The washer, Figs. 1296-7, consists of a perforated shcet-irun cylinder a, revolving on its AXi8 in a tank of water b. In frunt of tho tank, if3 bolted a hopper c, into which the beets full; behind ia a strainer. The cylinder leaves a space of only about in. at each end of the tank, that the roots may not get wedged in. The washed roots are thrown out by a helical grating d placed at the end opposite to the hopper. The rounded bottom of the tank is incliued towards an opening, by which the dirt and rootlots can be discharged. Another form of washer, shown in Fig. 1298, is designed to overcome the disadvantage manifested by the preceding, in requiring frequent stoppages while the water ie being changed. It consists of an archimedean screw working in a trough. The beete are fed in at a, and are carried by the screw against a descending stream of water in the direction indicated by the arrow, escaping at b perfectly clean.
The processes described thus far are of universal application : the stoning and washing of the roots are needful preliminary operations, whatever mode of extracting the juice may be adopted. Here the parallel eutle, and it is necessary to classify the succeeding methods of manipulation. They may bo grouped under the following heads :—(a) Rasping and Pressing, (b) Maceration, (c) Diffusion.
.Rasping and .Pressing.—The principles which govern this process are essentially mechanical. The aim of the operations is to first comminute the root so as to effect the rupture of the greatest possible number of cells, and then to separate the liberated but still absorbed juice from the solid matters by means of pressure, whether of a press or of a centrifugal bydro-extractor.
Raspers.—Machiues for reducing beets to a pulp are of multitudinoui forms, and it would be impracticable to describe all of them. They universally consist of a revolving drum armed with teeth, and differ mainly in having the dentition external in some cases and internal in others. The type of the first class is shown in Fig. 1299. The cylinder a, 24 in. diam., has its surface formed by a series of' saw-hlades (shown full-size in Fig. 1300), separated by wooden washers. The cylinder is divided into 2 or 3 compartments by intermediate false bottoms, and is driven at a speed of 800-1000 rev. a minute. It rotates in front of an inclined table, on which a pusher, placed before each compartment, is driven by an alternating motion, in such a way that each beetroot that falls from the washer is pleased agaiost the teeth, which reduce it to a pulp, more or less fine according to the dimensions, form, number, and wear of the saws.
1298.
The typical representative of the internal systeui of grating is Champonnois' rasper, shown under Starch, p. 1824, Fig. 1284. The beets are introduced by the hopper a, and are forced by the rapid rotation of the fliers b (800-1000 rev. a minute) against the short saw-like teeth of the reapers c. Water is at the same time injected at d. Fast and loose pulleys are shown at e f, and a fiy-wheel is fixed ou the end of the shaft g. The machine is reversed every 6 hours to equalize the wear, still the saws require sharpening after 48 hours' use. The pulp falls into a receptacle beneath.
Presses.—The pulp obtained from the raspers is carried or pumped up from the cistern in which it has collected, to be submitted to expression. e presses used are of two kinds, alternating (including screw and hydraulic) and continuous. For the hydraulic press, the pulp is placed in woollen sacks, containing 10-12 lb., superposed in the press with their mouths doubled under, and separated by iron plates; about 25 are collected, and the pile is put into a screw-press, called a " preparatory " press, which extracts about 45-50 per cent. of the juice. These pressed sacks are piled anew on the movable plate of a powerful hydraulic press, which takes 50 at a charge. Each preparatory press ean supply 4 hydraulic presses, which are ranged around it, so that ot the 4 presses, there will be one charging, one commencing to press, one in full pressure, and one discharging, at the same moment. Motion is communi cated to the 4 hydraulic presses by 4 pumps mounted on the same bed, and tended by the same workman who directs the pressing. An improvement upon the general form of hydraulic press is that devised by Lalouette, which enables 2 workmen and 1 boy to keep 5 presses at work. These presses turn out about 300 cwt. per 24 hours in the first pressing, and 600 in the second.
Hydraulic presses are rapidly falling into disuse in the beet-sugar industry, by reason of the superior merits of continuous presses, and the extended adoption of the diffusion system.
Continuous presses for beet were suggested by the roller-mills used in the oane-sugar industry. But the conditions in the two cases are widely different : the begass of the cane is solid, and readily parts from the juice ; whereas the pulp and juice of the beet have a strong tendency to combine, and the rollor-surface must therefore be permeable only by the juice. In Poizot et Druelle's press, the pulp passes between two cylinders, carried by endless cloths. The object is to unite the best features of the hydraulic press. To this end, a first gentle pressing is produced against the first cylinder by the elasticity of the principal cloth on which it is borne. Then, encountering a series of 4 little rollers, performing the functions of the preparatory press, it is next seized between the second and first cylinders, and deprived of the maximum quantity of juice. The press has been much improved since it first appeared. Manuel et Socin's press, made by Cail et Cie., has an ingenious modification by which the hair-cloth carrying the pulp is kept of a constant width. Each press, worked by one man, will treat the pulp of 1375-1570 cwt. of beet per diem, requiring scarcely 1 H.P. The juice, filtered through the hair-cloth, is free from pulp. The cost of manipulation is about 4d. per ton of root the yield is 26-28 per cent. of pulp. The juice can only be perfectly extracted by a second pressing. To effect this, two first-pressure presses are used for one second pressure. The pulp falls from the first into the trough of a screw, where it is mixed with a large quantity of water. Between the second and third presses, is another screw, which raises the softened pulp to the third press for a second pressing. The whole operation only occupies 25-30 seconds. The juice of the second pressing is used instead of water in the raspers, as the rapidity of the work prevents it undergoing any change, so that the juices are sent to the carbonization stage almost at the degree of density which they possessed while in the root, and the pulp retains but little sugar. Champonnois' press is composed of two permeable rollers partially immersed in a cast-iron tank, forming a watertight joint with their bases and with the portion emerging at the surface. The pulp can only escape between the rollers. A pump conveys the pulp leaving the raspers, and forces it into the tank under a pressure of 1-2 almos. The juice passes out between the rollers, while the exhausted pulp is raked away by No knives, which seize it imme diately at the exit, and falls by its own weight in front of the press, inclined for the purpose at 45°. The cylinders are driven in opposite directions. The filtering surface is formed by spiral windings of a triangular thread, the spaces being determined at 0.004-0.008 in. In this way, is produced a filter-surface having narrow openings on the outside and widening inwards. On leaving the press, the juice is received by a sieve, which prevents the loose pulp from mixing with the juice. The press has been further improved in the hands of Cail et Cie., and is now one of tl.e most perfect and least wetly in the market. Lebde's press is also composed of two filter-cylinders, in appearance somewhat resembling Champonnois', but essentially different in construction. It is formed of a series of portions of filtering surface, screwed on side by side, and enveloping the cylinder ; each portion consists of 10 little strips of copper, curved longitudinally, soldered at tho ends, and separated by intervals of 0'004-0.008 in. This press allows the filter-surface to be changed more easily than in the Champonnois press, without removing the cylinders ; but it is not so simple. Cuvelier's press, constructed by Lobbedez, has been at work for some years at Louez, near Arras, and gives 28-30 per cent. of pulp retaining very little sugar. Pieron's system hes been adopted at the Montigny factory : the preparatory press treats nearly 2000 tons of beetroot per 24 hours; the ordinary first press, nearly 800 tons ; and the second press, over 1500 tons. Sufficient has now been said to illustrate the principles and essential features of continuous presses for separating the juice from the pulp of mashed beets. Examples might be multiplied almost indefinitely.