Fehling’s reagent

What is Fehling’s reagent?

Fehling’s reagent consists of the following two aqueous solutions:

  • Solution A: Crystallised copper sulphate (SO4Cu) (35 g) and distilled water to make up to 1 litre.
  • Solution B: Seignette salt or mixed sodium and potassium tartrate (150 g), sodium hydroxide solution 40 %  (3 g) and water to make up to 1 litre.

These are stored separately until they are used (see Fehling’s Test), to avoid precipitation of copper hydroxide.

Fehling reagent test


Fehling, H. (1849), Die quantitative Bestimmung von Zucker und Stärkmehl mittelst Kupfervitriol. [The quantitative determination of sugar and starch flour using copper vitriol.] Justus Liebigs Ann. Chem., 72: 106-113. https://doi.org/10.1002/jlac.18490720112