MANUFACTURE OP CHARCOAL DUST. 63 



"At the Imperial Castle of La Motte-Beuvron, Sologne, the 

 carbonisation of bourrees is carried oil in a brick oven placed in a 

 central position in relation to the Forests or the Landes which are to 

 yield the material, and special regard is had to the roads as it is 

 desirable the oven should be near the best roads. Water also is 

 required to extinguish the charcoal when drawn from the oven. It 

 should therefore be of easy access. 



" In such ovens or kilns the upper aperture of the oven, into 

 which the bourrees are thrown, should be easily reached, and also 

 the lower opening, from which the carbon is withdrawn. This double 

 condition is attained by placing them where there are two surfaces 

 with unequal levels. The upper opening on a level with the 

 higher surface, while the lower is also on a level with the ground. 

 This arrangement is to be seen in many lime kilns. The earliest 

 kilns were not made in this way. The upper opening was above the 

 ground by the whole height of the kiln. The workman could not 

 throw in the bourrees at once, but was obliged to carry them up a 

 scaffolding. This additional labour increased the expense. 



" This inconvenience is prevented by erecting kilns of the kind 

 described : In default of a suitable slope, the kiln may be placed on 

 the ground, piling up earth to the half of its height and forming two 

 inclined planes, one leading to the upper opening, the other leading 

 down to the inferior one. Care should be taken to prevent rain from 

 collecting in the oven. 



" The bourrees are collected in isolated heaps in the neighbourhood 

 of the oven. It is considered that these should not be massed 

 together for fear of their taking fire ; and that they should as much 

 as possible be sheltered from rain. Wet bourrees are difficult to 

 carbonise, and yield less powder, especially if they have been exposed 

 to damp for any length of time. 



" The workman throws in the bourrees either by hand or with a 

 wooden fork. Thirty bourrSes are enough to fill a kiln. It is lighted 

 by the lateral opening ; immediately it ignites this opening is carefully 

 stopped with clay so as to exclude the air. The upper opening is 

 left half open, from which issues a thick white smoke chiefly formed 

 of vapour. So long as the smoke continues white, the workman 

 throws no more bourrSes, but whenever it loses a blueish tinge he 

 hastens to feed it up, as this is a certain indication of an advanced 

 degree of carbonisation. 



" He continues to work all day without withdrawing the charcoal, 

 and before leaving at night he puts in a fresh supply of bourrees. 



