If the char in this red-hot state were suddenly exposed to the air, the contact with oxygen would bring about combustion and the char would be quickly reduced to ashes, so a cooling process is necessary. It is, therefore, drawn from the cast-iron retorts into cooling pipes located directly beneath. These pipes are of thin sheet-iron and are about three by four and a half inches in section. There are three under each retort, and a mechanical device at the bottom allows only a small amount of char to escape at a time. This amount can be regulated at will by the operator, and in this way the char is held in the retorts the exact time necessary for its revivification. A current of cold air circulates continually around the cooling pipes, taking up the heat from the char and delivering it through pipes to the drier overhead, so that when the char leaves the bottom of the pipes its temperature is about 180 degrees Fahrenheit. From the cooling pipes, it drops on a belt conveyor from which it is carried by endless belt or chain bucket elevators to the top of the char filters to be used again. The manipulation of the char filters varies in different refineries, some running the liquor over the char for a longer period than others, but a fair average of the time required for filling, settling running liquors and syrups, sweetening off, washing, applying air and emptying, is eighty-six hours, the shortest time being seventy-two hours. Taking eighty-six hours as a basis, it will be seen that the char is handled and revivified eighty-one times each year after making due allowance for Sundays, holidays and annual clean-up periods. Each time the char is handled, a certain amount of it is broken into dust, and this is taken out by passing it over fine screens, and also by exhaust fans. Obviously, the amount of dust taken out each day must be replaced by its equivalent in new char. It is estimated that the original char put into the filters will last from five to six years before it finally becomes disintegrated and is taken out as dust. [Illustration: INTERIOR ARRANGEMENT OF CHAR DRIER] [Illustration: EXTERIOR VIEW OF CHAR KILNS—SHOWING OIL-BURNING APPARATUS] As approximately one pound of char is required for every pound of sugar melted, it will be seen that as the liquor is in contact with the char for only twenty-four hours out of seventy-two, a refinery turning out two million pounds of sugar per day should have filter capacity for six million pounds of char. The amount of the latter that is handled each year is, therefore, very great and requires a large and costly plant to take care of it properly. CRYSTALLIZATION PRODUCTION OF CRYSTALS BY CONCENTRATION The refining process has been described up to and including the purification and decolorizing of the sugar liquor, the last step being the delivery of the pure white liquor into the receiving tanks in the pan house.