FILTRATION 307 



juice is to be filtered en masse, about 150 sq. ft. per ton-cane-hour is required, 

 with proportionate increase if washing is to be followed. 



Carbonation. For first carbonated juice there will be required from 

 100 to 120 sq. ft. per ton-cane-hour, and for the second from 40 to 50 sq. ft., 

 whether in this case leaf presses or plate and frame presses are used. These 

 quantities seem very small when the greatly increased bulk of the solid 

 matter compared with that obtained in defecation is considered, but the 

 filtration is so much more rapid that the increase is not proportionate 

 thereto. With De Haan's scheme the area required on first filtration falls 

 to 80 sq. ft. per ton-cane-hour. 



Leaf Filters. When used on well settled cane juice in a defecation 

 process, from 30 to 40 sq. ft. per ton-cane-hour. 



Syrup Filtration. In both leaf and plate and frame presses there are 

 required from 30 to 40 sq. ft. per ton-cane-hour. 



Bagasse Filters. There will be required a volume of about 10 cu. ft. per 

 ton-cane-hour. 



Loss of Sugar in Press Cake. The weight of the press cake usually lies 

 between 1-25 and 1-75 on 100 cane. Of this about 25 per cent, is insoluble 

 and 75 per cent, is water and soluble. With juice 100 per cent, on cane, 

 unwashed cake and undiluted scums, the loss will be from I to 1-5 per cent, 

 of the sugar in the juice. In most Hawaiian factories this loss is reduced 

 to less than o 25 per cent, by dilution washing or double pressing. In Java, 

 Cuba and other districts a much higher loss is common. In factories follow- 

 ing the carbonation process where the weight of the cake is much greater, 

 washing is essential to prevent a very notable loss. 



Composition of Press Cake. Press cake consists of the suspended mechani- 

 cal impurities, i.e., cane fibre, sand, soil, etc., the coagulated colloids, including 

 cane wax and albuminoids, and phosphate of lime, as well as other bodies. 

 The percentage composition will vary greatly, and will be connected with the 

 milling practice, with the perforations in the mill strainers, with the variety 

 of the cane, and with the degree of exhaustion of the cake. Referred to dry 

 insoluble matter, or to the cake proper, the proportions will lie within the 

 following limits : Fibre, 30-40 per cent. ; soil, 10-15 per cent. ; cane wax, 

 20-30 per cent. ; albuminoids, 10-15 per cent. ; calcium phosphate, 10-15 

 per cent. Well pressed cake, firm and dry to the touch, contains from 60 

 to 70 per cent, of water, while the sugar in the cake will vary from 12 to I 

 per cent., dependent on the composition of the juice and the degree of ex- 

 haustion followed. 



REFERENCES IN CHAPTER XVII. 



1. Jour. Ind. Eng. Chem., 1912, 4, 528. 



2. " Beet Sugar Manufacture," New York, 1905. 



3. U.S. Senatorial Document, No. 50, 1845. 



