temperature minus the temperature of the cold water, multiply the quotient by the number of cubic feet of steam, and the product is the quantity of water required in cubic inches nearly.

EXAMPLE. What quantity of water at 52°, will it require to condense 6 cubic feet of steam at 226° to water at 90° ?

1212-90

90-52

×6= 177 cubic inches nearly.

One cubic inch of water produces about 1700 cubic inches of steam, at 212°; or the common pressure of the atmosphere; but the boiling point varies considerably according to the pressure on the surface of the fluid, and, of course, materially affect the density of the vapour produced, thus, in a vacuum, water boils at about 90°; under common pressure at 212°; and when pressed with a column of mercury 5 inches in height, it does not boil until heated to 217°; each inch of mercury producing by its pressure a rise of about 1° in the thermometer.

The pressure or force of steam in the boiler (less than the weight upon the safety valve) is generally indicated by a column of mercury in a bent iron tube, which causes the range of the float to be only half the range of the mercury, 2 inches of mercury being nearly equal to 1lb. pressure of steam in the boiler, thus:

4321

Each inch of the float indicates a pressure of 1 lb. nearly.

-Level of the mercury when there is no pressure of steam.

To Calculate the Effect of a Lever and Weight upon the Safety-valve of a Steam-boiler, &c.

The lever, in all cases, is supposed to be made, finished, and balanced, by a known weight or weights, on the short end, making that point where it rests, or is attached to the valve, the centre of motion; then, that weight which balances the lever, added to the weight of the lever, is the pressure on the valve when no other additional weight is annexed to the lever.

Then there are three different ways that it may be required to calculate the lever.

1.—When a certain pressure may be required upon the valve, the distance of the weight upon the lever, and distance of the valve from the centre of motion given, to find what weight will be required upon the lever at that distance.

2. When a certain pressure upon the valve is required, the weight upon the lever and distance of valve from the centre of motion given, to find where that weight must be placed.-And,

3.--When the distance of weight, distance of valve from centre of motion, and weight on the lever is given to find what pressure is upon that valve.

EXAMPLE 1.-Suppose the lever A B to be 24 inches in length, and the valve C placed 5 inches from the centre of motion A; what weight must be placed upon the lever, 21 inches from A, to equal 80 lbs. on the valve C, the weight of the lever being 2 lbs, and the weight D, which balances the lever, 44 lbs?

EXAMPLE 2.-Suppose, as in the last example, the weight upon the lever 17.5 libs. it is required, at what distance from A the weight must be placed to =80 libs. at C.

EXAMPLE 3. Suppose, as before, that a weight of 17.5 libs. is hung upon the lever, 21 inches from A, required the pressure at C, the distance from the centre of motion being 5 inches, and the weight of the lever, at that point, 6 lbs.

17.5 × 21

5

=

= 73.5+ 6.5 = 80 lbs.

A TABLE

Of the expansive Force of Steam, at each Degree of Temperature, from 212° to 300° Fahrenheit's Ther

mometer.

.50

Temp Inch.

212 .00

213

.50

214

1.01

215

1.71

.82

216 2.30

217 2.93

218 3.55

219 4.24

Pounds. Temp Inch. Pounds.

10.54 272 55.48 26.90 10.95 273 56.99 27.64 11.40 274 58.49 28.37 11.81 || 275 60.00 29.16 12.28 276 61.51 29.98 12.73 277 63.11 30.60 13.19 278 64.62 31.40 13.66 279 66.25 32.12 14.13 280 67.67 32.84 14.59 281 69.25 33.59 15.10 || 282 70.68 34.30 15.62 283 72.24 35.01 16.14 284 73.76 35.80

Pounds. Temp Inch. .00 242 21.75 .25 243 22.60 244 23.50 245 24.32 1.09 246 25.26 1.45 247 26.25 1.75 248 27.14 2.07 249 28.13 220 4.92 2.40 250 29.11 221 5.54 2.72 251 30.10 222 6.26 3.02 252 31.11 223 6.87 3.36 253 32.14 224 7.50 3.66 254 33.25 225 8.13 3.89 255 34.34 226 8:76 4.27 256 35.42 227 9.50 4.62 257 36.51 228 10.07 4.90 258 37.74 229 10.82 5.26 259 39.00 230 11.51 5.59 260 40.12 231 12.25 5.90 261 41.25 232 13.00 6.30 262 42.49 233 13.75 6.68 263 43.60 234 14.55 7.10 264 44.76 235 15.50 7.57 265 46.00 236 16.49 8.00 266 47.24 237 17.26 8.40 267 48.50 238 18.23 8.82 268 49.76 239 19.10 9.21 269 51.12 240 19.99 9.67 270 52.50 25.48 300 103.75 50.32 241 20.84 10.10 271 53.90 26.18

16.71 285
17.21 286
17.75 287
18.30 288 80.76 39.19
18.90 289 82.60 40.06
19.49 290 84.50 40.98
20.01 291 86.26

75.51 36.63

77.31
79.00 38.33

37.51

41.84

Proportions of Fuel.

The proportion that various substances bears to each other in producing heats sufficient to raise equal quantities of water, to equal temperatures, are nearly as follows:

And we find, from practice, that to keep up a uniform pressure of steam for an engine (the valve being loaded with 3 lbs. per square inch, or, 224°) requires, on an average, 14 lbs. of coal, per hour, for each horse power, hence:

And either of those quantities, being multiplied by the power of the engine, will give the average quantity of fuel required, per hour, nearly.

Boilers, for steam engines, are of a variety of forms, but, whatever may be the form adopted, not less than 16 superficial feet of boiler, or flue plate, ought to be exposed to the action of the fire for each horse power, and about 90 superficial inches of fire, or furnace bar; also, one-horse power requires about 12 imperial gallons of water per hour, or, 55 cubic inches, per minute, converted into steam.

To find the Height of a Column of Water, to supply a Steam-boiler, against any Pressure of Steam required.

RULE.-Multiply the pressure in pounds (upon a square inch of the boiler) by 2.5, and the product will be the height in feet above the surface of water in the boiler.