STEAM ENGINE 



5540 



STEAM ENGINE 



of water to absorb the heat. When the water 

 reaches the boiling point its molecules begin 

 to move apart, driven by the energy that was 

 in the coal but is now in a form in which, in 

 its efforts to expand the steam, it will turn 

 wheels for man. 



A century before the Christian Era there was 

 in Alexandria a man named Hero who experi- 

 mented with steam and constructed a device 

 like a Barker's mill, but whirled by steam in- 

 stead of water (see BARKER'S MILL). Nearly 

 2,000 years elapsed before the science of steam 

 engineering advanced, and then, in the first 

 year of the seventeenth century, an Italian 

 named Delia Porta wrote a book which told 

 how to build a fountain whose waters would 

 bubble up from the pressure of steam, and 

 stated that when the steam cooled it would 

 condense and draw up more water from below. 

 Upon this power of condensation inventors re- 

 lied as much as upon expansion, until the 

 nineteenth century. The first engine of actual 

 service, patented in England in 1698, was a 

 pump which was but an elaboration of Delia 

 Porta's -fountain, and the Newcomen engine, 

 the best known when James Watt began his 

 experiments in 1763, made no attempt at all 

 to utilize the expansive power of steam. 



Probably most people believe that James 

 Watt was the inventor of the steam engine, and 

 millions are familiar with the picture which 

 shows him in boyhood, watching the steam 

 clouds from the kettle. But Watt was only 

 the improver, not the inventor. What he ac- 

 complished for the world was to reduce the cost 

 of operating a condensing engine and to make 

 it practical for other things than pumping. 



The Newcomen engine set Watt to thinking, 

 because it consumed an enormous quantity of 

 steam, hence large amounts of fuel. It had a 

 cylinder and a piston (see the illustration for 

 explanation of these terms). The piston rod 

 hung from one end of a beam and the weight 

 to be lifted was suspended from the other end. 

 The beam was pivoted at the center so that, 

 like a seesaw, one end went up when the other 

 end went down. Steam was admitted below 

 the piston, whereupon the counterweight pulled 

 the piston up. Cold water was then injected 

 into the cylinder, so that the steam condensed 

 and made a partial vacuum beneath the piston. 

 The top of the piston was open to the air, 

 which of course exerted a pressure of nearly 

 fifteen pounds to the square inch on it, and 

 when the vacuum was created beneath it, 

 forced it down. 



Watt saw that the alternate heating and 

 cooling of the cylinder required large quanti- 

 ties of otherwise unnecessary heat. So he de- 

 vised an engine in which the condenser and the 

 cylinder were separate, and the latter always 

 remained hot. 

 As a result, three- 

 fourths of the 

 fuel cost for 

 steam engines was 

 eliminated. 



Watt took out 

 his first patents 

 in 1769, and from 

 that date we 

 count the era of 

 steam. He con- 

 tinued to make 

 improvements on 

 engines, perhaps 

 the most impor- 

 tant of which was 

 the introduction 

 of the principle 

 of double action, 

 in which steam is 

 used first on one 

 side of the piston, 

 then on the 

 other, as in the 

 engine shown in 

 the illustration. 

 He also learned 

 to shut off the 

 steam when the 



A SIMPLE STEAM ENGINE 

 Steam comes from the boiler 

 through the pipe t. If the 

 slide valve v is in the position 

 shown, steam rushes through 

 the port o into the cylinder d, 

 forcing up the piston p, thus 

 turning the crank c and sup- 

 plying power to the flywheel 

 /. As the piston rises, the 

 contents of the cylinder are 

 expelled into the exhaust port 

 k, from which they can es- 



cylinder was only cape to a condensing chamber 

 partly filled, re- or to the outer air. The turn- 

 lying on 



ing of the shaft h revolves the 

 eccentric e at end of shaft, 

 which thrusts the rod r down 

 and moves the slide valve to 

 the lower end of the steam 

 chest s, so that the port n 

 receives steam to force the 

 piston down again, and the 

 port o is connected with the 

 exhaust. The crosshead a, 

 sliding on the guide bars b, 

 keeps the piston rod j in a 

 straight line. 



expan- 

 sion to complete 

 the stroke. But 

 he never experi- 

 mented in the use 

 of high -pressure 

 steam ; his own 

 pressures were not 

 much greater than the fifteen pounds per 

 square inch of the air, while to-day pressures of 

 over 1,000 pounds are practical and are fre- 

 quently employed. 



The two most radical improvements in steam 

 engineering since Watt's day are the introduc- 

 tion of the compound engine and of the tur- 

 bine. In the former, high-pressure steam does 

 work in one cylinder, then passes to another, or 

 even to a third and a fourth. The turbine is 

 described in these volumes. C.H.H. 



