. Mineral Resources of the United States, 1914--Part II--Nonmetals . made indifferent localities may vary greatly. Natural cements are yellowto brown in color and have a lower specific gravity than Portlandcement. PORTLAND CEMENT. Portland cement was invented by Joseph Aspdin, of Leeds, Eng-land, and was thus named from its fancied resemblance, when set, tothe well-known oolitic limestone of Jurassic age quarried for buildingpurposes on Portland Isle, Dorsetshire, England. Portland cementis the product obtained by finely pulverizing clinker produced bycalcining to incipient fusion an intimate
. Mineral Resources of the United States, 1914--Part II--Nonmetals . made indifferent localities may vary greatly. Natural cements are yellowto brown in color and have a lower specific gravity than Portlandcement. PORTLAND CEMENT. Portland cement was invented by Joseph Aspdin, of Leeds, Eng-land, and was thus named from its fancied resemblance, when set, tothe well-known oolitic limestone of Jurassic age quarried for buildingpurposes on Portland Isle, Dorsetshire, England. Portland cementis the product obtained by finely pulverizing clinker produced bycalcining to incipient fusion an intimate mixture of properly propor-tioned argillaceous and calcareous substances, with only such addi-tions subsequent to calcining as may be necessary to control certainproperties. Such additions shall not exceed 3 per cent by weightof the calcined product. Chemically, Portland cement is a combina-tion consisting principally of silicates and aluminates of lime, and theraw materials must necessarily contain silica, alumina, and lime. MINERAL RESOURCES. 1914. PART II PLATE. MAP OF UNITED STATES SHOWING DISTRIBUTION OF PORTLAND, NATURAL, AND PUZZOLAN CEMENT PLANTSAND OUTLINES OF PORTLAND CEMENT COMMERCIAL DISTRICTS Prepared by Ernest F. Buroharrt1915 CEMENT. 223 Therefore, within these limitations, various raw materials are capableof being utilized for the manufacture of Portland cement. In Englandchalk and clay, and in Germany and France, marl and clay, and lime-stone and slate are employed. In the United States limestone andclay or shale, marl and clay, argillaceous limestone and purer lime-stone, as well as blast-furnace slag and limestone are used. The first process in the manufacture of Portland cement is the mix-ing of the raw materials. In order that this mixture may be uniformand homogeneous and the respective ingredients properly propor-tioned, they must be reduced to a fine powder. The method of re-duction depends to some extent, although less now than formerly,upon the charact
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