The Elements of economic geology

Bibliographic data

Monograph

Identifikator:: 1773832379

URN:: urn:nbn:de:zbw-retromon-172798

Document type:: Monograph

Author:: Gregory, John W. http://d-nb.info/gnd/11683014X

Title:: The Elements of economic geology

Place of publication:: London

Publisher:: Methuen

Year of publication:: 1928

Scope:: XIV, 312 S.; graph. Darst.

Digitisation:: 2021

Collection:: Economics Books

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Chapter

Document type:: Monograph

Structure type:: Chapter

Title:: Part III. Earthy minerals

Collection:: Economics Books

BUILDING STONES AND ROAD METALS 181 A sandstone should be compact, for, if porous, the water attacks the cement, and weakens the stone on freezing. Hence the brown sandstone used in New York is rejected if it weigh less than 130 lb. a cubic foot, or absorbs over 5 per cent. of water on 24 hours’ immersion, as either test indicates too high a porosity. Slate is often a durable building material. The main source of weakness is when its iron sulphide occurs as mar- casite instead of as the ordinary cubic pyrite. Slate might be more largely used, but for its dull colour. STONE PRESERVATION—The preservation of building stones depends mainly on preventing the entry of moisture. Paint is effective but expensive, as it has to be renewed, and re- moves the beauty of stonework. The exclusion of moisture is the purpose of numerous processes. Waterglass or silicate of soda fills the surface pores with silica. Sulphur dissolved in hot oil closes the pores with sulphur. The Szerelmy process uses silicate of soda containing a bituminous material. The drawback of any impermeable crust is that it flakes off owing to the expansion of the air within the stone. A coating of paraffin over the grains of the stone prevents the entrance of moisture by surface tension and yet allows the stone to breathe. The process is however too expensive for general application. A. P. Laurie has introduced the use of silicon ester (prepared by the action of alcohol on silicon tetrachloride) which deposits silica on the grains and not as a film; it leaves the pores open (¥. Soc. Chem. Ind.. xliv, 1925, p. 91 T.)., The baryta method was designed by Church for the Chapter House at Westminster Abbey; ! it was built in the thirteenth century of Upper Greensand from Reigate in Surrey, which is a siliceous sandstone containing grains of glauconite and cemented by from IO to 15 per cent. of carbonate of lime. The cement has been converted by sulphuric acid into gypsum (hydrous sulphate of lime). The building was sprayed—as the stone was too friable to withstand a brush—with a solu- tion of barium hydrate (3 per cent. of BaO in water), which converts the sulphate of lime into the insoluble barium sulphate : the calcium of the gypsum is left as hydrate, LA. H. Church, Memoranda Concerning Treatment of . . . Chapter House . . . Parl. Pap., 1904, Cd. 1889.

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