120 NOT ALTOGETHER ABOUT PLANTS 



law of solution. 12. Having dissolved a solid in a liquid, how can 

 you get it back in solid form again ? Give an example. 



Section 30. 1. What are molecules? 



Section 31. 1. What are the three states of matter? 2. What 

 is it that generally causes the change of matter from one state into 

 another ? 3. Of what advantage is it to man that water expands 

 when it freezes ? 4. Of what advantage is it that water also expands 

 when it becomes a gas ? 5. Watch water boil in a glass vessel and 

 describe what you see. 6. Give examples of substances which may 

 exist in three states ; in two ; in only one state. 7. Are liquids 

 generally heavier than solids, or the reverse ? Is wood always lighter 

 than water ? 8. Are some gases lighter than others ? How would 

 you prove this ? 9. Why does a steel ship float ? 



Section 32. 1. What happens to molecules when they burn? 

 2. Is water produced when wood burns ? How would you arrange 

 an experiment to find out ? 3. What is meant by diffusion? 4. What 

 is an element ? 5. What is a compound ? 6. Give examples of ele- 

 ments. 7. What are the elements which principally compose living 

 bodies ? 8. What are the elements which compose water ? 9. Of 

 what elements and compounds is air principally composed ? 



Section 33. 1. What are atoms? 2. Is the molecule of an ele- 

 ment the same thing as an atom ? Explain your answer. 3. Explain 

 the symbols H2O and CO2. 



Section 34. 1. Give examples of things which seem to be of one 

 substance but which are really mixtures of different substances. 

 2. What is the difference between a "mechanical mixture" and a 

 solution ? 3. Test a number of substances which are soluble in water, 

 and rank them in the order of their solubility. The substances being 

 in equal amounts by weight, the one which dissolves most quickly 

 ranks first in order of solubility, and so forth. 



Section 34 a. i. Explain how the law of solution acts in distribut- 

 ing material in the soil. 



A. 2. Describe the origin of soil, defining humus. 3. Define min- 

 erals, giving examples. 4. What is meant by glaciation ? 5. Describe 

 alluvial soils. 6. What physical kind of soil is best for agricultural 

 purposes ? Define loam. 



B. 7. What is the " soil problem " in relation to the human race ? 

 8. What elements does the plant get from the soil ? 



