Many types of chemicals have been studied as base fluids for synthetic lubricant^.^,^ These include esters, polyglycols, hydrocarbons, phosphate esters, silicones, silicate esters, polyphenyl ethers, halogenated JSL (1) 6-3 3 J S L 1-1

Rotary-engine lubrication studies have been conducted on four engines covering the two types of rotary engine now in production. Metallic or carbon-metallic apex seals were used. Results presented have been obtained with 13 different oil formulations, including passenger-car-engine oils corresponding to API SC, SD or SE categories, automatic-transmission fluids of the Dexron II type, and oils for two-stroke engines. Seven different test procedures have been used in these investigations, employing either engine bench test stands or vehicles on chassis dynamometers. Satisfactory rotary-engine performance has been obtained with oils containing from 0 to 1·2 per cent by weight of sulphated ash. The ability of the base stock to provide good film thickness has also been found of benefit in reducing rotary-engine wear. Passenger-car-engine oils can be excellent rotary-engine lubricants and those oils corresponding to the latest API SE classification exhibit better performance than previous API SC or SD oils. Automatic-transmission fluids have also given promising results.