280 



PROGRESS IN MICROSCOPY 



position of the eutectic mixture E. The fusion curves ME and NE 

 are plotted arbitrarily. If required, the melting point and composition 

 of an addition compound, the maximum or minimum of the curves 

 of a solid solution may also be determined. 



Pure Composition Pure 



Fig. 11.16. Kofler method for determination of eutectic composition. 



Kofler devised a striking method whereby the temperature com- 

 position of a binary mixture can be promptly determined without 

 any need for weighing. Let us assume that the index of pure A be 

 1-350 at t\ and the index of pure B be identical at t^ (Fig. 11.17). 

 In most melted mixtures and liquid bodies at normal temperature, 



O) 



\_ 



o 

 E 



t 



A 

 Pure 



M 



Composition 



B 

 Pure 



Fig. 11.17. Temperature variation versus the mixture composition keeping the index 



constant. 



the temperature variation versus the mixture composition keeping the 

 index constant (1530 in the case depicted in Fig. 11.17), is shown 

 by a straight line, such as ab. As an instance, for a mixture of com- 

 position A/, the mixture index is 1530 at the temperature /". This 



