EXTRACTION OF CANE-J1710E.—The juice in the cane exists in the plant enclosed in little cells, which are surrounded and protected by lig,nose (woody matter), the latter forming about of the total weight of the cane. The liberation of the juice may be effected (1) by rupturing these cells, so that their contents flow out ; (2) by combining the crushing process with maceration in water ; (3) by utilizing the membrane of the cells as a means of allowing the escape of the sugar and other " salts" in solution, by the process known as " diffusion." Cana-mills.—An account of all the introduced or proposed forms of mill for crushing sugar-cane would fill a large volume. Practical ends will be served by deecribing the typical forms.
Rousselot's 3-roller mill, as made by Fawcett, Preston, & Co., is shown in Figs. 1330-1332. The bed-plate D is seated on a strong timber framework, through which the large bolts I (Fig. 1330) pass, allowing the top roll to lift a little when any extraordinary strain occurs. The canes pass by the carrier H (Fig. 1331) down the elide E, through the rolls, and the beg,ass emerging at D is taken away by a carrier worked by the drum I. The ordinary frame of cast iron is not exposed to tension. The resistance of the CaDeS between the rolls A B C is taken from the top roll A through the cap and bolts, and compresses the frame, while the tendency to separate the bottom rolls is controlled by the horizontal tie-bolts; for all practical purposes, the frame might be made of oak instead of iron, as the working strains are thrown upon the wrought iron, instead of being borne by cast irou, as in other mills. The 3 cast-iron rollers are keyed on to the wrought iron shaft& The " returner-bar," or " knife," or " trash-turner," as it is variously denominated, is a flat or curved plate, placed at a distance of 21-3 in. below the bottom of the top roll, made to touch the circumference of the front roll, and to stand off about in. from the lower back roll, so as to allow the juice to run down. The mill shown in Fig. 1332 is composed of two cast-iron frames d, secured to the bed-plate e hy bolts at the four corners. Seats are prepared on the frames d for carrying the brasses for the shafts of the rolls a b e. The bolts i j pass through the frames and bed-plate and through the timber k, and take the strain of the top roll, and the bolts h, of which there aro 4 for each frame, take the strain on the caps g f. In this manner, the strain is borne
by the wrought-iron bolts instead of being thrown on the east-iron frames, enabling more juice to be extracted with safety than can be done with the ordinary cast-iron frame. The yield of sugar from the cane crushed in this mill at the central factory in St. Lucia, during the season ending in May 1881, is stated at 8 per cent. of the weight of the cane ; the cane there seldom gives juice of 10° B., yet by the careful use of a Rousselut mill and the necessary adjuncts, with a very limited consumption of animal black, 10,000 tons of cane give"800 tons of sugar of superior quality, averaging in London 25/. a ton, Formerly the returner-bars were much slighter than those ordered and supplied at present. When canes are passed through a mill without choking, everything. works smoothly ; but from the moment that a cane doubles up, trouble begins. The rolling friction of the mill is a light matter ; but the sliding friction in the confined space between the top roll, the front roll, the returner-bar, and the back roll, is very great. If the returner-bars aro slight, they bend by the pressure, and the jaw is relieved. The bar is taken out and straightened, and work is resumed. A pressure of 50 lb. a sq. in. drives the mill when there is no jamming ; but 80 lb. is required when it is "braked" by accumulation of trash between the rolls and the returner-plate ; orders are daily given for stronger returner-bars, so that where the massive rolls are " braked " with trash, that becomes hot and hard with friction, the resistance has to be overcome, and returner-bars are made to resist the force of a 60-H.P. engine, geared 20 to 1, and making 40 rev. Many engineers con tend that those who are trying to increase the yield in juice by very slow movement are in error, and recommend experimimt in the direction of lighter and repeated crushings, combined with maceration. By using two Dallis of moderate proportions, more effective work is said to be obtained, because there is less sliding friction ; and it is questioned whether the extra quantity of juice obtained by the extra force of a large mill is not at the expense of the quality.