The study of affinity from another aspect was contained in the attempts to find a measure of the chemical forces by the amount of heat given out in a chemical reaction. The importance of thermal phenomena in chemical reactions was realised by Lavoisier and Laplace (1784), who laid the foundations of thermochemistry (see Vol. III, p. 426). They assumed that the amount of heat evolved in a chemical reaction is equal to that absorbed in the reverse reaction, and measured some specific heats and the amount of heat evolved in reactions, in combustion, and respiration. Persoz1 regarded both Lavoisier’s ‘caloric’ theory of combustion and Berzelius’s electrochemical theory (see p. 169) as unsatisfactory, and concluded that ‘there is no means of explaining the heat developed in chemical reactions’.
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