268 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 54 



Kohn-Abrest also made two determinations of atomic weight by con- 

 verting metallic aluminum into oxide, as follows: 



.3429 grm. Al gave .6444 ALO3. 53.212 per cent. 

 .4168 " .7850 " 53.095 



Mean, 53.153, ± .0387 



Hence Al = 27.230. This can be combined with Thomsen's figure for 

 the Al : ratio, but its probable error is so high that it exerts no 

 appreciable influence. 



It is clear that the single determinations of Berzelius, Mather, Tissier, 

 Isnard and Terrell may now be safely left out of account, for the reason 

 that none of them could affect appreciably the final value for Al. The 

 ratios to consider are as follows : 



( 1 ) . 3 Ag : AICI3 : : 100 : 41.344, ± .0070 



(2). Percentage Al^Og in ammonium alum, 11.2793, ± .0008 



(3). SAgiAlBrs: :100:82.455, ± .0010 



(4). H:A1: :1:26.860, ± .0025 



(5). 2Al:3HjO: : 100: 99.742, ± .0160 



(6). AIJ.SOJ3: AlA: : 100: 29.832, ±: .0061 



(7). 0:A1::16:26.992, ±.0011 



The antecedent atomic weights are 



Ag = 107.880, ± .00029 S = 32.0667, ± .00075 



CI = 35.4584, ± .0002 N =14.0101, ±.000] 



Br = 79.9197, ± .0003 H = 1.00779. ± .00001 



Hence, 



From ratio 7 Al = 26.9920, ± .0011 



" 6 27.0607, ± .0115 



" 4 27.0695, ± .0025 



" 5 .' 27.0933, ± .0087 



" 3 27.0983, ± .0015 



" 2 27.1533, ± .0041 



" 1 27.4305, ± .0227 



General mean, Al = 27.0400, ± .0008 



The last value, from ratio 1, is worthless, but is of no influence in 

 the o^eneral combination. Xo one of the other values is entitled to ex- 

 elusive confidence. The atomic weight of aluminum needs reinvestigation. 



