M. H. Rose on Tantalum and its Compounds. 275 



And instances are not wanting in which a substance in crystal- 

 hzing carries with it a small quantity of another body whose 

 crystalline form is different from its own. 



Heinrich Rose is engaged on a complete investigation of tan- 

 talum and its compounds, and has already published* some of 

 his results. He prepared metallic tantalum by a method essen- 

 tially that of Berzelius, namely, by the action of sodium on the 

 double fluoride of tantalum and sodium. The two substances 

 are placed together in a well-covered crucible and heated ; the 

 action commences at a dull red heat, and is so violent that the 

 crucible becomes suddenly incandescent. The mass, on cooling, is 

 washed out, and metallic tantalum is left in the form of a dark 

 black powder. It is, however, not quite pure, but contains some 

 acid tantalate of soda. It conducts electricity very well, although 

 Berzelius found that it scarcely did so at all. It is not attacked 

 by any acids except nitrohydrofluoric, which dissolves it. It 

 is slowly oxidized by bisulphate of potash to tantalic acid. When 

 gently heated in chlorine, it glows and absorbs the gas very 

 rapidly, chloride of tantalum distils off, and there is left a residue 

 of acid tantalate of soda with which the metal is always conta- 

 minated. 



Tantalum is also obtained by passing phosphorus vapour over 

 heated tantalate of soda ; but the metal so obtained is not very 

 pure, and does not conduct electricity. 



With a view to determining the atomic weight of tantalum. 

 Rose prepared chloride of tantalum in a state of great purity by 

 methods which have been already described by him. When pure, 

 it is of a light yellow colour; it begins to volatilize at 144° C, 

 long before its melting-point, which is at 221° C, and sublimes 

 completely, condensing into a solid crystalline mass. In contact 

 with water it decomposes into tantalic acid and hydrochloric acid, 

 and its analysis was effected by treating it with water to which 

 ammonia was added, by which means the tantalic acid was more 

 readily and completely precipitated. In the filtrate from it the 

 hydrochloric acid was determined by nitrate of silver. 



The mean of a great many analyses executed in this manner 

 gave numbers from which the composition of tantalic acid is 

 deduced to be, — tantalum 81*14 per cent., oxygen 18-86 per 

 cent. This differs somewhat from the numbers obtained by Ber- 

 zelius. M. Rose shows that his method is defective. Berzelius 

 believed that the composition of tantalic acid was Ta^ O-^, and 

 that it was to be classed with alumina, oxide of iron, &c. Rose 

 has at various times inclined to consider it as TaO^ and Ta- 0^. 



* PoggendorflTs Jnna/CTt, August 30, 185G ; October 30, 1856; January 

 1857. 



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