INTRODUCTION. 



When the present work was undertaken the writers contem- 

 plated the use of anhydrous borax as the initial material in deter- 

 mining the atomic weight of certain elements, e.g., fluorine. After 

 numerous trials, a method was worked out which admitted of the 

 complete conversion of sodium tetraborate into sodium fluoride, 

 and the preliminary experiments made with this method gave a 

 value for fluorine which was practically identical with the present 

 international figure (19.0). However, as soon as the same method 

 was applied to borax, the purity and the anhydrous condition of 

 which were above suspicion, the atomic weight of fluorine (on 

 the assumption that B = 11.0) became too high. 



Although it was realized from the beginning that it would be 

 desirable to redetermine the atomic weight of boron before the 

 latter could properly be used in fixing other atomic weights, it 

 was not anticipated in view of the most reliable previous work 

 upon this constant that it would differ much from the accepted 

 value (11.0). 



A closer study of the literature bearing upon this subject soon 

 revealed that the inconsistencies and uncertainties in previous 

 determinations are much greater than might reasonably be 

 expected of a rather common, non-metallic, uniformly trivalent l 

 element of low atomic weight; and thus it has come to pass that 

 the major part of the present investigation is devoted to the 

 determination of the atomic weight of boron. The work outlined 

 in the following pages deals with the preparation of pure sub- 

 stances and the conversion, either directly or indirectly, of anhy- 

 drous sodium tetraborate into the chloride, fluoride, sulphate, 

 nitrate, and carbonate of sodium. The atomic weight of boron 

 was thus based upon the rather well-known atomic weights of 

 sodium, chlorine, sulphur, nitrogen, and carbon, and (with slight 

 variations) led to the value 10.900 for boron. 



Incidentally the work also seemed to furnish sufficient data 

 for a recalculation of the atomic weight of fluorine. The value 



1 Trivalent at least with respect to oxygen and the halogens. On the valence of boron 

 see A. Stock, E. Kuss, and O. Priess, Ber. 47, 3115-49 (1914). 



in 



