ATOMIC WEIGHTS 



313 



In the last mean the probable error is so low as to give it inordinate 

 weight, especially as Baxter and Coffin suspect the presence of basic im- 

 purities in the arsenate. It is better, therefore, to treat both series as 

 one, giving in mean AggAsO^ : 3AgBr: : 100: 121.793, ±.0013. Hence 

 As = 74.947. 



There are now the following ratios from which to compute the atomic 

 weight of arsenic. The single determination bj^ Berzelius has been arbi- 

 trarily assigned equal weight with that of Wallace's series : 



(1). 2AS203:3S0.: : 100: 48.525, ± .012 



(2). 3Ag: ASCI3: : 100: 56.014, ± .0035 



(3). 3Ag:AsBr3:: 100: 97.005, ±.012 



(4). 3 AS0O3 : 2K,CrA :: 100:99.039, ± .016 



(5). 3As,03:2KC103: : 100: 41.172, ± .009 



(6). Na4As„Oj:4NaCl: : 100: 66.098, ± .0030 



(7). Ag3AsO,:r:!Ag: : 100: 69.966, ± .0024 



( 8 ) . Ag3AsO, : 3 AgCl : : 100 : 92.9614, ± .00028 



(9). Ag3As04:3AgBr: : 100: 121.793, ± .0012 

 (10). Pb3As,Os:3PbCL: : 100: 92.731, ± .0019 

 (11). Pb3As,Os:3PbBr,: : 100: 122.441, ± .0076 



To reduce these ratios we have — 



Ag = 107.880, ± .00029 

 CI = 35.4584, ± .0002 

 Br = 79.9197, ± .0003 

 S = 32.0667, ± .00075 



Na = 23.0108, ± .00024 

 K = 39.0999, ± .0002 

 Cr = 52.0193, ± .0013 

 Pb = 206.970, ± .0017 



Hence, 



From ratio 3 As = 74.188, ± .0389 



" 6 74.895, ± .0066 



"11 74.916, ± .0286 



" 7 74.928. ± .0160 



" 8 74.934, ±.0018 



" 9 74.947, ± .0049 



" 2 75.008, ± .0108 



" 1 75.021, ± .0245 



" 4 75.032. ± .0160 



"10 75.050, ± .0099 



" 5 75.225, ± .0217 



General mean, As = 74.957, ± .0016 



This final mean is identical with the value found by Baxter and 

 Coffin as the result of their determinations. 



