Prof. R. Bunsen on Flame Reactions, 1 03 



titanium compounds form with soda a bead which at first effer- 

 vesces, and when hot is colourless and transparent, but on cool- 

 ing becomes opake. If to the hot bead stannous chloride be 

 added, and if it then be heated in the lower reducing flame, a grey 

 mass is formed, which dissolves on heating in hydrochloric acid, 

 yielding a pale-amethystine-coloured solution. 



27 & 28. Tantalum and Niobium Compounds exhibit the same 

 reactions as titanium. 



29. Silica Compounds. 



(a) Treated with soda in the oxidizing flame, the silicates dis- 

 solve with more or less effervescence. When treated whilst hot 

 with stannous chloride and fused, the mass does not yield a trace 

 of blue colour on solution in warm hydrochloric acid; and the 

 silicates may thus be distinguished from the compounds of titanic, 

 tantalic, or niobic acids. The blood-red colour obtained with 

 ferric oxide from these acids is also not yielded by silicates. 

 Gelatinous silica separates out when the fused mass is carefully 

 treated with water and acetic acid on the lamp-plate. Fine par- 

 ticles of any silicate yield, on fusion in a bead of microcosmic salt, 

 a mass of gelatinous silica when fused, which on cooling forms a 

 solid opake mass swimming in the transparent bead. 



30. Chromium Compounds. 



(a) In the spiral of platinum wire with soda the chromium com- 

 pounds give, when fused with repeated additions of nitre, a yellow 

 mass, which, when pulverized on the plate and treated with water, 

 yields a light-yellow solution. If this solution be carefully 

 poured off from the insoluble matter and acidified with acetic 

 acid, it turns a deep orange-colour, and yields, when absorbed 

 on strips of paper, a yellow precipitate with lead-salts, a red pre- 

 cipitate with mercuric salts, and a reddish-brown precipitate with 

 silver compounds. This solution turns green on addition of 

 ammonium-sulphide, or on treatment on the plate with aqua 

 regia, as likewise on addition of stannous chloride. 



(b) The borax bead is emerald-green in the oxidizing flame, 

 and does not undergo alteration when heated in the reducing 

 flame. 



31. Vanadium Compounds. 



(a) By treating the vanadium compounds with nitre and soda 

 in the platinum spiral, a bright yellow mass is obtained; this 

 gives a solution which, on addition of silver-nitrate and acidifi- 

 cation with acetic acid, yields a yellow precipitate. The fused 

 mass gives a yellow instead of a green solution when evaporated 

 with aqua regia, which becomes blue on addition of stannous 

 chloride. If the mass contains much vanadium, the solution 



