The filter.—The filter presses consist of a series of iron frames, every alternate one of which is hollow. The solid frames are covered with heavy duck cloth, which allows the juice to pass through but prevents the passage of the heavy deposit formed in the tanks. This deposit is called lime cake and is an excellent material for fertilizing the farm lands. After the presses have been filled with lime-cake, they are washed, emptied of the cake and made ready for filtering more juice. The presses are screwed together under great pres sure in order to prevent the possibility of any loss due to leaky joints in the press.
Second carbonatation.—From the presses of the first carbonatation the juice passes to the second carbonatation station to be treated as before, with the exception that only a small quantity of lime is added and the time of carbonatation is not so long. The action of the lime and the introduction of the gas at this station produce a clear liquid of bright amber color which filters with more ease than at the first station, and is then ready for the treat ment with sulfur gas. As the juice ]eaves the first presses it has a high alkalinity, which must be reduced before it is ready for boiling. The greatest epurating action has been found to be after the lime has been added twice to the juice and the juice carbonated after each addition. Usually .25 per cent to .50 per cent of lime is used in the second carbonatation.
In all operations in the process of making the sugar the juices must be kept hot and at specified temperatures. The cake formed at the second presses is softer, whiter and more chalky than that of the first presses, hut at the same time it is inferior for agricultural purposes.
Sulfuring.— Leaving the second presses, the juices are pumped to •the sulfur station to be further treated before the first evaporation. Here the juices are brought into contact with the gas secured by passing air over burning sulfur. This gas is carried into the tanks in the same way as in the tanks of the first and second stations. The action of this gas on the coloring substances that are in the beet juices varies, destroying only in part the coloring matter present. While sulfuring has hardly any effect on the purity of the juices, it gives a sparkle and has a brightening influence, and causes the juices to crystallize better. It is also important to note that the sulfurous acid decom poses the organic lime salts, while the carbonic acid does not.
Evaporating.— After sulfuring, the juices are filtered through special filter presses, or mechanical filters, and are then ready for the evaporators, in which they are boiled under a vacuum in order to concentrate them without the danger of destroying the sugar. About 80 per cent of the water in the original juice is taken out in the evaporators. The "effects," as they are called, are built in a series, usually four in number, and so connected with a vacuum pump that the heat of the first effect, where the juice boils at the ordinary temperature, causes the juice in the second to boil, but under a vacuum ; the second heats the third, the third heats the fourth. The following table will illustrate this :
Having reached the density of about 32° Baume, the juice in the fourth effect is pumped to the sulfur station for further treatment. The sulfuring of the "thick juice" takes place as with the thin juice. Having been reduced to the required alka linity, the thick juice is then ready for filtration and boiling in the pan.
Securing the inassecuitc.—The pan is a large tank built of cast iron, fourteen feet in diameter and fifteen feet high on the average. It is connected with a vacuum pump in order that the boiling of the juices may take place at low temperatures without the danger of destroying the sugar. As long as the juices have been treated properly in the first part of the process, there will be no trouble in producing a good grade of sugar in the pan. In order to get a high-purity massecuite from the first pan, it is necessary to have juices of high purity to start with. The massecuite is a mixture of sugar crystals, which are formed in the process of boiling, and sirup from which all of the sugar has not been crystallized. This mixture of sugar crystals and sirup secured from the first pan is run through the centrifugal machines, revolving at the rate of 1,200 revolutions per minute. The sirup is thrown out through the fine perforations in the walls of the machine and carried into tanks used only for col lecting this product. In the bottom of the centrif ugal machine is a covered opening through which the sugar is dropped into a scroll that carries it up to the sugar box, from whence it is passed through the drier before it is put in the sacks for the market.
The sirup is then sent to the pan floor to be boiled in the second pan, in order that it may be further concentrated and more sugar secured. When of the necessary density, it is run into large tanks and allowed to remain until all the sugar possible has been crystallized. This is the second massecuite, and the sugar from it is used to get a higher grade of sirup from which to produce a high grade of white sugar.
Treating the molasses.—The molasses from this is treated in various ways to get all the sugar pos sible, either by the "osomose process" or by the "Steffens process." The osmose consists of a series of frames separated by parchment paper ; the hot molasses passes through the press on one side of the paper and the hot water on the other side. The principle employed is the same as that of the diffu sion battery, with this exception, that in this case the impurities, or salts as they are called, are dis solved instead of the sugar. In the Steffens process, the molasses is treated with powdered lime, and the sugar forming a combination with the lime in the cold is separated from the mother liquor by means of presses, and is then diluted to a certain density; it is run into the juice of the first carbonatation and the combination of lime and sugar is broken up, setting the sugar free while the insoluble lime carbonate is formed as the lime-cake.
This, in general, is the process by which the sugar in the sugar-beet is converted into the gran ulated sugar used on our tables.