64 Mr David Forbes on the Chemical 



streak, reddish-brown. Lustre, brilliant and metallo-vitreous ; 

 translucent with a reddish-brown colour when in very thin 

 splinters. Hardness, 6*5. Specific gravity taken at 60° F, of 

 a small crystal = 4-99, and of a pure fragment of a large 

 crystal = 4-89. 



Heated in a glass-tube it does not change colour or lose 

 lustre. 



Before the blowpipe, infusible and unchanged. With borax 

 in the oxidating flame it gives a brownish-yellow glass some- 

 what lighter in colour when cold. In the reducing flame it is 

 unchanged, even on flaming. With phosphate of soda and 

 ammonia it gives a glass which is greenish-yellow whilst hot, 

 but nearly colourless on cooling. Gives no reaction either of 

 titanium or manganese, although it contains both these metals. 



The analysis was conducted as follows : — 



20-81 grains of the pure mineral impalpably powdered were 

 ignited in a gold crucible and lost 0*60 grains, becoming some- 

 what lighter in colour. 1 60 grains bisulphate of potash were 

 then added, gradually fused, and kept melted for several hours 

 until the mineral appeared completely decomposed. As much 

 as possible was removed from the crucible whilst in a pasty 

 state, softened with cold water in an agate mortar, and reduced 

 carefully to fine powder ; the crucible was likewise washed 

 with cold water, and the whole being made up to 16 oz., was 

 allowed to digest for 18 hours at the ordinary temperature in 

 a beaker. 



The clear supernatant fluid was carefully decanted off; 16 

 oz. more cold water added and allowed again to digest for 24 

 hours ; this was repeated a third time and the insoluble mat- 

 ter then thrown on to a filter, well washed with cold water, 

 dried, and incinerated. It weighed 8*03 grains. This residue 

 on heating became of a brilliant yellow colour, but was quite 

 white when cold, and possessed all the characters of columbic 

 acid.* 



The solution was now boiled for some time, when a precipi- 

 tate fell, which was washed, dried, and incinerated, and 



* As to whether the columhic acid might contain also tantalic acid I am not 

 prepared to say, as I believe there is not at present any accurate means of se- 

 parating these two substances. 



