THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Art. XXXII. — The Binary Systems of Alumina with Silica, 

 Lime and Magnesia ; by E. S. Shepherd and G. A. Rankin. 

 With Optical Study, by Fred. Eugene Wright. 



According to the calculation by Clarke,* the order of 

 relative importance of the oxides which make up the rock- 

 forming minerals stands, — silica, alumina, oxides of iron and 

 lime, etc. It seems desirable to begin with the study of the 

 systems of alumina, silica and lime, leaving the iron oxides until 

 more experience with the difficulties of this work should enable 

 us to meet the increased difficulties which are introduced by 

 the different oxidation stages of iron. The first paper of the 

 seriesf was published some time ago. We have now to present 

 the result of experiments with three other groups of oxides. 



The interest aroused by the study of the lime-silica series, 

 not only among those engaged in pure science, but also among 

 many in commercial work, would seem to warrant devoting 

 some space not only to the methods but also to the limitations 

 of this kind of investigation. 



In developing a system of such immense usefulness, it is of 

 the greatest importance that those who are interested in the 

 application of physical chemistry to extreme cases of rock 

 magmas shall have a firm grasp of the limitations, both of the 

 theory and experimental possibilities. None of the laws of 

 physical chemistry can be applied to such extreme conditions 

 without some modification. 



*Data of Geochemistry, F. W. Clarke, Bull. No. 330, U. S. Geol. Survey, 

 1908. 



•j-The Lime-Silica Series of Minerals, Day, Shepherd and Wright, 

 this Journal (4), xxii, 265, 1906. 



Am. Jour. Sci.— Fourth Series, Vol. XXVIII, No. 166.— October, 1909. 

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