827 



maximum in the green cind zero i)oints near 510 (ifi and 590 (i(i. 

 (Fig. 5 X points). 



xCaOFPaOg ACoOFcoOs 

 oZnOFPoOs 



.^_L 



450 



500 



550 

 Fie. 5. 



600 



650 680;, 



The rotation was too small for the determination of a temperature 

 curve. 



Titanium ferrite (Ti^Oj . FejOg, Ilmenite, regular). The same mirror 

 as used by Loria without result gave no measurable effect (? <^ 0,10- 



Ferroferrite (FeO . Fe^Oj, maguetite electrode of the firm Griesheim- 

 Elektron, 8^ ^ 500°). The dispersion curve is very similar to those 

 found bj LoRiA for a natural octahedral surface and by Weiss for 

 calcined amorphous FcgO^. The maximum d= rotations are, however, 

 somewhat less. The singular points of the three curves are located 

 as follows: 



Ferroferrite 



Zero-point I Maximum 



Natural Octahedral Surface 

 Calcined Amorphous 

 Magnetite Electi-ode 



464 {III 

 492 „ 

 496 „ 



ca. 575 mi 

 „ 615 ,, 

 „ 600 ., 



The position of the flat maximum is, of course, more or less 

 uncertain. Tiie agreement is, therefore, much better than e.g. with 

 the cementite samples. 



On heating the decrease in the rotation begins before 200° and 

 continues nearly linearly up to 430". A straight line extrapolation 

 of the curve cuts the axis of abscissae near 510° (Tab. 8). On cooling 

 the point near 200° was again observed and at ordinary temperature 

 the values of the rotation agreed with those before heating. 



Fennferrite [Fe^Oj . 2Fe503, martite, pseudomorphous with octa- 

 hedral magnetite, from Twin Peaks, Utah]. The above form of the 



