Лако-красочные материалы — производство

A strongly alkaline solution of 250 grams of technical sulfanilic acid in about 1 liter soda solution is boiled until all of the aniline has been driven off. The solution is then filtered and made strongly acid with hydrochloric acid. The precipitated material is filtered off after 12 hours, washed with a small amount of water, and redissolved in 400 cc. water containing enough soda ash (about 60 grams) to make the solution neutral. The hot solution is cooled to 0°C. with stirring, and the precipitate of sodium sulfanilate is filtered off. If the apparatus is available, the mother liquor is removed by centrifuging. The crystals are dissolved in 500 cc. distilled water, and the solution is filtered and acidified with pure hydrochloric acid (coned.). The solution is stirred so that only small crystals are formed. The precipitate is filtered off after a day and washed carefully with distilled water to wash out all of the sodium chloride. The material is then recrystallized once from hot dis­tilled water and dried at 120° to constant weight. The purified material is stored in a tight glass bottle with ground glass stopper. It is almost white and contains less than 0.01 per cent of impurities. A solution of the reagent is prepared by dissolving 173 grams in 100 cc. pure ammonia (20 per cent NH3) and diluting to 1 liter at 17.5°. This solution is stable in the dark for many months, but should be checked at intervals of 3 months. This standard solution is used in the preparation of 1 N nitrite solution.