EXERCISE 30 



WHAT IS THE NATURE OF HYDROGEN THE MORE ABUNDANT GAS FORMED IN 



THE DECOMPOSITION OF WATER? 



Materials. An apparatus like that shown in Fig. 36, page 64, of "Elements of General Science"; 

 some mossy or granulated zinc ; concentrated hydrochloric or sulphuric acid ; test tubes ; wide- 

 mouthed bottles ; pine splints. 



Directions. This experiment should be performed by the teacher. Since a mixture of hydrogen 

 and air is explosive, a flame should never be brought near the generator by one who is inexperienced 

 in handling the gas. 



Put into the generator bottle a small handful of fragments of zinc (granulated, mossy, or sheet 

 zinc, or iron). Place the stopper in the mouth of the bottle. Add enough water through the funnel 

 tube to cover the zinc and the end of the funnel tube. Now add about 10 cubic centimeters of con- 

 centrated hydrochloric or sulphuric acid. Observe what happens. Do not collect the gas which first 

 escapes from the tube. This is air or a mixture of air and hydrogen. Now collect two bottles of 

 the gas as in Exercise 29 ; cover these with glass plates and set aside for the tests c and d below. 

 More acid may be added if necessary. Also collect two test tubes of the gas for tests a and b. 



a. Hold a tube of the gas mouth downward for a minute, and then bring a flame to the mouth of 

 the tube. What occurs ? 



b. Hold a second tube of the gas mouth upward for one minute, and then bring a lighted match 

 near the mouth of the tube. Does anything happen ? What do the results of a and b show relative 

 to the weight of the gas in comparison with that of the air ? 



c. Bring a flame to the mouth of a bottle of the gas and see if the gas burns. Note the color 

 of the flame. 



d. Thrust a long flaming splint into the second bottle of the gas, the bottle having been inverted, 

 and note the result. Does the gas support the combustion of the splint? Hold the splint in the 

 bottle and see if it will be relighted by the burning gas. 



Additional problems. Soap bubbles may be made by use of hydrogen gas if the gas is first purified by 

 being passed through a solution of caustic soda. 

 Why is hydrogen used in dirigible balloons ? 



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