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CANE SUGAR.2. Return of Molasses.—In many factories molasses from first massecuitesare worked up with the syrup and are not boiled separately, a mixed strike ofsyrup and molasses being obtained; from this strike a high grade sugar willbe obtained, and often one boiling of the resulting molasses is enough, toseparate them into crystals and exhausted molasses. A high initial purity inthe juice is demanded for the best use of this process, which is most applicablein connection with crystallization in motion schemes.3. Return of Low Products.—The product obtained from massecuites oflow purity boiled blank contain generally less than 90 per cent, of sugar, andtheir sale as such is in general unremumerative; they are usually subjected toa process of refining in the factory either by being melted in the juices or bybeing used as 'seed' in the pan; when used in the latter way tho process ofgranulating the syrup is dispensed with; the fine grained low sugar is takeninto the pan in which there is already a quantity of syrup, and the depositof sugar from the concentrated syrup in the pan takes place on tho crystalsalready present.4. Suppression of Low Products.—By this term is meant processes wherelow products are entirely suppressed, not by the clumsy process of re-meltingthem but by obtaining an exhausted molasses without their appearance ; thisdepends on the carefully controlled return of the molasses combined withcooling in motion, and is discussed subsequently.Of these processes the last is the most rational one and is described indetail afterwards. It is shown also below that the purer the massecuite thepurer are the resulting molasses ; the return of low sugars increases the purityof the massecuites and hence of the molasses, while it is the object of theprocess of manufacture to reduce this as much as possible in each step ; inaddition continual return of low products keeps sugar in process longer, thusincreasing entrainment and other obscure losses and adds to the work of thecentrifugals as part of the sugar is cured at least twice.Standard Type of Vacuum Pan.—The vacuum pan is thename given to the vessel in which the final concentration takes place ; themeans of obtaining and maintaining the vacuum are precisely similar to thosegiven in the preceding chapter, and the principles detailed there are, mutatismutandis, applicable to the single effect pan. Some points of special interestare, however, discussed later. The vacuum pan was invented early in thenineteenth century by Howard, whose name is also associated with theinvention of the filter-press. As made by him the apparatus consisted of adouble-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 ofwater allowed to gravitate down from an overhead tank; no pump was at firstemployed.340