IV. On the thermodynamic theory of steam-engines with dry saturated steam, and its application to practice

In 1849 it was demonstrated, contemporaneously and independently, by Professor Clausius and the author of this paper, from the laws of thermodynamics, that when steam or other saturated vapour in expanding performs work, and receives no heat from without, a portion of it must be liquefied. That theoretical conclusion has since been confirmed by practical experience. The principal effect of the “steam-jacket” invented by Watt is to prevent that liquefaction. The presence of liquid water in any considerable quantity in the cylinder of a steam-engine acts injuriously, by taking heat from the steam while it is being admitted, and giving out that heat to the steam which is about to be discharged. Most of the heat so transferred is wasted.