SWEETENED CONDENSED MILK CONDENSING 91 



According to Kent 1 the relation of altitude to atmospheric 

 pressure per square inch is as follows: 



Pounds Pressure 

 Altitude Per Square Inch" 



At sea level ................................... 14.7 



J mile above sea level .......................... 14.02 



4- mile above sea level .................... . ..... 13.33 



j mile above sea level ......................... . 12.66 



1 mile above sea level .......................... 12.02 



1J miles above sea level ......................... 11.42 



H miles above sea level ............. . ......... , . 10.88 



2 miles above sea level ....... ." ................. 9.80 



"For a rough approximation we may assume that the pres- 

 sure 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 follows : 



Atmospheric pressure = 14.7 .5 = 14.2 pounds per square 

 inch. 



Absolute vacuum : : 14.2X2.04 = 28.97 inches. 



Absolute pressure = - - - 000*7 - : -- 1-95 pounds 



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, there- 

 fore, the low r er the pressure, the lower is 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 

 condenser. 



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



