300 sosMAN AND hostetter: reduction of iron oxides 



10 



20 30 



AMOUNT OF IRON IN MG 



Fig. 



Relation of magnetic pull to weight 

 of unabsorbed iron. 



and from figure 3, which repre- 

 sents graphically the data of 

 Table V. The surprising part 

 of the result is that practi- 

 cally the same ultimate mag- 

 netic pull is attained, although 

 one crucible contains nearly 

 twice as much iron as the 

 other. Furthermore, the iron 

 of Table V is concentrated in 

 a smaller area of platinum 

 surface than that of Table IV, 

 which might be expected to 

 make its magnetic effect more 

 than proportional to the 

 amount of iron, instead of 

 which it is found to be independent of the amount. The position 

 of the dissolved iron in the magnetic field is without any important 



effect, since turning the 

 crucible upside down 

 makes only a few hun- 

 dredths mg difference 

 in the final magnetic 

 pull. 



The summarized fig- 

 ures showing the 

 amounts of iron in the 

 various crucibles re- 

 ferred to, and their 

 magnetic effects, are 

 given in Table VI. 



It is evident from 

 Table VI that the mag- 

 netic pull must depend 

 not only upon the 

 amount of iron present, 

 but also upon other 



TIME IN MINUTES 



Fig. 3. Relation of magnetic pull to time of heat- 

 ing iron-plated platinum at 1400° (see Table V). 



