BORON AND FLUORINE. 47 



preferred by Brauner (19.02). 14 Jacquerod and Tourpaian 15 

 derived the atomic weight of fluorine from the weight of a normal 

 liter of silicon tetrafluoride and found F = 19.09. Even if the 

 method adopted by these investigators should be flawless it must 

 not be forgotten that the figure for fluorine depends on the atomic 

 weight of silicon, which was assumed to be 28.3. Any possible 

 error in the latter value, it is true, would scarcely be sufficient 

 to account for the high value for fluorine. It is safe to say, how- 

 ever, that the atomic weight of silicon is still too uncertain to 

 serve for reference in fixing other atomic weights. 



The paper by Me Adam and Smith has already been mentioned. 

 These authors converted weighed quantities of sodium fluoride 

 into sodium chloride by means of hydrochloric acid gas, and from 

 two analyses they derived two values for fluorine: 19.0176 and 

 19.0133 (with Na = 23.00 and 01 = 35.46). It may be gathered 

 from their paper that the second conversion was possibly not quite 

 complete. However, as the difference between these two values 

 is very small it is permissible to take the average, or 19.015. 

 This result is based on weighings in air. If the mean quantities 

 involved be reduced to the vacuum standard and the atomic 

 weight of fluorine be recalculated with the antecedents used in 

 the present paper, F will be 19.009. This value agrees quite 

 well with the value just found (19.005), particularly when it is 

 realized that the method applied by McAdam and Smith would 

 have a tendency to lead to a high value for fluorine. The sodium 

 fluoride (produced by heating the acid salt) had to be used in a 

 porous state and would have had a tendency to retain, or take 

 up, a trace of water. (This was actually found not to be the 

 case, however) . The weight of the resulting sodium chloride, on 

 the other hand, would have been too low if the conversion had 

 not been quite complete. Either, or both, of these errors if at 

 all operative to a measurable degree would have increased the 

 value of the ratio NaF : NaCl, and hence the atomic weight of 

 fluorine. For such reasons the agreement between McAdam and 

 Smith's value (19.009) and that obtained in the present investi- 

 gation (19.005) is all the more striking. 



" In Abegg-Auerbach's Handbuch d. anorg. Chem., Vol. IV, part 2, p. 12 (1913). 

 J; J. chim. phys. 11, 269-74 (1913). 



