It may be remarked here that in the older form of the wet process, developed in England and formerly used here to some extent, the thin slurry was run into "backs" or shallow reservoirs to settle, the clear liquid was run off, and the slurry, after further drying, was cut into bricks to be artificially dried and then burned in dome kilns. The adaptation of the rotary kiln to the burning of wet materials has put the original form of the wet process out of use in this country.

The fuel consumption in the wet process is appreciably greater than in the case of a dry mixture. The cooling and grinding of the clinker do not necessarily differ from the corresponding operations in the dry process.

21. The Semi-Dry Process

During the first thirty years of Portland cement production in the United States this process of manufacture was prominent, but the successful development of the rotary kiln has rendered it almost obsolete, and the modern cement mill is designed to use one of the processes already outlined with such minor modifications as the designer may consider advantageous.

With wet materials the semi-dry process consists in forming the mix into bricks after it has passed a pug mill, drying the bricks artificially either in drying ovens or in a portion of the burning kilns, and then burning the bricks in a stationary kiln. With dry materials, sufficient water is added after the preliminary grinding to permit pugging the mixture and making the bricks. The method is not only expensive in labor account, but considerable loss results from imperfect burning, and the uniform results attainable by the methods already described are not usually realized with this process.