SUGAR-CANE 



SUGAR-CANE 



60d 



possible excess may be saved to supply any defi- 

 ciency that may occur when richer cane is being 

 crushed. The average amount of bagasse produced 

 furnishes sufficient fuel to keep up steam for the 

 mill. With rich cane there may be a deficiency of 

 bagasse, which compels the use of some other kind 

 of fuel. 



Purifying the juice. — The mixed juices are 

 strained and then heated by being passed at once 

 through a super-heated steam heater, with the 

 result that some of the coagulable matter is thus 

 coagulated and the remainder rendered more 

 susceptible to purification by the addition of freshly 

 slaked lime, which constitutes the next operation. 

 The lime-water is added in measured quantities, 

 according to the composition of the juice, and at a 

 temperature of nearly 212°, this being the temper- 

 ature at which the maximum purification is 

 secured. The impurities settle rapidly, or rise as a 

 scum or "blanket," and the juice, often further 

 purified by boiling or skimming, is drawn off 

 into the evaporating pans. The blanket and pre- 

 cipitate go to the filter presses, where the re- 

 maining juice is pressed out through a long 

 series of cloth filters. Each element of the filter 

 press is a metal frame with its accompanying 

 cloth filter. The pressure is applied to the whole 

 series at once, usually by means of screws. The 

 filtered juice goes to the evaporators. The resulting 

 filtrate, known as press-cake, is used to form 

 fertilizer for the cane-fields. It is rich in lime and 

 nitrogen. 



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. 



Concentration. — 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- 



B39 



ence of crystals in a crystallizable syrup has much 

 to do with the formation of new ones, and in that 

 the presence in ,'i 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 ofl: 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 soriie- 

 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. 



