120 Introduction to the Study of Science 



with the result that the hydrogen is set free. Hydrochloric 

 acid makes the same sort of exchange. 



Exercise : To show properties and behavior of hydrogen. (1) Into 

 one bottle, held inverted, thrust a glowing, but not burning candle. 

 After you note the reaction, introduce a burning candle, which, se- 

 curely attached to a wire six inches long, should reach nearly to the 

 bottom of the bottle. The fire of the candle is extinguished, but the 

 gas in the bottle ignites. Withdraw the candle slowly, and it is 

 ignited by the burning gas. Does the flame of the gas show what sort 

 of gas it is? Hydrogen when not mixed with oxygen ignites without 

 explosion. 



(2) Place a .bottle upright on the table, open it for a moment, 

 and then throw a burning match into it. What happens? What 

 does the result indicate as to the cause of the difference in reaction 

 from that in the former test? Why does leaving the bottle uncov- 

 ered in an upright position make this difference in the contents of 

 the bottle ? Test your answer to the question by the following : 



(3) Hold a perfectly dry bottle mouth downward and directly over 

 the mouth of a bottle containing hydrogen. After a minute or so, cover 

 both bottles and stand in upright position. Drop into each a burning 

 match. What does the result show as to the content of the bottle 

 previously filled with air? What as regards that filled with hydrogen? 



When air and hydrogen mix in the bottles, the product is said to 

 be a mixture. But when oxygen and hydrogen unite in combustion, 

 the product, which is water, is said to be a compound. Are hydrogen 

 and oxygen more nearly like the separate gases when they form a 

 mixture or when they form a compound? You will find it helpful 

 to remember this distinction between mixture and compound. 



Does this test indicate which of the two, hydrogen or air, is the 

 heavier? What does the method of transferring hydrogen from one 

 bottle to another indicate as to its density in comparison with that 

 of air? 



(4) Test with burning candle to assure yourself that hydrogen 

 ignites without explosion when unmixed with oxygen, and burns with 

 a pale, bluish, almost invisible, but intensely hot flame. Observe 

 especially the heat produced. 



Summary of properties. Hydrogen is invisible, and has 

 neither taste nor odor. When you pour hydrogen from one 

 vessel into another, you must pour it upward as in a sort of 

 " looking-glass world." This indicates that it is lighter than 



