concentrated syrup is discharged down shoots into Such is the raw sugar of commerce: it varies greatly in quality, but really consists of a crystalline flour of pure sugar, moistened throughout with melasses, often to the extent of one-third of its weight, and often more than the crystals can contain. Hence as it attracts moisture from the damp air of the vessel and becomes more liquid, it escapes from the crevices of the casks. It is calculated that about 12 per cent. of sugar is lost in this way from the English colonies alone, or about 27,000 tons annually. | from the refuse syrup, or mother-liquor, of the first crop of crystals. The defects of the old system most plainly appear from the various modes adopted of calculating the loss. We have already given one or two estimates, and will conclude this section with one or two more. From every 1,000 parts of sugar-cane the old process yields from 60 to 80 parts raw sugar, and 25 to 30 of melasses; while according to chemical analysis the yield should be 180 to 200 parts of crystallized sugar. The following table has been drawn up from a large number of comparative results: Thus of the 180 to 200 parts of crystalline sugar in 1,000 parts of cane, there are obtained from 73 to 79 parts of raw sugar: 18 to 20 parts of melasses; cane trash, 28 to 33; and waste in the process of manufacture, from 48 to 61 parts. Mr. Kerr also states that of the 1,500 gallons of juice required to make a hogshead of sugar netting 15 cwt. in the English market, the planter does not get a return of more than 6 per cent. of moist muscovado sugar, and that of very inferior quality. SECTION III.-IMPROVED SYSTEM OF MANUFACTURING The various improvements in the rude process of manufacturing sugar described in the last section have for their objects the preservation of the juice from fermentation, and its concentration with as little agitation and exposure to the air, and at as low a temperature, as possible. Several proposals have been made for removing or diminishing the causes which lead to the rapid fermentation of the juice. Among other plans, Dr. Mitchell proposes to destroy the vitality of the glutinous fermenting matter, and to coagulate the albuminous substance in the tissue of the cane, by plunging the canes into some boiling liquid as soon as possible after they are cut. This plan would prevent the albumen, &c., from passing into the juice by expression. From some experiments made on this subject, it appears that a colourless juice was obtained; it was full of floating feculæ which immediately subsided, and the juice being decanted off and boiled down without the addition of any lime or temper, or any necessity for skimming, furIn places where the sugar is not packed in hogs-nished a pure white sugar. By this process, the juice heads for the sea voyage, it is set to drain in the curinghouse, in wooden moulds of deal. The syrup which drops from the moulds, or from the hogsheads, into a cistern, deposits on cooling a sugar, the grain of which resembles fine sand, and forming a layer on the bottom several inches in thickness. This inferior product is called by the French planters, fond de cisterne. It averages about 10 per cent. of the raw sugar, depending on the temperature at which the sugar is placed in the moulds. It has a moist and smeary character, and is an admixture of various salts, of gelatinous silica, mucus or gum deposited is diminished in quantity, but increased in density. Some of it was kept for 18 hours without undergoing any change. M. Payen recommends the use of sulphurous acid or of bisulphite of lime for preventing the rapid fermentation of the juice. He advises that the ends of the canes be dipped into a solution of the bisulphite as soon as they are cut. An infusion of tannin or nut-galls has also been recommended for the separation of the deliquescent matter and soluble salts. As the crushing-mill is generally on the ground, the juice is raised to the clarifying vessels by force pumps of peculiar construction, and with very little | cock which is opened for a short time on the admission agitation. For this purpose it is admitted into an apparatus called a monte-jus, Fig. 2098, from which it is forced up a pipe by the pressure of steam on the surface of the liquor. J is the vessel for receiving the juice, which passes into it by a pipe and cock P; s is a pipe for supplying steam for forcing the juice up AA; a is an aircock, through which the air escapes on the admission of the juice: the pipe attached to this cock dips 2 or 3 inches below the top of the cylinder, so that the juice never rises above that height; the space above being filled with air, acts as a cushion between the steam and the cane-juice, thereby preventing the juice from being heated to the temperature of the steam; M is a man-hole. It will be seen that the pipe A is not only continued to the bottom of the receiving vessel, but dips into a sunken receptacle, by which means all the juice is collected; for it is of importance not to leave layers of juice at the bottoms of vessels to ferment and damage the fresh juice afterwards added. Fig. 2098. Steam-heat is used for the clarifying vessel, into which the juice is raised by the monte-jus. This vessel consists of a hemispherical copper pan P, Fig. 2099, surrounded by a cast-iron jacket J, and steam is admitted into the space between the two, the supply being regulated by a valve v. On the top of the copper pan is fixed a light course LL, or copper band, from 15 to 18 inches deep, to prevent the scum from frothing over. The plug p in the bottom of the pan is furnished with two or three holes, through one of which the clarified