The work described in this paper was done during the war, at the suggestion of the aircraft engine firms, as a result of difficulties with lubricating oil systems at high altitudes. Failure of oil pressure, seizure of bearings, or excessive loss of oil sometimes occurred and these defects were attributed to air in the lubricating oil, this air being greatly increased in volume at high altitudes because of reduced atmospheric pressure.

The behaviour of air-oil mixtures therefore was studied to obtain fundamental information which could be applied to engine lubrication at high altitudes. The present paper deals with that part of the research which was done on a complete lubrication system under simulated altitude conditions.