Chemistry Magic 163 



materials. The molecules in plastics can be arranged in such an 

 orderly fashion that the material will be crystal-clear, or they 

 can be in disorder. It appears that when the molecules are in 

 the maximum of disorder the materials tend to be soft and 

 flexible. When the molecules are arranged in "military forma- 

 tion" the materials are hardest and strongest, but sometimes 

 brittle. For instance, there are the disorderly molecules of gum 

 rubber and the almost perfectly ordered molecules of sugar 

 and ice, which are brittle. A balance between these two ex- 

 tremes gives the chemist materials of desired strength and 

 toughness. 



The oldest plastic is cellulose nitrate, first made by treating 

 cotton with nitric acid. With camphor it made the inflam- 

 mable celluloid which was molded into combs, toothbrush 

 handles, wooden frames, and film. With alcohol it goes into 

 finishes that revolutionized the painting of automobiles around 

 twenty years ago. 



Another one, cellulose acetate, is made by dosing cellulose 

 with acetic acid and acetic anhydride. Like cellulose nitrate, 

 it is thermoplastic will soften up each time it is reheated to 

 a certain temperature. These plastics are tough, easily curved, 

 and more transparent than glass. 







The Hard Resilient Plastics 



The best-known plastics are the phenolic resins, including 

 bakelite, and the urea formaldehydes, which are much used 

 in bonding plywood. The phenolic resins are made by 

 combining phenol, from coal, and formaldehyde. They are 

 thermosetting when hardened they stay hard forever more. 

 They will resist solvents and other chemicals, and are used in 

 gears that will outwear steel. 



The urea resins, also thermosetting, are made by compound- 

 ing a nitrogen product, urea (principal organic constituent of 



