lo Schwartz & Kemp, PhyskaL Properties of Rubber. 



Ergs required to raise i cm. length through i°C. 

 = 0-415 X 0-965 X 0-4x4-2 X 10^ 

 = 6-'Jiy. 10". 



It is here assumed that the specific heat and 

 specific gravity remain unchanged on the application of 

 tension. The work done in extension is equal to i\We\ 

 where {W) is the tension applied gradually, and {e) is 

 the elongation. This is equal to the work done in dis- 

 placing the molecules relatively to one another, and is a 

 cause of heating. The work done in enlarging the inter- 

 molecular spaces is equal to 



A 



L' 



where {a) is Poisson's ratio, (Z^) the extended length, 

 (Z) the original length, and (/v") a constant. This work 

 increases the potential energy of the body, and is a source 

 of cooling since it absorbs energy. Thus the effects of 

 the two kinds of internal work are in opposition. If, 

 therefore, it is known at what tension neither heating nor 

 cooling occurs, it is possible to determine the numerical 

 value of (AT). This is done by equating the values of the 

 two kinds of molecular work for the given conditions. 



Therefore 



h It' e == A ^^3 ■ , 



at the neutral point. 



It is now possible to evaluate the above expressions 

 for different tensions, and to calculate the temperature 

 variations due to each particular load. The following 

 table is an example of such a calculation : — 



