ids para rubber. 



of as vulcanization. Pure sulphur does not combine with india- 

 rubber at temperatures below 270°F., but sulphur mono-chloride 

 readily reacts with it at ordinary temperatures. 



The elasticity, resiliency, colour, and odour of rubber vary con- 

 siderably, according to the age of the trees, and the methods of 

 collecting, coagulating, and curing the product. Rubber from 

 mature trees, if well prepared, is of a pale amber colour, has a 

 slight odour, and is very tough ; badly- prepared rubber or that 

 from young trees is frequently speckled, emits a foul odour, and 

 may on keeping become sticky, plastic, or brittle. 



Action or Heat on Indiarubber. 



Indiarubber becomes sticky if subjected to high temperatures. 

 It passes into quite a liquid state at ordinary temperatures under 

 certain conditions ; if sound rubber is subjected to 170 to 180°C, 

 it becomes more or less fluid. The melting point, if rubber can be 

 said to have one, is much higher than this if the resin has been 

 extracted. It is important that all drying and coagulating processes 

 should be so devised as to ensure the temperature being regulated, 

 and a maximum temperature considerably below that just quoted 

 should be guaranteed. 



Indiarubber articles, if exposed to high temperatures, are apt 

 to lose their strength, and to develop either sticky or brittle 

 properties. 



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