752 The Outline of Science 



test is this: Let the natural and the artificial products compete 

 fairly; let the {Esthetes decide how far they are physiologically 

 and psychologically equivalent; let us pay accordingly, if we 

 please ; but do not mix synthetic geraniol with attar of roses. 



Synthetic Rubber 



India-rubber or Caoutchouc is a gum that occurs in the 

 milky juice of many plants, and abundantly in a few, especially 

 in certain trees of the spurge and the fig orders. The milk flows 

 out when the tree is cut; and rubber-trees are now cultivated in 

 many places where they are not native. The material is used, 

 as everyone knows, for tyres, waterproofs, goloshes, hot-water 

 bottles, syringes, stoppers, and in hardened form as vulcanite. 

 It has almost been forgotten that the name "rubber" referred to 

 its early use as an eraser. Another gum known as gutta- 

 percha is used for isolating submarine cables and making golf- 

 balls. 



When rubber is heated in a retort it splits up into a benzine- 

 like liquid called "isoprene," and the synthetic chemist's problem 

 was first to make this isoprene artificially and second to change 

 it into caoutchouc. The whole story is an extraordinary one, 

 but we can only say that isoprene can be made artificially in 

 various ways, e.g. from the fusel-oil yielded by fermenting potato- 

 starch; and that isoprene can be changed into caoutchouc in va- 

 rious ways, e.g. by drying it over metallic sodium. In 1912 there 

 were exhibited in New York two automobile tyres of artificial 

 rubber which had run a thousand miles. But while the problem 

 has been solved scientificially, it has not been solved industrially. 

 For it does not pay to get isoprene from potatoes or from tur- 

 pentine. The most promising method is perhaps to heat coal 

 and lime in an electric furnace. They unite to form calcium car- 

 bide, which in contact with water yields acetylene, and from this 

 gas it is possible to make isoprene and therefore rubber. Yet it 

 remains more profitable to go to the rubber-tree ! 



