16 for receiving and discharging the liquid which the container 8 is to dispense in repeatable volumetric amounts the partition element 12 consists of a flexible film material which can be readily given a pre formed shape which is non yieldable in planar orientations linear directions but which is sufficiently thin to be collapsible under moderate fluid pressures one example of a satisfactory material is a thin e g 0 001 thickness 34 mylar 34 film as produced by e i dupont company at circleville ohio the material of partition element 12 and also the attachment medium which secures element 18 to the container interior bottom 14 must be impermeable to gasses and to liquids partition element 12 separates the entire interior volume of the housing 10 into a principal volume 18 between the opening 16 and the upper surface of the partition element 12 and a secondary or bladder volume 20 which lies between the under side of the partition element 12 and the interior bottom 14 of housing 10 the liquid to be dispensed is contained in the principal volume 18 the secondary volume 20 is vented at all times to the ambient environment it functions as a variable volume bladder in which the contained air pressure is always at a pressure corresponding to the ambient atmospheric pressure in the preferred embodiment depicted in fig1 and 2 an atmospheric vent means which consists of an aperture 22 is located in the bottom 14 of the container housing 10 in another embodiment depicted in fig3 the vent means consists of a tube 24 with two open ends 26 and 28 where one open end 28 is located in partition element 12 and.