OXYGEN. 



349 



been liquified under tremendous pressure at a very low temperature. 



Oxygen causes any red-hot substance plunged into it to burn brightly ; a 



match will readily inflame if a. spark be 



remaining, while phosphorus is exceedingly 



brilliant, and these appearances, with many 



others equally striking, are caused by the 



affinity for those substances possessed by 



the gas. Combustion is merely oxidation, 



just as the process of rusting is, only in the 



latter case the action is so slow that no 



sensible heat is produced. But when an Fi * -- showing retort placed in fl " 



aggregate of slowly oxidising masses are heaped together, heat is generated, 



and at length bursts into flame. This phenomenon is called " spontaneous 



combustion." Cases have been known in which the gases developed 



Fig- 335. The generation of oxygen from oxide of manganese and potash. 



in the human body by the abuse of alcoholic drinks have ended fatally ; 

 in like manner the body being completely charred. (Combustion must 

 not be confounded with ignition, as in the electric light.) Oxygen then, 

 we see, is a great supporter of combustion, though not a combustible itself 

 as coal is. When the chemical union of oxygen with another substance 

 is very rapid an explosion takes place. 



Oxidation occurs in various ways. Besides those already mentioned, 

 all verdigris produced on copper, all decays of whatever kind, disintegration, 

 and respiration, are the effects of oxygen. The following experiment for the 

 extraction of oxygen directly from the air was made by M. Boussingault, 

 who passed the gas upon a substance at a certain temperature, and released 

 it at a higher. The illustration on page 351 will show the way in which 

 the experiment was performed. 



