ISSO.] NATURAL SCIENCES OF PHILADELPHIA. 315 



cible, heated without access of air, it becomes a steel-gray color, its 

 iron having been reduced. Before the blowpipe it gives the violet 

 flame of potash and fuses to a black magnetic globule, which does 

 not intumesce when further heated. 



With the fluxes it reacts for silica and iron. It is readily dis- 

 solved by hot sulphuric acid, the pure white silica being left in the 

 original shape of the mica. It is dissolved in hydrochloric acid 

 upon long digestion . 



Chemical Composition. — In the investigation of the chemical 

 composition of Philadelphite the writer has had the valuable 

 advice of his friend, Prof. F. A. Genth, of the University of 

 Pennsylvania. The method used in the estimation of vanadium 

 is entirely due to him. The writer is also indebted to his friend, 

 Mr, Reuben Haines, of Germantown, for two analyses, and for 

 some interesting experiments. 



Of the four analyses given below, Numbers I and II are by Mr. 

 Haines; Nos. Ill and IV by the writer. Nos. I and II were 

 made upon the pulverized mineral, previously dried in an air-bath 

 at 100° C; the hygroscopic water, amounting to over 3 p. c, not 

 being included in the determinations. " In both the anal3^ses the 

 sample was dissolved in concentrated HCl, and the Si02 purified 

 by digestion with HCl. The Fe and Al were precipitated togetlier 

 by NH4HO and the Fe titrated by permanganate. The ferrous 

 oxide was found by dissolving the weighed mineral in sulphuric 

 acid in a closed flask from which the air was expelled by boiling 

 with sodic carbonate, and titrating as before. The magnesia was 

 weighed as pyrophosphate and the alkalies were separated by 

 Smith's method of fusion, and were determined by platinic chloride, 

 controlling the result by ignition of the platinic salt in hydrogen 

 and weighing as metallic platinum. Tlie combined H,0 is an 

 average of the results of experiments Nos. IV and VI (given 

 below) taken at a red heat on bottom of crucible." 



Analyses Xos. Ill and IV were made upon the ignited mineral, 

 this being considered its most constant state. The atomic water 

 was determined separately, and the analysis of tlie anhydrous 

 mineral reduced when the percentage of water was added. The 

 ignited mineral being v\ith difficulty soluble in acid, it was decom- 

 posed by fusion with sodic carbonate for anal^'sis. After repeated 

 evaporation of the silica with HCl, it was found still to contain 

 titanic acid, which was extracted by evaporation with concen- 

 trated H,iS04 and precipitated by dilution and boiling. Addi- 



