162 BULLETIN 42, UNITED STATES NATIONAL MUSEUM. 



pulling, thrusting, bending, twisting, and shearing, bars containing 1.2, 

 0.9, 0.6, 0.3 of carbon, three of each, were used to obtain an average. 

 The bars were all hammefed to 2 inches square, were all similarly pre- 

 pared and all similarly tested, so that the results are strictly compara- 

 ble. Throughout the entire series of experiments the stress is expressed 

 in pounds per square inch of the specimen's original area unless it is 

 otherwise stated. 



First. Pulling or tensile stress— strength. — Elastic stress, 62,033, 63,066, 

 58,100, 43,100 pounds; ultimate stress, 85,200, 106,603, 102,632, 61,312 

 pounds. 



Ductility. — Contraction of the specimen's area at fracture, 2.65, 6.11, 

 14.43, 61.52 per cent, of the original area. Ultimate extension, or the 

 amount that the specimen has stretched, 1.8, 5.1, 6.6, 16.5 per cent, of 

 its original length. In the order of their carbon contents the highest 

 being given first. 



Characteristics of fracture. — Bars 1.2, 0.9, 0.6, all broke more or less 

 suddenly, and are wholly granular and right-angled fractures; the 0.3, 

 or softest, broke very gradually, appearance wholly silky and of cup- 

 form. In the granular fractures some radiate from the center, whilst 

 others from or near the side of specimen presenting a fan-like appear- 

 ance. 



Second. Thrmting or compressive stress. — Specimens equal to 1, 2, 4, 

 and 8 diameters, showed the following results under elastic stress : 



Lensfth. 



One diameter 



Two diameter . . . 

 Four diameter . . . 

 Eight diameter . . 



Total mean 



Elastic stress. 



62, 833 59, 499 55, 833 



40, 667 



The stress becomes gradually reduced as the length is increased, the 

 hardest bars under thrusting giving the highest results, which was 

 found not to be the case under pulling stress. 



