Abstract: The invention provides for a cartridge for lubricant which is designed for use in an air line lubricator. The cartridge comprises a rigid sleeve defining an outlet nozzle for lubricant at its one end, with the other end being open and directed in use into the stream of pressure air flowing through the lubricator. A flexible sock with its mouth region secured within the sleeve acts physically to separate lubricant in the sleeve from the pressurized air, the body length of the sock being sufficient to permit exhaustion of lubricant from the sleeve. The sock may be secured within the sleeve at the outlet end thereof, midway there-along, or at its open end. In the latter case a method of charging the sleeve in accordance with a further aspect of the invention comprises locating a second sleeve within the cartridge sleeve so that during the charging process the sock is folded back on itself through the action of the secondary sleeve. After charging the secondary sleeve is withdrawn.