Micro-Metallography of Iron. 



63 



such large masses of iron to cool from a white beat appeared to 

 facilitate the production of the crystals of the secondary formation. 



Table II. Secondary Micro-crystallisation of Metallic Iron. 



In the case of both the primary and secondary crystals the pre- 

 dominant well-defined angles of the facets of the crystals hovered more 

 or less about the angle of 120. The majority of the angle readings, 

 nmde with the goniometer attached to the microscope, indicated 

 generally a hexagonal structure or form of crystallisation. There 

 were, however, also perfect cubical crystals observed. 



The rationale of this duplex crystallisation has apparently been as 

 follows : The mass of metallic iron on cooling having reached the 

 crystallising point at about 740 C., the periphery or skeletons of the 

 larger or primary crystals were then formed. As the period of 

 cooling was, however, very slow, the semi-fluid or viscous metal in 

 the interior of these primary crystals was, on fiually consolidating, 



