CHAPTER XIII 

 RUBBERS AND GUMS 



AT the time of the discovery of America the natives of 

 Central America and South America were found to be quite 

 familiar with the properties of rubber and were using rubber 

 for waterproofing garments and shoes and in making vessels 

 and utensils of various kinds. A few years ago a mass of 

 rubber was found in an olla, which was unburied in making 

 some excavations in an old Indian village in Arizona. The 

 conditions under which the rubber was found furnished quite 

 conclusive evidence that the particular mass of rubber was 

 not less than 300 years old. The mass of rubber had become 

 oxidized and brittle to a depth of about J^> inch. The inner 

 portion of the mass, however, retained apparently its full 

 elasticity. A French explorer sent specimens of rubber from 

 Ecuador to the French Academy of Sciences in 1736. Castil- 

 loa rubber was described in 1798, Hevea rubber in 1865, and 

 Ceara rubber in 1874. There are a few other important dates 

 in the development of the rubber industry. Priestley sug- 

 gested the use of rubber for erasers in 1770. The process of 

 waterproofing fabrics was invented by Macintosh in 1820. The 

 process of vulcanization of rubber was discovered by Good- 

 year in 1839 and was later modified by Hancock in England. 

 Previous to this discovery, rubber was of little commercial 

 importance and was used only in small quantities for the few 

 purposes to which it had been found to be adapted in its 

 unmodified condition. 



Vulcanization consists essentially in heating rubber with 

 sulphur. A combination takes place, whether of a physical 



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