SUGAR CULTURE AND MANUFACTURE. 



SUGAR CULTURE AND MANUFACTURE. 



890 



Many improvements have been effected upon the old methods o^ 

 clarifying and concentrating the syrup. The raw sugar is transferred 

 from the casks into large circular Mow-up citterns, in which it is mixed 

 with lime-water. The mass is heated by steam, forced by its own 

 pressure through small apertures in copper pipes, which are laid along 

 the bottom and sides of the vessel ; and the perfect solution of the 

 sugar is aided by stirring with long poles. The liquor is allowed to 

 flow from the blow-up cistern to a range of filtering-vessels in a room 

 beneath. The filters are tall vessels six or eight feet high, of cast-iron 

 or wood, having cisterns at top and bottom ; and a number of cloth or 

 canvas tubes, closed at their lower ends, but communicating at their 

 uppV ends, by which they are suspended, with the upper cistern. 

 Within each of these tubes is a bag of thick close cotton-cloth, which, 

 being much larger in diameter than the tube in which it is enclosed, 

 is necessarily folded together. By this device a very extensive filtering 

 Kurface is obtained in a small compass ; and, as the liquor from the 

 upper cistern cannot escape from the bags except by percolating 

 through the meshes of the cloth, it becomes, as it drops into the 

 lower cistern, very clear and transparent ; most of the solid impuri- 

 ties remaining in the bags. On leaving the filter, the syrup, though 

 clear and transparent, is of a reddish colour ; and the removal of this 

 tinge is effected by filtering the syrup through a mass of powdered 

 charcoal. The application of the bleaching power of charcoal to the 

 purification of sugar is one of the great improvements effected by 

 modern science. Powdered animal charcoal is placed in a large square 

 Teasel, which has a perforated false bottom, to the thickness of nearly 

 three feet. The syrup is conducted by pipes from the bag-filter to the 

 surface of the charcoal, through which it percolates slowly; it then 

 drops through the holes into the cavity beneath, where it is found 

 almost colourless. In some cases, before the sugar is placed in the 

 blow-up cistern, it is partially purified by mixing it into a pap with 

 hot water or steam, and exposing it to drain in large sugar-moulds, 

 similar to those used in the preparation of clayed sugar. In this case 

 the purification may be rendered more complete by the filtration of 

 moisture from a magma of sugar (a mags of wet sugar in a state 

 resembling mortar), applied in the same way as that of clay in the 

 claying process. Sometimes also a little blood is mixed with the 

 sugar in the blow-up cistern ; or, instead of it, a mixture of gelatinous 

 alumina and gypeum, called finings. Other refiners use both the blood 

 and finings. 



In the concentration of the clarified syrup, which forms the next 

 process, improvements of the greatest importance have been effected. 

 In the old plan of concentrating the syrup in open pans, they were 

 heated by fires to a temperature of from 230 to 250 Fahr. Many 

 plans were contrived for rendering the application of heat more 

 regular and controllable. It is well known that fluids will boil at a 

 much lower temperature in a partial vacuum than when exposed to 

 the ordinary pressure of the atmosphere ; and by the happy applica- 

 tion of this principle, Mr. Howard removed the chief difficulties 

 attending the evaporation of saccharine symp. The accompanying cut, 

 which represents one of the racuum-patu constructed on Howard's 



principle, may assist in the explanation of this admirable contrivance. 

 The apparatus consists of a copper vessel, a, b, the several parts of 

 whii'h are united by flanges, with packing between the joints to render 

 them perfectly air-tight. The middle portion, a, is cylindrical, from 

 -ii to seven feet in diameter; and the upper part, b, is convex or 

 dome-shaped. The bottom is also convex, but in a less degree. The 

 bottom is double, the cavity between the inner and outer casings 

 forming a receptacle for steam. The best kinds of pans have also a 

 spiral coil of copper pipe a little above the inner bottom, by which 

 steam may be' made to circulate through the body of syrup in the 

 pan, and thereby assist evaporation. The bottom cavity is supplied 

 with steam generated at a low pressure ; but the spiral pipe contains 



steam of high pressure, and consequently of great heat. There is a 

 short broad pipe called the neck, rising from the dome, from which 

 a communication is formed with an air-pump, by which'the pan may be 

 partially exhausted of air. A communication is also formed between 

 the interior of the pan and a vessel containing clarified syrup. A 

 quantity of liquid sugar is admitted. The air-pump continues at 

 work during the boiling of the syrup, motion being communicated to 

 it from a steam-engine ; and by this means the sugar is enabled to 

 boil at a temperature of only 130 to 150, or 100" lower than that 

 required in open vessels. To ascertain when the syrup is sufficiently 

 evaporated, the pan is supplied with a very ingenious appendage called 

 the proof-stick, the handle of which is shown as held by an attendant. 

