the system was initially at temperature t1,the same as that of atmosphere, and after work transfer let the temperature rise to t2. the pressure is always 1 atm. the process 1-2 undergone by the system is shown in fig.4.2 in generalized thermodynamic coordinates x,y. let the insulation now be removed. the system and the surroundings interact by heat transfer till the system returns to the original temperature t1, attaining the condition of thermal equilibrium with the atmosphere.