four or five feet high, (which will
secure them against further warping,) and left until they are dry enough
for burning,--that is, as dry as they can be made by exposure to the air.

*Burning.*--Tiles are burned in kilns in which, by the effect of flame
acting directly upon them, they are raised to a heat sufficient to melt
some of their more easily fusible ingredients, and give to them a
stone-like hardness.

Kilns are of various construction and of various sizes. As this book is
not intended for the instruction of those who are engaged in the general
manufacture of tiles, only for those who may find it necessary to
establish local works, it will be sufficient to describe a temporary
earthen kiln which may be cheaply built, and which will answer an
excellent purpose, where only 100,000 or 200,000 tiles per season will be
required.

Directions for its construction are set forth in a letter from Mr. T. Law
Hodges, of England, to the late Earl Spencer, published in the Journal of
the Royal Agricultural Society for the year 1843, as follows:

"The form of the clay-kiln is circular, 11 feet in diameter, and 7 feet
high. It is wholly built of damp, clayey earth, rammed firmly together,
and plastered, inside and out, with loam (clay?). The earth to form the
walls is dug out around the base, leaving a circular trench about four
feet wide and as many deep, into which the fire-holes of the kiln open. If
wood be the fuel used, three fire-holes will be sufficient; if coal, four
will be needed. About 1,200 common brick will be wanted to build these
fire-holes and flues; if coal is used, rather fewer bricks will be wanted,
but, then, some iron bars are necessary,--six bars to each fire-hole.

"The earthen walls are four feet thick at the floor of the kiln, seven
feet high, and tapering to a thickness of two feet at the top; this will
determine the slope of the exterior face of the kiln. The inside of the
wall is carried up perpendicularly, and the loam plastering inside
becomes, after the first burning, like a brick wall. The kiln may be
safely erected in March, or whenever the danger of injury from frost is
over. After the summer use of it, it must be protected, by faggots or
litter, against the wet and frost of winter. A kiln of these dimensions
will contain 32,500 1-1/4-inch tiles, * * * or 12,000 2-1/4-inch tiles. *
* *

"In good weather, this kiln can be filled, burnt, and discharged once in
every fortnight, and fifteen