284 The Properties of the Aluminium-Tin Alloys. [June 16, 



final member of this series of solids has the composition AlSn, and 

 begins to fall out from a solution of the same composition at 561 C. 

 The line ABCD connects the upper limits at which the separation of 

 solid matter takes place in fluid mixtures containing excess of aluminium 

 atoms. The line HKL marks the lower limit at which in our experi- 

 ments this separation was active. Within the area ADLKH the 

 mixture consists of solid, so-called aluminium-rich constituent, by which 

 is to be understood solid containing not less than one atom of aluminium 

 to one atom of tin, along with liquid of approximately the same com- 

 position. From mixtures containing about 18*5 per cent, of aluminium 

 and lower proportions than that the last member of the former series 

 AlSn is being separated from a fluid medium which contains excess of 

 tin atoms, and the solution is thereby gradually impoverished in respect 

 of aluminium until at the eutectic point, 228*73 (Heycockand Neville), 

 it retains only about 0'48 per cent, of that constituent. 



The existence of the compound AlSn as the terminal member of a 

 series of bodies separating out from the fluid mixtures of aluminium 

 and tin is inferred from the flattening of the liquidus curve at the part 

 CD, in the vicinity of an alloy of this composition, and the small 

 amount of heat liberated in mixtures richer in tin than AlSri as indicated 

 by the liquidus and solidus curves approximating closely to one another 

 to the right of that point. 



The part of the curve from F to the eutectic point G has not been 

 systematically examined by us, but analyses which we made on the 

 fusible portion of the alloys which is automatically expressed at higher 

 temperatures than the eutectic point, prove that the solvent power of 

 tin for aluminium becomes appreciably greater as the temperature is 

 increased. The liquid metal squeezed out between 300 and 400 C. is 

 a solution, when liquid, containing 3 to 4 per cent, of aluminium. The 

 ingots of composition Al = 42*5 per cent. ; 15 '4 per cent. ; 8 '04 

 per cent., yielded at 400 C. respectively beads of composition 



Al = 3-50 per cent. : 3'76 : 3' 



52. 



The saturated solution of aluminium in tin at 400 contains there- 

 fore 3 '5 9 per cent, of aluminium, equivalent to 1 part AlSn dissolved 

 in 5 parts of the solvent medium having the composition of the eutectic 

 (0'48 per cent. Al). The segregation resulting on very slow cooling 

 of these beads of saturated solution causes the very fluid eutectic residue 

 to be extruded in some cases so as to cover the solid bead with an 

 appendage of fine metallic hairs. The extent of this segregation will 

 be indicated by continuing the line LM in the curve to meet EFG 

 at the eutectic temperature G. The ease with which the compound 

 AlSn, aluminium stannide, becomes oxidised, makes it impossible so far 

 to isolate it from the metallic mixture in which it is produced. 



