[aerohead]

* The tribologists would have had access to Getman & Daniels' 'Outlinesof Theoretical Chemistry', 1st-Edition, 1913, which would avail them to technical information about molecular outer shell 'polar', 'non-polar' localized charges, which would aid them in identifying 'covalent bonding' chemistries, desired most inside engines.
* 'Table-top' lab experiments would ferret out non-viable candidates, narrowing the field for those which would ultimately be put to the most expensive tests, inside dynamometer test cells, using predecessors of the SAE J1082, SAE J607, SAE J1349, SAE J1995, SAE J2723, and ASTM D8114 Sequence VIE, 196-hour procedures, before accepted as acceptable motor oil additives, alongside: graphite, molybdenum, iron-oxygen-carbon-hydrogen, organic phosphates, organic sulfur, chlorine, boron-nitrogen, and Polyalphaolefin ( PAO ) 2.5 ( SYNFLUID ), Group-IV additives.
* Bear in mind that, in automotive engine tribology, any emphasis on 'Extreme Pressure' ( EP ) motor oil additives, is focused on 'valvetrain,' cam-lobe and valve-lifter protection.
* Transmissions have their own story.
* Differentials have their own story.