If the evaporating plant breaks down, there is danger of losing juice through fermentation. This is prevented by the use of antiseptics, such as formaldehyde.
Concentcation.—The juice is concentrated in a series of evaporating pans enclosed separately in vacuums of varying degrees, that of the first pan (6-inch vacuum) being less than that of the second (15-inch vacuum), and that of the third being nearly the highest that can be practically main tained by large pumping machinery (26- to 28-inch vacuum). These pans are raised on a high plat form so that the later operations may take advan tage of the force of gravity. The product of the evaporating process, known as massecuite, is a thick, grainy mass composed of crystallized sugar and molasses.
Crystallization.—The operation of converting the sucrose into the crystalline form in which it is sold, under the name of sugar, is carried out in what is known as the vacuum pan, a cast-iron cylinder with a conical bottom and domed top, the bottom containing the pan and its coils of steam pipe for heating the syrup and apparatus for keep ing the boiling mass in motion, and the top being supplied with large delivery pipes for the vapors which must move off slowly so as to prevent syrup entrainment. The highest possible vacuum must be available in the pan, and it must be under complete control, so that the temperature of the boiling can be promptly altered as required during the crystal lization of the sugar. This latter operation follows the known laws of crystallization, in that the pres ence of crystals in a crystallizable syrup has much to do with the formation of new ones, and in that the presence in a syrup of a multitude of minute crystals determines the accretion of further sugar on these crystals as a base. As the syrup ap proaches the necessary consistency, small samples are drawn off and tested for physical properties,— grain, consistency and the like. The approach of the boiling mass to this point is controlled by varying the vacuum and temperature, and by add ing more syrup, this latter being derived from the molasses. At the proper moment the "boiling" is "struck"; that is, the massecuite is delivered from the bottom of the pan through a valve at as low a temperature as possible, part, however, being left in the pan as a basis for the next boiling. Through
out all the apparatus for concentrating and crystallizing the syrup, are placed vacuum gages and temperature gages, and strongly glazed peek holes are provided for viewing the different pro cesses.
The proper manipulation of the vacuum pan determines not only how much sugar is secured by the centrifugals from the massecuite, but the ease with which it may be done. Improperly grained sugar may be difficult or even impossible of sepa ration in the centrifugals. The amount of sugar that crystallizes out, and the rapidity of the crys tallization, depend also on temperature and the perfection of the purification of the juice. Gummy matters not removed from the juice, for example, may delay or prevent crystallization of part of the sucrose. The massecuite may contain as low as 5 per cent of water. The cooled massecuite is dried in centrifugal machines about thirty inches in diameter, run at the rate of 800 to 1,300 revolu tions per minute, 1,000 being standard for thirty inch machines. The sugar passes down from the centrifugals as "first" sugar and, after weighing, is at once bagged.
Bagging.—For this operation the sugar is some times elevated again and spouted on to more or less automatic weighing machines. The bags into which it is spouted are sewed by machinery, being carried in succession on a horizontal carrier so that the free upper ends pass a horizontally-acting sewing machine needle.
Molasses.—The molasses extracted by the cen trifugals is cooled 'and allowed to stand days, weeks or even months, the result being that a further amount of sugar crystallizes out, yielding "second" and even " third " sugars. According to the com pleteness of the crystallizing, the molasses is rich or poor in saccharine substance. With the best work so little utilizable saccharine matter remains that the molasses is thrown away, or at best is used for fertilizer because of the mineral matter it contains in solution. Where the crystallization is imperfect, molasses of commercial value is a sec ondary product and may be marketed as such, or be converted into rum or alcohol. With the reduc tion of the duty on denatured alcohol, recently enacted by Congress, more attention is being given to the manufacture of such alcohol from the poorer grades of molasses.