juice passes down the hollow of Fig. 2099. CLARIFIER. the plug to the smaller channel of the two-way cock c. When the clear liquor is run off, the plug is removed by means of the handle h, and the thick scum and sediment pass off through the larger way. The condensed steam passes away by the pipe w. a is a of steam, to allow the air to escape. The clarifier being filled with juice, steam is admitted and the temperature raised to 176° Fahr. Any particles which rise to the top of the liquor are skimmed off, and milk of lime is poured in in quantities just sufficient to neutralize the acid, which is ascertained by the frequent use of litmus paper. The heat is continued until there is formed a thickness of 3 or 4 inches of scum, consisting of most of the impurities of the juice. In about 10 or 12 minutes from the first application of heat the scum should be well formed and about to break up. The moment it begins to crack the steam is shut off, and the liquor being left for 15 to 20 minutes, the lighter impurities will have mostly risen to the surface, and the heavier ones sunk to the bottom, while between the two is a pale and beautifully clear liquor. The hollow plug which is ground into the hole in the bottom of the pan, is now turned by its long handle h so as to throw open a hole in the side 3 or 4 inches from the bottom, and consequently above the subsided impurities: by this opening the clear liquor escapes, and proceeds along the small channel of the two-way cock until scum begins to appear; the cock is then turned on to the larger way, the plug is altogether removed, and the heavy matters and scum pass out through the hole, and are conveyed to a cistern, placed in bags, and the juice squeezed out. The juice in the clarifier is never allowed to rise above 208° or 209°, or the impurities would become so mixed up with the juice as to be incapable of separation; a result which will also be attained unless the process be speedily conducted. The clarified juice still contains matters in suspension, which require to be removed by filtration. The filters consist of fine copper-wire sieves in sets of 4 or more each, the one above fitting into the one below, the mesh of the lower sieves increasing in fineness. The bottom sieve has a flannel bag attached, for the separation of the finer impurities and the feculent matter. The flannel, or bag filter, is sometimes used without the sieves in an arrangement shown in Fig. 2100, in which s is the cistern for containing the juice, ff the filter bags. The filtered sugar liquor is next passed through filters of boneblack or animal charcoal, in large slightly conical vessels of copper or iron, from 6 to 12 feet high, each furnished with a perforated false bottom over which a filtering cloth is spread. The cistern is sometimes closed in at the top in order to preserve the warmth of the liquor, and thus facilitate its passage through the filter. In filling in the bone-black, the first few inches are pressed compactly down; after which it is filled lightly, but Fig. 2100. evenly, to within a short distance of the top, where a space is left for the accumulation of the cane juice. Fig. 2101 represents a vertical section of one of the charcoal filters used in France. Upon the false per lines, for the purpose of better running off the evaporated juice by the cock c. In these vessels the juicc I forated bottom a filtercloth is spread, and upon this the charcoal c is placed, first in Fig. 2101. well packed layers, and afterwards a little more loosely. Another cloth is placed on the top, and upon that a perforated plate of metal. The syrup to be filtered is let in from the cisterns, and the supply is regulated by a ball-cock be, a certain quantity being always kept at the top of the filter to prevent the charcoal from drying and dividing into vertical channels or cracks, and forming what the French call de fausses voies. To allow the syrup to accumulate in the bottom reservoir of the filter, it is necessary to let the air escape, for which purpose the tube tt is provided. At m is a man-hole for cleaning out the filter when required. The object of filtering is to remove all vegetable colouring matter and any excess of lime that may have been accidentally added in the clarification, together with mineral salts, such as sulphate of lime, originally present in the juice. About 5 tons of animal charcoal are required for every 100 tons of sugar made. After this the charcoal is reburnt, and thus its useful properties are restored to it. See BONE. The filtered liquor is now ready for evaporation, which according to the improved processes may be conducted either in the vacuum-pan or in open pans, containing a coil of steam-pipe. The usual plan is to concentrate the liquor in open pans to the density of 25° to 28° Baumé, up to which point it is not greatly acted on by the atmosphere. The evaporators used for this purpose are large iron vessels such as E, Fig. 2102, with copper pipes at the bottom bent round as shown in the plan, Fig. 2103, the extremities of which terminate in a straight gun-metal tube passing through stuffing-boxes HH: the pipe s, which conveys the steam, is at one end of the straight tube, and the pipe which discharges the condensed water at the other. By this arrangement the pipes can be raised up out of the vessel for the purpose of cleaning it thoroughly; for if the cane juice be allowed to hang about the pipes, it will become acid and infect the next charge. By means of the lever L the evaporator can be tilted into the position shown by the dotted is evaporated to about 27° B. before going into the vacuum-pan. Another arrangement for concentrating