'•68 Caoutchouc and its Applications. 



in many of its characteristic properties. It is no longer 

 affected by climatic temperature ; it is neither hardened by 

 cold nor softened by any heat which would not destroy it. 

 It ceases to be soluble in the solvents of common caoutchouc, 

 while its elasticity becomes greatly augmented and perma- 

 nent. 



The same effect may be produced by kneading sulphur into 

 caoutchouc by means of powerful rollers ; or the common 

 solvents, naphtha and spirit of turpentine, may be charged 

 with a sufficient amount of sulphur in solution to become a 

 compound solvent of rubber. In these cases articles may be 

 -made in any required forms before heating for the change of 

 condition. It is necessary, however, for this purpose, that 

 4he form should be carefully maintained during the exposure 

 -to the heat necessary to effect the vulcanization which leaves 

 it in a normal state. A vulcanized solid sphere of 2J inches 

 •in diameter, when forced between two rollers J inch apart 

 was found to maintain its form uninjured. In fact, it is the 

 exclusive property of vulcanized caoutchouc to be able to re- 

 tain any form impressed upon it, and to return to that form 

 on the removal of any disturbing force which has been brought 

 -to act upon it. 



Caoutchouc slightly expands and contracts in different 

 temperatures; it is also capable of being condensed under 

 pressure. A tube of 2J inches, impactly secured, was sub- 

 jected to a force of 200 tons. The result was a compression 

 amounting to yV J — great heat appeared to have been evolved, 

 and the excessive elas^ticity of the substance caused a fly- 

 wheel weighing five tons to recoil with an alarming violence. 



The evolution of heatf rom caoutchouc under condensation 

 is a property possessed by it in common with air and the 

 metals. It differs, however, from the latter in being able to 

 exhibit cold by reaction. Mr Brockedon stated that he had 

 raised the temperature of an ounce of water 2^ in about 15 

 minutes by collecting the heat evolved by the extension of 

 -caoutchouc thread : he refers this effect to the change in 

 -specific gravity. He contends that this heat thus produced 

 is not due to friction ; because the same amount of friction 

 is occasioned in the contraction as in the extension af the 



