Hertil klargøres der endnu en stor kolbe med beluftet uorganisk medium (ca. en tredjedel fuld) plus teststof og referencestof normalt i samme slutkoncentrationer som i de andre kolber.
Prepare another large bottle to contain aerated mineral medium (to about one-third of its volume) plus test chemical and reference chemical at final concentrations normally the same as those in the other large bottles.