MANUAL FOR SUGAR GROWERS. 



105 



air-pump, D, worked by a steam-engine. The steam 

 is condensed as quickly as possible by being 



Fig. 16.— Diagram of vacuum pan. 



brought into contact with cold water in C and E, 

 the condenser. From the table of pressures and 

 boiling-points on page 137, it will be seen that the 

 more effectually the air-pump and condenser pro- 

 duce a vacuum in A, the lower will be the boiling- 

 point of the syrup. 



In practice, the pressure in the interior of the 

 pan A is about one to two pounds less per square 

 inch, instead of fifteen pounds as in open vessels, and 

 the syrup boils at a temperature of 110° to 120° F. 

 An additional advantage of this low temperature is 

 that it allows the syrup to crystallise, or " grain," 

 even during the process of boiling, so that the syrup, 

 as discharged from the pan at the end of the opera- 

 tion of concentrating — masse cuite, as it is called — 

 is a mass of crystals. On allowing this to stand for 

 a few hours, further crystallisation takes place, and 

 the mass is then ready to be cured. 



