THE EVAPORATION OF THE JUICE TO SYRUP. 



The volume of 1 Ib. of air in cubic feet is given by the expression 



3697 (459-4 + Q 

 p 



where t is the temperature in "Fahrenheit degrees, and p is the pressure in pounds 

 per square inch. In the table below are given for a vacuum of 24 inches, for 

 cooling water at 60 P., and for discharge water at the indicated temperatures, 

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

 cooling water, condensed steam and gases, per pound of steam condensed : 



On examining these figures it will be observed that the volume of the 

 gases at first decreases with decreasing quantities of water, reaches a minimum 

 and tben rapidly increases; hence if the gases present in a condenser are propor- 

 tional to the amount of cooling water admitted, there is a definite temperature in 

 the waste water at which the volume of air is least; this temperature in the 

 waste water is then the OPTIMUM for the particular condition, and it controls 

 the proper amount of cooling water to be admitted. It is, however, quite 

 impossible to calculate for actual use where this optimum temperature lies, 

 since the amount of air entering the condenser is quite unknown ; in a tight 

 apparatus, and if the juice gives off no gas, and if the heating steam is air free, 

 then it could be calculated with reasonable accuracy. As the matter stands, 

 however, all that can be said is that such an optimum condition exists and that 

 it can probably be found by trial and error for each apparatus. 



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