Calorimetry represents the effort to measure heat (caloric, see Fig. 1.1) in any of its manifestations. 1 This attempt to measure heat directly distinguishes the present discussion from Chapters 3 and 4, in which the measurement of temperature did not lead to quantitative, caloric information. There is, however, no heat meter, meaning there is no instrument which allows one to find the heat content of a system directly, as has been mentioned already in Sect. 4.1. The measurement of heat must always be made in steps and summed from a chosen initial state. The most common reference state is that of the chemical elements, stable at 298.15 Κ [Δ/ff (298) = 0; see Fig. 2.14].