The steam engine: Newcomen and Watt

James Watt’s separate condenser, patented on 5 January 1769, let a steam engine do the same work while burning about two-thirds less coal.

Water in the mines

By 1700 Britain was burning more and more coal, and the easy seams near the surface were running out. Deeper mines filled with water, and pumping it out with horses was slow and expensive. In 1698 Thomas Savery patented a steam pump he called the Miner’s Friend, but it could not lift water very high and its boilers were dangerous. Thomas Newcomen, an ironmonger from Dartmouth in Devon, found a better way. In 1712 he and his partner John Calley built an engine to pump water from the Coneygree coal workings near Dudley, in the West Midlands. It is generally accepted as the first successful steam engine of its kind, and a full-size working replica now runs at the Black Country Living Museum on the same estate.

How Newcomen’s engine worked

Newcomen’s engine used the weight of the air rather than the push of steam. Low-pressure steam from a boiler filled a large cylinder beneath a piston. Then a jet of cold water was sprayed into the cylinder. The steam condensed into a few drops of water, leaving a partial vacuum, and the pressure of the atmosphere outside pushed the piston down. The piston was chained to one end of a huge wooden beam; as it went down, the other end rose and lifted a pump rod in the mine shaft. Steam was let in again, the weight of the pump rod pulled the beam back, and the cycle repeated about a dozen times a minute. Because the steam was at such low pressure there was little risk of the boiler bursting. By the time of Newcomen’s death there were more than a hundred of his engines in England and others in Europe.

The problem Watt saw

James Watt was a mathematical instrument maker with a workshop at the University of Glasgow, where the chemist Joseph Black became his friend and mentor. In the winter of 1763 to 1764 he was asked to repair the university’s small model Newcomen engine, which kept failing. Watt found that about 80 percent of the heat in the steam was used just to warm the cylinder back up after each spray of cold water had chilled it. The answer, which he worked out by 1765, was to condense the steam somewhere else. A separate condenser, kept permanently cold and joined to the cylinder by a pipe, drew the steam out and turned it to water, while the cylinder itself stayed hot. On 5 January 1769 Watt was granted a patent for “a new method of lessening the consumption of steam and fuel in fire-engines”. The Science Museum calls it the greatest single improvement ever made to the steam engine.

Boulton and Watt

Turning a model into a working engine took years and money. In 1774 Watt moved to Birmingham, and in 1775 he went into partnership with the manufacturer Matthew Boulton, whose Soho works had the skilled iron workers Watt needed. The first Boulton and Watt engines started work in 1776, one pumping water from a colliery near Tipton and one blowing air for John Wilkinson’s ironworks at Broseley. From 1777 many were sold to the copper and tin mines of Cornwall, where coal was expensive and saving fuel mattered most. Engines with Watt’s condenser burned about two-thirds less coal than Newcomen’s. Watt then designed ways to turn the beam’s up-and-down motion into rotation, so that engines could drive the machines in mills, breweries and ironworks, not only pumps. Watt’s patent lasted until 1800, and when it expired other makers rushed to use the separate condenser. Today the unit of power, the watt, is named after him.