The mills now in general use for squeezing the juice out of the sugar-canes are very powerful machines. Some idea of the strength of those mills will be formed from the fact, that one of the rollers weighs upward of 5 tons. The axles are 12 in. in di ameter, and notwithstanding that they are made of the best wrought iron, they are not secure against breakage. The manufacture of sugar has probably been carried to greater perfection in the islands of Java, Mauritius, and Cuba, than in any other parts of the world. In Java especially, in consequence of the great extent of the plantations, the planters have been able to erect very complete establishments for the manufacture of sugar.
The following very condensed account of the process of making sugar in Java will give some idea of the operation.
The canes, freed from all loose leaves, are passed through between the rollers under the greatest possible pressure that can be brought to bear upon them. The rollers re volve only from two to four times per minute. From 100 lbs. of canes, 65 to 75 lbs. of cane-juice will be expressed. This juice, which is of a sweetish taste, and of the color of dirty water, passes direct from the mill to a small reservoir, where it usually receives s small dose of quicklime, and without delay runs off to large iron or copper vessels, heated either by a fire underneath or by steam-pipes in the liquid. As the temperature of the juice rises, a thick scum comes to the top, which is either removed by skimming, or the warm juice is drawn off from below the scum. The concentration of the juice is partly effected in a series of large open hemispherical iron pans about six to eight ft. diameter, of which five or six are placed in a row, with a large fire under the one at the end. This one fire, which runs along under the whole row of pans, is found sufficient to make two or three of them nearest the fire boil violently, and in addition, it warms the juice in the pans furthest from the fire. As the juice firsts enters the pans furthest from the fire, it gets gradually heated, and the vegetable impurities rise in scum to the top, and are carefully removed. As the juice is ladled from one pan to the next, it boils with greater and greater vigor as it approaches nearer the fire, until in the pan immediately over the fire it seethes and foams with excessive violence; and this seems to be essential to the successful making of sugar. It is known that the presence of all
those impurities which constitute the scum interferes with the crystallizing of the sugar; and the rapid ascent of bubbles of steam through the liquid in the pans carries all im purities dispersed through the body of the liquid to the top, where they can be removed with facility. It is well known that great heat is very destructive to cane-juice; that is to say, it turns much of the crystallizable sugar into treacle or uncrystallizabie sugar, but the gain arising from getting rid of much of the impurity in the cane-juice more than compensates for the destruction of part of the sugar. After the concentration has been carried to a given point, and all the scum has been got rid of, the application of a high heat, which would act with an increasingly destructive effect as the condensation became greater, is suspended, and the liquor, now of the color of turbid port wine, and of the consistency of oil, is drawn into the vacuum-pan, where the concentration is completed at the lowest possible temperature, generally about 150° Fehr. The vacuum-pau is in universal use in all European sugar-refineries, and in all well-provided sugar-plantations. It is generally made of copper, of a spherical form, and from six to nine feet diameter. The bottom is double, leaving a space of an inch or two for the admission of steam be tween the two bottoms, and there is generally a long coiled copper pipe of three or four inches diameter above the inner bottom, so as to still further increase the amount of heating surface. This apparatus is made perfectly air and steam tight. Leading from its upper dome, there is a large pipe, communicating with a condenser into which a rush of cold water is continually passing, so as to condense all the steam or vapor that arises from the liquid boiling in the vacuum-pan. The water which is constantly rushing into the condenser is as steadily withdrawn again by pump. There is thus a constant vacuum in the pan, and, consequently, the liquid in it will boil at a much lower temperature than it would in an open pan or boiler. There is an extraordinary advantage in being able to effect the latter stages of concentration at a low temperature, for it is when the liquid becomes thick that the destructive results of a high temperature become most excessive.