The glass column works somewhat like a standard household water filter. A chemist pours a liquid chemical sample into the top of the upright glass tube. The sample slowly drips down through the packed bed of solid metal pieces.
As the liquid touches the reactive metal, a chemical reaction takes place. The solid metal gives away some of its electrons to the dissolved chemical in the liquid. This forced and continuous electron transfer is simply known as chemical reduction.
The metal pieces act as a strong reducing agent that pushes the dissolved chemical into a lower, stable charge state. A common misconception is that the reductor column itself measures the chemical directly. In real laboratory practice, the column only prepares the liquid sample.
It makes sure every single molecule is in the exact same lower oxidation state. Once the fully prepared liquid drips out the bottom, it is finally ready for the titration phase. In that next step, a chemist slowly adds a testing chemical. This final test reveals exactly how much of the target substance is present.