Major progress in the understanding of the thermal properties of matter in the 18th century was made by Joseph Black and his friends and colleagues. One of the key concepts that was developed was the heat capacityHeat capacity; the amount of heat per unit substance required to raise its temperature one degree. Another concept was the latent heatLatent heat associated with changes in the phase of the material. With the new understanding of both heat and work, James Watt[aut]Watt, James (1736-1819) and his friends were able to produce “steam enginesSteam engines” that used the vapor phase to produce useful work. The magisterial Lectures on the Elements of Chemistry, Delivered In the University of Edinburgh (1806), edited by John Robinson, is still worth reading. Chapter 4 brings this work to life in the 21st century.