Fehling's solution is a chemical reagent used to test for the presence of reducing sugars, such as glucose, fructose, and maltose. The solution is made up of two separate solutions, Fehling's A and Fehling's B, which are mixed together just before use. Here's how to prepare Fehling's solution: Fehling's A solution: Dissolve 69 g of copper(II) sulfate pentahydrate (CuSO4 · 5H2O) in about 500 ml of distilled water. In a separate container, dissolve 346 g of sodium hydroxide (NaOH) in about 500 ml of distilled water. Slowly pour the sodium hydroxide solution into the copper sulfate solution, stirring constantly. Dilute the resulting solution to 1 liter with distilled water. Store the solution in a dark bottle. Fehling's B solution: Dissolve 160 g of potassium sodium tartrate (KNaC4H4O6 · 4H2O) in about 500 ml of distilled water. In a separate container, dissolve 40 g of sodium hydroxide (NaOH) in about 500 ml of distilled water. Combine the two solutions and dilute to 1 liter with distilled water. Store the solution in a dark bottle. To use Fehling's solution, mix equal volumes of Fehling's A and Fehling's B solutions just before use, and heat the mixture until it boils. The solution will turn from blue to brick red if reducing sugars are present.