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| James Watt |
James Watt was born in 1736 in Greenock, Scotland. James was a thin, weakly
child who suffered from migraines and toothaches. He enjoyed mathematics in
grammar school, and also learned carpentry from his father. His father was a
carpenter by training, and built anything from furniture to ships, but primarily
worked in shipbuilding. Watt learned about the navigational aids on ships: quadrants,
compasses, telescopes. By his midteens he knew he wanted to become an instrument
maker. Watt's father had just lost a substantial investment due to a shipwreck,
and he could see the benefits of another occupation, so was supportive of Watt's
ambitions. Unfortunately, there were no opportunities for instrument training
in Greenock.
In 1754 Watt went to Glasgow, Scotland and became acquainted with Robert Dick
through a relative who worked at the University of Glasgow. Robert Dick, a University
scientist, was impressed with Watt's basic skills at instrument making, but
recognized the need for special training. Dick encouraged Watt to go to London
for training. Watt spent two weeks in London looking for an apprenticeship opportunity.
However the instrument makers protected their trade by rules of a body known
as the Worshipful Company of Clock-makers. The only employment was for fully-trained
instrument makers or trainees serving seven-year apprenticeships!
John Morgan, an instrument maker in the heart of London, did not always follow
the rules, and agreed to take Watt as an apprentice on the conditions of little
pay! Morgan recognized the capabilities of Watt, and agreed to shorten the apprenticeship
to a period of one year. Watt took the offer in 1755. Within two months, Watt's
abilities surpassed those of Morgan's official apprentice, who had been there
two years. Watt was eager to cram several years of training into one, and worked
10 hour days in the cold workshop. After hours, he worked for a small amount
of cash, and his father sent him a little, but he maintained long hours on little
food, and his health declined. During this time, Britain was at war with France,
and the military would force into service any able-bodied man. Watt avoided
the streets for this reason, which may have affected his health further. Watt
finished his apprenticeship year successfully, but his health collapsed almost
immediately afterwards.
Watt returned to Glasgow in 1756, now a trained instrument maker. His University
of Glasgow acquaintances learned of his return, and gave him some work. Watt
set up his shop, but found that other instrument makers shunned his credentials
and training. He was an outsider in Glasgow, after being trained in London.
The University professors recognized his abilities, and did not need to abide
by the traditions of the instrument makers. They arranged for permission to
set up a shop for Watt on University grounds and created the position "Mathematical
Instrument Maker to the University".
Even with the new position, Watt still had trouble finding enough work since
the other instrument makers were somewhat hostile. He started making musical
instruments to avoid competition. His musical instruments were improvements
over existing models and business began to grow. In 1758, an architect gave
him backing to open a new shop in the heart of Glasgow. His business and reputation
grew steadily and by 1763 he had apprentices of his own, but he was not out
of debt.
The job that changed history
Watt always had work from the University scientists, so he maintained through
the years his shop on the University property. Professor John Anderson was the
older brother of a grammar school companion, Andrew. One day in 1763, Professor
John Anderson brought Watt a new problem. The University had a lab-scale model
of the Newcomen pump to investigate why the full-scale pumps required so much
steam. The model suffered a problem. It would stall after a few strokes. Watt
recognized that the flaw was due to an undersized boiler that couldn't provide
enough steam to reheat the cylinder after a few strokes. (See Newcomen
pump details).
During troubleshooting of the lab-scale model, Watt discovered the main reason
the full-sized engines consumed such vast quantities of steam. However, implementation
of the solution did not come easily. The Newcomen pumps required such vast quantities
of steam since they were cooled during every stroke, then reheated. Watt needed
a way to condense the steam without cooling the cylinder. Watt turned over the
problem in his head for months and performed many experiments. He learned much
about steam properties, and independently discovered latent heat of vaporization
in his experiments. He also tabulated the vapor pressure of water at various
temperatures before the work of Clapeyron. One of his University friends was
Professor Black, who had discovered latent heat previously and had been lecturing
on it without Watt's knowledge. They shared many interesting conversations after
Watt told Professor Black of his "discovery". The concept for the
breakthrough to improve the Newcomen engine came in May of 1765, over two years
after Watt began to study the engine. Watt later described the moment of inspiration:
"I had gone to take a walk on a fine Sabbath afternoon, early in 1765. I had entered the green by the gate at the foot of Charlotte Street and had passed the old washing-house. I was thinking upon the engine at the time, and had gone as far as the herd's house, when the idea came into my mind that as steam was an elastic body it would rush into a vacuum, and if a communication were made between the cylinder and an exhausted vessel it would rush into it, and might be there condensed without cooling the cylinder. I then saw that I must get rid of the condensed steam and injection-water if I used a jet as in Newcomen's engine. Two ways of doing this occurred to me. First, the water might be run off by a descending pipe, if an offlet could be got at the depth of thirty-five or thirty-six feet, and any air might be extracted by a small pump. The second was to make the pump large enough to extract both water and air. . . . I had not walked farther than the golf-house when the whole thing was arranged in my mind."
