When it leaves the curing-house the sugar is packed in hogsheads for shipment as raw, brown, or muscovado sugar ; and in this state it is commonly exported from our West Indian colonies. As the molasses is very imperfectly separated from the crystallised sugar, a considerable diminution of weight takes place subsequent to the shipment, by the drainage from the hogsheads. This waste has been estimated to amount to no less than 12 per cent. The loss upon French colonial sugars used to be much greater even than this. Means have, however, been adopted of late years in some colonial sugar-works for reducing this loss.
Clayed sugar, also called Lisbon sugar, is raw sugar that has been subjected to a peculiar operation. The sugar is removed from the coolers into conical earthen moulds called formes, each of which has a small hole at the apex. These holes being stopped up, the formes are placed, apex downwards, in other earthmen vessels. The syrup, after being stirred round, is left for fifteen or twenty hours to crystallise. The plugs arc then withdrawn, to let out the unerystallised syrup ; and, the base of the crystallised loaf being removed, the forme is filled imp with pulverised white sugar. This is well pressed down, and then a quantity of clay mixed with water is placed upon the sugar, the formes being put into fresh empty pots. The moisture from the clay, filtering through the sugar, carries with it a portion of the colouring matter, which is more soluble than the crystals themselves. When the loaves are sufficiently purified to be removed from the formes, they are dried gradually in a stove, and crushed into a coarse powder for exportation. Claying is little practised in British plantations, from an opinion that the increase of labour and diminution of quantity of produce occasioned by it are not compensated by the improved quality of the sugar. It was however very generally practised by the French in St: Domingo. Hague's process consists in submitting the raw sugar, after being cured in the usual way, to the action of a vacuum filter. The apparatus consists of a shallow vessel, beneath which is a cavity connected with an air-pump. The bottom of the vessel is perforated with a number of small holes ; and when a quantity of muscovado sugar, mixed with a little water into a pasty mass, is laid in it, upon a piece of baireloth, the air is withdrawn from the cavity beneath the sugar. The pressure of the superincumbent atmosphere upon the
surface of the sugar then drives the moisture, and with it much of the colouring-matter, through the holes in the bottom of the vessel When the sugar is sufficiently whitened, the air-pump is stopped, the sugar and molasses are removed, and a fresh charge of muscovado is Another means of avoiding the loss consequent on the drainage from raw sugar during its voyage to this country, is the importation of sugar for the use of the refiner, in the form of concentrated cane-juice, containing nearly half its weight of granular sugar along with more or less molasses, according to the care taken in the boiling operations.
Before proceeding to the subject of sugar refining, it may be well to make a few observations on suggested improvements in the West Indian treatment of raw sugar. Chemists, and the better class of sugar-growers, have long known that a large amount of sugar is wasted by an imperfect management of the operations at the plantations. It is believed that 25 per cent. of the juice lodges in the cells of the megass or trash, and is lost ; it ought to be extracted, but is not. Even if not, the trash might form a better fuel for the boiling-houses (where it is now used) if first dried by the surplus heat of the chimneys, &.e. Dr. Seoffern, in 1847, ascertained that, in various ways, no less than two-thirds of the sugar is in some instances lost. In 1849 he introduced certain improvements, intended, by the use of new defecating agents, to increase the quantity of juice obtained from the cane, and of sugar obtained from the juice. Some of the agents used by him are poisonous however in their natural state, though innocuous in the process ; and this seems to have retarded the acceptance of his method. Some inventors say that the weight of juice extracted is only 50 per cent. of the weight of the original cane, whereas it ought to bo 90 per cent.; and they have devised a mode of treating the megass with hydraulic pressure, after the mill has done its work ; by this means the megass becomes a flattened mass of trash, as hard and nearly as dry as a deal board. It is also believed that, by a better con struction and management of apparatus more sugar and less molasses [MOLASSES] might be obtained from a given weight of juice.