For the Dieterici gas, the reduced inversion temperature is T ~ ~ I = 8 − − 4 / V ~ ~ m , and the relation between reduced pressure and reduced inversion temperature is p ~ ~ = ( 8 − − T ~ ~ I ) e 5 2 − − 4 8 − − T ~ ~ I . This is plotted on the right. The critical point falls inside the region where the gas cools on expansion. The outside region is where the gas warms on expansion.