With a separate condenser, the condensation process could take place constantly
and the steam cylinder could be pulled to a vacuum while remaining hot. The
vapor would rush into the condenser.
Watt would not work on the Sunday, as was the custom of the day. He controlled
his impatience, but first thing Monday morning he was in his shop. He crafted
a makeshift piston and condenser using a brass syringe. He filled the syringe
with steam. He pumped the air out of his makeshift condenser, and cooled it.
It worked! (Read more details on Watt's experiment).
Watt was 29 in 1765 when he discovered his idea would work. Yet it would be
11 years before he saw his invention in practice! He was modest, goodhearted,
and shy. He once wrote to his business partner, Boulton, many years later, "I
would rather face a loaded cannon than settle a disputed account or make a bargain."
He also understood the significance of his development. "I can think of
nothing but this engine", he said.
The waiting
Watt's University friends introduced him to John Roebuck, a industrialist who
held leases on coal deposits. Roebuck agreed to back the development of a full-scale
engine after he saw the model work. Watt devoted much time to troubleshooting
and developing a full-scale model. Roebuck did not employ machinists with the
experience that Watt's project required. Watt himself was a first rate instrument
maker, but he was ill-suited to manage the work crew to operate the pump. Over
the next four years, Watt was consumed with making an engine work. The experiments
were slow and costly. The greatest difficulty was maintaining the seal on the
large piston. In the Newcomen engine, the piston and cylinder were made up cast
iron, and the fit was of very poor quality. However, since the entire cylinder
was to be cooled, the piston was sealed by maintaining water on top of the piston
in the open cylinder. Any leakage in the Newcomen engine simply sucked some
water into the cylinder without defeating the driving force for the movement.
Such a solution was unacceptable with Watt's design where the piston was to
be maintained hot.
Although a full-scale working engine was constructed at Roebuck's coal mine,
the effort was taxing on energy as well as finances. Andrew Carnegie writes
in his biography of Watt:
The monster new engine, upon which so much depended, was ready for trial at last in September, 1769. About six months had been spent in its construction. Its success was indifferent. Watt had declared it to be a "clumsy job." The new pipe-condenser did not work well, the cylinder was almost useless, having been badly cast, and the old difficulty in keeping the piston-packing tight remained. Many things were tried for packing-cork, oiled rags, old hats (felt probably), paper, horse dung, etc., etc. Still the steam escaped, even after a thorough overhauling. The second experiment also failed. So great is the gap between the small toy model and the practical work-performing giant, a rock upon which many sanguine theoretical inventors have been wrecked! Had Watt been one of that class, he could never have succeeded. Here we have another proof of the soundness of the contention that Watt, the mechanic, was almost as important as Watt the inventor. (Carnegie, Andrew James Watt, New York: Doubleday, Page & Company, May, 1905.)
Roebuck was supportive of Watt and encouraged him to keep working on the pump.
Watt was able to get a large engine to work well enough to apply for a patent,
and Roebuck financed the engine patent that was granted in 1769. In exchange,
Roebuck agreed to pay off all of Watt debts for his instrument shops but would
take two-thirds of the money the invention made. Watt found this agreement acceptable
because the large experiments were slow and costly. The invention was far from
being ready for production. Then, Roebuck did another thing that helped Watt.
He indirectly introduced Watt to Matthew Boulton of Birmingham, England. This
last introduction was the one that helped the invention create the steam engine
revolution -- but the revolution didn't come easily or fast!
Boulton recognized that the engine had potential applications for much more
than pumping water! Boulton was an industrialist with an extraordinary vision
to have all craftsmen work in a common building -- a "manufactory"
(later shorted to "factory"). Previously, craftsmen had all maintained
individual shops. Further, Boulton had the desire to furnish the manufactory
with the best equipment and finest craftsmen. Boulton was certain that he could
sell the engine.
