EXERCISE IV. 

 OXYGEN— AN ELEMENT OF PLANT FOOD. 



Supplies for a Laboratory Section of Twelve. Two ounces of sodium peroxide; twelve test tubes; twelve pieces 

 of fine iron wire about five inches long, to the end of which have been fastened small bits of soft wood. 



1. Place enough sodium peroxide in a test tube to fill the rounded part. Add a little 

 water, (a) Observe any change. The chemical action which takes place when sodium peroxide 

 and water are brought together sets oxygen gas free. This gas, together with nitrogen (to 

 be studied later) forms the bulk of the atmosphere, (b) Observe the color of the gas given 

 off. Do not mistake the fine spray of water for oxygen. 



2. Hold a match, burning with a small flame, in the mouth of the tube. Observe the 

 effect on the flame. 



3. Let the match flame go out, leaving a glowing coal. Hold the coal in the mouth of 

 the tube. Observe what occurs. 



4. Fill a test tube with gas from the gas supply at the desk by holding it inverted over 

 the burner while you turn on the gas for a moment and then turn it off. Remove it and light 

 the gas which the tube contains, (a) Observe the color of the flame as the gas burns. In a 

 similar way, attempt to light oxygen gas as it is given off. (b) Observe whether or not it 

 will burn. 



5. On the supply table find a piece of iron wire, to one end of which has been fastened 

 a piece of soft wood. Light the wood with a match or by holding it in the Bunsen flame, (a) 

 As soon as lighted hold it in the mouth of a test tube filled with oxygen. Observe whether or 

 not the wire burns, (b) Remove the wire. Observe any change in its appearance.- 



6. Make a brief summary of the important points studied as suggested by the following: 

 (a) Does oxygen have color? (b) Will it allow other substances to burn in it? (c) Will 

 it burn? 



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