the juic for the vacuum-pan is shown in Fig. 2104, and it possesses the great advantage of employing the waste steam of the vacuum-pan. It consists of a series of straight copper pipes ss placed one above the other, with the ends fixed in cast-iron boxes or united by curved end pieces as in the figure. The steam generated within the vacuum-pan is admitted within these pipes; and the weak juice which is to be evaporated is allowed to trickle down in a shower over these pipes; an arrangement which reminds us of the thornwalls employed in Germany, for evaporating the weak brines used in the manufacture of common salt. [See SODIUM, Fig. 2009.] The weak juice is contained in a vat s, from which it passes along a pipe into a serrated trough f, and falling in drops from pipe to pipe it condenses the steam within, while itself becomes greatly heated, sends off vapour, and falls in a more concentrated form into the trough R, from whence it passes into a vat which feeds the vacuum-pan. There is, however, a remarkable adjustment of temperature in this apparatus, which is well adapted to the conditions of the process. As the cane-juice in passing over these pipes becomes more concentrated, and consequently more liable to injury from heat, the condensation of the steam within the pipes tends to mitigate the temperature, and to prevent the lower pipes from becoming too hot. The condensed water issues out through the pipe P, which is placed in connexion with a small air-pump, for the purpose of assisting the maintenance of the vacuum in the vacuum-pan, and the flow of steam along the pipes ss in the required direction. Thus, it will be seen that this apparatus is as ingenious as it is economical: the steam inside the Fig. 2104. CONDENSER AND EVAPORATOR. densed, thus enabling the vacuum-pan to perform twice as much work as it could otherwise get through. The concentrated juice is next passed into the vacuum-pan, where the evaporation is completed; unless a sugar of very superior quality be required, in which case the syrup is slightly heated for the purpose of increasing its fluidity, and is again passed through the charcoal filters. The vacuum-pan depends for its action on the principle that liquids boil at greatly reduced temperatures when relieved from the pressure of the atmosphere. [See EBULLITION.] The term vacuum-pan, however, is not very appropriate, for if all the air were removed at the commencement, the space would become rapidly filled with steam from the heated liquor, and an amount of pressure equal to that of the atmosphere be again established, unless means were taken for drawing off the vapour as fast as it formed, and even then an actual vacuum over the surface of a liquid could never be established. The vacuum-pan originally patented by Howard in 1812, has been of great value in the chemical arts, not only in the preparation of sugar, but also of medicinal extracts and other substances, the concentration of which, at their ordinary boiling points, was always dangerous, and generally led to the decomposition or deterioration of the vegetable juices. It has gone through a great variety of improvements since the date of its introduction. It is represented in its most approved form in a steel engraving, which is copied from the pan, manufactured by Messrs. Pontifex & Wood, which formed so conspicuous an object in the Great Exhibition. It is 8 feet in diameter, and is capable of boiling 80 tons of sugar in 24 hours. The section, Fig. 2105, will also assist the explanation. It consists of a copper pan, with a cast-iron jacket J, and arrangements for admitting steam between the two. Within the pan and corresponding with its curvature, is a worm or coil of copper pipe p, through which steam is passed for the purpose of boiling the juice. At the top of the pan and of the inner jacket is a Fig. 2105. VACUUM-PAN. ration of the juice, is removed by the condenser, Fig. 2104, already described, or the steam is drawn off into a condensing box, and condensed by the injection of cold water, as described under STEAMENGINE, Figs. 2043, 2044, 2053; by which means a partial vacuum is produced; and is further assisted by means of a powerful air-pump, which removes the water used in condensation, and also gets rid of the air which is carried in with the water. Now as air is far more difficult to remove than water, this method of condensation by injection is far inferior to that by the condenser, Fig. 2104, which does not require that water should come in contact with the steam, so that no air enters the pan; there is thus a saving of 40 to 50 per cent. of fuel, and consequently the vacuum-pan can be used in places where water is too scarce to command the large supply required for injection. There is also a saving in the size of the steam boilers required, in the freight, in the setting, and in the daily stoking. Besides this, the air-pump is not wanted, and thus the power required for working it is saved. A small air-pump is indeed generally attached to the condenser, in order the more quickly to get rid of the water formed by the condensation of steam in the pipes, and also to remove air from the pan at the commencement of the day's work. The condenser may be applied with advantage to steam-engines, producing a vacuum, according to the state of the atmosphere, of from 26 to 30 inches of mercury; and when attached to high-pressure engines used in the manufacture of sugar, not only may the waste steam of the engine be employed in evaporating the weak cane juice in the same manner as the steam from the vacuum-pan; but it saves and returns to the boilers the condensed water in a hot and pure state; and