CANE SUGAR. 



with the cooling of the massecuites in motion whereby the deposit of sugar 

 from supersaturated solution is accelerated and takes place on crystals already 

 formed." 



The development of this scheme is traced below. 



"When a strike of grained massecuite leaves the pan a portion of the sugar 

 is present as crystals and a portion is in solution ; on cooling, sugar is 

 deposited, and if the sugar is allowed to cool at rest new fine grain is formed 

 which is incapable of recovery as first product ; if such a strike is cooled in 

 motion the crystals already present are continually brought into contact with 

 fresh portions of the mother liquor and the sugar that is deposited forms on 

 the crystals initially present. The first schemes of crystallization in motion 

 had this for their object, and a very considerable increased return in first 

 product was obtained without in any way altering the system of repeated 

 boilings at that time general in cane sugar factories. Owing to the increased 

 yield in first product a first molasses of lower purity resulted and where a 

 factory took four boilings to obtain exhausted molasses the adoption of crystal- 

 lization in motion reduced the number of operations to two or to three, 

 besides obtaining a larger proportion of the output in the more valuable first 

 product. 



This point was made the subject of direct experiments by Prinsen 

 Oeerligs 3 in Java, who showed that a return of 64 per cent, of raw sugar was 

 obtained from massecuites cooled in motion compared with an average of 56 

 per cent, from similar massecuites cooled at rest, although the actual amount 

 of crystals present in all cases was very similar. This very simple scheme 

 gives most pronounced benefit when impurer juices are being worked, as 

 with these a more viscous mother liquor results and crystals deposited on 

 cooling go to form new fine grain, the less viscous mother liquors obtained 

 from purer juices allowing sugar separating on cooling to deposit on grain 

 already present. 



Although this scheme went far towards reducing the amount of low 

 products it could not entirely suppress them, as the primary massecuites 

 could not be boiled to a concentration so great that all the sugar capable of 

 recovery separated, and various schemes have been devised to the end that all 

 the output is obtained as high grade product. These schemes are discussed 

 below. 



Use of Exhausted Molasses. Eeference to the table of values 



s ms 



of the expression - shows that for a purity of 90, the 



s -4- m ms mp 



massecuite must contain 95 '48 per cent, of solids if it should give exhausted 

 molasses on curing ; such a massecuite would be impossible to obtain or to 

 work in the centrifugals ; but if to such a (hypothetical) massecuite exhausted 

 saturated molasses be added, no change in the massecuite, which can be itself 



356 



