DEFECATION AND CLARIFICATION.—Having, by any of the methods described, eXt/TtOted ELS much as possible of the juice from the cane, the next operation is to eliminate from that juice all matters regarded as impurities from the sugar-maker's point of view, i. e. everything except the auger and the water holding it in solution.
Preliminary Straining.—First of all, unless the juice has been extracted by diffusion, it is necessary to remove the gross impurities derived from the breaking-up of the canes. This may be done by a series of strainers, arranged so as to be easily removed, cleaned, and replaced. One of the best contrivances is a modification of the endless wire-web strainer, not essentially different from that on vehich the rag-pulp of paper-works is agitated and filtered from a great part of its water. The wire-gauze in common use has 40-60 threads per in., but it can be obtained of 80-90 : the finer the better, provided the web presents a clean surface as fast as necessary. The strained juice is received in a shallow tray placed immediately under the horizontal part of the straining web, and passes thence by a gutter to the clarifier.
The chief means introduced for cleansing the juice are heat, chemicals, and filtration.
Heat. —Heat alone will exercise beneficial effect both by checking acidity—scalding the juice prevents acetous ferrnentation setting in, probably by destroying the fungoid germs which are its necessary accompaniment (presumably its cause); and by evaporating a portion of the acids holding the albuminous matters in solution, whereby the albumen is coagulated and rendered insoluble. It is also a valuable aid to the action of chemicals upon the juice, increasing the energy of the reactions set up, and thus greatly reducing the duration of the operation. Hence heat is now universally availed of in recognized processes of defecation and olarification. But if the heat is applied injudiciously, much of the crystallizable sugar is inverted.
Steam Defecators and Clarifiers.—As the degree of heat employed is a matter of vital im portanoe, it is most conveniently applied in the form of steam, that being readily controlled. Figs. 1354 and 1355 represent respectively an elevation and plan of a steam defecator made by Fawcett, Preston, & Co., Liverpool. The part B is composed of a copper, spherically-shaped lining, mounted in a cast-iron casing, to which high-pressure steam is admitted. The upper part A is a
light curb of copper or iron to give capacity, and is clothed with lagging to prevent escape of heat. 0 D are pipes for juice and water; E is the steam-cock; F, the cock for drawing off the defecated contents ; and G, a swivel-mouth pipe to direct the contents of the defecator as required into the elear-juice gutter, the turbid-juice gutter, and the washings-gutter. As the steam condenses in the double bottom of the defecator, the water flows away throngh the condense-water box H.
Lately many planters have adopted another system of defecating. Instead of providing 4, 8, or 12 separate defecators, with corresponding equipment of double bott,oms, cocks, and pipes, they establish a powerful juice-heater, or vessel full of tubes fuced between two tube-plates. The steam outside the tubes, and the juice from the mill traverses the space inside the tubes. If the mill gives 1500 gal. of juice per hour, a heater with 300 sq. ft. of surface will deliver the whole into say 3 empty tanks of 500 gal. each ; there the juice is defecated and left to subside. By using a juice-heater and 3 tanks, the same result is obtained as by a costly steam-boiler working at high pressure and 4 very costly defecators with their mountings.
Figs. 1356 and 1357 represent elevation and plan of a steam clarifier and evaporator, made by Fawcett, Preston, & Co., Liverpool, which is used for treating the syrup after it leaves the triple effect (see p. 1895). It is a cylindrical vessel provided with a steam-worm B fitted in the lower part ; at the upper part, a border and gutter is formed, into which the scum is brushed as it rises on the syrup. The condensed steam in the shape of hot water passes through the box D, which has a float and cock to prevent uncondensed steam from passing uselessly away. The exterior A is lagged t,o economize steam by preventing the syrup from cooling. Every means must be adopted to save heat and fuel in a sugar factory, as it may be stated generally that 240 H.P. of steam are required to make a ton of sugar per hour, or 20 H.P. per hour for 12 hours ; and in many sugar producing countries, coal at the furnace-mouth costs 31. a ton.