in 1823 being associated with a William Lockwood and possibly others. In his 1824 cement patent, Joseph Aspdin called his invention "portland cement" because of its resemblance to Portland stone. Aspdin's cement was nothing like modern Portland cement, but a first step in the development of modern Portland cement, and has been called a "proto-portland cement". William Aspdin had left his father's company, to form his own cement manufactury. In the 1840s William Aspdin, apparently accidentally, produced calcium silicates which are a middle step in the development of Portland cement. In 1848, William Aspdin further improved his cement. Then, in 1853, he moved to Germany, where he was involved in cement making. William Aspdin made what could be called "meso-portland cement" (a mix of Portland cement and hydraulic lime). Isaac Charles Johnson further refined the production of "meso-portland cement" (middle stage of development), and claimed to be the real father of Portland cement. In 1859, John Grant of the Metropolitan Board of Works, set out requirements for cement to be used in the London sewer project. This became a specification for Portland cement. The next development in the manufacture of Portland cement was the introduction of the rotary kiln, patented by Frederick Ransome in 1885 (U.K.) and 1886 (U.S.); which allowed a stronger, more homogeneous mixture and a continuous manufacturing process. The Hoffmann "endless" kiln which was said to give "perfect control over combustion" was tested in 1860 and shown to produce a superior grade of cement. This cement was made at the Portland Cementfabrik Stern at Stettin, which was the first to use a Hoffmann kiln. The Association of German Cement Manufacturers issued a standard on Portland cement in 1878. Portland cement had been imported into the United States from Germany and England, and in the 1870s and 1880s, it was being produced by Eagle Portland cement near Kalamazoo, Michigan. In 1875, the first Portland cement was produced in the Coplay Cement Company Kilns under the direction of David O. Saylor in Coplay, Pennsylvania. By the early 20th century, American-made Portland cement had displaced most of the imported Portland cement. Composition ASTM C150 defines Portland cement as: The European Standard EN 197-1 uses the following definition: (The last two requirements were already set out in the German Standard, issued in 1909). Clinkers make up more than 90% of the cement, along with a limited amount of calcium sulfate (CaSO4,