28 
MR. J. MUIR ON THE TEMPERING OF IRON 
shows that the material now gave a yield-point at a stress only slio’htly higher than 
before. 
Diagram No. 7. (Tempering of Lowmoor Iron hardened l)y stretching.) 
Scale-.—I Unit = of an inch. _1- 
A temperature of 650° C. was next tried, and it was found that this temperature 
lowered the yield-point by a remarkably large amount, Curves Nos. II aud 12 showing 
that the material yielded at a stress distinctly less than that required to produce yielding- 
in the very first test of this specimen, which it may be recalled had been annealed by 
heating to 750° C. Curves II and 12 thus show that the overstraining and tempering 
which the specimen received as the result of the operations illustrated by Curves 1 
to 10 had brought the material into a condition more sensitive to the influence of 
temperature. 
The material was now hardened again by successive overstrain in the manner 
illustrated by Curves 13, 14 and 15, lOiagram 7, recoveiy from overstrain being 
