EXERCISE 29 



WHAT IS THE NATUKE OF OXYGEN THE LESS ABUNDANT GAS FORMED IN 



THE DECOMPOSITION OF WATER ? 



Materials. Some test tubes ; potassium chlorate ; a short piece of glass tubing ; a piece of rubber 

 tubing ; pine splints ; a few wide-mouthed bottles ; some glass plates about 2 inches square ; 

 sulphur ; iron picture wire ; a candle. 



Directions. This experiment may be performed by the teacher or by the pupils working in 

 groups of two. 



Place enough potassium chlorate in a test tube to make a layer about three fourths of an inch 

 deep, and arrange a delivery tube to collect over water 

 the gas which is formed when the potassium chlorate is 

 heated. Fill a test tube with the gas, after having allowed 

 the gas to form from the chlorate long enough to expel 

 the air from the generator. 



a. Note the odor and color of the gas. (The gas should 

 first be washed by shaking it with some water in a test 



tube sealed with the thumb.) Now take an ordinary match or a pine splint which is glowing, but not 

 flaming, and thrust it into the tube. Does the match burn brighter ? 



b. Try to light the gas with a flaming match to see if it will burn. 



c. Test the gas to see if it is lighter or heavier than air by holding a glowing splint above a tube 

 of oxygen, and then invert the tube and hold the glowing splint below the tube. What is the result ? 



d. Fill a bottle with the gas, collecting it over water as illustrated. Unbraid the end of a 10-inch 

 length of ordinary picture wire, heat it for a moment, and dip it into some 'sulphur or paraffin. 

 Ignite the sulphur or paraffin and thrust it into the bottle of gas, and observe what happens. 



e. By means of a wire, lower a short, burning candle into a second bottle of the gas. What 

 occurs ? 



Additional problems. Does oxygen support combustion of a piece of wood better than air does ? 

 Would the iron of iron-framed buildings be fireproof if the air were composed entirely of oxygen ? 

 Would it be of advantage for the blacksmith to use oxygen instead of air in the bellows to blow the 

 fire with which he heats his iron ? 



