762 



CHARCOAL 



coking place, -whose surrounding walls are heated by the flame which passes through 

 the intermediate space b. The place itself is divided by partitions of fire tiles into 

 three stages, through the apertures in which the flames of the fire c c, rise, and hwit 

 the exterior of the coking apartment. In order to confine the heat, there is in the 

 enclosing walls of the outer kiln, a cylindrical hollow space d, where the air is kept 

 stagnant Through the apertures left in the upper end at e, the turf is introduced ; 

 they are then shut with an iron plate /, -which is covered with ashes or sand. The 

 fire-place opens above this aperture, and its outlet is provided with a moveable iron 

 cover g, in which there is a small hole for the issue of the gases. The sole of the kiln 

 consists of a cast-iron slab h, which may be raised by means of a hook, i, upon it. This 

 is drawn back after the carbonisation is completed, whereby the charcoal falls from 

 the coking space into a subjacent vault. The volatile products are carried off by the 

 pipe k, and led into the condensing cistern ; the gases escaping to the fire-place, where 

 they are burned. The iron slab is protected from the corrosion of the acid vapours by 

 a layer of coal ashes. 



Charcoal obtained by the action of a rapid fire in close vessels is not so solid and so 

 good a fuel as that which is made in the ancient way by the slow calcination of pyra- 

 midal piles covered with earth. One of the most economical ovens for making wood 

 charcoal is that invented by M. Foucauld, which he calls a shroud, or abri. To con- 

 struct one of these, 30 feet in diameter at the base, 10 feet at its summit, and from 8 

 to 9 feet high, he forms, with wood 2 inches square, a frame 12 feet long, 3 feet broad 

 at one end, and 1 foot at the other. The figures 451, 452 will explain the construction. 



452 



a If 



454 



The uprights, A B and c D, of this frame are furnished with three pairs of wooden 

 handles a a a, by means of which they can be joined together, by passing through two 

 contiguous handles a wooden fork, the frame being previously provided with props, as 

 shown in Jiff. 452, and covered with loam mixed with grass. A flat cover of 10 feet 

 diameter, made of planks well joined, and secured by 4 cross bars, is mounted with 2 

 trap doors, M x, fig. 454, for giving egress to the smoke at the commencement of the 

 operation ; a triangular hole P, cut out in the cover, receives the end of the conduit Q 

 E s, (figs. 453 and 454) of wood formed of three deals destined to convey the gases 

 and condensed liquids into the casks F o H. Lastly, a door T, which may be opened and 

 shut at pleasure, permits the operator to inspect the state of the fire. The charcoal 

 calcined by this abri has been found of superior quality. 



When it is wished to change the place where the abri is erected, and to transport it 

 to a store of new-felled timber, the frame is taken down, after beating off the clay which 

 covers it ; the joints are then cut by a saw, as well as the ends of the fork which fixed 

 the frames to one another. This process is economical in use, and simple and cheap in 

 construction ; since all the pieces of the apparatus are easily moved about, and may be 

 readily mounted in the forests. For obtaining a compact charcoal, for the use of 

 artisans, this mixed process of Foucauld is said to be preferable to either the close iron 

 cylinder or the pile. 



For making gunpowder-charcoal the lighter woods, such as the willow, dogwood, 

 and alder answer best ; and in their carbonisation care should be taken to let the 



