I9I5-] 



IN RECENTLY HARDENED STEEL. 



61 



horizontal scratch was drawn across the poHshed fronts of the 

 bars G', H' by means of a straight-edge and sharp needle point 

 lightly applied. A microscope, magnifying about 200 diameters 

 and very solidly mounted, was brought into position and focused 

 on the horizontal scratch, which of course consisted of an inde- 

 pendent scratch on each bar, the two halves being initially in perfect 

 register. The microscope was provided with a filar micrometer 

 eyepiece carefully calibrated and adapted to measure accurately 

 any departure from register of the two half lines or scratches. 



Shrinkage of the hardened rod H was detected within two 

 minutes after scratching the brass bars, and was easily observable at 

 the end of two weeks. 



50 60 70 80 100 



Hours After Hardening 



Fig. S. 



Fig. 5 shows the progress of shrinking during the first 150 

 hours. The curve reached the 500 line a day or two later. The 

 hardened length of the rod was assumed to be 35 inches, so that its 

 actual shrinkage at the 500 line of the curve was 0.0175 inch. 



The rod was next scoured clean and tempered to light straw 

 color by electric warming, then to light blue color, and its total 

 shrinkage measured after each operation. Finally, it was thor- 

 oughly annealed by bedding in mineral wool, heating to very low 

 redness half an hour, and then gradually reducing the heating cur- 

 rent to nothing in the course of two or three hours, after which 



