368 CHAPTER XVIII 



of 24 ins. the pressure is 2*92 Ibs. per sq. in. Let the temperature of the water 

 in the condenser be 100 F, ; the pressure of water vapour at this temperature 

 is 0-95 Ibs. per sq. in. ; hence the air is at a pressure of 1-97 Ibs. per sq, in. 

 As the temperature of the water increases, so does its vapour pressure, and 

 consequently, under the stated conditions, the air will be at a lower pressure. 

 Since the volume of air is inversely proportional to the pressure, the volume 

 of the air becomes less as the temperature in the condenser falls. 



The annexed table illustrates the variation in the air pressure in a con- 

 denser where the vacuum is 24 inches, or pressure 2-92 Ibs. per sq. in., and 

 where the temperatures are as indicated. 



Temperature, Pressure of gases, Temperature, Pressure of gases, 



F Ibs. per sq. in. F* Ibs. per sq. in. 



80 .. 2-41 .. 1 20 .. 1*25 



go . . 2 -22 . . 130 . . o -70 



100 . . i -97 . . 140 . . o -04 



no . . i -65 



Accordingly, at a temperature of 140 F. the air occupies sixty times as 

 great a specific volume as at a temperature of 80 F. 



For the moment only the air introduced by the water will be considered. 

 Following on the determinations of Roscoe and Lunt, 21 and of Winkler, 22 

 the gases dissolved from air by water are : 



Temperature, Lbs. gases dissolved per 1,000 



F Ibs. of water. 



60 . . . . o -0266 



70 . . . . o -0241 



80 . . . . o -0217 



90 ... .. 0-0195 



For a 24-inch vacuum with cooling water at 60 F. the weights of water 

 required to obtain different temperatures in the condenser, and hence in the 

 discharge water, are as shown below, the weight of the air being also stated. 



Temperature of Weight of water Weight of air 



discharge water, per Ib. of steam from water, 



F. condensed. Ibs. 



80 -.." 50-4 .. 0-001365 



90 . . 33 *3 '000902 



100 .. 24 '7 .. 0*000669 



no .. 19-6 .. 0-000531 



120 .. 16 -i .. 0-000436 



130 .. 13*7 .. 0-000371 



140 . . n -8 .. o -000320 



The volume of i Ib. of air in cubic feet is given by the expression 



0'3697 (459*4 H- ) ^ere / j s the temperature in F and p is the pressure 



P 

 in Ibs. per sq. in. 



In the annexed table are given, for a vacuum of 24 ins. for cooling water 

 at 60 F., and for water discharged at the indicated temperatures, the cubic 

 feet of water, the cubic feet of air, and the combined volume of air and water, 

 per Ib. of steam condensed. 



