ON THE CEYSTALLINE STKUCTURE OF LEAL). 
239 
further strain was applied. Figs. 27 and 28 are photographs taken (at a magnifica¬ 
tion of 45 diameters) of a marked area on the specimen after the first and second 
straining respectively. 
The final experiment consisted in straining a single crystal in tension until fracture 
occurred, and examining the slip lines. It was found that even in this case, although 
the surface was to some extent broken up by Avavy bands, such as are described on 
p. 231, yet the general direction of the slip lines was constant all over the crystal, 
right up to the fracture. In other words, the rearrangement in structure of which 
the preAuous experiment had given evidence does not occur during the application of 
a strain, eA’en when that is continued up to the limit of fracture. 
From these experiments we Avould gather that the formation of the patches of new 
orientation always takes place after the stress has been removed and is not directly 
the result of a general revolution of some of the crystalline elements in the process of 
straining. From former experiments Ave haAm learned that in parts of the crystal 
where the strain has been severe the patches of iieAv orientation appear almost 
immediately after the stress is remoAmd and gradually extend from these into the 
remainder of the strained portion. There appears, therefore, to be no Inroad distinction 
between the change Avhich is Ausible (on re-etching) almost directly after straining 
and that which takes place after a certain lapse of time. Such differences as are found 
depend on the amount of strain to Avhich the material is subjected and the temperature 
at AAdiich it is kept; se^mre straining and a high temperature Ijoth tend to increase 
the subsecpient rate of change of structure. 
This re-crystallisation Avhicli has been shoAvn to go on in an individual crystal must 
be distinguished in one important particular from that Avhich AA-as oljseiwed by Eaaung 
and Rosenhaix to go on in strained specimens of lead composed of numeroTis crystals 
united together by a thin film of eutectic formed of part of the lead united AA'ith the 
metallic impuiities. In the present case the specimens were coinposed of practically 
pure lead and the action Avas one of a splitting up of tlie originally uniformly oriented 
crystal into numerous differently oriented parts, the action proceeding Avithout tlie 
aid of any eutectic. In ordinary lead Eaaung and IIosenhain found that certain 
crystals gradually increased in size by SAvalloAA'ing up their neighbours, and they have 
suggested that this Avas due to a “ solution and diffusion of the pure metal constituting 
the crystals into the fusible and mobile eutectic forming the intercrystalline cement.” 
It is interesting to note in this connection that in the case of a single crystal strained 
so as to shoAv newly oriented parts, such parts shoAv no inclination to groAv into one 
another. When once the Avhole of the specimen Ijecomes iieAvly oriented, further 
cooking produces no further change. This, so fiir as it goes, may he regarded as in 
agreement Avith the theoiy of difiusion through the eutectic, as there Avoidd in the 
case of an originally uniformly^ oriented ciystal be no eutectic between the iieAvly 
oriented parts, and hence no such groAvth Avould Ije possible. 
With regard to the formation of tAvin cry^stals Ave may, hoAvever, apply a similar 
