30 SCIENCE PROGRESS 



to decompose below their melting temperatures. Diopside 

 forms solid solutions with clinoenstatite, but not with forsterite 

 or pseudowoUastonite. The relationship of wollastonite and 

 the ternary compounds is discussed in a further paper by the 

 same authors {Amer. Journ. Set., 48, 165, 19 19). From a partial 

 investigation of the solidus, it is found that wollastonite can 

 take up I 7 per cent, of diopside and over 60 per cent, of aker- 

 manite in solid solution, while the high temperature form, 

 pseudowoUastonite, is capable of taking up only a trace and 

 23 per cent, respectively. 



A detailed examination of the wollastonite solid solutions has 

 been made and the inversion and decomposition temperatures 

 determined. The appearance of such phases as pseudowoUas- 

 tonite at temperatures far below the inversion-point is con- 

 sidered to be an example of the operation of Ostwald's rule 

 regarding unstable intermediate phases, which are so prominent 

 in the case of the silica minerals. 



The systems CaO-MgO-ALA and MgO-AlaO^-SiOa have 

 been re-examined by A. Meissner [Zement, 8, 296, 308, 191 9; 

 Journ. Chem. Soc, 118, 39, 1920), but, according to the avail- 

 able abstracts, the results are not, so far as the latter system 

 is concerned, in agreement with the results of G. A. Rankin and 

 H. E. Merwin [Amer. Journ. Set., 45, 301, 191 8). The problem 

 of the calcium ferrites and aluminates has undergone further 

 investigation by E. D. Campbell {Journ. Ind. Eng. Chem., 11, 

 116, 1 91 9). His results, which are in agreement with those of 

 R. B. Sosman and H. E. Merwin {Journ. Wash. Acad. Set., 6, 

 532, 1 91 6), indicate the existence of only two calcium ferrites, 

 2CaO . Fe203 and CaO . Fe203, there being no evidence of the 

 formation of the other compounds suggested by E. Kohlmeyer 

 and S. Hilpert {Ber.,A2, 2581, 1909). Mixed crystals of calcium 

 ferrite and aluminate have also been prepared, and it is found 

 that these can take up less lime in solid solution than the pure 

 aluminates (cf. E. S, Shepherd, G. A. Rankin, and F. E. Wright, 

 Zeit. anorg. Chem., 71, 19, 191 1 ; Amer. Journ. Set., 39, i, 191 5). 

 The application of recent synthetic work on the system 

 CaO — AlijOa — SiOa to the study of slags is discussed by 

 B. Neumann {Stahl u. Eisen, 38, 953, 191 8). 



Although several hydrated ferric oxides are usually described 

 in books on mineralogy, the nature of these minerals has long 

 been in doubt. Despite the opinion of J. M. van Bemmelen 

 {Zeit. anorg. Chem., 20, 185, 1899) that the amorphous " hy- 

 drates " were merely colloidal mixtures, these have been re- 

 garded by O. Ruff {Ber., 34, 3417, 1901) and others as definite 

 compounds. The minerals have been subjected to an elaborate 

 examination by E. Posnjak and H. E. Merwin {Amer. Journ. 

 Set., 47, 311, 1919), and they find that no series of hydrates 



