14 MATTER AND ENERGY 



19. Ductility Some solid substances may be drawn 



out into small wires ; they are said to be ductile. In 

 several cases a ductile substance is also malleable, but 

 this is not always true; a body whose malleability is 

 great may have small ductility, and the reverse is also 

 true. The ductility of platinum is very great, for it 

 may be drawn into wires that are only Q-^-Q-Q of an inch 

 in diameter. 



Experiment 14. Heat a small glass tube in a flame, holding 

 it at both ends. When the tube is well heated in the middle 

 (i.e. red hot and soft), remove it from the flame and quickly draw 

 the ends outward. Examine the portion that was heated. 



20. Tenacity. The property whereby a solid body 

 resists being pulled in pieces is called tenacity. This 

 property is similar to cohesion, though not so broad in 

 its meaning. Steel wire has great tenacity, a very small 

 wire being able to support a heavy mass. 



Experiment 15. Take a strip of fresh writing paper two 

 inches wide. Fold so as to make it one inch wide and of double 

 thickness. Grasp one end firmly, while some one else grasps the 

 other end. Now both pull steadily till the paper breaks in two 

 pieces. What do you conclude with regard to paper? 



21. Porosity. We have learned that all bodies of 

 matter are composed of molecules and pores or spaces 

 between molecules. The size of these pores varies 

 greatly in different substances, but in any body they 

 are much larger than the molecules. Even in dense 

 masses, such as a piece of lead or silver, these pores are 

 present, though the mass appears to have no such 

 spaces and none can be seen through a microscope. 



