84 Our Surroundings 



The sulphur match has been largely replaced by the safety 

 match. The head of this match is usually coated with a mix- 

 ture of sulphur, chlorate of potassium, powdered glass and glue, 

 but no phosphorus. A mixture of red phosphorus, less active 

 than yellow phosphorus, glue and other substances is placed on 

 the surface where the match is to be scratched. Safety matches 

 cannot be lighted except on this surface or on glass. 



It is a long way from the method of primitive people in 

 making fire by rubbing together two sticks to the modern method 

 with the safety match, but friction is employed in both cases. 

 Here is another illustration of the transformation of energy. 

 Again energy of motion is changed into heat energy. 



Experiment to Show the Necessity of Air (Oxygen), 

 Heat, and a Combustible Substance to Start Combustion. 

 Place a candle in a jar of air. Touch the wick of the candle with 

 small splints. Do they burn ? Light the candle and place the splints 

 in the flame. Do they burn ? Cover the jar for a while. Does the 

 candle continue to burn? If not, why? What do you conclude? 



Kindling Temperature. In order to make a fire, a cer- 

 tain degree of heat or temperature must be present. The kindling 

 temperature is the temperature at which a substance will take 

 fire. It varies much with different substances. 



Place a quart of water over a Bunsen burner and note how 

 long it takes for the water to boil; then in the same manner 

 determine how long it takes to boil a gallon of water over the 

 same burner. We find that the quart of water boils in a much 

 shorter time. Both amounts of water have the same temperature, 

 but the gallon of water contains four times as much heat. The 

 temperature of a body, therefore, has a far different meaning 

 than the amount of heat in a body. 



The most common combustible products are wood, coal, char- 

 coal, coke, oil, and gas. There are substances that will not 

 burn in ordinary air. Among these are iron, stone, and asbestos. 

 It is believed, however, that there is no substance that will not 

 burn if the degree of heat is sufficiently high. 



Experiment to Show Variation in Kindling Tempera- 

 tures. It is interesting to show the different kindling tern- 



