102 Day and Allen — Isomorphism and Thermal 



or range of temperature would be found within which the 

 vitreous condition would prove unstable and crystallization be 

 precipitated. The jar produced by an electric hammer pound- 

 ing upon the outside of the furnace during cooling proved to 

 be sufficient to bring down the entire charge as a beautiful 

 crystalline mass of radial, fibrous structure, brilliant luster, 

 rather high refractive index and increased volume. The pho- 

 tograph (fig. 2) will give some idea of the appearance of the 

 anhydrous crystalline borax in the crucible. Its specific grav- 

 ity proved to be 2'28 as compared with 2*37 for the glass, a 



(765°) 

 6800 



6700 



6600 



(740°) 



6500 



6400 



S 5900 



5800 

 (660°) 















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y 



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Time. 1 div. = 10 minutes. 



F£G. 3. 



somewhat unusual relation,* which may in part account for 

 the quasi-stability of the vitreous form during cooling. 



Observations were then undertaken upon the crystalline 

 borax with a thermoelement 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 660° and 765° is shown in the adjoining figure 

 (fig. 3, a). 



Having determined the melting point of crystalline anhydrous 

 borax satisfactorily, we examined more closely into the condi- 

 tions 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 into a 

 transparent glass without releasing the "latent" heat which it 



* Tammann. Loc. cit., p. 47 et seq. 



