This Demonstration illustrates the heat transfer between two vessels containing water, in thermal contact with one another. The left vessel contains kg at an initial temperature of ºC, while the right vessel contains kg at ºC. Color is used to indicate temperature, with blue corresponding to 0 ºC and red corresponding to 100 ºC. The two regions approach an equilibrium temperature, indicated by an intermediate color, usually close to purple. The equilibrium temperature is given by . The temperature of both reservoirs approaches equilibrium with an exponential time dependence. Thus and , where is time in some appropriate units. It is assumed that the heat capacity of water has a constant value of 3186 J/kg degree.