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Iron Oxide.—This compound is indicated by the red colour of the ash residue after ignition of the cocoa; but its presence, as well as that of the sulphate and carbonate of lime, is of such rare occurrence that comparatively little interest attaches to this part of the analysis. If either of the substances were indicated, their estimation could be effected by the usual process for the estimation of lime, sulphates, etc.
SUGARS are amongst the most widely-diffused substances in the vegetable kingdom ; but those which appear in commerce are capable of being divided into two classes—viz. that corresponding to sugar from the sugar-cane, and the class corresponding to glucose.
Origin.-Sucrose, or cane-sugar, has its source
ist. In certain grasses, to which the generic name Saccharum is applied, and which are cultivated chiefly in India, the East and West India Islands, Mauritius, South America, and China.
2nd. In Sorghum saccharatus, a native of India, cultivated in the United States under the name of Chinese sugar-cane, and known also as “Sorghum."
3rd. In the common beet (Beta vulgaris).
5th. In the sap of certain palms, such as the cocoa-nut (Cocos nucifera), the wild date-palm (Phænix sylvestris), and the Borassus flabelliformis, from which is derived a low-class sugar, known in commerce by the name of " Jaggery.”
6th. In the green stalks of maize or Indian corn (Zea mays).
The sugar derived from the above sources is that which is almost exclusively used for domestic purposes. It is crystalline,
soluble in one-third of its weight of cold water, and, when pure, has a specific gravity of 1'593 at 39° F. (4° C.)
The principal sugars corresponding to glucose are—Dextro glucose, produced by the hydration of starch under the influence of dilute acids, and existing ready-formed, sometimes with cane-sugar and sometimes with lævulose in fruits ; Maltose, produced by the action of malt-extract on starch; Lævulose, formed from cane-sugar, along with dextro-glucose, by the action of dilute mineral acidsthe two kinds existing in equal proportions in what is known as Invert Sugar; and Mannitose, produced by the oxidation of mannite.
Description.—Cane-sugar.—There are a great many varieties of sugar-cane or Saccharum officinarum, the most important being the common cane, having a yellow stem, and called by the West Indians “Creole,” or “Native Cane;” the purple cane, having a purple stem and richer juice, and called in India “karambou kari ;” and the gigantic cane, having a large, light-coloured stem, called in India, “karambou valli.” They are all the products of tropical or sub-tropical climates, flourishing best in moist and nutritious soils. They vary in height from 6 feet to 18 feet, the average being 10 or 12. The diameter of the stem is from 1/2 to 2 inches, and the joints on a single stem number from 40 to 80. They require from twelve to sixteen months to arrive at maturity. After being cut down, they strike again from the stole, the fresh stems being called “rattoons." The length of the joint diminishes every year, while the richness of the juice increases. At the end of five or six years, however, it is necessary to renew the plantation. As soon as the canes are ripe, they are cut down during dry weather, stripped of their leaves and watery top joints, which serve for shoots, then carried as quickly as possible to the millhouse, and crushed between rollers. The juice—which, as it flows from the mill, varies in specific gravity from 1'067 to 1'106—is then heated slightly, and treated either with milk of lime or sulphite of 'ime, by which the small quantity of acid present in the solution is
neutralised, the tendency to fermentation corrected, and a large quantity of impurities made to rise to the top in the form of scum. This being removed, the partly-clarified juice is evaporated down and crystallized, the product being imported into this country chiefly as raw sugar.
Cane-syrups show a greater tendency than beet-syrups to become acid and pass into the invert form of sugar in the process of boiling down, and the loss of crystallized sugar from this cause is very large. It has been estimated that sugar-cane contains about 18 per cent. of sugar, of which about one-third is left in the canes after crushing, and is therefore lost; that an acre of land will grow 30 tons of canes; but that, owing to the loss in crushing and boiling down, the acre does not produce more in actual practice than 27 tons of raw sugar. The molasses produced is to a great extent used in distilleries for the manufacture of rum. Large quantities of raw sugar imported into this country go into the hands of the refiners, whose business it is to cleanse or purify it. To effect this it is redissolved, generally in about half its weight of water, and the solution sometimes heated with bullocks' blood, which, on coagulation, has the effect of removing solid impurities, the coagulated mass being separated by filtration. Having been again heated, the syrup is run through a long column of animal charcoal, whence, having been partially decolourised and deprived of gummy matter, it is passed to a vacuum-pan, and concentrated until it becomes what is called “supersaturated,” after which it is allowed to crystallize. If it is required to make loafsugar, the air is admitted when the liquor has got beyond the crystallizing point, and the temperature is raised, by which some of the smaller crystals pass again into solution. This heated mixture of liquid and crystals is thrown as rapidly as possible into moulds, in which it is allowed to stand for a couple of days to drain and harden. At the end of this time a saturated solution of pure white sugar is passed through the moulds in order to wash the crystals and remove any impure syrup from the pores. The sugar is next removed from the moulds and placed in a stove heated by steam, for four or five days, or until thoroughly dry, when it is fit for the market.
Beetroot-sugar.-The process for the manufacture of sugar from beetroot is as follows: The roots are first washed, and then freed from the crowns, as well as from any decayed portion. They are then either crushed or subjected to what is called the “ diffusion process.” If the first plan be adopted, the roots are placed in a machine containing a large drum, the circumference of which is set with a number of saw-blades or teeth. This drum rotates, and as the roots are passed through they are rasped into a pulp, which falls into a cistern or hopper, where the juice is separated by pressure. In the diffusion process, the cleaned roots are sliced and placed in warm water for a time. The mixture of juice and water thus formed is then run into a second vessel containing more sliced roots, and so on to a third and a fourth, by which time it generally becomes sufficiently concentrated. The juice thus obtained is treated in the same way as the product of the crushing operation—that is, it is first heated with milk of lime to a temperature of 140° to 150° F. (60° C. to 66 C.) in order to clarify it, and, the scum having been removed, carbonic acid is forced into it to precipitate any lime which has been dissolved in the syrup, and in doing which it also carries down with it a quantity of colouring matter. The next operation is to pass the juice through animal charcoal, after which it is put into a vacuum-pan heated by steam, and evaporated to a syrup, having a specific gravity of from 1'200° to 1'300', and containing from 45 to 60 per cent. of sugar. The methods adopted for obtaining pure sugar from this syrup do not differ essentially from those employed in refining the product of the sugar-cane. The refiner of beet-sugar, however, finds his syrups to contain a much larger quantity of potash salts, which it is his object to leave behind as completely as possible in the mother liquor, from which his last crystallization of sugar has been obtained.
Maple-sugar.- The sugar-maple, Acer saccharinum--a tree abun