BORAX. 



31 



Observations were then undertaken upon the crystalline borax with 

 a thermo-element as before, to determine the melting temperature and 

 solid modifications, if such existed, but none of the latter were found. 

 The charge melted uniformly at 742 and the melting point was well 

 defined. A curve showing the minute-to-minute observations on the 

 crystalline borax between the temperatures 650 and 775 is shown in 

 fig. 5, a. 



Having determined the melting point of crystalline anhydrous 

 borax satisfactorilv, we examined more closely into the conditions 



Time - 1 division = 10 minutes 



Fig. 5. -a, Melting-point curve; b, c, d, curves showing undercooling and 

 crystallization at different temperatures. 



under which it solidified. As has been said, if the melted charge was 

 allowed to cool slowly, undisturbed, no return to the crystalline state 

 occurred. It merely thickened gradually into a transparent glass 

 without releasing the "latent" heat which it had taken on in melting 

 (fig. 7, b). If it was subjected to the jarring produced by the electric 

 hammer on the furnace wall, it cooled down a few degrees below the 

 melting point and then began to crystallize, the heat of fusion was set 

 free, and a rise in temperature immediately appeared, represented by a 

 hump upon the cooling curve, as shown in the figure (fig. 5, b, c, d) . Up 

 to this point the phenomenon differs but little from the usual behavior 

 of liquids which undercool in solidifying. We next varied the experi- 

 ment by first cooling quietly to about ioo below the melting point 







