394 CHAPTER XIX 



of 30 polarization gravity purity or of 40 gravity purity. The molasses 

 are removed from the process and the sugar treated as indicated above. 



Three-Massecuite Process. This scheme is similar to the above except 

 that the desaccharification is effected in three stages, the purities selected 

 being 80, 70 and 55-60. Evidently with initial purities below 80 the 

 two-massecuite scheme is obligatory, and it is to be preferred until the syrup 

 purity rises to 83-84, when the three-stage scheme should be worked, 

 since with higher purities it affords less material to be handled. It is at a 

 disadvantage, however, in requiring a more complicated system of piping, 

 tanks, and centrifugals. 



Operators differ in the ways adopted for boiling the low-grade strikes. 

 Generally these are boiled on a footing or pied-de-cuite of the 75 or 70 test 

 rriassecuite. Otherwise they may be boiled on a charge of syrup. The first 

 method is advantageous in that the resulting crystals are of the same size 

 as those from the high-grade strikes, and the massecuite may be dried with 

 the same centrifugal screen as used for these. 



As the molasses are in continual circulation in these schemes, they have 

 a tendency to finally become viscous. The stock in process should then be 

 liquidated and the routine begun again. 



Calculation of the Quantity of Massecuite produced. In this section all 

 calculations are referred to unit weight of gravity solids present in the original 

 syrup. The purities referred to are gravity polarization purities. The 

 essential equations required are : 



1. If p, be the purity of the syrup, p m be the purity of the molasses, 

 what are the proportions to give a mixed strike of P purity ? 



Let the strike contain unit weight of gravity solids, and let x be the gravity 

 solids of p f purity. 



Then p t x + (i - x) p m = P. 



For example, if p g = 80, p m = 45, and P = 75, x is found to be 0-857 

 or 85 7 per cent, of the solids in the strike are derived from the syrup, and 

 for every one part of solids in the syrup that will be produced there will be 

 I ~ 0-857 or 1*167 part solids in the massecuite. 



2. If 5 be the purity of the raw sugar produced, j be the purity of the 

 syrup, and m be the purity of the low grade massecuite, the sugar removed 

 from process to obtain the low-grade massecuite is given by the expression 

 s (j m) ^ 



j (s - m)' 



Then it follows that for every one part of solids in the syrup the low grade 



C I /I , .._ W\\ 4 



massecuite contains I ~ ( X parts of gravity solids. 

 j (s m) m^ 



S 7 



This formula reduces to the very simple form -. - ; for example, if 



s is 97, j is 80, and m is 55, the value of the expression is 0-405, or for every 

 ton of gravity solids in the syrup there is 0-405 ton of gravity solids in the 

 low-grade massecuite of 55 purity. 



Now consider the two-massecuite process described above. In the first 

 place all the syrup is reduced to 75 purity by the addition of the circulating 



* See Chapter XXVII. 



