"As predicted by friction theory, experiments showed that friction and surface damage of metals can be reduced by solid surface films. The ability of materials to form surface films that prevent welding was a very important factor in wear of dry and boundary lubricated surfaces. Films of graphitic carbon on cast irons, NiO on nickel alloys, and FeO and Fe(sub 3)O(sub 4) on ferrous materials were found to be beneficial. Abrasive films such as Fe(sub 2)O(sub 3) or MoO(sub 3) were definitely detrimental. It appears that the importance of oxide films to friction and wear processes has not been fully appreciated" (p. 93).

A study of the relations existing among pin-point autoignition, homogeneous autoignition, and knock has been made by means of the NACA high-speed camera and the full-view combustion apparatus. High-speed photographic records of combustion, together with corresponding pressure-time traces, of benzene, 2,2,3-trimethylbutane, S-4, and M-4 fuels at various engine conditions have shown the engine conditions under which each of these phenomena occur and the relation of these phenomena to one another.