CHEMICAL MICROSCOPY 



279 



crystals Ci and Ca are called limit mixed crystals. In Fig. 11.14, 

 (A) and (B) denote the isomorphic crystals of the constituent A and B, 

 (Ci) and (Ca) the limit mixed crystals. Figure 11.15 does not differ 

 much from Fig. 11.12. The mixtures on either side of the point K 



Composition 



Pure 



a> 

 a. 



E 



Pure 



Cornposition 



Preparation 



Fig. 11.14. Temperature-composition dia- 

 gram when substances A and B are not 

 miscible in any proportion in the solid 

 state (peritectic point K). 



Preparation 



Fig. 11.15. Temperature-composition dia- 

 gram when substances A and B are not 

 miscible in any proportion in the solid 

 state (eutectic point i; and mixed crystals). 



(peritectic point) are similar to those shown in Fig. 11.12. The 

 area to the left is the first one to melt as temperature rises. A simple 

 eutectic is shown in Fig. 11.15, the A crystals having a low B 

 content and conversely. The points Q and C, correspond to the limit 

 mixed crystals which are isomorphic to A and B, respectively. 



7. TEMPERATURE COMPOSITION DIAGRAM OF BINARY MIXTURES 



In general, plotting of the temperature composition diagram merely 

 consists in determining the melting points M and N of the two pure 

 substances A and B (Fig. 11.16) and both the melting point and com- 



19 



