Potassium benzoate can be prepared from benzoic acid and potassium carbonate or hydroxide. Benzoic acid is not very soluble, but both potassium carbonate and hydroxide are. Dissolve 140.2g potassium carbonate or 56.1g potassium hydroxide in 250 ml water, and add 146g benzoic acid. Bring the mixture to a boil. If potassium carbonate is used, CO2 gas will evolve. Continue boiling untill all benzoic acid has dissolved, occasionally adding some water to make up for what has evaporated. When all benzoic acid has dissolved, continue boiling untill the first crystals of potassium benzoate are observed (ie the saturation point has been reached). Then allow the solution to cool to room temperature. Potassium benzoate will crystalise in needle shaped crystals. Filter, and rinse the crystals twice with ice-cold water. The crystals may be dried in an oven at 100 deg C.