f4 



ConsiieraMc 

 rcMinblance. 



Tli9 Ameri- 

 can and Swe- 

 dish minerals 

 much alike. 



1^ external ap- 

 pearance. 



and compo- 

 nent parts. 



Treated with 

 alkalis. 



ON THB IDENTITY tF COLUMBIUM AND TANTALUM. 



obligingly fui-nished me with soaie oxide of the latter, 

 which remained in his possession. 



The resemblance was such in my first trials, as to induce 

 me to endeavour to procure a farther supply of colninbium ; 

 and by application to the Trustees of the British Museum, 

 I was allowed to detach a few o-rains from the original spe- 

 cimen analysed by Mr. Hatchett. 



Notwithstanding the quantity employed in my analyses 

 was thus limited, I have, nevertheless, by proportionate eco- 

 nomy of the materials, been enabled to render my experi- 

 ments sufficiently numerous, and have found so many points 

 of agreement in the modes by which each of these bodies 

 can or cannot be dissolved or precipitated, as to prove very 

 satisfactorily, that these Ameiican and Swedish specimens i»- 

 fact contain the same metal ; and since the reagents I have 

 employed are in the hands of every chemist, the properties 

 which I shall enumerate are such as will be most useful in 

 the practical examination of any other minerals, in which 

 this metal may be found to occur. 



In appearance the columbite Is so like tantallte, that It is 

 extremely difficult to discern a difference, that can be relied 

 upon. The external surface, as well as the colour and lus- 

 tre of the fracture, are precisely the snme; but columbite 

 breaks rather more easily by a blow, and the fracture of it 

 is less uniform, appearing in some parts Irregularly shat- 

 tered ; nevertheless, when the two are rubbed against each 

 other, the hardness appears to be the same, and the colour 

 of the scratch has the same tint of very dark brown. 



By analysis also, these bodies are found to consist of the 

 same three ingredients; a white oxide, combined with iron 

 and manganese. 



Either of these minerals, when reduced to powder, is very 

 readily acted upon by potash ; but as the iron contained In 

 them is not affected by alkalis, it appeared better to add a 

 small proportion of borax. 



Five grains of columbite, being mixed with twenty-five 

 grains of carbonate of potash and ten grains of borax were 

 fused together for a few minutes, and found to be perfectly 

 incorporated. The colour was of a deep green, from the 

 quantity of manganese present. The mass when cold could 



be 



