If slices of beet are placed in a vessel with about the same quantity of woter, the following changes take place. The water forces its way through the cellular membranes into the sugar-cells, displacing a portion of the saccharine solution, which passes out, thereby diminishing the sp. gr. of the juice left in the celLs, and increasing that of the water outside ; this interchange continues till the liquid the vessel has attained tho same sp. gr. as that in the cells : the diffusion is then complete. Supposing the juice in tho cells to be at sp. gr. 1.0435 (equal to 12 per cent. by sacoharometer), and the surrounding water 1•0000, when the diffusion is complete, the water will be sp. gr. 1.0237 (equal to 6 per cent. by saccharometer), and the now diluted juice in the cells the same. Conse quently complete exhaustion can only be accomplished by fractional diffusion, L e. by substituting for the liquid obtained another of less sp. gr., and this replacing of the more saturated liquid by a less saturated one must be continued until the desired degree of exhaustion is reached.
The first step in the process is to cut the roots into thin slices, great im portance attaching t,o their thickness being uniform. Tlie machine in com mon use, invented in 1850 for slicing beets for the hot maceration process, is shown in Fig. 1304. The cleaned roots fall into the hopper b, and encounter a plate a which turns horizontally, and carries 3 series of steel blades arranged at right angles. Tho roots are thus divided into rectangular prisms of varying length, without suffering any crushing or pressuro. The slic,e.s fall into the space c, and escape at d. With H.P., this machine is eaid to slice 100 tons of beet per 24 hours. By using two feed-hoppers, the effect is doubled. For diffusion, the slices aro about iu. thick and T4A; in. wide. The cutting disc is furnished with knife - edges, as shown in Fig. 1305.
In Robert's diffusion process, the ribbon-like slices of beet are con ducted to large closed vessels, mixed with the heated juice from a previous operation, and exhausted with cold water. The diluted juice is first heated to 75°-90° (167°-194° F.), so that the mixture assumes a mean tempe rature of 50° (122° F.), which is considered essential to success. Displacement of the Juice is performed by a flow of cold water throughout the whole battery (of 5 to 8 vessels), arranged as in Figs. 1306 and 1307. The cylinders are furnished at ton with manholes c for the introduction of the slices. Near the bottom, a hinged door f permits the exhausted slices to fall upon an endless web, which conveys them away. In the interior of the cylinder, is a case c pierced with boles, which prevents the pipes being obstructed by solid particles. The pipes a e put the vessels into com munication with the reheating boilers, while the conduits e g and c maintain the circulation in the various cylinders of the battery. The steam pipe furnished with a clack serves for the in troduction of stean3 to the several vessels. Pipes d
bring the water necessary to the operation, while the rich liquor passes away by f to the defecating boilers.
Each vessel receives 21 tons of slices, occupy ing a space of about 132 cub. ft. The vessels are not filled until the juice or the diffusion-water, as the case may be, has a temperature of 87°-97° (189° - 207° F.). The vessel is A filled with this hot liquid, and then the slices are fed in through e from trucks bolding about ton. On emptying the fourth truck, the reheated juice is allowed to run in at top, so that when the charging of the slices is completed, the vessel is full of juice. The proportions of juice and pulp entering the vessel should be carefully adjusted. Whilst charging, it is well to mix up the juice and pulp so that no part shall be left imperfectly exhausted, and the liquids shall have uniform circulation. As the contents of 6 or 7 trucks are needed to fill the vessel, and as the discharging of each occupies about 4 minutes, the whole charging requires nearly half an hour. The vessel once full, the cover e is closed, and the matters are left for about 20 rainutes. At this moment, the pressure of the colorful of water from the tanks above the factory is brought to bear upon the nearly exhausted pulp in the last vessel. As this vessel communicates with the 7 others forming the battery, the pressure can be conveyed to them all; the juice is thus displaced from the cylinder filled with fresh pulp, and proceeds while still hot to the defecating-boilers. In practice, eaoh vessel furnishes two full boilers of juice, varying ih density according to the duration and the number of vessels (5, 7, and even 10). Generally, the density fluctuates between 4° and 7° B., so that the juice is mixed with about 40 per cent. of water on the weight of beet.
The estimated cost of establishing a factory on the diffusion system to work 50 tons a day, according to Walkhoff, is :-1 slicing-machine, 144/. ; 10 cast-iron diffusors, weighing 1 ton each, 288/. ; 50 cast-iron valves, 180/. ; 20 traps, 52/. ; 30 elbow-pipes, 13/. ; 15 straight pipes, 22/. ; 600 screws, &c., 14/. ; 3 trucks, weighing 6 cwt., 50/. ; total, 763/. The oost of extracting 100 parts of juice may be calculated thus ;-6000 tons of beetroot, 5760/. ; transport and cleaning, 161/. ; interest and insurance at 10 per cent., 76/. ; 15 workmen per shift, or 30 per diem, 173/. ; removal of the residues (60 to 70 per cent. of the weight of beet), 4 workmen, 46/. ; repairs, sharpening knives, &c., 58/. ; residue-press, interest, repairs, &c., 50/. ; fuel for 8-H.P. steam-engine, 88 tons of coal, 127/. ; evaporation of 40 per cent. of water, requiring 480 tons of coal, 691/. ; total, 7142/. The product is 90 per cent. of juice at the initial density, or, on 6000 tons of root, 5400 tons of juice. The juice, therefore, costs about 26s. 5id. a ton ; thus diffusion presents no advautage in this respect over the beat systems of maceration.