USES. The use of gypsum seems to have been known at a very early period, for the Greeks were familiar with it, as shown by the writings of Theophrastus and Pliny. The commercial value of the mineral gypsum depends largely on the color, the whiter grades being calcined and used for plaster. This calcining is commonly done in large kettles, the material having been previously ground in crushers and mills. The kettles are usually about six feet deep and eight feet in diameter, and are filled to a depth of five feet. They are heated from below, and the gypsum is constantly stirred during the calcining process by revolving arms. Aside from its uses for ordinary plastering, it is also extensively em ployed in the manufacture of ornamental stucco work, as a filler in paper, in making imitations of marble, and sometimes for calcimining. Where a slow set is desired a retarder is sometimes used, such as glue, hair, lime, etc. Raw gypsum is also used as a basis for paints, the pigments being mixed with it. The impure crude gypsum finds application only for fertilizing purposes, and is extensively employed in both England and America for increasing the fertility of soils..
(See MANURES AND MANURING.) It is also em ployed at times to counteract the black alkali which forms in many of the soils of the arid region. Alabaster has been used for many years
for decorative purposes, and in the making of statuary, while satin spar has been employed for necklaces, inlaid work, and other ornaments.
The total quantity of gypsum produced in the United States in 1901 amounted to 1,246,649 short tons, valued at $1,577,493, and of this quantity 521,292 short tons were calcined. In the United States Kansas is the largest producer, with Michigan second. The imports in 1901 were valued at $326,670. Among the world's producers France leads, with the United States second and Canada third.
BIBLIOGRAPHY. Grimsley and Bailey, Gypsum Bibliography. Grimsley and Bailey, Gypsum Deposits of Kansas, issued by Kansas Geological Survey (Topeka, 1899) ; Wilkinson, "Technology of Cement Plaster," Transactions of the Ameri can Institute of Mining Engineers (New York, La Croix, "Le gypse de Paris et les mine raux qui l'accompagnent," Nouvelles archives des museum histoire naturelle (Paris, 1897). For statistics, consult volumes of the Mineral Re sources, issued by the United States Geological Survey (Washington, annual). See PLASTER OF PARIS.