1904.] Physical Characters of the Sodium Borates, etc. 



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satisfactory enough. The melting point curves for the glasses and 

 crystals are represented on fig. 2. The curve for the glasses presents 

 some features which are difficult to explain, since, so far as we are 

 aware, no such curve has before been described. 



FIG. 2. 



Molecules of Na e O to one Molecule of B 2 3 . 



The addition of sodium oxide to boric anhydride raises the melting 

 point continuously till a mixture of composition Na 2 0.4B 2 3 is reached. 

 There seems to be no depression of the melting point at all, thereby 

 differing from the case of ordinary solution, and indicating the 

 probability that there is no solid phase. 



The curve then remains fairly level till a composition Na 2 O.2B 2 3 is 

 reached, when it falls irregularly to 3Na 2 0.4B 2 Os. 



The last point we could obtain on this curve was with composition 

 Na 2 O.B 2 3 , where the melting point practically coincided with the 

 temperature of change from the glassy to the crystalline state of this 

 mixture. Indeed it is a little above it, but it was possible by fairly 

 rapid heating to melt the bead before the change had occurred. 



At present we are unable to state exactly what the meaning of this 

 melting point curve for the glasses may be. Glasses have hitherto been 

 supposed to possess no sharp melting point, but this does not seem to 

 be the case, as our results for each different temperature were remark- 

 ably close and well defined. 



