BORAX. 



33 



6500 

 (7251 



6000 



once crystallization was induced only io below it in a furnace of 



constant temperature. The 

 rapidity with which the crys- 

 tallization and the accompany- 

 ing release of the latent heat go 

 on depends in part upon the 

 rate of cooling and the char- 

 acter of the disturbance which 

 has been applied, i. c, upon 

 accidental rather than char- 

 acteristic conditions. It thus 

 happens that the amount of 

 the heat of fusion and its slow 

 rate of liberation in the case of 

 liquids which can be greatly 

 undercooled and become very 

 viscous may be such as to 

 deprive it of its usual signifi- 

 cance as defining a solidifying 

 point. It is, of course, a con- 

 sequence of the phase rule that 

 the solidifying temperature of 

 an undercooled liquid is estab- 

 lished, if only equilibrium be- 

 tween solid and liquid (and 

 vapor) is reached before com- 

 plete solidification is accom- 

 plished, but equilibrium is not 

 necessarily attained during so- 

 lidification, and the devices 

 usually employed (sowing with 

 crystals, agitating) are often 

 totally inadequate to effect it. 

 The temperature to which a 

 crystallizing liquid rises after 

 undercooling is not necessarily 

 constant or in any way related 

 to the melting point and is, 

 therefore, not, in general, enti- 

 tled to be regarded as a physi- 

 cal constant. 

 We then endeavored to ascertain whether the unstable domain had 



a lower limit also. For this purpose we mixed a quantity of the 



5500 



o 



> 

 o 

 l_ 

 o 



E 



c 5000 



u 



L. 



3 



0> 



a. 



E 

 u 



4500 



4000 



3500 



3200 



(400) 



20 



40 60 80 

 Time (minutes) 



100 



Fig. 7. Curves showing difference in spe- 

 cific heat between crystalline (ad) and 

 vitreous (bb) borax under like condi- 

 tions of cooling and reheating. 



