In the concentration of the clarified syrup, which forms the next process, improvements of the greatest importance have been effected. In the old plan of concentrating the syrup in open pans, they were heated by fires to a temperature of from 230' to 250° Fahr. Many plans were contrived for rendering the application of heat more regular and controllable. It is well known that fluids will boil at a much lower temperature in a partial vacuum than when exposed to the ordinary pressure of the atmosphere ; and by the happy applica tion of this principle, Mr. Howard removed the chief difficulties attending the evaporation of saccharine syrup. The accompanying cut, which represents one of the racsurn-pans constructed on Howard's principle, may assist in the explanation of this admirable contrivance. The apparatus consists of a copper vessel, a, b, the several parts of which are united by flanges, with packing between the joints to render them perfectly air-tight. The middle portion, a, is cylindrical, from six to seven feet in diameter ; and the upper part, b, is convex or dome-shaped. The bottom is also convex, but in a less degree. The bottom is double, the cavity between the inner and outer casings forming a receptacle for steam. The best kinds of pans have also a spiral coil of copper pipe a little above the inner bottom, by which steam may be made to circulate through the body of syrup in the pan, and thereby assist evaporation. The bottom cavity is supplied with steam generated at a low pressure ; but the spiral pipe contains steam of high pressure, and consequently of great heat. There is a short broad pipe called the neck, rising from the dome, from which a communication is formed with an air-pump, by whichthe pan may be partially exhausted of air. A communication is also formed between the interior of the pan and a vessel containing clarified syrup. A quantity of liquid sugar is admitted. The air-pump continues at work during the boiling of the syrup, motion being communicated to it from a steam-engine ; and by this means the sugar is enabled to boil at a temperature of only 130' to 150°, or 100' lower than that required in open vessels. To ascertain when the syrup is sufficiently evaporated, the pan is supplied with a very ingenious appeudage called the proof-stick, the handle of which is shown as held by an attendant. It consists of a tube extending into the pan, and terminating in a peculiar kind of valve, so formed that, by turuing a rod inserted in the tube, a sample of sugar may be drawn out without admitting air into the vessel. The sample thus obtained is tried by the touch, as described in explaining the process of evaporation in the West Indies ; and when it appears to be iu a satisfactory state, the sugar is allowed to flow, through an opening in the bottom of the pan, into a granu lating-vessel in a room below.
The practice of boiling the syrup at so low a temperature has occa sioned a curious difference in the next process, which is that of granu lating the concentrated liquor. In the West Indies, the vessels used for this purpose are called coolers, because the syrup is brought down to a lower temperature than in the boiling-coppers. The corresponding vessels used in refining sugar upon the old plan were similar to these, and were called by the same name ; but when the method of boiling at a low temperature is adopted, the granulators become heaters instead of coolers ; the sugar, when placed in them, being raised to a tem perature of 180° or 190°. This is done by the admission of steam into a cavity surrounding the granulating-vessel, a shallow open copper or pan, in which the thick pulpy mass is stirred quickly to promote the granulation.
From the granulators the sugar is transferred, by means of copper basins or pans, into moulds of a conical form, usually of iron. These moulds have orifices at their points, which are stopped up before they are filled with sugar. They are arranged with their open bases upper most ; and immediately after the sugar is poured in it is stirred round, to diffuse the crystals equally through the semifluid mass. They are then left for several hours, that the sugar may become solid : after which they are removed to another room ; and, their points being unstopped, they are set in earthen jars, that the uncrystallised fluid may drain from them ; or the same purpose is effected by placing them in racks, with gutters to receive the syrup. This syrup is re-boiled with raw sugar, so as to yield an inferior quality of sugar ; and when all the crystallisable matter has been extracted from it, the remainder is sold as treacle. It was formerly usual to "clay" the loaves in order more thoroughly to remove the molasses ; but this process is aban doned by most refiners for the superior method introduced by Mr. Howard of cleansing the loaf by causing a saturated solution of sugar in water to percolate through it. When the loaf of sugar is thoroughly purified by the repetition of this process, and is sufficiently dry, it is turned out of the mould ; the base being scraped to an even surface, and the apex applied to a kind of lathe, in which any part that may be slightly discoloured is cut off, leaving the end clean and smooth. The loaves are finally dried in an oven heated by steam-pipes to a tem perature of 130° or 140°, and then wrapped up in paper for sale.
It is needless to follow the processes by which the syrups and other refuse of the best sugar are converted into sugars of inferior quality, which are either sold as cheap loaf-sugar, or formed into large coarse loaves called bastards, which are crushed into powder for sale. It has been asserted that about two-thirds of the molasses found in the moulds under the old system were formed by the intense heat employed in concentrating the syrup ; a lose which is now, in a great measure, obviated. The effect of these improvements in diminishing the price and consequently increasing the consumption of refined sugar, is also very important ; the cost of refined sugar being now only about 20 per cent. greater than that of raw sugar, although formerly the difference of price was as much as 40 per cent.
In the preparation of refined sugar, as in that of raw, many improve ments, have recently been introduced ; but none equal in importance to Howard's capital invention of the vacuum pan. The chief of them is the draining of the sugar-loaves by centrifugal motion, on the system now so largely adopted in many branches of manufacture. [Dnvisa Mamma.] Several sugar moulds, with crystallised wet sugar in them, are arranged in a horizontal circle, each with its open apex out: wards; the frame containing them is made to rotate 800 times in a minute, and the centrifugal force thus generated drives all the moisture out of the sugar and out of the mould. Or the wet mass may be put at once into a centrifugal machine, and whirled round until it becomes a nearly dry white powder. In either case there is a great saving of time over the old method. Van Goethem, a Belgian sugar refiner, has been the chief agent in bringing about this improvement.