88 Dr. J. Muir. On Changes in Elastic Properties [Aug. 11, 



local extension. The third specimen was heated to 350° C, and 

 allowed to cool in the air. The behaviour of this specimen was very 

 similar to that of the quenched specimen. Rather less yielding was 

 obtained at low stresses, fracture occurred at 21,400 lbs. per square 

 inch, the ultimate extension was 0"'68 on 4 inches. The fracture was 

 abrupt, so that there was practically no local extension. 



Two specimens of cast tin were also tested, but owing to the low 

 melting point of tin quenching from 200° C. could only be tried. The 



Diageam No. 7. — (Aluminium.) 



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frque 



nched i 



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Extensions diminished by j^g^ 5 of &n inch for every spoo pounds 



of stress, 



Sc&Le :- iunit^ m V of An inch. & d , s. 



Diameter of specimens = 0""35. Length tested = 4' /- 00. 

 Specimen A. — As supplied. Broke four times in machine grips at 28,500 lbs. per 



square inch. Extension // '14 on 4 inches. 

 Specimen B. — Quenched from 550° C. Broke in the machine grips at 23,200 

 lbs. per square inch. Extension 0"*9 on 4 inches. 



quenched specimen showed rather greater extension at the lower 

 stresses; both specimens broke at 5250 lbs. per square inch; the 

 extensions were M *5 and 0"*8 on the 4-inch lengths, but local ex- 

 tension occurred in several places before fracture. 



In conclusion, it is proposed to consider how far the effects produced 

 by quenching described above may be accounted for by the stresses set 

 up in the material by the sudden cooling and consequent contraction, 

 the material, after quenching, being no longer in what has been termed 

 its " state of ease." 



When a long cylindrical rod cools, the cooling takes place radially, 

 and the end effects may be neglected. Taking any cross-section of the 

 rod, the outside ring will cool first and assume its elastic state ; the 



