THE EXPANSION OF STEAM.

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example, 147 lbs., or approximately 15 lbs., of its total pressure gofor nothing in counteracting the atmospheric resistance, before theslightest motion is possible. Thus, in the second case, at all pres-sures the motion of the steam is due solely to the difference of itsinherent pressure and that of the atmosphere. The ordinarymethod of estimating the velocity of the flow of gases or liquidsunder pressure is founded on the laws of falling bodies; it is a verybeautiful application of the law of gravitation, and it yields resultssimply and directly. A quantity of steam confined in a boiler, ofa given pressure and known density, would flow into a vacuumthrough an opening from the boiler with a certain initial velocity,and this velocity would be the same as that which would be givento a liquid of the same weight as the steam, flowing out under thesame pressure. The velocity of efflux referred to, when unretardedby physical obstructions, is precisely that which the liquid wouldacquire in falling through the height of a column of the same liquid1 inch square, equal in weight to the pressure of the steam persquare inch. By the laws of falling bodies it is known that thevelocity, v, acquired in falling freely through any height, h, is equalto eight times the square root of the height, or v = 8 vX Thus thevelocity of efflux into a vacuum is determinable, and the followingis the method of finding it:—

Given, the total pressure of the steam, which we suppose to besaturated, as in all ordinary cases it is; divide the pressure per squareinch by the weight of a cubic foot of the steam; the quotient is theheight of a uniform column of steam 1 foot square, equal in weightto the pressure of the steam per square inch. Multiply the quotientas found by 144, the number of square inches in a square foot ofbase, and the product is the height of a i-inch column of the steam,equal in weight to the given pressure of that steam on the squareinch.

To find the velocity with which saturated steam flows freely intoa vacuum. —Divide the total pressure per square inch in lbs. by theweight of a cubic foot of the steam in lbs., and find the square rootof the quotient; multiply this result by 96. The product is therequired velocity in feet per minute.

To find the velocity with which saturated steam freely flows intothe atmosphere, or into steam of inferior pressure .—Take the differ-ence of pressures of the two steams for the effective pressure, divide

the effective pressure in lbs. per square inch by the weight of a cubic

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