Why could ordinary chemical analysis interfere with the equilibria that Wilhelm Ostwald studied?

Wilhelm Ostwald studied chemical equilibria in systems where substances, such as two competing acids, existed in a delicate balance.1

Ordinary chemical analysis—specifically classical or "wet" methods—typically involves adding reagents to a sample to trigger a reaction, often resulting in a visible change like precipitation or color shift. Because these analytical procedures rely on consuming or altering the analyte through exhaustive chemical reactions, performing them directly on Ostwald's systems would have shifted the concentrations of the components and fundamentally changed the equilibrium state he was attempting to measure.21

To avoid this interference, Ostwald skillfully adapted the measurement of physical properties—such as refractive index, volume, and electrical conductivity—to indirectly analyze the reactions without disturbing the equilibrium.1