Copper is not attacked by mineral lubricating oil, least by sperm oil.[19] Dr. Watson states in regard to this action:
1. That of the oils used, viz., olive sperm, neat's-foot, and paraffine, the samples of paraffine oil on copper was least affected, and that sperm was next in order of inaction.
2. That the appearances of the paraffine oil and the copper were not changed after an exposure of 77 days.
He later[20] experimented further with the following results noted, after one day's exposure, with iron:—
1. Neat's-foot.—Considerable brown irregular deposit on metal. The oil slightly more brown than when first applied.
2. Sperm.—Slight brown deposit with irregular markings on the metal. Oil of dark brown color.
3. Olive.—Clear and bleached by exposure to light and air. The appearance of metal the same as when first immersed.
4. Paraffine.—Oil bright yellow and contains a little brown deposit.
The action of oils on iron exposed to their action for twenty-four hours and on copper after ten day's exposure was found to have been:—