1904.] Physical Characters of the Sodium Borates, etc. 293 



On analysis obtained : 

 Glass = 4-18 per cent. Na 2 O; crystals = 1O02 per cent. Na 2 0. 



(viii) Mixture of Composition about Na 2 0.40B 2 03. This could not 

 be crystallised at all. 



From these numbers it appears that with mixtures between 

 Na 2 0.4B 2 3 ' and Na 2 0.2B 2 O 3 the crystals and glass have absolutely 

 identical composition, but with mixtures containing more boric anhy- 

 dride than Na 2 O.4B 2 3 , only a part (decreasing in quantity as the 

 amount of boric anhydride present increases) crystallises, and this 

 part has approximately the composition Na 2 0.6B 2 O 3 . 



As the crystals of the mixture of this composition contain more 

 sodium than the glass, it seems probable that, could one obtain the 

 crystals really pure and not entangling any glass, the composition 

 might approach that of Na 2 0.4B 2 3 . 



The nearness in composition of the crystals obtained from mixtures 

 varying from Na 2 O.16B 2 3 to Na 2 0.6B 2 3 makes it seem fairly certain 

 that it is the same compound which separates out in all of them, and 

 that the differences in the analyses are due to the crystals being mixed 

 with more or less glass which it was impossible to remove. In experi- 

 ment (vi) the crystals and glass were particularly well separated, and 

 the result is shown by the great difference in their analyses. 



It seemed so curious that with mixtures of composition Na 2 O.2B 2 3 

 to Na 2 0.4B 2 3 the glass and crystals should give similar analytical 

 results, that we thought it worth while to try fractional crystallisation 

 of the glasses, to see if we could detect any differences between the 

 different crystalline portions. 



The analyses of these various portions gave the following results : 



(i) For a mixture of composition about Na 2 0.2B 2 3 



Per cent. NaX). 

 First portion glass = 29'7 



crystals = 29'3 

 Second portion glass = 29'9 



crystals = 29'2 

 Third portion glass =30-3 



crystals = 3O5 

 Fourth portion glass = 30 '2 



crystals = 30 '1 



(ii) For a mixture of composition about Na 2 0.4B 2 3 



Per cent. IS'a-O. 



First portion glass =18-7 



crystals = 18'6 



Second portion glass = 18*6 



crystals = 18*4 



