THE CONSTITUTION OF THE COPPER-TIN SERIES OF ALLOTS. 
9 
considerable confidence that the solidus, as we have drawn it, is a good first approxi¬ 
mation to the truth. 
The Substances occurring in the Alloys. 
The diao-ram of Plate 11 also contains a number of thick vertical and horizontal 
lines which divide up the area below the liquidus into closed compartments. Each 
of these compartments embraces all the temperatures and percentages for which the 
alloys are in a particular state of aggregation, and the phases making up the 
aggregates are indicated for each compartment. 
The following phases may occur :— 
Liquid, which is found in every compartment that lies between the liquidus and 
the solidus ; 
Crystals of five different types, which we designate a, /3, y, S, 77 , and H; 
The substance crystallising along the branch IK of the liquidus, which must be 
pure, or nearly pure, tin. 
The liquid may, of course, have any percentage weight of tin in it from 0 per cent, 
to 100 per cent. The a crystals are solid solutions, apparently isomorphous with pure 
copper. They may contain any percentage of tin not greater than 9 per cent. The 
S crystals are also solid solutions, perhaps isomorphous with the a. They range in 
composition from 22 ‘5 per cent, of tin to about 27 per cent. No uniform solid 
solutions are formed with percentages of tin between 9 per cent, and 22’5 per cent, of 
tin. The y crystals are also solid solutions of copper and tin or of compounds of the 
two metals. They do not appear to be isomorphous with the preceding. They range 
in composition from about 28 per cent, to about 57 per cent, of tin. The S material 
possesses a well-marked crystalline character and is very constant in appearance in all 
the alloys in which it is found. It may be a solid solution of varying composition 
like the preceding, but we are disposed to think that it is more j)robably the pure 
compound CrqSn. The y forms large crystalline plates, often bounded by plane faces 
making definite angles with each other. It occurs in all alloys between E and H, 
and in many of these alloys we have proved by isolation and analysis that it is the 
pure compound CugSn; it also occurs in the alloys between D and E, here it has 
the same crystalline form, but there is some reason to think that it may be a solid 
solution of varying composition. 
The H substance does not differ much in composition from the compound CuSn ; it 
plays an important part in anti-friction alloys. We have made many analyses of H, 
and find it very constant in composition; but it contains a few per cent, more copper 
than corresponds to the formula CuSn; it is probably CuSn containing some CugSn 
in solid solution. 
The substances a, S, y, y and H are found as primary crystals and mixed with liquid 
in ingots chilled between the liquidus and solidus ; the S substance never crystallises 
VOL. ecu.-A. C 
