RESINOGKAPHY 



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Fig. 8. Two "alloys," high in polystyrene containing small amounts of synthetic rubber as particles 

 of Type III, illustrating also two methods of preparation and two methods of lighting. Left: Polished 

 and etched (benzene in methyl alcohol ca. 1:4); bright-field reflected illumination. Right: Microtomed 

 thin section; bright-field, slightly oblique, transmitted illumination. 



Fig. 9. Polystyrene varjang across the field in proportion of isotactic (crystallizable) and atactic 

 (non-crystallizable). Light micrograph of unstirred sample between partially crossed polars, by trans- 

 mitted illumination. Melt quenched in air, warmed slowly until glassy phase, such as (G) was almost 

 entirely transformed to continuous rubbery (R) phase, held at slightly lower temperature to form some 

 colonies (X) of crystals, quenched again to freeze the 3 co-existent phases, not in equilibrium. Some 

 cracks are isotropic (shown black); some are anisotropic (shown white). 



The crystalline parts of Type IV are gen- (e.g., undulate extinction between crossed 

 erally aggregates of unicrystals (Types II & polars), and practical properties (e.g., inter- 

 Ill) (Figure 11). Such aggregates have their granular fracture). There is some evidence 

 characteristic habit (e.g., spherulitic), origin that at least some kinds of aggregates are a 

 (e.g., self -nucleating) , optical properties combination of crystalline (internal) forces 



530 



