. A text book of physics, for the use of students of science and engineering . e the constant mass of the gas, then m = v^ = v2d2 ; d2~ i\ •(1) Also m^m- Tx T2 • V*_PlT2 Vl PiTl Hence, from (1), ^=M? (2) d2 p2T1 If the temperature is constant, this reduces to <h = Pi d2 Pi If the pressure is constant, the result becomes d2 Tj If d0 is the density of the gas at normal pressure and temperature: 76 cm. of mercury and 0° Centigrade, the density d at any other (3) (4) 412 HEAT CHAP. pressure p cm. of mercury and temperature t degrees Centigradeis obtained from (2), giving da 76(£ + 273) d ~ 273^
. A text book of physics, for the use of students of science and engineering . e the constant mass of the gas, then m = v^ = v2d2 ; d2~ i\ •(1) Also m^m- Tx T2 • V*_PlT2 Vl PiTl Hence, from (1), ^=M? (2) d2 p2T1 If the temperature is constant, this reduces to <h = Pi d2 Pi If the pressure is constant, the result becomes d2 Tj If d0 is the density of the gas at normal pressure and temperature: 76 cm. of mercury and 0° Centigrade, the density d at any other (3) (4) 412 HEAT CHAP. pressure p cm. of mercury and temperature t degrees Centigradeis obtained from (2), giving da 76(£ + 273) d ~ 273^ 7 273j d, ,-* cZ = 76(/ + 273) —(5) Expt. 92.—Density of air. Reference is made to Fig. 405, in which Ais a glass globe furnished with a tap. The globe is connected by meansof a piece of thick rubber tube to a manometer BC. The manometercontains mercury, and the closed space above C is a Torricellian vacuum ;hence the gaseous pressure acting on the mercury surface at B is given bythe difference in levels of the mercury in the two limbs of the manometer, \\ (rx) D. ^ v^ Fig. 405.—Apparatus for determining the density of air. provided that the closed limb at C is not completely filled with mercuryThere is another connection, having a tap at E, and leading to two dryingtubes containing phosphorus pentoxide ; this substance removes anymoisture from the air before it enters the globe. The tube at D is opento the atmosphere. An exhausting air pump is connected to the apparatusthe connecting rubber tube being furnished with a clip at F; air may thusbe withdrawn from the globe A. (lose the tap E and exhaust the globe ; close the clip F and open Ethus permitting air to flow through the drying tubes and thence into thglobe. Repeat the operation several times so as to ensure that the globcontains dry air only. Since the globe is in communication with th^atmosphere, the pressure and temperature of the air it contains may bdobtained by reading the barometer and a thermometer pl
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