The normal condition of the battery in regular working order is :— The density of diffusion-juice in practical working is B. less than that of the raw juice, which gives au excess of mater to be evaporated amounting to 16-20 per cent. ; this entails an additional expense of about 8id. on every 1000 lb. of cane, estimating wood at 12s. 6d. a cord (8 ft. X 4 ft. x 4 ft., about tou), and coal at 3s. lid. a bar. (200 lb.).
The comparative characters of mill- and diffusion-juice are stated thus :— Diffusion ordinarily extracts nearly 83 per cent. of the juice, leaving 17 per cent. in the chips and refuse water. More can be obtained by continuing the process, but there is a point beyond which it does not pay to go, because, by drawing off more, less cane is worked up, and the greater amount of fuel required to evaporate the extra water is not paid for by the additional sugar. The 83 per cent. of juice sent to the clarifiers gives :— The loss by clarification, skimmings, and sediments amounts to about 6 per cent. on the juice, or 4.98 on the cane ; therefore the juice really obtained in green sugar is 78 per cent. of that pre sent in the cane. Of this,— The water required to work the diffusion apparatus is about one ton to every ton of cane ; it is important to have pure water, as it has a great influence on the quality of the juice. Water containing organic impurities in partial decomposition would add to the juice similar elements of fermentation to those which the process aims at leaving in the cells of the cane. About 6-7 per oent. of the water is saved, if, instead of emptying the water from the vessel containing exhausted chips, it is forced into the next. A peculiar difference exists between mill-juice and diffusion-juice, iu that the latter requires longer to crystallize when brought to syrup. BeAdes this, by the continued application of high temperature, part of the crystallizable sugar is inverted, as proved by the excess of molasses. In the matter of rapidity of crystallization, diffusion-juice apparently labours under a disadvantage as compared with mill-juice ; hut this is obviated by supplying more receivers for the syrups, anti by heating " cooling-room." The begass forms an excellent material for paper-making. The chic!' drawback to diffusion is the large quantity of water required, which, though much of it cau be utilized for condensing purposes, represents a proportionate extra evaporation and extra cistern space ; but under favourable circumstances, the larger yield of sugar more than compensates for the extra cost.
The Robert process is in use at the Asko. works, Ganjam, Madras, where the sugars made by it analyze :— The system has been quite abandoned in Louisiana, after prolonged trial.
Pumps and lionts-jus.—As the apparatus by which the juice is extracted from the cane is generally situated on the ground floors of the building where the operations are conducted, it becomes necessary to adopt means for raising the juice into the vessels where it is to undergo purification and concentration. This is not the case in Louisiana, where the mill is usually placed at sufficient height to permit the juice to descend by its own gravity throughout the operations. Force-pumps, worked from the mill, possess many disadvantages, including limited capacity, churning of the liquid and consequent admixture of air, and contamination of the liquid with the grease used in their lubrication. They soon gave place to the monte-jus (" juice-raiser "), copied from
the French. This is made in many different forms, one of which is shown in Fig. 1353. Its body consists of two chambers a b, separated by a steam-tight diaphragm ; the upper chamber a receives the juice to be elevated while the charge in the lower chamber b is in course of elevation. When the lower chamber b is empty, the valve c is raised by turning the handle d, while the tap of the air pipe e is opened. The juice contained in the upper chamber a immediately descends through the valve c, any air that may have been imprisoned in the chamber b escaping through the air-pipe e. This air-pipe extends about 6 in. into the lower chamber b, for the purpose of ascertaining when the chamber is sufficiently full, the escape of air through the pipe e being stopped as soon as the juice reaches its lower end. The cessation of the whistling noise made by the air rushing through the end of this pipe e constitutes the signal for screwing down the valve c, to prevent any further flow of juice into the lower chamber b. The air-tap is then closed, and the steam-tap f of the steam-pipe 9, communicating with the boilers, is opened, when the empty space between the surface of the juice and the top of the lower chamber b fills with steam, which drives the juice out through the discharge-pipe h. As this pipe is carried down to within a short distance of the bottom of the monte-jus, nearly the whole of the contained liquor is forced out of the lower chamber b. As soon as any indications of steam appear at the mouth of the discharge-pipe, the steam-tap f is shut, and the valve c and air-tap e are opened to let in a fresh charge. It will thus be seen that the action of the monte-jus is exceedingly simple, only one precaution being necessary, viz. to shut the valve c, through which the juice is running, in time. If the juice be allowed to reach the top plate of the chamber b, the steam, when let in through the pipe g, will mix with and boil the juice, but will not elevate it ; considerable difficulty and delay sometimes arise from this circumstance. As a precau tion against carelessness, an overflow-tap should be fitted to the shell of b, u. few inches below the top, so that the super abundant juice might be drawn off. The juice, as it comes from the monte-jus, is sufficiently warmed to retard fermentation on its way to the clarifiers.
While this instrument remains by far the most generally adopted means of raising juice, it has been objected that its interior is not readily accessible, and that it is therefore difficult to keep clean, whereby fermentation may be caused in the juice. It is also urged that the liquor is diluted by the admix ture of condensed steam. Hence, in many cases, the monte-jus has been replaced by centrifugal pumps. In favour of these, it is advanced that there are no valves nor other mechanism to become a refuge for dirt, no air nor steam is forced into the liquor, and, with properly adjusted arms, the juice is raised in a solid column without churning. Many statements, however, point to the fact that the churning is often seriously -worse than with the monte-jus. In the best central factories, steam in the monte-jus is feplaced by air under a pressure of 60 lb. a sq. in., thus obviating most of its drawbacks.