240 



CEMENTS, LIMES, AND PLASTERS. 



In the Sturtevant rock-emery mill the ordinary millstones or buhr- 

 stones are replaced by a " rock-emery" stone. This is composed of 



FIG. 45. Sturtevant horizontal rock-emery mill. 



a circular iron cup or shell. The center of the circle is made up of a 

 disc of buhrstone while the portion nearer the rim is set with slabs 



FIG. 46. Sturtevant rock-emery millstone. 



of "rock emery" cemented by metal poured in while molten. Radial 

 strips of buhrstone are set so as to continue the furrows of the cen- 

 tral buhrstone to the rim of the wheel. This is shown in Fig. 46. The 



