CANE SUGAR. 



of the hydrogen ions, and it is for this reason that it is possible to work juices 

 with so high an acidity ; the greater the amount of neutral salt the higher 

 can he the acidity. A heavily limed juice, with the lime 'cut ouf by excessive 

 sulphuring will contain a large amount of neutral salt, and can be worked 

 with a higher acidity than one not so heavily limed. This point is empirically 

 known to many West Indian sugar boilers. 



Th.e Demiiig 1 Process. This process which was introduced a 

 number of years ago has undergone numerous modifications from time to time, 

 and at the present time is worked under more than one combination. Included 

 in the scheme are two distinct ideas, the raising of the juice to a temperature 

 of about 230 F. under pressure (superheat clarification) and the use of a 

 specially designed form of a continuous settler. The different parts of the 

 apparatus are described below. 



FIG. 147. 



The Digester. The digester, aa Fig. 147, is a combination of return 

 current tubular horizontal heaters of conventional pattern ; they are worked 

 in pairs or in sets of three ; exhaust steam is employed as a heating agent in 

 that heater through which the juice first passes, and live steam in the later ones. 



The Alsorler. The absorber is a combined cooler and heater ; in the 

 earlier plants this consisted of a tubular element, in the interior of the 

 tubes of which the superheated juices from the digester circulated ; on the 

 outside of the tubes cold juice on its way to the digester passed; an inter- 

 change of heat occurred, and juice at a temperature of about 200 F. was 

 delivered to the settling tanks. The absorber shown at W, Fig. 1^7, is the 

 most recent form. It consists of a closed outer vessel wherein is maintained a 



258 



