1902.] 



produced by the sudden Cooling of Metals. 



87 



the local extensions at the points of fracture, or 1"*04, l" - 25, and 

 l"-98 respectively including the local extensions. 



Diagrams Nos. 6 and 7 may now be given without comment. They 

 illustrate tests made with brass and aluminium, and it is shown in 

 both cases that there is a loss of elasticity produced by quenching. 

 When the quenched material has been once loaded it is brought 

 approximately into the elastic condition, so that from a removal and 

 reapplication of load a straight stress-strain curve is obtained. 



Diagkram JSTo. 6. — (Brass.) 



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Extensions diminished by ioo°ooG bl - 6 of din inch for every 5,000 pounds) 



Scale :-l Unit = ^ u $ofa.n\mh.&. 



of stress) 



Diameter of specimens = 0"'44. Length under test = 4 // 000. 



Specimen A. — Brass as supplied. Broke 4 times in machine grips at about 

 48,500 lbs. per square inch. Extension from 0""87 on 4 inches 

 after the first break to 1"'68 after tbe fourth. 



Specimen B. — Brass quenched from 600° C. (B^ and from 700° (B 2 ). Broke at 

 42,500 lbs. per square inch after two breaks in the machine grips 

 at slightly lower stresses. Extension, 1"'33 on 4 inches. 



Three specimens of zinc, of diameter O'HO, were also tested. The 

 first — in the condition as supplied — broke at 21,000 lbs. per square 

 inch, the ultimate extension being 2"'04 on 4 inches. There was great 

 local extension, the specimen being drawn to a very narrow neck 

 before fracture. The second specimen was quenched from 350° C. 

 It yielded rather more for the lower loads than the first specimen, and 

 broke at 20,500 lbs. per square inch with an extension of 0"'41 on 4 

 inches. The fracture was quite abrupt, so that there was little or no 



