Adjoining this Refinery was the department in which charcoal was made and pulverized. Charcoal for gunpowder has to be made of a porous fine-grained wood, having very little ashes when burned; willow is generally preferred, and was used at first in the Powder Works, but the exigencies of the war taking away those who would ordinarily have supplied it, rendered it impracticable to procure a sufficient quantity. Recourse was had to the cotton wood, which was abundant; on trial its charcoal was found fully equal to that of the willow for the purpose, and was, thereafter always used. Charcoal for gunpowder must be made by what is termed the distilling process; that is, the wood must be heated in iron retorts to the proper degree, to have it of the best quality and free from sand or grit. For this purpose cast iron cylinders, or retorts, six feet long and four feet in diameter were used, placed over furnaces, each having one end solid and the other with a movable cover; into these were run the slip cylinders, which contained the kiln dried cotton wood, split up into sticks about one and a half inches in diameter, and entirely filling it. The slip cylinders were charged with the wood in an outside apartment, their covers put on, then readily moved by cranes to the retorts, into which they were pushed; the covers of which were then luted with clay and closely applied. The bottoms of the retorts being perforated, permitted the escape of the vapors and gases into the furnaces beneath, where inflaming, they supplied mainly the heat required in the operation. In about two hours the slip cylinders were withdrawn from the retorts and moved by the cranes over, and lowered into the cast iron coolers beneath the floor; these had water from the canal circulating around them; the covers being then put on to exclude the air, the mass of charcoal was rapidly cooled. As soon as a slip cylinder was removed from a retort a freshly charged one would take its place, and thus the process was continued. The slip cylinders were taken out of the coolers in succession by the cranes, and swung over a long and broad table upon which their contents were dropped; here the sticks of charcoal were separately examined and the imperfect rejected. The charcoal was then placed in pulverizing barrels with bronze balls, which revolving by machinery, soon reduced it more or less to a fine powder; it was then bolted, and with the sulphur and saltpetre taken to the weighing house. Here the three materials were arranged into sixty pounds charges, by mingling forty-five pounds of saltpetre, nine pounds of charcoal and six pounds of sulphur, which was then moistened and ready for incorporation.