30 
MR. J. MUIR OX THE TEMPERING OF IRON 
influence on the tempering of Lowmoor iron hardened by overstrain. Curve No. II 
.shows that 500° C. had lowered the yield-point to 21 or 21 ^ tons per square inch, 
while Curve 12 shows that, by keeping the specimen for two hours at about 500° C., 
the }deld-point was lowered to 19 tons per s(piare inch. Time has no doubt a slight 
effect on the similar tempering of steel; but in both cases temperature is distinctly 
the main determining cause. 
Picagram No. 8. (Tempering of Lowmoor Iron hardened by stretching.) 
tcnsjzn^ 
Scale-.—I Unit = of an inch.° - \ -■ 
Curve No. 15, Diagram 8 , which was olffained after lieating to 600° C, shows a 
very large drop in the yield-point similar to the drop obtained at 650° C. with the 
specimen whose history is given in Diagram 7. The yield-point shown by Curve 15 
is lower than that shown Ijy Curve 1 of Diagram 8 , that is, it is lower than the 3 Ueld- 
point given with material which had been annealed for a long time at 750° C., hut 
which had never been subjected to any tensile overstrain. 
