Page:The American Cyclopædia (1879) Volume XV.djvu/463

 SUGAR 447 in most of the principal commercial cities of the United States and of Europe. As for- merly practised, raw sugar was dissolved with lime water in a large open boiler, and, when warm, bullock's blood was added, which as it coagulated on boiling collected most of the lighter impurities and carried them to the sur- face in the form of a thick scum. This being removed, the liquor was partially evaporated by boiling, filtered through woollen cloth, then concentrated and grained on the general plan already described. The best sugar refiners do not now use blood or any other coagulating substance to collect suspended matters, but separate them entirely by filtration. The pro- cess in the best establishments is substantially as follows : On the ground floor the raw sugar is dissolved in hot water in large cisterns. "Water enough is added to produce a specific gravity of about 1'25, or 29 Baume. By a large pump near each cistern at the same level the solution is drawn off through a connecting pipe provided with a coarse wire strainer, which prevents all except the smaller solid particles from entering the pump. The sac- charine solution is pumped up into the highest story, which is usually the seventh or eighth, it being cheaper as well as more convenient to elevate the sugar in solution than in a solid state. It is pumped into vessels called " blow- up pans," because steam was formerly blown into them to heat them. They are now heated with close coils to about 208 or 210 F. Milk of lime is added to the solution in these pans for the purpose of neutralizing any acid which it may contain. From these pans the sirup passes down to the next floor and into filters by which it is completely deprived of all sus- pended solid particles. These filters consist of a great number of bags 4 or 5 in. in diameter and 8 or 10 ft. long, made of two thicknesses of cloth, an outer of coarse and an inner of fine material. They are enclosed in sets of about 200, in boxes, to prevent cooling. After a time they become foul, when they are turned inside out and washed. After leaving the bag filters, which it does at a temperature of from 170 to 180, the sirup is run through filters of animal charcoal or bone black. These are im- mense cylinders, 6 or 8 ft. in diameter and usually from 20 to 25 ft. high, filled with pul- verized bone black, which substance has the property of absorbing all the coloring matter in the sirup, which runs from the bag filters of a sherry wine color. After a time the char- coal becomes foul and loses its property of absorbing coloring matter, when it is taken to a neighboring room and reburned in kilns. The sirup which runs from the charcoal filters at a temperature of about 150, and, in a per- fectly colorless condition, is now pumped into vacuum pans and concentrated to the granu- lating or crystallizing point. These vacuum pans were invented by Howard and patented in 1812. They are large conical or ovoid ves- sels heated by steam and exhausted with air 769 VOL. xv. 29 pumps, by which the air and vapor are rapidly removed. In the later stages of the process the pressure is reduced to only 3 in. or less of mercury. The pans are sometimes supplied with an apparatus for condensing the steam by a cold spray. In making hard sugars, at the commencement the evaporation is con- ducted at a temperature of 170 to 180 F., but as soon as granulation begins it is lowered to 160, and just before the evaporation is completed it is reduced to 140, this being the lowest temperature at which crystallizing sugar boils at a pressure of 3 in. of mercury. An ingeniously devised sliding tube, by which a " proof " may be taken without admitting air, is attached to the vacuum pan. In making soft sugar the temperature is kept rather low- er. As soon as crystallization begins the sugar is run off, and if it is to be made into soft sugar, the sirup is discharged by means of centrifugal mills. If it is for hard sugar, it is run into a vat which has a gate in its bot- tom; from this it is run into conical moulds placed upon carriages, which are drawn under the gate.^ In the bottom of each mould there is an orifice which is kept closed by a stopper for several hours, until the sugar crystallizes, when it is removed and the sirup allowed to drain away. The loaf which remains has a slight yellow tint, which is removed by allow- ing a colorless solution of sugar to pass through it. The loaves are then taken out of the moulds and dried in ovens at a temperature of about 160. The sirup which drains from the moulds still contains a small percentage of cane sugar, but too small to recover with profit. It is therefore sold as sirup. It may be here remarked that raw molasses contains enough cane sugar to make it profitable for some es- tablishments to make a specialty of extracting it. The muscovado molasses from Cuba, Porto Rico, and Antigua is esteemed the best. Beet Sugar. In 1747 Marggraf, a Berlin chemist, found that the white beet yielded 6*2 per cent, and the red beet 4'6 per cent, of sugar, but the manufacture was not developed till the close of the year 1800. (See BEET.) The beets pre- ferred in Europe for the manufacture of sugar are varieties of the white Silesian, yielding a juice richer in sugar and more free from salts than that of other kinds of. beet. The weight of the larger ones is about 5 Ibs. each; and the yield per acre in France and Belgium is 14 or 15 tons, and about Magdeburg 10 to 12 tons of beets. The crop is successful over the greater part of Europe, but more particularly N. of lat. 45, and upon light dry soils, in a dry atmosphere. The richness of the juice is injured by direct application of manures to the growing crop, and it is less in large beets than in small ones. When the leaves begin to die, the beets are dug, the heads cut off, and the roots are thrown together and covered to protect them from light and frost. They may be thus kept for some time, though there is always risk of portions of the sugar passing