Ou the other hand, the rolls of the mills erected at Aba-el-Wakf, by Eastons and Anderson, in 1872, measured 48 in. diarn. and 5i ft. long, had a, surface-speed of 27-36 ft. a minute, took a feed 15-18 in. deep, and did excellent work. A comparative trial of a small rapid and a large slow mill on the same estate in Porto Rico, under like conditions, is interesting. The rapid mill had rollers 22 in. diam. by 48 in. long, and an average speed of 24 ft. a minute ; the slow rnill had rollers 36 in. diem. by 66 in. long, and an average speed of 9 ft. The rapid mill ground cane in good season, yielding juice of 10° B., and having 10 per cent. of woody fibre ; the slow mill had average good canes, a little over ripe and dry, yielding juice of 11° B., and 11 per cent. of woody fibre. The results were Tho loss in the begass of the rapid mill wae 7.53 per cent ; in that of the slow mill, 2.47, or a difference in favour of the latter of 5.06 per cent.
The De Mornay mill (Fig. 1333) presents various advantages, and will doubtless be more widely adopted in future. In Cuba and Demerara, it is unknown ; but it has been manufactured for S. America by Fawcett, Preston, & Co., and worked there with great sueee.ss. The canes enter between the rolls A B, and are carried onwards by the roll C, inclining upwarde until they are grasped by A D. There is no returner-bar in this mill to cameo abnormal friction and resistance, and no sliding or rubbing of the top roll on a mass of crushed cane. It is stated that this mill, when properly constructed and pro portioned, will grind cane with 50 lb. steam when the ordinary 3-roller mill fitted with a returner-bar requires 65 lb., or the difference between s, 15 and a 20-H.P. engine.
Figs. 1384 and 1335 show cnd and front views of the 3-roller mill made by Manlow, Alliott, Fryer, & Co., of Not tingham and Rouen. The bed and cheeke are entirely of cast iron, carefully proportioned to its work. Strong wrought-iron tie-bolts take the main tensional strains in the mill. The side roll-oaps, while well establiehed when the mill is working, are readily removable, and the rolls can be slid out without any lifting.
Cane-mille have been constructed with 4 and even 9 roll& In the 4-roll mill, where 2 rolls are placed above and two below, the driving-power is said to be not much greater than that required , for an ordinary 3-roll rnill, while more juice is obtained ; but this statement is very doubtful, and is negatived by the fact that 3-roll mills have quite superseded the 4-roll arrangement. In the 5-roll mill, 3 rolls are placed below, and 2 above ; 10 per cent. more juice is said to be extraetedty this plan, but much greater power is needed, and the begass ie much broken up.
Motors.—With regard to the suitability of the several kinds of power for driving cane-mills, it has been ascertained, by comparing the results of 44 mills in Guadeloupe, that :—with windmills of inferior construction, the canc-mills extracted only 50 per cent. of juice ; with ordinary wind mills, 56.4 per cent.; with animal power, 58.5 per cent.; with water power, 59.3 per cent. ; with
steam power, 61.8 per cent.
Figs. 1336 and 1337 show an economical combination of a vertical beam-engine arranged so as to work two large air pumps, and with power enough to work the cane-mill at the same time. This style of engine is applicable when the sugar-factory is organized so as to run day and night, as all should to work profitably. The engine is constantly at work, and its exhaust-steam is as constantly absorbed by the juice. It is evident that by using one large engine in stead of three (one each for the cane mill, the effect, and the strike pans), much loss by friction and expense of attendance are saved. Iu the figure, E represents an en tablature carrying the beam A, mounted by 8 columns on the bed-plate C ; H are two large airpumps in connection with the triple-effect and vacuum-pan ; a mas sive fly-wheel G is necessary to secure regularity of motion.
Fuels and Fur naces.—The use of coal and wood as fuel needs no remark. Whether wisely or not (see p. 1865), begass is largely em ployed for this pur pose. Approximately, 2 lb. of begass equal 1 lb. of coal, or 16 lb. of begass to evaporate 1 gal. of water. So that the refuse of the canes should give fuel sufficient to make the sugar, when the canes are not completely exhausted of the sac,charine juice. Ordinarily the begass requires pre liminary drying by the sun and wind, but furnaces have lately been introduced for burning it in the wet state, as it leaves the mill.
Marie's begass-furnace, made by 1Vlanlove & Co., is shown in Figs. 1338,1339, respectively in section and as attached to a boiler flre-box. The chamber A is constructed of cast-iron plates a stiffened by ribs b, bolted together by flanges, and encased in brickwork. The pyramidal crown B is also of cast-iron plates, bolted upon A, and surmounted by the hopper C, in which the begass is dried, and through which it is fed to the furnace. An inclined balance-door D is placed in the hopper, working on pivots at d, supported in the sides of the hopper, one having a lever-arm e, upon which is an adjustable counterweight f, to regulate the quantity of begass admitted. The fire bars g are incline,d; their lower ends extend through an opening h, and are supported by an inclined bridge i, bolted to extensions k of the side walls of the furnace. The upper part of h is surrounded by a flange /, the dimensions of the flanged opening being varied as circumstances may require. The doors m give access to the furnace. The most exposed parts of the sides a are lined internally with fire-brick, and the walls n are similarly faced. The begass-furnace is shown supported at front on feet o, and at back upon a wrought-iron girder p, whose ends are built into the walls that support the fire-box s of the boile,r. The lower part of the boiler fire-box is completely closed by brickwork r, supported on girders built into the side walls ; the interval between the begass-furnace and the flre-box being also built up, the air to support combustion must come in through the fire-bars g.