190 PROF. H. E. ROSCOE ON METALLIC NIOBIUM 



phuric acid, on the other hand, dissolves the metal quickly, 

 yielding a colourless solution. The metal does not take fire 

 in chlorine gas at the ordinary temperature ; but it does so 

 when gently heated, with formation of pentachloride and a 

 trace of oxychloride, owing to the unavoidable presence of 

 a small quantity of oxygen in the metal experimented with. 



The specific gravity o£ metallic niobium at 15°" 5 is 7 "06, 

 as a mean of two well-agreeing determinations made with 

 half a gram of substance. 



Niobium Trichloride, NbClj. — ^When the vapour of ni- 

 obium pentachloride is passed through a heated glass tube 

 it is slowly decomposed, a black deposit of trichloride 

 being formed on the sides *o£ the tube. Niobium trichlo- 

 ride is generally obtained as a black crystalline crust which 

 possesses an almost metallic lustre, and closely resembles 

 in appearance a film of sublimed iodine. It is some- 

 times deposited in long needle-shaped crystals which 

 exhibit a dichroic lustre. The trichloride is non- volatile ; 

 it is not deliquescent, nor is it decomposed by water or 

 ammonia ; but when brought into contact with dilute nitric 

 acid it is at once converted into niobic and hydrochloric 

 acids. Heated in the air it emits dense white fumes. 



For the purpose of analysis the trichloride, from several 

 different preparations, was in some cases decomposed by 

 nitric acid directly, and in others first fused with sodium 

 carbonate and the fused mass treated with nitric acid. 



No. I. 



Substance taken 0*278 1 



Nbj^Oj obtained o'i93o 



AgCl 0-5681 



Calculated. 



Niobium (Nb) 46-88 



Chlorine (CI3) S3'i2 



loo'oo 99'2i ioo'i6 99'35 



