42 GOODYEAR ON GUM- ELASTIC. 



They are cheaper substances than any of the vegetable gums, 

 as they are now obtained. 



Some of them, particularly coal-tar, was used at an early day 

 to a limited extent in the manufacture of caoutchouc. The 

 same causes which operated to bring about the more extensive 

 use of the resinous gums in this manufacture, have also led to 

 the use of bitumen and coal-tar in greater quantities in the 

 vulcanized compounds. The chief objection to their use is, 

 that they impart their peculiar odor to the fabrics ; but in some 

 of them which are used in the open air, where this odor is less 

 objectionable, bitumen or coal-tar may be used in equal propor- 

 tions with caoutchouc or India rubber. 



