'Ó8d 



in what the experimeiilally determined ciiive will differ from i(. 

 In the first place it is self-evident that through all kinds of 

 disturbing influences of these small pressures, as e.g. the presence 

 of traces of adsorbed gases or contaminations, and the slow pro- 

 gress of the dissociation, there is a great chance that the middle 

 part will not be found to be horizontal, but more or less sloping; 



FE,a 



3U4 



3 



V 



ffenO, 



Fig. 5. 



FfeA 



and in the second place the transition of the two sloping parts to 

 the horizontal part will not be found to be discontinuous, but always 

 continuous, especially when many observations are made in the 

 immediate neighbourhood of ƒ and <j. Instead of the above given 

 broken line the continuous curve of fig. 4 will, therefore, be found 

 in the most favoui-able case. 



When with these curves we compai-e the lines found by Sosman 

 and HosTETTER, which have been reproduced in fig. 5, we see that 

 the found curves closely resemble those which theory led us to 

 expect for only partial mixture of Fe203 and FejO^ in the solid state. 



Everything depends on this whether the non-horizontal course of 

 the middle [)ortion is essential or not, for if this is essential and 

 the observed pressures correspond with the states of equilibrium, 

 this course of the isotherm would really plead in favour of the 

 existence of a continuous mixed crystal seiies. Sosman and Hostetter 

 see a confirmation of the view that the mixing of FCjOj and FejO^ 

 is continuous in the fact that the indices of refraction of the mix- 

 tures change far from proportionally with the quantity FejO^ between 

 hematite {s = 2,78) and magnetite {11 = 2,42). 



They give namely the following results. 



