The experimental objections to the Thomsen–Berthelot principle include incomplete dissociation, reversibility, and spontaneous endothermic processes. Such cases were dismissed by orthadox thermochemist as outliers not covered by the principle, or the experiments were manipulated to fit it through with somewhat contrived justifications was later disproved. In 1873, Thomsen acknowledged that his theory might not have universal or definitive credibility. Later, under newly created chemical thermodynamics framework, the principle was explained to only be valid as an idealization under extreme conditions (i.e., absolute zero). Thomsen openly admitted that his initial understanding was merely a close estimate of the reality, emphasizing that while chemical reactions typically release heat, this heat isn't always a trustworthy indicator of the strength of the bonds formed. On the other hand, Berthelot, was more resistant and continued to assert the validity of the principle until 1894. In 1882 the German scientist Hermann von Helmholtz proved that affinity was not given by the heat evolved in a chemical reaction but rather by the maximum work, or free energy, produced when the reaction was carried out reversibly.