8 ANSWERS TO PRACTICAL QUESTIONS 



3. Why does not writing-paper blot? 



Because the pores are filled with size. (See Chemistry, 

 p. 161.) 



4. Why does paint prevent wood from shrinking? 

 Because it fills the pores of the wood. 



5. What is the shape of the surface of a glass of water and 

 one of mercury f 



Ordinarily the former is concave and the latter convex. 



6. Why can we not dry a towel perfectly by wringing ? 

 Because of the strength of the capillary force by which the 



water is held in the pores of the cloth. 



x 



7. Why will not water run through a fine sieve when the 

 wires have been greased? 



Because the grease repels the water and so prevents capil- 

 lary action. 



8. Why will camphor dissolve in alcohol and not in water? 

 Because there is a strong adhesion between the alcohol and 



camphor, and little, if any, between the water and camphor. 



9. Why will mercury rise in zinc tubes as water does in 

 glass tubes ? 



Because of the strong adhesion between zinc and mercury. 



10. Why is it so difficult to lift a board out of water ? 

 Because of the adhesion between the board and the water. 



1 1 . Why will ink spilled on the edge of a book extend further 

 inside than if spilled on the side of the leaves? 



Because the capillary pores of the paper are short, being 

 only the thickness of a leaf, while the capillary spaces between 

 the leaves are longer and continuous. 



12. If you should happen to spill some ink on the edge of 

 y cur book, ought you to press the leaves together? 



No. Because you would make the capillary spaces between 

 the leaves smaller, and so the ink would rise in them further. 



13. Why can you not mix oil and water ? 

 Because there is no adhesion between them. 



