INSTUr.MKNTS AM) CHEMICAL TI.STS 589 



</. Tin- substance is mixed with potaium bi-ulphate :iiil fused 

 in a closed tube, when bromine is liberated a.- reddish yellow vapors, 

 best seen by looking down in the top of the tube. 



Illustration. Use potassium bromide. 



Iodine, I. Atomic weight, 126.92. Fusing point ; 114.2 C. 



a. Flame test. Iodides when heated with copper oxide as in 

 case of chlorine yield a green flame. 



6. Iodides in solution yield a yellow precipitate of silver iodide, 

 with silver nitrate, nearly insoluble in ammonia, and which does 

 not darken on exposure to light. 



c. If the silver iodide from 6 is collected in the bottom of a test 

 tube, a few drops of dilute sulphuric acid, and a fragment of zinc 

 added, the silver will be reduced to metallic silver, and zinc iodide 

 will go in solution. The solution is decanted, a few drops of starch 

 paste (made by boiling starch in water) and fuming nitric acid 

 added. Iodine will be liberated, coloring the starch solution a deep 

 blue. 



d. Compounds containing iodine when mixed with bismuth sul- 

 phide and heated in the closed tube yield a brick-red sublimate of 

 bismuth iodide. 



e. If substances containing iodine are mixed with potassium 

 bisulphate and heated in the closed tube, iodine will be liberated 

 as violet vapors, best seen by looking down in the top of the tube. 



Illustration. Use potassium iodide. 



Fluorine, F. Atomic weight, 19. Fusing point, 223 C. 



a. Closed tube test. The ground mineral is mixed with two parts 

 of potassium bisulphate and heated in a closed tube, fluorine is lib- 

 erated and attacks the walls of the tube, forming a ring, like frosted 

 glas^ in appearance, due to a deposit of silica, SiO 2 . The hydro- 

 fluoric acid liberated by the fusion forms silicon tetrafluoride, 

 SiF 4 , with the silica contained in the glass ; this in turn is decom- 

 I > >s. 1 with water ; thus 3 SiF 4 4- 2 H 2 O = 2 H 2 SiF 6 + SiO 2 . After 

 the frosted ring appears, the bottom of the tube is broken off, and 

 the tube gently dipped in water, then dried carefully ; if the ring 

 returns and is non-volatile, it is due to fluorine and is not a subli- 

 mate of sulphates. The fusion with potassium bisulphate is not 

 applicable to silicates. 



6. Silicates are tested as follows: several S. Ph. beads are made 

 on wire and powdered; 4 parts of this powder are mixed with 

 one part of mineral and fused in the closed tube as directed in a 

 above. 



