Portland cement, on the other hand, is wholly an artificial product, made by calcining or burning a finely ground and carefully propor tioned mixture of calcareous (limey) matter with an argillaceous (clayey) or siliceous sub stance (sand, quartz, or slag) to the point of in cipient fusion, and grinding the resulting clinker to an impalpable powder, to which in some cases a small percentage of gypsum or other special ingredient is added.
Although Portland cement now far surpasses all other kinds of cement in structural import ance and in extent of use, natural and slag ce ments still figure to some extent in construction work. The difference in composition, strength, and lasting qualities, however, is great.
The first cements manufactured in modern times were made in England. As early as 1790, one Joseph Parker made a cement by burning lumps of chalky clay stones and finely pulveriz ing the clinker. This he called "Roman ce ment," either because it resembled the cement used by the Romans in its property of setting under water, or because of its similarity in color to the lavas found in the vicinity of Rome.
It is, however, to Joseph Aspdin, a brick mason of Leeds, that the credit of originating the first Portland Cement is due, and he is there fore generally recognized as the father of the modern Portland cement industry. After ex perimenting for some years along the lines indi cated by Parker, Aspdin produced a cement by mixing pulverized limestone with clay in certain proportions, calcining in kilns, and grinding very fine. This cement he named "Portland" because of its close resemblance in color to the famous stone quarried on the Isle of Portland in the English Channel, from which St. Paul's Cathedral, the Eddystone Lighthouse of Smea ton, and other prominent structures in England were built.
In 1824 Aspdin obtained a patent on his hy draulic cement. At this time, however, and for years thereafter, nothing was known of the proper proportioning of calcareous to argil laceous matter, or of the temperature necessary to insure a good product. Many experiments were made by English and French engineers in an endeavor to produce a cement that would command the attention of builders, but no per manent results of value were obtained. It was reserved for a German chemist, in 1828, to for mulate the first theory of the action of ingre dients and their proper combining proportions to make a true Portland cement. Without this knowledge, the securing of reliable material could never be depended upon. Improvements in standard were from time to time effected. Progress, however, was slow; and although the manufacture of Portland cement had been be gun in England in 1825 or 1827, it was not until the middle of the century that this cement se cured any wide recognition of its merits as a material of construction. In France, its manu
facture was begun in 1846; and in Germany, at Stettin, in 1855; but it was not until 1860 that any considerable quantity was made for the gen eral market in England or on the Continent, and even then but very little was made for exporta tion.
Portland cement was first brought to the United States in 1865; and during the following decade considerable quantities of the foreign product were imported, constituting the greater portion of such cement used in this country by architects and engineers. In the late seventies, however, the domestic product began to come into competition with the foreign article, and American Portland cement has now almost en tirely displaced that of foreign manufacture.
Thus, it was not until some years after the close of the Civil War that the great Portland cement industry in the United States had its beginning. For half a century prior to that time, natural cement—the first kind of cement manufactured in the United States—had practi cally a monopoly of construction work in this country. Its manufacture had been begun in 1818 by Canvass White, who secured a patent for a Roman cement made from natural rock; and this material was used in the original ma sonry work on the Erie canal.
The first Portland cement manufactured in the United States was made at Coplay, Pa., in 1872, by David 0. Saylor, who exhibited his product at the Centennial Exhibition in Phila delphia in 1876. This was the small beginning of the present enormous American Portland ce ment industry, whose later growth has in many respects been unprecedented in the history of American industrial development. Not, how ever, until twenty years or more had passed, did the industry in this country begin to show any very substantial increase or tendency to rise. Up to 1880, in fact, only six plants for the manu facture of Portland cement had been established in the United States—in Pennsylvania, New York, Maine, Indiana, and Michigan—and the entire American output aggregated a total of only 82,000 barrels. Not only were American methods of manufacture defective as compared with foreign standards, but at that time rein forced concrete was unknown, and the value and various adaptabilities of Portland cement con crete as a structural material were not dreamed of. Natural cement had almost the entire field to itself; and concrete, when it was used at all, was confined almost wholly to foundation and underground work. The slow progress of the Portland cement industry in America during these early days can be seen from a glance at Table I, which gives statistics of production in various years between 1880 and 1895.