1888. ] Recalescence of Steel, and allied Phenomena. 175 
It is a general practice in hardening steel to raise it to a 
bright red heat and chill immediately. I find that so long as 
it has been heated above ‘darkening’, it need not be chilled 
until just before reglow takes place. Chilling during reglow 
brings about a considerable degree of hardness : but chilling after 
the reglow leaves the steel as tough as though it had not been 
heated above the critical temperature at all. It may be that 
this temperature is Chernoff’s temperature ‘b’. 
Steel in which reglow is very marked very often cracks in 
hardening, especially if not heated very high before quenching. 
Such steel would be very interesting from the point of view of 
reglow: but the manufacturers clearly have no interest in making 
such steel. 
Chilled steel is, I think, recognised to have smaller density 
than the same steel before chilling. This is to be referred to 
the cooling of the outer rind on a swelled core, which cools and 
contracts later but leaves the external dimensions larger than they 
would be had the cooling been a slower process. In the case 
of bad steel, cracking by hardening is probably to be referred 
to actual expansion of the reglowing core within a cooled rind. 
The importance of this peculiarity from a practical point of view 
in the treatment of steel may well! be considerable. 
Thermo-electric peculiarities of steel. 
A study of the line for steel in Prof. Tait’s diagram shews 
that the peculiarities about a dull red heat could be partly 
explained if we could shew that the temperature of the steel 
fell at a certain point in the heating in spite of continued appli- 
cation of heat, and after falling for some time, then rose again 
continuously, whilst the thermometer in the enclosure containing 
the steel couple shewed continuous rise of temperature. We 
should, if this were the case, have to cut out a vertical strip so far 
as iron is concerned and close up the interval. 
If the peculiarity in steel is partly attributable to irregularities 
in heating or cooling, then a thermo-electric couple of, let us 
say, Pt Cu heated in a steel tube will shew the peculiarities 
ascribed by Prof. Tait to a change of sign in the Thomson specific 
heat of electricity. I have made this experiment and it shews 
most decisively that the peculiarity is not thermo-electric, or at 
least not wholly so. 
A piece of steel wire about lcm. diameter and 7 cms. long 
was softened and a hole 1 mm. diameter and 3 cms. long was 
drilled down its axis. A thermo-electric couple of Pt Cu com- 
posed of wires No. 36 B. W. G. was inserted, precautions being 
taken that there should be contact with the tube only at the 
