Mercury CompoundsA. Place 0.05 to 0.1 ml of a solution of the substance under examination on a well-scraped copper foil; a dark grey stain, which becomes shiny on rubbing, is produced. Heat the dried copper foil in a test-tube; the spot disappears.
B. To a solution of the substance under examination add carefully potassium iodide solution; a red precipitate is produced which is soluble in an excess of the reagent (mercuric compounds) or a yellow precipitate is produced which may become green on standing (mercurous compounds).
C. To the prescribed solution add 2 M sodium hydroxide until strongly alkaline; a dense, yellow precipitate is produced (mercuric compounds).
D. To a solution of the substance under examination add 6 M hydrochloric acid; a white precipitate is produced which is blackened by adding dilute ammonia solution (mercurous compounds).
NitratesA. Dissolve 15 mg of the substance under examination in 0.5 ml of water, add cautiously 1 ml of sulphuric acid, mix and cool. Incline the tube and carefully add, without mixing, 0.5 ml of ferrous sulphate solution; a brown colour is produced at the interface of the two liquids.
B. To a mixture of 0.1 m1 of nitrobenzene and 0.2 ml of sulphuric acid add a quantity of the powdered substance under examination equivalent to about 1 mg of nitrate ion or the prescribed quantity. Allow to stand for 5 minutes and cool in ice whilst adding slowly with stirring 5 ml of water and then 5 ml of sodium hydroxide solution. Add 5 ml of acetone, shake and allow to stand; the upper layer shows an intense violet colour.
Phosphates (Orthophosphates)A. To 5 ml of the prescribed solution, neutralised to pH 7.0, add 5 ml of silver nitrate solution; a light yellow precipitate forms, the colour of which is not changed by boiling and which is readily soluble in 10M ammonia and in dilute nitric acid.
B. Mix 1 ml of the prescribed solution with 1 ml of ammoniacal magnesium sulphate solution; a white crystalline precipitate is formed.
C. To 2 ml of the prescribed solution and 2 ml of dilute nitric acid and 4 ml of ammonium molybdate solution and warm the solution; a bright yellow precipitate is formed.
Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of Pharmaceutical Guidelines, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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