ATOMIC WEIGHTS 267 



By Banbigny ^ we have only two determinations, based upon the cal- 

 cination of anhydrous alnminum sulphate, Al, (804)3. 



3.6745 grm. salt gave 1.0965 AlA- 29.841 per cent. 

 2.539 " .7572 " 29.823 



Mean, 29.832, ± .0061 



Hence Al = 27.061. 



Thomsen's ^ value for the atomic weight of aluminum was derived 

 from Ms earlier work on the hydrogen-oxygen ratio. In that investiga- 

 tion one part of aluminum was found equivalent to 0.11190, ±.000015 

 of hydrogen, and 0.88787, ±.000018 of oxygen. The aluminum, however, 

 was impure, and the first step in the new research was to determine 

 its impurities. These were, in one gramme of metal, 0.00819 gramme 

 of silicon and .00322 of iron. Correcting for these, and also for the 

 change of volume in the soda solution following the solution of the 

 metal, the equivalent values become 0.99897 grm. Al, 0.11195 grm. H, 

 and 0.88824 grm. 0. From the oxygen ratio Al = 26.992, ±.0011. From 

 the hydrogen, the ratio H: Al: : 1 : 26.765, ±.0036 is derived. For the 

 same ratio Mallet found 26. 890, ±.0034. The two series, combined, give 

 a general mean of 26. 860, ±.0025. 



The determinations by Kohn-Abrest' are of very slender value. Im- 

 pure aluminum was dissolved in hydrochloric acid, the hydrogen evolved 

 was burned over hot copper oxide, and the water formed was weighed. 

 The weights of metal taken and the percentages of water produced are 

 given below : 



Weight Al. Per cent. H„0. 



.7909 98.08 



.7428 98.20 



.5477 97.86 



.5132 98.10 



.6571 98.44 



.4993 98.03 



.5384 97.98 



Mean, 98.10, ± .0473 



Corrected for the known impurities of the aluminum, this mean be- 

 comes 99.151. Hence Al = 27.255. 



Mallet's value for this ratio, reduced to the same standard, is 99.818. 

 ±.0170. Combining, the general mean is 99. 742, ±.0160. 



1 Compt. Rend., 97, 1369. 1883. 



2 Zeitsch. anorg. Chem., 15, 447. 1897. See also ante, p. 25. 



^Bull. Soc. Chim. (3), 33, 121. 1905. PTeliminary in Compt. Rend., 139, 669. 



