Abstract: Apparatus for introducing a widely variable predetermined quantity of liquid from a non-pressurized source into a flowing stream of a pressurized fluid. The unitary apparatus is readily detachably assembled to bulk shipping containers of different sizes and its pneumatically powered proportioning mechanism is quickly adjustable at will to pressurize and dispense a liquid at a selected one of many different precise rates into a pressurized fluid stream. The apparatus is readily and quickly adjusted to operate at a wide range of pressures and at many hundreds of pounds per square inch and to vary the ratios of the two fluids between one part in 1,000 and one part in 40,000. The proportioner has many applications including dispensing a fire fighting agent into a pressurized water line supplying fire hoses.