BORON AND FLUORINE 51 



with reference to oxygen and the halogens. The tribromide, for 

 example, was found to be incapable of combining with more 

 bromine either at room temperature or at 80. 



It may be added, however, that the ratios BX 3 : 3AgX and 

 BX 3 : 3Ag (X= halogen) are not particularly advantageous, for 

 practical reasons. As already indicated by the editors of Abra- 

 hall's paper, an experimental error in the ratio BBr 3 : 3Ag would 

 be magnified 23 times in the atomic weight of boron. 



In considering former analyses of borax itself, they may con- 

 veniently be discussed under three heads, as indicated in table 4. 

 The last two columns give the atomic weight of boron as recal- 

 culated by Clarke and by Brauner, respectively. 



A. THE DETERMINATION OF WATER IN CRYSTALLIZED BORAX. 



It is generally conceded that the determination of water of 

 crystallization in a salt is liable to lead to a doubtful atomic 

 weight, since the water-content may vary with atmospheric con- 

 ditions and since the salt may occlude traces of mother liquor. 

 These objections, no doubt, also apply to crystallized borax; at 

 the same time the dehydration of this salt seems to present even 

 more serious difficulties which were overlooked or, at any rate, 

 not fully appreciated by previous investigators; namely, the 

 volatility of the borate itself and the retention of water by the 

 end-product. The former was noticed, although underrated, 

 by Abrahall and by Armitage; the latter, i.e., the retention of 

 water, it would seem, was first suspected, but not remedied, by 

 Dobrovolsky. 



These difficulties, particularly the retention of water, have 

 been dwelt upon in the experimental part of the present work, 

 but on account of their importance will bear repetition. It is 

 evident from the earlier discussion of this question that borax 

 can not be dehydrated quantitatively by ignition in an open 

 vessel, such as a dish or a crucible, for the experimenter then 

 faces the dilemma of either not removing the water completely 

 or, if successful in this, of volatilizing some of the borax itself. 

 In this connection Abrahall' s own words may be of interest. 

 He says: 



"The determination of the atomic weight of boron by this method 

 necessitates the determination of the precise range of temperature 



