GYPSUM. 



BY STORY B. LADD. 



[Story B. Ladd, statistician, is one of the experts of the United States census bureau, in 

 which capacity ho has done important statistical work, including an invcstlKiition of 

 tlie gj^psum industry made by him for the twelfth census; he is the acknowletiged 

 authority on gypsum and its extraction and its products.] 



Gypsum, a natural product, is calcium sulphate, of the 

 chemical formula CaS04.2HoO, containing 40. 5 per cent of 

 sulphuric acid, 32.6 per cent of hme, and 20.9 per cent of water. 

 Anhydrite, a mineral like g^^^sum, ])ut as its name indicates, 

 containing no water, is composed of 58.8 per cent of sulphuric 

 acid and 41.2 per cent of lime. This absorbs water and 

 changes to gj-psum. When g^^^sum is properly calcined it 

 loses a part of the water of its composition and becomes plaster 

 of Paris, the name originatmg from the great deposits of gy])- 

 sum worked at Montmartre, a suburb of Paris. The transpar- 

 ent cr}^stallized variety of g}^sum is called selenite; its fine 

 massive variety, alabaster; and its fi])rous form, satin spar. 

 A loose earthy gjq^sum found in Kansas and other points in 

 the west is called gypsite. 



Gypsum crj^stallizes in the monoclinic system, has a 

 hardness of 2, and a specific gravity of 2.31. Its color is 

 white, although sometimes red, green, blue, gray, or bro^^^l. 

 When protected from the action of water it is extremely dur- 

 able, as evidenced by the niunerous monumental cfhgies, many 

 centuries old, in European churches and elsewhere. 



It is quite generally distributed and occurs in irregular 

 and often in ver}^ extensive and massive deposits. A deposit 

 of white cr^^stallme g}T)sum at Netherfield, England, is more 

 than 50 feet in thickness, and in the Thiiringerwald, Germany, 

 a great mass has been sunk through to a depth of 70 feet. The 

 g\T)sum deposits of Onondaga county, N. Y., show in places a 

 thickness of 60 feet. The snow-white alabaster found at 

 Volterra, in Tuscany, Italy, is used extensively at Florence and 

 Leghorn for works of art. It is white when newly broken and 



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