278 



PROGRESS IN MICROSCOPY 



As the solidified specimen is heated, the two eutectics, E^ and E., 

 melt. The eutectic E^ is between the substance A and the compound M, 

 the eutectic E2 being between the compound M and the substance B. 

 If the temperature is increased, the compound M melts and 



D 



O 



w 



a> 

 o 



E 

 .1' 



Pure 



I Composition 



B 

 Pure 



Pure 



Composition 



Pure 



Preparation 



Fig. 11.12. Binary temperature-compo- 

 sition diagram in a system showing simple 

 eutectic formation. 



Preparation 



Fig. 11.13. Temperature-composition dia- 

 gram for an addition compound system 

 (congruently melting addition compound). 



becomes a homogeneous liquid: fusion is congruent. In incon- 

 gruent fusion, the compound M cannot melt without being decomposed. 



(iv) The substances A and B do not react and are not miscib/e in 

 any proportion in the solid state. When the substances A and B are 

 not miscible in any proportion in the solid state, they yield two series 

 of mixed crystals, some are richer in A, some are richer in B as shown 

 in Fig. 11.14 and 11.15, respectively. In the first instance (Fig. 11.14), 

 the series of rnixed crystals richer in A have a B content ranging from 

 zero to the value shown by the abscissa of the point G. The crystals 

 richer in B evince their saturation limit in A (abscissa of the point Co). 

 The inter-space CyCo is a lack of miscibility, in the solid state, of the 

 two substances A and B (lack of syncrystaliization). The saturated 



