How did Joseph Black’s work on latent heat relate to James Watt’s steam-engine improvements?

Joseph Black’s research into latent heat—the energy absorbed or released during a change in the phase of a substance—was instrumental in the development of the Watt steam engine.12

While repairing a model of the Newcomen steam engine, James Watt observed that the engine was highly inefficient due to significant energy wastage. Watt realized that the primary defect of the Newcomen design was the loss of latent heat that occurred when steam was condensed within the main cylinder.2

By applying the concept of latent heat, Watt concluded that condensation must occur in a separate chamber to prevent the cylinder from cooling down during each cycle. This insight led to his invention of the separate condenser, which allowed the cylinder to remain hot while the condenser stayed cool, drastically improving the engine's efficiency. Although Black and Watt were close friends and corresponded frequently, they maintained that their respective scientific and engineering researches were conducted independently.231