As the wet char leaves the filter, it drops on a moving belt which carries it to large cast-iron hoppers leading to the driers immediately beneath, where the greater part of the moisture is expelled from the char prior to its being treated in the revivifying kilns. The driers are made up of a number of thin, hollow, cast-iron, triangular pipes, enclosed in a large, rectangular, outside casing. The wet bone-char passes over these hollow pipes as it falls slowly through the drier. The hot gases from the furnaces of the kilns below pass through these cast-iron pipes, giving off heat as they ascend, thus driving off the moisture in the char as it falls down over the outer surface of the pipes. At the same time, hot air obtained from cooling the char in the cooling pipes below the retorts is drawn through the drier, coming in direct contact with the char. The moisture given off by the char is absorbed by this hot air and carried out of the drier and building by fans or smokestacks. By this means the water in the char is reduced to ten per cent, and in this comparatively dry, hot state it runs freely by gravity from the bottom of the drier into a second set of hoppers, through which it drops into the retorts of the kiln. The hot gases, after drying the char, pass out at the top of the drier through a flue leading to a stack outside the building. [Illustration: TOP OF CHAR FILTERS—SHOWING PIPE CONNECTIONS] [Illustration: EXTERIOR VIEW OF CHAR DRIER] The kilns are large square boxes of brick, built around a strong supporting iron structure. On each side of these boxes are a number of large flat pipes of cast iron, nine feet long and twelve inches by three inches in section, the iron being three-quarters of an inch thick. These pipes are called retorts and are arranged vertically in the kilns, forty on each side. The space in the center between the retorts is known as the furnace and extends the entire length of the kiln, a distance of about sixteen feet. Intense fires are maintained in this central space and the flames playing around the retorts keep them red-hot. The upper ends of the retorts lead into the hoppers above and the lower ends to the cooling pipes below. As the char passes gradually through the red-hot retorts, it becomes heated to 900 degrees Fahrenheit and the organic matter it absorbed from the sugar liquor is changed into carbon. In this way the char becomes almost as good as new, or, as the term goes, revivified. Each kiln has a capacity of revivifying sixty thousand pounds of bone-char per day.