CLAY 



1411 



CLAY 



CLAY, the earth used in making brick, tile 

 and pottery. When dry, it is very hard and 

 compact; when moist, its particles stick to- 

 gether and this makes it possible to mold it 

 into any form desired. This peculiarity makes 

 clay one of the most valuable materials used 

 in the arts. All brick, pottery, tile and terra 

 cotta are made from it; it can be rolled into 

 thin sheets or drawn into rods which can be 

 bent and twisted into any form, which makes 

 it valuable in ornamental work. When moist 

 clay is baked at a high temperature it becomes 

 hard and will retain its form under high 

 pressure, but we all know that a vessel made 

 of clay is easily broken by a blow. 



Clay is composed of silica and aluminum, and 

 may contain small quantities of iron, calcium, 

 magnesium, potassium and sodium. Most clay 

 is formed by the decomposition of rock con- 

 taining feldspar. It varies in color from nearly 

 white to gray, dark blue and red. 



The color of clay depends upon the presence 

 of other substances than silica and aluminum. 

 If it contains iron it usually turns red when 

 burned. This -is why we have red brick, tiling 

 and pottery ware. Porcelain clay, or kaolin, is 

 usually white or light gray. Potter's clay and 

 pipe clay are similar to kaolin, but not so pure, 

 and are used in making the cheaper grades of 

 pottery. Fire clay will withstand intense heat, 

 and is used for lining furnaces, for smelting 

 iron and for making fire brick and crucibles. 



Tripoli and fuller's earth are varieties that are 

 easily reduced to a fine powder; the former is 

 sometimes used for polishing purposes. Clay 

 is used in the manufacture of soap, in finishing 

 paper to give it a glazed surface, in the manu- 

 facture of paint, and for adulterating food and 

 for making filters. 



Clay is an important constituent of soils. 

 It absorbs ammonia and other gases necessary 

 to the growth of plants and retains in the soil 

 the fertilizing substances supplied by manure. 

 Loam consists of clay mixed with sand and 

 humus, and without a certain proportion of 

 clay soil will not retain its fertility from sea- 

 son to season. Since water cannot pass through 

 clay, layers of it underlying the soil prevent 

 "leaching," that is, prevent the rain water 

 from .draining to lower layers of soil and gravel, 

 thus leaving the soil dry. 



Clay Modeling is a general feature of in- 

 struction in all kindergarten and primary 

 schools. For information relating to this 

 feature of education, see the article KINDER- 

 GARTEN. W.F.R. 



Related Subjects. Students will find it ad- 

 vantageous to read the following articles in 

 these volumes : 

 Brick Marl 

 Calcium Potassium 

 Feldspar Sodium 

 Iron Soil 

 Kaolin Terra Cotta 

 Magnesium Tile 



) "Ashland," Clay's Home at Lexington G 



HENRY (1777-1852), one of the 

 most distinguished leaders in American public 

 affairs during the critical period of the anti- 

 slavery controversy. He was born at a time 

 when his country was fighting for independence 

 from British rule, and died less than a decade 

 before the bitter struggle over the slavery 

 question reached its climax in the clash of arms 



between the North and the South. For thirty 

 years he gave his best efforts to warding off 

 that great conflict, thereby winning the title, 

 "The Great Pacificator," that will be asso- 

 ciated with him for all time. 



Henry Clay was born April 12, 1777, the son 

 of a Baptist clergyman of Hanover County, 

 Va., who died when the boy was four years 



