214 



COMMON SUBSTANCES 



Experiment 134. Secure a stick of oak wood, cut for a stove. 

 Split it lengthwise ; examine the freshly opened surface, using a 

 microscope if possible. Can you see fibers? Do you see groups 

 of fibers ? Examine the end of the stick, looking for masses of 



fibers. Do you see the openings 

 '' ~^ ; > for the sap ? 



Experiment 135 Put some 



bits of dry wood into a test 

 tube and apply heat (Fig. 140). 

 When the wood is thoroughly 

 black, cease to heat it. Examine 

 the remains. What is left in the 

 tube and what has gone from 

 the wood ? 



FIG. 140 



251. Cotton Cloth. Sev- 

 eral plants cotton, flax, and 

 hemp produce growths of 

 fine fibers that may be easily separated. These fibers 

 are twisted together to form rope, twine, and small 

 threads. Threads of cotton or linen are woven together 

 to form different sorts of cotton and linen fabrics. Plant 

 fibers of this sort are the same in chemical structure as 

 the fibers of wood ; they are therefore cellulose. 



252. Paper. Paper is a mass of fibers very firmly 

 pressed together. The fibers are obtained from cotton 

 or linen rags and from wood pulp (a mass of short 

 separated wood fibers). 



To make paper, the rags are cleansed and then torn and 

 shredded into tiny fibers by machines. Water is then 

 added to the mass of fibers, so that the mixture easily 

 flows. This mixture is poured out upon a flat surface, 

 made so that the water may partly drain out, leaving 



