Steam Engine
a machine driven by steam. It consists essentially of a boiler for generating steam; a cylinder, containing a piston; a piston rod; and a power wheel to be driven by the latter. By means of sliding valves, steam is admitted to the cylinder, first on one side of the piston, then on the other. The expansive force of the steam drives the piston to and fro. Any gas would answer the purpose, but steam produced from water is the cheapest and most efficient gas that can be employed. It is estimated that, under favorable circumstances, a pound of coal per hour can do as much work as a horse. Only about one-eighth of the heat value of fuel can be converted into actual work. The rest is lost by friction and waste.
The invention of the steam engine is credited popularly to James Watt. He invented improvements, but not the steam engine. Hero, a Greek scholar of Alexandria, left a manuscript, published about 120 B. C., in which he describes certain steam toys. The scientists, if we may term them such, of the Middle Ages, amused themselves with steam. A treatise by Da Porta in 1601 describes a steam fountain. A few years later a steam turbine was invented. Steam jets were employed during the seventeenth century to improve the draft of chimneys. A steam contrivance was invented capable of turning a spit on which meat was roasted.
The first practical engine appears to have been invented about 1650 by Edward Somerset, Marquis of Worcester. He used his "steam fountain" to pump water from the moat to the tower of Raglan Castle. His device was improved by engineers Savery and Smeaton. Further improvements were made by Newcomen, who took out a patent in 1705. As early as 1775 steam was used generally in pumping water from the mines of Europe. All the early inventions depended in part on atmospheric pressure. The piston was driven in one direction by steam, and was driven backward by atmospheric pressure. Steam was introduced into one end of the cylinder only. After it had driven the piston, it was condensed by a jet of cold water, thus forming a vacuum. Atmospheric pressure drove the piston back again. The sliding valve used to admit and cut off steam was formerly worked by hand. It is said that a boy named Humphrey Potter, in 1718, devised the scheme of attaching it to the piston rod so as to save himself the trouble of shoving it to and fro by hand.
About 1764 James Watt, a young instrument maker, began a series of improvements resulting in the steam engine practically as it is known today. He introduced steam first on one side of the piston, then on the other. He took out his first patent in 1769. The Watt engine may be said to have been perfected in 1782. This is the date assigned usually to the invention of the steam engine.
The amount of steam used for power purposes is now almost beyond computation. Fuel, steam, and engines are doing several times as much work as it would be possible for the entire human race to perform. Steam is doing work better and more cheaply than slaves could do it. It costs less to use steam than to feed men, to say nothing of their wages. In other words, the steam engine has made slavery unprofitable and drudgery unnecessary. In the manufactures of the United States alone (1910) steam is doing the work of 9,000,000 horses. If we take into consideration the use of steam for heating and for transportation as well, it may be seen readily that the steam engine is one of the great factors in modern civilization.
A new type of engine known as the steam turbine is now claiming attention. It is a revival of the steam toy of Hero of Alexandria. Instead of admitting steam first on one side and then on the other of the piston, resulting in a to-and-fro movement of the piston rod, steam is admitted to a turbine through a nozzle. It plays continuously on curved flanges, giving the shaft of the turbine a continuous twirling motion. The steam turbine is a modification of a water turbine long in use in mills. This new engine has stood preliminary tests so satisfactorily that it has been adopted already for use in ocean liners and battleships. The turbine requires very much less machinery and metal than the old style engine. There is a saving in the cost of building a turbine. It weighs less; it occupies less space. The saving in weight and bulk enables the shipowner to carry that much larger cargo. There is also economy in the use of steam. The ordinary steam engine uses from twenty-five to thirty pounds of steam per horse-power per hour. The best Corliss engine requires twelve and one-half pounds of steam, while the steam turbine, it is claimed, requires from six and one-half to ten pounds. The turbine gives increased speed. It is less liable to explosion. It requires less by way of repair. There is also another very decided advantage: the jar connected with the to-and-fro motion of the piston rod is obviated entirely. It is worthy of note, also, that experiments are on foot designed to replace, if possible, the bulky, dirty cargo of coal required for fuel by a composition of gun-cotton and nitroglycerin. It is proposed to burn large candles of these explosives in steam cylinders.
See Watt; Stephenson; Locomotive; Steam