SCIENCE OF COMMON THINGS. 229 



"Why water extinguishes a fire. Cause of the heat of a dunghill. 



15SS Why does a pair of bellows aid in kindling afire ? 



Because it drives the air more rapidly to theft-re, and 

 the plentiful supply of oxygen soon makes the tire burn 

 intensely. 



15S9 Why does water extinguish a fire 1 



1. Because the water forms a coating over the fuel, 

 which keeps it from the air ; and 



2. The conversion of water into steam draws off the 

 heat of the burning fuel. 



1530 Why does a Uast of air from a pair of bellows often extinguish a 

 red-hot coal of anthracite ? 



Because the cold air absorbs the heat of the coal so 

 quickly that it extinguishes it. 



1531 Why can you not light a candle or lamp with a match so long as 

 the sulphur on the end of it is burning f 



The chemical reason for this well known fact is, that 

 the sulphurous acid, formed by combustion of sulphur 

 in the air, surrounds the wick, and abstracts the oxygen 

 from the air, by passing to a higher state of oxidation ; 

 and this heavy vapor hangs about the wick and excludes 

 the air. 



153S Cannot wood be made to blaze without actual contact with fire? 



Yes ; if a piece of wood be held near the fire for a 

 little time, it will blaze, even though it does not touch 

 the fire. 



1533 Why will wood blaze, even if it does not touch the fire ? 



Because the heat of the fire drives out the inflam- 

 mable gas of the wood, which gas is ignited by contact 

 with the red-hot coals. 



1534 What causes the heat of fire 1 



The carbon of fuel (when heated) combines with the 

 oxygen of the air, and produces carbonic acid gas. 

 Again, the hydrogen of the fuel combining with other 

 portions of oxygen, condenses into water ; by which 

 chemical actions heat is evolved. 



1535 Whence does the heal of a dunghill arise f 



As the strawy etc., of the dunghill decays, it under- 



