MAKING NEW BAGS AND LINING THE WASHED BAGS
PRINTING THE EMPTY RAW-SUGAR BAGS
The impurities removed by the filter presses consist of sand, portions of bags and baskets, phosphates, hair, lime, salts and gums, in fact every kind of foreign matter that finds its way into raw sugar either in the process of manufacture or in transportation. A small amount of sugar accompanies this refuse, but as its recovery would cost more than it is worth, it is allowed to run to waste. The filter-press cake, as it is called, contains valuable fertilizing agents, and when conditions permit it is used for fertilizing purposes, otherwise it is run to waste.
BONE-CHAR FILTRATION
REMOVAL OF COLOR
To resume the course of the bag-filtered liquor, from which the superficial, the suspended and insoluble impurities have been removed and which is now the color of clear amber, the next step is bone-char filtration.
Bone-char, bone-coal or bone-black, as it is variously called, is made from the bones of animals. After the fat and glue are removed, the bones are subjected to a dry distillation which carbonizes them. These charred bones are then broken into very small pieces, or until they will pass through a ten-mesh screen and remain on a thirty-mesh screen; in other words, the size of the grains used in a sugar refinery vary from one-tenth to one-thirtieth of an inch. If properly manufactured, the grains are hard, porous, and have a great affinity for moisture.
Bone-char has the peculiar property of removing from the sugar liquor, in some unknown mechanical way, not only the soluble salts but the coloring matter as well. The elimination of the salts and coloring matter facilitates the subsequent crystallization.