SUGAR 



945 



8 or 8 feet high', furnished with doors ; beneath is a cistern with a pipe for receiving and 

 carrying off the filtered liquor ; and above the case is another cistern, c. Into the upper 

 cistern the syrup is introduced, and passes thence into the 1931 



mouths e, e, of the several filters, d, d. These consist each of a 

 bag of thick twilled cotton of cloth, about 2 feet in diameter 

 and 6 or 8 feet long, which is inserted into a narrow ' sheath,' 

 or bottomless bag of canvas, about 5 inches in diameter, for 

 the purpose of folding the filter-bag up into a small space, and 

 thus enabling a great extent of filtering surfaces to become 

 pressed into one box. The orifice of each compound bag is 

 tied round a conical brass mouth-piece or nozzle e, which screws 

 tight into a corresponding opening in the bottom of the upper 

 cistern. From 40 to 400 bags are mounted in each filter-case. 

 The liquor which first passes is generally turbid, and must be 

 pumped back into the upper cistern, for refiltration. The in- 

 terior of the case is furnished with a pipe for injecting steam, 

 which is occasionally used for warming the case. Fig. 1932 

 shows one mode of forming the funnel-shaped nozzles of the 

 bags, in which they are fixed by a bayonet-catch. Fig. 1933 

 shows the same made fast by means of a, screwed cap, which is 

 more secure. 



When the bags are fouled from the accumulation of clay and 

 a slimy substance on their inner surfaces, the filter is unpacked, 

 the bags withdrawn from the sheaths, and well washed in hot 

 water. This washing is usually performed with a dash-wheel, 

 or some one of the numerous kinds of washing-machines now 

 in use. Perhaps that of Manlove and Alliott, of Nottingham, 

 is in greatest favour. The dirty water, with the addition of a 

 little lime, is smartly boiled, and after some hours being 

 allowed for subsidence, the supernatant, clear, weak solution of 

 sugar is removed and used in the first process (solution), whilo 

 the muddy residue is placed in canvas bags and subjected to 

 pressure. The residue, technically called scum, is thrown away. 



Removal of colour. The liquor issuing from the bag-filters generally resembles in 

 colour dark sherry wine. To render this colourless it is passed through deep filtering- 

 beds of granulated burnt bones or animal-charcoal. When this substance was first 

 introduced, beds of a few inches in depth were considered sufficient, but the quantity 

 of charcoal used per ton of sugar has steadily increased, and filters of no less a depth 

 than 50 feet are now sometimes used. 



Cylinders of wrought or cast iron, varying in diameter from 5 to 10 feet, and in 

 height from 10 to 50, having a perforated false bottom a couple of inches above the 

 true one, are filled with granulated animal-charcoal. 



The grain varies from the size of turnip-seed to that of peas, some refiners pre- 

 ferring it fine, and others coarse. 



Liquor from the bag-filters is run on to the charcoal till the cylinder is perfectly 

 filled, when the exit tap at the bottom is opened, and a stream of -dense saccharine 

 fluid, perfectly colourless, issues forth. The amount of sugar which the charcoal 

 will discolour depends upon the age and composition of the charcoal, the degree 

 of perfection with which the previous revivification has been performed, and the 

 quality, colour, and density of the liquor to be operated upon. One ton of charcoal 

 is sometimes used to purify two tons of sugar ; and in at least one refinery, where in- 

 ferior sugar is operated on, two tons of charcoal serve for one ton of sugar. In most 

 provincial refineries about one ton of charcoal is used to one of sugar ; but in London, 

 from the dearness of fuel and other causes, a smaller proportion of charcoal is em- 

 ployed. The liquor from the charcoal filter, at first colourless, becomes slightly 

 tinged, and in course of time, varying from 24 hours to 72, the power of the charcoal 

 becomes exhausted, the partially decoloured syrup is passed through a fresli charcoal 

 filter, and the sugar is washed out from tho charcoal by means of hot water. The 

 charcoal is ready to be removed for revivification, which process has already been 

 described. 



Concentration. The next process in sugar-refining is the evaporation of the clari- 

 fied syrup to the granulating or crystallising point. The more rapidly this is 

 effected, and tho less the heat to which it is subjected, the better and greater is tha 

 product in sugar-loaves. No apparatus answers the refiner's double purpose of safety 

 and expedition so well as the vacuum-pan. 



The vacuum-pan, invented by Howard, and patented in the year 1812, is an 

 enclosed copper vessel, heated by steam, passing through one or more copper coils, 

 , VOL. III. 3 P 



