THE FILTRATION OF THE JUICE. 



Loss of Sugar in Presses. The loss of sugar in the presses 

 depends on the purity of the juice, as influencing the amount of cake formed, 

 and the degree to which the washing is carried. With the Taylor niters a 

 cake containing from 65 per cent, to 70 per cent, of water, and which cannot 

 be easily washed, is obtained ; a loss of 2 per cent, of the sugar in the juice 

 can easily occur here. With frame filter presses a cake containing from 

 50 to 55 per cent, of water and weighing from 1 to 1*5 per cent, of 

 the juice is obtained, and this cake without washing will contain from 

 8 to 1 per cent, of the sugar in the juice. This loss can be almost entirely 

 recovered by washing; the limit to which this washing can be carried 

 depends on the evaporative capacity of the factory, and on the filtering 

 area available. In the Hawaiian Islands many factories wash the cake 

 until it contains no more than 1 per cent, of sugar ; the loss in this case is 

 very small and less than '1 per cent, of the sugar in the juice. It should be 

 noticed that it is only in large factories that so complete an exhaustion can be 

 obtained. In a factory turning out annually 50,000 tons of sugar, a loss of 

 1 per cent, of the sugar entering with the juice indicates a loss of 500 tons 

 of sugar, and it will be economical to erect plant capable of dealing with this 

 loss; in a smaller factory making only 5000 tons of sugar, the erection of 

 plant to recover the 50 tons of sugar might be uneconomical, as the larger loss 

 would be recovered at a much lower pro rata cost. 



The very dilute last washings are often employed at the mill as a 

 macerating agent ; it should be remembered however that, as these washings 

 are alkaline, there is a tendency towards dissolving out gummy bodies from the 

 megass. In beet factories these washings are used in mixing the milk of lime r 

 of which much larger quantities are used than in cane factories. 



Double Pressing. In some factories the cake is not washed directly 

 in the presses, but is discharged without washing, and remixed with a quantity 

 of water ; the mud is then passed a second time through the presses. 



Difficulties in Filtration. In certain cases, a mud, from which it 

 is impossible to obtain a firm cake, results and such a cake is incapable of 

 washing ; the cause of this is probably to be found in the presence of gums or 

 of pectinous bodies in the juice, and is more likely to occur when unripe canes 

 are being milled ; in such a case, a better cake may sometimes be obtained by 

 forming in the scums a granular precipitate of oxalate of lime; about 1 per 

 cent, of a saturated solution of oxalic acid is added to the scums, followed by 

 enough lime to restore the alkaline reaction. 



Filter Press Pumps. In many instances the scums are forced 

 through the presses by means of montjus ; a montjus (Fig. 15Jj.), consists of a 

 cylindrical vessel a a ; it is filled by the funnel b ; the cock c communicates 



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