STATE GEOLOGIST, 187 
done successfully, however, with a Roman cement equipment, but requires 
more elaborate and expensive machinery and kilns. 
2nd. Roman cements, lower in lime than 1, and free from magnesia, 
can only be burnt at 1000° C. 
3rd. Roman cements, high in magnesia, should only be 
burnt at 950°C, as the great strength produced by making a magnesia 
Portland cement is counterbalanced by the danger of inconstancy in 
volume due to the two rates of hydration of lime and magnesia, the latter 
hydrating only after the first has assumed a stony hardness, thus break- 
ing the structure of the cement. In very sandy mortars and some kinds 
of work they might perhaps be used, but at this stage of our knowledge 
concerning cements they cannot be considered a safe proposition. 
Ath. Cements, dolomitic, less basic than the subsilicate, to be burnt 
only at or about 950°. 
These facts are well realized by natural cement manufacturers, who 
endeavor to burn their cements below the point at which decrease in 
strength occurs, and this they accomplish by leaving some of the calcium 
carbonate in dolomitic rocks undecomposed. It is hence unreasonable to 
demand of Roman cement manufacturers that they produce cement burnt 
to a point at which all volatile matter is expelled, but, of course, this does 
not mean that raw rock should be allowed to be ground together with the 
cement. 
Artificial Roman Cement. —The question has been raised as to the 
feasibility of producing an artificial Roman cement by blending clay and 
limestone in the proper proportion, burning the mixture to a low tempera- 
- ture, and grinding the resulting soft material to the usual fineness. There 
is no doubt as to the technical feasibility of this plan, and the large dolo- 
mitic limestone deposits of Ohio could thus be utilized without difficulty, 
but the commercial aspect is not promising, especially since the cost of 
production of Portland cement is being lowered so decidedly. This plan, 
however, might be carried out in countries without proper Portland or 
natural cement materials, but possessing dolomitic limestones. 
The Kilns.——The kilns used differ somewhat in size and shape 
in different localities. In the Louisville district they are cylindrical 
in shape, consisting of a cylindrical iron shell lined with fire-brick, about 
45 feet high, and 16 feet in diameter ; in the Rosendale district many kilns 
are IO feet in diameter (inside), and about 29 feet high; near Akron, 
N. Y., the writer saw a kiln oblong in section, 15 feet by 8 feet and 25 
feet high. -At Milwaukee a kiln is used, 11 feet in diameter (inside), 
and 36 feet high. In the Rosendale district the kilns usually are built 
together in a row of masonry braced by heavy timbers and iron rods. All 
the kilns are narrowed at the bottom to a neck, through which the calcined 
cement is discharged. The coal, usually anthracite, or a good grade of 
