The next process is concentrating and crystallizing the liquid, which is placed in vacuum pans generally made of cast iron. They have been made as large as 65 feet in circumference, but are often of copper and only 22 feet in circumference. The larger the pan the larger the sugar crystals, more refined sugar and less syrup. Small pans are mostly used in mould houses. When the syrup is first run into the vacuum pans the temperature is about 140 deg. Fahr., but it is lowered to 125 degrees when the liquid begins to granulate. More thin liquid is added till the pan is full. When fine grained sugar is desired the boiling must be conducted under higher temperature ; for coarse grained sugar a lower temperature is required. The vacuum pans hold many barrels of crude sugar and some refiners turn out 3000 bbls. daily.
The Centrifugal Separator. Formerly the sugar was passed from the vacuum pans through the intervening heater, which re ceived it directly into the moulds (as in the claying process), for separating the mother liquor from the crystals and making them. white ; but for this purpose centrifugal machines are now most generally used, thus substituting steam power for the slow process of gravity. This machine consists of a kind of round metallic basket, usually about thirty inches diameter (but some are now made larger), with sides of very finely perforated brass, twelve and fourteen inches high, and surrounded by an iron curb a few inches larger, which receives the syrup from the sugar in the basket and conducts it away. This basket is either suspended by a perpendicular shaft from above, or mounted on one from below, independent of the curb which surrounds it. After being filled from one-third to one-half its weight with semi-liquid sugar from the pan, it is made to revolve in a horizontal plane one thousand and fifteen hundred times per minute. The sugar immediately rises in vertical walls at the sides, the syrup being thrown out.
through the perforations, and from the native yellow color it begins to grow 'white immediately, and after a very few minutes, if it be of first quality, a little cold water from a sprinkler makes it beautifully pure and white. It is now in condition to be re moved and sold as confectioner's or coffee A sugar, or by further treatment to be made into the well-known granulated sugar of commerce.
Granulated Sugar. This very popular and strictly American style of sugar was first made and introduced about thirty years ago at the Boston Sugar Refinery. Although extremely popular in the United States since its origin, it has become popular in England only within a few years past. The apparatus at first consisted of a steam table fifteen or twenty feet long and three to five feet wide, on which the moist sugar was, by an ingenious pro cess or movement of wooden rakes, gradually worked the length of the table, becoming thoroughly dried in so doing. Afterward it was separated by sieves of different grades or mesh, into coarse and fine, and barreled and sold accordingly. This apparatus was
superseded ten or twelve years since by a large cylinder of wood or iron, some four feet in diameter and fifteen to eighteen feet long, slightly depressed at one end. The inner surface carries small projecting buckets, by which, as the cylinder revolves, the sugar, entering at the upper end, is lifted and poured through the heated interior. The heat is supplied by a small steam cylinder running through the length and center of the large one, and the position of the buckets is such as gradually to work the sugar through the length of the cylinder, during which it becomes. thoroughly dried. An arrangement of sieves, as before, completes the operation. The upper one has the coarsest mesh, to retain the largest grains, which are run directly from it into barrels and branded " extra granulated." The sugar which falls through this. first sieve drops into the next below, which has a mesh just fine enough to retain the grains next in size to those before mentioned, which are run into barrels and designated as " medium granu lated." The remaining sugar, too fine to be retained by either sieve, is packed in barrels under the name of " fine granulated." Powdered sugar is mostly manufactured from the coarsest granu lated sugar, after it has been thoroughly cooled. Tha powdered articles, are mostly manufactured in smaller establishments as a specialty.
Other grades of sugar are obtained from the liquor or syrup which is thrown out by the centrifugul, in the process of separa ting the crystallized sugar from the " mother liquid." This syrup contains 40 per cent. of sugar capable of being crystallized and available to commerce. This is worked over and over again by the refiners, till most of its sugar or sweetness is extracted. These different manipulations give rise to different grades of sugar offered on the market, and to what is called sugar-house syrup, which comes last in the order of manufacture. To illustrate ; suppose the refiner to take 1000 pounds of raw sugar, he obtains first 50 per cent. or 500 pounds of sugar suitable for the best granulated sugar; then, by working over the syrup which is left, he obtains 10 per eent. or 100 pounds, of " coffee A ; " then, again, by working over what is left from the last, he obtains 15 per cent. (of the original 1000 pounds), or 150 pounds, of " coffee extra C ; " the residue still remaining is again manipulated, and 15 per cent. or 150 Founds, of "coffee C yellow" is obtained; of what remains after this, 5 per cent. or 50 pounds, remaining to be accounted for in making up the 100 per cent. or 1000 pounds we started with, may be put down as the actual loss to the refiner, though this really varies, according to the quality of the raw sugar employed and the skill with which the refining processes are carried on.