A Calorimeter can be modeled as a large number of volume elements or cells in each of which the temperature may be considered uniform, and each of which can store heat and exchange heat with other cells. Application of the first law of thermodynamics to this set of cells leads to representations of the usual calorimetric equations for the energy change expressed in terms of measurable or estimatable heat capacities, heat transfer coefficients, temperatures, and work terms for the individual cells. Analysis of the results yields a framework within which most of the design and measurement problems of isoperibol calorimeters can be treated.