Housing is generally tubular and split into two longitudinal hinged halves. Housing receives threads on driver. Retention and anti-rotation means retain cartridge in other end of housing. Cartridge has zero draft tubular wall, and rounds to an extended tip with external threads at other end. Tip is hollow. Piston matching profile to tip and seals open end of cartridge. Liquid is contained between tip and piston. In use, driver engages piston to force liquid out tip. Cartridge differentiates between capacities of cartridge for housing. Driver and housing indicate rotary position of driver with respect to housing and prevent driver from reversing direction. Injector is designed to withstand pressures of operating system to which liquid is injected. Injector high accuracy for use with high concentrations and small cartridges. Cartridge and piston limits introduction of air when filling and limits retained liquid after cartridge used. Housing and driver indicate liquid remaining.