200 CAEBONISATION IN RETORTS AND CLOSE OVENS. 



to be carbonised in retorts or close furnaces, it should be as dry as 

 possible in order to economise both fuel and time ; and if it is to be 

 carbonised by any other method, which requires the admission of a 

 certain considerable quantity of air to produce the necessary tem- 

 perature, it should be just dry enough to develop that tempera- 

 ture -without burning too rapidly and being consumed to no pur- 

 pose. In the latter case, the quantity of moisture allowable will 

 be in direct proportion to the dryness and high temperature of 

 the air, the defective nature of the covering over the kiln, and 

 exposure to winds. 



Skction I. — Caebonisation in eetokts and close ovens. 



In every method of carbonization in retorts or close ovens the 

 double object is sought of obtaining the charcoal and of securing 

 the products of distillation, thus allowing no portion of the wood 

 to go to waste. 



A convenient and general form of oven used in England consists 

 of a cast-iron cylinder laid horizontally in masonry with a fire- 

 place below. The wood is put in at one end, which is then closed 

 with a well-fitting iron door that is carefully luted to render it com- 

 pletely gas-tight. For the first two or three hours the fire is kept 

 low to dry the charge of wood. It is then driven hard until carbo- 

 nization is complete ; but if the operation is conducted too quickly, 

 the yield of charcoal may be reduced by as much as 30 to 45 per 

 cent. A charge of 100 stacked cubic feet of wood requires 12 to 13 

 hours to give the best results. During carbonization the following 

 process takes place. First, the free moisture of the wood is driven 

 off ; then, as the temperature is raised and decomposition of the 

 wood occurs, acetic acid and water are given off, followed by tar 

 and volatile oils, and lastly by uncondensable gases, piz., carbon 

 monoxide and dioxide, and marsh and defiant gases. The pro- 

 ducts of distillation escape through a pipe at the other end, whence 

 they pass into the condenser. The condenser pipe gets rapidly 

 clogged with tarry matters ; it must therefore be composed of 

 short straight lengths that may be speedily cleaned out. At the 

 exit end of the condenser pipe there are two outlets, through the 

 lower one of which pass out the condensed products, consisting of 

 water, pyroligneous acid, ammonia, tar, naphtha, and various oils 

 and resinous matter ; through the upper the uncondensable gases 

 above mentioned, which, instead of being allowed to pass off into 

 the atmosphere and taint it, are conducted into the fireplace to 

 feed the fire. In order to utilise to its fullest extent the beat of the 