 It consists of a tube extending into the pan, and terminating in a 

 peculiar kind of valve, so formed that, by turning a rod inserted in 

 the tube, a sample of sugar may be drawn out without admitting air 

 into the vessel. The sample thus obtained is tried by the touch, as 

 described in explaining the process of evaporation in the West Indies ; 

 and when it appears to be in a satisfactory state, the sugar is allowed 

 to flow, through an opening in the bottom of the pan, into a granu- 

 lating-vessel in a room below. 



The practice of boiling the syrup at so low a temperature has occa- 

 sioned a curious difference in the next process, which is that of gratiu- 

 latiug the concentrated liquor. In the West Indies, the vessels used 

 for this purpose are called coolers, because the syrup is brought down 

 to a lower temperature than in the boiling-coppers. The corresponding 

 vessels used in refining sugar upon the old plan were similar to these, 

 and were called by the same name ; but when the method of boiling 

 at a low temperature is adopted, the granulators become heaters instead 

 of coolers ; the sugar, when placed in them, being raised to a tem- 

 perature of 180 or 190. This is done by the admission of steam 

 into a cavity surrounding the granulating-vessel, a shallow open 

 copper or pan, in which the thick pulpy mass is stirred quickly to 

 promote the granulation. 



From the granulators the sugar is transferred, by means of copper 

 basins or pans, into moulds of a conical form, usually of iron. These 

 moulds have orifices at their points, which are stopped up before they 

 are filled with sugar. They are arranged with their open bases upper- 

 most ; and immediately after the sugar is poured in it is stirred round, 

 to diffuse the crystals equally through the semifluid mass. They are 

 then left for several hours, that the sugar may become solid : after 

 which they are removed to another room; and, their points being 

 unstopped, they are set in earthen jars, that the uncrystallised fluid 

 may drain from them ; or the same purpose is effected by placing them 

 in racks, with gutters to receive the syrup. This syrup is re-boiled 

 with raw sugar, so as to yield an inferior quality of sugar ; and when 

 all the crystallisable matter has been extracted from it, the remainder 

 is sold as treacle. It was formerly usual to " clay " the loaves in order 

 more thoroughly to remove the molasses ; but this process is aban- 

 doned by most refiners for the superior method introduced by Mr. 

 Howard of cleansing the loaf by causing a saturated solution of sugar 

 in water to percolate through it. When the loaf of sugar is thoroughly 

 purified by the repetitiou of this process, and is sufficiently dry, it is 

 turned out of the mould ; the base being scraped to an even surface, 

 and the apex applied to a kind of lathe, in which any part that may be 

 slightly discoloured is cut off, leaving the end clean and smooth. The 

 loaves are finally dried in an oven heated by steam-pipes to a tem- 

 perature of 130 or 140, and then wrapped up in paper for sale. 



It is needless to follow the processes by which the syrups and other 

 refuse of the best sugar are converted into sugars of inferior quality, 

 which are either sold as cheap loaf-sugar, or formed into large coarse 

 loaves called bastards, which are crushed into powder for sale. It has 

 been asserted that about two-thirds of the molasses found in the moulds 

 under the old system were formed by the intense heat employed in 

 concentrating the syrup; a loss which is now, in a great measure, 

 obviated. The effect of these improvements in diminishing the price 

 and consequently increasing the consumption of refined sugar, is also 

 very important ; the cost of refined sugar being now only about 20 per 

 cent, greater than that of raw sugar, although formerly the difference 

 of price was as much as 40 per cent. 



In the preparation of refined sugar, as in that of raw, many improve- 

 ments have recently been introduced ; but none equal in importance 

 to Howard's capital invention of the vacuum pan. The chief of them is 

 the draining of the sugar-loaves by centrifugal motion, on the system 

 now so largely adopted in many branches of manufacture. [DRYING 

 MACHINES.] Several sugar moulds, with crystallised wet sugar in 

 them, are arranged in a horizontal circle, each with its open apex out- 

 wards ; the frame containing them is made to rotate 800 times in a 

 minute, and the centrifugal force thus generated drives all the moisture 

 out of the sugar and out of the mould. Or the wet mass may be put 

 at once into a centrifugal machine, and whirled round until it becomes 

 a nearly dry white powder. In either case there is a great saving of 

 time over the old method. Van Goethem, a Belgian sugar refiner, has 

 been the chief agent in bringing about this improvement. 



Sugar-Candy. This is the only kind of refined sugar made in China 

 and India ; and is made of the finest quality by the Chinese, who 

 export it in considerable quantities. Two sorts are met with at Canton, 

 called, respectively, Chinchew and Canton; the former being the 

 produce of the province of Fokien, and the latter of that of Canton. 



