The volatile alkyl halide, rising through the plugs, reacts with the mercuric nitrate to produce a light orange or vermilion color due to the formation of the mercuric iodide. A solution of 0.10 g of lead acetate in 1.0 mL of water is added to 6.0 mL of 1 M sodium hydroxide solution and stirred until the precipitate dissolves. To this solution is added a solution of 0.5 g of hydrated sodium thiosulfate in 1.0 mL of water. The strips of cloth are dried and rolled to fit the test tube. A saturated solution of mercuric nitrate is prepared in 24.5 mL of distilled water to which has been added 0.5 mL of concentrated nitric acid.
Mercury compounds are very toxic and require handling with special care.
Positive Test Formation of an orange or vermilion color on the test paper within a 10-min heating period is a positive test. A yellow color constitutes a negative or doubtful test. Sulfur-containing functional groups liberate hydrogen sulfie which interferes with the test.