Page:Popular Science Monthly Volume 60.djvu/163

Rh is very economical of labor and is very uniform in its action, which is an extremely desirable condition in the cement industry.

I am indebted to the obliging courtesy of the officers of the Virginia Portland Cement Co., of Craigsville, Augusta Co., Va., for the accompanying illustrations of a Portland Cement Plant.

Fig. 4 is a general view of the works, which it will be seen at once are very unlike the natural cement works, at Milwaukee. All the operations of a Portland cement works are under cover. Fig. 5 represents

the stone house where the materials are received and sorted, preparatory to being finely ground. A great variety of mills are used for grinding both the crude materials and the cement clinker. So far as the making of the cement is concerned, it does not matter in what kind of a mill the ingredients may be ground, provided they be ground fine and thoroughly mixed in the right proportions. If the mixture is burned dry, the mixing is accomplished by the use of screens and sieves; if it is burned wet, the grinding is done in a wet mill, the paste being floated off and allowed to settle in large tanks. The dry materials are blown into the kiln. The wet mud is allowed to drip into the upper end of the kiln as it is forced in by a pump.

Fig. 6 represents the rotary kiln. It consists of a slightly inclined steel cylinder, about 60 feet in length and 6 to 7 feet in diameter, lined with fire-brick, and revolving by means of powerful gears at the