82 SWEETENED CONDENSED MILK CONDENSING 



According to Kent x the relation of altitude to atmospheric 

 pressure per square inch is as follows : 



Pounds Pressure 



Altitude Per Square Inch 



At sea level - 14.7 



Y^ mile above sea level - 14.02 



J/2 mile above sea level - 13.33 



% mile above sea level - 12.66 



1 mile above sea level - 12.02 

 1 Y^ miles above sea level - -11.42 

 \y 2 miles above sea level - - 10.88 



2 miles above sea level - 9.80 



"For a rough approximation we may assume that the pressure 

 decreases one-half pound per square inch for every 1,000 feet of 

 ascent." 



The absolute pressure in the pan of a factory located at Omaha, 

 Neb., with an altitude of 1,016 feet above sea level, and condensing 

 in an actual vacuum of twenty-five inches, would then be as fol- 

 lows : 



Atmospheric pressure 14.7 .5 = 14.2 pounds per square 

 inch. 



Absolute vacuum = 14.2 X 2.04 = 28.97 inches. 



14. 2 X (28.97 25) 



Absolute pressure n>7 1.95 pounds 



^o. y/ 



per square inch. 



RELATION OF STEAM PRESSURE IN JACKET AND COILS, WATER 

 IN CONDENSER, TEMPERATURE IN PAN AND VACUUM, TO RAPIDITY 

 OF EVAPORATION. The temperature of the vapors in the vacuum 

 pan depends directly upon the pressure or vacuum under which 

 they are generated. The more nearly complete the vacuum and, 

 therefore, the lower the pressure, the lower the temperature, and, 

 other conditions being the same, the more rapid the evaporation. 

 The pressure in turn is governed by the capacity of the vacuum 

 pump, the tightness of the joints, the steam pressure in jacket and 

 coils and the amount and temperature of the water in the con- 

 denser. 



1 Mechanical Engineer's Pocket-Book, p. 581. 



