L'86 Messrs. C. H. Burgess and A. Holt, Junr. [Oct. 27, 



in which the ratio of the boric anhydride to the sodium carbonate is 

 not 2:1, also exhibit it in varying degree. 



Thus, all mixtures in which the ratio varies from 6 : 1 to 8 : 5, give a 

 glass when fused, and are all capable of being changed completely into 

 crystals on reheating, exactly like borax. Mixtures in which the boric 

 anhydride is present in greater proportion than 6:1, only change with 

 difficulty on prolonged heating ; and when they do, the crystals are 

 always found to be mixed with more or less truly glassy material, till, 

 when the ratio 40 : 1 is reached, it seems impossible to obtain crystals 

 at all. So far as we can ascertain, a mixture of this composition is 

 always a true glass in any circumstances. 



Mixtures, on the other hand, in which the ratio of boric anhydride 

 is less than 8:5, when fused, and allowed to cool, yield nearly opaque, 

 white substances, which seem to be micro-crystalline. Nevertheless, 

 these mixtures if heated to a high temperature, and then suddenly 

 chilled by being poured into mercury, also yield glasses. 



The glasses obtained by this sudden chilling seem to be very 

 unstable, as on gently heating by means of a Bunsen flame, they 

 change completely, and almost instantaneously, into crystals. 



There seems then to be a gradual alteration in the rapidity and 

 completeness with which this change occurs, and as it seemed probable 

 that the crystallisation of some borate rich in sodium was the cause of 

 it, we proceeded to determine what was the composition of the borate 

 richest in sodium which could be obtained by fusing boric anhydride 

 with sodium carbonate. 



When boric anhydride is fused with sodium carbonate, carbon 

 dioxide is evolved, and the product may be regarded as boric 

 anhydride combined with sodium oxide (Na20). Thus, by heating 

 boric anhydride with a large excess of sodium carbonate, and 

 determining the amount of carbonate decomposed, the greatest 

 proportion in which boric anhydride combines with sodium oxide 

 can be ascertained, and ought to give the composition of the richest 

 sodium borate obtainable by fusion. 



We have performed this experiment several times, and have obtained 

 the following results : 



(i) One part of B 2 3 combines with 1 '29 parts Na 2 O 

 (ii) One 1-34 



(in) One 1-32 



These results are probably a little too low, as the sodium carbonate 

 loses some carbon dioxide merely on heating alone, but this amount is 

 negligible, and does not in any way affect the conclusion that the 

 product obtained in this way is not sodium metaborate (NaB0 2 ), in 

 which the ratio of boric anhydride to sodium oxide is 1:1, and that 

 sodium orthoborate (Na 3 B0 3 ), in which the ratio is 1 : 3, cannot in any 

 case be formed by fusion of boric anhydride and sodium carbonate. 



