44 



THE ATOMIC WEIGHTS OF 



Na 2 SO 4 



Naj S0 4 



ZTSad 



B. THE ATOMIC WEIGHT OF FLUORINE. 



The various salts derived from borax in the determinations 

 recorded in table 1 may be grouped around the central substance, 

 borax, in such a manner as to bring out their relation, not only 

 to borax itself, but also to one another. This arrangement is 

 shown in the following diagram (figure 5) : 



This diagram 

 shows at a glance that 

 the results might be 

 correlated in a great 

 variety of ways. It is 

 easily seen that any 

 two salts on different 

 lines, radiating from 

 borax and represent- 

 ing independent de- 

 terminations, might 

 be compared, indi- 

 rectly, if their quan- 

 tities were computed 

 with reference to a 

 fixed quantity, say 100 grams, of borax; the "cross-ratios" thus 

 obtained might serve for checking purposes or for the calculation of 

 the atomic weights of other elements besides boron. However, the 

 experimental data did not seem to warrant the calculation of more 

 than one additional atomic weight, namely that of fluorine. Of the 

 possible cross-ratios only one, NaCl : NaF (indicated by a dotted 

 line in the diagram), has been used. Eight values for fluorine 

 have been calculated from the data recorded in table 1 and are 

 given in table 3, together with the ratios used. In four of these 

 the new value for boron (10.900) has been included for reference. 

 Three values are based on the atomic weights of sodium and 

 sulphur; one value, as already mentioned, has been computed 

 from a cross-ratio. The agreement between the individual values 

 is excellent and is largely due to the following factors: complete 

 dehydration of the borax, complete elimination of boric acid, 

 and avoidance of loss in the ignition of sodium fluoride. 



In this connection it may not be amiss to add a few words 

 concerning the value of cross-ratios in atomic weight determina- 



FIG. 5. 



