If the extinction of a solution is measured, its concentration can be calculated from the result. That relationship is expressed by the Beer-Lambert law. Along with the concentration c of a solution, the extinction also depends on the thickness d of the layer and on the substance-specific extinction coefficient ε.

In experiment C3.3.2.1, a dilution series is used to study the proportional relationship between extinction and concentration and to determine the extinction coefficient of blue copper tetraammine.