Testing Procedure (Method of analysis) for Benzoates, Bicarbonates and Bismuth Compounds

Benzoates

A. To 1 ml of a 10 percent w/v neutral solution of the substance under examination add 0.5 ml of ferric chloride test solution; a dull yellow precipitate, soluble in ether, is formed.

B. Moisten 0.2 g of the substance under examination with 0.2 to 0.3 ml of sulphuric acid and gently warm the bottom of the tube; a white sublimate is deposited on the inner walls of the tube and no charring occurs.

C. Dissolve 0.5 g of the substance under examination in 10 ml of water or use 10 ml of the prescribed solution and add 0.5 ml of hydrochloric acid; the precipitate obtained, after crystallization from water and drying at a pressure of 2 kPa, melts at about 122°C.

Bicarbonates

A. Solutions, when boiled, liberate carbon dioxide.

B. Treat a solution of the substance under examination with a solution of magnesium sulfate; no precipitate is formed (distinction from carbonates); boil, a white precipitate is formed.

C. Introduce into a test-tube 0.1 g of the substance under examination suspended in 2 ml of water or in 2 ml of the prescribed solution. Add 2 ml of 2 M acetic acid, close the tube immediately using a stopper fitted with a glass tube bent at two right-angles, heat gently and collect the gas in 5 ml of barium hydroxide solution; a white precipitate forms that dissolve on the addition of an excess of dilute hydrochloric acid.

Bismuth Compounds

A. To 0.5 g of the substance under examination add 10 ml of 2 M hydrochloric acid or use 10 ml of the prescribed solution. Heat to boiling for 1 minute, cool and filter, if necessary. To 1 ml of the filtrate add 20 ml of water; a white or slightly yellow precipitate is formed which on the addition of 0.05 to 0.1 ml of sodium sulfide solution turns brown.

B. To about 50 mg of the substance under examination add 10 ml of 2 M nitric acid or use 10 ml of the prescribed solution. Heat to boiling for 1 minute; allow cooling and filtering, if necessary. To 5 ml of the filtrate add 2 ml of a 10 percent w/v solution of thiourea; an orange-yellow color or an orange precipitate is produced. Add 4 ml of a 2.5 percent w/v solution of sodium fluoride; the solution is not decolorized within 30 minutes.

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