12 ANSWERS TO PRACTICAL QUESTIONS 



ADHESION. 



54 1. Why does cloth shrink when wet ? 



By adhesion the water is drawn into the pores of the cloth. 

 The fibers are thus expanded sidewise and shortened length- 

 wise. The cloth "fulls up" or thickens while it shortens and 

 narrows (shrinks) in the process. 



2. Why do sailors at a boat-race wet the sails ? 



The pores being full and expanded make the sails more 

 compact. They will, therefore, hold the wind better. 



3. WJiy does not writing-paper blot ? 



Because the pores are filled with sizing. (See Popular Chem- 

 istry, p. 216.) 



4. IVJiy does paint tend to prevent wood from shrink- 

 ing? 



Because it fills the pores of the wood at its surface. 



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

 and one of mercury? 



Ordinarily the former is concave and the latter convex. 



6. Why can ^ve not dry a toivel perfectly by wringing ? 



Because of the strength of the force of adhesion, by which 

 the water is held in the pores of the cloth. 



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

 the wires have been greased ? 



Because of reversed capillarity between oil and water. 



8. Why will camphor dissolve easily in alcohol and not 

 in water ? 



Because there is a strong adhesion between the- alcohol and 

 camphor, and but little between the water and camphor. 



,9. Why tvill mercury rise in zinc tubes as ivater does in 

 glass tubes ? 



Because of the strong adhesion between zinc and mercury. 



