38 
MESSRS. C. T. HEYCOCK AND F. H. NEVILLE ON 
a case of isomorphism in what may be called two conjugate solid solutions, but the 
great frequency of the regular system in the crystallisation of metals renders it more 
probable than it would otherwise be. 
The LC Alloys. —This small group, covering the atomic percentages from Sn 13'5 
to Sn If)'5, consists of alloys which polish to a yellowish-white. The unchilled alloys 
are compact, hard, and tough. 
We detect three well marked halts in the cooling curves of this group, one due to 
the latent lieat of crystallisation at the freezing-point, the second to the heat evolved 
at the C temperature l)y the reaction a + liquid the third at the C' temperature, 
due to the breaking iq3 of solid ^ into the C' complex, a reaction which we think is 
represented by the equation ^ = a -f- S. 
There must also, both in these and in the preceding group, be heat evolved when 
the temperature of the cooling alloy crosses the IG' line and the crystallisation of new 
a in large crystals out of the solid (i commences ; but this is a gradual process, and 
the heat evolved at any one temperature is apparently not enough to produce a 
perceptible effect on the line of tlie cooling curve. 
Like the preceding group, these alloys commence their solidification l)y the formation 
of a combs, but when the temperature has fallen to that of the point C and the a 
combs cease to form, there is more than enough liquid to transform all the a into /3; 
hence, with sufficiently slow cooling, ingots chilled between IG and the solidus Ic 
will he found to consist of yd combs immersed in a tin-rich mother-substance, while, 
when the temperature has fallen to a point on the solidus, the ingot will be a uniform 
mass of yS. The ingot will then remain uniform until the line IG' is reached, when 
the solid yd will have cooled to a point at which it is saturated with a, and that 
body will separate out in large crystals; the amount of these increases until the 
C' temperature is reached, at which temperature tlie yd becomes also saturated with S, 
and the eutectic separation commences. The two bodies, a and S, will now crystallise 
simultaneously and form the pearlite eutectic, similar to that in fig. 19. The chills of 
Sn 14 afford good illustrations of these changes. 
Sn 14. Chilled at 800° V.s.c. (fig. 28). 
These ingots are much distorted by granulation, but are compact enough for 
polishing. The simplest pattern is that developed by strong ammonia. This re-agent 
dissolves and darkens the a combs, and leaves the ground a very uniform dead white. 
One sees about 10 per cent, of a, arranged in very rectangular combs. The lobes are 
very rounded and often separated from each other, forming rows of rounded dots. A 
ferric chloride etch, fig. 28, shows the same combs light on a dark ground, and the 
ground is now seen to contain a good deal of dark chill primary, which is probably 
In essentials, the pattern resembles that of Sn 12 chilled at 805°, with tlie exception 
that in the chill of Sn 14 there is less a. 
