180 THE ATOMIC WEIGHTS. 



The results obtained were as follows. The third column gives the amount 

 of water formed from 10 grammes of aluminum. 



2.1704 grm. Al gave 2.1661 grm. H.^O. 9.9802 



2.9355 " 2.9292 " 9.9785 



5.2632 " 5.2562 " 9-9867 



Mean, 9.9818, ±.0017 



Hence Al = 26.867. 



From the last two series of experiments an independent value for the 

 atomic weight of oxygen may be calculated. It becomes = 15.895. 

 The closeness of this figure to some of the best determinations affords a 

 good indication of the accuracy of Mallet's work. 



In connection with Mallet's work it is worth noting that Torrey * pub- 

 lished a series of measurements of the H : Al ratio, representing determi- 

 nations made under his direction by elementary students. These meas- 

 urements are thirteen in number, and calculated with Regnault's old 

 value for the weight of hydrogen, range from 26.661 to 27.360, or in mean, 

 27.049, ± .323. Corrected by the latest value for the weight of H, this 

 mean becomes 26.967. The result, of course, has only confirmatory 

 significance. 



By Baubigny f we have only two determinations, based upon the 

 calcination of anhydrous aluminum sulphate, A1^(S0J3. 



3.6745 grm. salt gave 1.0965 AL^Oj. 29.84! per cent. 



2.539 " -7572 " 29.823 " 



Mean, 29.832, =h .0061 



Hence Al = 26.858. 



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 : 



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



(2.) Percentage of AljOg in ammonium alum, 11.2793, =t .0008 



(3-) 3Ag : AlBrg : : 100 : 82.455, ± .0010 



(4.) H : Al : : I : 26.890, ± .0034 



(5.) AI2 : 3U,0 : : 10 : 9.9818, d= .0017 



(6.) Percentage of Al^Og in Al2(S04)3, 29.832, ± .0061 



The antecedent values are — 



O =: 15.879, rt .0003 Br^ 79.344,^.0062 



Ag=: 107. 108, ± .0031 N =r 13.935, d= .0021 



CI = 35. 179, zfc .0048 S r= 31.828,^.0015 



* Am. Chem. Journ., 10, 74. 1888. 

 t Conipt. Rend., 97, 1369. 1883. 



