2i 4 RUBBER AND 



On cooling raw rubber to the freezing point of water 

 the substance becomes hard and brittle, but recovers 

 its ordinary properties when restored to the normal 

 temperature. At warm summer temperatures the 

 elasticity of the rubber is increased, but on further 

 raising the temperature the rubber becomes softer and 

 more extensible. If the heating is not carried too far, 

 the normal properties of the rubber are recovered on 

 cooling. Heated still further the rubber becomes soft 

 and sticky, becoming actually liquid at some point 

 above 200 C. If cooled again from such a temperature 

 the normal elasticity of the rubber is no longer 

 recovered. At still higher temperatures the rubber 

 undergoes dry distillation with destruction of the 

 molecule. 



Destructive Distillation. Synthesis. 



The destructive distillation of india-rubber gives rise 

 to isoprene C 5 H 8 , and to other bodies of the formula 

 (C 5 H 8 ) n . Isoprene is also the most important step in 

 the synthesis of rubber, for which a number of com- 

 mercial processes have recently been patented. Tilden, 

 many years ago, obtained true rubber from isoprene 

 which had been prepared by passing the vapour of 

 turpentine through heated tubes. The rubber appeared 

 spontaneously in the isoprene which had been kept for 

 some years in a closed bottle, and was also produced 

 more rapidly in small quantities by the action of 



