This test method is used for the determination of the hydrolytic stability of petroleum or synthetic-base hydraulic fluids. The sample of 75 g of fluid plus 25 g of water and a copper test specimen are placed in a pressure-type beverage bottle. The bottle is rotated, end for end, for 48 hours in an oven at 93°C (200°F). Layers are separated and insoluble are weighed. Weight change of copper is measured. Viscosity and acid number changes of fluid and acidity of water layer are determined. The equipment is rugged construction and the accuracy, precision, safety repeatability and reliability is ensured with appropriate design & instrumentation.