PORTLAND OZML!T. Portland cement is produced by cal cining a mixture containing from 75 to 80 per cent of carbonate of lime and 20 to 23 per cent of clay, at such a high temperature that the silica and alumina of the clay combines with the lime of the limestone. To secure a complete chemical combination of the clay and the lime, it is necessary that the raw materials shall be reduced to a powder and be thoroughly mixed before burning, and it is also necessary that the calcination shall take place at a high temperature.
In a general way portland cement differs from natural cement by being heavier, stronger, and usually slower-setting.
Portland cement derives its name from the resemblance which hardened mortar made of it bears to a stone found in the isle of Portland, off the south coast of England. Portland cement was made first in England about 1827, and in America about 1874.
Until about 1897 more portland cement was imported into this country than was made here; but since that date the imports have gradually fallen off and the domestic manufacture has increased very rapidly, so that in 1907 the imports of portland cement were less than 2 per cent of the domestic manufacture. The production of domestic portland cement increased more than twenty-fold from 1897 to 1907.
The domestic consumption per capita of portland increased one hundred-fold from 1880 to 1905, and the consumption per capita of all kinds of cement increased ten-fold in the same time. In 1887 only about one fifth of the cement used in this country was portland, in 1897, one third, and in 1907 over nine tenths was portland. The best American portland cement is better than the best imported, and is sold equally cheap or cheaper.
In 1905 portland cement was made at eighty-nine works in twenty-one States; but nearly one half of the production comes from the Lehigh Valley in northeastern Pennsylvania and northwestern New Jersey.