Sodium benzoate can be made from sodium carbonate (soda) or sodium hydroxide and benzoic acid which is often more easily available than it's salts. Benzoic acid is only sparingly soluble in water. Dissolve either 425 g hydrated sodium carbonate (common household soda) or 30 g sodium hydroxide in water. Add 100 g of benzoic acid and boil the solution. The benzoic acid will slowly dissolve. During boiling, occasionally add water to make up for what has evaporated. If sodium carbonate was used, carbon dioxide gas will evolve. After all the benzoic acid has dissolved, continue boiling allowing the water to evaporate untill crystallisation begins. Then stop heating and allow the solution to cool slowly to room temperature. Needle-shaped crystals of sodium benzoate will form upon cooling. Cool the solution further to 0 deg C, filtrate and rinse the crystals with ice-cold water. Purify the product by recrystallisation from water.