Download (4MB) - QUT Digital Collections

THE CLARIFICATION OR DEFECATION OE THE JUICE.maintained, the juice may be heated to a maximum temperature of no morethan 130° F., the further rise in temperature required being obtained by ajuice heater as described above.The method whereby juices are heated with extra steam taken from theevaporators is described in a subsequent chapter.Determination of Lime required for Clarification.—Thelime is usually applied as a cream standing about 20°-25° Brix, the quantityrequired being determined by one of three methods:—1. The raw juice is tested in the laboratory, and from the result theamount of lime required per clarifier is obtained. When working on theselines frequent tests should be made.2. To a clarifier half full of juice an amount of lime approximately thatwhich experience has shown to be necessary is added, and the reaction of thelimed juice to litmus paper observed. According to the reaction the same,more, or less lime is added when the clarifier is full. Working in this way theproper amount of lime required for a clarifier is soon found.3. Instead of using litmus paper, the limed juice is filtered into a testtube, and to the clear filtrate a drop of a solution of lime in sugar is added.The formation of a precipitate indicates the necessity for more lime, no precipitateoccurring with an overlimed or exactly tempered juice.These three methods do not give consonant results, for a juice limed sofar as to be just alkaline to litmus will give a further precipitation on theaddition of more lime; precipitation being only complete in the presence of aconsiderable excess of lime.The writer is inclined to regard clarification rather as a craft or art thanas a science, and pays attention to the following points:—1. Enough lime must be used to give a faint alkaline reaction to litmus.2. The precipitate must settle readily.3. No more lime should be used than will satisfy the above requirements.In the writer's opinion the best control is to place a sample of the juicefrom each tank in a four-ounce bottle, and to place each sample on a table convenientfor the observation of the employe responsible, who is guided by thereaction and the colour of the juice and by the setting of the precipitate.Choice of Lime.—The lime used should be as pure as possible; theobjectionable constituents that occur in limestones are silica, alumina, magnesiaand sulphate of lime. The first two, if present in limestone, may form acoating over the lime and prevent it slaking properly. Magnesia and sulphateof lime are particularly objectionable, as when introduced into the juice theyare deposited, on concentration, on the tubes of the evaporators as scale. Twoper cent. of magnesia should be the highest quantity allowable in a limeintended for use in a sugar factory.245