PROBLEM 40 G5 



When an iron nail is placed in a damp plar-o, it rusts. This is also an oxidation, 

 the iron of the nail uniting with the oxygen of the air. 



Conclusion. — 1*. Explain exactly what happens when a jj;low- 

 ing match is placed in pure oxygen. 



2. Is it correct to say that oxygen burns up? 



3. What !§ always released as a result of oxidation? 



4. Explain the difference between rapid oxidation (combustion) 

 and slow oxidation. 



Problem 39 : To test for carbon. 



Materials. — Meat, bread, starch, etc., glass plate, candle. Fig- 

 ure page 65, Civic Biology. 



Note. — All organic substances contain the chemical element carbon. This 

 may be proved by burning a substance. If it becomes charred or blackened, it 

 contains carbon. 



Method and Observations. — Test meat, bread, dried peas, and 

 starch for carbon. 



Hold a clean piece of glass over the flame of a candle. What 

 forms on the glass? Where does it come from? 



Conclusion. — Make a table showing substances tested, noting 

 whether or not they contain carbon. 



Problem 40 : To test for carbon dioxide. 



Note. — We have seen that substances that burn unite with the oxj'gen of the 

 air when they are oxidized. Let us next see what happens to the air when carbon 

 unites with oxygen. 



Materials. — Candle, limewater,^ wide-mouth bottle. 



Method. — Burn a candle (which has been proved to contain 

 carbon) in a wide-mouth bottle, then add a little limewater and 

 shake the bottle. 



Observations. — What change takes place in the limewater? 



Note. — a gas called carbcn dioxide causes limewater to become milky. 



Conclusion. — 1. How is carbon dioxide formed? 



2. What is the test for the presence of carbon dioxide? 



3. Explain this formula, C + 2 O = CO,. 



^ Limewater is made by adding a piece of quicklime the size of your fist to about 

 2 quarts of water. Filter before using. 

 HUNTER LAB. PROB. — 5 



