James Watt's Steam Engine

Power for the Industrial Revolution

It was there all along, waiting to be used. Generations of small boys, men too, had sat fascinated, watching what they called “steam” (though it wasn’t) puff from the spout of a kettle. There is a famous engraving by J. W. Steel of the young James Watt sitting before the fire in his parents’ house at Greenock, watching in wonder, chin in hands. His mother is at the back of the room, chattering; she hasn’t noticed the lid of the kettle being prised off by steam. Only the cat and James are watching, with clouds of the white vapour swirling about them.

The picture could have been made of other young boys. Robert Boyle, Edward Somerset, Christian Huyghens, Thomas Savery, Denis Papin, Thomas Newcomen, a dozen others, could have been drawn in the same wondering attitude, all of them fascinated by the properties of this “steam”, the vapour which came off the surface of water when it boiled. All of these, and others, experi­mented with it: it was left to James Watt to produce the first satisfactory “steam engine”.

The early experimenters found that the substance formed when water is vaporized (by boiling, or by any other method) was not, in fact, white and wet; it was dry, colourless and transparent. Only when it had been condensed from this dry steam by a surrounding cold atmosphere did it yield the familiar white cloud incorrectly called steam. Real steam, they discovered, had strange properties, not the least being the fact that it occupied almost two thousand times the space filled by the water from which it sprang. Obviously if it were contained in a vessel, not allowed to escape, a very high pressure would build up; and no doubt this could have a useful application.

The early experimenters, though, were more interested in the pressure of the atmosphere itself and the fact that steam, if in­geniously employed, could allow them to use it. They found that by boiling a little water in a flask with a stopcock in its outlet they could drive out the air, replace it with steam. Then, by closing the stopcock and cooling the vessel so that the steam reverted to water, they were left with a vacuum. If the stopcock were opened, air would rush in with a mighty noise as atmospheric pressure forced it in to fill up the vacuum. Nature, Aristotle had taught, three centuries before Christ, abhors a vacuum, will go to any lengths to fill it. Surely this “abhorrence” could be used to do work?

The power of the atmosphere had been dramatically shown by the German Otto von Guericke in the course of a startling experi­ment at Magdeburg in the seventeenth century. He made two hemispheres of copper, exactly alike and twelve feet in diameter, fitted them together to form a huge globe, with an airtight washer between the two halves. A pump was connected and air pumped from the globe. Then, in the presence of the Emperor Ferdinand, von Guericke demonstrated that a total of sixteen horses, eight harnessed in each direction, was required to pull the hemispheres apart.

At first only one horse was harnessed to each half; then a pair to each; whip them as the drivers might, the halves refused to separate. At last, with eight horses dragging at each, the two halves separated, with a sound like thunder. Von Guericke had proved that the force of the atmosphere, unopposed by a similar force inside the globe, kept the two halves together till brute strength tore them apart. Nature, with a roar, rushed in.

Robert Boyle proved that in a vacuum like this, water would boil at a lower temperature than usual. He placed some which had been allowed to cool to just below its boiling point into a sealed vessel; then by pumping out some of the vessel’s air he made it boil again. Mountaineers confirmed the discovery: on high peaks, where atmospheric pressure is less than at sea-level, water boils quickly, but at well below the accepted “boiling point” of 212 degrees Fahrenheit, or 100 degrees Centigrade. An egg can be boiled a long, long time, and still remain soft.

Denis Papin went on to prove the converse, with the first “pressure cooker”: his “Digester” for “softening meat and bones and extract­ing therefrom marrowy nourishing juices, that the most thrifty housewife declared had been abandoned as but poor prey by ye hungry dogs”. He had found that if water were boiled in a stout, closed container, so that the steam, finding no exit, built up a high pressure, the temperature at which it boiled would rise far above the usual 100 degrees C. Papin’s meat and bones would soon be cooking under water, yet at a higher temperature than water had ever attained.

But Papin, like others, was anxious to do more useful work with his steam than “digest” bones. He was finally able to publish the design of an engine for pumping water out of mine-shafts. The operation was slow and tedious, but it worked. A piston was forced up a vertically standing cylinder by the force of steam from water being boiled at its base. When the piston reached the top, its shaft, which projected beyond the cylinder, was hastily attached, via rope and pulley, to a bucket. The fire was then removed from under the cylinder: the water stopped boiling and the steam reverted to water, leaving a vacuum. The atmosphere, pushing against the upper side of the piston, rammed it down and at the same time raised Papin’s bucket, full of water from the mine-shaft. The bucket was made large enough to carry sixty pounds of water, but the cycle of operations took a whole minute to perform.

Thomas Savery made a similar engine, but with a separate boiler. Whereas Papin and others boiled water in their cylinder, then condensed the resulting steam in the same cylinder, Savery separated the functions. Now it was no longer necessary to move the fire out from under the cylinder: one turned off the cock which let in steam from a boiler.

Men’s minds were exercised so much with the problem of raising water—from mines, from wells, that they gave scant consideration to any other aspect of steam power. Savery’s engine, like those before him, was used solely for pumping: in fact, it had no moving parts, merely connected its vacuum to the water in the well or mine-shaft, and sucked. It performed its cycle four times a minute.

The last great predecessor of James Watt was Thomas Newcomen. He went back to the early designs of Papin and the others, using a moving piston, but whereas they had created their vacuum by letting their vessel cool by itself, or under a shower of cold water, Newcomen hit upon the idea of a spray of cold water actually inside the cylinder. This would condense the steam quickly, without seriously cooling the cylinder. The idea, with other ingenious improvements, made the Newcomen engine a practical affair, and with the new use of cast iron in its manufacture it became possible to make very large and strong engines which were soon being shipped all over the world. One was installed at Fresnes in France and we are told that in forty-eight hours it pumped as much water, with the help of its two “engineers” from England, as had been raised in a week, by fifty horses and twenty men working in shifts, day and night.

