. Public health and preventive medicine. ference inheight between the height of the column of outer air above the inlet and theheight to which the column of hotter air in the ventilating shaft would con-tract if it were reduced to the density of the outer air. Premising that thebarometric pressure is equal in both the outer and inner columns, and thereforemay be disregarded, and that air expands TJ^ (-002) of its volume for everydegree Fahrenheit through which its temperature is raised, let us suppose thatwe are dealing with a ventilating shaft 40 ft. high, and that the difference intemperatur
. Public health and preventive medicine. ference inheight between the height of the column of outer air above the inlet and theheight to which the column of hotter air in the ventilating shaft would con-tract if it were reduced to the density of the outer air. Premising that thebarometric pressure is equal in both the outer and inner columns, and thereforemay be disregarded, and that air expands TJ^ (-002) of its volume for everydegree Fahrenheit through which its temperature is raised, let us suppose thatwe are dealing with a ventilating shaft 40 ft. high, and that the difference intemperature between the internal and external air is 25° F. Then the calcula-tion is v2 = 2gh or v=\/2gh ; and since g is 322, 2f/ = 64-4, and its squareroot is 8*08 or roughly 8, and the formula becomes v = 8\//i. Then 7i = thecolumn of air above the inlet corresponding to the height of the outlet ventilat-ing shaft, 40 ft., minus the height to which the 40 ft. of hotter air would 40contract if reduced to the density of the outer air, Fig. 176.—Casellas air meter. Thus the formula now reads v= 8\/ 1+ 25 x -002 K) 40 1 + 25X-002 This simplified gives v = 8\/40 — 8-^27= 8x1-41. = 11-28 ft. per second. EFFICIENCY OF SANITARY APPLIANCES 393 This is a theoretical velocity, since no allowance has been made for actual velocity will be only one-half or three-fourths of the above. Asbefore, if discbarge is required, D = VA. To find whether the size of inlets and outlets is sufficient to give a propersupply of fresh air per head per hour, 1 >e Chaumonts formula is employed,namely, D = 200 x * X V002 x x X {t -T), where D = the delivery of air in cubic feet per hour. 3600 (60 x 60 seconds i»er hour) 200 = a constant = - - - - —. : l jrv X \/2 g. 144 (square 111. in a square ft.) = The sectional area of inlet and outlet in square inches. ./• = The height of the heated column of air in feet. / and T = The internal and external temperature respectively. Thus,
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