JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. II, DECEMBER 4, 1912 No. 20 



GEOCHEMISTRY. — The various forms of silica and their mutual 

 relations. Clarence N. Fenner, Geophysical Laboratory. 

 Communicated by Arthur L. Day. 



Character of the investigation 



Problems presented by the various forms of silica occurring 

 in nature, in the relations which they bear to each other, have 

 been the subject of investigation by a number of experimenters. 

 The results obtained have not been altogether concordant and 

 the present investigation was undertaken in order to reconcile 

 or explain these discrepancies if possible and to obtain such 

 additional information as would definitely establish the equili- 

 brium relations of the various forms. The investigation is not 

 yet concluded, but the general relations have been established 

 and can be stated with confidence. Later, the whole will be 

 presented at length and with full details of apparatus and methods 

 of work. 



The first subject of investigation was the determination of 

 the exact relations between quartz, tridymite, and cristobalite. 

 Two principal difficulties were encountered. First, the velocity 

 of transformation of one form into another is extremely small 

 at most temperatures; and second, it was found that silica pos- 

 sesses pre-eminently the property which Ostwald has expressed 

 in his principle of successive reactions, namely, that a given 

 form when subjected to conditions under which it is unstable, 



471 



