affinity for oxygen ; we have reason to 

 believe that the attraction of magnesium and 

 aluminium for oxygen is greater than that of potas- 

 sium for the same element ; but neither of those 

 metals oxidises either in air or water at common 

 temperatures, whilst potassium decomposes water 

 with great violence, and appropriates its oxygen. 



Phosphorus and hydrogen combine with oxygen 

 at ordinary temperatures, the first in moist air, the 

 second, when in contact with finely-divided plati- 

 num ; while charcoal requires a red heat before it 

 can enter into combination with oxygen. It is 

 evident that phosphorus and hydrogen are more 

 combustible than charcoal, that is, that their affi- 

 nity for oxygen at common temperatures is greater ; 

 and this is not the less certain, because it is found, 



