Annual Report 1961 - BEEP

-91-The Brix of the cake is obtained, as inMethod No. 3 by dividing pol % cake bypurity of expressed juice and multiplying by lOO.A number of retention figures were calculatedby each of the above methods and theresults obtained are given in Table 43.Table 43. Comparison of retention figures determined by different methods.Run No.MethodNo. IMethodNo. 2MethodNo. 3MethodNo. 4MethodNo. 5I23456789101112Av. runs 1-12Av. runs 6 - 12445965887574798067817560707458657194637477866882806674765362669260737482647874637073696967967010187lOO76III847183907580897193826980Of the four indirect methods used for thedetermination of retention in vacuum filters,Methods 4 and 5 yield inflated values.Methods 2 and 3, the latter in particular,give results which are, on the average, in closeagreement with the mean value found byMethod 1. It should however be stressed thatindividual retention values, when obtained indirectly,cannot be very reliable as they areaffected by too many sources of error. But ifretention is calculated twice daily, and theaverage of the twelve results obtained for theweek is worked out, the factory chemist willbe in a position to evaluate the efficiency offiltration from week to week.As already pointed out. the best method toutilize for the determination of mud solidsand the calculation of retention in vacuumfilters is that in which the mud solids are centrifuged,dried and weighed. Centrifugation isto be preferred to filtration, as employed inMethod I, which is delicate, tedious and timeconsuming and cannot consequently be usedfor the industrial control of filtration.In conclusion, it is recommended thatMethod 3 be adopted in all the sugar factorylaboratories of the island for the calculation ofretention. Two determinations should becarried out daily and the average value workedout for the week. This recommendation,however, is only temporary and will no longerbe valid as soon as sugar chemists have centrifugesat their disposal. They will then be ina position to determine mud solids directly andmore accurately.REFERENCESANON. (1954) The operation of rotary vacuum filters.Tech. Rep. 17, Sugar Res. Inst. Mackay.Laboratory Manual for Queensland Sugar Mills.3rd. ed. 1954, Brisbane, 104. 135-136.Laboratory Manual for Queensland Sugar Mills.4th ed. 1961, Brisbane, Ill, 146.