80 Introduction to the Study of Science 



dazzling brilliance in oxygen. These are only a few typical 

 instances, but you would find the same result with a large 

 range of substances. Only a few, as gold and platinum, are 

 not affected by oxygen in this way. On the whole it may be 

 concluded that oxygen unites freely with burning or sufficiently 

 heated substances introduced into it. 



Another characteristic of oxygen is to be noted. You col- 

 lected it in bottles first filled with water. The gas, making 

 its way through the water to the surface, that is, to the bottom 

 of the bottle, forced the water downward and out until the gas 

 alone filled the space. This indicates that oxygen is not very 

 soluble in water. It is, however, slightly soluble, which is 

 especially important when considered in connection with a 

 fact of common experience that only in the presence of moisture 

 is oxygen active in rusting iron and certain other metals, in 

 fermentation and decay, and -in the drying of such oils as lin- 

 seed. Perfectly dry iron does not rust. But there is always 

 enough moisture in the atmosphere to enable oxygen to begin 

 its work on iron and other metals when these are not protected 

 as by a moisture-proof oil. 



In slow combustion, or oxidation as it is commonly called, 

 oxygen becomes more active as the temperature rises. In a 

 haystack or pile of oil-saturated rags, the temperature may 

 become so high as to cause spontaneous combustion. Hay 

 that is not thoroughly dry is favorable to oxidation. Oxygen 

 of the air uniting with the moistened substance effects chemical 

 changes that bring about a rise in the temperature. Hay is a 

 poor conductor of heat, which, being therefore largely retained 

 within the stack, accelerates the process of combustion. The 

 result may be a charred stack of hay and possibly an outburst 

 of flame if the charred substance is suddenly exposed to the air 

 or to a greater supply of oxygen. Oiled waste is similarly 

 oxidized and when the kindling temperature is reached, ignition 

 occurs. Thus heat increases the facility of oxygen in combining 

 with many substances. 



