▁the ▁outside ▁air ▁is ▁allowed ▁to ▁mix ▁with ▁the ▁gas ▁inside ▁the ▁bott le ▁the ▁head space ▁no ▁longer ▁contains ▁pure ▁CO 2 . ▁ ▁Thus ▁the ▁partial ▁pressure ▁of ▁CO 2 ▁is ▁substantial ly ▁reduced , ▁from ▁ 2 ▁atmos pher es ▁to ▁the ▁partial ▁pressure ▁of ▁CO 2 ▁in ▁the ▁Earth ' s ▁atmosphere , ▁which ▁is ▁approximately ▁ 0 . 0 0 0 3 ▁atmos pher es . ▁ ▁In ▁accord ance ▁with ▁Henry ' s ▁Law , ▁the ▁excess ▁CO 2 ▁dissol ved ▁in ▁the ▁drink ▁comes ▁out ▁of ▁solution . ▁ ▁Event ually ▁it ▁reaches ▁a ▁new ▁dynamic ▁equilibrium ▁state , ▁with ▁a ▁much ▁lower ▁partial ▁pressure ▁of ▁CO 2 ▁in ▁the ▁head space ▁and ▁thus ▁a ▁much ▁lower ▁amount ▁of ▁CO 2 ▁held ▁in ▁solution . ▁ ▁P ump ing ▁pure ▁CO 2 ▁back ▁into ▁the ▁bott le ▁would ▁raise ▁that ▁partial ▁pressure , ▁and ▁force ▁more ▁CO 2 ▁back ▁into ▁solution . ▁ ▁The ▁F izz ▁K ee per , ▁however , ▁only ▁p umps ▁the ▁normal ▁atmos pher ic ▁mixture ▁of ▁g ases ▁into ▁the ▁bott le , ▁which ▁( by ▁Dal ton ' s ▁Law ) ▁does ▁not ▁raise ▁the ▁partial ▁pressure ▁of ▁CO 2 ▁far ▁above ▁ 0 . 0 0 0 3 ▁atmos pher es , ▁since ▁only ▁part ▁of ▁the ▁overall ▁increase ▁in ▁pressure ▁within ▁the ▁bott le ▁is ▁att rib utable ▁to ▁CO 2 . ▁ ▁Hence ▁little ▁to ▁no ▁CO 2 ▁goes ▁back ▁into ▁solution ▁and ▁effectively ▁none ▁of