Till: ORIGIN OF MINERALS 



241 



tho percentage of the original solution might be, upon cooling 

 cither salt or \v;itcr will separate from the solution as the case 

 may be and continue to do so, as the temperature is low* r. 1 , 

 until the constant percentage mixture of 77 parts water and 23 

 p:u-t> salt is reached at 22.4, when the solution will solidify 



as a whole. Such mixtures, which have a constant composition 

 and solidify as a whole at definite temperatures under like condi- 

 tions, are termed eutectic mixtures. Fig. 368 is a so-called fusion 

 diagram of a two-component system, water and salt. The plan, 

 one in which temperatures are measured vertically and percen- 

 tages horizontally, is divided into four fields of conditions by the 

 two curves AB and BC and the straight line DE. In field I, 



