Given the “hinged” wire loop on the bottom, 2nd picture, for placing one’s foot on when “pumping”, it could be used for pumping most any liquid, ….. water, motor oil, differential oil, etc. from a stationary place, ….. meaning, ….. when spraying insecticides and fertilizers one is always on the move.
Whatever it sprayed, it had to last a long time because that container doesn't look to be easily refilled. (which now causes me to add ........)
OOPS, just loked at pic again, ...... me now thinks its a "tire pump".