HISTORY OF CEMENT 113 



manufacturing natural cement on a commercial basis. Other 

 plants sprang up along the canals in New York state; also in 

 Ohio, and a plant was established near Louisville, Kentucky. 

 The output for a number of years was very small about 25,- 

 000 barrels per year. After the Civil War, during the recon- 

 struction period, an impetus was given to the cement indus- 

 try, and the production of natural cement reached its maxi- 

 mum in 1899, when 10,000,000 barrels were produced. Since 

 then, the production of cement from natural stone as found 

 in the quarries has been on the decline. At the present time 

 practically all cement used in America is artificial cement, or 

 Portland cement. 



104. Portland Cement. The process of making artificial 

 cement, or Portland cement, was discovered by Joseph Aspdin, 

 an Englishman, in 1829. The cement was given its name be- 

 cause it resembles the Portland rocks near Leeds, England. 

 In the United States it was first manufactured in 1870 at 

 Copley, Pennsylvania. Its use has increased so rapidly that 

 now the output amounts to about 100,000,000 barrels per year. 

 Portland cement manufacturing plants can now be found 

 thruout the country. Wherever there is an abundance of 

 suitable limestone and shale, or clay, and a supply of fuel and 

 labor, a cement plant can be successfully operated. Portland 

 cement is different from natural cement, in that the materials 

 of which it is made are carefully proportioned and artificially 

 mixed. The essential components of Portland cement are 

 silica, aluminum and lime, with small quantities of other ma- 

 terials. The silica and aluminum are in the clay. The ma- 

 terial is first ground, then mixed in proportion of three parts 

 of limestone to one of clay; it is then burned to a clinker and 



