Ford — Chemical Composition of BumoHierite. 429' 



Analysis No. II. Diimortierite from San Diego Co., Cal. 

 Specific gravity between 3*226 and 3 •43. 

 Ratios. 



SiO„ 30-58 -509 



ALO3 61-88 -600X6 = 3-600 



Fe^Og -36 -002X6 -012 



B.O3 5-93 -085X6 '510 



H'P 2-U -119X2 -238 



100-84 4-350 



4-350 :-509 = 60 : 7-02 



Analysis No. III. Diimortierite from Harlem, N. Y. 

 Specific gravity between 3'211 and 3"302. 

 Eatios, 



SiO, 31-24 -520 



A1^03-. 61-26 -596 x6 = 3-576 



Fe.03 -10 -0006X6 -004 



B,03 ... 6-14 -088 X6 -528 



H"„0 2-09 -116 X2 -232 



4-340 



4-340 : -520 = 60: 7-19 



Discussion of Analyses. — It would seem that the chief 

 problem in arriving at a formula for clumortierite would be 

 the determination of the roles played by boric oxide and 

 water, but the analyses indicate that these constituents are 

 present in such variable proportions as not to yield definite 

 ratios with the silica. In the first two analyses the ratios of 

 SiOg : B2O3 are respectively 7 : 1 and 6:1, with percentages of 

 H.,0 increasing with increase of ^fi^. It may be assumed, 

 therefore, that the boron in the mineral has not the nature of 

 an acid element, occurring in a definite proportion, bnt must 

 be considered rather as having' basic qualities, rephicing alu- 

 minium as an isomorphous constituent. Moreover, there is no 

 simple relation between the H„0 and the other oxides, which 

 fact, taken with that of the small amount of water present 

 and the difficulty with which it is driven off from the min- 

 eral, has led to the assumption that it, too, plays the part of a 

 basic constituent in the composition of the mineral. That 

 water does at times play such a role has been abundantly 

 proven. The results of the analyses were, therefore, treated 

 as follows : The ratio of each of the basic oxides was multi- 

 plied by a number which represented its equivalent in hydro- 

 gen, and in this way an expression for the acid from which 

 dumortierite is derived was obtained. Thus treated Analysis 

 ]^o. I gives the ratio of SiO, : H = 6-99 : 60, No. II, 7*02 : 60 



