G2 



vacuum is constantly maintained at about 635 to 710 millimeters and 

 the contents are easily boiled at very low temperature. 



The juice passes in succession from the tirst effect through to the last 

 one of the series and is gradually concentrated into it and emerges in 

 the form of a sirup of medium density, after which it is pumped into 

 the sirup storage tanks and held in readiness for final evaporation into 

 sugar in the vacuum pan. 



Vacuum pans. — The vacuum pan is similar in construction to a single 

 body of the multiple effects but is provided with a larger heating sur- 

 face and a better system of regulating the temperature and vacuum. 

 It is provided with a water leg ending in a hot well and connected with 

 a vacuum pump arranged the same as for the last body in a multiple 

 effect. They vary in size from a capacity of 1 to 50 tons of massecuite. 

 It is fitted with a device known as a proof-stick for taking samples of 

 the contents while being boiled. There are also gauges for determining 

 the height of the liquid in the body and they are sometimes fitted with 

 sight glasses for watching the contents while boiling. The most common 

 arrangement for heating the vacuum pan is by the installation of coils 

 of copper pipe running horizontally around the inside of the body up 

 as much as half way to the top of the pan and each coil so connected 

 that steam can be turned into it separately. This arrangement permits 

 the introduction of a small amount of sirup into the bottom of the pan 

 so that it can be rapidly concentrated to the point where the sugar in 

 it will begin to crystallize, after which additional juice can be admitted 

 from time to time and more heat turned on until the pan is entirely 

 filled with the crystalline mass mixed with a small portion of sinip and 

 forming what sugar boilers term "massecuite." When it reaches this 

 condition it is ready for a strike which consists of turning off the steam, 

 admitting air into the body of the vacuum pan, and opening the large 

 valve at the bottom so that the entire contents are delivered into the 

 sugar cars, mixers, or crystallizers, depending on the system used. 



Another arrangement for the heating of vacuum pans is known as the 

 "express system" in which the coils of copper pipe are displaced with a 

 steam belt composed of a large drum both surfaces of which slope to 

 the center of the pan where there is a large opening immediately above 

 the door in the bottom through which the sugar is discharged. The 

 tubes pass from the upper to the lower surfaces at an angle with the 

 walls of the pan. When the heated liquid in these tubes begins to 

 rise it passes toward the center of the body, rises, and goes to the 

 outside where it descends until it reaches the under surface and is 

 again forced through the tubes toward the center. This system is said 

 to give a much better circulation and more economical evaporation of 



