I have been assigned a task at work to investigate a scaly white residue found in a tank during an audit of the company's production facilities. We think that it is hard water residue, and I would like to try to determine its carbonate content by the method described in this article: https://www.researchgate.net/publication/233106952 ("Carbonate analysis in soils and minerals by acid digestion and two‐endpoint titration"). It looks pretty doable, except for the fact that I am not familiar with the part of the apparatus described by item "10" (described with the label "NaOH absorption") in Figure 1 of the linked paper. It looks like it involves a column packed with some medium that might become saturated with the 25 mL of 0.5 N sodium hydroxide that is to be placed in beaker "9," but I have never seen such a device used and am unsure of what exactly it is supposed to be. Could anybody give me a hint on how to make it?