66 BURNING OR OXIDATION 



forms of energy is equal to the energy originally stored away 

 in the powder. The better the gun is, the less will be the 

 energy dissipated in smoke and heat and noise. 



Chemical action as a source of heat. Heat is a strong 

 factor in bringing about chemical changes. Manganese dioxide 

 and potassium chlorate do not yield oxygen unless they are 

 heated ; wood does not change to charcoal unless it is heated. 

 But some chemical changes take place without strong heat; 

 bicycles and keys rust at ordinary temperature, and carpets 

 and draperies fade and lose their brilliant hues. 



Heat usually assists chemical action, and it is equally true 

 that chemical action sometimes produces heat. When hydro- 

 chloric acid is poured upon marble, the chemical change which 

 sets free carbon dioxide also sets free heat. You can easily 

 test this for yourself by holding your hand on a bottle in which 

 acid and marble are mixed. The heat produced by the chemical 

 action warms the bottle and the hand. The heat of chemical 

 change can be seen by us at any place where a building is being 

 erected or where alterations are being made. A laborer makes 

 mortar by mixing water, lime, and sand, and the mixture is 

 often so hot that it steams. Buildings in which lime is stored 

 frequently take fire, and the transportation of lime in ordinary 

 vessels is very dangerous. If rain leaks in upon the lime, or 

 if water reaches it in any way, chemical change occurs and the 

 heat produced is frequently sufficient to set fire to the building 

 or vessel. The only safe way to transport lime is to put it in 

 sealed metal containers through which water cannot soak or leak. 



