The Open Tube Test

Antimony Antimonides are oxidized to Sb,Oj, which is white and slowly volatile. The sublimate forms as (Sb) a dense, white smoke, which passes up the tube and partly settles on the upper side, partly it leaves the tube. It is volatile, but on further heating it changes to Sb,0 this compound is nonvolatile, infusible, and its color is pale straw-yellow when hot. 

Arsenic All arsenides are oxidized to give off arsenic trioxide (As,0,) which is white and readily volatile. (As) The sublimate forms as a ring in the cold part of the tube, and where it deposits on the warm glass it is distinctly crystalline. With a good magnifying lens tiny octahedrons can be visually observed. The typical garlic odour should not occur, since this is an indication of incompletely oxized samples. 

Bismuth When sulfides are present, bismuth combines with SO, forming a small white sublimate of (Bi) bismuth sulfate. When heated it melts to brown drops, the cooled drops are yellow and opaque. 

On increased heating they vanish due to the formation of Bi-silicates. The test for Bi is not very reliable and should be confirmed by heating on charcoal Lead Sulfides with a considerableamount of lead such as galena may give a small amount of (Pb) a sublimate of PbSO,. The color is white when cold, on strong heating it vanishes due to the 

Sulfur All sulfide minerals are oxidized and sulfur dioxide (SO,) is formed, which can be detected by its (S) odour or by the color change of wet pH-paper. Again brown moistened pyrolusite paper can be 

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White White sublimates could be either ammonium salts or As O, or Sb O, or lead chloride or Hg Clj. Repeat the test adding five times the amount of dry sodium carbonate to the assay, ammonium salts give off ammonia (NH,) while mercury chloride decomposes to metalhc mercury. T o distinguish between As- and Sb-oxides use the open tube test. 

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