4 Schwartz & Kemp, Physical Properties of Rubber. 



the change will be accompanied by a cooling, since the 



extra energy must be produced at the expense of the 



kinetic energy of the body ; or, in other words, at the 

 expense of its heat. 



In order to measure these thermo-dynamic effects 

 quantitatively, it is necessary to know on what physical 

 quantities they depend. The heat energy produced by 

 the relative movement of the molecular groups past one 

 another is proportional to the total work done upon the 

 specimen in extending it, and, if the rate of extension with 

 load is uniform, this is equal to \We, where ( JF) is the 

 weight (added gradually) which is required to produce the 

 extension, and {e) is the longitudinal extension. Chauveau' 

 states that the second kind of internal work (change in 

 the dimensions of the inter-molecular spaces) is simply a 

 function of the distance traversed by the lead, assuming 

 that the changes of volume experienced by the body are 

 proportional to its changes of shape. Work has to be 

 done on the body in order to separate the molecules of 

 which it is composed ; in other words, its potential energy 

 is increased. This is equivalent to saying it is a source 

 of cooling, for it absorbs heat energy and converts it into 

 strain energy or internal potential energy. 



Experiment shows that, when rubber is subjected to 

 tension, a cooling effect is first produced which decreases 

 in value to zero, ultimately changing to a heating effect 

 as the tension is increased. In compression, however, the 

 inter-molecular spaces are diminished in size, and heating 

 results from this cause as well as from the movement of 

 the molecules past one another ; these two effects are, 

 therefore, additive, both producing heating. 



* " Sur le mecanisme des phenomenes therniiques lies a la mise en jeu de 

 I'elasticite du Caoutchouc." Paris, 1' Academic des Sciences, Feb., 1899. 



