236 RUBBER AND 



Vulcanite. 



The manufacture of vulcanite resembles in principle 

 that of ordinary rubber goods at all stages, except that 

 a larger proportion of sulphur is added in the mixing 

 and that vulcanisation is carried out for a longer period 

 and at a higher temperature. As we proceed to stages 

 of vulcanisation beyond that for ordinary hard vulcan- 

 ised rubber, we pass through the tough and springy 

 condition of the substance employed as artificial 

 whalebone, and finally arrive at the hard and brittle 

 state of the vulcanite or ebonite employed for making 

 fountain pens and the mouthpieces of pipes to name 

 only two of a large variety of uses. In making whale- 

 bone-substitute the amount of sulphur added to the 

 rubber is from 12 to 14 per cent.; for the harder 

 ebonite from 24 to 35 per cent, is required. Vulcani- 

 sation is carried out either for a prolonged period 

 8 to 12 hours at a comparatively low temperature 

 about I35C, or for a shorter time at a higher tempera- 

 ture. 



The Testing of Rubber Goods. 



A number of ingenious devices are employed in 

 determining the quality of rubber goods as well as that 

 of raw rubber. The principal tests to which manu- 

 factured rubber is subjected are those for abrasion and 

 for stretching. In abrasion tests the sample is brought 



