HOW MATTER CHANGES 



143 



other combinations. This is called the Law of Definite 

 Proportions. 



If the proper weights of the given substances are well 

 mixed, so that each small particle is near those with which 

 it will unite, chemical combination takes place more rapidly. 

 Gases mix most readily, and liquids next; finely powdered 

 solids mix less readily than gases and liquids, but better 

 than large masses of solids. 



The burners of gas stoves and Bunsen burners, such as are 

 used in laboratories, are provided with holes for the admission 



FIG. 72. THE FIRE Box OF A FURNACE 



1. Why is a grate, and not a sheet of metal, provided for the coal 

 to rest upon? 2. At which door does air enter for the process of oxidation? 

 3. What is such an opening called? 4. How does the amount of air affect 

 combustion? 5. Explain the effect upon the fire when the other door is 

 left open. 



of air near the place where the gas enters. Thus air and 

 illuminating gas are mixed and come to the opening to- 

 gether, and when a flame is applied, every particle of illu- 

 minating gas is in contact with the oxygen of the air and 

 burns rapidly. Each particle of gas, however, will unite 

 with only a certain amount of oxygen, no matter how 

 much is furnished. (LABORATORY MANUAL, Exercises XV, 

 XVI.) 



