steam-engine work expansively, when the force of the steam is less than 60 inches of the mercurial column; because the above f+30 f hyp. log. is then less than 1 When an engine does not employ the expansive power of steam, we have 4873 (459 + t) × (1 £+30) = x the mechanical power of a cubic foot of water converted into steam. 15. Mr. Tredgold illustrates these formulæ by the following: Example. Let the force of the steam be 120 inches of mercury; the corresponding temperature is 292.8°. Then 4873 (459 + 292·8) ×(1 − (‡ × 120) + 30 1,830,000 lbs. raised one foot high. 120 = The quantity of coal is 84 +012 (2928212) 9.37 lbs. of coal. Now if the horse power be 16,000,000 lbs. raised one foot in a day of 8 hours; then 1,830,000, : 9.37 lbs. :: 16,000,000 : 82 lbs. Therefore, working with steam of 444 lbs. on the square inch on the piston, above the pressure of the atmosphere, 82 lbs. of Newcastle coal ought to do the day's work of a horse. But if the engine works expansively with the same force of steam, then 4873 (459292-8) x hyp. log. 2) =2,540,000 lbs. raised one foot high by 9.37 lbs. of coal; and consequently 59 lbs. of coal ought to do the day's work of a horse. 16. With regard to the maximum of useful effect in steamengines, it will be found, according to Mr. Tredgold, by taking v = 120 l, for the working velocity of an engine in feet per minute, being the length of the stroke in feet. If an engine has a 2 feet stroke, then v = 170 feet per minute, and the number of strokes per minute 424. By increasing the stroke to 3-4 feet, we get a velocity of 220 feet per minute, with 32 strokes per minute. If any variation be made from the maximum power, the decrease of effect is the same as in horse power; but, as Mr. T. remarks, we have this advantage in an engine-it can be made for any velocity, by attending to the relative proportions of its parts; those of a horse we cannot alter. 17. A horse, when he treads a mill-path at the rate of 24 miles an hour, will, on an average, raise about 150 lbs. by a cord hanging over a pulley; which is equivalent to 33,000 lbs. one foot high in a minute. Boulton and Watt estimate this at 32,000. Tredgold, still lower, at 27,500. Taking the first measure, however, as a basis of comparison; putting d for the diameter of the piston in inches, p for the pressure of the steam upon each square inch (diminished usually by about for friction and inertia), / for the length of the stroke of the piston in feet, n for the number of strokes in a minute: then the power of the engine in "Horse-powers" (H P), is (HP) = '0000238 d2 n p l, if it be a single stroke 2 keengine. 0000476 d n p l, if it be a double stroke S Example. Suppose d= 20 inches, 3 feet, n = 36, p = 50, and the engine one of double stroke. Then HP = l = 0000476 x 20 x 36 x 50 x 3 = 102.816, or nearly 103 horse-powers, the measure of the energy of the engine. Mr. Boulton states that 1 bushel of Newcastle coals, containing 84 pounds, will raise 30 million pounds 1 foot high; that it will grind and dress 11 bushels of wheat; that it will slit and draw into nails 5 cwt. of iron; that it will drive 1000 cotton spindles, with all the preparation machinery, with the proper velocity; and that these effects are equivalent to the work of 10 horses. 18. The rule usually given to adjust the weight of the fly wheel is this: Multiply the number of Horse-powers in the machine by 2000; divide the product by the square of the velocity in feet, per second, of the fly's circumference; the quotient will give its weight in hundred-weights. Thus, suppose the fly-wheel of a 20 horse-power engine to be 18 feet diameter, and to revolve 22 times in a minute ; what should be its weight ? CHAPTER XIV. USEFUL TABLES AND REMARKS ON STEAM-ENGINES, RAIL-ROADS, CANALS, AND TURNPIKE-ROADS. TABLE I.-Quantity of Coals equivalent to the horse power of 33,000 lbs. raised one foot per minute in high pressure steam-engines, when the greatest possible effect is obtained.* TABLE II.-Quantity of Coals equivalent to the horse power of 33,000 lbs. raised one foot per minute in condensing steam-engines, when the greatest possible effect is obtained. The curious tables here given, marked I. II. III., were extracted, with the author's permission, from Mr. Tredgold's work on Rail-roads. Remarks on Tables I, and II.-The columns showing the pounds an engine ought to raise one foot high, by the heat of one bushel of coals, are added chiefly for the purpose of comparison with actual practice. Now, it is stated, that after the most impartial examination for several years in succession, it is found that Woolf's engine at Wheal Abraham Mine, raised 44 millions of pounds of water, one foot high, with a bushel of coals. And, "the burning of one bushel of good Newcastle or Swansea coals, in Mr. Watt's reciprocating engines, working more or less expansively, was found, by the accounts kept at the Cornish mines, to raise from 24 to 32 millions of pounds of water one foot high; the greater or less effect depending upon the state of the engine, its size, and rate of working, and the quality of the coal." We shall further add the results of half a year's reports taken, without selection, from Lean's Monthly Reports on the work performed by the steam-engines in Cornwall, with each bushel of coals. The numbers show the pounds of water raised one foot high with each bushel, from January to June, 1818. 22 to 25 Common Engines average Wheal Vor (Woolf's Engine) January February. March. April. May. June. lbs. raised lbs. raised lbs. raised lbs. raised lbs. raised lbs. raised one foot. one foot. one foot. one foot. one foot. one foot. 22,188,000 22,424,000 21,898,000 22,982,000 23,608,000 23,836,000 30,834,000 26,158,000 29,511.000 26,064,000 29,032,000 30,336,000 Wheal Abraham (ditto) | 41,847,000 35,364,000 30,445,000 32,723,000 31,520,000 34,352,000 Ditto (ditto) 27,942,000 28,000,000 26,978,000 23,626,000 29,702,000 34,846,000 Wheal Unity (ditto) 31,900,000 32,306,000 Dalcouth Engine 42,622,000 41,354,000 40,499,000 41,888,000 38,233,000 38,143,000 32,239,000 36,180,000 35,715,000 33,934,000 33,714.000 34.291,000 36,396,000 31,830,000 31,427,000 33,564,000 33,967,000 30,105,000 38.733,000 39,375,000 41,867,000 41,823.000 40,615,000 42,098,000 Wheal Chance Engine 28,496,000 32,319,000 | 33,594,000 33,932,000 Wheal Abraham Engine 35.797,000 These numbers are less than the immediate power of the engines, by the friction and loss of effect in working the pumps; hence in comparing them with Mr. Tredgold's table, it may be inferred that he made his calculations from such data as can be realized in practice. It is known from experience, that a cubic foot of water can be converted into steam equal in force to the atmosphere, with 7 lbs. of Newcastle coals; but we also know the attention necessary to produce that effect, and therefore have assumed that 8 lbs. will be required for that purpose. 70 According to Mr. Lean's Monthly Report, for January, 1833, the following engines raise more than 50 millions of pounds, one foot high, by consuming a bushel of coals: Cardrew Downs Binner Downs 57,942,435 10.13 Ditto 65 65,617,011 5.28 Of the above, the engine of greatest operation, the first at Wheal Vor, raises the water 190 fathoms, at 7 lifts, drawing perpendicularly 160 fathoms, and the remainder diagonally. Main beam over the cylinder; stroke in the cylinder 10 feet; one balance-bob at the surface, and three underground. |