and was capable of exerting the power of 200 horses in action at once. In Cornwall they have some larger engines, but two engines should always be preferred, when the cylinder of one engine would exceed about sixty inches in diameter, for two engines give many advantages. 575.-When double engines are used for lifting water, they generally work one set of pumps by the outward end of the beam, and another set by a diagonal spear from the piston rod end. And in cases where it has not been convenient to divide the pumps into two sets, the ascending motion of the piston has been employed to raise a weight equal to the pressure of half the column of water in the pumps, but for such cases a single engine should be preferred. 576. The following table will give some idea of the work done by a given quantity of fuel, and of the nature of the engines most approved of in Cornwall; the results however can be correct only through the different errors of the mode of estimation balancing one another, for the weight of the column of water is less than the resistance, and the counter only registers the strokes and not the actual quantity of water raised.* * In the year 1811, a number of the respectable proprietors of the valuable tin and copper mines in Cornwall, resolved that the work which their respective steam engines were performing, should be ascertained, as it was suspected that some of them might not be doing duty adequate to the consumption of fuel; and for the greater certainty of attaining their object, it was agreed that a counter should be attached to each engine, (art. 563,) and all the engines be put under the superintendance of some respectable engineer, who should report monthly, the following particulars in columns: viz. The name of the mine; the size of the working cylinder; whether working single or double; the load per square inch in the cylinder; length of stroke in the cylinder; the number of pump lifts; the depth in fathoms of each lift; diameter of pumps in inches; time worked; consumption of coals in bushels; number of strokes during the time; length of stroke in pump; load in pounds; pounds lifted one foot high by a bushel of coals; number of strokes per minute; and lastly, a column for names of engineer and remarks. Messrs. Thomas and John Lean were appointed to the general superintendance; and the different proprietors, as well as the regular engineers of the respective mines, engaged to give them every facility and assistance in their power. The first monthly report was for August 1811. See Philo. Mag. Vol. XLVI. p. 116. Mines. A part of a monthly Report containing six of the most effective Engines, in December 1826, the whole number reported on forty-six. Wheal Drawing all the load perpendicularly. The engineers' names are given who plan the construction and superintend the execution and erection of the engines, for which they are paid in proportion to the power; they also attend to them afterwards, and direct such renewals or repairs as may be necessary, at fixed salaries. The principal manufacturers of engines for the Cornish mines are Messrs. Trevenan, Carne and Wood; Messrs. Harvey and Co; Messrs. Fox and Co; and Messrs. Price and Co. 577.-The depth of the pump shaft of a mine is divided into lifts of not more than twenty-five or thirty fathoms, if it can be avoided, with a cistern at each lift, consequently the water is raised from cistern to cistern. The size of the pumps is seldom greater than sixteen inches in diameter, and it will always be found better to make an additional set than to exceed this size. 578.-The engines most adapted for economy of fuel, are described in (art. 411, and 419,) those which are most simple in (art. 393 and 400,) and as it frequently happens that engines have to be removed from place to place, an engine supported by frames of cast iron is shewn in Plate XI. 579.-For drawing ores and coals, a double engine of from twenty to thirty horses' power is used; the size of the cylinder should be such, that the power shall be equal to the resistance, when the stress is the greatest; hence, engines for this purpose require more fuel to raise the same quantity of matter a given height, and there is also much loss of effect through stoppages, changes of motion, &c. When one pound of coal raises 70,000 pounds of ore, it is about the maximum quantity in irregular work of this kind. The weight of matter drawn at once is from three to seven cwt. The weight of a rope is about 27 c2 pounds per fathom; when c is the circumference in inches: the greatest stress on a rope should not be more than 700 times the weight of a fathom of the rope; and the stress on the engine should be equalized by the rope winding on to a spiral drum,* like the fusee of a watch, by which the expense of the engine, and the expenditure of fuel would be reduced. The engine should work expansively, (art. 419,) and be equalized by a fly wheel, (art. 540,) and regulated by a governor (art. 550.) When an inclined plane is necessary under ground, a small high pressure engine is sometimes used to draw the coals to the principal shaft, of the kind of engines described in (art. 371.) 580.-Engines are also employed to break ores by means of stampers, a process which seems capable of much improvement. Double engines are employed to raise the stampers by means of cams; and as the power of the engine is nearly uniform, the space * See Ency. Metho. Dict. de Chimie et Métallurgie, Seconde Partie, Planche 20; or Gilpin's Method, Transactions of the Society of Arts, Vol. XXV. p. 76. PP through which the stamper is raised should increase at first in the proportion due to an uniform force; otherwise the motion will be irregular, and the loss of power considerable. The weight of a stamper is usually made about 190 pounds, and the height it is raised about two feet; and not less than two-thirds of the stampers should be rising at any instant of time. Water Works. 581.-The same formulæ apply to water works as to other modes of raising water, when it is raised perpendicularly; but as this is seldom the case, instead of adding 1·5 feet for each lift, as in (art. 572,) add v2 L 140 d feet to the vertical height; where v is the velocity in feet per second, L the length of the main in feet, and d its diameter in inches: add also one-tenth of the height for the friction of the piston, and proceed in other respects as in the article referred to. son, 582.-The supply of a town should be ten cubic feet per day for each house, and for the averaged sized houses this is not more than comfort and cleanliness requires; or two cubic feet per day for each individual, besides what is required for watering streets, for breweries, engines, and various purposes; and for these purposes two cubic feet more ought to be delivered in summer, making a total of four cubic feet per day for each perfor the greatest quantity: in small and open towns a less quantity of water is required, but even in these, two cubic feet and a half ought to be calculated upon.* In raising water by forcing, the air vessel should always be in the direction of the motion of the fluid, and not to one side of it; want of attention to this causes those concussions to take place which tear the joints asunder, break the cranks, and spoil the machinery. Double engines with fly wheels are the most economical when fuel is dear, (art. 419,) and single engines where it is cheap, (art. 411 and 400.) See Plates XII, and XIII. * The following tablet is compiled chiefly from Leslie's Nat. Phil. with some additions, and a more reasonable esti Of Impelling Machinery for manufacturing Purposes. 583.-Iron manufacture. In this manufacture the steam engine is applied to blowing machines, forge hammers, rolling, flatting, and slitting machines, and various other purposes. 584.-Blowing machines. The object of this machine is to supply oxygen to furnaces, either for melting, or reducing ores to the metallic state; hence, in order that the effect may be the same, or nearly so, when the same fuel is used, the supply of oxygen should be the same. But in the same bulk of dry air, there is nearly ten per cent less oxygen at 85° than at 32°; and twelve per cent less when the air at 85° is saturated with vapour; consequently, if 1500 feet per minute be a sufficient supply for a furnace in winter, it may require 1625 feet per minute in summer, to have the same effect: and the difference ought clearly to be gained partly by the aperture being enlarged, and partly by increasing the intensity of the blast. The blast is usually produced by condensing the air, till it will sustain a column of from four to six inches and a half of mercury, (one and a half to two pounds per circular inch,) according to the quality of the coal; and the mean between these is most generally found to answer: the quantity discharged varies from 3000 to 1200 feet per minute. If v be the velocity of the piston of a blowing cylinder in feet per minute, p the force of compression in pounds per circular inch, and d the diameter of the blowing cylinder in inches, then allowing that the friction increases the power from 1 to 1-25, we have 1.25 |