272 Mr. G. T. Beilby on the Hard 
60. It is plain that the way in which work is done on the 
plastic metal must have an enormous influence on its structure 
and qualities in the hardened state. A wire which has been 
hardened by stretching is much inferior in tenacity to one 
which has been hardened by drawing through a die. This 
must result from a difference in the structural disposition of 
the two phases in the hardened metal. In the stretched wire 
the surface-layer during stretching must be alternately made 
and broken many times, and is finally left rough and open. 
In drawing, on the other hand, the flow of the surface as 
the wire is leaving the die ensures that it is strong and 
unbroken. 
61. One result of the intermixture of pbases in strained 
metal is that the crystalline aggregates, though isolated 
trom each other by the amorphous phase, are distributed in 
a form which ensures the quickest possible transformation of 
A —= C, when the transition temperature is reached. 
Consider the deformation of a crystallme grain which takes 
place by flattening. The lamellee of oriented units are spread 
out in all directions like the limbs of a disarticulated skeleton 
separated from each other by the amorphous phase. Each frag- 
ment of crystalline aggregate is made up of similarly oriented 
units, the adjoining fragments being for the most part similarly 
oriented. When the transition temperature is reached, the 
cerystallic force of these detached aggregates acts across the 
gaps between them, and compels the molecules of the amor- 
phous phase into the same orientation. A new skeleton with 
larger limbs and fully articulated is thus formed, and proceeds 
to clothe itself further by extending the area of the oriented 
molecules between its branches. In this way it is possible to 
explain the more vigorous growth of crystals in strained than 
in unstrained metal, which was supposed by Ewing and 
Rosenhain to result from a process of electrolysis in which an 
eutectic or foreign substance played a necessary part *, 
62. When a metal is rapidly cooled by quenching, strains 
may be set up which lead to a transformation of C into A 
phase. Muir has found that hardening by quenching results 
trom the overstraining of the successive layers of material in 
a rod or mass of metait. If the cooling is very rapid, a good 
deal of the strain will occur after the transition temperature 
is passed, and its results will remain therefore in a change of 
structure due to the transformation C-—— => M-——=A. 
63. With regard to the elastic properties of metal in the 
* Pal. rans. A, vol, cxcv: p. cel. 
+ Proc. Roy. Soc. vol. lxxi. p. 89. 
