MANUFACTURE OF CHARCOAL. 59 



exit of air must be regulated so that the heat may not be too great 

 or too low. When too low, the charcoal is of inferior quality ; when 

 too high, there is great waste, and the yield of charcoal is small. 



" The skill of a chai-coal maker is now seen in ascertaining what 

 progress the fire makes in the interior, in such a way that it can be 

 moderated in some places and increased in others. It is by the 

 smoke and cracks on the surface that this can be judged of. The 

 fire is moderated by stopping the openings, or increased by making 

 others. 



" The bad eSect of currents of wind is prevented by pallisades, or 

 bourrees, arranged like a wall, or by a simple clayonnage of branches. 



" The best constituted charcoal furnace is the one which, remaining 

 uniform and homogeneous throughout the operation, sinks and 

 breaks in regularly, allowing the smoke to escape in the same 

 quantities from all the openings disposed round the furnace. 



" The fire extends from above to below, and from the centre to the 

 circumference. At the end of 36 hours, in furnaces of the usual size, 

 the whole covering becomes incandescent. This is the time of the 

 ' grand feu.'' When this point is reached, M. Thomais says, that 

 a good charcoal burner will make it blaze furiously, and then put it 

 out dexterously. This, when done at the right time, produces a 

 great deal of charcoal. But to prevent failure, the furnaces should 

 be sheltered from currents of air, otherwise there is a chance of 

 considerable loss. 



" After the violent blaze, the charcoal making may be considered 

 finished. The fire is moderated by degrees by making openings 

 which allow the air to pass, and by replacing the warm dry earth of 

 the covering by earth which is cold and damp. The fire is 

 extinguished in five or six hours ; but another day is required 

 before the charcoal becomes cool and is fit to be carried away. 



*' To obtain a good yield of charcoal one must guard against 

 raising the temperature too much at the beginning of the operation. 

 The first part of the time is spent not in carbonising the wood, but 

 in getting rid of the moisture. If the faggots are strongly heated 

 before the water is dispelled, the latter being decomposed, two sorts 

 of gas are created, which, combining with the charcoal, issue from 

 the furnace in the form of carbonic acid, and carbonic oxide, and 

 carburetted hydrogen. From thence results a real loss of carbon, 

 which in this case is consumed in the same way as in our kitchen 

 stoves. The water decomposed by the fire acts on the incandescent 

 charcoal with more force than would the atmospheric air. 



