CARBON AND THE HYDROCARBONS 



848 



volatile substances (ash) forming a part of the organic matter, remain 

 behind with the charcoal. The, tar- like substances, which require a 

 high temperature in order to decompose them, also remain mixed with 

 charcoal. If a volatile organic substance, such as a gaseous compound 

 containing oxygen and hydrogen, be taken, the carbon separates on 

 passing the vapour through a tube heated to a high temperature. 

 Organic substances when burning with an insufficient supply of air 

 give off soot that is, charcoal proceeding from carbon compounds in 

 a state of vapour, the hydrogen of which has, by combustion, been 

 converted into water ; so, for instance, turpentine, naphthalene, and 

 other hydrocarbons which are with difficulty decomposed by heat, easily 

 yield carbon in the form of soot during combustion. Chlorine and 

 other substances which, like oxygen, are capable of taking up hydro 

 gen, and also substances which are capable of taking up water, can 

 also separate -carbon from (or char) most organic substances. 



Wood charcoal is prepared in large quantities in a similar manner 

 that is, by the partial combustion of wood. 4 In nature a similar 



Which wood undergoes at various temperatures when submitted to dry distillation by' 

 means of superheated steam 



4 The object of producing charcoal from wood has been explained in Note 1. 

 Wood charcoal is obtained in so-called stacks by partially burning the wood, or by 

 means of dry distillation (Note 1) without the access of air. It is principally manu- 

 factured for metallurgical processes, especially for smelting and forging iron. The 

 preparation of charcoal in stacks has one advantage, and that is that it may be done 

 on any spot in the forest. But in this way all the products of dry distillation are lost. 

 For charcoal burning, a pile or stack is generally .built, in which the logs are placed 

 close together, either horizontally, vertically, or inclined, forming a stack of from six 

 to fifty feet in diameter and even larger. Under the stack are several horizontal air 

 passages, and an opening in the middle to let out the smoke. The surface of the stack is 

 covered with earth and sods to a considerable thickness, especially the upper part, in 

 order to hinder the free passage of air and to concentrate the heat inside. When the 

 stack is kindled, the pile "begins to settle down by degrees, and it is then necessary .to 

 look after the turf casing and keep it in repair. As the combustion spreads throughout 

 the whole pile, the temperature rises and real dry distillation commences. It is then 

 necessary to stop the air holes, in order as much as possible to prevent unnecessary'Com- 

 bustion. The nature of the process is, that part of the fuel burns and develops the heat 

 required for subjecting the remainder to dry distillation. The charring is stopped when 

 the products of dry distillation, which are emitted, no longer burn with a brilliant flame, 

 but the pale blue flame of carbonic oxide appears. Dry wood in stacks yields about one* 

 fourth of its weight of charcoal. 



