METHODS AND MANIPULATION 57 when it is volatile (e.g. acetic acid). Citric acid is water-soluble and non-volatile and therefore cation exchange is a particularly suitable method of liberating it from its salts. Method. Prepare a slurry of a strong acid cation resin (such as Amberlite I.R-i2o(HO)*) in distilled water. Place a thin plug of glass wool at the base of a 50 ml. burette. Now pour the slurry into the burette until the latter is about half full. Open the tap of the burette and pour distilled water through the slurry until all the air bubbles have been removed. Drain off most of the water, but do not allow the resin to become uncovered at any time during this or subsequent operations. Now pass ioo ml. of io% hydrochloric acid solution through the resin and then wash it thoroughly by passing distilled water down the column until the washings leaving the burette are neutral to methyl orange. Close the tap of the burette. This column is now ready for use. Prepare
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