James Watt halved coal use by keeping one cylinder hot and another cold
Repairing a model engine at the University of Glasgow in 1763, James Watt noticed how much fuel it wasted reheating its own cylinder every stroke. His fix, a separate chamber to condense the steam, produced an engine burning half the coal for the same work, and helped power the Industrial Revolution.
Before Watt, mines relied on Thomas Newcomen's atmospheric engine of 1712. Steam filled a cylinder, a spray of cold water condensed it, and the resulting partial vacuum let air pressure drive the piston down, working a pump through a rocking beam. It could raise water from more than 300 feet down, and the very first one replaced a team of 500 horses. Seventy-five went into mines across Britain, France, Holland, Sweden and Russia. Its predecessor, Thomas Savery's device of 1698, could lift water only about 25 feet.
The weakness was heat. Chilling the cylinder at each stroke meant fresh steam condensed uselessly until the walls warmed again. In 1765 Watt conceived what he called a condenser: a separate vessel, kept cold in a water bath, into which steam was drawn off, leaving the working cylinder permanently hot. He added a steam jacket around the cylinder, let steam expand against the vacuum for extra efficiency, and spent years finding a way to seal the piston without the pool of water Newcomen had used.
Money was a struggle. John Roebuck of the Carron ironworks paid Watt's debts in return for two thirds of the profits and helped secure the 1769 patent, but by 1773 he faced insolvency and handed his share to Matthew Boulton to cancel a debt of £1200. The finished engine went on sale in 1776. Because earnings had been tied to coal saved, a London brewery driving its mills with horses pushed Watt to invent a new measure, the horsepower.
In 1781 a sun and planet gear converted the engine's back-and-forth stroke into rotation. Factories no longer needed a river and the right terrain for a water wheel; Boulton built the Soho Foundry around the new power. Watt stayed wary of high-pressure steam for safety reasons, even as rivals adopted it in the early 1800s.
Source: Watt steam engine
