The effective horse-power is determined by Mr. Browne according to the following scale : any Mr. Browne further says:- "The horse-power is taken at 33,000 lbs. lifted 1 foot high, and the actual horse-power employed, &c., at this rate per minute. The length of the lifts is given without allowance for head water; but to all forcing pumps one-half of the stroke is added in making up the duty. When the steam boilers are left uncovered for the purpose of drying the men's clothes, the following deductions are made from the actual consumption of coal: Engines working under 2 strokes per minute 4th. 2 and under 3 ith. The variation in the quality of coal, even from the same pit, is great; and the economy in attending to this will be found from one-twelfth to one-fifth of the consumption." According to the principles enunciated in the foregoing state ment, particulars of the twenty-two engines reported by Mr. Browne, for 1856, are given as follows: Average load on piston Load per square inch Number of strokes per minute 42,169 lbs. 2.9 Gals. of water drawn per minute by each engine 173 Millions of pounds lifted 1 ft. per 112 lbs. coal ... 42.3 From a series of experiments made by Mr. Wicksteed, it was found that the evaporative power of Welsh coal differs in the proportion of 32 per cent; Newcastle, large and screened, 19 per cent; Newcastle and Welsh mixed, 12 per cent; and small Newcastle, 11 per cent. A greater difference was, however, found during the late elaborate investigations relative to the economic value of coals suited for the Steam Navy, from which the following tables are extracted. TABLE I.-SHOWING THE AVERAGE VALUE OF COALS FROM DIFFERENT LOCALITIES, AS DEDUCED FROM EXPERIMENTS MADE FOR THE ADMIRALTY, TABLE II.-SHOWING THE AVERAGE COMPOSITION OF COALS FROM DIFFERENT 1.01 19 Aver. of 36 sam. from Wales 1.315 83.78 4.79 0.98 8 Scotland 1.259 78.53 5.61 1.00 1.11 9.69 4.03 54.22 7 Derbyshire 1.292 79.68 4.94 1:41 101 10.28 2.65 59.32 وو The amount of clinker in coal varies considerably; in some varieties it amounts to 87 lbs. per ton, whilst others are almost entirely free from it. F It may be remarked that no increase has been effected in the economical performance of the Cornish pumping engine for many years; nor, indeed, can any of a marked character be expected until steam of a higher pressure and expanded in a corresponding degree be employed. For accomplishing this object a longer cylinder will be advisable, and such modifications must be made in the valve gearing and mode of admitting steam on the piston as shall in a great measure avoid impact, and at the same time yield all the advantage due to high tension. To a certain extent the gearing may likewise be rendered less expensive, thereby economizing the original cost. This idea is already gaining ground among the Cornish engineers, and one of them has proposed to do away with the parallel motion, by running the piston-rod in guides; he also proposes to fix the steam-valve on the cylinder cover, and the equilibrium in the piston, as well as to work steam expansively on both sides of the piston, instead of on one side only. Whether these suggestions are in accordance with true economy, may be left to individual opinion; but a good engine should, undoubtedly, be distinguished by simplicity of construction, cheapness of first cost, and current maintenance, smoothness of action, ease of management, and economy of fuel. Or, in other words, a good engine should be so constructed as to ensure a high duty, and at the same time be so well-proportioned as to be light, and yet sufficiently strong to withstand any shock or strain it may be liable to experience. It might also be found advantageous to superheat the steam before admitting it into the cylinder; since any vesicular water would thus be volatilized, and all loss from condensation be avoided. PROPERTIES OF STEAM. The elastic force of steam is the most powerful and important mover of machinery yet discovered. It is produced at all temperatures, and possesses a certain mechanical force even at 32° Fah. It does not, however, become available for practical purposes until it has acquired a tension equal to a pressure of 15 lbs. per square inch on the enclosing vessel. 1.-The force of steam depends upon the pressure under which it is generated. 