CHAPTER III 



REVIEW OF PREVIOUS DETERMINATIONS OF THE 

 ATOMIC WEIGHT OF BORON. 



GENERAL CONSIDERATIONS. 



At this point it will be quite proper to consider the work of 

 other chemists upon the atomic weight of boron and, if possible, 

 point out the most probable errors which may have affected that 

 work. It is not thought that the observations, and value for 

 boron as given in this communication, are in any sense final, but 

 great confidence is placed in them; and since this new figure for 

 the atomic weight of boron is practically 1 per cent, lower than 

 the constant now in use, this investigation would, indeed, be 

 incomplete without a careful survey of previous determinations. 



It is to previous analyses of borax that attention must be 

 directed, for this compound of boron has been used extensively. 

 It may be assumed that the preparations of borax used in such 

 work in the past were of reasonable purity, the latter implying 

 not merely the absence of appreciable traces of foreign matter, 

 but also the proper proportion of the constituents of the salt 

 itself. While, in some cases, exception to this assumption might 

 be taken by the severe critic, it must be noted that many investi- 

 gators do not describe the preparation of the borax used by them 

 in sufficient detail to admit of a profitable criticism of the method 

 of preparation. 



In passing, it may be remarked that the analyses of boron 

 compounds, other than borax, have not added materially to the 

 existing knowledge of the atomic weight in question. Abrahall l 

 determined the ratio BBr 3 : 3Ag, which (according to Clarke) 

 leads to the value 10.819 for boron. The boron used in this prep- 

 aration of boron tribromide had been obtained by the method of 

 Wohler and Deville and must have been rather impure. Gautier 2 

 analyzed the sulphide, carbide, chloride, and bromide of boron 

 and obtained values the average of which is quite close to the 



v Journ. Chem. Soc., 61, 650 (1892). 'Ann. chim. phya. (7) 18, 352 (1899). 



48 



