IN POPULAR CHEMISTRY. 65 



One of several causes is the need of more O to supply the in- 

 creased oxidation in the blood necessitated by unusual exertion. 



23. How does O give us strength ? 



Our muscles, as well as the food from which they are 

 formed, consist of complex molecules. When they are oxidized, 

 potential energy becomes kinetic. 



24. Does the plant produce energy ? ' 



No ; it only absorbs solar energy, and becomes the medium 

 of its transformation. 



25. If we 1>nrn an organic body in a stove it gives off 

 heat; in the animal body it produces also motion. Ex- 

 plain. 



The force set free by the oxidation of the muscles, and of 

 the food within the body, is converted into muscular energy. 



2(>. Why does not blowing cold air on, a fire ivith a bel- 

 lows extinguish it ? 



It may extinguish it if the blast be strong enough. If not 

 strong enough to cool it below its kindling point, the heat of 

 oxidation more than balances the cooling from the air. 



27. IVJiy docs bloiving on a fire hlndle it, and on a 

 lighted lamp extinguish it ? 



The answer to the previous question applies to this one also. 



28. Why can we not ignite hard coal with a match ? 



The heat of the match is not enough to decompose the coal, 

 and thus set free gaseous constituents for the production of flame. 



29. Why ivill an excess of coal put out a fire ? 



The coal is heated at the expense of the fire, and may reduce 

 this below the kindling point unless the supply of O is rapid. 



30. Could a light be extinguislied by merely lowering 

 the temperature ? 



Yes ; by contact of a large body that is a good conductor 

 of heat. 



