CEMENT, a substance with which two bodies are joined together. Thee are many varieties, according to the special needs of different trades. In building the principal are known as Portland and Roman. There are many places in the United States in which are found the ingredients necessary for the manufac ture of the various cements described below, and many different varieties of the article are made. Where Portland cement is specified in a building contract the imported variety is meant.
Portland Cement was patented in Eng land by Joseph Aspdin in 1824. It is so called because it resembles in color Port land-stone. It is manufactured by cal cining a mixture of clayed mud from the Thames with a proper portion of chalk. The calcined mass is then reduced to a fine powder, and intimately mixed with the addition of water. The resulting paste is molded into bricks, dried and burnt. The heat during the process of calcining must be a white heat, other wise the carbonic acid and water may be expelled without the reaction between the lime and the clay necessary for the production of cement. The material is then assorted, all which has been too much or too little calcined being set aside and pulverized.
Roman Cement is a name given to cer tain hydraulic mortars, varying consid erably in their chemical composition, though physically possessing the same general character. Limestone is cal cined and mixed with sand in various proportions. Any limestone containing from 15 to 20 per cent. of clay will, when properly prepared, form this cement. Calcine any ordinary clay and mix it with two-thirds its quantity of lime, grind to powder, and calcine again. The epithet Roman is improperly given, since the preparation was entirely unknown to the Romans.
Hydraulic Cement is a kind of mortar used in building piers and walls under or exposed to water. There are many varieties, one of the best being composed of ground Portland-stone, 62 parts; sand, 35, and litharge, 3.
The production of cement in the United States in 1919 was: Portland, 80,287,000 barrels, valued at $135, 685,000; natural Cement, 528,000 bar rels, valued at $597,000. Pennsylvania ranks first in the production of Port land Cement, with 25,222,000 barrels in 1919.