CANE SUGAR. 



2. Return of Molasses. In many factories molasses from first massecuites 

 are worked up with the syrup and are not boiled separately, a mixed strike of 

 syrup and molasses being obtained; from this strike a high grade sugar will 

 be obtained, and often one boiling of the resulting molasses is enough to 

 separate them into crystals and exhausted molasses. A high initial purity in 

 the juice is demanded for the best use of this process, which is most applicable 

 in connection with crystallization in motion schemes. 



3. Return of Low Products. The product obtained from massecuites of 

 low purity boiled blank contain generally less than 90 per cent, of sugar, and 

 their sale as such is in general unremunerative ; they are usually subjected to 

 a process of refining in the factory either by being melted in the juices or by 

 being used as ' seed ' in the pan ; when used in the latter way the process of 

 granulating the syrup is dispensed with ; the fine grained low sugar is taken 

 into the pan in which there is already a quantity of syrup, and the deposit 

 of sugar from the concentrated syrup in the pan takes place on the crystals 

 already present. 



4. Suppression of Low Products. By this term is meant processes where 

 low products are entirely suppressed, not by the clumsy process of re-melting 

 them but by obtaining an exhausted molasses without their appearance ; this 

 depends on the carefully controlled return of the molasses combined with 

 cooling in motion, and is discussed subsequently. 



Of these processes the last is the most rational one and is described in 

 detail afterwards. It is shown also below that the purer the massecuite the 

 purer are the resulting molasses ; the return of low sugars increases the purity 

 of the massecuites and hence of the molasses, while it is the object of the 

 process of manufacture to reduce this as much as possible in each step ; in 

 addition continual return of low products keeps sugar in process longer, thus 

 increasing entrainment and other obscure losses and adds to the work of the 

 centrifugals as part of the sugar is cured at least twice. 



Standard Type of Vacuum Pan. The vacuum pan is the 

 name given to the vessel in which the final concentration takes place ; the 

 means of obtaining and maintaining the vacuum are precisely similar to those 

 given in the preceding chapter, and the principles detailed there are, mutatis 

 mutandis, applicable to the single effect pan. Some points of special interest 

 are, however, discussed later. The vacuum pan was invented early in the 

 nineteenth century by Howard, whose name is also associated with the 

 invention of the filter-press. As made by him the apparatus consisted of a 

 double-bottomed shallow iron pan, steam being admitted to the double-bottom ; 

 a partial vacuum was obtained by condensing the vapour given off by a jet of 

 water allowed to gravitate down from an overhead tank ; no pump was at first 

 employed. 



340 



