What is "acid egg"

The terms acid egg and montejus (or monte-jus) are sometimes used interchangeably to refer to a device with no moving parts formerly used instead of a pump in order to transfer difficult liquids. The principle is that a strong vessel containing the liquid is pressurized with gas or steam, forcing the liquid into a pipe (usually vertical upwards) thereby causing flow. When the liquid has been transferred, the pressure is released and more liquid is put in via gravity. It is thus cyclic in operation. The same principle has been used to lift water and called an air displacement pump or intermittent gas-lift pump, and has been applied to pumping oil up from the formation. Its use has largely been superseded by modern pumps, but it is still used sometimes for special tasks.