CHAPTER V 

 HYDROGEN 



AFTER considering the atmosphere, and particularly its most 

 active component, we naturally turn to water, which, like air, is 

 so closely associated with our daily life. We find that water is a 

 compound of oxygen with hydrogen, and the latter element, 

 therefore, next claims our attention. Hydrogen is of interest 

 upon its own account. It is often used for filling balloons. Illumi- 

 nating gas, of the kind (water gas) used in most large cities, 

 consists of hydrogen to the extent of about 40 per cent. 



Preparation by the Action of Metals on Water. Hydro- 

 gen is not easily liberated from water, since this oxide of hydrogen, 

 like many other oxides, is very stable. It is necessary to use some 

 element with which oxygen will combine even more 

 eagerly than with hydrogen, and to off er this element 

 in exchange for the hydrogen. 



If a piece of one of the very active metals, such 

 as potassium, sodium, or calcium is thrown into water, 

 hydrogen is liberated and comes off in bubbles. 

 The former two metals are lighter than water, and 

 run about on the surface. The action with potassium 

 FIG 24 * s so v il en t that the hydrogen usually catches fire, 

 and both with sodium and potassium much heat is 

 produced. The action often ends with a slight explosion, so that 

 a glass plate should be held up to protect the eyes. This experi- 

 ment is too dangerous to be tried by a novice. With calcium 

 the action is rapid, but not violent, and there is no danger. The 

 metal sinks to the bottom of the vessel (Fig. 24), so that a test- 

 tube or bottle filled with water can be inverted over the metal to 



catch the gas as it ascends. 



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