Page:The American Cyclopædia (1879) Volume IV.djvu/281

 CHARCOAL 273 temperature at which it was made : 1, hydro- gen ; 2, nitrogen ; 3, carbonic oxide ; 4, oxy- gen ; 5, marsh gas ; 6, nitrous oxide ; 7, car- bonic acid ; 8, olefiant gas ; 9, sulphurous acid ; 10, air; 11, sulphuretted hydrogen; 12, muri- atic acid; 13, hydrochloric acid ; 14, ammonia. When air-seasoned wood, that is to say, wood containing about 25 per cent, by weight of hygroscopic water, is slowly charred in heaps at a temperature of about 750 F., about one third of it is wholly consumed in produ- cing the heat required for the charring, leaving two thirds for the portion charred. The dry charcoal produced is 16 per cent, of the total weight of wood ; that is, of the sum of the weight consumed and the weight charred, or ( g 6 } 24 per cent, of the latter. When the wood is slowly distilled in ovens or retorts at the above temperature, then, as the same quantity of heat is required for producing the same effect, for every two pounds put into the retort one pound will be consumed beneath it to produce the heat for distillation. Of the two pounds thus distilled, 24 per cent, is ob- tained as dry charcoal ; or, of the total weight of wood used, that is, of the sum of the weights consumed and the weight distilled ($ of 24), 16 per cent, is obtained as dry charcoal. Con- sequently, for equal weights used of the same wood, the process of distillation in retorts and that of charring in heaps are equally economi- cal ; in the former case, however, the gaseous and liquid distillates belonging to two thirds of the wood are saved, while in the latter case they are lost. When the charring or distil- ling is very rapidly done, the resulting weight of dry charcoal is only 14 per cent, of that of the wood charred or distilled ; and the quan- tity of wood consumed in the production of. the heat required for the charring or distilling is equal to the weight of wood charred or dis- tilled ; consequently, in this case, only 7 per cent, of the total weight of wood used is ob- tained as dry charcoal. The proportion of charcoal obtained from wood varies with the kind of wood, and for the same kind of wood it varies with the temperature and with the duration of the charring or distillation ; the lower the temperature and the longer the du- ration of the process, the greater is the propor- tion of charcoal obtained. The charcoal also varies in chemical composition with the tem- perature and the duration of the charring or distilling process. The lower the temperature, other things being equal, the greater is the percentage of volatile matter and the smaller that of fixed carbon in the charcoal. The hygroscopic power of such charcoal is greater than of that prepared at higher temperatures. The longer the process of preparation is con- tinued, other things equal, the less is the per- centage of volatile matter and the more that of fixed carbon in the charcoal. The hygro- scopic power of such charcoal is less than of that prepared with shorter processes. No temperature at the command of man, and no time of distillation, will wholly expel the vola- tile constituents of charcoal, namely, the hy- drogen, oxygen, and nitrogen. The inflamma- bility of dry charcoal varies with the kind of wood from which it is made ; and for the same kind of wood it varies with the tempera- ture and with the duration of the charring or distillation ; the lower the temperature and the shorter the duration of the process, the more inflammable is the charcoal. The relative inflammability is measured by the temperature of ignition ; the lower, that temperature, the more inflammable is the charcoal. The in- flammability depends on the porosity of the charcoal and on the percentage of its volatile constituents, and both these are greater the lower the temperature of the charring or the distillation and the shorter the time. After a brief exposure of dry charcoal to the atmos- phere, its large absorption of hygroscopic moisture materially modifies the above rela- tions, and tends to equalize its inflammability, as the lower the temperature and the shorter the process of the charring or distillation, the more hygroscopic is the charcoal, and conse- quently the higher is its temperature of igni- tion. The temperatures of ignition of dry char- coal prepared at various temperatures are as follows: Temperature of the Charring 500 F. 600 1000 2000 3000 Temperature of Ignition. 650 F. 700 750 1100 1450 It is obvious that the dryer the, wood, the greater is the percentage of charcoal obtained from it, and the less is that of the wood re- quired to be consumed in producing the heat for the charring or distillation ; for the uncom- bined water in the part of the wood charred or distilled is entirely driven off as aqueous vapor during those processes ; while in the part of the wood consumed to produce the heat for the charring or distillation, the uncom- bined water is not only driven off, but also ab- sorbs for its evaporation a portion of the heat due to the combustion of the ligneous matter. A further portion of that heat is taken, too, for the evaporation of the water in the part of the wood charred or distilled, so that the greater the quantity of uncombined water in a given weight of wood, the greater is the percentage of the part required to be consumed in pro- ducing the heat for the charring or distilling. Thus, of the total weight of wood used, that is, the sum of the weight charred or distilled and consumed in producing the heat for the char- ring or distillation, the effect of the uncombined water is to diminish the charcoal product more largely than is due to the simple subtraction of that water by the amount of wood consumed for its evaporation. This is the only result attending the presence of water in the wood when the temperature of the charring or dis^