THE RUBBER INDUSTRY — GIBBONS 201 



and methods. Part of this was due, no doubt, to the contemporary 

 development of improved technique in other industries, and part to 

 the increasing demands made on the rubber industry to manufacture 

 better products and to adapt rubber to new uses. Textbooks and 

 handbooks on various subjects relating to rubber made their appear- 

 ance, and in general the technical part of the industry, at least, may 

 be said to have developed the art of self-expression. It was found 

 possible for rubber technologists to disseminate technical informa- 

 tion regarding the methods of testing their products and regarding 

 the general principles of manufacture without injuring the organ- 

 izations by whom they were engaged. 



The fruits of this happy union of science and the rubber industry 

 have been numerous. There was increased activity in the study of 

 rubber both in the universities and in the industry ; the results have 

 not only given us a greater insight into the structure of rubber and 

 the mechanism of vulcanization, but have also led to practical im- 

 provements in the manufacture of rubber products which have been 

 of outstanding importance to the world. In the remainder of this 

 paper we shall discuss these various developments by subjects rather 

 than chronologically. 



RUBBER STRUCTURE 



Harries, in his researches beginning in 1904, investigated the 

 ozonides and other derivatives of rubber, and his results are the most 

 convincing evidence we have for the basic structural unit of the rubber 

 hydrocarbon. The theories of Harries and other workers of this 

 period are based almost entirely on chemical reactions and particu- 

 larly on ozonization studies, and did not attempt to explain the long- 

 range extensibility and other important properties. 



According to Staudinger and Bondy (17), who used viscosity 

 methods, the molecular weight varies from 180,000 for Hevea crepe, 

 down to 11,700 for rubber oxidized with air. Determinations of 

 molecular weight by osmotic methods show values around 129,000 

 (14). Kraemer and Lansing (11), using both ultracentrifugal and 

 viscosity methods, found a molecular weight of over 400,000. In 

 spite of the quantitative discrepancy between molecular weight deter- 

 minations by different investigators, we are at least justified in con- 

 cluding that the value is extremely high. This high molecular weight 

 of rubber is important because, according to modern theory, many of 

 the unusual properties of rubber are accounted for by its high mole- 

 cular weight. A number of theories have been proposed during the 

 past few years based on space models contrived in an attempt to 

 explain the high extensibility and elasticity of rubber. The most 

 widely accepted theory was developed in detail by Kuhn and others 

 (12). According to them, rubber consisted of long threadlike mole- 



