24 THE PRINCIPLES Otf AGRICULTURE. 



QUESTIONS. 



How many different elementary substances are there in the earth? 

 Name those which are most common. Name as many others as 

 you can think of. What is meant by the symbol of a substance V 

 Name the symbols of the most common substances. 



What is an atom? Have atoms ever been seen? How do we know 

 that they exist? How are atoms represented? Give an idea 

 of the size of an atom. Can an atom be divided? Can it be 

 destroyed ? 



What is a molecule ? What causes atoms to form molecules ? How 

 is a molecule represented ? How are the atoms of a molecule 

 arranged ? 



Upon what does the nature of matter depend ? Must all substances 

 composed of carbon, hydrogen, and oxygen be alike? Can the 

 molecules of a body be broken or divided ? How can this be done ? 

 What effect does this have upon a body ? What would be the 

 effect of making a different arrangement of the atoms in the mole- 

 cules of a substance ? 



What is chemical action ? Give an example of chemical action, and 

 explain it. 



What are acids ? Bases ? Salts ? Name some of each. 



Give a chemical equation showing how bases are formed. 



What is cohesion ? What is adhesion ? Why does your hand become 

 wet when dipped in water ? Why are the feet kept dry by greas- 

 ing the boots? How is water purified by leaching through char- 

 coal ? Why are not two pieces of wood touching each other held 

 together by cohesion ? 



How many porous substances are there? How do we know that iron 

 is porous ? Why can salt be added to a glass full of water without 

 causing it to run over ? Why may two gases appear to occupy the 

 same space at the same time ? 



Explain the difference beween solids, liquids, and gases? Why is a 

 substance melted by heating it? How is it that heat expands and 

 cold contracts? Why does water expand in freezing? 



W T hat is the difference between organic and inorganic matter ? Is 

 hay organic or inorganic? A potato? Water? Milk? Sand? 

 Ordinary soil? 