2. The elastic or mechanical force of watery vapour increases in a greater ratio than its temperature. 3. The volume of steam derived from one cubic inch of water at a pressure of 15 lbs. per square inch becomes nearly 1,700 cubic inches; but each addition of external pressure diminishes the volume of steam, although causing it to act through smaller spaces with an increasing force. 4.-The velocity of steam flowing into a vacuum is considered to be equal to that of a body of the same density falling through a distance equal to the height of a column of steam corresponding to the given pressure. At 15 lbs. pressure this velocity is rated at 1,856 feet per second; but due allowance must at the same time be made for friction, &c. 5.—The expansive force of steam is very nearly inversely as the space a given quantity is made to occupy. 6. The total amount of heat in saturated steam is not a constant quantity; but as the temperature becomes augmented 30.5 per cent. of such augmentation is due to an addition of heat, and the remaining 69.5 to heat that was previously latent. 7.-The weight of steam is that of the water it contains; but the force and weight increase in different ratios. Stationary steam-engines are either high-pressure or condensing. In the former, the steam is admitted upon the piston at a greater pressure than that of the atmosphere, whilst the other side is in communication with it. The piston of a condensing engine is, on the contrary, entirely excluded from atmospheric contact, otherwise than that which may act against it through the nonproduction of a complete vacuum. For mining purposes, pumping engines are made either single or double acting. In singleacting engines the steam acts only on one side of the piston, motion being produced in an opposite direction by a counterpoise; whilst in the double-acting engine, steam from the boiler is admitted alternately on both sides of the piston. RULES AND TABLES. To convert degrees of the Reaumur thermometer into Fahrenheit, multiply the degrees of Reaumur by 9, divide by 4, and add 32 to the result. To convert degrees of Centigrade into Fahrenheit, multiply the degrees of Centigrade by 9, divide by 5, and add 32 to the quotient. Ex. 1.—Required to convert 40° Reaumur into Fahrenheit. 40 × 9 360 4 = =90; then 90 + 32 = 122° Fah. 4 Ex. 2.-Required to convert 55° Centigrade into Fahrenheit degrees. 55 x 9 495 5 = = 99; then 99 + 32 = 131° Fah. The foregoing rules apply to temperatures above 32° Fah., or 0° on the Reaumur and Centigrade scales. When the temperature is below the freezing point 0°, multiply and divide the given degrees as before, if they are Reaumur's degrees, and less than 143°, or Centigrade and less than 173°; subtract the quotient from 32°; the result will be the degrees of Fahrenheit above 0°. Ex. 2.-Convert 73° Centigrade into Fahrenheit. 7 × 9 32 5 But if the given degrees are not less than 1430 or 171° respectively, subtract 32° from the quotient; the remainder will be the degrees of Fahrenheit below 0° ̄. Ex. 1.-Convert 24° Reaumur into Fahrenheit. 24 × 9 4 Ex. 2.-Convert 30 × 9 5 LATENT HEAT.-To find the total heat of steam.-From the apparent heat of the steam subtract 32° x 305, and add 1123·7; the sum is the total latent and combined heat in Fahrenheit's degrees. Or, multiply the heat of steam Centigrade by 305, and add 606·5; the total is the latent and combined heat Centigrade. Ex. 1.-Required the total heat in steam of 230° Fah. = 230 32 × 305 + 1,123.7 1,184° Fah. Ex. 2.-Required the total heat in steam of 180° C. 180 × 305 + 606·5 661-4 Centigrade. To find the power of water in the form of steam.-1st. Multiply the pressure in lbs. per square inch by the relative volume of steam to water, and divide by 12; the quotient will give the lbs. raised one foot by one cubic inch of water as steam. 2nd. Multiply the lbs. pressure per square foot by the relative volume of steam to water for the lbs. raised one foot high by one cubic foot of water as steam. Ex.-Required the power of water as steam equal to 30 lbs. per square inch, its relative volume being 883. = Here, 30 x 883 ÷ 12 of water; or 30 × 144 in. by one cubic foot of water. 2,207 raised one foot by one cubic inch × 883 = 3,814,560 lbs. raised one foot |