From the trays, the thickened syrup flows into the tank F, and thence passes out into the revolving cylinder E. The cylinder is full of scroll-shaped iron plates, over both sides of which the thickened syrup flows as the cylinder revolves, and thus exposes a very large surface to the action of hot air, which is drawn through it hy means of a fan G. Motion is given to the whole apparatus by means of a small engine. In this cylinder, the syrup remains for about 20 minutes, and at the end of that time, flows from it at a temperature of about 91°-94° (195°-200° F.), and of such a consistency that it sets quite hard on cooling. By the use of dampers, the hot gases from the flue may be directed either under the boiler, returning through it to the heater, or direct to the heater. At J, is an auxiliary furnace for raising steam, when tho heat from the concretor flue is insufficient or not forthcoMing,—as, for instance, when beginning to crush canes, and before the juice has covered the trays. K is a emoke-door for cleaning out the boiler-tubes. L a chimney, either of brick or iron, for the last escape of tbe gases.
F. J. G. Minchin, of the Aare Sugar Works, Ganjam, Madras, gives the following result of using Fryer's concretor with diffusion-juice. It was in work 2 months, during which period there ran over it 1,030,680 gal. juice, and wero delivered from it 500,225 gal., hence it evaporated 530,455 gal. This gives a daily evaporation of 9557 gal. For this, wood fuel was used at the rate of about 15 tons per diem. The juice ran on at 6°-6i° B. cold, and ran off at 11°-12° B. cold. The concretor was used as an auxiliary to double-effect.
W. F. Ashby has published some statistics of the use of the concretor by the Umhloti Sugar Co., Natal, from which it appears that with the 1876-7 crop, 610,900 gal. of juice gave 507 tons
6 cwt. 3 qrs. 7 lb. of sugar, or 1.86 lb. per gal. of juice ; the 1877-8 crop gave, from 586,300 gal. of juice, 450 tons 15 cwt. 1 qr. 14 lb., or 1.72 lb. per gal. of juice.
B. By Cold.—More than 30 years ago, Kneller proposed to concentrate syrups by forcing cold air through them, and his plan was much improved by Chevallier. Sugar made in Chevallier's apparatus rivalled that of the vacuum-pan in every respect. A vessel holding 200 gal. of syrup (comprised of 3 parts of sugar to 1 of water) is estimated by Wray to turn out 12 tons of sugar daily. The cost of the apparatus is small ; the power required is trifling; ; the ordinary air of the estate could be used at once in dry weather, and would entail an insignificant expense for drying iu damp weather ; and the quality of the sugar is unsurpassed. In 1865, Alvaro Reynoso proposed to rapidly cool the syrup in suitable machines, and thus form a confused mass of particles of frozen water (ice) and dense syrup. The mixture is afterwards separated in centrifugals, and the -syrup deprived of ice is evaporated in vacuo ready for crystallization. It seerns most singular that, in the face of the many drawbacks and great cost incurred by concentration by heat, and in presence of the rnany improvements introduced of late years into refrigerating and cold-producing apparatus (see pp. 1017-20, 1134-42), so little effort is made by sugar-growers to adapt the latter system to their needs. A similar crystalline product, namely common salt (see p. 1718), is obtained by hundreds of tons from sea-water by the effect of natural cold, iu favourable localities ; and there would appear to be no valid reason why a modification of the plan should not succeed on an extensive scale with sugar solutions.