Brown— Composition of the Selensulphur from Hawaii. 133 



by James D. Dana while mineralogist to the Wilkes Exploring 

 Expedition at Kilauea in 1840. 



The fragment (U. S. N. M. Cat. No. 12901) consisted of a 

 slaggy, vesicular lava, almost a pumice in structure, impreg- 

 nated with an orange-red to sulphur yellow crystalline mineral, 

 and contained minute needle-like crystals in the cavities. It 

 yielded the following reactions: 



Before the blowpipe: Bluish flame, odor of burning sulphur 

 plus the pungency and odor of burning selenium (suggesting 

 scorching cabbage) ; residue reddish-brown, non-magnetic. 



In closed tube : Sublimate, similar to that of pure sulphur ; 

 banded appearance while hot ; on cooling, lower portion clear, 

 light yellow merging into a darker, grayish upper portion. 

 The yellow portion of the sublimate was insoluble in carbon 

 disulphide, but readily soluble in bromine. 



Qualitative analysis of the rock and mineral showed the 

 presence of silicon, phosphorus, sulphur, selenium, iron, alumi- 

 num, titanium, calcium, magnesium, sodium and potassium. 

 Tests on the largest amounts which could be spared failed to 

 show even traces of tellurium or of arsenic. 



The specimen was crushed to a coarse powder and the yellow 

 to orange-red portions, high in selensulphur, were picked out. 

 The selected material was then finely powdered, and amounted 

 to 8*2 grams. Determinations were made of the specific grav- 

 ity with a pyknometer, loss at 103°, sulphur content and 

 selenium content. 



The selensulphur was extracted from the finely powdered 

 mixture of rock and mineral with bromine and the selenium 

 determined by the method of W. Smith,* as follows : the bro- 

 mide of selenium was decomposed by the addition of succes- 

 sive small amounts of bromine water, the solutions were filtered 

 and the selenium precipitated from the combined filtrates by 

 potassium iodide and hydrochloric acid. The solution was 

 then boiled to convert all of the selenium to its black modifica- 

 tion, filtered through a Gooch crucible, the precipitate washed 

 with hot water, and the selenium finally weighed as the ele- 

 ment. In another portion of the mineral the sulphur was 

 oxidized to sulphuric acid by fusion with sodium peroxide, the 

 melt treated with hydrochloric acid and the insoluble residue 

 filtered off. Upon boiling the solution, red selenium separated, 

 and after standing over night the separation of the selenium 

 was complete. The selenium was then filtered off, and the sul- 

 phuric acid in the filtrate precipitated and weighed as barium 

 sulphate. 



In determining the loss at 103° traces of sulphur and 

 selenium were vaporized, as shown by the odor present when 

 * J. Ind. Eng. Chem., vii, 849, 1915. 



