Machine loaders are coming into use for trans ferring the bundles of cane from the primary car riers to those on the permanent ways. Chains or wire cords of the requisite length are provided, and these are fastened about the bundles of cane as they are assembled on the primary carriers. When these latter reach the permanent-way car riers, mechanical loaders attach their tackle to the bundles and lift them to the trucks, trolleys, or punts, as the case may be. These loaders are usu ally portable derricks. Where plantation railways are in use, they often have portable derricks attached to trucks. These are run on to sidings and from thence the trucks of the main train are loaded in succession. Naturally, all the mechanical contrivances are in use just in proportion to the price of efficient labor. Where labor is high they are in more common use than where it is cheap. In some countries that produce much sugar the modern labor-saving machines and implements are almost unknown. That they will be further per fected and come into wider use is certain.
There are more patterns of unloaders than of loaders, as might be expected from the fact that the problem is simpler. One of the commonest unloaders is a series of sprocket chains arranged on a frame and carrying at intervals perpendicular steel fingers a foot in length. The moving chains are lowered over the truck of cane and the motion of the steel fingers slides the cane off on to the mill carriers. As these fingers can be raised or lowered at will, the cane can be unloaded to accommodate the speed of the crushers. Another unloader consists of a fif teen-foot mechanical finger with a universal move ment. The end is forked and hooked downward, so that the cane can be raked off the truck on to the mill carrier.
Manufacture of cane-sugar.
To produce sugar from sugar-cane it is necessary extract the juice, purify it, and then evaporate it until the sugar will crystallize. Formerly these operations were conducted with very simple apparatus, and even now such crude methods are in use in the less progressive countries. The most primitive wooden or stone rollers driven by direct animal power, will express much of the juice from good ripe cane, and it may be concentrated without purification in simple open pans. The result is a poor sugar, much molasses, and the extraction of only a part of the sugar, much of it remaining in the bagasse and going to waste. The most perfect mills are only improvements of this simple process. The use of more powerful rollers was the first improvement; then came the multiplication of the rollers, not only because the repeated pressings would remove more juice from the already pressed fiber, but because between the crushings the fiber could be treated with hot liquids, that on being removed by the next set of rollers left the su crose in a more dilute solution in the bagasse. The amount of moisture that is left in the ba gasse is determined by the pressure; the amount of sugar is determined, however, by the con centration of the solution of sucrose in that moisture.
Shredding and crushing. — Endless carriers, several feet wide, receive the stalks and elevate them twelve to fifteen feet and dump them into a shredding machine or its equivalent. Here the cane-stalks are torn into fragments by revolving cylinders that somewhat resemble a peg-drum threshing machine in their action. The cane frag ments pass without further alteration to the first set of rollers. These three corrugated steel rollers are set to press out about three-fourths of the sucrose, an operation easily possible with the best mills. The fiber or bagasse from these rollers is macerated during about two minutes, as it passes on carriers to the second rollers, the macerating liquid being the heated juice from the final set of rollers used at about 150° Fahr., and sprayed at the rate of about six cubic feet per minute. About 10 per cent more of the sucrose is pressed from the macerated bagasse as it passes through the second set of rollers, which are like the first in action. These operations are repeated between the second and third sets of rollers, except that the macerating liquid is hot water in this case. The third rollers extract another 3 to 4 per cent of sucrose.
The bagasse from the third rollers is carried to the furnaces and is mechanically dumped into them at a rate that can be regulated, so that the 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.