lastly, by the addition of a small air-pump, it converts a high-pressure into a condensing engine, thus increasing the power of the engine and diminishing the cost of fuel required to work it. In addition to the above apparatus, there is an expansion vessel, for reducing the pressure of the steam to the point required in the vacuum-pan. It is a large cylinder of plate-iron c, Fig. 2106, into which Fig. 2106. EXPANSION VESSEL. We will now proceed with our description of the | the control of the sugar-boiler, who can work it various parts of the vacuum-pan. The copper worm without having to leave the vacuum-pan stage. The or coil of pipe through which steam passes for heating handle h in the steel-engraving is intended for a the juice, is marked p; the space between the pan and similar object. the jacket J is also occupied by steam. M is a manhole with a movable gun-metal top ground into its collar, and is taken off for the purpose of repairing or cleaning the pan. st is the valve for supplying steam to the worm; is a smaller valve for admitting steam into the interior of the pan for cleansing. ps is the proof-stick for drawing out a sample of sugar during the process of evaporation, without disturbing the vacuum: it consists of a piston with a receptacle in it for receiving the sample of sugar, into which it is plunged by being passed down a barrel soldered into the dome, and dipping below the surface of the liquor; and the piston is so arranged that it can be drawn out of the barrel to a sufficient extent to allow the sample of syrup to be taken out without admitting air into the vacuum. By means of a cock of similar construction, a little piece of butter may be introduced into the pan, to modify the violent ebullition to which the liquor is sometimes liable. is a thermometer for ascertaining the temperature at which the syrup within the pan is boiling; and b a barometer or vacuum gage for ascertaining the amount of pressure within the pan. s is a measure of the capacity of about 35 gallons, for regulating the quantity of juice admitted into the pan; it is furnished with a pipe and cock e dipping into a cistern below and which supplies the pan. s is the pipe and cock for conducting the measured juice into the pan. g is a glass gage partly enclosed in a brass tube for showing the quantity of juice in the measure; c' is a pipe and cock leading to the pan, through which the vacuum in the pan acts upon the juice in the cistern and draws it up into the measure, in filling which the cocks c and e' are opened and the juice is drawn up, and when the measure has received its proper quantity, these cocks are shut, and the cock s is opened; but as the cold liquor admitted into the measure will have condensed the vapour admitted into it from the pan, there will be a greater amount of rarefaction in the measure than in the pan when the cock c' is opened, so that juice will not flow into the pan until air is admitted into the measure, for which purpose the cock c'' in its cover is provided, and this being opened, the juice flows into the pan. o is an overflow vessel or receiver for catching any liquor that may boil over from the pan, the amount of the overflow being indicated by the gage g'; a cock at the bottom of o allows this juice to be racked off. A is a small air-cock in the arm-pipe, which conducts the vapour from the pan to the condenser. In the dome of the pan are small peep-glasses, e, one on each side, so that by looking through one, the other affords sufficient light to watch the progress of the boiling in the pan. The sugar is run out of the pan by a gun-metal saucer G, ground into a socket & attached to the pan; the saucer is raised or lowered by means of the lever . In some cases a cock is substituted for the saucer, and is brought by means of a windlass wheel within steam is admitted by the pipe s. At the top of the vessel is a valve v, loaded to the required pressure, through which steam escapes as soon as the pressure in the vessel rises above that point; the expanded steam is then led away to the vacuum-pan through the pipe P. is a valve for opening or closing the way between the boilers and the expansion vessel. r is a small safety self-regulating valve. Messrs. Pontifex & Wood have improved on the above common method of expanding, which occasions a waste of all the steam above the required pressure, by the contrivance of a peculiar valve c, which is a hollow cylinder, containing a solid piston or plunger loaded to the required weight by w, so that as soon as the pressure exceeds the counter-balancing weight, the piston, against the bottom of which the steam acts, rises and partially closes a valve which regulates the admission of the steam, and when the pressure is so reduced that the weight is able to force the piston down, the valve is again fully opened. In operating with the vacuum-pan the syrup is run in as quickly as possible, until the whole of the heating surface is covered: the steam is then turned on, and the temperature of from 180° to 190° maintained. When the syrup begins to granulate or form crystals the temperature is lowered to 1609, and just before the evaporation is completed, and the sugar ready to be let out, the temperature is reduced to 145°, or the lowest temperature at which proof-sugar boils at 3 inches above a perfect vacuum. The sugarboiler takes out a sample of syrup by means of the proof-stick, and drawing it out against the light between his finger and thumb, ascertains that the crystals are in a sufficiently forward state: he then adds another measure-full of syrup to the pan, and the same process is repeated until the whole charge is admitted. |