Fehlings Solution No. 1 was an aqueous solution of copper sulfate, while Fehling's No. 2 is a clear and colorless solution of aqueous potassium sodium tartarate and a strong alkali such as sodium hydroxide. It is used to differentiate between water-soluble carbohydrate and ketone functional groups, and as a test for monossaccharides. Solutions 1 and 2 were mixed just prior to use. Developed by German chemist Hermann von Fehling in 1849, it was used to detect the presence of glucose in the urine, a sign of diabetes.