428 TRANSACTIONS OF SECTION B. 
3. The Structural Changes brought about in certain Alloys by 
Annealing. By O. F. Hupson, M.Sc., A.R.C.S. 
A Jarge number of the useful alloys, particularly those which are rolled, drawn, 
or otherwise worked, consist of crystals of one kind only—viz. a solid solution. 
When alloys of this class are annealed, the structural changes that may be 
observed are : 
1. The cored structure usually characteristic of the alloy in the cast state 
gradually disappears, and the crystals become quite uniform in composition 
throughout. Structurally the alloy does not now differ from a pure metal, and 
other structural changes due to annealing are similar in both cases. 
2. If the alloy has been worked before it is annealed pronounced crystal 
growth is observed when the annealing takes place above a certain temperature, 
which varies with the alloy. In most cases also numerous twinned crystals are 
seen. In effect the alloy is recrystallised. If the temperature of annealing is 
raised the crystal growth becomes more pronounced, particularly from certain 
centres, and a very coarsely crystalline (overheated) metal or alloy may result. 
It is, however, to be noted that if the annealing is carried out at a suitable 
temperature a finer structure than the original is obtained. 
The recrystallisation of the strained alloy and the disappearance of the 
‘cores’ go on side by side until uniformity of composition is reached. 
In the case of alloys consisting of crystals of two or more kinds, those which 
are malleable are usually composed of crystals of two solid solutions. Generally 
the chief effect of annealing these alloys is to promote equilibrium between the 
two phases present. Crystal growth also takes place partly on lines similar to 
those indicated above and partly by the absorption of the smaller crystals in 
larger ones of the same kind. In some cases the annealing operation may result 
in a true recrystallisation. Complete phase and structural equilibrium in some 
alloys of this class are only attained after very prolonged annealing, and in 
many instances the alloys as used are in a meta-stable condition. 
The decrease in hardness and the lowering of the elastic limit due to the 
annealing of cold worked metals and alloys are almost complete before crystal 
growth becomes noticeable, and are apparently unaccompanied by structural 
chariges which can be observed by microscopical examination. 
4, Diffusion in Solid Solutions. 
By Cec H. Descu, D.Sc., Ph.D. 
Since the author’s report to the Dundee Meeting of the Association, Bruni 
and Meneghini have succeeded in demonstrating the occurrence of diffusion in 
a clear, crystalline solid in the case of sodium and potassium chlorides. <A 
mixture of these two salts, heated at 500° or 600°, yields a homogeneous solid 
solution, the formation of which is recognised by determining the heat of solu- 
tion in water, which differs from that of a mechanical mixture. 
The author’s further experiments with metallic alloys show that a sharp 
boundary is characteristic of diffusion in solids when a chemical compound is 
formed. An abrupt discontinuity of composition is also observed when one 
component is removed by solution, as in the dezincification of alloys of copper 
and zinc. 
5. Some Phenomena in the Formation of Eutectics. 
By F. E, E. Lameiovex and J. T. Scorr. 
6. The Electrical Conductivities of Sodium Amalgams. 
By Ernest Vanstone, M.Sc. 
Continuing the physico-chemical investigation of sodium amalgams, the author 
has determined their electrical conductivities when in the solid state. The 
amalgams were melted and drawn up into a capillary spiral 1 mm. diameter, 
