Abstract: Apparatus for the preparation of gas mixtures includes cylinder which is divided into two chambers by means of a fixed central barrier. This barrier has a central orifice for receiving a rod which has central portion of diameter corresponding with the diameter of the orifice. The rod has end portions which pass through end plates of the cylinder and these end portions have a small diameter than that of the central portion, the diameters of the end portions being equal. A valved passage for the gases of either chamber to be transferred to the other chamber is provided in the barrier and a stepper motor is used to move the rod over small distances; with means to introduce or withdraw gas from either chamber.

Abstract: Apparatus for the preparation of gas mixtures includes cylinder which is divided into two chambers by means of a fixed central barrier. This barrier has a central orifice for receiving a rod which has central portion of diameter corresponding with the diameter of the orifice. The rod has end portions which pass through end plates of the cylinder and these end portions have a small diameter than that of the central portion, the diameters of the end portions being equal. A valved passage for the gases of either chamber to be transferred to the other chamber is provided in the barrier and a stepper motor is used to move the rod over small distances; with means to introduce or withdraw gas from either chamber.

Abstract: A liquid dispensing device for use in the dispensing of micro-volumes of liquid for gas chromatography has a cylinder with an open end and has a piston slidable therein. The piston has a coaxial rod slidable within itself; and displacement member including a reversible stepper motor and clutch mechanism is provided to effect selectable linear displacement of the piston in the cylinder and/or the rod in the piston in order to vary to volume of the cylinder, the top end of which is in communication with the fluid sample to be injected.