Cement.—The cement of commerce may be divided into four classes: 1. Hydraulic lime, which is made from limestone containing a small proportion of clay (8 or 10 per cent.) by burning at a low temperature and slaking the product with water. 2. Hydraulic or natural rock cement, made from an impure limestone, containing a larger percentage of clay than that used for hydraulic lime, by being burned at a low temperature and then ground to powder. 3. Portland cement, which is made from an artificial mixture of carbonate of lime—chalk, ground limestone or marl—with certain proportions of clay, burned at a white heat, and the clinker ground to powder. 4. Slag cement, which is made by mixing finely ground volcanic ash or slag from a blast furnace with a small proportion of slaked lime.

Of these four classes, Portland cement is by far the most important, and the manufacture of slag cement is still in its infancy in the United States. The manufacture of cement in Kansas began at Fort Scott in 1868, and the next year the capacity of the plant was increased to 10 barrels a day, and the amount of capital invested was $4,000. At that time the nearest source of supply was Louisville, and the price of ordinary hydraulic cement was $10 a barrel. The Fort Scott company cut the price one-half, and soon had all the orders it could fill. When the Missouri, Kansas & Texas railroad was built to Fort Scott, the demand increased, railroad companies began to use cement in construction of their lines, and in 1871 the plant was enlarged to 50 barrels a day. Still the market widened with improved transportation facilities, and in 1879 the company was turning out 700 barrels daily. A second mill was erected in 1887, and in a short time it also was turning out 700 barrels a day, though the price had dropped to less than $1 a barrel. Improved methods were introduced, to cheapen the cost of production, and in 1900 Kansas mills had a capacity over 125,000 barrels for the year, which had been increased to nearly 240,000 in 1906.

The manufacture of Portland cement began in 1899. The first mill was erected at Iola and started with a capacity of 2,500 barrels a day, which was soon doubled. A second mill was established there in 1904. In 1905 mills were built at Independence and Neodesha. Mills are also in operation at Fredonia, Humboldt, Chanute, Yocemento and Bonner Springs. In 1908 three of the largest mills were consolidated under one management—the United States Portland Cement company, with a capital of over $12,500,000. The industry was greatly stimulated by the discovery of natural gas, and in 1910 the fifteen mills in the Kansas and Oklahoma gas belt turned out over 1,000,000 barrels a month. There is also a large quantity of cement plaster manufactured in Kansas. (See also articles on Geology and Gypsum.)