108 HOW WE USE HEAT 



just described. But even the'flint and steel was a big ad- 

 vance over the many centuries-old friction method with 

 the bow and drill. Your great-grandparents doubtless 

 thought of the wonderful way they had of making fire 

 compared to the people of early times, just as you now 

 think of the match as a wonderful device when compared 

 to the flint and steel of former days. Friction with a 

 match makes fire in a fraction of a second, but friction 

 with the bow and drill under the best of conditions re- 

 quired minutes to make fire. 



SELF-TESTING EXERCISE 



Select from the following list those words which best fit the blank spaces 

 in the sentences below. Arrange the words in proper numerical order. 

 A word may be used more than once. 



kindling go fire same 



temperature temperatures stops burns 



helps burn out better 



different combustible match incombustible 



below lower higher friction 



same chemical action fuel 



physical air (oxygen) stoves goes 



Fanning the kindlings placed on the glowing coals in a fireplace 



makes the fire (1) (2) Fanning a candle flame makes 



the fire (3) (4) In the first case there is much heat ; 



fanning brings in more (5) and so (6) the burning. In 



the second case there is little heat; fanning brings in so much 



air that the (7) is reduced (8) the (9) temperature 



and so (10) the burning. There can be no burning or com- 

 bustion unless a (11) substance is heated to its (12) 



(13) and supplied with (14) A common useful article 



making use of a combination of substances with different kindling 



temperatures is the (15) In early days of fire making 



(16) generated the heat. Today we have many devices using 



friction, but our ability to get fire so easily lies in the use of 



materials with (17) kindling (18) Sulphur takes (19) 



at a (20) temperature than wood. 



