The use of force-pumps of ordinary construction for raising cane-juice and syrups is to be condemned on the grounds of their limited capacity, the churning of the liquid and consequent admixture of air, and contamination of the liquid by the grease used in their lubrication. Hence the general adoption of the monts-jus ("juice-raiser"), one of whose many forms is illustrated in Fig. 62. The body of it consists of 2 chambers a b, separated by a steam-tight diaphragm; the upper chamber a receives the syrup to be elevated while the charge in the lower chamber 4 is in course of elevation, and it is made of suitable capacity for that purpose. When the lower chamber 6 is empty, the valve c is raised by turning the handle d, while the top of the air-pipe e is opened. The syrup contained in the upper chamber a immediately descends through the valve a, 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, of course, stopped as soon as the syrup 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 syrup into the lower chamber b. The air-tap is then closed, and the steam-tap f of the steam-pipe g, communicating with a steam boiler, is opened, when the empty space between the surface of the syrup and the top of the lower chamber b is immediately filled with steam, which at once commences to drive the syrup out through the discharge-pipe A. As this pipe is carried down to within a short distance of the bottom of the monte-jus, nearly the whole of the contained syrup is forced out of the lower chamber 6. As soon as any indications of steam appear at the mouth of the discharge-pipe, the steam-tap / 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 syrup is running, in time. If the syrup be allowed to reach the top plate of the chamber 6, the steam, when let in through the pipe g, will mix with and boil the syrup, but will not elevate it; considerable difficulty and delay sometimes arise from this circumstance. As a precaution against carelessness, an overflow tap i should be fitted to the shell of 6, a few inches below the top, so that the superabundant syrup might be drawn off. In the case of cane-juice, as it comes from the monte-jus, it is said to be sufficiently warmed to retard fermentation on its way to the clari-fiers.
While this instrument remains by, far the most generally adopted means of raising juices and syrups, its superiority has not been unchallenged. 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 juices by the presence of accumulated dirt within the monte-jus. It is also urged that the liquor is diluted by the admixture 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 or other mechanism to become a refuge for dirt; no air or steam is forced into the liquor; and, with properly adjusted arms, the juice or syrup 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 beat central sugar factories, steam in the monte-jus is replaced by air under a pressure of SO lb. per sq. in., thus obviating moat of the drawbacks that have been complained of.