Prof. R. Bun sen on Flame Reactions. 93 



4. Behaviour of the Arsenic Compounds. 



(a) Flame-coloration in upper reducing flame pale blue, giving 

 the well-known arsenical smell. 



(b) Reduction film black, dead or brilliant, thin film brown. 



(c) Oxide-film white; touched with perfectly neutral silver- 

 nitrate and then blown with ammoniacal air, it gives a canary- 

 yellow precipitate, soluble in ammonia. Together with the 

 lemon-yellow precipitate, a brick-red one of silver-arseniate occurs 

 when the film has previously been treated with bromine-vapour. 

 Stannous chloride with and without soda produces no change. 



(d) Iodide-film is deep yellow, disappears on breathing, but 

 returns on drying ; disappears in ammoniacal air and does not 

 return; reappears unaltered after the action of hydrochloric 

 acid. 



(e) Sulphide-film lemon-yellow, disappears easily on blowing 

 with ammonium-sulphide, and reappears on warming or blowing ; 

 insoluble in water, and does not disappear by breathing. 



(/) Reduction on charcoal splinter yields no metallic bead. 



5. Behaviour of the Bismuth Compounds. 



(a) Flame-coloration bluish, not characteristic. 



(b) Reduction film black, dead or brilliant; thin portion of 

 film brownish black. 



(c) Oxide-film light yellow; unalte?*ed by silver nitrate with 

 or without ammonia ; gives no reaction with stannous chloride, 

 but yields black precipitate of bismuth suboxide on addition of 

 caustic soda. 



(d) Iodide-film is very characteristic, and remarkable for the 

 number of tints which it assumes; the thick part is of a brown 

 or blackish-brown colour with a shade of lavender-blue; the thin 

 film varies from flesh-coloured to light pink ; it easily disappears 

 on breathing, and appears again on blowing; in a stream of am- 

 moniacal air it passes from pink to orange, and on blowing or 

 wartning it again attains a chestnut-brown colour; it resembles 

 the oxide-film in its behaviour to stannous chloride and caustic 

 soda. 



(e) Sulphide-film is of a burnt-umber colour, the thin parts are 

 of a lighter coffee-brown colour ; does not disappear on blowing, 

 and is not soluble in ammonium-sulphide. 



(/) On charcoal splinter with soda the bismuth compounds are 

 reduced to a metallic bead, yielding, when rubbed in the mortar, 

 bright shining yellowish splinters of metal soluble in nitric acid. 

 The solution gives, with stannous chloride and caustic soda, black 

 bismuth suboxide. 



