Improvements in Making Portland Cement.
Clay is taken as dug from the pit, without being dried, and mixed with the usual proportion of lime, a portion of which is used as limestone, the remainder as freshly burnt lime. The burnt lime is first added in such proportion that the water in the clay exactly suffices to slake it, and the heat given out effects the necessary drying. The limestone is then added and the mixture ground in a mill to the usual degree of fineness, made into bricks, calcined, and the “clinker” reduced to a fine state of division as usual.