The moulding is to a very large extent done by hand, sometimes in a wet
mould, sometimes in a dry sanded mould, and the bricks are first
air-dried, often under some slight shelter, as the rain or frost damages
them when fresh made; and then, when this process has made them solid
enough to handle, they are burned, and sorted into qualities. The
ordinary or stock brick of London and the neighborhood presents a
peculiarity the origin of which is not known, and which is not met with,
so far as I know, in other parts. Very fine coal or cinders is mixed
with the brick earth, and when the bricks are fired these minute
particles of fuel scattered through the material all of them burn, and
serve to bake the heart of the brick. Stock bricks are burnt in a clamp
made of the raw bricks themselves with layers of fuel, and erected on
earth slightly scooped out near the middle, so that as the bricks shrink
they drop together, and do not fall over sideways.

Most other varieties of bricks are kiln burnt. A very large number of
inventions for making bricks by machinery have been patented. If you
have occasion to look through the specifications of these patents, you
will find four or five main ideas appearing and reappearing, and only
here and there an invention which is to some extent different from the
others. A great majority of these inventions include machinery for
preparing the clay or brick earth, so that it may be dug up and filled
into a receptacle and worked up, screened from pebbles, and made fit for
use in a short time, so as not to have to wait a whole winter. This is
done in some sort of pug mill. A pug mill is a machine consisting of a
large cylinder with a central shaft passing through it from top to
bottom. Knives or blades are arranged spirally on the shaft, and other
blades project into the interior of the cylinder from the walls of it.
The material, after being screened, is fed into this at the top, and