Condensed Milk and Milk Powder 6i 



According to Kent 1 the relation of altitude to atmospheric 

 pressure per square inch is as follows: 



Altitude Pounds Pressure Per Square Inch 



At sea level 14.7 



yi mile above sea level 14.02 



Yi mile above sea level 13 .33 



24 mile above sea level 12.66 



1 mile above sea level 12.02 

 1% miles above sea level 11.42 

 iy 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 one thousand 

 feet of ascent." 



The absolute pressure in the pan of a factory located at 

 Omaha, Nebraska, with an altitude of ten hundred sixteen 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 = 14.2 X 2.04 = 28.97 inches. 



14.2 x (28.97 — 2 5) 

 Absolute pressure = ^ = 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 

 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 

 condenser. 



1 Mechanical Engineer's Pocket-book p. 581 



