CARBONIZATION IN OUDINARY KILKS. 203 



feet, and composed of -plates of sheet-iron which fit closely together 

 at the edges and are supported on a strong circular iron frame. This 

 oven, open at the bottom, is placed over a fire-place built up -with 

 brick or clay and provided with numerous holes through which the 

 heat from below can enter it. Some of these holes are covered over 

 with a sheet-iron plate to moderate the heat. The oven terminates 

 in a cliimnoy that can be closed or opened at pleasure. The wood 

 is stacked within the oven through a side-door. When lurid 

 vapours begin to issue from the chimney, an event that is not long 

 in occurring, the carbonisation is complete. All that has then to 

 be done is to close the chimney, put out the fire under the oven, and 

 allow this latter to cool down. The apparatus is extremely porta- 

 ble, and the fire-place may be built up anywhere without skilled 

 labour. 



As contrivances merely for the manufacture of charcoal, neither 

 of these two last-described or other similar apparatus are likely to 

 come into general use, as they can never supersede the inexpen- 

 sive wholesale methods of carbonization in ordinary kilns, which 

 can, besides, take in pieces of any size without requiring them to 

 be split up small. Those permitting of the utilization of the pro- 

 ducts of distillation must, however, at no distant date, enjoy a 

 certain extended application in India in meeting the large demand 

 that is sure to arise for acetic acid, wood spirits, ether, creosote, 

 tar, &c. 



Section II. — Carbonization in obdinaey kilns. 



In every system of carbonization in ordinary kilns, the covering 

 over the wood is a rough one (generally of leaves and earth), the 

 wood in the kilns has to keep up its own combustion, and the em- 

 placement of the kiln is not in any way built up. 



There are numerous forms of such kilns, but only four of them, 

 which are simple to build and manage, and are thoroughly practi- 

 cal and in very general use, will be described. They are (1) the 

 paraboloidal over-ground kiln, (2) the paraboloidal pit-kiln, (3) 

 the hill kiln, and (4) the prismatic kiln. 



Aetiole 1. — The paraboloidal ovee-giiotjnd kiln. 

 The shape of the kiln, when it is ready to be fired, is very near- 

 ly a paraboloid of revolution, tlje formula for the contents of whick 

 figure is 5rr' X 4^ or, expressed in terms of the circumference, G 



(which basal dimension alone can be measured;, -g^ — ^gTjg* 

 As the kiln is generally more acute than a paraboloid and has 



