94 



time. Treatments at temperatures above 250° C. were carried out by 

 heating in covered crucibles in an electric muffle furnace. For lower tem- 

 peratures the specimens were immersed in a bath of heated glycerine. 



Sections of the treated specimens were examined and photographed as 

 before. A measurement of crystals was made on the ground glass of the 

 camera and actual sizes calculated. In the chill cast specimens 7 -tin- 

 antimony crystals varied from 0.015 to 0.05 mm and €-tin-copper from 0.02 

 to 0.18 mm in their longest dimensions. In table I are summarized the 

 results of the various thermal treaments of the chilled pieces. Figs. 13 and 

 14 illustrate two of the treatments in the lower temperature ranges. 



♦All photomicrographs have been reduced one-third by the printer. 

 TABLE I 



