Physical Characters of the Sodium Borates, etc. 285 



" Some Physical Characters of the Sodium Borates, with a New 

 and Eapid Method for the Determination of Melting Points." 

 By CHARLES HUTCHENS BURGESS and ALFRED HOLT, Junr. 

 Communicated by Professor H. B. DIXON, F.RS. Eeceived 

 October 27 ; Read November 24, 1904. 



Some time ago we published a note* containing some new observa- 

 tions on the solubility of metallic oxides in fused boric anhydride. 

 Since its publication we have been further studying some of the points 

 therein mentioned, but have been in part anticipated by W. Guertler,f 

 who has examined many of the phenomena we remarked, in a more 

 complete manner. As, however, our experiments do not cover exactly 

 the same ground as his, we have arranged in the following paper the 

 results relating to the sodium borates, which we believe are completely 

 new, and, at the same time, present many interesting features towards 

 the study of these complex bodies. 



When a quantity of ordinary pure borax glass is heated for some 

 hours at a temperature which gives it about the consistency of a thick 

 syrup, it gradually changes to a mass of colourless crystals. The 

 crystallisation begins at two or three points on the surface of the mass, 

 generally around a particle of dirt, or minute fragment of imperfectly 

 fused borax, and spreads in more or less spherulitic growths throughout 

 the glassy portion. As the crystals grow, there appears to be a 

 contraction of volume, since the glass around them appears as raised 

 hummocks, and a subsequent investigation of the specific gravities of 

 the crystals and glass showed that this was really the case. 



The crystals do not seem to grow at a uniform rate. They start 

 rapidly, but as development continues, they take longer and longer to 

 form, so that many hours are occupied in changing from pure glass to 

 a holocrystalline aggregate. 



We have not been able to isolate any individual crystals, and so 

 study their characters, but the whole crystalline mass appears to be 

 composed of dense, matted clusters of very minute needles, which are 

 doubly refracting, and have a pearly lustre. They are about as 

 soluble in water as ordinary borax glass, are not hygroscopic, and melt 

 at a higher temperature than the glass, into which they are reconverted 

 on melting, and then cooling quickly. 



We find, however, that it is not borax glass alone which exhibits 

 this phenomenon of crystallisation on reheating, but that the glasses 

 obtained by fusing mixtures of boric anhydride and sodium carbonate, 



* ' Journ. Chem. 8oc. Proc.,' 1903, p. 221. 



f ' Zeit. Anorg. Chem.,' vol. 40, 2, pp. 225 and 268 ; vol. 40, 3, p. 337. 



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