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 

 massecuite. 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 wth 

 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, />„, be the purity of the molasses, 

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



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

 solids of p^ purity. 



Then p,x + {1 — x) p„, = P. 



For example, if p, = 80, p,,^ = 45, and P = y^, 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 -f- 0-857 or 1-167 P^rt solids in the massecuite. 



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

 s^Tup, 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 



j (s — rn)' 



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



massecuite contains i — ^ { X — parts of gravity solids. 



J {s — m) m 



s — i 



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



• ^ J — rn 



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 o - 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. 



