MECHANICAL TESTING OF RUBBER 91 



of revolutions at constant load indicates the difference 

 in tlie resistance to abrasion of the different pieces. 



Hardness Tests. — The hardness is measured by the in- 

 dentation produced by a steel ball pressed on to a disc of 

 the rubber by a constant weight ; or by the load required 

 to produce a given indentation. 



Resilience.— This is measured by the height of rebound 

 of a steel ball after dropping from a fixed height on to a 

 disc of the rubber, or by means of a pendulum-impact 

 tester, one arm of which carries a piece of the rubber to 

 be tested. 



There is no doubt that the mechanical testing of rubber 

 on these lines will furnish very important data, not only 

 for the manufacturer but also for the planter, by indicating 

 the methods of preparation which produce the highest 

 quality of rubber. 



