CANE SUGAR. 



pressure of 1-97 Ibs. per square inch. As the temperature of the water 

 increases so does its vapour pressure, and consequently the gases are at a lower 

 pressure. The volume occupied by air or any gas is inversely proportional to 

 the pressure ; hence the colder the condenser the less is the specific 

 volume of the gases. As illustrative of the variation in gas pressure 

 in a condenser, there is given below the pressure of the gases where the 

 vacuum is 24 inches or 2*92 Ibs. per square inch, and where the temperatures 

 are as shown. 



Hence when the temperature is 140 F. the gases will occupy sixty times as 

 great a specific volume as when the temperature is 80 F. Gases in condensers 

 arrive from the water used in cooling, from decompositions in the process of 

 boiling the juice, and from leaks in the apparatus. For the moment only the 

 first source will be considered. The gases dissolved from air by water, 

 following on the determinations of Roscoe and Lunt and of Winkler may be 

 thus expressed. 



Temperature 



60 

 70 

 80 

 90 



Lbs. Gases Dissolved per 1000 

 Lbs. of Water* 



0266 

 0241 

 0217 

 0195 



The amount of water used to obtain the condensation of the vapour is 

 given by the expression w = - - - , where w is the water used per unit 



t l 



and t 2 are the initial and 



weight of vapour, h is the total heat of the vapour, 

 final temperatures of the cooling water. 



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 in the table below, which also includes the 

 pounds of gases from the water. 



* The gases dissolved by water from air are very nearly in the proportion of two volumes 

 of nitrogen to one of oxygen ; it is here assumed that air itself is dissolved ; the calculation 

 is barely appreciably affected and the conclusion not at all. 



332 



