CHAPTER IX. 



GOODYEAR'S HEATED OR VULCANIZED INDIA RUBBER. 



Characteristics of the native gum. Goodyear's heated or vulcanized India rubber ; its elasticity ; 

 pliability ; durability ; insolubility ; unalterability ; inadhesiveness ; impermeability ; plasticity ; 

 facility of printing, and of being ornamented by painting, bronzing, gilding, japanning, and mix- 

 ing with colors ; non-electric property ; odor. Test of vulcanized and unvulcanized gum- 

 elastic. 



In order to have a correct understanding of w^hat the im- 

 provement consists in, which is treated of in this w^ork, as exist- 

 ing in such a variety of forms and aspects, it will be necessary 

 to bear in mind, what are the properties and defects of the gum 

 in its native state, as heretofore described under the head of 

 Native Gum-elastic ; and also that the utility of the numerous 

 fabrics and applications of this improvement depends upon the 

 change wrought in the gum by the vulcanizing process ; that the 

 cheapness of the production, and the durability of many of the 

 articles, depends upon the mechanical improvement of the lamin- 

 ated fibrous fabrics. 



A description of the method by which the change is wrought 

 in the gum, and the causes which led to its accomplishment, 

 have been heretofore given. The properties of the heated 

 or vulcanized gum-elastic, will be better understood and appre- 

 ciated, when contrasted with the defects and objections to the 

 gum in its native state, which are these : — 1st. It becomes rigid 

 and inflexible in cold weather. 2d. It is softened and decom- 

 posed in the sun and hot weather. 3d. It is very soluble and 

 quickly dissolved when brought in contact with any kind of 

 grease, essential or common oils ; and though more slowly, yet 

 as surely dissolved by perspiration. 4th. It is in its nature so 



