SOSMAN AND HOSTETTER: REDUCTION OF IRON OXIDES 301 



factors, perhaps its concentration, distribution in the platinum, 

 heat treatment, impurities, or other variables. As we were not 

 prepared to make any extensive study of the questions opened 

 by these results, we have been forced to conclude for the present 

 that the magnetic test alone gives only a qualitative indication 

 of the presence of iron, but no quantitative measure of the amount 

 present. 



TABLE VI 



The work of Isaac and Tammann^ indicates the cause of the 

 small magnetic effect produced by a considerable percentage of 

 iron when dissolved in platinum. They have found that the 

 magnetic transformation point, which is about 770° in pure iron, 

 is rapidly lowered by the addition of platinum, until at 50 weight 

 per cent platinum it is near 100°. Near pure platinum it would 

 seem to be below room temperature. It is possible, though not 

 proven by their results, that the magnetization of the alloys be- 

 tween 30 and per cent of iron is due to an "a form" of solid 

 solution crystals, with an inversion curve which falls rapidly 

 with increasing iron content, just as the inversion curve of the 

 a-form of pure iron and of the iron-rich alloys falls rapidly with 

 increasing content of platinum. 



Cause of reducing action of platinum. We have shown that 

 platinum acts on both hematite and magnetite at 1200° under 

 low pressures of oxygen, absorbing iron and -giving off oxygen. 



^ Isaac and Tammann. Zs. anor";. Chem., 55: 63-71. 1907. 



