How did Wilhelm Ostwald use physical measurements to study chemical reactions?

Wilhelm Ostwald sought to move chemistry beyond purely synthetic descriptions by applying physical measurements and mathematical reasoning to understand chemical affinities and activities.1

To study chemical equilibria without disrupting the reactions through traditional chemical analysis, Ostwald measured physical properties such as volume, refractive index, and electrical conductivity. By applying the law of mass action to these measurements, he was able to analyze chemical dynamics quantitatively.1

His approach was instrumental in substantiating the dissociation theory. For example, he tested his famous dissolution law by measuring the electrical conductivities of over 200 organic acids, demonstrating that their differing chemical activities were dependent on the concentration of active ions.1

Additionally, Ostwald investigated the temporal aspects of chemical reactions. He used reaction velocities as a measure of chemical activity and defined catalysis as the change in reaction velocity caused by a foreign compound, allowing him to measure catalytic activities systematically. This work eventually led to the development of the Ostwald process for the industrial production of nitric acid.1