But still this was only a pump. The development of turning this up-and-down, pumping motion into a rotary one, or even of seeing the need to do so, was still to come.

James Watt was born in Greenock, on the Clyde estuary in Scotland, in 1736. He studied the science of instrument-making in London and then returned to Scotland to work in the scientific workshop of Glasgow University. In the University laboratory was a working model of an early Newcomen engine, and soon Watt was devoting his considerable talent as maker of fine instruments to seeing how he could improve it. He found he could make parts that fitted better, moved more easily, wasted less heat and steam, but he realized that a rethinking of the design would have to be done as well. For a start, the heat used to make steam in the earlier engines was largely wasted when that steam was either allowed to escape or condensed in the cylinder. Both methods cooled the cylinder, so that heat from the next lot of steam was wasted when it encountered the cold walls. Watt realized he must cure this.

He began by making the boiler more efficient. He enclosed it in a heat-resistant wooden cover, passed a large number of flues through it, so a greater proportion of the hot gases of combustion would be used. He lagged his steam pipe with insulating material, to stop the heat escaping. Then he made his separate condenser, to which the steam, having done its work in moving a piston, was channelled, still hot. Here it reverted to water, warming in the process the water about to be made into steam, so that less heat was required. He built and patented his first engine, still for pumping water— in 1769, but it was not until 1774, after a long and discouraging bout of trial and error, that he was able to write his father that the “fire-engine” was at last working well, “and answers much better than any other that has been made”. By 1781 he was able to obtain another patent, setting out more improvements, including the “double-acting” principle, whereby steam was admitted to each side of the piston alternatively. By now his cylinder was kept hot by being enclosed in a “steam chest” connected to the boiler and from which steam was admitted to the cylinder by means of a slide valve. By experimenting with the opening and shutting of this valve, Watt was able to cut off the supply of steam from his boiler when the piston had travelled only a fraction of its full distance.

He showed that the “expansive” power of the steam could be profitably employed: the piston, to the amazement of his associates would travel the whole length of its stroke on the strength of “one wee spoonful” of steam which was let in, allowed to expand.

He went on at last to develop the “rotative engine” we know today: converting the up-and-down motion into a rotating one. At first, not trusting the time-honoured crank of spinning machine and foot-lathe, he invented an ingenious system whereby a “planet wheel” fastened rigidly to a “connecting rod” on the end of his piston rotated, like a planet about the sun, round a central wheel, keyed to the shaft that was to be driven.

Ingenious as this was, he discovered that the old spinning-wheel crank, which he had feared too weak for his engine, was better, and all his later engines incorporated a “crankshaft” and a “flywheel”. One final problem bedevilled him, but he solved it quickly: an engine with constant speed was highly desirable, and yet the steam engine tended to vary speed with its load. He invented the centrifugal governor, in which the tendency of heavy iron or brass balls to fly outwards when whirled round like chestnuts on a string could be made, by a system of levers, to narrow the steam Inlet and reduce speed.

The completed Watt engine, with double action, expansive working and governor, revolutionized industry. It came in time to operate the new cotton mills and also to give power to a mass of new metal- and wood-working tools. By linking the crankshaft of Watt’s engine through shafting and belts to all the machinery in a workshop or factory, it could be made to operate drills, lathes and the rest of the equipment with a speed, efficiency, undreamed of. It was left to Watt’s successors in the following century, men like George Stephenson, to use this exciting new source of power in a carriage running, because of its weight, on “rails”, and dragging a long line of other carriages, full of people and freight. From the Stockton and Darlington Railway, in 1827, the first to achieve this, railways proliferated over Europe and America, completely altering men’s way of life, shrinking continents to oranges. The idea was developed for the “steam-ship”, and oceans became ponds.

Today, with so many factories and workshops run by electricity; radio, television, stove and washing-machine run off the main; we must still remember that most electricity is generated by steam. Despite advances in nuclear powering, and the building of generating stations near waterfalls to use the power of descending water, electricity will continue to be generated by steam for years to come. Most power stations now use the fast-running steam “turbine”, in which high-pressure steam impels a device like a water-wheel: but this would have taken years longer to perfect had it not been for Watt.

The coming of his engine, The Mechanical Revolution, it has been called, gave the spur to the Industrial Revolution. Already a transition was taking place from the methods and economics of cottage industry and the domestic workshop on the one hand to larger-scale, factory production on the other; but this was hastened enormously by the advent of steam power. Coal made its contribution; it converted water into steam for the engine and also made possible metallurgical processes which allowed stronger, better, lighter engines to be built. In return, the steam engine operated the machinery of the mine so that more and more coal and iron were won from the earth.

The pace quickened: it has been said it was far too quick; that the huge increase in manufacturing spawned by the steam engine could not be kept up with by factory managements, nor by the economic systems of the World. This is true; men and women flocked into overcrowded towns to work in factories and brought about an overcrowding and concentration of misery with which we are still struggling. But this misery was the result, not of Watt’s invention, but of the greed which followed it, the greed of factory owners and of peasants, of rich men and poor. Had James Watt never lived, someone else would have invented the steam engine, years later. Destiny produced this quiet, simple man, this Scottish instrument-maker, just at the moment when his engine and all that followed from it would put Britain at the head of the world. Two world wars and a changing international climate have altered this, but the work of James Watt lingers on, every time we switch, on a light, take food from the fridge.