See his autobiography (1866); his writings, ed. by H. Greeley (1848, repr. 1969); biographies by D. L. Smiley (1962) and W. H. Townsend (1967).
His father died when he was four years old, and Clay's formal schooling was limited to three years. His stepfather secured (1792) for him a clerk's position in the Virginia high court of chancery. There he gained the regard of George Wythe, who directed his reading. Clay also read law under Robert Brooke, attorney general of Virginia, and in 1797 he was licensed to practice.
Moving in the same year to Lexington, Ky., he quickly gained wide reputation as a lawyer and orator. He served (1803-6) in the Kentucky legislature and was (1805-7) professor of law at Transylvania Univ. Having spent the short session of 1806-7 in the U.S. Senate, he returned (1807) to the state legislature, became (1808) speaker, and remained there until he was chosen to fill an unexpired term (1810-11) in the U.S. Senate.
In 1810 Clay was elected to the U.S. House of Representatives and served (1811-14) as speaker. As spokesman of Western expansionist interests and leader of the "war hawks," Clay stirred up enthusiasm for war with Great Britain and helped bring on the War of 1812. He resigned (1814) from Congress to aid in the peace negotiations leading to the Treaty of Ghent.
He again served (1815-21) in the House, again was speaker (1815-20), and began to formulate his "American system," a national program that ultimately included federal aid for internal improvements and tariff protection of American industries. In 1821, Clay, to pacify sectional interests, pushed the Missouri Compromise through the House. In the House for the last time (1823-25), he once more became (1823) speaker, and he did much to augment the powers of that office. In this session he secured the western extension of the National Road and, against much opposition, eloquently carried through the Tariff of 1824.
As a candidate for the presidency in 1824, Clay had the fourth largest number of electoral votes, and, with no candidate having a majority, the election went to the House, where the three highest were to be voted upon. It became Clay's duty to vote for one of his rivals. Despite the Western interests of Andrew Jackson and despite the instructions of the Kentucky legislature to vote for him, Clay's dislike for the military hero was so intense that he voted for John Quincy Adams. When President Adams appointed Clay Secretary of State, Jackson's friends cried "corrupt bargain" and charged Clay with political collusion. Evidence has not been found to prove this, but the accusation impeded Clay's future political fortunes. As Secretary of State (1825-29), he secured congressional approval—which came too late for the American delegates to attend—of U.S. participation in the Pan-American Congress of 1826.
In 1828, Clay again supported Adams for President, and Jackson's success bitterly disappointed him. Although he intended to retire from politics, Clay was elected (1831) to the U.S. Senate and now led the National Republicans, who were beginning to call themselves Whigs (because they opposed Jackson's "tyranny"; see Whig party). Hoping to embarrass Jackson, Clay led the opposition in the Senate to the President's policies, but when the election came Jackson was overwhelmingly reelected.
Clay's chagrin was buried in the crisis developing over the tariff. South Carolina's nullification of the tariffs of 1828 and 1832 as well as Jackson's threats of armed invasion of that state allowed Clay to gain politically—working, even at the cost of his own protectionist views, toward a compromise with the John C. Calhoun faction, he helped to promote the Compromise Tariff of 1833.
Clay opposed the Jackson regime at every turn, particularly on the bank issue. When Jackson had the deposits removed (1833) from the Bank of the United States to his "pet banks," Clay secured in the Senate passage of a resolution—later expunged (Jan., 1837) from the record—censuring the President for his act.
Refusing to run for President in 1836, Clay continued his opposition tactics against Van Buren's administration and fought the subtreasury system in vain. In 1840, Clay lost the Whig nomination to William H. Harrison, mainly because of Thurlow Weed's adroit politics. Clay supported Harrison and, when Harrison was elected, was offered the post of Secretary of State, but he chose to stay in the Senate. He now planned to reestablish the Bank of the United States, but the unexpected accession of John Tyler to the presidency and his vetoes of Clay's bills caused Clay to resign his Senate seat.
In 1844 he ran against James K. Polk, an avowed expansionist. Earlier Clay had publicly opposed the annexation of Texas, and he restated his position in the "Alabama letters," agreeing to annexation if it could be accomplished with the common consent of the Union and without war. This maneuver probably lost him New York state, with which he could have won the election. His failure was crushing for him and for the Whig party. In 1848 his party refused him its nomination, feeling that he had no chance, and his presidential aspirations were never fulfilled.
He reentered (1849) the Senate when the country faced the slavery question in the territory newly acquired following the Mexican War. Clay denounced the extremists in both North and South, asserted the superior claims of the Union, and was chiefly instrumental in shaping the Compromise of 1850. It was the third time that he saved the Union in a crisis, and thus he has been called the Great Pacificator and the Great Compromiser.
Publication of Clay's papers (ed. by J. Hopkins) was begun in 1959. See also his works (7 vol., 1896); C. Eaton, Henry Clay and the Art of American Politics (1957); biographies by C. Schurz (1887, repr. 1968), G. Van Deusen (1937), and B. Mayo (1937, repr. 1966).
Properties of the clays include plasticity, shrinkage under firing and under air drying, fineness of grain, color after firing, hardness, cohesion, and capacity of the surface to take decoration. On the basis of such qualities clays are variously divided into classes or groups; products are generally made from mixtures of clays and other substances. The purest clays are the china clays and kaolins. "Ball clay" is a name for a group of plastic, refractory (high-temperature) clays used with other clays to improve their plasticity and to increase their strength. Bentonites are clays composed of very fine particles derived usually from volcanic ash. They are composed chiefly of the hydrous magnesium-calcium-aluminum silicate called montmorillonite. See also fuller's earth.
