94 



TABLE 70. 



MECHANICAL PROPERTIES. 

 TABLE 70. Rubber and Leather. 



(a) RTJBBER, SHEET.* 



The specific gravity of rubber averages from 0.95 to 1.25, corresponding to an average weight 

 of 60 to 80 lb/ft 3 . 



Four-ply rubber belts show an average ultimate tensile strength of 0.63 to 0.65 kg/mm 2 or 

 890 to 930 lb./in 2 (Benjamin), and a working tensile stress of 0.07 to o.n kg/mm 2 or 100 to 150 

 lb./in 2 is recommended (Bach). 



(6) LEATHER, BELTING. 

 Oak tanned leather from the center or back of the hide: 



Minimum tensile strengths of belts f single 2.8 kg/mm 2 or 4000 lb./in 2 

 (Marks, p. 622) \ double 2.5 kg/mm 2 or 3600 lb./in 2 



Maximum elongation for one hour application of J single 13.5 per cent 

 1.6 kg/mm 2 or 2250 lb./in 2 stress \ double 12.5 percent. 



Modulus of elasticity of leather varies from an average value of 12.5 kg/mm 2 or 17,800 lb/in 2 

 (new) to 22.5 kg/mm 2 or 32,000 lb./in 2 (old). 



Chrome leather has a tensile strength of 6.0 to 9.1 kg/mm 2 or 8500 to 12,900 lb/in 2 . 



The specific gravity of leather varies from 0.86 to 1.02, corresponding to a weight of 53.6 

 to 63.6 lb./ft 3 . 



SMITHSONIAN TABLES. 



