Foote and Bradley — Chemical Composition of Nephelite. 439 



temperature, just the reverse of the common behavior of 

 hyd rated salts. The explanation has been that water exists in 

 zeolites in a condition of solid solution. Our data, obtained 

 entirely from analyses, supports this view but indicates also 

 that part of the silica is in a similar condition. It would be 

 possible theoretically, however, for the water to behave as 

 ordinary water of crystallization and still have the isomorphous 

 relations derived above. 



It is hoped that the deductions advanced in this article may 

 find similar application to other zeolites. 



In closing the authors desire to express their thanks to 

 Professor L. V. Pirsson for many valued suggestions. All the 

 material for this investigation was very generously furnished 

 by Professor W. E. Ford from the Brush collection, to whom 

 our thanks are also due. 



Chemical and Mineralogical Laboratories of the 

 Sheffield Scientific School of Yale University, 

 New Haven, Conn., Feb. 1912. 



Art. XXXVII. — The Chemical Composition of Nephelite ; 

 by H. W. Foote and W. M. Bradley. 



In a previous article,* we have shown from a series of 

 analyses that the composition of the mineral nephelite does not 

 correspond to the simple formula NaAlSi0 4 but that there is a 

 variable excess of silica beyond the amount required by the 

 formula. Since the material was entirely homogeneous, we 

 showed that the results could be accounted for very simply by 

 assuming that the excess of silica was present in some form in 

 solid solution. We did not attempt to determine the molec- 

 ular condition of the dissolved silica — whether it was present 

 as albite, for instance, or in any other form (p. 31). Recently, 

 two articles have appeared on the composition of nephelite, 

 one by Schallerf the other by Bowen.J Schaller prefers to 

 account for the excess of silica by assuming an isomorphous 

 mixture of nephelite with an hexagonal albite, while Bowen 

 assumes that albite itself accounts for the excess. The pres- 

 ence of kaliophilite with nephelite as an isomorphous mixture 

 of the ordinary type is of course to be assumed but has nothing 

 to do with the excess of silica in the ratios. The difference in 

 our views, then, amounts to this, that we assume silica is pres- 



*This Journal, xxxi, 25, 1911. f Wash. Acad. Sci., i, 109, 1911. 



{This Journal, xxxiii, 49, 1912. 



