THE COXSTITUTION OF THE COPPER-TIN SEPHES OF AI.LOYS. 
53 
same is true of all lower chills; for example, those at 556° and 380°, that is to say, of 
all ingots chilled below the D' temperature. But these ingots contain a new feature 
in the form of lace bars. The bars do not present the same variety of shade, and 
many of them are merely outlined and not completely filled in with the black, but 
their interior consists either of a fine ruling of black and white, or of a lace-work of 
the two. We are disposed to think that the lace bars are not bars imperfectly formed, 
but bars that have suffered a partial disintegration into two phases, which may be 
the final phases of S and y. On this view we may presume that the l^roader uniform 
bauds of the chill at 580° would have turned into lace bands if slowly cooled to a 
lower temperature before the chill. We do not reproduce the lace-bar eftect in Sn 21, 
as it is even better shown in Sn 22.^ 
Sn 22. 34’45 cent, of tin. 
At this percentage there is a slight singularity in Roberts-Austen and Stansfield’s 
transformation curve, and although our pyrometric determinations did not justify us 
in reproducing this singularity in our diagram (Plate 11), the microscopic study of the 
chills to some extent confirms their curve. The cliill patterns resemble those of the 
preceding alloy, but there are certain differences. 
Sn 22. Chilled at 733° (fig. 58). 
Tins shows very w^ell the characteristic clumsy y combs, generally dark on a lighter 
ground. One also sees bars of y, as a rule, in the mother-substance. 
Sn 22. Chilled at 7 10° (not reproduced). 
Tile solidus appears to lie at 700°, for the alloy at 710° has abundant primary 
combs in it of the true y type, with nothing rectangular about them. There is also 
a little chill primary. The combs are copper-ricli, but the heat oxidation employed 
to prove this point Iras, in places, modified the somewhat unstable material and caused 
the growth of bars of y. The y crystals will be found to be still more unstable when 
they contain a little more tin. 
Sn 22. Chilled at 690° (fig. 59). 
The ingot must have been quite solid at the moment of chilling, for the primaries 
have entirely gone and are replaced Iry large patches of uniform solid solution, but 
* [At a later date the ingot of fig. 57 was re-heated to a temperature between 500“ and 600°, cooled 
without chilling, polished and etched with FeCb. The re-heating has entirely altered the pattern; the 
broad twinned bands of have disappeared, by far the greater portion of the surface consists of white 8 
with some scanty lace bars of black »/. Unfortunately, this experiment was made too late for the 
reproduction of the photograph.—June 29, 1903.] 
