390 Penfield and Minor — Chemical Composition and 



vapors to pass off with the water.* There can be no doubt 

 about the water having come from hydroxyl, since it is not 

 driven off except at an intense heat. In an experiment on 

 topaz from Stoneham, Me., where the water was found to be 

 0*98 per cent, the powder suffered a loss of only 012 per cent 

 by heating for a long time in a platinum crucible at the highest 

 heat of a ring burner. 



The remainder of the analysis was conducted in the ordinary 

 manner. 



Material for analysis. — The specimens which we have 

 examined are from the following localities : 



Stoneham, Maine. — The material was colorless and trans- 

 parent and was taken from the center of a large crystal in the 

 Brush collection, catalogue number 185. Analyses have also 

 been made by Gentlrf and Whitfield.:}: The former found 

 18 - 83 and the latter 17*10 per cent of fluorine, also ]STa 3 1*25, 

 K a O 0*14: and H 2 0*20 per cent. A careful test that we have 

 made for alkalies has shown that they are absent. 



Pike's Peak, Colorado. — A perfectly colorless and trans- 

 parent cleavage piece from a large crystal. 



Nathrop, Colorado. — Wine yellow crystals in rhyolite, de- 

 scribed by Cross. § The habit is similar to fig. 4, page 493 of 

 the sixth edition of Dana's Mineralogy, or fig. 54, page 123 of 

 Hintze's Mineralogy. 



Utah. — Perfectly colorless transparent crystals from the 

 rhyolite of the Thomas Range, forty miles north of Sevier 

 Lake. The crystals were selected from a suite of specimens in 

 the Brush collection, and have been described by A. 1ST. Ailing. || 



San Luis Potosi, Mexico. — Colorless, transparent crystals 

 like those described by Biicking^[ and similar to the ones from 

 ISTathrop. 



Zacatecas, Mexico. — Colorless crystals similar to the preced- 

 ing. The material was generously supplied to us by Prof. A. 

 J. Moses, from the mineralogical collection of the Columbia 

 School of Mines, New York. 



Schneckenstein, Saxony. — Wine yellow crystals, selected 

 from a suite of specimens in the Brush collection. 



Adun-Chalon, Siberia. — The specimen corresponded to the 

 description given by Kokscharow.** A colorless and trans- 

 parent crystal in the Brush collection was used for the analysis. 



* A full description of this method is in preparation and will appear in a later 

 publication. 



f Trans. Am. Phil. Soc. Oct.. 1885, p. 43. 



% This Journal, III, xxix, p. 318, 1885. 



§This JourDal, III, xxxi, p. 432, 1886. 



|| This Journal, III, xxxiii, p. 146, 1887. 



«![ Zeitschr. Kryst., xh, p. 424, 1886 



** Materialien zur Min. Russlands, II, p. 232. 



