Ford — Chemical Comjyosition of Dumoriierite. 427 



direct determination of B^O, was not made. It is stated, 

 however, that but the smallest trace of B.Og was observed. It 

 may here be noted that it is not especially easy to get a satis- 

 factory qualitative test for boron in dumortierite, and without 

 a quantitative determination one might easily be led to a wholly 

 misleading conception as to the amount of B^Og present ; 

 hence it cannot be assumed that the absence of notable quan- 

 tities of boron in the Harlem mineral has been satisfactorily 

 proved. It has been found, as will be shown in the course of 

 this article, that the dumortierite from Harlem does contain 

 boron, and it also occurs in notable quantities in the mineral 

 from the original locality in France, as indicated by a distinct 

 qualitative test made by fusing on platinum wire with potas- 

 sium bisulphate and fluorspar; hence, boron seems to bean 

 unfailing constituent of dumortierite. 



All analyses thus far made agree in indicating that dumor- 

 tierite is a very basic silicate of aluminium, yielding a small 

 loss of weight on ignition, presumably water, but they show 

 marked variations as regards boron. The present investiga- 

 tion was undertaken, therefore, with the idea of making a 

 special feature of the boron determination and of establishing, 

 if possible, the exact chemical composition of the species. 



Material for Analysis. — It was possible to obtain material 

 from three independent sources. Clip, Arizona; Harlem, JN'ew 

 York ; and San Diego Co., California. From the first locality 

 material was obtained from specimens in the Brush collection, 

 and also from an abundant supply of the mineral sent by Mr. 

 Geo. L. English of Kew York. The dumortierite from Clij) 

 occurs as small columnar aggregates imbedded in a matrix of 

 granular quartz, associated with a little magnetite and cyanite. 

 Pure material was separated by pulverizing a large quantity of 

 the I'ock and treating, first with potassium mercuric iodide in 

 order to separate the quartz, then by suspension in barium 

 mercuric iodide so as to obtain the mineral in condition of 

 greatest possible purity. After separation in this manner the 

 dumortierite was picked over carefully by hand and then 

 allowed to stand for several days in hydrofluoric acid in order 

 to remove any remaining traces of quartz which might be 

 attached to the mineral. It may be stated that hydrofluoric acid 

 in the cold has practically no action on crystals of dumortierite. 



Material from Harlem was obtained from specimens in the 

 Brush collection and rendered pure by the means described 

 above. The material from San Diego Co., California, was 

 obtained from some specimens which were sent to Prof. S. L. 

 Penfield by Mr. E. Schernikow of ^ew York. The general 

 locality of the occurrence of this type of dumortierite has been 

 confirmed by Mr. W. Tassin of the U. S. ]S"ational Museum in 

 Washington, who kindly sent a specimen for comparison with 



