23 



or otherwise treated before use, the specimen representing 

 such material may be similarly treated before testing for 

 tensile strength. 



The elongation shall be measured on an original length of 

 $ inches. At least two test pieces shall be taken from each 

 melt or blow of finished material, one for tension and one 

 for bending. (Art. 153.) 



137. All samples or full-sized pieces must show uniform 

 fine-grained fractures of a blue steel-gray color, entirely 

 free from fiery lustre or a blackish cast. 



138. Medium Steel shall have an ultimate strength, when Medium sceei. 

 tested in samples of the dimensions above stated, of 60,000 



to 70,000 pounds per square inch, an elastic limit of not 

 less than one-half of the ultimate strength, and a minimum 

 elongation of 20 per cent, in 8 inches. But for eye-bar 

 material, not over 20 per cent, of the material must run 

 below 62,000 or above 68,000 pounds per square inch. 

 Steel for pins may have a minimum elongation of 15 per 

 cent. 



139. Before or after heating to a low cherry red and 

 cooling in water at 82 degrees Fah., this steel must stand 

 bending to a curve whose inner radius is one and a half 

 times the thickness of the sample, without cracking. 



140. Eye-bar material, ij inches and less in thickness, 

 shall, on test pieces cut from finished material, fill the above 

 requirements. For thicknesses greater than ij inches, 

 there will be allowed a reduction in the percentage of 

 elongation of I per cent, for each J of an inch increase of 

 thickness, to a minimum of 18 per cent. No bars over 2 

 inches in thickness will be used, except by special per- 

 mission. 



141. Full sized eye-bars shall show not less than 10 per 

 cent, elongation in the body of the bar, and an ultimate 

 strength not less than 56,000 pounds per square inch. 

 Should a bar break in the head, but develop 10 per cent, 

 elongation and the ultimate strength specified, it shall not 

 be cause for rejection, provided not more than one-third of 

 the total number of bars tested break in the head. 



