1 B6 Intelligence atid Miscellaneous Articles. 



fore and after calcination. When tantalic acid is heated, it acquires 

 a faint yellow colour ; niobic acid, on the contrary, a deep yellow ; 

 both became colourless on cooling. Tantalic acid forms on cooling 

 a white dull powder ; niobic acid, fragments possessed of great 

 lustre, similar to that presented by titanic acid precipitated by am- 

 monia and calcined ; with this difference, — that the titanic acid 

 exhibits a brownish tint, while the niobic acid remains colourless. 



Tantalic and niobic acids readily combine with the alkalies. 

 When fused with carbonated alkalies, they expel the carbonic acid. 

 These combinations are soluble in water, and also in an excess of a 

 solution of caustic or carbonated potash, but with difficulty in an 

 excess of caustic or carbonate of soda. The niobate of soda indeed 

 is almost insoluble in an excess of a solution of soda. Acids preci- 

 pitate the tantalic and niobic acids from these solutions. Sulphuric 

 acid precipitates both completely on the application of heat ; but in 

 the cold the tantalic acid is only partially thrown down by it, while 

 the niobic acid is entirely precipitated. Hydrochloric acid in the 

 cold only produces a turbidness in a solution of tantalate of soda ; 

 an excess of acid even causes this to disappear ; with the assistance 

 of heat it precipitates the tantalic acid, but not completely. In a 

 solution of niobate of soda it produces a considerable turbidness in 

 the cold, without precipitating the whole of the niobic acid, which 

 it effects however with the assistance of heat. Oxalic acid has no 

 effect on either of the alkaline solutions, while acetic acid produces 

 precipitates. Hydrochlorate of ammonia forms precipitates. 



W^hen an infusion of galls is added to a solution of tantalate of 

 soda, rendered slightly acid with hydrochloric or sulphuric acid, it 

 produces a bright yellow precipitate. In a solution of niobate of 

 soda it gives rise to a deep orange-yellow precipitate, which has 

 some resemblance to the precipitate formed under similar circum- 

 stances in a solution of titanic acid. Both the precipitates dissolve 

 in caustic alkalies. 



The tincture of galls is the best test for small quantities of tan- 

 talic or niobic acids in acid solutions ; but it should be observed, that 

 the presence of oxalic acid, or of any other non- volatile organic acid, 

 prevents the formation of the precipitate. 



The yellow fei-rocyanide of potassium produces in a solution of 

 tantalate of soda, rendered acid with a few drops of sulphuric acid, 

 a yellow flocculent precipitate, which is slightly soluble in a large 

 excess of hydrochloric acid. It gives rise to a decided red precipi- 

 tate in a solution of niobate of soda, resembling that produced in the 

 same solution by tincture of galls. The red ferrocyanide of potas- 

 sium forms a white flocculent precipitate in a solution of tantalate 

 of soda, a deep yellow one in a solution of niobate of soda. 



If a blade of zinc be immersed in a solution of tantalate of soda 

 rendered slightly acid, it produces no effect at first; but after some 

 time a white deposit is formed consisting of tantalic acid, which is 

 thrown down when the excess of acid begins to dissolve the oxide of 

 zinc formed. In a similar solution of niobate of soda the zinc pro- 

 duces a blue precipitate, which in the course of time becomes brown. 



Perchloride of tantalum, prepared from tantalic acid by means of 



