384 CHAPTER XIX 



or massecuite sufficient to keep the non-sugar in solution, whereby a means is 

 afforded for separating the solid crystals from the mother liquor or molasses. 

 Accumulated experience has shown that, in exhausted cane molasses, for 

 one part of non-sugar five-elevenths part of water (more or less) is required 

 to keep the non-sugar in solution, and that each part of water simultaneously 

 dissolves 1-8 part (more or less) of sugar. A product such as this forms a 

 typical exhausted molasses, from which sugar will no longer crystallize out 

 when water is removed. It will be of composition : Absolute solids, 80 per 

 cent. ; polarization, 27 ; sugar, 36 per cent. ; non-sugar, 44 per cent. ; absolute 

 purity, 45 ; gravity solids, 90 per cent. ; gravity purity, 40 ; polarization 

 gravity purity, 30. This composition is not to be taken as being fixed, but 

 merely as representative of good average conditions, and is one which is not 

 infrequently bettered in practice. 



Now, let % = absolute solids in a massecuite, 



s = solubility of sugar in the water remaining in the massecuite,, 

 p = absolute purity of the massecuite, 

 m = absolute purity of the molasses. 

 Then, (i x) = water in the massecuite, 



s (i x) = sugar in solution, i.e., in the molasses, 

 x (i p) non-sugar, a,nd 



s- ms 



s + m m s mp 



In the table next following are calculated out values of 100 x for m 0-45, 

 s = 1-8 and p = 0-45 to i-oo. This calculation has been made on a basis of 

 absolute solids or dry substance, and is initially referred to absolute purity, 

 as opposed to gravity polarization purity. After obtaining the values of 100 x 

 on this basis, translation was made empirically to a gravity solids polarization 

 basis, since it is to this that the routine control observations are referred. 



This table gives the percentage of solids to which syrups must be concen- 

 trated to afford a massecuite consisting of crystals and exhausted molasses, 

 and according to this reasoning all that is necessary to obtain all the crystals 

 in one operation is to push the concentration to the indicated limit, and then 

 to separate the crystals from the mother liquor, which now will be exhausted 

 molasses. This end cannot be achieved so simply in practice for the following 

 reasons : 



1. With the higher purities so great a concentration would result in so 

 thick a material that it could not be mechanically handled or even removed 

 from the vacuum pan. 



2. The hot massecuite would have to be cooled to allow the sugar kept 

 in solution to deposit. 



3. The deposit of sugar would take place very slowly, and much would 

 separate as fine grain incapable of immediate recovery. 



Accordingly, one of two schemes has to be employed to obtain all the 

 sugar that is capable of recovery. These are : 



i. Repeated Boilings. In this method the concentration in each operation 

 is carried only so far as to give a massecuite capable of manipulation. The 

 resulting crystals are removed and the residue (unexhausted molasses) is again 

 concentrated, with the production of a second crop of crystals, which is in its 



