drain off the water and let the clay
dry out sufficiently by subsequent evaporation. A machine of this
construction may be made of such a size that it may be put in motion by
hand, by means of a crank, and yet be capable of mixing, if properly
supplied, clay enough to mold 800 or 1000 pieces of drain pipe per
day."(24)

Mr. Parkes, in a report to the Royal Agricultural Society of England, in
1843, says:

"It is requisite that the clay be well washed and sieved before pugging,
for the manufacture of these tiles, or the operation of drawing them would
be greatly impeded, by having to remove stones from the small space
surrounding the die, which determines the thickness of the pipe. But it
results from this necessary washing, that the substance of the pipe is
uniformly and extremely dense, which, consequently, gives it immense
strength, and ensures a durability which cannot belong to a more porous,
though thicker, tile.

"The clay is brought from the pug-mill so dry that, when squeezed through
the machine, not a drop of water exudes,--moisture is, indeed, scarcely
apparent on the surface of the raw pipe. Hence, the tiles undergo little
or no change of figure while drying, which takes place very rapidly,
because of their firm and slight substance."

[Illustration: Fig. 42 - PUG-MILL.]

Fig. 42 - PUG-MILL.

_Tempering._--After the fine clay is relieved of the water with which it
was washed, and has become tolerably dry, it should be mixed with the
sand, or other tempering material, and passed through the _Pug-Mill_,
(Fig. 42,) which will thoroughly mix its various ingredients, and work the
whole into a homogeneous mass, ready for the tile machine. The _pug-mill_
is similar to that used in brick-yards, only, as the clay is worked much
stiffer for tiles than for bricks, iron knives must be substituted for the
wooden pins. These knives are so arranged as to cut the clay in every
part, and, by being set at an angle, they force it downward toward the
outlet gate at the bottom. The clay should be kept at the proper degree of
moisture from the time of tempering, and after passing through the
pug-mill it should be thoroughly beaten to drive out the air, and the
beaten mass should be kept covered with wet cloths to prevent drying.

*Moulding the Tiles.*--Machines for moulding tiles are of various styles,
with much variation in the details of their construction, but they all a