372 BELL SYSTEM TECHNICAL JOURNAL 



Brittleness Tests for Rubber and Gutta-Percha Compounds}'^ G. T. 

 KoHMAN and R. L. Peek, Jr. An insulating material compounded of 

 rubber, gutta-percha, or of similar substances becomes brittle at a 

 temperature, characteristic of the material, below which it may not 

 be used if liable to mechanical stress. This paper describes an 

 apparatus designed to determine this temperature by giving the sample 

 a sharp bend through a fixed angle. The highest temperature at 

 which fracture occurs in this test (the brittle temperature) is found to 

 be nearly independent of the bending angle and the sample's dimen- 

 sions provided the rate of bending is maintained at a nearly constant 

 (high) rate. A modified form of the apparatus is also described with 

 which the brittle temperature may be determined when the material 

 is under high hydrostatic pressure. The constancy of the brittle 

 temperature when determined under different conditions suggests 

 that it marks a change in the structure of the material. 



11 Ind. and Eng. Chem., Vol. 20, pp. 81-83, January, 1928. 



