Sugar-trash has been tried in England as a material from which to make paper, but without much success.
Sugar-refining.—Raw or muscovado sugar, as brought from the colonies, forms the common moist or brown sugar of the shops. The saccharine particles are always mixed with other matter, which imparts to the sugar a dark colour, a moist clammy feeling, and an empyreu untie odour. The object of the sugar-refiner is to remove these impurities, so as to obtain the sugar in the hard white semi-transparent state known as loaf-sugar.
The art of refining sugar, as well as that of extracting it from the cane, is supposed to have been brought to Europe from the East, probably from China ; but at what time is uncertain. The Venetians arc believed to have been the earliest sugar-refiners in Europe ; and it is known that they practised the art before the discovery of America. The Venetians originally operated upon the coarse black sugar brought from Egypt, and followed the Chinese practice of converting it into sugar-candy before they made loaf-sugar. Stow (` Survey of London ') states that sugar-refining was commenced in England about 1544. There were then two sugar-houses in London, but they yielded little profit, because there were many sugar-bakers in Antwerp who could supply refined sugar to England better and cheaper than it could be made at home. Subsequently, the commerce between England and Antwerp being stopped, these two sugar-houses supplied all England for twenty years, and became so profitable, that many other persons embarked in the business.
Few manufacturing operations have undergone more important changes than that of sugar-refining. As generally practised until within a recent period, the process commenced by mixing the raw sugar in a large open copper with lime-water, and adding to the mixture when warm a quantity of bullock's blood. The heat occasioned the serum of the blood to coagulate, and in so doing to collect most of the impuri ties floating in the liquor, and to raise them with it to the surface of the syrup in the form of a thick scum, which was carefully removed. This clarifying process was sometimes repeated with a fresh quantity of blood, or, as it is technically called, spice. When the liquor was thus rendered tolerably clear, and was partially evaporated by boiling, it was further cleansed by passing it through a filter of thick woollen cloth, which detained any particles of scum that might have been left after skimming the liquor. It was afterwards concentrated by boiling in a smaller open copper till sufficiently thick for graining ; after which it was formed into loaves in the manner hereafter described. For loaves of the finest quality a second refining followed this. In the preceding section allusion has been made to the methods of separating molasses from raw sugar by the vacuum-filter and the hydraulic-press, both of which have been applied to the preparation of sugar for refining; by the latter process sugar is now capable of yielding loaves equal to double-refmed by one process.
Many improvemeuts have been effected upon the old methods of clarifying and concentrating the syrup. The raw sugar is transferred from the casks into large circular blow-up cisterns, 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 upper 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 surface 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 largo square vessel, 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 awes, 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 mass 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 gypsum, called finings. Other refiners use both the blood and finings.