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James Watt  (30 January 1736 (19 January 1736 OS) - 25 August 1819) was a Scottish inventor, mechanical engineer, and chemist who improved on Thomas Newcomen's 1712 Newcomen steam engine with his Watt steam engine in 1781, which was fundamental to the changes brought by the Industrial Revolution in both his native Great Britain and the rest of the world. While working as an instrument maker at the University of Glasgow, Watt became interested in the technology of steam engines. He realised that contemporary engine designs wasted a great deal of energy by repeatedly cooling and reheating the cylinder. Watt introduced a design enhancement, the separate condenser, which avoided this waste of energy and radically improved the power, efficiency, and cost-effectiveness of steam engines.

In 1776, the first engines were installed and working in commercial enterprises. These first engines were used to power pumps and produced only reciprocating motion to move the pump rods at the bottom of the shaft. The design was commercially successful, and for the next five years Watt was very busy installing more engines, mostly in Cornwall for pumping water out of mines.  These early engines were not manufactured by Boulton and Watt, but were made by others according to drawings made by Watt, who served in the role of consulting engineer. The erection of the engine and its shakedown was supervised by Watt, at first, and then by men in the firm's employ. These were large machines. The first, for example, had a cylinder with a diameter of some 50 inches and an overall height of about 24 feet, and required the construction of a dedicated building to house it. Boulton and Watt charged an annual payment, equal to one third of the value of the coal saved in comparison to a Newcomen engine performing the same work.  The field of application for the invention was greatly widened when Boulton urged Watt to convert the reciprocating motion of the piston to produce rotational power for grinding, weaving and milling. Although a crank seemed the obvious solution to the conversion Watt and Boulton were stymied by a patent for this, whose holder, James Pickard, and associates proposed to cross-license the external condenser. Watt adamantly opposed this and they circumvented the patent by their sun and planet gear in 1781.  Over the next six years, he made a number of other improvements and modifications to the steam engine. A double acting engine, in which the steam acted alternately on the two sides of the piston was one. He described methods for working the steam "expansively" (i.e., using steam at pressures well above atmospheric). A compound engine, which connected two or more engines was described. Two more patents were granted for these in 1781 and 1782. Numerous other improvements that made for easier manufacture and installation were continually implemented. One of these included the use of the steam indicator which produced an informative plot of the pressure in the cylinder against its volume, which he kept as a trade secret. Another important invention, one which Watt was most proud of, was the parallel motion which was essential in double-acting engines as it produced the straight line motion required for the cylinder rod and pump, from the connected rocking beam, whose end moves in a circular arc. This was patented in 1784. A throttle valve to control the power of the engine, and a centrifugal governor, patented in 1788, to keep it from "running away" were very important. These improvements taken together produced an engine which was up to five times as efficient in its use of fuel as the Newcomen engine.  Because of the danger of exploding boilers, which were in a very primitive stage of development, and the ongoing issues with leaks, Watt restricted his use of high pressure steam - all of his engines used steam at near atmospheric pressure.  From an early age Watt was very interested in chemistry. In late 1786, while in Paris, he witnessed an experiment by Berthollet in which he reacted hydrochloric acid with manganese dioxide to produce chlorine. He had already found that an aqueous solution of chlorine could bleach textiles, and had published his findings, which aroused great interest among many potential rivals. When Watt returned to Britain, he began experiments along these lines with hopes of finding a commercially viable process. He discovered that a mixture of salt, manganese dioxide and sulphuric acid could produce chlorine, which Watt believed might be a cheaper method. He passed the chlorine into a weak solution of alkali, and obtained a turbid solution that appeared to have good bleaching properties. He soon communicated these results to James McGrigor, his father-in-law, who was a bleacher in Glasgow. Otherwise he tried to keep his method a secret.  With McGrigor and his wife Annie, he started to scale up the process, and in March 1788, McGrigor was able to bleach 1500 yards of cloth to his satisfaction. About this time Berthollet discovered the salt and sulphuric acid process, and published it so it became public knowledge. Many others began to experiment with improving the process, which still had many shortcomings, not the least of which was the problem of transporting the liquid product. Watt's rivals soon overtook him in developing the process, and he dropped out of the race. It was not until 1799, when Charles Tennant patented a process for producing solid bleaching powder (calcium hypochlorite) that it became a commercial success.  By 1794 Watt had been chosen by Thomas Beddoes to manufacture apparatus to produce, clean and store gases for use in the new Pneumatic Institution at Hotwells in Bristol. Watt continued to experiment with various gases for several years, but by 1797 the medical uses for the "factitious airs" had come to a dead end.  Watt combined theoretical knowledge of science with the ability to apply it practically. Humphry Davy said of him "Those who consider James Watt only as a great practical mechanic form a very erroneous idea of his character; he was equally distinguished as a natural philosopher and a chemist, and his inventions demonstrate his profound knowledge of those sciences, and that peculiar characteristic of genius, the union of them for practical application".  He was greatly respected by other prominent men of the Industrial Revolution. He was an important member of the Lunar Society, and was a much sought-after conversationalist and companion, always interested in expanding his horizons. His personal relationships with his friends and partners were always congenial and long-lasting.  Watt was a prolific correspondent. During his years in Cornwall, he wrote long letters to Boulton several times per week. He was averse to publishing his results in, for example, the Philosophical Transactions of the Royal Society however, and instead preferred to communicate his ideas in patents. He was an excellent draughtsman.  He was a rather poor businessman, and especially hated bargaining and negotiating terms with those who sought to use the steam engine. In a letter to William Small in 1772, Watt confessed that "he would rather face a loaded cannon than settle an account or make a bargain." Until he retired, he was always much concerned about his financial affairs, and was something of a worrier. His health was often poor. He was subject to frequent nervous headaches and depression.

Are there any other interesting aspects about this article?
Watt was a prolific correspondent. During his years in Cornwall, he wrote long letters to Boulton several times per week.