132 THE ATOMIC WEIGHTS. 



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 by nitric acid, 

 and the amount of oxide thus formed was determined. The 

 results were as follows : 



Mean, 69.9534, ± .O050 



In the second series ferric oxide was reduced by ignition 

 in a current of hydrogen, yielding the subjoined percentages 

 of metal : 



2-98353 gi-m. Fe.p3 gave 2 



2.4151S 

 2.99175 



3-5783 

 4.1922 

 3-IOI5 



2. 



Mean, 70.0354, ± .0055 



It is evident that one or both of these series must be 

 vitiated by constant errors, and that these probably arise 

 from impurities in the materials employed. Impurities in 

 the wire taken for the oxidation series could hardly have 

 been altogether avoided, and in the reduction series it is 

 possible that weighable traces of hydrogen may have been 

 retained by the iron. At all events it is probable that the 

 errors of both series are in contrary directions, and, there- 

 fore, in some measure compensatory. 



In 1844 there was also published an important paper by 

 Erdmann and Marchand.'" These chemists prepared ferric 

 oxide by the ignition of pure ferrous oxalate, and submitted 



* Journ. fiir Prakt. Chem., 33, i. 



