20 LABORATORY EXERCISES 



is the result? The fact that the limewater becomes milky 

 serves as a test for carbon dioxide. 



b. Through a glass tube blow your breath for some time into 

 about 5 cu. cm. of limewater. Have the limewater in a test tube. 

 What happens? What gas must be present in exhaled air? 



c. Prepare a cardboard cover for a wide-mouth bottle, and 

 make in the cardboard a hole just large enough to hold firmly 

 a pine splinter about half as thick as a pencil. The splinter 

 should be long enough to reach almost to the bottom of the 

 bottle. Light the splinter, and put it into the bottle, using the 

 cardboard both to cover the bottle and to hold the splinter. 



Let the burning go on as long as it will. Why does the 

 splinter not burn until it is all consumed? Is there any sign 

 that water is formed in the burning? Now remove the splinter, 

 put into the bottle about 5 cu. cm. of limewater, close the 

 bottle, and shake it. What is the result? What gas must be 

 formed when wood is burned? 



d. Burn a small candle (use a wire as a holder) in a bottle of 

 air, and make the same tests as in c. Give all the results, and 

 explain them. 



EXERCISE 16 



HEATING OF TIN IN AIR 



Apparatus and Materials. Small iron dish (cake tin or cover of 

 baking-powder box), stout wire or a small file, tin, ring stand, Balances. 



a. Weigh, all together, a small iron dish containing about 

 10 g. of tin, and a piece of stout iron wire that is to be used as a 

 stirring rod. Instead of the wire a small file may be used. 

 Support the dish on a ring stand (Fig. 11), and heat it strongly, 

 stirring the melted tin with the wire or the reverse end of the 

 file. What happens to the tin? If the wire or file becomes hot, 

 put one end into a cork, or a spool, and use this as a handle. 



