416 Dr. Thomas Thomson on the 



hard, brittle. Colour of streak, grayish black with a shade 



of brown. Specific gravity 7*300.''^ 



Its constituents, as determined by the analysis of Berze- 



lius, are 



Columbic acid, .... 83*2 



Protoxide of iron, . . . 7*2 



Protoxide of manganese, . 7*4 



Oxide of tin, 0*6 



98-4t 

 Dividing these numbers by the atomic weight of each, 

 we obtain. 



Atoms. 



Columbic acid, .... 3*23 or 2-018 

 Protoxide of iron, . . . 1*6 or 1- 

 Protoxide of manganese, . 1*64 or 1*025 

 These numbers leave no doubt, that the constitution of 

 tantalite is 



2 atoms columbic acid 

 1 atom protoxide of iron 

 1 atom protoxide of manganese 

 Thus, the number of atoms of the acid and of the bases 

 is equal. It is composed obviously of 

 1 atom columbate of iron 

 1 atom columbate of manganese 

 So that the formula indicating its constitution is /CI 4- 

 mn CI. 



It differs from columbite in containing 1 atom less of 

 protoxide of iron, united with the same proportion of 

 columbic acid and columbate of manganese. 



4. Ferrotantalite. 



Among the specimens of tantalite found in Ekeberg's 

 collection, there was one in powder, which had the colour 

 of rust, and which was marked as obtained from a single 

 tantalite cryslal, whose specific gravity was 7-936. This 

 powder Berzelius attempted to analyze in 1815; but the 

 result was unsatisfactory. In 1818, he received from Nor- 

 denskjold a specimen of a tantalite from Kimito, which, 

 when pounded, gave a cinnamon brown power, which he 



• Beitrage, v. 2. t Afhandlingar, iv. 262. 



