Testing Procedure (Method of analysis) for Potassium Salts, Salicylates and Silicates

Potassium Salts

A. Dissolve about 50 mg of the substance under examination in 1 ml of water or use 1 ml of the prescribed solution. Add 1 ml of dilute acetic acid and 1 ml of a freshly prepared 10 percent w/v solution of sodium cobaltinitrite; a yellow or orange-yellow precipitate is produced immediately.

B. Dissolve 0.1 g of the substance under examination in 2 ml of water or use 2 ml of the prescribed solution. Heat the solution with 1 ml of sodium carbonate solution; no precipitate is formed. Add 0.05 ml of sodium sulfide solution; no precipitate is formed. Cool in ice, add 2 ml of a 15 percent w/v solution of tartaric acid and allow to stand; a white, crystalline precipitate is produced.

C. Ignite a few mg of the substance under examination, cool and dissolve in the minimum quantity of water. To this solution add 1 ml of platinic chloride solution in the presence of 1 ml of hydrochloric acid; a yellow, crystalline precipitate is produced which on ignition leaves a residue of potassium chloride and platinum.

Salicylates

A. To 1 ml of a 10 percent w/v neutral solution add 0.5 ml of ferric chloride test solution; a violet color is produced which persists after the addition of 0.1 ml of dilute acetic acid.

B. Dissolve 0.5 g of the substance under examination in 10 ml of water or use 10 ml of the prescribed solution. Add 0.5 ml of hydrochloric acid; the precipitate obtained after recrystallization from hot water and drying at a pressure of 2 kPa melts at about 159°.

C. Dissolve 0.5 g of the substance under examination in 10 ml of water or use 10 ml of the prescribed solution. Add 2 ml of bromine solution; a cream-colored precipitate is formed.

Silicates

In a lead or platinum crucible mix by means of a copper wire to obtain a thin slurry the prescribed quantity of the substance under examination with 10 mg of sodium fluoride and a few drops of sulphuric acid. Cover the crucible with a thin transparent plate of plastic under which a drop of water is suspended and warm gently; within a short time, a white ring is formed around the drop of water.

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