Die deutsche Kali-Industrie 1930

The Elements of economic geology

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Monograph

Identifikator:: 1847185045

URN:: urn:nbn:de:zbw-retromon-241659

Document type:: Monograph

Title:: Die deutsche Kali-Industrie 1930

Edition:: (Als Ms. gedr.)

Place of publication:: Berlin

Publisher:: Hoppenstedt

Year of publication:: (1930)

Scope:: 94 Seiten

Digitisation:: 2022

Collection:: Economics Books

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Chapter

Document type:: Monograph

Structure type:: Chapter

Title:: [ II. Die drei großen Gruppen der deutschen Kali-Industrie ]

Collection:: Economics Books

THE GEOLOGY OF CEMENTS 189 New York; by L. H. Cole (Gypsum in Canada, Can. Dept. Mines, 1913, pp. 94-99) for those in British Columbia; by G. E. Pilgrim (Mem. &.S. India, 1908, xxxiv, p. 104), and by J. V. Harrison (Econ. Geol., 1924, p. 270) for the gypsum of Persia, and by Murray Stewart (Rec. G.S. India., 1919, 1, pp. 63, 67) for that of the Salt Range of the Punjab. The setting of gypsum is a delicate process requiring careful control of the temperature and amount of water, as too much leaves the crystals loose and the plaster friable. The water present should be not more than about a thousandth of that required to dissolve the material. The temperature in burning plaster of Paris should not rise above 260° F., at which the dihydrate (CaSO,, 2H,0), is converted into hemi- hydrate (2CaSO,, H,0) ; it readily dissolves in water, forming a supersaturated solution and crystals of dihydrate. Their formation sets free water, which dissolves more hemihydrate ; it releases more water as it crystallizes into dihydrate; and thus a small excess of water works through the material until all has set. The value of plaster of Paris in preparing casts and orna- mental mouldings is due to its expansion on solidification, so that the material is forced into the smallest crevices of the mould. The burning of gypsum mixed with alum or borax at 400° F. produces ** hard plaster.”

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