Unfortunately, Boulton could not work out a deal with Roebuck who had majority
control of the patent. Disheartened and in need of cash himself, Watt left the
instrument making business in 1771, and took up surveying. In March 1773, Roebuck
was in desperate need of cash. Boulton acquired Roebuck's rights to the engine
in 1773, four years after the engine was patented, and nine years after Watt
first discovered the separate condenser. Boulton was convinced the problems
could be solved.
A Perfect Partnership
Boulton and Watt's personalities complemented each other and they got along
well. Boulton's assembly of accomplished craftsmen provided the much-needed
expertise that Watt had lacked in his collaboration with Roebuck. As soon as
Watt finished his obligations for surveying, he moved to Birmingham to join
Boulton's shop. Watt maintained work on the engine as well as other tasks. In
November, 1774 he wrote to his father,
"The business I am here about has turned out rather successful; that is to say, the fire engine I have invented is now going, and answers much better than any other that has yet been made."
His letter was a modest statement of his true enthusiasm, for his concepts
were developing into a fantastic engine. Boulton's desire to hire the best craftsmen
had enabled the success.
Success at Last
In March 1776 the Bentley Mining Company started their newest piece of equipment,
a Boulton-Watt engine. The Bentley Mining Company had taken a substantial risk
by abandoning a half-built Newcomen engine and replacing it with the Boulton-Watt
engine. The day the engine started a newspaper reporter was present:
"From the first Moment of its setting to Work, it made about 14 to 15 Strokes per Minute, and emptied the Engine Pit (which is about 90 Feet deep and stood 57 Feet high in Water) in less than an hour". From "Aris's Birmingham Gazette, March 11, 1776.
(Technical note: water can be drawn by suction less than 33 feet, so the pumps were placed within that distance of the bottom.)
This Bentley Mining Company engine used a cylinder crafted by the best ironmaster
in Britain, John Wilkinson, who had recently developed a technique for boring
cylinders (cannons) and had adopted the technique to the steam cylinder of the
Boulton-Watt engine. The valves, piping, and fittings were manufactured at the
Soho Manufactory - a factory 2 miles from Birmingham partnered by Boulton and
Watt. The new engine used 1/4 of the steam that the Newcomen engines had required!
(See Watt Engine)
The new Boulton-Watt engine was a great success. Watt became very busy maintaining
business at Cornwall mines and setting up new pumps for the mines in the Cornwall
region.
More than Pumps
Boulton recognized the potential of the device for doing much more than pumping
water. He also recognized the limited market for the device to drive pumps.
In June 1781 he wrote to Watt:
"The people in London, Manchester and Birmingham are steam mill mad. I don't mean to hurry you, but I think in the course of a month or two, we should determine to take out a patent for certain methods of producing rotative motion…There is no other Cornwall to be found, and the most likely line for the consumption of our engines is the application of them to mills which is certainly an extensive field" (Sproule, Ann James Watt, Exley Publications, Herts, UK, 1992)
Watt answered this call, too. At age 45, Watt developed his next great invention
-- a method to convert reciprocating motion of the piston to rotating motion.
The invention was the sun and planet gear system. This invention was better
than a crankshaft which was already patented (an idea Watt said was stolen from
him). The sun and planet gear system permitted the rotative wheel to turn more
than once per stroke of the piston! Since the piston moved slowly, this was
an major improvement! An engine patented in 1782 by Boulton and Watt had another
major improvement -- the steam cylinder used valves above and below the piston
to connect independently to the boiler or the condenser; the piston performed
work on both the upward and downward stroke! This evened out the stroking of
the piston, performing equal work on each movement. Watt had another great improvement
on this engine. He had devised a mechanism to match the rocking motion of the
beam (which traces an arc) with the linear motion of the piston. This was known
as the "parallel motion" device, and was necessary to enable the piston
to push the beam on the upward stroke; the chains used in the previous single-acting
engines didn't transfer work on the upward stroke. He once told his son that
this was the invention of which he was most proud.(See Double-acting
Engine)
In 1782 a sawmill ordered an engine that was to replace 12 horses. Watt used
data from a sawmill to determine that a horse could lift 33,000 pounds the distance
of one foot in one minute -- and thus developed the units of hp.
Other major contributions developed by Watt include the steam throttling valve
and the mechanism to connect the throttle to the engine governor. Used together,
these devices regulated steam flow into the piston and kept a constant engine
speed.
By 1800, 84 British cotton mills used Boulton and Watt engines. So did wool
mills and flour mills! In his later years, Watt enjoyed the success and fame
he deserved.
Today, it is appropriate to recognize Watt's contributions when we used the
British (and American Engineering) units for power, hp, and the SI units for
power, the Watt.
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