CHAPTER XII 

 THE COMMON ELEMENTS OF THE EARTH 



158. Oxygen. Oxygen is the most abundant as well as 

 the most important of all the elements. Without it, there 

 could be no life. It has no color, odor, or taste. It does not 

 burn, but causes other substances to burn. It is a part of 

 the air we breathe, of the water we drink, and of almost 

 everything we use for food. As a pure element, however, 

 we have almost no practical use for oxygen. Physicians 



FIG. 74. BURNING IRON WIRE FIG. 75. UXYHYDROGEN LAMP 



FIG. 74. The end of a piece of iron wire tipped with a bit of burning 

 sulphur is put into a bottle of oxygen. The sulphur burns very brightly 

 and heats the end of the wire, which becomes dazzlingly bright and throws 

 off bright sparks. After the burning ceases, the inside of the jar is found 

 covered with a brown powder. 1. What could the powder be? 2. Why 

 does the burning stop before the iron is used up? 



FIG. 75. Acetylene, another combustible gas, is sometimes used instead 

 of hydrogen in such a lamp. The gas H is first turned on; it enters the tube 

 6, and is lighted at e. 1. How can it burn before the oxygen is turned on? 

 2. Oxygen passes through the tube a and out at c. Why is the flame hotter 

 after oxygen is turned on? 



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