II. HEAT IN RELATION TO THE HUMAN BODY 



COMBUSTION 



1. Put a long, narrow lamp chimney down over a short 

 lighted candle set in a dish containing a little water. Re- 

 peat several times, and state what occurs. Account for 

 the result. 



Repeat these tests, having a partition of tin reaching 

 down through the chimney at one side of the burning candle. 

 Hold an extinguished match that is still smoking at the top 

 of the chimney, first on one side of the tin and then on the 

 other, and observe the smoke. What is the significance of 

 the behavior of the smoke ? 



2. Let the teacher carefully melt a little potassium chlo- 

 rate in a test tube, and then heat it to boiling. Observe the 

 results as bits of match sticks are dropped into the hot 

 liquid. 1 



The gas, oxygen, is set free from the chlorate as result of 

 a chemical change, and the union of the oxygen with the 

 wood is another chemical change. 



What is true (a) of the nature of combustion; (b) of the 

 composition of air in order that it may support combustion 

 of the candle ? 



1 It will be a wise precaution to fold a strip of paper into several thick- 

 nesses, and wrap it about the upper end of the test tube as a holder. If the 

 tube be heated nearly its full length at first, there will be less likelihood of 

 breaking it when water from the crystals of the chlorate is driven off. 



9 



