82 Introduction to the Study of Science 



intense the heat. It is this property which makes oxygen 

 useful in many industries, being utilized in generating very 

 high temperatures needed in working with metals, as in welding, 

 cutting, and the like. It is combined in practically pure form 

 with some highly combustible substance, such as hydrogen 

 or acetylene gas. The flame of hydrogen and oxygen gives a 

 temperature of approximately 4000 F. ; while the oxyacety- 

 lene flame gives about 6500 F. at the hottest point. Students 

 will find in current magazines accounts of the various industrial 

 uses of oxygen and may report on such to the class. 



Abundance of oxygen. From the chemist's point of view 

 oxygen is one of the most active substances known. It unites 

 freely with practically all other substances. It is also one of 

 the most abundant of known elements. It forms about one 

 fifth of the atmosphere and eight ninths of the water; it 

 enters largely into the composition of almost all kinds of 

 rocks, and into all forms of living matter. It is estimated 

 to constitute about forty-eight per cent by weight of the 

 whole surface of the earth, of all that the earth contains, and 

 of the air enveloping it (page 433). 



SUMMARY 



Our knowledge of the nature of fire dates from the time of Lavoisier, 

 in the last quarter of the eighteenth century. 



Lavoisier showed that burning is oxidation. 



Only oxygen, which constitutes about one fifth of the volume of 

 the air, is useful in burning. The remaining four fifths is mainly 

 nitrogen, which is an indispensable element in the foods of plants and 

 animals. 



Oxygen is active in burning, nitrogen is inert and dilutes the oxy- 

 gen of the air. 



Oxygen may be obtained by heating various compounds, such as 

 potassium chlorate. 



Pure oxygen supports rapid combustion, even of iron. 



Oxygen is a colorless, odorless, tasteless gas, slightly soluble in 

 water. 



Oxygen dissolved in water causes the rusting of iron. 



