CHAPTER VI.

CURING THE SUGAR.

IT will be readily understood that the products of the various operations described in the preceding chapters, differ widely in character, and demand separate treatment in their preparation for the market. This treatment is generally known as "curing," and embraces the whitening or bleaching of the sugar. The several plans will be discussed in succession.

Simple Drainage.-This is the oldest and crudest method, and is on a par with the dirty-looking mass of sugar and impurities produced by the wasteful and slovenly copper wall. In order to remove a certain amount of the molasses and other impurities, the semi-liquid mass, dug out of the coolers as soon as it is sufficiently cold, is placed in casks with perforated bottoms; the holes in the casks are loosely filled with twisted leaves or rushes (the latter long enough to reach above the contents of the casks), in such a manner as to form the roughest imaginable kind of strainer. The casks stand meantime on rafters over an immense tank. Here the draining process slowly and imperfectly goes on, a portion of the molasses escaping into the tank below, but much still remaining in the mass of sugar, imprisoned the separation of the molasses is so incomplete, that very great leakage and waste continue while the sugar is on its way to European markets. Sugar which has been cured in this way is termed "muscovado," and is the most impure form of "raw" ("grocery," " moist," or "brown") sugar. It is still produced in some backward countries, but it is pretty

well obsolete in the English and French colonies, and its manufacture is decreasing rapidly in Louisiana.

Claying. The first improvement upon this barbarous system was introduced by the Spaniards and Portuguese in Cuba, and is based upon the fact that the impurities present in muscovado sugar are much more soluble in water than the crystalline sugar itself. Thus washing with water will effect considerable purification. The earliest manner of carrying this out was by placing the sugar in inverted cones with a minute aperture in the apex, which is stopped up during the filling and for about 12 hours afterwards; upon the mass of sugar in the cone, was placed a batter of clay and water (hence the term "claying "), the object being to ensure a very gradual percolation of the water through the mass. This water carries with it the uncrystallizable sugar and colouring matters imbedded between the crystals of the sugar. The resulting sugar is much lighter-coloured than muscovado, but the grain is very soft, and the operation is most wasteful. In Bengal, a wet rag is sometimes substituted for the clay batter.

Spirit-washing.-The very slight solubility of sugar in alcohol, coupled with the ready solubility in that medium of many of its impurities, suggested the practice called "spirit washing." This consists in substituting cold alcohol or alcohol and water for the simple water used in claying. The results are not perfect, however, and the costliness of the method soon caused its abandonment. It was principally employed in the East Indies.

Vacuum-chest.-The vacuum-chest consists of an iron box with a tray of wire gauze above, and connected with airpump suction below. The sugar is spread on the tray, and the downward suction produced by working the air-pump, creates a tendency in the fluid portion of the mass to separate itself. Effectual separation, however, can only be attained when the grain or crystal of the sugar dealt with is large, hard, and well formed; with small or soft grain, the

CHAPTER VII.

COMPLETE FACTORIES.

IT has been quite impossible in the preceding chapters to combine detailed descriptions of the many forms of apparatus used to effect the same purpose, with a connected account of the operations through which the material passes. It will therefore be interesting to follow the processes in general, by the aid of a few representations of complete factories on different systems.

Plate VII., Fig. 1, shows an elevation of a factory recently erected in Cuba, by Cail et Cie., Paris. The cane is crushed in the 3-roller mill a, worked by a 30-H.P. beam-engine b, connected by the gearing c. The expressed juice flows into a tank, and thence to the monte-jus d, by which it is raised to the 6 purifiers e (one shown) provided with supply and dischargepipes, and heated by steam coils, and where it undergoes defecation with lime. Hence it flows through 10 animalcharcoal filters f (one shown), and through their perforated false bottoms into a pipe leading to the tank g, whence it is transferred by another monte-jus to the receptacle, for delivery to the vessel i which regulates the supply to the concentrating-pans j. Leaving the pans, the syrup is pumped into the vacuum-pan k, when the concentration is completed. The separators / collect any water that may pass with steam from the vacuum-pan to the pipes in the concentrating-pans. The concentrated syrup is next treated with blood in the clarifiers m, re-filtered through f, re-concentrated in k, and run into moulds to crystallize. The crude crystallized sugar is crushed in a mill, and passed through the centrifugals o, the molasses being collected in a tank p for further treatment.