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Dr. W. C. Anderson and Mr. G. Lean. [June 16, 



and were cast as before in a chilled mould. One half of the ingot was 

 polished directly and etched for five minutes with a 2-per-cent. solution 

 of caustic potash. The other half was annealed at 400 C. for 

 twenty hours and then treated similarly. The two sets are referred 

 to as the cast and annealed metals. The series examined ranged in 

 composition from 99 per cent, aluminium to 1 per cent. When the 

 percentage of aluminium exceeds that required to saturate the tin, 

 which from our experiments is under 0'5, two constituents are always 

 visible in the solidified alloy. One of these, easily recognisable as 



DIAGHAM 2. Hydrogen Evolutions. 



that which solidified first, is abundant in those alloys which are rich 

 in aluminium and decreases in quantity as the percentage of aluminium 

 is lessened. In the cast metals, as illustrated in fig. 2, it is intimately 

 mixed with the second constituent, which is the eutectic, until the 

 aluminium has diminished to about 15 per cent., when it begins to 

 appear in isolated patches in the eutectic. The exact freezing point 

 of this eutectic mixture has been stated by Heycock and Neville to be 

 228-73 C. Annealing causes the constituent of higher melting point 

 to segregate into patches, and the eutectic becomes then more clearly 

 visible (fig. 3) even in alloys with a high percentage of aluminium. 

 The lowest temperature at which this segregation takes place actively 

 is above 250 and below 300 C. The photographs (figs. 4 and 5) 



