James Watt

(1736-1819)   James Watt was an engineer and inventor in the mid- to late 18th century.  He is most famous for his work with the steam engine.  It is a common misconception that Watt invented the steam engine when in fact several earlier models were in existence, however they were highly impractical.  Watt improved upon the most commonly used model invented by Thomas Newcomen. Newcomenís engine was used only to pump water out of coal mines, mainly because it was incapable of doing much else.  It, as well as other steam engines produced before the Watt engine, was very inefficient in that it used large quantities of steam (requiring large amounts of fuel) and produced a relatively small output of power.  This engine contained one boiler, which had to be heated to evaporate the water it contained into steam.  The steam would then enter a cylinder and build up enough pressure to move a piston.  The cylinder then had to be cooled to condense the steam back into water, creating a vacuum and forcing the piston back.  Much of the steam was lost in the alternate heating and cooling and not used for power output.  Watt set out to develop a practical, more economical engine. He was working as a mathematical instrument maker (what we would now call a mechanical engineer) for the university of Glasgow when he was asked to repair a small Newcomen engine.  In doing so he became fascinated with the steam engine and began the task of improving upon it.  He went about doing this in two ways.  First, by maintaining the temperature of the cylinder into which the steam entered.  If the cylinder were kept at a temperature close to that of the steam, less steam would be wasted in warming it.  He also found that the temperature of the water, of which the condensed steam was composed, and water injection itself (used to cool the steam) should be brought down to 100 degrees centigrade or lower. In 1765 Watt discovered the way he could accomplish these tasks.  If he opened a passage between the cylinder containing steam and another vessel that was completely empty (vacuum), the steam would have the tendency to flow into the vacuum until it had established equilibrium.  Furthermore, if the vacuum container were kept at a very cool temperature, more steam would enter and condense until the cylinder was emptied.  Less steam was wasted in this model because of the two separate compartments.  Watt also insulated his engine with wood so that a minimum of heat escaped.   The major question facing Watt at this point was how to retrieve the injection water, the air that entered with it and the condensed steam from the cooling container.  Using a pump or system of pumps to get the air, steam, and water out solved this problem. Wattís engine was more efficient and thus more economical because it made a better use of the available steam.  A greater amount of work output was produced for the same amount of steam as in the Newcomen engine.   Wattís method for improving the steam engine so that it was a practical source of power has become known as his theory of separate condensation.  His steam engine was so successful that it was commonly used for over a hundred years with no major changes made. The Watt engine was a large contributor to the Industrial Revolution.  It could do the work that it previously took a large number of men or horses to do.  In fact, Watt coined the term horsepower, which is used as a means of expressing the power of an engine. Watt is best known for his steam engine, although his accomplishments were by no means limited to that.  He also invented a double-acting engine, throttle valves, pressure gauge, and a governor for regulating engine speed, as well as many other devices.  He took the first steps in finding that water was a compound rather than an element.  Watt also had the power unit (the Watt) named in his honor. James Watt contributed greatly to the Industrial Revolution with his version of a steam engine.  He is often credited with the invention of the steam engine when in fact this is not the case.  He is the inventor of the first practical steam engine fit for accomplishing different types of tasks.  Other crude models existed before Wattís time, but they did not make the most of the massive quantities of steam, and so fuel, they required.  Watt invented many other devices in his time, but he is best known for the steam engine.                 Bibliography Biographical Encyclopedia of ScientistsóVol. 5, SchwaóZwory. Watt, James Concise Encyclopedia of the Sciences, John-David Yule, ed. World Book EncyclopediaóVol. 18, SoóSz.  Steam Engine World Book EncyclopediaóVol. 21, WóZ. Watt, James   HYPERLINK http://www.history.rochester.edu/steam/hart/   www.history.rochester.edu/steam/hart/   HYPERLINK http://www.history.rochester.edu/stream/lord/4-1.htm   www.history.rochester.edu/stream/lord/4-1.htm      

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