The Law of Mass Action

Peter Waage and Cato Maximillian Guldberg were Norwegian chemists interested in reactions that did not appear to go to completion.  In 1864 they jointly published a paper Studies Concerning Affinity that described the "law of mass action".

They based their conclusions on the measured equilibrium amounts of reactants and products in three reactions:

• the esterification reaction of ethyl alcohol and acetic acid based using the results of an experiment carried out by Berthelot and Giles in 1862.

C₂H₅OH + CH₃COOH C₂H₅OOCCH₃ + H₂O

• barium sulfate and potassium carbonate reacting to form barium carbonate and potassium sulfate, which they studied themselves.

BaSO₄ + K₂CO₃ K₂SO₄ + BaCO₃

• silica gel and sodium carbonate reacting to form sodium silicate and carbon dioxide studied by Scherer in 1860.

SiO₂ + Na₂CO₃ Na₂SiO₃ + CO₂

which they showed followed relationships very similar to that we today call the "equilibrium constant expression".

Reference:
Studies Concerning Affinity, P. Waage and C.M. Guldberg, Henry I. Abrash, Tanslator, California State University, Northridge, CA 91330, [Internet WWW http://dbhs.wvusd.k12.ca.us/Chem-History/Concerning-Affinity.html]