Qaoxilchouc or Indian Bubber. 289 



which is used in the experiment; for heat 

 increases the pliancy of the substance, and 

 cold, on the contrary, renders it more rigid \ so 

 that when a slip of this resin has been suffi- 

 ciently warmed, it may be extended to more 

 than twice its natural length, by a moderate 

 force applied to its extremities, after which it 

 will recover its original dimensions in a 

 moment, provided one of the ends of it be let 

 go as soon as it has been stretched. This dis- 

 position of the substance may be produced by 

 a degree of temperature, less than the heat of 

 the blood ; it is therefore necessary to prepare a 

 slip of it, by steeping it for a few minutes in 

 warm water^ or by holding it somewhat 

 longer in the fist ; either of these precautions 

 makes the resin pliant, and fits it for the ex- 

 periment ; which is performed in the following 

 manner. 



I made a piece of CaoutchoCic a little heavier 

 than an equal bulk of water, the temperature 

 of which was 45 degrees : the vessel con- 

 taining the resin and water was then placed 

 on the fire ; and when the contents of it were 

 heated to 130 degrees, the Caoutchouc floated 

 on the surface. \ 



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