ON DILUTE SOLUTIONS OF ALUMINIUM IN GOLD. 
275 
Description of the Microphotographs (Plate 4). 
2 . 
3. 
4. 
1. A1 15. 50 diameters. 
Plunged molten into bath at 470° C., annealed for 20 hours and chilled. 
A uniform solid solution of alpha. 
A1 15. 50 diameters. 
Annealed at 545° C. for 23 hours and chilled. 
The white is alpha, the dark matrix is beta. 
A1 18. 50 diameters. 
Plunged molten into bath at 520° C., annealed for 8 hours, chilled. 
Shows the decrease in the alpha as the content of A1 grows. 
A1 20. 18 diameters, oblique illumination. 
Plunged molten into bath at 535° C., annealed for 17 hours, chilled. 
Beta only. The relief effect is due to minute striations. 
5. A1 18. 350 diameters. 
Plunged molten into bath at 470° C., annealed 20 hours, chilled. 
The greater part of the beta of this ingot etches the usual uniform dark, but some patches 
give the bright ruling of the photo. This is, no doubt, due to a very perfect laminar 
crystallisation of the beta, or of a body derived from the beta. The smooth parts are 
alpha primaries. This bright ruling can be found in a good many alloys from A1 18 to 
A1 23 when chilled above 440° C. Almost equally perfect ruling can be found in the 
dark beta. 
6. A1 23. 20 diameters. 
Plunged molten into bath at 506° O., annealed for 3 hours, cooled to 410° C., annealed for 18 hours, 
chilled. 
The white is D, the ground is now, presumably, Y. The photo shows three crystal skeletons 
of D. It is typical of all the primaries of D. 
7. A1 25. 50 diameters. 
Plunged molten into bath at 535° C., annealed 20 hours, chilled. 
The white is D, the dark is beta. The small pattern, which must have formed rapidly during 
the chill, but a good deal of it at the eutectic temperature of the point C, seems to be 
made up hexagonal rods of beta surrounded by a margin of D. This is the nearest 
approach to the C eutectic that we have. 
8. A1 20. 160 diameters. 
Plunged molten into bath at 510° C., annealed 1 hour, cooled to 440° C.; annealed 3 hours, cooled 
to 418° C.; annealed 9 hours and chilled. 
The large dark bars are pseudo-primary of D that separated when temperature fell to the cL 
line. The small pattern is the L eutectoid of alpha and D. 
8a. A1 20. 160 diameters. 
The same ingot as that of fig. 8, but after the further treatment of dropping the ingot cold into 
bath at 400° C. and so provoking the recalescence. The ingot was annealed for 10 minutes 
at 400° C. 
The small white is the alpha left after the decomposition of the eutectoid. The dark ground 
is Y. The large white is the residue of the pseudo-primary of D; this would be removed 
by a longer anneal and would leave a pattern like that of fig. 17. 
9. A1 18. 300 diameters. 
Plunged molten into bath at 418° C., annealed 22 hours and chilled. 
A pre-recalescence pattern. The large white is primary alpha. The smaller complex is the L 
eutectoid of alpha and D. 
9a. A1 18. 300 diameters. 
The same ingot as that of fig. 9, but after recalescence brought about by heating for 10 minutes to 
400° C. 
The large primaries of alpha are no longer uniform, but are full of the recalescence pattern 
(compare with fig. 10). The small white is the residue of alpha left over after the 
decomposition of the L eutectoid. 
9b. A1 23. 350 diameters. 
Plunged molten into bath at 560° C., cooled in 2 hours to 420° C., chilled. 
A pre-recalescence pattern. The large dark masses are primary D, the complex is the L 
eutectoid. 
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