to have it as nearly uniform as possible. When most of the wood is
small, and only a small part of it is large, the large pieces are
usually split, to make it pack well. It has been found most satisfactory
to have three rows of vents around the kiln, which should be provided
with a cast-iron frame reaching to the inside of the furnace. The vents
near the ground are generally five inches high--the size of two
bricks--and four inches wide--the width of one--and the holes are closed
by inserting one or two bricks in them. They are usually the size of one
brick, and larger on the outside than on the inside. These holes are
usually from 0.45 m. to 0.60 m. apart vertically, and from 0.80 m. to
0.90 m. apart horizontally. The lower vents start on the second row of
the brickwork above the foundation, and are placed on the level with the
floor, so that the fire can draw to the bottom. There is sometimes an
additional opening near the top to allow of the rapid escape of the
smoke and gas at the time of firing, which is then closed, and kept
closed until the kiln is discharged. This applies mostly to the best
types of conical kilns. In the circular and conical ones the top
charging door is sometimes used for this purpose. Hard and soft woods
are burned indifferently in the kilns. Hard-wood coal weighs more than
soft, and the hard variety of charcoal is usually preferred for blast
furnaces, and for such purposes there is an advantage of fully 33-1/3
per cent. or even more in using hard woods. For the direct process in
the bloomaries, soft-wood charcoal is preferred. It is found that it is
not usually advantageous to build kilns of over 160 to 180 cubic meters
in capacity. Larger furnaces have been used, and give as good a yield,
but they are much more cumbersome to manage. The largest yield got from
kilns is from 50 to 60 bushels for hard wood to 50 for soft wood. The
average yield, however, is about 45 bushels. In meilers, two and a half
to three cords of wood are required for 100 bushels, or 30 to 40 bushels
to the cord. The kiln charcoal is very large, so that the loss in fine