S60 On the Acid contained in the North American Columhite. 



might be measured, would yield at 2000° a light suitable for 

 most purposes. Moreover, it would be very easy to form 

 from it an available photometer, by screening portions of the 

 shining surface. An ingenious artist would have very little 

 difficulty, by taking advantage of the movements of the lever, 

 in making a self-acting apparatus, in which the platinum 

 should be maintained at a uniform temperature, notwith- 

 standing any change taking place in the voltaic current. 

 University, New York, * 



Feb. 27, 1847. 



LV. On the Acid contained in the North American Columbite. 

 By Henry Rose*. 



nPHE columbite of North America has the same crystalline 

 -^ form as that from Bodenmais in Bavaria, but is distin- 

 guished from it in general by a far lower specific gravity ; 

 however, we find the same difference in the specific gravity of 

 the American mineral as occurs in the different crystals of the 

 Bodenmais columbite. The lightest crystals from the last 

 locality have the same specific gravity (5"704') as the heaviest 

 crystals from North America (5"708). 



1 have already communicated two analyses of North Ameri- 

 can columbites, of one of which however it was doubtful 

 whether it came from America. The following analysis of 

 American columbite was made by M. Grewink in my labora- 

 tory; it yielded, — 



Acid 80-06 . 



Protoxide of iron 12'59 



Protoxide of manganese .... 5*97 



Oxide of tin 096 



Oxide of copper and lead . . . O*** 



100'02 

 The specific gravity in fragments was 5'323; in powder, 5 "3202. 



This columbite comes nearest in composition and also in 

 specific gravity to that examined by M. Schlieper. 



I have on a former occasion shown that the different specific 

 "ravity of the crystals of the Bavarian columbite was owing 

 to the different proportions of niobic and pelopic acids which 

 are found in the different crystals. The specific gravity of 

 these two acids is widely different, but unequally so, according 

 to the temperatures to which they have been exposed previous 

 to weighing. 



Owing to want of material, I found it impossible to make a 



* Translated from Poggendorff's Annalen, 



