FEHLING'S SOLUTION, a solution used to determine the amount of glucose in a solution. It is prepared by dissolving in 200 cubic centimeters of distilled water, 34.64 grammes of pure crystallized cupric sulphate, previously powdered and pressed between blotting paper, and mixing it with 174 grammes of Rochelle salt dissolved in 400 cubic centimeters of a solution of pure caustic soda. The liquid must be kept in bottles protected from the light, and from absorption of CO₂ from the air.