Pug-mills appear to be used more than other classes of tempering machines. They are either vertical or horizontal, but in either case they have a central revolving shaft, fitted with radial knives extending nearly to the surrounding cyl inder in which the clay placed. or else fitted with a worm screw. Both knives and screw force the clay forward, as well as work it thor oughly, and by changing the angle of the adjusta ble knives the speed of the passing clay may be regulated. Water is admitted as desired and needed. When the clay is deficient in redness after burning, hematite may be added to the pug with clay. Pug-mills are compact. and re quire less power than ring-pits.
Washing is effected by a variety of processes. ranging from simple to complex. All of them involve a reduction of the clay in water to a semi-fluid state. or even to a state of suspen sion, which may be brought about by revolving paddles or blades, mounted on a- shaft in a cylinder or trough, or by any thorough stirring. The heavier, coarser impurities may be deposited in a vat by sedimentation. The water, with the remaining clay, may be removed by siphoning or carefully poured off, and the clay A Ilowed to settle. This process is sometimes called ebulli tion, particularly where it is repeated many times to recover fine-grained material. The pro cess of sedimentation may be altogether too slow, especially where large quantities of clay are to lie treated, and in such a case the clay and water. after being reduced, as described, to what is known as slip, may he passed through shak ing-screens of wireeloth, having forty meshes to the inch. It is then sent to an agitator, or large tank lilted with revolving paddles, to prevent sedimentation, from which tank the screened slip is forced by means of compressed air into a series of canvas-lined compartments, known as a press, where the is expelled by the force of the air. The press being loosened, the clay is removed in sheets or cakes one to two inches thick, weighing 30 to 40 pounds each, after which it is ready for the pug-mill. 1Vashing is used in the preparation of some sorts of (-lay for making into pottery.
BIIILIOGRApIIY. Bock, Die Ziegelindustrie (Leip zig. 1897) : Dinnoder. Handbuch der Ziegel-fahri kation (Halle, 1S97) : Ries, "The Clays of New York: Their Properties and Uses." in New York State Museum Bulletin No. 35 (Albany, 1900—eontains much general information on the properties of clay and the methods of manufac ture) ; Young, The Ceramic Arts (New York, 1878) ; Prime, Pottery and Porcelain of All Times and Nations (New York, 1878) ; Barber, Pottery and Porcelain of the United States (New York, 1900) ; Langenbeck, 7'he Chemistry of Pot tery (Easton, Pa., 1896). Among the more hn portant works issued by geological surveys of States are the following: Blatchley, "Clays of the Coal-Bearing Counties of Indiana," in Twen tieth Annual Report of the Geological Surrey of Indiana (Indianapolis• 1896) ; Branner, "Bib liography of Clays and the Ceramic Arts," in United States Geological Survey Bulletin No.
I '13 (Washington, 1896) : Buckley, "The Clays of Wisconsin," in Wisconsin Geological Survey Bulletins, vol. ii., part i. (Madison, 1901) ; Cook, The Clays of New Jersey," in New Jersey Geo logical Survey Report for 1878 (Trenton, 1878) ; Orton, "Clays and Clay-Working Industries of Ohio," in Ohio Geological Survey, vol. vi., part i. (Columbus, Ohio, 1893) ; Ries, "The ('lays of Alabama," in Atabatna. Geological Sur rey Bulletin No. 6 (Jacksonville, Fla., 1900) ; Ries, "The Clays and Clay Industries of North Carolina," in the North Carolina Geological Surrey Bulletin No. 13 (Raleigh, N. C.. 1897) ; Ries, "The Clays and Shales of Michigan," in Michigan Geological Surrey, vol. viii. (Lansing, 1901) ; Wheeler, "The Clays of Missouri." in Missouri Geological Surrey, vol. xi. (Jeffer son City, Mo., 1896). See ALUMINA; SHALE; PIPE-CLAY; KAOLIN; FIRE-CLA•; LOAM; SOIL; BRICK.
For the character, distribution, and methods of manufacture in the United States, consult: The Mineral Industry (New–Yo•k, 1892 et seq.) ; also, Davis, Practical Treatise on the Manufac ture of Bricks, Tiles, and Terra-Cotta (Phila delphia, 1895).
CLAY, ('Assns 11810.19631. An American abolitionist and politician, born in Madison County, Ky. Be graduated at Yale in 1832, returned to Kentucky to practice law, and was elected to the State Legislature in 1835, in 1837, and in 1840, but in 1841 failed of reelec tion on account of his strong anti-slavery opin ions. In 1844 he made speeches in the Northern States in advocacy of the election of 'Henry Clay to the Presidency, and ill the following year op posed the annexation of Texas, and established at Lexington, Ky., The True American, a vigor ous anti-slavery paper, which, however, was sup pressed by a mob, but was revived by Mr. Clay, and was published thereafter in Cincinnati. He volunteered for service in the Mexican War in 1846, and was taken prisoner. In 1850 he left the Whig Party, and was the Anti-Slavery can didate for Governor. In 1860 he supported Lin coln, and in 1861 was appointed Minister to Russia, but returned to the United States in 1862, and was made major-general of volunteers. In 1863, however, he resigned, and was again appointed Minister to Russia, where he remained until 1809. He supported Greeley in 1872 and Tilden in 1876, but went over to the Republican Party to vote for Blaine in 1884. In the cam paign of 1896 he was in the gold-standard wing of the Democratic Party. Consult his Life, Memoirs, Writings, and Speeches (Cincinnati, 1886).