_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 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: