144

MODERN STEAM PRACTICE.

accession of heat, at the rate of ^-gth of the volume at 32° for eachdegree of heat. If then we add (490 0 —32 0 ) 458° to the indicatedtemperature, the sum is directly as the total volume by expansion,and inversely as the density.

With a constant volume, or density, the increase of pressure isuniformly x^-g-th of that at 32 0 for each degree of temperatureacquired, and adding, as in the previous case, 458° to the indicatedtemperature, the sum is directly as the total pressure.

Though the law of the formation of saturated steam has been thesubject of much and varied experimenting, it can as yet be reachedonly by the aid of empirical formulas. The weight of a cubic footof steam at 212 0 , raised from water under the ordinary atmosphericpressure, namely, 147 lbs. per square inch, is "03666 lbs., and thisis an expression of the density of the steam, as weight is a directmeasure of mass or quantity of matter. A cubic foot of pure waterat 62° weighs 62721 lbs.; and the ascertained relative volume ofsaturated steam produced under the atmospheric pressure is 1700times that of the water at 62° of which it is made; therefore i - Ao thof the weight of a cubic foot of this water expresses the weight ofan equal bulk of the steam so formed, and it is in this way that theweight of steam already noted was determined. From these data,with the aid of the ratios already established, the relations of pres-sure, volume, and temperature may be found.

To find the relative volume of steam. —Add 458 to the temper-ature; divide the sum so found by the total pressure, and multiplyby 37"3. The product is the relative volume.

To find the total pressure of steam. —Add 458 to the tempera-ture; divide the sum by the relative volume, and multiply by 377.The product is the total pressure.

To find the temperature of steam. —Multiply the total pressureby the relative volume, and divide by 377; from the quotient sub-tract 458. The remainder is the temperature.

To find the vueight of steam. —Divide 62721 by the relativevolume; the quotient is the weight per cubic foot.

Motion of Steam. —It is well understood that steam unimpededmoves with great velocity from one locality to another, underslight differences of pressure. Steam may flow into a vacuum, orit may deliver itself into the atmosphere, or, further, it may flowinto steam of less density. The conditions of its flow in the firstand in the other cases are different; as in the second case, for