RECENT ADVANCES IN SCIENCE 41 



(cf. A. Lacroix, Bull. Soc. jr. Min. 9, 40, 1886; 40, 62, 191 7), 

 could be obtained by the cooling of a melt of the composition 

 FeSi0 3 . The fact that, except for the very few occurrences of 

 griinerite, ferrous metasilicate has not been found in anything 

 like a pure state in nature suggests its instability at its 

 melting point. The evidence of igneous rocks where ferrous 

 and magnesium compounds constantly occur in isomorphous 

 admixture both as orthosilicates and metasilicates, does, how- 

 ever, indicate that the stability of the magnesium silicates is 

 not greatly modified by the presence of ferrous oxide. 



Although a large volume of work has been done on the 

 crystallisation of silicates from melts, very little is known 

 concerning the nature of the compounds which exist in the 

 fused condition. Most of the attempts to gain information 

 about the latter have involved the measurement of certain 

 physical properties of undercooled liquids (glasses) composed 

 of the mixtures examined. Thus E. S. Larsen (Amer. Jour. 

 Set. 28, 263, 1909) found that the refractive indices and specific 

 gravities of the albite-anorthite series (continuous solid solu- 

 tion) lay on straight lines. A similar result was obtained 

 for the refractive indices of CaSi0 3 — MgSi0 3 (which form one 

 compound CaMgSi 2 6 stable at its melting-point) while the 

 density curve, although not straight, showed no cusps or other 

 critical points. This work has been re-interpreted by E. W. 

 Tillotson (Jour. Amer. Cer. Soc. 1, j6, 191 8), who maintains 

 that both properties in the latter system show breaks in the 

 curves, indicating the existence of compounds of the composi- 

 tions Ca 4 MgSi 5 Oi5 and CaMg 3 Si 4 0i 2 , the latter corresponding 

 to tremolite. Similar investigations of the ternary systems 

 Na 2 0-BaO-Si0 2 and Na 2 - CaO - Si0 2 indicate the exist- 

 ence of several compounds in the former system and of one 

 in the latter (2Na 2 0, 3CaO, 7Si0 2 ). This latter compound has 

 not the composition, 2Na 2 0, 3CaO, 5Si0 2 , of the compound, 

 which is indicated by the only maximum on the freezing-point 

 diagram (Kultascheff, Zeit. Anorg. Chem. 35, 187, 1903), while 

 in the case of the sodium barium series R. Wallace (ibid. 63, 8, 

 1909) found a continuous series of solid solutions. There 

 seem to be two serious objections to the deductions made from 

 this work. Firstly, the experimental errors are of a magni- 

 tude comparable with that of the deviations from the con- 

 tinuous curves, and secondly, since the work is carried out at 



