96 Prof. R. Bunsen on Flame Reactions. 



If this be moistened with a few milligrammes of a very dilute 

 cobalt solution and ignited, it appears of a beautiful green colour 

 on cooling. It need scarcely be added that the same reaction 

 can be effected with the metallic film. Stannous chloride with 

 and without soda, as well as silver-nitrate with and without am- 

 monia, give no reaction. 



(c) Iodide-film white, not easily recognizable either by itself 

 or after blowing with ammoniacal air. 



(d) Sulphide-film also white, not easily recognized either with 

 or without blowing with ammonium-sulphide. 



(e) The reduction of the metal cannot be accomplished, owing 

 to the volatility of zinc. 



11. Behaviour of the Indium Compounds, 



Indium is most easily and surely detected by the spectroscope ; 

 the flame reactions are given for the sake of completeness. 



(a) Flame -coloration intense, and pure indigo-colour. 



(b) Metallic film black, the thin parts brown, either dead or 

 brilliant; instantly disappears in presence of nitric acid. 



(c) Oxide-film yellowish white, scarcely visible; gives no re- 

 action with stannous chloride and silver solution. 



(d) Iodide-film also yellowish white, not visible either with or 

 without ammonia if present in small quantities. 



(e) Sulphide-film also yellowish white, difficult to see; unal- 

 tered by ammonium-sulphide. 



(/) Reduction on charcoal splinter with soda is difficult; 

 gives silver-white ductile globules slowly soluble in hydrochloric 

 acid. 



In the accompanying Table (p. 98 & 99) the film-reactions of 

 the foregoing elements are clearly seen. 



12. Behaviour of the Iron Compounds. 



(a) Reduction on charcoal splinter gives no metallic bead or 

 ductile lustrous particles ; the finely divided metal forms a black 

 brush on the end of the magnetized knife-blade ; this, when rub- 

 bed off on paper and dissolved in a drop of aqua regia, yields a 

 yellow spot when warmed over the flame, which, when moistened 

 with potassium-ferrocyanide, gives a deep coloration of prus- 

 sian blue. The yellow spot moistened with caustic soda and then 

 held for a few moments in a vessel with bromine-vapour gives, 

 on a second addition of soda, no coloration of a higher oxide. 



(b) Borax bead. — In the oxidizing flame, when hot, yellow to 

 brownish red ; when cold, yellow to brownish yellow ; reducing 

 flame bottle-green. 



