330 



TABLE 10. 



CohaUoferrite (CoO . Fe.Os, Hilpert, d^ = 520°). The malerial, a 

 black powder, yielded a sufiicientlj reflecting mirror. The rotation 

 is throughout the entire spectrum negative and reaches a numerical 

 minimum in the blue green. (F'ig. 5). Up to 250° I was unable to 

 detect any decrease in the rotation. 



Cupri/errite (CuO . Fe^Oa, Hilpert, ó^o = 420°). Loria has deter- 

 mined the dispersion curve (I.e. p. 897). On heating, the rotation 

 remains constant up to 200°. It then decreased at first slowly and 

 then somewhat niore rapidly up to 420° where it vanished. On 

 cooling, the rotation regained its original value. (Table 11). 



T A B L E 11. 

 8 =(p {t) X — 475 .ufi Cupriferrite (saturated) Hilpert 



Zincferrite. (Zn . Fe^Og, Franklinite, from Franivlin, New Jersey, 

 /9y = 62°). The sign of the rotation changes twice within the 



