d in the clay.

_Washing_ is the process of mixing the clay with a considerable quantity
of water, so as to form a thin paste, in which all stones and gravel will
sink to the bottom; the liquid portion is then drawn off into shallow pits
or vats, and allowed to settle, the clear water being finally removed by
pumping or by evaporation, according to the need for haste. For washing
small quantities of clay, a common mortar bed, such as is used by masons,
will answer, if it be supplied with a gate for draining off the muddy
water after the gravel has settled; but, if the work is at all extensive,
a washing mill will be required. It may be made in the form of a circular
trough, with scrapers for mixing the clay and water attached to a circular
horse-sweep.

"Another convenient mixing machine may be constructed in the following
manner: Take a large hollow log, of suitable length, say five or six feet;
hew out the inequalities with an adz, and close up the ends with pieces of
strong plank, into which bearing have been cut to support a revolving
shaft. This shaft should be sufficiently thick to permit being transfixed
with wooden pins long enough to reach within an inch or two of the sides
of the log or trough, and they should be so beveled as to form in their
aggregate shape an interrupted screw, having a direction toward that end
of the box where the mixed clay is designed to pass out. In order to
effect the mixing more thoroughly, these pins may be placed sufficiently
far apart to permit the interior of the box to be armed with other pins
extending toward the center, between which they can easily move. The whole
is placed either horizontally or vertically, and supplied with clay and
water in proper quantities, while the shaft is made to revolve by means of
a sweep, with horse power, running water or steam, as the case may be. The
clay is put into the end farthest from the outlet, and is carried forward
to it and mixed by the motion, and mutual action and re-action of the pins
in the shaft and in the sides of the box. Iron pins may, of course, be
substituted for the wooden ones, and have the advantage of greater
durability and of greater strength in proportion to their size, and the
number may therefore be greater in a machine of any given length. The
fluid mass of clay and water may be permitted to fall upon a sieve or
riddle, of heavy wire, and afterward be received in a settling vat, of
suitable size and construction, to