BORON. 175 



For reduction we have the antecedent atomic and molecular weights 



O = 15-879, -0003 Na = 22.881, .0046 



Ag= 107.108, .0031 NaCl=; 58.060, .0017 



Cl = 35.179,^.0048 AgCl= 142.287, rb .0037 

 Br = 79-344, =b .0062 



For the molecular weight of Na 2 B 4 7 we now have 



From (i) . . . .' Na 2 B 4 O 7 = 200. 198, .0377 



From (3) " = 200.439, .0263 



From (4) " = 200.756, .0419 



From (5) " = 200.260, .0518 



General mean Na 2 B 4 O t = 200.421, .0180 



Hence B = 10.876, .0051. 



From ratio (2), B = 10.753, .0207. The two values combined give 



B =1 10.863, .0050. 



Or, if = 16, B == 10.946. 



If we consider ratios (1), (3), (4), and (5) separately, they give the fol- 

 lowing values for B : 



From (i) B = 10.821 



From (3) " = 10.881 



From (4) " = 10.960 



From (5) " = 10.836 



Of these, the second and third involve the data from which, in a 

 previous section of this work, the ratio NaCl : AgCl was computed. In 

 using that ratio for measuring the molecular weights of its component 

 molecules, discordance was noted, which again appears here. The chief 

 uncertainty in it seems to be connected with ratio (4), which is therefore 

 entitled to comparatively little credence, although its rejection is not 

 necessary at this point. In ratio (2), Abrahall's determination, the high 

 probable error of B is due to the also high probable error of 3Br, and it 

 is quite likely that the result is undervalued. The general mean, B = 

 10.863, .0050, however, can hardly be much out of the way. It is cer- 

 tainly more probable than any one of the individual values. 



