CHARBAR CHARCOAL 271 meadow. They are found in the fossil state, and are important to the geologist as charac- terizing groups of strata, as those of the fresh- water marl beds of the tertiary formation. The seed vessel of these plants is very tough, and is covered by an integument consisting of five spiral valves. The stems are longitudinally striated, and always turn in a contrary direc- tion from the rings on the seed vessel. CHARBAR (or Chonbar) BAY, one of the best harbors on the coast of Beloochistan, in the In- dian ocean. Ras Charbar, the E. point of the bay, is in lat. 25 16' K, Ion. 60 35' E. On the E. side of its entrance is the town of Charbar, pop. 1,500, surrounded by a rampart of earth, and garrisoned by the sultan of Oman. North of this are the ruins of the Portuguese settle- ment of Teez, which was probably identical with the Tiz of Edrisi, and possibly occupied the site of the Trcesa of Nearchus. CHARCOAL, the solid residuum of the destruc- tive distillation of wood. Exclusive of hygro- scopic water and ash, it is composed of carbon, hydrogen, oxygen, and nitrogen, in proportions varying with the kind of wood, with its hy- groscopic condition, with the temperature of the distillation, and with the duration of the process. It is insipid and inodorous ; is a bad conductor of heat and a good conductor of elec- tricity ; is insoluble in water ; is attacked by nitric acid with difficulty, and is but little af- fected by the other acids or by the alkalies. Its carbon constituent is exceedingly refractory to heat, and if secluded in a retort will neither fuse nor volatilize under the highest tempera- ture that can be produced. It retains the or- ganic structure of the wood from which it was produced, except when prepared at very high temperature, when it becomes a black, shining, porous mass, resembling fossil coal, with a con- siderable increase in density, and without a trace of organic structure. Charcoal always contains a certain percentage of ash derived from the wood of which it is made, but that percentage is much less than what is due to the respective weights of the original wood and the resulting charcoal, showing that a portion of the mineral matter in the wood has been car- ried off by the fluid distillates. Charcoal is ex- cessively hygroscopic. A fresh preparation of it strongly attracts moisture from the moment it is exposed to the atmosphere, and the quan- tity thus absorbed at saturation varies with the temperature of distillation, and with the hygro- metric and barometric conditions of the atmos- phere. The lower the temperature at which the charcoal is produced, the greater the hu- midity of the air, and the higher the barometer, the greater is the percentage of moisture ab- sorbed at saturation by the charcoal. Charcoal is hard and brittle ; it rings when struck, and resists a strong pressure gradually applied, but is easily broken by a sudden blow, when it shingles like porcelain and shows a glossy, intensely black and glistening fracture, that scarcely soils the hand until after some expo- 172 VOL. iv. 18 sure to the air. The quantity of charcoal ob- tained from the same weight of wood in the same condition, and the ratio of its carbon constituent to its hydrogen, oxygen, and nitro- gen, vary with the temperature and time of distillation ; the lower the temperature and the shorter the time, the greater is the percentage of charcoal obtained, and this charcoal contains a greater percentage of hydrogen, oxygen, and nitrogen, and less of carbon ; but the high- est temperature and the longest application fail to wholly expel the volatile constituents of charcoal. The ordinary charcoal of commerce, prepared in heaps at the temperature of about 700 F., has the density of 0-42 including its pores, and of 1-50 excluding them. In the merchantable state it weighs 15 Ibs. per cubic foot, and requires 144J cubic feet of space to contain one ton. The following is its chemical constitution by weight, both including and ex- cluding its ash and hygroscopic moisture : Incluilre of ash and Hygroscopic moisture. Carbon 70 Hydrogen 5 Oxygen 11 Nitrogen 1 Ash 2 Hygroscopic I moisture ) Exclusive of i Hygroscopic u 80-46 5-75 12-64 1-15 11 100 100-00 When the distillation is done under a tempera- ture of about 1,500 F., charcoal has the density, exclusive of pores, of about 1*75, and the fol- lowing chemical constitution by weight, both including and excluding its ash and hygro- scopic moisture : Inclusive of ash and Hygroscopic moisture. Carbon 88-0 Hydrogen 2-5 Oxygen 5-0 Nitrogen 0-5 Ash 3-0 Hygroscopic | moisture f 6-0 100-0 Exclusive of ash and Hygroscopic moisture. 91-21 2-75 5-49 0-55 100-00 The ash of charcoal consists chiefly of carbon- ate of potash, silica, lime, and oxide of iron. When wood is distilled to the uttermost, at the temperature of 2500 F., the resulting dry charcoal, exclusive of its pores, has a density of about 2, and contains about 3 per cent, of volatile matter. The specific heat of good charcoal, free from hygroscopic moisture, in- creases with the temperature, and in the fol- lowing ratio: At 212 F. the specific heat is 0-2415 ; at 392, 0-2441 ; at 572, 0-2467 ; at 752, 0-2493; at 932, 0-2519 ; at 1112, 0-2545 ; at 1292, 0-2571 ; at 1472, 0-2597 ; at 1652, 0-2623; at 1832, 0-2649; at 2012, 0-2675 ; at 2192, 0-2701 ; at 2372, 0'2727 ; and at 2552, 0-2753. Charcoal absorbs the fixed gases as well as aqueous vapor with great avidity, the volumes at standard tempera- ture and pressure absorbed by the same char- coal varying with the temperature and pres-
