58 Mr Redfield on American Steam-Boats. 



four exhausting valves of the same dimensions. The diameter 

 of the main steam-pipe and side-pipes is 25 inches. 



The entire capacity of the cylinder, deducting the space oc- 

 cupied by the piston, and including one of the side apertures 

 extending to the valves, is equal to 252 cubic feet, which is 

 equal to 1890 standard wine gallons, or sixty-three barrels of 

 thirty gallons each. Should the engine perform twenly-six re- 

 volutions or double strokes per minute *, there will be exhausted 

 13,104 cubic feet = 3276 barrels per minute, and 786,240 

 cubic feet of steam, or 196,560 barrels will be exhausted every 

 hour, during the time in which the engine is in full motion ! 

 But the steam is allowed to enter freely from the boiler, only 

 during a part of each stroke, the throttle- valve being then closed, 

 and the steam which has previously entered the cylinder is al- 

 lowed to expand during the remainder of the stroke. If the 

 pressure of steam maintained in the boilers be equal to twenty 

 pounds per square inch above the mean pressure of the atmo- 

 sphere (and greater pressure is frequently employed in these 

 boats), the average effective pressure on the piston may be 

 safely estimated, even with less pressure, at about ten pounds 

 for each square inch of its superficies. To this must be added 

 the net pressure of the atmosphere, obtained by the use of the 

 condenser and air-pump, which is fully equal to ten pounds to 

 the inch, the vacuum in the condenser varying generally from 

 twelve and a half to thirteen and a half pounds to the inch, by 

 the barometrical guage. This estimate, which is obtained by 

 near approximations, will give an average pressure on the piston 

 equal to twenty pounds to the square inch ; but, lest we should 

 be charged with overrating, we will reduce it to sixteen pounds 

 effective pressure to the square inch, or 3421 inches of piston, 

 running fifty-two single strokes of ten feet each per minute. 

 Estimating now the full powers of a horse as equal to 150 

 pounds, moving at two and a half miles an hour, or to raising 

 33,000 pounds 1 foot per minute, we have the following formula : 

 3421 X 16 X 52 X 10 28462720 



33.000 " 33 000 



862 



• The engines of some of the Hudson River boats are often seen running 

 at the rate of twenty-eight double stroke? per minutej the velocity of the 

 piston being 560 feet per minute. 



