Mineralogy and Geology. 



279 



in 



Farther account of the Arkansite. — Mr. W. S. Clark, a student 

 Amherst College, having recently furnished me with a good sized spe- 

 cimen of this mineral,* in which it presents itself in very beautiful crys- 

 tals as well as massive, (the whole resembling a mass of Elba specular 

 iron ore,) I am able to add a few particulars to my first account of the 

 species.t The crystals differ considerably in the relative size or devel- 

 opment of the planes, from the modifica- 

 tion first described, and besides in present- 

 ing the new faces a, which result from the 

 truncation of the acute angles of the pri- 

 mary form. The planes M are here bet- 

 ter adapted to measurement than in the a 

 first specimens examined, though still obli- 

 ging us to employ the reflexions of a lamp 

 1'ght in place of the ordinary window bar. 

 The value obtained for M vvas constantly 

 between 101° and 101° 15', and that for a 

 on a, 123°. 



In my first account, I accidentally omitted to give the specific grav- 

 ity. It is 3-854. This result I have confirmed by fresh trials. 



The chemical examination has been so far extended by the present 

 supply of material, as to establish the conclusion that the before discov- 

 ered titanic acid in it is possessed of those traits which have induced Prof. 

 Rose to distinguish it as an acid of a new metal, called by him Niobium. 



In a perfectly powdered state, the mineral- is decomposed by four 

 h °urs boiling in concentrated sulphuric acid, its color gradually chan- 

 p n g during the digestion from dark ash grey to a pale yellowish white. 

 J 1 was transferred to a Berlin porcelain crucible and ignited. After full 

 J gnition for ten minutes, it was removed from the fire, when it was ob- 

 served that it still emitted fumes of sulphuric acid. On a farther heat- 

 ! n S however, these fumes ceased to be evolved. It was found to have 

 '°st only 1-89 p. c. of its original weight, and to possess a yellow color 

 w »«e hot, which faded out to white on cooling. 



A- It was now treated with dilute sulphuric acid and boiled for half 

 an hour; after which the liquid was poured off, and the insoluble mat- 

 ter was again thoroughly heated and weighed. It had lost scarcely 

 m °re than 1 p. c . by the process. The acid liquid gave with amrno- 

 n, a a slight flocculent precipitate. 



y - A portion of the insoluble powder A was fused with three parts 

 or carbonate of soda for half an hour. It melted perfectly, and had 



on cooling, a faint bluish tinge in spots. Water loosened it from the 



^ucible, but dissolved it only in the slightest portions. 



^ l °this solution either hydrochloric or sulphuric acid, a whitejirecipi- 



te Was produced, which did not disappear by boiling. ^ 

 f\e with alcoholic solution of nutgalls, a rich red brown or orange pre- 

 cl P«iate. 



On dropping 



ite precipi- 

 The liquid 



Tw f Io cahty at Magnet Cove. 

 lh 's Journal, tiger., vol. ii, p. 250. 



