The construction of this mill is very defective. A better form is that of placing the rollers in a horizontal position, and feeding the mill by sliding the canes gradually from an inclined board. The rollers, made very accurately of cast-iron, and fluted or grooved on the surface, are not placed in the same but are arranged in a triangular form, the periphery of the upper roller being very nearly iu contact with the two lower rollers, which are also very near together. The two lower rollers, which are called respectively the feeding and delivering rollers, have small flanges at their ends, between which the top roller is placed, so that the pressed canes may not be able to escape from the rollers and clog the machinery. The feed-board is an inclined plane,. com monly of cast-iron, the edge of which is nearly in contact with the feeding roller. The delivering board, which receives and conducts away the trash of the cane, is also of cast-iron, sloping downwards front the delivering roller. In sonic cases the liquor is raised from the glitter of the mill-bed by pumps connected with and worked by the machinery of the mill. Where circumstances render such an arrange ment practicable, labour may be saved by placing the crushing-mill on a high level, so that the liquor may run from it to the vessels in which it is to be purified, by inclined gutters. In Demerara a well-constructed engine and mill will produce about a hundred gallons of liquor per hour for each horse-power.
Cane-juice, as expressed by the mill, is an opaque, slightly viscid fluid, of a dull gray, olive, or olive-green colour, of a sweet balmy taste, and of a specific gravity varying from P033 to 1•I06. It holds in suspension particles of solid matter from the cane, a considerable portion of which is separable by filtration or repose. The juice Is so exceedingly fermentable, that in the climate of the West Indies it would often run into the acetous fermentation in twenty minutes after leaving the mill, if the process of clarifying were not immediately commenced.
We have next to treat of the extraction of the sugar from the juice. As practised in the East Indies, the liquor, after being strained so as to separate the coarser feculencies, is boiled down in open boilers into a thick inspissated juice ; the scum which rises during the operation being removed. When it is sufficiently bvaporated, it is removed into earthen pots to cool, and in these it becomes a dark-coloured, soft, viscid mass, called poor, or jarvery. Much of the molasses or un cryetallisable part of the juice is then separated, by putting the goer into a coarse cloth and subjecting it to pressure. The sugar is further purified by boiling it with water, with the addition of an alkaline solu tion and a quantity of milk. When this has been continued until scum no longer rises upon the liquor, it is evaporated, and sometimes strained, and afterwards transferred to earthen pots or jars. After it has been left for a few days to granulate, holes in the pots are unstopped, and the molasses drains off into vessels placed to receive it. The sugar is rendered atill purer and whiter by covering it with the moist leaves of some succulent aquatic plant, the moisture from which drains slowly through the sugar, and carries with it the dark-coloured molasses. A similar process to the above is said to be practised in Cochin China.
The separation of the sugar from the cane-juice is effected in a much simpler manner in the West Indies. The juice is conducted by gutters from the mill to large flat-bottomed pans, called clarifiers. Each of these is placed over a fire, which may be regulated or extinguished by a damper ; and each is supplied with a stop-cock or siphon for drawing off the liquor. When the clarifier is filled with juice, a little slaked lime is added to it ; the lime, which is called temper, being, in most cases, previously mixed with a little cane-juice to the consistence of cream. As the liquor in the clarifier becomes hot, the solid portions of the cane-juice coagulate, and are thrown up in the form of scum. The proper heat is indicated by the scum rising in blisters and break ing into white froth, which commonly happens about forty minutes after the fire is lighted. The damper is then closed, and the fire dies out ; and after an hour's repose, the liquor is ready for removal to the first of the evaporating pans.
From the clarifier the purified juice, bright, clear, and of a yellow wine colour, is transferred to the largest of a series of evaporating pans, three or more in number. These evaporators are placed over a long flue, heated by a fire at one end, over which the smallest of the coppers, called the !cache, is placed. In the process of boiling, impuri ties are thrown up in the form of scum, which is carefully removed. In the teethe, the liquor is boiled down to as thick a consistency as is considered necessary for granulation ; this point being most commonly ascertained by observing to what length a thread of the viscid syrup may be drawn between the thumb and finger. This trial by the touch, whence the teache is supposed to derive its name, is very imperfect ; for it sometimes happens that the syrup may have the required tenacity, and yet not be in a good state for crystallising. The latter point may be better ascertained by observing the incipient granulation of the syrup on the back of a ladle dipped in the teache. The thermometer, though useful, will not be a sure guide in determining the proper moment for striking, or emptying the teache; because a viscous syrup, containing much gluten and sugar, altered by lime, requires a higher temperature to enable it to granulate than a pure saccharine syrup. The concentrated syrup is ladled, or skipped, from the teache, either imme diately into open wooden boxes called coolers, or into a large cylindrical cooler, from which it is afterwards transferred to the granulating vessels. In these the sugar is brought to the state of a soft mass of crystals, imbedded in thick, viscid, but unerystallisable fluid. The separation Of this fluid is the next process, and is performed in the curing-house. This is a large building, the floor of which is excavated to form the molasses reservoir. Over this cistern is an open framing of joists, upon which stand a number of empty potting-casks ; each of these has eight or ten holes bored through the lower end, and in each hole is placed the stalk of a plantain-leaf. The soft concrete sugar is removed from the coolers into these casks, in which tho molasses gradually drains from the crystalline portion, percolating through the spongy plantain stalks.