THE CONSTITUTION OF THE COPPER-TIN SERIES OF ALLOYS. 
11 
Below the lines Ahlcdef, EgH' and the alloys are wholly solid, if they have 
been cooled with extreme slowness; we have succeeded in verifying this fact, hut, 
unless great care is taken to ensure slow cooling l^efore the chill, alloys chilled a little 
below these lines, which together make up the solidus, will be found to contain 
liquid at the moment of chilling. 
Classification of the Alloys into Groups. 
Vertical lines through the points B, L, C, D, E,/, G, H, I, divide the alloys into 
groups having special qualities. We will trace the complete cooling of an alloy from 
each group. 
(I.) The AB alloys, containing less than 5 atomic per cents, of tin, tliat is less than 
9 per cent, by weight. When these alloys begin to solidify they form, wliile above 
the line A6, a mixture of a crystals and liquid (fig. 2). When the temperature of an 
alloy has fallen below the line Ah, it consists of uniform a crystals embedded in a very 
little of a tin-rich mother-substance, which owes its existence to imperfect adjustment 
of the equilibrium between solid and liquid during the last stages of solidification. 
This small residue of liquid is absorbed by the a crystals at temperatures a little 
below hC and modifies the margin of these crystals, but in spite of some deceptive 
appearances, these alloys, at all temperatures below Ah, consist substantially of one 
phase, namely, the uniform solid solution a (fig. 7). 
(2.) The BL alloys, containing from 5 to 13 A atomic per cents, of tin, that is from 
9 to 22A per cent, by weight. These alloys, like the preceding group, commence 
their solidification by the formation of a crystals. Imt these never fill the whole 
volume, for when the temperature C (790°) is reached the reaction 
“k liqc = /3/ 
commences and continues until all the C liquid is exhausted. (The sub-indices h, C, I, 
indicate the compositions of the particular kind of a, liquid and respectively that 
take part in the reaction.) 
Tims, when tlie temperature falls below C, assuming that the ingot has l^een kept 
long enough at the C temperature, the alloy is wholly solid and consists of a crystals 
of the percentage h embedded in yd crystals of the percentage 1. Tliese yd crystals 
are uniform, and at lower temperatures play the part of a mother substance to the a 
crystals, wliich gi'ow at the expense of the yd wliile the solid alloy cools through the 
range of temperature hh'. This growth in the solid is very remarkable in alloys near 
the composition I, and accounts for the fantastic angular shapes seen in the a combs 
of the slowly cooled and unchilled alloys. Fig. 27, Plate 3, an ingot of Sn 13A, 
chilled at 558°, is a good example of this eftect. The a combs are light and the 
uniform solid /3 out of which they have grown, is dark. When the temperature falls 
below 500° (the eutectic line of Koberts-Austen and Stansejeld), the residual yd 
c; 2 
