Before the widespread use of petroleum oils in the late nineteenth century, tallow — animal fat — was a useful lubricant for steam locomotives. Firemen and engineers used tallow pots to lubricate the cylinders of moving locomotives. source
This tallow pot belonged to dad, Larkin Watson Buckland, Jr. and he used it during his days on the steam engines working both as a fireman and then an engineer on the Norfolk & Western.
The oil can below belonged to my grandfather, L.W. Buckland, SR who was also a fireman, then engineer.
See how they used the oil can on a steam engine. This photo taken from (source)
The Modern Railroad (1911)