416 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 54 



lEON. 



The atomic weight of iron has been mainly determined from the com- 

 position of ferric oxide, ferrous bromide and the two chlorides. 



Most of the earlier data relative to the percentage of metal and oxygen 

 in ferric oxide we may reject at once, as set aside by later investigations. 

 Among this no longer valuable material there is a series of experiments 

 by Berzelius, another by Dobereiner, and a third by Capitaine.' The 

 first work deserving of present consideration is that of Wackenroder,' 

 who reduced the oxide in hydrogen at a moderate red heat. The fol- 

 lowing percentages of iron were thus found : 



69.62 



69.954 



69.98 



69.98 



69.99 



70.04 



Mean, 69.927, ± .0905 



If we reject the first of these figures the mean becomes 69. 988, ±.0099, 

 which is more trustworthy. Hence re = 55.97. 



In 1844 Berzelius ' published two determinations of the ratio in ques- 

 tion. He oxidized iron by means of nitric acid, and Aveighed the oxide 

 thus formed. He thus found that when = 100 Fe = 350.27 and 

 350.369. 



Hence the following percentages of Fe in Fe^Og : 



70.018 

 70.022 



Mean, 70.020, ± .0013 



Hence Fe = 56.05. The "probable error" assigned to this pair of 

 measurements greatly overvalues them. It is better, therefore, to give 

 the mean equal weight with Wackenroder's, making it 70. 020, ±.0099. 



About the same time Svanberg and ivTorlin * published two elaborate 

 series of experiments; one relating to the synthesis of ferric oxide, the 

 other to its reduction. In the first set pure piano-forte wire was oxidized 



' For details concerning: these earlier researches, see Oudeman's monograph, pp. 140, 141. 



= .\rch. Pharm., 35, 279, and 36, 22. 1843. 



' Berz. Jahrcsb., 25, 43. Ann. Cheni. Pharni., 30, 432. 



■* Berz. Jahresb., 25, 42. 



