Since the beginnings of iron manufacture, charcoal has been a favorite fuel. Though during the past two centuries coke has grown to be the standard, with anthracite and some few bituminous coals finding use in certain favored localities, charcoal may be considered the fuel which developed the iron industry, at least until recent years. Charcoal As most of us know, charcoal is completely charred wood, usually hard wood, though sometimes resinous or other soft woods are used. Of well-dried timber more than 50 per cent by weight is moisture. This and certain other constituents are driven off by heat in the absence of air, which process is usually called “destructive distillation.” By primitive methods a considerable part of the wood was completely burned and wasted during the production of charcoal. Stacked in piles or long rows the cut wood was well covered with earth, except for a small opening at the top through which the fire was lighted down a center cavity left to the bottom of the pile. The air coming in through the opening at the top was sufficient to keep the wood smoldering. After a period, which had been shown by experience to give the best results, the opening was closed and the fire smothered. [Illustration: BEEHIVE COKE OVENS ] Brick ovens of the beehive shape were built at a later date where considerable charcoal was to be made. These were operated on much the same general principle as the _meillers_ or earth-covered piles, described above. The fire was lighted at the bottom of the central cavity of the corded wood, the only air at first coming from the top, though later in the process a little was admitted through holes in the walls. After about ten days, when gas ceased to come off, the kiln was tightly closed for a period of twenty days more for the fire to die out and the charcoal to cool. By both of these processes valuable constituents were burned or driven off by the heat and lost. These were mainly methyl alcohol, acetic acid, and wood tar. Modern industry so emphatically disapproves of any waste of materials that apparatus has been devised to produce charcoal which allows of recovery of the by-products at the same time. In northern Michigan, which is practically the only district in the United States in which the charcoal industry as an industry still survives, long steel tubes or retorts are built with brick fire-boxes under each end, much as a stationary boiler is set. Into these retorts are run steel cars loaded with the wood. The retorts being closed, the heat drives or distills off the moisture and gaseous compounds through pipes connecting them with condensing apparatus. After about twenty hours the wood has been charred, the doors of the kilns are suddenly opened and the cars are rushed into other and similar retorts for cooling, while fresh loads of wood replace them in the first. [Illustration: STANDARD BEEHIVE COKE OVEN ] [Illustration: BEEHIVE OVENS ]