CEMENT FOR A MODERN STREET. 149 



and Portland cement. The details of the process of manufacture will 

 now be given. 



In the United States the manufacture of natural cements is chiefly 

 carried on in the Lehigh Valley, near Louisville, Ky., at Akron, Ohio, 

 at Milwaukee, Wis., and at Glens Falls and other points in the State 

 of Xew York. While the rocks occurring at these different points are 

 not identical, either in geological age or in chemical composition, they 

 are in many respects similar. In geologic age they are of carboniferous 

 age or older and in chemical composition they consist of limestones in 

 V, hich clay occurs, either uniformly disseminated throughout the rock, 

 forming a very intimate admixture, or else interstratified with the 

 layers of limestone, so that when the rock is broken up and burned, the 

 resulting mixture of the constitiients of the rock is very intimate. Yet 

 intimate as tlie mixture is, both before and after burning and grind- 

 ing, in all the ledges the rock has to be sorted and mixed in the same 

 quarry with the greatest care, in order to insure a uniform product 

 from the same works. From the diiferent localities the output is 

 sufficiently different to give the Louisville, Milwaukee and other brands 

 distinctive, though unimportant, characteristics. 



At all the natural cement works substantially the same method of 

 manufacture is followed, although the details are modified to suit 

 different localities. 



One of the most extensive natural cement plants in the country is 

 ihat of the Milwaukee Cement Co., at Milwaukee, Wis., the officers of 

 which have kindly furnished the accompanying illustrations. Fig. 1 

 shows the tramway approaches to the kilns, which are arranged in a 

 double set of ten each. The rock is quarried in the immediate neigh- 

 borhood and is run in tram-cars, Avhich are seen in the middle fore- 

 ground, up the inclines to the top of the kilns into which the rock is 

 thrown. The trestle on the right is the dump for coal, which is also 

 loaded into tram cars, one of which is seen at the chute, and run up 

 the incline to the kilns. The rock and fuel are thus conveniently sup- 

 plied to the kilns at the top, while the burned cement is removed from 

 the kilns at the bottom. Fig. 3 shows one of the kilns on the left; the 

 grinding and shipping house in the center, with the inclines up which 

 the burned cement is hauled and the railroad tracks over which the 

 cement is shipped in all directions from Milwaukee. Fig. 3 represents 

 the grate at the bottom of the kiln, from which the burned cement is 

 removed, while fresh rock and fuel are supplied at the top, thus making 

 the action of the kilns continuous. 



Two obstacles make it impossible to prepare a theoretically perfect 

 cement from the natural rock. The first is a lack of uniformity in the 

 rock itself as it occurs in the quarry. This difficulty is obviated as 

 nearly as is po?si])lo by careful sorting. l)y which the least desirable rock 



