STUDY OF HYDROGEN. 15 



after removing it from the tray of 

 water. (If the hydrogen does not 

 come off in sufficient quantity, 

 add some more hydrochloric acid 

 to the zinc in the bottle.) 

 3. To obtain pure hydrogen, first pass it 

 through a solution of potassium per- 

 manganate in a glass bottle and then col- 

 lect it in a tray of water. This solution 

 removes the impurities from the hydro- 

 gen. (See Fig. 3.) 

 B. Properties of hydrogen. 



1. What are some of the physical properties 



of hydrogen? Hydrogen is the lightest 

 known substance. Why, therefore, are 

 the bottles kept upside down? 



2. Carefully lift one of the bottles of hydrogen 



and thrust up into the mouth a burning 

 splinter of wood. 



a. Does the carbon continue to burn? 



b. What do you notice? What is the 



color of the flame? 



c. How, then, does hydrogen differ from 



oxygen? from nitrogen? 



3. Remembering that a mixture of oxygen 



and hydrogen may cause a dangerous 

 explosion, collect a test-tube of hydro- 

 gen to make sure that all the oxygen has 

 been driven out of the bottle and deliv- 

 ery-tube. Remove the end of the de- 

 livery-tube from the water and attach 

 a piece of glass tubing that has been 



