six feet long encased in strong, coarse-meshed hempen sheaths. A single filter box may contain 400 or more of these bags, each attached to the filter head by means of a metal bell and socket.

An alternative method is to mix the liquid with diatomaceous. or infusorial earth ("kieselguhr," "celite ") and then filter by means of a filter press, usually of the "shell plate" type.

The filtrate from the bags is clear but not colorless. Most of the color is removed from this filtrate by passing it through boneblack filters. These are large, strong iron cylinders, often 10 feet in diameter and 20 to 30 feet high, filled with boneblack through which the sugar solution flows very slowly, usually at about the rate of one foot per hour. On account of the immense amounts of boneblack required in a modern refinery, this part of the process requires very careful control in order to use the boneblack or "char" as economically as possible. Freshly charred boneblack removes the color from the sugar solution almost completely, but with accumulation of impurities in the pores of the char it naturally becomes less effective until finally the filtrate shows so much color that it must be re-treated and the boneblack must be washed and sent to the "char house for reburning. Every reburning or "revivifying" leaves the pores of the boneblack somewhat clogged by the added carbon from the absorbed impurities, so that after 10 or 12 reburnings it is no longer economical to use. In the Weinrich oxidizing revivifier the reburning is carried out with a limited supply of air designed to burn out the carbon of the impurities but not that of the original char, and thus to prolong the usefulness of the boneblack.

The sugar solution which has passed the boneblack filter, and is both clear and practically colorless, is evaporated in vacuum pans of 1000 to 2000 cubic feet capacity, wherein the sugar solution is "boiled to grain" and concentrated to a low water content. In order to accomplish this satisfactorily a vacuum is first created in the pan, some sugar solution admitted, and

steam then passed through the heating coils and the solution concentrated until supersaturated. The exact point to which the concentration should be carried is determined by an experienced workman, who withdraws samples from the pan by means of a "proof stick," which is a long brass rod sliding through an air-tight fitting in the side of the pan and carrying a cup-like depression by means of which a small sample of the liquid in the pan can be removed without disturbing the vacuum. The test portion thus withdrawn from the pan is examined by drawing between the thumb and finger, and when the exact degree of viscosity necessary to insure the immediate production of "grain" is found, more of the sugar solution is admitted to the pan, thus chilling its contents and starting the crystallization, which is then continued as in the corresponding operation of raw sugar production described above, until the pan is charged with a magma of crystals and mother liquor, which is then dropped into the mixer on the floor below.

In the mixer or crystallizer the mass is thoroughly stirred while cooling and is then allowed to fall into the centrifugals, where the mother liquor, usually known as refinery sirup rather than molasses, is thrown out through the perforated walls of the rotating drum, leaving the mass of crystals, which is sprayed lightly with water for the further removal of the sirup, and usually with a solution of ultramarine or "permitted" blue dyestuff in order to offset the tendency toward a slightly yellowish color due to the very minute trace of mother liquor which still adheres to the crystals.

The washed sugar from the centrifugals is either barreled directly as "confectioner's sugar," pressed into cubical or domino form, or sent to the granulator to be made into the ordinary granulated sugar of commerce.

The granulator is a long inclined revolving cylinder heated by a current of hot air and provided with paddles to keep the

sugar stirred and screens to separate the crystals into standard sizes. After granulation and sifting the sugar is barreled and sent into commerce.

The Beet Sugar Industry

About the middle of the eighteenth century Margraf succeeded in separating about 6 per cent of sugar from beets, and later (1769) Archard in Austria established the first beet sugar factory; but the beet sugar industry first became of commercial importance when the European supply of imported sugar was shut off by the blockade established during the Napoleonic war. The industry is commonly considered as dating from about 1810.

At about this same time the polariscope was developed into a practicable apparatus for determining sugar, and it became possible to test individual sugar beets, and plant for seed the ones of highest sugar content. By breeding systematically with constant chemical control the average sugar content of the beet has been more than doubled, beets showing 16 to 18 per cent of sugar being now not uncommon, while in some cases from 20 to 24 per cent of sugar has been found. The sugar beet thrives in temperate climates. For the year 1912-1913 the countries showing largest production of sugar from beets were (in order): (1) Germany, (2) Austria, (3) Russia, (4) France, (5) the United States.

The

Beets of medium size are usually of better quality than large ones. The average composition of the sugar beet and its juice is given by Browne as follows (Table 61).

It will be noted that there is more water and less fiber in the sugar beet than in the sugar cane; there is also more ash (or salts) and more nitrogenous matter, but much less invert sugar, in the beet than in the cane. These differences in composition have an important bearing upon the differences in process of manufacture.

TABLE 61. COMPOSITION OF SUGAR BEET AND ITS JUICE (BROWNE)

The beets, after they are dug and have had their green tops removed, are hauled to the factory; they are first washed to remove adhering dirt and then passed over knives, which reduce them to fine slicings or chips.

The fine slicings are next carried by a conveyor to the diffusion battery, which consists of a series of tall, boiler-shaped cylinders called cells. These cells are connected by pipes, the outlet from the top of one cell passing downward into the bottom of the next and so on around. Each cell is filled with beet slicings through a manhole at the top and when full is tightly closed with a cover which is clamped into place. Twelve cells connected in series usually constitute a battery, and when they are filled, warm water of about 80° C. is passed through the system. The water circulating upwards through each cell removes the sugar from the beet slicings and becomes richer and richer in sugar with each succeeding cell. Heaters are placed between the cells, so that the circulating water is kept always at the right temperature. When the water has made a complete circuit through the cells of the battery, the slicings in the first cell are practically exhausted; this cell is then thrown out of circulation, emptied of exhausted chips, refilled with fresh slicings, and reconnected with the system, while the second cell under

goes replenishing. The process is thus a continuous one; IO cells are always in circulation, while one is always being emptied and one always being refilled.

The exhausted slicings from the diffusion cells are dried by the heat of the flue gases from the boilers and are then sold as a cattle food.

The diffusion juice as it leaves the last cell of the battery contains from 12 to 15 per cent sugar and is ready for clarification. The juice is first treated with a considerable excess of lime, and the dissolved lime precipitated by leading in a stream of carbon dioxide. This process is called "carbonatation."

After the first treatment with lime and carbon dioxide the precipitated calcium carbonate and other impurities are filtered off in filter presses and the juice subjected to a second carbonatation.

The juice from the second carbonatation is again filtered, when it is evaporated, grained, and centrifugaled, these processes being carried out essentially as described for cane juice.

There is a great difference in the physical properties of raw cane sugar and raw beet sugar. Raw cane sugar has usually a fragrant odor and a pleasant taste which many prefer to the refined product, while raw beet sugar has a bitter and nauseating taste and an odor suggestive of glue.

In this country beet sugar is usually refined in the same factories in which it is extracted from the beets.

The question is frequently raised whether cane and beet sugars are strictly identical. The answer depends upon the way in which the question is understood. The sugar in each case is sucrose, and if this were rendered absolutely pure, it would be the same whether derived from beet or cane. But absolute purity is not quite attained in the refining process. According to Prinsen-Geerlings, "All white cane sugars contain traces of reducing sugars," while beet sugars do not. This may result in a difference in the products obtained from cane versus beet sugars in making, for example, some kinds of confectionery.