Individual clay particles are always smaller than 0.004 mm. Clays often form colloidal suspensions when immersed in water, but the clay particles flocculate (clump) and settle quickly in saline water. Clays are easily molded into a form that they retain when dry, and they become hard and lose their plasticity when subjected to heat.
Clays are divided into two classes: residual clay, found in the place of origin, and transported clay, also known as sedimentary clay, removed from the place of origin by an agent of erosion and deposited in a new and possibly distant position. Residual clays are most commonly formed by surface weathering, which gives rise to clay in three ways—by the chemical decomposition of rocks, such as granite, containing silica and alumina; by the solution of rocks, such as limestone, containing clayey impurities, which, being insoluble, are deposited as clay; and by the disintegration and solution of shale. One of the commonest processes of clay formation is the chemical decomposition of feldspar.
Clay consists of a sheet of interconnected silicates combined with a second sheetlike grouping of metallic atoms, oxygen, and hydroxyl, forming a two-layer mineral such as kaolinite. Sometimes the latter sheetlike structure is found sandwiched between two silica sheets, forming a three-layer mineral such as vermiculite. In the lithification process, compacted clay layers can be transformed into shale. Under the intense heat and pressure that may develop in the layers, the shale can be metamorphosed into slate.
From prehistoric times, clay has been indispensable in architecture, in industry, and in agriculture. As a building material, it is used in the form of brick, either sun-dried (adobe) or fired. Clays are also of great industrial importance, e.g., in the manufacture of tile for wall and floor coverings, of porcelain, china, and earthenware, and of pipe for drainage and sewage. Highly absorbent, bentonite is much used in foundry work for facing the molds and preparing the molding sands for casting metals. The less absorbent bentonites are used chiefly in the oil industry, e.g., as filtering and deodorizing agents in the refining of petroleum and, mixed with other materials, as drilling muds to protect the cutting bit while drilling. Other uses are in the making of fillers, sizings, and dressings in construction, in clarifying water and wine, in purifying sewage, and in the paper, ceramics, plastics, and rubber industries.
Clay is one of the three principal types of soil, the other two being sand and loam. A certain amount of clay is a desirable constituent of soil, since it binds other kinds of particles together and makes the whole retentive of water. Excessively clayey soils, however, are exceedingly difficult to cultivate. Their stiffness presents resistance to implements, impedes the growth of the plants, and prevents free circulation of air around the roots. They are cold and sticky in wet weather, while in dry weather they bake hard and crack. Clods form very often in clayey soils. Clays can be improved by the addition of lime, chalk, or organic matter; sodium nitrate, however, intensifies the injurious effects. In spite of their disadvantages, the richness of clay soils makes them favorable to the growth of crops that have been started in other soil.
See R. E. Grim, Clay Mineralogy (2d ed. 1968); R. W. Grimshaw, The Chemistry and Physics of Clays and Allied Ceramic Materials (4th ed. 1971).
Clay is a naturally occurring material composed primarily of fine-grained minerals, which show plasticity through a variable range of water content, and which can be hardened when dried and/or fired. Clay deposits are mostly composed of clay minerals (phyllosilicate minerals), minerals which impart plasticity and harden when fired and/or dried, and variable amounts of water trapped in the mineral structure by polar attraction. Organic materials which do not impart plasticity may also be a part of clay deposits.
Clay minerals are typically formed over long periods of time by the gradual chemical weathering of rocks (usually silicate-bearing) by low concentrations of carbonic acid and other diluted solvents. These solvents (usually acidic) migrate through the weathering rock after leaching through upper weathered layers. In addition to the weathering process, some clay minerals are formed by hydrothermal activity. Clay deposits may be formed in place as residual deposits, but thick deposits usually are formed as the result of a secondary sedimentary deposition process after they have been eroded and transported from their original location of formation. Clay deposits are typically associated with very low energy depositional environments such as large lake and marine deposits.
Quick clay is a unique type of marine clay indigenous to the glaciated terrains of Norway, Canada and Sweden. It is a highly sensitive clay, prone to liquefaction, which has been involved in several deadly landslides.
Clays exhibit plasticity when mixed with water in certain proportions. When dry, clay becomes firm and when fired in a kiln, permanent physical and chemical reactions occur which, amongst other changes, causes the clay to be converted into a ceramic material. It is because of these properties that clay is used for making pottery items, both practical and decorative. Different types of clay, when used with different minerals and firing conditions, are used to produce earthenware, stoneware and porcelain. Early humans discovered the useful properties of clay in prehistoric times, and one of the earliest artifacts ever uncovered is a drinking vessel made of sun-dried clay. Depending on the content of the soil, clay can appear in various colors, from a dull gray to a deep orange-red.
Clays sintered in fire were the first form of ceramic. Bricks, cooking pots, art objects, dishware and even musical instruments such as the ocarina can all be shaped from clay before being fired. Clay is also used in many industrial processes, such as paper making, cement production and chemical filtering. Clay is also often used in the manufacture of pipes for smoking tobacco.
Clay, being relatively impermeable to water, is also used where natural seals are needed, such as in the cores of dams, or as a barrier in landfills against toxic seepage ('lining' the landfill, preferably in combination with geotextiles).
A recent article in The Journal of Antimicrobial Chemotherapy found that certain iron-rich clay was effective in killing bacteria.