94 WATER 



Materials: Sawdust, sand, filter paper. 



a. To use filter paper, fold it 

 in halves and then again in quar- 

 ters, as shown in the illustration. 

 Separate one thickness from the 

 other three and place in funnel. 

 Mix some sawdust, sand and 

 water. Then filter. Does the 

 water pass through clear? 



Review Questions, 19. 



1. What are two causes of the variation in the heat 

 which we receive from the sun? 



2. What causes contraction ? 



3. What part of the room is the warmest, near the 

 ceiling, on the level of your head, or near the floor? 



4. What are the advantages of deep breathing? 

 How can you prove your answer by figures? 



5. Name the parts of the air that are used by plants, 

 stating how they are used, and the parts of the air which 

 are taken in by animals, giving the use of each part. 



6. If you were given a long rubber tube, which 

 would reach across the room, and two glass tubes to fit 

 the ends of the rubber tube, tell how you could put two 

 shelves on the opposite sides of the room at exactly the 

 same level. 



7. How could you find out whether a body is porous? 



8. Name all of the porous bodies you can think of 

 and state the advantages or disadvantages which are due 

 to their porosity. 



9. What is meant by waterproofing. Give some 

 examples of waterproofing. 



