Temperature of Iron and Steel during Recalescence. 185 



while the anomalous temperature changes have their greatest 

 values in hard steel and rapidly diminish in magnitude with 

 the diminution of the percentage of carbon in the specimens. 



Herr Brinnell* is the one who first observed that hardened 

 steel re-tempers more quickly than annealed steel, and M, Os- 

 mond has found that heat is released in the heating of hardened 

 steel during the interval of temperature between 200° and 

 520°. I have found in corroboration that this releasing of heat 

 continually increases during heating from 200° to 350 c , and 

 thereafter decreases just as continually during the following- 

 heating up to about 500°. 



These observations appear to show : — 



(xi.) The re-tempering points d x and d 2 , mentioned above, 

 are not corresponded to by any isolated thermal points ; on 

 the contrary, heat is released during the whole interval of 

 temperature within which the re-tempering points in question 

 are situated. 



Approximate values of the coefficients of expansion of Iron 

 and Steel during the interval of temperature from 0°-800°, 

 and of the magnitude of the anomalous longitudinal changes. — 

 Figs 16-19 are grapldc reproductions of the length and 

 temperature curves in rods of Sandviken wire with different 

 percentages of carbon. These have been secured by simul- 

 taneous readings from the dilatometer and galvanometer at 

 every sixth second. 



Fig. 16. 



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Time. 1 min. 



1. Dilatation. 



2. Temperature rising. 



2 min. 



3. Contraction. 



4. Temperature falling. 



