ABSTRACT
In 1939, the prototypes were cleaned by rubbing all surfaces with a chamois leather that had first been soaked in ethanol and then in redistilled petrol. To clean the standards, clean chamois leather that has been saturated with the ethanol-ether mixture is used to rub each standard over its entire surface “fairly hard” by hand. Ultrasonic cleaning by solvents was found to be more effective than steam-jet cleaning in reducing carbon deposits and the adsorption of water. The reason for the difference in standard deviations and for a systematic difference in dimensional measurements for the two cleaning methods was not known. The vapor degreasing method and the Bureau International des Poids et Mesure cleaning/washing method were used on steel spheres the diameters of which were then measured optically. A. Bonhoure found also that single-piece stainless steel weights that had been used in hydrostatic measurements might change their mass value by an appreciable amount after steam cleaning.
